HD 73256
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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, 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, and is drifting further away with a radial velocity of +30 km/s.
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. The star appears overluminous for its class, which may be the result of a high metallicity. The star has roughly the same mass and a slightly smaller radius as the Sun, but is radiating 74% of the Sun's luminosity. It is around 2–3 billion years old and is spinning with a projected rotational velocity of 3.2 km/s.
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. Assuming the planet is perfectly grey with no greenhouse or tidal effects, and a Bond albedo of 0.1, the temperature would be about 1,300 K. This is close to 51 Pegasi b, and between the predicted temperatures of HD 189733 b and HD 209458 b (1,180–1,392 K), before they were measured. It is a candidate for "near-infrared characterisation with the VLTI Spectro-Imager".
In 2018, K. Ment and colleagues reported an attempt to confirm the existence of this planet using Keck/HIRES data, but were unable to detect it despite a likelihood of success. Thus the existence of this object is disputed.
In 2023, a different substellar companion on a wide orbit, likely a brown dwarf, was discovered using both radial velocity and astrometry. This study also reported a detection of HD 73256 b, but did not update its parameters or address the dispute.
| 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 | 2,690+60 −102 | 0.16±0.07 | 29+5 −3 or 152+8 −7° | — |