View source for U Hydrae

{{Short description|Variable star in the constellation Hydra}}
{{distinguish|Upsilon Hydrae}}
{{Starbox begin}}
{{Starbox image
| image = [[Image:UHyaLightCurve.png|250px]]
| caption = A [[Photometric system#Photometric letters|visual band]] [[light curve]] for U Hydrae, plotted from [[All Sky Automated Survey|''ASAS'']] data<ref name=ASASServer/>
}}
{{Starbox observe
 | epoch       = J2000
 | constell    = [[Hydra (constellation)|Hydra]]
 | ra          = {{RA|10|37|33.27295}}<ref name=vanLeeuwen2007/>
 | dec         = {{DEC|−13|23|04.3529}}<ref name=vanLeeuwen2007/>
 | appmag_v    = 4.89<ref name=Anderson2012/>
}}
{{Starbox character
 | type        = [[asymptotic giant branch|AGB]]<ref name=Rau2017/>
 | class       = {{nowrap|C-N5 C2 5-}}<ref name=barnbaum1996/>
 | b-v         = {{Val|2.80|0.51}}<ref name=Anderson2012/>
 | u-b         = 
 | variable    = [[semiregular variable star|SRb]]<ref name=Samus2017/>
}}
{{Starbox astrometry
 | radial_v    = {{Val|−25.8|1.7}}<ref name=Gontcharov2006/>
 | prop_mo_ra  = +42.59<ref name=vanLeeuwen2007/>
 | prop_mo_dec = −37.72<ref name=vanLeeuwen2007/>
 | parallax    = 4.80
 | p_error     = 0.23
 | parallax_footnote = <ref name=vanLeeuwen2007/>
 | absmag_v    = −1.70<ref name=Anderson2012/>
}}
{{Starbox detail
 | source      = 
 | mass        = 0.75<ref name=Rau2017/>
 | radius      = {{solar radius calculator|type=logLT|3.85|3200}}{{snd}}{{solar radius calculator|type=logLT|3.85|2600}}<ref name=Rau2017/>{{efn | name=radius | Applying the [[Stefan–Boltzmann law]] with a nominal [[sun|solar]] [[effective temperature]] of 5,772&nbsp;[[Kelvin|K]]: 
:<math>\sqrt{\biggl(\frac{5,772}{3,200}\biggr)^4 \cdot 10^{3.85}} = 273.75\ R_\odot</math><math>\sqrt{\biggl(\frac{5,772}{2,600}\biggr)^4 \cdot 10^{3.85}} = 414.67\ R_\odot</math>.}}
 | luminosity  = 3,476<ref name=Rau2017/>
 | temperature = {{Val|2600|-|3200|fmt=commas}}<ref name=Rau2017/>
 | gravity     = {{val|-0.28}}<ref name=Rau2017/>
 | metal_fe    = −0.1<ref name=Lambert1986/>
 | rotational_velocity = 
 | age_myr     = 
}}
{{Starbox catalog
 | names = {{odlist | V=U Hya | BD=−12°3218 | HD=92055 | HIP=52009 | HR=4163 | SAO=156110 }}<ref name=SIMBAD/>
}}
{{Starbox reference
 | Simbad=U+Hya
}}
{{Starbox end}}

'''U Hydrae''' is a single<ref name=Eggleton2008/> [[star]] in the [[celestial equator|equatorial]] [[constellation]] of [[Hydra (constellation)|Hydra]], near the northern constellation border with [[Sextans]]. It is visible to the [[naked eye]] under good observing conditions.  It is a [[semiregular variable star]] of sub-type SRb,<ref name=Samus2017/> with its brightness ranging from visual magnitude (V) 4.7 to 5.2 over a 450-day period, with some irregularity.<ref name="Monks"/> This object is located at a distance of approximately 680&nbsp;[[light year]]s from the [[Sun]] based on [[stellar parallax|parallax]].<ref name=vanLeeuwen2007/> It is drifting closer with a [[radial velocity]] of −26&nbsp;km/s.<ref name=Gontcharov2006/>

In 1871, [[Benjamin Apthorp Gould]] discovered that the star is a [[variable star]]. It was listed with its [[variable star designation]], U Hydrae, in [[Annie Jump Cannon|Annie Jump Cannon's]] 1907 work ''Second Catalog of Variable Stars''.<ref name="Cannon1907"/>

