7,784 research outputs found
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
Setting UBVRI Photometric Zero-Points Using Sloan Digital Sky Survey ugriz Magnitudes
We discuss the use of Sloan Digital Sky Survey (SDSS) ugriz point-spread
function (PSF) photometry for setting the zero points of UBVRI CCD images. From
a comparison with the Landolt (1992) standards and our own photometry we find
that there is a fairly abrupt change in B, V, R, & I zero points around g, r, i
~ 14.5, and in the U zero point at u ~ 16. These changes correspond to where
there is significant interpolation due to saturation in the SDSS PSF fluxes.
There also seems to be another, much smaller systematic effect for stars with
g, r > 19.5. The latter effect is consistent with a small Malmquist bias.
Because of the difficulties with PSF fluxes of brighter stars, we recommend
that comparisons of ugriz and UBVRI photometry should only be made for
unsaturated stars with g, r and i in the range 14.5 - 19.5, and u in the range
16 - 19.5. We give a prescription for setting the UBVRI zero points for CCD
images, and general equations for transforming from ugriz to UBVRI.Comment: 13 pages. 6 figures. Accepted for publication in the Astronomical
Journa
A Photometric Technique to Search for Be Stars in Open Clusters
We describe a technique to identify Be stars in open clusters using Stromgren
b, y, and narrow-band Halpha photometry. We first identify the B-type stars of
the cluster using a theoretical isochrone fit to the (b-y, y) color-magnitude
diagram. The strongest Be stars are easily identified in a (b-y, y-Halpha)
color-color diagram, but those with weaker Halpha emission (classified as
possible Be star detections) may be confused with evolved or foreground stars.
Here we present such photometry plus Halpha spectroscopy of members of the
cluster NGC 3766 to demonstrate the accuracy of our technique. Statistical
results on the relative numbers of Be and B-type stars in additional clusters
will be presented in a future paper.Comment: 15 pages, 6 figures, 1 table. Accepted by Ap
Data Analysis Techniques for Fan Performance in Highly-Distorted Flows from Boundary Layer Ingesting Inlets
The design of a unique distortion-tolerant fan for a high-bypass ratio boundary-layer ingesting propulsion system has been completed and a rig constructed and tested in the NASA Glenn 8x6 wind tunnel. Processing the data from the experiment presented some interesting challenges because of the complexity of the experimental setup and the flow through the test rig. The experiment was run in three phases, each of which employed a unique complement of inlet throat and fan face instrumentation to avoid the blockage that would have resulted from simultaneously installing all of the rakes. The measurement from the individual test points were subsequently combined to compute the overall stage performance. A CFD model of the experiment was used to gain understanding of the flow field and to test some of the techniques proposed for interpolating and extrapolating the measurements into regions where measurements were not made. This capability became extremely useful when it was discovered that there was an unexpected total temperature distortion in the tunnel. The CFD model was modified by inserting a total temperature profile at the upstream boundary that mimicked the measured distortion where measurements were available and that CFD solution was used to investigate methods to infer the complete total temperature field at the fan face
Spectral identification and quantification of salts in the Atacama Desert
This work was part-funded by a Research Incentive Grant from The Carnegie Trust (REF: 70335) and a Royal Society of Edinburgh Research Fellowship to C. Cousins. J, Harris acknowledges funding from STFC (consolidated grant ST/N000528/1).Salt minerals are an important natural resource. The ability to quickly and remotely identify and quantify salt deposits and salt contaminated soils and sands is therefore a priority goal for the various industries and agencies that utilise salts. The advent of global hyperspectral imagery from instruments such as Hyperion on NASA’s Earth-Observing 1 satellite has opened up a new source of data that can potentially be used for just this task. This study aims to assess the ability of Visible and Near Infrared (VNIR) spectroscopy to identify and quantify salt minerals through the use of spectral mixture analysis. The surface and near-surface soils of the Atacama Desert in Chile contain a variety of well-studied salts, which together with low cloud coverage, and high aridity, makes this region an ideal testbed for this technique. Two forms of spectral data ranging 0.35 – 2.5 μm were collected: laboratory spectra acquired using an ASD FieldSpec Pro instrument on samples from four locations in the Atacama desert known to have surface concentrations of sulfates, nitrates, chlorides and perchlorates; and images from the EO-1 satellite’s Hyperion instrument taken over the same four locations. Mineral identifications and abundances were confirmed using quantitative XRD of the physical samples. Spectral endmembers were extracted from within the laboratory and Hyperion spectral datasets and together with additional spectral library endmembers fed into a linear mixture model. The resulting identification and abundances from both dataset types were verified against the sample XRD values. Issues of spectral scale, SNR and how different mineral spectra interact are considered, and the utility of VNIR spectroscopy and Hyperion in particular for mapping specific salt concentrations in desert environments is established. Overall, SMA was successful at estimating abundances of sulfate minerals, particularly calcium sulfate, from both hyperspectral image and laboratory sample spectra, while abundance estimation of other salt phase spectral end-members was achieved with a higher degree of error.Publisher PD
A Possible Massive Asteroid Belt Around zeta Lep
We have used the Keck I telescope to image at 11.7 microns and 17.9 microns
the dust emission around zeta Lep, a main sequence A-type star at 21.5 pc from
the Sun with an infrared excess. The excess is at most marginally resolved at
17.9 microns. The dust distance from the star is probably less than or equal to
6 AU, although some dust may extend to 9 AU. The mass of observed dust is
\~10^22 g. Since the lifetime of dust particles is about 10,000 years because
of the Poytning-Robertson effect, we robustly estimate at least 4 10^26 g must
reside in parent bodies which may be asteroids if the system is in a steady
state and has an age of ~300 Myr. This mass is approximately 200 times that
contained within the main asteroid belt in our solar system.Comment: 12 pages, 3 figures, ApJL in pres
The Stellar Populations in the Outer Regions of M33. I. Metallicity Distribution Function
We present deep CCD photometry in the VI passbands using the WIYN 3.5m
telescope of a field located approximately 20' southeast of the center of M33;
this field includes the region studied by Mould & Kristian in their 1986 paper.
