9 research outputs found
Disentangling the Formation Pathways of Protostars
Star formation occurs within dense cores within molecular clouds, often associated with filamentary structures. However, there exist isolated instances of star formation, far from nearby forming stars. As a core collapses, a rotationally supported circumstellar disk emerges around a central, gravitating potential with the accretion of gas and dust playing a vital role in regulating the subsequent stellar mass assembly. With recent studies revealing nearly half of all solar-type star systems are multiples, this raises questions about the mechanisms behind their formation. Furthermore, despite numerous discoveries of exoplanets with state-of-the-art space telescopes, the initial stages of planetary formation remain elusive. High-resolution interferometric imaging using ALMA of protoplanetary disks has ubiquitously unveiled intricate substructures, hinting at ongoing planet formation processes. To understand the formation and evolution of stars and their planetary systems, it is essential to better characterize their progenitors, known as "protostars”, particularly the youngest known phases of protostars, so-called Class 0. During the early stages of star formation, when gravitational collapse initiates, the conservation of angular momentum leads to the formation of a rotationally supported disk. However, only a handful of Class 0 protostellar disks, which are highly embedded in gas and dust, have been rigorously detailed so far. Consequently, a more comprehensive analysis of Class 0/I systems is imperative for understanding their formation and evolution. This dissertation aims to address multiple outstanding questions in star formation, beginning with a detailed investigation of an extraordinary triple-source protostellar Class 0 system, L1448 IRS3B. Expanding the focus, BHR7, an isolated Class 0 source, is studied to map the transfer of angular momentum from 1000s of au down to the disk. BHR7 serves as an ideal testbed for non-ideal MHD theory and represents a prototypical isolated Class 0 source, free from contamination by nearby forming stars. Furthermore, a high-resolution survey is conducted in the Perseus region, encompassing 12 known multiple star systems, to determine the most probable formation pathways for each of these sources. Rigorous modeling techniques and statistical tests are employed to disentangle the formation pathways of the protostars. By undertaking these investigations, I aim to enhance our understanding of star formation processes, provide observational constraints on star formation theory, and shed light on the complex formation mechanisms underlying multiple star systems, which are thought to be the early stages of exoplanet progenitors
Kinematic Analysis of a Protostellar Multiple System: Measuring the Protostar Masses and Assessing Gravitational Instability in the Disks of L1448 IRS3B and L1448 IRS3A
We present new Atacama Large Millimeter/submillimeter Array (ALMA)
observations towards a compact (230~au separation) triple protostar system,
L1448 IRS3B, at 879~\micron with \contbeam~resolution. Spiral arm structure
within the circum-multiple disk is well resolved in dust continuum toward
IRS3B, and we detect the known wide (2300~au) companion, IRS3A, also resolving
possible spiral substructure. Using dense gas tracers, C17O, H13CO, and
H13CN, we resolve the Keplerian rotation for both the circum-triple disk in
IRS3B and the disk around IRS3A. Furthermore, we use the molecular line
kinematic data and radiative transfer modeling of the molecular line emission
to confirm that the disks are in Keplerian rotation with fitted masses of
for IRS3B-ab, ~Msun for IRS3A, and
place an upper limit on the central protostar mass for the tertiary IRS3B-c of
0.2~Msun. We measure the mass of the fragmenting disk of IRS3B to be 0.29~Msun
from the dust continuum emission of the circum-multiple disk and estimate the
mass of the clump surrounding IRS3B-c to be 0.07~Msun. We also find that the
disk around IRS3A has a mass of 0.04~Msun. By analyzing the Toomre~Q parameter,
