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R Hydrae

Mira Variable in Hydra

Right Ascension 13 : 29 : 42.7 (h:m)
Declination -23 : 16 : 52 (deg:m)
Distance (ly)
Visual brightness 3 .. 11 (mag)
Period 389.61 (days)
Spectra type M7 IIIe

This is the third Mira variable to be discovered, in 1704 by Giacomo Filippo (Jacques Philippe) Maraldi (1665-1729).

This star varies at a period of about 389 days, normally between 4.5 and 9.5 mag, but extremal values came close to mag 3 and mag 11. The period has been observed to decrease; Maraldi has reported it at about 500 days, and was little over 400 days in the early 20th century (1923-25: 415d). Since 1937, the period of this star has been quite stable near 389 days.

R Hydrae has a distant companion of mag 12 or 13 at PA 324 deg, separation 21.2". The pair, assigned Ho 381 or ADS 8920, exhibits common proper motion, and therefore is likely to be a physical pair.


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Hartmut Frommert
Christine Kronberg
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