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  • 21 Aug, 2019

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WASP-38b
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. It is invisible to the naked eye with an apparent visual magnitude of 9.4 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. The star is known to host one exoplanet, designated WASP-38b or formally named 'Iztok'.

The stellar classification of HD 146389 is F8, 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. 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. The star is 33% larger and 20% more massive than the Sun. It is radiating nearly three times the luminosity of the Sun at an effective temperature of 6,150 K.

Planetary system

The "hot Jupiter" class planet WASP-38 b, later named 'Iztok', was discovered around HD 146389 in 2010. The planet is losing significant amount of gas, estimated to 0.023 Earth masses per billion years. 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.

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
−43°.

The WASP-38 planetary system
Companion
(in order from star) 		Mass Semimajor axis
(AU) 		Orbital period
(days) 		Eccentricity Inclination Radius
b (Iztok) 2.691±0.036 MJ 0.07522
−0.00075 		6.871815
−0.000042 		0.0314
−0.0041 		89.69
−0.25° 		1.094
−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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