1
No.114

Apr. 2023

Variable Star Bulletin
SDSS J094002.56+274942.0: an SU UMa star with an orbital period of
3.92 hours and an apparently unevolved secondary
Taichi Kato1 , Tonny Vanmunster2
1 Department of Astronomy, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japantkato@kusastro.kyoto-u.ac.jp
2 Center for Backyard Astrophysics Belgium, Walhostraat 1A, B-3401 Landen, Belgium
tonny.vanmunster@gmail.com
Received 2023 Apr. 25
Abstract
We found that SDSS J094002.56+274942.0 underwent a superoutburst in 2019 February based on ourobservations and Zwicky Transient Facility (ZTF) data. This object showed shallow eclipses during thissuperoutburst and we established the orbital period to be 0.1635015(1) d in combination with the ZTF andAsteroid Terrestrial-impact Last Alert System (ATLAS) data in quiescence. Superhumps apparently started
to develop soon after the object reached the plateau phase and fully grown superhumps were recorded within
the initial 6 d of the plateau phase. Using the superhump and orbital periods, we obtained a mass ratio (q)of 0.39(3) and obtained an inclination of 70.5(5)◦ by eclipse modeling. These values reproduced the quiescentellipsoidal variations very well. Using the Gaia parallax and 2MASS observations, we conﬁrmed that thesecondary is indistinguishable from an unevolved main-sequence star. The resultant mass ratio and orbital
period were the highest among SU UMa stars, and this provided a proof that the 3:1 resonance can develop inless than 6 d even in q=0.39(3). The superoutburst faded relatively rapidly and was followed by a rebrightening,suggesting that the tidal eﬀect in a large-q system was insuﬃcient to maintain a long superoutburst and theremnant matter caused a rebrightening. The presence of such a system among dwarf novae is against theconventional idea that outbursts in dwarf novae are not long enough to develop superhumps, in contrast to
novalike variables, under a weak tidal eﬀect. The present observation also supports that the 3:1 resonance isthe cause of a long outburst, and not its consequence, even under extreme q. The rapid growth of the 3:1
resonance in a high-q system challenges the generally accepted results of hydrodynamic simulations.

1

Introduction

SU UMa-type dwarf novae are a class of cataclysmic variables (CVs) which show superhumps during long,bright outbursts (superoutbursts) [For general information of CVs and subclasses, see e.g., Warner (1995)]. Thisphenomenon is widely believed to be the consequence of the 3:1 resonance (Whitehurst 1988; Hirose and Osaki
1990; Lubow 1991) when the disk expands to this radius during a superoutburst. Whether the 3:1 resonance isthe cause or the consequence of a superoutburst has been discussed, and a series of analyses of the Kepler dataof V1504 Cyg and V344 Lyr (Osaki and Kato 2013a,b, 2014) established that the 3:1 resonance is the cause of asuperoutburst as originally proposed by Osaki (1989).
The size of the accretion disk is limited by tidal truncation, or in extreme cases, could be by the size of theRoche lobe. The size of the Roche lobe is a function of the mass ratio q = M1 /M2 and it has long been discussed,
both observationally and theoretically, what is the upper limit of q that enables the 3:1 resonance. Numericalsimulations such as by smoothed particle hydrodynamics (SPH) gave a limit of q <0.25–0.33 (e.g. Whitehurst
and King 1991; Murray 1998; Murray et al. 2000; Smith et al. 2007). CVs with longer orbital periods (Porb ) havelarger q and there is a natural upper limit for Porb for objects showing superhumps. The limit q=0.25 generally
corresponds to the period gap in CVs. This limit originally appeared to ﬁt SU UMa-type dwarf novae very well,among which systems above the period gap were very exceptional. It has been well-known, however, superhumps

