Astronomy:HD 93396

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Short description: Subgiant with an exoplanet; Sextans
HD 93396
Observation data
Epoch J2000.0   Equinox (celestial coordinates)
Constellation Sextans
Right ascension  10h 46m 49.74018s[1]
Declination −09° 23′ 56.4955″[1]
Apparent magnitude (V) 8.04±0.01[2]
Characteristics
Evolutionary stage Hertzsprung gap[3]
Spectral type G8/K0 IV[4]
B−V color index +0.83[2]
Variable type planetary transit[5]
Astrometry
Radial velocity (Rv)34.96±0.24[6] km/s
Proper motion (μ) RA: −79.160[1] mas/yr
Dec.: −78.507[1] mas/yr
Parallax (π)10.0049 ± 0.0202[1] mas
Distance326.0 ± 0.7 ly
(100.0 ± 0.2 pc)
Absolute magnitude (MV)+3.01[7]
Details
Mass1.43±0.07[8] M☉
Radius2.93±0.15[9] R☉
Luminosity6.01+0.13−0.07[1] L☉
Surface gravity (log g)3.72+0.04−0.05[3] cgs
Temperature5,375±25[10] K
Metallicity [Fe/H]+0.17±0.05[3] dex
Rotational velocity (v sin i)1.8[11] km/s
Age3.48±1.74[8] Gyr
Other designations
KELT-11, BD−08°2999, HD 93396, HIP 52733, SAO 137780[12]
Database references
SIMBADdata

HD 93396 (HIP 52733; TOI-664; KELT-11) is a solitary star located in the equatorial constellation Sextans. It has an apparent magnitude of 8.04,[2] making it readily visible in binoculars, but not to the naked eye. The object is located relatively close at a distance of 326 light-years based on Gaia DR3 parallax measurements,[1] but it is receding with a heliocentric radial velocity of 34.96 km/s.[6] At its current distance, HD 93396's brightness is diminished by an interstellar extinction of 0.17 magnitudes[13] and it has an absolute magnitude of +3.01.[7]

HD 93396 has a stellar classification of G8/K0 IV,[4] indicating that it is an evolved star with the characteristics of a G8 and K0 subgiant. At the age of 3.48 billion years, it is currently in the Hertzsprung gap,[8] meaning that the star is in the process of ceasing hydrogen fusion at its stellar core and it is evolving towards the red giant branch. It has 1.43 times the mass of the Sun[8] and a slightly enlarged radius 2.93 times that of the Sun's.[9] It radiates 6.01 times the luminosity of the Sun[1] from its photosphere at an effective temperature of 5,375 K,[10] giving it a yellowish-orange hue when viewed in the night sky. Like many planetary hosts, HD 93396 is metal enriched, having an iron abundance of [Fe/H] = +0.17 or 148% that of the Sun's.[3] It spins slowly with a projected rotational velocity of 1.8 km/s.[11]

Planetary system

In 2017, a sub-Saturn exoplanet was discovered transiting the star using the Kilodegree Extremely Little Telescope. It orbits very close to the star within a period of 4 days.[3] Although the planet only has 17% the mass of Jupiter, it is 35% larger than the jovian planet,[10] making it one of the most inflated and least dense exoplanets. Subsequent observations revealed that the planet's atmosphere contains water vapor and a high abundance of titanium and aluminum oxides.[14]

The KELT-11/HD 93396 planetary system
Companion
(in order from star) 		Mass Semimajor axis
(AU) 		Orbital period
(days) 		Eccentricity Inclination Radius
KELT-11b 0.171±0.015[10] MJ 0.0625+0.0030−0.0029[15] 4.7362034±0.0000083[16] 0 (fixed) [3] 85.8+2.4−1.8[3]° 1.35±0.10[10] RJ

