1
No.92

Feb. 2022

ISSN 0917-2211

Variable Star Bulletin
Analysis of the IW And star ASAS J071404+7004.3
Taichi Kato,1 Kiyoshi Kasai,2 Elena P. Pavlenko,3 , 4 Nikolaj V. Pit,3 Aleksei A. Sosnovskij,3Hiroshi Itoh,5 Hidehiko Akazawa,6 Stephen M. Brincat,7 Leonid E. Keir,8 Sergei N. Udovichenko,8Yusuke Tampo,1 Naoto Kojiguchi,1 Masaaki Shibata,1 Yasuyuki Wakamatsu,1 Tamás Tordai,9Tonny Vanmunster,10 Charles Galdies11
tkato@kusastro.kyoto-u.ac.jp
1 Department of Astronomy, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
2 Baselstrasse 133D, CH-4132 Muttenz, Switzerland
3 Federal State Budget Scientiﬁc Institution “Crimean Astrophysical Observatory of RAS”, Nauchny, 298409,
Republic of Crimea
4 V. I. Vernadsky Crimean Federal University, 4 Vernadskogo Prospekt, Simferopol, 295007, Republic of Crimea
5 Variable Star Observers League in Japan (VSOLJ), 1001-105 Nishiterakata, Hachioji, Tokyo 192-0153, Japan
6 Akazawa Funao Observartory, 107 Funao, Funaocho, Kurashiki, Okayama 710-0261, Japan
7 Flarestar Observatory, San Gwann SGN 3160, Malta
8 Astronomical Observatory of Odessa I. I. Mechnikov National University, Marazlievskaya 1v, 65014 Odessa,
Ukraine
9 Polaris Observatory, Hungarian Astronomical Association, Laborc utca 2/c, 1037 Budapest, Hungary
10 Center for Backyard Astrophysics Belgium, Walhostraat 1A, B-3401 Landen, Belgium
11 Institute of Earth Systems, University of Malta, Msida, MSD 2080, Malta

Received 2022 Feb. 23

Abstract
We made a time-resolved photometric campaign of the bright cataclysmic variable ASAS J071404+7004.3
in 2020. Inight et al. (2022, arXiv/2109.14514) recently published time-resolved optical spectroscopy, Xray observations and long- and short-term optical variations. Although their results were correct in many
parts, they classiﬁed ASAS J071404+7004.3 as a VY Scl-type novalike object. By comparing the ASASSN data of this object and the IW And-type object HO Pup, we showed that their type classiﬁcation wasincorrect. ASAS J071404+7004.3 showed outbursts from a standstill followed by shallow dips, which is thedeﬁning characteristic of an IW And star. This object predominantly showed states with low-amplitude dwarf
nova-type oscillations, some of which could be identiﬁed as the “heartbeat”-type state as a variety of the IW
And-type phenomenon. The low state described by Inight et al. (2022) was not a true low state of a VY Sclstar, but a dwarf nova-type state with increased outburst amplitudes. Both ground-based (our campaign) andTESS observations detected orbital variations whose periods [0.136589(5) d by the ground-based campaign
and 0.1366476(3) d by the TESS data] are in very good agreement with the one obtained by radial-velocity
studies by Inight et al. (2022). The standstill in 2019–2020 in ASAS J071404+7004.3 was not brighter thanits dwarf nova-type states. The brightest moment of this object occurred when the amplitudes of dwarf novatype variations were large, which challenges the widely accepted interpretation that standstills in Z Cam stars
occur when the mass-transfer rates are high.

