The Young SMC Cluster NGC 330 in the Optical and Infrared

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Session 51 -- Dwarf Galaxies
Display presentation, Tuesday, 10, 1995, 9:20am - 6:30pm

[51.12] The Young SMC Cluster NGC 330 in the Optical and Infrared

E.K.Grebel (Sternwarte Bonn), W.J.Roberts (CAS), W.Brandner (AI W\"urzburg), A.Moneti (ESTEC)

We analyzed UBVRI, H$\alpha$, Washington CMT$_1$T$_2$, and JHK CCD photometry as well as low-resolution spectroscopy of the young, populous cluster NGC 330 in the Small Magellanic Cloud. Though one of the most thoroughly studied clusters, there is significant disagreement about two of the most important parameters of NGC 330 -- metallicity and reddening. Reddening determinations for NGC 330 range from E$_{\rm B-V} = 0.03$ mag to 0.12 mag, while recent abundance determinations differ by more than 1 dex in [Fe/H].

Using our new objective theoretical technique of multicolor isochrone fitting (e.g., Roberts \& Grebel, this conference), we can determine for the first time reddening, abundance, age, and distance modulus in a single calculation. Application of our method to the independent Johnson and Washington data and isochrones shows excellent agreement. We derive the following results for NGC 330: E$_{\rm B-V,0} = 0.10\pm0.015$, [Fe/H] = $-0.67\pm0.24$ dex, DM = $18.90\pm0.07$, age $20\pm\sim1.5$ Myr. These physically and observationally compatible results provide some explanation for how discrepant values could be found by the several empirical and theoretical methods used in prior studies, as we discuss.

We also studied the Be star content of NGC 330. Among other things, its Be stars exhibit an infrared excess of up to 1 mag in V--K. We find correlations between infrared excess and our Balmer emission strength index that give insight into the atmosphere and environment of Be stars.

We compare the properties of the cluster stars to those of the surrounding field population. Several prior studies found the young field population to be more metal-rich than the cluster population. We do not find any significant difference: the region seems well mixed. These metallicities will be useful in studying the enrichment history of the SMC.

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