259 research outputs found
Science with the Keck Interferometer ASTRA Program
The ASTrometric and phase-Referenced Astronomy (ASTRA) project will provide
phase referencing and astrometric observations at the Keck Interferometer,
leading to enhanced sensitivity and the ability to monitor orbits at an
accuracy level of 30-100 microarcseconds. Here we discuss recent scientific
results from ASTRA, and describe new scientific programs that will begin in
2010-2011. We begin with results from the "self phase referencing" (SPR) mode
of ASTRA, which uses continuum light to correct atmospheric phase variations
and produce a phase-stabilized channel for spectroscopy. We have observed a
number of protoplanetary disks using SPR and a grism providing a spectral
dispersion of ~2000. In our data we spatially resolve emission from dust as
well as gas. Hydrogen line emission is spectrally resolved, allowing
differential phase measurements across the emission line that constrain the
relative centroids of different velocity components at the 10 microarcsecond
level. In the upcoming year, we will begin dual-field phase referencing (DFPR)
measurements of the Galactic Center and a number of exoplanet systems. These
observations will, in part, serve as precursors to astrometric monitoring of
stellar orbits in the Galactic Center and stellar wobbles of exoplanet host
stars. We describe the design of several scientific investigations capitalizing
on the upcoming phase-referencing and astrometric capabilities of ASTRA.Comment: Published in the proceedings of the SPIE 2010 conference on "Optical
and Infrared Interferometry II
Disentangling Confused Stars at the Galactic Center with Long Baseline Infrared Interferometry
We present simulations of Keck Interferometer ASTRA and VLTI GRAVITY
observations of mock star fields in orbit within ~50 milliarcseconds of Sgr A*.
Dual-field phase referencing techniques, as implemented on ASTRA and planned
for GRAVITY, will provide the sensitivity to observe Sgr A* with infrared
interferometers. Our results show an improvement in the confusion noise limit
over current astrometric surveys, opening a window to study stellar sources in
the region. Since the Keck Interferometer has only a single baseline, the
improvement in the confusion limit depends on source position angles. The
GRAVITY instrument will yield a more compact and symmetric PSF, providing an
improvement in confusion noise which will not depend as strongly on position
angle. Our Keck results show the ability to characterize the star field as
containing zero, few, or many bright stellar sources. We are also able to
detect and track a source down to mK~18 through the least confused regions of
our field of view at a precision of ~200 microarcseconds along the baseline
direction. This level of precision improves with source brightness. Our GRAVITY
results show the potential to detect and track multiple sources in the field.
GRAVITY will perform ~10 microarcsecond astrometry on a mK=16.3 source and ~200
microarcsecond astrometry on a mK=18.8 source in six hours of monitoring a
crowded field. Monitoring the orbits of several stars will provide the ability
to distinguish between multiple post-Newtonian orbital effects, including those
due to an extended mass distribution around Sgr A* and to low-order General
Relativistic effects. Early characterizations of the field by ASTRA including
the possibility of a precise source detection, could provide valuable
information for future GRAVITY implementation and observation.Comment: Accepted for publication in Ap
First Faint Dual-field Off-axis Observations in Optical Long Baseline Interferometry
Ground-based long baseline interferometers have long been limited in sensitivity in part by the short integration periods imposed by atmospheric turbulence. The first observation fainter than this limit was performed on 2011 January 22 when the Keck Interferometer observed a K = 11.5 target, about 1 mag fainter than its K = 10.3 atmospherically imposed limit; the currently demonstrated limit is K = 12.5. These observations were made possible by the Dual-Field Phase-Referencing (DFPR) instrument, part of the NSF-funded ASTrometry and phase-Referenced Astronomy project; integration times longer than the turbulence time scale are made possible by its ability to simultaneously measure the real-time effects of the atmosphere on a nearby bright guide star and correct for it on the faint target. We present the implementation of DFPR on the Keck Interferometer. Then, we detail its on-sky performance focusing on the accuracy of the turbulence correction and the resulting fringe contrast stability
ASTRA: ASTrometry and phase-Referencing Astronomy on the Keck interferometer