we find the IRS3A circumstellar disk is gravitationally stable (Q5), while
the IRS3B disk is consistent with a gravitationally unstable disk (Q1)
between the radii 200-500~au. This coincides with the location of the spiral
arms and the tertiary companion IRS3B-c, supporting the hypothesis that IRS3B-c
was formed in situ via fragmentation of a gravitationally unstable disk
The VLA/ALMA Nascent Disk and Multiplicity (VANDAM) Survey of Orion Protostars IV. Unveiling the Embedded Intermediate-Mass Protostar and Disk within OMC2-FIR3/HOPS-370
We present ALMA (0.87~mm and 1.3~mm) and VLA (9~mm) observations toward the
candidate intermediate-mass protostar OMC2-FIR3 (HOPS-370;
L~314~L) at 0.1" (40~au) resolution for the continuum
emission and ~0.25" (100 au) resolution of nine molecular lines. The dust
continuum observed with ALMA at 0.87~mm and 1.3~mm resolve a near edge-on disk
toward HOPS-370 with an apparent radius of ~100 au. The VLA observations detect
both the disk in dust continuum and free-free emission extended along the jet
direction. The ALMA observations of molecular lines (HCO, SO, CHOH,
CO, CO, NS, and HCN) reveal rotation of the apparent disk
surrounding HOPS-370 orthogonal to the jet/outflow direction. We fit radiative
transfer models to both the dust continuum structure of the disk and molecular
line kinematics of the inner envelope and disk for the HCO, CHOH, NS,
and SO lines. The central protostar mass is determined to be 2.5 M_sun
with a disk radius of 94~au, when fit using combinations of the HCO,
CHOH, NS, and SO lines, consistent with an intermediate-mass protostar.
Modeling of the dust continuum and spectral energy distribution (SED) yields a
disk mass of 0.035~M (inferred dust+gas) and a dust disk radius of
62~au, thus the dust disk may have a smaller radius than the gas disk, similar
to Class II disks. In order to explain the observed luminosity with the
measured protostar mass, HOPS-370 must be accreting at a rate between 1.7 and
3.210~M~yr.Comment: Accepted to ApJ; 51 pages, 12 Figures, 7 Table
Disks and Outflows in the Intermediate-mass Star Forming Region NGC 2071 IR
We present ALMA band 6/7 (1.3 mm/0.87 mm) and VLA Ka band (9 mm) observations
toward NGC 2071 IR, an intermediate-mass star forming region. We characterize
the continuum and associated molecular line emission towards the most luminous
protostars, i.e., IRS1 and IRS3, on ~100 au (0. 2") scales. IRS1 is partly
resolved in millimeter and centimeter continuum, which shows a potential disk.
IRS3 has a well resolved disk appearance in millimeter continuum and is further
resolved into a close binary system separated by ~40 au at 9 mm. Both sources
exhibit clear velocity gradients across their disk major axes in multiple
spectral lines including C18O, H2CO, SO, SO2, and complex organic molecules
like CH3OH, 13CH3OH and CH3OCHO. We use an analytic method to fit the Keplerian
rotation of the disks, and give constraints on physical parameters with a MCMC
routine. The IRS3 binary system is estimated to have a total mass of
1.4-1.5. IRS1 has a central mass of 3-5 based on both
kinematic modeling and its spectral energy distribution, assuming that it is
dominated by a single protostar. For both IRS1 and IRS3, the inferred ejection
directions from different tracers, including radio jet, water maser, molecular
outflow, and H2 emission, are not always consistent, and for IRS1, these can be
misaligned by ~50. IRS3 is better explained by a single precessing
jet. A similar mechanism may be present in IRS1 as well but an unresolved
multiple system in IRS1 is also possible.Comment: 36 pages, 21 figures, accepted by Ap
The VLA/ALMA Nascent Disk and Multiplicity (VANDAM) Survey of Orion Protostars. IV. Unveiling the Embedded Intermediate-Mass Protostar and Disk within OMC2-FIR3/HOPS-370
