# Optical Spectra of 73 Stripped-Envelope Core-Collapse Supernova

M. Modjaz, S. Blondin, R. P. Kirshner, T. Matheson, P. Berlind, F. B.

Bianco, M. L. Calkins, P. Challis, P. Garnavich, M. Hicken, et al.

► To cite this version:

M. Modjaz, S. Blondin, R. P. Kirshner, T. Matheson, P. Berlind, et al. Optical Spectra of 73 Stripped-Envelope Core-Collapse Supernova. The Astronomical Journal, 2014, 147 (5), pp.99-116. 10.1088/0004-6256/147/5/99. hal-01442008

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OPTICAL SPECTRA OF 73 STRIPPED-ENVELOPE CORE-COLLAPSE SUPERNOVAE

M. MODJAZ<fnref n="1" />, S. BLONDIN<fnref n="2" />, R. P. KIRSHNER<fnref n="3" />, T. MATHESON<fnref n="4" />, P. BERLIND<fnref n="5" />, F. B. BIANCO<fnref n="1" />, M. L. CALKINS<fnref n="5" />, P. CHALLIS<fnref n="3" />, P. GARNAVICH<fnref n="6" />, M. HICKEN<fnref n="3" />, S. JHA<fnref n="7" />, Y. Q. LIU<fnref n="1" />, AND G. H. MARION<fnref n="3" />

Received 2013 May 24; accepted 2014 January 12; published 2014 March 28

ABSTRACT

We present 645 optical spectra of 73 supernovae (SNe) of Types IIb, Ib, Ic, and broad-lined Ic. All of these types are attributed to the core collapse of massive stars, with varying degrees of intact H and He envelopes before explosion. The SNe in our sample have a mean redshift $\langle cz \rangle = 4200 \text{ km s}^{-1}$. Most of these spectra were gathered at the Harvard-Smithsonian Center for Astrophysics (CfA) between 2004 and 2009. For 53 SNe, these are the first published spectra. The data coverage ranges from mere identification (1–3 spectra) for a few SNe to extensive series of observations (10–30 spectra) that trace the spectral evolution for others, with an average of 9 spectra per SN. For 44 SNe of the 73 SNe presented here, we have well-determined dates of maximum light to determine the phase of each spectrum. Our sample constitutes the most extensive spectral library of stripped-envelope SNe to date. We provide very early coverage (as early as 30 days before V-band max) for photospheric spectra, as well as late-time nebular coverage when the innermost regions of the SN are visible (as late as 2 yr after explosion, while for SN 1993J, we have data as late as 11.6 yr). This data set has homogeneous observations and reductions that allow us to study the spectroscopic diversity of these classes of stripped SNe and to compare these to SNe-gamma-ray bursts. We undertake these matters in follow-up papers.

**Key words:** supernovae: general – surveys

*Online-only material:* color figures, figure set, machine-readable and VO tables

1. INTRODUCTION

Stripped-envelope core-collapse supernovae (SNe) mark the diverse deaths of massive stars and are sometimes accompanied by long-duration gamma-ray bursts (GRBs), while their nucleosynthesis products contribute to the universe's chemical enrichment. By stripped-envelope core-collapse SNe (SESNe; Clocchiatti et al. 1997), for short “stripped SNe,” we refer to SNe of Types IIb, Ib, Ic, and broad-lined Ic (SNe IIb, Ib, Ic and Ic-bl; reviews on spectral SN classification and the historical background can be found in Filippenko 1997 and Matheson et al. 2001). In this empirical classification scheme, SNe I do not show evidence of H lines, SNe Ib show conspicuous lines of He I, while SNe Ic do not, and neither subtype shows strong Si II or S II absorption lines, the hallmark of SNe Ia. SNe IIb are transition types, for which the Balmer lines decrease in strength over time, while He I lines, characteristic of SNe Ib, appear in their spectra (e.g., Filippenko et al. 1993).

Now, stripped SNe are recognized as core-collapse SNe whose massive progenitors have been stripped of progressively increasing amounts of their hydrogen and helium layers (e.g., Podsiadlowski et al. 1993; Nomoto et al. 1993; Clocchiatti et al. 1997; Matheson et al. 2001; Maurer et al. 2010, but see Dessart et al. 2012; Hachinger et al. 2012 and below), through either strong winds (Woosley et al. 1993) or binary interaction (Nomoto et al. 1995; Podsiadlowski et al. 2004) or a combination of both.

Positive identification of the progenitors of the stripped SN requires the identification of the pre-SN star and its disappearance after the SN fades. Recent reviews (Smartt et al. 2009; Eldridge

et al. 2013) show that pre-explosion *Hubble Space Telescope (HST)* images at the sites of SNe Ib, SNe Ic, and SNe Ic-bl have not yet conclusively detected a candidate for the progenitor star (except perhaps for a recent SN Ib; Cao et al. 2013).

Most recently, the connection between long-duration GRBs and broad-lined SNe Ic (see Woosley & Bloom 2006; Hjorth & Bloom 2011; Modjaz 2011 for reviews) has sparked interest in the nature and progenitors of SNe Ic with and without GRBs. Broad-lined SNe Ic are a class of SNe Ic that exhibit very broad and blended lines, indicating significant amount of mass at very large expansion velocities (15,000–30,000 km s⁻<fnref n="1" />) (Galama et al. 1998; Patat et al. 2001; Mazzali et al. 2006; Modjaz et al. 2006; Sanders et al. 2012b). The fundamental question remains, however, whether GRB-SNe Ic are a separate class of SNe Ic-bl requiring specific conditions (e.g., low metallicity; Yoon & Langer 2005; Woosley & Heger 2006; Stanek et al. 2006; Modjaz et al. 2008a) and/or constitute the extreme end of a continuum of SN Ic events, dictated by, for example, viewing angle effects in asymmetric explosions.

Despite their importance, there are only a handful of well-studied stripped SNe. The best-studied SN Ic has been SN 1994I (e.g., Filippenko et al. 1995; Richmond et al. 1996), which exploded in the nearby galaxy M51. Thus, it was well observed over many wavelength regimes and is commonly referred to as the “proto-typical” SN Ic. The same applies to SN 1993J (e.g., Filippenko et al. 1993; Matheson et al. 2000a, 2000b) in the nearby galaxy M81, the first SN IIb recognized as such (e.g., Nomoto et al. 1993), and often called the “proto-typical” SN IIb. To evaluate how typical these SNe are for their classes, however, one needs a broad sample for comparison.

<footnote n="1">¹Center for Cosmology and Particle Physics, New York University, 4 Washington Place, New York, NY 10003, USA; mmodjaz@nyu.edu</footnote>

<footnote n="2">²Aix Marseille Université, CNRS, LAM (Laboratoire d'Astrophysique de Marseille) UMR 7326, F-13388, Marseille, France</footnote>

<footnote n="3">³Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA</footnote>

<footnote n="4">⁴National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85719, USA</footnote>

<footnote n="5">⁵F. L. Whipple Observatory, 670 Mt. Hopkins Road, P.O. Box 97, Amado, AZ 85645, USA</footnote>

<footnote n="6">⁶Department of Physics, 225 Nieuwland Science Hall, University of Notre Dame, Notre Dame, IN 46556, USA</footnote>

<footnote n="7">⁷Department of Physics and Astronomy, Rutgers University, 136 Frelinghuysen Road, Piscataway, NJ 08854, USA</footnote>
The only comprehensive observational spectroscopic study
has been conducted by Matheson et al. (2001), who presented
84 spectra of 28 stripped SNe and unfiltered light curves for four
of their SNe Ib. While their spectroscopic observations are a
valuable source for understanding the distinctions between SNe
Ib and SNe Ic, their paucity of light curves renders it impossible
to assign a robust phase to most of their spectra.

Understanding the full range of massive stellar explosions re-
quires the study of a large and comprehensive SN sample with
homogeneous and densely time-covered data. It is important
to obtain secure spectroscopic identifications that may accu-
rately indicate the outer composition of the pre-explosion star,
including very early-time spectra that probe the outermost lay-
ers. Such data are presented in this work, which constitutes the
largest spectroscopic data set of stripped SNe to date. Since
1993, a vigorous program has been conducted at the CfA<fnref n="8" /> of
following up supernova discoveries with photometry and spec-
tra from the Fred Lawrence Whipple Observatory (FLWO) on
Mount Hopkins, Arizona. Early work emphasized SN Ia for their
cosmological utility. But more recent work, since 2004, has in-
cluded energetic studies of stripped-envelope core-collapse su-
pernovae. Photometric results on SN Ia are available in Riess
et al. (1999; CfA1), Jha et al. (2006; CfA2), Hicken et al. (2009;
CfA3) and Hicken et al. (2012; CfA4). Infrared observations of
Type Ia supernovae from the CfA are available in Wood-Vasey
et al. (2008) and in A. S. Friedman et al. (in preparation). A
first set of 432 CfA spectra of 32 SN Ia was published by Math-
eson et al. (2008), and a recent sample comprising 2603 CfA
spectra of 462 SN Ia was published by Blondin et al. (2012).
All published CfA spectra are publicly available through a CfA
Supernova Archive.<fnref n="9" />

Here we present the aggregate collection of spectroscopic
data of nearby ($z_{mean} = 0.0141 \pm 0.0097$) stripped-envelope
SNe collected between 1994 and 2009 (with 78% of all spectra
taken during 2004–2009). The plots of the spectra for all the
SNe in this paper are available in the online edition, and the
data will be made available through the above-mentioned CfA
Archive. A future companion paper presents the photometric
data of these stripped SNe (F. B. Bianco et al., in preparation).
A number of the CfA spectra of a few of these stripped SNe,
especially historic SNe, were published as single objects, as
well as part of slightly larger studies (see below for full list),
but we include those here, since in most cases the spectra were
re-reduced to be consistent with the full sample. Even for SNe
that have had spectra published by other groups, the spectra
presented here sometimes cover earlier epochs that were not
reported by others. The consistency of the method of observation
and the technique of reduction makes this an important data
set for studying the spectroscopic diversity of stripped SNe, as
well as providing a comparison sample for SNe associated with
GRBs, all of which we undertake in our follow-up paper. We
incorporated the data into the Supernova Identification (SNID)
code (Blondin & Tonry 2007) to aid in the (re)classification of
SNe, as discussed in Sections 4.1 and 4.2.

The format is as follows: In Section 2 we describe our spectro-
scopic observational and reduction techniques. In Section 3 we
present our full data set of optical spectra. In Section 4 we intro-
duce our stripped SN sample and give background information
about their discoveries and host galaxies, while discussing in
detail the SN classifications in Sections 4.1 and 4.2. We discuss

individual SNe, for which data have already been published, in
Section 5, and we conclude with Section 6.

## 2. SPECTROSCOPIC OBSERVATIONS AND DATA REDUCTION

While pre-2004 only the closest and therefore brightest
stripped SNe were followed, an intense follow-up program
started in 2004 (see Matheson et al. 2008 and Blondin et al.
2012 for detailed discussions of the CfA SN follow-up program
criteria). Our decision to monitor a particular newly discovered
SN IIb/Ib/Ic was broadly informed by the following considera-
tions: (1) accessibility (northern SNe with declination $\gtrsim -20^\circ$),
(2) SN brightness ($m < 18$ mag for spectroscopic observations
and $m < 20$ mag for optical photometry), and (3) SN phase
(SNe whose spectra indicated a young age were given higher
priority). Of course, (2) and (3) are correlated post-maximum,
since older SNe are dimmer.

The nearby SNe we monitored were discovered by a variety
of professional SN searches and amateurs using modern CCD
technology. Systematic SN searches include the Lick Observa-
tory SN Search (LOSS; Filippenko et al. 2001), the Texas SN
Search<fnref n="10" /> (Quimby 2006), and the Nearby SN Factory (Aldering
et al. 2002), among others. The successful LOSS and many
amateur SN searches possess a relatively small field of view
(FOV, 8.7 × 8.7 for LOSS) and have a database of galaxies that
they monitor nightly. Thus, they include well-known and, in-
evitably, more luminous galaxies (e.g., Li et al. 2001; Gallagher
et al. 2005; Mannucci et al. 2005). SNe that were discovered be-
cause their host galaxies were specifically targeted by traditional
searches are designated as “targeted.” The Texas SN Search and
the Nearby SN Factory are rolling searches that scan wide areas
that include hundreds or thousands of galaxies without select-
ing any individual galaxies as targets. These galaxy-impartial
searches are more likely to include SNe that erupt in low-
luminosity hosts. It is important to keep track of the provenance
of each SN to track selection effects that arise from the search
method (Modjaz et al. 2008a; Young et al. 2008; Sanders et al.
2012a). SNe that are discovered in galaxy-impartial searches or
that are discovered in background galaxies that are not the tar-
get of searches from a list we label “untargeted.” In our sample,
78% of the events were discovered in targeted surveys. Of those
targeted SNe, 39% were (co-)discovered by LOSS and 58% by
amateurs, where we have counted the SNe twice if they were
co-discovered by both LOSS and amateurs independently.

Our data acquisition and reduction techniques are in most
part identical to those discussed in Matheson et al. (2008) and
in Blondin et al. (2012); therefore, we only briefly summarize
their main aspects here. Most of the early-time spectroscopic
SN monitoring was performed via queue observers at the 1.5 m
Tillinghast telescope at the Fred Lawrence Whipple Observatory
(FLWO) that produced the vast majority (615 of 645 spectra)
of the low-resolution spectra presented here. In addition, we
observed SNe for late-time studies ($\gtrsim$3–6 months) with the
6.5 m Clay Telescope of the Magellan Observatory located at
Las Campanas Observatory (LCO), the 6.5 m MMT at FLWO,
and the 8.1 m Gemini-North Telescope in Hawaii via queue
observations (Program IDs GN-2005B-Q-11 & GN-2006B-
Q-16, GN-2007A-DD-4, GN-2008A-Q-17, PI: M. Modjaz).
The spectrographs utilized were the FAST (Fabricant et al.
1998) at the FLWO 1.5 m telescope, the LDSS-3 (Mulchaey
& Gladders 2005) at LCO, the Blue Channel (Schmidt et al.

<footnote n="8">⁸ http://www.cfa.harvard.edu/supernova/</footnote>

<footnote n="9">⁹ http://www.cfa.harvard.edu/supernova/SNarchive.html</footnote>

<footnote n="10">¹⁰ http://grad40.as.utexas.edu/~quimby/tss/index.html</footnote>
1989) at the MMT, and GMOS-North (Hook et al. 2003) at
Gemini-North.

