R Hydrae

R Hydrae, abbreviated R Hya,[2] is a single[10] star in the equatorial constellation of Hydra, about 2.7° to the east of Gamma Hydrae.[11] It is a Mira-type variable[2] that ranges in apparent visual magnitude from 3.5 down to 10.9 over a period of 389 days. At maximum brightness the star can be seen with the naked eye, while at minimum a telescope of at least 5 cm is needed. This star is located at a distance of approximately 410 light-years from the Sun based on parallax measurements,[1] but is drifting closer with a radial velocity of −10 km/s.[5]

Not to be confused with Rho Hydrae.
R Hydrae
Location of R Hydrae (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Hydra
Right ascension 13h 29m 42.782s[1]
Declination −23° 16′ 52.77″[1]
Apparent magnitude (V) 3.5 to 10.9 (variable)[2]
Characteristics
Spectral type M6e/M9e:[3]
B−V color index 1.317±0.254[4]
Variable type Mira[2] (period 388.87 days)
Astrometry
Radial velocity (Rv)−10.0±0.6[5] km/s
Proper motion (μ) RA: −57.68 mas/yr[1]
Dec.: +12.86 mas/yr[1]
Parallax (π)8.05 ± 0.69 mas[6]
Distance410 ± 30 ly
(120 ± 10 pc)
Absolute magnitude (MV)+0.95[4]
Details
Mass2[7] M☉
Radius460 R☉[7]
631[8] R☉
Luminosity7,375 L☉[8]
10,000[7] L☉
Temperature2,128 K[8]
2,830[7] K
Age0.5–1.0[7] Gyr
Other designations
R Hya, BD−22° 3601, HD 117287, HIP 65835, HR 5080, SAO 181695, WDS 13297-2317A[9]
Database references
SIMBADdata

This is an aging red giant star with a stellar classification of M6e/M9e:,[3] currently near the thermal-pulsing tip of the asymptotic giant branch.[7] The 1998 detection of weak technicium (Tc) lines in the spectrum suggests the star has recently gone through a third dredge-up.[12] However, a 2010 study failed to detect technicium in the atmosphere, indicating this oxygen-rich AGB star is Tc-poor.[13] O. J. Eggen found the star is a likely member of the Hyades supergroup, which suggests an age of 500 million to one billion years and a mass double that of the Sun.[7]

A visual band light curve for R Hydrae, from AAVSO data[14]

The first record of observations for this star was in 1662 by Johannes Hevelius. It was found to be variable by Giacomo Filippo Maraldi in 1702; thereafter he tracked its various appearances until 1712. The evidence suggests the period of variability during this period was ~495 days. In between 1770 and 1950, the period declined linearly down to 385 days. It has remained fairly stable since that time. The decline may be due to a prior thermal pulse caused by a helium flash under a hydrogen-fusing shell. The period change would have been accompanied by a decrease in the stellar radius. An alternative explanation is a relaxation of the stellar envelope brought on by a change in the structure within the star.[7]

The bow shock around R Hya[15]

An extended emission component has been detected in the infrared that indicates a detached, expanding dust shell surrounds the star. The inner boundary of this shell is located at 60–100 times the stellar radius, and it extends outward to at least 1,000 times the radius[12] with an expansion velocity of ~8 km/s.[16] The data indicate a mass loss rate of 2×10−7 M☉·yr−1, which declined by a factor of 20 around the year 1788.[16] Observations using the Spitzer Space Telescope show an extended double shell with a spiral structure, which extends out to 300″. It forms a bow shock where it interacts with the surrounding interstellar medium. The orientation of this feature is consistent with the star's proper motion.[17]

References
  1. 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. S2CID 18759600.
  2. "R Hya". International Variable Star Index. Retrieved 2021-12-01.
  3. Keenan, Philip C.; Garrison, Robert F.; Deutsch, Armin J. (1974). "Revised Catalog of Spectra of Mira Variables of Types ME and Se". Astrophysical Journal Supplement. 28: 271. Bibcode:1974ApJS...28..271K. doi:10.1086/190318.
  4. 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. S2CID 119257644.
  5. Gontcharov, G. A. (2006). "Pulkovo Compilation of Radial Velocities for 35 495 Hipparcos stars in a common system". Astronomy Letters. 32 (11): 759–771. arXiv:1606.08053. Bibcode:2006AstL...32..759G. doi:10.1134/S1063773706110065. S2CID 119231169.
  6. 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.
  7. Zijlstra, A. A.; et al. (2002). "The evolution of the Mira variable R Hydrae". Monthly Notices of the Royal Astronomical Society. 334 (3): 498. arXiv:astro-ph/0203328. Bibcode:2002MNRAS.334..498Z. doi:10.1046/j.1365-8711.2002.05467.x. S2CID 16663228.
  8. De Beck, E.; et al. (2010). "Probing the mass-loss history of AGB and red supergiant stars from CO rotational line profiles. II. CO line survey of evolved stars: derivation of mass-loss rate formulae". Astronomy and Astrophysics. 523: A18. arXiv:1008.1083. Bibcode:2010A&A...523A..18D. doi:10.1051/0004-6361/200913771. S2CID 16131273. A18.
  9. "V* R Hya". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2021-12-01.
  10. Pourbaix, D. (July 2008). Taming the binaries. A Giant Step: from Milli- to Micro-arcsecond Astrometry, Proceedings of the International Astronomical Union, IAU Symposium. Vol. 248. pp. 59–65. Bibcode:2008IAUS..248...59P. doi:10.1017/S1743921308018632.
  11. Sinnott, Roger W.; Perryman, Michael A. C. (1997). Millennium Star Atlas. Vol. 2. Sky Publishing Corporation and the European Space Agency. p. 866. ISBN 0-933346-83-2.
  12. Hashimoto, O.; et al. (January 1998). "A cold detached dust envelope around an oxygen-rich Mira-type AGB star R Hydrae". Astronomy and Astrophysics. 329: 213–218. Bibcode:1998A&A...329..213H.
  13. Uttenthaler, S.; Lebzelter, T. (February 2010). "Correlation between technetium and lithium in a sample of oxygen-rich AGB variables". Astronomy and Astrophysics. 510: A62. arXiv:0911.3507. Bibcode:2010A&A...510A..62U. doi:10.1051/0004-6361/200912548. S2CID 119231142. A62.
  14. "Download Data". aavso.org. AAVSO. Retrieved 1 October 2021.
  15. "Red Giant Plunging Through Space". Spitzer Science Center Press Release. November 30, 2006. Retrieved 2021-12-01.
  16. Decin, L.; et al. (June 2008). "Probing the mass-loss history of the unusual Mira variable R Hydrae through its infrared CO wind". Astronomy and Astrophysics. 484 (2): 401–412. Bibcode:2008A&A...484..401D. doi:10.1051/0004-6361:20079312.
  17. Speck, Angela K.; et al. (2006). Barlow, M. J.; Méndez, R. H. (eds.). Spitzer/MIPS Imaging of the Extremely Extended Dust Shell(s) around R Hya. Planetary Nebulae in our Galaxy and Beyond Proceedings IAU Symposium No. 234. Bibcode:2006IAUS..234..515S. doi:10.1017/S1743921306004017.

Further reading
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