Tau4 Serpentis

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τ4 Serpentis
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Serpens
Right ascension 15h 36m 28.1873s[1]
Declination +15° 06′ 05.128″[1]
Apparent magnitude (V) 5.89 to 7.07[2]
Spectral type M5II-III[1]
B−V color index 1.2[1]
Variable type SRB[2]
Radial velocity (Rv)−26 ± 5[1] km/s
Proper motion (μ) RA: −3.41[1] mas/yr
Dec.: 9.55[1] mas/yr
Parallax (π)6.27 ± 1.00[1] mas
Distanceapprox. 520 ly
(approx. 160 pc)
Absolute magnitude (MV)−0.03[3]
Luminosity155[3] L
Other designations
τ4 Ser, 17 Serpentis, BD+15° 2890, GC 20983, HD 139216, HIP 76423, SAO 101641, PPM 131543[1]
Database references

Tau4 Serpentis, Latinized from τ4 Serpentis, is a M-type bright giant star in the constellation of Serpens, approximately 520 light-years from the Earth.[1] It is classified as a semiregular late-type variable star, and its magnitude varies between +5.89 and +7.07 with a period of approximately 100 days.[2] τ4 is unique among the stars with the Bayer designation τ Serpentis as being the only one with no HR catalog number.


  1. ^ a b c d e f g h i j V* tau04 Ser -- Pulsating variable Star, database entry, SIMBAD. Accessed on line September 19, 2008.
  2. ^ a b c tau 4 Ser, database entry, The combined table of GCVS Vols I-III and NL 67-78 with improved coordinates, General Catalogue of Variable Stars, Sternberg Astronomical Institute, Moscow, Russia. Accessed on line September 19, 2008.
  3. ^ a b Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters, 38 (5): 331, arXiv:1108.4971, Bibcode:2012AstL...38..331A, doi:10.1134/S1063773712050015.