Observational details of the spectra and their reductions are
given in Table 1. The FAST spectra were obtained in the standard
COMBO setup (slit width of 3", 300 line mm⁻¹ grating), with an
observed wavelength range of 3500–7400 Å. The wavelength
resolution was ~7 Å, in other words, R = λ/Δλ ~ 800 at
the central wavelength of 5600 Å, corresponding to a velocity
resolution of ~400 km s⁻¹. During bright time, the FAST
spectrograph is not mounted on the FLWO 1.5 m; hence,
some of our spectroscopic time coverage has gaps of 10 or
more days. Moreover, FLWO undergoes a shutdown during
the month of August every year, due to Arizona monsoon
season; thus, we do not have monitoring data 1 month out
of the year. For MMT+Blue Channel, we used 1" or 2" slits
and the 300 line mm⁻¹ grating, and for Gemini+GMOS, the
0.75 slit and 400 line mm⁻¹ grating. For LDSS3+Magellan,
depending on the availability, we used the VPH-Blue, VPH-
Red, or VPH-All grisms, and usually slits of 0.75, 1", and 1.25
(matching the seeing conditions). For all setups, the resolution
was 5–10 Å, as determined from the width of night-sky lines.
Spectrophotometric standard stars (e.g., Massey et al. 1988;
Hamuy et al. 1992) were observed on the same nights for flux
calibration (see Table 1) and are also used to remove telluric
absorption features from the spectra (see, e.g., Wade & Horne
1988; Matheson et al. 2000a). Since the FAST spectrograph
suffered from second-order light contamination during our
observations, we observed standard stars of different colors. By
calibrating the data with blue standards for the blue wavelength
range and with red standards for the red, we minimized the
impact of the second-order light (Matheson et al. 2008). All
optical spectra were reduced and calibrated employing standard
techniques in IRAF and our own IDL routines for flux calibration
(see, e.g., Matheson et al. 2008). Table 1 gives the slit position
angle for each spectrum, as well as the absolute difference, |ΔΦ|,
with the parallactic angle. From 2000 on, after which most of
the discussed spectra were taken, the spectra were always taken
at or near the parallactic angle (Filippenko 1982). For the CfA
SN Ia samples taken with the same instruments, the relative flux
calibration has been demonstrated to have a precision of ~8%
across 4000–6500 Å (Matheson et al. 2008; Blondin et al. 2012).

Here we check the accuracy of the relative flux calibration of
our stripped SN spectra, employing a similar procedure as for
the CfA SN Ia data in Matheson et al. (2008) and in Blondin
et al. (2012). As outlined in the Appendix, stripped SNe have a
scatter of 0.24 mag (including all phases), about twice as large
as SNe Ia from the CfA SN Ia data, using our re-analysis.

3. CfA STRIPPED SN SPECTRA

We present a total of 645 spectra of 73 SNe in this section.

Since all 615 spectra from the 1.5 m Tillinghast were
obtained with the same instrument and telescope setup and were
reduced in the same manner, our data set constitutes the largest
homogeneous and densely time-sampled spectroscopic data set
of stripped-envelope SNe to date. The homogenous aspect of
our data is important for our ability to conclusively distinguish
between SNe Ib and SNe Ic, as we are able to consistently
test for the presence of the important line of He I λ7065 (see
Section 4.1) at the wavelengths where some of the telluric lines
are located, which we remove from all SN spectra in the same
manner. In addition, the MMT and Magellan spectra were also
obtained and reduced in the same manner as the data obtained
with the 1.5 m Tillinghast (e.g., observed at parallactic angle

after 1993, telluric absorption removed, etc.). In Figure 1, we
only show the CfA spectral series of four example SNe, namely,
one SN per stripped SN class (SN IIB, Ib, Ic, and Ic-bl). This is
done for brevity and for guidance regarding their format. The
rest of the spectra plots are available in the online version of
the paper and will be made available on the CfA SN Archive
website, along with the spectral data.

In all SN spectra figures and in the subsequent analysis,
the heliocentric SN velocity has been removed in order to
place the spectra in the SN rest frame. The SN velocity was
either determined from narrow emission lines in the galaxy/SN
spectrum (from superimposed H II regions) when detected, or
assumed to be equal to the heliocentric recession velocity
of the host galaxy nucleus (Table 2), with an uncertainty of
up to ±200–300 km s⁻¹ due to host galaxy’s rotation curve.
Furthermore, for SN for which the date of maximum light has
been measured (either in the literature or in our companion light
curve paper by F. B. Bianco et al., in preparation; see Table 3),
we list the rest-frame phases (i.e., Δt/(1 + z)) of the spectra,
where Δt denotes days with respect to maximum light. For most
of our SN, maximum light is measured in the V-band, except
for 6 SN which only have measured R-band maxima. For SN
without observed date of maximum light, we list on the figures
the UT dates of the obtained spectra.

4. CfA STRIPPED SN SAMPLE

We list our SN sample along with pertinent SNe and host
galaxy information in Table 2. The SN type listed in column 2 is
based on our own assessment by running the SN identification
code SNID (Blondin & Tonry 2007) with its extensive library
of template spectra (augmented with more recent spectra than
available when published in 2007) on the multi-epoch CfA
spectra, which lead in a number of cases to a different SN
classification than announced in the IAUC, as we discuss in
detail in Section 4.1. With some spectra of SNe, it may be hard
to tell whether the optical He optical lines are present—those
SNe we designate as SNe Ib/c (for a detailed discussion of the
SN classification see Section 4.1). Column 3 lists the discovery
reference as the IAUC or CBET number, while column 4 notes
the mode in which the SNe were discovered (“targeted” versus
“untargeted”). The mode of discovery will be important for
environmental studies, specifically for metallicity studies (e.g.,
see review by Modjaz 2011). Columns 5, 6, and 7 list the host
galaxy name and the SN offsets from the galaxy nucleus, which
are taken from the International Astronomical Union Circulars
(IAUC) and Central Bureau Electronic Telegrams (CBET)<fnref n="11" /> and
from the NASA/IPAC Extragalactic Database (NED). Column 8
lists the heliocentric recession velocity, while column 9 lists the
date of maximum light in the V band, unless noted otherwise, as
well as the corresponding reference publication in parentheses.
The CfA values for the dates of maximum values are based on
the fits to the CfA photometry using Monte Carlo simulations
(F. B. Bianco et al., in preparation).

We consulted the Updated Zwicky Catalogue (Falco et al.
1999) and the SDSS catalog for the heliocentric host galaxy
redshifts (czhelio), as well as already-published ones for the SNe
in our sample, and otherwise used those listed in the NED, giving
preference to optical redshifts over H I redshifts, if there was a
discrepancy. Some of the listed redshifts were determined by
ourselves via the superimposed H II-region emission lines in the
SN spectra, if there were no optical redshift determination for the

<footnote n="11">¹¹ http://cfa-www.harvard.edu/iau/cbat.html</footnote>
<table><caption>**Table 1**
Journal of Observations</caption><thead><tr><th>UT Date<sup>a</sup></th><th>HJD<sup>b</sup></th><th>Phase<sup>c</sup><br>(d)</th><th>Tel./Instr.<sup>d</sup></th><th>Range<sup>e</sup><br>(Å)</th><th>Disp.<sup>f</sup><br>(Å pixel<sup>-1</sup>)</th><th>Res.<sup>g</sup><br>(Å)</th><th>P.A.<sup>h</sup><br>(°)</th><th>|ΔΦ|<sup>i</sup><br>(°)</th><th>Air.<sup>j</sup></th><th>Flux Std.<sup>k</sup></th><th>See.<sup>l</sup><br>(")</th><th>Slit<sup>m</sup><br>(")</th><th>Exp.<sup>n</sup><br>(s)</th><th>Observer(s)<sup>o</sup></th></tr></thead><tbody><tr><td colspan="15" style="text-align:center; font-weight:bold;">SN 1994I</td></tr><tr><td>1994-04-03.49</td><td>2449445.99</td><td>-5.9</td><td>MMT+Blue Channel</td><td>3483-7697</td><td>3.51</td><td>7-8</td><td>...</td><td>81.2</td><td>1.38</td><td>...</td><td>...</td><td>...</td><td>120</td><td>GB</td></tr><tr><td>1994-04-03.39</td><td>2449445.89</td><td>-6.0</td><td>FLWO 1.5m+FAST</td><td>3705-7635</td><td>1.47</td><td>6-7</td><td>90.0</td><td>50.8</td><td>1.07</td><td>F67/F56</td><td>2</td><td>3.0</td><td>900</td><td>JPe</td></tr><tr><td>1994-04-05.32</td><td>2449447.82</td><td>-4.1</td><td>FLWO 1.5m+FAST</td><td>3704-7635</td><td>1.47</td><td>6-7</td><td>90.0</td><td>60.9</td><td>1.05</td><td>F67/F56</td><td>2-3</td><td>3.0</td><td>3×900</td><td>PBe</td></tr><tr><td>1994-04-06.39</td><td>2449448.89</td><td>-3.0</td><td>FLWO 1.5m+FAST</td><td>3707-7636</td><td>1.47</td><td>6-7</td><td>90.0</td><td>45.6</td><td>1.08</td><td>F67/F56</td><td>2-3</td><td>3.0</td><td>2×900</td><td>PBe</td></tr><tr><td>1994-04-07.38</td><td>2449449.88</td><td>-2.1</td><td>FLWO 1.5m+FAST</td><td>3707-7637</td><td>1.47</td><td>6-7</td><td>90.0</td><td>48.2</td><td>1.08</td><td>F67/F56</td><td>1-2</td><td>3.0</td><td>2×900</td><td>PBe</td></tr><tr><td>1994-04-08.33</td><td>2449450.83</td><td>-1.1</td><td>FLWO 1.5m+FAST</td><td>3706-7636</td><td>1.47</td><td>6-7</td><td>90.0</td><td>83.0</td><td>1.04</td><td>F67/F56</td><td>1-2</td><td>3.0</td><td>900</td><td>JPe</td></tr><tr><td>1994-04-10.27</td><td>2449452.77</td><td>+0.8</td><td>FLWO 1.5m+FAST</td><td>3705-7635</td><td>1.47</td><td>6-7</td><td>90.0</td><td>35.3</td><td>1.07</td><td>F67/F56</td><td>1-2</td><td>3.0</td><td>900</td><td>JPe</td></tr><tr><td>1994-04-110.5</td><td>2449454.00</td><td>+2.1</td><td>MMT+Blue Channel</td><td>3209-8760</td><td>1.91</td><td>7-8</td><td>...</td><td>82.9</td><td>1.62</td><td>...</td><td>...</td><td>...</td><td>300</td><td>JHuc, CHeI</td></tr><tr><td>1994-04-11.25</td><td>2449453.75</td><td>+1.8</td><td>FLWO 1.5m+FAST</td><td>3705-7635</td><td>1.47</td><td>6-7</td><td>90.0</td><td>26.8</td><td>1.09</td><td>F67/F56</td><td>1-2</td><td>3.0</td><td>2×900</td><td>PBe</td></tr><tr><td>1994-04-12.44</td><td>2449454.94</td><td>+3.0</td><td>FLWO 1.5m+FAST</td><td>3708-7638</td><td>1.47</td><td>6-7</td><td>90.0</td><td>11.9</td><td>1.26</td><td>F67/F56</td><td>1-2</td><td>3.0</td><td>2×900</td><td>PBe</td></tr><tr><td>1994-04-15.37</td><td>2449457.87</td><td>+5.9</td><td>FLWO 1.5m+FAST</td><td>4844-6839</td><td>0.75</td><td>3-4</td><td>170.0</td><td>35.8</td><td>1.08</td><td>HZ44</td><td>1-2</td><td>3.0</td><td>900</td><td>RJ, Fabricant</td></tr><tr><td>1994-04-16.35</td><td>2449458.85</td><td>+6.9</td><td>FLWO 1.5m+FAST</td><td>4843-6839</td><td>0.75</td><td>3-4</td><td>-177.0</td><td>71.0</td><td>1.04</td><td>HZ44</td><td>1-2</td><td>3.0</td><td>900</td><td>RJ, Fabricant</td></tr><tr><td>1994-04-30.35</td><td>2449472.85</td><td>+20.9</td><td>FLWO 1.5m+FAST</td><td>3707-7631</td><td>1.47</td><td>6-7</td><td>110.0</td><td>8.5</td><td>1.14</td><td>F67/F56</td><td>1-2</td><td>3.0</td><td>2×900</td><td>PBe</td></tr><tr><td>1994-05-01.39</td><td>2449473.89</td><td>+21.9</td><td>FLWO 1.5m+FAST</td><td>3708-7632</td><td>1.47</td><td>6-7</td><td>110.0</td><td>3.0</td><td>1.25</td><td>F67/F56</td><td>1-2</td><td>3.0</td><td>1800</td><td>PBe</td></tr><tr><td>1994-05-02.37</td><td>2449474.87</td><td>+22.9</td><td>FLWO 1.5m+FAST</td><td>3708-7631</td><td>1.47</td><td>6-7</td><td>110.0</td><td>0.2</td><td>1.22</td><td>F67/F56</td><td>1-2</td><td>3.0</td><td>1800</td><td>PBe</td></tr><tr><td>1994-05-03.28</td><td>2449475.78</td><td>+23.8</td><td>FLWO 1.5m+FAST</td><td>3706-7630</td><td>1.47</td><td>6-7</td><td>110.0</td><td>68.6</td><td>1.05</td><td>F67/F56</td><td>1-2</td><td>3.0</td><td>1800</td><td>JPe</td></tr><tr><td>1994-05-05.20</td><td>2449477.70</td><td>+25.7</td><td>FLWO 1.5m+FAST</td><td>3704-7628</td><td>1.47</td><td>6-7</td><td>110.0</td><td>45.8</td><td>1.08</td><td>F67/F56</td><td>1-2</td><td>3.0</td><td>1800</td><td>JPe</td></tr><tr><td>1994-05-07.31</td><td>2449479.81</td><td>+27.8</td><td>FLWO 1.5m+FAST</td><td>3707-7631</td><td>1.47</td><td>6-7</td><td>110.0</td><td>26.0</td><td>1.10</td><td>F67/F56</td><td>1-2</td><td>3.0</td><td>1800</td><td>PBe</td></tr><tr><td>1994-05-08.26</td><td>2449480.76</td><td>+28.8</td><td>FLWO 1.5m+FAST</td><td>3708-7632</td><td>1.47</td><td>6-7</td><td>110.0</td><td>88.0</td><td>1.24</td><td>F67/F56</td><td>1-2</td><td>3.0</td><td>1200</td><td>PBe</td></tr><tr><td>1994-05-09.26</td><td>2449481.76</td><td>+29.8</td><td>FLWO 1.5m+FAST</td><td>3707-7631</td><td>1.47</td><td>6-7</td><td>110.0</td><td>70.2</td><td>1.05</td><td>F67/F56</td><td>1-2</td><td>3.0</td><td>1800</td><td>JPe</td></tr><tr><td>1994-05-13.30</td><td>2449485.80</td><td>+33.8</td><td>FLWO 1.5m+FAST</td><td>3708-7632</td><td>1.47</td><td>6-7</td><td>110.0</td><td>15.1</td><td>1.11</td><td>F67/F56</td><td>1-2</td><td>3.0</td><td>900</td><td>PBe</td></tr><tr><td>1994-05-15.22</td><td>2449487.72</td><td>+35.7</td><td>FLWO 1.5m+FAST</td><td>3720-7643</td><td>1.47</td><td>6-7</td><td>110.0</td><td>86.1</td><td>1.04</td><td>F67/F56</td><td>2-3</td><td>3.0</td><td>900</td><td>SMu</td></tr><tr><td>1994-05-16.22</td><td>2449488.72</td><td>+36.7</td><td>FLWO 1.5m+FAST</td><td>3710-7634</td><td>1.47</td><td>6-7</td><td>110.0</td><td>85.7</td><td>1.04</td><td>F67/F56</td><td>2-3</td><td>3.0</td><td>2×900</td><td>SMu</td></tr><tr><td>1994-05-17.25</td><td>2449489.75</td><td>+37.8</td><td>FLWO 1.5m+FAST</td><td>3744-7668</td><td>1.47</td><td>6-7</td><td>110.0</td><td>44.3</td><td>1.05</td><td>F67/F56</td><td>2-3</td><td>3.0</td><td>900</td><td>SMu</td></tr><tr><td>1994-05-19.19</td><td>2449491.69</td><td>+39.7</td><td>FLWO 1.5m+FAST</td><td>3747-7670</td><td>1.47</td><td>6-7</td><td>110.0</td><td>72.2</td><td>1.05</td><td>F67/F56</td><td>2-3</td><td>3.0</td><td>1200</td><td>JPe</td></tr><tr><td>1994-06-04.27</td><td>2449507.77</td><td>+55.7</td><td>FLWO 1.5m+FAST</td><td>3799-7723</td><td>1.47</td><td>6-7</td><td>110.0</td><td>0.1</td><td>1.19</td><td>F67/F56</td><td>2-3</td><td>3.0</td><td>900</td><td>SMu</td></tr></tbody></table>

