1
No.93

Mar. 2022

ISSN 0917-2211

Variable Star Bulletin
On the identity of Tsesevich’s “YY Dra”
Taichi Kato,1 Elena P. Pavlenko2
tkato@kusastro.kyoto-u.ac.jp
1 Department of Astronomy, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
2 Federal State Budget Scientiﬁc Institution “Crimean Astrophysical Observatory of RAS”, Nauchny, 298409,
Republic of Crimea

Received 2022 Mar.07

Abstract
Hill et al. (2022, arXiv:2203.00221) recently published analysis of the intermediate polar DO Dra (YY Dra)
using TESS, ASAS-SN and ZTF data. They also attempted a search for the “lost” variable YY Dra using
modern catalogs of variable stars and found no corresponding one. This search drew our renewed attention
and we studied the original discovery paper of YY Dra by Tsesevich (Zessewitch). We found that two out offour variables reported by him were either lost or improperly studied. The coordinate oﬀset from the correct
position in another object was much larger than the expected error. Using the information of the publishedperiod and epoch of YY Dra, we suspect that Tsesevich used a couple of plates on which the object wasinvisible to derive the period rather than from a completely phased light curve. DO Dra sometimes spends
high states around 14 mag for a month to several months and it would not be surprising if Tsesevich observed
DO Dra in such a state and suspected it to be an Algol, urging him to examine the plate archive to obtainthe moments when the variable was undetected. We suspect that Tsesevich indeed observed DO Dra, rather
than a diﬀerent, lost eclipsing variable. The ﬁnal conclusion of this matter is almost impossible to reach dueto the consequence of the World War II, destructing the large part of plate collections. Until the humanity
becomes wise enough to restore this destruction and wise enough to be able to avoid further destruction ofhuman achievements, the designation YY Dra would better be conserved as a record of our negative history
and unambiguous DO Dra would better be used to designate the intermediate polar 3A 1148+719.

1

Introduction

Hill et al. (2022) recently reported on analysis of the intermediate polar DO Dra (YY Dra) using Transiting
Exoplanet Surveying Satellite (TESS)1 , All-Sky Automated Survey for Supernovae (ASAS-SN) Sky Patrol data
(Shappee et al. 2014; Kochanek et al. 2017), Zwicky Transient Facility (Masci et al. 2019) and other sources.
The discussion about the identity of Tsesevich’s “YY Dra” in Hill et al. (2022) drew our renewed attention. Thisobject was introduced to amateur variable star observers as a rarely outbursting new dwarf nova in the mid-1980s
by the American Association of Variable Stars (AAVSO), initially under the name of YY Dra and then DO Dra
twice in a row using the same chart issued in their monthly circulars. Knowing this complicated history, theidentity of these two designations has long been a matter of interest for many amateur observers and we would
like to clarify the matter a bit.

1 <https://tess.mit.edu/observations/>.

2
Original “YY Dra” was reported as one (SVS 504, Dra) of four variable stars discovered by Zessewitch (1934)2 .
The designation DO Dra was given in Kholopov et al. (1985) referring to the X-ray source 3A 1148+719 = 2A
1150+720 = PG 1140+719, following the identiﬁcation of this object as a cataclysmic variable (PG 1140+719:
Green et al. 1982, 3A 1148+719: Patterson et al. 1982), both giving YY Dra as the identiﬁcation, and thesubsequent identiﬁcation as a long-period dwarf nova (Wenzel 1983a,b). In Kholopov et al. (1985), it was written
as ̸=YY Dra. Following this oﬃcial naming of DO Dra by the General Catalogue of Variable Stars (GCVS) team,a debate arose. Patterson and Eisenman (1987) claimed that the cataclysmic variable is identical with YY Dra
and the name DO Dra should be abandoned (titled as “Let’s Forget DO Dra”). In response to this, the GCVS
team issued “Should we Really Forget DO Dra?” (Kholopov and Samus 1988), stating: “To conclude, we do notrecommend to forget DO Dra, and we do not recommend to forget YY Dra, either. If one really wants to forget
something, it would be better to forget until [as written] it is proven that DO Dra and YY Dra are the same,or until [as written] the real YY Dra is found”. Kholopov and Samus (1988) concluded: “As a group responsible
for the names of variable stars we are much interested in avoiding confusion and strongly recommended to use
the name DO Dra for E1140.8+7158”.3 A summary of this history was also described in Andronov et al. (2008);
Babina et al. (2020).
Following this recommendation, DO Dra has been treated as the oﬃcial designation of this cataclysmic
variable, and it has been widely used in IAU Circulars and in the community of amateur variable star observers.
The full papers by J. Patterson’s group were published as Patterson et al. (1992); Patterson and Szkody (1993),
clarifying the nature of this object as an intermediate polar. Patterson et al. (1992) also mentioned that there isno variable star in the vicinity corresponding to the Algol star “YY Dra”.

