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Into the Depths: A New Activity Metric for High-precision Radial Velocity Measurements Based on Line Depth Variations

Siegel, Jared C. and Rubenzahl, Ryan A. and Halverson, Samuel and Howard, Andrew W. (2022) Into the Depths: A New Activity Metric for High-precision Radial Velocity Measurements Based on Line Depth Variations. Astronomical Journal, 163 (6). Art. No. 260. ISSN 0004-6256. doi:10.3847/1538-3881/ac609a.

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The discovery and characterization of extrasolar planets using radial velocity (RV) measurements is limited by noise sources from the surfaces of host stars. Current techniques to suppress stellar magnetic activity rely on decorrelation using an activity indicator (e.g., strength of the Ca ii lines, width of the cross-correlation function, broadband photometry) or measurement of the RVs using only a subset of spectral lines that have been shown to be insensitive to activity. Here, we combine the above techniques by constructing a high-signal-to-noise activity indicator, the depth metric D(t), from the most activity-sensitive spectral lines using the "line-by-line" method of Dumusque (2018). Analogous to photometric decorrelation of RVs or Gaussian progress regression modeling of activity indices, time series modeling of D(t) reduces the amplitude of magnetic activity in RV measurements; in an αCenB RV time series from HARPS, the RV rms was reduced from 2.67 to 1.02 m s⁻¹. D(t) modeling enabled us to characterize injected planetary signals as small as 1 m s⁻¹. In terms of noise reduction and injected signal recovery, D(t) modeling outperforms activity mitigation via the selection of activity-insensitive spectral lines. For Sun-like stars with activity signals on the m s⁻¹ level, the depth metric independently tracks rotationally modulated and multiyear stellar activity with a level of quality similar to that of the FWHM of the CCF and logR'(HK). The depth metric and its elaborations will be a powerful tool in the mitigation of stellar magnetic activity, particularly as a means of connecting stellar activity to physical processes within host stars.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Siegel, Jared C.0000-0002-9337-0902
Rubenzahl, Ryan A.0000-0003-3856-3143
Halverson, Samuel0000-0003-1312-9391
Howard, Andrew W.0000-0001-8638-0320
Additional Information:© 2022. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Received 2021 November 19; revised 2022 March 8; accepted 2022 March 22; published 2022 May 11. We thank Jacob Bean and Andreas Seifahrt for helpful conversations and for spectra used for experimentation with this technique. We acknowledge NSF grant AST-2034278. R.A.R. is supported by an NSF Graduate Research Fellowship, grant No. DGE 1745301.
Group:Astronomy Department
Funding AgencyGrant Number
NSF Graduate Research FellowshipDGE-1745301
Subject Keywords:Exoplanet detection methods; Radial velocity
Issue or Number:6
Classification Code:Unified Astronomy Thesaurus concepts: Exoplanet detection methods (489); Radial velocity (1332)
Record Number:CaltechAUTHORS:20220512-561220000
Persistent URL:
Official Citation:Jared C. Siegel et al 2022 AJ 163 260
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:114706
Deposited By: George Porter
Deposited On:13 May 2022 17:33
Last Modified:13 May 2022 17:33

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