Direct Distances to Nearby Galaxies Using Detached Eclipsing Binaries and Cepheids. Iv. Variables in the Field M31d

We undertook a long term project, DIRECT, to obtain the direct distances to two important galaxies in the cosmological distance ladder – M31 and M33 – using detached eclipsing binaries (DEBs) and Cepheids. While rare and difficult to detect, DEBs provide us with the potential to determine these distances with an accuracy better than 5%. The extensive photometry obtained in order to detect DEBs provides us with good light curves for the Cepheid variables. These are essential to the parallel project to derive direct Baade-Wesselink distances to Cepheids in M31 and M33. For both Cepheids and eclipsing binaries, the distance estimates will be free of any intermediate steps. As a first step in the DIRECT project, between September 1996 and October 1997 we obtained 95 full/partial nights on the F. L. Whipple Observatory 1.2 m telescope and 36 full nights on the Michigan-Dartmouth-MIT 1.3 m telescope to search for DEBs and new Cepheids in the M31 and M33 galaxies. In this paper, fourth in the series, we 1 Based on the observations collected at the Michigan-Dartmouth-MIT (MDM) 1.3 m telescope and at the F. L. Whipple Observatory (FLWO) 1.2 m telescope – 2 – present the catalog of variable stars, most of them newly detected, found in the field M31D [(α, δ) = (11. • 03, 41. • 27), J2000.0]. We have found 71 variable stars: 5 eclipsing binaries, 38 Cepheids and 28 other periodic, possible long period or non-periodic variables. The catalog of variables, as well as their photometry and finding charts, is available via anonymous ftp and the World Wide Web. The complete set of the CCD frames is available upon request.