BM Andromedae

BM Andromedae (BM And) is a T Tauri star in the constellation Andromeda. Its apparent visual magnitude has irregular variations between a maximum of 11.63 and a minimum of 14.02.[2]

BM Andromedae
Observation data
Epoch J2000      Equinox J2000
Constellation Andromeda
Right ascension  23h 37m 38.47583s[1]
Declination +48° 24′ 11.83791″[1]
Apparent magnitude (V) 11.63 – 14.02 variable [2]
Characteristics
Spectral type F8ea-K5Vea[2]
Apparent magnitude (B) 12.40[3]
Apparent magnitude (V) 12.40[4]
Apparent magnitude (G) 12.4323[1]
Apparent magnitude (J) 10.524[5]
Apparent magnitude (H) 9.523[5]
Apparent magnitude (K) 8.810[5]
Variable type T Tauri star[6]
Astrometry
Radial velocity (Rv)−12.87±2.77[1] km/s
Proper motion (μ) RA: 3.569±1.436 [1] mas/yr
Dec.: 3.614±1.263[1] mas/yr
Parallax (π)3.3536 ± 0.8630[1] mas
Distanceapprox. 1,000 ly
(approx. 300 pc)
Other designations
2MASS J23373847+4824119
Database references
SIMBADdata

Spectrum

The exact spectral class of the star is not yet known. Different estimations gives a range F8-K5Vea,[2] meaning that there is agreement in identifying it as a main sequence star more luminous and with stronger emission lines than the usual, a typical classification for young stars that are near the main sequence phase.

The color indexes vary with the star's brightness, but the spectral class of BM Andromedae does not change with the decrease of luminosity. Strong H-alpha lines in the spectra are a sign of a gaseous envelope, while an infrared excess indicates the existence of an extended dust envelope.[6]

System

BM Andromedae is a young stellar object with a circumstellar cloud around it, one stage of the evolution from protostars to the main sequence phase. The cloud is made of a gaseous envelope and an extended dust envelope. The latter can reach a distance of 1 AU from the star and is strongly flattened and observed edge-on.[6]

It was also found that a correlation exists between the local interstellar magnetic field and the polarization of light emitted by BM Andromedae. Thus, the magnetic field could have played a role in the formation of the system.[6]

Variability

The envelope blocks a fraction of the light emitted by BM Andromedae, but it's not uniform so this fraction is variable in time. This explains both the brightness variability and the one of color indexes. It was also found that the dust envelope polarizes the light emitted by BM Andromedae; the more light is blocked, the stronger is the polarization.[6]

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References
  1. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  2. BM And, database entry, Combined General Catalog of Variable Stars (GCVS4.2, 2004 Ed.), N. N. Samus, O. V. Durlevich, et al., CDS ID II/250 Accessed on line 2018-10-25.
  3. "BM And". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved October 25, 2018.
  4. Database entry, Catalogue of Stellar Photometry in Johnson's 11-color system (2002 Ed.), J. R. Ducati, CDS ID Accessed on line 2018-10-25.
  5. Cutri, R. M.; Skrutskie, M. F.; Van Dyk, S.; et al. (June 2003). "VizieR Online Data Catalog: 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)". CDS/ADC Collection of Electronic Catalogues (2246): II/246. Bibcode:2003yCat.2246....0C.
  6. Grinin, V. P.; Kolotilov, E. A.; Rostopchina, A. (1995), "Dust around young stars. Photopolarimetric observations of the T Tauri star BM Andromedae.", Astronomy & Astrophysics Supplement Series, 112: 457, Bibcode:1995A&AS..112..457G.
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