2 Vulpeculae

2 Vulpeculae is a binary star^[12] system in the northern constellation of Vulpecula, located around 1,800 light years away^[2] from the Sun. It is visible to the naked eye as a faint, blue-white hued star with an apparent visual magnitude of 5.43.^[3]

2 Vulpeculae

A light curve for ES Vulpeculae, adapted from Lynds (1959)[1]
Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Vulpecula
2 Vul A
Right ascension	19h 17m 43.6354s[2]
Declination	+23° 01′ 31.9418″[2]
Apparent magnitude (V)	5.43[3]
2 Vul B
Right ascension	19h 17m 43.7343s[4]
Declination	+23° 01′ 30.8604″[4]
Characteristics
Spectral type	B1 IV[5]
B−V color index	0.020±0.003[3]
Variable type	β Cep[6]
Astrometry
2 Vul A
Radial velocity (Rv)	+1.0±4.2[3] km/s
Proper motion (μ)	RA: +0.956±0.041[2] mas/yr Dec.: −6.636±0.087[2] mas/yr
Parallax (π)	1.8212±0.0880 mas[2]
Distance	1,790 ± 90 ly (550 ± 30 pc)
Absolute magnitude (MV)	−2.35[3]
2 Vul B
Proper motion (μ)	RA: −0.170±0.038[4] mas/yr Dec.: −5.324±0.073[4] mas/yr
Parallax (π)	1.7131±0.0757 mas[4]
Distance	1,900 ± 80 ly (580 ± 30 pc)
Details
Mass	12.5±0.6[7] M☉
Luminosity (bolometric)	21,922[8] L☉
Temperature	26,850[8] K
Metallicity [Fe/H]	−0.06±0.10[9] dex
Rotational velocity (v sin i)	270[10] km/s
Age	12.6±0.7[7] Myr
Other designations
2 Vul, ES Vul, BD+22°3648, HD 180968, HIP 94827, HR 7318, SAO 87036, WDS 19177+2302[11]
Database references
SIMBAD	data

2 Vulpeculae is a double-lined spectroscopic binary;^[12] as of 2002, the pair had an angular separation of 1.72″ along a position angle of 127.2°.^[13]

The primary component of the binary is a rapidly rotating Be star^[14] with a stellar classification of B1 IV.^[5] It is a variable star with an amplitude of 0.06 magnitude and a period of 0.6096 days, tentatively classified as Beta Cephei variable.^[6] The variability was discovered in 1959,^[15] and it has been assigned the variable star designation ES Vulpeculae.^[6]