21Introduction

Inight et al. (2022) reported on the recently identiﬁed nearby, bright (V ∼ 12) cataclysmic variable (CV) ASAS
J071404+7004.3. This object was identiﬁed as the optical counterpart of the X-ray source 1RXS J071404.0+700413
by Kiraga and Stępień (2013) by examining light variations of ROSAT All Sky Survey sources (Voges et al. 1999)
using the northern twin (ASAS-N) of the All-Sky Automated Survey (ASAS: Pojmański 2002). This object was
unique among the objects identiﬁed by Kiraga and Stępień (2013) in that it was classiﬁed as a miscellaneous
variable star with a period of 22.44 d.
Inight et al. (2022) published time-resolved optical spectroscopy, X-ray observations and long- and short-term
optical variations. The object was conﬁrmed to be a CV with an orbital period of 0.1366454(1) d. Inight et al.
(2022) compared the long-term light curve of this object with the AAVSO light curves of prototypical objectsof CV subtypes: Z Cam (Z Cam star), V513 Cas (IW And star) and VY Scl (VY Scl star) and concluded thatthe object belongs to the VY Scl-type CVs based on the visual similarity of the light curve rather than detailed
comparisons.
This object was introduced to us by a baavss-alert message “Request for help in monitoring ASAS J071404+
7004.3” requested by Boris Gänsicke and posted by Jeremy Shears on 2020 February 71 . Upon this message,
one of the authors (TK) examined All-Sky Automated Survey for Supernovae (ASAS-SN) Sky Patrol data
(Shappee et al. 2014; Kochanek et al. 2017) and readily identiﬁed it as an IW And star (T. Kato, vsnet-alert
239442 on 2020 February 7) based on the heartbeat-type variation with shallow dips in 2017 and the presenceof standstills. This identiﬁcation was quickly reﬂected on the AAVSO Variable Star Index (VSX: Watson et al.
2006)3 . It is strange that there was no trace of examination of this type identiﬁcation in Inight et al. (2022) and
we clarify the reasons of the apparent discrepancy in the type classiﬁcation.
In the following section, we describe the results from ASAS-SN observations. We conducted our own campaign of time-resolved photometry by the VSNET Collaboration (Kato et al. 2004), which was aimed to detect
possible negative superhumps (T. Kato, vsnet-alert 239494 ) motivated by the presence of negative superhumps(a tilted disk) in the IW And star KIC 9406652 (Gies et al. 2013; Kimura et al. 2020a; Kimura and Osaki 2021)
and a possible suggestion that a tilted disk might be responsible for the IW And-type phenomenon (Kimura et al.
2020a). The log of observations is shown in table 1. The R and I bands refer to Kron-Cousins systems. We
also analyzed Transiting Exoplanet Survey Satellite (TESS) observations.5 The full light-curve is available at the
Mikulski Archive for Space Telescope (MAST6 ).
Table 1: Log of observations of ASAS J071404+7004.3.
Start∗
End∗mag†error‡
N§
obs∥ band#
58887.2403 58887.4579 11.562 0.003
246
Van
R
58887.2413 58887.4583 12.020 0.003
246
Van
V
58888.4555 58888.5833 11.594 0.003
168
Van
R
58888.4561 58888.5827 12.056 0.003
164
Van
V
58889.6340 58889.7702 11.841 0.003
156
Van
V
∗
JD−2400000.
†
Mean magnitude.
‡
1σ of the mean magnitude.
§
Number of observations.
∥Observer’s code: Aka (H. Akazawa), BSM (S. Brincat),
CRI (Crimean Astrophys. Obs.), GCH (C. Galdies), Ioh (H. Itoh),
KU1 (Kyoto U. rooftop obs.), Kai (K. Kasai), May (Mayaki Obs.),
Trt (T. Tordai), Van (T. Vanmunster).
#
Filter. “C” means unﬁltered.
1 Although baavss-alert mailing list on yahoo had a publicly accessible archive, this service has already been discontinued and themessage is not currently publicly available.
2 <http://ooruri.kusastro.kyoto-u.ac.jp/mailarchive/vsnet-alert/23944>.
3 <https://www.aavso.org/vsx/index.php?view=detail.top&oid=300502>.
4 <http://ooruri.kusastro.kyoto-u.ac.jp/mailarchive/vsnet-alert/23949>.
5 <https://tess.mit.edu/observations/>.
6 <http://archive.stsci.edu/>.

3
Table 1: Log of observations of ASAS J071404+7004.3 (continued).
Start∗
End∗mag†error‡
N§
obs∥ band#
58890.0932 58890.2128 11.816 0.002
359
Ioh
C
58890.2151 58890.3351 -0.286 0.003
163
CRI
C
58890.2334 58890.4270 11.844 0.005
100 BSMV
58890.2344 58890.4280 11.640 0.006
89
BSM
I
58890.4491 58890.5404 12.175 0.007
9Van
B
58890.4504 58890.5417 11.865 0.012
9VanV58892.2501 58892.5173 11.620 0.014
19
Van
R
58892.5180 58892.5190 12.152 0.001
5Van
V58893.0409 58893.2323 -0.431 0.001 1358 KU1
C58893.4654 58893.5545 -0.273 0.004
104
CRI
C
58893.5152 58893.5499 12.135 0.009
6Van
B
58893.5166 58893.5512 11.841 0.017
6VanV
58893.5676 58893.6573 12.060 0.002
330
May
R
58894.1140 58894.1698 -0.409 0.002
432
KU1
C
58894.3092 58894.3092 12.093
–
1
Van
CV
58894.3103 58894.5522 11.889 0.014
9VanV58894.5149 58894.5509 12.146 0.010
6Van
B58895.2431 58895.4151 11.871 0.006
86
BSM
V
58895.2440 58895.4160 11.690 0.007
79
BSM
I
58895.2490 58895.3544 11.832 0.005
60
GCH
V
58895.2499 58895.3552 11.616 0.006
60GCHI58895.3092 58895.5497 12.195 0.015
9VanB58895.3106 58895.5511 11.908 0.014
6
VanV
58896.2537 58896.4161 11.851 0.005
85
BSM
V
58896.2546 58896.4151 11.634 0.006
57
BSMI
58896.3134 58896.6055 12.136 0.015
7VanB58896.3150 58896.6069 11.849 0.009
7
VanV
58896.4278 58896.6302 11.854 0.007
66
GCH
V
58896.4286 58896.6293 11.629 0.005
66
GCH
I
58897.3853 58897.4572 -0.288 0.002
98
CRIC
58897.4273 58897.4846 11.838 0.006
35
GCH
V
58897.4282 58897.6063 11.639 0.007
62
GCH
I
58898.2358 58898.6443 -0.238 0.001 2003 CRI
C
58898.4455 58898.5999 12.109 0.020
6VanB58898.4469 58898.6014 11.845 0.017
6Van
V
58899.4977 58899.7251 12.182 0.014
7Van
B
58899.4990 58899.7239 11.907 0.008
9Van
V
58900.2339 58900.4157 11.910 0.004
165 BSM
V
58900.4976 58900.7262 12.237 0.009
8Van
B
58900.4993 58900.7247 11.950 0.005
8
Van
V
58900.5435 58900.6226 11.910 0.005
48
GCH
V
58900.5444 58900.6216 11.689 0.005
47
GCH
I
58901.2503 58901.6714 11.927 0.002
539
Kai
V
∗
JD−2400000.
†
Mean magnitude.
‡
1σ of the mean magnitude.
§
Number of observations.
∥Observer’s code: Aka (H. Akazawa), BSM (S. Brincat),
CRI (Crimean Astrophys. Obs.), GCH (C. Galdies), Ioh (H. Itoh),
KU1 (Kyoto U. rooftop obs.), Kai (K. Kasai), May (Mayaki Obs.),
Trt (T. Tordai), Van (T. Vanmunster).
#
Filter. “C” means unﬁltered.

