Rossiter–McLaughlin effect

<h2 id="description">Description</h2>
<p>The Rossiter–McLaughlin effect is a <a href="/facts/Astronomical_spectroscopy/NDGQ7mmM">spectroscopic</a> phenomenon observed when either an <a href="/facts/Eclipsing_binary/TYlDe1bD">eclipsing binary</a>'s secondary star or an <a href="/facts/Extrasolar_planet/zjfmqfUf">extrasolar planet</a> is seen to <a href="/facts/Astronomical_transit/4s6Mll1a">transit</a> across the face of the primary or parent star.
</p><p>As the main star rotates on its axis, one quadrant of its <a href="/facts/Photosphere/32a139LB">photosphere</a> will be seen to be coming towards the viewer, and the other visible quadrant to be moving away. These motions produce <a href="/facts/Blueshift/v8XBtGKH">blueshifts</a> and <a href="/facts/Redshift/Qfl4VjDF">redshifts</a>, respectively, in the star's <a href="/facts/Stellar_spectrum/NDGQ7mmM">spectrum</a>, usually observed as a broadening of the <a href="/facts/Spectral_line/HuI4Bj5f">spectral lines</a>. When the secondary star or planet transits the primary, it blocks part of the latter's disc, preventing some of the shifted light from reaching the observer. That causes the observed mean redshift of the primary star as a whole to vary from its normal value. As the transiting object moves across to the other side of the star's disc, the redshift anomaly will switch from being positive to being negative, or vice versa.
</p><p>The amplitude of the redshift anomaly depends on the mutual alignment between the primary star's equator and the secondary's path of transit. The maximum amplitude, which is determined by the primary's <a href="/facts/Stellar_rotation/N0VzIXLC">projected rotational velocity</a> <i>v</i> sin <i>i</i>, is achieved when the two are perfectly aligned; the secondary will start transiting the primary at the part of the star's disc with maximum blueshift, and end the transit at maximum redshift. Misalignment between the two leads to a decrease in the Rossiter–McLaughlin effect which is proportional to the cosine of the angle.
</p><p>The Rossiter–McLaughlin effect can only directly measure projected obliquity (typically indicated with <i>λ</i>) as it only measures the angle projected along the <a href="/facts/Line_of_sight/uhfdzGYv">line of sight</a>. For determination of the three-dimensional true obliquity (typically indicted with <i>ψ</i>), the projected obliquity needs to be combined with the values of inclination of the <a href="/facts/Axial_tilt/kt7KwL3v">primary's equator</a> obtained by comparing the projected rotational velocity with the true <a href="/facts/Rotation_period_(astronomy)/vHcCt6cu">rotation period</a>, and of the <a href="/facts/Orbital_inclination/TQCFWyfd">secondary's orbit</a> obtained from the impact parameter of transit and/or <a href="/facts/Doppler_spectroscopy/0uTvj3pq">doppler spectroscopy</a>, which instead measure the inclination angle relative to the line of sight.
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<h2 id="retrograde-motion-of-hot-jupiters">Retrograde motion of "hot Jupiters"</h2>
<p>This effect has been used to show that as many as 25% of <a href="/facts/Hot_jupiter/9wSFCuxk">hot Jupiters</a> are orbiting in a <a href="/facts/Retrograde_motion/1HCbwQqy">retrograde</a> direction with respect to their parent stars, strongly suggesting that dynamical interactions rather than <a href="/facts/Planetary_migration/rH6cEwNR">planetary migration</a> produce these objects if no additional processes are involved.<a class="footnote-ref" id="fnref:1" href="#fn:1"><sup>1</sup></a>
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<h2 id="history">History</h2>
<p>J. R. Holt in 1893 proposed a method to measure the <a href="/facts/Stellar_rotation/N0VzIXLC">stellar rotation</a> of stars by using <a href="/facts/Radial_velocity/B3NmbVLP">radial velocity</a> measurements. He predicted that when one star of an eclipsing binary eclipsed the other, it would first cover the advancing blueshifted half and then the receding redshifted half. That motion would create a <a href="/facts/Redshift/Qfl4VjDF">redshift</a> of the eclipsed star's spectrum followed by a <a href="/facts/Blueshift/v8XBtGKH">blueshift</a>, which would thus appear as a change in the measured radial velocity in addition to that caused by the orbital motion of the eclipsed star.<a class="footnote-ref" id="fnref:2" href="#fn:2"><sup>2</sup></a><a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a>
</p><p>The effect is named after <a href="/facts/Richard_Alfred_Rossiter/XlI7vqSY">Richard Alfred Rossiter</a> and <a href="/facts/Dean_Benjamin_McLaughlin/2QTfGV0h">Dean Benjamin McLaughlin</a>.<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a>
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<h2 id="further-reading">Further reading</h2>
<ul><li>Ohta, Y.; Taruya, A. & Suto, Y. (2005). "The Rossiter–McLaughlin Effect and Analytic Radial Velocity Curves for Transiting Extrasolar Planetary Systems". <i>The Astrophysical Journal</i>. 622 (1): 1118–1135. <a href="/facts/ArXiv_(identifier)/H6EtgnBe">arXiv</a>:<a href="https://arxiv.org/abs/astro-ph/0410499">astro-ph/0410499</a>. <a href="/facts/Bibcode_(identifier)/9HtdQSGB">Bibcode</a>:<a href="https://ui.adsabs.harvard.edu/abs/2005ApJ...622.1118O">2005ApJ...622.1118O</a>. <a href="/facts/Doi_(identifier)/muM9Etpq">doi</a>:<a href="https://doi.org/10.1086%2F428344">10.1086/428344</a>. <a href="/facts/S2CID_(identifier)/ldJsHa2Y">S2CID</a> <a href="https://api.semanticscholar.org/CorpusID:10420706">10420706</a>.</li>
<li>Anderson, D.; et al. (2010). "WASP-17b: An Ultra-Low Density Planet In A Probable Retrograde Orbit". <i>The Astrophysical Journal</i>. 709 (1): 159–167. <a href="/facts/ArXiv_(identifier)/H6EtgnBe">arXiv</a>:<a href="https://arxiv.org/abs/0908.1553">0908.1553</a>. <a href="/facts/Bibcode_(identifier)/9HtdQSGB">Bibcode</a>:<a href="https://ui.adsabs.harvard.edu/abs/2010ApJ...709..159A">2010ApJ...709..159A</a>. <a href="/facts/Doi_(identifier)/muM9Etpq">doi</a>:<a href="https://doi.org/10.1088%2F0004-637X%2F709%2F1%2F159">10.1088/0004-637X/709/1/159</a>. <a href="/facts/S2CID_(identifier)/ldJsHa2Y">S2CID</a> <a href="https://api.semanticscholar.org/CorpusID:53628741">53628741</a>.</li>
<li>Winn, J. (2006). "Exoplanets and the Rossiter-McLaughlin Effect". In C. Afonso; D. Weldrake; T. Henning (eds.). <i>Transiting Extrasolar Planets Workshop</i>. <a href="/facts/ASP_Conference_Proceedings/1hWIYXTL">ASP Conference Proceedings</a>. Vol. 366. p. 170. <a href="/facts/ArXiv_(identifier)/H6EtgnBe">arXiv</a>:<a href="https://arxiv.org/abs/astro-ph/0612744">astro-ph/0612744</a>. <a href="/facts/Bibcode_(identifier)/9HtdQSGB">Bibcode</a>:<a href="https://ui.adsabs.harvard.edu/abs/2007ASPC..366..170W">2007ASPC..366..170W</a>.</li></ul>

