R Geminorum
R Geminorum (R Gem) is a Mira variable and technetium star in the constellation Gemini. It is located approximately 850 parsecs (2,800 ly) away.
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Gemini |
| Right ascension | 07h 07m 21.271s |
| Declination | +22° 42′ 12.75″ |
| Apparent magnitude (V) | 6.0 - 14.0 |
| Characteristics | |
| Evolutionary stage | AGB |
| Spectral type | S2,9e-S8,9e(Tc) |
| Variable type | mira |
| Astrometry | |
| Radial velocity (Rv) | −45.2 km/s |
| Proper motion (μ) | RA: −8.765 mas/yr Dec.: 0.665 mas/yr |
| Parallax (π) | 1.1795 ± 0.0960 mas |
| Distance | 2,800 ± 200 ly (850 ± 70 pc) |
| Details | |
| Radius | 431 R☉ |
| Luminosity | 5,500 L☉ |
| Temperature | 2,400 K |
| Other designations | |
| Database references | |
| SIMBAD | data |
R Geminorum pulsates with an average period of 369.9 days, varying by up to eight magnitudes at visual wavelengths. When at maximum light its apparent visual magnitude is usually between 6 and 7, while at minimum light it is typically near magnitude 14.
R Geminorum is one of the brightest known examples of an S-type star, a type that is similar to M-type star, but whose spectra shows zirconium oxide, yttrium oxide and technetium. These exotic elements are formed in the star's core. Technetium has a half-life of just 4.2 million years, so it must have been brought up from the core relatively recently. R Gem has an unusual amount of it, even for an S-type star.