Alpha Serpentis
 Location of α Serpentis (circled) |
|
| Observation data Epoch J2000 Equinox J2000 |
|
|---|---|
| Constellation | Serpens |
| Right ascension | 15h 44m 16.07431s |
| Declination | +06° 25′ 32.2633″ |
| Apparent magnitude (V) | 2.623 |
| Characteristics | |
| Spectral type | K2 III |
| U−B color index | +1.248 |
| B−V color index | +1.167 |
| Astrometry | |
| Radial velocity (Rv) | +2.63 km/s |
| Proper motion (μ) |
RA: +133.84 mas/yr Dec.: +44.81 mas/yr |
| Parallax (π) | 44.10 ± 0.19mas |
| Distance | 74.0 ± 0.3 ly (22.68 ± 0.10 pc) |
| Absolute magnitude (MV) | +0.88 ± 0.03 |
| Details | |
| Radius | 12 R☉ |
| Luminosity | 70 L☉ |
| Surface gravity (log g) | 2.5 cgs |
| Temperature | 4,498 K |
| Metallicity [Fe/H] | 0.03 dex |
| Rotational velocity (v sin i) | 4.3 km/s |
| Other designations | |
| Database references | |
| SIMBAD | data |
Alpha Serpentis (α Serpentis, abbreviated Alpha Ser, α Ser), also named Unukalhai, is a double star in the head (Serpens Caput) of the equatorial constellation of Serpens. With an apparent visual magnitude of 2.6, this star is the brightest in the constellation and it can be viewed with the naked eye from most of the Earth. Parallax measurements yield an estimated distance of about 74 light-years (23 parsecs) from the Sun.
Alpha Serpentis is a giant star with a stellar classification of K2 III, having consumed the hydrogen at its core and evolved away from the main sequence. The interferometry-measured angular diameter of this star, after correcting for limb darkening, is 4.85 ± 0.05 mas, which, at its estimated distance, equates to a physical radius of about 12 times the radius of the Sun. The effective temperature of the outer envelope is 4,498 K, giving it an orange hue that is characteristic of a K-type star.
This star is radiating about 38 times the luminosity of the Sun, while a further 32 times the Sun's luminosity is being emitted in the infrared, for 70-fold total. A magnitude +11.8 companion is at an angular separation of 58 arcseconds from Alpha Serpentis, while a 13th magnitude star lies 2.3 arcminutes distant.
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