Presentation Open Access

Extremely precise HARPS-N solar RV to overcome the challenge of stellar signal

X. Dumusque

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    <subfield code="a">exoplanets; solar radial velocity; stellar activity</subfield>
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    <subfield code="u">Department of Astronomy of the University of Geneva</subfield>
    <subfield code="a">X. Dumusque</subfield>
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    <subfield code="a">Extremely precise HARPS-N solar RV to overcome the challenge of stellar signal</subfield>
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    <subfield code="a">Signal Correction to Reveal other Earths</subfield>
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    <subfield code="a">&lt;p&gt;Detecting and measuring the masses of&amp;nbsp;Earth-like&amp;nbsp;planets in the presence of stellar signals is the main challenge when using the radial-velocity (RV) technique. Even in the&amp;nbsp;&lt;em&gt;PLATO&lt;/em&gt;&amp;nbsp;era where&amp;nbsp;the satellite will provide the period of Earth-like&amp;nbsp;planetary&amp;nbsp;candidates,&amp;nbsp;measuring precisely their mass, which is critical to&amp;nbsp;1) confirm those candidates, 2)&amp;nbsp;constrain further planetary composition and thus planetary formation&amp;nbsp;and 3)&amp;nbsp;constrain further&amp;nbsp;planetary atmospheres,&amp;nbsp;will be extremely&amp;nbsp;challenging.&lt;/p&gt;


&lt;p&gt;Critical to a better understanding of RV variations induced by stellar signals and finding correction techniques is RV data with a sampling&amp;nbsp;and SNR&amp;nbsp;sufficient to probe&amp;nbsp;stellar signals&amp;nbsp;ranging from minutes to years. To address this challenge,&amp;nbsp;we can use the unprecedented data from the&amp;nbsp;solar telescope that feed sunlight into HARPS-N, which allows us to obtain Sun-as-a-star RVs at a sub-m/s precision.&lt;/p&gt;


&lt;p&gt;In this talk, I will discuss how to reduce properly the HARPS-N solar data to reach a precision of about 50 cm/s on the short and long-term. This implies optimizing the wavelength solution recipe, carefully selecting the most stable thorium lines, but also compensating for the ageing of thorium-argon lamps inducing a drift of thorium lines with time. I will show how those optimizations improve the quality of the data, and therefore will advise any team working in extremely precise RV to perform similar upgrades.&lt;/p&gt;


&lt;p&gt;The obtained solar data, published last October, have already been used in several studies that demonstrate that analyzing the HARPS-N solar&amp;nbsp;spectral (or cross-correlation functions) time-series using machine learning algorithms can mitigate stellar signals down to a level where Earth-like planets in the habitable zone could be detected (30 cm/s in semi-amplitude, signal three times larger than Earth).&lt;/p&gt;</subfield>
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