arXiv subjects

David Zurek

Publications and source records attributed to David Zurek.

39 records · Page 3Linked to original sources

arXiv2001

New Photometry for the Intermediate-age LMC Globular Cluster NGC 2121 and the Nature of the LMC Age Gap

We report new photometry for the cluster NGC 2121 in the Large Magellanic Cloud, which shows a prominent hydrogen core exhaustion gap at the turnoff, and a descending subgiant branch remniscent of Galactic open clusters. We achieve an excellent fit using the Girardi isochrones, finding an age of 3.2 +/- 0.5Gyr, with [Fe/H]=-0.6 +/- 0.2. The isochrones fit the color and shape of the turnoff and subgiant branch so precisely that we constrain the metallicity as well as the age. The smae isochrones also fit SL 663 and NGC 2155, although our photometry for these clusters has much larger errors. We find these clusters to be 0.8 Gyr younger, and 0.4 dex more metal rich, than recently reported in the literature. Consequently, we argue that NGC 2121, NGC 2155, and SL 663 are not properly assigned to the age gap in the LMC, but instead are among the first clusters to have formed int he relatively metal rich, younger group of LMC clusters. We propose a new definition of the LMC Age Gap as extending from 3.2 to 13 Gyr, with ESO121-SCO3 still the only remaining candidate for membership in the age gap.

astro-ph↗

arXiv1999

Two Groups of Nearly Coeval Star Clusters in the Small Magellanic Cloud

We report new photometry of populous intermediate-age clusters in the SMC using the {\sl Hubble Space Telescope}. In contrast to the accepted picture, these clusters appear to have formed in two brief intervals, one $8\pm 2$ Gyr ago, and a more recent burst $2\pm 0.5$ Gyr ago. When the ridgelines of the four clusters (NGC 339, 361, 416, and Kron 3) in the 8 Gyr burst are aligned, the dispersion in turnoff luminosities is $<0.2$ mag, corresponding to a maximum age spread of $\pm 0.7$ Gyr. When the ridgelines of three clusters (NGC 152, 411, and 419) in the 2 Gyr burst are aligned, the maximum dispersion of 0.2 mag in turnoff luminosity corresponds to a permitted age spread of $\pm 0.2$ Gyr. Within each group of clusters, the entire cluster loci (including red giant branches and clumps) are nearly identical, consistent with indistinguishable metallicities and ages. In contrast to the wide dispersion in ages previously reported in the literature, our sample with more precise photometry and age measurements supports a burst-punctuated rather than a continuous cluster formation history for the 2 Gyr and 8 Gyr SMC clusters.

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arXiv1998

Far-Ultraviolet Imaging of the Field Star Population in the Large Magellanic Cloud with HST

We present an analysis of the deepest pure-UV observations with the highest angular resolution ever performed, a set of 12 exposures with the HST WFPC2 and F160BW filter obtained in parallel observing mode, which cover $\sim$12 square arcminutes in the LMC, North of the bar and in the ``general field'' regime of the LMC. The 341 independent measurements of 198 objects represent an accumulated exposure of $\geq 2 10^4$ sec and reveal stars as faint as m$_{UV}\simeq$22 mag. The observations show that $\sim 2/3$ of the UV emission from the LMC is emitted by our HST-detected UV stars in the field, i.e., not in clusters or associations. We identified optical counterparts in the ROE/NRL photometric catalog for $\sim 1/3$ of the objects. The results are used to discuss the nature of these UV sources, to estimate the diffuse UV emission from the LMC as a prototype of dwarf galaxies, and to evaluate the contamination by field stars of UV observations of globular and open clusters in the LMC. We find that the projected density of UV stars in the general field of the LMC is a few times higher than in the Galactic disk close to the Sun. Combining our data with observations by UIT allows us to define the stellar UV luminosity function from $m_{UV}=8$ to 18 mag, and to confirm that the field regions in the LMC have been forming stars at a steady rate during the last 1 Gyr, with an IMF close to the Salpeter law.

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