| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Leo[1] |
| Right ascension | 11h 14m 33.1613s[2] |
| Declination | +25° 42′ 37.392″[2] |
| Apparent magnitude (V) | 7.762±0.012[3] |
| Characteristics | |
| Evolutionary stage | Main sequence[4] |
| Spectral type | K1V[5] |
| B−Vcolor index | 0.843±0.022[3] |
| Variable type | Planetary transit variable |
| Astrometry | |
| Radial velocity (Rv) | −1.579±0.0011[6] km/s |
| Proper motion (μ) | RA: −107.534±0.091mas/yr[2] Dec.: 48.662±0.090mas/yr[2] |
| Parallax (π) | 46.412±0.022 mas[7] |
| Distance | 70.27 ± 0.03 ly (21.55 ± 0.01 pc) |
| Absolute magnitude (MV) | 6.14[8] |
| Details | |
| Mass | 0.773+0.015 −0.018[7] M☉ |
| Radius | 0.728±0.008[7] R☉ |
| Luminosity (bolometric) | 0.351±0.007[7] L☉ |
| Surface gravity (log g) | 4.52 ± 0.06[3] cgs |
| Temperature | 5212±43[7] K |
| Metallicity [Fe/H] | −0.30±0.03[3] dex |
| Rotation | 38.5±1.0[3] |
| Rotational velocity (v sin i) | 0.92±0.05[3] km/s |
| Age | 3.9+2.6 −2.03[7] Gyr |
| Other designations | |
| BD+26° 2184,GJ 3651,HD 97658,HIP 54906,SAO 81730,GSC 01981-01168,2MASS J11143316+2542374[9] | |
| Database references | |
| SIMBAD | data |
HD 97658 is astar with anexoplanetary companion in theequatorialconstellation ofLeo. The star is too dim to be seen with the naked eye, having anapparent visual magnitude of 7.76.[3] It is located at a distance of 70 light years based onparallax, but is slowly drifting closer with aradial velocity of −1.6 km/s.[6]
This is an ordinaryK-type main-sequence star with astellar classification of K1V.[5] The star has 77% of the mass and 73% of the radius of the Sun.[7] Estimates of the star's age ranges from four to six billion years.[7] It is spinning with arotation period of around 39 days[3] and shows amagnetic activity cycle of 9.6 years, which is slightly shorter than thesolar cycle. The chromospheric activity is lower than average for stars of this class.[10]
HD 97658 is radiating 35% of the luminosity of the Sun from itsphotosphere at aneffective temperature of 5,212 K.[7] The star has a lowmetallicity – the atmospheric abundance of elements with a higheratomic number than helium, which explains why it lies 0.46 magnitudes below average for main sequence stars of its type.[4]
On November 1, 2010, asuper-Earth was announced orbiting the star along withGliese 785 b as part of the NASA-UC Eta-Earth program. The planet orbits in just under 9.5 days and was originally thought to have a minimum mass of 8.2 ± 1.2 M🜨.[4] Spurred by the possibility of transits, additional data was acquired for less than a year which found a lower mass for the star and hence reduced the minimum mass of the planet to 6.4 ± 0.7 M🜨, and improved certainty on the time of possible transit. Transits of the planet were apparently detected and announced on September 12, 2011; this would make HD 97658 the second-to-brightest star with a transiting planet after55 Cancri and indicating a low-density planet likeGliese 1214 b.[3] However, the occurrence of transits was quietly retracted on April 11, 2012,[11] and three days later it was announced that observations by the MOST space telescope could not confirm transits.[12] Transits of radii larger than 1.87 R🜨 were ruled out.
Further transit measurements were taken in April 2012 and were confirmed with transit readings made in the following year, March and April 2013. It was determined that HD 97658 b had a diameter 2.34 times that of Earth.[13] Using a radial velocity mass of 7.86 M🜨 and the radius measured from the transits taken in 2012 and 2013 and in early 2014, the density of the planet was calculated as 3.44 g cm−3.[13] It is likely therefore that the super-Earth exoplanet HD 97658 b has a large rocky core covered with a thick layer of volatiles, either a deep ocean of water or a thick atmosphere possibly made up of a mixture of helium and hydrogen.[13] The gravity on this exoplanet's surface is about 1.6 times greater than that of Earth's.[13][14]The planetary transmission spectrum of HD 97658 b taken in 2020 have revealed presence of clouds up to millibar pressure. Although no conclusion can be made on atmosphere composition, best model fitting is obtained with hydrogen-helium envelope withcarbon monoxide andmethane admixture.[10] No helium was detected at HD 97658 b in 2020 though.[15]
| Companion (in order from star) | Mass | Semimajor axis (AU) | Orbital period (days) | Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| b | 7.81+0.55 −0.44 M🜨 | 0.0796 ± 0.0012 | 9.49073±0.00015 | 0.03+0.034 −0.021 | 89.6±0.1° | 2.247+0.098 −0.095 R🜨 |
