Archived from the DIRECT project: http://cfa-www.harvard.edu/~kstanek/DIRECT/
Detached eclipsing binaries (DEBs) have the potential to establish distances to M31 and M33 with an unprecedented accuracy of better than 5% and possibly to better than 1%. These distances are now known to no better than 10-15%, as there are discrepancies of 0.2-0.3 mag between various distance indicators. Eclipsing binaries offer a single step distance determination to these galaxies and may therefore provide an accurate zero point calibration - a major step towards very accurate determination of the Hubble constant. DEBs have not been used so far as distance indicators to M31 and M33. Only now availability of large format CCD detectors and inexpensive CPUs makes it possible to organize a massive search for periodic variables, which is producing a handful of good DEB candidates. These can then be observed with the powerful new 6.5-10 meter telescopes.
As a first step of the DIRECT project, between September 1996 and November 1999 we obtained about 200 full/partial nights on the F. L. Whipple Observatory (FLWO) 1.2-meter telescope and the Michigan-Dartmouth-MIT (MDM) 1.3-meter telescope to search for detached eclipsing binaries and Cepheids in the M31 and the M33 galaxies. The second step involved obtaining precise light curves for 2 selected targets in M33 with the Kitt Peak 2.1 meter over 27 nights in 1999 and 2001. In 2002-2004, we obtained a total of 4 nights on the Keck II 10 meter telescope and 19 hours on the 8 meter Gemini telescope for the spectroscopic follow-up of the brightest DEB (V=19.5 mag). With infrared photometry from Gemini we constrained the extinction to the system and measured a 6% distance to M33: 964+/-54 kpc (24.92 +/- 0.12 mag).
The massive photometry provides us with good light curves for DEBs and for Cepheid variables, which is essential to the parallel project to derive direct Baade-Wesselink distances to Cepheids in M31 and M33. With both Cepheids and eclipsing binaries the distances to M31 and M33 will be free of any intermediate steps (hence the DIRECT).
Last Modification: January 6, 2024