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Title: Disc-accretion in star-forming regions
Author: Kalari, Venu Madhav
ISNI:       0000 0004 5989 0386
Awarding Body: Queen's University Belfast
Current Institution: Queen's University Belfast
Date of Award: 2015
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In this thesis, I present new ultraviolet/optical/infrared photometric and spectroscopic observations of pre-main sequence stars (PMS) that have formed either in metal-poor conditions, or in the vicinity of strong ionising radiation. This includes observations of 235 Classical T Tauri stars in the Lagoon Nebula; 63 Classical T Tauril Herbig Ae stars in the Carina Nebula open cluster Trumpler 14; 24 intermediate mass T Tauri stars in the low-Z Sh 2-284 star-forming region; and one Herbig 8[e] PMS candidate in the metal-poor 30 Doradus region. I measure the accretion rates of these PMS stars using the intensities of the U/Halpha band excess measured through either optical spectra of imaging. Where possible, I use archive infrared photometry in the 1.2-8 micron wavelength range to estimate the PMS disc evolutionary stage. The influence of the surrounding environment on the accretion rate evolution of pre-main sequence stars in these regions is explored using the spatial, and temporal distributions of accretion rate, mass, age and disc stage of PMS stars. In the wide-field photometric data of the Lagoon Nebula, I find that the spatial distributions of PMS stars is a continuum, ranging from dense clustering to relative isolation. Strongly accretion PMS stars are generally clumped together, in close proximity to their natal molecular cloud, whereas weaker, older accretors are relatively space apart. Ionising radiation from early-type stars appears to positively affect accretion rates on scales of 2-3 pc, but no evidence for triggered star formation is found. In addition, the accretion rates measured from Halpha imaging correlate well to those estimated from U-band photometry. In wide-field photometric data of Trumpler 14, I discover a population of PMS candidates nearly 25 Myrs old. I argue that these PMS candidates are a foreground population, approximately 5 Myr old that belong to the Carina Nebula cluster Trumpler 16. Using Halpha spectra of 24 intermediate mass T Tauri stars in Sh 2-284 (Z-0.004), I demonstrate that there is little evidence for a systematic change in accretion rates with metallicity, contrary to previous literature results at Z-0.006-0.002 in the Magellanic Clouds. I suggest that previous studies are likely affected by detection limits and biases. I also present ultraviolet/optical spectra of the Herbig 8[e] PMS candidate VFTS 822 located in the 30 Doradus region of the Large Magellanic Cloud. I discuss the impact of the discovery of VFTS 822 for star formation studies in the Magellanic Clouds, external Galaxies .
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available