44837884
SLUG—STOCHASTICALLY LIGHTING UP GALAXIES. I. METHODS AND VALIDATING TESTS
The effects of stochasticity on the luminosities of stellar populations are an often neglected but crucial element for understanding populations in the low-mass or the low star formation rate regime. To address this issue, we present SLUG, a new code to "Stochastically Light Up Galaxies." SLUG synthesizes stellar populations using a Monte Carlo technique that properly treats stochastic sampling including the effects of clustering, the stellar initial mass function, star formation history, stellar evolution, and cluster disruption. This code produces many useful outputs, including (1) catalogs of star clusters and their properties such as their stellar initial mass distributions and their photometric properties in a variety of filters, (2) two dimensional histograms of color-magnitude diagrams of every star in the simulation, and (3) the photometric properties of field stars and the integrated photometry of the entire simulated galaxy. After presenting the SLUG algorithm in detail, we validate the code through comparisons with STARBURST99 in the well-sampled regime, and with observed photometry of Milky Way clusters. Finally, we demonstrate SLUG's capabilities by presenting outputs in the stochastic regime. SLUG is publicly distributed through the Web site http://sites.google.com/site/runslug/.
36662401
AN INITIAL MASS FUNCTION STUDY OF THE DWARF STARBURST GALAXY NGC 4214
The production rate of ionizing photons in young (≤8 Myr), unresolved stellar clusters in the nearby irregular galaxy NGC 4214 is probed using multi-wavelength Hubble Space Telescope WFC3 data. We normalize the ionizing photon rate by the cluster mass to investigate the upper end of the stellar initial mass function (IMF). We have found that within the uncertainties the upper end of the stellar IMF appears to be universal in this galaxy, and that deviations from a universal IMF can be attributed to stochastic sampling of stars in clusters with masses ≾ 10^3 M_☉. Furthermore, we have found that there does not seem to be a dependence of the maximum stellar mass on the cluster mass. We have also found that for massive clusters, feedback may cause an underrepresentation in Hα luminosities, which needs to be taken into account when conducting this type of analysis.
118072730
Construction and test of the prototype chamber for region 1 of the LHCb muon station 2
A four gapMWPC prototypefor region 1 of the muonstation2, with non-staggered wires,wasbuilt andtested.Theconstructiondetailsandthetestresultsarepresented. 1 Intr oduction TheLHCb muonsystem[1] will useMulti-Wire ProportionalChambers(MWPC) for thefour regionsof stations2 and3, for regions3 and4 of station1 andfor regions1 and2 of stations4 and5. Thechambersvary in sizefor thedifferentstationsandregionsandthey have different readoutpadsizesin thoseregions(see[2] for moredetails). In this note,theconstructionof a MWPC prototypefor region 1 of station2 is described.The prototypeis an exact realization of a chamberfor this region. It hasfour symmetricgasgapsandthe characteristicslisted in table1. Table1: Somechamberparametersandoperationconditions. GasGapsize(mm) 5 Anode-Cathodespacing(mm) 2.5 Wire Diameter( m) 30 Sensiti vearea(mm ) 300 250 Wire pitch (mm) 1.5 Wire padsize(mm ) 6.3 250 Wire length(mm) 257 Cathodepadsize(mm ) 37.5 31.3 Wire Tension(gf) 60 10 NominalGasmixture (40%50%10%) Wire nominalpotential(V) 3150 The chamberhasa combinedreadoutof wire andcathodepadsasa consequenceof the requiredgranularity. 2 Chamber Construction The prototypewasbuilt in Rio (CEFET-RJ andLAPE/IF-UFRJ)with PCB-honeycomb-PCB panelsas describedin the Muon SystemTDR [1]. The panels’flatnesswas measured(INMETRO1 andBargoa2) to be within m, which is betterthanthe requiredspecifications (see[3]). Thewire fixation barswerealsomeasuredandgluedto thecathodepanels.Theanodeto cathodedistancewasinsuredbymeansof aprecisesteelspacerfixedto thosebars,during thegluing of thewires. For thepresentprototypethewire fixation barswerenot machinedto have a noseon theedgeswhich wasdonefor thepreviousprototypesto avoid dischar ges[3]. The resultsfor the dark currentandthe sparklimit show that this noseis not necessary . The darkcurrentmeasuredwasof theorderof thenA andthesparklimit wasof about3.45kV. The wiring wasdonein a latheasshown in thepictureof figure1. The wire tensionwas guaranteedusinga calibrateddevice asshown in figure 2. This device hasa DC motor that keepsthewire undertensionby applyinga torqueon thereel. TheDC voltageappliedto the motorwascalibratedwith a60gf weight. 1InstitutoNacionaldeMetrologia,Normalizaç̃aoe QualidadeIndustrial,Rio deJaneiro 2BargoaConectores, Rio deJaneiro
119246221
Photospheric parameters and C abundances in solar-like stars with and without planets
We have been analyzing a large sample of solar-like stars with and without planets in order to homogeneously measure their photospheric parameters and Carbon abundances. Our sample contains around 200 stars in the solar neighborhood observed with the ELODIE spectrograph, for which the observational data are publicly available. We performed spectral synthesis of prominent bands of C 2 and CI lines, aiming to accurately obtain the C abundances. We intend to contribute homogeneous results to studies that compare elemental abundances in stars with and without known planets. New arguments will be brought forward to the discussion of possible chemical anomalies that have been suggested in the literature, leading us to a better understanding of the planetary formation process. In this work we focus on the C abundances in both stellar groups of our sample.
