779 research outputs found
Les macroiinvertébrés dulçaquicoles de Nuku-Hiva (Marquises) : compte-rendu d'une mission en saison des pluies et proposition d'un protocole de surveillance
Dans le cadre du programme de lutte contre #Simulium buissoni, les macroinvertébrés des cours d'eau de l'île de Nuku-Hiva (Marquises) ont été échantillonnés. La faune apparaît pauvre et peu diversifiée, résultat probable des dimensions réduites et de la localisation de l'île, ainsi que des conditions hydrologiques particulièrement difficiles dans ces cours d'eau. Les Mollusques Gastéropodes et les Crustacés Décapodes occupent une place très importante dans les peuplements invertébrés et méritent d'être particulièrement étudiés. Les chevrettes (#Macrobrachium spp.) représentent le seul groupe exploité parmi ces invertébrés et exigent, à ce titre, d'être plus spécialement observées. Un protocole d'étude et de surveillance des peuplements invertébrés, en relation avec les traitements insecticides et constitué de quatre phases chronologiques, est ensuite proposé. (Résumé d'auteur
A probable pre-main sequence chemically peculiar star in the open cluster Stock 16
We used the Ultraviolet and Visual Echelle Spectrograph of the ESO-Very Large
Telescope to obtain a high resolution and high signal-to-noise ratio spectrum
of Stock 16-12, an early-type star which previous Delta-a photometric
observations suggest being a chemically peculiar (CP) star. We used spectral
synthesis to perform a detailed abundance analysis obtaining an effective
temperature of 8400 +/- 400 K, a surface gravity of 4.1 +/- 0.4, a
microturbulence velocity of 3.4 +0.7/-0.3 km/s, and a projected rotational
velocity of 68 +/- 4 km/s. We provide photometric and spectroscopic evidence
showing the star is most likely a member of the young Stock 16 open cluster
(age 3-8 Myr). The probable cluster membership, the star's position in the
Hertzsprung-Russell diagram, and the found infrared excess strongly suggest the
star is still in the pre-main-sequence (PMS) phase. We used PMS evolutionary
tracks to determine the stellar mass, which ranges between 1.95 and 2.3 Msun,
depending upon the adopted spectroscopic or photometric data results.
Similarly, we obtained a stellar age ranging between 4 and 6 Myr, in agreement
with that of the cluster. Because the star's chemical abundance pattern
resembles well that known of main sequence CP metallic line (Am) stars, the
object sets important constraints to the diffusion theory. Additional
spectroscopic and spectropolarimetric data allowed us to conclude that the
object is probably a single non-magnetic star.Comment: Accepted for publication in MNRAS; 8 pages, 5 figures, 1 tabl
Far-Ultraviolet Activity Levels of F, G, K, and M dwarf Exoplanet Host Stars
We present a survey of far-ultraviolet (FUV; 1150 - 1450 Ang) emission line
spectra from 71 planet-hosting and 33 non-planet-hosting F, G, K, and M dwarfs
with the goals of characterizing their range of FUV activity levels,
calibrating the FUV activity level to the 90 - 360 Ang extreme-ultraviolet
(EUV) stellar flux, and investigating the potential for FUV emission lines to
probe star-planet interactions (SPIs). We build this emission line sample from
a combination of new and archival observations with the Hubble Space
Telescope-COS and -STIS instruments, targeting the chromospheric and transition
region emission lines of Si III, N V, C II, and Si IV.
We find that the exoplanet host stars, on average, display factors of 5 - 10
lower UV activity levels compared with the non-planet hosting sample; this is
explained by a combination of observational and astrophysical biases in the
selection of stars for radial-velocity planet searches. We demonstrate that UV
activity-rotation relation in the full F - M star sample is characterized by a
power-law decline (with index ~ -1.1), starting at rotation periods
>~3.5 days. Using N V or Si IV spectra and a knowledge of the star's bolometric
flux, we present a new analytic relationship to estimate the intrinsic stellar
EUV irradiance in the 90 - 360 Ang band with an accuracy of roughly a factor of
~2. Finally, we study the correlation between SPI strength and UV activity in
the context of a principal component analysis that controls for the sample
biases. We find that SPIs are not a statistically significant contributor to
the observed UV activity levels.Comment: ApJS, accepted. 33 pages in emulateapj, 13 figures, 10 table
Stellar magnetism through the polarized eyes of the FORS1 instrument
During the last decade, the FORS1 instrument of the ESO Very Large Telescope
has been used to obtain low resolution circular polarized spectra for about 500
stars, with the aim of measuring their mean longitudinal magnetic fields.
