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Stellar Companions to the Exoplanet Host Stars HD 2638 and HD 164509

An important aspect of searching for exoplanets is understanding the binarity of the host stars. It is particularly important because nearly half of the solar-like stars within our own Milky Way are part of binary or multiple systems. Moreover, the presence of two or more stars within a system can place further constraints on planetary formation, evolution, and orbital dynamics. As part of our survey of almost a hundred host stars, we obtained images at 692 nm and 880 nm bands using the Differential Speckle Survey Instrument (DSSI) at the Gemini-North Observatory. From our survey, we detect stellar companions to HD 2638 and HD 164509. The stellar companion to HD 2638 has been previously detected, but the companion to HD 164509 is a newly discovered companion. The angular separation for HD 2638 is $0.512 \pm 0.002\arcsec$ and for HD 164509 is $0.697 \pm 0.002\arcsec$. This corresponds to a projected separation of $25.6 \pm 1.9$ AU and $36.5 \pm 1.9$ AU, respectively. By employing stellar isochrone models, we estimate the mass of the stellar companions of HD 2638 and HD 164509 to be $0.483 \pm 0.007$ $M_\sun$ and $0.416 \pm 0.007$ $M_\sun$, respectively, and their effective temperatures to be $3570 \pm 8$~K and $3450 \pm 7$~K, respectively. These results are consistent with the detected companions being late-type M dwarfs.