7 Vulpeculae

7 Vulpeculae is a binary star system approximately 910[5] light years away in the slightly northern constellation of Vulpecula.[6] 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.[4]

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 nature of the companion is unknown, but based upon its mass it may be a K- or M-type star. It could be a white dwarf that has undergone a mass transfer to the primary. Because of the lack of X-ray emission from the system, a third possibility is that the companion is a naked He star that has been stripped of its hydrogen envelope.[3]