U Aquarii

Not to be confused with Upsilon Aquarii.
U Aquarii

The visual band light curve of U Aquarii, from AAVSO data[1]
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Aquarius
Right ascension 22h 03m 19.69905s[2]
Declination −16° 37′ 35.2811″[2]
Apparent magnitude (V) 10.6 to 15.9[3]
Characteristics
Spectral type C-Hd[4]
U−B color index 0.07[5]
B−V color index 0.66[5]
Variable type R CrB[3]
Astrometry
Radial velocity (Rv)+89.49±1.54[6] km/s
Proper motion (μ) RA: 2.780[2] mas/yr
Dec.: −1.907[2] mas/yr
Parallax (π)0.0859 ± 0.0222 mas[2]
Distanceapprox. 38,000 ly
(approx. 12,000 pc)
Details
Mass4.5[7] M☉
Surface gravity (log g)2.28[7] cgs
Temperature5,500[5] K
Metallicity [Fe/H]−0.99[7] dex
Rotational velocity (v sin i)8.4[8] km/s
Other designations
U Aqr, BD−17°6424, HIP 108876, IRAS 22006-1652[9]
Database references
SIMBADdata

U Aquarii, abbreviated U Aqr, is a variable star in the equatorial constellation of Aquarius. It is invisible to the naked eye, having an apparent visual magnitude that ranges from 10.6 down to as low as 15.9.[3] Based on parallax measurements, the distance to this star is approximately 38 kly (12 kpc). In 1990, W. A. Lawson and associates provided a distance estimate of 43 kly (13.2 kpc) based on the assumption of a bolometric magnitude of −5.[5] It appears to lie several kiloparsecs below the galactic plane, and thus may belong to an old stellar population.[4]

The stellar classification of this star is C-Hd,[4] and it is classified as a R Coronae Borealis variable.[3] It is a carbon star with a hydrogen-deficient spectra that also shows evidence of s-process elements,[4] including overabundances of strontium and yttrium, but no barium.[10] This combination of properties is exceptionally rare; only one other example has been found as of 2012.[11] The elemental abundances are explained as the result of a single neutron exposure event, which is difficult to reconcile with a conjecture that this may be a post-AGB-type star.[10] In 1999, U Aqr was proposed to be a Thorne-Zytkow object, instead of being a simple R Coronae Borealis variable.[12]

  1. ^ Cite error: The named reference aavso was invoked but never defined (see the help page).
  2. ^ a b c d e Cite error: The named reference edr3 was invoked but never defined (see the help page).
  3. ^ a b c d Cite error: The named reference Samus_et_al_2017 was invoked but never defined (see the help page).
  4. ^ a b c d Cite error: The named reference Bond_et_al_1979 was invoked but never defined (see the help page).
  5. ^ a b c d Cite error: The named reference Lawson_et_al_1990 was invoked but never defined (see the help page).
  6. ^ Cite error: The named reference GaiaDR2 was invoked but never defined (see the help page).
  7. ^ a b c Cite error: The named reference starhorse was invoked but never defined (see the help page).
  8. ^ Cite error: The named reference majewski2017 was invoked but never defined (see the help page).
  9. ^ Cite error: The named reference SIMBAD was invoked but never defined (see the help page).
  10. ^ a b Cite error: The named reference Malaney1985 was invoked but never defined (see the help page).
  11. ^ Cite error: The named reference Goswami2012 was invoked but never defined (see the help page).
  12. ^ Cite error: The named reference Vanture_et_al_1999 was invoked but never defined (see the help page).