The Physical Properties of Young Stellar Objects in the Large Magellanic Cloud Observed with the Infrared Spectrograph on Spitzer

Abstract

We used an online fitting tool to fit model spectral energy distributions to photometric and spectroscopic data from Spitzer, for 15 young stellar objects (YSOs) in the Large Magellanic Cloud (LMC) . Evidence of confusion in the photometric data was found in 3 cases at 24 microns, and in all cases at 70 and 160 microns and, subsequently, this data was not included in the fits. 5 physical properties: central source mass , accretion rate, disk mass, total luminosity and envelope mass were determined for each source based on the best model fit. Uncertainties in the result were defined by the minimum and maximum values in subsequent good fits ,where the chi squared per data point minus the minimum chi squared per data point is less than 7. We found the following ranges for the physical properties of the sources in our sample: central source mass: 10.5-28.5 solar masses ; envelope accretion rate: 6.70*10^(-8)-2.45*10^(-2) solar masses per year; disk mass: 0-2.17 solar masses; total luminosity: 4.37*10^3-8.22*10^4 solar luminosities ; envelope mass 1.05*10^2-1.50*10^4. These are in reasonable agreement with results derived by other methods. The evolutionary stage of each source was determined using a classification scheme based on central source mass, envelope accretion rate and disk mass. 4 of our sources were found to be in stage II of their evolution; the remainder were found to be in stage I. The classification of our sources in this scheme also showed a reasonable correspondence with their classification in a scheme based on the relationship between total luminosity and envelope mass. Finally, we used the total derived mass of the sources in our sample to calculate the star formation rate in the LMC. We found a value of 1.24*10^(-3) solar masses per year, much lower than what we would expect. We attribute this to the fact that our source sample covers a very limited region in parameter space and is also found to contain only about 10 per cent of LMC YSOs in the mass range 11-20 solar masses.

Date of Award	31 Dec 2011
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Gary Fuller (Supervisor)