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J. Woillez,
R. Akeson,
M. Colavita,
J. Eisner,
A. Ghez,
J. Graham,
L. Hillenbrand,
R. Millan-Gabet,
J. Monnier,
J. -U. Pott, [......],
M. Hrynevych,
O. Martin,
D. Medeiros,
D. Morrison,
T. Panteleeva,
B Smith,
K. Summers,
K. Tsubota,
C. Tyau,
E. Wetherell
[show abstract]
[hide abstract]
ABSTRACT: 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.
Danchi, William C.; Delplancke, Françoise; Rajagopal, Jayadev K.: Optical and Infrared Interferometry II, SPIE, 773412-773412-10 (2010). 08/2012;
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[show abstract]
[hide abstract]
ABSTRACT: 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.
06/2012;
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R. Millan-Gabet,
E. Serabyn,
B. Mennesson,
W. A. Traub,
R. K. Barry,
W. C. Danchi,
M. Kuchner,
C. C. Stark,
S. Ragland,
M. Hrynevych, J. Woillez,
K. Stapelfeldt,
G. Bryden,
M. M. Colavita,
and A. J. Booth
[show abstract]
[hide abstract]
ABSTRACT: The Keck Interferometer Nuller (KIN) was used to survey 25 nearby main-sequence stars in the mid-infrared, in order to assess the prevalence of warm circumstellar (exozodiacal) dust around nearby solar-type stars. The KIN measures circumstellar emission by spatially blocking the star but transmitting the circumstellar flux in a region typically 0.1-4 AU from the star. We find one significant detection (η Crv), two marginal detections (γ Oph and α Aql), and 22 clear non-detections. Using a model of our own solar system's zodiacal cloud, scaled to the luminosity of each target star, we estimate the equivalent number of target zodis needed to match our observations. Our three zodi detections are η Crv (1250 ± 260), γ Oph (200 ± 80), and α Aql (600 ± 200), where the uncertainties are 1σ. The 22 non-detected targets have an ensemble weighted average consistent with zero, with an average individual uncertainty of 160 zodis (1σ). These measurements represent the best limits to date on exozodi levels for a sample of nearby main-sequence stars. A statistical analysis of the population of 23 stars not previously known to contain circumstellar dust (excluding η Crv and γ Oph) suggests that, if the measurement errors are uncorrelated (for which we provide evidence) and if these 23 stars are representative of a single class with respect to the level of exozodi brightness, the mean exozodi level for the class is <150 zodis (3σ upper limit, corresponding to 99% confidence under the additional assumption that the measurement errors are Gaussian). We also demonstrate that this conclusion is largely independent of the shape and mean level of the (unknown) true underlying exozodi distribution.
The Astrophysical Journal 05/2011; 734(1):67. · 6.02 Impact Factor
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R. Millan-Gabet,
E. Serabyn,
B. Mennesson,
W. A. Traub,
R. K. Barry,
W. C. Danchi,
M. Kuchner,
S. Ragland,
M. Hrynevych, J. Woillez,
K. Stapelfeldt,
G. Bryden,
M. M. Colavita,
A. J. Booth
[show abstract]
[hide abstract]
ABSTRACT: The Keck Interferometer Nuller (KIN) was used to survey 25 nearby main
sequence stars in the mid-infrared, in order to assess the prevalence of warm
circumstellar (exozodiacal) dust around nearby solar-type stars. The KIN
measures circumstellar emission by spatially blocking the star but transmitting
the circumstellar flux in a region typically 0.1 - 4 AU from the star. We find
one significant detection (eta Crv), two marginal detections (gamma Oph and
alpha Aql), and 22 clear non-detections. Using a model of our own Solar
System's zodiacal cloud, scaled to the luminosity of each target star, we
estimate the equivalent number of target zodis needed to match our
observations. Our three zodi detections are eta Crv (1250 +/- 260), gamma Oph
(200 +/- 80) and alpha Aql (600 +/- 200), where the uncertainties are 1-sigma.
The 22 non-detected targets have an ensemble weighted average consistent with
zero, with an average individual uncertainty of 160 zodis (1-sigma). These
measurements represent the best limits to date on exozodi levels for a sample
of nearby main sequence stars. A statistical analysis of the population of 23
stars not previously known to contain circumstellar dust (excluding eta Crv and
gamma Oph) suggests that, if the measurement errors are uncorrelated (for which
we provide evidence) and if these 23 stars are representative of a single class
with respect to the level of exozodi brightness, the mean exozodi level for the
class is <150 zodis (3-sigma upper-limit, corresponding to 99% confidence under
the additional assumption that the measurement errors are Gaussian). We also
demonstrate that this conclusion is largely independent of the shape and mean
level of the (unknown) true underlying exozodi distribution.
