The Effect of Freeze-Thaw Cycling and the Initial Mass of Water on the Unfrozen Water Content of Calcium Bentonites Modified by Copper Ions

This research was conducted with the use of the DSC method; it involved the examination of the unfrozen water content in two model (source) calcium bentonites (≥75% smectite), after one to three freeze-thaw cycles in the natural state, as well as after the ion exchange for a potentially toxic element (Cu2+). The freeze-thaw cycles do not affect the unfrozen water content at a given negative temperature in a statistically significant manner. However, a statistically significant influence of temperature, the initial mass of the water, and the clay type on the change of the unfrozen water content was found. Moreover, the empirical models of predicting the unfrozen water in the bentonite after the exchange for Cu2+ ion were created, for which the parameter was the mass of the water and the mass of the dry soil, at the temperature of −2 °C.

A Census of the Stellar Populations in the Sco-Cen Complex*

I have used high-precision photometry and astrometry from the early installment of the third data release of Gaia (EDR3) to perform a survey for members of the stellar populations within the Sco-Cen complex, which consist of Upper Sco, UCL/LCC, the V1062 Sco group, Ophiuchus, and Lupus. Among Gaia sources with σ π < 1 mas, I have identified 10,509 candidate members of those populations. I have compiled previous measurements of spectral types, Li equivalent widths, and radial velocities for the candidates, which are available for 3169, 1420, and 1740 objects, respectively. In a subset of candidates selected to minimize field star contamination, I estimate that the contamination is ≲1% and the completeness is ∼90% at spectral types of ≲M6–M7 for the populations with low extinction (Upper Sco, V1062 Sco, UCL/LCC). I have used that cleaner sample to characterize the stellar populations in Sco-Cen in terms of their initial mass functions, ages, and space velocities. For instance, all of the populations in Sco-Cen have histograms of spectral types that peak near M4–M5, which indicates that they share similar characteristic masses for their initial mass functions (∼0.15–0.2 M ⊙). After accounting for incompleteness, I estimate that the Sco-Cen complex contains nearly 10,000 members with masses above ∼0.01 M ⊙. Finally, I also present new estimates for the intrinsic colors of young stars and brown dwarfs (≲20 Myr) in bands from Gaia EDR3, the Two Micron All Sky Survey, the Wide-field Infrared Survey Explorer, and the Spitzer Space Telescope.

STUDY OF THE COAGULATION OF AEROSOL PARTICLES IN THE SCRUBBER ULTRASOUND CHAMBER

В данной работе представлены результаты исследования процесса коагуляции частиц аэрозоля моноаммонийфосфата в модельной ультразвуковой (УЗ) камере скруббера. Изучено поведение аэрозольных частиц внутри камеры на расстоянии 100 мм и 400 мм от ультразвукового излучателя с частотой излучения 22 кГц. Представленные результаты показывают практически отсутствие коагуляции частиц при интенсивности звукового давления 140 dB и процесс активной коагуляции при интенсивности звукового давления 150 dB для выбранного образца. Начальная массовая концентрация фосфата аммония в камере составляла 1 г/м3. Измерения дисперсного состава аэрозоля внутри камеры показали, что более интенсивно коагуляция проходила в области 400 мм. Через 30 минут воздействия значение среднего объемно-поверхностного диаметра частиц аэрозоля в камере изменилось на 238,4 %. This paper presents the results of the study of the coagulation of the monoammonium phosphate aerosol particles in the model ultrasonic scrubber chamber. The behavior of aerosol particles inside the chamber is studied at the distance of 100 mm and 400 mm from the ultrasonic emitter with 22 kHz of the radiation frequency. The presented results show almost complete absence of particle coagulation at the sound pressure intensity of 140 DB and the active coagulation process at the intensity of 150 dB for the selected sample. The initial mass concentration of ammonium phosphate in the chamber was 1 g / m3. Measuring the dispersed composition of the aerosol showed that coagulation proceeds more intensively in the region of 400 mm. After 30 minutes of exposure the value of the average surfactant diameter of the aerosol particles in the chamber has changed by 238.4%.

Variation in the Stellar Initial Mass Function from the Chromospheric Activity of M Dwarfs in Early-type Galaxies

Mass measurements and absorption-line studies indicate that the stellar initial mass function (IMF) is bottom-heavy in the central regions of many early-type galaxies, with an excess of low-mass stars compared to the IMF of the Milky Way. Here we test this hypothesis using a method that is independent of previous techniques. Low-mass stars have strong chromospheric activity characterized by nonthermal emission at short wavelengths. Approximately half of the UV flux of M dwarfs is contained in the λ1215.7 Lyα line, and we show that the total Lyα emission of an early-type galaxy is a sensitive probe of the IMF with a factor of ∼2 flux variation in response to plausible variations in the number of low-mass stars. We use the Cosmic Origins Spectrograph on the Hubble Space Telescope to measure the Lyα line in the centers of the massive early-type galaxies NGC 1407 and NGC 2695. We detect Lyα emission in both galaxies and demonstrate that it originates in stars. We find that the Lyα to i-band flux ratio is a factor of 2.0 ± 0.4 higher in NGC 1407 than in NGC 2695, in agreement with the difference in their IMFs as previously determined from gravity-sensitive optical absorption lines. Although a larger sample of galaxies is required for definitive answers, these initial results support the hypothesis that the IMF is not universal but varies with environment.