The color-magnitude diagram (CMD) extends to I~25 and shows a prominent red
giant branch (RGB), along with significant numbers of asymptotic giant branch
and young main sequence stars. The red clump of core helium burning stars is
also discernable near the limit of our CMD. The I-band apparent magnitude of
the red giant branch tip implies a distance modulus of (m-M)_I = 24.77 +/-
0.06, which combined with an adopted reddening of E(V-I)=0.06 +/- 0.02 yields
an absolute modulus of (m-M)_0 = 24.69 +/- 0.07 (867 +/- 28 kpc) for M33. Over
the range of deprojected radii covered by our field (~8.5 to ~12.5 kpc), we
find a significant age gradient with an upper limit of ~1 Gyr (~0.25 Gyr/kpc).
Comparison of the RGB photometry to empirical giant branch sequences for
Galactic globulars allows us to use the dereddened color of these stars to
construct a metallicity distribution function (MDF). The primary peak in the
MDF is at a metallicity of [Fe/H] ~ -1.0 with a tail to lower abundances. The
peak does show radial variation with a slope of d[Fe/H]/dR_{deproj} = -0.06 +/-
0.01 dex/kpc. This gradient is consistent with the variation seen in the inner
disk regions of M33. As such, we conclude that the vast majority of stars in
this field belong to the disk of M33, not the halo as previously thought.Comment: 34 pages, 13 figures, accepted to The Astronomical Journal, July
2004, high resolution version available at
ftp://www.astro.ufl.edu/pub/ata/sarajedini_m33.pd
Including Systematic Uncertainties in Confidence Interval Construction for Poisson Statistics
One way to incorporate systematic uncertainties into the calculation of
confidence intervals is by integrating over probability density functions
parametrizing the uncertainties. In this note we present a development of this
method which takes into account uncertainties in the prediction of background
processes, uncertainties in the signal detection efficiency and background
efficiency and allows for a correlation between the signal and background
detection efficiencies. We implement this method with the Feldman & Cousins
unified approach with and without conditioning. We present studies of coverage
for the Feldman & Cousins and Neyman ordering schemes. In particular, we
present two different types of coverage tests for the case where systematic
uncertainties are included. To illustrate the method we show the relative
effect of including systematic uncertainties the case of dark matter search as
performed by modern neutrino tel escopes.Comment: 23 pages, 10 figures, replaced to match published versio
Measuring Researcher-Production in Information Systems
While many studies have assessed IS researcher-production, most have focused on either ranking IS journals or assessing prolific researchers using a restricted time frame and a small inbasketld of journals (i.e., those journals selected for sampling). We found no research that has assessed the IS specificity of journals (i.e., the suitability of journals for publishing IS research) nor any that evaluated IS researcher-production measures. Based on a coding of over 26,000 articles and more than 1,900 authors, this study attempts such an evaluation by (1) determining the rate of publication of IS researchers in 58 journals perceived by at least one IS institution as IS specific, (2) profiling prolific and typical IS researchers using descriptive statistics, (3) evaluating the convergent validity of various researcher-production measures, (4) assessing the reliability of these researcher-production measures by varying baskets of Measuring Researcher-Production in Information Systems by C. Chua, L. Cao, K. Cousins, and D. W. Straub journals and time periods, and (5) comparing the sensitivity of measures across prolific and typical researchers. The study demonstrates that many journals perceived to be of high quality by IS researchers are not specifically targeted to information systems. Changing the evaluation procedure has a significant impact on measures of typical and prolific IS researchers. For typical IS researchers, measures of production are strongly convergent and are not sensitive to changes in journal baskets. However, for prolific researchers, measures of production are not convergent and highly sensitive to changes in journal baskets. The evaluation of both prolific and typical IS researchers is also highly sensitive to temporal effects. The differences in convergent validity and reliability demonstrate that prolific researchers are more sensitive to minor variations in the assessment procedure. Based on the empirical findings, the study closes with recommendations both for the evaluation of researcher-production and for developing institutional target journal lists, i.e., lists of journals viewed favorably by an institution
Improved to Transformation Equations for Main Sequence Stars
We report improved transformation equations between the and
photometric systems. Although the details of the transformations
depend on luminosity class, we find a typical rms scatter on the order of 0.001
magnitude if the sample is limited to main sequence stars. Furthermore, we find
an accurate transformation requires complex, multi-color dependencies for the
bluer bandpasses. Results for giant stars will be reported in a subsequent
paper.Comment: 7 pages, 8 figure
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