4
Table 1: Log of observations of ASAS J071404+7004.3 (continued).
Start∗
End∗mag†error‡
N§
obs∥ band#
58901.3029 58901.5823 11.874 0.002
318 BSM
V
58901.4978 58901.7253 12.107 0.007
7Van
B
58901.4988 58901.6578 11.872 0.017
5Van
V
58901.5416 58901.6152 11.915 0.007
30
GCH
V
58901.5447 58901.6132 11.685 0.004
29
GCH
I
58902.4975 58902.7253 12.183 0.010
9Van
B58902.4989 58902.7241 11.909 0.009
9Van
V
58903.4981 58903.7256 12.176 0.028
7Van
B
58903.4990 58903.6580 11.829 0.040
6Van
V
58904.2401 58904.5961 11.931 0.002
407
Kai
V
58904.4981 58904.7253 12.187 0.029
4Van
B
58904.4989 58904.4994 11.916 0.013
3Van
V
58905.2309 58905.4930 -2.011 0.002
436
May
R
58905.2415 58905.3582 11.831 0.003
161
Trt
V
58905.3755 58905.5422 -0.251 0.003
226
CRI
C
58906.1052 58906.3658 11.834 0.002
361
Aka
V
58906.2829 58906.4246 -0.247 0.002
192
CRI
C
58906.4837 58906.7254 12.082 0.003
4Van
B
58906.4853 58906.7242 11.827 0.026
3Van
V
58906.9395 58907.3708 11.814 0.003
292
Aka
V
58907.4842 58907.6261 12.119 0.009
5Van
B
58907.4855 58907.7099 11.876 0.015
9VanV
58908.3710 58908.5595 11.832 0.002
450
Trt
CV
58910.5706 58910.5711 11.628 0.006
3Van
R
58910.9375 58911.3143 11.800 0.003
270
Aka
V
58911.3220 58911.5347 -0.276 0.002
288
CRI
C
58911.4681 58911.4686 11.643 0.007
3Van
R
58911.9661 58912.0521 11.799 0.004
55
AkaV
58913.3184 58913.6768 11.791 0.001
871
Trt
V
58913.9270 58914.0178 11.776 0.006
73
AkaV
58914.0531 58914.2712 11.766 0.002
456
Ioh
V
58914.2568 58914.4465 11.793 0.004
209 BSMV
58914.9345 58915.0146 11.815 0.003
167
Ioh
V
58916.2513 58916.4514 11.926 0.003
253
Kai
V
58916.9406 58917.0958 11.924 0.003
147
Aka
V
58918.9692 58919.1906 11.842 0.002
359
Ioh
V
58919.9386 58920.0664 11.833 0.004
119
Aka
V
58920.2469 58920.4573 11.865 0.002
243 BSMV
58920.2670 58920.5717 11.878 0.002
401
Kai
V
58920.9181 58921.0824 11.881 0.003
151
Aka
V
58921.2463 58921.5264 -0.249 0.002
379
CRI
C
58921.2469 58921.4200 11.823 0.005
200 BSM
V
58921.3510 58921.3514 11.580 0.007
3
Van
R
∗
JD−2400000.
†
Mean magnitude.
‡
1σ of the mean magnitude.
§
Number of observations.
∥Observer’s code: Aka (H. Akazawa), BSM (S. Brincat),
CRI (Crimean Astrophys. Obs.), GCH (C. Galdies), Ioh (H. Itoh),
KU1 (Kyoto U. rooftop obs.), Kai (K. Kasai), May (Mayaki Obs.),
Trt (T. Tordai), Van (T. Vanmunster).
#
Filter. “C” means unﬁltered.

