21 research outputs found
On-sky wide field adaptive optics correction using multiple laser guide stars at the MMT
We describe results from the first astronomical adaptive optics system to use
multiple laser guide stars, located at the 6.5-m MMT telescope in Arizona. Its
initial operational mode, ground-layer adaptive optics (GLAO), provides uniform
stellar wavefront correction within the 2 arc minute diameter laser beacon
constellation, reducing the stellar image widths by as much as 53%, from 0.70
to 0.33 arc seconds at lambda = 2.14 microns. GLAO is achieved by applying a
correction to the telescope's adaptive secondary mirror that is an average of
wavefront measurements from five laser beacons supplemented with image motion
from a faint stellar source. Optimization of the adaptive optics system in
subsequent commissioning runs will further improve correction performance where
it is predicted to deliver 0.1 to 0.2 arc second resolution in the
near-infrared during a majority of seeing conditions.Comment: 13 pages, 1 table, 7 figures. Accepted for publication in
Astrophysical Journal. Expected March 200
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
Does the Debris Disk around HD 32297 Contain Cometary Grains?
We present an adaptive optics imaging detection of the HD 32297 debris disk
at L' (3.8 \microns) obtained with the LBTI/LMIRcam infrared instrument at the
LBT. The disk is detected at signal-to-noise per resolution element ~ 3-7.5
from ~ 0.3-1.1" (30-120 AU). The disk at L' is bowed, as was seen at shorter
wavelengths. This likely indicates the disk is not perfectly edge-on and
contains highly forward scattering grains. Interior to ~ 50 AU, the surface
brightness at L' rises sharply on both sides of the disk, which was also
previously seen at Ks band. This evidence together points to the disk
containing a second inner component located at 50 AU. Comparing the
color of the outer (50 /AU ) portion of the disk at L' with
archival HST/NICMOS images of the disk at 1-2 \microns allows us to test the
recently proposed cometary grains model of Donaldson et al. 2013. We find that
the model fails to match the disk's surface brightness and spectrum
simultaneously (reduced chi-square = 17.9). When we modify the density
distribution of the model disk, we obtain a better overall fit (reduced
chi-square = 2.9). The best fit to all of the data is a pure water ice model
(reduced chi-square = 1.06), but additional resolved imaging at 3.1 \microns is
necessary to constrain how much (if any) water ice exists in the disk, which
can then help refine the originally proposed cometary grains model.Comment: Accepted to ApJ January 13, 2014. 12 pages (emulateapj style), 9
figures, 1 tabl
The Large Binocular Telescope Interferometer & Adaptive Optics System: On-sky Performance and Results
Increasing spatial resolution and contrast capabilities will make possible new direct detections of exoplanets, exozodis, and circumstellar disks. The Large Binocular Telescope Interferometer (LBTI) has been engineered to sit at the combined focus of the Large Binocular Telescope's two 8.4m apertures. Both apertures are equipped with 672-actuator deformable secondary mirrors, the first of the next generation of ``extreme'' adaptive optics (AO) systems. We present an overview of the LBTI AO instrument suite and detail current on-sky performance
The Gray Needle: Large Grains in the HD 15115 Debris Disk from LBT/PISCES/Ks and LBTI/LMIRcam/L' Adaptive Optics Imaging
We present diffraction-limited \ks band and \lprime adaptive optics images of
the edge-on debris disk around the nearby F2 star HD 15115, obtained with a
single 8.4 m primary mirror at the Large Binocular Telescope. At \ks band the
disk is detected at signal-to-noise per resolution element (SNRE) \about 3-8
from \about 1-2\fasec 5 (45-113 AU) on the western side, and from \about
1.2-2\fasec 1 (63-90 AU) on the east. At \lprime the disk is detected at SNRE
\about 2.5 from \about 1-1\fasec 45 (45-90 AU) on both sides, implying more
symmetric disk structure at 3.8 \microns . At both wavelengths the disk has a
bow-like shape and is offset from the star to the north by a few AU. A surface
brightness asymmetry exists between the two sides of the disk at \ks band, but
not at \lprime . The surface brightness at \ks band declines inside 1\asec
(\about 45 AU), which may be indicative of a gap in the disk near 1\asec. The
\ks - \lprime disk color, after removal of the stellar color, is mostly grey
for both sides of the disk. This suggests that scattered light is coming from
large dust grains, with 3-10 \microns -sized grains on the east side and 1-10
\microns dust grains on the west. This may suggest that the west side is
composed of smaller dust grains than the east side, which would support the
interpretation that the disk is being dynamically affected by interactions with
the local interstellar medium.Comment: Apj-accepted March 27 2012; minor correction
First Light LBT AO Images of HR 8799 bcde at 1.65 and 3.3 Microns: New Discrepancies between Young Planets and Old Brown Dwarfs
As the only directly imaged multiple planet system, HR 8799 provides a unique
opportunity to study the physical properties of several planets in parallel. In
this paper, we image all four of the HR 8799 planets at H-band and 3.3 microns
with the new LBT adaptive optics system, PISCES, and LBTI/LMIRCam. Our images
offer an unprecedented view of the system, allowing us to obtain H and 3.3$
micron photometry of the innermost planet (for the first time) and put strong
upper-limits on the presence of a hypothetical fifth companion. We find that
all four planets are unexpectedly bright at 3.3 microns compared to the
equilibrium chemistry models used for field brown dwarfs, which predict that
planets should be faint at 3.3 microns due to CH4 opacity. We attempt to model
the planets with thick-cloudy, non-equilibrium chemistry atmospheres, but find
that removing CH4 to fit the 3.3 micron photometry increases the predicted L'
(3.8 microns) flux enough that it is inconsistent with observations. In an
effort to fit the SED of the HR 8799 planets, we construct mixtures of cloudy
atmospheres, which are intended to represent planets covered by clouds of
varying opacity. In this scenario, regions with low opacity look hot and
bright, while regions with high opacity look faint, similar to the patchy cloud
structures on Jupiter and L/T transition brown-dwarfs. Our mixed cloud models
reproduce all of the available data, but self-consistent models are still
necessary to demonstrate their viability.Comment: Accepted to Ap