121956644
A fast voltage preamplifier for use with MWPCs
Abstract We report the development of a voltage preamplifier for use with ionizing particles detection. It has been designed to match the requirements of a test station for muon Multiwire Proportional Chambers (MWPC) of the LHCb experiment at CERN. Simulation results and bench test measurements are presented, which exhibit the main circuit features: gain close to 500, rise time below 20 ns, bandwidth exceeding 30 MHz, input noise lower than 10 nV / Hz . Other results that demonstrate the applicability of the device in other contexts, specially with X-Ray imaging systems based on position sensitive detectors and proportional counters, are presented.
347666
Novel considerations about the non-equilibrium regime of the tricritical point in a metamagnetic model: Localization and tricritical exponents
a b s t r a c t We have investigated the time-dependent regime of a two-dimensional metamagnetic model at its tri- critical point via Monte Carlo simulations. First, we obtained the temperature and magnetic field corre- sponding to the tricritical point of the model by using a refinement process based on optimization of the coefficient of determination in the log-log fit of magnetization decay as a function of time. With these es- timates in hand, we obtained the dynamic tricritical exponents θ and z and the static tricritical exponents ν and β by using the universal power-law scaling relations for the staggered magnetization and its mo- ments at an early stage of the dynamic evolution. Our results at the tricritical point confirm that this model belongs to the two-dimensional Blume-Capel model universality class for both static and dynamic behav- iors, and they also corroborate the conjecture of Janssen and Oerding for the dynamics of tricritical points.
118450072
Accurate and homogeneous abundance patterns in solar-type stars of the solar neighbourhood: a chemo-chronological analysis
Aims. We report the derivation of abundances of C, Na, Mg, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sr, Y, Zr, Ba, Ce, Nd, and Sm in a sample of 25 solar-type stars of the solar neighbourhood, correlating the abundances with the stellar ages, kinematics, and orbital parameters. Methods. The spectroscopic analysis, based on data of high resolution and high signal-to-noise ratio, was differential to the Sun and applied to atomic line equivalent widths supplemented by the spectral synthesis of C and C2 features. We also performed a statistical study by using the method of tree clustering analysis, searching for groups of stars sharing similar elemental abundance patterns. We derived the stellar parameters from various criteria, with average errors of 30 K, 0.13 dex, and 0.05 dex, respectively, for Teff, log g ,a nd [Fe/H]. The average error of the [X/Fe] abundance ratios is 0.06 dex. Ages were derived from theoretical HR diagrams and membership of the stars in known kinematical moving groups. Results. We identified four stellar groups: one having, on average, over-solar abundances (� [X/H]� =+ 0.26 dex), another with undersolar abundances (� [X/H]� = −0.24 dex), and two with intermediate values (� [X/H]� = −0.06 and +0.06 dex) but with distinct chemical patterns. Stars sharing solar metallicity, age, and Galactic orbit possibly have non-solar abundance ratios, a possible effect either of chemical heterogeneity in their natal clouds or migration. A trend of [Cu/Fe] with [Ba/Fe] seems to exist, in agreement with previous claims in the literature, and maybe also of [Sm/Fe] with [Ba/Fe]. No such correlation involving C, Na, Mn, and Zn is observed. The [X/Fe] ratios of various elements show significant correlations with age. [Mg/Fe], [Sc/Fe], and [Ti/Fe] increase with age. [Mn/Fe] and [Cu/Fe] display a more complex behaviour, first increasing towards younger stars up to the solar age, and then decreasing, a result we interpret as possibly related to time-varying yields of SN Ia and the weak s-process in massive stars. The steepest negative age relation is due to [Ba/Fe], but only for stars younger than the Sun, and a similar though less significant behaviour is seen for Zr, Ce, and Nd. [Sr/Fe] and [Y/Fe] show a linearly increasing trend towards younger stars. The [Cu/Ba] and [Sm/Ba] therefore decrease for younger stars. We found that [Ba/Mg], [Ba/Zn], and [Sr,Y,Ba/Sm] increase but only for stars younger than the Sun, whereas the [Sr/Mg], [Y/Mg], [Sr/Zn], and [Y/Zn] ratios increase linearly towards younger stars over the whole age range.