TW Horologii

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
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 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☉
Radius303[9][a] 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 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.[14]

Based on the detection of excess ultraviolet excess, it is most likely a binary star system.[15] 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]

  1. ^ Cite error: The named reference Tabur was invoked but never defined (see the help page).
  2. ^ a b c d e f Cite error: The named reference GaiaDR2tw was invoked but never defined (see the help page).
  3. ^ a b c d e f Cite error: The named reference Anderson2012 was invoked but never defined (see the help page).
  4. ^ a b c d Cite error: The named reference Samus2017 was invoked but never defined (see the help page).
  5. ^ a b Cite error: The named reference barnbaum was invoked but never defined (see the help page).
  6. ^ Cite error: The named reference UBV was invoked but never defined (see the help page).
  7. ^ a b Cite error: The named reference guandalini was invoked but never defined (see the help page).
  8. ^ a b Cite error: The named reference kervella2019 was invoked but never defined (see the help page).
  9. ^ a b c d Cite error: The named reference dust_agb was invoked but never defined (see the help page).
  10. ^ Cite error: The named reference mcdonald2017 was invoked but never defined (see the help page).
  11. ^ Cite error: The named reference SIMBAD was invoked but never defined (see the help page).
  12. ^ a b Cite error: The named reference Streicher2009 was invoked but never defined (see the help page).
  13. ^ Cite error: The named reference Marcos2013 was invoked but never defined (see the help page).
  14. ^ Cite error: The named reference Lebzelter2003 was invoked but never defined (see the help page).
  15. ^ Cite error: The named reference Ortiz2016 was invoked but never defined (see the help page).


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