141 research outputs found
Precision Photometric and Astrometric Calibration Using Alternating Satellite Speckles
Photometric and astrometric calibration of high-contrast images is essential for the characterization of companions at small angular separation from their stellar host. The main challenge to performing accurate relative photometry and astrometry of high-contrast companions with respect to the host star is that the central starlight cannot be directly used as a reference, as it is either blocked by a coronagraphic mask or saturating the detector. Our approach is to add fiducial incoherent faint copies of the host star in the image plane and alternate the pattern of these copies between exposures. Subtracting two frames with different calibration patterns removes measurement bias due to static and slowly varying incoherent speckle halo components, while ensuring that calibration references are inserted on each frame. Each calibration pattern is achieved by high-speed modulation of a pupil-plane deformable mirror to ensure incoherence. We implemented the technique on-sky on the Subaru Coronagraphic Extreme Adaptive Optics instrument with speckles which were of the order of 10³ times fainter than the central host. The achieved relative photometric and astrometric measurement precisions for 10 s exposure were respectively 5% and 20 milliarcsecond. We also demonstrate, over a 540 s measurement span, that residual photometric and astrometric errors are uncorrelated in time, indicating that residual noise averages as the inverse square root of the number of exposures in longer time-series data sets
Quasar Radio-Loudness and the Elliptical Core Problem
The dichotomy between radio-loud and radio-quiet QSOs is not simply one of
host morphology. While spiral galaxies almost exclusively host radio-quiet
QSOs, ellipticals can host either radio-louds or radio-quiets. We find that a
combination of accretion rate and host scale determines which type of QSO a
given elliptical galaxy will host. QSOs with high x-ray luminosities (above
10^44.5 erg/s at 0.5 keV) are mostly radio-loud. But those with low
luminosities divide fairly neatly in size (measured by the half-light radius,
r_e). Those larger than about 10 kpc are radio-loud, while smaller ones are
radio-quiet. It has recently been found that core and coreless ellipticals are
also divided near this limit. This implies that for low-luminosity QSOs,
radio-louds are found in core ellipticals, while radio-quiets are in coreless
ellipticals and spirals. This segregation also shows up strongly for
low-redshift objects, and in general, there is a loss over time of coreless,
radio-loud QSOs. Since the presence or absence of a core may be tied to the
galactic merger history, we have an evolutionary explanation for the
differences between radio-loud and radio-quiet QSOs.Comment: 8 pages, 4 figures. To be published in MNRA
Conceptual Design of the Coronagraphic High Angular Resolution Imaging Spectrograph (CHARIS) for the Subaru Telescope
Recent developments in high-contrast imaging techniques now make possible
both imaging and spectroscopy of planets around nearby stars. We present the
conceptual design of the Coronagraphic High Angular Resolution Imaging
Spectrograph (CHARIS), a lenslet-based, cryogenic integral field spectrograph
(IFS) for imaging exoplanets on the Subaru telescope. The IFS will provide
spectral information for 140x140 spatial elements over a 1.75 arcsecs x 1.75
arcsecs field of view (FOV). CHARIS will operate in the near infrared (lambda =
0.9 - 2.5 microns) and provide a spectral resolution of R = 14, 33, and 65 in
three separate observing modes. Taking advantage of the adaptive optics systems
and advanced coronagraphs (AO188 and SCExAO) on the Subaru telescope, CHARIS
will provide sufficient contrast to obtain spectra of young self-luminous
Jupiter-mass exoplanets. CHARIS is in the early design phases and is projected
to have first light by the end of 2015. We report here on the current
conceptual design of CHARIS and the design challenges
The Optical Design of CHARIS: An Exoplanet IFS for the Subaru Telescope
High-contrast imaging techniques now make possible both imaging and
spectroscopy of planets around nearby stars. We present the optical design for
the Coronagraphic High Angular Resolution Imaging Spectrograph (CHARIS), a
lenslet-based, cryogenic integral field spectrograph (IFS) for imaging
exoplanets on the Subaru telescope. The IFS will provide spectral information
for 138x138 spatial elements over a 2.07 arcsec x 2.07 arcsec field of view
(FOV). CHARIS will operate in the near infrared (lambda = 1.15 - 2.5 microns)
and will feature two spectral resolution modes of R = 18 (low-res mode) and R =
73 (high-res mode). Taking advantage of the Subaru telescope adaptive optics
systems and coronagraphs (AO188 and SCExAO), CHARIS will provide sufficient
contrast to obtain spectra of young self-luminous Jupiter-mass exoplanets.
