Distances to M31 and M33 (original) (raw)

Archived from the DIRECT project: http://cfa-www.harvard.edu/\~kstanek/DIRECT/

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Determining the distances to nearby galaxies

The two nearby galaxies - M31 and M33, are stepping stones to most of our current effort to understand the evolving universe at large scales. They are essential to the calibration of the extragalactic distance scale and for constraining population synthesis models for early galaxy formation and evolution. There is one simple requirement for all this - accurate distances.

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 200full/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 forDEBs 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).

DIRECT papers:

(as of January 2007)

Paper: The First DIRECT Distance Determination to a Detached Eclipsing Binary in M33, by Bonanos, Stanek, Kudritzki, Macri et al. was published in the Astrophysical Journal (November 2006) (also preprint:astro-ph:0606279)
Paper: The RR Lyrae Distance to the Draco Dwarf Spheroidal Galaxy, by Bonanos et.al. was published in the Astronomical Journal (February 2004) (also preprint:astro-ph/0310477)
Invited Talk: The DIRECT Project, by Macri, was published in the proceedings of the IAU Colloquium 193, "Variable stars in the Local Group", D.W. Kurtz & K. Pollard, eds. (2004) (also preprint:astro-ph/0310016)
Contributed Talk: Determining Accurate Distances to Nearby Galaxies, by Bonanos, was published in the proceedings of the 6th Hellenic Astronomical Conference (September 2003) (Preprint:astro-ph/0312310)
Paper: The DIRECT Distances to Nearby Galaxies Using Detached Eclipsing Binaries and Cepheids. IX. Variables in the Field M31Y Discovered with Image Subtraction by Bonanos et.al. was published in the Astronomical Journal (July 2003) (Preprint:astro-ph/0303307)
Paper: DIRECT Distances to Nearby Galaxies Using Detached Eclipsing Binaries and Cepheids. VIII. Additional Variables in the Field M33B Discovered with Image Subtraction by Mochejska_et.al._ was published in the Astronomical Journal_(November 2001)_ (Preprint:astro-ph/0107279)

More DIRECT stuff:

(October 2003)

Get the light curves and finding charts of variables found in the Draco dwarf spheroidal galaxy.
Get the light curves and finding chart for Hubble's Variable 19 in M33

Authors: Alceste Bonanos and Krzysztof Stanek
Curator: Hartmut Frommert

Hartmut Frommert
[contact]

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Last Modification: January 6, 2024