5
Table 1: Log of observations of ASAS J071404+7004.3 (continued).
Start∗
End∗mag†error‡
N§
obs∥ band#
58921.9225 58922.0375 11.836 0.012
12
AkaV
58922.2563 58922.4496 11.929 0.002
229
Kai
V
58922.9169 58923.0817 11.905 0.004
141
Aka
V
58923.2440 58923.3678 11.919 0.003
124 BSMV
58923.2583 58923.3547 11.664 0.007
42
GCH
I
58923.2913 58923.6167 11.944 0.003
318
Kai
V
58924.2966 58924.6162 11.939 0.002
438
Kai
V
58925.9374 58926.0609 11.835 0.004
118
Aka
V
58926.2837 58926.6095 11.904 0.003
306
Kai
V
58926.9214 58927.0259 11.822 0.004
100
Aka
V
58927.9136 58928.0794 11.862 0.004
158
Aka
V
58928.2683 58928.5974 11.908 0.002
405
Kai
V
58928.9217 58929.0517 11.855 0.003
124
Aka
V
58929.9151 58930.0732 11.820 0.003
150
Aka
V
58931.2772 58931.5853 11.876 0.002
379
Kai
V
58931.9134 58932.0502 11.806 0.005
130
Aka
V
58932.2744 58932.5878 11.867 0.002
430
Kai
V
58932.9478 58933.0523 11.815 0.004
100
Aka
V
58933.2719 58933.5594 11.882 0.002
370
Kai
V
58933.9427 58934.0441 11.838 0.005
97
AkaV
58934.2866 58934.5844 11.890 0.003
399
Kai
V
58935.2794 58935.5188 11.902 0.002
330
Kai
V
58939.2897 58939.5744 11.906 0.003
346
Kai
V
58940.2760 58940.5717 11.885 0.002
322
Kai
V
58941.2824 58941.5637 11.907 0.003
253
Kai
V
58942.2825 58942.5454 11.927 0.003
332
Kai
V
58943.2586 58943.4255 12.081 0.002
326
May
R
58945.2525 58945.4978 11.939 0.002
440
May
R
58945.2642 58945.4158 11.800 0.002
190 BSMV
58945.2677 58945.3942 11.585 0.003
82
GCH
I58945.2915 58945.5449 11.830 0.002
302
Kai
V
58946.2911 58946.5505 11.833 0.002
340
Kai
V
58946.9222 58947.2099 11.827 0.002
610
Ioh
V
58947.2909 58947.5459 11.878 0.002
335
Kai
V
58947.9265 58948.2262 11.884 0.002
649
Ioh
V
58948.2619 58948.4155 11.931 0.003
185 BSMV
58948.2682 58948.4491 11.698 0.003
134 GCHI
58948.2861 58948.5414 11.963 0.002
335
Kai
V
58949.2820 58949.4997 12.034 0.002
428
May
R
58949.2993 58949.4091 11.624 0.005
56GCH
I
58950.0043 58950.1393 11.758 0.002
340
Ioh
V
58953.9519 58954.2054 11.876 0.002
695
Ioh
V
∗
JD−2400000.
†
Mean magnitude.
‡
1σ of the mean magnitude.
§
Number of observations.
∥Observer’s code: Aka (H. Akazawa), BSM (S. Brincat),
CRI (Crimean Astrophys. Obs.), GCH (C. Galdies), Ioh (H. Itoh),
KU1 (Kyoto U. rooftop obs.), Kai (K. Kasai), May (Mayaki Obs.),
Trt (T. Tordai), Van (T. Vanmunster).
#
Filter. “C” means unﬁltered.

62

Results and discussions

2.1

Long-term light curve

Although the ASAS-SN light curves were shown in Inight et al. (2022), they were either too small (their ﬁgure12) or the important feature was not shown (their ﬁgure 2), we provide the full ASAS-SN light curve (ﬁgures 1,
2 and 3) together with TESS observations and the VSNET campaign data to show important features.
The most obvious feature is the long-lasting standstill between BJD 2458720 and 2459000 (ﬁgure 3, the second
panel). It was rather a pity that the start of this standstill was not recorded. This standstill was terminated byan outburst which occurred during TESS observations.
The other parts after BJD 2456950 were dominated by low-amplitude dwarf nova-type variations (startingfrom the fourth panel of ﬁgure 1, most of ﬁgure 2 except the ﬁnal part and ﬁgure 3 except the second panel andafter BJD 2459550). The 22.44 d period in Kiraga and Stępień (2013) apparently referred to these low-amplitude
dwarf nova-type variations. Although such low-amplitude dwarf nova-type variations are also seen in IX Vel(Kato 2021b), the cycle length in ASAS J071404+7004.3 is longer compared to IX Vel with 13–20 d and the
proﬁle is diﬀerent in that variations in ASAS J071404+7004.3 tend to have slower rise and steeper decline as seenin the third panel of ﬁgure 2. This feature was interpreted as “inside out” (outburst) in Inight et al. (2022).

