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]
| 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 | |
| Database references | |
| SIMBAD | data |
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]
References
edit- ^ "Download Data", aavso.org, AAVSO, retrieved 9 April 2023.
- ^ a b c d e Brown, A. G. A.; et al. (Gaia collaboration) (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics. 649: A1. arXiv:2012.01533. Bibcode:2021A&A...649A...1G. doi:10.1051/0004-6361/202039657. S2CID 227254300. (Erratum: doi:10.1051/0004-6361/202039657e). Gaia EDR3 record for this source at VizieR.
- ^ a b c Samus, N. N.; et al. (2017), "General Catalogue of Variable Stars", Astronomy Reports, 5.1, 61 (1): 80–88, Bibcode:2017ARep...61...80S, doi:10.1134/S1063772917010085, S2CID 125853869.
- ^ Meinunger, L. (May 1980), "Spectra of Four Blue Irregular Variables in Andromeda", Information Bulletin on Variable Stars, 1795: 1, Bibcode:1980IBVS.1795....1M.
- ^ a b c d e Szkody, Paula; et al. (December 2013), "A Study of the Unusual Z Cam Systems IW Andromedae and V513 Cassiopeia", Publications of the Astronomical Society of the Pacific, 125 (934): 1421–1428, arXiv:1311.1557, Bibcode:2013PASP..125.1421S, doi:10.1086/674170, S2CID 118631716.
- ^ "IW ANd". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2023-04-07.
- ^ a b Kato, Taichi (January 2019), "Three Z Camelopardalis-type dwarf novae exhibiting IW Andromedae-type phenomenon", Publications of the Astronomical Society of Japan, 71 (1): 20, arXiv:1811.05038, Bibcode:2019PASJ...71...20K, doi:10.1093/pasj/psy138, 20.
- ^ Meinunger, L. (1975), "Veränderliche in einem Feld um ν Andromedae", Mitteilungen über Veränderliche Sterne, 7: 1–21, Bibcode:1975MitVS...7....1M.
- ^ a b Liu, Wu; et al. (May 1999), "Spectroscopic Confirmation of 55 Northern and Equatorial Cataclysmic Variables. I. 27 Confirmed Cataclysmic Variables", The Astrophysical Journal Supplement Series, 122 (1): 243–255, Bibcode:1999ApJS..122..243L, doi:10.1086/313210, S2CID 122899189.
- ^ a b c Kato, Taichi; et al. (February 2003), "IW And is a Z Cam-Type Dwarf Nova", Information Bulletin on Variable Stars, 5376: 1, arXiv:astro-ph/0204353, Bibcode:2003IBVS.5376....1K.
- ^ Meinunger, L.; Andronov, I. L. (September 1987), "Photometric Study of the Blue Variables IW, IZ and IO Andromedae", Information Bulletin on Variable Stars, 3081: 1, Bibcode:1987IBVS.3081....1M.
- ^ Hameury, J. -M.; Lasota, J. -P. (September 2014), "Anomalous Z Cam stars: a response to mass-transfer outbursts", Astronomy & Astrophysics, 569: A48, arXiv:1407.3156, Bibcode:2014A&A...569A..48H, doi:10.1051/0004-6361/201424535, S2CID 119238557, A48.
- ^ Lee, Chien-De; et al. (April 2021), "HO Puppis: Not a Be Star, but a Newly Confirmed IW And-type Star", The Astrophysical Journal, 911 (1): 51, arXiv:2102.09748, Bibcode:2021ApJ...911...51L, doi:10.3847/1538-4357/abe871, S2CID 231979353, 51.
- ^ Kato, Taichi; Kojiguchi, Naoto (December 2020), "BC Cassiopeiae: First detection of IW Andromedae-type phenomenon among post-eruption novae", Publications of the Astronomical Society of Japan, 72 (6): 98, arXiv:2009.12993, Bibcode:2020PASJ...72...98K, doi:10.1093/pasj/psaa096, 98.