27 research outputs found
Studying young stellar objects with near-IR non-redundant aperture masking and millimeter interferometry
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
The frequency of binary star interlopers amongst transitional discs
Using Non-Redundant Mask interferometry (NRM), we searched for binary companions to objects previously classified as transitional discs (TD). These objects are thought to be an evolutionary stage between an optically thick disc and optically thin disc. We investigate the presence of a stellar companion as a possible mechanism of material depletion in the inner region of these discs, which would rule out an ongoing planetary formation process in distances comparable to the binary separation. For our detection limits, we implement a new method of completeness correction using a combination of randomly sampled binary orbits and Bayesian inference. The selected sample of 24 TDs belongs to the nearby and young star-forming regions: Ophiuchus (˜130 pc), Taurus-Auriga (˜140 pc) and IC348 (˜220 pc). These regions are suitable to resolve faint stellar companions with moderate to high confidence levels at distances as low as 2 au from the central star. With a total of 31 objects, including 11 known TDs and circumbinary discs from the literature, we have found that a fraction of 0.38 ± 0.09 of the SEDs of these objects are likely due to the tidal interaction between a close binary and its disc, while the remaining SEDs are likely the result of other internal processes such as photoevaporation, grain growth, planet-disc interactions. In addition, we detected four companions orbiting outside the area of the truncation radii and propose that the IR excesses of these systems are due to a disc orbiting a secondary companion
The ALMA Early Science View of FUor/EXor objects. IV. Misaligned Outflows in the Complex Star-forming Environment of V1647 Ori and McNeil's Nebula
We present Atacama Large Millimeter/sub-millimeter Array (ALMA) observations
of the star-forming environment surrounding V1647 Ori, an outbursting FUor/EXor
pre-MS star. Dust continuum and the (J = 2 - 1) CO, CO, CO
molecular emission lines were observed to characterize the V1647 Ori
circumstellar disc and any large scale molecular features present. We detect
continuum emission from the circumstellar disc and determine a radius r = 40
au, inclination i = 17 and total disc mass of
M of ~0.1 M. We do not identify any disc structures
associated with nearby companions, massive planets or fragmentation. The
molecular cloud environment surrounding V1647 Ori is both structured and
complex. We confirm the presence of an excavated cavity north of V1647 Ori and
have identified dense material at the base of the optical reflection nebula
(McNeil's Nebula) that is actively shaping its surrounding environment. Two
distinct outflows have been detected with dynamical ages of ~11,700 and 17,200
years. These outflows are misaligned suggesting disc precession over ~5500
years as a result of anisotropic accretion events is responsible. The
collimated outflows exhibit velocities of ~2 km s, similar in velocity
to that of other FUor objects presented in this series but significantly slower
than previous observations and model predictions. The V1647 Ori system is
seemingly connected by an "arm" of material to a large unresolved structure
located ~20 to the west. The complex environment surrounding V1647 Ori
suggests it is in the early stages of star formation which may relate to its
classification as both an FUor and EXor type object.Comment: 18 pages, 14 figures, 4 tables; accepted for publication in MNRA
The ALMA Early Science View of FUor/EXor Objects - V. Continuum Disc Masses and Sizes
Low-mass stars build a significant fraction of their total mass during short outbursts of enhanced accretion known as FUor and EXor outbursts. FUor objects are characterized by a sudden brightening of ∼5 mag at visible wavelengths within 1 yr and remain bright for decades. EXor objects have lower amplitude outbursts on shorter time-scales. Here we discuss a 1.3 mm Atacama Large Millimeter/submillimeter Array (ALMA) mini-survey of eight outbursting sources (three FUors, four EXors, and the borderline object V1647 Ori) in the Orion Molecular Cloud. While previous papers in this series discuss the remarkable molecular outflows observed in the three FUor objects and V1647 Ori, here we focus on the continuum data and the differences and similarities between the FUor and EXor populations. We find that FUor discs are significantly more massive (∼80–600 MJup) than the EXor objects (∼0.5–40 MJup). We also report that the EXor sources lack the prominent outflows seen in the FUor population. Even though our sample is small, the large differences in disc masses and outflow activity suggest that the two types of objects represent different evolutionary stages. The FUor sources seem to be rather compact (Rc \u3c 20–40 au) and to have a smaller characteristic radius for a given disc mass when compared to T Tauri stars. V1118 Ori, the only known close binary system in our sample, is shown to host a disc around each one of the stellar components. The disc around HBC 494 is asymmetric, hinting at a structure in the outer disc or the presence of a second disc
