Non-local thermal equilibrium spectra of atmospheric molecules for exoplanets
Authors: Wright Sam , Waldmann Ingo , Yurchenko Sergey 
Published: September 2022

&lt;p&gt;Here we present a study of non-local thermodynamic equilibrium (LTE) effects on the exoplanetary spectra of a collection of molecules that are key in the investigation of exoplanet atmospheres: water, methane, carbon monoxide, and titanium oxide. These molecules are chosen as examples of different spectral ranges (infrared and ultraviolet), molecular types (diatomics and polyatomics), and spectral types (electronic and rovibrational); the importance of different vibrational bands in forming distinct non-LTE spectral features is investigated. Most notably, such key spectral signatures for distinguishing between the LTE and non-LTE cases include: for CH&lt;sub&gt;4&lt;/sub&gt;&lt;span class=&quot;Apple-converted-space&quot;&gt;&amp;#160;&lt;/span&gt;the 3.15&amp;#160;&lt;span class=&quot;inline-formula no-formula-id&quot;&gt;&lt;span id=&quot;MathJax-Element-1-Frame&quot; class=&quot;MathJax&quot; tabindex=&quot;0&quot; role=&quot;presentation&quot; data-mathml=&quot;&lt;math xmlns=&amp;quot;http://www.w3.org/1998/Math/MathML&amp;quot;&gt;&amp;#x03BC;&quot;&gt;&lt;span id=&quot;MathJax-Span-1&quot; class=&quot;math&quot;&gt;&lt;span id=&quot;MathJax-Span-2&quot; class=&quot;mrow&quot;&gt;&lt;span id=&quot;MathJax-Span-3&quot; class=&quot;mi&quot;&gt;&amp;#956;&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;m band region; for H&lt;sub&gt;2&lt;/sub&gt;O the 2.0 and 2.7&amp;#160;&lt;span id=&quot;MathJax-Element-2-Frame&quot; class=&quot;MathJax&quot; tabindex=&quot;0&quot; role=&quot;presentation&quot; data-mathml=&quot;&lt;math xmlns=&amp;quot;http://www.w3.org/1998/Math/MathML&amp;quot;&gt;&amp;#x03BC;&quot;&gt;&lt;span id=&quot;MathJax-Span-4&quot; class=&quot;math&quot;&gt;&lt;span id=&quot;MathJax-Span-5&quot; class=&quot;mrow&quot;&gt;&lt;span id=&quot;MathJax-Span-6&quot; class=&quot;mi&quot;&gt;&amp;#956;&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;m band regions; for TiO, a strong variation in intensity in the bands between 0.5 and 0.75&amp;#160;&lt;span id=&quot;MathJax-Element-3-Frame&quot; class=&quot;MathJax&quot; tabindex=&quot;0&quot; role=&quot;presentation&quot; data-mathml=&quot;&lt;math xmlns=&amp;quot;http://www.w3.org/1998/Math/MathML&amp;quot;&gt;&amp;#x03BC;&quot;&gt;&lt;span id=&quot;MathJax-Span-7&quot; class=&quot;math&quot;&gt;&lt;span id=&quot;MathJax-Span-8&quot; class=&quot;mrow&quot;&gt;&lt;span id=&quot;MathJax-Span-9&quot; class=&quot;mi&quot;&gt;&amp;#956;&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;m; and a sole CO signature between 5 and 6&amp;#160;&lt;span id=&quot;MathJax-Element-4-Frame&quot; class=&quot;MathJax&quot; tabindex=&quot;0&quot; role=&quot;presentation&quot; data-mathml=&quot;&lt;math xmlns=&amp;quot;http://www.w3.org/1998/Math/MathML&amp;quot;&gt;&amp;#x03BC;&quot;&gt;&lt;span id=&quot;MathJax-Span-10&quot; class=&quot;math&quot;&gt;&lt;span id=&quot;MathJax-Span-11&quot; class=&quot;mrow&quot;&gt;&lt;span id=&quot;MathJax-Span-12&quot; class=&quot;mi&quot;&gt;&amp;#956;&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;m. The analysis is based on the ExoMol cross-sections&amp;#160;and takes advantage of the extensive vibrational assignment of these molecular line lists in the ExoMol data base. We examine LTE and non-LTE cross-sections&amp;#160;under conditions consistent with those on WASP-12b and WASP-76b using the empirically motivated bi-temperature Treanor model.&lt;/span&gt;&lt;/p&gt;
&lt;p&gt;An example variation between the LTE case and Non-LTE case with our approach can be seen here for an important Methane band shown at high resolution and low pressure:&lt;/p&gt;
&lt;p&gt;&lt;span class=&quot;inline-formula no-formula-id&quot;&gt;&lt;img src=&quot;&quot; alt=&quot;&quot; width=&quot;437&quot; height=&quot;316&quot; /&gt;&lt;/span&gt;&lt;/p&gt;
&lt;p&gt;&amp;#160;&lt;/p&gt;
&lt;p&gt;&amp;#160;&lt;/p&gt;