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
Radius 476±120 - 493±129 [6]   R☉
Luminosity 6,300 [7]   L☉
Surface gravity (log g)−1.02 [8]   cgs
Temperature 2,500 [8]   K
Metallicity [Fe/H]−1.01 [9]   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, [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]

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. [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]

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References

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  7. ↑ 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 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.
  9. ↑ 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.
  10. ↑ 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.
  11. ↑ 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.
  12. ↑ 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 .
  13. ↑ 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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