Magnetic field estimates were obtained by different authors, using different
software tools. Several interesting detections were obtained at a 3 sigma
level; some of them were eventually confirmed by follow-up investigations, some
of them were not. This raises issues about the reliability of the stated
uncertainties of some of the published field values. To investigate these
problems, we have developed a semi-automatic procedure for magnetic field
determination, which includes self-consistent checks for field detection
reliability. We have applied our procedure to the full content of single star
("fast mode") circular spectropolarimetric measurements of the FORS1 archive,
and explored the details and interagreement of various methods for data
reduction. We have finally produced a catalogue of FORS1 longitudinal field
measurements which includes about 1000 entries. Here we critically review the
previously published FORS1 measurements, and, based on our results, we suggest
that the incidence of the magnetic field in various classes of stars should be
revised.Comment: To appear in the proceedings of the conference "Stellar Polarimetry:
From Birth to Death" held in Madison, Wisconsin, in June 201
Magnetic field measurements and their uncertainties: the FORS1 legacy
During the last decade, the FORS1 instrument of the ESO VLT has been
extensively used to study stellar magnetism. A number of interesting
discoveries of magnetic fields in several classes of stars have been announced,
many of which obtained at a ~3 sigma level; some of the discoveries are
confirmed by measurements obtained with other instruments, some are not. Here
we investigate the reasons for the discrepancies between the results obtained
with FORS1 and those obtained with other instruments.
Using the ESO FORS pipeline, we have developed a semi-automatic procedure for
magnetic field determination. We have applied this procedure to the full
content of circular spectropolarimetric measurements of the FORS1 archive. We
have devised and applied a number of consistency checks to our field
determinations, and we have compared our results to those previously published
in the literature.
We find that for high signal-to-noise ratio measurements, photon noise does
not account for the full error bars. We discuss how field measurements depend
on the specific algorithm adopted for data reduction, and we show that very
small instrument flexures, negligible in most of the instrument applications,
may be responsible for some spurious field detections in the null profiles.
Finally, we find that we are unable to reproduce some results previously
published in the literature. Consequently, we do not confirm some important
discoveries of magnetic fields obtained with FORS1 and reported in previous
publications.
Our revised field measurements show that there is no contradiction between
the results obtained with the low-resolution spectropolarimeter FORS1 and those
obtained with high-resolution spectropolarimeters. FORS1 is an instrument
capable of performing reliable magnetic field measurements, provided that the
various source of uncertainties are properly taken into account.Comment: Accepted for publication in A&
Phylogenetic analysis of grapevine cv. Ansonica growing on the island of Giglio, Italy, by AFLP and SSR markers
The geographic origin of the grapevine cultivar Ansonica (Vitis vinifera L.) grown on the island of Giglio, Tuscany, Italy, was investigated with molecular tools, i.e. AFLP and SSR (microsatellite) analysis. The scored polymorphic DNA bands were statistically analysed and the results were expressed in dendrograms showing the degree of genomic similarity among the tested cultivars: three Ansonica vines sampled in some of the oldest vineyards of the island one Ansonica specimen grown in Tuscany, one Inzolia specimen grown in Sicily, 23 cultivars grown in different Mediterranean regions and 40 Greek cultivars. The results obtained from AFLP or SSR approaches led to equivalent conclusions: the three grapevines sampled in Giglio were indistinguishable and showed genetic similarity with cv. Ansonica grown in the Tuscan mainland and with cv. Inzolia from Sicily, Airen from Spain, Clairette from France and Roditis from Greece. The SSR analysis showed that Sideritis and Roditis have the highest genomic similarity with Ansonica among the 40 tested Greek cultivars. The molecular analysis gives conclusive evidence for the Greek origin of Ansonica grown on the island, as previously proposed on the basis of morphological and historical studies
Phylogenetic analysis of grapevine cv. Ansonica growing on the island of Giglio, Italy, by AFLP and SSR markers
The geographic origin of the grapevine cultivar Ansonica (Vitis vinifera L.) grown on the island of Giglio, Tuscany, Italy, was investigated with molecular tools, i.e. AFLP and SSR (microsatellite) analysis. The scored polymorphic DNA bands were statistically analysed and the results were expressed in dendrograms showing the degree of genomic similarity among the tested cultivars: three Ansonica vines sampled in some of the oldest vineyards of the island, one Ansonica specimen grown in Tuscany, one Inzolia specimen grown in Sicily, 23 cultivars grown in different Mediterranean regions and 40 Greek cultivars. The results obtained from AFLP or SSR approaches led to equivalent conclusions: the three grapevines sampled in Giglio were indistinguishable and showed genetic similarity with cv. Ansonica grown in the Tuscan mainland and with cv. Inzolia from Sicily, Airen from Spain, Clairette from France and Roditis from Greece. The SSR analysis showed that Sideritis and Roditis have the highest genomic similarity with Ansonica among the 40 tested Greek cultivars. The molecular analysis gives conclusive evidence for the Greek origin of Ansonica grown on the island, as previously proposed on the basis of morphological and historical studies
