ET Andromedae

ET Andromedae is a binary star system star in the northern constellation of Andromeda.[13] It has an apparent visual magnitude of 6.48,[2] placing it at the nominal limit for visibility with the naked eye. The distance to this system can be estimated from its annual parallax shift of 5.42 mas,[1] which yields a value of 602 light years.

ET Andromedae
Observation data
Epoch J2000      Equinox J2000
Constellation Andromeda
Right ascension 23h 17m 56.011185s[1]
Declination +45° 29′ 20.1197″[1]
Apparent magnitude (V) 6.48[2]
Characteristics
Spectral type A0 Vp SiSr[3] or B9p SI[4]
B−V color index −0.037±0.006[2]
Variable type α2 CVn
Astrometry
Radial velocity (Rv)−0.30±4.10[2] km/s
Proper motion (μ) RA: +24.740[1] mas/yr
Dec.: −11.038[1] mas/yr
Parallax (π)5.4200 ± 0.0572[1] mas
Distance602 ± 6 ly
(185 ± 2 pc)
Absolute magnitude (MV)0.58[5]
Orbit[6]
Period (P)48.304±0.007 d
Eccentricity (e)0.50±0.05
Periastron epoch (T)2443720.11±0.64 JD
Argument of periastron (ω)
(secondary)		49.8±6.0°
Semi-amplitude (K1)
(primary)		25.7±2.0 km/s
Details
Mass3.25[7] M☉
Radius2.7[8] R☉
Luminosity91.06[2] L☉
Surface gravity (log g)3.81[9] cgs
Temperature11,444[9] K
Rotation1.62 d[10]
Rotational velocity (v sin i)65[11] km/s
Age284[5] Myr
Other designations
BD+44° 4373, HD 219749, HIP 115036, HR 8861, SAO 52876, PPM 64037, TYC 3636-2562-1, GSC 03636-02562, 2MASS J23175600+4529201[12]
Database references
SIMBADdata

Variations in the radial velocity of this star suggest it is a single-lined spectroscopic binary system. This yields orbital elements with a period of 48.3 days and an eccentricity of 0.50. The a sin i value for the primary is 14.8 Gm (0.099 AU), where a is the semimajor axis and i is the (unknown) orbital inclination.[6]

The visible component is a well-studied magnetic chemically peculiar star[14] with a stellar classification of A0 Vp SiSr.[3] The SiSr notation indicates unusual abundances of silicon and strontium in the spectrum. It has a magnetic field with an average surface value of 3.2 kT.[15] The abundance of silicon varies depending on the viewing angle.[14] The star is an Alpha2 Canum Venaticorum variable with a period of 1.618875 days.[16]

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.
  2. Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters, 38 (5): 331, arXiv:1108.4971, Bibcode:2012AstL...38..331A, doi:10.1134/S1063773712050015, S2CID 119257644.
  3. Abt, Helmut A.; Morrell, Nidia I. (1995). "The Relation between Rotational Velocities and Spectral Peculiarities among A-Type Stars". Astrophysical Journal Supplement. 99: 135. Bibcode:1995ApJS...99..135A. doi:10.1086/192182.
  4. Cowley, A.; et al. (April 1969). "A study of the bright A stars. I. A catalogue of spectral classifications". Astronomical Journal. 74: 375–406. Bibcode:1969AJ.....74..375C. doi:10.1086/110819.
  5. Gontcharov, G. A. (November 2012). "Spatial distribution and kinematics of OB stars". Astronomy Letters. 38 (11): 694–706. arXiv:1606.09028. Bibcode:2012AstL...38..694G. doi:10.1134/S1063773712110035. S2CID 119108982.
  6. Ouhrabka, M.; Grygar, J. (May 1979). "Spectroscopic evidence for the binary nature of the Ap star". Information Bulletin on Variable Stars. 1600: 1. Bibcode:1979IBVS.1600....1O.
  7. Ducati, J. R.; et al. (2011). "The mass ratio and initial mass functions in spectroscopic binaries" (PDF). Astronomy and Astrophysics. 525: A26. Bibcode:2011A&A...525A..26D. doi:10.1051/0004-6361/200913895.
  8. Pasinetti Fracassini, L. E.; et al. (2001). "Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS)". Astronomy & Astrophysics (Third ed.). 367 (2): 521–24. arXiv:astro-ph/0012289. Bibcode:2001A&A...367..521P. doi:10.1051/0004-6361:20000451. S2CID 425754.
  9. Adelman, Saul J. (2002). "On the Periods of the Magnetic CP Stars". Baltic Astronomy. 11: 475–485. Bibcode:2002BaltA..11..475A.
  10. Kreidl, T. J. (October 1993), "A Null Detection of Rapid Oscillations in the Ap Star ET And", Information Bulletin on Variable Stars, 3945: 1, Bibcode:1993IBVS.3945....1K
  11. Strom, Stephen E.; et al. (2005). "B Star Rotational Velocities in h and χ Persei: A Probe of Initial Conditions during the Star Formation Epoch?". The Astronomical Journal. 129 (2): 809–828. arXiv:astro-ph/0410337. Bibcode:2005AJ....129..809S. doi:10.1086/426748. S2CID 15059129.
  12. "HD 13530". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 20 August 2018.
  13. Watson, Christopher (4 February 2010). "ET Andromedae". AAVSO Website. American Association of Variable Star Observers. Retrieved 5 November 2014.
  14. Adelman, Saul J. (May 2000). "UVBY photometry of the magnetic CP stars HD 36668, 36 Lyncis, HD 86592, and HR 8861". Astronomy and Astrophysics. 357: 548–552. Bibcode:2000A&A...357..548A.
  15. Glagolevskij, Yu. V. (September 2007). "Magnetic-field dependence of chemical anomalies in CP stars". Astrophysical Bulletin. 62 (3): 244–256. Bibcode:2007AstBu..62..244G. doi:10.1134/S1990341307030054. S2CID 122706004.
  16. Samus', N. N.; Kazarovets, E. V.; Durlevich, O. V.; Kireeva, N. N.; Pastukhova, E. N. (2017), "General catalogue of variable stars: Version GCVS 5.1", Astronomy Reports, 61 (1): 80–88, Bibcode:2017ARep...61...80S, doi:10.1134/S1063772917010085, S2CID 125853869.
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