75 research outputs found
Star Spot Induced Radial Velocity Variability in LkCa 19
We describe a new radial velocity survey of T Tauri stars and present the
first results. Our search is motivated by an interest in detecting massive
young planets, as well as investigating the origin of the brown dwarf desert.
As part of this survey, we discovered large-amplitude, periodic, radial
velocity variations in the spectrum of the weak line T Tauri star LkCa 19.
Using line bisector analysis and a new simulation of the effect of star spots
on the photometric and radial velocity variability of T Tauri stars, we show
that our measured radial velocities for LkCa19 are fully consistent with
variations caused by the presence of large star spots on this rapidly rotating
young star. These results illustrate the level of activity-induced radial
velocity noise associated with at least some very young stars. This
activity-induced noise will set lower limits on the mass of a companion
detectable around LkCa 19, and similarly active young stars.Comment: ApJ accepted, 27 pages, 12 figures, aaste
A Critique of Current Magnetic-Accretion Models for Classical T-Tauri Stars
Current magnetic-accretion models for classical T-Tauri stars rely on a
strong, dipolar magnetic field of stellar origin to funnel the disk material
onto the star, and assume a steady-state. In this paper, I critically examine
the physical basis of these models in light of the observational evidence and
our knowledge of magnetic fields in low-mass stars, and find it lacking.
I also argue that magnetic accretion onto these stars is inherently a
time-dependent problem, and that a steady-state is not warranted.
Finally, directions for future work towards fully-consistent models are
pointed out.Comment: 2 figure
High Resolution Spectroscopy during Eclipse of the Young Substellar Eclipsing Binary 2MASS 0535-0546. I. Primary Spectrum: Cool Spots versus Opacity Uncertainties
We present high-resolution Keck optical spectra of the very young substellar
eclipsing binary 2MASS J05352184-0546085, obtained during eclipse of the
lower-mass (secondary) brown dwarf. The observations yield the spectrum of the
higher-mass (primary) brown dwarf alone, with negligible (~1.6%) contamination
by the secondary. We perform a simultaneous fine-analysis of the TiO-epsilon
band and the red lobe of the KI doublet, using state-of-the-art PHOENIX Dusty
and Cond synthetic spectra. Comparing the effective temperature and surface
gravity derived from these fits to the {\it empirically} determined surface
gravity of the primary (logg=3.5) then allows us to test the model spectra as
well as probe the prevailing photospheric conditions. We find that: (1) fits to
TiO-epsilon alone imply Teff=2500 \pm 50K; (2) at this Teff, fits to KI imply
logg=3.0, 0.5 dex lower than the true value; and (3) at the true logg, KI fits
yield Teff=2650 \pm 50K, ~150K higher than from TiO-epsilon alone. On the one
hand, these are the trends expected in the presence of cool spots covering a
large fraction of the primary's surface (as theorized previously to explain the
observed Teff reversal between the primary and secondary). Specifically, our
results can be reproduced by an unspotted stellar photosphere with Teff=2700K
and (empirical) logg=3.5, coupled with axisymmetric cool spots that are 15%
cooler (2300K), have an effective logg=3.0 (0.5 dex lower than photospheric),
and cover 70% of the surface. On the other hand, the trends in our analysis can
also be reproduced by model opacity errors: there are lacks in the synthetic
TiO-epsilon opacities, at least for higher-gravity field dwarfs. Stringently
discriminating between the two possibilities requires combining the present
results with an equivalent analysis of the secondary (predicted to be
relatively unspotted compared to the primary).Comment: To appear in ApJ. 11 pages, 5 figure
Colloidal Gels: Equilibrium and Non-Equilibrium Routes
We attempt a classification of different colloidal gels based on
colloid-colloid interactions. We discriminate primarily between non-equilibrium
and equilibrium routes to gelation, the former case being slaved to
thermodynamic phase separation while the latter is individuated in the
framework of competing interactions and of patchy colloids. Emphasis is put on
recent numerical simulations of colloidal gelation and their connection to
experiments. Finally we underline typical signatures of different gel types, to
be looked in more details in experiments.Comment: topical review, accepted in J. Phys. Condens. Matte
The model of dynamo with small number of modes and magnetic activity of T Tauri stars
The model that describes operation of dynamo in fully convective stars is
presented. It is based on representation of stellar magnetic field as a
superposition of finite number of poloidal and toroidal free damping modes. In
the frame of adopted low of stellar differential rotation we estimated minimal
value of dynamo number D, starting from which generation of cyclic magnetic
field in stars without radiative core is possible. We also derived expression
for period of the cycle. It was found that dynamo cycles of fully convective
stars and stars with thin convective envelopes differ in a qualitative way: 1)
distribution of spots over latitude during the cycle is different in these
stars; 2) the model predicts that spot formation in fully convective stars
should be strongly suppressed at some phases of the cycle.