2
are present in longer-Porb systems in novalike variables (systems with a thermally stable high-state disk), such asin Bruch (2022); Stefanov et al. (2022); Bruch (2023) using modern Transiting Exoplanet Survey Satellite (TESS:
Ricker et al. 2015) data. Although the case of RZ Gru (Porb =0.4563 d) in Bruch (2022) may be exceptional
and it may have shown a phenomenon diﬀerent from (ordinary) superhumps, many novalike variables are known
to show superhumps at least up to Porb =0.18 d (Bruch 2023). Since the majority of long-Porb systems showing
superhumps are novalike systems, there has been an idea that a weaker eﬀect of a resonance requires longer
time to develop, and systems in high states for a suﬃciently long time (i.e. novalike variables) only can showsuperhumps. In this interpretation, the high states (outbursts) in dwarf novae are not long enough to develop
superhumps, somewhat in line with the above-mentioned idea that the 3:1 resonance is the consequence of a longoutburst, not the cause.
In recent years, however, a number of SU UMa-type dwarf novae have been discovered above the period
gap. The only traditionally known system was TU Men (Stolz and Schoembs 1984)1 . The q value for TU Men,however, is unfortunately not well-determined (Smak 2006). There is evidence for CNO-processing in this object(Godon and Sion 2021) and TU Men may not be considered an ordinary CV following the standard evolutionary
track. Modern examples without evidence of an evolved secondary include CRTS J035905.9+175034 [q=0.281(15):Littleﬁeld et al. (2018)] and BO Cet [q=0.31–0.34: Kato et al. (2021); Kato (2023a)]. Superhumps in both objects
started to develop soon after superoutbursts reached the plateau phase as in other SU UMa stars (Osaki andKato 2013a). There was no indication of a signiﬁcant delay in the development of superhumps, which would be
expected if the 3:1 resonance is the consequence of a long outburst.
SDSS J094002.56+274942.0 was spectroscopically selected as a CV (Szkody et al. 2007). The spectrum by
Szkody et al. (2007) was that of an ordinary dwarf nova. Krajci and Wils (2010) noticed an outburst detected by
Catalina Real-Time Transient Survey (CRTS) in 2009 and performed time-resolved photometry. Krajci and Wils
(2010) detected orbital modulations (ellipsoidal variations) with a period of 0.16352 d during the fading part ofthis outburst. Although Krajci and Wils (2010) suggested that the disk or the hot spot may have been (partially)
eclipsed during the brighter stages of this outburst, the nature of the observed dip was unclear due to the poor
phase coverage. Krajci and Wils (2010) discussed that TiO bands expected from the secondary type (M4–5) wereinvisible in the spectrum of Szkody et al. (2007). Krajci and Wils (2010) noted a possibility of an early M-type
secondary, which would suggest an evolved core, with little TiO absorption. Based on this identiﬁcation of Porb ,SDSS J094002.56+274942.0 has long been regarded as an SS Cyg-type dwarf nova. Hou et al. (2020) observed
this object three times by the LAMOST survey. No Ciii/Niii emission lines were recorded. Feii emission lines
were recorded once and Hα lines was double-peaked on a single occasion. All spectra were obtained in quiescenceand one of them was presented in Han et al. (2020).
During an inspection of Zwicky Transient Facility (ZTF: Masci et al. 2019)2 data, one of the authors (T.K.)
noted that ZTF incidentally obtained time-resolved photometry during a long outburst in 2019 February. Combined with time-resolved observations by the second author (T.V.) reported to VSNET Collaboration (Kato et al.
2004), T.K. found that this outburst was a superoutburst and that this object showed superhumps (vsnet-chat9373)3 .

2

Data analysis

The observations by T.V. were obtained with a 0.40-m f/5.1 Newton telescope and an unﬁltered Starlight Xpress
Trius SX-46 CCD camera with KAF-16200 (3×3 bin) chip, located in Extremadura, Spain. We used ZTF andAsteroid Terrestrial-impact Last Alert System (ATLAS: Tonry et al. 2018) forced photometry (Shingles et al.
2021) data for our analysis. Some unﬁltered snapshot observations reported to VSOLJ were also used (hereafter
CCD). Some ATLAS and CCD observations had false bright detections, which were removed after comparison
with the observations on the same night or with other observers. Although TESS also observed this object inquiescence, these observations were strongly contaminated by nearby brighter stars and we did not use themsince they were not particularly useful in determining Porb in the presence of ZTF and ATF observations with alonger baseline. The log of time-resolved observations is listed in table 1. When analyzing the quiescent data, we
1 The case of U Gem was claimed by Smak and Waagen (2004), but T.K. considered it questionable (Kato et al. 2014b) and thecase is far from being established [see also Patterson et al. (2005)].
2 The ZTF data can be obtained from IRSA <https://irsa.ipac.caltech.edu/Missions/ztf.html> using the interface <https://irsa.ipac.caltech.edu/docs/program_interface/ztf_api.html> or using a wrapper of the above IRSA API<https://github.com/MickaelRigault/ztfquery>.
3 <http://ooruri.kusastro.kyoto-u.ac.jp/mailarchive/vsnet-chat/9373>.

