Theta Apodis

Theta Apodis (θ Apodis, θ Aps) is a variable star in the southern circumpolar constellation of Apus. It is a variable star with an apparent visual magnitude range of 4.65 to 6.20,[3] which, according to the Bortle Dark-Sky Scale, means it is a faint star but visible to the naked eye from dark suburban skies. The distance to Theta Apodis is approximately 350 light-years (110 parsecs), based upon parallax measurements made from the Gaia telescope.[6] It is unusual in that it is a red star with a high proper motion (greater than 50 milliarcseconds a year).[10]

A light curve for Theta Apodis, adapted from Moon et al. (2008)[11]
θ Apodis
Location of θ Apodis (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Apus
Right ascension 14h 05m 19.87784s[1]
Declination −76° 47′ 48.3204″[1]
Apparent magnitude (V) 4.65 - 6.20[2]
Characteristics
Spectral type M7 III[3]
U−B color index +1.07[4]
B−V color index +1.48[4]
Variable type SRb[3]
Astrometry
Radial velocity (Rv)+9.0[5] km/s
Proper motion (μ) RA: −83.823[6] mas/yr
Dec.: −34.694[6] mas/yr
Parallax (π)9.2261 ± 0.6873 mas[6]
Distance350 ± 30 ly
(108 ± 8 pc)
Absolute magnitude (MV)0.7[3]
Details
Mass2.9[7] M☉
Radius208[8] R☉
Luminosity3,748[8] L☉
Surface gravity (log g)−0.086[8] cgs
Temperature3,131[8] K
Metallicity [Fe/H]−0.20[7] dex
Other designations
CD–76 615, FK5 1363, HD 122250, HIP 68815, HR 5261, SAO 257112[9]
Database references
SIMBADdata

This is an evolved red giant that is currently on the asymptotic giant branch,[12] with a stellar classification of M7 III.[3] It shines with a luminosity approximately 3879 times that of the Sun and has a surface temperature of 3,131 K.[8] It is a semiregular pulsating variable and its brightness changes over a range of 0.56 magnitudes with a period of 119[3] days. A longer period of around 1,000 days has also been detected.[11] It is losing mass at the rate of 1.1 × 10−7 times the mass of the Sun per year through its stellar wind. Dusty material ejected from this star is interacting with the surrounding interstellar medium, forming a bow shock as the star moves through the galaxy. The stand-off distance for this front is located at about 0.134 ly (0.041 pc) from Theta Apodis.[12]

Theta Apodis has been identified as an astrometric binary, indicating that it has an orbiting companion that causes gravitational perturbation of the primary star.[13]

References
  1. van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357, S2CID 18759600.
  2. "VSX". Retrieved 2018-10-29.
  3. Yeşilyaprak, C.; Aslan, Z. (December 2004), "Period-luminosity relation for M-type semiregular variables from Hipparcos parallaxes", Monthly Notices of the Royal Astronomical Society, 355 (2): 601–607, Bibcode:2004MNRAS.355..601Y, doi:10.1111/j.1365-2966.2004.08344.x.
  4. Wisse, P. N. J. (May 1981), "Three colour observations of southern red variable giant stars", Astronomy and Astrophysics Supplement Series, 44: 273–303, Bibcode:1981A&AS...44..273W.
  5. Feast, M. W.; Woolley, R.; Yilmaz, N. (1972), "The kinematics of semi-regular red variables in the solar neighbourhood", Monthly Notices of the Royal Astronomical Society, 158: 23–46, Bibcode:1972MNRAS.158...23F, doi:10.1093/mnras/158.1.23.
  6. 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.
  7. Anders, F.; Khalatyan, A.; Chiappini, C.; Queiroz, A. B.; Santiago, B. X.; Jordi, C.; Girardi, L.; Brown, A. G. A.; Matijevič, G.; Monari, G.; Cantat-Gaudin, T.; Weiler, M.; Khan, S.; Miglio, A.; Carrillo, I.; Romero-Gómez, M.; Minchev, I.; De Jong, R. S.; Antoja, T.; Ramos, P.; Steinmetz, M.; Enke, H. (2019). "Photo-astrometric distances, extinctions, and astrophysical parameters for Gaia DR2 stars brighter than G = 18". Astronomy and Astrophysics. 628: A94. arXiv:1904.11302. Bibcode:2019A&A...628A..94A. doi:10.1051/0004-6361/201935765. S2CID 131780028.
  8. 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, S2CID 73594365.
  9. "tet Aps -- Semi-regular pulsating Star", SIMBAD, Centre de Données astronomiques de Strasbourg, retrieved 2012-07-08.
  10. Jiménez-Esteban, F. M.; Caballero, J. A.; Dorda, R.; Miles-Páez, P. A.; Solano, E. (2012). "Identification of red high proper-motion objects in Tycho-2 and 2MASS catalogues using Virtual Observatory tools". Astronomy & Astrophysics. 539: 12. arXiv:1201.5315. Bibcode:2012A&A...539A..86J. doi:10.1051/0004-6361/201118375. S2CID 53404166.
  11. Moon, T. T. (2008). "Combining Visual and Photoelectric Observations of Semiregular Red Variables". Journal of the American Association of Variable Star Observers. 36 (1): 77. arXiv:0711.4873. Bibcode:2008JAVSO..36...77M.
  12. Cox, N. L. J.; et al. (January 2012), "A far-infrared survey of bow shocks and detached shells around AGB stars and red supergiants", Astronomy & Astrophysics, 537: A35, arXiv:1110.5486, Bibcode:2012A&A...537A..35C, doi:10.1051/0004-6361/201117910, S2CID 56041336. See table 1, IRAS 14003-7633.
  13. Eggleton, P. P.; Tokovinin, A. A. (September 2008). "A catalogue of multiplicity among bright stellar systems". Monthly Notices of the Royal Astronomical Society. 389 (2): 869–879. arXiv:0806.2878. Bibcode:2008MNRAS.389..869E. doi:10.1111/j.1365-2966.2008.13596.x. S2CID 14878976.
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