V391 Pegasi
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| Observation data Epoch J2000.0 |
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|---|---|---|
| Constellation (pronunciation) |
Pegasus | |
| Right ascension | 22h 04m 12.2s | |
| Declination | +26° 25' 08" | |
| Apparent magnitude (V) | +14.57 | |
| Characteristics | ||
| Spectral type | sdB | |
| Variable type | EC 14026 star | |
| Astrometry | ||
| Distance | 4570 ly (1400 pc) | |
| Absolute magnitude (MV) | +3.84 | |
| Details | ||
| Mass | 0.5±0.05 M☉ | |
| Radius | 0.23±0.03 R☉ | |
| Surface gravity (log g) | 5.15 | |
| Luminosity | 15.4[citation needed] L☉ | |
| Temperature | 29300±500 K | |
| Age | >10 × 109 years | |
| Planet | ||
| Companion |
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| Mass (MJ) |
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| Orbital period (days) |
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| Semimajor axis (AU) |
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| Eccentricity |
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| Other designations | ||
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HS 2201+2610
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V391 Pegasi (HS 2201+2610) is a subdwarf B star (also known as an "extreme horizontal branch star") with an apparent magnitude of +14.57 and located 1400 parsecs (4570 light years) distant. It is small with only half the mass and one-over-four-and-one-thirds the diameter of the Sun. It has luminosity 15.4 times the Sun.[citation needed] It is old, over 10 Gyr old. It is a pulsating variable star of the EC 14026 type.
Subdwarf B stars such as V391 Pegasi are thought to be the result of premature ejection of the hydrogen envelope of a red giant star before the onset of helium fusion. The reasons for why some stars undergo this process instead of going through the red giant stage and becoming white dwarfs are not well known.
[edit] Planetary system
In 2007, a gas giant planet designated V391 Pegasi b was found in orbit by variable timing method. This planet around "extreme horizontal branch" star provided clues about what could actually happen to the planets in our solar system when our Sun turns to a red giant hood in next five billion years.
| Planet (in order from star) |
Mass (MJ) |
Orbital period (days) |
Semimajor axis (AU) |
Eccentricity |
|---|---|---|---|---|
| b | >3.2±0.7 | 1170±44 | 1.7±0.1 | 0.00 |
[edit] References
- R. Østensen, J.-E. Solheim, U. Heber, R. Silvotti, S. Dreizler, H. Edelmann (2001). "Detection of pulsations in three subdwarf B stars". Astronomy and Astrophysics 368: 175–182. doi:.
- C. S. Jeffery (2005). "Pulsations in Subdwarf B Stars". Journal of Astrophysics and Astronomy 26: 261. doi:.
