1,453 research outputs found
Research on Computational and Display Requirements for Human Control of Space Vehicle Boosters, Phase III. Part II - Computer Programs and Data Package Final Report, 1 Mar. - 31 Aug. 1967
Hybrid computer program for real time trajectory determination of human controlled space vehicle booste
An infrared imaging search for low-mass companions to members of the young nearby beta Pic and Tucana/Horologium associations
We present deep high dynamic range infrared images of young nearby stars in
the Tucana/Horologium and beta Pic associations, all ~ 10 to 35 Myrs young and
at ~10 to 60 pc distance. Such young nearby stars are well-suited for direct
imaging searches for brown dwarf and even planetary companions, because young
sub-stellar objects are still self-luminous due to contraction and accretion.
We performed our observations at the ESO 3.5m NTT with the normal infrared
imaging detector SofI and the MPE speckle camera Sharp-I. Three arc sec north
of GSC 8047-0232 in Horologium a promising brown dwarf companion candidate is
detected, which needs to be confirmed by proper motion and/or spectroscopy.
Several other faint companion candidates are already rejected by second epoch
imaging. Among 21 stars observed in Tucana/Horologium, there are not more than
one to five brown dwarf companions outside of 75 AU (1.5" at 50 pc); most
certainly only < 5 % of the Tuc/HorA stars have brown dwarf companions (13 to
78 Jupiter masses) outside of 75 AU. For the first time, we can report an upper
limit for the frequency of massive planets (~ 10 M_jup) at wide separations (~
100 AU) using a meaningfull and homogeneous sample: Of 11 stars observed
sufficiently deep in beta Pic (12 Myrs), not more than one has a massive planet
outside of ~ 100 AU, i.e. massive planets at large separations are rare (< 9
%).Comment: Astronomische Nachrichten, in pres
Using Virtual Observatory techniques to search for Adaptive Optics suitable AGN
Until recently, it has been possible only for nearby galaxies to study the
scaling relations between central black hole and host galaxy in detail. Because
of the small number densities at low redshift, (luminous) AGN are
underrepresented in such detailed studies. The advent of adaptive optics (AO)
at large telescopes helps overcoming this hurdle, allowing to reach small
linear scales over a wide range in redshift. Finding AO-suitable targets, i.e.,
AGN having a nearby reference star, and carrying out an initial multiwavelength
classification is an excellent use case for the Virtual Observatory. We present
our Virtual-Observatory approach to select an AO-suitable catalog of
X-ray-emitting AGN at redshifts 0.1<z<1.Comment: 4 pages, 5 figures, submitted to "EURO-VO AIDA workshop:
Multiwavelength astronomy and Virtual Observatory", ESAC, Spain, 1-3 Dec.
200
A Sample of X-Ray active extragalactic Sources suitable for NIR Adaptive Optics Observations
Recent X-ray surveys have now resolved most of the X-ray background (XRB)
into discrete sources. While this represents a break- through in the
understanding of the XRB, the astrophysical nature of these sources still
remains mysterious. In this article we present a sample of X-ray/optically
selected extragalactic objects which are suitable for adaptive optics
observations in the near infrared (NIR) at highest angu- lar resolution. The
sample is based on a cross-correlation of the Sloan Digital Sky Survey and the
ROSAT All Sky Survey. The NIR properties can help to disentangle the nature of
the X-ray bright, partially absorbed and spectroscopically passive background
objects and their hosts.Comment: 4 pages with 1 figure, LateX, uses newpasp.sty, to appear in "AGN
Physics with the Sloan Digital Sky Survey", ed. G. T. Richards and P. B. Hall
(San Francisco: ASP), 200
On the orientation of the Sagittarius A* system
The near-infrared emission from the black hole at the Galactic center (Sgr
A*) has unique properties. The most striking feature is a suggestive periodic
sub-structure that has been observed in a couple of flares so far. Using
near-infrared polarimetric observations and modelling the quasi-periodicity in
terms of an orbiting blob, we try to constrain the three dimensional
orientation of the Sgr A* system. We report on so far unpublished polarimetric
data from 2003. They support the observations of a roughly constant mean
polarization angle of 60 degr \pm 20 degr from 2004-2006. Prior investigations
of the 2006 data are deepened. In particular, the blob model fits are evaluated
such that constraints on the position angle of Sgr A* can be derived.
