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Detection of a Low-mass Stellar Companion to the Accelerating A2IV Star HR 1645

De Rosa, Robert J. and Wang, Jason J. (2019) Detection of a Low-mass Stellar Companion to the Accelerating A2IV Star HR 1645. Astronomical Journal, 158 (6). Art. No. 226. ISSN 1538-3881.

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The ~500 Myr A2IV star HR 1645 has one of the most significant low-amplitude accelerations of nearby early-type stars measured from a comparison of the Hipparcos and Gaia astrometric catalogs. This signal is consistent with either a stellar companion with a moderate mass ratio (q ~ 0.5) on a short period (P < 1 yr), or a substellar companion at a separation wide enough to be resolved with ground-based high-contrast imaging instruments; long-period equal-mass ratio stellar companions that are also consistent with the measured acceleration are excluded with previous imaging observations. The small but significant amplitude of the acceleration made HR 1645 a promising candidate for targeted searches for brown dwarf and planetary-mass companions around nearby, young stars. In this paper we explore the origin of the astrometric acceleration by modeling the signal induced by a wide-orbit M8 companion discovered with the Gemini Planet Imager, as well as the effects of an inner short-period spectroscopic companion discovered a century ago but not since followed up. We present the first constraints on the orbit of the inner companion, and demonstrate that it is a plausible cause of the astrometric acceleration. This result demonstrates the importance of vetting of targets with measured astrometric acceleration for short-period stellar companions prior to conducting targeted direct imaging surveys for wide-orbit substellar companions.

Item Type:Article
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URLURL TypeDescription Paper
De Rosa, Robert J.0000-0002-4918-0247
Wang, Jason J.0000-0003-0774-6502
Additional Information:© 2019 The American Astronomical Society. Received 2019 March 30; revised 2019 October 7; accepted 2019 October 16; published 2019 November 13. Supported by NSF grants AST-1411868 (R.D.R., E.L.N., K.B.F., B.M., and J.P.), AST-141378 (G.D.), AST-1518332 (R.D.R., J.J.W., T.M.E., J.R.G., P.G.K.), and AST1411868 (J.H., J.P.). Supported by NASA grants NNX14AJ80G (R.D.R., E.L.N., S.C.B., B.M., F.M., and M.P.), NNX15AC89G, and NNX15AD95G (R.D.R., B.M., J.E.W., T.M.E., G.D., J.R.G., P.G.K.). This work benefited from NASA's Nexus for Exoplanet System Science (NExSS) research coordination network sponsored by NASA's Science Mission Directorate. J.R. is supported by the French National Research Agency in the framework of the Investissements dAvenir program (ANR-15-IDEX-02), through the funding of the "Origin of Life" project of the University Grenoble-Alpes. Portions of this work were performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. Based on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), National Research Council (Canada), CONICYT (Chile), Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina), Ministério da Ciência, Tecnologia e Inovação (Brazil), and Korea Astronomy and Space Science Institute (Republic of Korea). 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. This research has made use of the SIMBAD database and the VizieR catalog access tool, both operated at the CDS, Strasbourg, France. This research has made use of the "Modern Mean Dwarf Stellar Color and Effective Temperature Sequence" available at This research has benefited from the SpeX Prism Library (and/or SpeX Prism Library Analysis Toolkit), maintained by Adam Burgasser at, the IRTF Spectral Library, maintained by Michael Cushing, the Brown Dwarfs in New York City database led by Jackie Faherty, Emily Rice, and Kelle Cruz, and the Montreal Brown Dwarf and Exoplanet Spectral Library, maintained by Jonathan Gagné. Facility: Gemini:South (GPI). - Software: Astropy (The Astropy Collaboration et al. 2013), Matplotlib (Hunter 2007).
Funding AgencyGrant Number
Heising-Simons Foundation51 Pegasi b Fellowship
Agence Nationale pour la Recherche (ANR)ANR-15-IDEX-02
University Grenoble-AlpesUNSPECIFIED
Department of Energy (DOE)DE-AC52-07NA27344
Gaia Multilateral AgreementUNSPECIFIED
Subject Keywords:Astrometry; Radial velocity; Close binary stars; Coronographic imaging; Visual binary stars
Issue or Number:6
Classification Code:Unified Astronomy Thesaurus concepts: Astrometry (80); Radial velocity (1332); Close binary stars (254); Coronographic imaging (313); Visual binary stars (1777)
Record Number:CaltechAUTHORS:20191114-094358200
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Official Citation:Robert J. De Rosa et al 2019 AJ 158 226
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:99828
Deposited By: Tony Diaz
Deposited On:14 Nov 2019 18:05
Last Modified:14 Nov 2019 18:05

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