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Effective Temperature (effective + temperature)
Selected AbstractsPrediction of thermal sensation based on simulation of temperature distribution in a vehicle cabinHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 3 2001Takuya Kataoka Abstract Thermal comfort in an automobile is predicted with numerical simulation. The flow field and temperature distribution are solved with a grid system based on many small cubic elements which are generated automatically with cabin and passenger configuration. Simulation of temperature is combined with simulation of cooling cycle and calculation of heat transfer at the wall including solar radiation to treat transient and actual driving conditions of the vehicle. In order to evaluate thermal comfort, transitional effective temperature is calculated from simulated thermal conditions and physiologic values which are calculated by a simple model of a human thermal system. This system can well predict thermal sensation of passengers in a short period of time. © 2001 Scripta Technica, Heat Trans Asian Res, 30(3): 195,212, 2001 [source] Effects of temperature on the post-diapause embryonic development and the hatching time in three grasshopper species (Orth., Acrididae)JOURNAL OF APPLIED ENTOMOLOGY, Issue 2 2004S. G. Hao Abstract: A study was conducted to determine the effects of six constant temperatures (15, 20, 25, 30, 35 and 40°C) on the post-diapause embryonic development and the hatching time in three grasshopper species ,Omocestus haemorrhoidalis (Charp.), Calliptamus abbreviatus Ikonn. and Chorthippus fallax (Zub.) , from the Inner Mongolian steppe. The results indicate that the species differ in the developmental rates, survival curves and cumulative hatching probabilities. The eggs of O. haemorrhoidalis had the fastest developmental rate with a low developmental threshold temperature of 9.9°C and the sum of effective temperature (SET) 211.2 degree-days (DD). The corresponding values were 10.9°C and 210.6 DD for C. abbreviatus, 10.5°C and 240.2 DD for Ch. fallax respectively. The SET at which 50% of post-diapause eggs hatched were 252.0 DD for O. haemorrhoidalis, 262.8 DD for C. abbreviatus, and 273.3 DD for Ch. fallax. The predicted maximal hatch ability of O. haemorrhoidalis (91.17%), C. abbreviatus (75.67%) and Ch. fallax (94.07%) occurred at 23.7, 29.0 and 31.3°C, respectively. The thermal death points of each species were reached at 43.3, 45.0 and 48.6°C. The optimal temperature ranges were 12.2,35.2°C for O. haemorrhoidalis, 21.7,36.3°C for C. abbreviatus and 20.9,41.7°C for Ch. fallax respectively. These results suggest that O. haemorrhoidalis adapt to hatch at a lower temperature range, C. abbreviatus adapt to mid-temperature range, while Ch. fallax adapt to hatch at a higher temperature range. Although the SET of Ch. fallax is more than that of the other two species, it is not sufficient to explain the hatching sequence of the species in springtime. The results also indicate that Ch. fallax and O. haemorrhoidalis have wider adaptive temperature range than C. abbreviatus. [source] THE APPLICATION OF ELECTRON SPIN RESONANCE AS A GUIDE TO THE MATURATION AND TYPING OF ORGANIC MATTER IN THE NORTH SEAJOURNAL OF PETROLEUM GEOLOGY, Issue 1 2003R. A. McTavish In early electron spin resonance (ESR) analysis of North Sea wells, maturation of organic matter (OM) was expressed in terms of maximum palaeotemperature (MPT) based on North American calibrations that did not consider the influences of kerogen composition or overpressure. In the North Sea, the MPTs were anomalous in overpressured sequences and relative to other indices of OM maturation such as vitrinite reflectance, so the ESR method was abandoned there in geochemical studies. However, early empirical study of North Sea ESR data indicated that, in relation to functions that linked temperature and pore pressure, some ESR parameters were predictable without reference to MPTs. In order to re-evaluate ESR parameters as indices of OM maturation, the physical factors (temperature and pressure) which affect OM maturation are related in the present paper to the ESR parameters "g" (spectral position) and Ng (spin density) at six well locations in the northern North Sea. A third ESR parameter, W (line width), is not an effective guide to maturation levels due to its complex relationship to the physical factors and kerogen types. However, cross-plots of W versus "g" and Ng appear to be as effective as pyrolysis for kerogen typing. Levels of maturation investigated in the North Sea wells range through the equivalent vitrinite reflectance values of about 0.50,1.50%. The values of "g" and Ng have been differentiated for kerogen type, but undifferentiated values of "g" have also been studied. Regression analysis has shown