tokens: (James et al. 2000 ). In this paper, we present the discovery of KELT J041621-620046, which is a bright ( J ∼ 10.2) 0.45 + 0.40 M eclipsing binary. This system is one of the brightest known detached M-M EB, with a very short orbital period of 1.11 days. With only about three dozen M-M EBs known, most with V > 14, KELT J041621-620046 provides the opportunity to test theoretical models for higher-mass M dwarfs. Section 2 presents the discovery photometry and the follow-up photometric and spectroscopic observations used. Section 3 presents the analysis and principal results of this study, including direct measurement of the two stars’ masses, radii, and other properties. In Section 4 , we briefly discuss the results in the context of the predictions of stellar models and of empirical relations for radius and temperature anomalies in LMSs. We summarize the results in Section 5 . 2. Observations 2.1. Kilodegree Extremely Little Telescope The Kilodegree Extremely Little Telescope (KELT) is an all-sky photometric survey designed to detect transiting planets around bright host stars (7 V 11). The survey uses two telescopes: the KELT-North in Soniata, AZ and the KELT-South at the South African Astronomical Observatory. Each telescope uses a 4096 × 4096 pixel Apogee CCD camera with a 42 mm aperture, producing a 26° × 26° field of view (Pepper et al. 2007 , 2012 ). See Kuhn et al. ( 2016 ) for a detailed description of the KELT-South data reduction pipeline. KELT J041621-620046 is located in KELT-South field 20, which is centered on J2000 α = 04 h 36 m 00 s δ = −53°00′00′′. KELT J041621-620046 itself is located at α = 04 h 16 m 21652 δ = −62°00′4644 J2000 and was observed by KELT-South 4182 times from UT 2010 February 28 until UT 2013 April 7. The discovery KELT light-curve is shown in Figure 1 . It is also known in various catalogs by the names 2MASS J04162165-6200463, UCAC4 140-003916, and WISE J041621.52-620047.1 (see Table 1 ). Figure 1. Top: the KELT-South light-curve of KELT J041621-620046 phase-folded to the discovery ephemeris ( T 0 = 2455255.950528 in JD TT , P = 1.1112884 days). The binned data are shown in red. Bottom: a zoom-in of the primary (left) and secondary (right) eclipses. The data used to create this figure are available . Table 1 Stellar Properties of KELT J041621-620046 Obtained from the Literature and from this Work Note. a See Zhou et al. ( 2015 ) for a description on how log( L H α / L bol ) was measured. 2.2. Photometric Follow-up To better measure the KELT J041621-620046 system, we obtained higher precision photometric follow-up of the primary and secondary eclipses from the KELT Follow-Up Network. All follow-up photometry except the Anglo-Australian Telescope (AAT) observations were reduced using the AstroImageJ 24 24 http://www.astro.louisville.edu/software/astroimagej (AIJ) package (Collins Kielkopf 2013 ; Collins et al. 2017 ) and the reported time stamps are BJD TDB . The AAT observations were reduced following the
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