Astronomy:HD 176693

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Short description: Star in the constellation Draco
HD 176693
Observation data
Equinox J2000.0]] (ICRS)
Constellation Draco
Right ascension  18h 59m 08.684s[1]
Declination 48° 25′ 23.60″[1]
Apparent magnitude (V) 8.83[2]
Characteristics
Evolutionary stage Main sequence
Spectral type F8V[3]
B−V color index 0.51[4]
Astrometry
Radial velocity (Rv)−54.76±0.18[5] km/s
Proper motion (μ) RA: 4.704±0.013[1] mas/yr
Dec.: 9.263±0.016[1] mas/yr
Parallax (π)11.2176 ± 0.0126[1] mas
Distance290.8 ± 0.3 ly
(89.1 ± 0.1 pc)
Details[6]
Mass1.05±0.04 M☉
Radius1.253±0.051 R☉
Luminosity1.864[7] L☉
Surface gravity (log g)4.318+0.08−0.089 cgs
Temperature6,080±65 K
Metallicity [Fe/H]−0.138+0.043−0.042 dex
Rotation12.89±0.19 d
Rotational velocity (v sin i)2.8±1.0 km/s
Age7.15±1.61[4] Gyr
Other designations
BD+48 2806, HD 176693, Kepler-408, KOI-1612, KIC 10963065, TYC 3545-1227-1, GSC 03545-01227, 2MASS J18590868+4825236, Gaia EDR3 2131593785132997632[8]
Database references
SIMBADdata

HD 176693, also known as Kepler-408, is a star with a close orbiting exoplanet in the northern constellation of Draco. It is located at a distance of 291 light years from the Sun based on parallax measurements, but it is drifting closer with a radial velocity of −55 km/s.[5] The star is predicted to come as close as 23.1 light-years in 1.6 million years.[9] It has an apparent visual magnitude of 8.83,[2] which is too faint to be viewed with the naked eye.

The spectrum of HD 176693 matches an F-type main-sequence star with a stellar classification of F8V.[3] The star is older than the Sun, at 7.15 billion years. It is slightly and uniformly[10] depleted in heavy elements compared to the Sun, having about 75% of the solar abundance of iron and other heavy elements.[6] HD 176693 is a chromospherically inactive star,[4] although there is weak evidence for tidal spin-up due to star-planet interaction.[11]

HD 176693 is 5% more massive than the Sun and has a 25% larger radius.[6] It is radiating 1.9[7] times the luminosity of the Sun from its photosphere at an effective temperature of 6,080 K. The star is spinning with a rotation period of 12.89 days.[6] As of 2016, multiplicity surveys have not detect any stellar companions to HD 176693.[12]

Planetary system

In 2014, a transiting Sub-Earth planet b was detected on a tight 2.5 day orbit. Initially reported with a relatively low confidence of 97.9%,[13] it was confirmed in 2016.[14]

The planetary orbit is inclined to the equatorial plane of the star by 41.7+5.1−3.5°. Such strong spin-orbit misalignment is unique for a sub-Earth transiting planet, and needs either additional giant planets in the system or a history of close stellar encounters to explain it.[6] The planet may also be a captured body originating from elsewhere.[15]

The Kepler-408 planetary system[6]
Companion
(in order from star) 		Mass Semimajor axis
(AU) 		Orbital period
(days) 		Eccentricity Inclination Radius
b ≥ 0.02[13] MJ — 2.465024±0.000005 — 81.85±0.10° 0.86±0.04 R⊕

