19 research outputs found
Photometric Monitoring of Open Clusters I. The Survey
Open clusters, which have age, abundance, and extinction information from
studies of main-sequence turn off stars, are the ideal location in which to
determine the mass-luminosity-radius relation for low-mass stars. We have
undertaken a photometric monitoring survey of open clusters in the Galaxy
designed to detect low-mass eclipsing binary systems through variations in
their relative light curves. Our aim is to provide an improved calibration of
the mass-luminosity-radius relation for low-mass stars and brown dwarfs, to
test stellar structure and evolution models, and to help quantify the
contribution of low-mass stars to the global mass census in the Galaxy. In this
paper we present our survey, describing the data and outlining the analysis
techniques. We study six nearby open clusters, with a range of ages from to 4 Gyr and metallicities from approximately solar to -0.2dex. We monitor
a field-of-view of > 1 square degree per target cluster, well beyond the
characteristic cluster radius, over timescales of hours, days, and months with
a sampling rate optimised for the detection of eclipsing binaries with periods
of hours to days. Our survey depth is designed to detect eclipse events in a
binary with a primary star of \lesssim 0.3~M_{\sun}. Our data have a
photometric precision of mmag at .Comment: 50 pages, 18 figures, accepted for publication in A
Astro2020 science white paper:fundamental physics with brown dwarfs: the mass-radius relation
The lowest-mass stars, brown dwarfs and giant exoplanets span a minimum in
the mass-radius relationship that probes the fundamental physics of extreme
states of matter, magnetism, and fusion. This White Paper outlines scientific
opportunities and the necessary resources for modeling and measuring the
mass-radius relationship in this regime.Comment: 7 pages, submitted to Astro2020 Science White Paper cal
Simulations of the galaxy population constrained by observations from z=3 to the present day: implications for galactic winds and the fate of their ejecta
We apply Monte Carlo Markov Chain (MCMC) methods to large-scale simulations of galaxy formation in a LambdaCDM cosmology in order to explore how star formation and feedback are constrained by the observed luminosity and stellar mass functions of galaxies. We build models jointly on the Millennium and Millennium-II simulations, applying fast sampling techniques which allow observed galaxy abundances over the ranges 7<log(M*/Msun)<12 and z=0 to z=3 to be used simultaneously as constraints in the MCMC analysis. When z=0 constraints alone are imposed, we reproduce the results of previous modelling by Guo et al. (2012), but no single set of parameters can reproduce observed galaxy abundances at all redshifts simultaneously, reflecting the fact that low-mass galaxies form too early and thus are overabundant at high redshift in this model. The data require the efficiency with which galactic wind ejecta are reaccreted to vary with redshift and halo mass quite differently than previously assumed, but in a similar way as in some recent hydrodynamic simulations of galaxy formation. We propose a specific model in which reincorporation timescales vary inversely with halo mass and are independent of redshift. This produces an evolving galaxy population which fits observed abundances as a function of stellar mass, B- and K-band luminosity at all redshifts simultaneously. It also produces a significant improvement in two other areas where previous models were deficient. It leads to present day dwarf galaxy populations which are younger, bluer, more strongly star-forming and more weakly clustered on small scales than before, although the passive fraction of faint dwarfs remains too high
Stellar Diameters and Temperatures II. Main Sequence K & M Stars
We present interferometric diameter measurements of 21 K- and M- dwarfs made
with the CHARA Array. This sample is enhanced by literature radii measurements
to form a data set of 33 K-M dwarfs with diameters measured to better than 5%.
For all 33 stars, we compute absolute luminosities, linear radii, and effective
temperatures (Teff). We develop empirical relations for \simK0 to M4 main-
sequence stars between the stellar Teff, radius, and luminosity to broad-band
color indices and metallicity. These relations are valid for metallicities
between [Fe/H] = -0.5 and +0.1 dex, and are accurate to ~2%, ~5%, and ~4% for
Teff, radius, and luminosity, respectively. Our results show that it is
necessary to use metallicity dependent transformations to convert colors into
stellar Teffs, radii, and luminosities. We find no sensitivity to metallicity
on relations between global stellar properties, e.g., Teff-radius and
Teff-luminosity. Robust examinations of single star Teffs and radii compared to
evolutionary model predictions on the luminosity-Teff and luminosity-radius
planes reveals that models overestimate the Teffs of stars with Teff < 5000 K
by ~3%, and underestimate the radii of stars with radii < 0.7 R\odot by ~5%.
