2,805 research outputs found
The Palomar 200-inch f/9 Cassegrain CCD camera
This article describes the design and construction of a CCD camera for the f/9 Cassegrain focus of the 200-inch (5m) Hale Telescope at Palomar Observatory. This instrument utilizes a set of 18-inch (0.45m) diameter lenses to change the Cassegrain focal ratio from f/16 to f/9, and the optical design prescription of these lenses is reported. For CCDs having 24 micrometers pixels, the f/9 focus gives a reciprocal plate scale of 9 pixels per arcsecond, which is well suited to precision photometry as well as future application to adaptive optics. In addition to the CCD and shutter, the instrument also incorporates an offset guider and an 8-position filter wheel
Design of a high-speed UV-transmitting camera for the Keck LRIS
Preliminary optical designs have been developed for the blue channel of the Low Resolution Imaging Spectrograph (LRIS) for the Keck Ten Meter Telescope. This paper discusses the configuration- driving factors and performance of the designs, as well as coating and fabrication issues
The Palomar 200-inch f/9 Cassegrain CCD camera
This article describes the design and construction of a CCD camera for the f/9 Cassegrain focus of the 200-inch (5m) Hale Telescope at Palomar Observatory. This instrument utilizes a set of 18-inch (0.45m) diameter lenses to change the Cassegrain focal ratio from f/16 to f/9, and the optical design prescription of these lenses is reported. For CCDs having 24 micrometers pixels, the f/9 focus gives a reciprocal plate scale of 9 pixels per arcsecond, which is well suited to precision photometry as well as future application to adaptive optics. In addition to the CCD and shutter, the instrument also incorporates an offset guider and an 8-position filter wheel
Striking Photospheric Abundance Anomalies in Blue Horizontal-Branch Stars in Globular Cluster M13
High-resolution optical spectra of thirteen blue horizontal-branch (BHB)
stars in the globular cluster M13 show enormous deviations in element
abundances from the expected cluster metallicity. In the hotter stars (T_eff >
12000 K), helium is depleted by factors of 10 to 100 below solar, while iron is
enhanced to three times the solar abundance, two orders of magnitude above the
canonical metallicity [Fe/H] ~= -1.5 dex for this globular cluster. Nitrogen,
phosphorus, and chromium exhibit even more pronounced enhancements, and other
metals are also mildly overabundant, with the exception of magnesium, which
stays very near the expected cluster metallicity. These photospheric anomalies
are most likely due to diffusion --- gravitational settling of helium, and
radiative levitation of the other elements --- in the stable radiative
atmospheres of these hot stars. The effects of these mechanisms may have some
impact on the photometric morphology of the cluster's horizontal branch and on
estimates of its age and distance.Comment: 11 pages, 1 Postscript figure, uses aaspp4.sty, accepted for
publication in ApJ Letter
Counts and Colors of Faint Galaxies in the U and R Bands
Ground-based counts and colors of faint galaxies in the U and R bands in one
field at high Galactic latitude are presented. Integrated over flux, a total of
1.2x10^5 sources per square degree are found to U=25.5 mag and 6.3x10^5 sources
per square degree to R=27 mag, with d log N/dm ~ 0.5 in the U band and d log
N/dm ~ 0.3 in the R band. Consistent with these number-magnitude curves,
sources become bluer with increasing magnitude to median U-R=0.6 mag at 24<U<25
mag and U-R=1.2 mag at 25 < R < 26 mag. Because the Lyman break redshifts into
the U band at z~3, at least 1.2x10^5 sources per square degree must be at
redshifts z<3. Measurable U-band fluxes of 73 percent of the 6.3x10^5 sources
per square degree suggest that the majority of these also lie at z < 3. These
results require an enormous space density of objects in any cosmological model.Comment: 17 pages, MNRAS in pres
Rotations and Abundances of Blue Horizontal-Branch Stars in Globular Cluster M15
High-resolution optical spectra of eighteen blue horizontal-branch (BHB)
stars in the globular cluster M15 indicate that their stellar rotation rates
and photospheric compositions vary strongly as a function of effective
temperature. Among the cooler stars in the sample, at Teff ~ 8500 K, metal
abundances are in rough agreement with the canonical cluster metallicity, and
the v sin i rotations appear to have a bimodal distribution, with eight stars
at v sin i < 15 km/s and two stars at v sin i ~ 35 km/s. Most of the stars at
Teff > 10000 K, however, are slowly rotating, v sin i < 7 km/s, and their iron
and titanium are enhanced by a factor of 300 to solar abundance levels.
