7,303 research outputs found
Predicted Colors and Flux Densities of Protostars in the Herschel PACS and SPIRE Filters
Upcoming surveys with the Herschel Space Observatory will yield far-IR
photometry of large samples of young stellar objects, which will require
careful interpretation. We investigate the color and luminosity diagnostics
based on Herschel broad-band filters to identify and discern the properties of
low-mass protostars. We compute a grid of 2,016 protostars in various physical
congurations, present the expected flux densities and flux density ratios for
this grid of protostars, and compare Herschel observations of three protostars
to the model results. These provide useful constraints on the range of colors
and fluxes of protostar in the Herschel filters. We find that Herschel data
alone is likely a useful diagnostic of the envelope properties of young starsComment: Part of HOPS KP papers to the Herschel special A&A issu
Current-voltage characteristics of quasi-one-dimensional superconductors: An S-curve in the constant voltage regime
Applying a constant voltage to superconducting nanowires we find that its
IV-characteristic exhibits an unusual S-behavior. This behavior is the direct
consequence of the dynamics of the superconducting condensate and of the
existence of two different critical currents: j_{c2} at which the pure
superconducting state becomes unstable and j_{c1}<j_{c2} at which the phase
slip state is realized in the system.Comment: 4 pages, 5 figures, replaced with minor change
Financial Transaction Tax: Small is Beautiful
The case for taxing financial transactions merely to raise more revenues from the financial sector is not particularly strong. Better alternatives to tax the financial sector are likely to be available. However, a tax on financial transactions could be justified in order to limit socially
undesirable transactions when more direct means of doing so are unavailable for political or
practical reasons. Some financial transactions are indeed likely to do more harm than good,
especially when they contribute to the systemic risk of the financial system. However, such a
financial transaction tax should be very small, much smaller than the negative externalities in
question, because it is a blunt instrument that also drives out socially useful transactions.
There is a case for taxing over-the-counter derivative transactions at a somewhat higher rate
than exchange-based derivative transactions. More targeted remedies to drive out socially
undesirable transactions should be sought in parallel, which would allow, after their
implementation, to reduce or even phase out financialtransaction taxes
CARMA Large Area Star Formation Survey: Observational Analysis of Filaments in the Serpens South Molecular Cloud
We present the N2H+(J=1-0) map of the Serpens South molecular cloud obtained
as part of the CARMA Large Area Star Formation Survey (CLASSy). The
observations cover 250 square arcminutes and fully sample structures from 3000
AU to 3 pc with a velocity resolution of 0.16 km/s, and they can be used to
constrain the origin and evolution of molecular cloud filaments. The spatial
distribution of the N2H+ emission is characterized by long filaments that
resemble those observed in the dust continuum emission by Herschel. However,
the gas filaments are typically narrower such that, in some cases, two or three
quasi-parallel N2H+ filaments comprise a single observed dust continuum
filament. The difference between the dust and gas filament widths casts doubt
on Herschel ability to resolve the Serpens South filaments. Some molecular
filaments show velocity gradients along their major axis, and two are
characterized by a steep velocity gradient in the direction perpendicular to
the filament axis. The observed velocity gradient along one of these filaments
was previously postulated as evidence for mass infall toward the central
cluster, but these kind of gradients can be interpreted as projection of
large-scale turbulence.Comment: 12 pages, 4 figures, published in ApJL (July 2014
Protostellar accretion traced with chemistry. High resolution C18O and continuum observations towards deeply embedded protostars in Perseus
Context: Understanding how accretion proceeds is a key question of star
formation, with important implications for both the physical and chemical
evolution of young stellar objects. In particular, very little is known about
the accretion variability in the earliest stages of star formation.
Aims: To characterise protostellar accretion histories towards individual
sources by utilising sublimation and freeze-out chemistry of CO.
Methods: A sample of 24 embedded protostars are observed with the
Submillimeter Array (SMA) in context of the large program "Mass Assembly of
Stellar Systems and their Evolution with the SMA" (MASSES). The size of the
CO emitting region, where CO has sublimated into the gas-phase, is
measured towards each source and compared to the expected size of the region
given the current luminosity. The SMA observations also include 1.3 mm
continuum data, which are used to investigate whether a link can be established
between accretion bursts and massive circumstellar disks.
