  | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Hydra |
| Right ascension | 13h 29m 42.7819s[1] |
| Declination | −23° 16′ 52.775″[1] |
| Apparent magnitude (V) | 3.5 to 10.9 (variable)[2] |
| Characteristics | |
| Spectral type | M6e/M9e:[3] |
| B−Vcolor index | 1.317±0.254[4] |
| Variable type | Mira[2](period 388.87 days) |
| Astrometry | |
| Radial velocity (Rv) | −10.0±0.6[5] km/s |
| Proper motion (μ) | RA: −53.79mas/yr[1] Dec.: +16.15mas/yr[1] |
| Parallax (π) | 7.93±0.18 mas[1] |
| Distance | 411 ± 9 ly (126 ± 3 pc) |
| Absolute magnitude (MV) | +0.95[4] |
| Details | |
| Mass | 2[6] M☉ |
| Radius | 377[7][a] R☉ |
| Luminosity | 10,000[6] L☉ |
| Temperature | 2,830[6] K |
| Age | 0.5–1.0[6] Gyr |
| Other designations | |
| R Hya,BD−22° 3601,HD 117287,HIP 65835,HR 5080,SAO 181695,WDS 13297-2317A[8] | |
| Database references | |
| SIMBAD | data |
R Hydrae, abbreviated R Hya,[2] is a single[9]star in theequatorialconstellation ofHydra, about 2.7° to the east ofGamma Hydrae.[10] It is aMira-type variable[2] that ranges inapparent visual magnitude from 3.5 down to 10.9 over a period of 389 days. At maximum brightness the star can be seen with thenaked eye, while at minimum a telescope of at least 5cm is needed. This star is located at a distance of approximately 410 light-years from theSun[1] but is drifting closer with aradial velocity of −10 km/s.[5]
This is an agingred giant star with astellar classification of M6e/M9e:,[3] currently near the thermal-pulsing tip of theasymptotic giant branch.[6] The 1998 detection of weak technicium (Tc) lines in the spectrum suggests the star has recently gone through a thirddredge-up.[11] However, a 2010 study failed to detect technicium in the atmosphere, indicating this oxygen-rich AGB star is Tc-poor.[12]O. J. Eggen found the star is a likely member of theHyades supergroup, which suggests an age of 500 million to one billion years and a mass double that of the Sun.[6]
The first record of observations for this star was in 1662 byJohannes Hevelius. It was found to be variable byGiacomo Filippo Maraldi in 1702; thereafter he tracked its various appearances until 1712. The evidence suggests the period of variability during this period was ~495 days. In between 1770 and 1950, the period declined linearly down to 385 days. It has remained fairly stable since that time. The decline may be due to a priorthermal pulse caused by ahelium flash under a hydrogen-fusing shell.[jargon] The period change would have been accompanied by a decrease in the stellar radius. An alternative explanation is a relaxation of the stellar envelope brought on by a change in the structure within the star.[6]
An extended emission component has been detected in theinfrared that indicates a detached, expandingdust shell surrounds the star. The inner boundary of this shell is located at 60–100 times the stellar radius, and it extends outward to at least 1,000 times the radius[11] with an expansion velocity of~8 km/s.[15] The data indicate a mass loss rate of2×10−7 M☉·yr−1, which declined by a factor of 20 around the year 1788.[15] Observations using theSpitzer Space Telescope show an extended double shell with a spiral structure, which extends out to300″. It forms abow shock where it interacts with the surroundinginterstellar medium. The orientation of this feature is consistent with the star'sproper motion.[16]
{{cite conference}}: CS1 maint: DOI inactive as of November 2024 (link)