These conclusions additionally suggest that the models overestimate the effects
that the stellar metallicity may have on the astrophysical properties of an
object. By comparing the interferometrically measured radii for single stars to
those of eclipsing binaries, we find that single and binary star radii are
consistent. However, the literature Teffs for binary stars are systematically
lower compared to Teffs of single stars by ~ 200 to 300 K. Lastly, we present a
empirically determined HR diagram for a total of 74 nearby, main-sequence, A-
to M-type stars, and define regions of habitability for the potential existence
of sub-stellar mass companions in each system. [abridged]Comment: 73 pages, 12 Tables, 18 Figures. Accepted for publication in The
Astrophysical Journa
Astro2020 science white paper:fundamental physics with brown dwarfs: the mass-radius relation
Galaxy formation in the Planck cosmology - I. Matching the observed evolution of star formation rates, colours and stellar masses
We have updated the Munich galaxy formation model to the Planck first-year cosmology, while modifying the treatment of baryonic processes to reproduce recent data on the abundance and passive fractions of galaxies from z = 3 down to z = 0. Matching these more extensive and more precise observational results requires us to delay the reincorporation of wind ejecta, to lower the surface density threshold for turning cold gas into stars, to eliminate ram-pressure stripping in haloes less massive than ∼1014 M⊙, and to modify our model for radio mode feedback. These changes cure the most obvious failings of our previous models, namely the overly early formation of low-mass galaxies and the overly large fraction of them that are passive at late times. The new model is calibrated to reproduce the observed evolution both of the stellar mass function and of the distribution of star formation rate at each stellar mass. Massive galaxies (log M⋆/M⊙ ≥ 11.0) assemble most of their mass before z = 1 and are predominantly old and passive at z = 0, while lower mass galaxies assemble later and, for log M⋆/M⊙ ≤ 9.5, are still predominantly blue and star forming at z = 0. This phenomenological but physically based model allows the observations to be interpreted in terms of the efficiency of the various processes that control the formation and evolution of galaxies as a function of their stellar mass, gas content, environment and time
Confronting theoretical models with the observed evolution of the galaxy population out to z=4
[abridged] We construct lightcones for the semi-analytic galaxy formation
simulation of Guo et al. (2011) and make mock catalogues for comparison with
deep high-redshift surveys. Photometric properties are calculated with two
different stellar population synthesis codes (Bruzual & Charlot 2003; Maraston
2005) in order to study sensitivity to this aspect of the modelling. The
catalogues are publicly available and include photometry for a large number of
observed bands from 4000{\deg}A to 6{\mu}m, as well as rest-frame photometry
and intrinsic properties of the galaxies. Guo et al. (2011) tuned their model
to fit the low-redshift galaxy population but noted that at z > 1 it
overpredicts the abundance of galaxies below the "knee" of the stellar mass
function. Here we extend the comparison to deep galaxy counts in the B, i, J, K
and IRAC 3.6{\mu}m, 4.5{\mu}m and 5.8{\mu}m bands, to the redshift
distributions of K and 5.8{\mu}m selected galaxies, and to the evolution of
rest-frame luminosity functions in the B and K bands. The B, i and J counts are
well reproduced, but at longer wavelengths the overabundant high-redshift
galaxies produce excess faint counts. The predicted redshift distributions for
K and 5.8{\mu}m selected samples highlight the effect of emission from
thermally pulsing AGB stars. The full treatment of Maraston (2005) predicts
three times as many z~2 galaxies in faint 5.8{\mu}m selected samples as the
model of Bruzual & Charlot (2003), whereas the two models give similar
predictions for K-band selected samples. Although luminosity functions are
adequately reproduced out to z~3 in rest-frame B, the same is true at
rest-frame K only if TP-AGB emission is included, and then only at high
luminosity. Fainter than L* the two synthesis models agree but overpredict the
number of galaxies, another reflection of the overabundance of ~10^10M\odot
model galaxies at z > 1.Comment: 13 pages, 6 figures, accepted by MNRA
Prise de position de la Société Francophone du Diabète (SFD) sur la prise en charge médicamenteuse de l'hyperglycémie du patient diabétique de type 2
peer reviewe
Successful response to pegylated interferon alpha in a patient with recurrent paraganglioma
International audienceNo abstract availabl
Head-to-head comparison between 18F-FDOPA PET/CT and MR/CT angiography in clinically recurrent head and neck paragangliomas
International audiencePurpose: Head and neck paragangliomas (HNPGLs) can relapse after primary treatment. Optimal imaging protocols have not yet been established for posttreatment evaluation. The aim of the present study was to assess the diagnostic value of 18F-FDOPA PET/CT and MR/CT angiography (MRA/CTA) in HNPGL patients with clinical relapse during their follow-up.Methods: Sixteen consecutive patients presenting with local pain, tinnitus, dysphagia, hoarse voice, cranial nerve involvement, deafness, or retrotympanic mass appearing during follow-up after the initial treatment of HNPGLs were retrospectively evaluated. Patients underwent both 18F-FDOPA PET/CT and MRA (15 patents) or CTA (1 patent). Both methods were first assessed under blinded conditions and afterwards correlated. Head and neck imaging abnormalities without histological confirmation were considered true-positive results based on a consensus between radiologists and nuclear physicians and on further 18F-FDOPA PET/CT and/or MRA.Results: 18F-FDOPA PET/CT and MRA/CTA were concordant in 14 patients and in disagreement in 2 patients. 18F-FDOPA PET/CT and MRA/CTA identified, respectively, 12 and 10 presumed recurrent HNPGLs in 12 patients. The two lesions diagnosed by PET/CT only were confirmed during follow-up by otoscopic examination and MRA performed 29 and 17 months later. 18F-FDOPA PET/CT images were only slightly influenced by the posttreatment sequelae, showing a better interobserver reproducibility than MRA/CTA. Finally, in 2 of the 16 studied patients, 18F-FDOPA PET/CT detected two additional synchronous primary HNPGLs.Conclusion: 18F-FDOPA PET/CT is highly sensitive in posttreatment evaluation of patients with HNPGLs, and also offers better interobserver reproducibility than MRA/CTA and whole-body examination. We therefore suggest that 18F-FDOPA PET/CT is performed as the first diagnostic imaging modality in symptomatic patients with suspicion of HNPGL relapse after primary treatment when 68Ga-labeled somatostatin analogues are not available