A Study of the Physics of the Interstellar Medium using the Herschel-SPIRE Instrument
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Date
2014-10-03
Authors
Makiwa, Gibion
Journal Title
Journal ISSN
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Publisher
Lethbridge, Alta. : University of Lethbridge, Dept. of Physics & Astronomy
Abstract
Stars form in cold and dense regions of the interstellar medium where Rayleigh scattering heavily attenuates short wavelength radiation but allows long wavelength radiation to escape. Long-wavelength radiation from star forming regions, after travelling many lightyears to reach us, is absorbed by the water vapor in the Earth's atmosphere before it can reach ground-based telescopes. Thus, prior to the far-infrared space telescope, Herschel, our view of the submillimeter universe was through very narrow spectral windows that are only accessible from high mountain sites. Herschel, with its three instruments, was designed to operate in the far-infrared and observe radiation from star forming regions. Unlike ground based telescopes, Herschel has provided the first unfettered access to the entire far-infrared electromagnetic spectrum.
In this work, I have analyzed Herschel observations of three starless cores (L1521E, L1521F and L1689B), one Class 0 protostar (IRAS16293-2422) and one Class I protostar (Elias 29). These observations were obtained with the Spectral and Photometric Imaging Receiver (SPIRE) photometer and spectrometer. The measured low-spectral resolution spectra of starless cores have been used to obtain more accurate spectral energy distributions (SEDs) which have enabled the calculation of dust temperatures, emissivity spectral indices, and masses associated with these cores.
The map-making capability of the SPIRE instrument provided fully sampled spectral maps of IRAS16293-2422 and Elias 29. A wealth of molecular line emission was detected from both protostars. These include 12CO, 13CO, C18O, CI, H2O, HCO+ and CS. Integrated line intensity maps show that both line and continuum emission from IRAS16293-2422 originate from a compact region surrounding the protobinary system. An SED constructed from flux density points obtained with various instruments has been fitted with radiative transfer models to obtain physical parameters associated with IRAS16293-2422. Integrated line intensity maps for Elias 29 have confirmed the previously reported result that there are three components along the line of sight. The spatial extent of molecular emission from these sources is an important constraint in radiative transfer models that are used to better understand the physical conditions in the early stages of star formation.
Far-infrared broadband observations of starless cores, Class 0 and Class I protostars obtained with the Herschel-SPIRE instrument have provided for the first time the ability to study the first stages of star formation. Continuum observations of starless cores have been used to construct SEDs from which more accurate dust temperatures and emissivity indices have been derived. Fully Nyquist sampled observations have been used to study the spatial extent of dust and line emission from Class 0 and Class I protostars.
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Keywords
Star formation, Interstellar medium, Starless cores, Protostars, SPIRE , long wave radiation , infrared space telescope , Spectral and Photometric Imaging Receiver , spectral energy distribution , protostars , starless cores