Astronomy:TW Horologii

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Short description: Star in the constellation Horologium
TW Horologii
250px
A visual band light curve for TW Horologii, plotted from data published by Tabur et al. (2009)[1]
Observation data
Equinox J2000.0]] (ICRS)
Constellation Horologium
Right ascension  03h 12m 33.16062s[2]
Declination −57° 19′ 17.5710″[2]
Apparent magnitude (V) 5.71[3] (5.52 to 5.95)[4]
Characteristics
Evolutionary stage Asymptotic giant branch
Spectral type C-N4IIIb: (C23.5)[5]
U−B color index +2.93[6]
B−V color index +2.419±0.014[3]
Variable type SRb[4]
Astrometry
Radial velocity (Rv)+14.3±2.9[3] km/s
Proper motion (μ) RA: +18.492[2] mas/yr
Dec.: +13.298[2] mas/yr
Parallax (π)2.3755 ± 0.1295[2] mas
Distance1,370 ± 70 ly
(420 ± 20 pc)
Absolute magnitude (MV)−1.79[3]
Absolute bolometric
magnitude (Mbol)		−4.62[7]
Details
Mass3.29±0.65[8] M☉
Radius300[9][lower-alpha 1] R☉
Luminosity6,700[9] L☉
Surface gravity (log g)0.049[10] cgs
Temperature3,000[9] K
Other designations
TW Hor, CD−57°626, FK5 118, HD 20234, HIP 14930, HR 977, SAO 233037[11]
Database references
SIMBADdata

TW Horologii is a carbon star and semiregular variable in the southern constellation of Horologium,[12] near the eastern constellation border with Reticulum. It has a ruddy hue and, with an apparent visual magnitude that ranges from 5.52 down to 5.95,[4] is visible to the naked eye and one of the brightest carbon stars.[12] Based on parallax measurements, it is located at a distance of approximately 1,370 light years from the Sun.[2] It is drifting further away with a radial velocity of +14 km/s.[3] In the past this star has been considered a member of the open cluster NGC 1252, but this now seems unlikely.[13]

This star was designated Sigma2 Horologii by Johann Elert Bode in his 1801 Uranographia, but this is now no longer used.[14]

This is an aging red giant star on the asymptotic giant branch[7] with a stellar classification of C-N4IIIb: and a C2 index of C23.5. It has been listed as a standard star for that MK spectral class.[5] The star is classified as a semiregular variable of type SRb and has a periodicity of 158 days.[4] It has expanded to 303 times the radius of the Sun and, on average, is radiating 6,700 times the Sun's luminosity from its swollen photosphere at an effective temperature of 3,000 K.[9] If it replaced the Solar System, the perihelion of Mars would be inside the star. The short-lived element technetium has been observed in the spectrum, an indicator of thermal pulses during helium shell burning.[15]

Based on the detection of excess ultraviolet excess, it is most likely a binary star system.[16] An analysis of the motion of TW Horologii suggests a low-mass companion, although the UV excess suggests it is hot.[8]

In 2013 the luminosity of Mira variables, based on Hipparcos parallaxes, was used to calibrate a Period-luminosity relationship for carbon stars. The absolute magnitude of TW Horologii was calculated to be −1.79.[3]

Notes

  1. ↑ Applying the Stefan–Boltzmann law with a nominal solar effective temperature of 5,772 K:
    (5,7723,000)4⋅6,700=303 R⊙.

