HD 176693
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| 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 mas/yr[1] Dec.: 9.263±0.016 mas/yr[1] |
| Parallax (π) | 11.2176 ± 0.0126 mas[1] |
| Distance | 290.8 ± 0.3 ly (89.1 ± 0.1 pc) |
| Details[6] | |
| Mass | 1.05±0.04 M☉ |
| Radius | 1.253±0.051 R☉ |
| Luminosity | 1.864[7] L☉ |
| Surface gravity (log g) | 4.318+0.08 −0.089 cgs |
| Temperature | 6,080±65 K |
| Metallicity [Fe/H] | −0.138+0.043 −0.042 dex |
| Rotation | 12.89±0.19 d |
| Rotational velocity (v sin i) | 2.8±1.0 km/s |
| Age | 7.15±1.61[4] Gyr |
| Other designations | |
| Database references | |
| SIMBAD | data |
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]
| 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
- ^ a b c d 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.
- ^ a b Høg, E.; et al. (March 2000), "The Tycho-2 catalogue of the 2.5 million brightest stars", Astronomy and Astrophysics, 355: L27–L30, Bibcode:2000A&A...355L..27H, doi:10.1888/0333750888/2862.
- ^ a b 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, arXiv:1306.6011, Bibcode:2013MNRAS.434.1422M, doi:10.1093/mnras/stt1095, S2CID 59269553.
- ^ a b c Booth, R. S.; et al. (2020), "Chromospheric emission of solar-type stars with asteroseismic ages", Monthly Notices of the Royal Astronomical Society, 491 (1): 455–467, arXiv:1910.12557, Bibcode:2020MNRAS.491..455B, doi:10.1093/mnras/stz3039.
- ^ a b Gaia Collaboration (May 2022), "Gaia DR3 Part 1. Main source", VizieR Online Data Catalog, Bibcode:2022yCat.1355....0G, doi:10.26093/cds/vizier.1355.
- ^ a b c d e f Kamiaka, Shoya; et al. (2019), "The Misaligned Orbit of the Earth-sized Planet Kepler-408b", The Astronomical Journal, 157 (4): 137, arXiv:1902.02057, Bibcode:2019AJ....157..137K, doi:10.3847/1538-3881/ab04a9, S2CID 118909208.
- ^ a b 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, arXiv:1906.12308, Bibcode:2019MNRAS.488.1558B, doi:10.1093/mnras/stz1804.
- ^ "Kepler-408", SIMBAD, Centre de données astronomiques de Strasbourg, retrieved 1 July 2021
- ^ Bailer-Jones, C.A.L.; et al. (2018), "New stellar encounters discovered in the second Gaia data release", Astronomy & Astrophysics, 616: A37, arXiv:1805.07581, Bibcode:2018A&A...616A..37B, doi:10.1051/0004-6361/201833456, S2CID 56269929.
- ^ 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, arXiv:2005.09846, Bibcode:2020MNRAS.495.3961L, doi:10.1093/mnras/staa1420.
- ^ Metcalfe, Travis S.; Egeland, Ricky (2019), "Understanding the Limitations of Gyrochronology for Old Field Stars", The Astrophysical Journal, 871 (1): 39, arXiv:1811.11905, Bibcode:2019ApJ...871...39M, doi:10.3847/1538-4357/aaf575, S2CID 119405127.
- ^ 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, arXiv:1604.05744, Bibcode:2016AJ....152....8K, doi:10.3847/0004-6256/152/1/8, S2CID 119110229.
- ^ a b 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, arXiv:1401.4195, Bibcode:2014ApJS..210...20M, doi:10.1088/0067-0049/210/2/20, S2CID 10760418.
- ^ Campante, T. L.; et al. (2016), "Spin–Orbit Alignment of Exoplanet Systems: Ensemble Analysis Using Asteroseismology", The Astrophysical Journal, 819 (1): 85, arXiv:1601.06052, Bibcode:2016ApJ...819...85C, doi:10.3847/0004-637X/819/1/85, S2CID 56307453.
- ^ 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, arXiv:2008.08587, Bibcode:2020ApJ...902L...5P, doi:10.3847/2041-8213/abb952, S2CID 221186597.
