Star formation studies using the Herschel-SPIRE Imaging FTS

Abstract

The study of low mass star formation in our local Galaxy is particularly suited to HERSCHEL. The SPIRE spectrometer and photometer aboard the spacecraft operate in the ~ 200 - 600�m range and are well suited to probe the cold, dusty environments in molecular clouds where prestellar cores reside. The SPIRE FTS spectrometer is an interferometer, and this instrument design has strengths and weaknesses which are im- portant to understand when using data from the instrument. Herschel is set to continue groundbreaking work in the infrared, building upon earlier work from ISO, IRAS, and SPITZER, probing deep into star forming regions and improving our knowledge of the processes within. In this PhD thesis, we outline the current body of knowledge in low mass star formation. We examine the properties of the SPIRE FTS as a spectrometerusing a small, laboratory designed desktop FTS. We study the intrinsic properties of the instrument, as a way of understanding issues we are likely to see when using the SPIRE FTS in ight. With these issues firmly in mind, we examine the creation and use of SLIDE - an interactive IDL-based tool for processing SPIRE FTS data. SLIDE can extract line and continuum information from SPIRE FTS SEDs. We outline the creation, testing and use of SLIDE and provide examples of the use of SLIDE in astronomy with some examples from the literature. We then use the line information we extract from a variety of sources with the spectrometer, to examine how SED fitting from photometer data could be affected by line contamination. We simulate a wide range of greybodies with noise and line con- tamination and examine how SED fitting is affected. Our simulations conclude that line contamination is not enough to affect the recovery of temperature and spectral index B significantly. Finally we use the information we have deduced to examine SPIRE FTS SEDs of L1689B - a prestellar core located in Ophiuchus. Our SED fitting of the core confirms that this core is starless with no internal heating source, and the spectral index profile over the core morphology is consistent with an increasing density of fractal aggregrate grains towards the centre. The increase in grain density and spectral index profile is also in agreement with previous CO depletion data. Fractal grain growth of this nature is consistent with dust grain models