3,783 research outputs found
Analysing and Resisting American Citizensâ Insensitivity to Civilian Casualties of American Wars
Relationship of program to group cohesiveness among a group of four emotionally disturbed boys
Thesis (M.S.)--Boston Universit
Land deed, Marshall County, MS, 6 February 1856
https://egrove.olemiss.edu/aldrichcorr_c/1104/thumbnail.jp
Variables in the Southern Polar Region Evryscope 2016 Dataset
The regions around the celestial poles offer the ability to find and
characterize long-term variables from ground-based observatories. We used
multi-year Evryscope data to search for high-amplitude (~5% or greater)
variable objects among 160,000 bright stars (Mv < 14.5) near the South
Celestial Pole. We developed a machine learning based spectral classifier to
identify eclipse and transit candidates with M-dwarf or K-dwarf host stars -
and potential low-mass secondary stars or gas giant planets. The large
amplitude transit signals from low-mass companions of smaller dwarf host stars
lessens the photometric precision and systematics removal requirements
necessary for detection, and increases the discoveries from long-term
observations with modest light curve precision. The Evryscope is a robotic
telescope array that observes the Southern sky continuously at 2-minute
cadence, searching for stellar variability, transients, transits around exotic
stars and other observationally challenging astrophysical variables. In this
study, covering all stars 9 < Mv < 14.5, in declinations -75 to -90 deg, we
recover 346 known variables and discover 303 new variables, including 168
eclipsing binaries. We characterize the discoveries and provide the amplitudes,
periods, and variability type. A 1.7 Jupiter radius planet candidate with a
late K-dwarf primary was found and the transit signal was verified with the
PROMPT telescope network. Further followup revealed this object to be a likely
grazing eclipsing binary system with nearly identical primary and secondary K5
stars. Radial velocity measurements from the Goodman Spectrograph on the 4.1
meter SOAR telescope of the likely-lowest-mass targets reveal that six of the
eclipsing binary discoveries are low-mass (.06 - .37 solar mass) secondaries
with K-dwarf primaries, strong candidates for precision mass-radius
measurements.Comment: 32 pages, 17 figures, accepted to PAS
PCN153 A Trial for Evaluating Breast Cancer Tumor Marker Use Impact: A Value of Research Analysis
The Solar Neighborhood. XXXIX. Parallax Results from the CTIOPI and NOFS Programs: 50 New Members of the 25 Parsec White Dwarf Sample
We present 114 trigonometric parallaxes for 107 nearby white dwarf (WD)
systems from both the Cerro Tololo Inter-American Observatory Parallax
Investigation (CTIOPI) and the U. S. Naval Observatory Flagstaff Station (NOFS)
parallax programs. Of these, 76 parallaxes for 69 systems were measured by the
CTIOPI program and 38 parallaxes for as many systems were measured by the NOFS
program. A total of 50 systems are confirmed to be within the 25 pc horizon of
interest. Coupled with a spectroscopic confirmation of a common proper motion
companion to a Hipparcos star within 25 pc as well as confirmation parallax
determinations for two WD systems included in the recently released Tycho Gaia
Astrometric Solution (TGAS) catalog, we add 53 new systems to the 25 pc WD
sample a 42% increase. Our sample presented here includes four strong
candidate halo systems, a new metal-rich DAZ WD, a confirmation of a recently
discovered nearby short-period (P = 2.85 hr) double degenerate, a WD with a new
astrometric pertubation (long period, unconstrained with our data), and a new
triple system where the WD companion main-sequence star has an astrometric
perturbation (P 1.6 yr).Comment: 32 pages, 12 figures. Figure 4 in the manuscript is a representative
set of plots - plots for all WDs presented here are available
(allfits_photo.pdf, allfits_photo_DQ.pdf, and allfits_photo_DZ.pdf). Accepted
for publication in The Astronomical Journa
EVR-CB-001: An evolving, progenitor, white dwarf compact binary discovered with the Evryscope
We present EVR-CB-001, the discovery of a compact binary with an extremely
low mass () helium core white dwarf progenitor (pre-He
WD) and an unseen low mass () helium white dwarf (He
WD) companion. He WDs are thought to evolve from the remnant helium-rich core
of a main-sequence star stripped during the giant phase by a close companion.
Low mass He WDs are exotic objects (only about .2 of WDs are thought to be
less than .3 ), and are expected to be found in compact binaries.
Pre-He WDs are even rarer, and occupy the intermediate phase after the core is
stripped, but before the star becomes a fully degenerate WD and with a larger
radius () than a typical WD. The primary component of
EVR-CB-001 (the pre-He WD) was originally thought to be a hot subdwarf (sdB)
star from its blue color and under-luminous magnitude, characteristic of sdBs.
The mass, temperature (), and surface gravity
() solutions from this work are lower than values for
typical hot subdwarfs. The primary is likely to be a post-RGB, pre-He WD
contracting into a He WD, and at a stage that places it nearest to sdBs on
color-magnitude and - diagrams. EVR-CB-001 is expected to
evolve into a fully double degenerate, compact system that should spin down and
potentially evolve into a single hot subdwarf star. Single hot subdwarfs are
observed, but progenitor systems have been elusive.Comment: 14 pages, 11 figures. Published in The Astrophysical Journa
Variables in the Southern Polar Region Evryscope 2016 Data Set
The regions around the celestial poles offer the ability to find and characterize long-term variables from ground-based observatories. We used multi-year Evryscope data to search for high-amplitude (â5% or greater) variable objects among 160,000 bright stars (mv Ï limiting magnitude of g = 16 in dark time. In this study, covering all stars 9 Mâ) secondaries with K-dwarf primaries, strong candidates for precision massâradius measurements
Elemental abundances of Galactic bulge planetary nebulae from optical recombination lines
(abridged) Deep long-slit optical spectrophotometric observations are
presented for 25 Galactic bulge planetary nebulae (GBPNe) and 6 Galactic disk
planetary nebulae (GDPNe). The spectra, combined with archival ultraviolet
spectra obtained with the International Ultraviolet Explorer (IUE) and infrared
spectra obtained with the Infrared Space Observatory (ISO), have been used to
carry out a detailed plasma diagnostic and element abundance analysis utilizing
both collisional excited lines (CELs) and optical recombination lines (ORLs).
Comparisons of plasma diagnostic and abundance analysis results obtained from
CELs and from ORLs reproduce many of the patterns previously found for GDPNe.
In particular we show that the large discrepancies between electron
temperatures (Te's) derived from CELs and from ORLs appear to be mainly caused
by abnormally low values yielded by recombination lines and/or continua.
Similarly, the large discrepancies between heavy element abundances deduced
from ORLs and from CELs are largely caused by abnormally high values obtained
from ORLs, up to tens of solar in extreme cases. It appears that whatever
mechanisms are causing the ubiquitous dichotomy between CELs and ORLs, their
main effects are to enhance the emission of ORLs, but hardly affect that of
CELs. It seems that heavy element abundances deduced from ORLs may not reflect
the bulk composition of the nebula. Rather, our analysis suggests that ORLs of
heavy element ions mainly originate from a previously unseen component of
plasma of Te's of just a few hundred Kelvin, which is too cool to excite any
optical and UV CELs.Comment: 35 pages, 27 figures and 16 tables, accepted for publication in MNRA
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