3

Table 1: Time-resolved photometry of SDSS J094002.56+274942.0.
Start∗End∗
Mean mag.
58522.3249 58522.5274
14.60058523.3216 58523.4898
14.74258523.7527 58523.9151
14.68858524.4699 58524.4930
14.81558524.7530 58524.9168
14.78258526.3213 58526.5304
15.03058526.7307 58526.8945
14.936∗
BJD−2400000.
†
Number of observations.

Error
0.004
0.006
0.007
0.003
0.006
0.006
0.011

N†
95
41
56
28
57
245
57

ObserverVanmunster
Vanmunster
ZTF
Vanmunster
ZTF
Vanmunster
ZTF

Filter
CV
CV
r
CV
r
CV
r

used locally-weighted polynomial regression (LOWESS: Cleveland 1979) to remove long-term trends. The periods
were determined using the phase dispersion minimization (PDM: Stellingwerf 1978) method, whose errors were
estimated by the methods of Fernie (1989); Kato et al. (2010).

3

Results

3.1

Long-term behavior

Long-term light curves are shown in ﬁgures 1 and 2. This object showed outbursts relatively infrequently. The
2019 February outburst (fourth panel in ﬁgure 1) was a long one, which later turned out to be a superoutburst(subsection 3.3), while the other three were short. The 2009 outburst observed by Krajci and Wils (2010) was
also a short one. The rarity of outbursts suggests a low mass-transfer rate.
The details of the 2019 February long outburst are shown in ﬁgure 3. This outburst had an approximate
duration of 20 d and was followed by a rebrightening on 2019 March 3 (BJD 2458546). The overall shape of thisoutburst is compatible with that of a superoutburst, which will be examined in subsection 3.3.

3.2

Orbital period and proﬁleWe used ZTF and ATLAS observations in quiescence (all bands were combined after zero-point adjustments)and obtained the same ellipsoidal variations detected by Krajci and Wils (2010) (ﬁgure 4). The orbital phase
was deﬁned by
Min(BJD) = 2458953.7169(10) + 0.1635015(1)E.
(1)
The zero phase was determined by an MCMC analysis (Kato et al. 2010) of the eclipses detected during the2019 superoutburst (see subsection 3.3) since eclipses during an outburst are a better indicator of the center ofthe disk particularly when a hot spot is present. This ephemeris, however, very well expressed the primary (butshallower) minimum of the ellipsoidal variations in quiescence. The phase 0.75 peak was brighter than the phase
0.25 one probably due to the hot spot. The secondary (but deeper) minimum occurred somewhat before thephase 0.5.

3.3

Eclipses and superhumps in superoutburst

We show phase-averaged light curves during the 2019 February outburst in ﬁgure 5. The orbital phases wereobtained using equation (1). The four runs (ZTF and the ﬁnal night by Vanmunster) were slightly longer than
Porb and full orbital phases were sampled in these cases. This ﬁgure corresponds to ﬁgure 3 in Krajci and Wils
(2010) (but phase-averaged). Eclipses were present in all runs covering the expected eclipse phase and we used
these data to determine the zero phase of equation (1). The eclipses became asymmetric during the third and ﬁfth
runs, probably reﬂecting the evolution of superhumps. In the sixth and seventh runs, the presence of superhumps
having a period longer than Porb is apparent. The result of a PDM analysis of the combined sixth and seventhruns is shown in ﬁgure 6 after removing the eclipse parts (phases within ±0.06). There was some ambiguity in thediﬀerence in the zero points between these two runs (they were by diﬀerent observers using diﬀerent equipment

4

14
ZTF r

ZTF g

ZTF i

57300

57350

57400

ATLAS oATLAS c

CCD

16

18

57250

57450

57500

57550

57600

14

16

18

57650

57700

57750

57800

57850

57900

57950

14

16

18

58000

58050

58100

58150

58200

58250

58300

14

16

18

58350

58400

58450

58500

58550

58600

58650

58700

Figure 1: Light curve of SDSS J094002.56+274942.0 in 2015–2019. CCD refers to unﬁltered snapshot observations.

5

14

16

18

58750

58800

58850

58900

58950

59000

59050

14

16

18

59100

59150

59200

59250

59300

59350

59400

14

16

18

59450

59500

59550

59600

59650

59700

59750

59800

14

16

18

59800

59850

59900

59950

60000

60050

60100

60150

Figure 2: Light curve of SDSS J094002.56+274942.0 in 2019–2023. The symbols are the same as in ﬁgure 1.