that there are linear relationships between the ESR parameters "g" and Ng, and the physical factors present-day temperature (To), "effective" temperature (Te), and differential pressure (Pd). Correlation coefficients for both "g" (undifferentiated and differentiated) and Ng (differentiated) relative to the physical factors are high; the highest values are for "g" and Ng relative to Te and Pd (r =,0.950 for "g" differentiated or undifferentiated, r = 0.944,0.976 for Ng differentiated, respectively). However, correlation coefficients were lower for "g" and Ng relative to To. More frequent high correlation coefficients and larger sample populations suggest that "g" (undifferentiated) is a more reliable index of OM maturation than Ng(differentiated). However, the estimation of levels of OM maturation is improved if both indices are used together. The ESR method appears to be effective both for estimating levels of OM maturation and for kerogen typing. It has a number of potential advantages over other geochemical methods: firstly, it is more sensitive for estimating OM maturation than most other methods; secondly, it can be used to analyze organic matter which is as old as Proterozoic; thirdly, it does not destroy the samples analyzed. [source] Monoenergetic electron beam generation in a laser-driven plasma accelerationLASER PHYSICS LETTERS, Issue 2 2006M. Adachi Abstract We obtained a 7-MeV monoenergetic electron beam from a plasma with the electron density ne of 1.5 × 1020 cm,3 produced by a 2-TW 50-fs laser pulse. In both higher and lower sides of the density region of 4 × 1019 ÷ 4 × 1020 cm,3, energy spectra of electrons were bi-Maxwellian distribution function whose maximum electron energy and effective electron temperature were 30 MeV and approximately MeV, respectively. Observed first Stokes satellites in the forward scattering light spectra, and the density dependences of maximum electron energy and the effective temperature suggest that electrons are first accelerated by SMLWFA and are further accelerated by direct laser acceleration (DLA) in the ne region of more than 2 × 1020 cm,3; a cascade acceleration by SMLWFA and DLA. A Stokes satellite peak observed with the monoenergetic beam suggests that the monoenergetic beam would be accelerated by SMLWFA. (© 2006 by Astro, Ltd. Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) [source] HD 209621: abundances of neutron-capture elements,MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2010Aruna Goswami ABSTRACT High-resolution spectra obtained from the Subaru Telescope High Dispersion Spectrograph have been used to update the stellar atmospheric parameters and metallicity of the star HD 209621. We have derived a metallicity of [Fe/H]=,1.93 for this star, and have found a large enhancement of carbon and of heavy elements, with respect to iron. Updates on the elemental abundances of four s-process elements (Y, Ce, Pr, Nd) along with the first estimates of abundances for a number of other heavy elements (Sr, Zr, Ba, La, Sm, Eu, Er, Pb) are reported. The stellar atmospheric parameters, the effective temperature, Teff, and the surface gravity, log g (4500 K, 2.0), are determined from local thermodynamic equilibrium analysis using model atmospheres. Estimated [Ba/Eu]=+0.35, places the star in the group of CEMP-(r+s) stars; however, the s-elements abundance pattern seen in HD 209621 is characteristic of CH stars; notably, the second-peak s-process elements are more enhanced than the first-peak s-process elements. HD 209621 is also found to show a large enhancement of the third-peak s-process element lead (Pb) with [Pb/Fe]=+1.88. The relative contributions of the two neutron-capture processes, r and s, to the observed abundances are examined using a parametric model-based analysis, which hints that the neutron-capture elements in HD 209621 primarily originate in s-process. [source] Spectroscopic and photometric observations of the selected Algol-type binaries , II.MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2008V2080 Cygni, V2365 Ophiuchi ABSTRACT This paper is the second in the planned series of investigations. We present new radial velocities and photometric observations of V2080 Cyg and V2365 Oph. New UBV photometric data and radial velocities were analysed for the systems' parameters. While V2080 Cyg consists of two nearly equal F-type main-sequence stars, V2365 Oph has two different components, namely an early A-type primary and a G-type secondary star. New ephemerides are calculated for both systems. The masses of the component stars have been derived as 1.19 ± 0.02 and 1.16 ± 0.02 M, for V2080 Cyg and 1.97 ± 0.02 and 1.06 ± 0.01 M, for V2365 Oph. The effective temperatures and reddening of the systems have been estimated from Johnson wide-band UBV photometric calibrations. The radii have been