1,714 research outputs found
A rotating disk around the very young massive star AFGL 490
We observed the embedded, young 8--10 Msun star AFGL 490 at subarcsecond
resolution with the Plateau de Bure Interferometer in the C17O (2--1)
transition and found convincing evidence that AFGL 490 is surrounded by a
rotating disk. Using two-dimensional modeling of the physical and chemical disk
structure coupled to line radiative transfer, we constrain its basic
parameters. We obtain a relatively high disk mass of 1 Msun and a radius of ~
1500 AU. A plausible explanation for the apparent asymmetry of the disk
morphology is given.Comment: 4 pages, 5 figure
NGC 2264 IRS1: The central engine and its cavity
We present a high-resolution study of NGC 2264 IRS1 in CS(2-1) and in the
3-mm continuum using the IRAM Plateau de Bure Interferometer. We complement
these radio data with images taken at 2.2, 4.6, and 11.9 micron. The combined
information allow a new interpretation of the closest environment of NGC 2264
IRS1. No disk around the B-type star IRS1 was found. IRS1 and its low-mass
companions are located in a low-density cavity which is surrounded by the
remaining dense cloud core which has a clumpy shell-like structure. Strong
evidence for induced on-going star formation was found in the surroundings of
IRS1. A deeply embedded very young stellar object 20 arcsec to the north of
IRS1 is powering a highly collimated bipolar outflow. The object 8 in the
closer environment of IRS1 is a binary surrounded by dusty circumbinary
material and powering two bipolar outflows.Comment: 17 pages, 6 figures, The paper is accepted and will appear in the
Astrophysical Journal, Vol 599, No 1 (issue December 10). A high-resolution
postscript version of this paper is available here (
http://www.astro.uni-jena.de/Users/martin/publi.html). Furthermore, you can
find a high resolution PDF file here (
http://www.tls-tautenburg.de/research/tls-research/pub2003.html
Sistemas para reducir el bebedero en la inyección de materiales plásticos
Se describen diferentes sistemas para reducir el bebedero en la inyección de materiales plásticos
Reorientation of Spin Density Waves in Cr(001) Films induced by Fe(001) Cap Layers
Proximity effects of 20 \AA thin Fe layers on the spin density waves (SDWs)
in epitaxial Cr(001) films are revealed by neutron scattering. Unlike in bulk
Cr we observe a SDW with its wave vector Q pointing along only one {100}
direction which depends dramatically on the film thickness t_{Cr}. For t_{Cr} <
250 \AA the SDW propagates out-of-plane with the spins in the film plane. For
t_{Cr} > 1000 \AA the SDW propagates in the film plane with the spins
out-of-plane perpendicular to the in-plane Fe moments. This reorientation
transition is explained by frustration effects in the antiferromagnetic
interaction between Fe and Cr across the Fe/Cr interface due to steps at the
interface.Comment: 4 pages (RevTeX), 3 figures (EPS
Impact, Attention, Influence: Early Assessment of Autonomous Driving Datasets
Autonomous Driving (AD), the area of robotics with the greatest potential
impact on society, has gained a lot of momentum in the last decade. As a result
of this, the number of datasets in AD has increased rapidly. Creators and users
of datasets can benefit from a better understanding of developments in the
field. While scientometric analysis has been conducted in other fields, it
rarely revolves around datasets. Thus, the impact, attention, and influence of
datasets on autonomous driving remains a rarely investigated field. In this
work, we provide a scientometric analysis for over 200 datasets in AD. We
perform a rigorous evaluation of relations between available metadata and
citation counts based on linear regression. Subsequently, we propose an
Influence Score to assess a dataset already early on without the need for a
track-record of citations, which is only available with a certain delay.Comment: Daniel Bogdoll and Jonas Hendl contributed equally. Accepted for
publication at ICCRE 202
Using helium 10830 {\AA} transits to constrain planetary magnetic fields
Planetary magnetic fields can affect the predicted mass loss rate for
close-in planets that experience large amounts of UV irradiation. In this work,
we present a method to detect the magnetic fields of close-in exoplanets
undergoing atmospheric escape using transit spectroscopy at the 10830 Angstrom
line of helium. Motivated by previous work on hydrodynamic and
magneto-hydrodynamic photoevaporation, we suggest that planets with magnetic
fields that are too weak to control the outflow's topology lead to blue-shifted
transits due to day-to-night-side flows. In contrast, strong magnetic fields
prevent this day-to-night flow, as the gas is forced to follow the magnetic
field's roughly dipolar topology. We post-process existing 2D photoevaporation
simulations to test this concept, computing synthetic transit profiles in
helium. As expected, we find that hydrodynamically dominated outflows lead to
blue-shifted transits on the order of the sound speed of the gas. Strong
surface magnetic fields lead to unshifted or slightly red-shifted transit
profiles. High-resolution observations can distinguish between these profiles;
however, eccentricity uncertainties generally mean that we cannot conclusively
say velocity shifts are due to the outflow for individual planets. The majority
of helium observations are blue-shifted, which could be a tentative indication
that close-in planets generally have surface dipole magnetic field strengths
gauss. More 3D hydrodynamic and magneto-hydrodynamic are needed
to confirm this conclusion robustly.Comment: Published in MNRA
Syzygies of torsion bundles and the geometry of the level l modular variety over M_g
We formulate, and in some cases prove, three statements concerning the purity
or, more generally the naturality of the resolution of various rings one can
attach to a generic curve of genus g and a torsion point of order l in its
Jacobian. These statements can be viewed an analogues of Green's Conjecture and
we verify them computationally for bounded genus. We then compute the
cohomology class of the corresponding non-vanishing locus in the moduli space
R_{g,l} of twisted level l curves of genus g and use this to derive results
about the birational geometry of R_{g, l}. For instance, we prove that R_{g,3}
is a variety of general type when g>11 and the Kodaira dimension of R_{11,3} is
greater than or equal to 19. In the last section we explain probabilistically
the unexpected failure of the Prym-Green conjecture in genus 8 and level 2.Comment: 35 pages, appeared in Invent Math. We correct an inaccuracy in the
statement of Prop 2.
A VLA Search for Water Masers in Six HII Regions: Tracers of Triggered Low-Mass Star Formation
We present a search for water maser emission at 22 GHz associated with young
low-mass protostars in six HII regions -- M16, M20, NGC 2264, NGC 6357, S125,
and S140. The survey was conducted with the NRAO Very Large Array from 2000 to
2002. For several of these HII regions, ours are the first high-resolution
observations of water masers. We detected 16 water masers: eight in M16, four
in M20, three in S140, and one in NGC 2264. All but one of these were
previously undetected. No maser emission was detected from NGC 6357 or S125.
There are two principle results to our study. (1) The distribution of water
masers in M16 and M20 does not appear to be random but instead is concentrated
in a layer of compressed gas within a few tenths of a parsec of the ionization
front. (2) Significantly fewer masers are seen in the observed fields than
expected based on other indications of ongoing star formation, indicating that
the maser-exciting lifetime of protostars is much shorter in HII regions than
in regions of isolated star formation. Both of these results confirm
predictions of a scenario in which star formation is first triggered by shocks
driven in advance of ionization fronts, and then truncated approximately 10^5
years later when the region is overrun by the ionization front.Comment: 30 pages, 20 figures, 3 tables. Accepted for publication by ApJ. Full
resolution figures and PS and PDF versions with full-res figures available at
http://eagle.la.asu.edu/healy/preprints/hhc0
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