6

14

16

18

58510

58520

58530

58540

58550

58560

Figure 3: Light curve of SDSS J094002.56+274942.0 during the 2019 February superoutburst. Blue plots aretime-resolved photometry by T.V. The other symbols are the same as in ﬁgure 1.

and ﬁlters). We adopted a correction of 0.050 mag to the ZTF data so that the maxima and minima of these
two runs become the same. This ambiguity, however, did not strongly aﬀect the result. The resultant period
was 0.1825(7) d. With this period, the peaks of the superhump maxima from the two sets of the data well agree
although the waveforms were somewhat diﬀerent, probably due to the beat phenomenon between the orbital andsuperhump periods (ﬁgure 6). The nominal (statistical) error could be an underestimate due to a systematic
error arising from the beat phenomenon and intrinsic variations. A result from a short (0.57 d) baseline would
be more strongly aﬀected by these eﬀects than in ordinary superhump analyses using longer baselines, such as in
Kato et al. (2009). We, however, disregard this possibility in the following discussions and use the nominal error.
Although superhumps apparently grew before the sixth run, we could not determine the period before thisrun partly due to the overlapping orbital signal. There was a gap more than 1 d before the sixth run and it
appears that the major increase of the superhump amplitude occurred during this observational gap.

4

Discussion

4.1

Mass ratio and the secondary

With Porb of 0.1635015 d = 3.924 hr, a CV on the standard evolutionary sequence is expected to have a secondary
mass of M2 =0.303 M⊙ (main sequence) and near-infrared absolute magnitudes of MJ =6.87, MH =6.45 andMK =6.29 (Knigge 2006, 2007). These near-infrared absolute magnitudes can be directly comparable to theobserved 2MASS magnitudes (Cutri et al. 2003) and the Gaia parallax yielding a distance modulus of 9.5(2) mag(Gaia Collaboration et al. 2022). The observed J=16.15(11), H=15.61(16) and Ks =15.48(18) correspond to theabsolute magnitudes of MJ =6.7(2), MH =6.1(3) and MK =6.0(3). These values exclude a possibility of an evolved
donor as in other SU UMa stars with very long Porb [such as ASASSN-18aan (Porb =0.149454 d, Wakamatsu et al.
2021) and ASASSN-15cm (Porb =0.2084652 d, Kato 2023b)]. The secondary star in SDSS J094002.56+274942.0
appears to be indistinguishable from a normal main-sequence star. Assuming a white dwarf with an average mass
M1 =0.82M⊙ in short-period CVs (Savoury et al. 2011; Zorotovic et al. 2011; McAllister et al. 2019; Pala et al.
2022), the expected mass of the secondary translates to q=0.37.
What is inferred from the superhump observation? It is well established that superhump periods vary (Katoet al. 2009) and it is important which stage is used for estimating q from the superhump period (Kato and Osaki
2013; Kato 2022a). In the case of SDSS J094002.56+274942.0, the superhump observations were apparently
made just around the peak of the superhump amplitude. It is known that stage A–B transition [see Kato et al.
(2009); Kato (2022b) for superhump stages] does not match the peak of the superhump amplitude in long-Porb

7

θ
1.0

0.8

0.6

P=0.16350
0.16340.16350.1636

0.1637

1.0

1.5

(d)

−0.2

0.0

0.2

−0.5

0.0

0.5

Figure 4: Orbital proﬁle of SDSS J094002.56+274942.0 in quiescence. (Upper): PDM analysis. The bootstrap
result using randomly contain 50% of observations is shown as a form of 90% conﬁdence intervals in the resultant
θ statistics. (Lower): Phase plot.

80(BJD−2400000)
58522.4(Vanmunster)

58523.4(Vanmunster)

58523.8

1(ZTF r)58524.5(Vanmunster)

58524.8(ZTF r)58526.4

2(Vanmunster)

58526.8(ZTF r)

−0.5

0.0

0.5

1.0

1.5

Figure 5: Phased proﬁles during the 2019 February superoutburst. The orbital phase is deﬁned by equation (1).
The values to the right refer to the center of observational runs.

9

1.0
θ

0.8

0.6

0.4

0.2

P=0.1825

0.0
0.16

0.18

0.20

0.22

(d)

−0.2

−0.1

Vanmunster
0.0

ZTF r
0.1

0.2

−0.5

0.0

0.5

1.0

1.5

Figure 6: Superhumps in SDSS J094002.56+274942.0. The data for BJD 2458526.33–2458526.90 were used after
removing eclipse parts. (Upper): PDM analysis. (Lower): Phase plot.

