Studying young stellar objects with near-IR non-redundant aperture masking and millimeter interferometry
Date
2018
Authors
Ruiz Rodriguez, Dary Alexandra
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Abstract
Circumstellar disks and outflows play a central role in the
growth of low-mass
(M < 2 M_sun) stars and the formation of planetary systems. These
disks are
ubiquitous at young ages (< 1 Myr), as they are naturally formed
during the
gravitational collapse of protostellar cores due to the
conservation of angular
momentum. Circumstellar disks feed the forming stars and provide
an environment
for small grains to eventually grow into rocky planets and the
cores of
giant planets at a wide range of stellocentric distances (
~0.1-100 au). In parallel
to the growth solids in the disk, bipolar outflows and winds are
generated
on similar physical scales. Outflows carry angular momentum away
and help
the accretion of circumstellar material onto the central object.
They also play
an important role in the dissipation of the envelope that marks
the transition
from the Class I (a deeply embedded protostar) to Class II stage
(an optically
visible T Tauri star). Eventually, the primordial disk disperses,
leaving a
star surrounded by a remnant debris (Class III) object and likely
a system of
planetesimals and planets.
This thesis incorporates high-sensitivity millimeter-wavelength
interferometry
and near-infrared Non-Redundant Mask (NRM) Interferometry to
assess molecular
outflow and disks properties in Class I-II objects. It explores
the physical
mechanisms dispersing the disk and envelope system (e.g.,
outflows and dynamical
interactions in binary systems) and the properties of
protoplanetary
disks as a function of stellar mass at an age of 2-3 Myr.
We investigate the properties of the Class I molecular outflows
present in HBC
494 and V883 Ori, two young stellar objects experiencing episodic
events of
extreme accretion known as FU Ori outbursts. These outflows help
to disperse
the surrounding envelope at very early stages while removing
angular momentum
from the disk. We estimate the kinematic properties and describe
physical
structures of the outflows using the 12CO and 13CO emissions
lines. Similarly,
the C18O emission line is used to describe envelope material from
both sources.
An outstanding result is the wide-opening angle of the outflow
cavities of ~150 deg. for both sources. Outflows masses in both
FUors are on the same order of magnitude, while V883 Ori shows an
outflow component that is much slower (characteristic velocity of
only 0.65 km s^-1) than seen in other FUors such as
HBC 494. To date, interferometric studies of FUors are scarce and
more observations
needed in order to compare with other objects at a similar
sensitivity
and resolution.
In addition, using NRM, we searched for binary companions to
objects previously
classified as Transitional Disks (TD, disks with inner opacity
holes)
in nearby (d < 300 pc) star-forming regions (Ophiuchus,
Taurus-Auriga, and
IC348) and investigate the interaction with (sub)stellar
companions as a possible
mechanism for the depletion of their inner disks. We implement a
new
method of completeness correction using a combination of randomly
sampled
binary orbits and Bayesian inference. We find that ~ 0.38 +/-
0.09 of the TDs
are actually circumbinary disks, while the remaining objects are
transitional
disks where the inner holes are the result of other internal
processes such as
photoevaporation, and/or planet-disk interactions.
Finally, we present an ALMA 1.3 mm survey of Class II sources in
the benchmark 2-3 Myr stellar cluster IC 348 to investigate the
properties of disks at the time 50% of the disks have already
been completely dispersed. We find that the detection rate in 1.3
mm continuum is a strong function of stellar mass. Most
targets with masses 0.3 < M_sun remain undetected down to a
3-sigma sensitivity of
0.45 mJy, corresponding to a disk dust mass of ~0.9 M_earth. A
stacking analysis
of the non-detections suggests that the typical dust mass around
most 2-3 Myr
old M-type stars is 0.2 M_earth (or 0.07 M_JUP of gas + dust,
assuming a standard
gas to dust mass ratio of 100). A Bayesian analysis is used to
statistically compare
IC 348 to other star-forming regions. As a general result, this
analysis
shows that IC 348 disks are a factor of 5 fainter on average than
in Taurus,
Cha I, and Lupus. While IC 348 and sigma Ori have similar
distributions. On the
other hand, Upper Sco disks are definitely fainter on average
than IC 348. The
resulting cumulative distribution functions confirm a clear
evolution (depletion
of mm-sized grains) of the circumstellar disks in these regions
over a period of
1-10 Myr.
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Keywords
Interferometry, T-Tauri Stars, Disks
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