| 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: +2.471mas/yr[2] Dec.: −5.904mas/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 abinary star system in the northernconstellation ofAndromeda, abbreviated IW And. It is the prototype of a class ofvariable stars known as IW And variables, which is an anomalous sub-class of theZ Camelopardalis (Z Cam) variables.[7] The brightness of this system ranges from anapparent visual magnitude of 13.7 down to 17.3,[3] which requires atelescope to view. The system is located at a distance of approximately 2,860 light years from theSun based onparallax measurements.[2]
The irregular variability of this star was discovered byL. Meinunger in 1975.[8][9] Thespectra was found to resemble a blue–huedOB star with some peculiarities. It is a confirmedcataclysmic variable (CV) but its properties differ markedly from other sub-classes of that type.[10] Thephotometric behavior of the star is dissimilar to that of adwarf orpolar 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 weakemission of thehydrogen–alpha line was discovered byW. Liu and associates in 1999.[9]
This is a close binary system with anorbital period of 223 minutes (3.7 hours). The primary component is awhite dwarf star with 75% of themass of the Sun. The secondary component has 27% of the Sun's mass and is overflowing itsRoche lobe, resulting in mass transfer to anaccretion disk orbiting the primary. Theaccretion rate for the primary is3×10−9 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. Theduty cycle of its standstill is unusually long for a variable of this class.[10] Outbursts during these standstills may be explained byflares on the secondary, which result in brief surges in mass transfer.[12]
Other variables displaying IW And–type behavior have since been discovered, includingHO Puppis,[13]BC Cassiopeiae,[14]IM Eridani, V507 Cygni, and FY Vulpecula.[7]
