INFRARED SPECTROSCOPY OF INTERMEDIATE-MASS YOUNG STELLAR OBJECTS

In this paper, we present Spitzer Infrared Spectrograph spectroscopy for 14 intermediate-mass young stellar objects (YSOs). We use Spitzer spectroscopy to investigate the physical properties of these sources and their environments. Our sample can be divided into two types of objects: young isolated, embedded objects with spectra that are dominated by ice and silicate absorption bands, and more evolved objects that are dominated by extended emission from polycyclic aromatic hydrocarbons (PAHs) and pure H(2) rotational lines. We are able to constrain the illuminating FUV fields by classifying the PAH bands below 9 mu m. For most of the sources we are able to detect several atomic fine structure lines. In particular, the [Ne II] line appearing in two regions could originate from unresolved photodissociation regions or J-shocks. We relate the identified spectral features to observations obtained from NIR through submillimeter imaging. The spatial extent of several H(2) and PAH bands is matched with morphologies identified in previous Infrared Array Camera observations. This also allows us to distinguish between the different H(2) excitation mechanisms. In addition, we calculate the optical extinction from the silicate bands and use this to constrain the spectral energy distribution fit, allowing us to estimate the masses of these YSOs.