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HD 201585 is a star located in the equatorial constellation Equuleus. It has an apparent magnitude of 8.23, making it readily visible in small telescopes but not to the naked eye. Gaia DR3 parallax measurements imply a distance of 594 light-years and it is currently receding with a heliocentric radial velocity of 14 km/s. At its current distance, HD 201585's brightness is diminished by three-tenths of a magnitudes due to interstellar extinction and it has an absolute magnitude of +1.81. HD 201585 is the star's Henry Draper Catalogue designation. It is also designated as MASCARA-1 meaning that it is the first star observed by the MASCARA exoplanet search program.

HD 201585 has a stellar classification of A3, indicating that it is an A-type star. However, later observations of the star's physical properties revealed a cooler class of A8. It has 1.9 times the mass of the Sun and 2.1 times the radius of the Sun. It radiates 12 times the luminosity of the Sun from its photosphere at an effective temperature of 7,490 K, giving it the typical white hue of an A-type star. HD 201585 either has a solar metallicity or an iron abundance of = +0.15, depending on the source. Unfortunately, the latter value is poorly constrained. The star is estimated to be approximately 800 million years old and like most hot stars, it spins rapidly with a projected rotational velocity of 109 km/s.

Planetary system

HD 201585 b, also known as MASCARA-1b, was discovered around 2016 after astronomer G. J. J. Talens and colleagues observed planetary transit signals coming from HD 201585; its discovery was announced on July 13, 2017. It is a hot Jupiter with 3.7 times the mass of Jupiter and 1.60 times the radius of Jupiter. MASCARA-1b has a measured equilibrium temperature of 2,594±2 K. A 2022 study conducted on the planet found that it was unusually reflective for a hot Jupiter, having a geometric albedo of 0.171+0.066
−0.068. Attempts to characterize its spectrum around the same year in a different study have failed due to MASCARA-1b's high surface gravity, resulting in a compact planetary atmosphere.

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. ^ Høg, E.; Fabricius, C.; Makarov, V. V.; Urban, S.; Corbin, T.; Wycoff, G.; Bastian, U.; Schwekendiek, P.; Wicenec, A. (March 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. S2CID 17128864.
3. ^ Turon, C.; et al. (July 1993). "Version 2 of the HIPPARCOS Input Catalogue". Bulletin d'Information du Centre de Donnees Stellaires. 43: 5. Bibcode:1993BICDS..43....5T. ISSN 1169-8837. S2CID 129205012.
4. ^ Anderson, E.; Francis, Ch. (May 2012). "XHIP: An extended hipparcos compilation". Astronomy Letters. 38 (5): 331–346. arXiv:1108.4971. Bibcode:2012AstL...38..331A. doi:10.1134/S1063773712050015. eISSN 1562-6873. ISSN 1063-7737. S2CID 119257644.
5. ^ Talens, G. J. J.; Albrecht, S.; Spronck, J. F. P.; Lesage, A.-L.; Otten, G. P. P. L.; Stuik, R.; Van Eylen, V.; Van Winckel, H.; Pollacco, D.; McCormac, J.; Grundahl, F.; Fredslund Andersen, M.; Antoci, V.; Snellen, I. A. G. (13 July 2017). "MASCARA-1 b. A hot Jupiter transiting a bright m_V = 8.3 A-star in a misaligned orbit". Astronomy & Astrophysics. 606. EDP Sciences: A73. arXiv:1707.04262. Bibcode:2017A&A...606A..73T. doi:10.1051/0004-6361/201731282. ISSN 0004-6361. S2CID 119259578.
6. ^ 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; Souto, Diogo; Zamora, Olga; Beaton, Rachael L.; Bovy, Jo; Donor, John; Pinsonneault, Marc H.; Poovelil, Vijith Jacob; Sobeck, Jennifer (August 17, 2020). "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). American Astronomical Society: 120. arXiv:2007.05537. Bibcode:2020AJ....160..120J. doi:10.3847/1538-3881/aba592. ISSN 1538-3881. S2CID 220496397.
7. ^ Hooton, M. J.; et al. (September 10, 2022). "Spi-OPS: Spitzer and CHEOPS confirm the near-polar orbit of MASCARA-1 b and reveal a hint of dayside reflection". Astronomy & Astrophysics. 658. EDP Sciences: A75. arXiv:2109.05031. Bibcode:2022A&A...658A..75H. doi:10.1051/0004-6361/202141645. ISSN 0004-6361. S2CID 237490820.
8. Saffe, C.; Miquelarena, P.; Alacoria, J.; Flores, M.; Jaque Arancibia, M.; Calvo, D.; Martín Girardi, G.; Grosso, M.; Collado, A. (March 2021). "Chemical analysis of early-type stars with planets". Astronomy & Astrophysics. 647: A49. arXiv:2101.04416. Bibcode:2021A&A...647A..49S. doi:10.1051/0004-6361/202040132. eISSN 1432-0746. ISSN 0004-6361. S2CID 231582834.
9. "HD 201585". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved September 22, 2023.
10. Gontcharov, George A.; Mosenkov, Aleksandr V. (28 September 2017). "Verifying reddening and extinction for Gaia DR1 TGAS main sequence stars". Monthly Notices of the Royal Astronomical Society. 472 (4): 3805–3820. arXiv:1709.01160. Bibcode:2017MNRAS.472.3805G. doi:10.1093/mnras/stx2219. eISSN 1365-2966. ISSN 0035-8711. S2CID 118879856.
11. Casasayas-Barris, N.; et al. (June 19, 2022). "Transmission spectroscopy of MASCARA-1b with ESPRESSO: Challenges of overlapping orbital and Doppler tracks". Astronomy & Astrophysics. 664. EDP Sciences: A121. arXiv:2206.09443. Bibcode:2022A&A...664A.121C. doi:10.1051/0004-6361/202143016. ISSN 0004-6361. S2CID 249889798.

v t e Constellation of Equuleus
Equuleus in Chinese astronomy List of stars in Equuleus
Stars	Bayer α (Kitalpha) β γ δ ε ζ λ Flamsteed 4 6 9 Variable R U SY HR 8038 8067 8090 8095 8149 8191 HD 200779 200964 201585 202908 203473 Other HAT-P-65 WASP-90
Exoplanets MASCARA-1b
Galaxies	NGC 7015 7040 7046
Category

• Equuleus
• A-type main-sequence stars
• Planetary systems with one confirmed planet
• Durchmusterung objects
• Henry Draper Catalogue objects
• Hipparcos objects
• TIC objects