Confidence contours in the position-inclination angle plane are derived. On a
3sigma level the position angle of the equatorial plane normal is in the range
60 degr - 108 degr (east of north) in combination with a large inclination
angle. This agrees well with recent independent work in which radio
spectral/morphological properties of Sgr A* and X-ray observations,
respectively, have been used. However, the quality of the presently available
data and the uncertainties in our model bring some ambiguity to our
conclusions.Comment: 10 pages, 4 figures; Research Note accepted by A&A for publicatio
K-band polarimetry of an Sgr A* flare with a clear sub-flare structure
Context: The supermassive black hole at the Galactic center, SgrA*, shows
frequent radiation outbursts, often called 'flares'. In the near-infrared some
of these flares were reported as showing intrinsic quasi-periodicities. The
flux peaks associated with the quasi-periodic behavior were found to be highly
polarized. Aims: The aim of this work is to present new evidence to support
previous findings of the properties of the polarized radiation from SgrA* and
to again provide strong support for the quasi-periodicity of ~18+-3 min
reported earlier. Methods: Observations were carried out at the European
Southern Observatory's Very Large Telescope on Paranal, Chile. We used the
NAOS/CONICA adaptive optics/near-infrared camera instrument. By fitting the
polarimetric lightcurves with a hot-spot model, we addressed the question of
whether the data are consistent with this model. To fit the observed data we
used a general relativistic ray-tracing code in combination with a simple
hot-spot/ring model. Results: We report on new polarization measurements of a
K-band flare from the supermassive black hole at the Galactic center. The data
provide very strong support for a quasi-periodicity of 15.5+-2 min. The mean
polarization of the flare is consistent with the direction of the electric
field vector that was reported in previous observations. The data can be
modeled successfully with a combined blob/ring model. The inclination i of the
blob orbit must be i > 20 deg on a 3sigma level, and the dimensionless spin
parameter of the black hole is derived to be a > 0.5.Comment: accepted by A&A Letters for publication; 5 pages, 9 figure
Simultaneous NIR/sub-mm observation of flare emission from SgrA*
We report on a successful, simultaneous observation and modeling of the
sub-millimeter to near-infrared flare emission of the Sgr A* counterpart
associated with the super-massive black hole at the Galactic center. Our
modeling is based on simultaneous observations that have been carried out on 03
June, 2008 using the NACO adaptive optics (AO) instrument at the ESO VLT and
the LABOCA bolometer at the APEX telescope. Inspection and modeling of the
light curves show that the sub-mm follows the NIR emission with a delay of
1.5+/-0.5 hours. We explain the flare emission delay by an adiabatic expansion
of the source components.Comment: 12 pages, 9 figures, 3 tables, in press with A&
Coordinated NIR/mm observations of flare emission from Sagittarius A*
We report on a successful, simultaneous observation and modelling of the
millimeter (mm) to near-infrared (NIR) flare emission of the Sgr A* counterpart
associated with the supermassive black hole at the Galactic centre (GC). We
present a mm/sub-mm light curve of Sgr A* with one of the highest quality
continuous time coverages and study and model the physical processes giving
rise to the variable emission of Sgr A*.Comment: 14 pages, 16 figure
VLT-SINFONI observations of Mrk 609 - A showcase for X-ray active galaxies chosen from a sample of AGN suitable for adaptive optics observations with natural guide stars
We will present first results of ESO-VLT AO-assisted integral-field
spectroscopy of a sample of X-ray bright AGN with redshifts of 0.04 < z < 1. We
constructed this sample by cross-correlating the SDSS and ROSAT surveys and
utilizing typical AO constraints. This sample allows for a detailed study of
the NIR properties of the nuclear and host environments with high spectral
resolution on the 100 pc scale. These objects can then be compared directly to
the local (z<0.01) galaxy populations (observed without AO) at the same linear
scale. As a current example, we will present observations of the z=0.034
Seyfert 1.8 galaxy Mrk 609 with the new AO-assisted integral-field spectrometer
SINFONI at the VLT. The successful observations show, that in the future -
while having observed more objects - we will be able to determine the presence,
frequency and importance of nuclear bars and/or circum-nuclear star forming
rings in these objects and address the question of how these X-ray luminous AGN
and their hosts are linked to optically/UV-bright QSOs, low-z QSOs/radio
galaxies, or ULIRGs.Comment: 9 pages, 7 figures, submitted to "Adaptive Optics-Assisted
Integral-Field Spectroscopy", Rutten R.G.M., Benn C.R., Mendez J., eds., May
2005, La Palma (Spain), New Astr. Re
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