TW Horologii

A visual band light curve for TW Horologii, plotted from data published by Tabur et al. (2009)[1]
Observation data
Epoch J2000      Equinox J2000
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
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 mas[2]
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☉
Radius163.6+18.7
−27.9[2] R☉
Luminosity4,390±281[2] L☉
Surface gravity (log g)0.049[9] cgs
Temperature3,674+360
−194[2] K
Other designations
TW Hor, CD−57°626, FK5 118, HD 20234, HIP 14930, HR 977, SAO 233037[10]
Database references
SIMBADdata

TW Horologii is a carbon star and semiregular variable in the southern constellation of Horologium,[11] 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.[11] 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.[12]

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 164[2] times the radius of the Sun and, on average, is radiating 4,390 times the Sun's luminosity from its swollen photosphere at an effective temperature of 3,674 K.[2] The short-lived element technetium has been observed in the spectrum, an indicator of thermal pulses during helium shell burning.[13]

Based on the detection of excess ultraviolet excess, it is most likely a binary star system.[14] 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]

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. arXiv:0908.3228. Bibcode:2009MNRAS.400.1945T. doi:10.1111/j.1365-2966.2009.15588.x.
  2. 1 2 3 4 5 6 7 8 9 10 11 Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  3. 1 2 3 4 5 6 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. S2CID 119257644.
  4. 1 2 3 4 Samus, N. N.; et al. (2017). "General Catalogue of Variable Stars". Astronomy Reports. 5.1. 61 (1): 80–88. Bibcode:2017ARep...61...80S. doi:10.1134/S1063772917010085. S2CID 125853869.
  5. 1 2 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. Bibcode:1996ApJS..105..419B. doi:10.1086/192323.
  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. 1 2 Guandalini, R.; Cristallo, S. (2013). "Luminosities of carbon-rich asymptotic giant branch stars in the Milky Way". Astronomy & Astrophysics. 555: 7. arXiv:1305.4203. Bibcode:2013A&A...555A.120G. doi:10.1051/0004-6361/201321225. S2CID 54918450. A120.
  8. 1 2 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. arXiv:1811.08902. Bibcode:2019A&A...623A..72K. doi:10.1051/0004-6361/201834371. S2CID 119491061.
  9. ↑ 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. arXiv:1706.02208. Bibcode:2017MNRAS.471..770M. doi:10.1093/mnras/stx1433.
  10. ↑ "V* TW Hor". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 19 March 2016.
  11. 1 2 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.
  12. ↑ 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. arXiv:1306.1643. Bibcode:2013MNRAS.434..194D. doi:10.1093/mnras/stt996.
  13. ↑ 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. arXiv:astro-ph/0310018. Bibcode:2003A&A...411..533L. doi:10.1051/0004-6361:20031458. S2CID 18879265.
  14. ↑ 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. arXiv:1606.09086. Bibcode:2016MNRAS.461.3036O. doi:10.1093/mnras/stw1547.
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