We have analyzed historical lightcurve of WTTS star V410 Tau and found that
long term activity of the star is not periodic process. Rather one can speak
about quasi cyclic activity with characteristic time of yr and chaotic
component over imposed. We concluded also that redistribution of cool spots
over longitude is the reason of long term variations of V410 Tau brightness. It
means that one can not compare directly results of photometric observations
with predictions of our axially symmetric (for simplicity) model which allows
to investigate time evolution of spot's distribution over latitude. We then
discuss what kind of observations and in which way could be used to check
predictions of the dynamo theory.Comment: 18 pages, 5 figures, accepted to Astron. Let
Multisite observations of SU Aurigae
We present results from the 1996 MUSICOS (MUlti-SIte COntinuous Spectroscopy)
campaign on the T Tauri star SU Aurigae. We find a 2.7-d periodicity in the He
I (587.6 nm) line and somewhat longer, less well-pronounced periodicities in
the Balmer lines and in Na D. Our observations support the suggestion that the
wind and infall signatures are out of phase on SU Aur. We present Doppler
images of SU Aur that have been obtained from least-squares deconvolved
profiles. Images taken about one rotation apart show only limited overlap, in
particular at low latitudes. This is in part due to limitations in
signal-to-noise, and in part due to line profile deformations that arise from
short-lived and/or non-surface features. The agreement at high latitudes is
better and suggests that at least some longer-lived features are present. The
analysis of Stokes V profiles yields a marginal magnetic field detection during
one of the phases.Comment: 22 pages, 20 figures, accepted for publication in MNRA
Monotherapy efficacy of blood-brain barrier permeable small molecule reactivators of protein phosphatase 2A in glioblastoma
Glioblastoma is a fatal disease in which most targeted therapies have clinically failed. However, pharmacological reactivation of tumour suppressors has not been thoroughly studied as yet as a glioblastoma therapeutic strategy. Tumour suppressor protein phosphatase 2A is inhibited by non-genetic mechanisms in glioblastoma, and thus, it would be potentially amendable for therapeutic reactivation. Here, we demonstrate that small molecule activators of protein phosphatase 2A, NZ-8-061 and DBK-1154, effectively cross the in vitro model of bloodâbrain barrier, and in vivo partition to mouse brain tissue after oral dosing. In vitro, small molecule activators of protein phosphatase 2A exhibit robust cell-killing activity against five established glioblastoma cell lines, and nine patient-derived primary glioma cell lines. Collectively, these cell lines have heterogeneous genetic background, kinase inhibitor resistance profile and stemness properties; and they represent different clinical glioblastoma subtypes. Moreover, small molecule activators of protein phosphatase 2A were found to be superior to a range of kinase inhibitors in their capacity to kill patient-derived primary glioma cells. Oral dosing of either of the small molecule activators of protein phosphatase 2A significantly reduced growth of infiltrative intracranial glioblastoma tumours. DBK-1154, with both higher degree of brain/blood distribution, and more potent in vitro activity against all tested glioblastoma cell lines, also significantly increased survival of mice bearing orthotopic glioblastoma xenografts. In summary, this report presents a proof-of-principle data for bloodâbrain barrierâpermeable tumour suppressor reactivation therapy for glioblastoma cells of heterogenous molecular background. These results also provide the first indications that protein phosphatase 2A reactivation might be able to challenge the current paradigm in glioblastoma therapies which has been strongly focused on targeting specific genetically altered cancer drivers with highly specific inhibitors. Based on demonstrated role for protein phosphatase 2A inhibition in glioblastoma cell drug resistance, small molecule activators of protein phosphatase 2A may prove to be beneficial in future glioblastoma combination therapies.</p
Insecticide resistance status in Anopheles gambiae in southern Benin
BACKGROUND: The emergence of pyrethroid resistance in Anopheles gambiae has become a serious concern to the future success of malaria control. In Benin, the National Malaria Control Programme has recently planned to scaling up long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS) for malaria prevention. It is, therefore, crucial to monitor the level and type of insecticide resistance in An. gambiae, particularly in southern Benin where reduced efficacy of insecticide-treated nets (ITNs) and IRS has previously been reported. METHODS: The protocol was based on mosquito collection during both dry and rainy seasons across forty districts selected in southern Benin. Bioassay were performed on adults collected from the field to assess the susceptibility of malaria vectors to insecticide-impregnated papers (permethrin 0.75%, delthamethrin 0.05%, DDT 4%, and bendiocarb 0.1%) following WHOPES guidelines. The species within An. gambiae complex, molecular form and presence of kdr and ace-1 mutations were determined by PCR. RESULTS: Strong resistance to permethrin and DDT was found in An. gambiae populations from southern Benin, except in Aglangandan where mosquitoes were fully susceptible (mortality 100%) to all insecticides tested. PCR showed the presence of two sub-species of An. gambiae, namely An. gambiae s.s, and Anopheles melas, with a predominance for An. gambiae s.s (98%). The molecular M form of An. gambiae was predominant in southern Benin (97%). The kdr mutation was detected in all districts at various frequency (1% to 95%) whereas the Ace-1 mutation was found at a very low frequency (<or= 5%). CONCLUSION: This study showed a widespread resistance to permethrin in An. gambiae populations from southern Benin, with a significant increase of kdr frequency compared to what was observed previously in Benin. The low frequency of Ace-1 recorded in all populations is encouraging for the use of bendiocarb as an alternative insecticide to pyrethroids for IRS in Benin
Ătude du relargage des mĂ©taux dans les eaux d'infiltration d'un champ d'Ă©pandage par construction d'un plan d'expĂ©riences D-optimal pondĂ©rĂ©
National audienceThis study aimed to determine the climatic factors influencing metal solubilization in the percolation waters from a field that had received intensive pig slurry applications. We first set up a D-optimal experimental design specially fitted to this study. The experimental design allowed to take into account some specific conditions in relation with the experimental domain under study. On the one hand, these conditions consisted of constraints corresponding to parts of the domain which cannot be studied, and on the other hand, of difficulties in achieving some levels of factors. Carrying out in vitro experiments enabled to evidence that temperature and volume of rainfalls were the most important factors acting on metal solubilization. © EDP Sciences, Wiley-VCH
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