Imaging & Spectroscopy

Direct Imaging Explorations For Companions Around Mid-Late M Stars From The Subaru/IRD Strategic Program

By Keith Cowing
Status Report
February 27, 2023
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Direct Imaging Explorations For Companions Around Mid-Late M Stars From The Subaru/IRD Strategic Program
Color-magnitude diagram of the detected companion candidates (we expediently add a suffix of ’B’ of the primary star ’A’) overlaid with photometric libraries of field low-mass stars/substellar-mass objects (Dupuy & Liu 2012; Dupuy & Kraus 2013) as well as BT-Settl isochrones (cerulean blue solid: 1 Gyr, dashed: 5 Gyr, and dotted lines: 10 Gyr; Allard et al. 2012) and blackbody radiation (gray dashed line). We corrected the Keck/NIRC2 magnitudes into MKO/NSFCam filters to compare with the libraries using species (Stolker et al. 2020). We also added the expected L 0 -band absolute magnitudes of the background stars around LSPM J1922+0702 (bgs1 and bgs2) assuming the same distance as the target star in the left panel. The right panel shows the zoomed-in diagram without the background stars. — astro-ph.SR

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 observations with pyramid wavefront 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 ∼2−20~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 MJup) 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 JWST to search for smaller-mass companions below the NIRC2 detection limits.

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

Comments: 16 pages, 8 figures, accepted for publication in AJ
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2302.13354 [astro-ph.SR] (or arXiv:2302.13354v1 [astro-ph.SR] for this version)
Submission history
From: Taichi Uyama
[v1] Sun, 26 Feb 2023 17:10:56 UTC (4,138 KB)

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