7 Vulpeculae

7 Vulpeculae is a binary star system approximately 910^[6] light years away in the slightly northern constellation of Vulpecula.^[7] It is a challenge to view with the naked eye, having an apparent visual magnitude of 6.3.^[2] The system currently has a heliocentric radial velocity of −38 km/s.^[5]

7 Vulpeculae

Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Vulpecula
Right ascension	19h 29m 20.8974s[1]
Declination	20° 16′ 47.0583″[1]
Apparent magnitude (V)	6.337[2]
Characteristics
Spectral type	B4–5 III–IVe[3] + sdB/sdO[4]
U−B color index	−0.585[2]
B−V color index	−0.157[2]
Astrometry
Radial velocity (Rv)	−38.0±4.3[5] km/s
Proper motion (μ)	RA: 2.555±0.069[1] mas/yr Dec.: −15.383±0.071[1] mas/yr
Parallax (π)	3.5826±0.04 mas[6]
Distance	910 ± 10 ly (279 ± 3 pc)
Absolute magnitude (MV)	−1.66+0.44 −0.51[3]
Orbit[4]
Period (P)	69.30±0.07 d
Semi-major axis (a)	0.5553±0.0096 AU
Eccentricity (e)	0
Inclination (i)	98.7±1.2°
Longitude of the node (Ω)	151.0±0.6°
Periastron epoch (T)	2,454,248.1±2.7 HJD[3]
Argument of periastron (ω) (secondary)	90°
Semi-amplitude (K1) (primary)	8.7±0.2 km/s
Semi-amplitude (K2) (secondary)	77.2±1.5 km/s
Details[3]
7 Vul A
Mass	4.25±0.23[4] M☉
Radius	5.2 R☉
Surface gravity (log g)	3.75±0.02 cgs
Temperature	15,600±200 K
Rotational velocity (v sin i)	300±30 km/s
Age	50–80 Myr
7 Vul B
Mass	0.477±0.020[4] M☉
Other designations
7 Vul, BD+19 4039, HD 183537, HIP 95818, HR 7409, SAO 87269[7]
Database references
SIMBAD	data

This star at the eastern end of an asterism called the coathanger, or "Brocchi's Cluster", the other stars and the centre of quite faint open cluster NGC6802 are at near-identical angular separation, viewed from the Solar System. This is in the south of Vulpecula, visible the world over, particularly from space and very dark skies or dark skies with most instruments.

This is a single-lined spectroscopic binary star system with an orbital period of 69.3 days and an eccentricity of 0.16.^[3] The visible component is a Be star with a stellar classification of B4–5 III–IVe that appears to be nearing the end of its main sequence lifetime. The system shows a rapid projected rotational velocity of 300 km/s, which is just below the estimated critical velocity for a binary of 367 km/s.^[3]

There is a small variability in the magnitude over a 0.559-day cycle;^[2] this is likely the rotation period of the primary star.^[2]

The companion is a hot subdwarf, either a subdwarf B or subdwarf O star, with a mass of 48% the Sun's mass. It has a close orbital separation of half an astronomical unit and take 69 days to complete an orbit.^[4]