R Andromedae

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R Andromedae
Andromeda IAU.svg
Red circle.svg
Location of R Andromedae (circled)
Observation data
Epoch J2000       Equinox J2000
Constellation Andromeda
Right ascension 00h 24m 01.946s [1]
Declination +38° 34′ 37.37″ [1]
Apparent magnitude  (V)5.8 - 15.2 [2]
Characteristics
Spectral type S3,5e-S8,8e(M7e) [2]
B−V color index 1.97 [3]
Variable type Mira [2]
Astrometry
Radial velocity (Rv)−6.40 [4] km/s
Proper motion (μ)RA: −16.021±0.148 [1] mas/yr
Dec.: −32.794±0.141 [1] mas/yr
Parallax (π)2.6444±0.1600  mas [1]
Distance 1,230 ± 70  ly
(380 ± 20  pc)
Absolute magnitude  (MV)−5.19 [5]
Details
Mass 3.7 [6]   M☉
Radius 730 [7] [a] or 476±120 –493±129 [8]   R☉
Luminosity 6,300 [7]   L☉
Surface gravity (log g)−1.02 [9]   cgs
Temperature 1,900 –2,500 [9]   K
Metallicity [Fe/H]−1.01 [10]   dex
Other designations
HR 90, BD +37°58, HD 1967, SAO 53860, HIP 1901.
Database references
SIMBAD data

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, [11] 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. [12] The star is losing mass due to stellar winds at a rate of 1.09×10−6 M☉/yr. [5]

Contents

Variability

R Andromedae light curve R Andromedae light curve.png
R Andromedae light curve

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. [13] 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. [14]

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 . [8] Other measurements based on the spectral energy distribution of the star give a luminosity of 6,000 L☉ and a very cool temperature of 1,900  K , [7] which imply a very large radius of 730 R☉. [a] R Andromedae is one of the largest known stars.

Notes

  1. 1 2 Applying the Stefan–Boltzmann law with a nominal solar effective temperature of 5,772  K:
    .

References

  1. 1 2 3 4 5 Brown, A. G. A.; et al. (Gaia collaboration) (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics . 649: A1. arXiv: 2012.01533 . Bibcode:2021A&A...649A...1G. doi: 10.1051/0004-6361/202039657 . S2CID   227254300. (Erratum:  doi:10.1051/0004-6361/202039657e). Gaia EDR3 record for this source at VizieR .
  2. 1 2 3 4 Samus, N. N.; Durlevich, O. V.; 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.
  3. ↑ "R And". SIMBAD . Centre de données astronomiques de Strasbourg . Retrieved October 7, 2018.
  4. ↑ 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. arXiv: 1208.3048 . Bibcode:2012A&A...546A..61D. doi:10.1051/0004-6361/201219219. S2CID   59451347. A61.
  5. 1 2 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. arXiv: 1002.2458 . Bibcode:2010A&A...513A...4G. doi:10.1051/0004-6361/200911764. S2CID   119193286.
  6. ↑ Khalatyan, A.; Anders, F.; Chiappini, C.; Queiroz, A. B. A.; Nepal, S.; Dal Ponte, M.; Jordi, C.; Guiglion, G.; Valentini, M.; Torralba Elipe, G.; Steinmetz, M.; Pantaleoni-González, M.; Malhotra, S.; Jiménez-Arranz, Ó.; Enke, H.; Casamiquela, L.; Ardèvol, J. (2024). "Transferring spectroscopic stellar labels to 217 million Gaia DR3 XP stars with SHBoost". Astronomy and Astrophysics. 691: A98. arXiv: 2407.06963 . Bibcode:2024A&A...691A..98K. doi:10.1051/0004-6361/202451427.
  7. 1 2 3 Ramstedt, S.; Olofsson, H. (2014). "The12CO/13CO ratio in AGB stars of different chemical type". Astronomy & Astrophysics. 566: A145. arXiv: 1405.6404 . Bibcode:2014A&A...566A.145R. doi:10.1051/0004-6361/201423721. S2CID   59125036.
  8. 1 2 van Belle, G. T.; et al. (1997). "Angular Size Measurements of Carbon Miras and S-Type Stars". The Astronomical Journal. 114 (5): 2150–2156. Bibcode:1997AJ....114.2150V. doi:10.1086/118635.
  9. 1 2 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. arXiv: 1606.09086 . Bibcode:2016MNRAS.461.3036O. doi: 10.1093/mnras/stw1547 . S2CID   118619933.
  10. ↑ Gáspár, András; Rieke, George H.; Ballering, Nicholas (2016). "The Correlation between Metallicity and Debris Disk Mass". The Astrophysical Journal. 826 (2): 171. arXiv: 1604.07403 . Bibcode:2016ApJ...826..171G. doi: 10.3847/0004-637X/826/2/171 . S2CID   119241004.
  11. ↑ Merrill, P. W. (1952). "Technetium in the stars". Science . 115 (2992): 479–489 [484]. Bibcode:1952Sci...115..479.. doi:10.1126/science.115.2992.479. PMID   17792758.
  12. ↑ Yamamura, Issei; et al. (January 2000). "Identification of SH ∆v=1 Ro-vibrational Lines in R Andromedae". The Astrophysical Journal. 528 (1): L33 –L36. arXiv: astro-ph/9911080 . Bibcode:2000ApJ...528L..33Y. doi: 10.1086/312420 . PMID   10587489.
  13. ↑ 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. Bibcode:1980ApJS...43..379K. doi: 10.1086/190673 .
  14. ↑ 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. Bibcode:1974ApJS...28..271K. doi: 10.1086/190318 .
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