300 research outputs found
A balloon-borne 1 meter telescope for far-infrared astronomy
The flight of a balloon-borne one-meter telescope for infrared astronomy in the wavelength interval of 40 to 240 microns is discussed. The gyro-stabilized telescope mapped the intensity of the far infrared radiation from NGC 7538, Mars, the Orion Nebula, and W3 with a resolution of one minute and from selected regions of these sources with a resolution of 30 seconds. The infrared detection is described and its capabilities are analyzed. The instrumentation, orientation system, and modes of observation of the telescope are defined
The near-infrared reflected spectrum of source I in Orion-KL
Source I in the Orion-KL nebula is believed to be the nearest example of a
massive star still in the main accretion phase. It is thus one of the best
cases for studying the properties of massive protostars to constrain high-mass
star formation theories. Near-infrared radiation from source I escapes through
the cavity opened by the OMC1 outflow and is scattered by dust towards our line
of sight. The reflected spectrum offers a unique possibility of observing the
emission from the innermost regions of the system and probing the nature of
source I and its immediate surroundings. We obtained moderately high
spectral-resolution (R~9000) observations of the near-infrared diffuse emission
in several locations around source I/Orion-KL. We observed a widespread rich
absorption line spectrum that we compare with cool stellar photospheres and
protostellar accretion disk models. The spectrum is broadly similar to strongly
veiled, cool, low-gravity stellar photospheres in the range Teff~3500-4500 K,
luminosity class I-III. An exact match explaining all features has not been
found, and a plausible explanation is that a range of different temperatures
contribute to the observed absorption spectrum. The 1D velocity dispersions
implied by the absorption spectra, sigma~30 km/s, can be explained by the
emission from a disk around a massive, mstar~10 Msun, protostar that is
accreting at a high rate, mdot~3x10^{-3} Msun/yr. Our observations suggest that
the near-infrared reflection spectrum observed in the Orion-KL region is
produced close to source I and scattered to our line of sight in the OMC1
outflow cavity. The spectrum allows us to exclude source I being a very large,
massive protostar rotating at breakup speed. We suggest that the absorption
spectrum is produced in a disk surrounding a ~10 Msun protostar, accreting from
its disk at a high rate of a few 10^{-3} Msun/yr.Comment: Accepted for publication on A&
High-resolution infrared spectroscopy as a tool to detect false positives of transit search programs
Transit search programs such as CoRoT and Kepler now have the capability of
detecting planets as small as the Earth. The detection of these planets however
requires the removal of all false positives. Although many false positives can
be identified by a detailed analysis of the LCs, the detections of others
require additional observations. An important source of false positives are
faint eclipsing binaries within the PSF of the target stars. We develop a new
method that allows us to detect faint eclipsing binaries with a separation
smaller than one arcsec from target stars. We thereby focus on binaries that
mimic the transits of terrestrial planets. These binaries can be either at the
same distance as the target star (triple stars), or at either larger, or
smaller distances. A close inspection of the problem indicates that in all
relevant cases the binaries are brighter in the infrared than in the optical
regime. We show how high resolution IR spectroscopy can be used to remove these
false positives. For the triple star case, we find that the brightness
difference between a primary and an eclipsing secondary is about 9-10 mag in
the visual but only about 4.5-5.9 magnitudes in the K-band. We demonstrate how
the triple star hypothesis can be excluded by taking a high-resolution IR
spectrum. Simulations of these systems show that the companions can be detected
with a false-alarm probability of 2%, if the spectrum has a S/N-ratio > 100. We
show that high-resolution IR spectra also allows to detect most of the false
positives caused by foreground or background binaries. If high resolution IR
