AAVSO: American Association of Variable Star Observers

Binaries with Mass Ratios Near Unity: The First BVRI Observations, Analysis and Period Studies of TX Canis Minoris and DW Canis Minoris

Volume 49 number 2 (2021)

Ronald G. Samec
Pisgah Astronomical Research Institute, 112 Idlewood Acres, Hartwell, GA 30643; ronaldsamec@gmail.com
Daniel Caton
Dark Sky Observatory, Physics and Astronomy Department, Appalachian State University, 525 Rivers Street, Boone, NC 28608-2106; catondb@appstate.edu
Jacob Ray
Dark Sky Observatory, Physics and Astronomy Department, Appalachian State University, 525 Rivers Street, Boone, NC 28608-2106; catondb@appstate.edu
Riley Waddell
Dark Sky Observatory, Physics and Astronomy Department, Appalachian State University, 525 Rivers Street, Boone, NC 28608-2106; catondb@appstate.edu
Davis Gentry
Dark Sky Observatory, Physics and Astronomy Department, Appalachian State University, 525 Rivers Street, Boone, NC 28608-2106; catondb@appstate.edu
Danny Faulkner
Johnson Observatory, 1414 Bur Oak Court, Hebron, KY 41048; dfaulkner@answersingenesis.org

Abstract

CCD BVRI light curves of TX CMi and DW CMi were taken in 2020 on 20, 21 January, 22, 23 February, and 4 April with the 0.81-m reflector of Appalachian State University by Daniel Caton, Ronald Samec and Danny Faulkner. Six times of minimum light were determined from our present observations of TX CMi. Fifty-five total times of minimum light were included in the 61-year period study. From these we determined that the period for TX CMi is increasing. Eight times of minimum light were determined for DW CMi and thirty-five total times of minimum light were included in the 19.3-year period study. The period is weakly decreasing with a quadratic term of –1.9 × 10^–11. This could be due to mass transfer to M1 (q = M2 / M1) for DW CMi. A Wilson-Devinney (W-D) analysis of TX CMi reveals that the system is a W UMa binary with a mass ratio near unity, q ~1.00. Its Roche Lobe fill-out is ~10%. One spot was needed in the modeling. The temperature difference of the components is only ~90 K, so the stars are nearly twins, with the secondary component the slightly cooler one. The inclination is high, 86.9 ± 0.1˚. A W-D analysis reveals that DW CMi is a W-type W UMa binary a mass ratio near unity, q ~1.1. Its Roche Lobe fill-out is ~10%. One weak spot was needed in the modeling. The temperature difference of the components is T2 – T1 ~260 K, making the binary of W-type.