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 Vallenari, A. et al. (2022). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy & Astrophysics. doi:10.1051/0004-6361/202243940  Gaia DR3 record for this source at VizieR.
  2. ↑ 2.0 2.1 2.2 Høg, E.; Fabricius, C.; Makarov, V. V.; Urban, S.; Corbin, T.; Wycoff, G.; Bastian, U.; Schwekendiek, P. et al. (March 2000). "The Tycho-2 catalogue of the 2.5 million brightest stars". Astronomy and Astrophysics 355: L27–L30. ISSN 0004-6361. Bibcode: 2000A&A...355L..27H. 
  3. ↑ 3.0 3.1 3.2 3.3 3.4 3.5 3.6 Pepper, Joshua et al. (April 18, 2017). "KELT-11b: A Highly Inflated Sub-Saturn Exoplanet Transiting the V = 8 Subgiant HD 93396". The Astronomical Journal 153 (5): 215. doi:10.3847/1538-3881/aa6572. Bibcode: 2017AJ....153..215P. 
  4. ↑ 4.0 4.1 Houk, Nancy; Swift, Carrie (1999). Michigan catalogue of two-dimensional spectral types for the HD Stars; vol. 5. Bibcode: 1999mctd.book.....H. 
  5. ↑ "VSX : Detail for KELT-11". https://www.aavso.org/vsx/index.php?view=detail.top&oid=1546458. 
  6. ↑ 6.0 6.1 Chubak, Carly; Marcy, G. (January 2011). "Accurate Radial Velocities of 2284 FGKM Stars and 127 Standards". American Astronomical Society 43. 434.12. Bibcode: 2011AAS...21743412C. 
  7. ↑ 7.0 7.1 Anderson, E.; Francis, Ch. (May 2012). "XHIP: An extended hipparcos compilation". Astronomy Letters 38 (5): 331–346. doi:10.1134/S1063773712050015. ISSN 1063-7737. Bibcode: 2012AstL...38..331A. 
  8. ↑ 8.0 8.1 8.2 8.3 Ghezzi, L. (June 2018), "Retired A Stars Revisited: An Updated Giant Planet Occurrence Rate as a Function of Stellar Metallicity and Mass", The Astrophysical Journal 860 (2): 18, doi:10.3847/1538-4357/aac37c, Bibcode: 2018ApJ...860..109G 
  9. ↑ 9.0 9.1 Kervella, P.; Thévenin, F.; Di Folco, E.; Ségransan, D. (April 8, 2004). "The angular sizes of dwarf stars and subgiants: Surface brightness relations calibrated by interferometry". Astronomy & Astrophysics 426 (1): 297–307. doi:10.1051/0004-6361:20035930. ISSN 0004-6361. Bibcode: 2004A&A...426..297K. 
  10. ↑ 10.0 10.1 10.2 10.3 10.4 Beatty, Thomas G.; Stevens, Daniel J.; Collins, Karen A.; Colón, Knicole D.; James, David J.; Kreidberg, Laura; Pepper, Joshua; Rodriguez, Joseph E. et al. (June 27, 2017). "Determining Empirical Stellar Masses and Radii from Transits and Gaia Parallaxes as Illustrated by Spitzer Observations of KELT-11b". The Astronomical Journal 154 (1): 25. doi:10.3847/1538-3881/aa7511. ISSN 1538-3881. Bibcode: 2017AJ....154...25B. 
  11. ↑ 11.0 11.1 Brewer, John M.; Fischer, Debra A.; Valenti, Jeff A.; Piskunov, Nikolai (August 26, 2016). "Spectral Properties of Cool Stars: Extended Abundance Analysis of 1,617 Planet-search Stars". The Astrophysical Journal Supplement Series 225 (2): 32. doi:10.3847/0067-0049/225/2/32. ISSN 0067-0049. Bibcode: 2016ApJS..225...32B. 
  12. ↑ "HD 93396". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=HD+93396. 
  13. ↑ 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. doi:10.1093/mnras/stx2219. ISSN 0035-8711. Bibcode: 2017MNRAS.472.3805G. 
  14. ↑ Colón, Knicole D.; Kreidberg, Laura; Line, Michael; Welbanks, Luis; Madhusudhan, Nikku; Beatty, Thomas; Tamburo, Patrick; Stevenson, Kevin B. et al. (November 23, 2020). "An Unusual Transmission Spectrum for the Sub-Saturn KELT-11b Suggestive of a Subsolar Water Abundance". The Astronomical Journal 160 (6): 280. doi:10.3847/1538-3881/abc1e9. Bibcode: 2020AJ....160..280C. 
  15. ↑ Changeat, Q.; Edwards, B.; Al-Refaie, A. F.; Morvan, M.; Tsiaras, A.; Waldmann, I. P.; Tinetti, G. (November 13, 2020). "KELT-11 b: Abundances of Water and Constraints on Carbon-bearing Molecules from the Hubble Transmission Spectrum". The Astronomical Journal 160 (6): 260. doi:10.3847/1538-3881/abbe12. Bibcode: 2020AJ....160..260C. 
  16. ↑ Ivshina, Ekaterina S.; Winn, Joshua N. (April 8, 2022). "TESS Transit Timing of Hundreds of Hot Jupiters". The Astrophysical Journal Supplement Series 259 (2): 62. doi:10.3847/1538-4365/ac545b. ISSN 0067-0049. Bibcode: 2022ApJS..259...62I. 



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