Short description: Variable star in the constellation Equuleus

U Equulei

A visual band light curve for U Equulei, plotted from OMC data[1]

Observation data
Equinox J2000.0]] (ICRS)
Constellation | Equuleus
Right ascension |  20h 57m 16.28s[2]
Declination | 02° 58′ 44.6″[2]
Apparent magnitude (V) | 9 - 13[3]
Characteristics
Evolutionary stage | (post?) AGB[4]
Spectral type | G - K III[4]
B−V color index | +1.6[4]
Variable type | Lb[3]
Astrometry
Radial velocity (Rv)| −75[5] km/s
Proper motion (μ)|  RA: 10.490[6] mas/yr
Dec.: −10.433[6] mas/yr
Parallax (π)| 0.0985 ± 0.0750[6] mas
Distance| 3,340±700[7] pc
Details
Luminosity| 6,000[7] L☉
Temperature| 5,005[6] K
Other designations

IRAS 20547+0247, 2MASS J20571628+0258445, Gaia DR2 1731164844433296128

Database references
SIMBAD| data

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.

## Contents

* 1 Properties
* 2 Theoretical Planet
* 3 See also
* 4 References

## 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.[8]

## 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.[9] 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.[10]

## See also

* List of stars in Equuleus

## References

1. ↑ "OMC Archive". The Astronomical Data Centre at CAB. https://sdc.cab.inta-csic.es/omc/secure/form_busqueda.jsp?resetForm=true.
2. ↑ 2.0 2.1 Cutri, Roc M.; Skrutskie, Michael F.; Van Dyk, Schuyler D.; Beichman, Charles A.; Carpenter, John M.; Chester, Thomas; Cambresy, Laurent; Evans, Tracey E. et al. (2003). "VizieR Online Data Catalog: 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)". CDS/ADC Collection of Electronic Catalogues 2246: II/246. Bibcode: 2003yCat.2246....0C. http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=II/246.
3. ↑ 3.0 3.1 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. doi:10.1086/429369. Bibcode: 2005ApJ...624..983G.
4. ↑ 4.0 4.1 4.2 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.
5. ↑ 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. doi:10.1088/0004-6256/145/1/22. Bibcode: 2013AJ....145...22K.
6. ↑ 6.0 6.1 6.2 6.3 Brown, A. G. A. (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics 616: A1. doi:10.1051/0004-6361/201833051. Bibcode: 2018A&A...616A...1G. Gaia DR2 record for this source at VizieR.
7. ↑ 7.0 7.1 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. doi:10.1093/mnras/stu2383. Bibcode: 2015MNRAS.447.1673V.
8. ↑ Lewis, B. M. (2002). "On Dead OH/IR Stars". The Astrophysical Journal 576 (1): 445–449. doi:10.1086/341534. Bibcode: 2002ApJ...576..445L.
9. ↑ 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. doi:10.1046/j.1365-8711.1999.02784.x. Bibcode: 1999MNRAS.308.1133S.
10. ↑ 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. doi:10.1093/mnras/stw2931.

* v
* t
* e

Constellation of Equuleus

* List of stars in Equuleus

Stars|

| Bayer|

* α (Kitalpha)
* β
* γ
* δ
* ε

|

Flamsteed|

* 2 (λ)
* 3 (ζ)
* 4
* 6
* 9

Variable|

* R
* S
* U
* SY

HR|

* 8038
* 8067
* 8090
* 8095
* 8149
* 8191

HD|

* 200964
* 202908

Other|

* 2MASS J0523−1403
* Gliese 229
* WASP-49
* WASP-61

Galaxies|

| NGC|

* 7015
* 7040
* 7046

|

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