427 research outputs found
The Performance of the Robo-AO Laser Guide Star Adaptive Optics System at the Kitt Peak 2.1-m Telescope
Robo-AO is an autonomous laser guide star adaptive optics system recently
commissioned at the Kitt Peak 2.1-m telescope. Now operating every clear night,
Robo-AO at the 2.1-m telescope is the first dedicated adaptive optics
observatory. This paper presents the imaging performance of the adaptive optics
system in its first eighteen months of operations. For a median seeing value of
, the average Strehl ratio is 4\% in the band
and 29\% in the J band. After post-processing, the contrast ratio under
sub-arcsecond seeing for a primary star is five and
seven magnitudes at radial offsets of and
, respectively. The data processing and archiving pipelines
run automatically at the end of each night. The first stage of the processing
pipeline shifts and adds the data using techniques alternately optimized for
stars with high and low SNRs. The second "high contrast" stage of the pipeline
is eponymously well suited to finding faint stellar companions.Comment: 12 pages, 16 figures, to be submitted to PAS
High-efficiency Autonomous Laser Adaptive Optics
As new large-scale astronomical surveys greatly increase the number of
objects targeted and discoveries made, the requirement for efficient follow-up
observations is crucial. Adaptive optics imaging, which compensates for the
image-blurring effects of Earth's turbulent atmosphere, is essential for these
surveys, but the scarcity, complexity and high demand of current systems limits
their availability for following up large numbers of targets. To address this
need, we have engineered and implemented Robo-AO, a fully autonomous laser
adaptive optics and imaging system that routinely images over 200 objects per
night with an acuity 10 times sharper at visible wavelengths than typically
possible from the ground. By greatly improving the angular resolution,
sensitivity, and efficiency of 1-3 m class telescopes, we have eliminated a
major obstacle in the follow-up of the discoveries from current and future
large astronomical surveys.Comment: Published in ApJL. 6 pages, 4 figures, and 1 tabl
Two Small Planets Transiting HD 3167
We report the discovery of two super-Earth-sized planets transiting the
bright (V = 8.94, K = 7.07) nearby late G-dwarf HD 3167, using data collected
by the K2 mission. The inner planet, HD 3167 b, has a radius of 1.6 R_e and an
ultra-short orbital period of only 0.96 days. The outer planet, HD 3167 c, has
a radius of 2.9 R_e and orbits its host star every 29.85 days. At a distance of
just 45.8 +/- 2.2 pc, HD 3167 is one of the closest and brightest stars hosting
multiple transiting planets, making HD 3167 b and c well suited for follow-up
observations. The star is chromospherically inactive with low rotational
line-broadening, ideal for radial velocity observations to measure the planets'
masses. The outer planet is large enough that it likely has a thick gaseous
envelope which could be studied via transmission spectroscopy. Planets
transiting bright, nearby stars like HD 3167 are valuable objects to study
leading up to the launch of the James Webb Space Telescope.Comment: Accepted by ApJL. 6 pages, 1 figure, 2 table
Robotic Laser-Adaptive-Optics Imaging of 715 Kepler Exoplanet Candidates using Robo-AO
The Robo-AO Kepler Planetary Candidate Survey is designed to observe every
Kepler planet candidate host star with laser adaptive optics imaging to search
for blended nearby stars, which may be physically associated companions and/or
responsible for transit false positives. In this paper we present the results
from the 2012 observing season, searching for stars close to 715 representative
Kepler planet candidate hosts. We find 53 companions, 44 of which are new
discoveries. We detail the Robo-AO survey data reduction methods including a
method of using the large ensemble of target observations as mutual
point-spread-function references, along with a new automated
companion-detection algorithm designed for large adaptive optics surveys. Our
survey is sensitive to objects from 0.15" to 2.5" separation, with contrast
ratios up to delta-m~6. We measure an overall nearby-star-probability for
Kepler planet candidates of 7.4% +/- 1.0%, and calculate the effects of each
detected nearby star on the Kepler-measured planetary radius. We discuss
several KOIs of particular interest, including KOI-191 and KOI-1151, which are
both multi-planet systems with detected stellar companions whose unusual
planetary system architecture might be best explained if they are "coincident
multiple" systems, with several transiting planets shared between the two
stars. Finally, we detect 2.6-sigma evidence for <15d-period giant planets
being 2-3 times more likely be found in wide stellar binaries than smaller
close-in planets and all sizes of further-out planets.Comment: Accepted by ApJ. Minor updates & improved statistical analysis; no
changes to results. 15 pages, 13 figure
Magnetic Inflation and Stellar Mass. I. Revised Parameters for the Component Stars of the Kepler Low-mass Eclipsing Binary T-Cyg1-12664
Several low-mass eclipsing binary stars show larger than expected radii for their measured mass, metallicity, and age. One proposed mechanism for this radius inflation involves inhibited internal convection and starspots caused by strong magnetic fields. One particular eclipsing binary, T-Cyg1-12664, has proven confounding to this scenario. Çakırlı et al. measured a radius for the secondary component that is twice as large as model predictions for stars with the same mass and age, but a primary mass that is consistent with predictions. Iglesias-Marzoa et al. independently measured the radii and masses of the component stars and found that the radius of the secondary is not in fact inflated with respect to models, but that the primary is, which is consistent with the inhibited convection scenario. However, in their mass determinations, Iglesias-Marzoa et al. lacked independent radial velocity measurements for the secondary component due to the star's faintness at optical wavelengths. The secondary component is especially interesting, as its purported mass is near the transition from partially convective to a fully convective interior. In this article, we independently determined the masses and radii of the component stars of T-Cyg1-12664 using archival Kepler data and radial velocity measurements of both component stars obtained with IGRINS on the Discovery Channel Telescope and NIRSPEC and HIRES on the Keck Telescopes. We show that neither of the component stars is inflated with respect to models. Our results are broadly consistent with modern stellar evolutionary models for main-sequence M dwarf stars and do not require inhibited convection by magnetic fields to account for the stellar radii
Exact Synchronization for Finite-State Sources
We analyze how an observer synchronizes to the internal state of a
finite-state information source, using the epsilon-machine causal
representation. Here, we treat the case of exact synchronization, when it is
possible for the observer to synchronize completely after a finite number of
observations. The more difficult case of strictly asymptotic synchronization is
treated in a sequel. In both cases, we find that an observer, on average, will
synchronize to the source state exponentially fast and that, as a result, the
average accuracy in an observer's predictions of the source output approaches
its optimal level exponentially fast as well. Additionally, we show here how to
analytically calculate the synchronization rate for exact epsilon-machines and
provide an efficient polynomial-time algorithm to test epsilon-machines for
exactness.Comment: 9 pages, 6 figures; now includes analytical calculation of the
synchronization rate; updates and corrections adde
The Robo-AO software: fully autonomous operation of a laser guide star adaptive optics and science system
Robo-AO is the first astronomical laser guide star adaptive optics (AO) system designed to operate completely
independent of human supervision. A single computer commands the AO system, the laser guide star, visible and
near-infrared science cameras (which double as tip-tip sensors), the telescope, and other instrument functions.
Autonomous startup and shutdown sequences as well as concatenated visible observations were demonstrated in
late 2011. The fully robotic software is currently operating during a month long demonstration of Robo-AO at
the Palomar Observatory 60-inch telescope
Selection of an optimal neural network architecture for computerâ aided detection of microcalcificationsâ Comparison of automated optimization techniques
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/134870/1/mp5036.pd
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