4,348 research outputs found
The Impact of Contaminated RR Lyrae/Globular Cluster Photometry on the Distance Scale
RR Lyrae variables and the stellar constituents of globular clusters are
employed to establish the cosmic distance scale and age of the universe.
However, photometry for RR Lyrae variables in the globular clusters M3, M15,
M54, M92, NGC2419, and NGC6441 exhibit a dependence on the clustercentric
distance. For example, variables and stars positioned near the crowded
high-surface brightness cores of the clusters may suffer from photometric
contamination, which invariably affects a suite of inferred parameters (e.g.,
distance, color excess, absolute magnitude, etc.). The impetus for this study
is to mitigate the propagation of systematic uncertainties by increasing
awareness of the pernicious impact of contaminated and radial-dependent
photometry.Comment: To appear in ApJ
Use of combinatorial analysis for the study of new material for solar cells applications
This paper presents a combinatorial method for the deposition and
characterization of new metallic precursors for photovoltaic materials.
Onedimensional thin film alloy “libraries” were electrodeposited on Mo-coated
glass. The library elements were deposited in two consecutive baths and then
heated in a reducing atmosphere to promote interdiffusion of the elements. At
the end of this process, the libraries possessed a composition gradient along
their lengths, with single elements at their two opposite ends and one or more
alloys and/or a solid state solution in between. This continuous range of
compositions can therefore be considered a collection of specific precursors
that can be interrogated by examining their corresponding locations, with the
crystallographic structure along the library changing in accordance with the
phase diagram for the metals. The libraries were then sulphurised or selenised
by heating in a sulphur-rich or selenium rich atmosphere; this converted the
metallic precursors in a continuous range of materials, candidates for potential
solar cells absorbers. The libraries were analysed by X-ray diffraction and
energy dispersive X-ray spectrometry. The X-ray diffraction results show phase
changes across the libraries, which can be correlated with the original
precursor concentration at that particular p
Searching Beyond the Obscuring Dust Between the Cygnus-Aquila Rifts for Cepheid Tracers of the Galaxy's Spiral Arms
A campaign is described, open to participation by interested AAVSO members,
of follow-up observations for newly-discovered Cepheid variables in
undersampled and obscured regions of the Galaxy. A primary objective being to
use these supergiants to clarify the Galaxy's spiral nature. Preliminary
multiband photometric observations are presented for three Cepheids discovered
beyond the obscuring dust between the Cygnus & Aquila Rifts (40 \le l \le 50
degrees), a region reputedly tied to a segment of the Sagittarius-Carina arm
which appears to cease unexpectedly. The data confirm the existence of
exceptional extinction along the line of sight at upwards of A_V~6 magnitudes
(d~2 kpc, l~47 degrees), however, the noted paucity of optical spiral tracers
in the region does not arise solely from incompleteness owing to extinction. A
hybrid spiral map of the Galaxy comprised of classical Cepheids, young open
clusters & H II regions, and molecular clouds, presents a consistent picture of
the Milky Way and confirms that the three Cepheids do not populate the main
portion of the Sagittarius-Carina arm, which does not emanate locally from this
region. The Sagitarrius-Carina arm, along with other distinct spiral features,
are found to deviate from the canonical logarithmic spiral pattern. Revised
parameters are also issued for the Cepheid BY Cas, and it is identified on the
spiral map as lying mainly in the foreground to young associations in
Cassiopeia. A Fourier analysis of BY Cas' light-curve implies overtone
pulsation, and the Cepheid is probably unassociated with the open cluster NGC
663 since the distances, ages, and radial velocities do not match.Comment: Accepted for Publication (JAAVSO
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The Use of Reddit as an Inexpensive Source for High-Quality Data
Today, researchers have the ability to conduct their investigations in a number of different manners, including both traditional testing using university subject pool participants and the more recent method of online recruitment. Although the use of internet participants is becoming more popular, this area of research is still very much in its infancy and needs further examination. Additionally, alternative web-based platforms need to be investigated because much of the literature has focused on using Amazon.com’s Mechanical Turk (MTurk). Therefore, the current study recruited an internet population using the website Reddit, and compared them to a traditional undergraduate sample to learn more about this web-based platform. The results demonstrated similarities and distinctions between the two samples. Furthermore, previous findings in the psychological well-being literature were replicated. As a whole, the participants recruited from Reddit provided high-quality data that were inexpensive and comparable to the responses gathered using undergraduate participants. We conclude that this website appears to be a promising tool for the field of psychological assessment, research, and evaluation. Accessed 4,072 times on https://pareonline.net from May 30, 2017 to December 31, 2019. For downloads from January 1, 2020 forward, please click on the PlumX Metrics link to the right
The z=0.0912 and z=0.2212 Damped Lyman Alpha Galaxies Along the Sight-Line Toward the Quasar OI 363
New optical and infrared observations along the sight-line toward the quasar
OI 363 (0738+313) are presented and discussed. Excluding systems which lack
confirming UV spectroscopic observations of the actual Lyman alpha line, this
sight-line presently contains the two lowest-redshift classical damped Lyman
alpha (DLA) quasar absorption line systems known (i.e. with N(HI) \ge 2 x
10^{20} atoms cm^{-2}), one at z(abs)=0.0912 and the other at z(abs)=0.2212.
The z=0.09 DLA galaxy appears to be an extended low surface brightness galaxy
which is easily visible only in infrared images and shows rich morphological
structure. Subtraction of the quasar nuclear and host light yields L_K \approx
0.08L_K* at z=0.09. The impact parameter between the galaxy and quasar
sight-line is very small, b<3.6 kpc (<2 arcsec), which makes measurements
difficult. The z=0.22 DLA galaxy is an early-type dwarf with a K-band
luminosity of L_K \approx 0.1L_K* at impact parameter b=20 kpc. In general,
these results serve to support mounting evidence that DLA galaxies are drawn
from a wide variety of gas-rich galaxy types. (Abridged)Comment: 27 pages, 6 figures, 2 in color. Submitted to Ap
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