1,135 research outputs found
Detection Rates for Close Binaries Via Microlensing
Microlensing is one of the most promising methods of reconstructing the
stellar mass function down to masses even below the hydrogen-burning limit. The
fundamental limit to this technique is the presence of unresolved binaries,
which can in principle significantly alter the inferred mass function. Here we
quantify the fraction of binaries that can be detected using microlensing,
considering specifically the mass ratio and separation of the binary. We find
that almost all binary systems with separations greater than of
their combined Einstein ring radius are detectable assuming a detection
threshold of . For two M dwarfs, this corresponds to a limiting separation
of \gsim 1 \au. Since very few observed M dwarfs have companions at
separations \lsim 1 \au, we conclude that close binaries will probably not
corrupt the measurements of the mass function. We find that the detectability
depends only weakly on the mass ratio. For those events for which individual
masses can be determined, we find that binaries can be detected down to .Comment: 19 pages including 6 figures. Uses phyyzx format. Send requests for
higher quality figures to [email protected]
Large Magellanic Cloud Microlensing Optical Depth with Imperfect Event Selection
I present a new analysis of the MACHO Project 5.7 year Large Magellanic Cloud
(LMC) microlensing data set that incorporates the effects of contamination of
the microlensing event sample by variable stars. Photometric monitoring of
MACHO LMC microlensing event candidates by the EROS and OGLE groups has
revealed that one of these events is likely to be a variable star, while
additional data has confirmed that many of the other events are very likely to
be microlensing. This additional data on the nature of the MACHO microlensing
candidates is incorporated into a simple likelihood analysis to derive a
probability distribution for the number of MACHO microlens candidates that are
true microlensing events. This analysis shows that 10-12 of the 13 events that
passed the MACHO selection criteria are likely to be microlensing events, with
the other 1-3 being variable stars. This likelihood analysis is also used to
show that the main conclusions of the MACHO LMC analysis are unchanged by the
variable star contamination. The microlensing optical depth toward the LMC is =
1.0 +/- 0.3 * 10^{-7}. If this is due to microlensing by known stellar
populations, plus an additional population of lens objects in the Galactic
halo, then the new halo population would account for 16% of the mass of a
standard Galactic halo. The MACHO detection exceeds the expected background of
2 events expected from ordinary stars in standard models of the Milky Way and
LMC at the 99.98% confidence level. The background prediction is increased to 3
events if maximal disk models are assumed for both the MilkyWay and LMC, but
this model fails to account for the full signal seen by MACHO at the 99.8%
confidence level.Comment: 20 pages, 2 postscript figues, accepted by Ap
Effect of a polyphenol–vacuum packaging on lipid deterioration during an 18-month frozen storage of Coho Salmon (Oncorhynchus kisutch)
10 páginas, 3 tablas, 2 figuras.-- The final publication is
available at www.springerlink.comA packaging system combining a polyphenolrich
film and vacuum (PPRF–VP) was applied to farmed
coho salmon (Oncorhynchus kisutch) muscle for an 18-
month storage (−18 °C). For it, two different concentrations
of polyphenol compounds (namely, p-coumaric and ferulic
acids) obtained from a barley husk extract were applied
(PPRF–VP conditions) and compared to vacuum packaging
without polyphenol presence (vacuum control; VP condition)
and to packaging in the absence of vacuum and
polyphenols (control; CP condition). The study was
addressed to lipid hydrolysis and oxidation development
and to lipid changes related to nutritional value. Both
PPRF–VP conditions provided an inhibitory effect (p<
0.05) on conjugated diene and fluorescent compound
formation in frozen salmon. Compared to CP condition,
vacuum packaging (PPRF–VP and VP conditions) led to
lower (p<0.05) peroxide and anisidine values and to an
inhibitory effect (p<0.05) on α- and γ-tocopherol losses.
No effect (p>0.05) of polyphenol presence and vacuum
packaging could be inferred on free fatty acid formation
(hydrolysis development) and on polyunsaturated fatty acid
retention (polyene index assessment). A low rancid odour
development was observed in all kinds of fish samples, this
being lower (p<0.05) in fish kept under vacuum (PPRF–VP
and VP) conditions.Peer reviewe
Quality assessment of sardines during storage by measurement of fluorescent compounds
5 páginas, 2 figuras, 5 tablasSardine alterations during chilled storage (0°C) were investigated by measuring the fluorescence ratio between two excitation/emission maxima (393/463 nm, 327/415 nm) and compared with common quality indices. Sardines were also maintained at 15°C to accelerate all reactions occurring at 0°C. Other quality indices (total volatile base-nitrogen, free fatty acids, formation of conjugated dienes, and thiobarbituric acid values) were determined and the use of the fluorescence ratio (fluorescence shift, δF) was analyzed. A high correlation was found between the δF and the total volatile base-nitrogen (r = 0.93, at 0°C; r = 0.92, at 15°C).Xunta de Galicia (Project XUGA 402 01B93).Peer reviewe
Differential lipid damage in various muscle zones of frozen hake (Merluccius merluccius)
5 páginas, 5 tablas, 1 figura.-- The final publication is
available at www.springerlink.comA comparison of the lipid damage produced
in different hake zones was carried out during frozen
storage at –11 and –18 7C. Three light muscle zones and
the dark muscle were considered. Lipid oxidation [conjugated
dienes; thiobarbituric acid index (TBA-i); fluorescence
formation] and hydrolysis (free fatty acids,
FFA) were determined. The most predominant lipid
damage in all zones was hydrolysis, at the end of storage
reaching values of about 40% (for the light muscle
zones) and 12% (for the dark muscle) of the total lipids
at –11 7C. Significant (P~0.05) correlation value
(rp0.67–0.85) relationships between the frozen storage
time and the FFA content were obtained for the four
muscle zones at both temperatures. A comparison of
the regression lines slopes in the different zones
showed that a lower (P~0.05) lipolitic activity was produced
in the dark muscle compared to the three light
zones at both temperatures. A low lipid oxidation development
was produced in the three light muscle
parts, so that no significant differences between them
could be assessed. However, the dark muscle showed a
higher oxidation development (TBA-i and fluorescence
formation) as a result of a higher lipid content and the
presence of prooxidant constituents.European Community, Research Projects
FAIR-CT95–1111 and AIR 3-CT94–1921.Peer reviewe
Is the Large Magellanic Cloud a Large Microlensing Cloud?
