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{{Short description|Variable star in the constellation Hydra}}
{{Starbox begin
{{Starbox begin
| name=V Hydrae
| name=V Hydrae
Line 16: Line 17:
| ra={{RA|10|51|37.25661}}<ref name=hipparcos/>
| ra={{RA|10|51|37.25661}}<ref name=hipparcos/>
| dec={{DEC|&minus;21|15|00.3245}}<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|accessdate=2016-10-12}}</ref>
| 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]]
| constell=[[Hydra (constellation)|Hydra]]
}}
}}
{{Starbox character
{{Starbox character
| class=C6,3e-C7,5e(N6e)<ref name=gcvs/>
| 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|author1=Ducati|first1=J. R.|year=2002}}</ref>
| 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=
| 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|author1=Samus|first1=N. N.|last2=Durlevich|first2=O. V.|year=2009}}</ref>
| 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
{{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|author1=Gontcharov|first1=G. A.|year=2006|doi=10.1134/S1063773706110065}}</ref>
| 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_ra={{nowrap|&minus;11.02 ± 1.14<ref name=hipparcos/>}}
| prop_mo_dec={{nowrap|2.29 ± 1.16<ref name=hipparcos/>}}
| prop_mo_dec={{nowrap|2.29 ± 1.16<ref name=hipparcos/>}}
| parallax=1.44
| parallax=1.44
| p_error=1.41
| 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|author1=Van Leeuwen|first1=F.|year=2007|doi=10.1051/0004-6361:20078357}}</ref>
| 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|author1=Gordon|first1=Courtney P.|year=1968|doi=10.1086/128694}}</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
{{Starbox orbit
| reference = <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|author1=Sahai|first1=R.|last2=Scibelli|first2=S.|last3=Morris|first3=M. R.|year=2016|doi=10.3847/0004-637X/827/2/92}}</ref>
| 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 = 8.5
| period = {{val|17.45|0.34|0.29}}
| eccentricity = ≥0.6
| eccentricity = {{Val|0.024|0.027|0.017}}
| inclination =
| inclination = {{val|37.7|2.2|2.0}}
| node = {{val|159.7|43.0|3.3}}
| axis =
| periarg = {{val|343|147|122}}
| axis_unitless =
| periastron = [[Julian Day|JD]] {{=}} {{val|2458684|2128|2582|fmt=commas}}
| axis_unitless = {{val|11.2|1.2|1.5|ul=AU}}
}}
}}
{{Starbox detail
{{Starbox detail
| component1 = A
| component1 = A
| mass=1.0<ref name=zh/>
| mass={{val|1.9|1.0}}<ref name=planquart2024/>
| 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>{{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>
| radius=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|author1=Zhao-Geisler|first1=R.|last2=Quirrenbach|first2=A.|last3=Köhler|first3=R.|last4=Lopez|first4=B.|year=2012|doi=10.1051/0004-6361/201118150}}</ref>
| 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/>
| temperature=2,650<ref name=zh/>
| gravity=&minus;0.5<ref name=zh/>
| gravity=&minus;0.5<ref name=zh/>
Line 52: Line 55:
| rotational_velocity=11 - 14<ref name=zh/>
| rotational_velocity=11 - 14<ref name=zh/>
| component2 = B
| component2 = B
| mass2=<1<ref name=sahai2016/>
| mass2= {{val|2.63|0.63|0.69}}<ref name=planquart2024/>
| radius2=
| radius2=1.5<ref name=planquart2024/>
| luminosity2=
| luminosity2=
| temperature2 =
| temperature2 =9,950<ref name=planquart2024/>
| metal2=
| metal2=
| rotation2=
| rotation2=
Line 68: Line 71:
{{Starbox end}}
{{Starbox end}}


'''V Hydrae''' ('''V Hya''') is a [[carbon star]] in the [[constellation]] [[Hydra (constellation)|Hydra]].
'''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==
==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"/>]]
⚫
[[File:Artist's Illustration of Scenario for Plasma Ejections from V Hydrae.jpg|thumb|left|upright=1.0|Artist's illustration of plasma ejections from V Hydrae]]
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.<ref name="Chandler1888A"/> Later that year, Chandler included the star with its [[variable star designation]], V Hydrae, in his ''Catalogue of Variable Stars''.<ref name="Chandler1888B"/>
⚫
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 6,160 days 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|author1=Olivier|first1=Enrico A.|last2=Whitelock|first2=Patricia|last3=Marang|first3=Fred|year=2001|doi=10.1046/j.1365-8711.2001.04511.x}}</ref>