measured by simultaneous fitting the UBV light curves using Wilson,Devinney code and are 1.60 ± 0.01 R, for both components of V2080 Cyg and 2.19 ± 0.01 and 0.934 ± 0.004 R, for V2365 Oph. The absolute parameters of the stars in both systems lie within the same ranges in the mass,radius, mass,effective temperature, mass,luminosity and luminosity,effective temperature planes as in detached Algol systems. A comparison between the properties of the systems of interest and the predictions of theoretical evolutionary models is undertaken in the log g,logTeff, log R, log M and radius,log age diagrams. The model predictions match the measured properties of V2080 Cyg for an age of about 5.6 Gyr and a ,solar' metal abundance (Z= 0.019), indicating the components near the end of their core hydrogen-burning phases. However, the position of the components of V2365 Oph on the Hertzsprung,Russell (HR) diagram is best reproduced with evolutionary models for somewhat metal-deficient (Z= 0.004) stars. We found an age of about 700 Myr, with the primary component slightly evolved off the zero-age main-sequence and the secondary one still very close to it. From the basic stellar parameters we have also redetermined the distances to V2080 Cyg and V2365 Oph as 78 ± 1 and 251 ± 8 pc, which are in agreement with, and more accurate than, Hipparcos values. The observations show that at least one of the components of V2365 Oph is an intrinsic variable with a period and peak-to-peak amplitude of 0.07 d and 0.05 mag, respectively. In accordance with its position in the HR diagram, the primary component should be considered as a , Scuti star and it is believed to be the variable star in the system. [source] Accurate fundamental parameters for lower main-sequence starsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2006Luca Casagrande ABSTRACT We derive an empirical effective temperature and bolometric luminosity calibration for G and K dwarfs, by applying our own implementation of the Infrared Flux Method to multiband photometry. Our study is based on 104 stars for which we have excellent BV(RI)CJHKS photometry, excellent parallaxes and good metallicities. Colours computed from the most recent synthetic libraries (ATLAS9 and MARCS) are found to be in good agreement with the empirical colours in the optical bands, but some discrepancies still remain in the infrared. Synthetic and empirical bolometric corrections also show fair agreement. A careful comparison to temperatures, luminosities and angular diameters obtained with other methods in the literature shows that systematic effects still exist in the calibrations at the level of a few per cent. Our Infrared Flux Method temperature scale is 100-K hotter than recent analogous determinations in the literature, but is in agreement with spectroscopically calibrated temperature scales and fits well the colours of the Sun. Our angular diameters are typically 3 per cent smaller when compared to other (indirect) determinations of angular diameter for such stars, but are consistent with the limb-darkening corrected predictions of the latest 3D model atmospheres and also with the results of asteroseismology. Very tight empirical relations are derived for bolometric luminosity, effective temperature and angular diameter from photometric indices. We find that much of the discrepancy with other temperature scales and the uncertainties in the infrared synthetic colours arise from the uncertainties in the use of Vega as the flux calibrator. Angular diameter measurements for a well-chosen set of G and K dwarfs would go a long way to addressing this problem. [source] Offline, multidetector intensity interferometers , II.MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2006Implications, applications ABSTRACT Intensity interferometry removes the stringent requirements on mechanical precision and atmospheric corrections that plague all amplitude interferometry techniques at the cost of severely limited sensitivity. A new idea we recently introduced, very high redundancy, alleviates this problem. It enables the relatively simple construction (,1 cm mechanical precision) of a ground-based astronomical facility able to transform a two-dimensional field of point-like sources to a three-dimensional distribution of microarcsec resolved systems, each imaged in several optical bands. Each system will also have its high-resolution residual timing, high-quality (inside each band) spectra and light curve, emergent flux, effective temperature, polarization effects and perhaps some thermodynamic properties, all directly measured. All the above attributes can be measured in a single observation run of such a dedicated facility. We conclude that after three decades of abandonment, optical intensity interferometry deserves another review, also as a ground-based