A.C.I.D - an Improved LSD Technique for Accurate Line Profile Retrieval.

Stellar activity and planetary effects induce radial velocity (RV) offsetsand cause temporal distortions in the shape of the stellar line profile. Hence,accurately probing the stellar line profile offers a wealth of information onboth the star itself and any orbiting planets. Typically, Cross-CorrelationFunctions (CCFs) are used as a proxy for the stellar line profile. The shape ofCCFs, however, can be distorted by line blending and aliasing limiting thestellar and planetary physics that can be probed from them. Least-squaresdeconvolution (LSD) offers an alternative that directly fits the mean lineprofile of the spectrum to produce a high-precision profile. In this paper, weintroduce our novel method ACID (Accurate Continuum fItting and Deconvolution)that builds on LSD techniques by simultaneously fitting the spectral continuumand line profile as well as performing LSD in effective optical depth. Tests onmodel data revealed ACID can accurately identify and correct the spectralcontinuum to retrieve an injected line profile. ACID was also applied toarchival HARPS data obtained during the transit of HD189733b. The applicationof the Reloaded Rossiter-McLaughlin technique to both ACID profiles and HARPSCCFs shows ACID residual profiles improved the out-of-line RMS by over 5compared to CCFs. Furthermore, ACID profiles are shown to exhibit a Voigtprofile shape that better describes the expected profile shape of the stellarline profile. This improved representation shows that ACID better preserves thestellar and planetary physics encoded in the stellar line profile shape forslow rotating stars.