30 research outputs found
Instrumental calibration projector for the Large Synoptic Survey Telescope
Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2011.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student submitted PDF version of thesis.Includes bibliographical references (p. 125-126).The Large Synoptic Survey Telescope (LSST) is a next-generation ground-based survey telescope whose science objectives demand photometric precision at the 1% level. Recent efforts towards 1% photometry have advocated in-situ instrumental calibration schemes that use a calibrated detector, rather than a celestial source, as the fundamental reference point for all measurements of system throughput. Results have been promising, but report systematic errors due to stray and scattered light from the flat-field screens used. The LSST calibration scheme replaces the traditional Lambertian-scattering flat-field screen with an array of projectors whose light is constrained in angle, thereby minimizing scattered light incident on the detector. This thesis presents the construction and testing of a single prototype projector within the LSST array. In particular, we evaluate the use of Engineered Diffusers to define the angular radiance of incident light, and of either a Fresnel lens or parabolic mirror to collimate that light. We find that flat-top Engineered Diffusers produce light that is constrained in angle, but which shows persistent pixel-to-pixel non-uniformity at the 5-10% level, and colorto- color non-uniformity at the 5-15% level; unless compensated, chromatic non-uniformity renders them unsuitable for our purposes. The additional chromatic aberrations introduced by Fresnel lens collimators render such transmissive collimators infeasible. Nevertheless, we demonstrate the soundness of the flat-field projector concept by constructing an alternative projector prototype, based on an integrating sphere, that satisfies each criterion well within our tolerances. The magnitude of improvement granted by the integrating sphere projector suggests that future work further investigate this approach.by Amali L. Vaz.S.B
The TRENDS High-Contrast Imaging Survey. VII. Discovery of a Nearby Sirius-like White Dwarf System (HD 169889)
Monitoring the long-term radial velocity (RV) and acceleration of nearby
stars has proven an effective method for directly detecting binary and
substellar companions. Some fraction of nearby RV trend systems are expected to
be comprised of compact objects that likewise induce a systemic Doppler signal.
In this paper, we report the discovery of a white dwarf companion found to
orbit the nearby ( mas) G9 V star HD 169889.
High-contrast imaging observations using NIRC2 at Keck and LMIRCam at the LBT
uncover the (, ) companion
at an angular separation of 0.8'' (28 au). Thirteen years of precise Doppler
observations reveal a steep linear acceleration in RV time series and place a
dynamical constraint on the companion mass of . This "Sirius-like" system adds to the census of white dwarf
companions suspected to be missing in the solar neighborhood.Comment: Accepted to Ap
Image Flux Ratios of Gravitationally Lensed HS 0810+2554 with High Resolution Infrared Imaging
We report near simultaneous imaging using LMIRCam on the LBTI of the
quadruply imaged lensed quasar HS 0810+2554 at wavelengths of 2.16, 3.7 and
m with a Full Width Half Max (FWHM) spatial resolution of
, and
respectively, comparable to HST optical imaging. In
the rest frame of the quasar, the observed wavelengths
correspond to 0.86, 1.48, and m respectively. The two brightest
images in the quad, A and B, are clearly resolved from each other with a
separation of . The flux ratio of these two images (A/B)
trends from 1.79 to 1.23 from 2.16 to m. The trend in flux ratio is
consistent with the m flux originating from a small sized accretion
disk in the quasar that experiences only microlensing. The excess flux above
the contribution from the accretion disk at the two longer wavelengths
originates from a larger sized region that experiences no microlensing. A
simple model employing multiplicative factors for image B due to stellar
microlensing and sub-structure millilensing is presented. The
result is tightly constrained to the product . Given the
observational errors, the 60\% probability contour for this product stretches
from , to , , where the later is
consistent with microlensing only.Comment: accepted A
Speckle statistics in adaptive optics images at visible wavelengths
Residual speckles in adaptive optics (AO) images represent a well-known
limitation on the achievement of the contrast needed for faint source
detection. Speckles in AO imagery can be the result of either residual
atmospheric aberrations, not corrected by the AO, or slowly evolving
