28 Cygni

This article is about b2 Cygni. For other stars with this Bayer designation, see b Cygni.
28 Cygni

A light curve for V1624 Cygni, plotted from TESS data[1]
Observation data
Epoch J2000      Equinox J2000
Constellation Cygnus
Right ascension 20h 09m 25.61909s[2]
Declination +36° 50′ 22.5961″[2]
Apparent magnitude (V) 4.93[3]
Characteristics
Spectral type B2.5 V[4] or B2 IV(e)[5] + sdO[6]
B−V color index −0.139±0.004[3]
Variable type SX Ari[7]
Astrometry
Radial velocity (Rv)−0.36±2.59[8] km/s
Proper motion (μ) RA: +2.728[2] mas/yr
Dec.: +15.562[2] mas/yr
Parallax (π)5.2947 ± 0.2255 mas[2]
Distance620 ± 30 ly
(189 ± 8 pc)
Absolute magnitude (MV)−2.56[3]
Details
Mass9.5±0.3[9] M☉
Radius5.7[10] R☉
Luminosity1,353.22[11] L☉
Surface gravity (log g)3.983[12] cgs
Temperature11,338[11] K
Rotational velocity (v sin i)320[10] km/s
Age22.1±2.8[9] Myr
Other designations
b2 Cygni, 28 Cygni, V1624 Cygni, BD+36°3907, HD 191610, HIP 99303, HR 7708, SAO 69518[13]
Database references
SIMBADdata

28 Cygni is a binary[6] star in the northern constellation of Cygnus. It is a faint blue-white hued star but visible to the naked eye with an apparent visual magnitude of 4.93.[3] The distance to 28 Cyg, as estimated from its annual parallax shift of 5.3 mas,[2] is around 620 light years. It has an absolute magnitude of −2.56,[3] which means that if the star were just 10 parsecs (33 light-years) away it would be brighter than Sirius, the brightest star in the night sky.

This primary object is a B-type main-sequence star with a stellar classification of B2.5 V, per Lesh (1968).[4] Slettebak (1982) found a class of B2 IV(e),[5] which would suggest this is a more evolved subgiant star. It is a Be star, which means the spectrum displays emission lines due a disk of ejected gas in a Keplerian orbit around the star. The star displays short-term variability with two or more periods,[10] and is classified as an SX Arietis variable by Samus et al. (2017).[7] It is spinning rapidly with a projected rotational velocity of 320 km/s; estimated at round 80% of the critical rotation rate. This is giving the star an oblate shape with an equatorial bulge out to 6.5 times the Sun's radius, compared to 5.7 at the poles.[10] The central star is orbited by a secondary companion star, which is a subdwarf O star.[6] After previous failed attempts to find the star,[14] the companion was detected using interferometry, but the orbital parameters are unknown.[6]

  1. ^ Cite error: The named reference MAST was invoked but never defined (see the help page).
  2. ^ a b c d e f Cite error: The named reference GaiaDR2 was invoked but never defined (see the help page).
  3. ^ a b c d e Cite error: The named reference Anderson2012 was invoked but never defined (see the help page).
  4. ^ a b Cite error: The named reference Lesh1968 was invoked but never defined (see the help page).
  5. ^ a b Cite error: The named reference slettebak1982 was invoked but never defined (see the help page).
  6. ^ a b c d Cite error: The named reference Klement was invoked but never defined (see the help page).
  7. ^ a b Cite error: The named reference Samus2017 was invoked but never defined (see the help page).
  8. ^ Cite error: The named reference Becker2015 was invoked but never defined (see the help page).
  9. ^ a b Cite error: The named reference Tetzlaff2011 was invoked but never defined (see the help page).
  10. ^ a b c d Cite error: The named reference Baade2018 was invoked but never defined (see the help page).
  11. ^ a b Cite error: The named reference McDonald2012 was invoked but never defined (see the help page).
  12. ^ Cite error: The named reference fremat2005 was invoked but never defined (see the help page).
  13. ^ Cite error: The named reference SIMBAD was invoked but never defined (see the help page).
  14. ^ Cite error: The named reference Wang2018 was invoked but never defined (see the help page).