10

Table 2: Eclipse modeling during superoutburst.
q
0.37
0.39
0.42

Inclination (◦ )
71.0
70.5
70.0

systems and stage A (judged from the superhump period) extends slight after the maximum of the superhump
amplitude [V1006 Cyg: Kato et al. (2016, see supplementary ﬁgure) and MN Dra: Kato et al. (2014a)]. We
therefore consider that the superhump period (PSH ) recorded in SDSS J094002.56+274942.0 reﬂects that of stage
A superhumps. The observed ϵ∗ ≡ 1 − Porb /PSH was 0.104(4). This corresponds to q=0.39(3) [see table 1 in
Kato (2022a)]. Considering the uncertainty in determining the superhump period and an assumption of the whitedwarf mass, this value appears to be consistent with a normal main-sequence secondary. The superhump period
at least does not favor a light-weight secondary with an evolved core (as already conﬁrmed by the near-infraredabsolute magnitudes).

4.2

Inclination and ellipsoidal variations

Eclipses observed during the superoutburst provide an excellent opportunity for modeling the binary since the disk
radius is expected to be the radius of the 3:1 resonance. Assuming an optically thick standard disk, inclinations
needed to reproduce the observed eclipse depth (0.11 mag) are given in table 2. We used three q values (0.37from the standard evolutionary sequence and an average-mass white dwarf, 0.39 from stage A superhumps and0.42 as the upper limit). The uncertainties of inclinations were 0.5◦ and the values were rounded to 0.5◦ .
We followed the case of ASASSN-15cm (Kato 2023b) in modeling the quiescent light curve. Using Ellipsoidal
Modulation Light Curve Generator by M. Uemura (2006), which was based on Orosz and Bailyn (1997a,b), we
could reproduce ellipsoidal variations ZTF r and g observations in ﬁgure 7. We used Teﬀ =3500 K, log g=4.727,
assuming a main-sequence secondary in Knigge (2006, 2007) and gravity darkening and limb-darkening coeﬃcients
given in Claret and Bloemen (2011) (solar metallicity and a microturbulent velocity of 2 km s−1 as typical values
were used). As in the case of ASASSN-15cm, outbursts in SDSS J094002.56+274942.0 were rare and the masstransfer rate is expected to be low. The contribution from the disk appears to be negligible in quiescence. Both
q=0.37 and q=0.42 cases suﬃciently ﬁt the observations with the inclinations determined by eclipse analysis. It
turned out that quiescent ellipsoidal variations could not constrain the binary parameter better than what we
obtained from superhump and eclipse analysis. This result, however, conﬁrmed that our basic picture (unevolved
main-sequence secondary) is correct.

4.3

Implications of the present discovery

As stated in section 1, it has long been considered that CVs above the period gap showing superhumps are almost
entirely novalike variables with a thermally stable (high-state) disk. It has been considered that superhumps
can grow only in such systems in suﬃciently long high states under a weaker resonance eﬀect. Indeed, someestablished SU UMa-type dwarf novae above the period gap have a secondary with an evolved core such as
in OT J002656.6+284933 (=CSS101212:002657+284933, PSH =0.13225 d: Kato et al. 2017), ASASSN-18aan(Porb =0.149454 d: Wakamatsu et al. 2021) and ASASSN-15cm (Porb =0.208466 d: Kato 2023b). Wakamatsu
et al. (2021) suggested that the 3:1 resonance in long-Porb dwarf novae is more diﬃcult to develop around thestability border than in the case of the 2:1 resonance. The present discovery of an SU UMa-type dwarf nova with
Porb =0.1635015 d with a normal main-sequence secondary is against this interpretation. Even with q=0.39(3),this dwarf nova apparently started developing superhumps soon after it reached the plateau phase and fully
developed superhumps were recorded within 6 d of the start of the plateau phase. This behavior is common toother SU UMa-type dwarf novae and there was no signiﬁcant diﬀerence in the development of superhumps. Thiscase supports the idea that the 3:1 resonance triggered a superoutburst even in this extreme case.
The superoutburst, however, terminated rather quickly and was followed by a rebrightening. These features
suggest that the hot state was diﬃcult to maintain by the 3:1 resonance in an extreme q case — a mechanism
proposed in V1006 Cyg and CS Ind which simulated a WZ Sge-type phenomenon (Kato et al. 2016, 2019) — and

11

0.0

ZTF r

0.2

0.4

ZTF g

0.6

0.8

1.0

−0.4 −0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

Figure 7: Orbital proﬁle of SDSS J094002.56+274942.0 in quiescence using ZTF r and g data. The orbital
phase is deﬁned by equation (1). The plots were shifted by 0.4 mag between diﬀerent bands. The solid curves
represent ellipsoidal variations expected for q=0.43, i=70.0◦ (skyblue) and q=0.37, i=71.0◦ (pink) (see text).

