1,831 research outputs found
On the abundance of Lithium in T Coronae Borealis
We have obtained high resolution echelle spectroscopy of the recurrent nova T
CrB. We find that the surface lithium abundance in T CrB is signifcantly
enhanced compared to field M giants, where it is not detectable. We offer
possible explanations for this in terms of either a delay in the onset of
convection in the giant star, enhanced coronal activity due to star-spots or
the enhancement of Li resulting from the nova explosion(s).Comment: 3 pages, 1 figure (a and b), accepted by MNRA
On the lithium content of the globular cluster M92
I use literature data and a new temperature calibration to determine the Li
abundances in the globular cluster M 92. Based on the same data, Boesgaard et
al. have claimed that there is a dispersion in Li abundances in excess of
observational errors. This result has been brought as evidence for Li depletion
in metal-poor dwarfs. In the present note I argue that there is no strong
evidence for intrinsic dispersion in Li abundances, although a dispersion as
large as 0.18 dex is possible. The mean Li abundance, A(Li)=2.36, is in good
agreement with recent results for field stars and TO stars in the metal-poor
globular cluster NGC 6397. The simplest interpretation is that this constant
value represents the primordial Li abundance.Comment: A&A accepte
Evolution of lithium beyond the solar age: a Li survey of the old open cluster NGC 188
We have determined Li abundances for 11 G-type stars in the 6-8 Gyr old open
cluster NGC 188. These data significantly enlarge the number of cluster stars
with Li measurements, allowing us to extend the investigation of Li depletion
in open clusters to ages well beyond the age of the Sun. We have also inferred
the cluster metallicity which turns out to be solar. We find that solar-type
stars in NGC 188 are only slightly more Li depleted than the much younger
Hyades and no more Li depleted than stars of similar temperature in the 2-4 Gyr
younger cluster M 67. At variance with M 67, NGC 188 members show virtually no
scatter in their Li abundances. Surprisingly, no solar- type star in NGC 188
appears as Li depleted as the Sun or as the most Li depleted stars in M 67. We
discuss the implications of these results for mechanisms of internal mixing and
Li depletion in main sequence stars.Comment: to appear in A&
GPS-based CERN-LNGS time link for Borexino
We describe the design, the equipment, and the calibration of a new GPS based
time link between CERN and the Borexino experiment at the Gran Sasso Laboratory
in Italy. This system has been installed and operated in Borexino since March
2012, and used for a precise measurement of CNGS muon neutrinos speed in May
2012. The result of the measurement will be reported in a different letter.Comment: 13 pages, 11 figure
Element abundances of unevolved stars in the open cluster M 67
We determined the metallicity ([Fe/H]), together with O, Na, Mg, Al, Si, Ca,
Ti, Cr and Ni abundances for a sample of 10 unevolved or slightly evolved stars
belonging to the open cluster M 67. We find an average metallicity [Fe/H]=0.03
+/- 0.01, in very good agreement with previous determinations. All the [X/Fe]
abundance ratios are very close to solar. The star-to-star scatter in [Fe/H]
and [X/Fe] ratios for all elements, including oxygen, is lower than 0.05 dex,
implying that the large dispersion in lithium reported in previous studies is
not due to differences in these element abundances. We also find that, when
using a homogeneous scale, the abundance pattern of unevolved stars in our
sample is very similar to that of evolved stars, suggesting that, at least in
this cluster, RGB and clump stars have not undergone any chemical processing.
Finally, our results show that M 67 has a chemical composition that is
representative of the solar neighborhood.Comment: 18 pages, 5 figures, accepted for publication in A&
The energetics of the gradual phase
Reseachers compare results with those in the chapter by Moore et al. (1980), who reached five main conclusions about the gradual phase: (1) the typical density of the soft X-ray emitting plasma is between 10 to the 11th power and 10 to the 12th power cm-3 for compact flares and between 10 to the 10th power and 10 to the 11th power cm-3 for a large-area flare; (2) cooling is by conduction and radiation in roughly equal proportions; (3) continual heating is needed in the decay phase of two-ribbon flares; (4) continual heating is probably not needed in compact events; (5) most of the soft-X-ray-emitting plasma results from chromospheric evaporation. The goal was to reexamine these problems with the data from the Solar Maximum Mission (SMM) and other supporting instruments as well as to take advantage of recent theoretical advances. SMM is capable of measuring coronal temperatures more accurately and with a better cadence than has been possible before. The SMM data set is also unique in that the complete transit of an active region was observed, with soft X-ray and UV images being taken every few minutes. Researcher's were therefore able to establish the pre-flare conditions of the region and see whether anything has changed as a result of the flare. The assumptions made in attempting to determine the required plasma parameters are described. The derived parameters for the five prime flares are presented, and the role of numerical simulations is discussed
Design of a Base-Board for arrays of closely-packed Multi-Anode Photo-Multipliers
We describe the design of a Base-Board to house Multi-Anode Photo-Multipliers
for use in large-area arrays of light sensors. The goals, the design, the
results of tests on the prototypes and future developments are presented.Comment: 16 pages, 5 figures, submitted to Nucl. Instrum. and Meth.
Dual analysis of host and pathogen transcriptomes in ostreid herpesvirus 1-positive Crassostrea gigas
Ostreid herpesvirus type 1 (OsHV-1) has become a problematic infective agent for the Pacific oyster Crassostrea gigas. In particular, the OsHV-1 \u3bcVar subtype has been associated with severe mortality episodes in oyster spat and juvenile oysters in France and other regions of the world. Factors enhancing the infectivity of the virus and its interactions with susceptible and resistant bivalve hosts are still to be understood, and only few studies have explored the expression of oyster or viral genes during productive infections. In this work, we have performed a dual RNA sequencing analysis on an oyster sample with a high viral load. High sequence coverage allowed us to thoroughly explore the OsHV-1 transcriptome and identify the activated molecular pathways in C.gigas. The identification of several highly induced and defence-related oyster transcripts supports the crucial role played by the innate immune system against the virus and opportunistic microbes possibly contributing to subsequent spat mortality
The Discovery of a Companion to the Very Cool Dwarf Gl~569~B with the Keck Adaptive Optics Facility
We report observations obtained with the Keck adaptive optics facility of the
nearby (d=9.8 pc) binary Gl~569. The system was known to be composed of a cool
primary (dM2) and a very cool secondary (dM8.5) with a separation of 5" (49
Astronomical Units). We have found that Gl~569~B is itself double with a
separation of only 0".1010".002 (1 Astronomical Unit). This detection
demonstrates the superb spatial resolution that can be achieved with adaptive
optics at Keck. The difference in brightness between Gl~569~B and the companion
is 0.5 magnitudes in the J, H and K' bands. Thus, both objects have
similarly red colors and very likely constitute a very low-mass binary system.
For reasonable assumptions about the age (0.12~Gyr--1.0~Gyr) and total mass of
the system (0.09~M--0.15~M), we estimate that the orbital
period is 3 years. Follow-up observations will allow us to obtain an
astrometric orbit solution and will yield direct dynamical masses that can
constrain evolutionary models of very low-mass stars and brown dwarfs
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