Phi2 Hydrae
Star in the constellation Hydra
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Phi2 Hydrae, Latinized from φ2 Hydrae, is a star in the constellation Hydra. It originally received the Flamsteed designation of 1 Crateris before being placed in the Hydra constellation.[11] Based upon an annual parallax shift of 2.9 mas as seen from Earth, it is located roughly 1,110 light years from the Sun. The star is faintly visible to the naked eye with an apparent visual magnitude of about 6.1.[4] It forms a triangle with the fainter φ1 Hydrae and the brighter φ3 Hydrae, between μ Hydrae and ν Hydrae.
| Period (days) |
Amplitude (magnitude) |
|---|---|
| 11.0 | 0.008 |
| 110.3 | 0.012 |
| 153.6 | 0.015 |
| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
|---|---|
| Constellation | Hydra[2] |
| Right ascension | 10h 36m 16.65890s[3] |
| Declination | −16° 20′ 39.5764″[3] |
| Apparent magnitude (V) | 6.1[4] |
| Characteristics | |
| Evolutionary stage | AGB[5] |
| Spectral type | M1 III[6] |
| U−B color index | +1.95[7] |
| B−V color index | +1.64[7] |
| Variable type | SR[8] |
| Astrometry | |
| Radial velocity (Rv) | +15.7±2.9[4] km/s |
| Proper motion (μ) | RA: −30.651[3] mas/yr Dec.: +4.212[3] mas/yr |
| Parallax (π) | 2.929±0.1349 mas[3] |
| Distance | 1,110 ± 50 ly (340 ± 20 pc) |
| Absolute magnitude (MV) | −0.80[2] |
| Details | |
| Mass | 6.4[3] M☉ |
| Radius | 85[9] R☉ |
| Luminosity | 1,470[9] L☉ |
| Surface gravity (log g) | 1.25[3] cgs |
| Temperature | 3,873[9] K |
| Other designations | |
| φ2 Hya, BD−15°3087, HD 91880, HIP 51905, HR 4156, SAO 156093[10] | |
| Database references | |
| SIMBAD | data |
This is an evolved red giant star with a stellar classification of M1 III.[5] It is currently on the asymptotic giant branch,[5] and is a semiregular variable that undergoes changes in luminosity according to three pulsation periods,[8] although it is formally still only a suspected variable.[12] The star is radiating an estimated 1,470 times the Sun's luminosity from its photosphere at an effective temperature of 3,873 K.
Phi2 Hydrae has a faint visual companion: a magnitude 12.20 star at an angular separation of 3.50 arc seconds along a position angle of 280°, as of 1959.[13] The companion has a similar Gaia Data Release 3 parallax to Phi2 Hydrae[14] and is at a distance of 329+5
−4 pc.[15]