IW Andromedae

IW Andromedae

A visual band light curve for IW Andromedae, plotted from AAVSO data[1]
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]
Distance2,860 ± 80 ly
(880 ± 30 pc)
Details
White dwarf
Mass0.75[5] M☉
Radius0.015[5] R☉
Temperature25,000[5] K
Donor star
Mass0.27[5] M☉
Other designations
IW And, 2MASS J01010890+4323257, AAVSO 0055+42[6]
Database references
SIMBADdata

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]

  1. ^ Cite error: The named reference aavso was invoked but never defined (see the help page).
  2. ^ a b c d e Cite error: The named reference GaiaEDR3 was invoked but never defined (see the help page).
  3. ^ a b c Cite error: The named reference Samus_et_al_2017 was invoked but never defined (see the help page).
  4. ^ Cite error: The named reference Meinunger_1980 was invoked but never defined (see the help page).
  5. ^ a b c d e Cite error: The named reference Szkody_et_al_2013 was invoked but never defined (see the help page).
  6. ^ Cite error: The named reference SIMBAD was invoked but never defined (see the help page).
  7. ^ a b Cite error: The named reference Kato_2019 was invoked but never defined (see the help page).
  8. ^ Cite error: The named reference Meinunger_1975 was invoked but never defined (see the help page).
  9. ^ a b Cite error: The named reference Liu_et_al_1999 was invoked but never defined (see the help page).
  10. ^ a b c Cite error: The named reference Kato_et_al_2003 was invoked but never defined (see the help page).
  11. ^ Cite error: The named reference Meinunger_Andronov_1987 was invoked but never defined (see the help page).
  12. ^ Cite error: The named reference Hameury_Lasota_2014 was invoked but never defined (see the help page).
  13. ^ Cite error: The named reference Chien-De_et_al_2021 was invoked but never defined (see the help page).
  14. ^ Cite error: The named reference Kato_Kojiguchi_2020 was invoked but never defined (see the help page).