2

New attempts

There have been attempts to search for the original Tsesevich’s YY Dra considering that the published position
was in error. One of the authors (TK) noticed in 2000 that the coordinates of the Algol RW UMa precessedby 50 years have the right ascension very similar to that of YY Dra with a diﬀerence in declination by 20◦ .
Furthermore, the published epoch of the minimum of YY Dra agrees with E=−3544 of the element of RW UMa
in GCVS (T. Kato, vsnet-chat 38074 ). This ﬁnding was brought through the discussion with N. N. Samus. His
message (vsnet-chat 38055 ) might help understanding the situation, and we quote it here for reader’s convenience:
Tsessevich’s observations used Simeiz plates. A part of Simeiz collection perished in the WorldWar II, another part survived and is now in Pulkovo. The Pulkovo collection does not contain plates
around the dates of minima originally announced by Tsessevich. Also, some plates could survive andbe taken to Odessa, but, again, they could not be found so far.
Tsessevich was a VERY experienced person and could not mix up an eclipser with a dwarf nova.
Upon the query about the possible confusion with RW UMa, Samus replied (vsnet-chat 38196 ). We also quote it
here:Your ﬁnding is very interesting. However, I don’t believe that RW UMa and YY Dra are the same.
Tsessevich told me that his star was “In a half degree” – I could not understand his remark, but now
I know that his position was exactly in a half degree from the center of his plates, Z Dra” 7 . [...] As
far as I remember, no other minima of YY Dra are known.
2 The author name W. Zessewitch is the German spelling of V. Tsesevich (Ceseviq, Vladimir Platonoviq in the original
language). This paper was written in English. There is also a variety of Latin transcription (Tsessevich) of his name, in which “-sse-”
apparently came from the German spelling (in German, “-se-” is pronounced as “-ze-” in English, and “-sse-” was apparently used toreﬂect the original sound). We use the better known spelling Tsesevich, which agrees with the spelling in the original language, inthe present paper when referring to the discoverer.
3 A similar situation occurred when “GM Sgr” optically brightened and was identiﬁed with an X-ray source (Stubbings et al. 1999).
The name GM Sgr had already been used to designate this variable (Goranskij 1978, 1990; Downes et al. 1995). In this case, theoriginal GM Sgr was identiﬁed to be a diﬀerent variable (see also Kato and Uemura 1999; Orosz 2000) and a new designation of
V4641 Sgr was assigned (Samus et al. 1999).
4 <http://vsnet.kusastro.kyoto-u.ac.jp/vsnet/Mail/chat3000/msg00807.html>.
5 <http://vsnet.kusastro.kyoto-u.ac.jp/vsnet/Mail/chat3000/msg00805.html>.
6 <http://vsnet.kusastro.kyoto-u.ac.jp/vsnet/Mail/chat3000/msg00819.html>.
7 Since the original article would be diﬃcult to reach, we clarify that this remark by Tsesevich was not present in Zessewitch(1934). Zessewitch (1934) only reported the position 21h 42m 42s +56◦ 15.′ 2 (1855.0), Amplitude: 12.9–[14.5, Algol-type. Tsesevich
apparently used Bonner Durchmustering to derive the coordinates.

