71 research outputs found
Efficient dynamic optimization of logic programs
A summary is given of the dynamic optimization approach to speed up learning for logic programs. The problem is to restructure a recursive program into an equivalent program whose expected performance is optimal for an unknown but fixed population of problem instances. We define the term 'optimal' relative to the source of input instances and sketch an algorithm that can come within a logarithmic factor of optimal with high probability. Finally, we show that finding high-utility unfolding operations (such as EBG) can be reduced to clause reordering
The Orbit of the Companion to HD 100453A: Binary-Driven Spiral Arms in a Protoplanetary Disk
HD 100453AB is a 10+/-2 Myr old binary whose protoplanetary disk was recently
revealed to host a global two-armed spiral structure. Given the relatively
small projected separation of the binary (1.05", or ~108 au), gravitational
perturbations by the binary seemed to be a likely driving force behind the
formation of the spiral arms. However, the orbit of these stars remained poorly
understood, which prevented a proper treatment of the dynamical influence of
the companion on the disk. We observed HD 100453AB between 2015-2017 utilizing
extreme adaptive optics systems on the Very Large Telescope and Magellan Clay
Telescope. We combined the astrometry from these observations with published
data to constrain the parameters of the binary's orbit to a=1.06"+/-0.09",
e=0.17+/-0.07, and i=32.5+/- 6.5 degrees. We utilized publicly available ALMA
CO data to constrain the inclination of the disk to i~28 degrees, which is
relatively co-planar with the orbit of the companion and consistent with
previous estimates from scattered light images. Finally, we input these
constraints into hydrodynamical and radiative transfer simulations to model the
structural evolution of the disk. We find that the spiral structure and
truncation of the circumprimary disk in HD 100453 are consistent with a
companion-dirven origin. Furthermore, we find that the primary star's rotation,
its outer disk, and the companion exhibit roughly the same direction of angular
momentum, and thus the system likely formed from the same parent body of
material.Comment: 28 pages, 11 figures, Accepted to Ap
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
The TWA 3 Young Triple System: Orbits, Disks, Evolution
We have characterized the spectroscopic orbit of the TWA 3A binary and
provide preliminary families of probable solutions for the TWA 3A visual orbit
as well as for the wide TWA 3A--B orbit. TWA 3 is a hierarchical triple located
at 34 pc in the 10 Myr old TW Hya association. The wide component
separation is 1."55; the close pair was first identified as a possible binary
almost 20 years ago. We initially identified the 35-day period orbital solution
using high-resolution infrared spectroscopy which angularly resolved the A and
B components. We then refined the preliminary orbit by combining the infrared
data with a re-analysis of our high-resolution optical spectroscopy. The
orbital period from the combined spectroscopic solution is 35 days, the
eccentricity is 0.63, and the mass ratio is 0.84; although this
high mass ratio would suggest that optical spectroscopy alone should be
sufficient to identify the orbital solution, the presence of the tertiary B
component likely introduced confusion in the blended optical spectra. Using
millimeter imaging from the literature, we also estimate the inclinations of
the stellar orbital planes with respect to the TWA 3A circumbinary disk
inclination and find that all three planes are likely misaligned by at least
30 degrees. The TWA 3A spectroscopic binary components have spectral
types of M4.0 and M4.5; TWA 3B is an M3. We speculate that the system formed as
a triple, is bound, and that its properties were shaped by dynamical
interactions between the inclined orbits and disk.Comment: Accepted to Ap
Magellan Adaptive Optics first-light observations of the exoplanet beta Pic b. II. 3-5 micron direct imaging with MagAO+Clio, and the empirical bolometric luminosity of a self-luminous giant planet
Young giant exoplanets are a unique laboratory for understanding cool,
low-gravity atmospheres. A quintessential example is the massive extrasolar
planet Pic b, which is 9 AU from and embedded in the debris disk of the
young nearby A6V star Pictoris. We observed the system with first light
of the Magellan Adaptive Optics (MagAO) system. In Paper I we presented the
first CCD detection of this planet with MagAO+VisAO. Here we present four
MagAO+Clio images of Pic b at 3.1 m, 3.3 m, , and
, including the first observation in the fundamental CH band. To
remove systematic errors from the spectral energy distribution (SED), we
re-calibrate the literature photometry and combine it with our own data, for a
total of 22 independent measurements at 16 passbands from 0.99--4.8 m.
Atmosphere models demonstrate the planet is cloudy but are degenerate in
effective temperature and radius. The measured SED now covers 80\% of the
planet's energy, so we approach the bolometric luminosity empirically. We
calculate the luminosity by extending the measured SED with a blackbody and
integrating to find log(/) . From our
bolometric luminosity and an age of 233 Myr, hot-start evolutionary tracks
give a mass of 12.70.3 , radius of 1.450.02 , and
of 170823 K (model-dependent errors not included). Our
empirically-determined luminosity is in agreement with values from atmospheric
models (typically dex), but brighter than values from the field-dwarf
bolometric correction (typically dex), illustrating the limitations in
comparing young exoplanets to old brown dwarfs.Comment: Accepted to ApJ. 27 pages, 22 figures, 19 table
Resolving the Dusty Circumstellar Structure of the Enigmatic Symbiotic Star CH Cygni with the MMT Adaptive Optics System
We imaged the symbiotic star CH Cyg and two PSF calibration stars using the
unique 6.5m MMT deformable secondary adaptive optics system. Our
high-resolution (FWHM=0.3"), very high Strehl (98%+-2%) mid-infrared (9.8 and
11.7 um) images of CH Cyg allow us to probe finer length scales than ever
before for this object. CH Cyg is significantly extended compared to our
unresolved PSF calibration stars (Mu UMa and Alpha Her) at 9.8 and 11.7 um. We
estimated the size of the extension by convolving a number of simple Gaussian
models with the Mu UMa PSF and determining which model provided the best fit to
the data. Adopting the Hipparcos distance for this object of 270 pc, we found a
nearly Gaussian extension with a FWHM at 9.8 um of ~40.5+-2.7 AU (0.15+-0.01")
and a FWHM at 11.7 um of 45.9+-2.7 AU (0.17+-0.01"). After subtracting out the
Gaussian component of the emission (convolved with our PSF), we found a faint
\~0.7" asymmetric extension which peaks in flux ~0.5" north of the stars. This
extension is roughly coincident with the northern knotlike feature seen in HST
WFPC2 images obtained in 1999.Comment: 18 pages, 7 figures, accepted by the Astrophysical Journa
Status of MagAO and review of astronomical science with visible light adaptive optics
We review astronomical results in the visible (lambda <1 micron) with
adaptive optics and note the status the MagAO system and the recent upgrade to
visible camera's Simultaneous/Spectra Differential Imager (SDI to SDI+) mode.
