U Equulei (U Equ / IRAS 20547 +0247) is a variable star in the Equuleus constellation with an apparent magnitude of +14.50 in the B band. It lies at an estimated distance of 5,000 light-years (1,500 parsecs) from the Solar System.
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Equuleus |
| Right ascension | 20h 57m 16.28s[2] |
| Declination | 02° 58′ 44.6″[2] |
| Apparent magnitude (V) | 9 - 13[3] |
| Characteristics | |
| Evolutionary stage | (post?) AGB[4] |
| Spectral type | G - K III[4] |
| B−V color index | +1.6[4] |
| Variable type | Lb[3] |
| Astrometry | |
| Radial velocity (Rv) | −75[5] km/s |
| Proper motion (μ) | RA: 10.490[6] mas/yr Dec.: −10.433[6] mas/yr |
| Parallax (π) | 0.0985 ± 0.0750 mas[6] |
| Distance | 3,340±700[7] pc |
| Details | |
| Luminosity | 6,000[7] L☉ |
| Temperature | 5,005[6] K |
| Other designations | |
| Database references | |
| SIMBAD | data |
Properties
U Equulei is, or was, an OH/IR star, and strong OH and H2O masers have been observed. These vary to a greater extent than almost any other star observed, and it is possible that the stage of maser activity is essentially finished.[8]
Theoretical Planet
Lionel Siess and Mario Livio suggested that the accretion of a giant planet towards the increasing red giant has made the star's outer layers rotate fast enough to cause an outpouring equatorial- or disk-expansion, responsible for the star's peculiar environment.[9] The spectroscopic study has indicated the star is surrounded by the dust shell, but shape of the shell cannot be measured due to large distance to the star.[10]