R Crucis

R Crucis is a variable star in the southern constellation of Crux. It has a yellow-white hue and is often too faint to see with the naked eye, having an apparent visual magnitude that fluctuates around 6.89.[2] This object is located at a distance of approximately 1,600 light years from the Sun based on parallax,[6] but it is drifting closer with a radial velocity of −13.5 km/s.[2]

R Crucis
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Crux
Right ascension  12h 23m 37.68840s[1]
Declination −61° 37′ 44.8570″[1]
Apparent magnitude (V) 6.89[2]
Characteristics
Spectral type F6-G2Ib-II[3] or F7Ib/II[4]
B−V color index 0.67±0.02[2]
Variable type δ Cep[5]
Astrometry
Radial velocity (Rv)−13.5±3.0[2] km/s
Proper motion (μ) RA: -9.404[1] mas/yr
Dec.: −0.430[1] mas/yr
Parallax (π)1.98 ± 0.54[6] mas
Distanceapprox. 1,600 ly
(approx. 500 pc)
Details
Radius44.6[7] R☉
Surface gravity (log g)1.65[8] cgs
Temperature5,812±22[8] K
Metallicity [Fe/H]+0.06[8] dex
Other designations
R Cru, CD−60°4138, HD 107805, HIP 60455, SAO 251878[9]
Database references
SIMBADdata

This is a Classical Cepheid, or Delta Cephei variable, that ranges in brightness from visual magnitude 6.40 down to 7.23 with a period of 5.82575 days.[5] It is a supergiant star with a stellar classification that varies over each pulsation cycle, giving it a class range of F6-G2Ib-II.[3] The star has a mean radius 44.6 times the radius of the Sun (44.6 R☉), but the radius varies by 5 R☉ during each pulsation.[10] It has a near solar metallicity and the atmospheric abundances indicate it is likely past first dredge-up.[8]

A candidate companion star has been detected at an angular separation of 7.6″, which corresponds to a projected separation of 6,330 AU. The Hubble WFC3 shows a closer companion at a separation of 1.9″.[11] The system is a source for X-ray emission but the contributing component is unclear.[12]

References
  1. 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.
  2. 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.
  3. Watson, Christopher (4 January 2010). "R Crucis". AAVSO Website. American Association of Variable Star Observers. Retrieved 12 March 2014.
  4. Houk, Nancy (1979). Michigan catalogue of two-dimensional spectral types for the HD stars. 1. Ann Arbor, Michigan: Department of Astronomy, University of Michigan. Bibcode:1978mcts.book.....H.
  5. 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.
  6. van Leeuwen, F. (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.
  7. Moskalik, P.; Gorynya, N. A. (2005). "Mean Angular Diameters and Angular Diameter Amplitudes of Bright Cepheids". Acta Astronomica. 55: 247. arXiv:astro-ph/0507076. Bibcode:2005AcA....55..247M.
  8. Usenko, I. A.; et al. (July 2014). "Spectroscopic studies of southern-hemisphere Cepheids: Three Cepheids in Crux (BG Cru, R Cru, and T Cru)". Astronomy Letters. 40 (7): 435–448. Bibcode:2014AstL...40..435U. doi:10.1134/S106377371407007X.
  9. "R Cru". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2020-02-14.
  10. Moskalik, P.; Gorynya, N. A. (June 2005). "Mean Angular Diameters and Angular Diameter Amplitudes of Bright Cepheids". Acta Astronomica. 55: 247–260. arXiv:astro-ph/0507076. Bibcode:2005AcA....55..247M.
  11. Evans, Nancy Remage; et al. (May 2016). "Hubble Space Telescope Snapshot Survey for Resolved Companions of Galactic Cepheids". The Astronomical Journal. 151 (5): 14. arXiv:1603.02224. Bibcode:2016AJ....151..129E. doi:10.3847/0004-6256/151/5/129. 129.
  12. Engle, Scott G.; et al. (March 2017). "The Secret Lives of Cepheids: δ Cep—The Prototype of a New Class of Pulsating X-Ray Variable Stars". The Astrophysical Journal. 838 (1): 9. arXiv:1702.06560. Bibcode:2017ApJ...838...67E. doi:10.3847/1538-4357/aa6159. 67.
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