The Photometry of Undersampled Point Spread Functions

An undersampled point spread function may interact with the microstructure of a solid-state detector such that the total flux detected can depend sensitively on where the PSF center falls within a pixel. Such intra-pixel sensitivity variations will not be corrected by flat field calibration and may limit the accuracy of stellar photometry conducted with undersampled images, as are typical for Hubble Space Telescope observations. The total flux in a stellar image can vary by up to 0.03 mag in F555W WFC images depending on how it is sampled, for example. For NIC3, these variations are especially strong, up to 0.39 mag, strongly limiting its use for stellar photometry. Intra-pixel sensitivity variations can be corrected for, however, by constructing a well-sampled PSF from a dithered data set. The reconstructed PSF is the convolution of the optical PSF with the pixel response. It can be evaluated at any desired fractional pixel location to generate a table of photometric corrections as a function of relative PSF centroid. A caveat is that the centroid of an undersampled PSF can also be affected by the pixel response function, thus sophisticated centroiding methods, such as cross-correlating the observed PSF with its fully-sampled counterpart, are required to derive the proper photometric correction.Comment: 20 pages, 14 postscript figures, submitted to the PAS

Effect of aluminum substitution on the reflectance spectra of hematite

Hematite and aluminous hematite were synthesized and the diffuse reflectance spectra were recorded for the region between 0.35 and 1.20 microns. Results show that the near-IR based minimum for the aluminous hematite is shifted longward by about 0.02 microns and is much more shallow. Also, the aluminous specimen is considerably more reflective shortward of approximately 0.55 microns where the ferritic specimen is strongly absorbing. This is noteworthy since the visible slope and the red shoulder are often used in the construction of false color and band ratio images

General Hospitals, Specialty Hospitals and Financially Vulnerable Patients

Examines whether specialty hospitals draw well-insured patients away from general and safety-net hospitals, reducing their ability to cross-subsidize less profitable services and uncompensated care, in three cities. Notes challenges and implications

Reliability of the O\u27Connor Block Test

The O\u27Connor Block test is widely known and is manufactured and sold without any very definite information as to its reliability and validity. In fact it seems to be used without great uniformity in method of administration. Whenever mechanical ability is discussed one is likely to hear of this test along with several others. No published studies of the O\u27Connor Block test of any great importance have been made on its relative merits and its reliability and validity. Several years ago exploratory studies on this test, along with others designed to measure mechanical aptitude and ingenuity, were conducted in the Driving Laboratory at Iowa State College. Various mechanical tests were used to ascertain their possible relation to driving. Although the O\u27Connor Block Test seems to be looked upon with some askance in some quarters, it did seem to screen out persons who would require considerable extra attention while learning to drive. This cue was followed up still further and a study using the O\u27Connor test was reported by Miller and Lauer (1946). A low positive correlation with driving performance was obtained but the subjects were largely Orientals and their driving performance rather irregular. Also there was some question as to the reliability of the test

Bremsstrahlung in alpha-Decay Reexamined

A high-statistics measurement of bremsstrahlung emitted in the alpha decay of 210Po has been performed, which allows to follow the photon spectra up to energies of ~ 500 keV. The measured differential emission probability is in good agreement with our theoretical results obtained within the quasi classical approximation as well as with the exact quantum mechanical calculation. It is shown that due to the small effective electric dipole charge of the radiating system a significant interference between the electric dipole and quadrupole contributions occurs, which is altering substantially the angular correlation between the alpha particle and the emitted photon.Comment: 10 pages, 5 figures, v2: fix of small typo

Are radio galaxies and quiescent galaxies different? Results from the analysis of HST brightness profiles