CHARIS will undergo CDR in October 2013 and is projected to have first light by
the end of 2015. We report here on the current optical design of CHARIS and its
unique innovations.Comment: 15 page
Recommended from our members
Zebrafish orthologs of human muscular dystrophy genes
BACKGROUND: Human muscular dystrophies are a heterogeneous group of genetic disorders which cause decreased muscle strength and often result in premature death. There is no known cure for muscular dystrophy, nor have all causative genes been identified. Recent work in the small vertebrate zebrafish Danio rerio suggests that mutation or misregulation of zebrafish dystrophy orthologs can also cause muscular degeneration phenotypes in fish. To aid in the identification of new causative genes, this study identifies and maps zebrafish orthologs for all known human muscular dystrophy genes. RESULTS: Zebrafish sequence databases were queried for transcripts orthologous to human dystrophy-causing genes, identifying transcripts for 28 out of 29 genes of interest. In addition, the genomic locations of all 29 genes have been found, allowing rapid candidate gene discovery during genetic mapping of zebrafish dystrophy mutants. 19 genes show conservation of syntenic relationships with humans and at least two genes appear to be duplicated in zebrafish. Significant sequence coverage on one or more BAC clone(s) was also identified for 24 of the genes to provide better local sequence information and easy updating of genomic locations as the zebrafish genome assembly continues to evolve. CONCLUSION: This resource supports zebrafish as a dystrophy model, suggesting maintenance of all known dystrophy-associated genes in the zebrafish genome. Coupled with the ability to conduct genetic screens and small molecule screens, zebrafish are thus an attractive model organism for isolating new dystrophy-causing genes/pathways and for use in high-throughput therapeutic discovery
CHARIS Science: Performance Simulations for the Subaru Telescope's Third-Generation of Exoplanet Imaging Instrumentation
We describe the expected scientific capabilities of CHARIS, a high-contrast
integral-field spectrograph (IFS) currently under construction for the Subaru
telescope. CHARIS is part of a new generation of instruments, enabled by
extreme adaptive optics (AO) systems (including SCExAO at Subaru), that promise
greatly improved contrasts at small angular separation thanks to their ability
to use spectral information to distinguish planets from quasistatic speckles in
the stellar point-spread function (PSF). CHARIS is similar in concept to GPI
and SPHERE, on Gemini South and the Very Large Telescope, respectively, but
will be unique in its ability to simultaneously cover the entire near-infrared
, , and bands with a low-resolution mode. This extraordinarily broad
wavelength coverage will enable spectral differential imaging down to angular
separations of a few , corresponding to 0.\!\!''1. SCExAO
will also offer contrast approaching at similar separations,
0.\!\!''1--0.\!\!''2. The discovery yield of a CHARIS survey will
depend on the exoplanet distribution function at around 10 AU. If the
distribution of planets discovered by radial velocity surveys extends unchanged
to 20 AU, observations of 200 mostly young, nearby stars targeted
by existing high-contrast instruments might find 1--3 planets. Carefully
optimizing the target sample could improve this yield by a factor of a few,
while an upturn in frequency at a few AU could also increase the number of
detections. CHARIS, with a higher spectral resolution mode of , will
also be among the best instruments to characterize planets and brown dwarfs
like HR 8799 cde and And b.Comment: 13 pages, 7 figures, proceedings from SPIE Montrea
The low-order wavefront sensor for the PICTURE-C mission
The PICTURE-C mission will fly a 60 cm off-axis unobscured telescope and two high-contrast coronagraphs in successive high-altitude balloon flights with the goal of directly imaging and spectrally characterizing visible scattered light from exozodiacal dust in the interior 1-10 AU of nearby exoplanetary systems. The first flight in 2017 will use a 10[superscript -4] visible nulling coronagraph (previously flown on the PICTURE sounding rocket) and the second flight in 2019 will use a 10[superscript -7] vector vortex coronagraph. A low-order wavefront corrector (LOWC) will be used in both flights to remove time-varying aberrations from the coronagraph wavefront. The LOWC actuator is a 76-channel high-stroke deformable mirror packaged on top of a tip-tilt stage. This paper will detail the selection of a complementary high-speed, low-order wavefront sensor (LOWFS) for the mission. The relative performance and feasibility of several LOWFS designs will be compared including the Shack-Hartmann, Lyot LOWFS, and the curvature sensor. To test the different sensors, a model of the time-varying wavefront is constructed using measured pointing data and inertial dynamics models to simulate optical alignment perturbations and surface deformation in the balloon environment.United States. National Aeronautics and Space Administration (Grant NNX15AG23G S01
Host Galaxies of Luminous Type 2 Quasars at z ~ 0.5
We present deep Gemini GMOS optical spectroscopy of nine luminous quasars at
redshifts z ~ 0.5, drawn from the SDSS type 2 quasar sample. Our targets were
selected to have high intrinsic luminosities (M_V < -26 mag) as indicated by
the [O III] 5007 A emission-line luminosity (L_[O III]). Our sample has a
median black hole mass of ~ 10^8.8 M_sun inferred assuming the local
M_BH-sigma_* relation and a median Eddington ratio of ~ 0.7, using stellar
velocity dispersions sigma_* measured from the G band. We estimate the
contamination of the stellar continuum from scattered quasar light based on the
strength of broad H-beta, and provide an empirical calibration of the
contamination as a function of L_[O III]; the scattered light fraction is ~ 30%
of L_5100 for objects with L_[O III] = 10^9.5 L_sun. Population synthesis
indicates that young post-starburst populations (< 0.1 Gyr) are prevalent in
luminous type 2 quasars, in addition to a relatively old population (> 1 Gyr)
which dominates the stellar mass. Broad emission complexes around He II 4686 A
with luminosities up to 10^8.3 L_sun are unambiguously detected in three out of
the nine targets, indicative of Wolf-Rayet populations. Population synthesis
shows that ~ 5-Myr post-starburst populations contribute substantially to the
luminosities (> 50% of L_5100) of all three objects with Wolf-Rayet detections.
We find two objects with double cores and four with close companions. Our
results may suggest that luminous type 2 quasars trace an early stage of galaxy
interaction, perhaps responsible for both the quasar and the starburst
activity.Comment: 20 pages, 13 figures, 7 tables; accepted to Ap
- …