Delta Cephei
 Location of δ Cep (circled) |
|
| Observation data Epoch J2000.0 Equinox J2000.0 |
|
|---|---|
| Constellation | Cepheus |
| δ Cep A | |
| Right ascension | 22h 29m 10.26502s |
| Declination | +58° 24′ 54.7139″ |
| Apparent magnitude (V) | 4.07 (3.48–4.37) / 7.5 |
| δ Cep C | |
| Right ascension | 22h 29m 09.248s |
| Declination | +58° 24′ 14.76″ |
| Apparent magnitude (V) | 6.3 |
| Characteristics | |
| Spectral type | F5Ib-G1Ib + B7-8 |
| U−B color index | 0.36 |
| B−V color index | 0.60 |
| Variable type | Cepheid |
| Astrometry | |
| Radial velocity (Rv) | -16.8 km/s |
| Proper motion (μ) |
RA: +15.35 mas/yr Dec.: +3.52 mas/yr |
| Parallax (π) | 3.77 ± 0.16mas |
| Distance |
887 ± 26 ly (272 ± 8pc) |
| Absolute magnitude (MV) | –3.47 ± 0.10 (–3.94 - –3.05) |
| Details | |
| δ Cep A | |
| Mass | 4.5 ± 0.3 M☉ |
| Radius | 44.5 R☉ |
| Luminosity | ∼2000 L☉ |
| Temperature | 5,500–6,800 K |
| Metallicity [Fe/H] | +0.08 dex |
| Rotational velocity (v sin i) | 9 km/s |
| Age | ~100 Myr |
| δ Cep B | |
| Mass | 0.2 - 1.2 M☉ |
| Orbit | |
| Primary | δ Cep A |
| Companion | δ Cep B |
| Period (P) | 6.03 yr |
| Eccentricity (e) | 0.647 |
|
Semi-amplitude (K1) (primary) |
1.509 ± 0.2 km/s |
| Other designations | |
| Database references | |
| SIMBAD | data |
Delta Cephei (δ Cep, δ Cephei) is the Bayer designation for a quadruple star system located approximately 887 light-years away in the northern circumpolar constellation of Cepheus, the King. At this distance, the visual magnitude of the star is diminished by 0.23 as a result of extinction caused by gas and dust along the line of sight. It is the prototype of the Cepheid variable stars that undergo periodic changes in luminosity.
Delta Cephei was discovered to be variable by John Goodricke during 1784. He describes his first observation on October 19, 1784, followed by a regular series of observations most nights until December 28. Further observations were made during the first half of 1785, the variability was described in a letter dated June 28, 1785, and formally published on January 1, 1786. This was the second variable star of this type, with eta Aquilae being discovered just a few weeks earlier, on September 10, 1784.
As well as being the prototype, Delta Cephei is among the closest stars of this type of variable to the Sun, with only Polaris being nearer. Its variability is caused by regular pulsations in the outer layers of the star. It varies from magnitude 3.48 to 4.37, and its stellar classification also varies, from about F5 to G3. The pulsation period is 5.366249 days, with a rise to maximum occurring quicker than the subsequent decline to minimum.
Because the period of this class of variable is dependent on the star's luminosity, Delta Cephei is of particular importance as a calibrator for the period-luminosity relationship, since its distance is now one of the most precisely established for a Cepheid. This accuracy is thanks in part to its membership of a star cluster and the availability of precise Hubble Space Telescope/Hipparcos parallaxes. Hence, in 2002, the Hubble Space Telescope was used to determine the distance to Delta Cephei within a 4% margin of error: 273 parsecs (890 light-years) . However, a re-analysis of Hipparcos data found a larger parallax than before, leading to a shorter distance of 244 ± 10 pc, which is equivalent to 800 light-years.
...
Wikipedia