How to Constrain Your M Dwarf. II. The Mass–Luminosity–Metallicity Relation from 0.075 to 0.70 Solar Masse
The mass-luminosity relation for late-type stars has long been a critical
tool for estimating stellar masses. However, there is growing need for both a
higher-precision relation and a better understanding of systematic effects
(e.g., metallicity). Here we present an empirical relationship between Mks and
mass spanning . The relation is derived from 62
nearby binaries, whose orbits we determine using a combination of Keck/NIRC2
imaging, archival adaptive optics data, and literature astrometry. From their
orbital parameters, we determine the total mass of each system, with a
precision better than 1% in the best cases. We use these total masses, in
combination with resolved Ks magnitudes and system parallaxes, to calibrate the
mass-Mks relation. The result can be used to determine masses of single stars
with a precision of 2-3%, which we confirm by a comparison to dynamical masses
from the literature. The precision is limited by scatter around the best-fit
relation beyond mass uncertainties, perhaps driven by intrinsic variation in
the mass-Mks relation or underestimated measurement errors. We find the effect
of [Fe/H] on the mass-Mks relation is likely negligible for metallicities in
the Solar neighborhood (0.0+/-2.2% change in mass per dex change in [Fe/H]).
This weak effect is consistent with predictions from the Dartmouth Stellar
Evolution Database, but inconsistent with those from MESA Isochrones and
Stellar Tracks. A sample of binaries with a wider range of abundances will be
required to discern the importance of metallicity in extreme populations (e.g.,
in the Galactic Halo or thick disk).Comment: Published in ApJ/AAS Journals. Comments welcome. Code for computing
mass posteriors from Ks+distance at https://github.com/awmann/M_-M_K
How to Constrain Your M Dwarf. II. the Mass-Luminosity-Metallicity Relation from 0.075 to 0.70 Solar Masses
The mass–luminosity relation for late-type stars has long been a critical tool for estimating stellar masses.
However, there is growing need for both a higher-precision relation and a better understanding of systematic
effects (e.g., metallicity). Here we present an empirical relationship between MKS and M* spanning
0.075 Me < M* < 0.70 Me. The relation is derived from 62 nearby binaries, whose orbits we determine using
a combination of Keck/NIRC2 imaging, archival adaptive optics data, and literature astrometry. From their orbital
parameters, we determine the total mass of each system, with a precision better than 1% in the best cases. We use
these total masses, in combination with resolved KS magnitudes and system parallaxes, to calibrate the MKS–M* relation. The resulting posteriors can be used to determine masses of single stars with a precision of 2%–3%, which
we confirm by testing the relation on stars with individual dynamical masses from the literature. The precision is
limited by scatter around the best-fit relation beyond measured M* uncertainties, perhaps driven by intrinsic
variation in the MKS–M* relation or underestimated uncertainties in the input parallaxes. We find that the effect of
[Fe/H] on the MKS–M* relation is likely negligible for metallicities in the solar neighborhood (0.0% ± 2.2%
change in mass per dex change in [Fe/H]). This weak effect is consistent with predictions from the Dartmouth
Stellar Evolution Database, but inconsistent with those from MESA Isochrones and Stellar Tracks (at 5σ). A
sample of binaries with a wider range of abundances will be required to discern the importance of metallicity in
extreme populations (e.g., in the Galactic halo or thick disk).A.W.M. was supported through Hubble Fellowship grant
51364 awarded by the Space Telescope Science Institute,
which is operated by the Association of Universities for
Research in Astronomy, Inc., for NASA, under contract NAS
5-26555. T.J.D. acknowledges research support from Gemini
Observatory. This work was supported by a NASA Keck PI
Data Award (award nos. 1554237, 1544189, 1535910, and
1521162), administered by the NASA Exoplanet Science
Institut