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| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Auriga |
| Right ascension | 06h39m 19.82634s[1] |
| Declination | +42° 29′ 19.9617″[1] |
| Apparent magnitude (V) | 4.79[2] |
| Characteristics | |
| Spectral type | K3 III[3] or K3 Iab:[4] |
| U−B color index | +1.30[2] |
| B−V color index | +1.23[2] |
| R−I color index | 0.6 |
| Astrometry | |
| Radial velocity (Rv) | 16.09 ± 0.19[5] km/s |
| Proper motion (μ) | RA: -0.87[1] mas/yr Dec.: -54.97[1] mas/yr |
| Parallax (π) | 7.84 ± 0.29 mas[1] |
| Distance | 420 ± 20 ly (128 ± 5 pc) |
| Absolute magnitude (MV) | −0.72[6] |
| Details | |
| Radius | 27[7] R☉ |
| Luminosity | 304[6] L☉ |
| Surface gravity (log g) | 2.30[8] cgs |
| Temperature | 4,410[8] K |
| Metallicity [Fe/H] | –0.10[8] dex |
| Rotational velocity (v sin i) | 1.0[9] km/s |
| Other designations | |
ψ2 Aur, 50 Aurigae, BD+42 1585, HD 47174, HIP 31832, HR 2427, SAO 41239.[10] | |
| Database references | |
| SIMBAD | data |
Psi2 Aurigae, Latinized from ψ2 Aurigae, is a star in the constellation Auriga. It is faintly visible to the naked eye with an apparent visual magnitude of 4.79.[2] Based upon parallax measurements, this star is approximately 420 light-years (130 parsecs) away from the Earth. At that distance, the brightness of the star is diminished by 0.07 in magnitude from extinction caused by interstellar gas and dust.[5]
Most studies categorized this as a K-type giant star with a stellar classification of K3 III.[3] However, the results of a study published in 2003 list it with a classification of K3 Iab:, which would instead suggest it is a supergiant star.[4][10] The measured angular diameter of this star, after correction for limb darkening, is 1.97 ± 0.02 mas.[11] At the estimated distance of this star,[1] this yields a physical size of about 27 times the radius of the Sun.[7] It is radiating 304[6] times the Sun's luminosity from its enlarged photosphere at an effective temperature of 4,410 K.[8]
It was also known to be part of a much bigger constellation named Telescopium Herschelii. It was also the constellation's second-brightest star before it was unrecognized by the International Astronomical Union (IAU).
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