3
The above explanation by N. N. Samus was partially presented as a form of private communication in
Virnina (2011). There was some more details according to Samus’ (1988). Samus noticed in 1983 fall [i.e. after
publication by Wenzel (1983a,b)] about the bright eclipsing binary YY Dra, which had been virtually forgotten
or lost and no one else had observed, while working on the 4-th Edition of the GCVS. Samus’ (1988) wrote that
the X-ray source 3A 1148+719 had been found in this region and that Wenzel (1983a,b) successfully identiﬁed itwith an eruptive (cataclysmic in modern term) variable star. Samus’ (1988) wrote that some researchers applied
the name YY Dra to this cataclysmic variable, while others considered that the true YY Dra was a diﬀerent star
which was not be able to be recovered possibly due to the error in the position. If there had been a chart by thediscoverer, the question could have been answered, but there was none in the literature. Although Samus was wellfamiliar with Tsesevich and his knowledge in variable stars was highly evaluated, Samus was not sure whether
Tsesevich remembered the position of a star which he observed long time ago. Samus discussed this matter withhis colleague M. S. Frolov and Frolov immediately replied about Tsesevich’s unique ability of remembrance about
when and how the period varied of RR Lyr stars Frolov asked. Samus called Odessa, and Tsesevich replied that
he remembered YY Dra. Here, Tsesevich replied “in a half degree” and asked to send a good plate to Odessa, on
which he could mark YY Dra. A plate was quickly sent to Odessa, but Tsesevich had already been in a clinic.
On October 26 he asked to bring the plate to the clinic, but after two days he passed away, bringing the mysteryof YY Dra with himself.
Virnina (2011) considered that the position of the original YY Dra was in error and attempted to ﬁnd an
eclipsing binary in the 10◦ ×10◦ area surrounding Z Dra by new observations. This search yielded only contact
binaries, which were apparently diﬀerent from the one discovered by Tsesevich.
Since all-sky photometric data such as ASAS-SN became publicly available, at least two groups independently
searched the possible counterpart of Tsesevich’s YY Dra: Hill et al. (2022) and Koji Mukai in the 2021 update8
of his “The Intermediate Polars” page9 . Mukai searched the ASAS-SN variable star database (Jayasinghe et al.
2018, 2019) matching the period in the 10◦ ×10◦ ﬁeld as in Virnina (2011) and found none. Hill et al. (2022)
searched the Catalina Surveys Periodic Variable Star Catalog (Drake et al. 2014) and the ASAS-SN variable star
database for the entire sky observable from Russia. There was no object compatible with Tsesevich’s YY Draeven if they loosened the constraints on the amplitude and the period. Hill et al. (2022) wrote: “We cannot ruleout the possibility that YY Dra really is an eclipsing binary whose position, period, and range of variation were
all massively erroneous. This explanation, however, would require an unlikely conﬂuence of errors and would
probably be untestable, in that it would leave the search for YY Dra almost completely unconstrained”.

3

Discussion

We here provide new perspectives regarding this matter.