alternative to the science goals of space interferometers. [source] The effect of stellar rotation on colour,magnitude diagrams: on the apparent presence of multiple populations in intermediate age stellar clustersMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY: LETTERS (ELECTRONIC), Issue 1 2009N. Bastian ABSTRACT A significant number of intermediate age clusters (1,2 Gyr) in the Magellanic Clouds appear to have multiple stellar populations within them, derived from bimodal or extended main-sequence turn-offs. If this is interpreted as an age spread, the multiple populations are separated by a few hundred million years, which would call into question the long-held notion that clusters are simple stellar populations. Here, we show that stellar rotation in stars with masses between 1.2 and 1.7 M, can mimic the effect of a double or multiple population, whereas in actuality only a single population exists. The two main causes of the spread near the turn-off are the effects of stellar rotation on the structure of the star and the inclination angle of the star relative to the observer. Both effects change the observed effective temperature, hence colour, and flux of the star. In order to match observations, the required rotation rates are 20,50 per cent of the critical rotation, which are consistent with observed rotation rates of similar mass stars in the Galaxy. We provide scaling relations which can be applied to non-rotating isochrones in order to mimic the effects of rotation. Finally, we note that rotation is unlikely to be the cause of the multiple stellar populations observed in old globular clusters, as low-mass stars (<1 M,) are not expected to be rapid rotators. [source] New constraints from the H, line for the temperature of the transiting planet host star OGLE-TR-10,ASTRONOMISCHE NACHRICHTEN, Issue 6 2008M. Ammler-von Eiff Abstract The spectroscopic analysis of systems with transiting planets gives strong constraints on planetary masses and radii as well as the chemical composition of the systems. The properties of the system OGLE-TR-10 are not well-constrained, partly due to the discrepancy of previous measurements of the effective temperature of the host star. This work, which is fully independent from previous works in terms of data reduction and analysis, uses the H, profile in order to get an additional constraint on the effective temperature. We take previously published UVES observations which have the highest available signal-to-noise ratio for OGLE-TR-10. A proper normalization to the relative continuum is done using intermediate data products of the reduction pipeline of the UVES spectrograph. The effective temperature then is determined by fitting synthetic H, profiles to the observed spectrum. With a result of Teff = 6020 ± 140 K, the H, profile clearly favours one of the previous measurements. The H, line is further consistent with dwarf-like surface gravities as well as solar and super-solar metallicities previously derived for OGLE-TR-10. The H, line could not be used to its full potential, partly because of the varying shape of the UVES échelle orders after flat field correction. We suggest to improve this feature when constructing future spectrographs. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Time-series photometric spot modelling , VI.ASTRONOMISCHE NACHRICHTEN, Issue 3 2003A new computer code, its application to 23 years of photometry of the active giant IM Pegasi Abstract We present and apply a new computer program named SpotModeL to analyze single and multiple bandpass photometric data of spotted stars. It is based on the standard analytical formulae from Budding and Dorren. The program determines the position, size, and temperature of up to three spots by minimizing the fit residuals with the help of the Marquardt-Levenberg non-linear least-squares algorithm. We also expand this procedure to full time-series analysis of differential data, just as real observations would deliver. If multi-bandpass data are available, all bandpasses can be treated simultaneously and thus the spot temperature is solved for implicitly. The program may be downloaded and used by anyone. In this paper, we apply our code to an ,23 year long photometric dataset of the spotted RS CVn giant IM Peg. We extracted and modelled 33 individual light curves, additionally, we fitted the entire V dataset in one run. The resulting spot parameters reflect the long term light variability and reveal two active longitudes on the substellar point and on the antipode. The radius and longitude of the dominant spot show variations with 29.8 and 10.4 years period, respectively. Our multicolour data suggests that the spot temperature is increasing with the brightening of the star. The average spot temperature from V, IC is 3550 ± 150 K or approximately 900 K below the effective temperature of the star. [source] Seasonal synchrony of life cycles between the exotic predator, Pseudoscymnus tsugae (Coleoptera: Coccinellidae) and its prey, the hemlock woolly adelgid Adelges tsugae (Homoptera:Adelgidae)AGRICULTURAL AND FOREST ENTOMOLOGY, Issue 4 2000Carole A. S. -J. Abstract 1 The seasonal synchrony between the exotic predator, Pseudoscymnus tsugae and its prey, the hemlock woolly adelgid, Adelges tsugae, was investigated in field cages and in the forest in Connecticut, U.S.A. from 1997,1999. 