2,878 research outputs found
Mass Loss In M67 Giants: Evidence From Isochrone Fitting
We present a study of the stellar content of the open cluster M67. We have
computed new evolutionary sequences of stellar models with solar abundance that
cover all phases of evolution from the Zero-Age Main Sequence to the bright end
of the Asymptotic Giant Branch (AGB). We examine the fit between the calculated
and the observed red giant branch (RGB) in particular, and discuss factors that
most influence its quality. The distinct color gap between the RGB and the
clump giants is compared with the temperature gap between the He-burning tracks
and the computed 5 Gyr isochrone. This purely differential approach strongly
indicates that the clump giants have M \lta 0.70\msun\ , implying an amount
of mass loss ( \msun) well in excess of that found in globular
cluster stars. Observational constraints on mass loss processes favor the
interpretation that mass loss in cool low-mass giant stars increases with
metallicity.Comment: 21pp., plain TeX astro-ph/yymmnn
An experimental test of all theories with predictive power beyond quantum theory
According to quantum theory, the outcomes of future measurements cannot (in
general) be predicted with certainty. In some cases, even with a complete
physical description of the system to be measured and the measurement
apparatus, the outcomes of certain measurements are completely random. This
raises the question, originating in the paper by Einstein, Podolsky and Rosen,
of whether quantum mechanics is the optimal way to predict measurement
outcomes. Established arguments and experimental tests exclude a few specific
alternative models. Here, we provide a complete answer to the above question,
refuting any alternative theory with significantly more predictive power than
quantum theory. More precisely, we perform various measurements on distant
entangled photons, and, under the assumption that these measurements are chosen
freely, we give an upper bound on how well any alternative theory could predict
their outcomes. In particular, in the case where quantum mechanics predicts two
equally likely outcomes, our results are incompatible with any theory in which
the probability of a prediction is increased by more than ~0.19. Hence, we can
immediately refute any already considered or yet-to-be-proposed alternative
model with more predictive power than this.Comment: 13 pages, 4 figure
Derived Parameters for NGC 6791 from High-Metallicity Isochrones
We have computed 8, 10, and 12 Gyr isochrones and physically consistent
models of zero-age red horizontal branch stars for stellar masses between 0.55
and 1.3~\msun, all at [Fe/H] . Comparison to the NGC 6791 BVI
photometry of Ka{\l}u\.zny & Udalski (1992) and Montgomery, Janes & Phelps
(1994) yields an age of Gyr at an apparent distance modulus
13.49 < \dmv < 13.70. The color offsets required to fit the isochrones,
combined with the spectroscopic results of Friel & Janes, imply that the
foreground reddening to NGC 6791 lies in the range 0.24 > \ebv >0.19 with
[Fe/H] .
The zero-age horizontal branch models suggest that the red horizontal branch
stars of NGC 6791 have masses \lesssim 0.7\msun. The masses are similar to
those found for M67 red clump stars by Tripicco, Dorman & Bell (1993) and for
globular cluster red horizontal branch stars, despite higher and lower masses
(respectively) in those cases. This suggests the presence of a mechanism that
tends to reduce stellar envelopes on the zero-age horizontal branch {\it to} a
given mass rather than {\it by} a given amount.Comment: 23 pages, postscript fil
Dietary Cholesterol Concentration and Duration Degrade Long-Term Memory of Classical Conditioning of the Rabbit's Nictitating Membrane Response
A rabbit model of Alzheimer's disease based on feeding a cholesterol diet for eight weeks shows sixteen hallmarks of the disease, including learning and memory changes. Although we have shown 2% cholesterol and copper in water can retard learning, other studies show feeding dietary cholesterol before learning can improve acquisition whereas feeding cholesterol after learning can degrade long-term memory. We explored this issue by manipulating cholesterol concentration and duration following classical trace conditioning of the rabbit's nictitating membrane response and assessed conditioned responding after eight weeks on cholesterol. First, rabbits given trace classical conditioning followed by 0.5%, 1%, or 2% cholesterol for eight weeks showed body weight and serum cholesterol levels that were a function of dietary cholesterol. Although all concentrations of cholesterol showed some sign of retarding long-term memory, the level of memory retardation was correlated with serum cholesterol levels. Second, rabbits given trace conditioning followed by different durations of a 2% cholesterol diet combined with different durations of a 0% control diet for 8 weeks showed duration and timing of a 2% cholesterol diet were important in affecting recall. The data support the idea that dietary cholesterol may retard long-term memory
Keyring models: an approach to steerability
If a measurement is made on one half of a bipartite system, then, conditioned
on the outcome, the other half has a new reduced state. If these reduced states
defy classical explanation -- that is, if shared randomness cannot produce
these reduced states for all possible measurements -- the bipartite state is
said to be steerable. Determining which states are steerable is a challenging
problem even for low dimensions. In the case of two-qubit systems a criterion
is known for T-states (that is, those with maximally mixed marginals) under
projective measurements. In the current work we introduce the concept of
keyring models -- a special class of local hidden state models. When the
measurements made correspond to real projectors, these allow us to study
steerability beyond T-states.