An expression is provided for the self-lensing optical depth of the thin LMC
disk surrounded by a shroud of stars at larger scale heights. The formula is
written in terms of the vertical velocity dispersion of the thin disk
population. If tidal forcing causes 1-5 % of the disk mass to have a height
larger than 6 kpc and 10-15 % to have a height above 3 kpc, then the
self-lensing optical depth of the LMC is , which is
within the observational uncertainties. The shroud may be composed of bright
stars provided they are not in stellar hydrodynamical equilibrium.
Alternatively, the shroud may be built from low mass stars or compact objects,
though then the self-lensing optical depths are overestimates of the true
optical depth by a factor of roughly 3. The distributions of timescales of the
events and their spatial variation across the face of the LMC disk offer
possibilities of identifying the dominant lens population. In propitious
circumstances, an experiment lifetime of less than 5 years is sufficient to
decide between the competing claims of Milky Way halos and LMC lenses. However,
LMC disks can sometimes mimic the microlensing properties of Galactic halos for
many years and then decades of survey work are needed. In this case
observations of parallax or binary caustic events offer the best hope for
current experiments to deduce the lens population. The difficult models to
distinguish are Milky Way halos in which the lens fraction is low (< 10 %) and
fattened LMC disks composed of lenses with a typical mass of low luminosity
stars or greater. A next-generation wide-area microlensing survey, such as the
proposed ``SuperMACHO'' experiment, will be able to distinguish even these
difficult models with just a year or two of data.Comment: 25 pages, 4 figures, The Astrophysical Journal (in press
The Origin of Primordial Dwarf Stars and Baryonic Dark Matter
I present a scenario for the production of low mass, degenerate dwarfs of
mass via the mechanism of Lenzuni, Chernoff & Salpeter (1992).
Such objects meet the mass limit requirements for halo dark matter from
microlensing surveys while circumventing the chemical evolution constraints on
normal white dwarf stars. I describe methods to observationally constrain this
scenario and suggest that such objects may originate in small clusters formed
from the thermal instability of shocked, heated gas in dark matter haloes, such
as suggested by Fall & Rees (1985) for globular clusters.Comment: TeX, 4 pages plus 2 postscript figures. To appear in Astrophysical
Journal Letter
Eclipsing binaries in the MACHO database: New periods and classifications for 3031 systems in the Large Magellanic Cloud
Eclipsing binaries offer a unique opportunity to determine fundamental
physical parameters of stars using the constraints on the geometry of the
systems. Here we present a reanalysis of publicly available two-color
observations of about 6800 stars in the Large Magellanic Cloud, obtained by the
MACHO project between 1992 and 2000 and classified as eclipsing variable stars.
Of these, less than half are genuine eclipsing binaries. We determined new
periods and classified the stars, 3031 in total, using the Fourier parameters
of the phased light curves. The period distribution is clearly bimodal,
reflecting refer to the separate groups of more massive blue main sequence
objects and low mass red giants. The latter resemble contact binaries and obey
a period-luminosity relation. Using evolutionary models, we identified
foreground stars. The presented database has been cleaned of artifacts and
misclassified variables, thus allowing searches for apsidal motion, tertiary
components, pulsating stars in binary systems and secular variations with
time-scales of several years.Comment: 11 figures, 9 pages, accepted for publication in Ap
Quality enhancement of chilled fish by including alga Bifurcaria bifurcata extract in the icing medium
9 páginas, 4 tablasBifurcaria bifurcata is a widely extended brown macroalga, whose antimicrobial and antioxidant properties have previously been described. In this study, ethanolic extracts of B. bifurcata were included in the icing medium employed for the chilled storage of megrim (Lepidorhombus whiffiagonis). For it, two different concentrations of this brown macroalga extract (0.67 and 2.50 g lyophilized alga L−1 aqueous solution; B-1 and B-2 batches, respectively) were tested for a 14-day storage. The effect of the alga extract was compared with a counterpart batch stored in traditional ice prepared only from water (B-0 batch). Significant (p < 0.05) inhibitions of microbial activity (aerobes, psychrotrophs, lipolytic bacteria, proteolytic bacteria and Enterobacteriaceae) as well as of pH and trimethylamine formation were observed as a result of the incorporation of the alga extract in the icing medium, being this effect especially relevant in the B-2 batch. Concerning lipid damage development, a significantly (p < 0.05) lower formation of free fatty acids (lipid hydrolysis development) and of fluorescent compounds (tertiary lipid oxidation development) in samples corresponding to both alga-including batches could also be observed; this inhibitory effect was more intense in fish belonging to the B-2 batch. The icing medium proposed in this work constitutes a promising strategy in order to apply algae extracts to enhance fish quality retention during the different steps of storage and commercialization of marine speciesThis work was supported by the Consejo Superior de Investigaciones CientÃficas (CSIC; Spain) through the project PIE 201370E001Peer reviewe
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