Investigating Jets and their Role in Star Formation

In this thesis, I present the results of a number of studies using high-resolution observations from world-class telescopes. The aim of these studies is to investigate protostellar jets and their role in star formation. In a case study of the bipolar jet from the T Tauri star DO Tau, we observe significant asymmetries in the morphology and kinematics of the jet and counterjet. The collimation of the jet supports the idea that magnetic fields collimate the jet, rather than pressure from the infalling envelope. If magnetic fields are responsible for jet collimation, then they may also drive jet launching. By measuring the radial velocities across the jet, we can calculate an upper limit on the jet launching radii. Our results support an X-wind or narrow disk wind model. Jet axis wiggling is also observed and is consistent with jet precession, which may be caused by an unseen companion in the disk or by launching the disk wind. In a study of four Class 0/I jets (HH 1, HH 34, HH 46 and HH 111) using high-resolution HST images, we were able to detect the inner knots of the red-shifted lobes in all four sources in more detail than previous studies. We compare these images to archival data to measure the proper motions in each jet. Jet axis wiggling is observed in three of these sources and the wiggling pattern in the HH 111 jet is consistent with jet precession and the presence of a companion in the disk. We also measure the extinction in each jet, which is quite high close to the star but decreases further out along each jet. Extinction measurements are important in the interpretation of emission line ratios, which reveal plasma conditions along the jet and hence the mass and momentum transfer. These two case studies illustrate the power of high resolution observations in differentiating between models of jet launching, and also reveal that protostellar jet trajectories could be a useful tool in identifying newly forming substellar companions close to the star. Finally, a survey of over 100 stars was conducted using high-resolution X-Shooter spectra. This study examines He I line profiles which vary between the two star forming regions examined in the sample, suggesting a trend with age. We also find that the maximum absorption velocity appears to be correlated with the source inclination and with the accretion rates of the sources. Our study confirms the results of past works (Edwards et al., 2006; Kwan et al., 2007; Fischer et al., 2008) and supports the idea that these winds are accretion powered. This survey gives context to our two case studies, by examining the link between accretion and ejection. High resolution observations are critical to advance understanding of the role of protostellar jets in star formation, as illustrated by the contribution of this thesis. The recently launched JWST facility marks the start of an era which will see exciting progress in this field, as its near-IR instruments peer deep into the embedded accretion-ejection engine.