V Hydrae
  | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Hydra |
| Right ascension | 10h 51m 37.25661s[1] |
| Declination | −21° 15′ 00.3245″[1] |
| Apparent magnitude (V) | 6.0 - 12.3[2] |
| Characteristics | |
| Spectral type | C6,3e-C7,5e(N6e)[3] |
| B−V color index | +5.43[4] |
| Variable type | SRa[3] |
| Astrometry | |
| Radial velocity (Rv) | −14.80[5] km/s |
| Proper motion (μ) | RA: −11.02 ± 1.14[1] mas/yr Dec.: 2.29 ± 1.16[1] mas/yr |
| Parallax (π) | 1.44 ± 1.41 mas[1] |
| Distance | approx. 2,000 ly (approx. 700 pc) |
| Absolute magnitude (MV) | −3.5 to +1.8[6] |
| Orbit[7] | |
| Period (P) | 17.45+0.34 −0.29 yr |
| Semi-major axis (a) | 11.2+1.2 −1.5 AU |
| Eccentricity (e) | 0.024+0.027 −0.017 |
| Inclination (i) | 37.7+2.2 −2.0° |
| Longitude of the node (Ω) | 159.7+43.0 −3.3° |
| Periastron epoch (T) | JD = 2,458,684+2,128 −2,582 |
| Argument of periastron (ω) (secondary) | 343+147 −122° |
| Details | |
| A | |
| Mass | 1.9±1.0[7] M☉ |
| Radius | 420[8]–430[9] R☉ |
| Luminosity | 7,850[10] L☉ |
| Surface gravity (log g) | −0.5[10] cgs |
| Temperature | 2,650[10] K |
| Rotational velocity (v sin i) | 11 - 14[10] km/s |
| B | |
| Mass | 2.63+0.63 −0.69[7] M☉ |
| Radius | 1.5[7] R☉ |
| Temperature | 9,950[7] K |
| Other designations | |
| Database references | |
| SIMBAD | data |
V Hydrae (V Hya) is a carbon star in the constellation Hydra. To date perhaps uniquely in our galaxy it has plasma ejections/eruptions on a grand scale that could be caused by its near, unseen companion.
Variability
[edit]
In the 1870s, Benjamin Apthorp Gould suspected that the star is variable, based on observations with opera glasses. In May of 1888, Seth Carlo Chandler confirmed that the star is variable, citing observations from 1797 through 1879, and he derived a period of 535 days, which is very close to the currently accepted value.[12] Later that year, Chandler included the star with its variable star designation, V Hydrae, in his Catalogue of Variable Stars.[13]
V Hydrae is a semiregular variable star of type SRa, sometimes considered to be a Mira variable. It pulsates with a period of 530 days and a brightness range of 1-2 magnitudes, but also shows deep fades at intervals of about 17.5 years when it may drop below magnitude 12.[2][14]
Evolutionary stage
[edit]V Hydrae is a late carbon star, an asymptotic giant branch (AGB) star that has dredged up sufficient material from its interior to have more carbon in its atmosphere than oxygen. The rate of mass loss from V Hydrae indicates that it is almost at the end of the AGB stage and about to lose its atmosphere completely and form a planetary nebula. It is sometimes considered to be a post-AGB object.[15]
Companions
[edit]V Hydrae has a visible binary companion 46" distant. It is a magnitude 11.5 K0 giant.[6]
V Hydrae also has an unseen companion inferred by its ultraviolet excess and radial-velocity monitoring.[7][16][9] It has been suggested that the steep drops in brightness every 17 years or so are caused by obscuration by a cloud associated with the companion passing in front of the giant star.[16] A study in 2024 used astrometry and radial velocity measurements and constrained the orbital parameters of the companion, as well as its mass, being 36% larger than the mass of the primary and equivalent to 2.6 times the mass of the Sun.[7]
Bullets
[edit]
V Hydrae has high-speed outflows of material collimated into jets, and also a disk of material around the star. Since the star itself is considered to be at the end of the Asymptotic Giant Branch (AGB) phase of evolution and starting to generate a planetary nebula, the mechanism for the ejection of this material can give key insights to the formation of planetary nebulae. Microwave spectra of rotational transitions of carbon monoxide show that portions of the envelope, probably the jets, are moving away from the star at 200 km/sec. This is far faster than the ~15 km/sec stellar wind that is typically seen around AGB stars.[17]
References
[edit]- ^ a b c d e 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.
