Magnetised stellar wind and their influence in the upper atmosphere of HD 209458b

VILLARREAL D'ANGELO, CAROLINA S.; ESQUIVEL, ALEJANDRO; SCHNEITER, MATIAS; SGRÓ, MARIO

Conferencia; BCool 2018: Seventh BCool meeting; 2018

<!-- /* Font Definitions */@font-face{font-family:"Cambria Math";panose-1:2 4 5 3 5 4 6 3 2 4;mso-font-charset:0;mso-generic-font-family:auto;mso-font-pitch:variable;mso-font-signature:-536870145 1107305727 0 0 415 0;}@font-face{font-family:Calibri;panose-1:2 15 5 2 2 2 4 3 2 4;mso-font-charset:0;mso-generic-font-family:auto;mso-font-pitch:variable;mso-font-signature:-536870145 1073786111 1 0 415 0;}@font-face{font-family:alpha;panose-1:0 0 0 0 0 0 0 0 0 0;mso-font-alt:"Times New Roman";mso-font-charset:0;mso-generic-font-family:roman;mso-font-format:other;mso-font-pitch:auto;mso-font-signature:0 0 0 0 0 0;} /* Style Definitions */p.MsoNormal, li.MsoNormal, div.MsoNormal{mso-style-unhide:no;mso-style-qformat:yes;mso-style-parent:"";margin:0in;margin-bottom:.0001pt;mso-pagination:widow-orphan;font-size:12.0pt;font-family:"Times New Roman";mso-fareast-font-family:Calibri;mso-fareast-theme-font:minor-latin;}.MsoChpDefault{mso-style-type:export-only;mso-default-props:yes;font-family:Calibri;mso-ascii-font-family:Calibri;mso-ascii-theme-font:minor-latin;mso-fareast-font-family:Calibri;mso-fareast-theme-font:minor-latin;mso-hansi-font-family:Calibri;mso-hansi-theme-font:minor-latin;mso-bidi-font-family:"Times New Roman";mso-bidi-theme-font:minor-bidi;mso-fareast-language:EN-US;}@page WordSection1{size:8.5in 11.0in;margin:70.85pt 70.85pt 70.85pt 70.85pt;mso-header-margin:.5in;mso-footer-margin:.5in;mso-paper-source:0;}div.WordSection1{page:WordSection1;}-->Lyman  alpha observations during an exoplanet transit have proved to be veryuseful to study the interaction between the stellar wind and the planetaryatmosphere. They have been extensively used to constrain planetary systemparameters that are not directly observed, such as the planetary mass lossrate. In this way, Ly alpha observations can be a powerful tool to infer theexistence of a planetary magnetic field, since it is expected that the latterwill affect the escaping planetary material.To explore the effect that magnetic fields have on the Ly alpha absorption ofHD 209458b, we run a set of 3D MHD simulations including dipolar magneticfields for the planet and the star. We assume values for the surface magneticfield at the poles of the planet in the range of [0-5] G, and from 1 to 5 G atthe poles of the star.Our models also include collisional and photo-ionisation, radiativerecombination, and an approximation for the radiation pressure. Our resultsshow that the magnetic field of the planet and the star change the shape of theLy alpha absorption profile, since it controls the extent of the planetarymagnetosphere and the amount of neutral material inside it. The model that best reproduces the absorption observed in HD 209458b (withcanonical values for the stellar wind parameters) corresponds to a dipoleplanetary field of less than 1 gauss at the poles.