We investigate the properties of young (≤108 yr) M33 star clusters from the samples presented in the first two papers of this series using far‐UV photometry. Previously, UBV colors were used to derive cluster ages, luminosities, and masses, assuming an extinction interpolated from neighboring stars. Fifteen of 44 clusters imaged in the Hubble Space Telescope WFPC2 with the F170W filter are detected. The far‐UV magnitudes provided by this filter are used to rederive young cluster ages by comparing integrated photometry with stellar evolutionary models. Overall, we find ages consistent with those from our second paper from UBV photometry. However, the addition of the F170W flux provides three major improvements over previous work: (1) This band is more sensitive to the temperature range of clusters younger than ∼108 yr. (2) UBV colors for young clusters with contaminated V‐band fluxes (from red supergiants or from line emission by surrounding excited gas) provide only an upper age limit. The addition of the far‐UV flux allows us to extract precise ages. (3) Far‐UV flux helps to constrain cluster extinction. New theoretical M/LV ratios are presented for cluster ages between 4 × 106 and 1010 yr and metallicities of (Z = 0.02, Y = 0.28), (Z = 0.008, Y = 0.25), (Z = 0.004, Y = 0.24), (Z = 0.001, Y = 0.23), and (Z = 0.0004, Y = 0.23), extracted from the recent models of C. Chiosi. These M/LV values are used to estimate cluster masses from derived ages and measured luminosities. We find young clusters to have masses in the range 6 × 102–2 × 104 M⊙. These values are smaller than the most massive old clusters in M33 (which have masses up to a few times 105 M⊙) in the sample presented in our second paper.
[1]
H. Ford,et al.
Star Clusters in M33. II. Global Properties
,
1999
.
[2]
H. Ford,et al.
Star Clusters in M33. I. Detection, Morphology, and Photometry
,
1999
.
[3]
A. Vallenari,et al.
HST photometry: Can UV colors probe the galaxy ages?
,
1997
.
[4]
P. Massey,et al.
Hot, luminous stars in selected regions of NGC 6822, M31, and M33
,
1995
.
[5]
Forrest J. Rogers,et al.
Spin-Orbit Interaction Effects on the Rosseland Mean Opacity
,
1992
.
[6]
B. Madore,et al.
New Cepheid distances to nearby galaxies based on BVRI CCD photometry. II, The Local Group galaxy M33
,
1991
.
[7]
J. Barbero,et al.
The Age Calibration of Integrated Ultraviolet Colors and Young Stellar Clusters in the Large Magellanic Cloud
,
1990
.
[8]
M. Cassé,et al.
Astrophysical ages and dating methods
,
1990
.
[9]
R. Capuzzo-Dolcetta,et al.
Evolutionary population synthesis - An application to Magellanic Cloud clusters
,
1989
.
[10]
J. Mathis,et al.
The relationship between infrared, optical, and ultraviolet extinction
,
1989
.
[11]
E. Fitzpatrick.
Interstellar extinction variations in the Large Magellanic Cloud
,
1985
.
[12]
Blair D. Savage,et al.
Observed Properties of Interstellar Dust
,
1979
.