1,420 research outputs found
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
Wireless internet architecture and testbed for wineglass
One of the most challenging issues in the area of mobile communication is the deployment of IPbased
wireless multimedia networks in public and business environments. The public branch may involve public
mobile networks, like UMTS as 3G system, while the business branch introduces local radio access networks by
means of W-LANs. Conventional mobile networks realise mobile specific functionality, e.g. mobility management
or authentication and accounting, by implementing appropriate mechanisms in specific switching nodes (e.g.
SGSN in GPRS). In order to exploit the full potential of IP networking solutions a replacement of these
mechanisms by IP-based solutions might be appropriate. In addition current and innovative future services in
mobile environments require at least soft-guaranteed, differentiated QoS. Therefore the WINE GLASS project
investigates and implements enhanced IP-based techniques supporting mobility and QoS in a wireless Internet
architecture. As a means to verify the applicability of the implemented solutions, location-aware services
deploying both IP-mobility and QoS mechanisms will be implemented and demonstratedPeer ReviewedPostprint (published version
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.
Complete determination of the reflection coefficient in neutron specular reflection by absorptive non-magnetic media
An experimental method is proposed which allows the complete determination of
the complex reflection coefficient for absorptive media for positive and
negative values of the momenta. It makes use of magnetic reference layers and
is a modification of a recently proposed technique for phase determination
based on polarization measurements. The complex reflection coefficient
resulting from a simulated application of the method is used for a
reconstruction of the scattering density profiles of absorptive non-magnetic
media by inversion.Comment: 14 pages, 4 figures, reformulation of abstract, ref.12 added,
typographical correction
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
Millimeter observations and modeling of the AB Aurigae system
(Abriged) We present the results of millimeter observations and a suitable
chemical and radiative transfer model of the AB Aur (HD 31293) circumstellar
disk and surrounding envelope. The integral molecular content of this system is
studied by observing CO, CO, CS, HCO, DCO, HCO, HCN, HNC,
and SiO rotational lines with the IRAM 30-m antenna, while the disk is mapped
in the HCO(1-0) transition with the Plateau de Bure interferometer. Using a
flared disk model with a vertical temperature gradient and an isothermal
spherical envelope model with a shadowed midplane and two unshielded cones
together with a gas-grain chemical network, time-dependent abundances of
observationally important molecules are calculated. Then a 2D non-LTE line
radiative transfer code is applied to compute excitation temperatures of
several rotational transitions of HCO, CO, CO, and CS molecules. We
synthesize the HCO(1-0) interferometric map along with single-dish CO(2-1),
CO(2-1), HCO(1-0), HCO(3-2), CS(2-1), and CS(5-4) spectra and
compared them with the observations. Our disk model successfully reproduces
observed interferometric HCO(1-0) data, thereby constraining the following
disk properties: (1) the inclination angle \iota=17^{+6}_{-3}\degr, (2) the
position angle \phi=80\pm30\degr, (3) the size AU,
(4) the mass M_\mathrm{disk}=1.3\cdot10^{-2} M_{\sun} (with a factor of
uncertainty), and (5) that the disk is in Keplerian rotation.
Furthermore, indirect evidence for a local inhomogeneity of the envelope at
\ga600 AU is found...Comment: 62 pages, 13 figures, 7 tables, accepted for publication in Ap
Disk and outflow signatures in Orion-KL: The power of high-resolution thermal infrared spectroscopy
We used the CRIRES spectrograph on the VLT to study the ro-vibrational
12CO/13CO, the Pfund beta and H2 emission between 4.59 and 4.72mu wavelengths
toward the BN object, the disk candidate source n, and a proposed dust density
enhancement IRC3. We detected CO absorption and emission features toward all
three targets. Toward the BN object, the data partly confirm the results
obtained more than 25 years ago by Scoville et al., however, we also identify
several new features. While the blue-shifted absorption is likely due to
outflowing gas, toward the BN object we detect CO in emission extending in
diameter to ~3300AU. Although at the observational spectral resolution limit,
the 13CO line width of that feature increases with energy levels, consistent
with a disk origin. If one attributes the extended CO emission also to a disk
origin, its extent is consistent with other massive disk candidates in the
literature. For source n, we also find the blue-shifted CO absorption likely
from an outflow. However, it also exhibits a narrower range of redshifted CO
absorption and adjacent weak CO emission, consistent with infalling motions. We
do not spatially resolve the emission for source n. For both sources we conduct
a Boltzmann analysis of the 13CO absorption features and find temperatures
between 100 and 160K, and H2 column densities of the order a few times
10^23cm^-2. The observational signatures from IRC3 are very different with only
weak absorption against a much weaker continuum source. However, the CO
emission is extended and shows wedge-like position velocity signatures
consistent with jet-entrainment of molecular gas, potentially associated with
the Orion-KL outflow system. We also present and discuss the Pfund beta and H2
emission in the region.Comment: 12 pages, 15 pages, accepted for A&A, you find a high-resolution copy
at http://www.mpia-hd.mpg.de/homes/beuther/papers.htm
Controlled Crystallization of the Amorphous Phase in Silicon Nitride Ceramics
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65986/1/j.1151-2916.1987.tb05676.x.pd
- …