384 research outputs found
Differential Imaging with a Multicolor Detector Assembly: A New ExoPlanet Finder Concept
Simultaneous spectral differential imaging is a high contrast technique by
which subtraction of simultaneous images reduces noise from atmospheric
speckles and optical aberrations. Small non-common wave front errors between
channels can seriously degrade its performance. We present a new concept, a
multicolor detector assembly (MCDA), which can eliminate this problem. The
device consists of an infrared detector and a microlens array onto the flat
side of which a checkerboard pattern of narrow-band micro-filters is deposited,
each micro-filter coinciding with a microlens. Practical considerations for
successful implementation of the technique are mentioned. Numerical simulations
predict a noise attenuation of 10^-3 at 0.5" for a 10^5 seconds integration on
a mH=5 star of Strehl ratio 0.9 taken with an 8-m telescope. This reaches a
contrast of 10^-7 at an angular distance of 0.5" from the center of the star
image.Comment: 13 pages, 5 figures, accepted APJ
Angular Differential Imaging: a Powerful High-Contrast Imaging Technique
Angular differential imaging is a high-contrast imaging technique that
reduces quasi-static speckle noise and facilitates the detection of nearby
companions. A sequence of images is acquired with an altitude/azimuth telescope
while the instrument field derotator is switched off. This keeps the instrument
and telescope optics aligned and allows the field of view to rotate with
respect to the instrument. For each image, a reference PSF is constructed from
other appropriately-selected images of the same sequence and subtracted to
remove quasi-static PSF structure. All residual images are then rotated to
align the field and are combined. Observed performances are reported for Gemini
North data. It is shown that quasi-static PSF noise can be reduced by a factor
\~5 for each image subtraction. The combination of all residuals then provides
an additional gain of the order of the square root of the total number of
acquired images. A total speckle noise attenuation of 20-50 is obtained for
one-hour long observing sequences compared to a single 30s exposure. A PSF
noise attenuation of 100 was achieved for two-hour long sequences of images of
Vega, reaching a 5-sigma contrast of 20 magnitudes for separations greater than
8". For a 30-minute long sequence, ADI achieves 30 times better signal-to-noise
than a classical observation technique. The ADI technique can be used with
currently available instruments to search for ~1MJup exoplanets with orbits of
radii between 50 and 300 AU around nearby young stars. The possibility of
combining the technique with other high-contrast imaging methods is briefly
discussed.Comment: 27 pages, 7 figures, accepted for publication in Ap
The Multidimensional Mortality Awareness Measure & Model (MMAMM): Development and validation of a new self-report questionnaire & psychological framework
For each of eight literature-identified conceptual dimensions of mortality awareness, questionnaire items were generated, producing 89 in all. 359 participants responded to these items and to questionnaires measuring health attitudes, risk-taking, rebelliousness and demographic variables. Multivariate correlational analyses investigated the underlying structure of the item pool and the construct validity as well as the reliability of the emergent empirically derived subscales. Five components, rather than eight, were identified. Given the item content of each, the associated mortality awareness subscales were labelled as: legacy, fearfulness, acceptance, disempowerment, and disengagement. Each attained an acceptable level of internal reliability. Relationships with other variables supported the construct validity of these empirically derived subscales and more generally of this five-factor model. In conclusion, this new multidimensional measure and model of mortality awareness extends our understanding of this important aspect of human existence and supports a more integrative and optimistic approach to mortality awareness than previously available
Morphological Evolution of Distant Galaxies from Adaptive Optics Imaging
We report here on a sample of resolved, infrared images of galaxies at z~0.5
taken with the 10-m Keck Telescope's Adaptive Optics (AO) system. We regularly
achieve a spatial resolution of 0.05'' and are thus able to resolve both the
disk and bulge components. We have extracted morphological information for ten
galaxies and compared their properties to those of a local sample. The
selection effects of both samples were explicitly taken into account in order
