1,242 research outputs found
The composition of HB stars : RR Lyrae variables
We used moderately high-resolution, high S/N spectra to study the chemical
composition of 10 field ab-type RR Lyrae stars. A new temperature scale was
determined from literature Infrared Flux Method measures of subdwarfs and the
Kurucz (1992) model atmospheres, and used to calibrate colors for both dwarfs
and RR Lyraes. The applicability of Kurucz (1992) model atmospheres in the
analysis of RR Lyraes at minimum light was analyzed: we found that they are
able to reproduce colors, excitation and ionization equilibria as well as the
wings of Halpha. We derived abundances for 21 species. The metal abundances of
the program stars span the range -2.50<[Fe/H]<+0.17$. Lines of most elements
are found to form in LTE conditions. Fe lines satisfy very well the excitation
and ionization equilibria. RR Lyraes share the typical abundance pattern of
other stars of similar [Fe/H]: alpha-elements are overabundant by about 0.4dex
and Mn is underabundant by about 0.6dex in stars with [Fe/H]<-1. Significant
departures from LTE are found only for a few species. We used our new [Fe/H]
abundances, as well as values from Butler and coworkers (corrected to our
system), and from high resolution spectroscopy of globular clusters giants, to
obtain a new calibration of the DeltaS index: [Fe/H]= -0.194(\pm 0.011)DeltaS
-0.08(\pm 0.18) and to update the metallicity calibration of the Ca II K line
index: [Fe/H]= 0.65(\pm 0.17)W'(K) -3.49(\pm 0.39). Finally, our new
metallicity scale was used to revise the [Fe/H] dependence of the absolute
magnitude of RR Lyrae stars, Mv: Mv = 0.20(\pm 0.03)[Fe/H] + 1.06(\pm 0.04).Comment: 59 pages, Latex using aaspp.sty, ps-files of text, tables (21) and
figures (23) available from ftp://boas3.bo.astro.it/pub/gisella To appear in
October 1995 Astronomical Journa
Red thick disks of nearby galaxies
Edge on systems reveal the properties of disk galaxies as a function of
height, z, above the plane. Four local edge-on galaxies, that are close enough
to have been resolved into stars by the Hubble Space Telescope, show thick
disks, composed of a red stellar population, which is old and relatively metal
rich. Color gradients, d(V-I)/dz, are zero or slightly positive. Favored models
may have an explicit thick disk formation phase
Cell-Cell Death Communication by Signals Passing Through Non-Aqueous Environments: A Reply
The effects of the emission of low intensity light from cells and organelles, known as biophotons, or ultraweak photon emission, are not well understood and subject to debate. Potapovich & Kostyuk recently proposed that the induction of oxidative stress generates non-chemical death signals which can induce cell death in neighbouring, chemically isolated cells (termed detector cells). Given the significance of these results, here we attempt to replicate their findings. We found treatment of “inductor cells” with duroquinone dissolved in ethanol does indeed induce significant cell death in neighbouring “detector” cells relative to distant control cells (64.53% ± 14.42 vs 99.72% ± 6.09 cell viability), closely reproducing their original results. However, this was no longer true if the induction drug was dissolved in a less volatile solvent, suggesting that their original findings may have been a result of volatile solvent-based transmission as opposed to light-based non-chemical signalling
Evolution in the Clustering of Galaxies to r = 26 (TAPIR GRP-390)
We present results for the two-point angular correlation function of galaxies
to a limiting magnitude of r=26. The final sample is 97% complete to r=26.0,
yielding 5730 galaxies over a 90.1 sq. arcmin field. The correlation function
for our faint galaxies can be parameterised by a power law, ,
in agreement with the clustering statistics of shallower catalogues. The
derived amplitude, , is small, but non-zero. We combine this measurement
with the latest statistical constraints on faint galaxy redshifts from
gravitational lensing studies, which imply that the bulk of the r<26 field
galaxies should be at redshifts of order 1. Our derived is significantly
lower than that predicted from the local bright galaxy correlation function
using the lensing-determined galaxy redshift distribution and modest growth of
clustering. This simplistic model does not include the variation in observed
morphological mix as a function of redshift and apparent magnitude in our
sample. At our faintest limits we reach sufficiently high redshifts that
differential corrections will result in the observed galaxy mix being
dominated by star bursting dwarf and low surface brightness irregulars, rather
than the early-type systems used to define the local bright galaxy correlation
function. Adopting the correlation function measured locally for these low
surface brightness galaxies and assuming modest clustering evolution, we obtain
reasonable agreement between our model and observations. This model supports
the scenario in which the high number density of faint galaxies is produced by
normally clustered star forming dwarf galaxies at modest redshifts.Comment: 13 pages LaTeX (article style), 3 figures (tar compressed and
