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High resolution observations of the L1551, B335 and L723 bipolar molecular outflows using maximum entropy image reconstruction.
A Sub-millimeterwave ``Flare'' from GG Tau?
We have monitored the millimeter and submillimeter emission from the young
stellar object GG Tau, a T Tauri binary system surrounded by a massive
circumbinary disk. We find that between 1992 and 1994, the flux has increased
significantly at 800, 1100, and 1300 microns, resulting in a steepening of the
observed spectral energy distribution at those wavelengths. Such an increase
appears consistent with a modest increase in disk luminosity (a factor of two).
The increase in the effective disk temperature might arise from a slight change
in the disk heating processes. Alternatively, the flux increase may reflect a
sudden change in the underlying dust optical properties.Comment: 15 pages, AASTex v.4.0 format, four postscript figures, four tables,
to appear in The Astrophysical Journa
Multi-Generational Star Formation in L1551
The L1551 molecular cloud contains two small clusters of Class 0 and I
protostars, as well as a halo of more evolved Class II and III YSOs, indicating
a current and at least one past burst of star formation. We present here new,
sensitive maps of 850 and 450 um dust emission covering most of the L1551
cloud, new CO J=2-1 data of the molecular cloud, and a new, deep, optical image
of [SII] emission. No new Class 0/I YSOs were detected. Compact sub-millimetre
emitters are concentrated in two sub-clusters: IRS5 and L1551NE, and the
HL~Tauri group. Both stellar groups show significant extended emission and
outflow/jet activity. A jet, terminating at HH 265 and with a very weak
associated molecular outflow, may originate from LkHa 358, or from a binary
companion to another member of the HL Tauri group. Several Herbig Haro objects
associated with IRS5/NE were clearly detected in the sub-mm, as were faint
ridges of emission tracing outflow cavity walls. We confirm a large-scale
molecular outflow originating from NE parallel to that from IRS5, and suggest
that the "hollow shell" morphology is more likely due to two interacting
outflows. We confirm the presence of a prestellar core (L1551-MC) of mass 2-3
Mo north-west of IRS5. The next generation cluster may be forming in this core.
The L1551 cloud appears cometary in morphology, and appears to be illuminated
and eroded from the direction of Orion, perhaps explaining the multiple
episodes of star formation in this cloud. The full paper (including figures)
can be downloaded at http://www.jach.hawaii.edu/~gms/l1551/l1551-apj641.pdf, or
viewed at http://www.jach.hawaii.edu/~gms/l1551/.Comment: Accepted for publication in The Astrophysical Journal, April 2006
(vol. 641). 27 pages, 17 figure
The Local Environment of the FUor-like Objects AR 6A and 6B
We present new 12CO J=3-2 and HCN J=3-2 molecular line maps of the region
surrounding the young star AR 6 using the 15 metre James Clerk Maxwell
Telescope. AR 6 was previously found to be a double source with both components
exhibiting several characteristics of FU Orionis (FUor) eruptive variable
stars. Our data indicates that AR 6, like FU Orionis itself, does not possess a
CO outflow and likewise, does not show evidence for large amounts of molecular
g as in its circumstellar environment. We conclude that from the near-IR to the
sub-mm, AR 6 is similar to FU Orionis in several respects. We interpret the
lack of significant dust and molecular gas in the circumstellar environment of
AR 6, together with the large near-IR thermal excess, as evidence that the
sources have exhausted their natal envelopes, that they have at least small hot
circumstellar disks, and that they are more evolved than Class I protostars.
This, in itself, suggests that, since FUor eruptions have also been observed in
stars with large dust mass envelopes (e.g. V346 Nor) and with CO outflows (e.g.