04/2011;
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J.-U. Pott, J. Woillez,
S. Ragland,
P. L. Wizinowich,
J. A. Eisner,
J. D. Monnier,
R. L. Akeson,
A. M. Ghez,
J. R. Graham,
L. A. Hillenbrand, [......],
J. Herstein,
M. Hrynevych,
D. Medeiros,
D. Morrison,
T. Panteleeva,
B. Smith,
K. Summers,
K. Tsubota,
C. Tyau,
and E. Wetherell
[show abstract]
[hide abstract]
ABSTRACT: We report on the successful science verification phase of a new observing mode at the Keck Interferometer, which provides a line-spread function width and sampling of 150 km s–1 at the K'-band, at a current limiting magnitude of K' ~ 7 mag with a spatial resolution of λ / 2 B 2.7 mas and a measured differential phase stability of unprecedented precision (3 mrad at K = 5 mag, which represents 3 μ as on the sky or a centroiding precision of 10–3). The scientific potential of this mode is demonstrated by the presented observations of the circumstellar disk of the evolved Be-star 48 Lib. In addition to indirect methods such as multi-wavelength spectroscopy and polarimetry, the spectro-interferometric astrometry described here provides a new tool to directly constrain the radial density structure in the disk. For the first time, we resolve several Pfund emission lines, in addition to Br γ, in a single interferometric spectrum, with adequate spatial and spectral resolution and precision to analyze the radial disk structure in 48 Lib. The data suggest that the continuum and Pf-emission originates in significantly more compact regions, inside the Br γ-emission zone. Thus, spectro-interferometric astrometry opens the opportunity to directly connect the different observed line profiles of Br γ and Pfund in the total and correlated flux to different disk radii. The gravitational potential of a rotationally flattened Be star is expected to induce a one-armed density perturbation in the circumstellar disk. Such a slowly rotating disk oscillation has been used to explain the well-known periodic V/R spectral profile variability in these stars, as well as the observed V/R cycle phase shifts between different disk emission lines. The differential line properties and linear constraints set by our data are consistent with theoretical models and lend direct support to the existence of a radius-dependent disk density perturbation. The data also show decreasing gas rotation velocities at increasing stellocentric radii as expected for Keplerian disk rotation, assumed by those models.
The Astrophysical Journal 08/2010; 721(1):802. · 6.02 Impact Factor
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J. A. Eisner,
R. Akeson,
M. Colavita,
A. Ghez,
J. Graham,
L. Hillenbrand,
R. Millan-Gabet,
J. D. Monnier,
J. -U. Pott,
S. Ragland,
P. Wizinowich, J. Woillez
[show abstract]
[hide abstract]
ABSTRACT: 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"
08/2010;
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S. Ragland,
R. Akeson,
M. Colavita,
R. Millan-Gabet, J. Woillez,
P. Wizinowich,
E. Appleby,
B. Berkey,
A. Cooper,
C. Felizardo, [......],
M. Hrynevych,
D. Medeiros,
D. Morrison,
T. Panteleeva,
J.-U. Pott,
B. Smith,
K. Summers,
K. Tsubota,
C. Tyau,
E. Wetherell
[show abstract]
[hide abstract]
ABSTRACT: The Keck Interferometer (KI) combines the two 10m diameter Keck telescopes providing milliarcsecond angular resolution. KI has unique observing capabilities such as sensitive K-band V2, L-band V2 and N-band nulling operations. The instrument status of the Keck Interferometer since the last SPIE meeting in 2008 is summarized. We discuss the performance of new visibility observing capabilities including L-band and self-phase referencing modes. A simultaneous dual-beam-combiner mode in the K and L-band has been demonstrated, nearly doubling operational efficiency for bright targets. Operational improvements including simplified reliable operations with reduced personnel resources are highlighted. We conclude with a brief review of the current and future developmental activities of KI. Details of ASTRA developments, nulling performance and science results are presented elsewhere at this conference.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
07/2010;
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J. Woillez,
R. Akeson,
M. Colavita,
J. Eisner,
A. Ghez,
J. Graham,
L. Hillenbrand,
R. Millan-Gabet,
J. Monnier,
J-U. Pott, [......],
M. Hrynevych,
O. Martin,
D. Medeiros,
D. Morrison,
T. Panteleeva,
B. Smith,
K. Summers,
K. Tsubota,
C. Tyau,
E. Wetherell