spectroscopy is combined with photometric methods, virtually all false
positives can be detected without RV measurements. It is thus possible to
confirm transiting terrestrial planets with a modest investment of observing
time.Comment: 6 pages, 7 figure
Computing and data processing
The applications of computers and data processing to astronomy are discussed. Among the topics covered are the emerging national information infrastructure, workstations and supercomputers, supertelescopes, digital astronomy, astrophysics in a numerical laboratory, community software, archiving of ground-based observations, dynamical simulations of complex systems, plasma astrophysics, and the remote control of fourth dimension supercomputers
ESO Imaging Survey: infrared observations of CDF-S and HDF-S
This paper presents infrared data obtained from observations carried out at
the ESO 3.5m New Technology Telescope (NTT) of the Hubble Deep Field South
(HDF-S) and the Chandra Deep Field South (CDF-S). These data were taken as part
of the ESO Imaging Survey (EIS) program, a public survey conducted by ESO to
promote follow-up observations with the VLT. In the HDF-S field the infrared
observations cover an area of ~53 square arcmin, encompassing the HST WFPC2 and
STIS fields, in the JHKs passbands. The seeing measured in the final stacked
images ranges from 0.79" to 1.22" and the median limiting magnitudes (AB
system, 2" aperture, 5sigma detection limit) are J_AB~23.0, H_AB~22.8 and
K_AB~23.0 mag. Less complete data are also available in JKs for the adjacent
HST NICMOS field. For CDF-S, the infrared observations cover a total area of
\~100 square arcmin, reaching median limiting magnitudes (as defined above) of
J_AB~23.6 and K_AB~22.7 mag. For one CDF-S field H-band data are also
available. This paper describes the observations and presents the results of
new reductions carried out entirely through the un-supervised, high-throughput
EIS Data Reduction System and its associated EIS/MVM C++-based image processing
library developed, over the past 5 years, by the EIS project and now publicly
available. The paper also presents source catalogs extracted from the final
co-added images which are used to evaluate the scientific quality of the survey
products, and hence the performance of the software. This is done comparing the
results obtained in the present work with those obtained by other authors from
independent data and/or reductions carried out with different software packages
and techniques. The final science-grade catalogs and co-added images are
available at CDS.Comment: Accepted for publication in A&A, 13 pages, 12 figures; a full
resolution version of the paper is available from
http://www.astro.ku.dk/~lisbeth/eisdata/papers/4528.pdf ; related catalogs
and images are available through http://www.astro.ku.dk/~lisbeth/eisdata
Implication of the overlap representation for modelling generalized parton distributions
Based on a field theoretically inspired model of light-cone wave functions,
we derive valence-like generalized parton distributions and their double
distributions from the wave function overlap in the parton number conserved
s-channel. The parton number changing contributions in the t-channel are
restored from duality. In our construction constraints of positivity and
polynomiality are simultaneously satisfied and it also implies a model
dependent relation between generalized parton distributions and transverse
momentum dependent parton distribution functions. The model predicts that the
t-behavior of resulting hadronic amplitudes depends on the Bjorken variable
x_Bj. We also propose an improved ansatz for double distributions that embeds
this property.Comment: 15 pages, 8 eps figure
A long look at the BALQSO LBQS 2212-1759 with XMM-Newton
Very long (172 ks effective exposure time) observations of the BALQSO LBQS
2212-1759 with XMM-Newton yield a stringent upper-limit on its 0.2-10 keV
(rest- frame 0.64-32.2 keV) flux, F < 6 E-17 erg/cm2/s, while simultaneous UV
and optical observations reveal a rather blue spectrum extending to 650 A in
the source rest frame. These results are used to set a tight upper-limit on its
optical to X-ray spectral index alpha_{ox} < -2.56. Given the HI-BAL nature of
LBQS 212-1759, its X-ray weakness is most likely due to intrinsic absorption.