Since mid-2013 there has been a rapid increase visible AO with over 50 refereed
science papers published in just 2015-2016 timeframe. The main focus of this
paper is another large (D=6.5m Magellan telescope) AO system (MagAO) which has
been very productive in the visible (particularly at the H-alpha emission
line). MagAO is an advanced Adaptive Secondary Mirror (ASM) AO system at the
Magellan in Chile. This ASM secondary has 585 actuators with <1 msec response
times (0.7 ms typically). MagAO utilizes a 1 kHz pyramid wavefront sensor
(PWFS). The relatively small actuator pitch (~22 cm/subap, 300 modes, upgraded
to 30 pix dia. PWFS) allows moderate Strehls to be obtained in the visible
(0.63-1.05 microns). Long exposures (60s) achieve <30mas resolutions and 30%
Strehls at 0.62 microns (r') with the VisAO camera (0.5-1.0 microns) in 0.5"
seeing with bright R < 9 mag stars (~10% Strehls can be obtained on fainter
R~12 mag guide stars). Differential Spectral Imaging (SDI) at H-alpha has been
very important for accreting exoplanet detection. There is also a 1-5micron
science camera (Clio; Morzinski et al. 2016). These capabilities have led to
over 35 MagAO refereed science publications. Here we review the key steps to
having good performance in the visible and review the exciting new AO visible
science opportunities and science results. The recent rapid increase in the
scientific publications and power of visible AO is due to the maturity of the
next-generation of AO systems and our new ability probe circumstellar regions
with very high (10-30 mas) spatial resolutions that would otherwise require
much larger (>10m) diameter telescopes in the infrared.Comment: 18 pages, Proc. SPIE 10703, Adaptive Optics IV, June 2018 Austin TX.
arXiv admin note: substantial text overlap with arXiv:1407.509
Into the Blue: AO Science with MagAO in the Visible
We review astronomical results in the visible ({\lambda}<1{\mu}m) with
adaptive optics. Other than a brief period in the early 1990s, there has been
little astronomical science done in the visible with AO until recently. The
most productive visible AO system to date is our 6.5m Magellan telescope AO
system (MagAO). MagAO is an advanced Adaptive Secondary system at the Magellan
6.5m in Chile. This secondary has 585 actuators with < 1 msec response times
(0.7 ms typically). We use a pyramid wavefront sensor. The relatively small
actuator pitch (~23 cm/subap) allows moderate Strehls to be obtained in the
visible (0.63-1.05 microns). We use a CCD AO science camera called "VisAO".
On-sky long exposures (60s) achieve <30mas resolutions, 30% Strehls at 0.62
microns (r') with the VisAO camera in 0.5" seeing with bright R < 8 mag stars.
These relatively high visible wavelength Strehls are made possible by our
powerful combination of a next generation ASM and a Pyramid WFS with 378
controlled modes and 1000 Hz loop frequency. We'll review the key steps to
having good performance in the visible and review the exciting new AO visible
science opportunities and refereed publications in both broad-band (r,i,z,Y)
and at Halpha for exoplanets, protoplanetary disks, young stars, and emission
line jets. These examples highlight the power of visible AO to probe
circumstellar regions/spatial resolutions that would otherwise require much
larger diameter telescopes with classical infrared AO cameras.Comment: 14 pages, 8 figures, to appear in Proc. SPIE 914
Mid-Infrared Imaging of the Post-AGB Star AC Herculis with the MMT Adaptive Optics System
We utilized the MMT's unique deformable secondary adaptive optics system to
produce high-resolution (FWHM=0.3"), very high Strehl mid-infrared (9.8, 11.7 &
18 micron) images of the post-AGB star AC Her. The very high (98+/-2%) Strehls
achieved with Mid-IR AO led naturally to an ultra-stable PSF independent of
airmass, seeing, or location on the sky. We find no significant difference
between AC Her's morphology and our unresolved PSF calibration stars (mu UMa &
alpha Her) at 9.8, 11.7, & 18 microns. Our current observations do not confirm
any extended Mid-IR structure around AC Her. These observations are in conflict
with previously reported Keck (seeing-limited) 11.7 and 18 micron images which
suggested the presence of a resolved ~0.6" edge-on circumbinary disk. We
conclude that AC Her has no extended Mid-IR structure on scales greater than
0.2" (R<75 AU). These first results of Mid-IR AO science are very encouraging
for future high accuracy Mid-IR imaging with this technique.Comment: To appear in the November 20, 2003 issue of the Astrophysical Journal
Letters. The preprint has 7 pages and 3 figures (one in color; but prints OK
in B&W
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