3,665 research outputs found
Cooler and bigger than thought? Planetary host stellar parameters from the InfraRed Flux Method
Effective temperatures and radii for 92 planet-hosting stars as determined
from the InfraRed Flux Method (IRFM) are presented and compared with those
given by other authors using different approaches. The IRFM temperatures we
have derived are systematically lower than those determined from the
spectroscopic condition of excitation equilibrium, the mean difference being as
large as 110 K. They are, however, consistent with previous IRFM studies and
with the colors derived from Kurucz and MARCS model atmospheres. Comparison
with direct measurements of stellar diameters for 7 dwarf stars, which
approximately cover the range of temperatures of the planet-hosting stars,
suggest that the IRFM radii and temperatures are reliable in an absolute scale.
A better understanding of the fundamental properties of the stars with planets
will be achieved once this discrepancy between the IRFM and the spectroscopic
temperature scales is resolved.Comment: 15 pages, 4 figures. Accepted for publication in Ap
Abundances of Baade's Window Giants from Keck/HIRES Spectra: I. Stellar Parameters and [Fe/H] Values
We present the first results of a new abundance survey of the Milky Way bulge
based on Keck/HIRES spectra of 27 K-giants in the Baade's Window (, ) field. The spectral data used in this study are of much higher resolution
and signal-to-noise than previous optical studies of Galactic bulge stars. The
[Fe/H] values of our stars, which range between -1.29 and , were used to
recalibrate large low resolution surveys of bulge stars. Our best value for the
mean [Fe/H] of the bulge is . This mean value is similar to the
mean metallicity of the local disk and indicates that there cannot be a strong
metallicity gradient inside the solar circle. The metallicity distribution of
stars confirms that the bulge does not suffer from the so-called ``G-dwarf''
problem. This paper also details the new abundance techniques necessary to
analyze very metal-rich K-giants, including a new Fe line list and regions of
low blanketing for continuum identification.Comment: Accepted for publication in January 2006 Astrophysical Journal. Long
tables 3--6 withheld to save space (electronic tables in journal paper). 53
pages, 10 figures, 9 table
Abundances in Stars from the Red Giant Branch Tip to the Near Main Sequence in M71: II. Iron Abundance
We present [Ffe/H] abundance results that involve a sample of stars with a
wide range in luminosity from luminous giants to stars near the turnoff in a
globular cluster. Our sample of 25 stars in M71 includes 10 giant stars more
luminous than the RHB, 3 horizontal branch stars, 9 giant stars less luminous
than the RHB, and 3 stars near the turnoff. We analyzed both Fe I and Fe II
lines in high dispersion spectra observed with HIRES at the W. M. Keck
Observatory. We find that the [Fe/H] abundances from both Fe I and Fe II lines
agree with each other and with earlier determinations. Also the [Fe/H] obtained
from Fe I and Fe II lines is constant within the rather small uncertainties for
this group of stars over the full range in Teff and luminosity, suggesting that
NLTE effects are negligible in our iron abundance determination. In this
globular cluster, there is no difference among the mean [Fe/H] of giant stars
located at or above the RHB, RHB stars, giant stars located below the RHB and
stars near the turnoff.Comment: Minor changes to conform to version accepted for publication, with
several new figures (Paper 2 of a pair
Crafting a critical technical practice
In recent years, the category of practice-based research has become an essential component of discourse around public funding and evaluation of the arts in British higher education. When included under the umbrella of public policy concerned with the creative industries", technology researchers often find themselves collaborating with artists who consider their own participation to be a form of practice-based research. We are conducting a study under the Creator Digital Economies project asking whether technologists, themselves, should be considered as engaging in practice-based research, whether this occurs in collaborative situations, or even as a component of their own personal research [1]
Oxygen Abundances in Two Metal-Poor Subgiants from the Analysis of the 6300 A Forbidden O I Line
Recent LTE analyses (Israelian et al. 1998 and Bosegaard et al. 1999) of the
OH bands in the optical-ultraviolet spectra of nearby metal-poor subdwarfs
indicate that oxygen abundances are generally higher than those previously
determined. The difference increases with decreasing metallicity and reaches
delta([O/Fe]) ~ +0.6 dex as [Fe/H] approaches -3.0.
Employing high resolution (R = 50000), high S/N (~ 250) echelle spectra of
the two stars found by Israelian et al. (1998) to have the highest
[O/Fe]-ratios, viz, BD +23 3130 and BD +37 1458, we conducted abundance
analyses based on about 60 Fe I and 7-9 Fe II lines. We determined from Kurucz
LTE models the values of the stellar parameters, as well as abundances of Na,
Ni, and the traditional alpha-elements, independent of the calibration of color
vs scales. We determined oxygen abundances from spectral synthesis of
the stronger line (6300 A) of the [O I] doublet.
The syntheses of the [O I] line lead to smaller values of [O/Fe], consistent
with those found earlier among halo field and globular cluster giants. We
obtain [O/Fe] = +0.35 +/- 0.2 for BD +23 3130 and +0.50 +/- 0.2 for BD +37
1458. In the former, the [O I] line is very weak (~ 1 mA), so that the quoted
[O/Fe] value may in reality be an upper limit.
