R Hydrae

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The bow shock around R Hya [1]
R Hydrae
Observation data
Epoch J2000      Equinox J2000
Constellation Hydra
Right ascension 13h 29m4 2.80s
Declination -23° 16' 53.0"
Apparent magnitude (V) 3.5 to 10.9 (variable)[2]
Spectral type M6e/M9e:
B−V color index 1.3
Variable type Mira
 period= 388.87 days[2]
Radial velocity (Rv) −10.4[3] km/s
Parallax (π) 8.05 ± 0.69 mas
Distance 410 ± 30 ly
(120 ± 10 pc)
Mass 2[4] M
Radius 460 (variable)[4] R
Luminosity 10,000 (variable)[4] L
Temperature 2,830[4] K

R Hydrae, also known as R Hya,[2] is a Mira-type variable star in the constellation Hydra.[2][3]

The magnitude of R Hydrae varies over a period of 389 days, between 3.21 and 11.00. The period of R Hydrae changes slowly.

At maximum brightness the star can be seen with the naked eye, while at minimum a telescope of at least 5 cm is needed.

R Hydrae is approximately 2000 light years from Earth. R Hydrae's spectral class is M7IIIe.[3]


  1. ^ Spitzer Science Center Press Release: Red Giant Plunging Through Space
  2. ^ a b c d AAVSO
  3. ^ a b c SIMBAD
  4. ^ a b c d Zijlstra, A. A.; Bedding, T. R.; Mattei, J. A. (2002). "The evolution of the Mira variable R Hydrae". Monthly Notices of the Royal Astronomical Society 334 (3): 498. arXiv:astro-ph/0203328. Bibcode:2002MNRAS.334..498Z. doi:10.1046/j.1365-8711.2002.05467.x. 

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