L1551 IRS5), FUor events probably occur at many different stages in the early,
formative phase of a star's life, and lends support to the idea that FUor
outbursts are repetitive like their shorter-lived relatives occurring in EXor
eruptive variables. Finally, we show that, being part of the 'Spokes' young
stellar cluster, AR 6 is unlike many FUors which typically are located in more
sparsely populated regions.Comment: Accepted for publication in The Astronomical Journal (October 2008
CSO Bolocam 1.1 mm continuum mapping of the Braid Nebula star formation region in Cygnus OB7
We present a 1.1 mm map of the Braid Nebula star formation region in Cygnus OB7 taken using Bolocam on the Caltech Submillimeter Observatory. Within the 1 deg2 covered by the map, we have detected 55 cold dust clumps all of which are new detections. A number of these clumps are coincident with IRAS point sources although the majority are not. Some of the previously studied optical/near-IR sources are detected at 1.1 mm. We estimate total dust/gas masses for the 55 clumps together with peak visual extinctions. We conclude that over the whole region, approximately 20% of the clumps are associated with IRAS sources suggesting that these are protostellar objects. The remaining 80% are classed as starless clumps. In addition, both FU Orionis (FUor) like objects in the field, the Braid Star and HH 381 IRS, are associated with strong millimeter emission. This implies that FUor eruptions can occur at very early stages of pre-main-sequence life. Finally, we determine that the cumulative clump mass function for the region is very similar to that found in both the Perseus and Ï? Ophiuchus star-forming regions. © 2011. The American Astronomical Society. All rights reserved
V2494 cyg: A unique FU ori type object in the cygnus OB7 complex
A photometric and spectral study of the variable star V2494 Cyg in the L 1003 dark cloud is presented. The brightness of the star, formerly known as HH 381 IRS, increased by 2.5 mag in R (probably in the 1980s) and since then has remained nearly constant. Since the brightness increase, V2494 Cyg has illuminated a bipolar cometary nebula. The stellar spectrum has several features typical of the FU Ori (FUor) type, plus it exhibits very strong Ha and forbidden emissionlines with high-velocity components. These emission lines originate in the Herbig-Haro (HH) jet near the star. The kinematic age of the jet is consistent with it forming at the time of the outburst leading to the luminosity increase. V2494 Cyg also produces a rather extended outflow; it is the first known FUor with both an observed outburst and a parsec-sized HH flow. The nebula, illuminated by V2494 Cyg, possesses similar morphological and spectral characteristics to Hubble's variable nebula (R Monocerotis/NGC 2261). © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society
Magnetic Fields in Star-Forming Molecular Clouds III. Submillimeter Polarimetry of Intermediate Mass Cores and Filaments in Orion B
Using the imaging polarimeter for the Submillimeter Common User Bolometric
Array at the James Clerk Maxwell Telescope, we have detected polarized thermal
emission at 850 micron from dust toward three star-forming core systems in the
Orion B molecular cloud: NGC 2071, NGC 2024 and LBS 23N (HH 24). The
polarization patterns are not indicative of those expected for magnetic fields
dominated by a single field direction, and all exhibit diminished polarization
percentages toward the highest intensity peaks. NGC 2024 has the most organized
polarization pattern which is centered consistently along the length of a chain
of 7 far-infrared sources. We have modeled NGC 2024 using a helical field
geometry threading a curved filament and also as a magnetic field swept up by
the ionization front of the expanding HII region. In the latter case, the field
is bent by the dense ridge, which accounts for both the polarization pattern
and existing measurements of the line-of-sight field strength toward the
northern cores FIR 1 to FIR 4. The direction of the net magnetic field
direction within NGC 2071 is perpendicular to the dominant outflow in that
region. Despite evidence that line contamination exists in the 850 micron
continuum, the levels of polarization measured indicate that the polarized
emission is dominated by dust.Comment: 39 pages, 9 postscript figures (6 color), 3 tables; accepted for
publication in Ap
Cross-National Differences in Victimization : Disentangling the Impact of Composition and Context
Varying rates of criminal victimization across countries are assumed to be the outcome of countrylevel structural constraints that determine the supply ofmotivated o¡enders, as well as the differential composition within countries of suitable targets and capable guardianship. However, previous empirical tests of these ‘compositional’ and ‘contextual’ explanations of cross-national di¡erences
have been performed upon macro-level crime data due to the unavailability of comparable individual-level data across countries. This limitation has had two important consequences for cross-national crime research. First, micro-/meso-level mechanisms underlying cross-national differences cannot be truly inferred from macro-level data. Secondly, the e¡ects of contextual measures (e.g. income inequality) on crime are uncontrolled for compositional heterogeneity. In this
paper, these limitations are overcome by analysing individual-level victimization data across 18 countries from the International CrimeVictims Survey. Results from multi-level analyses on theft and violent victimization indicate that the national level of income inequality is positively related to risk, independent of compositional (i.e. micro- and meso-level) di¡erences. Furthermore, crossnational variation in victimization rates is not only shaped by di¡erences in national context, but
also by varying composition. More speci¢cally, countries had higher crime rates the more they consisted of urban residents and regions with lowaverage social cohesion.