Magnetism, X-rays, and Accretion Rates in WD 1145+017 and other Polluted White Dwarf Systems
This paper reports circular spectropolarimetry and X-ray observations of
several polluted white dwarfs including WD 1145+017, with the aim to constrain
the behavior of disk material and instantaneous accretion rates in these
evolved planetary systems. Two stars with previously observed Zeeman splitting,
WD 0322-019 and WD 2105-820, are detected above 5 sigma and > 1 kG, while
WD 1145+017, WD 1929+011, and WD 2326+049 yield (null) detections below this
minimum level of confidence. For these latter three stars, high-resolution
spectra and atmospheric modeling are used to obtain limits on magnetic field
strengths via the absence of Zeeman splitting, finding B* < 20 kG based on data
with resolving power R near 40 000. An analytical framework is presented for
bulk Earth composition material falling onto the magnetic polar regions of
white dwarfs, where X-rays and cyclotron radiation may contribute to accretion
luminosity. This analysis is applied to X-ray data for WD 1145+017, WD
1729+371, and WD 2326+049, and the upper bound count rates are modeled with
spectra for a range of plasma kT = 1 - 10 keV in both the magnetic and
non-magnetic accretion regimes. The results for all three stars are consistent
with a typical dusty white dwarf in a steady-state at 1e8 - 1e9 g/s. In
particular, the non-magnetic limits for WD 1145+017 are found to be well below
previous estimates of up to 1e12 g/s, and likely below 1e10 g/s, thus
suggesting the star-disk system may be average in its evolutionary state, and
only special in viewing geometry.Comment: 14 pages, 7 figures, 3 tables; accepted to MNRA
An In-Depth Spectroscopic Analysis of the Blazhko Star RR Lyr. I. Characterisation of the star: abundance analysis and fundamental parameters
The knowledge of accurate stellar parameters is a keystone in several fields
of stellar astrophysics, such as asteroseismology and stellar evolution.
Although the fundamental parameters can be derived both from spectroscopy and
multicolour photometry, the results obtained are sometimes affected by
systematic uncertainties. In this paper, we present a self-consistent spectral
analysis of the pulsating star RR Lyr, which is the primary target for our
study of the Blazhko effect. We used high-resolution and high signal-to-noise
ratio spectra to carry out a consistent parameter determination and abundance
analysis for RR Lyr. We provide a detailed description of the methodology
adopted to derive the fundamental parameters and the abundances. Stellar
pulsation attains high amplitudes in RR Lyrae stars, and as a consequence the
stellar parameters vary significantly over the pulsation cycle. The abundances
of the star, however, are not expected to change. From a set of available
high-resolution spectra of RR Lyr we selected the phase of maximum radius, at
which the spectra are least disturbed by the pulsation. Using the abundances
determined at this phase as a starting point, we expect to obtain a higher
accuracy in the fundamental parameters determined at other phases. The set of
fundamental parameters obtained in this work fits the observed spectrum
accurately. Through the abundance analysis, we find clear indications for a
depth-dependent microturbulent velocity, that we quantified. We confirm the
importance of a consistent analysis of relevant spectroscopic features,
application of advanced model atmospheres, and the use of up-to-date atomic
line data for the determination of stellar parameters. These results are
crucial for further studies, e.g., detailed theoretical modelling of the
observed pulsations.Comment: 12 pages, accepted for publication in Astronomy & Astrophysic
Suppressed Far-UV stellar activity and low planetary mass-loss in the WASP-18 system
WASP-18 hosts a massive, very close-in Jupiter-like planet. Despite its young age (R′HK activity parameter lies slightly below the basal level; there is no significant time-variability in the log R′HK value; there is no detection of the star in the X-rays. We present results of far-UV observations of WASP-18 obtained with COS on board of HST aimed at explaining this anomaly. From the star’s spectral energy distribution, we infer the extinction (E(B − V) ≈ 0.01mag) and then the ISM column density for a number of ions, concluding that ISM absorption is not the origin of the anomaly. We measure the flux of the four stellar emission features detected in the COS spectrum (C II, C III, C IV, Si IV). Comparing the C II/C IV flux ratio measured for WASP-18 with that derived from spectra of nearby stars with known age, we see that the far-UV spectrum of WASP-18 resembles that of old (>5Gyr), inactive stars, in stark contrast with its young age. We conclude that WASP-18 has an intrinsically low activity level, possibly caused by star-planet tidal interaction, as suggested by previous studies. Re-scaling the solar irradiance reference spectrum to match the flux of the Si IV line, yields an XUV integrated flux at the planet orbit of 10.2 erg s−1 cm−2. We employ the rescaled XUV solar fluxes to model of the planetary upper atmosphere, deriving an extremely low thermal mass-loss rate of 10−20MJ Gyr−1. For such high-mass planets, thermal escape is not energy limited, but driven by Jeans escape
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