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Persistent Starspot Signals on M Dwarfs: Multiwavelength Doppler Observations with the Habitable-zone Planet Finder and Keck/HIRES

Robertson, Paul and Stefansson, Gudmundur and Mahadevan, Suvrath and Endl, Michael and Cochran, William D. and Beard, Corey and Bender, Chad F. and Diddams, Scott A. and Duong, Nicholas and Ford, Eric B. and Fredrick, Connor and Halverson, Samuel and Hearty, Fred and Holcomb, Rae and Juan, Lydia and Kanodia, Shubham and Lubin, Jack and Metcalf, Andrew J. and Monson, Andrew and Ninan, Joe P. and Palafoutas, Jonathan and Ramsey, Lawrence W. and Roy, Arpita and Schwab, Christian and Terrien, Ryan C. and Wright, Jason T. (2020) Persistent Starspot Signals on M Dwarfs: Multiwavelength Doppler Observations with the Habitable-zone Planet Finder and Keck/HIRES. Astrophysical Journal, 897 (2). Art. No. 125. ISSN 1538-4357.

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Young, rapidly rotating M dwarfs exhibit prominent starspots, which create quasiperiodic signals in their photometric and Doppler spectroscopic measurements. The periodic Doppler signals can mimic radial velocity (RV) changes expected from orbiting exoplanets. Exoplanets can be distinguished from activity-induced false positives by the chromaticity and long-term incoherence of starspot signals, but these qualities are poorly constrained for fully convective M stars. Coherent photometric starspot signals on M dwarfs may persist for hundreds of rotations, and the wavelength dependence of starspot RV signals may not be consistent between stars due to differences in their magnetic fields and active regions. We obtained precise multiwavelength RVs of four rapidly rotating M dwarfs (AD Leo, G227-22, GJ 1245B, GJ 3959) using the near-infrared (NIR) Habitable-zone Planet Finder and the optical Keck/HIRES spectrometer. Our RVs are complemented by photometry from Kepler, TESS, and the Las Cumbres Observatory network of telescopes. We found that all four stars exhibit large spot-induced Doppler signals at their rotation periods, and investigated the longevity and optical-to-NIR chromaticity for these signals. The phase curves remain coherent much longer than is typical for Sunlike stars. Their chromaticity varies, and one star (GJ 3959) exhibits optical and NIR RV modulation consistent in both phase and amplitude. In general, though, we find that the NIR amplitudes are lower than their optical counterparts. We conclude that starspot modulation for rapidly rotating M stars frequently remains coherent for hundreds of stellar rotations and gives rise to Doppler signals that, due to this coherence, may be mistaken for exoplanets.

