W Hydrae

W Hydrae is a Mira-type variable star in the constellation Hydra. The star is nearly located within the Solar neighborhood, at 320 light years from the Solar System. It has a visual apparent magnitude range of 5.6 to 10. In the near-infrared J band it has a magnitude of -1.7,^[4] is the 7th brightest star in the night sky, and is even brighter than Sirius.

W Hydrae

The visual band light curve of W Hydrae, from AAVSO data[1]
Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Hydra
Right ascension	13h 49m 01.998s
Declination	−28° 22′ 03.49″
Apparent magnitude (V)	7.7 - 11.6[2]
Characteristics
Spectral type	M7.5e-M9ep[3]
Apparent magnitude (J)	-1.7[4]
Variable type	Mira
Astrometry
Parallax (π)	10.18±2.36 mas[5]
Distance	320+98 −59 ly (98+30 −18 pc)[5]
Details
Mass	2.14+1.07 −0.71[6] M☉
Radius	436+134 −80[7][a] R☉
Luminosity	9,290+2,460 −1,940[6] L☉
Temperature	3,000[6] K
Other designations
W Hya, CCDM J13491-2822A, HD 120285, RAFGL 1650, CPD-27° 4792, HIP 67419, SAO 181981, AAVSO 1343-27, IRAS 13462-2807, GC 18659, TYC 6728-19-1.
Database references
SIMBAD	data

Water masers and dust

Spectrum of water vapour towards W Hydrae obtained with APEX

The star also shows signs of intense water emissions, indicative of the presence of a wide disk of dust and water vapour.^[8] Such emissions cover a zone spanning between 10.7 Astronomical Units (within Saturn's orbital zone) and 1.2 parsecs (or nearly 247,500 Astronomical Units, as far away as the Oort Cloud in Solar System).

Notes

1. Radius calculated using a distance of 98+30
   −18 parsecs and an angular diameter of 41.4 milliarcseconds (0.041 arcsec). 98 • 0.041 = diameter of 4.06 AU, which is multiplied by 107.5 to convert from AU to R_☉.