2.2

Problem of type classiﬁcation in Inight et al. (2022)

The main reason why Inight et al. (2022) reached an inadequate classiﬁcation was that they only consulted therelatively old literature Hameury and Lasota (2014) when referring to IW And stars. It is queer that Inight et al.
(2022) referred to the category IW And stars, which term was not mentioned in Hameury and Lasota (2014),
but was later deﬁned by Kato (2019). These authors apparently dismissed this later deﬁnition and subsequent
progress (e.g. Kimura et al. 2020b; Kato et al. 2020, 2021). In Kato (2019); Kimura et al. (2020b), the IW And
stars were deﬁned to have the features: (1) Standstills are terminated by brightening in IW And-type objects,
unlike fading in Z Cam stars. (2) There are quasi-periodic cycles consisting of a (quasi-)standstill with damping
oscillations — brightening which terminates the standstill — often a deep dip (not always present within the same
object) and returning to a (quasi-)standstill. When deep dips are not present, the light curve looks like a periodic
pattern with gradual rise with an increasing rate to a maximum followed by rapid fading. This pattern is referred
to as “heartbeat-type oscillations”. It can be conﬁrmed that this is a variety of IW And-type variation since thesame object shows both typical IW And-type cycles with deep dips and these heartbeat-type oscillations. The
depths of the dips form a continuum from zero (heartbeat-type oscillations) to a few magnitudes in the typical IW
And-type cycles. This feature was described for the two objects in FY Vul and HO Pup in Kimura et al. (2020b),
and Inight et al. (2022) probably missed modern knowledge of IW And stars. Considering these features, thelight curve of ASAS J071404+7004.3 is very similar to that of HO Pup (ﬁgures 4 and 5). Just for information,
Lee et al. (2021) correctly described HO Pup as an IW And star. The presence of long standstills (second panel
in ﬁgure 3 and possibly before BJD 2456930 in ﬁgure 1) is also similar to the IW And star BO Cet, which showeda long standstill (this object was therefore initially classiﬁed as a novalike) lasting for years (Kato et al. 2021).
The second reason is that Inight et al. (2022) did not describe the characteristics of subclasses of CVs
correctly. Inight et al. (2022) described IW And stars as showing continual outbursts (not unlike dwarf novae)
during the high state (i.e. during the “standstill”). The most obvious feature of the IW And stars, however, isthe presence of outbursts at the end of standstills, not during standstills.
Low states in VY Scl stars were also poorly deﬁned (without a reference) and poorly compared with ASAS
J071404+7004.3 in Inight et al. (2022). Typical low states of VY Scl stars lasts months to years and there
are usually no strong sign of dwarf-nova outbursts during decline despite that the mass-transfer rates decrease.
Examples of the light curves and a schematic representation of the lack of dwarf-nova outbursts can be foundin Leach et al. (1999). This feature has long been known and the cause of the apparent inconsistency with the
disk-instability model has been sought. Leach et al. (1999) suggested heating from a hot white dwarf suppresses
thermal instability of the disk. Hameury and Lasota (2002) considered that the magnetism of a white dwarf
could truncate the disk, thereby suppressing thermal instability. The presence of magnetism of white dwarfs in
VY Scl stars in general, however, has not been apparent by observations. In any case, Inight et al. (2022) did
not consider this well-known observational feature of VY Scl stars. The fading episode in ASAS J071404+7004.3

7

11

12

13

55950

56000

56050

56100

56150

56200

56250

11

12

13

56250

56300

56350

56400

56450

56500

56550

11

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13

56600

56650

56700

56750

56800

56850

11

12

13

56900

56950

57000

57050

57100

57150

Figure 1: Long-term light curve of ASAS J071404+7004.3 using the ASAS-SN data. All data are in V band. After
BJD 2456950, low-amplitude (0.7 mag) dwarf-nova oscillations appeared. After BJD 2457100, the amplitudes ofthese oscillations became larger (1.6 mag) and the period became shorter.

8

11

12

13

57200

57250

57300

57350

57400

57450

11

12

13

57500

57550

57600

57650

57700

57750

57800

11

12

13

57800

57850

57900

57950

58000

58050

58100

11

12

13

58150

58200

58250

58300

58350

58400

Figure 2: Long-term light curve of ASAS J071404+7004.3 using the ASAS-SN data (2). Blue and green symbols
represent V and g observations, respectively. This segment is dominated by low-amplitude dwarf nova-type
variations with variable amplitudes and periods. The periods became as short as 10 d. In the latter part of thissegment, the periods became longer and the rise to outbursts became slower than the decline. Some outbursts
were followed by small dips. This part corresponds to the IW And-type behavior. See ﬁgure 5 for a comparison
to the IW And star HO Pup.

