Spectrophotometric Distances to Galactic HII Regions

A. P. Moisés$^{1}$, A. Damineli$^{1}$, E. Figuerêdo$^{1}$, R. D. Blum$^{2}$, P. S. Conti$^{3}$ and C. L. Barbosa$^{4}$

$^{1}$IAG-USP, Rua do Mat~ao, 1226, 05508-900, S~ao Paulo, SP Brazil
$^{2}$NOAO Gemini Science Center, 950 N Cherry Ave., Tuczon, AZ 85719 USA.
$^{3}$JILA, University of Colorado, Boulder, CO 80309-0440, USA.
$^{4}$IP&D-UNIVAP, Av. Shishima Hifumi, 2911, 12244-000 S. J. dos Campos, SP Brazil

We present a near infrared study of the stellar content of 35 HII regions in the Galactic plane, 24 of them have been classified as giant HII regions. We have selected these optically obscured star forming regions from the catalogs of Russeil (2003), Conti & Crowther (2004) and Bica et al. (2003). In this work, we have used the near infrared domain J−, H− and Ks− band color images to visually inspect the sample. Also, color-color and color-magnitude diagrams were used to indicate ionizing star candidates, as well as, the presence of young stellar objects such as classical TTauri Stars (CTTS) and massive young stellar objects (MYSOs). We have obtained Spitzer IRAC images for each region to help further characterize them. Spitzer and near infrared morphology to place each cluster in an evolutionary phase of development. Spitzer photometry was also used to classify the MYSOs. Comparison of the main sequence in color-magnitude diagrams to each observed cluster was used to infer whether or not the cluster kinematic distance is consistent with brightnesses of the stellar sources. We find qualitative agreement for a dozen of the regions, but about half the regions have near infrared photometry that suggests they may be closer than the kinematic distance. A significant fraction of these already have spectrophotometric parallaxes which support smaller distances. These discrepancies between kinematic and spectrophotometric distances are not due to the spectrophotometric methodologies, since independent non-kinematic measurements are in agreement with the spectrophotometric results. For instance, trigonometric parallaxes of star-forming regions were collected from the literature and show the same effect of smaller distances when compared to the kinematic results. In our sample of HII regions, most of the clusters are evident in the near infrared images. Finally, it is possible to distinguish among qualitative evolutionary stages for these objects.

Reference: Accepted for publication in MNRAS
Status: Manuscript has been accepted

Weblink: http://adsabs.harvard.edu/abs/2010arXiv1009.3924M


Email: apmoises@astro.iag.usp.br