HD 73256 is a variable star in the southern constellation of Pyxis. It has the variable star designation CS Pyxidis. With a baseline apparent visual magnitude of 8.08,[2] it requires binoculars or a small telescope to view. The star is located at a distance of 120 light years from the Sun based on parallax,[1] and is drifting further away with a radial velocity of +30 km/s.[2]
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Pyxis |
| Right ascension | 08h 36m 23.01654s[1] |
| Declination | −30° 02′ 15.4462″[1] |
| Apparent magnitude (V) | 8.08[2] |
| Characteristics | |
| Spectral type | G8 IV-V Fe+0.5[3] |
| B−V color index | 0.782±0.002[2] |
| Variable type | BY Dra[4] |
| Astrometry | |
| Radial velocity (Rv) | 29.66±0.14[1] km/s |
| Proper motion (μ) | RA: −182.193(17) mas/yr[1] Dec.: 67.373(21) mas/yr[1] |
| Parallax (π) | 27.2441 ± 0.0217 mas[1] |
| Distance | 119.72 ± 0.10 ly (36.71 ± 0.03 pc) |
| Absolute magnitude (MV) | 5.20[2] |
| Details[5] | |
| Mass | 1.01±0.03 M☉ |
| Radius | 0.94±0.02 R☉ |
| Luminosity | 0.74±0.01 L☉ |
| Surface gravity (log g) | 4.49±0.03 cgs |
| Temperature | 5,532±36 K |
| Metallicity [Fe/H] | 0.29±0.05[6] dex |
| Rotational velocity (v sin i) | 3.22±0.32[6] km/s |
| Age | 2.5±2.3 Gyr |
| Other designations | |
| Database references | |
| SIMBAD | data |
The stellar classification of this star is G8IV-VFe+0.5, which suggests a slightly evolved G-type main-sequence star with a mild overabundance of iron in the spectrum. It is a BY Draconis variable with a period of 13.97 days, showing a variation of 0.03 in magnitude due to chromospheric activity.[4] The star appears overluminous for its class, which may be the result of a high metallicity.[6] The star has roughly the same mass and a slightly smaller radius as the Sun, but is radiating 74% of the Sun's luminosity.[5] It is around 2–3 billion years old and is spinning with a projected rotational velocity of 3.2 km/s.[6]
Planetary system
In 2003, S. Udry and colleagues reported the discovery of a planet in orbit around HD 73256 using data from the CORALIE spectrograph. This object is a hot Jupiter with at least 1.87 times the mass of Jupiter in an orbit with a period of 2.55 days.[6] Assuming the planet is perfectly grey with no greenhouse or tidal effects, and a Bond albedo of 0.1, the temperature would be about 1300 K. This is close to 51 Pegasi b; between the predicted temperatures of HD 189733 b and HD 209458 b (1180-1392K), before they were measured. It is a candidate for "near-infrared characterisation with the VLTI Spectro-Imager".[8]
In 2018, K. Ment and colleagues reported an attempt to confirm the existence of this planet using Keck/HIRES data, but were unable to do so despite a likelihood of success. Thus the existence of this object is disputed.[9]
In 2023, a different substellar companion on a wide orbit, likely a brown dwarf, was discovered using both radial velocity and astrometry. This study did also detect HD 73256 b, but did not update its parameters or address the dispute.[10]
| Companion (in order from star) | Mass | Semimajor axis (AU) | Orbital period (days) | Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| b (disputed) | >1.87 ± 0.49 MJ | 0.037 | 2.54858 ± 0.00016 | 0.029 ± 0.02 | — | — |
| c | 16±1 MJ | 3.8±0.1 | 2690+60 −102 | 0.16±0.07 | 29+5 −3 or 152+8 −7° | — |