ASTRA (ASTrometric and phase-Referencing Astronomy) is an upgrade to the
existing Keck Interferometer which aims at providing new self-phase referencing
(high spectral resolution observation of YSOs), dual-field phase referencing
(sensitive AGN observations), and astrometric (known exoplanetary systems
characterization and galactic center general relativity in strong field regime)
capabilities. With the first high spectral resolution mode now offered to the
community, this contribution focuses on the progress of the dual field and
astrometric modes.Comment: 10 pages, 6 figures, 2 tables, SPIE 201
Confronting Standard Models of Proto--Planetary Disks With New Mid--Infrared Sizes from the Keck Interferometer
We present near and mid-infrared interferometric observations made with the
Keck Interferometer Nuller and near-contemporaneous spectro-photometry from the
IRTF of 11 well known young stellar objects, several observed for the first
time in these spectral and spatial resolution regimes. With AU-level spatial
resolution, we first establish characteristic sizes of the infrared emission
using a simple geometrical model consisting of a hot inner rim and mid-infrared
disk emission. We find a high degree of correlation between the stellar
luminosity and the mid-infrared disk sizes after using near-infrared data to
remove the contribution from the inner rim. We then use a semi-analytical
physical model to also find that the very widely used "star + inner dust rim +
flared disk" class of models strongly fails to reproduce the SED and
spatially-resolved mid-infrared data simultaneously; specifically a more
compact source of mid-infrared emission is required than results from the
standard flared disk model. We explore the viability of a modification to the
model whereby a second dust rim containing smaller dust grains is added, and
find that the two-rim model leads to significantly improved fits in most cases.
This complexity is largely missed when carrying out SED modelling alone,
although detailed silicate feature fitting by McClure et al. 2013 recently came
to a similar conclusion. As has been suggested recently by Menu et al. 2015,
the difficulty in predicting mid-infrared sizes from the SED alone might hint
at "transition disk"-like gaps in the inner AU; however, the relatively high
correlation found in our mid-infrared disk size vs. stellar luminosity relation
favors layered disk morphologies and points to missing disk model ingredients
instead
Tests with a Carlina-type diluted telescope; Primary coherencing
Studies are under way to propose a new generation of post-VLTI
interferometers. The Carlina concept studied at the Haute- Provence Observatory
is one of the proposed solutions. It consists in an optical interferometer
configured like a diluted version of the Arecibo radio telescope: above the
diluted primary mirror made of fixed cospherical segments, a helium balloon (or
cables suspended between two mountains), carries a gondola containing the focal
optics. Since 2003, we have been building a technical demonstrator of this
diluted telescope. First fringes were obtained in May 2004 with two
closely-spaced primary segments and a CCD on the focal gondola. We have been
testing the whole optical train with three primary mirrors. The main aim of
this article is to describe the metrology that we have conceived, and tested
under the helium balloon to align the primary mirrors separate by 5-10 m on the
ground with an accuracy of a few microns. The servo loop stabilizes the mirror
of metrology under the helium balloon with an accuracy better than 5 mm while
it moves horizontally by 30 cm in open loop by 10-20 km/h of wind. We have
obtained the white fringes of metrology; i.e., the three mirrors are aligned
(cospherized) with an accuracy of {\approx} 1 micron. We show data proving the
stability of fringes over 15 minutes, therefore providing evidence that the
mechanical parts are stabilized within a few microns. This is an important step
that demonstrates the feasibility of building a diluted telescope using cables
strained between cliffs or under a balloon. Carlina, like the MMT or LBT, could
be one of the first members of a new class of telescopes named diluted
telescopes.Comment: 18 pages, 17 figures, A&A, accepte
First VLTI infrared spectro-interferometry on GCIRS 7 - Characterizing the prime reference source for Galactic center observations at highest angular resolution
Investigating the environment of the massive black hole SgrA* at the center
of the Galaxy requires the highest angular resolution available to avoid source
confusion and to study the physical properties of the individual objects.
