769 research outputs found
A Close Companion Search Around L Dwarfs Using Aperture Masking Interferometry and Palomar Laser Guide Star Adaptive Optics
We present a close companion search around 16 known early L dwarfs using aperture masking interferometry with Palomar laser guide star adaptive optics (LGS AO). The use of aperture masking allows the detection of close binaries, corresponding to projected physical separations of 0.6-10.0 AU for the targets of our survey. This survey achieved median contrast limits of ΔK ~ 2.3 for separations between 1.2λ/D-4λ/D and ΔK ~ 1.4 at 2/3λ/D. We present four candidate binaries detected with moderate-to-high confidence (90%-98%). Two have projected physical separations less than 1.5 AU. This may indicate that tight-separation binaries contribute more significantly to the binary fraction than currently assumed, consistent with spectroscopic and photometric overluminosity studies. Ten targets of this survey have previously been observed with the Hubble Space Telescope as part of companion searches. We use the increased resolution of aperture masking to search for close or dim companions that would be obscured by full aperture imaging, finding two candidate binaries. This survey is the first application of aperture masking with LGS AO at Palomar. Several new techniques for the analysis of aperture masking data in the low signal-to-noise regime are explored
An aperture masking mode for the MICADO instrument
MICADO is a near-IR camera for the Europea ELT, featuring an extended field
(75" diameter) for imaging, and also spectrographic and high contrast imaging
capabilities. It has been chosen by ESO as one of the two first-light
instruments. Although it is ultimately aimed at being fed by the MCAO module
called MAORY, MICADO will come with an internal SCAO system that will be
complementary to it and will deliver a high performance on axis correction,
suitable for coronagraphic and pupil masking applications. The basis of the
pupil masking approach is to ensure the stability of the optical transfer
function, even in the case of residual errors after AO correction (due to non
common path errors and quasi-static aberrations). Preliminary designs of pupil
masks are presented. Trade-offs and technical choices, especially regarding
redundancy and pupil tracking, are explained.Comment: SPIE 2014 Proceeding -- Montrea
Phase Errors in Diffraction-Limited Imaging: Contrast Limits for Sparse Aperture Masking
Bispectrum phase, closure phase and their generalisation to kernel-phase are
all independent of pupil-plane phase errors to first-order. This property, when
used with Sparse Aperture Masking (SAM) behind adaptive optics, has been used
recently in high-contrast observations at or inside the formal diffraction
limit of large telescopes. Finding the limitations to these techniques requires
an understanding of spatial and temporal third-order phase effects, as well as
effects such as time-variable dispersion when coupled with the non-zero
bandwidths in real observations. In this paper, formulae describing many of
these errors are developed, so that a comparison can be made to fundamental
noise processes of photon- and background-noise. I show that the current
generation of aperture-masking observations of young solar-type stars, taken
carefully in excellent observing conditions, are consistent with being limited
by temporal phase noise and photon noise. This has relevance for plans to
combine pupil-remapping with spatial filtering. Finally, I describe calibration
strategies for kernel-phase, including the optimised calibrator weighting as
used for LkCa 15, and the restricted kernel-phase POISE technique that avoids
explicit dependence on calibrators.Comment: 11 pages, 5 figures, resubmitted to MNRAS after responding to
referee's comment
Discovery of Seven Companions To Intermediate-Mass Stars With Extreme Mass Ratios in the Scorpius-Centaurus Association
We report the detection of seven low-mass companions to intermediate-mass stars (SpT B/A/F; M similar to 1.5-4.5M(circle dot)) in the Scorpius-Centaurus (Sco-Cen) Association using nonredundant aperture masking interferometry. Our newly detected objects have contrasts Delta L' approximate to 4-6, corresponding to masses as low as similar to 20 M-Jup and mass ratios of q approximate to 0.01-0.08, depending on the assumed age of the target stars. With projected separations rho approximate to 10-30 AU, our aperture masking detections sample an orbital region previously unprobed by conventional adaptive optics imaging of intermediate-mass Sco-Cen stars covering much larger orbital radii (similar to 30-3000 AU). At such orbital separations, these objects resemble higher-mass versions of the directly imaged planetary mass companions to the 10-30 Myr, intermediate-mass stars HR 8799, beta Pictoris, and HD 95086. These newly discovered companions span the brown dwarf desert, and their masses and orbital radii provide a new constraint on models of the Formation of low-mass stellar and substellar companions to intermediate-mass stars.NASA through the Sagan Fellowship ProgramNSF Astronomy and Astrophysics Postdoctoral Fellowship AST-1203023Clay FellowshipNASA through Hubble Fellowship 51257.01AURA, Inc., for NASA NAS 5-26555W. M. Keck FoundationAstronom
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
Mapping the Shores of the Brown Dwarf Desert III: Young Moving Groups
We present the results of an aperture masking interferometry survey for
substellar companions around 67 members of the young (~8-200Myr) nearby
(~5-86pc) AB Doradus, Beta Pictoris, Hercules-Lyra, TW Hya, and
Tucana-Horologium stellar associations. Observations were made at near infrared
wavelengths between 1.2-3.8 microns using the adaptive optics facilities of the
Keck II, VLT UT4, and Palomar Hale Telescopes. Typical contrast ratios of
~100-200 were achieved at angular separations between ~40-320mas, with our
survey being 100% complete for companions with masses below 0.25\msolar across
this range. We report the discovery of a \msolar companion to
HIP14807, as well as the detections and orbits of previously known stellar
companions to HD16760, HD113449, and HD160934. We show that the companion to
HD16760 is in a face-on orbit, resulting in an upward revision of its mass from
\mjupiter to \msolar. No substellar
companions were detected around any of our sample members, despite our ability
to detect companions with masses below 80\mjupiter for 50 of our targets: of
these, our sensitivity extended down to 40\mjupiter around 30 targets, with a
subset of 22 subject to the still more stringent limit of 20\mjupiter. A
statistical analysis of our non-detection of substellar companions allows us to
place constraints on their frequency around ~0.2-1.5\msolar stars. In
particular, considering companion mass distributions that have been proposed in
the literature, we obtain an upper limit estimate of ~9-11% for the frequency
of 20-80\mjupiter companions between 3-30AU at 95% confidence, assuming that
their semimajor axes are distributed according to in this range.Comment: Accepted by Ap
Precision Masses of the low-mass binary system GJ 623
We have used Aperture Masking Interferometry and Adaptive Optics (AO) at the
Palomar 200'' to obtain precise mass measurements of the binary M dwarf GJ 623.
AO observations spread over 3 years combined with a decade of radial velocity
measurements constrain all orbital parameters of the GJ 623 binary system
accurately enough to critically challenge the models. The dynamical masses
measured are m_{1}=0.371\pm0.015 M_{\sun} (4%) and m_{2}=0.115\pm0.0023
M_{\sun} (2%) for the primary and the secondary respectively. Models are not
consistent with color and mass, requiring very low metallicities.Comment: 7 pages, 5 figures. Accepted for Ap
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