12that the matter left in the disk due to the early quenching of the superoutburst resulted a rebrightening, which
is usually a feature in short-Porb systems (Kato et al. 1998; Kato 2015).
Continued monitoring of this object is required, and better determination of the superhump period and its
evolution will clarify what is happening in long-Porb and high-q SU UMa-type dwarf novae.

Acknowledgements
This work was supported by JSPS KAKENHI Grant Number 21K03616. The authors are grateful to the ZTF and
ATLAS teams for making their data available to the public. We are grateful to VSOLJ observers (particularly
Yutaka Maeda) who reported snapshot CCD photometry of SDSS J094002.56+274942.0. We are also gratefulto Makoto Uemura for sharing the code of Ellipsoidal Modulation Light Curve Generator, Naoto Kojiguchi for
helping downloading the ZTF and TESS data and Yasuyuki Wakamatsu for converting the data reported to the
VSNET Collaboration.
Based on observations obtained with the Samuel Oschin 48-inch Telescope at the Palomar Observatory as
part of the Zwicky Transient Facility project. ZTF is supported by the National Science Foundation under Grant
No. AST-1440341 and a collaboration including Caltech, IPAC, the Weizmann Institute for Science, the Oskar
Klein Center at Stockholm University, the University of Maryland, the University of Washington, Deutsches
Elektronen-Synchrotron and Humboldt University, Los Alamos National Laboratories, the TANGO Consortiumof Taiwan, the University of Wisconsin at Milwaukee, and Lawrence Berkeley National Laboratories. Operations
are conducted by COO, IPAC, and UW.
The ztfquery code was funded by the European Research Council (ERC) under the European Union’s Horizon
2020 research and innovation programme (grant agreement n◦ 759194 – USNAC, PI: Rigault).
This work has made use of data from the Asteroid Terrestrial-impact Last Alert System (ATLAS) project.
The ATLAS project is primarily funded to search for near earth asteroids through NASA grants NN12AR55G,
80NSSC18K0284, and 80NSSC18K1575; byproducts of the NEO search include images and catalogs from thesurvey area. This work was partially funded by Kepler/K2 grant J1944/80NSSC19K0112 and HST GO-15889,
and STFC grants ST/T000198/1 and ST/S006109/1. The ATLAS science products have been made possible
through the contributions of the University of Hawaii Institute for Astronomy, the Queen’s University Belfast,
the Space Telescope Science Institute, the South African Astronomical Observatory, and The Millennium Instituteof Astrophysics (MAS), Chile.

List of objects in this paper
BO Cet, V1006 Cyg, V1504 Cyg, MN Dra, U Gem, RZ Gru, V344 Lyr, TU Men, WZ Sge, SU UMa, ASASSN15cm, ASASSN-18aan, CRTS J035905.9+175034, CSS101212:002657+284933, OT J002656.6+284933, SDSS
J094002.56+274942.0

References
Bruch, A. (2022) TESS light curves of cataclysmic variables – I – Unknown periods in long-known stars. MNRAS
514, 4718
Bruch, A. (2023) TESS light curves of cataclysmic variables – II – Superhumps in old novae and novalike variables.
MNRAS 519, 352
Claret, A., & Bloemen, S. (2011) Gravity and limb-darkening coeﬃcients for the Kepler, CoRoT, Spitzer, uvby,
UBVRIJHK, and Sloan photometric systems. A&A 529, A75
Cleveland, W. S. (1979) Robust locally weighted regression and smoothing scatterplots. J. Amer. Statist. Assoc.
74, 829
Cutri, R. M. et al. (2003) 2MASS All Sky Catalog of point sources (NASA/IPAC Infrared Science Archive)
Fernie, J. D. (1989) Uncertainties in period determinations. PASP 101, 225