This is a carbon-rich [[red giant star]] on the [[asymptotic giant branch]]<ref name=Rau2017/> – a [[carbon star]] – with [[s-process]] elements appearing in the [[stellar spectrum|spectrum]]. It has a [[stellar classification]] of {{nowrap|C-N5}} with a carbon star class of {{nowrap|C2 5-}}.<ref name=barnbaum1996/> The star is losing mass at the rate of {{Val|1.2e−7|ul=solar mass}}·yr<sup>−1</sup>, with an outflow velocity of {{val|6.9|u=km/s}}. [[Technetium star|Technetium]] has been detected in the spectrum, suggesting the star has experienced a third [[dredge-up]] episode due to thermal pulses of the [[helium fusion|helium-burning]] shell some time within the last 100,000&nbsp;years.<ref name=Izumiura2011/>

An [[ultraviolet astronomy|ultraviolet]] (UV) excess has been detected coming from an extended elliptical ring that surrounds this star. It has a mean [[angular radius]] of {{Val|110|ul=arcsecond}} and lines up with a detached shell of dusty material that was previously detected in the [[infrared astronomy|infrared]] band. The material was most likely ejected from the star due to [[Stellar mass loss|mass loss]] episodes. The probable cause of the UV emission is from the movement of the star through space and possibly [[Shock (mechanics)|shock]]-excited molecules of H<sub>2</sub>. The emission does not show a bow-shock-like structure.<ref name=Sanchez2015/>

==Notes==
{{notelist}}

==References==
{{reflist|30em|refs=

<ref name=ASASServer>{{cite web |title=ASAS All Star Catalogue |url=http://www.astrouw.edu.pl/asas/?page=aasc |publisher=The All Sky Automated Survey |access-date=8 December 2021}}</ref>


<ref name=SIMBAD>{{cite simbad | title=U Hya | access-date=19 March 2016}}</ref>

<ref name=Lambert1986>{{cite journal
 | title=The Chemical Composition of Carbon Stars. I. Carbon, Nitrogen, and Oxygen in 30 Cool Carbon Stars in the Galactic Disk
 | last1=Lambert | first1=David L. | last2=Gustafsson | first2=Bengt
 | last3=Eriksson | first3=Kjell | last4=Hinkle | first4=Kenneth H.
 | display-authors=1 | journal=Astrophysical Journal Supplement
 | volume=62 | page=373 | date=October 1986
 | doi=10.1086/191145 | bibcode=1986ApJS...62..373L }}</ref>

<ref name=Anderson2012>{{cite journal
 | title=XHIP: An extended hipparcos compilation
 | last1=Anderson | first1=E. | last2=Francis | first2=Ch.
 | journal=Astronomy Letters | arxiv=1108.4971
 | volume=38 | issue=5 | pages=331 | year=2012
 | bibcode=2012AstL...38..331A | doi=10.1134/S1063773712050015 | s2cid=119257644 }}</ref>

<ref name=vanLeeuwen2007>{{cite journal
 | title=Validation of the new Hipparcos reduction
 | last1=van Leeuwen | first1=F.
 | journal=Astronomy and Astrophysics
 | volume=474 | issue=2 | pages=653–664 | date=2007
 | arxiv=0708.1752 | bibcode=2007A&A...474..653V
 | doi=10.1051/0004-6361:20078357 | s2cid=18759600 }}</ref>

<ref name=Samus2017>{{cite journal
 | display-authors=1 | last1=Samus | first1=N. N.
 | last2=Kazarovets | first2=E. V. | last3=Durlevich | first3=O. V.
 | last4=Kireeva | first4=N. N. | last5=Pastukhova | first5=E. N.
 | title=General Catalogue of Variable Stars
 | version=5.1 | journal=Astronomy Reports
 | year=2017 | volume=61 | issue=1 | pages=80–88
 | bibcode=2017ARep...61...80S | doi=10.1134/S1063772917010085 | s2cid=125853869 }}</ref>

<ref name="Cannon1907">{{cite journal
 | last1=Cannon | first1=Annie J. | title=Second catalogue of variable stars
 | journal=Annals of Harvard College Observatory | date=1907 | volume=55 | pages=1–94
 | bibcode=1907AnHar..55....1C | url=https://articles.adsabs.harvard.edu/pdf/1907AnHar..55....1C
 | access-date=18 December 2024}}</ref>

<ref name=Gontcharov2006>{{cite journal
 | last1=Gontcharov | first1=G. A.
 | title=Pulkovo Compilation of Radial Velocities for 35495 Hipparcos stars in a common system
 | journal=Astronomy Letters
 | volume=32| issue=11| pages=759–771| date=November 2006
 | bibcode=2006AstL...32..759G | arxiv=1606.08053
 | doi=10.1134/S1063773706110065 | s2cid=119231169
 }}</ref>

