7 Vulpeculae

7 Vulpeculae is a binary star system approximately 940[1] light years away in the northern constellation of Vulpecula.[5] It is a challenge to view with the naked eye, having an apparent visual magnitude of 6.34.[2] The system is moving closer to the Earth with a heliocentric radial velocity of −38 km/s.[4]

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]
U−B color index −0.585[2]
B−V color index −0.157[2]
Astrometry
Radial velocity (Rv)−38.0±4.3[4] km/s
Proper motion (μ) RA: 2.555±0.069[1] mas/yr
Dec.: −15.383±0.071[1] mas/yr
Parallax (π)3.4729 ± 0.0479[1] mas
Distance940 ± 10 ly
(288 ± 4 pc)
Absolute magnitude (MV)−1.66+0.44
−0.51[3]
Orbit[3]
Period (P)69.30±0.07 d
Eccentricity (e)0.161±0.035
Periastron epoch (T)2,454,248.1±2.7 HJD
Argument of periastron (ω)
(secondary)		247±16°
Semi-amplitude (K1)
(primary)		8.9±0.4 km/s
Details[3]
7 Vul A
Mass5.5±0.5 M☉
Radius5.2 R☉
Surface gravity (log g)3.75±0.02 cgs
Temperature15,600±200 K
Rotational velocity (v sin i)300±30 km/s
Age50–80 Myr
7 Vul B
Mass0.50 – 0.77[3] M☉
Other designations
7 Vul, BD+19 4039, HD 183537, HIP 95818, HR 7409, SAO 87269[5]
Database references
SIMBADdata

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. It shows a rapid rotation rate with a projected rotational velocity of 300 km/s, which is just below the estimated critical velocity of 367 km/s.[3]

There is a small variability in the magnitude of this star that occurs over 0.559 days 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. However, it could be a white dwarf that has previously undergone a mass transfer event with the now visible component. 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]

References
  1. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  2. Harmanec, P.; et al. (2020). "A new study of the spectroscopic binary 7 Vul with a Be star primary". Astronomy and Astrophysics. 639. Table A.1. arXiv:2005.11089. Bibcode:2020A&A...639A..32H. doi:10.1051/0004-6361/202037964.
  3. Vennes, S.; et al. (2011). "On the nature of the Be star HR 7409 (7 Vul)". Monthly Notices of the Royal Astronomical Society. 413 (4): 2760–2766. arXiv:1101.2622. Bibcode:2011MNRAS.413.2760V. doi:10.1111/j.1365-2966.2011.18350.x.
  4. Anderson, E.; Francis, Ch. (2012). "XHIP: An extended hipparcos compilation". Astronomy Letters. 38 (5): 331. arXiv:1108.4971. Bibcode:2012AstL...38..331A. doi:10.1134/S1063773712050015.
  5. "7 Vul". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 28 August 2012.
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