Therefore in these two stars a discrepancy exists between the [O/Fe]- ratios
derived from [O I] and the OH feature, and the origin of this difference
remains unclear. Until the matter is clarified, we suggest it is premature to
conclude that the ab initio oxygen abundances of old, metal-poor stars need to
be revised drastically upward.Comment: 38 pages, 5 tables, 14 figures To appear in July 1999 AJ Updated
April 16, 1999. Fixed typo
Repelling sandhill cranes from corn: whole-kernel experiments with captive birds
Sandhill cranes (Grus canadensis) are opportunistic omnivores that incorporate both waste and unharvested cereal grains (Gramineae) in their diets. Limited hunting of cranes to reduce crop damage has had questionable results, and lethal control of depredating species is increasingly contentious. Our objectives were to evaluate anthraquinone-based Flight ControlTM and methyl anthranilate-based ReJeX-iTTM AG-36 as nontoxic avian foraging repellents in separate 2-choice pen tests with captive greater sandhill cranes (G. c. tabida) fed with whole-kernel corn (Zea mays). In both tests, crane pairs consumed, respectively, 8.6 and 9.8 times more untreated than treated corn. Total corn consumption did not differ among the treatment and control groups during the 8-day experiment. Though both repellents were effective at deterring cranes from treated corn, neither has been tested on corn under field conditions
Ideal MHD theory of low-frequency Alfven waves in the H-1 Heliac
A part analytical, part numerical ideal MHD analysis of low-frequency Alfven
wave physics in the H-1 stellarator is given. The three-dimensional,
compressible ideal spectrum for H-1 is presented and it is found that despite
the low beta (approx. 10^-4) of H-1 plasmas, significant Alfven-acoustic
interactions occur at low frequencies. Several quasi-discrete modes are found
with the three-dimensional linearised ideal MHD eigenmode solver CAS3D,
including beta-induced Alfven eigenmode (BAE)- type modes in beta-induced gaps.
The strongly shaped, low-aspect ratio magnetic geometry of H-1 causes CAS3D
convergence difficulties requiring the inclusion of many Fourier harmonics for
the parallel component of the fluid displacement eigenvector even for shear
wave motions. The highest beta-induced gap reproduces large parts of the
observed configurational frequency dependencies in the presence of hollow
temperature profiles
Global Alfven Eigenmodes in the H-1 heliac
Recent upgrades in H-1 power supplies have enabled the operation of the H-1
experiment at higher heating powers than previously attainable. A heating power
scan in mixed hydrogen/helium plasmas reveals a change in mode activity with
increasing heating power. At low power (<50 kW) modes with beta-induced Alfven
eigenmode (BAE) frequency scaling are observed. At higher power modes
consistent with an analysis of nonconventional Global Alfven Eigenmodes (GAEs)
are observed, the subject of this work. We have computed the mode continuum,
and identified GAE structures using the ideal MHD solver CKA and the
gyrokinetic code EUTERPE. An analytic model for ICRH-heated minority ions is
used to estimate the fast ion temperature from the hydrogen species. Linear
growth rate scans using a local flux surface stability calculation, LGRO, are
performed. These studies demonstrate growth from circulating particles whose
speed is significantly less than the Alfven speed, and are resonant with the
mode through harmonics of the Fourier decomposition of the strongly-shaped
heliac magnetic field. They reveal drive is possible with a small, hot
energetic tail of the hydrogen species. Local linear growth rate scans are also
complemented with global calculations from CKA and EUTERPE. These qualitatively
confirm the findings from the LGRO study, and show that the inclusion of finite
Larmor radius effects can reduce the growth rate by a factor of three, but do
not affect marginal stability. Finally, a study of damping of the global mode
with the thermal plasma is conducted, computing continuum, and the damping
arising from parallel electric fields. We find that continuum damping is of
order 0.1% for the configuration studied. The inclusion of resistivity lifts
the damping to 19%. Such large damping is consistent with experimental
observations that in absence of drive the mode decays rapidly (~0.1 ms).Comment: 18 pages, 15 figures, submitted 07/04/2017 to Plasma Physics and
Controlled Fusio
Avian Survey Methods for Use at Airports
Adverse effects and damage caused by interactions between humans and wildlife are increasing (DeStephana and DeGraaf 2003). To manage wildlife effectively- whether to mitigate damage. to enhance safety, or to reach conservation goals-wildlife biologists must identify hazards posed by or to members of a particular species (i.e., a population) or guild, and then prioritize management goals and specific actions. We examine the special problem of managing birds to reduce hazards to aviation, particularly those species known to cause structural damage to aircraft when struck and that ·pose problems to airport facilities (Dolbeer et al. 2000, Cleary and Dolbeer 2005, DeVault et al. 2011). Effective management of hazardous species at airports requires knowledge of species abundance and how abundance varies over time. In this context, the quality of the sampling methodology used will influence a biologist\u27s ability to accurately quantify avian hazards and to understand the ecological interactions of populations or guilds using airport environments
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