Item Type:Article
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URLURL TypeDescription Paper
Robertson, Paul0000-0003-0149-9678
Stefansson, Gudmundur0000-0001-7409-5688
Mahadevan, Suvrath0000-0001-9596-7983
Endl, Michael0000-0002-7714-6310
Cochran, William D.0000-0001-9662-3496
Beard, Corey0000-0001-7708-2364
Bender, Chad F.0000-0003-4384-7220
Diddams, Scott A.0000-0002-2144-0764
Duong, Nicholas0000-0001-6730-9115
Ford, Eric B.0000-0001-6545-639X
Fredrick, Connor0000-0002-0560-1433
Halverson, Samuel0000-0003-1312-9391
Hearty, Fred0000-0002-1664-3102
Holcomb, Rae0000-0002-5034-9476
Juan, Lydia0000-0003-1035-3232
Kanodia, Shubham0000-0001-8401-4300
Lubin, Jack0000-0001-8342-7736
Metcalf, Andrew J.0000-0001-5000-1018
Monson, Andrew0000-0002-0048-2586
Ninan, Joe P.0000-0001-8720-5612
Palafoutas, Jonathan0000-0002-3411-8897
Roy, Arpita0000-0001-8127-5775
Schwab, Christian0000-0002-0091-7105
Terrien, Ryan C.0000-0002-4788-8858
Wright, Jason T.0000-0001-6160-5888
Alternate Title:Persistent starspot signals on M dwarfs: multi-wavelength Doppler observations with the Habitable-zone Planet Finder and Keck/HIRES
Additional Information:© 2020 The American Astronomical Society. Received 2020 April 17; revised 2020 May 15; accepted 2020 May 19; published 2020 July 9. The authors thank the anonymous referee for a prompt and thorough review, as well as for comments that significantly improved the quality of this manuscript. This work was partially supported by funding from the Center for Exoplanets and Habitable Worlds. The Center for Exoplanets and Habitable Worlds is supported by the Pennsylvania State University, the Eberly College of Science, and the Pennsylvania Space Grant Consortium. This work was supported by NASA Headquarters under the NASA Earth and Space Science Fellowship Program through grants NNX16AO28H and 80NSSC18K1114. We acknowledge support from NSF grants AST-1006676, AST-1126413, AST-1310875, AST-1310885, AST-1517592, the NASA Astrobiology Institute (NAI; NNA09DA76A), and PSARC in our pursuit of precision radial velocities in the NIR. Computations for this research were performed on the Pennsylvania State University's Institute for Computational and Data Sciences. We acknowledge support from the Heising-Simons Foundation via grant 2017-0494 and 2019-1177. This is University of Texas Center for Planetary Systems Habitability Contribution 0003. We wish to thank Kento Masuda for informative discussions on determining stellar inclinations from projected rotational velocities, stellar radii, and rotation periods. These results are based on observations obtained with the Habitable-zone Planet Finder Spectrograph on the Hobby–Eberly Telescope. We thank the Resident Astronomers and Telescope Operators at the HET for the skillful execution of our observations of our observations with HPF. The Hobby–Eberly Telescope is a joint project of the University of Texas at Austin, the Pennsylvania State University, Ludwig-Maximilians-Universität München, and Georg-August Universität Gottingen. The HET is named in honor of its principal benefactors, William P. Hobby and Robert E. Eberly. The HET collaboration acknowledges the support and resources from the Texas Advanced Computing Center. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. The authors also thank the Keck Observing Assistants and Telescope Operators for their assistance in collecting these data. This research has made use of the Keck Observatory Archive (KOA), which is operated by the W. M. Keck Observatory and the NASA Exoplanet Science Institute (NExScI), under contract with the National Aeronautics and Space Administration. This work makes use of observations from the LCOGT network through the observing program KEY2017AB-005. This paper includes data collected by the TESS mission. Funding for the TESS mission is provided by the NASA Explorer Program. This work has made use of data from the European Space Agency (ESA) mission Gaia (, processed by the Gaia Data Processing and Analysis Consortium (DPAC, Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. Facilities: HET - McDonald Observatory's Hobby-Eberly Telescope, Keck:I (HIRES) - , LCOGT - , TESS. - Software: AstroImageJ (Collins et al. 2017), Astropy (Astropy Collaboration et al. 2013), Astroquery (Ginsburg et al. 2019), celerite (Foreman-Mackey et al. 2017), (Foreman-Mackey 2016), emcee (Foreman-Mackey et al. 2013), HxRGproc (Ninan et al. 2018), Isochrones (Morton 2015), Jupyter (Kluyver et al. 2016), matplotlib (Hunter 2007), numpy (Van Der Walt et al. 2011), pandas (McKinney 2010), radvel (Fulton et al. 2018), SERVAL (Zechmeister et al. 2018).
Funding AgencyGrant Number
Center for Exoplanets and Habitable WorldsUNSPECIFIED
Pennsylvania State UniversityUNSPECIFIED
Eberly College of ScienceUNSPECIFIED
Pennsylvania Space Grant ConsortiumUNSPECIFIED
NASA Earth and Space Science FellowshipNNX16AO28H
Heising-Simons Foundation2017-0494
Heising-Simons Foundation2019-1177
W. M. Keck FoundationUNSPECIFIED
Gaia Multilateral AgreementUNSPECIFIED
Subject Keywords:M dwarf stars ; Radial velocity ; Stellar photometry ; High resolution spectroscopy ; Exoplanets ; Starspots ; Time series analysis ; Gaussian Processes regression
Issue or Number:2
Classification Code:Unified Astronomy Thesaurus concepts: M dwarf stars (982); Radial velocity (1332); Stellar photometry (1620); High resolution spectroscopy (2096); Exoplanets (498); Starspots (1572); Time series analysis (1916); Gaussian Processes regression (1930)
Record Number:CaltechAUTHORS:20200710-141852176
Persistent URL:
Official Citation:Paul Robertson et al 2020 ApJ 897 125
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:104335
Deposited By: Tony Diaz
Deposited On:10 Jul 2020 22:08
Last Modified:10 Jul 2020 22:08

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