**Notes.**

<sup>a</sup> UT at midpoint of observation(s).

<sup>b</sup> Heliocentric Julian Date at midpoint of observation(s).

<sup>c</sup> Rest-frame age of spectrum in days relative to V-band maximum. For 29 SNe with no reliable estimate for the time of maximum, we indicate the rest-frame days relative to the first spectrum preceded by an "@" symbol.

<sup>d</sup> Telescope and instrument used for this spectrum: FAST = FLWO 1.5m+FAST, IMACS = Magellan Baade+IMACS, LDSS2 = Magellan Clay+LDSS2, LDSS3 = Magellan Clay+LDSS3, MMTblue = MMT+Blue Channel, MMTred = MMT+Red Channel.

<sup>e</sup> Observed wavelength range of spectrum.

<sup>f</sup> Spectral dispersion in Å per pixel.

<sup>g</sup> Approximate FWHM spectral resolution in Å.

<sup>h</sup> Observed position angle during the observation(s).

<sup>i</sup> Absolute difference between the observed position angle and the average parallactic angle over the course of the observation(s).

<sup>j</sup> Airmass of the observation.

<sup>k</sup> Standard stars: BD17 = BD+17°4708, BD26 = BD+26°2606, BD28 = BD+28°4211, BD33 = BD+33°2642, CD32 = CD-32 9927, EG131 = EG 131, EG274 = EG 274, F15 = Feige 15, F25 = Feige 25, F34 = Feige 34, F56 = Feige 56, F66 = Feige 66, F67 = Feige 67, F110 = Feige 110, G191 = G191B2B, H102 = Hiltner 102, H600 = Hiltner 600, HD19 = HD 192281, HD21 = HD 217086, HD84 = HD 84937, HZ44 = HZ 44, HZ14 = HZ 14, L3218 = LTT 3218, L3864 = LTT 3864, L4816 = LTT 4816, vMa2 = van Maanen 2.

<sup>l</sup> Seeing is based upon estimates by the observers.

<sup>m</sup> Spectroscopic slit width.

<sup>n</sup> Exposure time. Separate exposures are indicated.

<sup>o</sup> Observers: EA = E. Adams, VA = V. Antoniou, HA = H. Arce, JA = J. P. Anderson, ZB = Z. Balog, PBa = P. Barmby, EB = E. Barton, JB = J. Battat, PBe = P. Berlind, GB = G. Bernstein, WBI = W. P. Blair, SB = S. Blondin, AB = A. E. Bragg, CB = C. Briceño, WBr = W. Brown, NC = N. Caldwell, MC = M. L. Calkins, BC = B. J. Carter, PC = P. Challis, JC = J. R. Cho, CC = C. Clemens, ACo = A. Cody, ACr = A. Crook, TC = T. Currie, RC = R. M. Cutri, KD = K. Dendy, AD = A. Diamond-Stanic, JDon = J. L. Donley, JDow = J. J. Downes, KE = K. Eriksen, GE = G. Esquerdo, DF = D. Fabricant, EF = E. E. Falco, RF = R. Fesen, JF = J. Foster, JGa = J. Gallagher, AG = A. Garg, PG = P. M. Garnavich, IG = I. Ginsburg, JGr = J. Graves, NG = N. Grogin, TG = T. Groner, VH = V. Hradecky, HH = H. Hao, CHei = C. Heinke, CHeI = C. Heller, JHe = J. Hernández, MH = M. Hicken, CHi = C. Hill, JHuc = J. P. Huchra, JHug = J. P. Hughes, CHu = C. Hutcheson, RH = R. Hutchins, RJ = R. Jansen, SJ = S. Jha, SKa = S. J. Kannapan, SKe = S. Kenyon, RK = R. P. Kirshner, DK = D. M. Koranyi, JK = J. Kuraszkiewicz, HL = H. Landt, TL = T. Lappin, NL = N. Lepore, LM = L. Macri, JM = J. A. Mader, AM = A. Mahdavi, EM = E. Mamajek, SMa = S. A. Mao, NM = N. Martinbeau, TM = T. Matheson, MM = M. Modjaz, FM = F. Munshi, SMu = S. Muscarella, GN = G. Narayan, PN = P. Nutzman, CP = C. A. Pantoja, BP = B. M. Patten, KP = K. Penev, JPe = J. Peters, WP = W. Peters, MP = M. Phelps, JPi = J. Piñeda, AR = A. G. Riess, KR = K. Rines, MS = M. Schrödter, JS = J. D. Silverman, IS = I. Song, ST = S. Tokarz, MT = M. Torres, CT = C. Tremonti, AV = A. Vaz, LW = L. Wells, MW = M. Westover.

(This table is available in its entirety in machine-readable and Virtual Observatory (VO) forms in the online journal. A portion is shown here for guidance regarding its form and content.)

host galaxy (for SN 2005kf, 2007ag, 2007ce) or if the systemic galaxy recession velocities listed in NED were different from those at the SN position by more than ± 200 km s⁻¹ presumably because of the galaxy’s rotation curve (for SN 2004gq, 2005az, 2005bf, 2005la, 2006T, 2006lv).

The last column lists the Julian Date of V-band maximum (but in 6 cases, R-band maximum, as noted in the table) or upper limits on the date, as well as the appropriate references. From a sample of well-observed V and R light curves of SESNe (e.g., Drout et al. 2011 and references therein), it appears
<figure><img src="image_2.png" /><figcaption>**Figure 1.** Example of CfA spectra of one SN per stripped SN type: SN 2008bo (Iib), 2004gq (Ib), 2005az (Ic), 2007ce (Ic-bl). The flux units are in $f_\lambda$ (erg s$^{-1}$ cm$^{-1}$ Å$^{-1}$) that have been normalized with additive offsets for clarity. The observation dates are indicated with respect to the V-band maximum light, $t_{Vmax}$ (see Table 2 for SNe with measured date of maximum and corresponding references). For SNe without known date of maximum light (here, e.g., 2007ce), we list the UT dates of observations instead of phases. The spectra, some of which are binned, are in the rest frame of the SN's host galaxy, as listed in Table 2 and described in the text.</figcaption></figure>

(The complete figure set (72 images) is available in the online journal.)

that the R-band maximum occurs 1–3 days later than V-band maximum.

A number of the CfA spectra of the following SNe were published as single objects: SN 1994I (Millard et al. 1999), 1997ef (Iwamoto et al. 2000), 2000H (Branch et al. 2002), 2003jd (Valenti et al. 2008a), 2005bf (Tominaga et al. 2005; Modjaz et al. 2008b), 2006aj (Modjaz et al. 2006, 2008b), and 2008D (Modjaz et al. 2009). Furthermore, a sample of CfA late-time spectra of stripped SNe were published and analyzed in Modjaz et al. (2008b) and Milisavljevic et al. (2010). While a few SNe have been observed by others and spectra published elsewhere (e.g., SN 1998dt, 2002ap, 2004aw, 2005la, 2006jc, 2007gr, 2008ax, 2009jf), we are here contributing new and hitherto unpublished CfA data for those SNe. Furthermore, even for a number of SNe (SN 1998dt, 20000H, 2004aw, 2005la, 2007bg, 2008ax) that have had spectra published by other authors, our spectra presented here start earlier than any of the published ones. Also, the CfA spectra for some of

the SNe that have been already published (SN 1994I, 1997ef, 2003jd, 2005bf, 2006aj, 2006jc, 2008D) are among the earliest spectra in the literature, which emphasizes the importance of the CfA SN follow-up program and its legacy value. We discuss the publication context of these SNe individually in Section 5.

### 4.1. SN Type Identification

Given our strength of having obtained multi-epoch spectra for a large number of SNe, as well as knowing the date of maximum light such that we can assign phases to the spectra, we now attempt to obtain secure SN type identifications for the SNe in our sample. SNe are classified based on the presence and absence of specific characteristic elements in their optical spectra at maximum light (Filippenko 1997; Matheson et al. 2001). For illustration, we plot in Figure 2 some of the main types of SNe at around maximum light. In the following,
<table><caption>**Table 2**

