Observations, Analyses and 19 Year Period Study of a Shallow Very Short Period Binary, DW CMI with a Mass Ratio Near Unity

CCD, BVRI light curves of DW Cmi of were taken on 20, 21, and 22, 23 February, and 4 April, 2020, at Appalachian State University’s Dark Sky Observatory, North Carolina with the 32-inch (0.81 m) reflector. DW CMi was found to possibly be a W-type W UMa binary with a weakly decreasing period. The ephemeris is: JD Hel Min I = (2458868.67380 ± 0.00042d) + (0.30755479 ± 0.00000009)×E - (0.000000000019 ± 0.000000000005)×E². A Wilson-Devinney analysis reveals that the system has a mass ratio near unity, q ~ 1.1. Its Roche Lobe fill-out is ~10%. One weak spot was needed in the modeling, a northern, -30 degree latitude, 31 degree radius, spot with a t-fact of 0.94. The temperature difference of the components is T₂ – T₁ ~ 260 K, making the binary of W-type. More information is given in this preliminary report.