HD 128717

Last updated
HD 128717
Observation data
Epoch J2000       Equinox J2000
Constellation Draco [1]
Right ascension 14h 36m 21.3187s [2]
Declination +57° 33′ 38.382″ [2]
Apparent magnitude  (V)8.29±0.01 [3]
Characteristics
Evolutionary stage main sequence [2]
Spectral type F8 [4]
Astrometry
Radial velocity (Rv)−4.851±0.004 [5] km/s
Proper motion (μ)RA: −82.125 mas/yr [2]
Dec.: +67.259 mas/yr [2]
Parallax (π)13.5609±0.0216  mas [2]
Distance 240.5 ± 0.4  ly
(73.7 ± 0.1  pc)
Absolute magnitude  (MV)4.16 [6]
Orbit [7]
Period (P)9.37+0.06
−0.05 years
Semi-major axis (a)4.85+0.02
−0.01  au
Eccentricity (e)0.850±0.002
Inclination (i)130.3+1.6
−1.9°
Longitude of the node (Ω)131.7+3.3
−3.4°
Periastron epoch (T)2023.6716±0.0009
Argument of periastron (ω)
(secondary)		−105.7+0.4
−0.3°
Details [7]
A
Mass 1.212+0.058
−0.068  M☉
Radius 1.248±0.024  R☉
Luminosity 2.10±0.07  L☉
Surface gravity (log g)4.329+0.025
−0.030  cgs
Temperature 6,210±40  K
Metallicity [Fe/H]+0.16±0.08  dex
Rotation 7.8±0.6 days
Rotational velocity (v sin i)6.1±0.5 km/s
Age 1.4±0.3  Gyr
B
Mass 19.8±0.5  MJup
Other designations
BD+58°1514, HD 128717, HIP 71425, TYC 3866-1234-1 [8]
Database references
SIMBAD data

HD 128717 is a star in the constellation of Draco. With an apparent magnitude of +8.29, it is too faint to be seen with the naked eye. Parallax measurements by the Gaia spacecraft imply a distance of 240 light-years (73.7 parsecs ). It is moving towards the Solar System at a velocity of 4.851 km/s.

Contents

Characteristics

With a spectral class of F8, [4] HD 128717 is a late-type F-type star. It is estimated to be 1.4 billion years old, has 1.21 times the mass of the Sun and 1.25 times the radius. It radiates 2.1 times the Sun's luminosity from its photosphere at an effective temperature of 6,210  K , [7] giving it the typical yellowish-white hue of a late-type F-type star. [9]

The space velocity components of HD 128717 are U =−30, V=−10 and W=−4km/s. It is orbiting the Milky Way galaxy with an orbital eccentricity of 0.06. Its distance from the galactic center varies between 7.40 kiloparsecs (24.1 kilolight-years) and 8.38 kpc (27.3 kly). This orbit lies close to the galactic plane, and the star travels no more than 70 parsecs (230 light-years) above or below this plane. [10]

Companion

Astrometric data collected by the Gaia spacecraft on its third data release revealed that HD 128717 appears to wobble around an empty space, indicating that it has an object in orbit whose gravitational force is pulling it. The object was first noted by the Gaia team in 2022, [11] and the paper by Sahlmann et al in 2024 identified HD 128717 "as a strong candidate for hosting a super-Jupiter". [12] In the same year, Alessandro Sozzetti reported, in a conference, the confirmation of the object using radial velocity observations. [13] The companion was independently confirmed by Pinamonti et al. (2025), which named it as Gaia-6b since it was the sixth planetary candidate detected by Gaia that has been later confirmed. [7]

HD 128717 b is a brown dwarf with 19.8 times the mass of Jupiter. It has an orbital period of 9.37 years and a highly-eccentric orbit: At apoastron, its orbital separation is 9.0  astronomical units, while at periastron it is 0.73 au. [a] The reasons for such a high eccentricity remain unclear. [7]

Notes

  1. ↑ Calculating using the equations a(1 + e) and a(1 − e) for apoastron and periastron, respectively, where a is the semi-major axis and e is the eccentricity.