References

  1. ↑ Tabur, V.; Bedding, T. R.; Kiss, L. L.; Moon, T. T.; Szeidl, B.; Kjeldsen, H. (December 2009). "Long-term photometry and periods for 261 nearby pulsating M giants". Monthly Notices of the Royal Astronomical Society 400 (4): 1945–1961. doi:10.1111/j.1365-2966.2009.15588.x. Bibcode: 2009MNRAS.400.1945T. 
  2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 Brown, A. G. A. (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics 616: A1. doi:10.1051/0004-6361/201833051. Bibcode: 2018A&A...616A...1G.  Gaia DR2 record for this source at VizieR.
  3. ↑ 3.0 3.1 3.2 3.3 3.4 3.5 Anderson, E.; Francis, Ch. (2012). "XHIP: An extended hipparcos compilation". Astronomy Letters 38 (5): 331. doi:10.1134/S1063773712050015. Bibcode: 2012AstL...38..331A. 
  4. ↑ 4.0 4.1 4.2 4.3 Samus, N. N. et al. (2017). "General Catalogue of Variable Stars". Astronomy Reports. 5.1 61 (1): 80–88. doi:10.1134/S1063772917010085. Bibcode: 2017ARep...61...80S. 
  5. ↑ 5.0 5.1 Barnbaum, Cecilia et al. (1996). "A Moderate-Resolution Spectral Atlas of Carbon Stars: R, J, N, CH, and Barium Stars". Astrophysical Journal Supplement 105: 419. doi:10.1086/192323. Bibcode: 1996ApJS..105..419B. 
  6. ↑ Nicolet, B. (1978). "Catalogue of homogeneous data in the UBV photoelectric photometric system". Astronomy and Astrophysics Supplement Series 34: 1–49. Bibcode: 1978A&AS...34....1N. 
  7. ↑ 7.0 7.1 Guandalini, R.; Cristallo, S. (2013). "Luminosities of carbon-rich asymptotic giant branch stars in the Milky Way". Astronomy & Astrophysics 555: 7. doi:10.1051/0004-6361/201321225. A120. Bibcode: 2013A&A...555A.120G. 
  8. ↑ 8.0 8.1 Kervella, Pierre; Arenou, Frédéric; Mignard, François; Thévenin, Frédéric (2019). "Stellar and substellar companions of nearby stars from Gaia DR2. Binarity from proper motion anomaly". Astronomy and Astrophysics 623: A72. doi:10.1051/0004-6361/201834371. Bibcode: 2019A&A...623A..72K. 
  9. ↑ 9.0 9.1 9.2 9.3 Siderud, Emelie (2020). Dust emission modelling of AGB stars. https://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-423949. 
  10. ↑ McDonald, I.; Zijlstra, A. A.; Watson, R. A. (2017). "Fundamental parameters and infrared excesses of Tycho-Gaia stars". Monthly Notices of the Royal Astronomical Society 471 (1): 770. doi:10.1093/mnras/stx1433. Bibcode: 2017MNRAS.471..770M. 
  11. ↑ "V* TW Hor". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=V%2A+TW+Hor. 
  12. ↑ 12.0 12.1 Streicher, Magda (October 2009). "The Pendulum Clock". Monthly Notes of the Astronomical Society of South Africa 68 (9–10): 202–206. Bibcode: 2009MNSSA..68..202S. 
  13. ↑ de la Fuente Marcos, R. et al. (September 2013). "NGC 1252: a high altitude, metal poor open cluster remnant". Monthly Notices of the Royal Astronomical Society 434 (1): 194–208. doi:10.1093/mnras/stt996. Bibcode: 2013MNRAS.434..194D. 
  14. ↑ E-Rara.ch, 2026, https://www.e-rara.ch/zut/content/zoom/3341806 
  15. ↑ Lebzelter, T.; Hron, J. (December 2003). "Technetium and the third dredge up in AGB stars. I. Field stars". Astronomy and Astrophysics 411 (3): 533–542. doi:10.1051/0004-6361:20031458. Bibcode: 2003A&A...411..533L. 
  16. ↑ Ortiz, Roberto; Guerrero, Martín A. (September 2016). "Ultraviolet emission from main-sequence companions of AGB stars". Monthly Notices of the Royal Astronomical Society 461 (3): 3036–3046. doi:10.1093/mnras/stw1547. Bibcode: 2016MNRAS.461.3036O. 



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