DH Cephei

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	22^h 46^m 54.111^s[2]
Declination	+58° 05′ 03.53″[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: −2.599 mas/yr[2] Dec.: −2.236 mas/yr[2]
Parallax (π)	0.3397 ± 0.0138 mas[2]
Distance	9,600 ± 400 ly (2,900 ± 100 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
Mass	25.0[9] or 38.4±2.5 M☉
Radius	8.31[9] R☉
Luminosity	2.34×10^5[9] L☉
Surface gravity (log g)	4.3±0.3 cgs
Temperature	44,000 K
Rotational velocity (v sin i)	175 km/s
B
Mass	16.8[9] or 33.4±2.2 M☉
Radius	7.76[9] R☉
Luminosity	1.86×10^5[9] L☉
Surface gravity (log g)	4.3±0.2 cgs
Temperature	43,000 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
SIMBAD	data

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 9.6 kilolight-years (2.9 kiloparsecs) from the Sun.[2] At present it is moving closer to the Earth with a radial velocity of −33 km/s.[6]

A visual band light curve for DH Cephei, adapted from Lines et al. (1986)[11]

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.[12] This is a detached binary[12] 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]

In 1949, Joseph Algernon Pearce derived the orbital elements for DH Cephei (then known as HD 215835) and predicted that the binary pair would show eclipses, although he had no data to prove that.[13] Graham Hill et al. confirmed the predicted variability of star's brightness, in 1976.[14] 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.[15] Their measured X-ray luminosity is 3.2×10^31 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) (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics. 649: A1. arXiv:2012.01533. Bibcode:2021A&A...649A...1G. doi:10.1051/0004-6361/202039657. S2CID 227254300. (Erratum: doi:10.1051/0004-6361/202039657e). Gaia EDR3 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, vol. 3, Sky Publishing Corporation and the European Space Agency, p. 1071, ISBN 0-933346-84-0.
11. Lines, L. C.; Lines, R. D.; Guinan, E. F.; Robinson, C. R. (September 1986), "B and V Light Curves of the Massive Close Binary DH Cephei", Information Bulletin on Variable Stars, 2932: 1, Bibcode:1986IBVS.2932....1L, retrieved 1 January 2022.
12. 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.
13. Pearce, J. A. (April 1949). "HD 215835 - a new massive eclipsing system". Astronomical Journal. 54: 135–136. Bibcode:1949AJ.....54..135P. doi:10.1086/106226. Retrieved 20 January 2025.
14. Hill, G.; Hilditch, R. W.; Pfannenschmidt, E. L. (1976). "Photoelectric measures of variable stars observed at Mt. Kobau (1970 - 73)". Publications of the Dominion Astrophysical Observatory Victoria. 15: 1–35. Bibcode:1976PDAO...15....1H. Retrieved 20 January 2025.
15. 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.