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Photometric Survey of Stellar Clusters in the Outer Part of M33. II. Analysis of HST/ACS Images

Zloczewski K., Kaluzny J.

Acta Astronomica

2009

Vol. 59, No. 1

47--67

We have used deep ACS/WFC images of M33 to check the nature of extended objects detected by the ground based survey of Zloczewski etal (2008). A total of 24 candidates turned out to be genuine compact stellar clusters. In addition we detected 91 new clusters. Equatorial coordinates, integrated magnitudes and angular sizes are listed for all 115 objects. Forty-two clusters have sufficiently red colors to be candidates for old globulars. For four clusters we extracted resolved stellar photometry. Object 33-3-018 located in the outer disk of M33 turned out to be a young cluster with an age estimated at 200-350 Myr. Cluster ZK-90 has an age of 3-5 Gyr. The remaining two clusters have intermediate ages ranging from one to a few Gyr.

Reddening and Age for 12 Concentrated Large Magellanic Cloud Clusters Determined from Integrated Spectroscopy

Palma T., Ahumada A. V., Clariá J. J., Santos Jr. J. F. C., Bica E.

Acta Astronomica

2008

Vol. 58, No. 4

359--372

We present flux-calibrated integrated spectra in the optical range (3700-6800 å) for a sample of 12 concentrated Large Magellanic Cloud (LMC) star clusters, five of which do not have previous age and reddening determinations. We estimate simultaneously age and foreground reddening by comparing the continuum distribution and line strengths of the cluster spectra with those of template spectra. Cluster reddening values and ages are also derived from the available interstellar extinction maps and from the equivalent width (EW) method, respectively. The latter includes the use of age/metallicity calibrations and diagnostic diagrams involving the sum of EWs of selected spectral lines. In general, cluster ages derived from both methods show good agreement and range from 40 Myr to 800 Myr, while the foreground reddening values vary from E(B-V)= 0.0 mag to 0.16 mag. The present cluster sample complements previous ones, in an effort to create a spectral library for the LMC with several clusters per age bin.

Photometric Survey for Stellar Clusters in the Outer Part of M33

Zloczewski K., Kaluzny J., Hartman J.

Acta Astronomica

2008

Vol. 58, No. 1

23--39

We present a catalog of 4780 extended sources from the outer field of M33. The catalog includes 73 previously identified clusters or planetary nebulae, 1153 likely background galaxies, and 3554 new candidate stellar clusters. The survey is based on deep ground-based images obtained with the MegaCam instrument on the CFHT telescope. We provide g'r'i' photometry for detected objects as well as estimates of the FWHM and ellipticity of their profiles. The sample includes 122 new, relatively bright, likely globular clusters. Follow-up observations of fainter candidates from our list may extend the faint-end of the observed luminosity function of globular clusters in M33 by up to 3 magnitudes. The catalog includes several cluster candidates located in the outskirts of the galaxy. These objects are promising targets for deep photometry with the HST. We present a color-magnitude diagram for one detected object, showing that it is an extended and low-surface-brightness old cluster located at an angular distance of 27' from the center of M33.