[show abstract]
[hide abstract]
ABSTRACT: 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.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
07/2010;
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[show abstract]
[hide abstract]
ABSTRACT: We present near-infrared observations of T Tauri and Herbig Ae/Be stars with a spatial resolution of a few milli-arcseconds and a spectral resolution of ~2000. Our observations spatially resolve gas and dust in the inner regions of protoplanetary disks, and spectrally resolve broad-linewidth emission from the Brackett gamma transition of hydrogen gas. We use the technique of spectro-astrometry to determine centroids of different velocity components of this gaseous emission at a precision orders of magnitude better than the angular resolution. In all sources, we find the gaseous emission to be more compact than or distributed on similar spatial scales to the dust emission. We attempt to fit the data with models including both dust and Brackett gamma-emitting gas, and we consider both disk and infall/outflow morphologies for the gaseous matter. In most cases where we can distinguish between these two models, the data show a preference for infall/outflow models. In all cases, our data appear consistent with the presence of some gas at stellocentric radii of ~0.01 AU. Our findings support the hypothesis that Brackett gamma emission generally traces magnetospherically driven accretion and/or outflows in young star/disk systems. Comment: 48 pages, including 17 figures. Accepted for publication by ApJ
06/2010;
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R. K. Barry,
W. C. Danchi,
W. A. Traub,
J. L. Sokoloski,
J. P. Wisniewski,
E. Serabyn,
M. J. Kuchner,
R. Akeson,
E. Appleby,
J. Bell, [......],
M. Shao,
R. Smythe,
K. Summers,
M. Swain,
K. Tsubota,
C. Tyau,
E. Wetherell,
P. Wizinowich, J. Woillez,
and G. Vasisht
[show abstract]
[hide abstract]
ABSTRACT: 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 μm in a nulling mode. The nulling technique is the sparse aperture equivalent of the conventional coronagraphic technique used in filled aperture telescopes. In this mode the stellar light itself is suppressed by a destructive fringe, effectively enhancing the contrast of the circumstellar material located near the star. By fitting the unique KIN data, we have obtained an angular size of the mid-infrared continuum emitting material 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.
The Astrophysical Journal 12/2008; 677(2):1253. · 6.02 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: 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&A
05/2008;
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[show abstract]
[hide abstract]
ABSTRACT: The Keck Interferometer (KI) combines the two 10m Keck telescopes with a
baseline separation of 85m, and is one of the two large aperture optical
long baseline interferometric (OLBI) facilities in the world. The KI is
funded by the National Aeronautics and Space Administration (NASA). The
10m telescope diameters provide a unique sensitivity advantage and has
lead to several 'first OLBI' science in the IR such as visibility
measurements of an AGN. The visibility (V2) and Nuller modes, are in
operation and offered to the Keck community. Now a new major development
effort is underway to broaden the astrophysical applications of this
unique instrument: the ASTRA upgrade.
ASTRA stands for the ASTrometric and phase-Referenced Astronomy upgrade
of the KI project. ASTRA has been funded by the NSF-Major Research
Instrumentation program and will be implemented in three steps over the
next 3 years. Besides the NSF engagement a number of science institutes
contribute to the ASTRA collaboration to advance and profit from
large-aperture OLBI.
This contribution will present the three modes of ASTRA each of which
will overcome current sensitivity limitations by continuous correction
for phase distortions induced by the turbulent atmosphere: (i)
self-referenced spectroscopy stabilizes fringes on-axis and enable
higher spectral resolution up to a few thousands (ii) dual-field
visibility measurements stand for integration beyond the atmospheric
coherence time to reach K=15mag on science targets while locking the
fringe tracker on an offset guide star (iii) the narrow-angle astrometry
mode eventually will measure distances between a pair of stars within
the iso-planatic patch to an accuracy of less than 100 uas.
02/2008; 211.
