View source for V Hydrae

{{Short description|Variable star in the constellation Hydra}}
{{Starbox begin
| name=V Hydrae
}}
{{Starbox image
| image=
{{Location mark
|image=Hydra constellation map.svg|alt=|float=center|width=320
|label=|position=right
|mark=Red circle.svg|mark_width=8|mark_link=V Hya
|x=550|y=340
}}
|caption=Location of V Hydrae (circled)
}}
{{Starbox observe
| epoch=J2000
| ra={{RA|10|51|37.25661}}<ref name=hipparcos/>
| dec={{DEC|&minus;21|15|00.3245}}<ref name=hipparcos/>
| appmag_v=6.0 - 12.3<ref name=vsx>{{cite web|url=http://www.aavso.org/vsx/index.php?view=detail.top&oid=15964 |title=V Hydrae |author =Watson, Christopher |date=4 January 2010  |work=The International Variable Star Index|publisher=[[American Association of Variable Star Observers]]|access-date=2016-10-12}}</ref>
| constell=[[Hydra (constellation)|Hydra]]
}}
{{Starbox character
| class=C6,3e-C7,5e(N6e)<ref name=gcvs/>
| b-v=+5.43<ref name=ducati>{{cite journal|bibcode=2002yCat.2237....0D|title=VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system|journal=CDS/ADC Collection of Electronic Catalogues|volume=2237|last1=Ducati|first1=J. R.|year=2002}}</ref>
| u-b=
| variable=[[Semiregular variable|SRa]]<ref name=gcvs>{{cite journal|bibcode=2009yCat....102025S|title=VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)|journal=VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S|volume=1|display-authors=etal|last1=Samus|first1=N. N.|last2=Durlevich|first2=O. V.|year=2009}}</ref>
}}
{{Starbox astrometry
| radial_v=&minus;14.80<ref>{{cite journal|bibcode=2006AstL...32..759G|title=Pulkovo Compilation of Radial Velocities for 35 495 Hipparcos stars in a common system|journal=Astronomy Letters|volume=32|issue=11|pages=759–771|last1=Gontcharov|first1=G. A.|year=2006|doi=10.1134/S1063773706110065|arxiv = 1606.08053 |s2cid=119231169}}</ref>
| prop_mo_ra={{nowrap|&minus;11.02 ± 1.14<ref name=hipparcos/>}}
| prop_mo_dec={{nowrap|2.29 ± 1.16<ref name=hipparcos/>}}
| parallax=1.44
| p_error=1.41
| parallax_footnote = <ref name=hipparcos>{{cite journal|bibcode=2007A&A...474..653V|title=Validation of the new Hipparcos reduction|journal=Astronomy and Astrophysics|volume=474|issue=2|pages=653–664|last1=Van Leeuwen|first1=F.|year=2007|doi=10.1051/0004-6361:20078357|arxiv = 0708.1752 |s2cid=18759600}}</ref>
| absmag_v=&minus;3.5 to +1.8<ref name=gordon>{{cite journal|bibcode=1968PASP...80..597G|title=The Absolute Magnitudes of Carbon Stars|journal=Publications of the Astronomical Society of the Pacific|volume=80|pages=597|last1=Gordon|first1=Courtney P.|year=1968|issue=476|doi=10.1086/128694|doi-access=free}}</ref>
}}
{{Starbox orbit
| reference = <ref name=planquart2024>{{cite journal|bibcode=2024A&A...682A.143P|arxiv=2405.07820|title=A dynamic view of V Hydrae. Monitoring of a spectroscopic-binary AGB star with an alkaline jet|journal=Astronomy & Astrophysics |volume=682|pages=A143|display-authors=etal|last1=Planquart|first1=L.|last2=Jorissen|first2=A.|year=2024|doi=10.1051/0004-6361/202347947}}</ref>
| period = 17.5
| eccentricity = ~0.0
| inclination =
| axis =
| axis_unitless =
}}
{{Starbox detail
| component1 = A
| mass=1.0<ref name=zh/>
| radius=420<ref name=luttermoser>{{cite journal|bibcode=1992ApJ...384..634L|title=A VLA 3.6 centimeter survey of N-type carbon stars|journal=Astrophysical Journal|volume=384|pages=634|last1=Luttermoser|first1=Donald G.|last2=Brown|first2=Alexander|year=1992|doi=10.1086/170905}}</ref>–430<ref name=sahai2016/>
| luminosity=7,850<ref name=zh>{{cite journal|bibcode=2012A&A...545A..56Z|arxiv=1207.3767|title=Dust and molecular shells in asymptotic giant branch stars|journal=Astronomy & Astrophysics|volume=545|pages=A56|last1=Zhao-Geisler|first1=R.|last2=Quirrenbach|first2=A.|last3=Köhler|first3=R.|last4=Lopez|first4=B.|year=2012|doi=10.1051/0004-6361/201118150|s2cid=53992211}}</ref>
| temperature=2,650<ref name=zh/>
| gravity=&minus;0.5<ref name=zh/>
| metal=
| rotational_velocity=11 - 14<ref name=zh/>
| component2 = B