We present ALMA (0.87 and 1.3 mm) and VLA (9 mm) observations toward the candidate intermediate-mass protostar OMC2-FIR3 (HOPS-370; L_(bol) ~ 314 L_⊙) at ~0."1 (40 au) resolution for the continuum emission and ~0."25 (100 au) resolution of nine molecular lines. The dust continuum observed with ALMA at 0.87 and 1.3 mm resolves a near edge-on disk toward HOPS-370 with an apparent radius of ~100 au. The VLA observations detect both the disk in dust continuum and free–free emission extended along the jet direction. The ALMA observations of molecular lines (H₂CO, SO, CH₃OH, ¹³CO, C¹⁸O, NS, and H¹³CN) reveal rotation of the apparent disk surrounding HOPS-370 orthogonal to the jet/outflow direction. We fit radiative transfer models to both the dust continuum structure of the disk and molecular line kinematics of the inner envelope and disk for the H₂CO, CH₃OH, NS, and SO lines. The central protostar mass is determined to be ~2.5 M_⊙ with a disk radius of ~94 au, when fit using combinations of the H₂CO, CH₃OH, NS, and SO lines, consistent with an intermediate-mass protostar. Modeling of the dust continuum and spectral energy distribution yields a disk mass of 0.035 M_⊙ (inferred dust+gas) and a dust disk radius of 62 au; thus, the dust disk may have a smaller radius than the gas disk, similar to Class II disks. In order to explain the observed luminosity with the measured protostar mass, HOPS-370 must be accreting at a rate of (1.7−3.2) × 10⁻⁵ M_⊙ yr⁻¹
The VLA/ALMA Nascent Disk and Multiplicity (VANDAM) Survey of Orion Protostars. I. Identifying and Characterizing the Protostellar Content of the OMC-2 FIR4 and OMC-2 FIR3 Regions
We present ALMA (0.87~mm) and VLA (9~mm) observations toward OMC2-FIR4 and
OMC2-FIR3 within the Orion integral-shaped filament that are thought to be the
nearest regions of intermediate mass star formation. We characterize the
continuum sources within these regions on 40~AU (0\farcs1) scales and
associated molecular line emission at a factor of 30 better resolution
than previous observations at similar wavelengths. We identify six compact
continuum sources within OMC2-FIR4, four in OMC2-FIR3, and one additional
source just outside OMC2-FIR4. This continuum emission is tracing the inner
envelope and/or disk emission on less than 100~AU scales. HOPS-108 is the only
protostar in OMC2-FIR4 that exhibits emission from high-excitation transitions
of complex organic molecules (e.g., methanol and other lines) coincident with
the continuum emission. HOPS-370 in OMC2-FIR3 with L~~360~\lsun, also
exhibits emission from high-excitation methanol and other lines. The methanol
emission toward these two protostars is indicative of temperatures high enough
to thermally evaporate methanol from icy dust grains; overall these protostars
have characteristics similar to hot corinos. We do not identify a clear outflow
from HOPS-108 in \twco, but find evidence of interaction between the
outflow/jet from HOPS-370 and the OMC2-FIR4 region. The multitude of
observational constraints indicate that HOPS-108 is likely a low to
intermediate-mass protostar in its main mass accretion phase and it is the most
luminous protostar in OMC2-FIR4. The high resolution data presented here are
essential for disentangling the embedded protostars from their surrounding
dusty environments and characterizing them
The Disk Orientations of Perseus Protostellar Multiples at ∼8 au Resolution
We present a statistical characterization of circumstellar disk orientations toward 12 protostellar multiple systems in the Perseus molecular cloud using the Atacama Large Millimeter/submillimeter Array at Band 6 (1.3 mm) with a resolution of ∼25 mas (∼8 au). This exquisite resolution enabled us to resolve the compact inner-disk structures surrounding the components of each multiple system and to determine the projected 3D orientation of the disks (position angle and inclination) to high precision. We performed a statistical analysis on the relative alignment of disk pairs to determine whether the disks are preferentially aligned or randomly distributed. We considered three subsamples of the observations selected by the companion separations a 500 au, and a 500 au) subsample appears to be consistent with a distribution of 40%–80% preferentially aligned sources. Similarly, the full sample of systems with companions ( a 500 au) are statistically different