21 Persei

21 Persei is a single,[10] variable star in the northern constellation of Perseus, located about 331 light years away from the Sun. It is visible to the naked eye as a faint, white-hued star with an apparent visual magnitude of 5.10 km/s.[2] The object is moving further from the Earth with a heliocentric radial velocity of +8.5 km/s.[6] It has the variable star designation LT Persei; 21 Persei is the Flamsteed designation.

21 Persei

Location of 21 Persei (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Perseus
Right ascension	02^h 57^m 17.28228^s[1]
Declination	31° 56′ 03.1976″[1]
Apparent magnitude (V)	5.10[2]
Characteristics
Spectral type	A2VspSiEu[3]
U−B color index	−0.24[4]
B−V color index	−0.01[4]
Variable type	α² CVn[5]
Astrometry
Radial velocity (Rv)	+8.50[6] km/s
Proper motion (μ)	RA: +1.319[1] mas/yr Dec.: -30.384[1] mas/yr
Parallax (π)	9.8477 ± 0.2575[1] mas
Distance	331 ± 9 ly (102 ± 3 pc)
Absolute magnitude (MV)	0.14[2]
Details
Mass	3.57[7] M☉
Luminosity	88.65[2] L☉
Surface gravity (log g)	4.05[7] cgs
Temperature	12,585[7] K
Metallicity [Fe/H]	+0.90[8] dex
Rotational velocity (v sin i)	20[7] km/s
Other designations
21 Per, LT Per, BD+31°509, FK5 2205, GC 3544, HD 18296, HIP 13775, HR 873, SAO 56031[9]
Database references
SIMBAD	data

This is an Ap star with a stellar classification of A2VspSiEu,[3] where the A2V indicates it is an A-type main-sequence star, 's' means narrow "sharp" absorption, and SiEu shows abundance anomalies of the elements silicon and europium. The star is an Alpha² Canum Venaticorum variable, meaning that the star has a strong magnetic field chromium, silicon, and strontium spectral lines. 21 Persei's period of variability is approximately 2.88 days.[11]

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. 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. Vizier catalog entry
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. Mermilliod, J. C. (2006). "VizieR Online Data Catalog: Homogeneous Means in the UBV System (Mermilliod 1991)". VizieR On-line Data Catalog: II/168. Originally Published in: Institut d'Astronomie. 2168. Bibcode:2006yCat.2168....0M.Vizier catalog entry
5. Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/gcvs. Originally Published in: 2009yCat....102025S. 1. Bibcode:2009yCat....1.2025S.
6. Gontcharov, G. A. (2006). "Pulkovo Compilation of Radial Velocities for 35 495 Hipparcos stars in a common system". Astronomy Letters. 32 (11): 759. arXiv:1606.08053. Bibcode:2006AstL...32..759G. doi:10.1134/S1063773706110065.
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. Vizier catalog entry
8. Wu, Yue; Singh, H. P.; Prugniel, P.; Gupta, R.; Koleva, M. (2010). "Coudé-feed stellar spectral library – atmospheric parameters". Astronomy & Astrophysics. 525: A71. arXiv:1009.1491. Bibcode:2011A&A...525A..71W. doi:10.1051/0004-6361/201015014.
9. "21 Per". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2019-03-29.
10. Eggleton, P. P.; Tokovinin, A. A. (September 2008), "A catalogue of multiplicity among bright stellar systems", Monthly Notices of the Royal Astronomical Society, 389 (2): 869–879, arXiv:0806.2878, Bibcode:2008MNRAS.389..869E, doi:10.1111/j.1365-2966.2008.13596.x.
11. Catalano, F. A.; Renson, P.; Leone, F. (1993). "Third supplement to the catalogue of observed periods of Ap stars". Astronomy and Astrophysics Supplement Series. 98 (2): 269–273. Bibcode:1993A&AS...98..269C.