17 research outputs found
Surveying the Giant HII Regions of the Milky Way with SOFIA: IV. Sgr D, W42, and a Reassessment of the Giant HII Region Census
This is the fourth paper exploring the infrared properties of giant HII
regions with the FORCAST instrument on the Stratospheric Observatory For
Infrared Astronomy (SOFIA). Our survey utilizes the census of 56 Milky Way
giant HII regions identified by Conti & Crowther (2004), and in this paper we
present the 20 and 37 micron imaging data we have obtained from SOFIA for
sources Sgr D and W42. Based upon the SOFIA data and other multi-wavelength
data, we derive and discuss the detailed physical properties of the individual
compact sources and sub-regions as well as the large scale properties of Sgr D
and W42. However, improved measurements have revealed much closer distances to
both regions than previously believed, and consequently both sources are not
powerful enough to be considered giant HII regions any longer. Motivated by
this, we revisit the census of giant HII regions, performing a search through
the last two decades of literature to update each source with the most recent
and/or most accurate distance measurements. Based on these new distance
estimates, we determine that 14 sources in total (25%) are at sufficiently
reliable and closer distances that they are not powerful enough to be
considered giant HII regions. We briefly discuss the observational and physical
characteristics specific to Sgr D and W42 and show that they have properties
distinct from the giant HII regions previously studied as a part of this
survey.Comment: 31 pages, 8 figures, 7 tables; accepted for publication in Ap
HOPS 361-C's Jet Decelerating and Precessing Through NGC 2071 IR
We present a two-epoch Hubble Space Telescope (HST) near-infrared (NIR) study
of NGC 2071 IR highlighting HOPS 361-C, a protostar producing an arced 0.2
parsec-scale jet. Proper motions for the brightest knots decrease from 350 to
100 km/s with increasing distance from the source. The [Fe II] and Pa
emission line intensity ratio gives a velocity jump through each knot of 40-50
km/s. We show a new [O I] 63 m spectrum taken with the German REciever
for Astronomy at Terahertz frequencies (GREAT) instrument aboard Stratospheric
Observatory for Infrared Astronomy (SOFIA), which give a low jet inclination.
Proper motions and jump velocities then estimate total flow speed throughout
the jet.
We model knot positions and speeds with a precessing jet that decelerates
within the host molecular cloud. The measurements are matched with a precession
period of a few thousand years and half opening angle of 15. The [Fe
II] 1.26 m to 1.64 m line intensity ratio gives the
extinction to each knot ranging from 5-30 mag. Relative to 14 mag of
extinction through the cloud from CO emission maps, the jet is well
embedded at a fractional depth from 1/5 to 4/5, and can interact with the
cloud. Our model suggests the jet is locally dissipated over 0.2 pc. This may
be because knots sweep through a wide angle, giving the cloud time to fill in
cavities opened by the jet. This contrasts with nearly unidirectional
protostellar jets that puncture host clouds and can propagate significantly
further than a quarter pc.Comment: 24 pages, 9 figures, submitted to 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~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
Investigating Protostellar Accretion-Driven Outflows Across the Mass Spectrum: JWST NIRSpec IFU 3-5~m Spectral Mapping of Five Young Protostars
Investigating Protostellar Accretion (IPA) is a Cycle 1 JWST program using
the NIRSpec+MIRI IFUs to obtain 2.9--28 m spectral cubes of five young
protostars with luminosities of 0.2 to 10,000 L in their primary
accretion phase. This paper introduces the NIRSpec 2.9--5.3 m data of the
inner 840-9000 au with spatial resolutions from 28-300 au. The spectra show
rising continuum emission, deep ice absorption, emission from H, H~I, and
[Fe~II], and the CO fundamental series in emission and absorption. Maps of the
continuum emission show scattered light cavities for all five protostars. In
the cavities, collimated jets are detected in [Fe~II] for the four ~L protostars, two of which are additionally traced in
Br-. Knots of [Fe~II] emission are detected toward the most luminous
protostar, and knots of [FeII] emission with dynamical times of ~yrs are
found in the jets of the others. While only one jet is traced in H, knots
of H and CO are detected in the jets of four protostars. H is seen
extending through the cavities showing they are filled by warm molecular gas.
Bright H emission is seen along the walls of a single cavity, while in
three cavities, narrow shells of H emission are found, one of which has an
[Fe~II] knot at its apex. These data show cavities containing collimated jets
traced in atomic/ionic gas surrounded by warm molecular gas in a wide-angle
wind and/or gas accelerated by bow shocks in the jets.Comment: 30 pages, 11 figure