DH Cephei

DH Cephei is a variable binary star[5] system in the northern circumpolar constellation of Cepheus, positioned about two degrees to the east of the star system Delta Cephei.[10] With an apparent visual magnitude of 8.61,[3] it is too faint to be visible without a telescope. Based on parallax measurements, this system is located at a distance of approximately 10.6 kilolight-years (3.2 kiloparsecs) from the Sun.[2] At present it is moving closer to the Earth with a radial velocity of −33 km/s.[6]

DH Cephei

DH Cephei is at the center of this image of the NGC 7380 complex[1]
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Cepheus
Right ascension 22h 46m 54.11086s[2]
Declination +58° 05′ 03.5317″[2]
Apparent magnitude (V) 8.61[3] (8.63 – 8.70)[4]
Characteristics
Evolutionary stage Main sequence
Spectral type O5.5 V + O6 V[5]
B−V color index 0.334±0.041[6]
Variable type Ellipsoidal[7][4]
Astrometry
Radial velocity (Rv)−33.4±3.2[6] km/s
Proper motion (μ) RA: −2.63[2] mas/yr
Dec.: −2.10[2] mas/yr
Parallax (π)0.3082 ± 0.0348[2] mas
Distanceapprox. 11,000 ly
(approx. 3,200 pc)
Absolute magnitude (MV)−4.66±0.25 (A)
−4.55±0.25 (B)[8]
Orbit[3]
Period (P)2.11095 d
Semi-major axis (a)≥9.79±0.17 R☉
Eccentricity (e)0.0 (fixed)
Periastron epoch (T)2,456,525.564±0.006 HJD
Details[3]
A
Mass25.0[9] or
38.4±2.5 M☉
Radius8.31[9] R☉
Luminosity2.34×105[9] L☉
Surface gravity (log g)4.3±0.3 cgs
Temperature44,000 K
Rotational velocity (v sin i)175 km/s
B
Mass16.8[9] or
33.4±2.2 M☉
Radius7.76[9] R☉
Luminosity1.86×105[9] L☉
Surface gravity (log g)4.3±0.2 cgs
Temperature43,000 K
Rotational velocity (v sin i)160 km/s
Other designations
DH Cep, BD+57° 2607, HD 215835, HIP 112470, WDS 22469+5805[1]
Database references
SIMBADdata

This is a double-lined spectroscopic binary system consisting of two near-identical, massive, O-type main sequence stars.[5] Evolutionary tracks place the stars close to the zero age main sequence, with an age of less than two million years.[11] This is a detached binary[11] with a close orbit having a period of 2.11 days, and the orbit is assumed to have circularized. The orbital plane is estimated to be inclined by an angle of 47°±1° to the line of sight from the Earth, which yields mass estimates of 38 and 34 times the mass of the Sun.[3] Although initially suspected to be an eclipsing binary and given a variable star designation,[8] it doesn't appear to be eclipsing.[3] Instead, the system displays ellipsoidal light variations that are caused by tidal distortions.[7]

This system lies at the center of the young open cluster NGC 7380. It is the primary ionizing source for the surrounding H II region designated S142. The pair are a source of X-ray emission, which may be the result of colliding stellar winds.[12] Their measured X-ray luminosity is 3.2×1031 erg s−1.[9] The location and rare class of these stars make them an important object for astronomical studies.[8]

References
  1. "HD 215835". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2020-10-20.
  2. 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.
  3. Martins, F.; et al. (November 2017), "Properties of six short-period massive binaries: A study of the effects of binarity on surface chemical abundances", Astronomy & Astrophysics, 607: 13, arXiv:1709.00937, Bibcode:2017A&A...607A..82M, doi:10.1051/0004-6361/201731593, S2CID 7835895, A82.
  4. Samus, N. N.; et al. (2017), "General Catalogue of Variable Stars", Astronomy Reports, 5.1, 61 (1): 80–88, Bibcode:2017ARep...61...80S, doi:10.1134/S1063772917010085, S2CID 125853869.
  5. Sota, A.; et al. (March 2014), "The Galactic O-Star Spectroscopic Survey (GOSSS). II. Bright Southern Stars", The Astrophysical Journal Supplement, 211 (1): 84, arXiv:1312.6222, Bibcode:2014ApJS..211...10S, doi:10.1088/0067-0049/211/1/10, S2CID 118847528, 10.
  6. 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, S2CID 119257644.
  7. Penny, Laura R.; et al. (July 1997), "Tomographic Separation of Composite Spectra. IV. The Physical Properties of the Massive Close Binary DH Cephei", The Astrophysical Journal, 483 (1): 439–448, Bibcode:1997ApJ...483..439P, doi:10.1086/304239.
  8. Hilditch, R. W.; et al. (October 1996), "New masses for the O-type binary DH Cephei, and the temperatures of O-stars.", Astronomy and Astrophysics, 314: 165–172, Bibcode:1996A&A...314..165H.
  9. Krtička, J.; et al. (July 2015), "X-ray irradiation of the winds in binaries with massive components", Astronomy & Astrophysics, 579: 15, arXiv:1505.03411, Bibcode:2015A&A...579A.111K, doi:10.1051/0004-6361/201525637, S2CID 119120927, A111.
  10. Sinnott, Roger W.; Perryman, Michael A. C. (1997), Millennium Star Atlas, 3, Sky Publishing Corporation and the European Space Agency, p. 1071, ISBN 0-933346-84-0.
  11. Sturm, E.; Simon, K. P. (February 1994). "Spectroscopic analysis of hot binaries. I. The components of DH Cephei". Astronomy and Astrophysics. 282: 93–105. Bibcode:1994A&A...282...93S.
  12. Lata, Sneh; et al. (March 2016), "Variable stars in young open star cluster NGC 7380", Monthly Notices of the Royal Astronomical Society, 456 (3): 2505–2517, arXiv:1511.08892, Bibcode:2016MNRAS.456.2505L, doi:10.1093/mnras/stv2800, S2CID 118473907.

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