HD 1

HD 1 (HIP 422) is the first star in the Henry Draper Catalogue. It is located in the constellation Cepheus. With an apparent magnitude of 7.42, it is too dim to be seen with the unaided eye, but can be seen with binoculars. HD 1 is currently located 1,190 light-years based on parallax, but is drifting closer to the Solar System with a radial velocity of −27.33 km/s.

This article is about a star in the Henry Draper Catalogue. For other uses, see HD 1 (disambiguation).

HD 1
location of HD 1 (circled)
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Cepheus
Right ascension 00h 05m 08.84s[1]
Declination +67° 50′ 23.97″[1]
Apparent magnitude (V) 7.42±0.01[2]
Characteristics
Evolutionary stage red giant branch[3]
Spectral type G9-K0IIIa[3]
B−V color index +1.288[4]
Astrometry
Radial velocity (Rv)−27.33±0.48[1] km/s
Proper motion (μ) RA: 8.159±0.060 mas/yr[1]
Dec.: −4.165±0.064 mas/yr[1]
Parallax (π)2.7368 ± 0.0371 mas[1]
Distance1,190 ± 20 ly
(365 ± 5 pc)
Absolute magnitude (MV)-0.01[4]
Orbit[5]
Period (P)2,315±2.7 d
Eccentricity (e)0.488±0.013
Semi-amplitude (K1)
(primary)		4.35±0.08 km/s
Details
Mass3.0[3] M☉
Radius26.64[1] R☉
Luminosity225.789[1] L☉
Surface gravity (log g)1.81[6] cgs
Temperature4,334[1] K
Metallicity [Fe/H]+0.24[6] dex
Rotational velocity (v sin i)5.6±1.2[3] km/s
Age350[3] Myr
Other designations
BD+67 1599, HD 1, HIP 422, SAO 10963, GSC 04294-00080
Database references
SIMBADdata

Properties

This star has a stellar classification of "G9-K0IIIa", which means that its spectrum is intermediate between a G9 and K0 giant star. It has exhausted hydrogen at its core and evolved away from the main sequence. It has 3 times the Sun's mass, but has expanded to 26.64 times the Sun's radius. It radiates at 225 solar luminosities, and has an effective temperature of 4,334 K, which gives it an orange hue. It rotates slightly faster than most giants, and has a metallicity greater than the Sun.

Binary system

HD 1 was originally considered to be a single star. Later observations show that it is actually a single-lined spectroscopic binary, with a period of 6.2 years and a high eccentricity of 0.50 ± 0.01.[5]

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. Kharchenko, N. V. (2001-10-01). "All-sky compiled catalogue of 2.5 million stars". Kinematika I Fizika Nebesnykh Tel. 17 (5): 409–423. Bibcode:2001KFNT...17..409K. ISSN 0233-7665.
  3. Strassmeier, K. G.; Weber, M.; Granzer, T.; Dall, T. H. (2010-04-01). "HD 1: The number-one star in the sky". Astronomische Nachrichten. 331 (4): 368–377. Bibcode:2010AN....331..368S. doi:10.1002/asna.201011356. ISSN 0004-6337.
  4. Anderson, E.; Francis, Ch. (2012-05-01). "XHIP: An extended hipparcos compilation". Astronomy Letters. 38 (5): 331–346. arXiv:1108.4971. Bibcode:2012AstL...38..331A. doi:10.1134/S1063773712050015. ISSN 1063-7737.
  5. Griffin, R. F.; McClure, R. D. (2009-02-01). "Spectroscopic binary orbits for the Henry Draper Catalogue stars". The Observatory. 129: 28–32. Bibcode:2009Obs...129...28G. ISSN 0029-7704.
  6. Anders, F.; Khalatyan, A.; Chiappini, C.; Queiroz, A. B.; Santiago, B. X.; Jordi, C.; Girardi, L.; Brown, A. G. A.; Matijevic, G.; Monari, G.; Cantat-Gaudin, T. (2019-08-01). "Photo-astrometric distances, extinctions, and astrophysical parameters for Gaia DR2 stars brighter than G = 18". Astronomy and Astrophysics. 628: A94. arXiv:1904.11302. Bibcode:2019A&A...628A..94A. doi:10.1051/0004-6361/201935765. ISSN 0004-6361.
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