HD 176693
Star in the constellation Draco
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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.[6] The star is predicted to come as close as 23.1 light-years in 1.6 million years.[10] It has an apparent visual magnitude of 8.83,[3] which is too faint to be viewed with the naked eye.
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Draco[1] |
| Right ascension | 18h 59m 08.684s[2] |
| Declination | 48° 25′ 23.60″[2] |
| Apparent magnitude (V) | 8.83[3] |
| Characteristics | |
| Evolutionary stage | Main sequence |
| Spectral type | F8V[4] |
| B−V color index | 0.51[5] |
| Astrometry | |
| Radial velocity (Rv) | −54.76±0.18[6] km/s |
| Proper motion (μ) | RA: 4.704±0.013 mas/yr[2] Dec.: 9.263±0.016 mas/yr[2] |
| Parallax (π) | 11.2176±0.0126 mas[2] |
| Distance | 290.8 ± 0.3 ly (89.1 ± 0.1 pc) |
| Details[7] | |
| Mass | 1.05±0.04 M☉ |
| Radius | 1.253±0.051 R☉ |
| Luminosity | 1.864[8] 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[5] 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[9] | |
| Database references | |
| SIMBAD | data |
The spectrum of HD 176693 matches an F-type main-sequence star with a stellar classification of F8V.[4] The star is older than the Sun, at 7.15 billion years. It is slightly and uniformly[11] depleted in heavy elements compared to the Sun, having about 75% of the solar abundance of iron and other heavy elements.[7] HD 176693 is a chromospherically inactive star,[5] although there is weak evidence for tidal spin-up due to star-planet interaction.[12]
HD 176693 is 5% more massive than the Sun and has a 25% larger radius.[7] It is radiating 1.9[8] 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.[7] As of 2016, multiplicity surveys have not detect any stellar companions to HD 176693.[13]
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%,[14] it was confirmed in 2016.[15]
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.[7] The planet may also be a captured body originating from elsewhere.[16]
| Companion (in order from star) |
Mass | Semimajor axis (AU) |
Orbital period (days) |
Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| b | ≥ 0.02[14] MJ | — | 2.465024±0.000005 | — | 81.85±0.10° | 0.86±0.04 R🜨 |
