1,697 research outputs found
Galactic Bulge Microlensing Optical Depth from EROS-2
We present a new EROS-2 measurement of the microlensing optical depth toward
the Galactic Bulge. Light curves of clump-giant stars
distributed over of the Bulge were monitored during seven Bulge
seasons. 120 events were found with apparent amplifications greater than 1.6
and Einstein radius crossing times in the range 5 {\rm d}.
This is the largest existing sample of clump-giant events and the first to
include northern Galactic fields. In the Galactic latitude range
1.4\degr<|b|<7.0\degr, we find with . These results are in good
agreement with our previous measurement, with recent measurements of the MACHO
and OGLE-II groups, and with predictions of Bulge models.Comment: accepted A&A, minor revision
A New Minimal-Stress Freely-Moving Rat Model for Preclinical Studies on Intranasal Administration of CNS Drugs
Purpose. To develop a new minimal-stress model for intranasal administration in freely moving rats and to evaluate in this model the brain distribution of acetaminophen following intranasal versus intravenous administration. Methods. Male Wistar rats received one intranasal cannula, an intra-cerebral microdialysis probe, and two blood cannulas for drug administration and serial blood sampling respectively. To evaluate this novel model, the following experiments were conducted. 1) Evans Blue was administered to verify the selectivity of intranasal exposure. 2) During a 1 min infusion 10, 20, or 40 Όl saline was administered intranasally or 250 ”l intravenously. Corticosterone plasma concentrations over time were compared as biomarkers for stress. 3) 200 ”g of the model drug acetaminophen was given in identical setup and plasma, and brain pharmacokinetics were determined. Results. In 96 % of the rats, only the targeted nasal cavity was deeply colored. Corticosterone plasma concentrations were not influenced, neither by route nor volume of administration. Pharmacokinetics of acetaminophen were identical after intravenous and intranasal administration, although the Cmax in microdialysates was reached a little earlier following intravenous administration. Conclusion. A new minimal-stress model for intranasal administration in freely moving rats has been successfully developed and allows direct comparison with intravenous administration. KEY WORDS: acetaminophen; brain; intranasal infusion; microdialysis; pharmacokinetics
Observation of periodic variable stars towards the galactic spiral arms by EROS II
We present the results of a massive variability search based on a photometric
survey of a six square degree region along the Galactic plane at (, ) and (, ). This
survey was performed in the framework of the EROS II (Exp\'erience de Recherche
d'Objets Sombres) microlensing program. The variable stars were found among
1,913,576 stars that were monitored between April and June 1998 in two
passbands, with an average of 60 measurements. A new period-search technique is
proposed which makes use of a statistical variable that characterizes the
overall regularity of the flux versus phase diagram. This method is well suited
when the photometric data are unevenly distributed in time, as is our case.
1,362 objects whose luminosity varies were selected. Among them we identified 9
Cepheids, 19 RR Lyrae, 34 Miras, 176 eclipsing binaries and 266 Semi-Regular
stars. Most of them are newly identified objects. The cross-identification with
known catalogues has been performed. The mean distance of the RR Lyrae is
estimated to be kpc undergoing an average absorption of
magnitudes. This distance is in good agreement with the one
of disc stars which contribute to the microlensing source star population.Our
catalogue and light curves are available electronically from the CDS,
Strasbourg and from our Web site http://eros.in2p3.fr.Comment: 15 pages, 11 figures, accepted in A&A (april 2002
Recommended from our members
Risk measures for direct real estate investments with non-normal or unknown return distributions
The volatility of returns is probably the most widely used risk measure for real estate. This is rather surprising since a number of studies have cast doubts on the view that volatility can capture the manifold risks attached to properties and corresponds to the risk attitude of investors. A central issue in this discussion is the statistical properties of real estate returnsâin contrast to neoclassical capital market theory they are mostly non-normal and often unknown, which render many statistical measures useless. Based on a literature review and an analysis of data from Germany we provide evidence that volatility alone is inappropriate for measuring the risk of direct real estate.
