HN Andromedae

HN Andromedae (often abbreviated to HN And) is a variable star in the constellation Andromeda. Its apparent visual magnitude varies between 6.67 and 6.76[2] in a cycle of 69.51 days.[9] It is classified as an α2 Canum Venaticorum variable.[2]

HN Andromedae
Observation data
Epoch J2000      Equinox J2000
Constellation Andromeda
Right ascension  01h 24m 18.6762s[1]
Declination +43° 08′ 31.6293″[1]
Apparent magnitude (V) 6.67 – 6.76 variable[2]
Characteristics
Spectral type A2pSrCrEu[2]
Apparent magnitude (B) 6.704[3]
Apparent magnitude (V) 6.676[3]
Apparent magnitude (G) 6.6505[1]
Apparent magnitude (J) 6.457[4]
Apparent magnitude (H) 6.534[4]
Apparent magnitude (K) 6.495[4]
Variable type α2 CVn[2]
Astrometry
Radial velocity (Rv)3.0±3.3[5] km/s
Proper motion (μ) RA: −4.355±0.190 [1] mas/yr
Dec.: −13.258±0.169[1] mas/yr
Parallax (π)3.437 ± 0.098[1] mas
Distance950 ± 30 ly
(291 ± 8 pc)
Orbit[6]
Period (P)106.357±0.009 days
Eccentricity (e)0.122±0.010
Periastron epoch (T)HJD 2444952.21±1.32
Argument of periastron (ω)
(secondary)		279.76±4.75°
Semi-amplitude (K1)
(primary)		26.85±0.29 km/s
Details
Mass2.76±0.18[6] M☉
Radius3.86±0.66[6] R☉
Luminosity93[7] L☉
Surface gravity (log g)3.3[8] cgs
Temperature9,617[7] K
Rotational velocity (v sin i)<2.35[6] km/s
Other designations
2MASS J01241868+4308315, BD+42 293, HD 8441, HIP 6560, TYC 2825-2536-1, SAO 37177
Database references
SIMBADdata

System

The HN Andromedae system is triple, as seen in periodic radial velocity variations. The primary component is a star that is leaving the main sequence with an absolute magnitude Mv=−0.03±0.42, dominates the observed spectrum[6] and its spectral classification is A2pSrCrEu,[2] meaning that it has stronger than usual absorption lines of strontium, chromium and europium. It is also a chemically peculiar star and classified as an Ap star.[8]

The other two components contribute just 0.23 magnitudes to the apparent magnitude of HN Andromedae. One has an orbital period of 106.3 days, and some orbital parameters can be computed. The other has an orbital period longer than 5000 days.[6]

Variability

The variability of HN Andromedae can be totally ascribed to the primary component, and is compatible with its stellar rotation; this gives the classification as an α2 Canum Venaticorum variable.[6] Magnetic fields in this star are strong and variable, and this is thought to happen when the magnetic dipole axis in the star is not aligned to the rotation axis.[9] Also, the distribution of metals, and consequently the surface brightness, is not uniform on the surface, and this causes the brightness observed variation.

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. HN 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 2018-10-17.
  3. 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.
  4. 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.
  5. Gontcharov, G. A. (November 2006). "Pulkovo Compilation of Radial Velocities for 35 495 Hipparcos stars in a common system". Astronomy Letters. 32 (11): 759–771. arXiv:1606.08053. Bibcode:2006AstL...32..759G. doi:10.1134/S1063773706110065.
  6. North, P.; Carquillat, J. -M.; Ginestet, N.; Carrier, F.; Udry, S. (1998), "Multiplicity among peculiar A stars. I. The AP stars HD 8441 and HD 137909, and the AM stars HD 43478 and HD 96391", Astronomy and Astrophysics Supplement, 130 (2): 223–232, Bibcode:1998A&AS..130..223N, doi:10.1051/aas:1998365.
  7. Joshi, S.; Martinez, P.; Chowdhury, S.; Chakradhari, N. K.; Joshi, Y. C.; Van Heerden, P.; Medupe, T.; Kumar, Y. B.; Kuhn, R. B. (2016). "The Nainital-Cape Survey. IV. A search for pulsational variability in 108 chemically peculiar stars". Astronomy and Astrophysics. 590: A116. arXiv:1603.03517. Bibcode:2016A&A...590A.116J. doi:10.1051/0004-6361/201527242.
  8. Adelman, S. J.; Caliskan, H. (2004). "Revised Elemental Abundances of the MCP Star HD 8441". Baltic Astronomy. 13: 35–39. Bibcode:2004BaltA..13...35A.
  9. Pyper, D. M.; Adelman, S. J. (October 2017). "On the Photometric Variability of Very Sharp-lined Cool mCP Stars". Publications of the Astronomical Society of the Pacific. 129 (980): 104203. Bibcode:2017PASP..129j4203P. doi:10.1088/1538-3873/aa7c9e.
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