- ^ a b Watson, Christopher (4 January 2010). "V Hydrae". The International Variable Star Index. American Association of Variable Star Observers. Retrieved 2016-10-12.
- ^ a b 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.
- ^ Ducati, J. R. (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". CDS/ADC Collection of Electronic Catalogues. 2237. Bibcode:2002yCat.2237....0D.
- ^ 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.
- ^ a b Gordon, Courtney P. (1968). "The Absolute Magnitudes of Carbon Stars". Publications of the Astronomical Society of the Pacific. 80 (476): 597. Bibcode:1968PASP...80..597G. doi:10.1086/128694.
- ^ a b c d e f g Planquart, L.; Jorissen, A.; et al. (2024). "A dynamic view of V Hydrae. Monitoring of a spectroscopic-binary AGB star with an alkaline jet". Astronomy & Astrophysics. 682: A143. arXiv:2405.07820. Bibcode:2024A&A...682A.143P. doi:10.1051/0004-6361/202347947.
- ^ Luttermoser, Donald G.; Brown, Alexander (1992). "A VLA 3.6 centimeter survey of N-type carbon stars". Astrophysical Journal. 384: 634. Bibcode:1992ApJ...384..634L. doi:10.1086/170905.
- ^ a b Sahai, R.; Scibelli, S.; Morris, M. R. (2016). "High-speed Bullet Ejections during the AGB-to-Planetary Nebula Transition: HST Observations of the Carbon Star, V Hydrae". The Astrophysical Journal. 827 (2): 92. arXiv:1605.06728. Bibcode:2016ApJ...827...92S. doi:10.3847/0004-637X/827/2/92. S2CID 119209118.
- ^ a b c d Zhao-Geisler, R.; Quirrenbach, A.; Köhler, R.; Lopez, B. (2012). "Dust and molecular shells in asymptotic giant branch stars". Astronomy & Astrophysics. 545: A56. arXiv:1207.3767. Bibcode:2012A&A...545A..56Z. doi:10.1051/0004-6361/201118150. S2CID 53992211.
- ^ "Download Data". aavso.org. AAVSO. Retrieved 1 October 2021.
- ^ Chandler, S. C. (May 1888). "On a new variable of long period". Astronomical Journal. 8 (171): 24. doi:10.1086/101016. Retrieved 22 December 2024.
- ^ Chandler, S. C. (September 1888). "Catalogue of Variable Stars". Astronomical Journal. 8: 81–94. Bibcode:1888AJ......8...81C. doi:10.1086/101060. Retrieved 22 December 2024.
- ^ Olivier, Enrico A.; Whitelock, Patricia; Marang, Fred (2001). "Dust-enshrouded asymptotic giant branch stars in the solar neighbourhood". Monthly Notices of the Royal Astronomical Society. 326 (2): 490. arXiv:astro-ph/0103294. Bibcode:2001MNRAS.326..490O. doi:10.1046/j.1365-8711.2001.04511.x. S2CID 15509666.
- ^ Knapp, G. R.; Crosas, M.; Young, K.; Ivezić, Željko (2000). "Atomic Carbon in the Envelopes of Carbon-rich Post–Asymptotic Giant Branch Stars". The Astrophysical Journal. 534 (1): 324–334. arXiv:astro-ph/9912496. Bibcode:2000ApJ...534..324K. doi:10.1086/308731. S2CID 2963393.
- ^ a b Sahai, R.; Findeisen, K.; Gil De Paz, A.; Sánchez Contreras, C. (2008). "Binarity in Cool Asymptotic Giant Branch Stars: A GALEX Search for Ultraviolet Excesses" (PDF). The Astrophysical Journal. 689 (2): 1274–1278. arXiv:0807.1944. Bibcode:2008ApJ...689.1274S. doi:10.1086/592559. S2CID 12437723.
- ^ Knapp, G.R.; Jorissen, A.; Young, K. (October 1997). "A 200 km/sec Molecular Wind in the Peculiar Carbon Star V Hya". Astronomy and Astrophysics. 326: 318–328. Bibcode:1997A&A...326..318K. Retrieved 16 November 2020.