Mid-Infrared Imaging and Spectroscopy of Dust
Structures Periodically Formed Around WR140
based on Observations with Subaru/COMICS

Itsuki Sakon, Takashi Onaka, Ryou Ohsawa, Kentaro Asano (Univ. of Tokyo),
Takaya Nozawa (IPMU), Takashi Kozasa (Hokkaido University),
Takuya Fujiyoshi(NAOJ), Yoshiko Okamoto(Ibaraki University),
Hirokazu Kataza (ISAS/JAXA),Hidehiro Kaneda (Nagoya University)

26th Grain Formation Workshop

September 1-3, 2010

Dust formation by massive stars
SCIENTIFIC BACKGROUND・ Dust Formation by massive stars
important to explore the origin of dust in the early universe- How much amount of dust is formed in the ejecta of supernovae- How much fraction of it can survive the circumstellar environment- Can the dust be formed efficiently before the SN explosions and contributeas the budget of interstellar dust
(Dust formation by optical transients  Ohwasa-san’s talk)・The amount of 0.1Msolar/SN dust formation is needed to account for the dust
content of high red-shift galaxies (Morgan & Edmunds 2003).
・ The dust condensation in the ejecta of core-collapse SNe is theoreticallysuggested (Kozasa et al.1991; Todini & Ferrera 2001; Nozawa et al. 2003, 2010).
・ Observational Evidence for the dust formation in SN ejecta- Type II SN2003gd; 0.02Msolar(Sugerman et al. 2006) -> 4x10-5Msolar(Meikle et al. 2007)- Type II SN1987A ; 7.5x10-4Msolar (Ercolano et al.2007)- Cas A ; 0.003Msolar (Hines et al. 2004) or 0.02-0.054Msolar (Rho et al. 2004)

 much smaller amount of dust formation is suggested observationallyIntroduction: Dust formation by SN2006jc
An Example of the Latest Results on the Dust Formation by Core-collapse SNeAKARI/Infrared Camera (IRC) observations of SN2006jc in UGC4904

800K component; Newly formed dust in the ejecta of SN2006jcThot.car. = 800±10 (K)Mhot.car. = 6.9±0.5 x 10-5 Msolar
300K component; pre-existing circumstellar dust
Twarm.car. = 320±10 (K)[3µm(blue), 7µm(green), 11µm(red)]
Mwarm.car. = 2.7 +0.7x 10-3 Msolar-0.5

 The amount of newly formed dust is more than 3 orders of magnitudes smaller than
the amount needed for a SN to contribute efficiently to the early-Universe dust budget
Dust condensation in the mass loss wind associated with the prior events to the SN
explosion could make a significant contribution to the dust formation by a massive stars.
(Sakon et al. 2009, ApJ, 692, 546)

Introduction: Dust Emission around SN2008ax
SN2008ax in NGC 4490 (d = 9.6Mpc; Pastorello et al. 2008)
Type IIb (Chornock et al. 2008) discovered by Mostardi et al.(2008) on 2008 Mar 3.45-- the optical light curve similar to that of the He-rich Type IIb SNe 1996cb and 1993J-- an OB/WR progenitorstar (Mms = 10-14M☉) in an interacting binary system properties of the circumstellar dust shell Possible dust formation in the SN ejecta
NIR imaging of SN2008ax with AKARI/IRC on ~100days

0.33±0.03 mJy at N3(3µm) and 0.41±0.03 mJy at N4(4µm) bands
 Ta.car.=767±45K; Ma.car.=1.2+0.4-0.3 10-5 M☉
 Ta.sil.=885±60K; Ma.sil.=6.8+2.5-1.7 10-5 M☉
Infrared light echo from the dust formed as a result of the WR binary activities

Dust formation by Wolf-Rayet Binaries
Dust Formation in the wind-wind collision of massive Wolf-Rayet binary systems
Wolf-Rayet stars; extremely luminous (L>105L☉, Teff≫20,000K)
average mass-loss rate ; δM ~ 10-5M☉/yrterminal velocity ; v∞ ~ 1,000 - 4,500km/s
Periodic dust formation in binary WC+O system with eccentric orbits
dust production rate; δM ~ 10-6M☉/yr (van der Hucht et al. 1987; Williams 1995)“spectroscopic event”

WR ‘dusters’ --- WR9, WR25, WR48a, WR76, WR80, WR95, WR98a, WR102e, WR106, WR121,
WR125, WR137, WR140, etc (Marchenko & Moffat 2007; Wood et al. 2003)

Dust formation by WR140
WR140; long-period (P=7.93y; Marchenko et al. 2003) colliding-wind WR binary(WC7 class Wolf-Rayet star + O4 type star) located at d~1.85kpc“spectroscopic events” in 1993, 2001 and 2009
Observations; Cooled Mid-infrared Camera and Spectrometer (COMICS) / Subaru
N- and Q-band imaging and low-resolution spectroscopy of WR140
1st epoch; Aug. 2009 & 2nd epoch Nov. 2009 & 3rd epoch June 2010

, submitted

12.5µm image of WR140 taken withMichelle/Gemini-North on Nov. – Dec.
in 2003 (Marchenko & Moffat 2007).

11.7µm image of WR140 taken withCOMICS/Subaru on 1st Aug. in 2009
(Sakon et al. 2009).

