Delta Cephei
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| Observation data Epoch J2000 |
|
|---|---|
| Constellation | Cepheus |
| Right ascension | 22h 29m 10.27s |
| Declination | +58° 24′ 54.7″ |
| Apparent magnitude (V) | 4.07 (3.48–4.37) |
| Spectral Characteristics | |
| Spectral type | F5 Iab (F5Ib-G2Ib) |
| U-B color index | 0.36 |
| B-V color index | 0.60 |
| Variable type | Cepheid variable |
| Astrometry | |
| Radial velocity (Rv) | -16.8 km/s |
| Proper motion (μ) | RA: 16.47±0.69 mas/yr Dec.: 3.55±0.64 mas/yr |
| Parallax (π) | 3.66 ± 0.15 mas |
| Distance | 891 ly (273 pc) |
| Absolute magnitude (MV) | -3.47 |
| Physical Characteristics | |
| Mass | 5 M☉ |
| Radius | 41.6[1] R☉ |
| Luminosity | 2,000 L☉ |
| Temperature | 5,500–6,800 K |
| Metallicity | ? % Sun |
| Rotation | ~9 km/s. |
| Age | ~108 years |
| Other designations | |
Delta Cephei (δ Cep / δ Cephei) is a star in the constellation Cepheus.
Delta Cephei is the prototype of the Cepheid variables, hence its Latin proper name Cepheidus Prototypus, and it is also the closest star of this type to the Sun. Its variability was discovered by John Goodricke in 1784, the second Cepheid variable discovered following Eta Aquilae earlier the same year.
Unlike the eclipsing binary Algol, Delta Cephei's variability is due to pulsation of the star. It varies from magnitude 3.6 to 4.3, and its spectral type also varies, from about F5 to G3. The period is 5.36634 days; rise to maximum is quicker than the subsequent decline to minimum. It was later discovered that there are two types of Cepheid variables, and Delta Cephei is now known as a type I (Classical) Cepheid.
Stars of this type are believed to form with masses of 3–30 times that of our Sun, and then have passed through the main sequence as B-class stars. With the hydrogen burnt up in their core, these unstable stars are now passing through later stages of nuclear burning.[2]
Knowing the distance of Delta Cephei and others in its class is fundamental to calibrating their period-luminosity relationship; unfortunately, these efforts were until recently marred by only fair parallax accuracy. In 2002 however, the Hubble Space Telescope was used to determine the distance to Delta Cephei (and RR Lyrae, another standard candle) within ~4%: 273 parsecs, or 890 light-years.[3]
There is a companion star, separated from Delta Cephei by 41 arc seconds.
[edit] References
- ^ "Database of Galactic Classical Cepheids", David Dunlop Observatory, 1995.
- ^ Turner, David G, "Monitoring the Evolution of Cepheid Variables", Journal of the AAVSO, 26, 1998, 101-111.
- ^ Benedict, et al., "Astrometry with the Hubble space telescope: a parallax of the fundamental distance calibrator δ Cephei"
[edit] External links
- Alcyone ephemeris.
- SEDS page.
- Delta Cephei by Professor Jim Kaler.
- AAVSO variable star of the month.
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