2 In early spring, egg to adult development took 45 d at 18.7 °C, 39.7 d at 20.2 °C and 31.5 d at 22.7 °C. Earliest emerging F1 adults mated and oviposited in the same year. whereas F1 and F2 females emerging later in the summer mated and reserved most of their egg complement for the following year. 3 A second generation of P. tsugae is possible in Connecticut but may be delayed by cool mid-spring temperatures. Individuals of three generations of P. tsugae, including overwintering survivors, may coexist in July and August and adults can be found year-round with A. tsugae in infested hemlock forests. 4 A linear regression model for development from egg to adult under field temperatures gave good agreement with results from constant temperature findings. The model predicted a lower development threshold of 9.5 °C and a sum of effective temperatures of 405 day °C. Development time of P. tsugae is shorter relative to its prey A. tsugae and generation time ratios of predator to prey was 0.16,0.5, with an advantage conferred on the coccinellid. 5 Overwintering ability and behaviour were determined in 1998,1999 and adults remained on infested hemlock branches throughout a mild winter, becoming reproductively active in mid-April. Peak oviposition period extended from April to July, in synchrony with peak oviposition and developing stages of two generations of A. tsugae. [source] Evaluation of the protonation thermochemistry obtained by the extended kinetic method,JOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 8 2006Guy Bouchoux Abstract An evaluation of the results obtained by the extended kinetic method for a series of representative bases is presented here. Analysis of the original experimental data is conducted using the orthogonal distance regression (ODR) statistical treatment. A comparison with the proton affinities and protonation entropies obtained from variable temperature equilibrium constant measurements demonstrate deviations, which may be ascribed to random and systematic errors. Considerable random errors are associated with the extended kinetic method if the number of reference bases and the range of effective temperatures are too low. It is also confirmed that large systematic errors on proton affinities and protonation entropies are obtained when large protonation entropy is associated with the considered system. It is, however, encouraging to note that the gas phase basicities obtained by the extended kinetic method are generally comparable to that obtained by other methods within a few kJ/mol. Copyright © 2006 John Wiley & Sons, Ltd. [source] Obtaining thermochemical data by the extended kinetic methodJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 9 2004Guy Bouchoux Abstract A microcanonical analysis of the extended kinetic method is performed using statistical rate calculations based on orbiting transition state theory. The model systems simulate polydentate bases M which exhibit losses of entropy upon protonation of up to 35 kJ mol,1 K,1. It is shown that the correlations using the natural logarithm of the ratio of rate constants vs the proton affinity of the reference bases, at several effective temperatures, lead to correct proton affinity and protonation entropy of the base M of interest. A systematic underestimate of the latter quantity (by 5,15%), mainly due to the use of a linear rather than a polynomial curve fitting procedure, is noted, however. When considering experimental data, more severe underestimates are observed for the protonation entropies of polydentate bases (by 50,90%). The origins of these considerable discrepancies are beyond the limits of the present modeling and remain to be determined. Copyright © 2004 John Wiley & Sons, Ltd. [source] Post-common-envelope binaries from SDSS , I. 101 white dwarf main-sequence binaries with multiple Sloan Digital Sky Survey spectroscopyMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2007A. Rebassa-Mansergas ABSTRACT We present a detailed analysis of 101 white dwarf main-sequence binaries (WDMS) from the Sloan Digital Sky Survey (SDSS) for which multiple SDSS spectra are available. We detect significant radial velocity variations in 18 WDMS, identifying them as post-common-envelope binaries (PCEBs) or strong PCEB candidates. Strict upper