Thermal and nonthermal dust sputtering in hydrodynamical simulations of the multiphase interstellar medium

We study the destruction of interstellar dust via sputtering in supernova (SN) shocks using three-dimensional hydrodynamical simulations. With a novel numerical framework, we follow both sputtering and dust dynamics governed by direct collisions, plasma drag and betatron acceleration. Grain-grain collisions are not included and the grain-size distribution is assumed to be fixed. The amount of dust destroyed per SN is quantified for a broad range of ambient densities and fitting formulae are provided. Integrated over the grain-size distribution, nonthermal (inertial) sputtering dominates over thermal sputtering for typical ambient densities. We present the first simulations that explicitly follow dust sputtering within a turbulent multiphase interstellar medium. We find that the dust destruction timescales $\tau$ are 0.35 Gyr for silicate dust and 0.44 Gyr for carbon dust in solar neighborhood conditions. The SN environment has an important impact on $\tau$. SNe that occur in preexisting bubbles destroy less dust as the destruction is limited by the amount of dust in the shocked gas. This makes $\tau$ about 2.5 times longer than the estimate based on results from a single SN explosion. We investigate the evolution of the dust-to-gas mass ratio (DGR), and find that a spatial inhomogeneity of $\sim$ 14\% develops for scales below 10 pc. It locally correlates positively with gas density but negatively with gas temperature even in the exterior of the bubbles due to incomplete gas mixing. This leads to a $\sim$ 30\% lower DGR in the volume filling warm gas compared to that in the dense clouds.Comment: 20 pages, 16 figures, accepted versio

CrH and FeH bands in atmospheres of the ultracool objects

Absorption CrH and FeH bands are of importance for study of atmospheres of ultracool dwarfs (Teff < 2200 K). Results from calculations of synthetic spectra of these objects using the new theoretical CrH and FeH opacities obtained by Burrows et al. [2] and Dulick et al. [3], respectively, are discussed. Comparison of the CrH and FeH spectra computed with the JOLA approximation and Burrows data is carried out. Dependencies of SEDs of ulracool dwarfs on temperature, gravity, dust opacity are discussed. We compare our synthetic SEDs with an observed spectrum of Kelu-1 (L2)

Can star cluster environment affect dust input from massive AGB stars?

This is the final version. Available from American Astronomical Society via the DOI in this record. We examine the fraction of massive asymptotic giant branch (AGB) stars remaining bound in their parent star clusters (SCs) and the effect of irradiation of these stars by an intracluster ultraviolet (UV) field. We employ a set of N-body models of dynamical evolution of SCs rotating in a galactic potential at the solar galactocentric radius. The cluster models are combined with stellar evolution formulae, a library of stellar spectra, and simple models for SiO photodissociation in the circumstellar environment (CSE). The initial stellar masses of clusters are varied from to . Results derived for individual clusters are combined using a mass distribution function for young SCs. We find that about 30% of massive AGB stars initially born in clusters become members of the field population, while the rest evolve in SCs. They are irradiated by strong intracluster UV radiation, resulting in the decrease of the photodissociation radius of SiO molecules, in many stars down to the dust formation zone. In the absence of dust shielding, the UV photons penetrate in the CSE deeper than in 64% and deeper than in 42% of all massive AGB stars. If this suppresses subsequent dust formation, the current injection rate of silicate dust from AGB stars in the local Galaxy decreases from to at most. A lower revised value of 40% for the expected fraction of presolar silicate grains from massive AGB stars is still too high to explain the non-detection of these grains in meteorites

H-ATLAS/GAMA: the nature and characteristics of optically red galaxies detected at submillimetre wavelengths