Magnesium maintains a nearly constant abundance over the entire range of Teff,
and helium is depleted by factors of 10 to 30 in three of the hotter stars.
Diffusion effects in the stellar atmospheres are the most likely explanation
for these large differences in composition. Our results are qualitatively very
similar to those previously reported for M13 and NGC 6752, but with even larger
enhancement amplitudes, presumably due to the increased efficiency of radiative
levitation at lower intrinsic [Fe/H]. We also see evidence for faster stellar
rotation explicitly preventing the onset of the diffusion mechanisms among a
subset of the hotter stars.Comment: 11 pages, 1 figure, 1 table, accepted to ApJ
Results from Solar Reflective Band End-to-End Testing for VIIRS F1 Sensor Using T-SIRCUS
Verification of the Visible Infrared Imager Radiometer Suite (VIIRS) End-to-End (E2E) sensor calibration is highly recommended before launch, to identify any anomalies and to improve our understanding of the sensor on-orbit calibration performance. E2E testing of the Reflective Solar Bands (RSB) calibration cycle was performed pre-launch for the VIIRS Fight 1 (F1) sensor at the Ball Aerospace facility in Boulder CO in March 2010. VIIRS reflective band calibration cycle is very similar to heritage sensor MODIS in that solar illumination, via a diffuser, is used to correct for temporal variations in the instrument responsivity. Monochromatic light from the NIST T-SIRCUS was used to illuminate both the Earth View (EV), via an integrating sphere, and the Solar Diffuser (SD) view, through a collimator. The collimator illumination was cycled through a series of angles intended to simulate the range of possible angles for which solar radiation will be incident on the solar attenuation screen on-orbit. Ideally, the measured instrument responsivity (defined here as the ratio of the detector response to the at-sensor radiance) should be the same whether the EV or SD view is illuminated. The ratio of the measured responsivities was determined at each collimator angle and wavelength. In addition, the Solar Diffuser Stability Monitor (SDSM), a ratioing radiometer designed to track the temporal variation in the SD BRF by direct comparison to solar radiation, was illuminated by the collimator. The measured SDSM ratio was compared to the predicted ratio. An uncertainty analysis was also performed on both the SD and SDSM calibrations
An Analysis of Genetic Diversity and Inbreeding in Wuchereria bancrofti: Implications for the Spread and Detection of Drug Resistance
Estimates of genetic diversity in helminth infections of humans often have to rely on genotyping (immature) parasite transmission stages instead of adult worms. Here we analyse the results of one such study investigating a single polymorphic locus (a change at position 200 of the β-tubulin gene) in microfilariae of the lymphatic filarial parasite Wuchereria bancrofti. The presence of this genetic change has been implicated in benzimidazole resistance in parasitic nematodes of farmed ruminants. Microfilariae were obtained from patients of three West African villages, two of which were sampled prior to the introduction of mass drug administration. An individual-based stochastic model was developed showing that a wide range of allele frequencies in the adult worm populations could have generated the observed microfilarial genetic diversity. This suggests that appropriate theoretical null models are required in order to interpret studies that genotype transmission stages. Wright's hierarchical F-statistic was used to investigate the population structure in W. bancrofti microfilariae and showed significant deficiency of heterozygotes compared to the Hardy-Weinberg equilibrium; this may be partially caused by a high degree of parasite genetic differentiation between hosts. Studies seeking to quantify accurately the genetic diversity of helminth populations by analysing transmission stages should increase their sample size to account for the variability in allele frequency between different parasite life-stages. Helminth genetic differentiation between hosts and non-random mating will also increase the number of hosts (and the number of samples per host) that need to be genotyped, and could enhance the rate of spread of anthelmintic resistance
Spectral variability of the binary HR 4049
The H profile varies with the orbital period. The two strong shell
type emission peaks are identified as from one single broad emission feature
with an absorption centered around -7.5~\kms. The intensity variations are
largely attributed to a differential amount of reddening towards the H
emitting region and the stellar continuum. The radial velocities suggest that
the H emission moves in phase with the primary, but with a slightly
lower velocity amplitude.
We propose two competing models that could account for the observed velocity
and intensity variations of the H profile. Model I: light from the
primary reflects on a localized spot near the inner radius of the circumbinary
disc which is closest to the primary. Model II: H emission originates
in the outer layers of the extended atmosphere of the primary due to activity.
These activities are locked to the position of the primary in its orbit.
We discuss the similarities of variability and shape of the H
emission of HR~4049 with those of early type T-Tauri stars (e.g SU~Aur).Comment: 14 pages + 8 pages appendix, 17 figures, 4 tables A&A accepte
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