| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Hydra |
| Right ascension | 10h 24m 36.768s[4] |
| Declination | −19° 05′ 32.96″[4] |
| Apparent magnitude (V) | 8.08[5] |
| Characteristics | |
| Evolutionary stage | Main sequence |
| Spectral type | F5V[6] |
| B−Vcolor index | 0.466±0.014[5] |
| Variable type | β Per[7] |
| Astrometry | |
| Radial velocity (Rv) | −7.13±0.2[8] km/s |
| Proper motion (μ) | RA: −14.017mas/yr[4] Dec.: −10.686mas/yr[4] |
| Parallax (π) | 9.7366±0.0643 mas[4] |
| Distance | 335 ± 2 ly (102.7 ± 0.7 pc) |
| Absolute magnitude (MV) | 3.25[5] |
| Orbit[9] | |
| Primary | HS Hya A |
| Companion | HS Hya B |
| Period (P) | 1.56804098 ± 0.00000014 days |
| Semi-major axis (a) | ≥ 7.656±0.014 R☉ |
| Semi-amplitude (K1) (primary) | 121.73±0.30 km/s |
| Semi-amplitude (K2) (secondary) | 125.38±0.35 km/s |
| Orbit[10] | |
| Primary | HS Hya AB |
| Companion | HS Hya C |
| Period (P) | 190.530±0.015 days |
| Semi-major axis (a) | ≥ 34.5±1.1 R☉[9] |
| Eccentricity (e) | 0.246±0.029 |
| Periastronepoch (T) | 2,448,047.2±3.4 HJD |
| Argument of periastron (ω) (secondary) | 111.2±7.6° |
| Semi-amplitude (K1) (primary) | 9.02±0.31 km/s |
| Details | |
| HS Hya A | |
| Mass | 1.31±0.03[10] M☉ |
| Radius | 1.275±0.007[9] R☉ |
| Temperature | 6,500±50[9] K |
| HS Hya B | |
| Mass | 1.27±0.03[10] M☉ |
| Radius | 1.216±0.007[9] R☉ |
| Temperature | 6,400±50[9] K |
| HS Hya C | |
| Mass | 0.56+0.12 −0.09[10] M☉ |
| Other designations | |
| BV 701,HS Hya,BD−18 2927,HD 90242,HIP 50966,SAO 155964,PPM 222916[11] | |
| Database references | |
| SIMBAD | data |
HS Hydrae is atriple star[9] system in theequatorialconstellation ofHydra. The inner pair were aneclipsing binary during the period 1920 until 2019,[12] withHS Hya being thevariable star designation. With a baseapparent visual magnitude of 8.08,[5] HS Hya is too dim to be viewed with the naked eye. During the primary eclipse, the magnitude dropped to 8.61; the secondary eclipse lowered the magnitude to 8.55.[7] Based onparallax measurements, the system is located at a distance of approximately 335 light years from theSun.[4] It is drifting closer with a meanradial velocity of−7 km/s.[8]
This star was determined to be anAlgol variable as part of a survey of bright southern stars byW. Strohmeierand and associates in 1965, demonstrating it is a binary system with anorbital inclination close to the line of sight from the Earth.[13]D. M. Popper found an eclipse periodicity of 1.568024 days for the pair with a combined estimatedclass of F3–F4.[14] A longer-term analysis of the system's radial velocities in 1997 showed a third member of the system is likely orbiting the inner pair. This is probably a smallred dwarf with about half the mass of the Sun and anorbital period of ~190 days.[9]
In 1997, observations with theHipparcos satellite showed the depth of both eclipses was lower than they were 20 years earlier. In 2012,P. Zasche andA. Paschke showed that theinclination of theorbital plane for the inner pair had changed by 15° since its discovery. The third member of the system is causing the orbit of the inner pair toprecess, resulting in a change of inclination of 7.8° over the same period.[15] By 2022, the eclipses have come to an end, with the final observed events captured by theTESSspace telescope in 2019. Examination of earlier data showed that the eclipses had begun in the early 1920s, and the system is predicted to resume eclipses in 2195.[12]
The combinedstellar classification of this system is F5V,[6] matching anF-type main-sequence star. The inner pair form a detached binary system[7] that showellipsoidal variation due totidal interaction.[12] The primary member, designated component A, has 1.31[10] times the mass and 1.28[9] times the radius of the Sun. The marginally smaller secondary, component B, has 1.27[10] times the mass with 1.22[9] times the radius of the Sun. The unseen third member, component C, has about 56% of the Sun's mass.[10]