We use a unique data sample by IPD, which includes the total returns of 939 properties across different usage types (56% office, 20% retail, 8% others and 16% residential properties) from 1996 to 2009, the German IPD Index, and the German Property Index. The analysis of the distributional characteristics shows that German real estate returns in this period were not normally distributed and that a logistic distribution would have been a better fit. This is in line with most of the current literature on this subject and leads to the question which indicators are more appropriate to measure real estate risks. We suggest that a combination of quantitative and qualitative risk measures more adequately captures real estate risks and conforms better with investor attitudes to risk. Furthermore, we present criteria for the purpose of risk classification
The EROS2 search for microlensing events towards the spiral arms: the complete seven season results
The EROS-2 project has been designed to search for microlensing events
towards any dense stellar field. The densest parts of the Galactic spiral arms
have been monitored to maximize the microlensing signal expected from the stars
of the Galactic disk and bulge. 12.9 million stars have been monitored during 7
seasons towards 4 directions in the Galactic plane, away from the Galactic
center. A total of 27 microlensing event candidates have been found. Estimates
of the optical depths from the 22 best events are provided. A first order
interpretation shows that simple Galactic models with a standard disk and an
elongated bulge are in agreement with our observations. We find that the
average microlensing optical depth towards the complete EROS-cataloged stars of
the spiral arms is , a number that is
stable when the selection criteria are moderately varied. As the EROS catalog
is almost complete up to , the optical depth estimated for the
sub-sample of bright target stars with () is easier to interpret. The set of microlensing events
that we have observed is consistent with a simple Galactic model. A more
precise interpretation would require either a better knowledge of the distance
distribution of the target stars, or a simulation based on a Galactic model.
For this purpose, we define and discuss the concept of optical depth for a
given catalog or for a limiting magnitude.Comment: 22 pages submitted to Astronomy & Astrophysic
Removing the Microlensing Blending-Parallax Degeneracy Using Source Variability
Microlensing event MACHO 97-SMC-1 is one of the rare microlensing events for
which the source is a variable star, simply because most variable stars are
systematically eliminated from microlensing studies. Using observational data
for this event, we show that the intrinsic variability of a microlensed star is
a powerful tool to constrain the nature of the lens by breaking the degeneracy
between the microlens parallax and the blended light. We also present a
statistical test for discriminating the location of the lens based on the
\chi^2 contours of the vector \Lambda, the inverse of the projected velocity.
We find that while SMC self lensing is somewhat favored over halo lensing,
neither location can be ruled out with good confidence.Comment: 15 text pages + 2 tables + 7 figures. Published in the Astrophysical
Journa
Discovery of a peculiar Cepheid-like star towards the northern edge of the Small Magellanic Cloud
For seven years, the EROS-2 project obtained a mass of photometric data on
variable stars. We present a peculiar Cepheid-like star, in the direction of
the Small Magellanic Cloud, which demonstrates unusual photometric behaviour
over a short time interval. We report on data of the photometry acquired by the
MARLY telescope and spectroscopy from the EFOSC instrument for this star,
called EROS2 J005135-714459(sm0060n13842), which resembles the unusual Cepheid
HR 7308. The light curve of our target is analysed using the Analysis of
Variance method to determine a pulsational period of 5.5675 days. A fit of
time-dependent Fourier coefficients is performed and a search for proper motion
is conducted. The light curve exhibits a previously unobserved and spectacular
change in both mean magnitude and amplitude, which has no clear theoretical
explanation. Our analysis of the spectrum implies a radial velocity of 104 km
s and a metallicity of -0.40.2 dex. In the direction of right
ascension, we measure a proper motion of 17.46.0 mas yr using EROS
astrometry, which is compatible with data from the NOMAD catalogue. The nature
of EROS2 J005135-714459(sm0060n13842) remains unclear. For this star, we may
have detected a non-zero proper motion for this star, which would imply that it
is a foreground object. Its radial velocity, pulsational characteristics, and
photometric data, however, suggest that it is instead a Cepheid-like object
located in the SMC. In such a case, it would present a challenge to
conventional Cepheid models.Comment: Correction of typos in the abstrac
- âŠ