to derive the unbiased result that disks at z~0.5 are ~0.6 mag arcsec^-2
brighter than, and about the same size as, local disks. The
no-luminosity-evolution case is ruled out at 90% confidence. We also find, in a
more qualitative analysis, that the bulges of these galaxies have undergone a
smaller amount of surface brightness evolution and have also not changed
significantly in size from z~0.5 to today. This is the first time this type of
morphological evolution has been measured in the infrared and it points to the
unique power of AO in exploring galaxy evolution.Comment: 27 pages, 7figures, 2 tables. Accepted for publication in the
Astrophysical Journa
Direct Imaging of Multiple Planets Orbiting the Star HR 8799
Direct imaging of exoplanetary systems is a powerful technique that can
reveal Jupiter-like planets in wide orbits, can enable detailed
characterization of planetary atmospheres, and is a key step towards imaging
Earth-like planets. Imaging detections are challenging due to the combined
effect of small angular separation and large luminosity contrast between a
planet and its host star. High-contrast observations with the Keck and Gemini
telescopes have revealed three planets orbiting the star HR 8799, with
projected separations of 24, 38, and 68 astronomical units. Multi-epoch data
show counter-clockwise orbital motion for all three imaged planets. The low
luminosity of the companions and the estimated age of the system imply
planetary masses between 5 and 13 times that of Jupiter. This system resembles
a scaled-up version of the outer portion of our Solar System.Comment: 30 pages, 5 figures, Research Article published online in Science
Express Nov 13th, 200
A Search for Wide Companions to the Extrasolar Planetary System HR 8799
The extrasolar planetary system around HR 8799 is the first multiplanet
system ever imaged. It is also, by a wide margin, the highest mass system with
>27 Jupiters of planetary mass past 25 AU. This is a remarkable system with no
analogue with any other known planetary system. In the first part of this paper
we investigate the nature of two faint objects imaged near the system. These
objects are considerably fainter (H=20.4, and 21.6 mag) and more distant
(projected separations of 612, and 534 AU) than the three known planetary
companions b, c, and d (68-24 AU). It is possible that these two objects could
be lower mass planets (of mass ~5 and ~3 Jupiters) that have been scattered to
wider orbits. We make the first direct comparison of newly reduced archival
Gemini adaptive optics images to archival HST/NICMOS images. With nearly a
decade between these epochs we can accurately assess the proper motion nature
of each candidate companion. We find that both objects are unbound to HR 8799
and are background. We estimate that HR 8799 has no companions of H<22 from
~5-15 arcsec. Any scattered giant planets in the HR 8799 system are >600 AU or
less than 3 Jupiters in mass. In the second part of this paper we carry out a
search for wider common proper motion objects. While we identify no bound
companions to HR 8799, our search yields 16 objects within 1 degree in the
NOMAD catalog and POSS DSS images with similar (+/-20 mas/yr) proper motions to
HR 8799, three of which warrant follow-up observations.Comment: 22 pages, 8 figures, submitted to the Astrophysical Journa
Obsessive passion: a compensatory response to unsatisfied needs
The present research investigated the role of two sources of psychological need satisfaction (inside and outside a passionate activity) as determinants of harmonious (HP) and obsessive (OP) passion. Four studies were carried out with different samples of young and middle-aged adults (e.g., athletes, musicians; total N=648). Different research designs (cross-sectional, mixed, longitudinal) were also used. Results showed that only a rigid engagement in a passionate activity (OP) was predicted by low levels of need satisfaction outside the passionate activity (in an important life context or in life in general), whereas both OP and a more favorable and balanced type of passion, HP were positively predicted by need satisfaction inside the passionate activity. Further, OP led to negative outcomes, and HP predicted positive outcomes. These results suggest that OP may represent a form of compensatory striving for psychological need satisfaction. It appears important to consider two distinct sources of need satisfaction, inside and outside the passionate activity, when investigating determinants of optimal and less optimal forms of activity engagemen
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An optimal point spread function subtraction algorithm for high-contrast imaging: a demonstration with angular differential imaging
