Near-IR spectroscopic follow-up of PGIR20emh/AT2020rjf

ATel #13973; S. Tinyanont (UCSC), S. Jha (Rutgers), C. Ashall (IfA), Y. Camacho-Neves, K. G. Dettman, L. Kwok, T. Barna (Rutgers), J. Hinkle (IfA)
on 26 Aug 2020; 22:21 UT
Credential Certification: Samaporn Tinyanont (st@astro.caltech.edu)

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The bright, likely Galactic microlensing event, PGIR20emh/AT2020rjf was discovered by the Palomar Gattini-IR survey (De et al. 2020; Moore and Kasliwal 2019) on UT 2020-07-18 (ATel#13969). On UT 2020-08-24, we obtained a near-infrared spectrum of AT2020rjf using the Near-InfraRed Echellette Spectrometer (NIRES) on the 10-meter Keck 2 telescope. We also observed an A0 V star HIP81457 for the telluric and flux calibration. The spectrum was reduced and calibrated using Spextool (Cushing et al. 2004)and Xtellcor (Vacca et al. 2003). The spectrum showed a bright IR continuum, peaking around 1.4 micron, which corresponds to a blackbody temperature of around 2000 K. The spectrum showed strong absorption features from the first and second overtones of CO molecules in the K and H bands, along with the CN absorption at 1.1 micron. These spectral features are consistent with the interpretation in ATel#13969 that the lensed source is a cool red dwarf.