13,909 research outputs found
Spectral Variations in Early-Type Galaxies as a Function of Mass
We report on the strengths of three spectral indicators - Mg_2, Hbeta, and
Hn/Fe - in the integrated light of a sample of 100 field and cluster E/S0
galaxies. The measured indices are sensitive to age and/or and metallicity
variations within the galaxy sample. Using linear regression analysis for data
with non-uniform errors, we determine the intrinsic scatter present among the
spectral indices of our galaxy sample as a function of internal velocity
dispersion. Our analysis indicates that there is significantly more intrinsic
scatter in the two Balmer line indices than in the Mg_2 index, indicating that
the Balmer indices provide more dynamic range in determining the age of a
stellar population than does the Mg_2 index. Furthermore, the scatter is much
larger for the low velocity dispersion galaxies, indicating that star formation
has occurred more recently in the lower mass galaxies.Comment: 4 pages, 1 figure, 1 table, to appear in the Astrophysical Journal
Letter
The Limits of Quintessence
We present evidence that the simplest particle-physics scalar-field models of
dynamical dark energy can be separated into distinct behaviors based on the
acceleration or deceleration of the field as it evolves down its potential
towards a zero minimum. We show that these models occupy narrow regions in the
phase-plane of w and w', the dark energy equation-of-state and its
time-derivative in units of the Hubble time. Restricting an energy scale of the
dark energy microphysics limits how closely a scalar field can resemble a
cosmological constant. These results, indicating a desired measurement
resolution of order \sigma(w')\approx (1+w), define firm targets for
observational tests of the physics of dark energy.Comment: 4 pages, 2 figure
Experiment to evaluate feasibility of utilizing Skylab-EREP remote sensing data for tectonic analysis of the Bighorn Mountains region, Wyoming-Montana
There are no author-identified significant results in this report
Incorporation of privacy elements in space station design
Privacy exists to the extent that individuals can control the degree of social contact that they have with one another. The opportunity to withdraw from other people serves a number of important psychological and social functions, and is in the interests of safety, high performance, and high quality of human life. Privacy requirements for Space Station crew members are reviewed, and architectual and other guidelines for helping astronauts achieve desired levels of privacy are suggested. In turn, four dimensions of privacy are discussed: the separation of activities by areas within the Space Station, controlling the extent to which astronauts have visual contact with one another, controlling the extent to which astronauts have auditory contact with one another, and odor control. Each section presents a statement of the problem, a review of general solutions, and specific recommendations. The report is concluded with a brief consideration of how selection, training, and other procedures can also help Space Station occupants achieve satisfactory levels of seclusion
Spectrophotometry of nearby field galaxies: the data
We have obtained integrated and nuclear spectra, as well as U, B, R surface
photometry, for a representative sample of 196 nearby galaxies. These galaxies
span the entire Hubble sequence in morphological type, as well as a wide range
of luminosities (M_B=-14 to -22). Here we present the spectrophotometry for
these galaxies. The selection of the sample and the U, B, R surface photometry
is described in a companion paper (Paper I). Our goals for the project include
measuring the current star formation rates and metallicities of these galaxies,
and elucidating their star formation histories, as a function of luminosity and
morphology. We thereby extend the work of Kennicutt (1992a) to lower luminosity
systems. We anticipate that our study will be useful as a benchmark for studies
of galaxies at high redshift.
We describe the observing, data reduction and calibration techniques, and
demonstrate that our spectrophotometry agrees well with that of Kennicutt. The
spectra span the range 3550--7250 A at a resolution (FWHM) of ~6 A, and have an
overall relative spectrophotometric accuracy of +/- 6 per cent. We present a
spectrophotometric atlas of integrated and nuclear rest-frame spectra, as well
as tables of equivalent widths and synthetic colors.
We study the correlations of galaxy properties determined from the spectra
and images. Our findings include: (1) galaxies of a given morphological class
display a wide range of continuum shapes and emission line strengths if a broad
range of luminosities are considered, (2) emission line strengths tend to in-
crease and continua tend to get bluer as the luminosity decreases, and (3) the
scatter on the general correlation between nuclear and integrated H_alpha
emission line strengths is large.Comment: Accepted for publication in ApJS (scheduled for Vol.127, 2000 March);
63 pages, LateX, 9 figures and 6 tables included, a spectrophotometric atlas
is provided as GIF images, fig 1 as a JPEG image, in a single tar-file; a
full 600 dpi version is available at http://www.astro.rug.nl/~nfgs
The luminosity function of Palomar 5 and its tidal tails
We present the main sequence luminosity function of the tidally disrupted
globular cluster Palomar 5 and its tidal tails. For this work we analyzed
imaging data obtained with the Wide Field Camera at the INT (La Palma) and data
from the Wide Field Imager at the MPG/ESO 2.2 m telescope at La Silla down to a
limiting magnitude of approximately 24.5 mag in B. Our results indicate that
preferentially fainter stars were removed from the cluster so that the LF of
the cluster's main body exhibits a significant degree of flattening compared to
other GCs. This is attributed to its advanced dynamical evolution. The LF of
the tails is, in turn, enhanced with faint, low-mass stars, which we interpret
as a consequence of mass segregation in the cluster.Comment: 4 pages, 3 figures, to be published in the proceedings of the
conference "Satellites and tidal streams" held at La Palma, Canary Islands,
May 26 - 30, 200
Identification of photons in double beta-decay experiments using segmented germanium detectors - studies with a GERDA Phase II prototype detector
The sensitivity of experiments searching for neutrinoless double beta-decay
of germanium was so far limited by the background induced by external
gamma-radiation. Segmented germanium detectors can be used to identify photons
and thus reduce this background component.
The GERmanium Detector Array, GERDA, will use highly segmented germanium
detectors in its second phase. The identification of photonic events is
investigated using a prototype detector. The results are compared with Monte
Carlo data.Comment: 20 pages, 7 figures, to be submitted to NIM-
Pulse shape simulation for segmented true-coaxial HPGe detectors
A new package to simulate the formation of electrical pulses in segmented
true-coaxial high purity germanium detectors is presented. The computation of
the electric field and weighting potentials inside the detector as well as of
the trajectories of the charge carriers is described. In addition, the
treatment of bandwidth limitations and noise are discussed. Comparison of
simulated to measured pulses, obtained from an 18-fold segmented detector
operated inside a cryogenic test facility, are presented.Comment: 20 pages, 16 figure
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