<ref name=Eggleton2008>{{cite journal
 | last1=Eggleton | first1=P. P. | last2=Tokovinin | first2=A. A.
 | title=A catalogue of multiplicity among bright stellar systems
 | journal=Monthly Notices of the Royal Astronomical Society
 | volume=389 | issue=2 | pages=869–879 | date=September 2008
 | doi=10.1111/j.1365-2966.2008.13596.x
 | doi-access=free | bibcode=2008MNRAS.389..869E | arxiv=0806.2878 | s2cid=14878976 }}</ref>

<ref name="Monks">{{cite book
 | last1=Monks | first1=Neale
 | title=Go-To Telescopes Under Suburban Skies
 | date=2010 | publisher=Springer
 | isbn=978-1-4419-6851-7 | page=65
 | url=https://books.google.com/books?id=waO6tUtfblsC&pg=PA65 }}</ref>

<ref name=Sanchez2015>{{cite journal
 | title=First Detection of Ultraviolet Emission from a Detached Dust Shell: Galaxy Evolution Explorer Observations of the Carbon Asymptotic Giant Branch Star U Hya
 | last1=Sanchez | first1=Enmanuel | last2=Montez | first2=Rodolfo Jr.
 | last3=Ramstedt | first3=Sofia | last4=Stassun | first4=Keivan G.
 | display-authors=1 | journal=The Astrophysical Journal Letters
 | volume=798 | issue=2 | id=L39 | pages=5 | date=January 2015
 | arxiv=1412.7542 | bibcode=2015ApJ...798L..39S 
 | doi=10.1088/2041-8205/798/2/L39 | s2cid=118434298 }}</ref>

<ref name=Rau2017>{{cite journal
 | title=The adventure of carbon stars. Observations and modeling of a set of C-rich AGB stars
 | last1=Rau | first1=G. | last2=Hron | first2=J.
 | last3=Paladini | first3=C. | last4=Aringer | first4=B.
 | last5=Eriksson | first5=K. | last6=Marigo | first6=P.
 | last7=Nowotny | first7=W. | last8=Grellmann | first8=R.
 | display-authors=1 | journal=Astronomy & Astrophysics
 | volume=600 | id=A92 | pages=21 | date=April 2017
 | arxiv=1701.04331 | bibcode=2017A&A...600A..92R 
 | doi=10.1051/0004-6361/201629337 | s2cid=49571205 }}</ref>

<ref name=Izumiura2011>{{cite journal
 | title=Extended dust shell of the carbon star U Hydrae observed with AKARI
 | display-authors=1 | last1=Izumiura | first1=H.
 | last2=Ueta | first2=T. | last3=Yamamura | first3=I.
 | last4=Matsunaga | first4=N. | last5=Ita | first5=Y.
 | last6=Matsuura | first6=M. | last7=Nakada | first7=Y.
 | last8=Fukushi | first8=H. | last9=Mito | first9=H.
 | last10=Tanabé | first10=T. | last11=Hashimoto | first11=O.
 | journal=Astronomy & Astrophysics
 | volume=528 | id=A29 | pages=14 | date=April 2011
 | doi=10.1051/0004-6361/201015163 | bibcode=2011A&A...528A..29I | doi-access=free }}</ref>

<ref name=barnbaum1996>{{cite journal
 | display-authors=1 | last1=Barnbaum | first1=Cecilia
 | last2=Stone | first2=Remington P. S. | last3=Keenan | first3=Philip C.
 | title=A Moderate-Resolution Spectral Atlas of Carbon Stars: R, J, N, CH, and Barium Stars
 | journal=Astrophysical Journal Supplement
 | volume=105 | pages=419 |year=1996
 | bibcode=1996ApJS..105..419B | doi=10.1086/192323 }}</ref>

}}

{{Stars of Hydra}}
<!-- Properties -->

{{DEFAULTSORT:U Hydrae}}
[[Category:Carbon stars]]
[[Category:Asymptotic-giant-branch stars]]
[[Category:Semiregular variable stars]]
<!-- Identifiers -->
[[Category:Hydra (constellation)]]
[[Category:Durchmusterung objects]]
[[Category:Henry Draper Catalogue objects|092055]]
[[Category:Hipparcos objects|052009]]
[[Category:Bright Star Catalogue objects|4163]]
[[Category:Objects with variable star designations|Hydrae, U]]