30 research outputs found
Spectrophotometric Distances to Galactic H\,{\sc{ii}} Regions
We present a near infrared study of the stellar content of 35 H\,{\sc{ii}}
regions in the Galactic plane. In this work, we have used the near infrared
domain , and 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 {\it Spitzer} IRAC images for each region to help
further characterize them. {\it Spitzer} and near infrared morphology to place
each cluster in an evolutionary phase of development. {\it 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 H\,{\sc{ii}} 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.Comment: 59 pages, 146 figures and 4 tables. MNRAS accepte