13
Gaia Collaboration et al. (2022) Gaia Data Release 3. Summary of the contents and survey properties. A&A(arXiv:2208.00211)
Godon, P., & Sion, E. M. (2021) White dwarf photospheric abundances in cataclysmic variables. I. SS Aurigae
and TU Mensae. ApJ 908, 173
Han, Z., Boonrucksar, S., Qian, S., Xiaohui, F., Wang, Q., Zhu, L., Dong, A., & Zhi, Q. (2020) Spectroscopic
properties of the dwarf nova-type cataclysmic variables observed by LAMOST. PASJ 72, 76
Hirose, M., & Osaki, Y. (1990) Hydrodynamic simulations of accretion disks in cataclysmic variables – superhump
phenomenon in SU UMa stars. PASJ 42, 135
Hou, W., Luo, A.-L., Li, Y.-B., & Qin, L. (2020) Spectroscopically identiﬁed cataclysmic variables from the
LAMOST survey. I. The sample. AJ 159, 43
Kato, T. (2015) WZ Sge-type dwarf novae. PASJ 67, 108
Kato, T. (2022a) Evolution of short-period cataclysmic variables: implications from eclipse modeling and stage
a superhump method (with New Year’s gift). VSOLJ Variable Star Bull. 89, (arXiv:2201.02945)
Kato, T. (2022b) Analysis of TESS observations of V844 Her during the 2020 superoutburst. VSOLJ Variable
Star Bull. 102, (arXiv:2205.05284)
Kato, T. (2023a) SU UMa-type supercycle in the IW And-type dwarf nova BO Cet above the period gap. VSOLJ
Variable Star Bull. 106, (arXiv:2302.02593)
Kato, T. (2023b) ASASSN-15cm: an SU UMa star with an orbital period of 5.0 hours. VSOLJ Variable Star
Bull. 109, (arXiv:2302.09713)
Kato, T. et al. (2014a) Survey of period variations of superhumps in SU UMa-type dwarf novae. VI: The ﬁfth
year (2013–2014). PASJ 66, 90
Kato, T. et al. (2014b) Survey of period variations of superhumps in SU UMa-type dwarf novae. V: The ﬁfth
year (2012–2013). PASJ 66, 30
Kato, T., Hambsch, F.-J., Monard, B., Nelson, P., Stubbings, R., & Starr, P. (2019) CS Indi: SU UMa-type
dwarf nova with long precursor outburst. PASJ 71, L4
Kato, T. et al. (2009) Survey of period variations of superhumps in SU UMa-type dwarf novae. PASJ 61, S395
Kato, T. et al. (2010) Survey of period variations of superhumps in SU UMa-type dwarf novae. II. The second
year (2009–2010). PASJ 62, 1525
Kato, T., Nogami, D., Baba, H., & Matsumoto, K. (1998) in ASP Conf. Ser. 137, Wild Stars in the Old West,
ed. S. Howell, E. Kuulkers, & C. Woodward (San Francisco: ASP) p. 9
Kato, T., & Osaki, Y. (2013) New method to estimate binary mass ratios by using superhumps. PASJ 65, 115
Kato, T. et al. (2016) V1006 Cygni: Dwarf nova showing three types of outbursts and simulating some featuresof the WZ Sge-type behavior. PASJ 68, L4
Kato, T. et al. (2021) BO Ceti: Dwarf nova showing both IW And and SU UMa-type features. PASJ 73, 1280
Kato, T. et al. (2017) OT J002656.6+284933 (CSS101212:002657+284933): An SU UMa-type dwarf nova withlongest superhump period. PASJ 69, L4
Kato, T., Uemura, M., Ishioka, R., Nogami, D., Kunjaya, C., Baba, H., & Yamaoka, H. (2004) Variable Star
Network: World center for transient object astronomy and variable stars. PASJ 56, S1
Knigge, C. (2006) The donor stars of cataclysmic variables. MNRAS 373, 484
Knigge, C. (2007) Erratum: The donor stars of cataclysmic variables. MNRAS 382, 1982

