9,356 research outputs found
Photoheliograph requirements for a spectrograph, November 1967 - June 1968
Preliminary design requirements and constraints for ATM photoheliograp
Transient localization in the kicked Rydberg atom
We investigate the long-time limit of quantum localization of the kicked
Rydberg atom. The kicked Rydberg atom is shown to possess in addition to the
quantum localization time a second cross-over time where quantum
dynamics diverges from classical dynamics towards increased instability. The
quantum localization is shown to vanish as either the strength of the kicks at
fixed principal quantum number or the quantum number at fixed kick strength
increases. The survival probability as a function of frequency in the transient
localization regime is characterized by highly irregular,
fractal-like fluctuations
PANIC: A Near-infrared Camera for the Magellan Telescopes
PANIC (Persson's Auxiliary Nasmyth Infrared Camera) is a near-infrared camera
designed to operate at any one of the f/11 folded ports of the 6.5m Magellan
telescopes at Las Campanas Observatory, Chile. The instrument is built around a
simple, all-refractive design that reimages the Magellan focal plane to a plate
scale of 0.125'' pixel^{-1} onto a Rockwell 1024x1024 HgCdTe detector. The
design goals for PANIC included excellent image quality to sample the superb
seeing measured with the Magellan telescopes, high throughput, a relatively
short construction time, and low cost. PANIC has now been in regular operation
for over one year and has proved to be highly reliable and produce excellent
images. The best recorded image quality has been ~0.2'' FWHM.Comment: 8 pages, 5 figures. To appear in "Astronomical Telescopes and
Instrumentation," Proc SPIE (Glasgow), June 2004. Version with higher
resolution figures is available at
http://cfa-www.harvard.edu/~pmartini/professional/publications/panic.pd
The luminosity function of the brightest galaxies in the IRAS survey
Results from a study of the far infrared properties of the brightest galaxies in the IRAS survey are described. There is a correlation between the infrared luminosity and the infrared to optical luminosity ratio and between the infrared luminosity and the far infrared color temperature in these galaxies. The infrared bright galaxies represent a significant component of extragalactic objects in the local universe, being comparable in space density to the Seyferts, optically identified starburst galaxies, and more numerous than quasars at the same bolometric luminosity. The far infrared luminosity in the local universe is approximately 25% of the starlight output in the same volume
Extremely red objects in the fields of high redshift radio galaxies
We are engaged in a program of infrared imaging photometry of high redshift radio galaxies. The observations are being done using NICMOS2 and NICMOS3 arrays on the DuPont 100-inch telescope at Las Campanas Observatory. In addition, Persson and Matthews are measuring the spectral energy distributions of normal cluster galaxies in the redshift range 0 to 1. These measurements are being done with a 58 x 62 InSb array on the Palomar 5-m telescope. During the course of these observations we have imaged roughly 20 square arcminutes of sky to limiting magnitudes greater than 20 in the J, H, and K passbands (3 sigma in 3 square arcseconds). We have detected several relatively bright, extremely red, extended objects during the course of this work. Because the radio galaxy program requires Thuan-Gunn gri photometry, we are able to construct rough photometric energy distributions for many of the objects. A sample of the galaxy magnitudes within 4 arcseconds diameter is given. All the detections are real; either the objects show up at several wavelengths, or in subsets of the data. The reddest object in the table, 9ab'B' was found in a field of galaxies in a rich cluster at z = 0.4; 9ab'A' lies 8 arcseconds from it
Phase rigidity and avoided level crossings in the complex energy plane
We consider the effective Hamiltonian of an open quantum system, its
biorthogonal eigenfunctions and define the value that characterizes the
phase rigidity of the eigenfunctions . In the scenario with
avoided level crossings, varies between 1 and 0 due to the mutual
influence of neighboring resonances. The variation of may be
considered as an internal property of an {\it open} quantum system. In the
literature, the phase rigidity of the scattering wave function
is considered. Since can be represented in the interior
of the system by the , the phase rigidity of the
is related to the and therefore also to the mutual
influence of neighboring resonances. As a consequence, the reduction of the
phase rigidity to values smaller than 1 should be considered, at least
partly, as an internal property of an open quantum system in the overlapping
regime. The relation to measurable values such as the transmission through a
quantum dot, follows from the fact that the transmission is, in any case,
resonant with respect to the effective Hamiltonian. We illustrate the relation
between phase rigidity and transmission numerically for small open
cavities.Comment: 6 pages, 3 figure
Theory of friction: contribution from fluctuating electromagnetic field
We calculate the friction force between two semi-infinite solids in relative
parallel motion (velocity ), and separated by a vacuum gap of width . The
friction force result from coupling via a fluctuating electromagnetic field,
and can be considered as the dissipative part of the van der Waals interaction.
