  | |
| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
|---|---|
| Constellation | Gemini |
| Right ascension | 06h 09m 43.9853s [1] |
| Declination | +23° 06′ 48.472″ [1] |
| Apparent magnitude (V) | 5.71 - 5.77 [2] |
| Characteristics | |
| Evolutionary stage | Blue supergiant star |
| Spectral type | B3Ia [3] |
| U−B color index | −0.63 [4] |
| B−V color index | +0.21 [4] |
| Variable type | α Cyg [5] [2] |
| Astrometry | |
| Radial velocity (Rv) | 16.00±4.3 [6] km/s |
| Proper motion (μ) | RA: −0.064 [1] mas/yr Dec.: −2.685 [1] mas/yr |
| Parallax (π) | 0.3878±0.0616 mas [1] |
| Distance | approx. 8,000 ly (approx. 2,600 pc) |
| Absolute magnitude (MV) | −6.26 [7] |
| Details | |
| Mass | 21 [7] M☉ |
| Radius | 55 [8] R☉ |
| Luminosity | 204,000 [8] L☉ |
| Surface gravity (log g) | 2.45 [8] cgs |
| Temperature | 16,500 [8] K |
| Rotational velocity (v sin i) | 80 [8] km/s |
| Other designations | |
| 3 Geminorum, PU Gem, HR 2173, HIP 29225, HD 42087, BD+23°1226, AAVSO 0603+23 | |
| Database references | |
| SIMBAD | data |
3 Geminorum is a blue supergiant star in the constellation Gemini. It is a small amplitude pulsating variable and a close double star, with a mean combined apparent visual magnitude of about 5.7.
3 Geminorum was found to be an α Cygni variable in 1998 and given the designation PU Geminorum. It varies by a few tenths of a magnitude [5] with a main period of 6.807 days [2] and a secondary period of 25 days. [8]
3 Geminorum is also a close double star. The brighter component is the variable blue supergiant. The companion is 2.5 magnitudes fainter. The separation is about 0.6 arc-seconds. [10] There is also a much fainter, approximately 14th magnitude, star 14" away. [11]
Faint Hα emission lines have been detected in the spectrum of 3 Geminorum, [12] but this is not usually expressed in published spectral classifications. [3] An "e" is only occasionally appended to the spectral type to reflect the emission lines. [13] [5] 3 Geminorum has frequently been classified as a normal supergiant (luminosity class Ib), [14] although a bright supergiant (Ia) luminosity class is now preferred. [3]
3 Geminorum can be occulted by the Moon. Observations of these occultations can give information about the angular diameter of a star, or about close companions. Occultations of 3 Geminorum have been observed, but no double or diameter information has been published. [15]
