Rotation and Hα Emission in a Young SMC Cluster: A Spectroscopic View of NGC 330

Abstract We present an analysis of high-resolution optical spectra recorded for 30 stars of the split extended main-sequence turnoff of the young (∼40 Myr) Small Magellanic Cloud globular cluster NGC 330. Spectra were obtained with the Michigan/Magellan Fiber System and Magellan Inamori Kyocera Echelle spectrographs located on the Magellan-Clay 6.5 m telescope. These spectra revealed the presence of Be stars, occupying primarily the cool side of the split main sequence. Rotational velocity ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>v</mml:mi> <mml:mi>sin</mml:mi> <mml:mi>i</mml:mi> </mml:math> ) measurements for most of the targets are consistent with the presence of two populations of stars in the cluster: one made up of rapidly rotating Be stars ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo stretchy="false">〈</mml:mo> <mml:mi>v</mml:mi> <mml:mi>sin</mml:mi> <mml:mi>i</mml:mi> <mml:mo stretchy="false">〉</mml:mo> <mml:mo>≈</mml:mo> <mml:mn>200</mml:mn> </mml:math> km s −1 ) and the other consisting of warmer stars with slower rotation ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo stretchy="false">〈</mml:mo> <mml:mi>v</mml:mi> <mml:mi>sin</mml:mi> <mml:mi>i</mml:mi> <mml:mo stretchy="false">〉</mml:mo> <mml:mo>≈</mml:mo> <mml:mn>50</mml:mn> </mml:math> km s −1 ). Core emission in the H δ photospheric lines was observed for most of the H α emitters. The shell parameter computed for the targets in our sample indicates that most of the observed stars should have inclinations below 75°. These results confirm the detection of Be stars obtained through photometry but also reveal the presence of narrow H α and H δ features for some targets that cannot be detected with low-resolution spectroscopy or photometry. Asymmetry variability of H α line profiles on the timescales of a few years is also observed and could provide information on the geometry of the decretion disks. Observations revealed the presence of nebular H α emission, strong enough in faint targets to compromise the extraction of spectra and to impact narrow-band photometry used to assess the presence of H α emission.