Alruba
Star in the constellation Draco
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Alruba,[10] a name derived from Arabic for "the foal", is a suspected astrometric binary[11] star system in the northern circumpolar constellation of Draco. It is just barely visible to the naked eye as a dim point of light with an apparent visual magnitude of 5.76.[3] Based on parallax measurements obtained during the Gaia mission, it is located at a distance of about 457 light-years (140 parsecs) from the Sun. The system is drifting closer with a radial velocity of −2 km/s.[6]
 | |
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Draco[1] |
| Pronunciation | /ælˈruːbə/ |
| Right ascension | 17h 43m 59.17049s[2] |
| Declination | +54° 48′ 06.1637″[2] |
| Apparent magnitude (V) | 5.76[3] |
| Characteristics | |
| Evolutionary stage | Main sequence[4] |
| Spectral type | A0V[5] |
| Astrometry | |
| Radial velocity (Rv) | −2.0[6] km/s |
| Proper motion (μ) | RA: 17.450[2] mas/yr Dec.: −18.125[2] mas/yr |
| Parallax (π) | 7.1436±0.0605 mas[2] |
| Distance | 457 ± 4 ly (140 ± 1 pc) |
| Absolute magnitude (MV) | −0.3[1] |
| Details | |
| Mass | 2.97±0.07[4] M☉ |
| Luminosity | 146.7+29.6 −24.7[4] L☉ |
| Surface gravity (log g) | 3.80±0.10[7] cgs |
| Temperature | 9,226+107 −106[4] K |
| Metallicity [Fe/H] | −0.40±0.11[7] dex |
| Rotational velocity (v sin i) | 170[4] km/s |
| Age | 58[8] Myr |
| Other designations | |
| Alruba, BD+53°1978, CPD–51°9815, HD 161693, HIP 86782, HR 6618, SAO 30538[9] | |
| Database references | |
| SIMBAD | data |
The visible component is an A-type main-sequence star with a stellar classification of A0 V.[5] It is about 58 million years old[8] with three times the mass of the Sun[4] and has a high rate of spin, showing a projected rotational velocity of 170 km/s.[4] The star is radiating 147 times the luminosity of the Sun[4] from its photosphere at an effective temperature of 9,226 K.[4] The system is a source for X-ray emission, which is most likely coming from the unseen companion.[12]
Nomenclature
In the Henry Draper catalogue this system has the designation HD 161693, while it has the identifier HR 6618 in the Bright Star Catalogue.[9]
It bore the traditional Arabic name الربع Al Rubaʽ "the foal" (specifically a young camel born in the spring), a member of the Mother Camels asterism in early Arabic astronomy.[13][14]
In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[15] to catalogue and standardize proper names for stars. The WGSN approved the name Alruba for this star on 1 June 2018 and it is now so entered on the List of IAU-approved Star Names.[10]