TV Geminorum

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TV Geminorum
Gemini constellation map.svg
Red circle.svg
Location of TV Geminorum (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Gemini
Right ascension 06h 11m 51.41401s[1]
Declination 21° 52′ 05.6452″[1]
Apparent magnitude (V) 6.27 - 7.50[2]
Spectral type K5.5 - M1.3 Iab[3] + B4 III:[2]
U−B color index +1.77[4]
B−V color index +2.25[4]
Variable type SRc[3]
Radial velocity (Rv)+20.42[5] km/s
Proper motion (μ) RA: 0.29[1] mas/yr
Dec.: −2.41[1] mas/yr
Parallax (π)1.05 ± 0.58[1] mas
Distance1,500[6] pc
Absolute magnitude (MV)-6.31[7]
Mass14[8] M
Radius623 ± 158[9], 620 - 710[6] (-770[7]R
Diameter623 ± 158[9], 620 - 710[6] (-770[7]D
Luminosity62,000 - 89,000[6] L
Temperature3,500 - 3,850[6] K
Other designations
TV Gem, BD+21°1146, SAO 78092, HD 42475, HR 2190, HIP 29416
Database references

TV Geminorum (TV Gem / HD 42475 / HR 2190) is a variable red supergiant in the constellation Gemini. Its visual magnitude varies from 6.3 to 7.5.


TV Gem is less than a degree SW of η Geminorum. It is a member of the Gemini OB1 stellar association at around 4,500 light years from Earth.[7]


TV Geminorum is classified as a semi-regular variable star, meaning that its brightness changes are not predictable, but do show some periodicity. The General Catalogue of Variable Stars does not list a period,[3] but the International Variable Star Index gives an uncertain period of 229 days.[2] A detailed study of TV Gem between 1997 and 2014 detects periods of 411 days and 3,137 days.[6]


TV Geminorum changes its size, temperature, and luminosity as its brightness varies. The temperature changes between 3,500 K and 3,850 K, the radius between 620 D and 710 D, and the bolometric luminosity between 62,000 L and 89,000 L. The majority of the electromagnetic radiation is emitted at wavelengths longer than the visual band, being only around 20,000 times brighter than the sun at visual wavelengths.

The pulsations are not correlated with the brightness changes in the expected way; other pulsating variables are brightest when they are hottest and smallest, but TV Gem does not follow this rule. It has been suggested that the luminosity variations are affected by the formation of supergranules surrounding the star.[6] The spectral type varies in line with the temperature changes, from as early as K5.5 to as late as M1.3. The type M1.3 is assigned by a numerical calculation from photometry.[10] The MK spectral class is M0 - M1.5 Iab.[11]

If TV Gem was at the centre of the solar system, the four inner planets, including the Earth, would be encompassed within the star. It is losing mass at an annual rate of 3.5×10−7M.[12]


TV Gem appears to have a very close hot companion. Its existence is inferred from an ultraviolet excess in the spectral energy distribution. The spectral type determined from the ultraviolet portion of the spectrum is B4, appearing to be a giant although it is thought that this is caused by the stellar wind from an underlying main sequence star. It is estimated to have an apparent magnitude of 11.2 and an absolute magnitude of −1.4.[13]

See also


  1. 1.0 1.1 1.2 1.3 1.4 Van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics 474 (2): 653. arXiv:0708.1752. Bibcode 2007A&A...474..653V. doi:10.1051/0004-6361:20078357.
  2. 2.0 2.1 2.2 Watson, C. L. (2006). "The International Variable Star Index (VSX)". The Society for Astronomical Sciences 25th Annual Symposium on Telescope Science. Held May 23–25 25: 47. Bibcode 2006SASS...25...47W.
  3. 3.0 3.1 3.2 Samus, N. N.Expression error: Unrecognized word "etal". (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/gcvs. Originally published in: 2009yCat....102025S 1. Bibcode 2009yCat....102025S.
  4. 4.0 4.1 Ducati, J. R. (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". CDS/ADC Collection of Electronic Catalogues 2237. Bibcode 2002yCat.2237....0D.
  5. Famaey, B.; Jorissen, A.; Luri, X.; Mayor, M.; Udry, S.; Dejonghe, H.; Turon, C. (2005). "Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data. Revisiting the concept of superclusters". Astronomy and Astrophysics 430: 165. arXiv:astro-ph/0409579. Bibcode 2005A&A...430..165F. doi:10.1051/0004-6361:20041272.
  6. 6.0 6.1 6.2 6.3 6.4 6.5 Wasatonic, Richard P.; Guinan, Edward F.; Durbin, Allyn J. (2015). "V-Band, Near-IR, and TiO Photometry of the Semi-Regular Red Supergiant TV Geminorum: Long-Term Quasi-Periodic Changes in Temperature, Radius, and Luminosity". Publications of the Astronomical Society of the Pacific 127 (956): 1010. Bibcode 2015PASP..127.1010W. doi:10.1086/683261.
  7. 7.0 7.1 7.2 Levesque, Emily M.; Massey, Philip; Olsen, K. A. G.; Plez, Bertrand; Josselin, Eric; Maeder, Andre; Meynet, Georges (2005). "The Effective Temperature Scale of Galactic Red Supergiants: Cool, but Not As Cool As We Thought". The Astrophysical Journal 628 (2): 973. arXiv:astro-ph/0504337. Bibcode 2005ApJ...628..973L. doi:10.1086/430901.
  8. Stothers, R.; Leung, K. C. (1971). "Luminosities, masses and periodicities of massive red supergiants". Astronomy and Astrophysics 10: 290. Bibcode 1971A&A....10..290S.
  9. Mondal, Soumen; Chandrasekhar, T. (2005). "Angular Diameter Measurements of Evolved Variables by Lunar Occultations at 2.2 and 3.8 Microns". The Astronomical Journal 130 (2): 842-852. arXiv:astro-ph/0504326. Bibcode 2005AJ....130..842M. doi:10.1086/430457.
  10. White, N. M.; Wing, R. F. (1978). "Photoelectric two-dimensional spectral classification of M supergiants". Astrophysical Journal 222: 209. Bibcode 1978ApJ...222..209W. doi:10.1086/156136.
  11. Keenan, Philip C.; McNeil, Raymond C. (1989). "The Perkins catalog of revised MK types for the cooler stars". Astrophysical Journal Supplement Series 71: 245. Bibcode 1989ApJS...71..245K. doi:10.1086/191373.
  12. Mauron, N.; Josselin, E. (2011). "The mass-loss rates of red supergiants and the de Jager prescription". Astronomy and Astrophysics 526: A156. arXiv:1010.5369. Bibcode 2011A&A...526A.156M. doi:10.1051/0004-6361/201013993.
  13. Buss, Richard H.; Snow, Theodore P. (1988). "Hot components and circumstellar grains in M supergiant syncretic binaries". Astrophysical Journal 335: 331. Bibcode 1988ApJ...335..331B. doi:10.1086/166931.