Alpha Pictoris
 Location of α Pictoris (circled) |
|
| Observation data Epoch J2000 Equinox J2000 |
|
|---|---|
| Constellation | Pictor |
| Right ascension | 06h 48m 11.45512s |
| Declination | −61° 56′ 29.0008″ |
| Apparent magnitude (V) | 3.27 |
| Characteristics | |
| Spectral type | A8 Vn kA6 |
| U−B color index | +0.13 |
| B−V color index | +0.21 |
| Astrometry | |
| Radial velocity (Rv) | +20.6 km/s |
| Proper motion (μ) |
RA: –66.07 mas/yr Dec.: +242.97 mas/yr |
| Parallax (π) | 33.78 ± 1.78mas |
| Distance | 97 ± 5 ly (30 ± 2 pc) |
| Absolute magnitude (MV) | 0.86 |
| Orbit | |
| Period (P) |
1618+1407 −325 days |
| Semi-major axis (a) |
36+15 −2 mas |
| Eccentricity (e) | 0.39+0.35 −0.17 |
| Inclination (i) | 118±3° |
| Longitude of the node (Ω) | 24±5° |
| Periastron epoch (T) | 953+707 −640 |
|
Argument of periastron (ω) (secondary) |
92+22 −44° |
| Details | |
| Mass | 2.04 M☉ |
| Radius | 1.6 R☉ |
| Luminosity | 13 L☉ |
| Surface gravity (log g) | 3.48 cgs |
| Temperature | 7530 K |
| Metallicity [Fe/H] | –0.11 dex |
| Rotational velocity (v sin i) | 206 km/s |
| Age | 660 Myr |
| Other designations | |
Alpha Pictoris (α Pic, α Pictoris) is the brightest star in the southern constellation of Pictor. It has an apparent visual magnitude of 3.27, which is bright enough to be viewed from urban areas in the southern hemisphere. This star is close enough for its distance to be measured using parallax shifts, which yields a value of roughly 97 light-years (30 parsecs) from the Sun, with a 5% margin of error. Alpha Pictoris has the distinction of being the south pole star of the planet Mercury.
With an estimated age of 660 million years, this is a relatively young Lambda Boötis star. The stellar classification of A8 Vn kA6 shows this peculiarity, with the kA6 notation indicating weaker than normal K-lines in the spectrum. The 'n' following the main sequence luminosity class of V indicates the absorption lines in the spectrum are broad and nebulous. This is caused by the rapid spin of the star, which has a high projected rotational velocity of 206 km/s. Spectroscopy shows narrow, time-varying absorption features being caused by circumstellar gas moving toward the star. This is not the result of interstellar matter, but a shell of gas along the orbital plane. Alpha Pictoris is categorized as a rapidly rotating shell star that may have recently ejected mass from its outer atmosphere.
Alpha Pictoris is larger than the Sun, with twice the mass and a 60% greater radius. It is radiating 13 times as much luminosity as the Sun from its outer atmosphere at an effective temperature of 7530 K. At this heat, the star glows with the white hue of an A-type star. The space velocity components of this star in the galactic coordinate system are U = -22, V = -20 and W = -9 km/s.
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