Programme "Scientific projects"

Establishing the Triangulum Galaxy (M33) as an anchor of the Extragalactic Distance Scale

National Observatory of Athens


The aim of this work is to obtain an accurate distance to the Triangulum galaxy (M33) and establish it as an anchor of the extragalactic distance scale. The method relies on binary star systems in configurations exhibiting periodic eclipses, which are classical astronomical distance indicators for determining accurate and precise fundamental distances.

We applied this technique to an eclipsing binary in M33 in 2006 and obtained a distance that was 13% longer than previous Cepheid-based distances. To resolve this discrepancy, in the present study, we analyzed new data we obtained on a second system to obtain a precise, independent distance and confirm our previous result. Our preliminary analysis of the light and radial velocity curve revealed that the components have masses of 16 and 24 solar masses, at a distance of 892 Β± 21 kpc, which is consistent with our first measurement.

The determination of an accurate distance to M33 will help calibrate the Cepheid period-luminosity relation and resolve the ongoing controversy about the distance scale, with its ramifications for cosmology and stellar ages.

Final report (in Greek)



Alcestis Bonanou, Astronomer, National Observatory of Athens

Project Team:

Norberto Castro Rodriguez, Astronomer, National Observatory of Athens

Lucas Macri, Professor of Astronomy, Texas A & M University

Krzysztof Stanek, Professor of Astronomy, The Ohio State University

Lofos Nymphon

11810 Thissio Athens

Tel.: +30 210 34 90 000

Fax: +30 210 34 90 120