Short description: Star in the constellation Andromeda
R Andromedae (R And) is a Mira-type variable star in the constellation Andromeda. Its spectral class is type S because it shows absorption bands of zirconium monoxide (ZrO) in its spectrum. It was among the stars found by Paul Merrill to show absorption lines of the unstable element technetium,[10] establishing that nucleosynthesis must be occurring in stars. The SH molecule was found for the first time outside earth in the atmosphere of this star.[11] The star is losing mass due to stellar winds at a rate of 1.09×10−6 M☉/yr.[5]
Variability
R Andromedae shows periodic variations in its brightness approximately every 409 days. The maximum brightness is not the same every cycle and can reach a peak magnitude of mv = 5.8, with the lowest known minima nearly 10 magnitudes fainter. The rise to maximum brightness is approximately twice as fast as the fall to minimum brightness. It is classified as a Mira variable. Those stars contract and expand regularly, changing size and temperature, and this causes the brightness variations.[2]
Properties
R Andromedae has a spectral type that varies as its brightness changes. At a typical maximum it is assigned a spectral type of S5/4.5e. This makes it an S-type star, a red giant similar to class M stars but with unusually strong molecular bands of ZrO in its spectrum compared to the titanium oxide (TiO) bands seen in other cool giants. S stars are intermediate between carbon stars and the more typical oxygen-rich giants. The S5 indicates its relative temperature, while the number after the slash is a measure of the relative C:O ratio, 4.5 meaning carbon is about 97% as abundant as oxygen. ZrO bands in R Andromedae are about twenty times stronger than those of TiO.[12] When it is fainter, the spectral type has been classified as late as S8,8e. On this older classification system for S stars, the number after the comma is an indication of the relative strength of ZrO and TiO bands which used to be considered to show the C:O ratio.[13]
R Andromedae, like all Mira variables, is an asymptotic giant branch star, one that has exhausted its core helium and is burning it in a shell outside the core and hydrogen in a shell closer to the surface. These stars undergo dredge-up events which cause convection of fusion products to the surface and anomalies such as enhanced carbon and zirconium. Asymptotic giant branch stars are very cool and luminous red giants; R Andromedae varies in temperature and luminosity but is typically about 2,500 K and 6,300 L☉. The angular diameter of R Andromedae has been measured at 8.63±1.42 mas and 8.32±1.27 mas on different dates, corresponding to radii of 493±129 R☉ and 476±120 R☉ respectively, assuming a distance of 532 pc.[6]
References
- ↑ 1.0 1.1 1.2 1.3 1.4 Brown, A. G. A. (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics 649: A1. doi:10.1051/0004-6361/202039657. Bibcode: 2021A&A...649A...1G. Gaia EDR3 record for this source at VizieR.
- ↑ 2.0 2.1 2.2 2.3 Samus, N. N. et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S 1. Bibcode: 2009yCat....102025S.
- ↑ "R And". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=R+And.
- ↑ de Bruijne, J. H. J.; Eilers, A.-C. (October 2012). "Radial velocities for the HIPPARCOS-Gaia Hundred-Thousand-Proper-Motion project". Astronomy & Astrophysics 546: 14. doi:10.1051/0004-6361/201219219. A61. Bibcode: 2012A&A...546A..61D.
- ↑ 5.0 5.1 Guandalini, R. (April 2010). "Infrared photometry and evolution of mass-losing AGB stars. III. Mass loss rates of MS and S stars". Astronomy and Astrophysics 513: A4. doi:10.1051/0004-6361/200911764. Bibcode: 2010A&A...513A...4G.
- ↑ 6.0 6.1 van Belle, G. T. et al. (1997). "Angular Size Measurements of Carbon Miras and S-Type Stars". The Astronomical Journal 114 (5): 2150–2156. doi:10.1086/118635. Bibcode: 1997AJ....114.2150V. https://cdr.lib.unc.edu/downloads/w9505947n.
- ↑ Ramstedt, S.; Olofsson, H. (2014). "The12CO/13CO ratio in AGB stars of different chemical type". Astronomy & Astrophysics 566: A145. doi:10.1051/0004-6361/201423721. Bibcode: 2014A&A...566A.145R.
- ↑ 8.0 8.1 Ortiz, Roberto; Guerrero, Martín A. (2016). "Ultraviolet emission from main-sequence companions of AGB stars". Monthly Notices of the Royal Astronomical Society 461 (3): 3036. doi:10.1093/mnras/stw1547. Bibcode: 2016MNRAS.461.3036O.
- ↑ Gáspár, András; Rieke, George H.; Ballering, Nicholas (2016). "The Correlation between Metallicity and Debris Disk Mass". The Astrophysical Journal 826 (2): 171. doi:10.3847/0004-637X/826/2/171. Bibcode: 2016ApJ...826..171G.
- ↑ Merrill, P. W. (1952). "Technetium in the stars". Science 115 (2992): 479–489 [484]. doi:10.1126/science.115.2992.479. PMID 17792758. Bibcode: 1952Sci...115..479..
- ↑ Yamamura, Issei et al. (January 2000). "Identification of SH ∆v=1 Ro-vibrational Lines in R Andromedae". The Astrophysical Journal 528 (1): L33–L36. doi:10.1086/312420. PMID 10587489. Bibcode: 2000ApJ...528L..33Y.
- ↑ Keenan, P. C.; Boeshaar, P. C. (1980). "Spectral types of S and SC stars on the revised MK system". The Astrophysical Journal Supplement Series 43: 379. doi:10.1086/190673. Bibcode: 1980ApJS...43..379K.
- ↑ Keenan, Philip C.; Garrison, Robert F.; Deutsch, Armin J. (1974). "Revised Catalog of Spectra of Mira Variables of Types ME and Se". The Astrophysical Journal Supplement Series 28: 271. doi:10.1086/190318. Bibcode: 1974ApJS...28..271K.
External links
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