Gaia DR3 1382578220583890176 (J1623+4431): orbit and analysis package for an M-dwarf binary with a candidate white-dwarf companion

Public DESI and SDSS-V spectra show that the active M3.5–M4 dwarf Gaia DR31382578220583890176 (G = 16.7, d = 127.9pc) is in a circular P = 0.600119d orbit with K1 =155.6 ± 0.9kms−1. With M1 = 0.293 ± 0.007M⊙ from the MK–mass relation, the mass function(0.234M⊙) requires an unseen companion of at least 0.55M⊙. An ordinary single star of that masswould supply 4.5 times the observed K-band flux, and no second spectrum or eclipse is detected.The M dwarf’s blue absorption lines show a dilution anomaly relative to active comparison stars; illustrative white-dwarf models (∼5100K, 0.6M⊙) are compatible with its approximate scale, but thesignal is not a calibrated detection, so I regard it as tentative. A white dwarf is the most naturalcompanion, making the system a candidate post-common-envelope binary. I give an ephemeris andthe rotational-velocity predictions that follow-up spectroscopy could test