The JCMT BISTRO Survey: A Spiral Magnetic Field in a Hub-filament Structure, Monoceros R2
We present and analyze observations of polarized dust emission at 850 μm toward the central 1
7 1 pc hub-filament structure of Monoceros R2 (Mon R2). The data are obtained with SCUBA-2/POL-2 on the James Clerk Maxwell Telescope (JCMT) as part of the B-fields in Star-forming Region Observations survey. The orientations of the magnetic field follow the spiral structure of Mon R2, which are well described by an axisymmetric magnetic field model. We estimate the turbulent component of the magnetic field using the angle difference between our observations and the best-fit model of the underlying large-scale mean magnetic field. This estimate is used to calculate the magnetic field strength using the Davis–Chandrasekhar–Fermi method, for which we also obtain the distribution of volume density and velocity dispersion using a column density map derived from Herschel data and the C18O (J = 3 - 2) data taken with HARP on the JCMT, respectively. We make maps of magnetic field strengths and mass-to-flux ratios, finding that magnetic field strengths vary from 0.02 to 3.64 mG with a mean value of 1.0 \ub1 0.06 mG, and the mean critical mass-to-flux ratio is 0.47 \ub1 0.02. Additionally, the mean Alfv\ue9n Mach number is 0.35 \ub1 0.01. This suggests that, in Mon R2, the magnetic fields provide resistance against large-scale gravitational collapse, and the magnetic pressure exceeds the turbulent pressure. We also investigate the properties of each filament in Mon R2. Most of the filaments are aligned along the magnetic field direction and are magnetically subcritical
The JCMT Gould Belt Survey: SCUBA-2 Data Reduction Methods and Gaussian Source Recovery Analysis
The James Clerk Maxwell Telescope (JCMT) Gould Belt Survey (GBS) was one of the first legacy surveys with the JCMT in Hawaii, mapping 47 deg2 of nearby (<500 pc) molecular clouds in dust continuum emission at 850 and 450 μm, as well as a more limited area in lines of various CO isotopologues. While molecular clouds and the material that forms stars have structures on many size scales, their larger-scale structures are difficult to observe reliably in the submillimeter regime using ground-based facilities. In this paper, we quantify the extent to which three subsequent data reduction methods employed by the JCMT GBS accurately recover emission structures of various size scales, in particular, dense cores, which are the focus of many GBS science goals. With our current best data reduction procedure, we expect to recover 100% of structures with Gaussian σ sizes of ≤30'' and intensity peaks of at least five times the local noise for isolated peaks of emission. The measured sizes and peak fluxes of these compact structures are reliable (within 15% of the input values), but source recovery and reliability both decrease significantly for larger emission structures and fainter peaks. Additional factors such as source crowding have not been tested in our analysis. The most recent JCMT GBS data release includes pointing corrections, and we demonstrate that these tend to decrease the sizes and increase the peak intensities of compact sources in our data set, mostly at a low level (several percent), but occasionally with notable improvement