RS Cancri

RS Cancri, also known as HR 3639 and HD 78712, is a star about 490 light years from the Earth in the constellation Cancer. It is a semiregular variable star, ranging in brightness from magnitude 5.4 to 7.3 over a period of about 229 days. During the time intervals when it is brighter than magnitude 6, it may be faintly visible to the naked eye of an observer far from city lights.

RS Cancri

A visual band light curve for RS Cancri, plotted from AAVSO data[1]
Observation data
Epoch J2000      Equinox J2000
Constellation Cancer
Right ascension 09h 10m 38.79702s[2]
Declination +30° 57′ 47.2911″[2]
Apparent magnitude (V) 5.4 - 7.3[3]
Characteristics
Spectral type M6S[4]
Variable type SRb[3]
Astrometry
Proper motion (μ) RA: −10.723±0.423[2] mas/yr
Dec.: −33.822±0.360[2] mas/yr
Parallax (π)6.6490 ± 0.4946 mas[2]
Distance490 ± 40 ly
(150 ± 10 pc)
Absolute magnitude (MV)5.4 - 7.3[3]
Details
Radius225[5] R☉
Luminosity4950[6] L☉
Temperature3200[6] K
Other designations
HD 78712, HR 3639, HIP 45058, SAO 61306[7]
Database references
SIMBADdata

The variability of RS Cancri was discovered by Edward Pickering based upon 15 observations made in 1892 and 1898. S. Seliwanow derived a period of 129.5 days for the star, in 1923.[8] In 2005, Saul Adelman and John Dennis found that the star showed two periods well determined by their data, 121.8±0.9 and 248±7 days, as well as a poorly-determined third period of about 500 days.[9]

RS Cancri is an S-type star,[4] on the asymptotic giant branch.[10] Its spectrum shows technetium, implying the star has undegone the third dredge-up.[11] RS Cancri has a stellar wind, and is losing mass at a rate of 1.7 × 10−7 solar masses per year.[5]

RS Cancri has a circumstellar shell. It is a good target for studies of such a shell, because its rather high galactic latitude (+42 degrees) means that it is cleanly separated from the interstellar dust and gas seen along most lines of sight through the galactic plane. Dust within the shell produces far-infrared continuum emission that was resolved by IRAS.[12] Both atomic and molecular gas within the shell are also measurably extended, and have been mapped.[5]

The extensive molecular envelope surrounding RS Cancri was first detected in 1977, by Kwok-Yung (Fred) Lo and Kenneth Bechis, who used the 36 foot radio telescope on Kitt Peak to detect the J=1-0 line of carbon monoxide (CO).[13] Years later, when observations of spectral lines could be made with more sensitive equipment, it was noticed that the shapes of the spectral lines suggested that RS Cancri has two distinct stellar wind components, expanding into space at different speeds.[14] Interferometric observations have shown that the two winds consist of a ~2 km/sec wind arising from an equatorial disk within the envelope, and an ~8 km/sec bipolar wind.[15] In subsequent decades, additional molecules such as SiO, SO, SO2, H2O HCN and PN have been detected.[6]

References
  1. "Download Data". aavso.org. AAVSO. Retrieved 21 March 2023.
  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. (2017). "General catalogue of variable stars: Version GCVS 5.1". Astronomy Reports. 61 (1): 80. Bibcode:2017ARep...61...80S. doi:10.1134/S1063772917010085. S2CID 125853869.
  4. Keenan, Philip C. (November 1954). "Classification of the S-Type Stars". Astrophysical Journal. 120: 484–505. Bibcode:1954ApJ...120..484K. doi:10.1086/145937.
  5. Hoai, D. T.; Matthews, L. D.; Winters, J. M.; Nhung, P. T.; Gérard, E.; Libert, Y.; Le Bertre, T. (May 2014). "The multi-scale environment of RS Cancri from CO and H I observations". Astronomy and Astrophysics. 565: A54. Bibcode:2014A&A...565A..54H. doi:10.1051/0004-6361/201423529.
  6. Winters, J. M.; Hoai, D. T.; Wong, K. T.; Kim, W. J.; Nhung, P. T.; Tuan-Anh, P.; Lesaffre, P.; Darriulat, P.; Le Bertre, T. (February 2022). "Molecules, shocks, and disk in the axi-symmetric wind of the MS-type AGB star RS Cancri". Astronomy and Astrophysics. 658: A135. Bibcode:2022A&A...658A.135W. doi:10.1051/0004-6361/202141662.
  7. "V* RS Cnc -- S Star". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2023-03-21.
  8. Howarth, J. J. (December 2005). "The semi-regular variable RS Cancri: one period, two, or many?". Journal of the British Astronomical Association. 115 (6): 334–337. Bibcode:2005JBAA..115..334H.
  9. Adelman, Saul J.; Dennis, John W., III (2005). "The S-Type Asymptotic Giant Branch Stars RS Cnc, ST Her, OP Her And HR Peg". Baltic Astronomy. 14: 41–50. Bibcode:2005BaltA..14...41A.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  10. Nhung, Pham Tuyet; Thi Hoai, Do; Winters, Jan Martin; Darriulat, Pierre; Gérard, Eric; Le Bertre, Thibaut (May 2015). "On the central symmetry of the circumstellar envelope of RS Cnc". Research in Astronomy and Astrophysics. 15 (5): 713. Bibcode:2015RAA....15..713N. doi:10.1088/1674-4527/15/5/008.
  11. Lebzelter, Th.; Hron, J. (November 1999). "A search for Technetium in semiregular variables". Astronomy and Astrophysics. 351: 533–542. Bibcode:1999A&A...351..533L.
  12. Young, K.; Phillips, T. G.; Knapp, G. R. (June 1993). "Circumstellar Shells Resolved in the IRAS Survey Data. I. Data Processing Procedure, Results, and Confidence Tests". Astrophysical Journal Supplement. 86: 517–640. Bibcode:1993ApJS...86..517Y. doi:10.1086/191789.
  13. Lo, K. Y.; Bechis, K. P. (November 1977). "Variable 2.5 mm CO emission from chi Cygni and Mira". Astrophysical Journal. 218 (L27–L30): L27. Bibcode:1977ApJ...218L..27L. doi:10.1086/182569.
  14. Knapp, G. R.; Young, K.; Lee, E.; Jorissen, A. (July 1998). "Multiple Molecular Winds in Evolved Stars. I. A Survey of CO(2-1) and CO(3-2) Emission from 45 Nearby Asymptotic Giant Branch Stars". The Astrophysical Journal Supplement Series. 117 (1): 209–231. Bibcode:1998ApJS..117..209K. doi:10.1086/313111.
  15. Libert, Y.; Winters, J. M.; Le Bertre, T.; Gérard, E.; Matthews, L. D. (June 2010). "HI and CO in the circumstellar environment of the S-type star RS Cancri". Astronomy and Astrophysics. 515: A112. arXiv:1003.1636. Bibcode:2010A&A...515A.112L. doi:10.1051/0004-6361/200912731. Retrieved 24 March 2023.
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