949 research outputs found
A two-band approach to n phase error corrections with LBTI's PHASECam
PHASECam is the Large Binocular Telescope Interferometer's (LBTI) phase
sensor, a near-infrared camera which is used to measure tip/tilt and phase
variations between the two AO-corrected apertures of the Large Binocular
Telescope (LBT). Tip/tilt and phase sensing are currently performed in the H
(1.65 m) and K (2.2 m) bands at 1 kHz, and the K band phase telemetry
is used to send tip/tilt and Optical Path Difference (OPD) corrections to the
system. However, phase variations outside the range [-, ] are not
sensed, and thus are not fully corrected during closed-loop operation.
PHASECam's phase unwrapping algorithm, which attempts to mitigate this issue,
still occasionally fails in the case of fast, large phase variations. This can
cause a fringe jump, in which case the unwrapped phase will be incorrect by a
wavelength or more. This can currently be manually corrected by the observer,
but this is inefficient. A more reliable and automated solution is desired,
especially as the LBTI begins to commission further modes which require robust,
active phase control, including controlled multi-axial (Fizeau) interferometry
and dual-aperture non-redundant aperture masking interferometry. We present a
multi-wavelength method of fringe jump capture and correction which involves
direct comparison between the K band and currently unused H band phase
telemetry.Comment: 17 pages, 10 figure
Study and analysis of satellite power systems configurations for maximum utilization of power Fifth quarterly progress report, 18 May - 18 Jul. 1966
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First Light with ALES: A 2-5 Micron Adaptive Optics Integral Field Spectrograph for the LBT
Integral field spectrographs are an important technology for exoplanet
imaging, due to their ability to take spectra in a high-contrast environment,
and improve planet detection sensitivity through spectral differential imaging.
ALES is the first integral field spectrograph capable of imaging exoplanets
from 3-5m, and will extend our ability to characterize self-luminous
exoplanets into a wavelength range where they peak in brightness. ALES is
installed inside LBTI/LMIRcam on the Large Binocular Telescope, taking
advantage of existing AO systems, camera optics, and a HAWAII-2RG detector. The
new optics that comprise ALES are a Keplerian magnifier, a silicon lenslet
array with diffraction suppressing pinholes, a direct vision prism, and
calibration optics. All of these components are installed in filter wheels
making ALES a completely modular design. ALES saw first light at the LBT in
June 2015.Comment: 13 pages, 9 figures, Proc. SPI
PhoSim-NIRCam: Photon-by-photon image simulations of the James Webb Space Telescope's Near-Infrared Camera
Recent instrumentation projects have allocated resources to develop codes for
simulating astronomical images. Novel physics-based models are essential for
understanding telescope, instrument, and environmental systematics in
observations. A deep understanding of these systematics is especially important
in the context of weak gravitational lensing, galaxy morphology, and other
sensitive measurements. In this work, we present an adaptation of a
physics-based ab initio image simulator: The Photon Simulator (PhoSim). We
modify PhoSim for use with the Near-Infrared Camera (NIRCam) -- the primary
imaging instrument aboard the James Webb Space Telescope (JWST). This photon
Monte Carlo code replicates the observational catalog, telescope and camera
optics, detector physics, and readout modes/electronics. Importantly,
PhoSim-NIRCam simulates both geometric aberration and diffraction across the
field of view. Full field- and wavelength-dependent point spread functions are
presented. Simulated images of an extragalactic field are presented. Extensive
validation is planned during in-orbit commissioning
Variations of the 10 um Silicate Features in the Actively Accreting T Tauri Stars: DG Tau and XZ Tau
Using the Infrared Spectrograph aboard the Spitzer Space Telescope, we
observed multiple epochs of 11 actively accreting T Tauri stars in the nearby
Taurus-Auriga star forming region. In total, 88 low-resolution mid-infrared
spectra were collected over 1.5 years in Cycles 2 and 3. The results of this
multi-epoch survey show that the 10 um silicate complex in the spectra of two
sources - DG Tau and XZ Tau - undergoes significant variations with the
silicate feature growing both weaker and stronger over month- and year-long
timescales. Shorter timescale variations on day- to week-long timescales were
not detected within the measured flux errors. The time resolution coverage of
this data set is inadequate for determining if the variations are periodic.
Pure emission compositional models of the silicate complex in each epoch of the
DG Tau and XZ Tau spectra provide poor fits to the observed silicate features.
These results agree with those of previous groups that attempted to fit only
single-epoch observations of these sources. Simple two-temperature, two-slab
models with similar compositions successfully reproduce the observed variations
in the silicate features. These models hint at a self-absorption origin of the
diminution of the silicate complex instead of a compositional change in the
population of emitting dust grains. We discuss several scenarios for producing
such variability including disk shadowing, vertical mixing, variations in disk
heating, and disk wind events associated with accretion outbursts.Comment: 6 pages, emulate apj format, accepted for publication in ApJ Letter
Disentangling the Origin and Heating Mechanism of Supernova Dust: Late-Time Spitzer Spectroscopy of the Type IIn SN 2005ip
This paper presents late-time near-infrared and {\it Spitzer} mid-infrared
photometric and spectroscopic observations of warm dust in the Type IIn SN
2005ip in NGC 2906. The spectra show evidence for two dust components with
different temperatures. Spanning the peak of the thermal emission, these
observations provide strong constraints on the dust mass, temperature, and
luminosity, which serve as critical diagnostics for disentangling the origin
and heating mechanism of each component. The results suggest the warmer dust
has a mass of \msolar, originates from newly formed
dust in the ejecta, or possibly the cool, dense shell, and is continuously
heated by the circumstellar interaction. By contrast, the cooler component
likely originates from a circumstellar shock echo that forms from the heating
of a large, pre-existing dust shell ~\msolar~by the late-time
circumstellar interaction. The progenitor wind velocity derived from the blue
edge of the He 1 1.083 \micron~P Cygni profile indicates a progenitor eruption
likely formed this dust shell 100 years prior to the supernova explosion,
which is consistent with a Luminous Blue Variable (LBV) progenitor star.Comment: 12 pages, 10 figures, Accepted to Ap
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High Interest Rates: Causes and Effects
This report describes the major market and policy forces that determine the general level of interest rates. The discussion is related to the recent economic experience of high interest rates and inflation, but may be generally applied to any economic environment
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