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E. Serabyn,
A. Booth,
M. M. Colavita,
S. Crawford,
J. Garcia,
J. Gathright,
M. Hrynevych,
C. Koresko,
R. Ligon,
B. Mennesson,
T. Panteleeva,
S. Ragland,
K. Summers,
W. Traub,
K. Tsubota,
E. Wetherell,
P. Wizinowich, J. Woillez
[show abstract]
[hide abstract]
ABSTRACT: The Keck Interferometer Nuller (KIN) is now largely in place at the Keck Observatory, and functionalities and performance are increasing with time. The main goal of the KIN is to examine nearby stars for the presence of exozodiacal emission, but other sources of circumstellar emission, such as disks around young stars, and hot exoplanets are also potential targets. To observe with the KIN in nulling mode, knowledge of the intrinsic source spectrum is essential, because of the wide variety of wavelengths involved in the various control loops - the AO system operates at visible wavelengths, the pointing loops use the J-band, the high-speed fringe tracker operates in the K-band, and the nulling observations take place in the N-band. Thus, brightness constraints apply at all of these wavelengths. In addition, source structure plays a role at both K-band and N-band, through the visibility. In this talk, the operation of the KIN is first briefly described, and then the sensitivity and performance of the KIN is summarized, with the aim of presenting an overview of the parameter space accessible to the nuller. Finally, some of the initial observations obtained with the KIN are described.© (2006) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
06/2006;
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G Perrin, J Woillez,
O Lai,
J Guérin,
T Kotani,
P L Wizinowich,
D Le Mignant,
M Hrynevych,
J Gathright,
P Léna, [......],
C Marlot,
M Marteaud,
B-T Melse,
J Nishikawa,
J-M Reess,
S T Ridgway,
F Rigaut,
K Roth,
A T Tokunaga,
D Ziegler
[show abstract]
[hide abstract]
ABSTRACT: Here we report successful interferometric coupling of two large telescopes with single-mode fibers. Interference fringes were obtained in the 2- to 2.3-micrometer wavelength range on the star 107 Herculis by using the two Keck 10-meter telescopes, each feeding their common interferometric focus with 300 meters of single-mode fibers. This experiment demonstrates the potential of fibers for future kilometric arrays of telescopes and is the first step toward the 'OHANA (Optical Hawaiian Array for Nanoradian Astronomy) interferometer at the Mauna Kea observatory in Hawaii. It opens the way to sensitive optical imagers with resolutions below 1 milli-arc second. Our experimental setup can be directly extended to large telescopes separated by many hundreds of meters.
Science 02/2006; 311(5758):194. · 31.20 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: The `OHANA (Optical Hawaiian Array for Nanaoradian Astronomy)
instrument, by replacing conventional mirrors with single mode fibers,
proposes an alternative design for astronomical interferometers. After
four years of developments, a first successful combination was achieved
on June 17, 2005, between the two 10-meter Keck telescopes, thus
validating the fiber technology. Further developments are under way to
combine new baselines on the Mauna Kea and achieve an unprecedented
angular resolution at optical wavelength.
The sensitivity associated to the angular resolution should foster
interest in interferometric observations in a broader community. For
example, the extragalactic science that started two years ago on both
the Keck Interferometer and the Very Large Telescope Interferometer
would further benefit from an increased angular resolution provided by
the `OHANA instrument. Observations of the inner parts of type 1 Active
Galactic Nuclei, toward the Broad Line Region and the base of Radio
Jets, should provide confirmation or new insight on the geometry and
physics of the central black hole environment.
The extension of `OHANA to all baselines, leading to an imaging array on
the Hawaiian summit, will require a new operational model and a larger
support of the summit partners. The resulting 800-meter baselines
instrument would fulfill the role of a scientific and technical test bed
for a future Extremely Large Optical Interferometer. In 10 to 20 years,
this next generation facility, dedicated to interferometric
observations, based on 4 to 8-meter class telescopes, spread over
kilometric baselines, would be made possible with the single mode fiber
transport solution.
The `OHANA project is supported in France by the Ministry of Research,
Paris Observatory and Institut National des Sciences de l'Univers (INSU)
of CNRS. The authors are thankful to the `OHANA collaboration, and to
CARA and NASA/JPL for providing successful nights and key support to the
project.
11/2005; 37:1308.
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B. Mennesson ,
R. Akeson ,
E. Appleby ,
J. Bell ,
A. Booth ,
M.M. Colavita ,
S. Crawford ,
M.J. Creech-Eakman ,
W. Dahl ,
J. Fanson , [......],
E. Serabyn ,
M. Shao ,
R. Smythe ,
K. Summers ,
M. Swain ,
K. Tsubota ,
C. Tyau ,
G. Vasisht ,
P. Wizinowich , J. Woillez
[show abstract]
[hide abstract]
ABSTRACT: The Keck Interferometer Nuller (KIN) is one of the major scientific and technical precursors to the Terrestrial Planet Finder Interferometer (TPF-I) mission. KIN's primary objective is to measure the level of exo-zodiacal mid-infrared emission around nearby main sequence stars, which requires deep broad-band nulling of astronomical sources of a few Janskys at 10 microns. A number of new capabilitites are needed in order to reach that goal with the Keck telescopes: mid-infrared coherent recombination, interferometric operation in “split pupil” mode, N-band optical path stabilization using K-band fringe tracking and internal metrology, and eventually, active atmospheric dispersion correction. We report here on the progress made implementing these new functionalities, and discuss the initial levels of extinction achieved on the sky.