limits to the orbital periods are calculated, ranging from 0.43 to 7880 d. Given the sparse temporal sampling and relatively low spectral resolution of the SDSS spectra, our results imply a PCEB fraction of ,15 per cent among the WDMS in the SDSS data base. Using a spectral decomposition/fitting technique we determined the white dwarf effective temperatures and surface gravities, masses and secondary star spectral types for all WDMS in our sample. Two independent distance estimates are obtained from the flux-scaling factors between the WDMS spectra, and the white dwarf models and main-sequence star templates, respectively. Approximately one-third of the systems in our sample show a significant discrepancy between the two distance estimates. In the majority of discrepant cases, the distance estimate based on the secondary star is too large. A possible explanation for this behaviour is that the secondary star spectral types that we determined from the SDSS spectra are systematically too early by one to two spectral classes. This behaviour could be explained by stellar activity, if covering a significant fraction of the star by cool dark spots will raise the temperature of the interspot regions. Finally, we discuss the selection effects of the WDMS sample provided by the SDSS project. [source] Testing the accuracy of synthetic stellar librariesMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2007Lucimara P. Martins ABSTRACT One of the main ingredients of stellar population synthesis models is a library of stellar spectra. Both empirical and theoretical libraries are used for this purpose, and the question about which one is preferable is still debated in the literature. Empirical and theoretical libraries are being improved significantly over the years, and many libraries have become available lately. However, it is not clear in the literature what are the advantages of using each of these new libraries, and how far behind models are compared to observations. Here we compare in detail some of the major theoretical libraries available in the literature with observations, aiming at detecting weaknesses and strengths from the stellar population modelling point of view. Our test is twofold: we compared model predictions and observations for broad-band colours and for high-resolution spectral features. Concerning the broad-band colours, we measured the stellar colour given by three recent sets of model atmospheres and flux distributions, and compared them with a recent UBVRIJHK calibration which is mostly based on empirical data. We found that the models can reproduce with reasonable accuracy the stellar colours for a fair interval in effective temperatures and gravities. The exceptions are (1) the U,B colour, where the models are typically redder than the observations, and (2) the very cool stars in general (V,K, 3). Castelli & Kurucz is the set of models that best reproduce the bluest colours (U,B, B,V) while Gustafsson et al. and Brott & Hauschildt more accurately predict the visual colours. The three sets of models perform in a similar way for the infrared colours. Concerning the high-resolution spectral features, we measured 35 spectral indices defined in the literature on three high-resolution synthetic libraries, and compared them with the observed measurements given by three empirical libraries. The measured indices cover the wavelength range from ,3500 to ,8700 Å. We found that the direct comparison between models and observations is not a simple task, given the uncertainties in parameter determinations of empirical libraries. Taking that aside, we found that in general the three libraries present similar behaviours and systematic deviations. For stars with Teff, 7000 K, the library by Coelho et al.is the one with best average performance. We detect that lists of atomic and molecular line opacities still need improvement, specially in the blue region of the spectrum, and for the cool stars (Teff, 4500 K). [source] Revisiting two local constraints of the Galactic chemical evolutionMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2006M. Haywood ABSTRACT I review the uncertainties in two observational local constraints of the Galactic disc chemical evolution: the metallicity distribution of long-lived dwarfs and the age,metallicity relation. Analysing most recent data, it is shown first that the observed metallicity distribution at solar galactocentric radius, designed with standard methods, is more fit to a closed-box model than to the infall metallicity distribution. We argue that this is due to the specific contribution of the thick-disc population, which has been overlooked both in the derivation of the observed metallicity distribution and in the standard chemical evolution models. Although this agreement disqualifies the metallicity distribution as