Direct imaging of exoplanets is limited by bright quasi-static speckles in the point spread function (PSF) of the central star. This limitation can be reduced by subtraction of reference PSF images. We have developed an algorithm to construct an optimal reference PSF image from an arbitrary set of reference images. This image is built as a linear combination of all available images and is optimized independently inside multiple subsections of the image to ensure that the absolute minimum residual noise is achieved within each subsection. The algorithm developed is completely general and can be used with many high contrast imaging observing strategies, such as angular differential imaging (ADI), roll subtraction, spectral differential imaging, reference star observations, etc. The performance of the algorithm is demonstrated for ADI data. It is shown that for this type of data the new algorithm provides a gain in sensitivity by up 22 to a factor 3 at small separation over the algorithm previously used
Therapeutic limitations in tumor-specific CD8+ memory T cell engraftment
BACKGROUND: Adoptive immunotherapy with cytotoxic T lymphocytes (CTL) represents an alternative approach to treating solid tumors. Ideally, this would confer long-term protection against tumor. We previously demonstrated that in vitro-generated tumor-specific CTL from the ovalbumin (OVA)-specific OT-I T cell receptor transgenic mouse persisted long after adoptive transfer as memory T cells. When recipient mice were challenged with the OVA-expressing E.G7 thymoma, tumor growth was delayed and sometimes prevented. The reasons for therapeutic failures were not clear. METHODS: OT-I CTL were adoptively transferred to C57BL/6 mice 21 – 28 days prior to tumor challenge. At this time, the donor cells had the phenotypical and functional characteristics of memory CD8+ T cells. Recipients which developed tumor despite adoptive immunotherapy were analyzed to evaluate the reason(s) for therapeutic failure. RESULTS: Dose-response studies demonstrated that the degree of tumor protection was directly proportional to the number of OT-I CTL adoptively transferred. At a low dose of OT-I CTL, therapeutic failure was attributed to insufficient numbers of OT-I T cells that persisted in vivo, rather than mechanisms that actively suppressed or anergized the OT-I T cells. In recipients of high numbers of OT-I CTL, the E.G7 tumor that developed was shown to be resistant to fresh OT-I CTL when examined ex vivo. Furthermore, these same tumor cells no longer secreted a detectable level of OVA. In this case, resistance to immunotherapy was secondary to selection of clones of E.G7 that expressed a lower level of tumor antigen. CONCLUSIONS: Memory engraftment with tumor-specific CTL provides long-term protection against tumor. However, there are several limitations to this immunotherapeutic strategy, especially when targeting a single antigen. This study illustrates the importance of administering large numbers of effectors to engraft sufficiently efficacious immunologic memory. It also demonstrates the importance of targeting several antigens when developing vaccine strategies for cancer
Constraints on the architecture of the HD 95086 planetary system with the Gemini Planet Imager
We present astrometric monitoring of the young exoplanet HD 95086 b obtained
with the Gemini Planet Imager between 2013 and 2016. A small but significant
position angle change is detected at constant separation; the orbital motion is
confirmed with literature measurements. Efficient Monte Carlo techniques place
preliminary constraints on the orbital parameters of HD 95086 b. With 68%
confidence, a semimajor axis of 61.7^{+20.7}_{-8.4} au and an inclination of
153.0^{+9.7}_{-13.5} deg are favored, with eccentricity less than 0.21. Under
the assumption of a co-planar planet-disk system, the periastron of HD 95086 b
is beyond 51 au with 68% confidence. Therefore HD 95086 b cannot carve the
entire gap inferred from the measured infrared excess in the SED of HD 95086.
We use our sensitivity to additional planets to discuss specific scenarios
presented in the literature to explain the geometry of the debris belts. We
suggest that either two planets on moderately eccentric orbits or three to four
planets with inhomogeneous masses and orbital properties are possible. The
sensitivity to additional planetary companions within the observations
presented in this study can be used to help further constrain future dynamical
simulations of the planet-disk system.Comment: Accepted for publication in ApJ
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