We combine Herschel/SPIRE sub-millimeter (submm) observations with existing multi-wavelength data to investigate the characteristics of low redshift, optically red galaxies detected in submm bands. We select a sample of galaxies in the redshift range 0.01≤z≤0.2, having >5σ detections in the SPIRE 250 micron submm waveband. Sources are then divided into two sub-samples of red and blue galaxies, based on their UV-optical colours. Galaxies in the red sample account for ≈4.2 per cent of the total number of sources with stellar masses M∗≳1010 Solar-mass. Following visual classification of the red galaxies, we find that ≳30 per cent of them are early-type galaxies and ≳40 per cent are spirals. The colour of the red-spiral galaxies could be the result of their highly inclined orientation and/or a strong contribution of the old stellar population. It is found that irrespective of their morphological types, red and blue sources occupy environments with more or less similar densities (i.e., the Σ5 parameter). From the analysis of the spectral energy distributions (SEDs) of galaxies in our samples based on MAGPHYS, we find that galaxies in the red sample (of any morphological type) have dust masses similar to those in the blue sample (i.e. normal spiral/star-forming systems). However, in comparison to the red-spirals and in particular blue systems, red-ellipticals have lower mean dust-to-stellar mass ratios. Besides galaxies in the red-elliptical sample have much lower mean star-formation/specific-star-formation rates in contrast to their counterparts in the blue sample. Our results support a scenario where dust in early-type systems is likely to be of an external origin

Gas-to-Dust mass ratios in local galaxies over a 2 dex metallicity range

This paper analyses the behaviour of the gas-to-dust mass ratio (G/D) of local Universe galaxies over a large metallicity range. We combine three samples: the Dwarf Galaxy Survey, the KINGFISH survey and a subsample from Galametz et al. (2011) totalling 126 galaxies, covering a 2 dex metallicity range, with 30% of the sample with 12+log(O/H) < 8.0. The dust masses are homogeneously determined with a semi-empirical dust model, including submm constraints. The atomic and molecular gas masses are compiled from the literature. Two XCO are used to estimate molecular gas masses: the Galactic XCO, and a XCO depending on the metallicity (as Z^{-2}). Correlations with morphological types, stellar masses, star formation rates and specific star formation rates are discussed. The trend between G/D and metallicity is empirically modelled using power-laws (slope of -1 and free) and a broken power-law. We compare the evolution of the G/D with predictions from chemical evolution models. We find that out of the five tested galactic parameters, metallicity is the galactic property driving the observed G/D. The G/D versus metallicity relation cannot be represented by a power-law with a slope of -1 over the whole metallicity range. The observed trend is steeper for metallicities lower than ~ 8.0. A large scatter is observed in the G/D for a given metallicity, with a dispersion of 0.37 dex in metallicity bins of ~0.1 dex. The broken power-law reproduces best the observed G/D and provides estimates of the G/D that are accurate to a factor of 1.6. The good agreement of the G/D and its scatter with the three tested chemical evolution models shows that the scatter is intrinsic to galactic properties, reflecting the different star formation histories, dust destruction efficiencies, dust grain size distributions and chemical compositions across the sample. (abriged)Comment: 23 pages, 12 figures, accepted in Astronomy & Astrophysic