References

  1. ↑ 1.0 1.1 1.2 1.3 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 Høg, E. et al. (March 2000), "The Tycho-2 catalogue of the 2.5 million brightest stars", Astronomy and Astrophysics 355: L27–L30, doi:10.1888/0333750888/2862, Bibcode: 2000A&A...355L..27H. 
  3. ↑ 3.0 3.1 Molenda-Żakowicz, J. et al. (2013), "Atmospheric parameters of 169 F-, G-, K- and M-type stars in the Kepler field", Monthly Notices of the Royal Astronomical Society 434 (2): 1422, doi:10.1093/mnras/stt1095, Bibcode: 2013MNRAS.434.1422M. 
  4. ↑ 4.0 4.1 4.2 Booth, R. S. et al. (2020), "Chromospheric emission of solar-type stars with asteroseismic ages", Monthly Notices of the Royal Astronomical Society 491: 455–467, doi:10.1093/mnras/stz3039, Bibcode: 2020MNRAS.491..455B. 
  5. ↑ 5.0 5.1 Gaia Collaboration (May 2022), "Gaia DR3 Part 1. Main source", VizieR Online Data Catalog, doi:10.26093/cds/vizier.1355, Bibcode: 2022yCat.1355....0G. 
  6. ↑ 6.0 6.1 6.2 6.3 6.4 6.5 Kamiaka, Shoya et al. (2019), "The Misaligned Orbit of the Earth-sized Planet Kepler-408b", The Astronomical Journal 157 (4): 137, doi:10.3847/1538-3881/ab04a9, Bibcode: 2019AJ....157..137K. 
  7. ↑ 7.0 7.1 Brito, Ana; Lopes, Ilídio (2019), "The partial ionization zone of heavy elements in F-stars: A study on how it correlates with rotation", Monthly Notices of the Royal Astronomical Society 488 (2): 1558–1571, doi:10.1093/mnras/stz1804, Bibcode: 2019MNRAS.488.1558B. 
  8. ↑ "Kepler-408". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=Kepler-408. 
  9. ↑ Bailer-Jones, C.A.L. et al. (2018), "New stellar encounters discovered in the second Gaia data release", Astronomy & Astrophysics 616: A37, doi:10.1051/0004-6361/201833456, Bibcode: 2018A&A...616A..37B. 
  10. ↑ Ramírez, I. et al. (2020), "Detailed chemical compositions of planet-hosting stars – I. Exploration of possible planet signatures", Monthly Notices of the Royal Astronomical Society 495 (4): 3961–3973, doi:10.1093/mnras/staa1420, Bibcode: 2020MNRAS.495.3961L. 
  11. ↑ Metcalfe, Travis S.; Egeland, Ricky (2019), "Understanding the Limitations of Gyrochronology for Old Field Stars", The Astrophysical Journal 871 (1): 39, doi:10.3847/1538-4357/aaf575, Bibcode: 2019ApJ...871...39M. 
  12. ↑ Kraus, Adam L. et al. (2016), "The Impact of Stellar Multiplicity on Planetary Systems. I. The Ruinous Influence of Close Binary Companions", The Astronomical Journal 152 (1): 8, doi:10.3847/0004-6256/152/1/8, Bibcode: 2016AJ....152....8K. 
  13. ↑ 13.0 13.1 Marcy, Geoffrey W. et al. (2014), "Masses, Radii, and Orbits of Small Kepler Planets: The Transition from Gaseous to Rocky Planets", The Astrophysical Journal Supplement Series 210 (2): 20, doi:10.1088/0067-0049/210/2/20, Bibcode: 2014ApJS..210...20M. 
  14. ↑ Campante, T. L. et al. (2016), "Spin–Orbit Alignment of Exoplanet Systems: Ensemble Analysis Using Asteroseismology", The Astrophysical Journal 819 (1): 85, doi:10.3847/0004-637X/819/1/85, Bibcode: 2016ApJ...819...85C. 
  15. ↑ Petrovich, Cristobal et al. (2020), "A Disk-driven Resonance as the Origin of High Inclinations of Close-in Planets", The Astrophysical Journal Letters 902 (1): L5, doi:10.3847/2041-8213/abb952, Bibcode: 2020ApJ...902L...5P. 

Coordinates: Sky map 18h 59m 08.6847s, +48° 25′ 23.5990″



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