Observation data Epoch J2000 Equinox J2000 | |
---|---|
Constellation | Hercules |
Right ascension | 17h 05m 23.1475s [1] |
Declination | +33° 00′ 44.940″ [1] |
Apparent magnitude (V) | 12.759 [2] |
Characteristics | |
Spectral type | K2V |
Astrometry | |
Radial velocity (Rv) | -11.83 km/s |
Proper motion (μ) |
RA: −14.002(9)
mas/
yr
[1] Dec.: −36.751(11) mas/ yr [1] |
Parallax (π) | 6.1863 ± 0.0093 mas [1] |
Distance | 527.2 ± 0.8
ly (161.6 ± 0.2 pc) |
Details [3] | |
Mass | 0.750+0.015 −0.014 M☉ |
Radius | 0.7202+0.0095 −0.01 R☉ |
Luminosity | 0.27±0.04 [4] L☉ |
Surface gravity (log g) | 4.599±0.013 cgs |
Temperature | 4835+39 −35 K |
Metallicity | 0.044+0.060 −0.051 |
Rotation | 14.66±0.03 d [4] |
Rotational velocity (v sin i) | 0.5±0.5 [4] km/s |
Age | 12.4+4.4 −6.4 [4] Gyr |
Other designations | |
Database references | |
SIMBAD | data |
HAT-P-18 is a K-type main-sequence star about 530 light-years away. The star is very old and has a concentration of heavy elements similar to solar abundance. [4] A survey in 2015 detected very strong starspot activity on HAT-P-18. [6]
In 2010 a transiting hot Saturn-sized planet was detected. [2] Its equilibrium temperature is 841 K. [7]
In 2014, observations utilizing the Rossiter–McLaughlin effect detected an exoplanet, HAT-P-18b, on a retrograde orbit, with an angle between orbital plane of the planet and the parent star equatorial plane equal to 132±15°. [8]
Transit-timing variation measurements in 2015 did not detect additional planets in the system. [9]
In 2016, the transmission optical spectra of the planet indicated that the atmosphere is lacking detectable clouds or hazes, and is blue in color due to Rayleigh scattering of light. [10] The atmosphere seems to gradually evaporate, but at a slow rate - less than 2% of planetary mass is lost per one billion years. [11] By contrast, spectra taken in 2022 has showed an extensive hazes and clear evidence of water vapour, along with the tail of escaping helium. [12]
The dayside temperature of HAT-P-18b was measured in 2019 to be 1004+78
−94
K.
[13]
Companion (in order from star) |
Mass |
Semimajor axis ( AU) |
Orbital period ( days) |
Eccentricity | Inclination | Radius |
---|---|---|---|---|---|---|
b | 0.183+0.034 −0.032 MJ |
0.04649± | 5.508029±0.0000042 | 0.106+0.15 −0.084 |
88.79±0.21 ° | 0.947±0.044 RJ |
Observation data Epoch J2000 Equinox J2000 | |
---|---|
Constellation | Hercules |
Right ascension | 17h 05m 23.1475s [1] |
Declination | +33° 00′ 44.940″ [1] |
Apparent magnitude (V) | 12.759 [2] |
Characteristics | |
Spectral type | K2V |
Astrometry | |
Radial velocity (Rv) | -11.83 km/s |
Proper motion (μ) |
RA: −14.002(9)
mas/
yr
[1] Dec.: −36.751(11) mas/ yr [1] |
Parallax (π) | 6.1863 ± 0.0093 mas [1] |
Distance | 527.2 ± 0.8
ly (161.6 ± 0.2 pc) |
Details [3] | |
Mass | 0.750+0.015 −0.014 M☉ |
Radius | 0.7202+0.0095 −0.01 R☉ |
Luminosity | 0.27±0.04 [4] L☉ |
Surface gravity (log g) | 4.599±0.013 cgs |
Temperature | 4835+39 −35 K |
Metallicity | 0.044+0.060 −0.051 |
Rotation | 14.66±0.03 d [4] |
Rotational velocity (v sin i) | 0.5±0.5 [4] km/s |
Age | 12.4+4.4 −6.4 [4] Gyr |
Other designations | |
Database references | |
SIMBAD | data |
HAT-P-18 is a K-type main-sequence star about 530 light-years away. The star is very old and has a concentration of heavy elements similar to solar abundance. [4] A survey in 2015 detected very strong starspot activity on HAT-P-18. [6]
In 2010 a transiting hot Saturn-sized planet was detected. [2] Its equilibrium temperature is 841 K. [7]
In 2014, observations utilizing the Rossiter–McLaughlin effect detected an exoplanet, HAT-P-18b, on a retrograde orbit, with an angle between orbital plane of the planet and the parent star equatorial plane equal to 132±15°. [8]
Transit-timing variation measurements in 2015 did not detect additional planets in the system. [9]
In 2016, the transmission optical spectra of the planet indicated that the atmosphere is lacking detectable clouds or hazes, and is blue in color due to Rayleigh scattering of light. [10] The atmosphere seems to gradually evaporate, but at a slow rate - less than 2% of planetary mass is lost per one billion years. [11] By contrast, spectra taken in 2022 has showed an extensive hazes and clear evidence of water vapour, along with the tail of escaping helium. [12]
The dayside temperature of HAT-P-18b was measured in 2019 to be 1004+78
−94
K.
[13]
Companion (in order from star) |
Mass |
Semimajor axis ( AU) |
Orbital period ( days) |
Eccentricity | Inclination | Radius |
---|---|---|---|---|---|---|
b | 0.183+0.034 −0.032 MJ |
0.04649± | 5.508029±0.0000042 | 0.106+0.15 −0.084 |
88.79±0.21 ° | 0.947±0.044 RJ |