References

  1. ↑ 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. XHIP record for this object at VizieR.
  2. 1 2 3 4 5 6 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.
  3. ↑ Høg, E.; Fabricius, C.; Makarov, V. V.; Urban, S.; Corbin, T.; Wycoff, G.; Bastian, U.; Schwekendiek, P.; Wicenec, A. (2000). "The Tycho-2 catalogue of the 2.5 million brightest stars". Astronomy and Astrophysics. 355: L27 –L30. Bibcode:2000A&A...355L..27H. ISSN   0004-6361.
  4. 1 2 Cannon, A. J.; Pickering, E. C. (1993). "VizieR Online Data Catalog: Henry Draper Catalogue and Extension (Cannon+ 1918-1924; ADC 1989)". VizieR Online Data Catalog. 3135: III/135A. Bibcode:1993yCat.3135....0C.
  5. ↑ Jönsson, Henrik; Holtzman, Jon A.; Prieto, Carlos Allende; Cunha, Katia; García-Hernández, D. A.; Hasselquist, Sten; Masseron, Thomas; Osorio, Yeisson; Shetrone, Matthew; Smith, Verne; Stringfellow, Guy S.; Bizyaev, Dmitry; Edvardsson, Bengt; Majewski, Steven R.; Mészáros, Szabolcs (2020-08-17). "APOGEE Data and Spectral Analysis from SDSS Data Release 16: Seven Years of Observations Including First Results from APOGEE-South". The Astronomical Journal. 160 (3): 120. arXiv: 2007.05537 . Bibcode:2020AJ....160..120J. doi: 10.3847/1538-3881/aba592 . ISSN   0004-6256.
  6. ↑ Holmberg, J.; Nordström, B.; Andersen, J. (July 2009). "The Geneva-Copenhagen survey of the solar neighbourhood. III. Improved distances, ages, and kinematics". Astronomy and Astrophysics. 501 (3): 941–947. arXiv: 0811.3982 . Bibcode:2009A&A...501..941H. doi:10.1051/0004-6361/200811191. ISSN   0004-6361.
  7. 1 2 3 4 5 Pinamonti, M.; Sozzetti, A.; Barbato, D.; Desidera, S.; Biazzo, K.; Bonomo, A. S.; Lanza, A. F.; Naponiello, L.; Affer, L. (2025-12-04). "The GAPS programme at TNG LXXI. HD 128717 B/Gaia-6 B: a long-period eccentric low-mass brown dwarf from astrometry and radial velocities". Astronomy and Astrophysics. arXiv: 2512.04606 .
  8. ↑ "HD 128717". SIMBAD . Centre de données astronomiques de Strasbourg.
  9. ↑ "The Colour of Stars". Australia Telescope, Outreach and Education. Commonwealth Scientific and Industrial Research Organisation. December 21, 2004. Archived from the original on 2013-12-03. Retrieved 2012-01-16.
  10. ↑ Nordström, B.; Mayor, M.; Andersen, J.; Holmberg, J.; Pont, F.; Jørgensen, B. R.; Olsen, E. H.; Udry, S.; Mowlavi, N. (May 2004). "The Geneva-Copenhagen survey of the Solar neighbourhood. Ages, metallicities, and kinematic properties of ∼14 000 F and G dwarfs". Astronomy and Astrophysics. 418: 989–1019. arXiv: astro-ph/0405198 . Bibcode:2004A&A...418..989N. doi:10.1051/0004-6361:20035959. ISSN   0004-6361.
  11. ↑ Collaboration, Gaia; Arenou, F.; Babusiaux, C.; Barstow, M. A.; Faigler, S.; Jorissen, A.; Kervella, P.; Mazeh, T.; Mowlavi, N.; Panuzzo, P.; Sahlmann, J.; Shahaf, S.; Sozzetti, A.; Bauchet, N.; Damerdji, Y. (2022-06-11). "Gaia Data Release 3. Stellar multiplicity, a teaser for the hidden treasure". Astronomy and Astrophysics. 674: A34. arXiv: 2206.05595 . Bibcode:2023A&A...674A..34G. doi:10.1051/0004-6361/202243782. ISSN   0004-6361.
  12. ↑ Sahlmann, Johannes; Gómez, Pablo (2024-04-14). "Machine learning-based identification of Gaia astrometric exoplanet orbits". Monthly Notices of the Royal Astronomical Society. 537 (2): 1130–1145. arXiv: 2404.09350 . doi: 10.1093/mnras/staf018 . ISSN   0035-8711.
  13. ↑ Sozzetti, Alessandro (July 2024). "Ground-based RV follow-up of Gaia DR3 astrometric exoplanet candidates around bright stars". EAS2024, European Astronomical Society Annual Meeting: 1626. Bibcode:2024eas..conf.1626S.
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