Alpha Vulpeculae

Alpha Vulpeculae (α Vulpeculae, abbreviated Alpha Vul, α Vul), officially named Anser /ˈænsər/,^[10] is the brightest star in the constellation of Vulpecula. It is approximately 291 light-years from Earth. It forms a wide optical binary with 8 Vulpeculae.^[11]

α Vulpeculae

Location of α Vulpeculae (circled)
Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Vulpecula
Right ascension	19h 28m 42.3299s[1]
Declination	+24° 39′ 53.661″[1]
Apparent magnitude (V)	4.40[2]
Characteristics
Evolutionary stage	red giant[3]
Spectral type	M1 III[4]
U−B color index	+1.81[2]
B−V color index	1.487[5]
Variable type	suspected[3]
Astrometry
Radial velocity (Rv)	−84.91±0.26[5] km/s
Proper motion (μ)	RA: −126.197±0.071[1] mas/yr Dec.: −106.865±0.111[1] mas/yr
Parallax (π)	11.2238±0.1129 mas[1]
Distance	291 ± 3 ly (89.1 ± 0.9 pc)
Absolute magnitude (MV)	−0.36[6]
Details[7]
Mass	0.97 M☉
Radius	43.14 R☉
Luminosity	415.9 L☉
Surface gravity (log g)	1.30 cgs
Temperature	3,690 K
Metallicity [Fe/H]	-0.38[8] dex
Rotational velocity (v sin i)	4.6[5] km/s
Age	11.30 Gyr
Other designations
Anser, α Vul, 6 Vulpeculae, BD+24°3759, FK5 1508, HD 183439, HIP 95771, HR 7405, SAO 87261, CCDM J19288+2442A, WDS J19287+2440A[9]
Database references
SIMBAD	data

Alpha Vulpeculae is a red giant of spectral class M1 and has an apparent magnitude of +4.4. It has been analyzed as a member of the Arcturus stream, a group of stars with high proper motion and metal-poor properties thought to be the remnants of a small galaxy consumed by the Milky Way.^[12]

Nomenclature

α Vulpeculae (Latinised to Alpha Vulpeculae) is the system's Bayer designation.

It bore the traditional name Anser, derived from when the constellation had the name Vulpecula cum Ansere 'the little fox with the goose'.^[13] In 2016, the IAU organized a Working Group on Star Names (WGSN)^[14] to catalog and standardize proper names for stars. The WGSN approved the name Anser for this star on 30 June 2017 and it is now so included in the List of IAU-approved Star Names.^[10]

Description

Amateur image of the dark nebula LDN 778 (center) and Alpha Vulpeculae, (red giant, top center).

α Vulpeculae has evolved away from the main sequence after exhausting its core hydrogen and is now a red giant, probably on the red giant branch.^[3] It is about 11.3 billion years since it first formed.^[7] It has an effective surface temperature of 3,690 K and a bolometric luminosity of 416 L_☉, meaning that its radius is 43 R_☉.

α Vulpeculae has been suspected to be variable in brightness by about a tenth of a magnitude, but this has never been confirmed.^[15] Analysis of the isotopic ratios in its photosphere show that it has a mass less than 1.5 M_☉ and has not yet evolved to the asymptotic giant branch and experienced a third dredge up.^[3]