S Apodis

S Apodis , also known as HD 133444 is a variable star located in the southern circumpolar constellation Apus. It has an apparent magnitude ranging from 9.6 to 17,[3] which is below the limit for naked eye visibility. The object is located relatively far at a distance of approximately 15,000 light years based on Gaia DR3 parallax measurements,[2] but it is drifting closer with a heliocentric radial velocity of −75 km/s.[7]

S Apodis

The visual band light curve of S Apodis, from AAVSO data[1]
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Apus
Right ascension 15h 09m 24.53660s[2]
Declination −72° 03′ 45.1828″[2]
Apparent magnitude (V) 9.6 - 17.0[3]
Characteristics
Evolutionary stage post-AGB[4]
Spectral type R3[5]
U−B color index +0.66[6]
B−V color index +1.26[6]
Variable type R Coronae Borealis[3]
Astrometry
Radial velocity (Rv)−75.0[7] km/s
Proper motion (μ) RA: −6.632 mas/yr[2]
Dec.: −2.155 mas/yr[2]
Parallax (π)0.2243 ± 0.0171 mas[2]
Distance15,000 ± 1,000 ly
(4,500 ± 300 pc)
Absolute bolometric
magnitude (Mbol)		−2.68 (at max)[8]
Details
Mass0.6 or 1[9] M☉
Radius132±9[10] R☉
Luminosity960[11] L☉
Temperature4,500 - 5,115[12] K
Other designations
S Aps, CD−71°1120, CPD−71°1743, HD 133444, HIP 74179, 2MASS J15092452-7203451[13]
Database references
SIMBADdata

HD 133444 has been known to be a variable star since 1896.[14] However, its nature as a carbon star was not observed until 1967 by astronomer Brian Warner.[15] In 1973, HD 133444 was listed as a R Coronae Borealis variable. [16] These are extremely hydrogen-deficient supergiants thought to have arisen as the result of the merger of two white dwarfs[17] and fewer than 100 have been discovered as of 2013.[18] A decade later, S Apodis was observed to have a change it its pulsation mode.[9]

S Apodis has a stellar classification of R3, indicating that it is a R-type carbon star. It has a mass of either 0.6 M☉ or 1 M☉,[9] depending on the model. However, it has expanded to an average radius 132 times that of the Sun.[10] It radiates 960 times the luminosity of the Sun[11] from its photosphere at an effective temperature of 4,500–5,115 K,[12] giving it an orange hue. An infrared excess has been detected around the star, indicating the presence of circumstellar dust. The dust has a temperature of 730 K.[19]

