Master's Thesis Defense by Louise Dyregaard Nielsen – Niels Bohr Institute - University of Copenhagen

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Master's Thesis Defense by Louise Dyregaard Nielsen

"Understanding Early Star Formation: Probing Kinematic and Thermal Properties of the Very Low Luminosity Object DC2742-04-IRS"

Abstract:
How and under which circumstances star formation happens is one of the
fundamental questions in astronomy. Probing the internal parts of stellar
nurseries is a difficult task due to the inherent faint, obscured and
short-life nature of these environments. Very Low Luminosity Objects (VeLLOs)
are believed to be the manifestation of the earliest stages of star formation.

The first VeLLOs were discovered as a result of the Spitzer Space Telescope
Legacy project ”From Molecular cores to Planet Forming Disks” (Evans et al.
2003), offering unprecedented sensitivity at 3.6-160 microns. Dense cores that
were otherwise deemed starless turned out to harbour central objects with
internal luminosities less than 0.1 L_sun known under the collective VeLLOs.
The central object in the core will heat up the gas around it and possibly also
drive a bipolar outflow.

The embedded object DC2742-04-IRS may have an internal luminosity as low as
0.001 L_sun (Dunham et al. 2008), which makes it the faintest VeLLO discovered
to this date. Deep H-band imaging performed with Hubble Space Telescope shows a
faint scattering light nebula with the Spitzer source located in the centre of
this bipolar outflow. This thesis uses photometric and spectral sub-mm data
taken with the Atacama Pathfinder EXperiment (APEX) to probe temperature,
density and dynamical structure in the immediate environment of DC2742-04-IRS.
Additional unpublished Herschel Space Telescope data (100-500 microns) are also
used.

The excitation temperatures found are consistent with temperatures found in
other VeLLOs, all under 10 K. The column density measured both with spectral
lines and continuum emission is N(H2) ≈ 1.6·1023 cm^2 calculated envelope mass
is to be 0.7 M_sun very flat close to the central object, which might imply
that the core is not undergoing collapse.

The line profiles of the optically thick 12CO(3-2) show signs of outflow, which
is an important signature of active star formation. The molecular outflow seems
to be well-aligned with the outflow seen in the HST data. This make
DC2742-04-IRS an extremely low mass object driving an outflow. A general offset
between the sub-mm peak intensities and the IR Spitzer source is present in all
data sets which might indicate that the IR and sub-mm source are not related.

Supervisor: Jes K. Jørgensen