Astronomy:V361 Hydrae
| Observation data Equinox J2000.0]] (ICRS) | |
|---|---|
| Constellation | Hydra |
| Right ascension | 14h 05m 33.018s[1] |
| Declination | −27° 01′ 34.01″[1] |
| Apparent magnitude (V) | 15.3[2] |
| Characteristics | |
| Evolutionary stage | horizontal branch[3] |
| Spectral type | sdB+[4] |
| Variable type | V361 Hya[5] |
| Astrometry | |
| Proper motion (μ) | RA: −7.8[2] mas/yr Dec.: −9.4[2] mas/yr |
| Parallax (π) | −0.7258 ± 0.3350[6] mas |
| Distance | ~7,200[7] ly (2,231[7] pc) |
| Details | |
| Mass | 0.47[7] M☉ |
| Radius | 0.101[7] R☉ |
| Luminosity | 13.3[7] L☉ |
| Surface gravity (log g) | 6.10[8] cgs |
| Temperature | 34,700[8] K |
| Other designations | |
EC 14026−2647, UCAC4 315-074628 | |
| Database references | |
| SIMBAD | data |
V361 Hydrae is a hot subdwarf variable star, the prototype of a class of pulsating variables. It is very approximately 2,200 parsecs away in the constellation of Hydra. The star is classified as an extreme horizontal branch star; it is small, with only half the mass and a tenth the diameter of the Sun, but is 13 times as luminous as the Sun.
Discovery
This star was first noted in the Edinburgh-Cape Blue Object Survey, a search for blue objects in the southern celestial hemisphere published in 1997, and it was catalogued as EC 14026−2647. Together with several similar objects from the survey, it was found to pulsate with a period of just a few minutes. These stars were initially referred to as EC 14026 stars and tentatively grouped with the PV Telescopii variables. In 2000, this star was given the variable star designation V361 Hydrae[9] and in 2008 a new class of variable stars was formally created, the V361 Hydrae variables.[10]
V361 Hydrae itself varies in brightness by about a tenth of a magnitude[5] with a period of 144 seconds.[4]
Formation
Subdwarf B stars such as V361 Hydrae are thought to be the result of the ejection of the hydrogen envelope of a red giant star at or just before the onset of helium fusion. The ejection left only a tiny amount of hydrogen on the surface—less than 1/1000 of the total stellar mass. The future for the star is to eventually cool down to make a low-mass white dwarf. Most stars retain more of their hydrogen after the first red giant phase, and eventually become asymptotic giant branch stars. The reason that some stars lose so much mass is not well known.[11] At the tip of the red-giant branch, the red giant precursors of the subdwarf stars reach their maximum radius, on the order of 0.7 AU. After this point, the hydrogen envelope is lost and helium fusion begins—this is known as the helium flash.[12]
Possible companion
The spectrum of V361 Hydrae is unusual and difficult to interpret. While it is clearly a hot hydrogen-deficient subdwarf, the spectrum contains a full series of hydrogen absorption lines that are typical of a class F or G main sequence star and these are presumed to originate from an otherwise-unseen companion.[4][8]
References
- ↑ 1.0 1.1 Vallenari, A. et al. (2022). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy & Astrophysics. doi:10.1051/0004-6361/202243940 Gaia DR3 record for this source at VizieR.
- ↑ 2.0 2.1 2.2 Zacharias, N. (2012). The fourth US Naval Observatory CCD Astrograph Catalog (UCAC4). VizieR On-line Data Catalog. 1322. Bibcode: 2012yCat.1322....0Z.
- ↑ Guyot, N.; Van Grootel, V.; Charpinet, S.; Farnir, M.; Dupret, M.-A.; Brassard, P. (2025). "The theoretical pulsation spectra of hot B subdwarfs: Static and evolutionary STELUM models". Astronomy and Astrophysics 696. doi:10.1051/0004-6361/202452423. Bibcode: 2025A&A...696A..13G.
- ↑ 4.0 4.1 4.2 Kilkenny, D.; O'Donoghue, D.; Koen, C.; Stobie, R. S.; Chen, A. (1997-06-01). "The Edinburgh-Cape Blue Object Survey - II. Zone 1 - the North Galactic CAP". Monthly Notices of the Royal Astronomical Society 287 (4): 867–893. doi:10.1093/mnras/287.4.867. ISSN 0035-8711. Bibcode: 1997MNRAS.287..867K.
- ↑ 5.0 5.1 Samus, N. N. et al. (2017). "General Catalogue of Variable Stars". Astronomy Reports. GCVS 5.1 61 (1): 80–88. doi:10.1134/S1063772917010085. Bibcode: 2017ARep...61...80S.
- ↑ Brown, A. G. A. (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics 616: A1. doi:10.1051/0004-6361/201833051. Bibcode: 2018A&A...616A...1G. Gaia DR2 record for this source at VizieR.
- ↑ 7.0 7.1 7.2 7.3 7.4 Stassun, Keivan G. et al. (2019). "The Revised TESS Input Catalog and Candidate Target List". The Astronomical Journal 158 (4): 138. doi:10.3847/1538-3881/ab3467. Bibcode: 2019AJ....158..138S.
- ↑ 8.0 8.1 8.2 Geier, S. (2020). "The population of hot subdwarf stars studied with Gaia. III. Catalogue of known hot subdwarf stars: Data Release 2". Astronomy and Astrophysics 635: A193. doi:10.1051/0004-6361/202037526. Bibcode: 2020A&A...635A.193G.
- ↑ Kazarovets, E. V.; Samus, N. N.; Durlevich, O. V. (2000). "The 75th Name-List of Variable Stars". Information Bulletin on Variable Stars 4870: 1. Bibcode: 2000IBVS.4870....1K.
- ↑ Jeffery, C. Simon (2008). "Variable Star Designations for Extreme Helium Stars". Information Bulletin on Variable Stars 5817: 1. Bibcode: 2008IBVS.5817....1J.
- ↑ Silvotti, R.; Schuh, S.; Kim, S.-L.; Lutz, R.; Reed, M.; Benatti, S.; Janulis, R.; Lanteri, L. et al. (2018). "The SDB pulsating star V391 Peg and its putative giant planet revisited after 13 years of time-series photometric data". Astronomy and Astrophysics 611: A85. doi:10.1051/0004-6361/201731473. Bibcode: 2018A&A...611A..85S.
- ↑ Silvotti, R.; Schuh, S.; Janulis, R.; Solheim, J.-E.; Bernabei, S.; Østensen, R.; Oswalt, T. D.; Bruni, I. et al. (2007). "A giant planet orbiting the 'extreme horizontal branch' star V391 Pegasi". Nature 449 (7159): 189–191. doi:10.1038/nature06143. PMID 17851517. Bibcode: 2007Natur.449..189S. https://ruj.uj.edu.pl/xmlui/handle/item/156623.
Sources
- C. S. Jeffery (2005). "Pulsations in Subdwarf B Stars". Journal of Astrophysics and Astronomy 26 (2–3): 261–271. doi:10.1007/BF02702334. Bibcode: 2005JApA...26..261J.
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