<h2 id="external-links">External links</h2>
<ul><li> Media related to Rossiter–McLaughlin effect at Wikimedia Commons</li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1"><p>Triaud, A. H. M. J.; et al. (2010). "Spin-orbit angle measurements for six southern transiting planets: New insights into the dynamical origins of hot Jupiters". Astronomy & Astrophysics. 524: A25. arXiv:1008.2353. Bibcode:2010A&A...524A..25T. doi:10.1051/0004-6361/201014525. S2CID 59320239. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li>
<li id="fn:2"><p>Holt, J. R. (August 1893). "Spectroscopic Determination of Stellar Rotation". Astronomy and Astro-Physics. 12 (7): 646. Bibcode:1893AstAp..12..646H. <a href="https://archive.org/details/sim_astronomy-and-astro-physics_1893-08_12_7/page/646/mode/2up" target="_blank">https://archive.org/details/sim_astronomy-and-astro-physics_1893-08_12_7/page/646/mode/2up</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li>
<li id="fn:3"><p>Triaud, A. H. M. J.; et al. (2013). "The EBLM project I. Physical and orbital parameters, including spin-orbit angles, of two low-mass eclipsing binaries on opposite sides of the brown dwarf limit". Astronomy and Astrophysics. 549 A18. arXiv:1208.4940. Bibcode:2013A&A...549A..18T. doi:10.1051/0004-6361/201219643. <a href="https://doi.org/10.1051%2F0004-6361%2F201219643" target="_blank">https://doi.org/10.1051%2F0004-6361%2F201219643</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li>
<li id="fn:4"><p>Boué, G.; et al. (2013). "New analytical expressions of the Rossiter-McLaughlin effect adapted to different observation techniques". Astronomy & Astrophysics. 550 A53. arXiv:1211.3310. Bibcode:2013A&A...550A..53B. doi:10.1051/0004-6361/201220146. <a href="https://doi.org/10.1051%2F0004-6361%2F201220146" target="_blank">https://doi.org/10.1051%2F0004-6361%2F201220146</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li>
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Rossiter–McLaughlin effect open-in-new

Rossiter–McLaughlin effect