9

11

12

dip

13

dip

58450

dip

58500

58550

58600

58650

58700

11

12

13

58750

58800

TESS (1)

VSNET campaign

58850

58900

TESS (2)

58950

59000

11

12

13

59050

59100

59150

59200

59250

59300

59350

11

12

13

TESS (3)

59350

59400

TESS (4)
59450

59500

59550

59600

59650

Figure 3: Long-term light curve of ASAS J071404+7004.3 using the ASAS-SN data, TESS data (yellow) andthe VSNET campaign data (red). Blue and green symbols for the ASAS-SN data represent V and g observations,
respectively. The TESS and VSNET data were binned to 1 d. The initial three runs of of the TESS data were
shifted by −0.1 mag to match the ASAS-SN data. The ﬁrst panel shows the typical behavior of an IW And star.
Slowly rising standstills were terminated by outbursts (shown by the upper blue ticks), followed by small dips(shown by the lower ticks). See ﬁgure 5 for a comparison to the IW And star HO Pup. The second panel shows
the standstill phase. An outburst in the TESS data (2) marked the end of the standstill phase. The third panel
is also dominated by dwarf nova-type variations.

10
was simply a dwarf nova phase with larger amplitudes (as in Z Cam stars) when the mass-transfer rate dropped
slightly. It is also apparent from ﬁgure 4 that excursions to fainter magnitudes while maintaining dwarf nova-type
outbursts happen in other IW And stars. This is probably what happened ASAS J071404+7004.3 after BJD
2457100.
The confusion with the VY Scl-type phenomenon is not, however, surprising. Even the authority of CVs
Brian Warner considered dwarf nova-type AM CVn stars, which are currently known as helium counterpart of
SU UMa/WZ Sge-type stars in hydrogen-rich CVs (see e.g. Tsugawa and Osaki 1997; Kotko et al. 2012), to beanalogous to VY Scl stars at least in the past (Warner 1995).

2.3

Analysis of ground-based time-resolved campaign

We obtained more than 25000 measurements between 2020 February 7 and 2020 April 14. Although someobservations are apparently common to the “intensive photometric monitoring of the system using small-aperture
telescopes throughout February and March 2020” described in Inight et al. (2022), the majority of the data wereobtained by VSOLJ observers, the Crimean Astrophysical Observatory and the Kyoto University team, which
are not present in the AAVSO International Database7 (ﬁgures 6 and 7). Inight et al. (2022) did not show
any result of period analysis of these ground-based observations. This interval corresponded to the standstill(ﬁgure 3, the second panel) and we only searched for periodicities around the orbital period. We used locallyweighted polynomial regression (LOWESS: Cleveland 1979) to remove the long-term trend and applied thePhase Dispersion Minimization (PDM, Stellingwerf 1978) method. The errors of periods by the PDM method
were estimated by the methods of Fernie (1989) and Kato et al. (2010). This analysis (ﬁgure 8) detected anorbital period of 0.136589(5) d, which agrees with the value by Inight et al. (2022) to better than 0.0005%.

2.4

Period analysis of TESS data

TESS observations have four segments. We performed PDM analysis as in the same way for the ground-based
campaign (ﬁgures 9, 10, 11 and 12). All segments showed only the orbital signal. We can conclude that that there
were neither positive nor negative superhumps regardless of the outbursting phase. This result excludes (at leastin this object) a possible suggestion that a tilted disk might be responsible for the IW And-type phenomenon(Kimura et al. 2020a). It has been pointed out that a model involving a tilted disk could not reproduce thevariation of the disk radius observed in the IW And star KIC 9406652 (Kimura and Osaki 2021). The absenceof negative superhumps has also been reported in other IW And stars (IM Eri: Kato et al. 2020; ST Cha:
Kato and Kojiguchi 2021; HO Pup: Lee et al. 2021).
The proﬁle of the orbital variation slightly varied. During the long standstill and one outburst, the proﬁle
was almost sinusoidal (ﬁgures 9, 10). During another outburst cycle, the maximum of the orbital hump had
double peaks (ﬁgure 11). During the most recent standstill with some variability, the orbital proﬁle became
asymmetric (ﬁgure 12). There were no apparent changes in the PDM θ diagrams and these changes were not a
result of positive/negative superhumps. Orbital proﬁles from the TESS observations are shown in ﬁgure 13. It
appears that the phases of maxima and minima varied slightly. These changes may reﬂect the changes in thestate of the accretion disk or the accretion geometry, and need to be studied in detail.
There were no “embedded precursors” as observed in ST Cha (Kato and Hambsch 2021). There was noenhancement of the orbital signal nor appearance of a long period as observed in a long outburst of the SS Cyg
star V363 Lyr (Kato 2021a).
We summarize the values of orbital periods in table 2. We obtained the photometric orbital period fromthe combined TESS data to be 0.1366476(3) d, which is in very good agreement with the one obtained by theradial-velocity study by Inight et al. (2022).

2.5

Are standstills brighter than dwarf nova-type states?

In ﬁgure 14, we show the trend of mean magnitudes (averaged in ﬂux) as we did for IX Vel (Kato 2021b) and ST
Cha (Kato and Kojiguchi 2021). The result shows that the 2019–2020 standstill was not brighter than the dwarf
nova-type states (IW And-type states) before and after this. This indicates that either standstill or IW And
state does not occur as the result of changing mass-transfer rates. This conclusion is the same as in Inight et al.
(2022). It would be interesting to note that dwarf nova-type state with relatively large amplitudes in 2015–2016
7 <https://www.aavso.org>.