We consider the dependence of the friction force on the temperature , and
present a detailed discussion of the limiting cases of small and large and
.Comment: 15 pages, No figure
Casimir attractive-repulsive transition in MEMS
Unwanted stiction in micro- and nanomechanical (NEMS/MEMS) systems due to
dispersion (van der Waals, or Casimir) forces is a significant hurdle in the
fabrication of systems with moving parts on these length scales. Introducing a
suitably dielectric liquid in the interspace between bodies has previously been
demonstrated to render dispersion forces repulsive, or even to switch sign as a
function of separation. Making use of recently available permittivity data
calculated by us we show that such a remarkable non-monotonic Casimir force,
changing from attractive to repulsive as separation increases, can in fact be
observed in systems where constituent materials are in standard NEMS/MEMS use
requiring no special or exotic materials. No such nonmonotonic behaviour has
been measured to date. We calculate the force between a silica sphere and a
flat surface of either zinc oxide or hafnia, two materials which are among the
most prominent for practical microelectrical and microoptical devices. Our
results explicate the need for highly accurate permittivity functions of the
materials involved for frequencies from optical to far-infrared frequencies. A
careful analysis of the Casimir interaction is presented, and we show how the
change in the sign of the interaction can be understood as a result of multiple
crossings of the dielectric functions of the three media involved in a given
set-up.Comment: 6 pages, 4 figure
Distant radio galaxies in the near IR
We are carrying out a program of near IR imaging and spectroscopy of radio galaxies with redshifts of 1.5 and greater. One of its principal goals is to constrain the ages and star formation histories of massive galaxies at early epochs. The radio galaxies are drawn from the survey of 1Jy class sources by McCarthy et al (1989) and McCarthy (1990). The sample contains 18 radio galaxies with redshifts greater than 2 and an additional 10 objects with 1.5 less than z less than 2.0. The redshifts were obtained from long slit spectra with the CTIO 4 m. While the galaxies are quite faint (r approximately = 21-24.5) all have Lyman alpha emission with rest frame equivalent widths of 100 - 1000 A. Multicolor photometry in the g,r,i and J,H,K bands has been obtained with the 2.5-m Du Pont Telescope on Las Campanas and with the Hale 5 m telescope at Palomar. We have recently obtained near IR spectra, using the 4 m telescopes at KPNO and CTIO, of a few objects with the goal of determining the Lyman alpha/H-alpha ratio and hence the reddening
The Y-Band at 1.035 um: Photometric Calibration and the Dwarf Stellar/Sub-Stellar Color Sequence
We define and characterize a photometric bandpass (called "Y") that is
centered at 1.035 um, in between the traditionally classified ``optical'' and
``infrared'' spectral regimes. We present Y magnitudes and Y-H and Y-K colors
for a sample consisting mostly of photometric and spectral standards, spanning
the spectral type range sdO to T5V. Deep molecular absorption features in the
near-infrared spectra of extremely cool objects are such that the Y-H and Y-K
colors grow rapidly with advancing spectral type especially from late M through
mid L, substantially more rapidly than J-H or H-K which span a smaller total
dynamic range. Consistent with other near-infrared colors, however, Y-H and Y-K
colors turn blueward in the L6-L8 temperature range with later T-type objects
having colors similar to those of warmer M and L stars. Use of the Y-band
filter is nonetheless promising for easy identification of low-mass stars and
brown dwarfs, especially at young ages. The slope of the interstellar reddening
vector within this filter is A_Y = 0.38 x A_V. Reddening moves stars nearly
along the YHK dwarf color sequence making it more difficult to distinguish
unambiguously very low mass candidate brown dwarf objects from higher mass
stars seen, e.g. through the galactic plane or towards star-forming regions.
Other diagrams involving the Y-band may be somewhat more discriminating.Comment: accepted at PAS
- …