ST Cephei
Star in the constellation of Cepheus
From Wikipedia, the free encyclopedia
ST Cephei (ST Cep), also known as BD+56°2793,[2] is a red supergiant and a variable star located in the constellation Cepheus. It has a variable apparent magnitude between 7.75 and 8.90, and is over a hundred times the radius of the Sun.[7]
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Cepheus |
| Right ascension | 22h 30m 10.73791s[1] |
| Declination | +57° 00′ 03.0712″[1] |
| Apparent magnitude (V) | 7.75 - 8.90[2] |
| Characteristics | |
| Spectral type | M2Ia-Iab[3] |
| B−V color index | 2.28[4] |
| Variable type | LC[2] |
| Astrometry | |
| Radial velocity (Rv) | −66.6[5] km/s |
| Proper motion (μ) | RA: −3.568[1] mas/yr Dec.: −3.096[1] mas/yr |
| Parallax (π) | 0.2162±0.0239 mas[1] |
| Distance | approx. 15,000 ly (approx. 4,600 pc) |
| Absolute magnitude (MV) | −3.73[6] |
| Details | |
| Mass | 9[7] M☉ |
| Radius | 175[7] - 290[4] R☉ |
| Luminosity | 12,246[8] L☉ |
| Surface gravity (log g) | 0.92[7] cgs |
| Temperature | 4200[7] K |
| Metallicity [Fe/H] | 0.02[1] dex |
| Other designations | |
| BD+56°2793, HD 239978, SAO 34529[9] | |
| Database references | |
| SIMBAD | data |
Distance
ST Cephei is very far from the Solar System, and its parallax was not measured by the Hipparcos satellite. Its membership in the Cepheus OB2-B stellar association allows its distance to be estimated at 830 parsecs, or 2,715 light years.[citation needed]
Characteristics
ST Cephei is a red supergiant of spectral type M3I—previously cataloged as M2I—with an effective temperature of 3,600 Kelvin. It is a large supergiant; estimates of its radius range from 175[7] to 290 solar radii.[4] Considering an intermediate radius between both values, if it were in the place of the Sun, its surface would extend to the Earth's orbit. Despite this, its size is far from the two known hypergiants in this constellation, μ Cephei and VV Cephei.[2][7][4]
The bolometric luminosity of ST Cephei is 8,400 times greater than that of the Sun. It has a mass 9 times greater than the Sun, at the limit from which stars end their lives by exploding as supernovae. Like other analogous supergiants, it loses mass; Its loss of stellar mass—in the form of dust, since the atomic and molecular gas could not be evaluated—is quantified at 2.5×10−9 M☉/year.[7]
In 1910 it was announced that Evelyn Leland had discovered that the star is a variable star.[11] That same year it was given its variable star designation, ST Cephei.[12] Listed as an LC irregular variable star, the brightness of ST Cephei varies by about two magnitudes, with no period recognized.[2]