GCIRS7 has been used as wavefront and astrometric reference. Our studies
investigate, for the first time, its properties at 2&10um using VLTI/AMBER and
MIDI. We aim at analyzing the suitability of IRS7 as an IF-phase-reference for
the upcoming generation of dual-field facilities at optical interferometers. We
observed with (R~30) and 50m (proj.) baseline, resulting in 9 and 45mas
resolution for NIR and MIR, resp. The first K-band fringe detection of a GC
star suggests that IRS7 could be marginally resolved at 2um, which would imply
that the photosphere of the supergiant is enshrouded by a molecular and dusty
envelope. At 10um, IRS7 is strongly resolved with a visibility of approximately
0.2. The MIR is dominated by moderately warm (200 K), extended dust, mostly
distributed outside of a radius of about 120 AU (15 mas) around the star. A
deep 9.8-silicate absorption in excess of the usual extinction law with respect
to the NIR extinction has been found. This confirms recent findings of a
relatively enhanced, interstellar 9.8-silicate absorption with respect to the
NIR extinction towards another star in the central arcsec, suggesting an
unusual dust composition in that region. Our VLTI observations show that
interferometric NIR phase-referencing experiments with mas resolution using
IRS7 as phase-reference appear to be feasible, but more such studies are
required to definitely characterize the close environment around this star. We
demonstrate that interferometry is required to resolve the innermost
environment of stars at the Galactic center.Comment: 6 pages, 2 figures, accepted for publication in A&
Scientific, Technical and Economic Committee for Fisheries (STECF) - Report of the STECF Study Group on the Evaluation of Fishery Multi-annual Plans (SGMOS 09-02)
SG-MOS 09-02 was held in IPIMAR, Lisbon, (Portugal), on 23-27 November 2009. The aim of the
workshop was to provide Evaluations of three multiannual fisheries management plans:- R(EC) No
388/2006 ¿ multi-annual plan for sole in the Bay of Biscay; R(EC) No 209/2007 ¿ multi-annual plan for sole
in the Western Channel R(EC) No676/2007 ¿ multi-annual plan for sole and plaice in the North Sea.
STECF reviewed the report during its Plenary meeting on 26-30 April 2010.JRC.DG.G.4-Maritime affair
Milliarcsecond N-Band Observations of the Nova RS Ophiuchi: First Science with the Keck Interferometer Nuller
We report observations of the nova RS Ophiuchi (RS Oph) using the Keck
Interferometer Nuller (KIN), approximately 3.8 days following the most recent
outburst that occurred on 2006 February 12. These observations represent the
first scientific results from the KIN, which operates in N-band from 8 to 12.5
microns in a nulling mode. By fitting the unique KIN data, we have obtained an
angular size of the mid-infrared continuum of 6.2, 4.0, or 5.4 mas for a disk
profile, gaussian profile (FWHM), and shell profile respectively. The data show
evidence of enhanced neutral atomic hydrogen emission and atomic metals
including silicon located in the inner spatial regime near the white dwarf (WD)
relative to the outer regime. There are also nebular emission lines and
evidence of hot silicate dust in the outer spatial region, centered at ! 17 AU
from the WD, that are not found in the inner regime. Our evidence suggests that
these features have been excited by the nova flash in the outer spatial regime
before the blast wave reached these regions. These identifications support a
model in which the dust appears to be present between outbursts and is not
created during the outburst event. We further discuss the present results in
terms of a unifying model of the system that includes an increase in density in
the plane of the orbit of the two stars created by a spiral shock wave caused
by the motion of the stars through the cool wind of the red giant star. These
data show the power and potential of the nulling technique which has been
developed for the detection of Earth-like planets around nearby stars for the
Terrestrial Planet Finder Mission and Darwin missions.Comment: 41 pages, 10 figure
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