HU Delphini

HU Delphini, also known as Gliese 791.2, is a star system in the constellation of Delphinus. Its apparent magnitude is 13.07.[2] With a trigonometric parallax of 113.4 ± 0.2 mas,[2] it is about 28.76 light-years (8.82 parsecs) away from the Solar System.

HU Delphini
Observation data
Epoch J2000      Equinox J2000
Constellation Delphinus
Right ascension  20h 29m 48.344s[1]
Declination +09° 41 20.25[1]
Apparent magnitude (V) 13.07[2]
Characteristics
Spectral type M4.5V[3]
U−B color index +1.29[4]
B−V color index +1.64[4]
Variable type Flare star[5]
Astrometry
Radial velocity (Rv)-34.24 ± 0.07[2] km/s
Proper motion (μ) RA: 673.1[2] mas/yr
Dec.: 122.0[2] mas/yr
Parallax (π)113.4 ± 0.2[2] mas
Distance28.76 ± 0.05 ly
(8.82 ± 0.02 pc)
Absolute magnitude (MV)13.46 / 16.73[2]
Orbit[2]
Period (P)538.6 ± 0.1 d
Semi-major axis (a)0.1037 ± 0.0005″
Eccentricity (e)0.558 ± 0.005
Inclination (i)145.4 ± 0.6°
Longitude of the node (Ω)102.2 ± 1.1°
Periastron epoch (T)JD 2451022.7 ± 0.9
Argument of periastron (ω)
(secondary)
12.2 ± 1.5°
Semi-amplitude (K1)
(primary)
4.09 ± 0.08 km/s
Semi-amplitude (K2)
(secondary)
8.54 ± 0.13 km/s
Details[2]
HU Del A
Mass0.237 ± 0.004 M
Metallicity [Fe/H]0.07 dex
HU Del B
Mass0.114 ± 0.002 M
Other designations
HU Del, GJ 791.2, CCDM J20298+0941AB, LHS 3556[5]
Database references
SIMBADdata
ARICNSA
B

HU Delphini is a binary star with a well-defined period of 538.6 days. The orbit has been derived from astrometry as well as through spectral observations, although that has been difficult because of the high projected rotational velocity. It is also fairly eccentric, at 0.558.[2]

Both stars in the system are red dwarfs. The primary component of the system is only 23.7% as massive as the Sun,[2] so it is fully convective.[3] As a result, there are frequent starspots on its surface. While the normal surface temperature of the primary is 3000 K, the starspots themselves are cooler: only 2700 K. It is also a flare star.[3] The secondary star has a mass of 11.4% that of the Sun.[2]

See also

References

  1. Cutri, R. M. (2003). "2MASS All-Sky Catalog of Point Sources". VizieR On-line Data Catalog. Bibcode:2003yCat.2246....0C.
  2. Benedict, G. F.; Henry, T. J.; Franz, O. G.; McArthur, B. E.; Wasserman, L. H.; Jao, Wei-Chun; Cargile, P. A.; Dieterich, S. B.; Bradley, A. J.; Nelan, E. P.; Whipple, A. L. (2016). "The Solar Neighborhood. XXXVII. The Mass–Luminosity Relation for Main-Sequence M Dwarfs". The Astronomical Journal. 152 (5): 141. arXiv:1608.04775. Bibcode:2016AJ....152..141B. doi:10.3847/0004-6256/152/5/141.
  3. Barnes, J. R.; Jeffers, S. V.; Jones, H. R. A.; Pavlenko, Ya. V.; Jenkins, J. S.; Haswell, C. A.; Lohr, M. E. (2015). "Starspot Distributions on Fully Convective M Dwarfs: Implications for Radial Velocity Planet Searches". The Astrophysical Journal. 812: 42. arXiv:1509.05284. Bibcode:2015ApJ...812...42B. doi:10.1088/0004-637X/812/1/42.
  4. Nicolet, B. (1978). "Photoelectric photometric Catalogue of homogeneous measurements in the UBV System". Astronomy and Astrophysics Supplement Series. 34: 1–49. Bibcode:1978A&AS...34....1N.
  5. "GJ 791.2". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 11 June 2017.
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