Stripped SN Sample: SN and Host Galaxy Information</caption><thead><tr><th>SN Name</th><th>SN Type<sup>a</sup></th><th>Disc. Ref</th><th>Disc. Type<sup>b</sup></th><th>Host Galaxy</th><th>SN Offsets<sup>c</sup><br>(")</th><th>c<sub>zhelio</sub><br>(km s<sup>-1</sup>)</th><th>JD of SN V-max (Ref<sup>d</sup>)</th></tr></thead><tbody><tr><td>1993J</td><td>Ib</td><td>IAUC 5731</td><td>T</td><td>M81</td><td>45W</td><td>160S</td><td>-140</td><td>2449095.0 (R94)</td></tr><tr><td>1994I</td><td>Ic</td><td>IAUC 5961</td><td>T</td><td>M51</td><td>14E</td><td>12S</td><td>461</td><td>2449451.4 (R96)</td></tr><tr><td>1995F</td><td>Ib</td><td>IAUC 6165</td><td>T</td><td>NGC 2726</td><td>2E</td><td>1S</td><td>1440</td><td>...</td></tr><tr><td>1995bb</td><td>Ib/c</td><td>IAUC 6271</td><td>Non-T</td><td>Anonymous</td><td>&lt;1.5</td><td>&lt;1.5</td><td>1610</td><td>...</td></tr><tr><td>1996cb</td><td>Iib</td><td>IAUC 6524</td><td>T</td><td>NGC 3510</td><td>20.9W</td><td>65.7N</td><td>800</td><td>2450454.4 (Q99)</td></tr><tr><td>1997X</td><td>Ib</td><td>IAUC 6552</td><td>T</td><td>NGC 4691</td><td>7.2E</td><td>0.3N</td><td>1072</td><td>...</td></tr><tr><td>1997dq</td><td>Ic</td><td>IAUC 6770</td><td>T</td><td>NGC 3810</td><td>43W</td><td>29N</td><td>993</td><td>&lt;2450754 (IAUC)</td></tr><tr><td>1997ef</td><td>Ic-bl</td><td>IAUC 6778</td><td>T</td><td>UGC 4107</td><td>10E</td><td>20S</td><td>3400</td><td>2450793.8 (I00)</td></tr><tr><td>1998dt</td><td>Iib</td><td>IAUC 7006</td><td>T</td><td>NGC 945</td><td>23.1W</td><td>39.5S</td><td>4580</td><td>2451068.5<sup>e</sup> (M01)</td></tr><tr><td>1998fa</td><td>Iib</td><td>IAUC 7073</td><td>T</td><td>UGC 3513</td><td>4.0W</td><td>3.8N</td><td>7460</td><td>2451180.5<sup>e</sup> (M01)</td></tr><tr><td>2000H</td><td>Iib</td><td>IAUC 7361</td><td>T</td><td>IC 454</td><td>19.6E</td><td>0.2S</td><td>3894</td><td>2451585.5 (B02)</td></tr><tr><td>2001ai</td><td>Ib</td><td>IAUC 7605</td><td>T</td><td>NGC 5278</td><td>2.0W</td><td>9.0S</td><td>7753</td><td>...</td></tr><tr><td>2001ej</td><td>Ib</td><td>IAUC 7719</td><td>T</td><td>UGC 3829</td><td>4W</td><td>7N</td><td>4135</td><td>&lt;2452188 (CfA)</td></tr><tr><td>2001gd</td><td>Iib</td><td>IAUC 7761</td><td>T</td><td>NGC 5033</td><td>52W</td><td>161N</td><td>1024</td><td>&lt;2452267 (CfA)</td></tr><tr><td>2002ap</td><td>Ic-bl</td><td>IAUC 7810</td><td>T</td><td>M74</td><td>258W</td><td>108S</td><td>659</td><td>2452313.4 (F03)</td></tr><tr><td>2002ji</td><td>Ib</td><td>IAUC 8025</td><td>T</td><td>NGC 3655</td><td>22.4W</td><td>14.0S</td><td>1624</td><td>...</td></tr><tr><td>2003jd</td><td>Ic-bl</td><td>IAUC 8232</td><td>T</td><td>MCG-01-59-21</td><td>8.3E</td><td>7.7S</td><td>5635</td><td>2452943.3 (V08, CfA)</td></tr><tr><td>2004aw</td><td>Ic</td><td>IAUC 8310</td><td>T</td><td>NGC 3997</td><td>27.7E</td><td>19.8S</td><td>4721</td><td>2453091.5 (T06, CfA)</td></tr><tr><td>2004ao</td><td>Ib</td><td>IAUC 8299</td><td>T</td><td>UGC 10862</td><td>6.3E</td><td>23.8S</td><td>1691</td><td>&lt;2453079 (CfA)</td></tr><tr><td>2004dk</td><td>Ib</td><td>IAUC 8377</td><td>T</td><td>NGC 6118</td><td>4.4E</td><td>43.5N</td><td>1573</td><td>2453238.0 (D11)</td></tr><tr><td>2004dn</td><td>Ic</td><td>IAUC 8381</td><td>T</td><td>UGC 2069</td><td>0.5W</td><td>26.1S</td><td>3777</td><td>2453230.5 (D11)</td></tr><tr><td>2004eu</td><td>Ic<sup>f</sup></td><td>IAUC 8446</td><td>Non-T</td><td>MCG+07-5-39</td><td>1.5E</td><td>2.7N</td><td>6486</td><td>...</td></tr><tr><td>2004fe</td><td>Ic</td><td>IAUC 8417</td><td>T</td><td>NGC 132</td><td>2.1W</td><td>7.9S</td><td>5361</td><td>2453319.3 (CfA)</td></tr><tr><td>2004ff</td><td>Iib</td><td>IAUC 8425</td><td>T</td><td>ESO552-G40</td><td>8.7E</td><td>12.3S</td><td>6664</td><td>2453316.0<sup>e</sup> (D11)</td></tr><tr><td>2004ge</td><td>Ic</td><td>IAUC 8425</td><td>T</td><td>UGC 3555</td><td>11.2W</td><td>2.8S</td><td>4644</td><td>2453341.5<sup>e</sup> (D11)</td></tr><tr><td>2004gk</td><td>Ic</td><td>IAUC 8443</td><td>T</td><td>IC 3311</td><td>6.2E</td><td>1.4S</td><td>-122</td><td>&lt;2453338 (CfA)</td></tr><tr><td>2004gq</td><td>Ib</td><td>IAUC 8452</td><td>T</td><td>NGC 1832</td><td>22.3E</td><td>22.4N</td><td>1859</td><td>2453361.0 (D11)</td></tr><tr><td>2004gt</td><td>Ic</td><td>IAUC 8454</td><td>T</td><td>NGC 4038</td><td>34W</td><td>10S</td><td>1642</td><td>2453362.0 (S)</td></tr><tr><td>2004gv</td><td>Ib</td><td>IAUC 8454</td><td>T</td><td>NGC 856</td><td>13.8W</td><td>4.0S</td><td>5974</td><td>2453366.2 (S)</td></tr><tr><td>2005U</td><td>Iib</td><td>IAUC 8473</td><td>T</td><td>Arp 299</td><td>3.7W</td><td>4.9S</td><td>3021</td><td>...</td></tr><tr><td>2005ar</td><td>Ib</td><td>IAUC 8493</td><td>T</td><td>CGCG011-033</td><td>4.6E</td><td>5.6N</td><td>7629</td><td>...</td></tr><tr><td>2005az</td><td>Ic</td><td>IAUC 8503</td><td>Non-T</td><td>NGC 4961</td><td>8W</td><td>5.5N</td><td>2622</td><td>2453473.9 (CfA)</td></tr><tr><td>2005bf</td><td>Ib</td><td>IAUC 8507</td><td>T</td><td>MCG+00-27-00</td><td>11.7E</td><td>32.6S</td><td>5430</td><td>2453499.0<sup>e</sup> (CfA)</td></tr><tr><td>2005da</td><td>Ic-bl</td><td>IAUC 8570</td><td>Non-T</td><td>UGC 11301</td><td>108.4W</td><td>34.8N</td><td>4496</td><td>...</td></tr><tr><td>2005hg</td><td>Ib</td><td>IAUC 8623</td><td>T</td><td>UGC 1394</td><td>3.7W</td><td>19.6S</td><td>6388</td><td>2453684.4 (CfA)</td></tr><tr><td>2005kf</td><td>Ic</td><td>IAUC 8630</td><td>Non-T</td><td>J074726.40+265532.4</td><td>0.8E</td><td>0.6S</td><td>4522</td><td>&lt;2453699 (CfA)</td></tr><tr><td>2005kl</td><td>Ic</td><td>CBET 300</td><td>T</td><td>NGC 4369</td><td>6W</td><td>4N</td><td>1045</td><td>2453703.7 (CfA)</td></tr><tr><td>2005la</td><td>Ib-n/Iib-n</td><td>IAUC 8639</td><td>Non-T</td><td>KUG1249+278</td><td>6W</td><td>6S</td><td>5570</td><td>2453694.5<sup>e</sup> (P08a)</td></tr><tr><td>2005mf</td><td>Ic</td><td>IAUC 8648</td><td>T</td><td>UGC 04798</td><td>5.9W</td><td>13.3N</td><td>8023</td><td>2453734.56 (CfA)</td></tr><tr><td>2005nb</td><td>Ic-bl</td><td>CBET 357</td><td>Non-T</td><td>UGC 7230</td><td>1.5W</td><td>5.N</td><td>7127</td><td>&lt;2453747.9 (CfA)</td></tr><tr><td>2006T</td><td>Iib</td><td>IAUC 8666</td><td>T</td><td>NGC 3054</td><td>22E</td><td>21S</td><td>2650</td><td>2453782.1 (CfA)</td></tr><tr><td>2006aj</td><td>Ic-bl</td><td>IAUC 8674</td><td>Non-T</td><td>J032139.68+165201.7</td><td>&lt;0.2</td><td>&lt;0.2</td><td>10052</td><td>2453794.7 (M06)</td></tr><tr><td>2006ck</td><td>Ic</td><td>IAUC 8713</td><td>T</td><td>UGC 08238</td><td>10.2W</td><td>3.0S</td><td>7312</td><td>&lt;2453879 (CfA)</td></tr><tr><td>2006el</td><td>Iib</td><td>IAUC 8741</td><td>T</td><td>UGC 12188</td><td>12.9E</td><td>18.2S</td><td>5150</td><td>2453984.7 (CfA, D11)</td></tr><tr><td>2006ep</td><td>Ib</td><td>IAUC 8744</td><td>T</td><td>NGC 214</td><td>43W</td><td>11.3S</td><td>4505</td><td>2453988.7 (CfA)</td></tr><tr><td>2006fo</td><td>Ib</td><td>IAUC 8750</td><td>Non-T</td><td>UGC 02019</td><td>6.0W</td><td>0.6N</td><td>6214</td><td>&lt;2454006 (CfA, D11)</td></tr><tr><td>2006jc</td><td>Ib-n</td><td>IAUC 8762</td><td>T</td><td>UGC 04904</td><td>11W</td><td>7S</td><td>1670</td><td>2454020.0 (F07)</td></tr><tr><td>2006lc</td><td>Ib</td><td>CBET 693</td><td>Non-T</td><td>NGC 7364</td><td>1.4E</td><td>10.0S</td><td>4863</td><td>&lt;2454045 (CfA)</td></tr><tr><td>2006ld</td><td>Ib</td><td>IAUC 8766</td><td>Non-T</td><td>UGC 348</td><td>1E</td><td>18S</td><td>4179</td><td>&lt;2454044 (CfA)</td></tr><tr><td>2006lv</td><td>Ib</td><td>IAUC 8771</td><td>T</td><td>UGC 6517</td><td>10E</td><td>12N</td><td>2570</td><td>&lt;2454043 (CfA)</td></tr><tr><td>2007C</td><td>Ib</td><td>CBET 798</td><td>T</td><td>NGC 4981</td><td>9E</td><td>22S</td><td>1767</td><td>2454115.9 (CfA)</td></tr><tr><td>2007D</td><td>Ic-bl</td><td>IAUC 8794</td><td>T</td><td>UGC 2653</td><td>4.9E</td><td>2.8S</td><td>6944</td><td>2454123.3 (CfA)</td></tr><tr><td>2007I</td><td>Ic-bl</td><td>IAUC 8798</td><td>Non-T</td><td>J115913.13-013616.1</td><td>0.8E</td><td>0.8S</td><td>6487</td><td>&lt;2454117 (CfA)</td></tr><tr><td>2007ag</td><td>Ib</td><td>CBET 868</td><td>T</td><td>UGC 5392</td><td>4.0E</td><td>15.5N</td><td>6017</td><td>2454170.3 (CfA)</td></tr><tr><td>2007bg</td><td>Ic-bl</td><td>IAUC 8834</td><td>Non-T</td><td>Anonymous</td><td>&lt;0.2</td><td>&lt;0.2</td><td>10370</td><td>2454206.7<sup>e</sup> (Y10)</td></tr><tr><td>2007ce</td><td>Ic-bl</td><td>IAUC 8843</td><td>Non-T</td><td>J121018.03+484331.8</td><td>&lt;0.5</td><td>&lt;0.5</td><td>13890</td><td>&lt;2454226 (CfA)</td></tr><tr><td>2007cl</td><td>Ic<sup>f</sup></td><td>IAUC 8851</td><td>T</td><td>NGC 6479</td><td>3.2W</td><td>8.2N</td><td>6650</td><td>2454250.9 (CfA)</td></tr><tr><td>2007gr</td><td>Ic</td><td>IAUC 8864</td><td>T</td><td>NGC 1058</td><td>24.8W</td><td>15.8N</td><td>518</td><td>2454338.5 (H09)</td></tr><tr><td>2007hb</td><td>Ic</td><td>CBET 1064</td><td>T</td><td>NGC 819</td><td>39.9W</td><td>3.9N</td><td>6669</td><td>&lt;2454363 (CfA)</td></tr><tr><td>2007iq</td><td>Ic/Ic-bl</td><td>CBET 1043</td><td>Non-T</td><td>UGC 3416</td><td>19W</td><td>5S</td><td>4003</td><td>&lt;2454363 (CfA)</td></tr><tr><td>2007kj</td><td>Ib</td><td>CBET 1092</td><td>T</td><td>NGC 7803</td><td>6W</td><td>10S</td><td>5366</td><td>2454382.5 (CfA)</td></tr><tr><td>2007ru</td><td>Ic-bl</td><td>CBET 1149</td><td>T</td><td>UGC 12381</td><td>4.4E</td><td>39.8S</td><td>4636</td><td>2454440.5 (CfA, S09)</td></tr><tr><td>2007rz</td><td>Ic</td><td>CBET 1158</td><td>T</td><td>NGC 1590</td><td>8.6E</td><td>0.1N</td><td>3897</td><td>&lt;2454454 (CfA)</td></tr><tr><td>2007uy</td><td>Ib-pec</td><td>IAUC 8908</td><td>T</td><td>NGC 2770</td><td>20.6E</td><td>15.5S</td><td>2100</td><td>2454481.8 (CfA)</td></tr><tr><td>2008D</td><td>Ib</td><td>CBET 1202</td><td>T</td><td>NGC 2770</td><td>38.3W</td><td>55.6N</td><td>2100</td><td>2454494.6 (S08, M09, CfA)</td></tr></tbody></table>
<table><caption>**Table 2**
(Continued)</caption><thead><tr><th rowspan="2">SN Name</th><th rowspan="2">SN Type<sup>a</sup></th><th rowspan="2">Disc. Ref</th><th rowspan="2">Disc. Type<sup>b</sup></th><th rowspan="2">Host Galaxy</th><th colspan="2">SN Offsets<sup>c</sup></th><th rowspan="2">cZhelio<br>(km s<sup>-1</sup>)</th><th rowspan="2">JD of SN V-max (Ref<sup>d</sup>)</th></tr><tr><th>(")</th><th>(")</th></tr></thead><tbody><tr><td>2008an</td><td>Ic</td><td>CBET 1268</td><td>T</td><td>UGC 10936</td><td>4.9E</td><td>9.8S</td><td>8124</td><td>&lt;2454524 (CfA)</td></tr><tr><td>2008aq</td><td>IIb</td><td>CBET 1271</td><td>T</td><td>MCG-02-33-20</td><td>15.2E</td><td>45.2S</td><td>2389</td><td>&lt;2454527 (CfA)</td></tr><tr><td>2008ax</td><td>IIb</td><td>CBET 1280</td><td>T</td><td>NGC 4490</td><td>53.1E</td><td>25.8S</td><td>630</td><td>2454549.5 (P08b;C11)</td></tr><tr><td>2008bo</td><td>IIb</td><td>CBET 1324</td><td>T</td><td>NGC 6643</td><td>31E</td><td>15N</td><td>1484</td><td>2454569.7 (CfA)</td></tr><tr><td>2008cw</td><td>IIb</td><td>CBET 1395</td><td>Non-T</td><td>J163238.16+412730.8</td><td>1E</td><td>2N</td><td>9724</td><td>&lt;2454622 (CfA)</td></tr><tr><td>2009er</td><td>Ib-pec</td><td>CBET 1811</td><td>T</td><td>J153930.49+242614.8</td><td>8W</td><td>9S</td><td>10500</td><td>2454982.6 (CfA)</td></tr><tr><td>2009iz</td><td>Ib</td><td>CBET 1947</td><td>T</td><td>UGC 2175</td><td>12.3W</td><td>14.5N</td><td>4257</td><td>2455109.4 (CfA)</td></tr><tr><td>2009jf</td><td>Ib</td><td>CBET 1952</td><td>T</td><td>NGC 7479</td><td>53.8W</td><td>36.5N</td><td>2443</td><td>2455122.8 (CfA, V11)</td></tr></tbody></table>

**Notes.**

<sup>a</sup> The SN types were re-determined by us via running SNID on all our SN spectra and are sometimes different from those listed in the IAU list of SNe (see Table 3). The SN Type “Ic-bl” stands for broad-lined SNe Ic. SN 2006jc is an SN Ib-n (“n” for narrow) that showed narrow He lines in emission. See the text for details.