The expansion velocity of the dust shell; 2.7±0.3 ×103 km s-1 ,consistent with Williams et al. 2009

Dust Structures around WR140
Revealed by Subaru/COMICS Observations
Subaru/COMICS N11.7 band (11.7µm)

August in 2009
orbital phase φ=1.065

Dust Structures around WR140
Revealed by Subaru/COMICS Observations
Subaru/COMICS N11.7 band (11.7µm)

November in 2009
orbital phase φ=1.097

Dust Structures around WR140
Revealed by Subaru/COMICS Observations
Subaru/COMICS N11.7 band (11.7µm)

June in 2010
orbital phase φ=1.170

Properties of Dust formed during the 2001 periastron at φ=1.097
The results of the photometry of dust shellformed during the 2001 periastron at theorbital phase of φ=1.107 (9 Nov 2009)
N11.7(11.7µm) 0.21±0.02 mJy
Q17.7(17.7µm) 0.15±0.04 mJy

X; amorphous carbon (X=acar)
Qabsacar (λ) ; absorption cross section(Colangeli et al. 1995)
ρacar =1.87 (g cm-3)
aacar= 0.01µm
R=1.85 kpc
temperature of amorphous carbon
Tacar = 350±60 K
total mass of amorphous carbon in the dust shell-8
Macar =0.99-0.35+0.5 ×10 M☉

Properties of Dust formed during the 2001 periastron at φ=1.170

The results of the photometry of dust shellformed during the 2001 periastron at theorbital phase of φ=1.170 (June 2009)
N11.7(11.7µm) 0.160±0.02 mJy
Q17.7(17.7µm) 0.125±0.04 mJy

temperature of amorphous carbon
Tacar = 330±60 K
total mass of amorphous carbon
Macar =0.95-0.35 ×10-8 M☉

Properties of Dust formed during the 2001 periastronThe temperature of amorphous carbon at φ=1.097 (9 Nov 2009)； Tacar = 350±60 K
φ=1.170 (4 Jun 2010)； Tacar = 330±60 K・Equations on the radiative equilibrium (Williams et al. 2009)

Energy output
via thermal emission

energy input from the O5 starenergy input from the WC7 star

Qa(a,T) ; the Planck mean absorption cross-section
a; the radius of a dust grain
Tg; the temperature of a dust grainr; the distance between the dust and either of the two stars (O-type star or WR star)
RO, RWR; effective radii of the O-type star and the WR starTO, TWR; effective temperature of the O-type star and the WR star・Qa(a,Tg) ∝ Tg1.2 holds for the amorphous carbon grains in the relevant temperature range
 The radiative equilibrium grain temperature(Tg) is expected to decrease with distancefrom the stars as Tg ∝ r - 2/5.2.
Tg = 980K at φ=0.039 (Williams et al. 2009)
The obtained dust temperature of Tg=350±60K
at φ=1.107 is generally in good agreement withthe expected relation of Tg ∝ r - 2/5.2.

Properties of Dust formed during the 2001 periastron-0.35 ×10-8 M
total mass of amorphous carbon in the dust shell at φ=1.097；Macar =0.99+0.5☉-0.4 ×10-8 M
φ=1.170；Macar =0.90+0.5☉(Williams et al. 2009; asumming Tg∝r-0.38)
orbital phase; φMacar (M☉)
0.01
2×10-80.02
3×10-80.12
6×10-80.14
6.5×10-8
0.56<2×10-8(this study)
orbital phase; φMacar (M☉)-0.35 ×10-8
1.097
0.99+0.5-8
1.170
0.90-0.4+0.6 ×10
Interpretations by Williams et al. (2009)0<φ<0.03 ; dust formation begins and new dust condenses
0.03<φ<0.12 ; growth of recently formed grains at their equilibrium temperature
cf. typical size of dust grains in WR140 grow to 0.069µm (Marchenko et al. 2003)
0.14<φ; the rate of destruction by thermal sputtering overtakes that of growth by
implantation of carbon ions (Zubko 1998) and dust grains are destroyed
At most 1×10-8M☉ of amorphous carbon dust survives at the orbital phase of φ=1.097~1.170.

Summary
Near- to Mid-Infrared observations of SN2006jc and SN2008ax with AKARI/IRC
・The amount of newly formed dust is more than 3 orders of magnitudes smaller than the amountneeded for a SN to contribute efficiently to the early-Universe dust budget.
・Dust condensation in the mass loss wind associated with the prior events to the SN explosion
could make a significant contribution to the dust formation by a massive stars
MIR observations of WR140 at the orbital phase of φ=1.097 and 1.170 with Subaru/COMICS
・The expansion velocity of dust clouds is ~2700km/s, consistent with Williams et al. (2009).
・Q-band imaging of dust structures at such later epoch was obtained for the first time.
・The result of our photometry at 11.7µm and 17.7µm of dust structures formed around theWR140 during the previous periaston in 2001 is consistent with the presence of amorphous
carbons of T~350±60K with the mass of 1×10-8M☉ at the epoch of φ=1.097 and T~350±60K with themass of 0.9×10-8M☉ at the epoch of φ=1.170
 In the case of WR140, 1×10-8M☉ of amorphous carbon dust, at most, survives at the orbital
phase of φ=1.097 and 1.170