Alphard
- For the programming language, see Alphard (programming language).
- For the vehicle, see Toyota Alphard.
 Alphard is the α star in the constellation of Hydra. | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Hydra |
| Right ascension | 09h 27m 35.2s |
| Declination | -08° 39′ 31″ |
| Apparent magnitude (V) | +1.98 |
| Characteristics | |
| Spectral type | K3 II-III |
| U−B color index | 1.72 |
| B−V color index | 1.44 |
| Variable type | ? |
| Astrometry | |
| Radial velocity (Rv) | -4 km/s |
| Proper motion (μ) | RA: -14.49 mas/yr Dec.: 33.25 mas/yr |
| Parallax (π) | 18.4 ± 0.78 mas |
| Distance | 177 ± 8 ly (54 ± 2 pc) |
| Absolute magnitude (MV) | −1.70 |
| Details | |
| Mass | ? M☉ |
| Radius | 34.5 R☉ |
| Luminosity | 400 L☉ |
| Temperature | 4,400 K |
| Metallicity | ? |
| Rotation | <17 km/s. |
| Age | ? years |
| Other designations | |
Alphard (α Hya / α Hydrae / Alpha Hydrae) is the brightest star in the constellation Hydra, marking the heart of the snake.
Alphard is an orange giant star. The name Alphard is from the Arabic الفرد (al-fard), "the solitary one", there being no other bright stars near it.
Precise radial velocity measurements [1] have shown variations in the stellar radial velocities and spectral line profiles. The oscillations are multi-periodic with periods from several hours up to several days. The short-term oscillations were assumed to be a result of stellar pulsations, similar to the solar ones. A correlation between the variations in the asymmetry of the spectral line profile and the radial velocity has also been found. The multi-periodic oscillations make HD 81797 (Alphard) an object of interest for asteroseismologic investigations.
References
- ^ Setiawan, J., Roth, M., Weise, P., Dölinger, M. P. (2006) Multi-periodic oscillations of HD 32887 and HD 81797. Memorie della Societa Astronomica Italiana, 77, p.510
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