U Equulei

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)78 km/s
Distance5,000 ly
(1,500[3] pc)
Other designations
IRAS 20547+0247, 2MASS J20571628+0258445
Database references
SIMBADdata

U Equulei (U Equ / IRAS 20547 +0247) is a variable star in the constellation of Equuleus of 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 a peculiar star whose optical spectrum is one of the strangest observed. Their spectra, obtained in 1994, are dominated by strong absorption units metallic oxides somewhat similar to red giant of spectral type M. The bands due to TiO, AlO, and appear to have a source VO-from circumstellar material surrounding the star-and photospheric . There appears to be falling into the star material or mass ejection therefrom, it is thought that gas can be contained in a disk-shaped structure. U Equulei also shows other peculiarities. Its emissions maser of OH and H2O vary in speed and intensity. Also, its high radial velocity (78 km / s) and galactic latitude (-26 °) suggest a link with the population of galactic halo.[2][3] Although the spectrum is superficially similar to class M stars,[4] this is thought to be due to an underlying G or early K class giant star surrounded by a dusty disc.[3]

U Equulei is ranked as an irregular variable of long period (LB) whose brightness-B-band magnitude varies between +14.5 and +15.5. Although in 1994 the visual magnitude was about +9, post - 1996, 1998 and 1999 - showed a decrease in magnitude to +13. Variations in visual magnitude and the origin of circumstellar material remain unexplained, however, the strange nature of its optical spectrum suggests that the star may have entered a stage of rapid development.[4]

U Equ 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.[5]

Theoretical Planet

Lionel Siess and Mario Livio suggested that the accretion of a giant planet towards increasing red giant has been able to make the star's outer layers rotate fast enough to cause an outpouring equatorial-or disk-expansion, responsible for the peculiar environment U Equulei.[6]

See also

References

  1. 1 2 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. 1 2 3 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
  3. 1 2 3 4 5 6 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. 1 2 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.
  5. ↑ Lewis, B. M. (2002). "On Dead OH/IR Stars". The Astrophysical Journal 576: 445. Bibcode:2002ApJ...576..445L. doi:10.1086/341534.
  6. ↑ 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.
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