Results: Depending on the adopted sublimation temperature of the CO ice,
between 20% and 50% of the sources in the sample show extended CO
emission indicating that the gas was warm enough in the past that CO sublimated
and is currently in the process of refreezing; something which we attribute to
a recent accretion burst. Given the fraction of sources with extended CO
emission, we estimate an average interval between bursts of 20000-50000 yr,
which is consistent with previous estimates. No clear link can be established
between the presence of circumstellar disks and accretion bursts, however the
three closest known binaries in the sample (projected separations <20 AU) all
show evidence of a past accretion burst, indicating that close binary
interactions may also play a role in inducing accretion variability.Comment: Accepted for publication in A&A, 21 pages, 13 figure
Radioactive Probes of the Supernova-Contaminated Solar Nebula: Evidence that the Sun was Born in a Cluster
We construct a simple model for radioisotopic enrichment of the protosolar
nebula by injection from a nearby supernova, based on the inverse square law
for ejecta dispersion. We find that the presolar radioisotopes abundances
(i.e., in solar masses) demand a nearby supernova: its distance can be no
larger than 66 times the size of the protosolar nebula, at a 90% confidence
level, assuming 1 solar mass of protosolar material. The relevant size of the
nebula depends on its state of evolution at the time of radioactivity
injection. In one scenario, a collection of low-mass stars, including our sun,
formed in a group or cluster with an intermediate- to high-mass star that ended
its life as a supernova while our sun was still a protostar, a starless core,
or perhaps a diffuse cloud. Using recent observations of protostars to estimate
the size of the protosolar nebula constrains the distance of the supernova at
0.02 to 1.6 pc. The supernova distance limit is consistent with the scales of
low-mass stars formation around one or more massive stars, but it is closer
than expected were the sun formed in an isolated, solitary state. Consequently,
if any presolar radioactivities originated via supernova injection, we must
conclude that our sun was a member of such a group or cluster that has since
dispersed, and thus that solar system formation should be understood in this
context. In addition, we show that the timescale from explosion to the creation
of small bodies was on the order of 1.8 Myr (formal 90% confidence range of 0
to 2.2 Myr), and thus the temporal choreography from supernova ejecta to
meteorites is important. Finally, we can not distinguish between progenitor
masses from 15 to 25 solar masses in the nucleosynthesis models; however, the
20 solar mass model is somewhat preferred.Comment: ApJ accepted, 19 pages, 3 figure
Herschel/PACS Imaging of Protostars in the HH 1-2 Outflow Complex
We present 70 and 160 micron Herschel science demonstration images of a field
in the Orion A molecular cloud that contains the prototypical Herbig-Haro
objects HH 1 and 2, obtained with the Photodetector Array Camera and
Spectrometer (PACS). These observations demonstrate Herschel's unprecedented
ability to study the rich population of protostars in the Orion molecular
clouds at the wavelengths where they emit most of their luminosity. The four
protostars previously identified by Spitzer 3.6-40 micron imaging and
spectroscopy are detected in the 70 micron band, and three are clearly detected
at 160 microns. We measure photometry of the protostars in the PACS bands and
assemble their spectral energy distributions (SEDs) from 1 to 870 microns with
these data, Spitzer spectra and photometry, 2MASS data, and APEX sub-mm data.
The SEDs are fit to models generated with radiative transfer codes. From these
fits we can constrain the fundamental properties of the protostars. We find
luminosities in the range 12-84 L_sun and envelope densities spanning over two
orders of magnitude. This implies that the four protostars have a wide range of
envelope infall rates and evolutionary states: two have dense, infalling
envelopes, while the other two have only residual envelopes. We also show the
highly irregular and filamentary structure of the cold dust and gas surrounding
the protostars as traced at 160 microns.Comment: 6 pages, 4 figures, accepted for publication in the A&A Herschel
special issu
HOPS 383: An Outbursting Class 0 Protostar in Orion
We report the dramatic mid-infrared brightening between 2004 and 2006 of HOPS
383, a deeply embedded protostar adjacent to NGC 1977 in Orion. By 2008, the
source became a factor of 35 brighter at 24 microns with a brightness increase
also apparent at 4.5 microns. The outburst is also detected in the
submillimeter by comparing APEX/SABOCA to SCUBA data, and a scattered-light
nebula appeared in NEWFIRM K_s imaging. The post-outburst spectral energy
distribution indicates a Class 0 source with a dense envelope and a luminosity
between 6 and 14 L_sun. Post-outburst time-series mid- and far-infrared
photometry shows no long-term fading and variability at the 18% level between
2009 and 2012. HOPS 383 is the first outbursting Class 0 object discovered,
pointing to the importance of episodic accretion at early stages in the star
formation process. Its dramatic rise and lack of fading over a six-year period
hint that it may be similar to FU Ori outbursts, although the luminosity
appears to be significantly smaller than the canonical luminosities of such
objects.Comment: Accepted by ApJ Letters, 6 pages, 4 figures; v2 has an updated email
address for the lead autho
THE DETECTION, PHARMACOKINETICS AND BEHAVIORAL EFFECTS OF DIISOPROPYLAMINE DICHLOROACETATE (DADA) IN THE HORSE: A PRELIMINARY REPORT
1. Drug administration studies using diisopropylamine dichloroacetate (DADA) and diisopropylamine (DIPA) were conducted in Thoroughbred and Standardbred horses to assess physiological effects and develop detection methods.
2. Four horses received 0.08 mg DADA/kg body wt and showed no changes in heart and respiratory rates or body temperature as measured over a 1-hr period after administration. A transient diuretic effect was found to occur in 2 mares dosed with 0.80 mg DADA/kg body wt.
3. A qualitative detection method using thin-layer chromatography was developed to detect DIPA, the major metabolite of DADA in equine urine. A quantitative detection method (lower limit of detection 0.5/zg/ml urine) for this metabolite was also developed using gas chromatography.
4. Neither DADA or the free base, DIPA, were detectable in equine blood samples using the abovementioned methodologies
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