Explanatory Notes on the Catalog

Objects in the Catalog

The 2021 version of the catalog consists of IPs and IP candidates, based on information that was public as of 2021 October 31.

To classify an object as "ironclad" IP, one requirement I have put is that the orbital period must be directly measured, using a method that has a physical association with the binary orbit. That is, I require either the radial velocity curve from optical spectroscopy or eclipse timings. If the orbital period is infered through photometric modulations (with a period in the right range) or from the spacing of spin and beat periods, that can be used to "confirm" the IP nature of an object, but it is not sufficient to consider the classification "ironclad.". In addition, large uncertainties in one of the periods (typically the possible aliases of the orbital period) is allowable in a "confirmed" system but not in an "ironclad" system. I have now collected notes on individual confirmed but not ironclad IPs.

At the other end of the star rating scale, once an object is proposed as an IP in a refereed publication, it remains in the catalog even if it turns out not to be the case. Thus, the catalog includes several X-ray binaries, one transisional millisecond pulsar, double-generate systems, confirmed polars, and several asynchronous polars. These are all rated one star, although calling then "doubtful" may not be the best terminology.

In between these extremes, there are IP candidates at various levels of confidence. For convenience, I have started a wishlist of observations that might allow to confirm some of them as IPs.

Then there are systems for which too little is known that I have not included in the catalog.

Nomencalture

Whenever available, I use the official designation in the General Catalog of Variable Stars. As for other names, I try to prioritize the names used in papers dedicated to the objects. While it is common for objects to have many designations from many catalogs, they are not given prominence unless one is used as the main designation of that object in a publication.

As a special case, there is one object for which competing names have been used. Starting with the 2021 version of the catalog, I have switched to using the name DO Dra; see, however, my note on YY Dra.

Links

Starting with the 2021 version of the catalog, I have added links, where available, to The International Variable Star Index of the AAAVSO, and to Swift Bat 157-Month Hard X-ray Survey Ccatalog

Position

Starting with the 2021 version of the catalog, I use the Gaia (specifically, EDR3) positions whenever available, obtained from the ESA Gaia archive. These are indicated by the notation "(Gaia)" after the RA and Dec values.

In some case, you may find a noticeable difference between the Gaia and published positions, even when the latter are from reliable sources. This likely indicates the object is nearby and has a significant proper motion, and the Gaia-era location is therefore offset from the published (typically equinox and epoch 2000) position.

Some objects do not have a Gaia counterpart. This is often the case for distant objects (e.g., near the Galactic center). As a special case, XY Ari, which sits behind a molecular cloud, does not have a Gaia counterpart, either.

Apparent Magnitudes and X-ray Fluxes

Starting with the 2021 version of the catalog, I rely heavily on large-scale catalog to indicate the (typical) apparent magnitudes and X-ray fluxes. Whenever available, I list

G magnitude from Gaina EDR3
Hard X-ray (14-195 keV) flux from BAT 157-month survey.
X-ray fluxes in the traditional band (~0.5-10 keV) mainly from XMM-Newton Serendipitous Survey Catalog or Swift X-ray Telescope Point Source catalog.

IPs, by definition, are variable on all time scales, so obvious caveats apply.

Bibliography

The reference list is now listed (approximately) chronologically, with a brief note indicating what kind of information the paper might contain.

In generally, I prioritize refereed publications; non-refereed publications (including conference proceedings, ATels etc.) are included only when some key piece of information is only available in those forms.

The reference list is not complete.

I do not include catalog papers, unless there is a specific note about an individual object of interest.
My highest priority is on papers that relate to the IP nature (or otherwise) of the cataloged objects. Some known IPs are also classical novae or dwarf novae, and papers exclusively on nova eruptions or dwarf nova outbursts have lower priority in the context of this catalog.
Those I calssify as "doubtful" have a low priority in terms of bibliography. Once I judge an object not to be an IP, I stop keeping track of new publications.

I thank all my collaborators over the years, but specially Dr. Domitilla de Martino who checked the new version of the catalog in progress, and provided valuable feedbacks, and for pointing out typos in several pages. I also thank Prof. John Thorstensen for his assistance in checking the catalog, in particular cross-checking the coordinates and his assistance in the formatting of the Ascii version of the catalog.

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