R Hydrae

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R Hydrae
Hydra constellation map.svg
Red circle.svg

Location of R Hydrae (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Hydra
Right ascension 13h 29m 42.80s
Declination −23° 16′ 53.0″
Apparent magnitude (V) 3.5 to 10.9 (variable)[1]
Spectral type M6e/M9e:
B−V color index 1.3
Variable type Mira[1] (period 388.87 days)
Radial velocity (Rv) −10.4[2] km/s
Parallax (π) 8.05 ± 0.69 mas
Distance 410 ± 30 ly
(120 ± 10 pc)
Mass 2[3] M
Radius 460 (variable)[3] R
Luminosity 10,000 (variable)[3] L
Temperature 2,830[3] K
Other designations
HD 117287, HIP 65835, HR 5080, SAO 181695, BD−22° 3601
Database references
The bow shock around R Hya [4]

R Hydrae, also known as R Hya,[1] is a Mira-type variable star in the constellation Hydra.[1][2]

The magnitude of R Hydrae varies over a period of 389 days, between 3.5 and 10.9. 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 400 light years from Earth. Its spectral class is M7IIIe.[2]


  1. ^ a b c d AAVSO
  2. ^ a b c SIMBAD
  3. ^ 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. Bibcode:2002MNRAS.334..498Z. arXiv:astro-ph/0203328Freely accessible. doi:10.1046/j.1365-8711.2002.05467.x. 
  4. ^ Spitzer Science Center Press Release: Red Giant Plunging Through Space

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