Using keyring models, we completely solve the steering problem for real
projective measurements when the state arises from mixing a pure two-qubit
state with uniform noise. We also give a partial solution in the case when the
uniform noise is replaced by independent depolarizing channels.Comment: 15(+4) pages, 5 figures. v2: references added, v3: minor change
Empirically Constrained Color-Temperature Relations. II. uvby
(Abriged) A new grid of theoretical color indices for the Stromgren uvby
photometric system has been derived from MARCS model atmospheres and SSG
synthetic spectra for cool dwarf and giant stars. At warmer temperatures this
grid has been supplemented with the synthetic uvby colors from recent Kurucz
atmospheric models without overshooting. Our transformations appear to
reproduce the observed colors of extremely metal-poor turnoff and giant stars
(i.e., [Fe/H]<-2). Due to a number of assumptions made in the synthetic color
calculations, however, our color-temperature relations for cool stars fail to
provide a suitable match to the uvby photometry of both cluster and field stars
having [Fe/H]>-2. To overcome this problem, the theoretical indices at
intermediate and high metallicities have been corrected using a set of color
calibrations based on field stars having accurate IRFM temperature estimates
and spectroscopic [Fe/H] values. Encouragingly, isochrones that employ the
transformations derived in this study are able to reproduce the observed CMDs
(involving u-v, v-b, and b-y colors) for a number of open and globular clusters
(including M92, M67, the Hyades, and 47Tuc) rather well. Moreover, our
interpretations of such data are very similar, if not identical, with those
given by VandenBerg & Clem (2003, AJ, 126, 778) from a consideration of BV(RI)c
observations for the same clusters. In the present investigation, we have also
analyzed the observed Stromgren photometry for the classic Population II
subdwarfs, compared our "final" (b-y)-Teff relationship with those derived
empirically in a number of recent studies, and examined in some detail the
dependence of the m1 index on [Fe/H].Comment: 70 pages, 26 figures. Accepted for publication in AJ (Feb 2004).
Postscript version with high resolution figures and complete Table 3
available at http://astrowww.phys.uvic.ca/~jclem/uvb
The Production of Sodium and Aluminum in Globular Cluster Red Giant Stars
We study the production of Na and Al around the hydrogen shell of two
red-giant sequences of different metallicity in order to explain the abundance
variations seen in globular cluster stars in a mixing scenario. Using detailed
stellar models together with an extensive nuclear reaction network, we have
calculated the distribution of the various isotopic abundances around the
hydrogen shell at numerous points along the red-giant branch. These
calculations allow for the variation in both temperature and density in the
shell region as well as the timescale of the nuclear processing, as governed by
the outward movement of the hydrogen shell. The reaction network uses updated
rates over those of Caughlin \& Fowler (1988). We find evidence for the
production of Na and Al occurring in the NeNa and MgAl cycles. In particular,
Na is significantly enhanced throughout the region above the hydrogen shell.
The use of the newer reaction rates causes a substantial increase in the
production of Al above the hydrogen shell through heavy leakage from the
NeNa cycle and should have an important effect on the predicted surface
abundances. We also find that the nuclear processing is considerably more
extensive at lower metallicities.Comment: 4 pages with 4 EPS figures embedded, accepted by ApJL March 28, 199
Possible Applications of Surface Electromagnetic Waves to Measure Absorption Coefficients
We Show that Surface Electromagnetic Waves Can Probably Be Used to Measure the Absorption Coefficients of Materials overlaying Metals. the Proposed Experimental Method is Illustrated in the Infrared Frequency Range using Water, Teflon, and Polyethylene as Sample Materials
- …