237 research outputs found
The unlikely rise of masking interferometry: leading the way with 19th century technology
The exquisite precision delivered by interferometric techniques is rapidly
being applied to more and more branches of optical astronomy. One particularly
successful strategy to obtain structures at the scale of the diffraction limit
is Aperture Masking Interferometry, which is presently experience a golden age
with implementations at a host of large telescopes around the world. This
startlingly durable technique, which turns 144 years old this year, presently
sets the standard for the recovery of faint companions within a few resolution
elements from the core of a stellar point spread function. This invited review
will give a historical introduction and overview of the modern status of the
technique, the science being delivered, and prospects for new advances and
applications.Comment: This is an invited review for SPIE Amsterdam in 2012. It presents a
brief history of masking interferometry, and some thoughts on future
progress. 11 pages, 4 figs, lots of ref
A Demonstration of Wavefront Sensing and Mirror Phasing from the Image Domain
In astronomy and microscopy, distortions in the wavefront affect the dynamic
range of a high contrast imaging system. These aberrations are either imposed
by a turbulent medium such as the atmosphere, by static or thermal aberrations
in the optical path, or by imperfectly phased subapertures in a segmented
mirror. Active and adaptive optics (AO), consisting of a wavefront sensor and a
deformable mirror, are employed to address this problem. Nevertheless, the
non-common-path between the wavefront sensor and the science camera leads to
persistent quasi-static speckles that are difficult to calibrate and which
impose a floor on the image contrast. In this paper we present the first
experimental demonstration of a novel wavefront sensor requiring only a minor
asymmetric obscuration of the pupil, using the science camera itself to detect
high order wavefront errors from the speckle pattern produced. We apply this to
correct errors imposed on a deformable microelectromechanical (MEMS) segmented
mirror in a closed loop, restoring a high quality point spread function (PSF)
and residual wavefront errors of order nm using 1600 nm light, from a
starting point of nm in piston and mrad in tip-tilt. We
recommend this as a method for measuring the non-common-path error in
AO-equipped ground based telescopes, as well as as an approach to phasing
difficult segmented mirrors such as on the \emph{James Webb Space Telescope}
primary and as a future direction for extreme adaptive optics.Comment: 9 pages, 6 figure
Properties of the close binary and circumbinary torus of the Red Rectangle
New diffraction-limited speckle images of the Red Rectangle in the wavelength
range 2.1--3.3 microns with angular resolutions of 44--68 mas and previous
speckle images at 0.7--2.2 microns revealed well-resolved bright bipolar
outflow lobes and long X-shaped spikes originating deep inside the outflow
cavities. This set of high-resolution images stimulated us to reanalyze all
infrared observations of the Red Rectangle using our two-dimensional radiative
transfer code. The new detailed modeling, together with estimates of the
interstellar extinction in the direction of the Red Rectangle enabled us to
more accurately determine one of the key parameters, the distance D=710 pc with
model uncertainties of 70 pc, which is twice as far as the commonly used
estimate of 330 pc. The central binary is surrounded by a compact, massive
(M=1.2 Msun), very dense dusty torus with hydrogen densities reaching
n_H=2.5x10^12 cm^-3 (dust-to-gas mass ratio rho_d/rho~0.01). The bright
component of the spectroscopic binary HD 44179 is a post-AGB star with mass
M*=0.57 Msun, luminosity L*=6000 Lsun, and effective temperature T*=7750 K.
