The WFI Halpha spectroscopic survey

TL;DR

This paper reports on a spectroscopic survey of Halpha emitters in galactic and SMC open clusters, revealing the nature of emission line stars and the prevalence of Be stars at low metallicity using the ESO Wide Field Imager.

Contribution

It introduces a new large-scale Halpha survey in the SMC and provides initial results on Be star ratios in 84 open clusters, improving understanding of stellar rotation and emission features.

Findings

Small number of true circumstellar emission line stars in NGC6611.

Faster rotation of B-type stars in the SMC compared to the Milky Way.

First large-scale Halpha survey of the SMC with 3 million spectra.

Abstract

This document presents the results from our spectroscopic survey of Halpha emitters in galactic and SMC open clusters with the ESO Wide Field Imager in its slitless spectroscopic mode. First of all, for the galactic open cluster NGC6611, in which, the number and the nature of emission line stars is still the object of debates, we show that the number of true circumstellar emission line stars is small. Second, at low metallicity, typically in the Small Magellanic Cloud, B-type stars rotate faster than in the Milky Way and thus it is expected a larger number of Be stars. However, till now, search for Be stars was only performed in a very small number of open clusters in the Magellanic Clouds. Using the ESO/WFI in its slitless spectroscopic mode, we performed a Halpha survey of the Small Magellanic Cloud. 3 million low-resolution spectra centered on Halpha were obtained in the whole SMC. Here, we present the method to exploit the data and first results for 84 open clusters in the SMC about the ratios of Be stars to B stars.