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.
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 8.38kpc (27.3kly). 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]
↑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.
↑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. ISSN0004-6361.
12Cannon, 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.
12345Pinamonti, 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.
↑"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.
↑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. ISSN0004-6361.
↑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. ISSN0004-6361.
