U Equulei
{{Short description|Variable star in the constellation Equuleus}}
{{Starbox begin
|name = U Equulei
}}
{{Starbox image
| image = 250px
| caption = A visual band light curve for U Equulei, plotted from OMC data
}}
{{Starbox observe
|epoch = J2000
|constell = Equuleus
}}
{{Starbox character
|type = (post?) AGB
|u-b =
|variable = Lb
}}
{{Starbox astrometry
|parallax = 0.0985
|p_error = 0.0750
|dist_ly =
|dist_pc = {{val|3340|700|fmt=commas}}
}}
{{Starbox detail
|mass =
}}
{{Starbox catalog
|names = IRAS 20547+0247, 2MASS J20571628+0258445, Gaia DR2 1731164844433296128
}}
{{Starbox reference
|Simbad=U+Equulei
}}
{{Starbox end}}
U Equulei (U Equ / IRAS 20547 +0247) is a variable star in the Equuleus constellation with an apparent magnitude of +14.50 in the B band. It lies at an estimated distance of 5,000 light-years (1,500 parsecs) from the Solar System.
Properties
U Equulei is, or was, an OH/IR star, and strong OH and H2O masers have been observed. These vary to a greater extent than almost any other star observed, and it is possible that the stage of maser activity is essentially finished.
Theoretical Planet
Lionel Siess and Mario Livio suggested that the accretion of a giant planet towards the increasing red giant has made the star's outer layers rotate fast enough to cause an outpouring equatorial- or disk-expansion, responsible for the star's peculiar environment. The spectroscopic study has indicated the star is surrounded by the dust shell, but shape of the shell cannot be measured due to large distance to the star.
See also
References
{{Reflist|refs=
{{cite DR2|1731164844433296128}}
{{cite journal | last1=Geballe | first1=T.R. | last2=Barnbaum | first2=C. | last3=Noll | first3=Keith S. | last4=Morris | first4=M. | title=Infrared Spectroscopy of U Equulei's Warm Circumstellar Gas | journal=The Astrophysical Journal | volume=624 | issue=2 | pages=983–984 |date=September 2012 | doi=10.1086/429369 |arxiv = astro-ph/0502154 |bibcode = 2005ApJ...624..983G | s2cid=14707061 }}
{{cite journal|last=Siess|first=Lionel|author2=Mario Livio |title=The accretion of brown dwarfs and planets by giant stars – II. Solar-mass stars on the red giant branch|journal=Monthly Notices of the Royal Astronomical Society|date=October 1999|volume=308|issue=4|pages=1133–1149|doi=10.1046/j.1365-8711.1999.02784.x|doi-access=free |arxiv = astro-ph/9905235 |bibcode = 1999MNRAS.308.1133S |s2cid=12893455}}
{{cite journal|bibcode=1996A&A...310..259B|title=The unusual circumstellar environment of the evolved star, U Equulei|journal=Astronomy and Astrophysics|volume=310|pages=259|last1=Barnbaum|first1=C.|last2=Omont|first2=A.|last3=Morris|first3=M.|year=1996}}
{{cite journal |arxiv=1403.7230 |doi=10.1093/mnras/stu2383 |title=New light on Galactic post-asymptotic giant branch stars – I. First distance catalogue |year=2015 |last1=Vickers |first1=Shane B. |last2=Frew |first2=David J. |last3=Parker |first3=Quentin A. |last4=Bojičić |first4=Ivan S. |journal=Monthly Notices of the Royal Astronomical Society |volume=447 |issue=2 |pages=1673–1691 |doi-access=free |bibcode=2015MNRAS.447.1673V |s2cid=119245776 }}
{{cite journal|bibcode=2002ApJ...576..445L|title=On Dead OH/IR Stars|journal=The Astrophysical Journal|volume=576|pages=445–449|last1=Lewis|first1=B. M.|year=2002|issue=1|doi=10.1086/341534|s2cid=121803017 |doi-access=free}}
{{cite journal|arxiv=1611.03306|title=Do Water Fountain Jets Really Indicate the Onset of the Morphological Metamorphosis of Circumstellar Envelopes|year=2016|doi=10.1093/mnras/stw2931|last1=Yung|first1=Bosco H. K.|last2=Nakashima|first2=Jun-Ichi|last3=Hsia|first3=Chih-Hao|last4=Imai|first4=Hiroshi|journal=Monthly Notices of the Royal Astronomical Society|volume=465|issue=4|pages=4482–4499|doi-access=free |s2cid=119058467}}
}}
{{Stars of Equuleus}}
{{DEFAULTSORT:U Equulei}}