11

13

14

15

57000

57050

57100

57150

57200

57250

57300

13

14

15

57350

57400

57450

57500

57550

57600

13

14

15

57650

57700

57750

57800

57850

57900

13

14

15

57950

58000

58050

58100

58150

58200

Figure 4: Long-term light curve of HO Pup using the ASAS-SN data. Blue and green symbols represent
V and g observations, respectively. The third panel corresponds to “heartbeat-type” oscillations in IW And
stars, accompanied by slower rise and steeper decline. This type of variation is considered to be IW And-type
cycles simply lacking post-outburst dips. After BJD 2458080, typical IW And-type behavior is seen: standstills
terminated by outbursts, followed by dips. It is also apparent that the depths of the dips vary and the dips
became inapparent after BJD 2458180, indicating that heartbeat-type oscillations and the typical IW And-type
behavior form a smooth continuum.

12

13

14

15

58250

58300

58350

58400

58450

58500

58550

13

14

15

58550

58600

58650

58700

58750

58800

58850

13

14

15

58900

58950

59000

59050

59100

59150

13

14

15

59200

59250

59300

59350

59400

59450

Figure 5: Long-term light curve of HO Pup using the ASAS-SN data (2). Blue and green symbols represent
V and g observations, respectively. Most of the time, this star showed heartbeat-type oscillations with variableintervals. This segment is very similar to ASAS J071404+7004.3 between BJD 2458150 and 2458630 (ﬁgures 2
and 3).

13

11.4
11.6
11.8
12.0
12.2
12.4

58888

58890

58892

58894

58896

58898

58900

58902

58904

11.4
11.6
11.8
12.0
12.2
12.4
58904

58906

58908

58910

58912

58914

58916

58918

58920

11.4
11.6
11.8
12.0
12.2
12.4

58922

58924

58926

58928

58930

58932

58934

58936

58938

11.4
11.6
11.8
12.0

B

12.2
12.4
58938

58940

58942

58944

58946

58948

58950

V

R
58952

I

C
58954

Figure 6: Light curve of ASAS J071404+7004.3 using the ground-based observations obtained by our campaign.
The zero points were adjusted by correcting the diﬀerences between observers and bands. The color indicesagainst V were determined only for B and I by simultaneous observations, and they are reﬂected on this ﬁgure.
The colors corresponded to B − V =+0.08 and V − I=+0.19. We assumed that the mean magnitudes were thesame for V , R and C since there were no simultaneous data for these bands and since the color indices between
these bands are expected to be close to zero in this unreddened and disk-dominated CV.

14

11.4
11.6
11.8
12.0
12.2
12.4

58919.858920.058920.2

58920.4

58920.6

58920.8

58921.058921.2

58921.4

58921.6

58921.8

58922.058922.2

58922.4

58922.6

58922.858923.058923.2

58923.4

58923.6

11.4
11.6
11.8
12.0
12.2
12.4
11.4
11.6
11.8
12.0
12.2
12.4
11.4
11.6
11.8
12.0
12.2
12.4

Figure 7:
Example of enlarged light curve of ASAS J071404+7004.3 using the ground-based observations
obtained by our campaign. The symbols are the same as ﬁgure 6.

15

θ
1.00

0.99

0.98

P=0.13659

0.97
0.130

0.132

0.134

0.136

0.138

0.140

0.142

0.144

(d)

−0.02

0.00

0.02

−0.5

0.0

0.5

1.0

1.5

Figure 8: Period analysis of our campaign in 2020 February–April. (Upper): We analyzed 100 samples which
randomly contain 50% of observations, and performed the PDM analysis for these samples. The bootstrap resultis shown as a form of 90% conﬁdence intervals in the resultant PDM θ statistics. (Lower): Orbital variation.

16

θ
1.00

0.98

0.96

0.94

P=0.13664
0.92
0.130

0.132

0.134

0.136

0.138

0.140

0.142

0.144

(d)

−0.02

0.00

0.02

−0.5

0.0

0.5

1.0

1.5

Figure 9: Period analysis of TESS data between BJD 2458842 (2019 December 25) and 2458868 (2020 January
20). These observations correspond to the long standstill phase. (Upper): PDM analysis. (Lower): Orbital
variation.

17

θ
1.00

0.95

0.90

0.85

P=0.13664
0.130

0.132

0.134

0.136

0.138

0.140

0.142

0.144

(d)

−0.02

0.00

0.02

−0.5

0.0

0.5

1.0

1.5

Figure 10: Period analysis of TESS data between BJD 2459010 (2020 June 9) and 2459035 (2020 July 4). Theseobservations covered the outburst that terminated the long standstill phase. (Upper): PDM analysis. (Lower):
Orbital variation.

