YY Draconis

Researchers have used both "YY Dra" and "DO Dra" to refer to the same object. I have long prefered the former, but with this version of the IP catalog, I'm switching to the latter as the primary designation. The two main reasons are: (1) The GCVS team still considers DO Dra to be the correct name; and (2) a larger fraction of the papers use the designation DO Dra. Since the primary function of the name of an astronomical object is to tell the readers what object you are describing, the most important consideration is for the community to agree to use a single designation.

Here is the history and current status of the two designations, for the record.

This low luminosity IP was identified as the optical counterpart of an X-ray source, and initially announced, by Patteron et al. (1982), who considered the optical counterpart to be known variable star, YY Dra, supposedly of Algol type. However, the GCVS team disagreed and assigned a new variable star designation, DO Dra, to this CV. This happened before the first comprehensive refereed publication (Patterson et al. 1992) was published, noting that this was an intermediate polar. The disagreements regarding the designation are summarized in a pair of IBVS articles.

Patterson & Eisenman (1987) argued that the CV is the previoulsy cataloged variable star, YY Dra.
- The cataloged position of YY Dra is coincident with that of CV, to within the errors of variable stars discovered in old photographic plates.
- Mis-classification of variable star type is common, when based on sparse data.
- At the high Galactic latitude of YY Dra, the very presence of an Algol type star and its positional coincidence with the X-ray source is statistically unlikely.
Kholopov & Samus (1988) argued that the YY Dra was not a CV, and hence a new designation is warranted for the CV.
- Tsesevich could not have misclassified a dwarf nova as an Algol type star.
- Both the position and the brightness of the variable star, on the other hand, could be in error.
- Patterson's arguments are primarily statistical in nature, and cannot definitively prove that the CV is YY Dra.

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 statment might be true. However, the long-term variability of IPs is an active research field that has yieled many suprises in recent years. Thus, it would be presumptious for any of us to think that we would know IPs from their >1 day variability alone.

Is there a lost Algol star somewhere near the LLIP?

I have performed a quick search for such an object for this page, as follows. Virnina (2011) reported on "Tsessevich Project: an Attempt to Find the System YY Dra," which provides additional details about the original discovery: it was made on 10 x 10 deg plates centered on Z Dra. There are 177 entries listed in the ASAS-SN variable star database, none of which matches the supposed 4.2 day period of "YY Dra." If a 4-day period Algol really did exist in this area of the sky, it almost certainly would have been discovered by ASAS-SN (see the latest paper on the ASAS-SN variable star catalog).
Hill et al. (2022) performed a far more comprehensive and systematic search using the Catalina Surveys Periodic Varible Star Catalog and the ASAS-SN Catalog of Variable Stars. They point out that a periodic variable star of the characteristics of "YY Dra" should have been recovered, quite easily, by these surveys. However, no matches were found, discounting a star of similar characteristics in the far southern (declination -53) sky, unobservable from Russia. Hill et al. (2022) therefore argue that YY Dra and DO Dra is one and the same.

Motivated by Hill et al. (2022), Kato & Pavlenko (2022) revisited Tsessevich's original report as well as related materials and considered it likely that the original classification was based on relatively few points. They suggest that the star Tsessevich observed was the LLIP, DO Dra, in a long-lasting bright, with occasional non-detections.

Please send your comments, suggestions etc. to Koji.Mukai@nasa.gov and/or Koji.Mukai@umbc.edu

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YY Draconis