* Astronomy

Title: Time-resolved Spectroscopy of the Polar EU Cancri in the Open Cluster Messier 67
Authors: Kurtis A. Williams (1), Steve B. Howell (2), James Liebert, Paul S. Smith (3), Andrea Bellini (4), Kate H.R. Rubin (5), Michael Bolte (6) ((1) Texas A&M University-Commerce, (2) NASA Ames, (3) Steward Obs., (4) STSci, (5) MPIA, (6) UCO/Lick)

We present time-resolved spectroscopic and polarimetric observations of the AM Her system EU Cnc. EU Cnc is located near the core of the old open cluster Messier 67; new proper motion measurements indicate that EU Cnc is indeed a member of the star cluster, this system therefore is useful to constrain the formation and evolution of magnetic cataclysmic variables. The spectra exhibit two-component emission features with independent radial velocity variations as well as time-variable cyclotron emission indicating a magnetic field strength of 41 MG. The period of the radial velocity and cyclotron hump variations are consistent with the previously-known photometric period, and the spectroscopic flux variations are consistent in amplitude with previous photometric amplitude measurements. The secondary star is also detected in the spectrum. We also present polarimetric imaging measurements of EU Cnc that show a clear detection of polarisation, and the degree of polarisation drops below our detection threshold at phases when the cyclotron emission features are fading or not evident. The combined data are all consistent with the interpretation that EU Cnc is a low-state polar in the cluster Messier 67. The mass function of the system gives an estimate of the accretor mass of M_WD >= 0.68 solar masses with M_WD ~ 0.83 solar masses for an average inclination. We are thus able to place a lower limit on the progenitor mass of the accreting WD of >= 1.43 solar masses.

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