3.1

Reliability of Tsesevich’s classiﬁcation and magnitudes

We studied three other variables discovered in Zessewitch (1934). The ﬁrst object listed was YY Dra. The second
one is AI Cep and was listed as a β Lyrae-type with an element of Min = 2426550.256+4.22524E. According
to Albo (1964), Tsesevich discovered this object during observation of SU Cep. This ephemeris agrees with themodern one and Tsesevich apparently observed the full orbital cycle. The only small diﬀerence (0.003%) of theperiod from the modern one suggests that he should have used a very long (tens of years) baseline. According toAlbo (1964), Tsesevich obtained this epoch for AI Cep from 296 visual observations. Another epoch of 2415615.385
was listed, which was based on two photographic observations. They were published in V. P. Ceseviq, Odessa
Izv. (Odessa Proceedings) 4, vyp. 1 (1954). This indicates that the objects reported in Zessewitch (1934) usedvery heterogenous types of observations. The small number of photographic observations reported for AI Cep
suggests that Tsesevich’s conclusion for each object in Zessewitch (1934) was not based on a large number ofplates.
The third object is NSV 14669 and the coordinates were given as 23h 34m 23s +23◦ 38′ (1855.0). The object
Tsesevich found is currently identiﬁed with GSC 02251-00965, which is 1′ away from the Tsesevich’s position. Thisobject was listed as having a range of 12.5–[14.0 and was classiﬁed as Longperiodic. The ASAS-SN data show that
this object is constant (T. Kato, vsnet-chat 900410 ). and the absolute magnitude (Gaia Collaboration et al. 2021)
8 <https://asd.gsfc.nasa.gov/Koji.Mukai/iphome/systems/yydra.html>
9 <https://asd.gsfc.nasa.gov/Koji.Mukai/iphome/iphome.html>.
10 <http://ooruri.kusastro.kyoto-u.ac.jp/mailarchive/vsnet-chat/9004>.

4
is too faint for a long-period variable. We could not ﬁnd an alternative candidate in the vicinity both using variable
star catalogs [The International Variable Star Index (VSX): Watson et al. (2006); Asteroid Terrestrial-impact
Last Alert System (ATLAS): Heinze et al. (2018); ZTF: Ofek et al. (2020)] and 2MASS catalog (Cutri et al.
2003). This case is as problematic as YY Dra, and either variation detected by Tsesevich was an illusion or thecoordinates were perfectly wrong. This case alone indicates that Tsesevich’s reports were not as complete assupposed by Kholopov and Samus (1988).
The fourth object is NSV 14776 and the coordinates were given as 23h 50m 16s +23◦ 16.′ 4 (1855.0). The
object is currently identiﬁed with a Mira star NSVS J235727.2+240732 = ASAS J235727+2407.6 = ASASSN-V
J235727.38+240731.3. Although the reported range and classiﬁcation (11.1–[14, Longperiodic) agree with themodern one, the position is nearly 4′ diﬀerent. This diﬀerence is too large even if Tsesevich used a printed atlasof Bonner Durchmustering.
As judged from this analysis, two objects out of four in Zessewitch (1934) were either lost or misclassiﬁed,
casting doubt on the reliability of Tsesevich’s report.

3.2

Information from period and epoch

The large number of signiﬁcant digits in the period of 4.21123 d for YY Dra would suggest that observations
with a long (tens of years) baseline was used as in AI Cep. Considering that Tsesevich should have known
that the duration of an Algol-type eclipse is an order of 10% of its period, he must have been aware that thereported uncertainty of the period (assuming ±5 at the end ﬁgure) corresponds to a baseline of 4.21×0.1/0.00005≃8000 cycles ≃90 years. This is much longer than the time (10 years) between the epoch (2419852.4) listed in
the table and the date of publication. We therefore consider that Tsesevich did not make a formal analysis bycreating a completely phased light curve. He probably instead used widely separated epochs of the plate on which
the object was invisible and determined the unique period by ﬁnding the greatest common divisor between theintervals. This interpretation is consistent with the listed epoch corresponding to 1913 March 25, when he wasat an age of 5 (Samus’ 1988) and he probably spotted an old isolated exposure on which the object was invisible.
This interpretation is strengthened by the given precision of the epoch: he gave the end ﬁgure only to 0.1 d incontrast to AI Cep, having a period similar to that of YY Dra, for which he gave an epoch down to 0.001 d. The
given epoch indicates that it was not derived from continuous observations of an eclipse, but only conveyed theinformation that the plate was taken at night in Russia.
The actual intervals used by Tsesevich are diﬃcult to estimate since we do not know at what time of nights
when these plates were exposed. If he only used integer intervals (this would be a reasonable assumption, since
the duration of an eclipse of a 4-d Algol is comparable to the duration of a night), an interval of 1575N d, where
N is the integer, would be a candidate since the given period is exactly 1575/374.
As stated earlier, there would remain a possibility that he confused the element with that of RW UMa. As
Samus noted, the only information from Tsesevich was that it was “in a half degree”, and “a half degree fromZ Dra” was an interpretation by Samus. We cannot rule out that Tsesevich meant something else and the actual
variable was far from the given location.
The Algol (rather than β Lyr etc.) classiﬁcation would not be inconsistent if he observed DO Dra, since
the object is either visible or invisible (in outburst/high state or quiescence). As judged from the rest of objects
in Zessewitch (1934), the magnitudes were unlikely too bright as suggested by Kholopov and Samus (1988). Allother objects in Zessewitch (1934) have Guide Star Catalog (GSC: Lasker et al. 1990) counterparts and thelimiting magnitudes should have been brighter than 15 mag. YY Dra should have been as bright. According
to the DASCH light curve of DO Dra presented in Hill et al. (2022), this object was detected at intermediatebrightness slightly below 14 mag in the early 1920s. Long-lasting similarly bright states were recently observed in2017 January (V above 14.5) for a month and in 2021 May when the object was near or above V =14. Tsesevich
might have observed such a long-lasting bright state when DO Dra was almost always visible on the plates heexamined with occasional “invisible” moments, which could have been suﬃcient to convince him of the Algol-typenature and to urge him to obtain the moments in historical plates when the object was undetected.