aberrations induced by the optical system. We take advantage of the high
temporal cadence (1 ms) of the data acquired by the System for Coronagraphy
with High-order Adaptive Optics from R to K bands-VIS forerunner experiment at
the Large Binocular Telescope to characterize the AO residual speckles at
visible wavelengths. An accurate knowledge of the speckle pattern and its
dynamics is of paramount importance for the application of methods aimed at
their mitigation. By means of both an automatic identification software and
information theory, we study the main statistical properties of AO residuals
and their dynamics. We therefore provide a speckle characterization that can be
incorporated into numerical simulations to increase their realism and to
optimize the performances of both real-time and postprocessing techniques aimed
at the reduction of the speckle noise
The Multiplicity of M-Dwarfs in Young Moving Groups
We image 104 newly identified low-mass (mostly M-dwarf) pre-main sequence
members of nearby young moving groups with Magellan Adaptive Optics (MagAO) and
identify 27 binaries with instantaneous projected separation as small as 40
mas. 15 were previously unknown. The total number of multiple systems in this
sample including spectroscopic and visual binaries from the literature is 36,
giving a raw multiplicity rate of at least for this
population. In the separation range of roughly 1 - 300 AU in which infrared AO
imaging is most sensitive, the raw multiplicity rate is at least
for binaries resolved by the MagAO infrared camera (Clio). The
M-star sub-sample of 87 stars yields a raw multiplicity of at least
over all separations, for secondary
companions resolved by Clio from 1 to 300 AU ( for all known
binaries in this separation range). A combined analysis with binaries
discovered by the Search for Associations Containing Young stars shows that
multiplicity fraction as a function of mass and age over the range of 0.2 to
1.2 and 10 - 200 Myr appears to be linearly flat in both parameters
and across YMGs. This suggests that multiplicity rates are largely set by 100
Myr without appreciable evolution thereafter. After bias corrections are
applied, the multiplicity fraction of low-mass YMG members () is
in excess of the field.Comment: 25 page
Large Binocular Telescope Interferometer Adaptive Optics: On-sky performance and lessons learned
The Large Binocular Telescope Interferometer is a high contrast imager and
interferometer that sits at the combined bent Gregorian focus of the LBT's dual
8.4~m apertures. The interferometric science drivers dictate 0.1'' resolution
with contrast at , while the imaging science
drivers require even greater contrasts, but at scales 0.2''. In imaging
mode, LBTI's Adaptive Optics system is already delivering contrast of
at in good conditions. Even in poor seeing, it can
deliver up to 90\% Strehl Ratio at this wavelength. However, the performance
could be further improved by mitigating Non-Common Path Aberrations. Any NCPA
remedy must be feasible using only the current hardware: the science camera,
the wavefront sensor, and the adaptive secondary mirror. In preliminary
testing, we have implemented an ``eye doctor'' grid search approach for
astigmatism and trefoil, achieving 5\% improvement in Strehl Ratio at , with future plans to test at shorter wavelengths and with more modes. We
find evidence of NCPA variability on short timescales and discuss possible
upgrades to ameliorate time-variable effectsComment: Published in Proceedings of SPIE, vol 9148: Adaptive Optics Systems
I
Sub-percent Photometry: Faint DA White Dwarf Spectophotometric Standards for Astrophysical Observatories
We have established a network of 19 faint (16.5 mag 19 mag) northern
and equatorial DA white dwarfs as spectrophotometric standards for present and
future wide-field observatories. Our analysis infers SED models for the stars
that are tied to the three CALSPEC primary standards. Our SED models are
consistent with panchromatic Hubble Space Telescope () photometry to
better than 1%. The excellent agreement between observations and models
validates the use of non-local-thermodynamic-equilibrium (NLTE) DA white dwarf
atmospheres extinguished by interstellar dust as accurate spectrophotometric
references. Our standards are accessible from both hemispheres and suitable for
ground and space-based observatories covering the ultraviolet to the near
infrared. The high-precision of these faint sources make our network of
standards ideally suited for any experiment that has very stringent
requirements on flux calibration, such as studies of dark energy using the
Large Synoptic Survey Telescope (LSST) and the Wide-Field Infrared Survey
Telescope ().Comment: 46 pages, 23 figures, 8 tables, accepted for publication in ApJ