U Lacertae

U Lacertae is a spectroscopic binary star in the constellation Lacerta.

U Lacertae

Location of U Lacertae (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Lacerta
Right ascension	22h 47m 43.42677s[1]
Declination	+55° 09′ 30.3036″[1]
Apparent magnitude (V)	9.40[2]
Characteristics
Spectral type	M4epIab + B[3]
U−B color index	+1.46[2]
B−V color index	+2.34[2]
Variable type	SRc[3]
Astrometry
Radial velocity (Rv)	−68[4] km/s
Proper motion (μ)	RA: −3.207 [5] mas/yr Dec.: −3.150 [5] mas/yr
Parallax (π)	0.3519±0.0708 mas[5]
Distance	2,750[6] pc
Absolute magnitude (MV)	−5.6[7]
Details
Mass	22[7] M☉
Radius	1,013[8] R☉
Luminosity	152,000[8] L☉
Temperature	3,535[8] K
Other designations
U Lac, HIP 112545, PPM 411, GSC 03988-01641, IRC+50446, TYC 3988-1641-1, BD+54°2863, HD 215924, 2MASS J22474341+5509303, AAVSO 2243+54
Database references
SIMBAD	data

Despite being in the constellation of Lacerta, U Lacertae is considered to be a member of the Cepheus OB1 association.^[9] It has been listed as a member of the open cluster ASCC 123.^[10]

U Lacertae is a binary star consisting of a red supergiant and a small hot companion, similar to VV Cephei. The companion has been identified from a high excitation component in the spectrum and from radial velocity variations, but the orbit is unknown.^[11]

A visual band light curve for U Lacertae, plotted from AAVSO data^[12]

In 1894, T. H. E. C. Espin announced that the star, then called BD +54° 2863, might be a variable star.^[13] T. W. Blackhouse confirmed its variability in 1897.^[14] It was listed with its variable star designation, U Lacertae, in Annie Jump Cannon's 1907 work Second Catalog of Variable Stars.^[15] U Lacertae is classified as a semiregular variable.^[3] The periodicity is uncertain but a main period of 150 days and a long secondary period of 550 – 690 days have been suggested.^[16] A study of Hipparcos satellite photometry found an amplitude of 0.77 magnitudes and found no periodicity.^[17] The General Catalogue of Variable Stars lists an amplitude of 2.7 magnitudes.^[3]

Water masers have been detected around U Lacertae, common in the extended atmospheres of very luminous cool stars.^[18]

See also

• List of largest known stars
• VV Cephei