| mass2=<1<ref name=sahai2016>{{cite journal|bibcode=2016ApJ...827...92S|arxiv=1605.06728|title=High-speed Bullet Ejections during the AGB-to-Planetary Nebula Transition: HST Observations of the Carbon Star, V Hydrae|journal=The Astrophysical Journal|volume=827|issue=2|pages=92|last1=Sahai|first1=R.|last2=Scibelli|first2=S.|last3=Morris|first3=M. R.|year=2016|doi=10.3847/0004-637X/827/2/92|s2cid=119209118 |doi-access=free }}</ref>
| radius2=
| luminosity2=
| temperature2 =
| metal2=
| rotation2=
| age2=
}}
{{Starbox catalog
| names=[[Variable star designation|V]]&nbsp;Hya, [[Bonner Durchmusterung|BD]]&minus;20°3283, [[Hipparcos catalogue|HIP]]&nbsp;53085, [[2MASS]]&nbsp;J10513724-2115002, [[IRAS]]&nbsp;10491-2059, [[Washington Double Star Catalog|WDS]]&nbsp;J10516-2115
}}
{{Starbox reference
| Simbad=V+Hydrae
}}
{{Starbox end}}
'''V Hydrae''' ('''V Hya''') is a [[carbon star]] in the [[constellation]] [[Hydra (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==
[[File:VHyaLightCurve.png|thumb|left|A [[Photometric_system#Photometric_letters|visual band]] [[light curve]] for V Hydrae, plotted from AAVSO data<ref name="aavso"/>]]
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.<ref name=vsx/><ref name=olivier>{{cite journal|bibcode=2001MNRAS.326..490O|arxiv=astro-ph/0103294|title=Dust-enshrouded asymptotic giant branch stars in the solar neighbourhood|journal=Monthly Notices of the Royal Astronomical Society|volume=326|issue=2|pages=490|last1=Olivier|first1=Enrico A.|last2=Whitelock|first2=Patricia|last3=Marang|first3=Fred|year=2001|doi=10.1046/j.1365-8711.2001.04511.x|doi-access=free |s2cid=15509666}}</ref>
==Evolutionary stage==
V Hydrae is a late [[carbon star]], an [[asymptotic giant branch]] (AGB) star that has [[dredge-up|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.<ref name=knapp>{{cite journal|doi=10.1086/308731|title=Atomic Carbon in the Envelopes of Carbon-rich Post–Asymptotic Giant Branch Stars|journal=The Astrophysical Journal|volume=534|pages=324–334|year=2000|last1=Knapp|first1=G. R.|last2=Crosas|first2=M.|last3=Young|first3=K.|last4=Ivezić|first4=Željko|issue=1|arxiv = astro-ph/9912496 |bibcode = 2000ApJ...534..324K |s2cid=2963393}}</ref>
==Companions==
V Hydrae has a visible binary companion 46" distant. It is a magnitude 11.5 K0 giant.<ref name=gordon/>
V Hydrae also has an unseen companion inferred by its ultraviolet excess and radial-velocity monitoring.<ref name=planquart2024/><ref name=sahai2008>{{cite journal|bibcode=2008ApJ...689.1274S|title=Binarity in Cool Asymptotic Giant Branch Stars: A GALEX Search for Ultraviolet Excesses|journal=The Astrophysical Journal|volume=689|issue=2|pages=1274–1278|last1=Sahai|first1=R.|last2=Findeisen|first2=K.|last3=Gil De Paz|first3=A.|last4=Sánchez Contreras|first4=C.|year=2008|doi=10.1086/592559|arxiv = 0807.1944 |s2cid=12437723|url=http://eprints.ucm.es/35616/1/gildepaz81libre.pdf}}</ref><ref name=sahai2016/>  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.<ref name=sahai2008/>
==Bullets==
[[File:Artist's illustration of scenario for plasma ejections from V Hydrae.jpg|thumb|left|upright=1.0|Artist's illustration of [[plasma ejection]]s from V Hydrae.]]
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 nebula]]e. 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.<ref>{{cite journal |last1=Knapp |first1=G.R. |last2=Jorissen |first2=A. |last3=Young |first3=K. |title=A 200 km/sec Molecular Wind in the Peculiar Carbon Star V Hya |journal=Astronomy and Astrophysics |date=October 1997 |volume=326 |pages=318–328 |bibcode=1997A&A...326..318K |url=http://adsabs.harvard.edu/full/1997A%26A...326..318K |access-date=16 November 2020}}</ref>
==References==
{{reflist|refs=
<ref name="aavso">{{cite web |title=Download Data |url=https://www.aavso.org/data-download |website=aavso.org |publisher=AAVSO |access-date=1 October 2021}}</ref>
}}
{{Stars of Hydra}}
{{DEFAULTSORT:V Hydrae}}
[[Category:Hydra (constellation)]]
[[Category:Carbon stars]]
[[Category:Objects with variable star designations|Hydrae, V]]
[[Category:Asymptotic-giant-branch stars]]
[[Category:Semiregular variable stars]]
[[Category:Hipparcos objects|053085]]
[[Category:Durchmusterung objects]]