Based on the orbital elements of the binary, we identify its invisible
component with a helium white dwarf with Mwd~0.35 Msun, Lwd~100 Lsun, and
Twd~6x10^4 K. The hot white dwarf ionizes the low-density bipolar outflow
cavities inside the dense torus, producing a small HII region observed at radio
wavelengths. We propose an evolutionary scenario for the formation of the Red
Rectangle nebula, in which the binary initially had 2.3 and 1.9 Msun components
at a separation of 130 Rsun. The nebula was formed in the ejection of a common
envelope after Roche lobe overflow by the present post-AGB star.Comment: 20 pages, 10 figures, accepted by Astronomy and Astrophysics, also
available at
http://www.mpifr-bonn.mpg.de/div/ir-interferometry/publications.htm
Simulating a dual beam combiner at SUSI for narrow-angle astrometry
The Sydney University Stellar Interferometer (SUSI) has two beam combiners,
i.e. the Precision Astronomical Visible Observations (PAVO) and the
Microarcsecond University of Sydney Companion Astrometry (MUSCA). The primary
beam combiner, PAVO, can be operated independently and is typically used to
measure properties of binary stars of less than 50 milliarc- sec (mas)
separation and the angular diameters of single stars. On the other hand, MUSCA
was recently installed and must be used in tandem with the for- mer. It is
dedicated for microarcsecond precision narrow-angle astrometry of close binary
stars. The performance evaluation and development of the data reduction
pipeline for the new setup was assisted by an in-house computer simulation tool
developed for this and related purposes. This paper describes the framework of
the simulation tool, simulations carried out to evaluate the performance of
each beam combiner and the expected astrometric precision of the dual beam
combiner setup, both at SUSI and possible future sites.Comment: 28 pages, 23 figures, accepted for publication in Experimental
Astronomy. The final publication is available at http://link.springer.co
Direct Detection of the Brown Dwarf GJ 802B with Adaptive Optics Masking Interferometry
We have used the Palomar 200" Adaptive Optics (AO) system to directly detect
the astrometric brown dwarf GJ 802B reported by Pravdo et al. 2005. This
observation is achieved with a novel combination of aperture masking
interferometry and AO. The dynamical masses are 0.1750.021 M and
0.0640.032 M for the primary and secondary respectively. The
inferred absolute H band magnitude of GJ 802B is M=12.8 resulting in a
model-dependent T of 1850 50K and mass range of
0.057--0.074 M.Comment: 4 Pages, 5 figures, emulateapj format, submitted to ApJ
The VAMPIRES instrument: Imaging the innermost regions of protoplanetary disks with polarimetric interferometry
Direct imaging of protoplanetary disks promises to provide key insight into
the complex sequence of processes by which planets are formed. However imaging
the innermost region of such disks (a zone critical to planet formation) is
challenging for traditional observational techniques (such as near-IR imaging
and coronagraphy) due to the relatively long wavelengths involved and the area
occulted by the coronagraphic mask. Here we introduce a new instrument --
VAMPIRES -- which combines non-redundant aperture-masking interferometry with
differential polarimetry to directly image this previously inaccessible
innermost region. By using the polarisation of light scattered by dust in the
disk to provide precise differential calibration of interferometric
visibilities and closure phases, VAMPIRES allows direct imaging at and beyond
the telescope diffraction limit. Integrated into the SCExAO system at the
Subaru telescope, VAMPIRES operates at visible wavelengths (where polarisation
is high) while allowing simultaneous infrared observations conducted by HICIAO.
Here we describe the instrumental design and unique observing technique and
present the results of the first on-sky commissioning observations, validating
the excellent visibility and closure phase precision which are then used to
project expected science performance metrics
High Angular Resolution Stellar Imaging with Occultations from the Cassini Spacecraft II: Kronocyclic Tomography
We present an advance in the use of Cassini observations of stellar
occultations by the rings of Saturn for stellar studies. Stewart et al. (2013)
demonstrated the potential use of such observations for measuring stellar
angular diameters. Here, we use these same observations, and tomographic
imaging reconstruction techniques, to produce two dimensional images of complex
stellar systems. We detail the determination of the basic observational
reference frame. A technique for recovering model-independent brightness
profiles for data from each occulting edge is discussed, along with the
tomographic combination of these profiles to build an image of the source star.
Finally we demonstrate the technique with recovered images of the {\alpha}
Centauri binary system and the circumstellar environment of the evolved
late-type giant star, Mira.Comment: 8 pages, 8 figures, Accepted by MNRA
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