U Lacertae

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]
Distance2,750[6] pc
Absolute magnitude (MV)−5.6[7]
Details
Mass22[7] M☉
Radius1,013[8] R☉
Luminosity152,000[8] L☉
Temperature3,535[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
SIMBADdata

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

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]

U Lacertae is a variable star 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.[13] A study of Hipparcos satellite photometry found an amplitude of 0.77 magnitudes and found no periodicity.[14] 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.[15]

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