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HD 1, also known as HIP 422, is the first star catalogued in the Henry Draper Catalogue. It is located in the northern circumpolar constellation Cepheus and has an apparent magnitude of 7.42,[2] making it readily visible in binoculars, but not to the naked eye. The object is located relatively far away at a distance of 1,220 light years but is approaching the Solar System with a spectroscopic radial velocity of −27.3 km/s.[4]
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Cepheus |
| Right ascension | 00h 05m 08.84054s[1] |
| Declination | +67° 50′ 23.9805″[1] |
| Apparent magnitude (V) | 7.42±0.01[2] |
| Characteristics | |
| Evolutionary stage | red giant branch[1][3] |
| Spectral type | G9-K0 IIIa[3] |
| Astrometry | |
| Radial velocity (Rv) | −27.3±0.5[4] km/s |
| Proper motion (μ) | RA: +7.480 mas/yr[1] Dec.: −5.045 mas/yr[1] |
| Parallax (π) | 2.668 ± 0.0485 mas[1] |
| Distance | 1,220 ± 20 ly (375 ± 7 pc) |
| Absolute magnitude (MV) | −0.01[5] |
| Orbit[6] | |
| Period (P) | 6.345±0.007 yr |
| Eccentricity (e) | 0.488±0.013 |
| Periastron epoch (T) | 2,452,213±9 JD |
| Argument of periastron (ω) (secondary) | 224±2.2° |
| Semi-amplitude (K1) (primary) | 4.35±0.08 km/s |
| Details | |
| Mass | 3.0[3] M☉ |
| Radius | 30[7] R☉ |
| Luminosity | 226±5[4] L☉ |
| Surface gravity (log g) | 1.81[8] cgs |
| Temperature | 5,844±122[9] K |
| Metallicity [Fe/H] | +0.24[8] dex |
| Rotational velocity (v sin i) | 5.6±1.2[3] km/s |
| Age | 350[3] Myr |
| Other designations | |
| Database references | |
| SIMBAD | data |
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Originally thought to be a single object, observations from Griffin & McClure (2009) reveal it to be a single-lined spectroscopic binary. The components take approximately 6 years to circle each other in an eccentric orbit.[6] The visible component is an evolved red giant branch[1] (RGB) star with a stellar classification of G9-K0 IIIa,[3] a spectral class intermediate between a G9 and K0 giant star. It has 3 times the mass of the Sun, but at the age of 350 million years[3] it has expanded to 30 times its girth.[7] It radiates 226 times the luminosity of the Sun[4] from its enlarged photosphere at an effective temperature of 5,844 K,[9] giving it a yellowish-orange hue. HD 1A is metal enriched, with an iron abundance 74% above solar levels.[8] The objects spins modestly with a projected rotational velocity of 5.6 km/s.[3]
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