U Hydrae

Not to be confused with Upsilon Hydrae.
U Hydrae

A visual band light curve for U Hydrae, plotted from ASAS data[1]
Observation data
Epoch J2000      Equinox J2000
Constellation Hydra
Right ascension 10h 37m 33.27295s[2]
Declination −13° 23′ 04.3529″[2]
Apparent magnitude (V) 4.89[3]
Characteristics
Evolutionary stage AGB[4]
Spectral type C-N5 C2 5-[5]
B−V color index 2.80±0.51[3]
Variable type SRb[6]
Astrometry
Radial velocity (Rv)−25.8±1.7[7] km/s
Proper motion (μ) RA: +42.59[2] mas/yr
Dec.: −37.72[2] mas/yr
Parallax (π)4.80 ± 0.23 mas[2]
Distance680 ± 30 ly
(208 ± 10 pc)
Absolute magnitude (MV)−1.70[3]
Details
Mass0.75[4] M☉
Radius274 – 415[4][a] R☉
Luminosity3,476[4] L☉
Surface gravity (log g)−0.28[4] cgs
Temperature2,600–3,200[4] K
Metallicity [Fe/H]−0.1[8] dex
Other designations
U Hya, BD−12°3218, HD 92055, HIP 52009, HR 4163, SAO 156110[9]
Database references
SIMBADdata

U Hydrae is a single[10] star in the equatorial constellation of Hydra, near the northern constellation border with Sextans. It is a semiregular variable star of sub-type SRb,[6] with its brightness ranging from visual magnitude (V) 4.7 to 5.2 over a 450-day period, with some irregularity.[11] This object is located at a distance of approximately 680 light years from the Sun based on parallax.[2] It is drifting closer with a radial velocity of −26 km/s.[7]

This is a carbon-rich red giant star on the asymptotic giant branch[4] – a carbon star – with s-process elements appearing in the spectrum. It has a stellar classification of C-N5 with a carbon star class of C2 5-.[5] The star is losing mass at the rate of 1.2×10−7 M☉·yr−1, with an outflow velocity of 6.9 km/s. Technetium has been detected in the spectrum, suggesting the star has experienced a third dredge-up episode due to thermal pulses of the helium-burning shell some time within the last 100,000 years.[12]

An ultraviolet (UV) excess has been detected coming from an extended elliptical ring that surrounds this star. It has a mean angular radius of 110″ and lines up with a detached shell of dusty material that was previously detected in the infrared band. The material was most likely ejected from the star due to mass loss episodes. The probable cause of the UV emission is from the movement of the star through space and possibly shock-excited molecules of H2. The emission does not show a bow-shock-like structure.[13]

  1. ^ Cite error: The named reference ASASServer was invoked but never defined (see the help page).
  2. ^ a b c d e f Cite error: The named reference vanLeeuwen2007 was invoked but never defined (see the help page).
  3. ^ a b c Cite error: The named reference Anderson2012 was invoked but never defined (see the help page).
  4. ^ a b c d e f g Cite error: The named reference Rau2017 was invoked but never defined (see the help page).
  5. ^ a b Cite error: The named reference barnbaum1996 was invoked but never defined (see the help page).
  6. ^ a b Cite error: The named reference Samus2017 was invoked but never defined (see the help page).
  7. ^ a b Cite error: The named reference Gontcharov2006 was invoked but never defined (see the help page).
  8. ^ Cite error: The named reference Lambert1986 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. ^ Cite error: The named reference Eggleton2008 was invoked but never defined (see the help page).
  11. ^ Cite error: The named reference Monks was invoked but never defined (see the help page).
  12. ^ Cite error: The named reference Izumiura2011 was invoked but never defined (see the help page).
  13. ^ Cite error: The named reference Sanchez2015 was invoked but never defined (see the help page).


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