Welcome to the M33 CFHT variability survey web page

We have surveyed the Local Group galaxy M33 for variable stars, using the wide-field camera MegaCam on the Canada-France-Hawaii telescope. This page contains information about the survey and over time, it will develop into an interface for accessing our data.

The survey, in a nutshell:
    1 square degree,
    3 filters (Sloan-like g'r'i')
    3 seasons
    33 epochs

We use image subtraction to detect variability. We have found 36000 variable objects, and we have over 80000 light curves.
We use DAOPHOT to extract fluxes. There are roughly 2.5 million sources detected in each passband. We have point source photometry for 4.7 million different sources; about 1 million sources detected in all 3 filters.

In 2008 and 2009 we obtained more epochs with the 2.5m Isaac Newton Telescope (La Palma). The specific aim was to find double-mode Cepheids (a.k.a. "beat Cepheids"). The sampling is quite different from the CFHT data (several epochs per night over a few nights, mostly in r band, little g and i). These images are now calibrated and will be used to calibrate the CFHT data.

Data access:

A paper describing the search for variables is published (Hartman et al. 2006, MNRAS 371, 1405), also available on astro-ph.
Over time, we will add more information as the work progresses (catalogs for each types of variables -- Cepheids, Miras, etc. -- periods, calibrated photometry), but for now you can download several tables (published in Hartman et al. 2006) that contain information about the variables found.

WARNING: The photometry is not yet calibrated. We provide "semi-instrumental" magnitudes. We used a constant zero point (provided by the observatory) for all images. From one chip to another, there can be differences of a few tenths of a magnitude.

The files are publicly available and you can do whatever you want with the data. It is nice to let us know what you do though.

There are two different groups of variables. One is for stars that have a counterpart in the deep reference image (most "regular" variables like Cepheids, Miras, LBVs, red giants, etc.). Download the summary file and the light curves (gzipped, 30 Mb).
The other group is for stars that do not have a counterpart (one-off things, possible novae, fast microlensing events, etc.). Download the summary file and the light curves (gzipped, 23 Mb).


Here is a link to papers that use or cite the data

You can also check out some cool movies, made by Joel Hartman .

This is the whole galaxy, with the movie region highlighted [Credit: T.A.Rector (NRAO/AUI/NSF and NOAO/AURA/NSF) and M.Hanna (NOAO/AURA/NSF)]:

Field of view

Here is the movie for this region.

Zooming in on a sub-region .

Survey logo from Cool Text: Logo and Graphics Generator