U Equulei

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.

U Equulei
Observation data
Epoch J2000      Equinox J2000
Constellation Equuleus
Right ascension 20h 57m 16.28s[1]
Declination 02° 58′ 44.6″[1]
Apparent magnitude (V) 9 - 13[2]
Characteristics
Evolutionary stage (post?) AGB[3]
Spectral type G - K III[3]
B−V color index +1.6[3]
Variable type Lb[2]
Astrometry
Radial velocity (Rv)−75[4] km/s
Proper motion (μ) RA: 10.490[5] mas/yr
Dec.: −10.433[5] mas/yr
Parallax (π)0.0985 ± 0.0750[5] mas
Distance3,340±700[6] pc
Details
Luminosity6,000[6] L☉
Temperature5,005[5] K
Other designations
IRAS 20547+0247, 2MASS J20571628+0258445, Gaia DR2 1731164844433296128
Database references
SIMBADdata

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.[7]

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.[8] 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.[9]

See also

References
  1. Cutri, R. M.; Skrutskie, M. F.; Van Dyk, S.; Beichman, C. A.; Carpenter, J. M.; Chester, T.; Cambresy, L.; Evans, T.; Fowler, J.; Gizis, J.; Howard, E.; Huchra, J.; Jarrett, T.; Kopan, E. L.; Kirkpatrick, J. D.; Light, R. M.; Marsh, K. A.; McCallon, H.; Schneider, S.; Stiening, R.; Sykes, M.; Weinberg, M.; Wheaton, W. A.; Wheelock, S.; Zacarias, N. (2003). "VizieR Online Data Catalog: 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)". VizieR On-line Data Catalog: II/246. Originally Published in: 2003yCat.2246....0C. 2246. Bibcode:2003yCat.2246....0C.
  2. Geballe, T.R.; Barnbaum, C.; Noll, Keith S.; Morris, M. (September 2012). "Infrared Spectroscopy of U Equulei's Warm Circumstellar Gas". The Astrophysical Journal. 624 (2): 983–984. arXiv:astro-ph/0502154. Bibcode:2005ApJ...624..983G. doi:10.1086/429369. S2CID 14707061.
  3. Barnbaum, C.; Omont, A.; Morris, M. (1996). "The unusual circumstellar environment of the evolved star, U Equulei". Astronomy and Astrophysics. 310: 259. Bibcode:1996A&A...310..259B.
  4. Kim, Jaeheon; Cho, Se-Hyung; Kim, Sang Joon (2013). "Simultaneous Observations of SiO and H2O Masers toward Known Stellar H2O Maser Sources". The Astronomical Journal. 145 (1): 22. Bibcode:2013AJ....145...22K. doi:10.1088/0004-6256/145/1/22.
  5. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  6. Vickers, Shane B.; Frew, David J.; Parker, Quentin A.; Bojičić, Ivan S. (2015). "New light on Galactic post-asymptotic giant branch stars – I. First distance catalogue". Monthly Notices of the Royal Astronomical Society. 447 (2): 1673–1691. arXiv:1403.7230. Bibcode:2015MNRAS.447.1673V. doi:10.1093/mnras/stu2383. S2CID 119245776.
  7. Lewis, B. M. (2002). "On Dead OH/IR Stars". The Astrophysical Journal. 576 (1): 445–449. Bibcode:2002ApJ...576..445L. doi:10.1086/341534.
  8. Siess, Lionel; Mario Livio (October 1999). "The accretion of brown dwarfs and planets by giant stars – II. Solar-mass stars on the red giant branch". Monthly Notices of the Royal Astronomical Society. 308 (4): 1133–1149. arXiv:astro-ph/9905235. Bibcode:1999MNRAS.308.1133S. doi:10.1046/j.1365-8711.1999.02784.x. S2CID 12893455.
  9. Yung, Bosco H. K.; Nakashima, Jun-Ichi; Hsia, Chih-Hao; Imai, Hiroshi (2016). "Do Water Fountain Jets Really Indicate the Onset of the Morphological Metamorphosis of Circumstellar Envelopes". Monthly Notices of the Royal Astronomical Society. 465 (4): 4482–4499. arXiv:1611.03306. doi:10.1093/mnras/stw2931. S2CID 119058467.
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