If this is the case, and assuming that the intrinsic alpha_{ox} of LBQS
2212-1759 is -1.63 - a value appropriate for a radio-quiet quasar of this
luminosity - one can set a lower limit on the X-ray absorbing column N_{H} >
3.4 E25 cm-2. Such a large column has a Thomson optical depth to electron
scattering tau > 23, sufficient to extinguish the optical and UV emission. The
problem only gets worse if the gas is neutral since the opacity in the Lyman
continuum becomes extremely large, > 2 E8, conflicting with the source
detection below 912 A. This apparent contradiction probably means that our
lines-of-sight to the X-ray and to the UV emitting regions are different, such
that the gas covers completely the compact X-ray source but only partially the
more extended source of ultraviolet photons. An extended (~ 1') X-ray source is
detected 2' to the south-east of the QSO. Given its thermal spectrum and
temperature (1.5 < T < 3.0 keV}, it is probably a foreground (0.29 < z < 0.46)
cluster of galaxies.Comment: 9 pages, 3 figures, A&A latex, accepted for publication in Astronomy
& Astrophysic
The Quintuplet Cluster I. A K-band spectral catalog of stellar sources
Three very massive clusters are known to reside in the Galactic Center
region, the Arches cluster, the Quintuplet cluster and the Central parsec
cluster. We obtained spectroscopic observations of the Quintuplet cluster with
the Integral Field Spectrograph SINFONI-SPIFFI at the ESO-VLT. The spectral
range comprises the near-IR K-band from 1.94 to 2.45 micrometer. The 3D data
cubes of the individual fields were flux-calibrated and combined to one
contiguous cube, from which the spectra of all detectable point sources were
extracted. We present a catalog of 160 stellar sources in the inner part of the
Quintuplet cluster.Comment: 14 pages, 9 figures, 3 tables, accepted by A&
Implications of quantum automata for contextuality
We construct zero-error quantum finite automata (QFAs) for promise problems
which cannot be solved by bounded-error probabilistic finite automata (PFAs).
Here is a summary of our results:
- There is a promise problem solvable by an exact two-way QFA in exponential
expected time, but not by any bounded-error sublogarithmic space probabilistic
Turing machine (PTM).
- There is a promise problem solvable by an exact two-way QFA in quadratic
expected time, but not by any bounded-error -space PTMs in
polynomial expected time. The same problem can be solvable by a one-way Las
Vegas (or exact two-way) QFA with quantum head in linear (expected) time.
- There is a promise problem solvable by a Las Vegas realtime QFA, but not by
any bounded-error realtime PFA. The same problem can be solvable by an exact
two-way QFA in linear expected time but not by any exact two-way PFA.
- There is a family of promise problems such that each promise problem can be
solvable by a two-state exact realtime QFAs, but, there is no such bound on the
number of states of realtime bounded-error PFAs solving the members this
family.
Our results imply that there exist zero-error quantum computational devices
with a \emph{single qubit} of memory that cannot be simulated by any finite
memory classical computational model. This provides a computational perspective
on results regarding ontological theories of quantum mechanics \cite{Hardy04},
\cite{Montina08}. As a consequence we find that classical automata based
simulation models \cite{Kleinmann11}, \cite{Blasiak13} are not sufficiently
powerful to simulate quantum contextuality. We conclude by highlighting the
interplay between results from automata models and their application to
developing a general framework for quantum contextuality.Comment: 22 page
Acceleration Schemes for Ab-Initio Molecular Dynamics and Electronic Structure Calculations
We study the convergence and the stability of fictitious dynamical methods
for electrons. First, we show that a particular damped second-order dynamics
has a much faster rate of convergence to the ground-state than first-order
steepest descent algorithms while retaining their numerical cost per time step.
Our damped dynamics has efficiency comparable to that of conjugate gradient
methods in typical electronic minimization problems. Then, we analyse the
factors that limit the size of the integration time step in approaches based on
plane-wave expansions. The maximum allowed time step is dictated by the highest
frequency components of the fictitious electronic dynamics. These can result
either from the large wavevector components of the kinetic energy or from the
small wavevector components of the Coulomb potential giving rise to the so
called {\it charge sloshing} problem. We show how to eliminate large wavevector
instabilities by adopting a preconditioning scheme that is implemented here for
the first-time in the context of Car-Parrinello ab-initio molecular dynamics
simulations of the ionic motion. We also show how to solve the charge-sloshing
problem when this is present. We substantiate our theoretical analysis with
numerical tests on a number of different silicon and carbon systems having both
insulating and metallic character.Comment: RevTex, 9 figures available upon request, to appear in Phys. Rev.
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