HD 2421

HD 2421 is a multiple star system in the constellation Andromeda. It is faintly visible to the naked eye with a combined apparent visual magnitude of 5.17.[2] Based on parallax measurements, it is located at a distance of approximately 290 light years from the Sun.[1] The system is drifting further away with a radial velocity of ~2 km/s.[4]

HD 2421
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Andromeda
Right ascension 0h 28m 13.6588s[1]
Declination +44° 23′ 40.1085″[1]
Apparent magnitude (V) 5.173[2]
Characteristics
Spectral type A2Vs + F2V[3]
Astrometry
Radial velocity (Rv)2.0±0.9[4] km/s
Proper motion (μ) RA: 82.361±0.197[1] mas/yr
Dec.: −16.244±0.119[1] mas/yr
Parallax (π)11.2634 ± 0.1621[1] mas
Distance290 ± 4 ly
(89 ± 1 pc)
Orbit[5]
Period (P)3.95529±0.00003 d
Semi-major axis (a)≥ 0.0176±0.0006 AU[6]
Eccentricity (e)0.135±0.011
Periastron epoch (T)2448523.14±0.04
Argument of periastron (ω)
(secondary)		280±4°
Argument of periastron (ω)
(primary)		91±8°
Semi-amplitude (K1)
(primary)		49.1±0.6 km/s
Semi-amplitude (K2)
(secondary)		81.1±1.0 km/s
Details
A
Mass2.31[7] M☉
Luminosity9,875[3] L☉
Surface gravity (log g)4.26[3] cgs
Rotational velocity (v sin i)3.0±0.2 km/s
Age413[7] Myr
B
Surface gravity (log g)4.26[3] cgs
Temperature7,200[3] K
Rotational velocity (v sin i)8.0±0.4[3] km/s
Other designations
BD+43°92, HD 2421, HIP 2225, HR 104, SAO 36390[8]
Database references
SIMBADdata

This is a double-lined spectroscopic binary with an orbital period of 3.96 days and an eccentricity of 0.135. The variable radial velocity was first reported by Robert Horace Baker in 1909 and the first orbit computed by Stella Udick in 1912.[9] A refined orbit was published in 1993 resulting in updated orbital parameters, and in the assessment of a period shift with respect to the 1912 observations.[5]

The primary member of the pair, designated component A, has a stellar classification of A2 Vs, indicating a sharp-lined A-type main-sequence star. The element abundances are similar to those in the Sun.[3] The fainter and cooler secondary, component B, is also a sharp-lined star with a class of F2V,[3] matching an F-type main-sequence star.

A steady variation in the motion of the system suggests the influence of a third component. In 2015 a faint companion, component C, was detected ~ 0.1″ to the southwest of the main pair. This star has about 1.1 times the mass of the Sun, and, if gravitationally bound, is orbiting with a period of around 16 years at a distance of 10.5 AU.[6]

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. Høg, E.; Fabricius, C.; Makarov, V. V.; Urban, S.; Corbin, T.; Wycoff, G.; Bastian, U.; Schwekendiek, P.; Wicenec, A. (2000). "The Tycho-2 catalogue of the 2.5 million brightest stars". Astronomy & Astrophysics. 355: L27–L30. Bibcode:2000A&A...355L..27H.
  3. Adelman, Saul J.; et al. (June 2015). "Elemental Abundance Analyses with DAO Spectrograms. XXXVIII. The SB2 Stars HR 104 (A2 V) and θ Aql (B9.5 III)". Publications of the Astronomical Society of the Pacific. 127 (952): 509. Bibcode:2015PASP..127..509A. doi:10.1086/682075.
  4. Wilson, R. E. (1953). General catalogue of stellar radial velocities. Centre de Données astronomiques de Strasbourg. III/21 Accessed on line 2018-12-03.
  5. Hill, Graham; et al. (1993). "The double-lined spectroscopic binary HR 104". Publications of the Astronomical Society of the Pacific. 105: 748–750. Bibcode:1993PASP..105..748H. doi:10.1086/133225.
  6. Heyne, T.; et al. (January 2020). "Spectroscopic characterization of nine binary star systems as well as HIP 107136 and HIP 107533". Astronomische Nachrichten. 341 (1): 99–117. arXiv:1912.05343. Bibcode:2020AN....341...99H. doi:10.1002/asna.202013683.
  7. David, Trevor J.; Hillenbrand, Lynne A. (2015). "The Ages of Early-Type Stars: Strömgren Photometric Methods Calibrated, Validated, Tested, and Applied to Hosts and Prospective Hosts of Directly Imaged Exoplanets". The Astrophysical Journal. 804 (2): 146. arXiv:1501.03154. Bibcode:2015ApJ...804..146D. doi:10.1088/0004-637X/804/2/146. S2CID 33401607.
  8. "HD 2421". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2018-03-03.
  9. Udick, Stella (1912). "The orbit of B.D. +43° 92". Publications of the Allegheny Observatory of the University of Pittsburgh. 2 (18): 191–196. Bibcode:1912PAllO...2..191U.
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