1,105 research outputs found
Disentangling the entangled: Observations and analysis of the triple non-coeval protostellar system VLA1623
Commonplace at every evolutionary stage, Multiple Protostellar Systems (MPSs)
are thought to be formed through fragmentation, but it is unclear when and how.
The youngest MPSs, which have not yet undergone much evolution, provide
important constraints to this question. It is then of interest to disentangle
early stage MPSs. In this letter we present the results of our work on VLA1623
using our observations and archival data from the Submillimeter Array (SMA).
Our continuum and line observations trace VLA1623's components, outflow and
envelope, revealing unexpected characteristics. We construct the SED for each
component using the results of our work and data from literature, as well as
derive physical parameters from continuum and perform a simple kinematical
analysis of the circumstellar material. Our results show VLA1623 to be a triple
non-coeval system composed of VLA1623A, B & W, with each source driving its own
outflow and unevenly distributed circumstellar material. From the SED, physical
parameters and IR emission we conclude that VLA1623A & W are Class 0 and I
protostars, respectively, and together drive the bulk of the observed outflow.
Furthermore, we find two surprising results, first the presence of a rotating
disk-like structure about VLA1623A with indications of pure Keplerian rotation,
which, if real, would make it one of the first evidence of Keplerian disk
structures around Class 0 protostars. Second, we find VLA1623B to be a bonafide
extremely young protostellar object between the starless core and Class 0
stages.Comment: 22 pages, 4 figures, 1 Table, Accepted to Ap
Widening of Protostellar Outflows: an Infrared Outflow Survey in Low Luminosity Objects
We present an outflow survey toward 20 Low Luminosity Objects (LLOs), namely
protostars with an internal luminosity lower than 0.2 Lsun. Although a number
of studies have reported the properties of individual LLOs, the reasons for
their low luminosity remain uncertain. To answer this question, we need to know
the evolutionary status of LLOs. Protostellar outflows are found to widen as
their parent cores evolve, and therefore, the outflow opening angle could be
used as an evolutionary indicator. The infrared scattered light escapes out
through the outflow cavity and highlights the cavity wall, giving us the
opportunity to measure the outflow opening angle. Using the
Canada-France-Hawaii Telescope, we detected outflows toward eight LLOs out of
20 at Ks band, and based on archival Spitzer IRAC1 images, we added four
outflow-driving sources from the remaining 12 sources. By fitting these images
with radiative transfer models, we derive the outflow opening angles and
inclination angles. To study the widening of outflow cavities, we compare our
sample with the young stellar objects from Arce & Sargent 2006 and Velusamy et
al. 2014 in the plot of opening angle versus bolometric temperature taken as an
evolutionary indicator.Our LLO targets match well the trend of increasing
opening angle with bolometric temperature reported by Arce & Sargent and are
broadly consistent with that reported by Velusamy et al., suggesting that the
opening angle could be a good evolutionary indicator for LLOs. Accordingly, we
conclude that at least 40% of the outflow-driving LLOs in our sample are young
Class 0 objects.Comment: Accepted for publication in AJ, 13 pages, 9 figure
The Overshooting Hypothesis of Agricultural Prices: The Role of Asset Substitutability
By allowing for various degrees of asset substitutability between bonds and agricultural products, this paper reexamines the robustness of the overshooting hypothesis of agricultural product prices. It is found, in both a closed economy and an open economy, that the crucial factor determining whether agricultural prices overshoot or undershoot their long-run response following an expansion in the money stock depends upon the extent of asset substitutability between bonds and agricultural goods.asset substitutability, commodity prices, overshooting, Demand and Price Analysis,
Multi-wavelength Stellar Polarimetry of the Filamentary Cloud IC5146: I. Dust Properties
We present optical and near-infrared stellar polarization observations toward
the dark filamentary clouds associated with IC5146. The data allow us to
investigate the dust properties (this paper) and the magnetic field structure
(Paper II). A total of 2022 background stars were detected in -, -,
-, and/or -bands to mag. The ratio of the polarization
percentage at different wavelengths provides an estimate of ,
the wavelength of peak polarization, which is an indicator of the small-size
cutoff of the grain size distribution. The grain size distribution seems to
significantly change at 3 mag, where both the average and dispersion
of decrease. In addition, we found
0.6-0.9 m for mag, which is larger than the 0.55 m
in the general ISM, suggesting that grain growth has already started in low
regions. Our data also reveal that polarization efficiency (PE ) decreases with as a power-law in -, -, and
-bands with indices of -0.710.10, -1.230.10 and -0.530.09.
However, -band data show a power index change; the PE varies with
steeply (index of -0.950.30) when mag but softly
(index of -0.250.06) for greater values. The soft decay of PE in
high regions is consistent with the Radiative Aligned Torque model,
suggesting that our data trace the magnetic field to mag.
Furthermore, the breakpoint found in -band is similar to the where we
found the dispersion significantly decreased. Therefore, the
flat PE- in high regions implies that the power index changes result
from additional grain growth.Comment: 31 pages, 17 figures, and 3 tables; accepted for publication in Ap
The Mid-Infrared Extinction Law in the Ophiuchus, Perseus, and Serpens Molecular Clouds
We compute the mid-infrared extinction law from 3.6-24 microns in three
molecular clouds: Ophiuchus, Perseus, and Serpens, by combining data from the
"Cores to Disks" Spitzer Legacy Science program with deep JHKs imaging. Using a
new technique, we are able to calculate the line-of-sight extinction law
towards each background star in our fields. With these line-of-sight
measurements, we create, for the first time, maps of the chi-squared deviation
of the data from two extinction law models. Because our chi-squared maps have
the same spatial resolution as our extinction maps, we can directly observe the
changing extinction law as a function of the total column density. In the
Spitzer IRAC bands, 3.6-8 microns, we see evidence for grain growth. Below
, our extinction law is well-fit by the Weingartner & Draine
(2001) diffuse interstellar medium dust model. As the extinction
increases, our law gradually flattens, and for , the data are
more consistent with the Weingartner & Draine model that uses
larger maximum dust grain sizes. At 24 microns, our extinction law is 2-4 times
higher than the values predicted by theoretical dust models, but is more
consistent with the observational results of Flaherty et al. (2007). Lastly,
from our chi-squared maps we identify a region in Perseus where the IRAC
extinction law is anomalously high considering its column density. A steeper
near-infrared extinction law than the one we have assumed may partially explain
the IRAC extinction law in this region.Comment: 38 pages, 19 figures in pre-print format. Accepted for publication in
ApJ. A version with full-resolution figures can be found here:
http://peggysue.as.utexas.edu/SIRTF
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