⚫
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==
==Evolutionary stage==
V Hydrae is a 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|year=2000|last1=Knapp|first1=G. R.|last2=Crosas|first2=M.|last3=Young|first3=K.|last4=Ivezić|first4=Željko}}</ref>
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==
==Companions==
V Hydrae has a visible binary companion 46" distant. It is a magnitude 11.5 K0 giant.<ref name=gordon/>
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 in an 8.5 year orbit, inferred by its ultraviolet excess and eruptions associated with the periastron passage.<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|author1=Sahai|first1=R.|last2=Findeisen|first2=K.|last3=Gil De Paz|first3=A.|last4=Sánchez Contreras|first4=C.|year=2008|doi=10.1086/592559}}</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/>
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/> A study in 2024 used [[astrometry]] and [[Doppler spectroscopy|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]].<ref name="planquart2024" />


==Bullets==
==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]] 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. The ejections have been modelled as ''bullets'' of material fired out each time the compact companion passes close to the extended giant star during a highly eccentric orbit. The bullets are ejected in opposite directions in different orbits due to a flip-flop of the ejection mechanism.<ref name=sahai2016/>
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==
==References==
{{reflist}}
{{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>

<ref name="Chandler1888A">{{cite journal |last1=Chandler |first1=S. C. |title=On a new variable of long period |journal=Astronomical Journal |date=May 1888 |volume=8 |issue=171 |page=24 |doi=10.1086/101016 |bibcode=1888AJ......8...24C |url=https://articles.adsabs.harvard.edu/pdf/1888AJ......8...24C |access-date=22 December 2024}}</ref>

<ref name="Chandler1888B">{{cite journal |last1=Chandler |first1=S. C. |title=Catalogue of Variable Stars |journal=Astronomical Journal |date=September 1888 |volume=8 |pages=81–94 |doi=10.1086/101060 |bibcode=1888AJ......8...81C |url=https://articles.adsabs.harvard.edu/pdf/1888AJ......8...81C |access-date=22 December 2024}}</ref>

}}


{{Stars of Hydra}}
{{Stars of Hydra}}


{{DEFAULTSORT:V Hydrae}}
[[Category:Hydra (constellation)]]
[[Category:Hydra (constellation)]]
[[Category:C-type stars]]
[[Category:Carbon stars]]
[[Category:Objects named with variable star designations|Hydrae, V]]
[[Category:Objects with variable star designations|Hydrae, V]]
[[Category:Asymptotic-giant-branch stars]]
[[Category:Asymptotic-giant-branch stars]]
[[Category:Semiregular variable stars]]
[[Category:Semiregular variable stars]]
[[Category:Hipparcos objects|053085]]
[[Category:Hipparcos objects|053085]]
[[Category:Durchmusterung objects]]

Latest revision as of 16:43, 1 January 2025

V Hydrae
Location of V Hydrae (circled)
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]
Distanceapprox. 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
Mass1.9±1.0[7] M☉
Radius420[8]–430[9] R☉
Luminosity7,850[10] L☉
Surface gravity (log g)−0.5[10] cgs
Temperature2,650[10] K
Rotational velocity (v sin i)11 - 14[10] km/s
B
Mass2.63+0.63
−0.69[7] M☉
Radius1.5[7] R☉
Temperature9,950[7] K
Other designations
V Hya, BD−20°3283, HIP 53085, 2MASS J10513724-2115002, IRAS 10491-2059, WDS J10516-2115
Database references
SIMBADdata

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]
A visual band light curve for V Hydrae, plotted from AAVSO data[11]

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]
Artist's illustration of plasma ejections 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 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]
  1. ^ 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.
  2. ^ a b Watson, Christopher (4 January 2010). "V Hydrae". The International Variable Star Index. American Association of Variable Star Observers. Retrieved 2016-10-12.
  3. ^ 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.
  4. ^ 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.
  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.
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