<sup>b</sup> Discovery type: “T” = SN host galaxy was targeted; “Non-T” = SN host galaxy was not targeted.

<sup>c</sup> Offsets from the center of host galaxy as listed in discovery IAUCs or as derived by comparing SN and host-galaxy coordinates.

<sup>d</sup> References: R94 = Richmond et al. (1994). R96 = Richmond et al. (1996). Q99 = Qiu et al. (1999). I00 = Iwamoto et al. (2000). M01 = Matheson et al. (2001). CfA = CfA photometry presented in F. Bianco et al. (in preparation), where the date of V-band maximum is derived by fitting Monte Carlo realizations the V-band photometric data points near peak with a second-degree polynomial. For cases where literature data were available for the same SN, those data were also included in the fit. B02 = Branch et al. (2002). F03 = Foley et al. (2003). V08 = Valenti et al. (2008a). T06 = Taubenberger et al. (2006). D11 = Drout et al. (2011). S = M. D. Stritzinger et al. (in preparation). T05 = Tominaga et al. (2005). Note that the V-band light curve of SN 2005bf had two distinct maxima, and that we are using the first maximum as our reference. P08a = Pastorello et al. (2008). M06 = Modjaz et al. (2006). F07 = Foley et al. (2007). Y10 = Young et al. (2010). H09 = Hunter et al. (2009b). S09 = Sahu et al. (2009). S08 = Soderberg et al. (2008). M09 = Modjaz et al. (2009). P08b = Pastorello et al. (2008). C11 = Chornock et al. (2011). V11 = Valenti et al. (2011). Upper limits on date of maximum are indicated and are based on the CfA data.

<sup>e</sup> SNe with measured and listed maximum only in R band.

<sup>f</sup> We cannot exclude the potential possibility of the emergence of He I lines in these SNe Ic, since our spectra were taken either before or well after maximum light.

<sup>g</sup> SN 2005bf showed a pronounced double-peak light curve—here we are using the main, second, maximum.

we adopt the line identifications for stripped SNe of Branch et al. (2002); Elmhamsdi et al. (2006); Branch et al. (2006); Dessart et al. (2012), as well as those of Baron et al. (1999); Tominaga et al. (2005); Sauer et al. (2006); Valenti et al. (2008b); Tanaka et al. (2009) for the specific SNe that they published and are included in this work. We note that our line identifications are not definitive since we have not conducted spectral synthesis calculations; furthermore, we discuss below some of the features for which contradictory identification exists in the literature.

A number of crucial SN spectral features are heavily time dependent, making the identification based on a single spectrum, upon which the IAUC/CBETS are based, sometimes difficult. For example, for SNe IIb, the Balmer lines become weaker and the He I lines stronger over time; for SNe Ib, the He I lines usually emerge over time, due to non-thermal excitation by gamma rays from the <sup>56</sup>Ni decay chain (for early discussions about the distinction between SNe Ib and SNe Ic see Lucy 1991; Wheeler et al. 1994; Clocchiatti et al. 1996; Matheson et al. 2001, and more recently, e.g., Modjaz et al. 2009; Leloudas et al. 2011; Dessart et al. 2011; Hachinger et al. 2012; Dessart et al. 2012, and for SNe IIb, see Pastorello et al. 2008; Chornock et al. 2011; Arcavi et al. 2011; Milisavljevic et al. 2013). Given those caveats, some authors question the validity of sub-classifying SNe into SNe Ib and SNe Ic in the first place, and they tend to lump the SN subtypes together into the expression “SN Ibc.”

We find that high signal-to-noise spectra taken at many epochs with known phases, as we have for this sample, are tremendously useful for arriving at a secure classification. In our follow-up paper that includes quantitative line strength ratios and analysis (M. Modjaz et al., in preparation; Y. Liu et al., in preparation), we find that the SN types of SNe Ib and SNe Ic are useful

and separate categories for most of the SNe.<sup>12</sup> The distinction between spectra of SNe Ib and SNe Ic in the optical is most readily visible when considering not only the strong line of He I λ5876, but in addition at least two other He I lines, namely, He I λ6678 and He I λ7065. There are of course additional He I lines in the near-infrared (NIR) that ought to be used, such as He I λ10830 and He I λ20581 (see discussion in Taubenberger et al. 2006; Modjaz et al. 2009; Hunter et al. 2009a; Valenti et al. 2011; Hachinger et al. 2012; Dessart et al. 2012), but these lines are outside the spectral wavelength range of all of our spectra. Usually, authors concentrate on He I λ5876, since it is the strongest optical He I line, but it has the drawback that it overlaps with Na I D at a similar wavelength (Sauer et al. 2006; Valenti et al. 2008b and references therein). These three main optical He I lines are visible as early as 10 days before maximum light in some SNe Ib and fully developed in all SNe Ib by maximum light and at +15 and +30 days (Y. Liu et al., in preparation). The He I lines then disappear when the SNe start to transition into the nebular phase; especially, He I λ6678 and He I λ7065 become very weak beyond $t_{Vmax} > 50–70$ days. Nevertheless, any observed continuum between SN types that may correspond to a continuum of envelope masses or of <sup>56</sup>Ni mixing will be discussed in detail in our follow-up papers (M. Modjaz et al., in preparation; Y. Liu et al., in preparation), as

<footnote n="12"><sup>12</sup> There may be even two kinds of SNe Ib (Y. Liu et al., in preparation)—ones with strong He I lines, increasing in strength over time, which include SN 1998dt, 1999dn, 2004ao, 2004dk, 2004gq, 2005hg, 2006ep, 2008D, and ones with weak He I absorption lines, which disappear two weeks after maximum, such as SN 2009jf (Valenti et al. 2011) and 2002ji (as shown here), but where strong He I λ20581 is detected (Valenti et al. 2011; H. Marion et al. 2013, private communication), securely indicating presence of He.</footnote>
<table><caption>**Table 3**
New or Refined Classifications for Stripped SNe</caption><thead><tr><th>SN Name</th><th>Old SN Type</th><th>References for Old SN Type</th><th>New SN Type<sup>a</sup></th><th>References for New SN Type</th></tr></thead><tbody><tr><td>1990U<sup>b</sup></td><td>Ic</td><td>IAUC 5111, Matheson et al. (2001)</td><td>Ib</td><td>This work</td></tr><tr><td>1995F</td><td>Ic</td><td>IAUC 6138, SN catalogs</td><td>Ib</td><td>This work</td></tr><tr><td>1997X</td><td>Ic</td><td>IAUC 6554</td><td>Ib</td><td>This work</td></tr><tr><td>1997dq</td><td>Ib</td><td>IAUC 6770, SN catalogs</td><td>Ic</td><td>This work</td></tr><tr><td>1997dq</td><td>Ic-bl</td><td>Matheson et al. (2001); Mazzali et al. (2004)</td><td>Ic</td><td>This work</td></tr><tr><td>1997ef</td><td>Ib?</td><td>SN catalogs</td><td>Ic-bl</td><td>IAUC 6783, 6786; Iwamoto et al. (2000)</td></tr><tr><td>2001ai</td><td>Ic</td><td>IAUC 7605, SN catalogs</td><td>Ib</td><td>This work</td></tr><tr><td>2002ji</td><td>Ic</td><td>IAUC 8025</td><td>Ib</td><td>This work; M. Marion et al. (in preparation)</td></tr><tr><td>2004ff</td><td>Ic</td><td>IAUC 8428</td><td>IIb</td><td>Leloudas et al. (2011); This work</td></tr><tr><td>2005U</td><td>II</td><td>IAUC 8475</td><td>IIb</td><td>ATEL 431; This work</td></tr><tr><td>2005az</td><td>Ib</td><td>IAUC 8503</td><td>Ic</td><td>Kelly & Kirshner (2012); This work</td></tr><tr><td>2005bf</td><td>Ic/b</td><td>IAUC 8509, 8520, IAU SN list</td><td>Ib</td><td>IAUC 8521,8522; Tominaga et al. (2005); Folatelli et al. (2006)</td></tr><tr><td>2005eo</td><td>Ic</td><td>IAUC 8605, IAU SN list</td><td>Ia</td><td>This work</td></tr><tr><td>2006lc</td><td>Ib/c</td><td>Leloudas et al. (2011)</td><td>Ib</td><td>This work</td></tr><tr><td>2006el</td><td>Ib</td><td>SN catalog</td><td>IIb</td><td>CBET 614,626; This work</td></tr><tr><td>2006fo</td><td>Ic</td><td>IAUC 8750</td><td>Ib</td><td>Leloudas et al. (2011); This work</td></tr><tr><td>2007C</td><td>Ib/c</td><td>Leloudas et al. (2011)</td><td>Ib</td><td>This work</td></tr><tr><td>2007D<sup>c</sup></td><td>Ic</td><td>SN catalogs</td><td>Ic-bl</td><td>IAUC 8794; This work</td></tr><tr><td>2007bg<sup>c</sup></td><td>Ic</td><td>SN catalogs</td><td>Ic-bl</td><td>IAUC 8834; Young et al. (2010); This work</td></tr><tr><td>2007ce<sup>c</sup></td><td>Ic</td><td>SN catalogs</td><td>Ic-bl</td><td>IAUC 8843; This work</td></tr><tr><td>2007iq</td><td>Ic</td><td>CBET 1101</td><td>Ic/Ic-bl</td><td>This work</td></tr><tr><td>2007kj</td><td>Ib/c</td><td>Leloudas et al. (2011)</td><td>Ib</td><td>This work</td></tr><tr><td>2007rw</td><td>IIb</td><td>CBET 1155</td><td>II</td><td>Arora et al. (2011); This work</td></tr><tr><td>2007uy</td><td>Ib</td><td>CBET 1191</td><td>Ib-pec</td><td>This work; Roy et al. (2013)</td></tr><tr><td>2008aq</td><td>IIb?</td><td>IAU SN list</td><td>IIb</td><td>CBET 1271; This work</td></tr><tr><td>2008bo</td><td>IIb/Ib</td><td>SN catalogs</td><td>IIb</td><td>CBET 1325; This work</td></tr><tr><td>2009er</td><td>Ib</td><td>CBET 1817</td><td>Ib-pec</td><td>This work</td></tr><tr><td>2009iz</td><td>Ib/c</td><td>CBET 1947</td><td>Ib</td><td>This work</td></tr></tbody></table>

**Notes.**

<sup>a</sup> These are the SN types reported in Table 2.

<sup>b</sup> No new data of this SN are presented here, but a re-classification of the spectra from Matheson et al. (2001) via SNID were obtained with a larger template library.

<sup>c</sup> These SN were announced as SN Ic-bl in the IAUCs, but the SN catalogs list them as SN Ic. See the text for details.

well as the approach of quantifying the diversity within the spectral classification classes by constructing average spectra for different SN types and measuring line strength changes over time.

Because of the time-dependent nature of the emergence of the He I lines, there are three SNe Ic (2004eu, 2005kl, 2007cl) out of 19 SNe Ic in our sample, for which we cannot exclude the potential emergence of He lines during times for which we have no spectra (Table 2). For SN 2007cl, our only spectrum was taken 7 days before V-band maximum, and for SN 2005kl, we have spectra at $t_{Vmax} = -4, +70, \text{ and } +155$ days. While these spectra do not exhibit He I lines and are well matched by SN Ic spectra via SNID, we cannot exclude the possibility that they may have developed He I lines around maximum light and later, since we do not possess spectra at those phases. For 2004eu, we cannot exclude that its spectra were taken before maximum light, since we have no light-curve data. Thus, for the majority of the SNe Ic in our sample (namely, 16 out of 19 SNe Ic), we are confident that they are bona fide SNe Ic based on their optical spectra.

Nevertheless, even for “bona fide” SNe Ic, recent detailed radiative transfer calculations by Hachinger et al. (2012) and Dessart et al. (2012) suggest that the lack of obvious optical lines of He I in SN Ic spectra may not necessarily be evidence for helium deficiency in their ejecta. They suggest that if there is not sufficient mixing of $^{56}$Ni SNe may not exhibit optical He I lines, but may still have some He in their ejecta (less than 0.06–0.14 $M_{\odot}$, depending on mixing and the models). They

further suggest that the NIR lines of He I, especially the He I $\lambda$20581 line, may be better probes of He content than optical lines, though NIR spectra of SESNe are still rare. Further predictions of Dessart et al.’s model for the case that both SNe Ic and SNe Ib have the same progenitors, but are only distinguished by the amount of mixing of $^{56}$Ni, will be discussed in Y. Liu et al. (in preparation).

The question of the SN IIb versus SN Ib classification is more complex, since in some SN, very early-time spectra long before maximum light are needed to detect strong $H\alpha$ (Pastorello et al. 2008; Chornock et al. 2011; Arcavi et al. 2011; Milisavljevic et al. 2013), and these are rare. However, we do have a number of very early pre-maximum spectra of SN Ib, which do not show strong $H\alpha$. For SN 2004gq, 2005hg, 2008D, 2009iz (at $t_{Vmax} \approx -14$ to $-10$ days), and SN 2005bf, 2006ep, 2009jf, 2009er (at around $t_{Vmax} \approx -7$ days), a weak absorption line that could be identified with $H\alpha$ is much weaker than He I $\lambda$5876 (see Y. Liu et al., in preparation), such that we can exclude for those SN (i.e., for at least 8 SN out of 26 SN Ib in our sample) a scenario in which much hydrogen might have gone undetected (though for quantitative conclusions radiative transfer calculations are needed).

However, in all of those cases there is a weak absorption at 6100–6200 Å that could be identified with either high-velocity $H\alpha$ (Branch et al. 2002) or Si II (Tanaka et al. 2009).

In addition, the burgeoning field of environmental studies has uncovered systematic environmental trends for different subtypes of SNe, thus strongly suggesting that the empirical
<figure><img src="image_3.png" /><figcaption>**Figure 2.** Montage of the main types of stripped SN at around maximum light, along with a SN II and a SN Ia, for comparison, in order to illustrate the SN classification scheme. The main distinguishing spectral features are marked in color and annotated. For clarity, superimposed H II region lines are clipped. The SNe plotted are: SN 1999em (SN II; Leonard et al. 2001), SN 1996cb (SN IIb; This work), SN 2004gq (SN Ib; This work), SN 2004fe (SN Ic; This work), SN 2002ap (SN Ic-bl; This work; see also Gal-Yam et al. 2002; Mazzali et al. 2002; Foley et al. 2003), and SN 1994D (SN Ia; Patat et al. 1996; Blondin et al. 2012). How much diversity there is within the spectral classification classes and whether there is a continuum between types corresponding to a continuum of envelope masses will be the subject of our follow-up paper that includes quantitative comparisons (Y. Liu et al., in preparation). Note that some of the identifying spectral features are time-dependent (see the text).

