Epoch J2000.0 Equinox J2000.0
|Right ascension||05h 32m 12.75251s|
|Declination||+18° 35′ 39.2436″|
|Apparent magnitude (V)||4.23 - 4.54|
|U−B color index||+2.23|
|B−V color index||+2.08|
|Radial velocity (Rv)||+23.75 km/s|
|Proper motion (μ)||RA: 1.86 mas/yr
Dec.: −4.48 mas/yr
|Parallax (π)||1.82 ± 0.26 mas|
|Distance||approx. 1,800 ly
(approx. 550 pc)
|Absolute magnitude (MV)||−5.20|
|Radius||601 ± 83 R☉|
|Luminosity (bolometric)||43,000 L☉|
|Surface gravity (log g)||-0.21 cgs|
119 Tauri, also known as CE Tauri and nicknamed the Ruby Star even though it is not approved by the IAU for use, is a star in the constellation Taurus. It has a diameter about over 600 times that of the Sun. CE Tau is close enough that its distance can be determined accurately by parallax and so the actual diameter can be determined directly from the angular diameter.
119 Tauri has a spectral class of M2 and a luminosity class of Iab-Ib, intermediate between an intermediate-luminosity supergiant and a less luminous supergiant. It is approximately 1,800 light years from Earth. The star is classified as a semiregular variable star and its brightness varies from magnitude +4.23 to +4.54 with a period of 165 days. With a colour index of +2.07, it is one of the reddest naked eye stars in the night sky.
CE Tauri lies 4.6 degrees off the ecliptic. This makes it a candidate for occultations by the Moon and (extremely rarely) by one of the bright planets. The star's angular diameter has been measured by lunar occultation, giving limb-darkened angular diameters of 9.1±0.8 and 10.9±1.0 mas. An occultation has also been observed in H-alpha, giving a diameter of 17±1 mas, which indicates that there is circumstellar hydrogen producing emission across at least that size. The diameter has also been measured directly by very-long-baseline interferometry (VLBI), leading to limb-darkened diameters of 9.3±0.5 9.83±0.07, 9.97±0.08, and 10.68±0.21. Although CE Tauri is classified as a pulsating variable, observations using the same equipment and wavelengths have not not detected changes in the angular diameter over time.
Angular diameter measurements can be combined with absolute observed fluxes to derive an accurate effective temperature, in this case 3,400 K. Combined with a distance, the linear size of the star can be calculated. CE Tauri is found to have a radius of 601 R☉. Then the bolometric luminosity is the star is found to be 43,000 L☉. Comparison with stellar evolutionary tracks shows CE Tauri to be an 8 M☉ asymptotic giant branch (AGB) star, although the presence of technetium is considered doubtful so it may be an early-AGB star or even near the top of the red giant branch.
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