Observation data Epoch J2000 Equinox J2000 | |
---|---|
Constellation | Hercules |
Right ascension | 16h 15m 50.36526s [1] |
Declination | 10° 01′ 57.2844″ [1] |
Apparent magnitude (V) | 9.447±0.024 [2] |
Characteristics | |
Spectral type | F8 [3] |
B−V color index | 0.476 |
J−H color index | 0.181 |
J−K color index | 0.289 |
Astrometry | |
Radial velocity (Rv) | −9.06±0.53 [1] km/s |
Proper motion (μ) |
RA: −31.073
[1]
mas/
yr Dec.: −39.171 [1] mas/ yr |
Parallax (π) | 7.3115 ± 0.0429 mas [1] |
Distance | 446 ± 3
ly (136.8 ± 0.8 pc) |
Details | |
Mass | 1.203±0.036 [4] M☉ |
Radius | 1.331+0.030 −0.025 [4] R☉ |
Luminosity | 2.838±0.024 [1] L☉ |
Surface gravity (log g) | 4.25+0.012 −0.013 [2] cgs |
Temperature | 6,150±80 [4] K |
Metallicity [Fe/H] | 0.06 [5] dex |
Rotational velocity (v sin i) | 8.6±0.4 [2] km/s |
Age | 350 Myr
[5] 400±500 [6] Myr |
Other designations | |
Database references | |
SIMBAD | data |
HD 146389 (also known as WASP-38), is a star with a yellow-white hue in the northern constellation of Hercules. The star was given the formal name Irena by the International Astronomical Union in January 2020. [8] [9] It is invisible to the naked eye with an apparent visual magnitude of 9.4 [2] The star is located at a distance of approximately 446 light years from the Sun based on parallax, but is drifting closer with a radial velocity of −9 km/s. [1] The star is known to host one exoplanet, designated WASP-38b or formally named 'Iztok'.
The stellar classification of HD 146389 is F8, [3] which is an F-type star of uncertain luminosity class. The age of the star is uncertain. It shows a low lithium abundance, which suggests an age of more than 5 billion years. However, the rotation rate indicates an age closer to one billion. [2] The study in 2015 utilizing Chandra X-ray Observatory, have failed to detect any X-ray emissions from the star during planetary eclipse, which may indicate an unusually low coronal activity or the presence of absorbing gas ring formed by atmosphere escaping planet WASP-38 b. [10] The star is 33% larger and 20% more massive than the Sun. [4] It is radiating nearly three [1] times the luminosity of the Sun at an effective temperature of 6,150 K. [4]
The "hot Jupiter" class planet WASP-38 b, later named 'Iztok', was discovered around HD 146389 in 2010. [2] The planet is losing significant amount of gas, estimated to 0.023 Earth masses per billion years. [3] In 2013, it was found the planetary orbit is surprisingly well aligned with the rotational axis of the parent star, despite the noticeable orbital eccentricity. [11] [4]
A 2012 study, utilizing a
Rossiter–McLaughlin effect, have determined the orbital plane of WASP-38b is poorly constrained but probably aligned with the equatorial plane of the star, misalignment equal to 15+33
−43°.
[12]
Companion (in order from star) |
Mass |
Semimajor axis ( AU) |
Orbital period ( days) |
Eccentricity | Inclination | Radius |
---|---|---|---|---|---|---|
b (Iztok) | 2.691±0.036 MJ | 0.07522+0.00074 −0.00075 |
6.871815+0.000045 −0.000042 |
0.0314+0.0046 −0.0041 |
89.69+0.3 −0.25 ° |
1.094+0.029 −0.028 RJ |