IW Andromedae
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| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Andromeda |
| Right ascension | 01h 01m 08.907s[2] |
| Declination | 43° 23′ 25.79″[2] |
| Apparent magnitude (V) | 13.7 to 17.3[3] |
| Characteristics | |
| Spectral type | sdOB[4] |
| Variable type | Z Cam(?)[3] |
| Astrometry | |
| Proper motion (μ) | RA: +2.471 mas/yr[2] Dec.: −5.904 mas/yr[2] |
| Parallax (π) | 1.1413±0.0326 mas[2] |
| Distance | 2,860 ± 80 ly (880 ± 30 pc) |
| Details | |
| White dwarf | |
| Mass | 0.75[5] M☉ |
| Radius | 0.015[5] R☉ |
| Temperature | 25,000[5] K |
| Donor star | |
| Mass | 0.27[5] M☉ |
| Other designations | |
| IW And, 2MASS J01010890+4323257, AAVSO 0055+42[6] | |
| Database references | |
| SIMBAD | data |
IW Andromedae is a binary star system in the northern constellation of Andromeda, abbreviated IW And. It is the prototype of a class of variable stars known as IW And variables, which is an anomalous sub-class of the Z Camelopardalis (Z Cam) variables.[7] The brightness of this system ranges from an apparent visual magnitude of 13.7 down to 17.3,[3] which requires a telescope to view. The system is located at a distance of approximately 2,860 light years from the Sun based on parallax measurements.[2]
The irregular variability of this star was discovered by L. Meinunger in 1975.[8][9] The spectra was found to resemble a blue–hued OB star with some peculiarities. It is a confirmed cataclysmic variable (CV) but its properties differ markedly from other sub-classes of that type.[10] The photometric behavior of the star is dissimilar to that of a dwarf or polar nova as it shows rapid brightening of up to three magnitudes in periods of around a day,[11] but stays in a low excitement state about 72% of the time.[10] Evidence for weak emission of the hydrogen–alpha line was discovered by W. Liu and associates in 1999.[9]
This is a close binary system with an orbital period of 223 minutes (3.7 hours). The primary component is a white dwarf star with 75% of the mass of the Sun. The secondary component has 27% of the Sun's mass and is overflowing its Roche lobe, resulting in mass transfer to an accretion disk orbiting the primary. The accretion rate for the primary is 3×10−9 M☉·yr−1.[5]
T. Kato and associates in 2003 found the light curve matched a Z Cam variable, with the previously observed inactive states being caused by a characteristic standstill. The duty cycle of its standstill is unusually long for a variable of this class.[10] Outbursts during these standstills may be explained by flares on the secondary, which result in brief surges in mass transfer.[12]
Other variables displaying IW And–type behavior have since been discovered, including HO Puppis,[13] BC Cassiopeiae,[14] IM Eridani, V507 Cygni, and FY Vulpecula.[7]