18

θ
1.00

0.98

0.96

0.94

0.92

P=0.13665
0.130

0.132

0.134

0.136

0.138

0.140

0.142

0.144

(d)

−0.02

0.00

0.02

−0.5

0.0

0.5

1.0

1.5

Figure 11: Period analysis of TESS data between BJD 2459390 (2021 June 25) and 2459418 (2021 July 23). Theseobservations covered one complete outburst and one outburst during decline of the heartbeat phase. (Upper):
PDM analysis. (Lower): Orbital variation.

19

θ
1.00

0.98

0.96

0.94

P=0.13674
0.130

0.132

0.134

0.136

0.138

0.140

0.142

0.144

(d)

−0.02

0.00

0.02

−0.5

0.0

0.5

1.0

1.5

Figure 12: Period analysis of TESS data between BJD 2459579 (2021 December 23) and 2459606 (2022 January
27). These observations correspond to a slightly variable standstill phase. (Upper): PDM analysis. (Lower):
Orbital variation.

20

0.5

(BJD−2400000)
58849

0.4

58862

59016
0.3

59029

59397
0.2

59412

59596
0.1

59600

0.0
−0.5

0.0

0.5

1.0

1.5

Figure 13: Variation of the orbital proﬁle in TESS data. The data with 14-d segments centered on the dates
given to the right of the averaged light curves were used. The epoch and period were from Inight et al. (2022).

21

Table 2: Orbital period of ASAS J071404+7004.3
Data
Radial velocity
TESS (1)
TESS (2)TESS (3)TESS (4)TESS combined
VSNET campaign

Interval (JD−2400000)
56597–59197
58842–58868
59010–59035
59390–59418
59579–59606
58842–59606
58887–58954

Period (d)0.1366454(1)0.136635(10)0.136644(7)0.136648(3)0.136741(4)0.1366476(3)0.136589(5)SourceInight et al. (2022)
this paper
this paper
this paper
this paper
this paper
this paper(BJD 2457260–2457700) occurred when the mean magnitude was the brightest. This phenomenon challenges theclassical (and widely accepted) interpretation that standstills in Z Cam stars occur when the mass-transfer rates
are high (Meyer and Meyer-Hofmeister 1983).

2.6

Notes on interpretations in Inight et al. (2022)

Inight et al. (2022) suggested that there is an outer part of the disk that occasionally becomes suﬃciently cool forhydrogen to recombine to explain the dwarf nova-like variations of ASAS J071404+7004.3 (this is an explanation
for dwarf-nova outbursts, although Inight et al. (2022) did not adopt the dwarf-nova classiﬁcation for this object)rather than periodic mass-transfer variations from the secondary as modeled by Hameury and Lasota (2014).
Inight et al. (2022) stated that this outburst starts at the inner edge of this area and subsequently spreads
outwards. This picture is essentially what was proposed for IW And stars in Kato (2019) (it was written as “thestandstill in these objects is somehow maintained in the inner part of the disk and the thermal instability startingfrom the outer part of the disk terminates the standstill to complete the cycle” in the abstract). It is, however,diﬃcult to consider a disk whose outer part becomes cool for a long time when the mass-transfer hits the outeredge of the disk. Kimura et al. (2020b) considered a tilted disk in which the majority of mass stream hits theinner disk and the outer disk is cool most of the time. Although model simulations by Kimura et al. (2020b)
reproduced a limit cycle similar to IW And stars, they could not reproduce the observed disk radius variation(Kimura et al. 2020a) and the frequent occurrence of heating waves in the cool part of the disk was somewhat
diﬀerent from what are observed in IW And stars. The existence of the cool region in the disk of IW And stars
during (quasi-)standstills has been conﬁrmed by M. Shibata et al. in preparation and the picture by Kato (2019)
and Inight et al. (2022) appear to be correct. We still need an explanation why the outer disk can remain coolin the presence of mass-transfer reaching the outer part of the disk.
Inight et al. (2022) also concluded that the emission lines in ASAS J071404+7004.3 could be reproducedby considering the wind. It would be worth noting that Tampo et al. (2022) considered the same kind of windduring the superoutburst of the WZ Sge star V455 And and reproduced singly peaked emission lines as observed,
which are not expected for this high-inclination CV.

Acknowledgements
This work was supported by JSPS KAKENHI Grant Number 21K03616. The author is grateful to the ASAS-SN
team for making their data available to the public. This research has made use of the AAVSO Variable Star
Index and NASA’s Astrophysics Data System.

List of objects in this paper
IW And, V455 And, Z Cam, V513 Cas, BO Cet, AM CVn, SS Cyg, IM Eri, V363 Lyr, HO Pup, VY Scl, WZ
Sge, SU UMa, IX Vel, FY Vul, ASAS J071404+7004.3, KIC 9406652

22

11

12

13

11.4

11.6

11.8

12.0

12.2

12.4
56000

56500

57000

57500

58000

58500

59000

59500

Figure 14: (Upper): ASAS-SN light curve of ASAS J071404+7004.3. (Lower): Trend determined by LOWESS.
A smoothing parameter of f =0.06 was used.

23

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license.

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