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 22h 46m 54.111s[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]
Distance9,600 ± 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
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

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] 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.[13] 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]

  1. ^ a b Cite error: The named reference SIMBAD was invoked but never defined (see the help page).
  2. ^ a b c d e Cite error: The named reference GaiaEDR3 was invoked but never defined (see the help page).
  3. ^ a b c d e f Cite error: The named reference Martins2017 was invoked but never defined (see the help page).
  4. ^ a b Cite error: The named reference Samus2017 was invoked but never defined (see the help page).
  5. ^ a b c Cite error: The named reference Sota2014 was invoked but never defined (see the help page).
  6. ^ a b c Cite error: The named reference Anderson2012 was invoked but never defined (see the help page).
  7. ^ a b Cite error: The named reference Penny1997 was invoked but never defined (see the help page).
  8. ^ a b c Cite error: The named reference Hilditch1996 was invoked but never defined (see the help page).
  9. ^ a b c d e f g Cite error: The named reference Krtička2015 was invoked but never defined (see the help page).
  10. ^ Cite error: The named reference Sinnott1997 was invoked but never defined (see the help page).
  11. ^ Cite error: The named reference Lines was invoked but never defined (see the help page).
  12. ^ a b Cite error: The named reference Sturm1994 was invoked but never defined (see the help page).
  13. ^ Cite error: The named reference Lata2016 was invoked but never defined (see the help page).