6,306 research outputs found
SPIRAL Phase A: A Prototype Integral Field Spectrograph for the AAT
We present details of a prototype fiber feed for use on the Anglo-Australian
Telescope (AAT) that uses a dedicated fiber-fed medium/high resolution (R >
10000) visible-band spectrograph to give integral field spectroscopy (IFS) of
an extended object. A focal reducer couples light from the telescope to the
close-packed lenslet array and fiber feed, allowing the spectrograph be used on
other telescopes with the change of a single lens. By considering the
properties of the fibers in the design of the spectrograph, an efficient design
can be realised, and we present the first scientific results of a prototype
spectrograph using a fiber feed with 37 spatial elements, namely the detection
of Lithium confirming a brown dwarf candidate and IFS of the supernova remnant
SN1987A.Comment: 41 pages, 15 figures, 3 tables; accepted by PAS
The Velocity Dispersion Profile of the Remote Dwarf Spheroidal Galaxy Leo I: A Tidal Hit and Run?
(abridged) We present kinematic results for a sample of 387 stars located
near Leo I based on spectra obtained with the MMT's Hectochelle spectrograph
near the MgI/Mgb lines. We estimate the mean velocity error of our sample to be
2.4 km/s, with a systematic error of < 1 km/s. We produce a final sample of 328
Leo I red giant members, from which we measure a mean heliocentric radial
velocity of 282.9 +/- 0.5 km/s, and a mean radial velocity dispersion of 9.2
+/- 0.4 km/s for Leo I. The dispersion profile of Leo I is flat out to beyond
its classical `tidal' radius. We fit the profile to a variety of equilibrium
dynamical models and can strongly rule out models where mass follows light.
Two-component Sersic+NFW models with tangentially anisotropic velocity
distributions fit the dispersion profile well, with isotropic models ruled out
at a 95% confidence level. The mass and V-band mass-to-light ratio of Leo I
estimated from equilibrium models are in the ranges 5-7 x 10^7 M_sun and 9-14
(solar units), respectively, out to 1 kpc from the galaxy center. Leo I members
located outside a `break radius' (about 400 arcsec = 500 pc) exhibit
significant velocity anisotropy, whereas stars interior appear to have
isotropic kinematics. We propose the break radius represents the location of
the tidal radius of Leo I at perigalacticon of a highly elliptical orbit. Our
scenario can account for the complex star formation history of Leo I, the
presence of population segregation within the galaxy, and Leo I's large outward
velocity from the Milky Way. The lack of extended tidal arms in Leo I suggests
the galaxy has experienced only one perigalactic passage with the Milky Way,
implying that Leo I may have been injected into its present orbit by a third
body a few Gyr before perigalacticon.Comment: ApJ accepted, 23 figures, access paper as a pdf file at
http://www.astro.lsa.umich.edu/~mmateo/research.htm
Adaptive foveated single-pixel imaging with dynamic super-sampling
As an alternative to conventional multi-pixel cameras, single-pixel cameras
enable images to be recorded using a single detector that measures the
correlations between the scene and a set of patterns. However, to fully sample
a scene in this way requires at least the same number of correlation
measurements as there are pixels in the reconstructed image. Therefore
single-pixel imaging systems typically exhibit low frame-rates. To mitigate
this, a range of compressive sensing techniques have been developed which rely
on a priori knowledge of the scene to reconstruct images from an under-sampled
set of measurements. In this work we take a different approach and adopt a
strategy inspired by the foveated vision systems found in the animal kingdom -
a framework that exploits the spatio-temporal redundancy present in many
dynamic scenes. In our single-pixel imaging system a high-resolution foveal
region follows motion within the scene, but unlike a simple zoom, every frame
delivers new spatial information from across the entire field-of-view. Using
this approach we demonstrate a four-fold reduction in the time taken to record
the detail of rapidly evolving features, whilst simultaneously accumulating
detail of more slowly evolving regions over several consecutive frames. This
tiered super-sampling technique enables the reconstruction of video streams in
which both the resolution and the effective exposure-time spatially vary and
adapt dynamically in response to the evolution of the scene. The methods
described here can complement existing compressive sensing approaches and may
be applied to enhance a variety of computational imagers that rely on
sequential correlation measurements.Comment: 13 pages, 5 figure
Changing patterns in electroweak precision with new color-charged states: Oblique corrections and the boson mass
The recent measurement by the CDF Collaboration of the boson mass is in
significant tension with the Standard Model expectation, showing a discrepancy
of seven standard deviations. A larger value of affects the global
electroweak fit, particularly the best-fit values of the Peskin-Takeuchi
parameters , (and perhaps ) that measure oblique corrections from new
physics. To meet this challenge, we propose some simple models capable of
generating non-negative and , the latter of which faces the greatest
upward pressure from the CDF measurement in scenarios with . Our models
feature weak multiplets of scalars charged under , which cannot attain nonzero vacuum expectation values
but nevertheless produce e.g. given some other mechanism to split
the electrically charged and neutral scalars. We compute the oblique
corrections in these models and identify ample parameter space supporting the
CDF value of .Comment: 27 pages, 4 figure
Temporal inabilities and decision-making capacity in depression
We report on an interview-based study of decision-making capacity in two classes of patients suffering from depression. Developing a method of second-person hermeneutic phenomenology, we articulate the distinctive combination of temporal agility and temporal inability characteristic of the experience of severely depressed patients. We argue that a cluster of decision-specific temporal abilities is a critical element of decision-making capacity, and we show that loss of these abilities is a risk factor distinguishing severely depressed patients from mildly/moderately depressed patients. We explore the legal and clinical consequences of this result
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