We present a study of the optical brightness profiles of early type galaxies, using a number of samples of radio galaxies and optically selected elliptical galaxies. For the radio galaxy samples--B2 of Fanaroff-Riley type I and 3C of Fanaroff-Riley type II-- we determined a number of parameters that describe a "Nuker-law" profile, which were compared with those already known for the optically selected objects. We find that radio active galaxies are always of the "core" type (i.e. an inner Nuker law slope gamma < 0.3). However, there are core-type galaxies which harbor no significant radio source and which are indistinguishable from the radio active galaxies. We do not find any radio detected galaxy with a power law profile (gamma > 0.5). This difference is not due to any effect with absolute magnitude, since in a region of overlap in magnitude the dichotomy between radio active and radio quiescent galaxies remains. We speculate that core-type objects represent the galaxies that have been, are, or may become, radio active at some stage in their lives; active and non-active core-type galaxies are therefore identical in all respects except their eventual radio-activity: on HST scales we do not find any relationship between boxiness and radio-activity. There is a fundamental plane, defined by the parameters of the core (break radius r_b and break brightness mu_b), which is seen in the strong correlation between r_b and mu_b. The break radius is also linearly proportional to the optical Luminosity in the $I$ band. Moreover, for the few galaxies with an independently measured black hole mass, the break radius turns out to be tightly correlated with M_{BH}. The black hole mass correlates even better with the combination of fundamental plane parameters r_b and mu_b, which represents the central velocity dispersion.Comment: Accepted for publication in A&A, 20 Pages, 9 figure

An integrated study of earth resources in the State of California based on ERTS-1 and supporting aircraft data

There are no author-identified significant results in this report

M32+/-1

WFPC-2 images are used to study the central structure of M31, M32, and M33. The dimmer peak, P2, of the M31 double nucleus is centered on the bulge to 0.1", implying that it is the dynamical center of M31. P2 contains a compact source discovered by King et al. (1995) at 1700 A. This source is resolved, with r_{1/2} approx0.2 pc. It dominates the nucleus at 3000 A, and is consistent with late B-early A stars. This probable cluster may consist of young stars and be an older version of the cluster of hot stars at the center of the Milky Way, or it may consist of heavier stars built up from collisions in a possible cold disk of stars orbiting P2. In M32, the central cusp rises into the HST limit with gamma approx0.5, and the central density rho_0>10^7M_sol pc^-3. The V-I and U-V color profiles are flat, and there is no sign of an inner disk, dust, or any other structure. This total lack of features seems at variance with a nominal stellar collision time of 2 X 10^10 yr, which implies that a significant fraction of the light in the central pixel should come from blue stragglers. InM33, the nucleus has an extremely steep gamma=1.49 power-law profile for 0.05"<r<0.2" that becomes shallower as the HST resolution limit is approached. The profile for r<0.04" has either a gamma approx 0.8 cusp or a small core with r_c ~<0.13 pc. The central density is rho_0 > 2 10^6M_sol pc^-3, and the implied relaxation time is only ~3 X 10^6 yr, indicating that the nucleus is highly relaxed. The accompanying short collision time of 7 X 10^9 yr predicts a central blue straggler component quantitatively consistent with the strong V-I and B-R color gradients seen with HST and from the ground.Comment: 44 pages, 22 figures (7 as separate JPEG images), submitted to The Astronomical Journal. Full postscript image available at http://www.noao.edu/noao/staff/lauer/lauer_paper

Terrestrial impact melts as analogues for the hematization of Martian surface materials

Visible and near-IR reflectivity and Mossbauer data were obtained on powders of hydrothermally-altered impact melt sheets from West Clearwater Lake, Manicouagan, and Ries (Polsingen) impact structures. The data support previous interpretations that Martian bright regions spectra can be interpreted by a ferric-bearing phase that has a relatively featureless absorption edge together with some well-crystalline (bulk) hematite to account for the 860 nm hematite band. The data also show that bands at wavelengths longer than 900 nm, which are characteristic of Martian dark regions, occur when both hematite and pyroxene are present. It thus follows that hematization of Mars can be attributed, at least in part, to hydrothermal alterations of impact melt sheets. Impact heating could also form bulk-Hm from nanophase ferric oxides