V455 And
V515 And
AE Aqr
FO Aqr
V349 Aqr
XY Ari
V405 Aur
V647 Aur
HT Cam
MU Cam
DW Cnc
V709 Cas
V1025 Cen
V1033 Cas
TV Col
TX Col
UU Col
V2069 Cyg
V2306 Cyg
DO Dra
PQ Gem
V418 Gem
DQ Her
V1323 Her
V1460 Her
V1674 Her
EX Hya
NY Lup
V2400 Oph
V2731 Oph
V3037 Oph
V598 Peg
GK Per
AO Psc
HZ Pup
V667 Pup
WX Pyx
V1223 Sgr
V4743 Sgr
CC Scl
V1062 Tau
AX J1740.1
AX J1832.3
AX J1853.3
CTCV J2056
CXO J174954
IGR J04571
IGR J08390
IGR J15094
IGR J16500
IGR J16547
IGR J17014
IGR J17195
IGR J18151
IGR J18173
IGR J18308
IGR J19267
PBC J0927.8
PBC J1841.1
RX J1804
RX J2015
RX J2113
RX J2133
RX J2306
Swift J0717
Swift J1839
Swift J2006
Swift J2138

Full Catalog

Related Systems

Home Reviews IPs & Candidates Issues Links Gallery News

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.


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.


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


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

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


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.

Home Reviews IPs & Candidates Issues Links Gallery News

Please send your comments, suggestions etc. to Koji.Mukai@nasa.gov and/or Koji.Mukai@umbc.edu
NASA Logo, National Aeronautics and Space Administration