U Equulei

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.

U Equulei

A visual band light curve for U Equulei, plotted from OMC data[1]
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
IRAS 20547+0247, 2MASS J20571628+0258445, Gaia DR2 1731164844433296128
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]

See also

• List of stars in Equuleus