the best supportive (indirect) evidence for infall, we argue that the evolution must be more complex than described by either the closed-box or the standard infall models. It is then shown that recent determinations of the age,metallicity distribution (AMD) from large Strömgren photometric surveys are dominated by noise resulting from systematic biases in metallicities and effective temperatures. These biases are evaluated and a new AMD is obtained, where particularities of the previous determinations are phased out. The new age,metallicity relation shows a mean increase limited to about a factor of 2 in Z over the disc age. It is shown that below 3 Gyr, the dispersion in metallicity is about 0.1 dex, which, given the observational uncertainties in the derived metallicities, is compatible with the small cosmic dispersion measured on the interstellar medium and meteoritic pre-solar dust grains. A population that is progressively older and more metal rich arises at a metallicity greater than that of the Hyades, to reach [Fe/H],+0.5 dex at ages greater than 5 Gyr. We suggest that this is best explained by radial migration. A symmetrical widening of the metallicity interval towards lower values is seen at about the same age, which is attributed to a similar cause. Finally, the new derived ages are sufficiently consistent that an age,metallicity relation within the thick disc is confirmed. These new features altogether draw a picture of the chemical evolution in the solar neighbourhood where dynamical effects and complexity in the AMD dominate, rather than a generalized high dispersion at all ages. [source] Magnetic braking of Ap/Bp stars: application to compact black-hole X-ray binariesMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2006Stephen Justham ABSTRACT We examine the proposal that the subset of neutron-star and black-hole X-ray binaries that form with Ap or Bp star companions will experience systemic angular-momentum losses due to magnetic braking, not otherwise operative with intermediate-mass companion stars. We suggest that for donor stars possessing the anomalously high magnetic fields associated with Ap and Bp stars, a magnetically coupled, irradiation-driven stellar wind can lead to substantial systemic loss of angular momentum. Hence, these systems, which would otherwise not be expected to experience ,magnetic braking', evolve to shorter orbital periods during mass transfer. In this paper, we detail how such a magnetic braking scenario operates. We apply it to a specific astrophysics problem involving the formation of compact black-hole binaries with low-mass donor stars. At present, it is not understood how these systems form, given that low-mass companion stars are not likely to provide sufficient gravitational potential to unbind the envelope of the massive progenitor of the black hole during a prior ,common-envelope' phase. On the other hand, intermediate-mass companions, such as Ap and Bp stars, could more readily eject the common envelope. However, in the absence of magnetic braking, such systems tend to evolve to long orbital periods. We show that, with the proposed magnetic braking properties afforded by Ap and Bp companions, such a scenario can lead to the formation of compact black-hole binaries with orbital periods, donor masses, lifetimes and production rates that are in accord with the observations. In spite of these successes, our models reveal a significant discrepancy between the calculated effective temperatures and the observed spectral types of the donor stars. Finally, we show that this temperature discrepancy would still exist for other scenarios invoking initially intermediate-mass donor stars, and this presents a substantial unresolved mystery. [source] A comparison of DA white dwarf temperatures and gravities from Lyman and Balmer line studiesMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2001M.A. Barstow We present measurements of the effective temperatures and surface gravities for a sample of hot DA white dwarfs, using the Lyman line data available from the HUT, ORFEUS and FUSE FUV space missions. Comparing the results with those from the standard Balmer line technique, we find that there is a general good overall agreement between the two methods. However, significant differences are found for a number of stars, but not always of a consistent nature in that sometimes the Balmer temperature exceeds that derived from the Lyman lines and in other instances it is lower. We conclude that, with the latest model atmosphere calculations, these discrepancies probably do not arise from an inadequate theoretical treatment of the Lyman lines but rather from systematic effects in the observation and data reduction processes, which dominate the statistical errors in these spectra. If these systematic data reduction effects