References
  1. "Download Data". aavso.org. AAVSO. Retrieved 1 October 2021.
  2. Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
  3. Samus’, N. N.; Kazarovets, E. V.; Durlevich, O. V.; Kireeva, N. N.; Pastukhova, E. N. (January 2017). "General catalogue of variable stars: Version GCVS 5.1". Astronomy Reports. 61 (1): 80–88. Bibcode:2017ARep...61...80S. doi:10.1134/S1063772917010085. eISSN 1562-6881. ISSN 1063-7729. S2CID 125853869.
  4. Szczerba, R.; Siódmiak, N.; Stasińska, G.; Borkowski, J. (29 March 2007). "An evolutionary catalogue of galactic post-AGB and related objects". Astronomy & Astrophysics. 469 (2): 799–806. arXiv:astro-ph/0703717. Bibcode:2007A&A...469..799S. doi:10.1051/0004-6361:20067035. eISSN 1432-0746. ISSN 0004-6361. S2CID 16505186.
  5. Cannon, Annie Jump; Pickering, Edward Charles (1920). "The Henry Draper catalogue : 12h, 13h, and 14h". Annals of Harvard College Observatory. 95: 1. Bibcode:1920AnHar..95....1C.
  6. Ducati, J. R. (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". VizieR Online Data Catalog. Bibcode:2002yCat.2237....0D.
  7. Skuljan, L.; Cottrell, P. L. (11 January 1999). "Spectroscopic and photometric observations of the R Coronae Borealis stars S Apodis and RZ Normae throughout their recent declines". Monthly Notices of the Royal Astronomical Society. 302 (2): 341–348. Bibcode:1999MNRAS.302..341S. doi:10.1046/j.1365-8711.1999.02123.x. eISSN 1365-2966. ISSN 0035-8711. S2CID 120220227.
  8. Bergeat, J.; Knapik, A.; Rutily, B. (August 2002). "Carbon-rich giants in the HR diagram and their luminosity function". Astronomy & Astrophysics. 390 (3): 967–986. Bibcode:2002A&A...390..967B. doi:10.1051/0004-6361:20020525. eISSN 1432-0746. ISSN 0004-6361. S2CID 122775604.
  9. Kilkenny, D. (1 December 1983). "A possible change in pulsation mode of the R Corona Borealis star, S Apodis". Monthly Notices of the Royal Astronomical Society. 205 (4): 907–912. Bibcode:1983MNRAS.205..907K. doi:10.1093/mnras/205.4.907. eISSN 1365-2966. ISSN 0035-8711. S2CID 123036693.
  10. Kervella, P.; Thévenin, F.; Di Folco, E.; Ségransan, D. (October 2004). "The angular sizes of dwarf stars and subgiants. Surface brightness relations calibrated by interferometry". Astronomy & Astrophysics. 426 (1): 297–307. arXiv:astro-ph/0404180. Bibcode:2004A&A...426..297K. doi:10.1051/0004-6361:20035930. eISSN 1432-0746. ISSN 0004-6361. S2CID 6077801.
  11. McDonald, I.; Zijlstra, A. A.; Boyer, M. L. (21 November 2012). "Fundamental parameters and infrared excesses of Hipparcos stars: Parameters and IR excesses from Hipparcos". Monthly Notices of the Royal Astronomical Society. 427 (1): 343–357. arXiv:1208.2037. Bibcode:2012MNRAS.427..343M. doi:10.1111/j.1365-2966.2012.21873.x. eISSN 1365-2966. ISSN 0035-8711. S2CID 118665352.
  12. Bergeat, J.; Knapik, A.; Rutily, B. (April 2001). "The effective temperatures of carbon-rich stars". Astronomy & Astrophysics. 369 (1): 178–209. Bibcode:2001A&A...369..178B. doi:10.1051/0004-6361:20010106. eISSN 1432-0746. ISSN 0004-6361. S2CID 121435880.
  13. "S Apodis". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved February 25, 2023.
  14. Pickering, E. C.; Fleming, W. P. (April 1896). "Harvard College Observatory, circular no. 6. New variable stars". The Astrophysical Journal. 3: 296. Bibcode:1896ApJ.....3..296P. doi:10.1086/140219. eISSN 1538-4357. ISSN 0004-637X. S2CID 121212070.
  15. Warner, B. (1 October 1967). "The Hydrogen-Deficient Carbon Stars". Monthly Notices of the Royal Astronomical Society. 137 (2): 119–139. Bibcode:1967MNRAS.137..119W. doi:10.1093/mnras/137.2.119. eISSN 1365-2966. ISSN 0035-8711. S2CID 121153173.
  16. Feast, M. W.; Glass, I. S. (1 March 1973). "Infra-red Photometry of R Coronae Borealis Type Variables and Related Objects". Monthly Notices of the Royal Astronomical Society. 161 (3): 293–303. Bibcode:1973MNRAS.161..293F. doi:10.1093/mnras/161.3.293. eISSN 1365-2966. ISSN 0035-8711. S2CID 120889102.
  17. Zhang, Xianfei; Jeffery, C. Simon (7 September 2012). "Can R Coronae Borealis stars form from the merger of two helium white dwarfs?". Monthly Notices of the Royal Astronomical Society: Letters. 426 (1): L81–L85. arXiv:1208.3907. Bibcode:2012MNRAS.426L..81Z. doi:10.1111/j.1745-3933.2012.01330.x. ISSN 1745-3925. S2CID 118613556.
  18. Tisserand, P.; Clayton, G. C.; Welch, D. L.; Pilecki, B.; Wyrzykowski, L.; Kilkenny, D. (26 February 2013). "The ongoing pursuit of R Coronae Borealis stars: the ASAS-3 survey strikes again". Astronomy & Astrophysics. 551: A77. arXiv:1211.2475. Bibcode:2013A&A...551A..77T. doi:10.1051/0004-6361/201220713. eISSN 1432-0746. ISSN 0004-6361. S2CID 59060842.
  19. García-Hernández, D. A.; Rao, N. Kameswara; Lambert, D. L. (31 July 2013). "Dust Around R Coronae Borealis Stars. II. Infrared Emission Features in an H-poor Environment". The Astrophysical Journal. 773 (2): 107. arXiv:1307.0294. Bibcode:2013ApJ...773..107G. doi:10.1088/0004-637X/773/2/107. eISSN 1538-4357. ISSN 0004-637X. S2CID 119243395.
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