HD 146389

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'.

WASP-38 / Irena
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]
Distance446 ± 3 ly
(136.8 ± 0.8 pc)
Details
Mass1.203±0.036[4] M☉
Radius1.331+0.030
−0.025[4] R☉
Luminosity2.838±0.024[1] L☉
Surface gravity (log g)4.25+0.012
−0.013[2] cgs
Temperature6,150±80[4] K
Metallicity [Fe/H]0.06[5] dex
Rotational velocity (v sin i)8.6±0.4[2] km/s
Age350 Myr[5]
400±500[6] Myr
Other designations
BD+10°2980, Gaia DR2 4453211899986180352, HD 146389, SAO 102042, 2MASS J16155036+1001572, WASP 38[7]
Database references
SIMBADdata

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]

Planetary system

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]

The WASP-38 planetary system[2]
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

References
  1. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  2. Barros, S. C. C.; et al. (2011). "WASP-38b: A transiting exoplanet in an eccentric, 6.87d period orbit". Astronomy & Astrophysics. 525: A54. arXiv:1010.0849. Bibcode:2011A&A...525A..54B. doi:10.1051/0004-6361/201015800. S2CID 5723076.
  3. Ehrenreich, D.; Désert, J.-M. (2011). "Mass-loss rates for transiting exoplanets". Astronomy & Astrophysics. 529: A136. arXiv:1103.0011. Bibcode:2011A&A...529A.136E. doi:10.1051/0004-6361/201016356. S2CID 119302960.
  4. Brown, D. J. A.; et al. (2012). "Analysis of Spin-Orbit Alignment in the Wasp-32, Wasp-38, and Hat-P-27/Wasp-40 Systems". The Astrophysical Journal. 760 (2): 139. arXiv:1303.5649. Bibcode:2012ApJ...760..139B. doi:10.1088/0004-637X/760/2/139. S2CID 54033638.
  5. Delgado Mena, E.; et al. (April 2015). "Li abundances in F stars: planets, rotation, and Galactic evolution". Astronomy & Astrophysics. 576: A69. arXiv:1412.4618. Bibcode:2015A&A...576A..69D. doi:10.1051/0004-6361/201425433. S2CID 56051637. A69.
  6. Bonfanti, A.; et al. (2015). "Revising the ages of planet-hosting stars". Astronomy and Astrophysics. 575: A18. arXiv:1411.4302. Bibcode:2015A&A...575A..18B. doi:10.1051/0004-6361/201424951. S2CID 54555839.
  7. "HD 146389". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2020-01-18.
  8. "IAU Catalog of Star Names (IAU-CSN)". IAU Division C Working Group on Star Names (WGSN). January 1, 2021. Retrieved 2021-01-18.
  9. "The IAU announces names for WASP exoplanets". WASP Planets. 5 January 2020. Retrieved 2021-01-18.
  10. Salz, M.; et al. (2015). "High-energy irradiation and mass loss rates of hot Jupiters in the solar neighborhood". Astronomy & Astrophysics. 576: A42. arXiv:1502.00576. Bibcode:2015A&A...576A..42S. doi:10.1051/0004-6361/201425243. S2CID 55139248.
  11. Simpson, E. K.; et al. (2011). "The spin-orbit angles of the transiting exoplanets WASP-1b, WASP-24b, WASP-38b and HAT-P-8b from Rossiter-Mc Laughlin observations". Monthly Notices of the Royal Astronomical Society. 414 (4): 3023–3035. arXiv:1011.5664. Bibcode:2011MNRAS.414.3023S. doi:10.1111/j.1365-2966.2011.18603.x. S2CID 46522188.
  12. Albrecht, Simon; et al. (2012), "Obliquities of Hot Jupiter host stars: Evidence for tidal interactions and primordial misalignments", The Astrophysical Journal, 757 (1): 18, arXiv:1206.6105, Bibcode:2012ApJ...757...18A, doi:10.1088/0004-637X/757/1/18, S2CID 17174530
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