*(A color version of this figure is available in the online journal.)*</figcaption></figure>

SN classification scheme appears physically insightful and motivated. Specifically, SNe Ib and SNe Ic appear to trace differently their respective host galaxy's distributions of Hα emission (Anderson & James 2008; Anderson et al. 2012) and the brightest blue regions (Kelly et al. 2008; Kelly & Kirshner 2012), with SNe Ic having higher correlations with both parameters than SNe Ib, and both more than SNe II. These observations have been interpreted by these and other authors to indicate higher progenitor masses for more stripped SNe, with SNe II at the lowest mass end and increasing upward toward SNe Ib and finally SNe Ic (see also Raskin et al. 2008 and Leloudas et al. 2010), even for the binary scenario (Smith et al. 2011). Kelly & Kirshner (2012) find that the environments of SNe IIb and SNe Ic-bl seem to be different from their respective cousins, SNe Ib and SNe Ic, despite the fact that the SN IIb/SN Ib distinction may be debated (Milisavljevic et al. 2013). Arcavi et al. (2010) find that the population of SNe harvested via the untargeted survey Palomar Transient Factory (PTF) is different in low-luminosity versus high-luminosity galaxies such that only SNe IIb, Ib, and Ic-bl are hosted by low-luminosity galaxies, but no SNe Ic. Furthermore, the field of directly measured metallicities is a rapidly developing research area (Modjaz et al. 2008a; Prieto et al. 2008; Anderson et al. 2010; Modjaz et al. 2011; Leloudas et al. 2011; Kelly & Kirshner 2012; Sanders et al. 2012a, see review in Modjaz 2011), since

metallicity is one of the most basic parameters expected to determine the lives and deaths of massive stars (Heger et al. 2003). While there are indications that the oxygen abundances measured directly at the explosion sites of SNe Ib and SNe Ic are statistically different, also including those from untargeted surveys (Modjaz et al. 2011; Kelly & Kirshner 2012, but see Leloudas et al. 2011; Sanders et al. 2012a), with in turn SN Ic-bl sites having lower oxygen abundances than those of their cousins SNe Ic (Modjaz et al. 2011; Sanders et al. 2012a), more data based on statistically larger data sets from the same untargeted survey are needed.

Thus, for the purposes of this paper, we take the SN identifications at face value and use the standard SN spectral identification tool SNID (Blondin & Tonry 2007) with its extensive library of template spectra (augmented with more recent spectra than available when published in 2007). SNID is based on cross-correlation of the target spectrum with a set of individual “template” spectra of a pre-determined SN type, and we apply it to all our spectra of each SN in our sample to determine the type of the SN, which we then report in Table 2.

## 4.2. New or Refined Classifications for Stripped SNe

To determine the subtypes of the SNe with SNID, we followed classification criteria similar to those of Blondin & Tonry (2007), namely, requiring that the SNID rlap<fnref n="13" /> value be at least 10 and the three best-matching spectra from SNID all be of the same subtype. In cases where we possessed multiple spectra per SN we performed SNID on the highest S/N spectra, but also checked that the ID was consistent for spectra of the same SN at different phases. We find that for a number of SNe in our sample, our ID either refines or differs from that reported in the IAU and CBET circulars<fnref n="14" /> and therefore from that in some of the catalogs (e.g., the continuously updated Asiago SN catalog, Barbon et al. 1989, or Sternberg Astronomical Institute Supernova Catalogue<fnref n="15" />), as well as from the literature. We present a summary of our SN type refinements in Table 3 and discuss cases below, where our ID differs from those presented in the literature.

For spectra of SN 1990U, as published by Matheson et al. (2001), we find better SNID matches to the spectra of SN Ib 2008D, also based on the detection of the He I lines in 1999U, and thus revise its classification to SN Ib, though we do not present any new spectra here.

While SN 1997dq was first typed as an SN Ib (IAUC 6770, and is still listed as a SN Ib in the Sternberg Astronomical Institute Supernova Catalogue), Matheson et al. (2001) suggested it to be an SN Ic-bl, arguing that its spectra look very similar to those of SN 1997ef, a bona fide SN Ic-bl. This line of argument that was later fleshed out by Mazzali et al. (2004), who suggested that both the sparse light curve and the spectra of Matheson et al. (2001) were both similar to those of SN 1997ef. Thus, many publications since then refer to this SN as an SN Ic-bl (e.g., Soderberg et al. 2006; Guetta & Della Valle 2007; Modjaz et al. 2008a; Taubenberger et al. 2009; Maurer et al. 2010). However, based on our seven spectra, including those that were taken earlier than by Matheson et al. (2001), used in conjunction with

<footnote n="13">¹³ In SNID, the rlap value is a measure of the strength of the correlation between the best-matching spectrum and the input spectrum.</footnote>

<footnote n="14">¹⁴ We note that the IAU SN list website (http://www.cbat.eps.harvard.edu/lists/Supernovae.html) might not always include the updated SN type announced in later IAUC/CBETs and usually lists broad-lined SNe Ic as SNe Ic.</footnote>

<footnote n="15">¹⁵ http://www.sai.msu.su/sn/sncat/</footnote>
SNID, we find better matches with after-maximum spectra of SNe Ic than with SNe Ic-bl and therefore assign the type “SN Ic” to this SN.

SN 1999ex, for which three optical and NIR spectra were obtained by Hamuy et al. (2002), is still being used as an important SN for comparison. Hamuy et al. (2002) compared SN 1999ex with SN 1984L, 1987M, and 1994I and concluded that it was similar to a SN Ic but with stronger He lines, or a SN Ib with “moderate strength” He I lines, leading them to classify it as “intermediate” SN Ib/c. However, subsequent papers, including those that perform spectral synthesis with SYNOW (Branch et al. 2002; Elmhamdi et al. 2006; Branch et al. 2006), conclude that the presence of He I is solid and identify the line at 6200 Å as Hα, making SN 1999ex a SN Ib (or even an SN Iib). While we do not present any new spectra of SN 1999ex, here we run SNID on the three spectra of Hamuy et al. (2002), which were taken at $\Delta t_{Vmax} = -5, 0, \text{ and } 9$ days. The spectra are matched well by spectra of other SN Ib (e.g., SN 2005bf, 2007Y) as well as a few SN Iib (e.g., SN 2000H, 2008ax, though SN Iib show a double-dip profile at Hα, while SN 1999ex only shows a single dip). Thus, for the remainder of this paper, we regard SN 1999ex as a SN Ib and do not call it an intermediate type SN Ib/c.

For SN 2002ji, we note that our re-classification from an SN Ic to an SN Ib is supported by the detection of He I λ20581 in its NIR spectra (H. Marion et al., in preparation).

For 2004dk, we note that based on an early spectrum, Harutyunyan et al. (2008) list it as an SN Ic in their paper (probably since the He lines had not fully developed two weeks before maximum light), while our spectra spanning $t_{Vmax} = +17-50$ days, as well as those mentioned in IAUC 8404 announcing the SN Ib classification, show the four optical He I lines.

For SN 2004gt, we do not see all optical lines of He I in our six photospheric spectra (spanning the phases $t_{Vmax} = 16-48$ days, where usually all He lines are apparent in SNe Ib) and therefore refine the classification from “SN Ib/c” to “SN Ic.”

In addition, our multi-epoch spectra support the reclassification of two SNe as proposed by Leloudas et al. (2011): SN 2006fo from an SN Ic to an SN Ib, as well as the reclassification of SN 2004ff from SN Ic to SN Iib, based on our pre-maximum spectrum, which shows strong Hα at $V_{Rmax} = -4$ days. However, for three SNe, our IDs differ from those suggested in Leloudas et al. (2011), namely, their reclassification of SN 2006lc, 2007C, and 2007kj from SN Ib to SN Ib/c. Their reclassifications are mostly based on the fact that Leloudas et al. found good matches with spectra of SN 1999ex (G. Leloudas 2013, private communication), which they call an SN Ib/c following Hamuy et al. (2002). For all three of these SNe, our own multi-epoch spectra clearly show the multiple optical lines of He I (He I λ4471, He I λ5876, He I λ6678 and He I λ7065), and the spectra are fit by SNID with a number of SN Ib (SN 1999dn, 1999ex, 2005hg). Indeed, when obtaining the spectra of SN 2007C and 2007kj from Leloudas et al. (2011) and running SNID with our updated set of templates on them, we find in both cases very good matches with clear SN Ib (SN 2005bf, 2008D) besides SN 1999ex, which we find to be a SN Ib (see above). Thus, we classify these SN as SN Ib, in line with the classification based on our own spectra.

Furthermore, our spectra support the reclassification of SN 2005az in Kelly & Kirshner (2012) from an SN Ib to an SN Ic based on our 24 spectra (that range in phase from $t_{Vmax} = -8$ to +87 days), since not all optical He I lines are visible in the spectra that usually are visible in normal SNe Ib and since SNID

<figure><img src="image_4.png" /><figcaption>**Figure 3.** Time evolution of the CfA Spectra of SN Ib-pec 2007uy, as in Figure 1.</figcaption></figure>

finds better matches with SNe Ic (e.g., SN Ic 2004aw, 2007gr) than with SNe Ib. The strongest line at ~5800 Å could be either due to He I λ5876 for a bona fide SN Ib (if all the other optical He lines were also visible), or due to Na I D, or due to a blend (Baron et al. 1999; Sauer et al. 2006; Valenti et al. 2008b).

For SN 2005eo, SNID finds many very good matches with normal SNe Ia at two to three weeks after maximum, and a few, but worse, matches with young SNe Ic (around maximum). Furthermore, the maximum observed in the R-band light curve of SN 2005eo in Drout et al. (2011) is consistent with the second R-band maximum (or hump) observed in the light curves of SNe Ia (as shown in F. Bianco et al., in preparation), making the phases derived from the spectra based on SNID SN Ia template fitting be fully consistent with the spectral phases read off directly from the light curve. Thus, we reclassify this SN from an SN Ic to an SN Ia, remove it from our stripped SN sample, and are reminded that spectra of young SNe Ic can look similar to those of older SNe Ia (e.g., Blondin & Tonry 2007).

We note that while SN 2007D, 2007bg, and 2007ce were announced as SNe Ic-bl, as confirmed by our spectra and by Young et al. (2010) for SN 2007bg, they are simply listed as SNe Ic on the IAU SN website and in the various catalogs.

While SN 2007iq was classified as an SN Ic based on a spectrum taken on 2007 October 15 (CBET 1101), our CfA spectrum was taken 1 month earlier (on 2007 September 14). Running SNID on our spectrum yields good matches with spectra of both old SNe Ic and old SNe Ic-bl. Thus, we conclude that a unique identification of this SN based on spectra presumably taken well after maximum light is not secure and reclassify this SN from an SN Ic to an SN Ic/Ic-bl.

For the four spectra of SN 2007rw, SNID finds better matches with SN II spectra (both SN IIP and SN IIL) than with SN 1993J, an SN Iib, and we see strong Hα in its nebular phase spectra. Thus, we revise its SN type from Iib to II, in agreement with Arora et al. 2011, and remove it from our stripped SN sample.

We present our spectral time series of SN 2007uy in Figure 3. While SN 2007uy was initially classified as an SN Ib by us
<figure><img src="image_5.png" /><figcaption>**Figure 4.** Comparison of spectra of SN 2007uy with those of other SN Ib at maximum light and at $t_{Vmax} = 2$ weeks. We show the spectra of SN 2004gq (in blue), a classical SN Ib, at 2 epochs closest to those of SN 2007uy, and color code the He lines with orange to guide the eye. We also show spectra of SN 2009er (from this work) which has a very similar spectrum to SN 2007uy, at 2 weeks after maximum. Data shown for SN 1999dn include those from Benetti et al. (2011).</figcaption></figure>

(A color version of this figure is available in the online journal.)

based on our earliest spectrum at $t_{Vmax} = -13$ days (Blondin & Calkins 2008), its subsequent evolution is unlike that of any observed SN Ib, except one. The spectral feature that could be identified as He I λ5876 is not as strong as usually seen in SN Ib, and the absorption line at ~6100 Å is very strong, much stronger than observed in both SNe Ib and SNe Ic. Indeed, SNID finds many matches with SNe Ia (where the line at ~6100 Å is consistent with the strength of Si II λ6355 in SNe Ia) and only few matches with SNe Ib at later epochs (around and within two weeks after maximum, including SN 2009er; see below). Nevertheless, there are reasons to believe that SN 2007uy is an SN Ib, albeit a very peculiar one, as we discuss below. In any case, SN 2007uy is an H-stripped core-collapse object, since its nebular spectra unambiguously show the presence of intermediate-mass elements (oxygen, calcium), and no H, which is characteristic of stripped core-collapse SNe, with line profiles consistent with other SNe Ib (see also Milisavljevic et al. 2010; Roy et al. 2013). Its nebular spectra do not show the iron blends that are characteristic of SN Ia nebular spectra.