uuencoded using uufiles csh script) PostScript figures available via
anonymous ftp from goldie.tapir.caltech.edu in directory pub/Roger (files
wtheta1.ps, wtheta2.ps, wtheta3.ps
Calibration of metallicity effects on the integrated colors of globular clusters and early-type galaxies
New infrared observations of globular clusters have been obtained which show that both infrared and optical colors are strongly correlated with metallicity and which provide an empirical calibration of abundance effects in composite stellar systems. Models have been constructed, based on the isochrones of Ciardullo and Demarque, with Z-values between 0.0001 and 0.04, and slope of the initial mass function s between 0 and 4. Metal-poor models with s ≤ 2.35 (the Salpeter function) give good agreement with the empirical calibration. Metal-rich models are compared with observations of the central regions of early-type galaxies, and imply that galaxies which have -19 ≥ M_v ≥ -23 correspond to a range in metallicity of 0.0 ≤ [M/H] ≤ +0.3. Models with s = 2.35 adequately fit the observations; proper accounting of metallicity effects on narrow-band infrared features does not require s < 2, as previously published models have suggested. An upper limit on s of 3.2 is determined
Shapes and Shears, Stars and Smears: Optimal Measurements for Weak Lensing
We present the theoretical and analytical bases of optimal techniques to
measure weak gravitational shear from images of galaxies. We first characterize
the geometric space of shears and ellipticity, then use this geometric
interpretation to analyse images. The steps of this analysis include:
measurement of object shapes on images, combining measurements of a given
galaxy on different images, estimating the underlying shear from an ensemble of
galaxy shapes, and compensating for the systematic effects of image distortion,
bias from PSF asymmetries, and `"dilution" of the signal by the seeing. These
methods minimize the ellipticity measurement noise, provide calculable shear
uncertainty estimates, and allow removal of systematic contamination by PSF
effects to arbitrary precision. Galaxy images and PSFs are decomposed into a
family of orthogonal 2d Gaussian-based functions, making the PSF correction and
shape measurement relatively straightforward and computationally efficient. We
also discuss sources of noise-induced bias in weak lensing measurements and
provide a solution for these and previously identified biases.Comment: Version accepted to AJ. Minor fixes, plus a simpler method of shape
weighting. Version with full vector figures available via
http://www.astro.lsa.umich.edu/users/garyb/PUBLICATIONS
Non-chemical Signalling Between Mitochondria
A wide variety of studies have reported some form of non-chemical or non-aqueous communication between physically isolated organisms, eliciting changes in cellular proliferation, morphology, and/or metabolism. The sources and mechanisms of such signalling pathways are still unknown, but have been postulated to involve vibration, volatile transmission, or light through the phenomenon of ultraweak photon emission. Here, we report non-chemical communication between isolated mitochondria from MCF7 (cancer) and MCF10A (non-cancer) cell lines. We found that mitochondria in one cuvette stressed by an electron transport chain inhibitor, antimycin, alters the respiration of mitochondria in an adjacent, but chemically and physically separate cuvette, significantly decreasing the rate of oxygen consumption compared to a control (p = <0.0001 in MCF7 and MCF10A mitochondria). Moreover, the changes in O2-consumption were dependent on the origin of mitochondria (cancer vs non-cancer) as well as the presence of "ambient" light. Our results support the existence of non-chemical signalling between isolated mitochondria. The experimental design suggests that the non-chemical communication is light-based, although further work is needed to fully elucidate its nature
The luminosity of supernovae of type Ia from TRGB distances and the value of H_0
Distances from the tip of the red-giant branch (TRGB) in the halo Population
of galaxies - calibrated through RR Lyr stars as well as tied to Hipparcos
parallaxes and further supported by stellar models - are used to determine the
luminosity of six nearby type Ia supernovae (SN 2011fe, 2007sr, 1998bu, 1989B,
1972E, and 1937C). The result is M_V^corr = -19.41 +/- 0.05. If this value is
applied to 62 SNe Ia with 3000< v < 20,000 km/s a large-scale value of the
Hubble constant follows of H_0 = 64.0 +/- 1.6 +/- 2.0. The SN HST Project gave
H_0 = 62.3 +/- 1.3 +/- 5.0 from ten Cepheid-calibrated SNe Ia (Sandage et al.
2006). The agreement of young Population I (Cepheids) and old, metal-poor
Population II (TRGB) distance indicators is satisfactory. The combined weighted
result is H_0 = 63.7 +/- 2.3 (i.e. +/-3.6%). The result can also be reconciled
with WMAP5 data (Reid et al. 2010).Comment: 9 pages, 3 figures, 3 tables, accepted for publication in Astronomy
and Astrophysic
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