can be adequately controlled, the Lyman line temperature and gravity measurements are consistent with those obtained from the Balmer lines when allowance is made for reasonable observational uncertainties. [source] Masses and luminosities of O- and B-type stars and red supergiantsASTRONOMISCHE NACHRICHTEN, Issue 4 2010M.M. Hohle Abstract Massive stars are of interest as progenitors of supernovae, i.e. neutron stars and black holes, which can be sources of gravitational waves. Recent population synthesis models can predict neutron star and gravitational wave observations but deal with a fixed supernova rate or an assumed initial mass function for the population of massive stars. Here we investigate those massive stars, which are supernova progenitors, i.e. with O- and early B-type stars, and also all supergiants within 3 kpc. We restrict our sample to those massive stars detected both in 2MASS and observed by Hipparcos, i.e. only those stars with parallax and precise photometry. To determine the luminosities we calculated the extinctions from published multi-colour photometry, spectral types, luminosity class, all corrected for multiplicity and recently revised Hipparcos distances. We use luminosities and temperatures to estimate the masses and ages of these stars using different models from different authors. Having estimated the luminosities of all our stars within 3 kpc, in particular for all O- and early B-type stars, we have determined the median and mean luminosities for all spectral types for luminosity classes I, III, and V. Our luminosity values for supergiants deviate from earlier results: Previous work generally overestimates distances and luminosities compared to our data, this is likely due to Hipparcos parallaxes (generally more accurate and larger than previous ground-based data) and the fact that many massive stars have recently been resolved into multiples of lower masses and luminosities. From luminosities and effective temperatures we derived masses and ages using mass tracks and isochrones from different authors. From masses and ages we estimated lifetimes and derived a lower limit for the supernova rate of ,20 events/Myr averaged over the next 10 Myr within 600 pc from the sun. These data are then used to search for areas in the sky with higher likelihood for a supernova or gravitational wave event (like OB associations) (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Expanding atmosphere models for SSS spectra of novaeASTRONOMISCHE NACHRICHTEN, Issue 2 2010D.R. van Rossum Abstract Super Soft Source (SSS) spectra are powered by nuclear burning on the surface of a white dwarf. The released energy causes a radiatively-driven wind that leads to a radially extended atmosphere around the white dwarf. Significant blue shifts in photospheric absorption lines are found in the spectra of novae during their SSS phase, being an evidence of continued mass loss in this phase. We present spherically symmetric PHOENIX models that account for the expansion of the ejecta. A comparison to a plane parallel, hydrostatic atmosphere model demonstrates that the mass loss can have a significant impact on the model spectra. The dynamic model yields less pronounced absorption edges, and harder X-ray spectra are the result. Therefore, lower effective temperatures are needed to explain the observed spectra. Although both types of models are yet to be fine-tuned in order to accurately determine best fit parameters, the implications on the chemical abundances are going in opposite directions. With the expanding models the requirement for strong depletion of the crucial elements that cause these edges is now avoidable (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Radial velocity and light curves analysis of the eclipsing binary NN VirASTRONOMISCHE NACHRICHTEN, Issue 9 2004R. Pazhouhesh Abstract The eclipsing binary NN Vir is a short period system showing an EW-type light curve. Photometric observations of NN Vir were done by Gomez-Ferrellad & Garcia-Melendo (1997) at Esteve Duran Observatory. We used photometric data of NN Vir for light curve analysis. The available spectroscopic data of NN Vir is new and we also used the first radial velocity data of this system obtained by Rusinski & Lu (1999) for analysis. The radial velocity and light curves analysis was made with the latest version ofWilson program(1998) and the geometric and physical elements of the system are derived. By searching the simultaneous solutions of the system, we have determined the masses and radii of the components : 1.89(M,) and 1.65(R,) for the primary component; 0.93(M,) and 1.23(R,) for the secondary component. We estimated effective temperatures of 7030(K) for the primary and 6977(K) for the secondary component. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | |||||||||||||