In Figure 4, we plot spectra of SN 2007uy at maximum and at two weeks after, i.e., phases were the helium lines are well developed in normal SNe Ib, along with spectra of SN Ib 2004gq, a normal SN Ib, and SN 2009er, at the same phases. The normal SN Ib 2004gq clearly shows the set of three helium lines, while SN 2007uy shows weak absorption at wavelengths consistent with those three helium lines at somewhat higher velocities than observed in other SNe Ib (by ~1000–2000 km s⁻¹). For the spectrum at $t_{Vmax} = 13$ days, if the lines at ~5500 Å and 6100 Å

<figure><img src="image_6.png" /><figcaption>**Figure 5.** Time evolution of the CfA Spectra of SN Ib-pec 2009er, as in Figure 1.</figcaption></figure>

are due to He I λ5876 and He I λ6678 (respectively), they would have to be blended with other lines to explain their observed large widths (15,000 km s⁻¹ and 30,000 km s⁻¹, respectively) in SN 2007uy. Indeed, the strong, unidentified line that was at 6000–6100 Å between $t_{Vmax} = -6$ and −3 days may have merged with He I λ6678 on $t_{Vmax} = 13$ days to give rise to the very wide absorption line; unfortunately, we have no data during that observing gap to witness and test this development. We have found one other SN Ib with similar spectra at two weeks after maximum, namely, SN 2009er, which appears to be a case of an in-between object between normal SNe Ib (such as SN2004gq and SN1999dn, the latter having a notable, but less deep, absorption at 6200–6300 Å) and the extreme case of SN 2007uy. SN 2009er shows on $t_{Vmax} = 15$ days the same broad line at ~6100 Å as SN 2007uy (which is seen clearly in Figures 5 and 4), but in the blue part of the spectrum, SN 2009er has a less smeared-out spectrum, i.e., the lines are less blended than in SN 2007uy; for example, the blue edge of the line that may be identified with He I λ5876 is more well defined in SN 2009er than it is in SN 2007uy, leading to many more matches with normal SNe Ib via SNID for SN 2009er than for SN 2007uy. While it is outside the scope of this paper to conclusively identify the deep feature at 6100 Å, we note that Benetti et al. (2011) have an extensive discussion of the similar, but much weaker and narrow, feature in SN 1999dn, which has been attributed by different authors using different spectral synthesis codes to either Hα (Branch et al. 2002; James & Baron 2010; Benetti et al. 2011), CII (Deng et al. 2000), or a blend of Si II λ6355 and Fe II lines (Ketchum et al. 2008). Lastly, in SN2007uy the noted strong absorption line at ~6100 Å is not similar to the strong Hα line seen in SN IIb, as SNID does not get any good matches with SNIIb for SN 2007uy and thus SN2007uy cannot be called an SN IIb. When SN 2007uy was re-observed on $t_{Vmax} = 46$ days and after, that line is no longer detected in the spectra.

Thus, we denote SN 2007uy as an “SN Ib-pec,” i.e., a peculiar SN Ib. Recently, Roy et al. (2013) presented a spectral series of
<figure><img src="image_7.png" /><figcaption>**Figure 6.** Distribution of redshifts of the 73 SN in the CfA stripped SN sample, including published ones, with a mean redshift value of $0.0141 \pm 0.0097$. The redshift-distribution of SN with phase information is overplotted in gray. The SN at negative recession velocities are the nearby SN Iib 1993J (at $-140 \text{ km s}^{-1}$) and Ic 2004gk (at $-122 \text{ km s}^{-1}$), while the highest redshift ones consist of three broad-lined SN Ic (XRF 060218/SN 2006aj at $z = 0.03353$, and SN Ic-bl 2007bg at $z = 0.0346$ and 2007ce at $z = 0.04633$) and one SN Ib (SN 2009er at $z = 0.0350$).</figcaption></figure>

this SN (including two of our CfA spectra<fnref n="16" />). In large part their observations are consistent with ours (except when they refer to the fleeting feature, which is fleeting because it is a feature in the spectrum of SN 2008D), and they attribute its peculiar spectral behavior to a very aspherical explosion in this SESN.

The pre-maximum spectra of SN 2009er are characterized by very broad lines (see Figure 5), similar to SN Ib 2008D, which showed SN Ic-bl like spectra after explosion, i.e., 15 to 10 days before maximum, but developed narrow-line spectra with helium by maximum light (Mazzali et al. 2008; Modjaz et al. 2009; Malesani et al. 2009). Our two spectra at $\Delta t_{Vmax} = +15$ and $+16$ days are well matched by those of a number of normal SNe Ib (1990I, 1998dt, 2004gq) at similar phases, but SN 2009er exhibits weaker He I line strengths and a stronger absorption feature at 6200–6400 Å than other SNe Ib, and similar to SN 2007uy (see above and Figure 4). Thus, we call SN 2009er an SN Ib-pec and caution that its early-time spectra and evolution are unusual, as well as its light-curve shape and luminosity (H. Marion 2013, private communication; F. B. Bianco et al., in preparation).

In conclusion, our sample consists of 13 SNe Iib, 26 SNe Ib (where we have included SN Ib-pec 2007uy and 2009er), 19 SNe Ic, 11 SNe Ic-bl, and 4 for SNe either for which we could not determine an unique type based on our spectra (SN 1995bb, 2007iq) or which belong to an interacting SN type without much hydrogen (SN 2005la, 2006jc).

### 4.3. SN Sample Properties: Redshifts and Phases

Figure 6 presents the redshift distribution of the CfA SESN sample, including published ones, which has a mean redshift of $0.0141 \pm 0.0097$. The SNe at negative recession velocities are the nearby SN Iib 1993J (at $-140 \text{ km s}^{-1}$) and SN Ic 2004gk (at $-122 \text{ km s}^{-1}$), while the ones at the highest redshifts consist of one SN Ib (SN 2009er at $z = 0.0350$) and three broad-lined SNe Ic, namely, XRF 060218/SN 2006aj at $z = 0.03353$, SN Ic-bl 2007bg at $z = 0.0346$, and SN 2007ce at $z = 0.04633$.

<figure><img src="image_8.png" /><figcaption>**Figure 7.** Distribution of number of spectra per SN for all 73 SN in the CfA stripped SN sample. Note that while the maximum number of spectra per SN lies at a value of 2 spectra, there is a large tail of SN with many spectra, such that the average number of spectra per SN for all SN in our sample is 9 and for SN with observed maximum 12 (see the text for more details).</figcaption></figure>

With the full set of 645 spectra for 73 SNe in our sample (see Figure 7 for the distribution), the average number of spectra per SN is 9. For the 44 SNe with observed light-curve maximum, we possess a total of 508 spectra, which corresponds to an average of 12 spectra per SN with measured date of maximum light. Figure 8 shows the distribution of the phases of the spectra of 44 SNe in the CfA stripped SN sample, including those of already-published ones. The spectra counted here are at a phase earlier than 30 days after maximum, and we plot them also as a function of SN type. Note the large number of pre-maximum spectra for all types, especially for SNe Ib and SNe Ic, while SNe Iib and SNe Ic-bl have the earliest spectra, taken as early as 20 days before V-band maximum. We also obtained a number of spectra that are at later spectral phases: for spectra with $30 < t_{Vmax} < 60$ days, there are ~4 SN spectra for each day (combining all types), with a long tail of SN spectra before and during the nebular phase (not shown). Furthermore, in Figure 9, we show the phase of the first spectrum that we took of the SN. Note that the rarer subtypes in our sample (SN Iib and SN Ic-bl) have had their first spectrum taken at earlier phases than those of their more common SN cousins (SN Ib and SN Ic, respectively). We are not using the date of explosion as our reference point for assigning ages to the spectra, since the explosion dates are unconstrained for most of the SNe in our sample, except for a few special SNe (e.g., GRB-SNe, SN 2008D, and nearby SNe).

## 5. NOTES ON INDIVIDUAL SNe WITH PUBLISHED EARLY-TIME SPECTRA

Here we list the specific SNe for which early-time spectra have been published in the literature (either based on our work or those of others) and relate those published data to our data set presented here. We also note any published late-time spectra, but do not discuss further the nebular spectra SN samples by Maeda et al. (2008); Modjaz et al. (2008b); Taubenberger et al. (2009); Milisavljevic et al. (2010).

SN 1993J. This SN Iib in M81 was a well-observed SN (e.g., Filippenko et al. 1993; Trammell et al. 1993; Wheeler et al. 1993; van Dyk et al. 1994; Richmond et al. 1994; Barbon et al. 1995; Matheson et al. 2000a, 2000b; Maund et al. 2004), and here we present nine very late-time ($t_{Vmax} = 590–2958$ days) CfA spectra on this SN, some of which were included in Milisavljevic et al. (2012).

<footnote n="16">¹⁶ We note that the CfA spectrum taken on 2008 April 1 of SN 2007uy as published in Milisavljevic et al. (2010; labeled “92 days [after discovery]”) and used in Roy et al. (2013; labeled “+96 days [after explosion]”) is accidentally that of SN 2008D, observed at the same time in the same galaxy, and not of SN 2007uy. Here we present the correct CfA spectrum of SN 2007uy (labeled as “$t_{Vmax} = 76$ days”) in Figure 3.</footnote>
<figure><img src="image_9.png" /></figure>

**Figure 8.** Distribution of the spectral phases of the 44 SN in the CfA Stripped SN sample with measured V-max dates, including published ones. The spectral phases earlier than 30 days after maximum are shown, as well as the distribution for different stripped SN sub-types. In this plot, we include SN Ib-pec 2007uy and 2009er among SN Ib while SN Ib-n 2006jc and SN Ib-n/IIb-n 2005la are not shown among the subtypes, but included in all SN. The number of SN corresponding to a given type is indicated in the legend. Note the large number of pre-maximum spectra for all types, especially for SN IIb and SN Ic-bl.

(A color version of this figure is available in the online journal.)

SN 1994I. A number of the spectra of this SN Ic presented here have been published and analyzed by Millard et al. (1999), but they were re-reduced to be consistent with the rest of this spectroscopic sample. Since SN 1994I was a bright SN in the nearby M51, it was well observed by a number of other groups over many wavelength regimes (e.g., Filippenko et al. 1995; Richmond et al. 1996; Immler et al. 1998), leading to its designation as the “proto-typical” or “standard” SN Ic.

SN 1996cb. This SN IIb was well observed by Qiu et al. (1999), who presented BVR light curves and 19 spectra that span −18 days < $t_{Vmax}$ < 154 days. M01 present spectra at later times. Here we present a total of 22 spectra, which start two days earlier than those of Qiu et al. (1999) and are among the earliest spectra of SNe IIb hitherto taken (i.e., 20 days before maximum light), as well as fully nebular spectra taken one year after the explosion.

SN 1997dq. Matheson et al. (2001) presented five spectra of this SN Ic. Here we present seven spectra of SN 1997dq, which span 7 weeks, among which our first spectrum was taken one day earlier than the earliest spectrum presented in Matheson et al. (2001).

SN 1997ef. Some of our early spectra presented here have been published and analyzed by Iwamoto et al. (2000), but the spectra presented herein were re-reduced to be consistent with the rest of this spectroscopic sample. These data constitute the most complete spectroscopic data set for this SN that was among the first to be typed as a broad-lined SN Ic. Nebular spectra of this SN have been presented in Matheson et al. (2001) and in Mazzali et al. (2004).

SN 1997X. While Munari et al. (1998) presented two early-time spectra of this SN Ib, here we present six early-time spectra that start three days before those in Munari et al.

<figure><img src="image_10.png" /></figure>

**Figure 9.** Similar to Figure 8, but now for distribution of phases of the first spectrum. Note the large number of pre-maximum spectra for all types, especially for SN IIb and SN Ic-bl.

(A color version of this figure is available in the online journal.)

SN 1998dt. While Matheson et al. (2001) published two spectra of this SN Ib taken with Lick 3m+KAST, which were at $t_{Rmax}$ = +8 and +33 days, here we present seven new CfA spectra that are at earlier phases between $t_{Rmax}$ = 0 and +17 days.

SN 1998fa. Four spectra of this SN IIb were presented in Matheson et al. (2001) (starting 1999 January 10 till 1999 February 12), as well as an R-band light curve. Here we present three spectra, which start two weeks before those presented in Matheson et al.

SN 2000H. While Branch et al. (2002) published spectra based on observations collected at the European Southern Observatory and at the Asiago Observatory that started after maximum light, here we present seven new CfA spectra of this SN IIb that range in earlier phases from $t_{Vmax}$ = −2 to +17 days. Note that the date of maximum light is uncertain: while Branch et al. (2002) favor 2000 February 11 as the date of V-band max from unpublished ESO photometry, the Asiago Catalogue lists 2000 February 2 as the date of max. Here we adopt the later date consistent with Branch et al., since otherwise the spectral evolution of SN 2000H would be very different from that of the rest of SNe IIb, as shown in our companion paper (Y. Liu et al., in preparation).

SN 2001gd. This SN IIb emitted strong radio emission with modulations (e.g., Stockdale et al. 2003; Ryder et al. 2004; see Stockdale et al. 2007 and references therein), as well as strong X-ray emission (Immler & Kuntz 2005). However, since the date of maximum is not measured, the authors use spectral similarity with SN 1993J to estimate its explosion date, which is highly uncertain. Here we present two spectra of this SN that show its transformation into the nebular phase.

SN 2002ap. This SN Ic-bl in M74 was well observed (e.g., Gal-Yam et al. 2002; Leonard et al. 2002; Mazzali et al. 2002; Berger et al. 2002; Foley et al. 2003), and here we present 15 new unpublished CfA spectra for this SN.

SN 2003jd. A number of the 24 CfA FLWO spectra presented here have been published and analyzed by Valenti et al. (2008a), but are shown here for completeness. We note that Mazzali et al. (2005) published their two late-time spectra.
SN 2004aw. While Taubenberger et al. (2006) published their own spectra of this SN Ic, here we present 15 new CfA spectra, among which the earliest one at $t_{Vmax} = -6$ days was taken three days earlier than that in Taubenberger et al.

SN 2004dk. While Harutyunyan et al. (2008) presented their spectrum taken two weeks before V-band maximum light of this SN Ib, here we present three CfA spectra that span $t_{Vmax} = +17-50$ days.

SN 2004dn. While Harutyunyan et al. (2008) presented their spectrum taken one week before V-band maximum light of this SN Ic/Ic-bl, here we present four CfA spectra that were taken one month later and that span $t_{Vmax} = 30-55$ days.

SN 2004fe. While Harutyunyan et al. (2008) presented their spectrum taken one week before V-band maximum light of this SN Ic, here we present 10 CfA spectra that were taken at the same time and later, spanning $t_{Vmax} = -6$ to +242 days.

SN 2005la. While Pastorello et al. (2008) published their own four spectra of this peculiar and transitional SN Ib-n/IIn, starting 17 days after R-band max, here we present five CfA spectra that were taken at earlier phases, starting at 14 days after R-band maximum.

SN 2005bf. A number of the CfA spectra presented here have been published and analyzed by Tominaga et al. (2005), but are presented herein with details and for completeness. SN 2005bf had peculiar late-time spectra (Maeda et al. 2007; Modjaz et al. 2008b) and a pronounced and unique double-peaked light curve (Tominaga et al. 2005; Folatelli et al. 2006). Here we are using the second, main peak as the main peak for V-band maximum, since the time evolution of its spectral features is more in line with those of other SNe Ib than otherwise (except the increasing He I velocities over time; Tominaga et al. 2005; Y. Liu et al., in preparation).