Proceedings of the International Astronomical Union 09/2005; 1:227 - 232.
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W Jaffe,
K Meisenheimer,
H J A Röttgering,
Ch Leinert,
A Richichi,
O Chesneau,
D Fraix-Burnet,
A Glazenborg-Kluttig,
G-L Granato,
U Graser, [......],
F Paresce,
J-W Pel,
G Perrin,
F Przygodda,
M Schoeller,
H Sol,
L B F M Waters,
G Weigelt, J Woillez,
P T De Zeeuw
[show abstract]
[hide abstract]
ABSTRACT: Active galactic nuclei (AGNs) display many energetic phenomena--broad emission lines, X-rays, relativistic jets, radio lobes--originating from matter falling onto a supermassive black hole. It is widely accepted that orientation effects play a major role in explaining the observational appearance of AGNs. Seen from certain directions, circum-nuclear dust clouds would block our view of the central powerhouse. Indirect evidence suggests that the dust clouds form a parsec-sized torus-shaped distribution. This explanation, however, remains unproved, as even the largest telescopes have not been able to resolve the dust structures. Here we report interferometric mid-infrared observations that spatially resolve these structures in the galaxy NGC 1068. The observations reveal warm (320 K) dust in a structure 2.1 parsec thick and 3.4 parsec in diameter, surrounding a smaller hot structure. As such a configuration of dust clouds would collapse in a time much shorter than the active phase of the AGN, this observation requires a continual input of kinetic energy to the cloud system from a source coexistent with the AGN.
Nature 06/2004; 429(6987):47-9. · 36.28 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: We present the results of observations of the AGN in the Seyfret galaxy NGC 1068 at 43 GHz (7 mm wavelength) with 50 mas resolution. The results are consistent with the claim of Gallimore et al. (2004) that the nuclear component is dominated by thermal emission. This adds to the growing body of evidence that this component is dominated by a hot inner region of the obscuring torus rather than the base of the radio jet. However, possible detection of linear polarization from this component suggests some emission from the synchrotron emitting jet or that the polarization arises from Thompson scattering of the thermal emission by the nuclear plasma.
http://dx.doi.org/10.1051/0004-6361:20078781.
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[show abstract]
[hide abstract]
ABSTRACT: Context. The massive black hole Sgr A* at the very center of the Galaxy, and its immediate stellar and non-stellar environment, have been studied in the past decade with increasing intensity and wavelength coverage, revealing surprising results. This research requires the highest angular resolution available to avoid source confusion and to study the physical properties of the objects.Aims. GCIRS 7 is the dominating star of the central cluster in the NIR, so it has been used as wavefront and astrometric reference. Our studies investigate, for the first time, its properties at 2 and 10 $\mu$m using the VLTI. We aim at analyzing the suitability of GCIRS 7 as an interferometric phase-reference for the upcoming generation of dual-field facilities at optical interferometers.Methods. VLTI-AMBER and MIDI instruments were used to spatially resolve GCIRS 7 and to measure the wavelength dependence of the visibility using the low spectral resolution mode ($\lambda$ / $\Delta \lambda \approx$ 30) and projected baseline lengths of about 50 m, resulting in an angular resolution of about 9 mas and 45 mas for the NIR and MIR, respectively.Results. The first $K$-band fringe detection of a GC star suggests that GCIRS 7 could be marginally resolved at 2 micron, which would imply that the photosphere of the supergiant is enshrouded by a molecular and dusty envelope. At 10 $\mu$m, GCIRS 7 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$\,\mu$m-silicate absorption in excess of the usual extinction law with respect to the NIR extinction has been found.Conclusions. Our VLTI observations show that interferometric NIR phase-referencing experiments with mas resolution using GCIRS 7 as phase reference appear to be feasible, but more such studies are required to definitely characterize the close environment around this star. The MIR data confirm recent findings of a relatively enhanced, interstellar 9.8$\,\mu$m-silicate absorption with respect to the NIR extinction towards another star in the central arc-seconds, suggesting an unusual dust composition in that region. We demonstrate that the resolution and sensitivity of modern large-aperture optical telescope arrays is required to resolve the innermost environment of stars at the Galactic center.
http://dx.doi.org/10.1051/0004-6361:200809829.