4Conclusion

We have shown that the results by Tsesevich were not as complete and previously supposed. In his discovery
paper of YY Dra, two out of four objects were either lost or improperly studied. The coordinate oﬀset from thecorrect position in another object was much larger than the expected error. Using the information of published5
period and epoch of YY Dra, we suspect that Tsesevich used a couple of plates on which the object was invisible
to derive the period rather than from a completely phased light curve. Judging from them, his conclusion on
YY Dra was not incompatible with what is expected for the current DO Dra.
In response to Koji Mukai’s judgement (typos corrected) “The main substantive point of Kholopov & Samus
can be quickly dismissed. This object is not a (normal) dwarf nova; it is a Low Luminosity IP with occasional(dwarf nova-like) outbursts. If this was a normal dwarf nova, their statement might be true”, we note that DO Dra
pretty much behaves like a normal dwarf nova (Wenzel 1983a,b). The only apparent diﬀerence from a normal
dwarf nova is the shortness (a few days) of outbursts compared to what is expected for its orbital period. If theorbital period and the nature of the secondary were unknown, the behavior of DO Dra would be indistinguishable
from dwarf novae below the period gap showing only normal outbursts and high/low states in quiescence (suchas IR Com). In this point, Kholopov and Samus (1988) was correct. We consider what was probably wrong with
Kholopov and Samus (1988) was that they assumed that Tsesevich used a much more comprehensive data set
than we suspect in this paper.
At the time of writing of this paper, crises are unfolding in Ukraine11 .
As we have seen, the ﬁnal conclusion on Tsesevich’s YY Dra is almost impossible to reach due to the result of the World War II. The same thingalso happened in various ﬁelds of science. For example, some of type specimens in biology were completely lost (see e.g. Eggli and Leuenberger 2008;
Müller and Tennent 2018). We wish that no further destruction of our treasures should occur. The illustration is the Ukrainian dove for Peace designed
by Moscow-born designer Natasha Alimova to support Ukraine during the
Maidan revolution of 2014. TK learned this symbol from the page by the
BirdLife International12 and I would like to share it to be with the people,
including the second author with her colleagues in Ukraine and Russia, suffering from hard moments.

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. We are grateful to Aleksandra Zubareva who made us accessible
to Samus’ (1988). TK is grateful to N. N. Samus about the discussion in 2000.

List of objects in this paper
SU Cep, AI Cep, IR Com, Z Dra, YY Dra, DO Dra, RR Lyr, β Lyr, β Per, GM Sgr, V4641 Sgr, RW
UMa, NSV 14669, NSV 14776, 3A 1148+719, ASAS J235727+2407.6, E 1140.8+7158, GSC 02251-00965, NSVS
J235727.2+240732, PG 1140+719

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