SN 2006aj. SN 2006aj/GRB 060218 was a well-observed SN Ic-bl/GRB (Campana et al. 2006; Modjaz et al. 2006; Pian et al. 2006; Sollerman et al. 2006; Mirabal et al. 2006; Cobb et al. 2006; Kocevski et al. 2007; Mazzali et al. 2007; Taubenberger et al. 2009). Our CfA spectra were presented in Modjaz et al. (2006) and in Modjaz et al. (2008b) and are included here for completeness.

SN 2006lc. While Östman et al. (2011) presented their spectrum taken on 2006 December 13 of this SN Ib, here we present four CfA spectra that were taken two months prior and that span 2006 October 26 to 2006 October 31.

SN 2006fo. While Östman et al. (2011) presented their three spectra of this SN Ib, here we present three CfA spectra that range from $t_{Vmax} = -3$ days to +75 days.

SN 2006jc. SN 2006jc was a well-observed SN since it was a peculiar SN Ib with He lines in emission, indicating interaction between the SN ejecta and a dense helium shell (e.g., Foley et al. 2007; Pastorello et al. 2007; Immler et al. 2007) and early onset of dust production (e.g., Smith et al. 2008). Here we present 19 unpublished CfA spectra that are between $t_{Rmax} = +6$ and +66 days.

SN 2007bg. While Young et al. (2010) presented their four spectra of this SN Ic-bl starting at $t_{Vmax} = +5$ days, here we present one spectrum that was taken at $t_{Vmax} = +4$ days.

SN 2007gr. SN 2007gr was a well-observed SN Ic (e.g., Valenti et al. 2008a; Hunter et al. 2009b; Tanaka et al. 2008) in the nearby NGC 1058, with which progenitor detection was attempted (Crockett et al. 2008b). While Paragi et al. (2010) claimed it to be an engine-driven explosion without an observed GRB, Soderberg et al. (2010) argue based on their radio light curves and X-ray data that it may well be an ordinary SN Ic

explosion. Here we present 17 new CfA spectra that range from $t_{Vmax} = +7$ days to +69 days.

SN 2007ru. Sahu et al. (2009) presented their own nine spectra of this SN Ic-bl starting at $t_{Vmax} = -2$ days, and here we present three spectra that start at $t_{Vmax} = -2$ day.

SN 2007rz. Our CfA late-time spectrum of SN Ic 2007rz was presented in Milisavljevic et al. (2010), and here we also present one early-time spectrum. The late-time spectra are contaminated by host galaxy light, especially on the blue end.

SN 2007uy. While one late-time CfA MMT spectrum of this SN was presented and analyzed in Milisavljevic et al. (2010),<fnref n="17" /> we present here the additional nine early-time spectra of this SN, which range from $t_{Vmax} = -13$ days to +55 days. As discussed in detail in Section 4.1, while He lines appear to be present in its spectra and its nebular spectra show line profiles similar to other SESNe, its photospheric evolution is unlike that of any other SN Ib. Thus, we designate it as SN Ib-pec. While Roy et al. (2013) presented their five spectra of this SN, our spectral series starts 10 days earlier than the one in Roy et al. (2013).

SN 2008D. SN 2008D and its X-ray outburst 080109 have been well studied (e.g., Soderberg et al. 2008; Mazzali et al. 2008; Modjaz et al. 2009; Malesani et al. 2009; Maund et al. 2009; Tanaka et al. 2009). Nine out of the 10 FLWO and MMT spectra, which are among the earliest for an SN Ib (starting at $t_{Vmax} = -16$ days), were already presented in Modjaz et al. (2009), along with spectra from other institutions and telescopes, but are included here for completeness.

SN 2008ax. SN 2008ax was a very well observed SN Iib (e.g., Pastorello et al. 2008; Roming et al. 2009; Taubenberger et al. 2011; Chornock et al. 2011) in the nearby (9.6 Mpc) NGC 4490, with a potential progenitor detection (Crockett et al. 2008a). Here we present 25 CfA spectra that start as early as 20 days before V-band maximum light, i.e., only 0.8 days after the estimated shock breakout on 2008 March 3.32 (Pastorello et al. 2008; Chornock et al. 2011), and up to 1.5 days earlier than the earliest published spectra so far (Pastorello et al. 2008; Chornock et al. 2011). Our late-time spectra were included in and presented by Milisavljevic et al. (2010).

SN 2008bo. While our two MMT late-time spectra of this SN Iib were presented and analyzed in Milisavljevic et al. (2010), we present here our additional 10 early-time spectra, including a number of pre-maximum spectra.

SN 2009jf. While Valenti et al. (2011) and Sahu et al. (2009) presented very early-time spectra for this nearby SN Ib, here we present 14 new CfA spectra ranging from $t_{Vmax} = -7$ days to +393 days.

## 6. CONCLUSIONS

While the importance of studying stripped SNe and of understanding their connection to GRBs has been long acknowledged, their study has been mostly confined to individual SNe. Here we present the largest spectroscopic data set of stripped core-collapse SNe to date, which comprises 645 densely time-sampled and homogeneous optical low-dispersion spectra of 73 SNe Iib, Ib, Ic, and Ic-bl, obtained through the CfA Supernova Program between 1994 and 2009. For comparison, the hitherto largest publication of early-time spectra of stripped-envelope core-collapse SNe by Matheson et al. (2001) consisted

<footnote n="17">¹⁷ We note that the CfA spectrum of SN 2007uy shown in Milisavljevic et al. (2010; labeled “92 days [after discovery]”) and used in Roy et al. (2013; labeled “+96 days [after explosion]”) is accidentally that of SN 2008D and not of SN 2007uy.</footnote>
of 84 spectra of 29 SNe, while the SUSPECT<fnref n="18" /> database con-
tains 292 spectra of 37 SESNe (including a number of SNe
from our sample, as well as those from Matheson et al. 2001).
The recently established WISE REP database (Yaron & Gal-
Yam 2012)<fnref n="19" /> incorporates some of the SUSPECT database
and contains additional spectra, though it is harder to esti-
mate their total number of SESN spectra due to instances of
double-counting. Our sample spans a large range in relatively
low redshift ((z) = 0.0141 ± 0.0097) and includes spectra as
early as −30 days before and as late as +611 days after V-band
maximum (for SN 1993J up to thousands of days). Most of the
SNe in our sample have spectra before maximum light (36 out
of the 44 SNe with maximum light measured), and the mean
number of spectra per SN is 9 for all SNe and 12 for SNe with
measured maximum light. While not representative of SN rates,
our sample consists of 13 SNe IiB, 26 SNe Ib (where we have
included SN Ib-pec 2007uy and 2009er), 19 SNe Ic, 11 SNe
Ic-bl, and 4 SNe either for which we could not determine an
unique type based on our spectra (SN 1995bb, 2007iq) or which
belong to an interacting SN type, probably without much hydro-
gen (SN 2005la, 2006jc). The 615 spectra of stripped SNe taken
with the FAST spectrograph at the FLWO 1.5 m telescope were
reduced in a consistent manner, making this a crucial sample for
detailed spectroscopic studies of SESNe and their connection
to SNe-GRBs (see our companion paper, M. Modjaz et al., in
preparation), as well as for comparisons to theoretical models
and radiative transfer codes (e.g., Yoon et al. 2010; Dessart et
al. 2011; Hachinger et al. 2012; Dessart et al. 2012) and for inclu-
sions in SN identification schemes, both spectroscopic (e.g.,
Howell et al. 2005; Blondin & Tonry 2007; Harutyunyan et
2008) and photometric ones that need to include the spectrally
derived k-corrections (e.g., Bernstein et al. 2011).

We are grateful for the efforts of the observers at the 1.5 m
FLWO, 6.5 m MMT, and Magellan telescopes (listed in Table 1),
who obtained some of the data presented here, as well as
the staffs of the F. L. Whipple, MMT, and Las Campanas
Observatories, who assisted with and supported the CfA SN
long-term projects. We thank Dan Green at the IAU CBAT
for the dissemination of SN discoveries and information, and
the passionate supernova searchers, both professionals and
amateurs. A specific person to whom M.M. is deeply grateful is
Weidong Li, who was instrumental to the prolific nearby Lick
Observatory SN Search over the past 14 yr, as well as a dedicated
and cheerful SN astronomer. We would also like to thank Alex
Filippenko, Ryan Foley, Nathan Smith, Craig Wheeler, Rob
Fesen, Avishay Gal-Yam, Claes Fransson, Luc Dessart, Shri
Kulkarni, and Alicia Soderberg for discussions. Thanks to Max
Stritizinger on behalf of the Carnegie Supernova Project for
providing us with the dates of maximum for SN 2004gt and
2004gv, to G. Leloudas for providing spectra of SN 2007C and
2007kj before publication, and to David Fierroz for helping to
collate SN offsets.

M.M. acknowledges support from Hubble Fellowship grant HST-HF-51277.01-A, awarded by STScI, which is operated by AURA under NASA contract NAS5-26555, and from the NYU ADVANCE Women-in-Science Travel Grant funded by the NSF ADVANCE-PAID award Number HRD-0820202, during which part of this work was performed. Supernova research at Harvard University, including the CfA Supernova Archive,

has been supported in part by the National Science Foundation
grants AST06-06772, AST09-07903, and AST-1211196. R.P.K.
is grateful to the John Simon Guggenheim Foundation and
was supported by NSF grants PHY99-07949 and NSF PHY11-
25915 to the Kavli Institute for Theoretical Physics. S.W.J.
is supported at Rutgers University in part by NSF CAREER
award AST-084715, and F.B.B. is supported by a James Arthur
fellowship at the CCPP NYU.

Furthermore, this research has made use of NASA's Astro-
physics Data System Bibliographic Services (ADS), the Hyper-
LEDA database, and the NASA/IPAC Extragalactic Database
(NED), which is operated by the Jet Propulsion Laboratory, Cal-
ifornia Institute of Technology, under contract with the National
Aeronautics and Space Administration.

This paper is partly based on observations obtained at the
Gemini Observatory, which is operated by the Association
of Universities for Research in Astronomy, Inc., under a co-
operative agreement with the NSF on behalf of the Gemini
partnership: the National Science Foundation (United States),
the Particle Physics and Astronomy Research Council (United
Kingdom), the National Research Council (Canada), CONICYT
(Chile), the Australian Research Council (Australia), CNPq
(Brazil), and CONICET (Argentina).

APPENDIX

RELATIVE FLUX CALIBRATION

Here we check the accuracy of the relative flux calibration
of our stripped SN spectra across the spectrum, employing a
similar, but improved, procedure as for the CfA SN Ia data
in Matheson et al. (2008) and in Blondin et al. (2012). We
compared the B−V colors calculated from our stripped SN
spectra with those based on the corresponding calibrated CfA
light curves of the same stripped SNe in the Bessel standard
star system (F. B. Bianco et al., in preparation). We show
the results in Figure 10. For some spectra that are heavily
contaminated by H II regions, we first removed the H II region
emission lines and then computed spectra-based (B − V) colors
by multiplying the spectra with Bessel B and V filter functions.
Furthermore, we only used spectra that were taken at parallactic
angle in order to test for effects on spectrophotometry other
than the known differential light loss produced by atmospheric
dispersion. Moreover, we computed photometry-based colors
only if they were available within one day of the spectra.
Lastly, we propagated the photometry uncertainties into the
color calculations, a new feature compared to similar plots of
Matheson et al. (2008) and Blondin et al. (2012), and plot them
in Figure 10. For our stripped SN sample, which consists of
116 data points, we find that the scatter around zero difference
between spectra-based and photometry-based colors is ~2 times
smaller for spectra at phases less than 20 days (~0.15 mag) than
for phases larger than 20 days (~0.37 mag). This factor of two is
consistent with the conclusions based on SN Ia data presented in
Matheson et al. (2008) and Blondin et al. (2012). As mentioned
in those works, the likely reasons are twofold: (1) over time,
the spectra become dominated by strong emission lines, such
that any deviation of the actual filter response function from the
assumed one, with which we convolved our spectra, introduces
errors; and (2) the SNe get fainter over time, which makes host
galaxy contamination more significant. We find no significant
difference for the color comparison between SNe Ib and SNe Ic.

For comparison, we overplot the corresponding colors for the
SN Ia data. For consistency, we downloaded the SN Ia data

<footnote n="18">¹⁸ http://bruford.nhn.ou.edu/~suspect/</footnote>

<footnote n="19">¹⁹ http://www.weizmann.ac.il/astrophysics/wiserep/</footnote>
<figure><img src="image_11.png" /><figcaption>**Figure 10.** Comparison of the colors of stripped SN in our sample derived from spectroscopy (this work) and from photometry (F. B. Bianco et al., in preparation) over all phases, in order to evaluate the relative flux calibration of the CfA spectra. Note that the axes are inverted compared to corresponding figures in Matheson et al. (2008) and Blondin et al. (2012) for the CfA data of SN Ia. The full stripped SN sample has a scatter (0.24 mag) that is a factor of ~2 higher than for the full SN Ia sample (0.12 mag, using spectra from Blondin et al. 2012 and photometry from Riess et al. 1999; Jha et al. 2006; Hicken et al. 2009, re-analyzed in the same way as the stripped SN data).</figcaption></figure>

(A color version of this figure is available in the online journal.)

from the CfA SN Archive (using spectra from Blondin et al. 2012 and photometry from Riess et al. 1999; Jha et al. 2006; Hicken et al. 2009) and re-analyzed them by applying the same procedure as used for the stripped SN data (see above), yielding 348 data points for SNe Ia. In order to quantify any systematic deviation from the diagonal, i.e., the one-to-one correspondence of both colors, we performed a simple weighted least-squares fit to each SN sample (for all phases, over the same color range as for stripped SNe) and computed the scatter around the fitted line. While both SN samples appear to show somewhat bluer colors from spectra than from photometry for a few SNe, the formal weighted fits yield only slight deviations from a diagonal (see fitted lines, slope for SNe Ia: $1.037 \pm 0.019$; slope for stripped SNe: $1.033 \pm 0.038$). SNe Ia have less scatter around the fitted line (from our analysis: 0.12 mag, including all phases) than stripped SNe (0.24 mag, including all phases). However, these values may not necessarily imply that the relative flux calibration for the stripped SN spectra is twice worse than for SN Ia spectra, given that the *photometry data* of stripped SNe are also worse than for SNe Ia, as evidenced by the larger error bars for the stripped SN data than for SN Ia. Furthermore, the fact that the stripped SN sample has a factor of two worse scatter than the SN Ia sample could partly be due to the fact that there are more older stripped SNe than older SNe Ia in this comparison: 34% and 27% of the data points for the stripped SNe and for the SNe Ia, respectively, are at phases later than 20 days.

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