Direct Imaging Explorations for Companions around Mid–Late M Stars from the Subaru/IRD Strategic Program

Creators: Uyama, Taichi; Beichman, Charles; Kuzuhara, Masayuki; Janson, Markus; Kotani, Takayuki; Mawet, Dimitri; Sato, Bun'ei; Tamura, Motohide; Ishikawa, Hiroyuki Tako; Cale, Bryson; Currie, Thayne; Harakawa, Hiroki; Henning, Thomas; Hirano, Teruyuki; Hodapp, Klaus; Hori, Yasunori; Ishizuka, Masato; Jacobson, Shane; Kasagi, Yui; Kokubo, Eiichiro; Konishi, Mihoko; Kudo, Tomoyuki; Kurokawa, Takashi; Kusakabe, Nobuhiko; Kwon, Jungmi; Machida, Masahiro; Nakagawa, Takao; Narita, Norio; Nishikawa, Jun; Ogihara, Masahiro; Omiya, Masashi; Serizawa, Takuma; Ueda, Akitoshi; Vievard, Sébastien; Wang, Ji

Abstract

The Subaru telescope is currently performing a strategic program (SSP) using the high-precision near-infrared (NIR) spectrometer IRD to search for exoplanets around nearby mid/late M dwarfs via radial velocity (RV) monitoring. As part of the observing strategy for the exoplanet survey, signatures of massive companions such as RV trends are used to reduce the priority of those stars. However, this RV information remains useful for studying the stellar multiplicity of nearby M dwarfs. To search for companions around such "deprioritized" M dwarfs, we observed 14 IRD-SSP targets using Keck/NIRC2 with pyramid wave-front sensing at NIR wavelengths, leading to high sensitivity to substellar-mass companions within a few arcseconds. We detected two new companions (LSPM J1002+1459 B and LSPM J2204+1505 B) and two new candidates that are likely companions (LSPM J0825+6902 B and LSPM J1645+0444 B), as well as one known companion. Including two known companions resolved by the IRD fiber injection module camera, we detected seven (four new) companions at projected separations between ∼2 and 20 au in total. A comparison of the colors with the spectral library suggests that LSPM J2204+1505 B and LSPM J0825+6902 B are located at the boundary between late M and early L spectral types. Our deep high-contrast imaging for targets where no bright companions were resolved did not reveal any additional companion candidates. The NIRC2 detection limits could constrain potential substellar-mass companions (∼10–75 M_(Jup)) at 10 au or further. The failure with Keck/NIRC2 around the IRD-SSP stars having significant RV trends makes these objects promising targets for further RV monitoring or deeper imaging with the James Webb Space Telescope to search for smaller-mass companions below the NIRC2 detection limits.

Additional Information

© 2023. 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. The authors would like to thank the anonymous referee for the constructive comments and suggestions to improve the quality of the paper. We are grateful to Tomas Stolker, who helped arrange the internal settings of species. T.U. is supported by a Grant-in-Aid for the Japan Society for the Promotion of Science (JSPS) Fellows and JSPS KAKENHI grant No. JP21J01220. M.T. is supported by JSPS KAKENHI grant Nos. 18H05442, 15H02063, and 22000005. T.H. is supported by JSPS KAKENHI grant Nos. 19K14783 and 21H00035. E.K. is supported by JSPS KAKENHI grant No. 18H05438. This research is partially supported by NASA ROSES XRP award 80NSSC19K0294, JSPS KAKENHI grant No. JP18H05439, and JST CREST grant No. JPMJCR1761. Some of the research described in this publication was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. Parts 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. Part of this research is based on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan. 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. This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC; https://www.cosmos.esa.int/web/gaia/dpac/consortium). 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 NASA's Astrophysics Data System Bibliographic Services. This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France. Our modeling of the distortion of the IRD-FIM camera used M5 images that benefited from observations made with the NASA/ESA Hubble Space Telescope, and obtained from the Hubble Legacy Archive, which is a collaboration between the Space Telescope Science Institute, the Space Telescope European Coordinating Facility (ST-ECF/ESA) and the Canadian Astronomy Data Centre (CADC/NRC/CSA). Software: astropy (Astropy Collaboration et al. 2013, 2018).

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