Застосування задачі інвестора щодо торгівлі цінними паперами

У статті досліджено застосування проблеми інвестора до торгівлі цінними паперами в одноперіодній і багатоперіодній моделях. Інвестор повинен визначити на етапі t суму Xt, яку він вкладає в купівлю цінних паперів (акцій або опціонів), якщо з попередніх історичних статистичних даних йому відомий розподіл випадкової величини St – ціни акцій, за умови, що E(St) < ∞ в період t, а дохід інвестора визначається випадковою величиною Yt+1 на етапі t. Крім цього інвестору відомо банківські процентні ставки як на депозит, так і на кредит. Актуальність даного дослідження набуває особливого значення в умовах кризових явищ; зокрема, на перший план виходить дослідження зв’язку між оптимальним інвестування у цінні папери (з точки зору максимізації прибутку) та управлінням і обчисленням ризику такого інвестування. Дане завдання може бути вирішено за рахунок існування близького зв’язку між оптимальним інвестуванням та вимірюванням ризику, що дається стохастичною оптимізацією. Це можливо бо середнє значення ризику AVaR (як для одноперіодної так і для багатоперіодної моделей) виявилось пов’язаним із простою стохастичною проблемою із кусково-неперервною функцією доходу/втрат та, як раніше було доведено, максимальне значення цієї функції досягається. Постановка задачі включає розгляд двох можливих сценаріїв: коли дохід Yt+1 в кінці періоду більше вкладених інвестицій Xt на початку періоду та коли дохід менше вкладених інвестицій і відбувається дефіцит. Результатом роботи стало формулювання чотирьох тверджень щодо величин оптимальних інвестицій в акції і опціони в одноперіодній та багатоперіодній моделях та щодо потенційних максимальних прибутків при застосуванні такої стратегії. Виявилось, що величину оптимальних інвестицій можна напряму виразити через VaR деякого рівня альфа, а цей рівень виражається через величини кредитних і депозитних ставок і є характеристикою стану національного економічного середовища. Результати теоретичного дослідження було проілюстровано на реальних фінансових даних для двох моделей фінансових ринків. У першій моделі рух акцій підкорюється геометричному броунівському руху (GBM модель). Другою моделлю стала модель, у якій рух ризикованих активів описується узагальненою дифузією з новим фрактальним часом (FAT модель). Результати оптимальних інвестицій для обох моделей було порівняно із справедливою ціною, отриманою за формулою Блека - Шоулза. Результати дослідження, проведеного в даній роботі, було використано для розробки рекомендацій щодо прийняття рішень відносно оптимальних інвестувань у цінні папери (акції, опціони) для отримання спекулятивних доходів у біржовій торгівлі.The article investigates the application of the investor problem to securities trading in single-period and multi-period models. The investor has to determine at stage t the sum Xt he invests in the purchase of securities (shares or options), if from previous historical data he knows the distribution function of a random variable t St – the share price, provided that with E(St) < ∞ in period t. The investor's income is a random variable Yt+1 at stage t. In addition, the investor knows the bank interest rates on both deposit and loan. The relevance of this study is of particular importance in a crisis; in particular, the study of the relationship between the optimal investment in securities (in terms of profit maximization) and the management and measuring of the risk of such investment comes to the fore. This problem can be solved by the existence of a close relationship between the optimal investment and the measurement of risk given by stochastic optimization. It is possible because the average value-at-risk AV@R is related to a simple stochastic optimization problem with a piecewise linear profit/cost function and maximal value is attained. The problem includes consideration of two possible scenarios: when the income Yt+1 at the end of the period is more than the investment Xt at the beginning of the period and when the income is less than the investment and there is a shortfall. The result of the work is the formulation of four statements about the values of optimal investments in stocks and options in the single-period and multi-period models and about the potential maximum profits for such applying such a strategy. It turned out that the value of optimal investment can be directly expressed in terms of VaR of some probability level, and this level is expressed in terms of credit and deposit interest rates an characterizes the state of the national economic environment. The results of the theoretical study were illustrated on real financial data using two models of financial markets. In the first model, the stock movement obeys the geometric Brownian motion (GBM model). The second model was a model in which the movement of risky assets is described by generalized diffusion with a new fractal time (FAT model). The results of optimal investments for both models were compared with the fair price obtained by the Black-Scholes formula. The results of the study conducted in this work were used to develop recommendations for making decisions about optimal investments in securities (stocks, options) to obtain speculative income in stock trading

Lifting the Dusty Veil II: A Large-Scale Study of the Galactic Infrared Extinction Law

We combine near-infrared (2MASS) and mid-infrared (Spitzer-IRAC) photometry to characterize the IR extinction law (1.2-8 microns) over nearly 150 degrees of contiguous Milky Way midplane longitude. The relative extinctions in 5 passbands across these wavelength and longitude ranges are derived by calculating color excess ratios for G and K giant red clump stars in contiguous midplane regions and deriving the wavelength dependence of extinction in each one. Strong, monotonic variations in the extinction law shape are found as a function of angle from the Galactic center, symmetric on either side of it. These longitudinal variations persist even when dense interstellar regions, known a priori to have a shallower extinction curve, are removed. The increasingly steep extinction curves towards the outer Galaxy indicate a steady decrease in the absolute-to-selective extinction ratio (R_V) and in the mean dust grain size at greater Galactocentric angles. We note an increasing strength of the 8 micron extinction inflection at high Galactocentric angles and, using theoretical dust models, show that this behavior is consistent with the trend in R_V. Along several lines of sight where the solution is most feasible, A_lambda/A_Ks as a function of Galactic radius is estimated and shown to have a Galactic radial dependence. Our analyses suggest that the observed relationship between extinction curve shape and Galactic longitude is due to an intrinsic dependence of the extinction law on Galactocentric radius.Comment: Accepted to Ap