HD 73256

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]

Not to be confused with HD 73526.
HD 73256
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]
Distance119.72 ± 0.10 ly
(36.71 ± 0.03 pc)
Absolute magnitude (MV)5.20[2]
Details[5]
Mass1.01±0.03 M☉
Radius0.94±0.02 R☉
Luminosity0.74±0.01 L☉
Surface gravity (log g)4.49±0.03 cgs
Temperature5,532±36 K
Metallicity [Fe/H]0.29±0.05[6] dex
Rotational velocity (v sin i)3.22±0.32[6] km/s
Age2.5±2.3 Gyr
Other designations
CS Pyx, CD−29°6456, HD 73256, HIP 42214, SAO 176159[7]
Database references
SIMBADdata

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]

The HD 73256 planetary system[6][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°		 —

See also

References
  1. Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
  2. Anderson, E.; Francis, Ch. (2012). "XHIP: An extended hipparcos compilation". Astronomy Letters. 38 (5): 331. arXiv:1108.4971. Bibcode:2012AstL...38..331A. doi:10.1134/S1063773712050015. S2CID 119257644.
  3. Gray, R. O.; et al. (July 2006). "Contributions to the Nearby Stars (NStars) Project: spectroscopy of stars earlier than M0 within 40 pc-The Southern Sample". The Astronomical Journal. 132 (1): 161–170. arXiv:astro-ph/0603770. Bibcode:2006AJ....132..161G. doi:10.1086/504637. S2CID 119476992.
  4. Samus, N. N.; et al. (2017). "General Catalogue of Variable Stars". Astronomy Reports. 5.1. 61 (1): 80–88. Bibcode:2017ARep...61...80S. doi:10.1134/S1063772917010085. S2CID 125853869.
  5. Bonfanti, A.; et al. (2015). "Revising the ages of planet-hosting stars". Astronomy and Astrophysics. 575. A18. arXiv:1411.4302. Bibcode:2015A&A...575A..18B. doi:10.1051/0004-6361/201424951. S2CID 54555839.
  6. Udry, S.; et al. (2003). "The CORALIE survey for southern extra-solar planets X. A Hot Jupiter orbiting HD 73256". Astronomy and Astrophysics. 407 (2): 679–684. arXiv:astro-ph/0304248. Bibcode:2003A&A...407..679U. doi:10.1051/0004-6361:20030815. S2CID 118889984.
  7. "HD 73256". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2020-11-28.
  8. Renard, Stéphanie; Absil, Olivier; Berger, Jean-Philippe; Bonfils, Xavier; Forveille, Thierry; Malbet, Fabien (2008). "Prospects for near-infrared characterisation of hot Jupiters with the VLTI Spectro-Imager (VSI)" (PDF). Proceedings of SPIE. Optical and Infrared Interferometry. 7013: 70132Z–70132Z–10. arXiv:0807.3014. Bibcode:2008SPIE.7013E..2ZR. doi:10.1117/12.790494. S2CID 119268109.
  9. Ment, Kristo; et al. (November 2018). "Radial Velocities from the N2K Project: Six New Cold Gas Giant Planets Orbiting HD 55696, HD 98736, HD 148164, HD 203473, and HD 211810". The Astronomical Journal. 156 (5): 45. arXiv:1809.01228. Bibcode:2018AJ....156..213M. doi:10.3847/1538-3881/aae1f5. S2CID 119243619. 213.
  10. Philipot, F.; Lagrange, A.-M.; et al. (August 2023). "Multi techniques approach to identify and/or constrain radial velocity sub-stellar companions". Astronomy & Astrophysics. arXiv:2308.05417.
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