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

This is a double-lined spectroscopic binary system consisting of two near-identical, massive, O-type main sequence stars. Evolutionary tracks place the stars close to the zero age main sequence, with an age of less than two million years. This is a detached binary 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 to the line of sight from the Earth, which yields mass estimates of 38 and 34 times the mass of the Sun. Although initially suspected to be an eclipsing binary and given a variable star designation, it doesn't appear to be eclipsing. Instead, the system displays ellipsoidal light variations that are caused by tidal distortions.

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. Their measured X-ray luminosity is . The location and rare class of these stars make them an important object for astronomical studies.
Q50053
binary star
Concept
Q1067416
circumpolar constellation
Concept
Q10468
Cepheus
CEL
Q13024
Delta Cephei
CEL
Q124313
apparent visual magnitude
Concept
Q906561
parallax
Concept
Q240105
radial velocity
Concept
Q50053
spectroscopic binary
Concept
Q911809
O-type main sequence star
Concept
Q3450
Evolutionary track
Concept
Q3450
zero age main sequence
Concept
Q50053
detached binary
Concept
Q800358
orbital plane
Concept
Q180892
mass of the Sun
Concept
Q50053
eclipsing binary
Concept
Q593448
variable star designation
Concept
Q1332364
ellipsoidal
Concept
Q11387
open cluster
Concept
Q584325
NGC 7380
DIS
Q186161
ionizing source
Concept
Q11282
H II region
Concept
Q1852
X-ray emission
Concept
Q654396
stellar wind
Concept
Q5797093
DH Cephei
CEL
7380-01-01T00:00:00Z^^http://www.w3.org/2001/XMLSchema#dateTime
7380
DATE
+8.61^^http://www.w3.org/2001/XMLSchema#decimal
8.61
NUMBER
+33^^http://www.w3.org/2001/XMLSchema#decimal
33
NUMBER
+2.11^^http://www.w3.org/2001/XMLSchema#decimal
2.11
NUMBER
+38^^http://www.w3.org/2001/XMLSchema#decimal
38
NUMBER
+34^^http://www.w3.org/2001/XMLSchema#decimal
34
NUMBER
+142^^http://www.w3.org/2001/XMLSchema#decimal
142
NUMBER
constellation
type of variable star
instance of
instance of