14
Krajci, T., & Wils, P. (2010) Photometry of the dwarf nova SDSS J094002.56+274942.0 in outburst. J. American
Assoc. Variable Star Obs. 38, 33
Littleﬁeld, C., Garnavich, P., Kennedy, M., Szkody, P., & Dai, Z. (2018) A comprehensive K2 and ground-based
study of CRTS J035905.9+175034, an eclipsing SU UMa system with a large mass ratio. AJ 155, 232
Lubow, S. H. (1991) A model for tidally driven eccentric instabilities in ﬂuid disks. ApJ 381, 259
Masci, F.-J. et al. (2019) The Zwicky Transient Facility: Data processing, products, and archive. PASP 131,018003
McAllister, M. et al. (2019) The evolutionary status of cataclysmic variables: eclipse modelling of 15 systems.
MNRAS 486, 5535
Murray, J., Warner, B., & Wickramasinghe, D. (2000) Superhumps in systems with intermediate mass ratios.
New Astron. Rev. 44, 51
Murray, J. R. (1998) Simulations of superhumps and superoutbursts. MNRAS 297, 323
Orosz, J. A., & Bailyn, C. D. (1997a) Optical observations of GRO J1655−40 in quiescence. I. A precise mass
for the black hole primary. ApJ 477, 876
Orosz, J. A., & Bailyn, C. D. (1997b) Erratum: Optical observations of GRO J1655−40 in quiescence. I. A precise
mass for the black hole primary. ApJ 482, 1086
Osaki, Y. (1989) A model for the superoutburst phenomenon of SU Ursae Majoris stars. PASJ 41, 1005
Osaki, Y., & Kato, T. (2013a) The cause of the superoutburst in SU UMa stars is ﬁnally revealed by Kepler
light curve of V1504 Cygni. PASJ 65, 50
Osaki, Y., & Kato, T. (2013b) Study of superoutbursts and superhumps in SU UMa stars by the Kepler light
curves of V344 Lyrae and V1504 Cygni. PASJ 65, 95
Osaki, Y., & Kato, T. (2014) A further study of superoutbursts and superhumps in SU UMa stars by the Kepler
light curves of V1504 Cygni and V344 Lyrae. PASJ 66, 15
Pala, A. F. et al. (2022) Constraining the evolution of cataclysmic variables via the masses and accretion ratesof their underlying white dwarfs. MNRAS 510, 6110
Patterson, J. et al. (2005) Superhumps in cataclysmic binaries. XXV. qcrit , ϵ(q), and mass-radius. PASP 117,
1204
Ricker, G. R. et al. (2015) Transiting Exoplanet Survey Satellite (TESS). J. of Astron. Telescopes, Instruments,
and Systems 1, 014003
Savoury, C. D. J. et al. (2011) Cataclysmic variables below the period gap: mass determinations of 14 eclipsingsystems. MNRAS 415, 2025
Shingles, L. et al. (2021) Release of the ATLAS Forced Photometry server for public use. Transient Name Server
AstroNote 7, 1
Smak, J. I. (2006) On the mass ratio of TU Men. Acta Astron. 56, 277
Smak, J., & Waagen, E. O. (2004) The 1985 superoutburst of U Geminorum. Detection of superhumps. Acta
Astron. 54, 433
Smith, A. J., Haswell, C. A., Murray, J. R., Truss, M. R., & Foulkes, S. B. (2007) Comprehensive simulations ofsuperhumps. MNRAS 378, 785
Stefanov, S. Y., Latev, G., Boeva, S., & Moyseev, M. (2022) Superhumps in the cataclysmic variable BG Triangulum. MNRAS 516, 2775
Stellingwerf, R. F. (1978) Period determination using phase dispersion minimization. ApJ 224, 953

15
Stolz, B., & Schoembs, R. (1984) The SU UMa star TU Mensae. A&A 132, 187
Szkody, P. et al. (2007) Cataclysmic variables from Sloan Digital Sky Survey. VI. The sixth year (2005). AJ 134,
185
Tonry, J. L. et al. (2018) ATLAS: A High-cadence All-sky Survey System. PASP 130, 064505
Wakamatsu, Y. et al. (2021) ASASSN-18aan: An eclipsing SU UMa-type cataclysmic variable with a 3.6-hrorbital period and a late G-type secondary star. PASJ 73, 1209
Warner, B. (1995) Cataclysmic Variable Stars (Cambridge: Cambridge University Press)
Whitehurst, R. (1988) Numerical simulations of accretion disks. I – Superhumps: A tidal phenomenon of accretion
disks. MNRAS 232, 35
Whitehurst, R., & King, A. (1991) Superhumps, resonances and accretion discs. MNRAS 249, 25
Zorotovic, M., Schreiber, M. R., & Gänsicke, B. T. (2011) Post-common-envelope binaries from SDSS. XI. The
white dwarf mass distributions of CVs and pre-CVs. A&A 536, A42

This work is licensed under a Creative Commons “Attribution-NonCommercial-ShareAlike 4.0 International”
license.

VSOLJ
c/o Keiichi Saijo National Science Museum, Ueno-Park, Tokyo Japan
Editor Seiichiro Kiyota
e-mail:skiyotax@gmail.com