Spectroscopic Optical Observations in the Search of CN20 Exciting Star(s)

Abstract

Using molecular lines and radio continuum observations, Ortega et al. (2016) studied the bright-rimmed cloud (BRC) at the border of the infrared dust bubble CN20 (H ii region G000.640+0.623). To study star formation in the cloud, most likely triggered by the action of CN20, these authors used photometric criterial (Comerón & Pasquali 2012) to search for stars which could excite the bubble. Then they roughly estimated the resulting ionizing photon flux impinging upon the illuminated face of the BRC. Figure 1 (upper panel) displays the southern portion of CN20 as seen in 8 μm (from Spitzer-IRAC) and 24 μm (from Spitzer-MIPS) in red and green, respectively. Crosses are the positions of stars that according to the photometric criteria of Comerón & Pasquali (2012) could be O-type (S1, S2, and S3). In particular, Ortega et al. (2016) selected S1 as the most probable star to be the main ionizing source of the region, which was suggested to be an O9.5V. In this work we present results from spectroscopic observations towards these stars to accurately determine their spectral type.