Wolf-Rayet Galaxies in SDSS-IV MaNGA. II. Metallicity Dependence of the High-mass Slope of the Stellar Initial Mass Function

As hosts of living high-mass stars, Wolf-Rayet (WR) regions or WR galaxies are ideal objects for constraining the high-mass end of the stellar initial mass function (IMF). We construct a large sample of 910 WR galaxies/regions that cover a wide range of stellar metallicity (from Z ∼ 0.001 to 0.03) by combining three catalogs of WR galaxies/regions previously selected from the SDSS and SDSS-IV/MaNGA surveys. We measure the equivalent widths of the WR blue bump at ∼4650 Å for each spectrum. They are compared with predictions from stellar evolutionary models Starburst99 and BPASS, with different IMF assumptions (high-mass slope α of the IMF ranging from 1.0 to 3.3). Both singular evolution and binary evolution are considered. We also use a Bayesian inference code to perform full spectral fitting to WR spectra with stellar population spectra from BPASS as fitting templates. We then make a model selection among different α assumptions based on Bayesian evidence. These analyses have consistently led to a positive correlation of the IMF high-mass slope α with stellar metallicity Z, i.e., with a steeper IMF (more bottom-heavy) at higher metallicities. Specifically, an IMF with α = 1.00 is preferred at the lowest metallicity (Z ∼ 0.001), and an Salpeter or even steeper IMF is preferred at the highest metallicity (Z ∼ 0.03). These conclusions hold even when binary population models are adopted.

The key impact of the host star’s rotational history on the evolution of TOI-849b

Context. TOI-849b is one of the few planets populating the hot-Neptune desert and it is the densest Neptune-sized one discovered so far. Its extraordinary proximity to the host star, together with the absence of a massive H/He envelope on top of the 40.8 M⊕ rocky core, calls into question the role played by the host star in the evolution of the system. Aims. We aim to study the impact of the host star’s rotational history on the evolution of TOI-849b, particularly focussing on the planetary migration due to dynamical tides dissipated in the stellar convective envelope, and on the high-energy stellar emission. Methods. Rotating stellar models of TOI-849 are coupled to our orbital evolution code to study the evolution of the planetary orbit. The evolution of the planetary atmosphere is studied by means of the JADE code, which uses realistic X-ray and extreme-ultraviolet (XUV) fluxes provided by our rotating stellar models. Results. Assuming that the planet was at its present-day position (ain = 0.01598 AU) at the protoplanetary disc dispersal, with mass 40.8 M⊕, and considering a broad range of host star initial surface rotation rates (Ωin ∈ [3.2, 18] Ω⊙), we find that only for Ωin ≤ 5 Ω⊙ do we reproduce the current position of the planet, given that for Ωin > 5 Ω⊙ its orbit is efficiently deflected by dynamical tides within the first ∼40 Myr of evolution. We also simulated the evolution of the orbit for values of ain ≠ 0.01598 AU for each of the considered rotational histories, confirming that the only combination suited to reproduce the current position of the planet is given by ain = 0.01598 AU and Ωin ≤ 5 Ω⊙. We tested the impact of increasing the initial mass of the planet on the efficiency of tides, finding that a higher initial mass (Min = 1 MJup) does not change the results reported above. Based on these results we computed the evolution of the planetary atmospheres with the JADE code for a large range of initial masses above a core mass of 40.8 M⊕, finding that the strong XUV-flux received by the planet is able to remove the entirety of the envelope within the first 50 Myr, even if it formed as a Jupiter-mass planet.

On the initial velocity of the glacial-stone material movement, the air-blast, the nature of the carrier medium and the range of action of sudden explosion-like gas-dynamic surge of the Kolka glacier

Начальная массовая скорость компактного движения выброшенного ледово-каменного материала ледника Колка, достигнутая на стадии газового ускорения в эпицентральной зоне взрывоподобного внезапного газодинамического выброса ледника, составляла около 300 м/с. Именно столь высокие значения величины начальной массовой скорости выброса основного количества ледово-каменного материала определили возможность образования сопутствовавшей выбросу ударной воздушной волны, которая и на большом расстоянии от эпицентра выброса (порядка 15 км) все еще имела значительную интенсивность. Воздушным был характер несущей среды для всего Геналдонского лавинообразного потока в пределах выделенной прежде всего по этому признаку зоны транзита на всем многокилометровом ее протяжении, а для начальной и основной стадий выброса – и за пределами этой зоны (до Скалистого хребта). Дальность же действия взрывоподобного внезапного газодинамического выброса ледника Колка 20 сентября 2002 года, безусловно, не ограничивалась лишь вместилищем ледника Колка или Колкинским цирком, как иногда полагают, а захватывала огромную территорию Колкинского и Геналдонского ущелий и была ограничена (да и то не полностью) лишь непреодолимой механической преградой Скалистого хребта. Цель работы. В плане сопоставления с взрывоподобными направленными газодинамическими выбросами ледников рассматривается вопрос об истории изучения направленных вулканических взрывов, установленных полстолетием ранее. Методы работы. Проведен анализ имеющихся данных и существующих походов их оценок. Результаты работы. Показана огромная мощность взрывоподобных направленных газодинамических выбросов ледника Колка, вполне сопоставимых в данном отношении с крупными направленными вулканическими взрывами. The initial mass velocity of the compact movement of the ejected glacial-stone material of the Kolka glacier, reached at the stage of gas acceleration in the epicentral zone of the sudden explosion-like gas-dynamic surge of the glacier, was about 300 m/s. Exactly such high values of the initial mass velocity of the surge of the main amount of glacial-stone material that determined the possibility of the formation of an accompanying ejection of the air-blast, which had a significant intensity even at a great distance from the surge epicenter (about 15 km). The nature of the carrier medium for the entire Genaldon avalanche flow was aerial within the transit zone distinguished primarily according this character along its entire length of many kilometers; and for the initial and main stages of the surge the nature was the same outside this zone (up to the Skalisty (Rocky) Ridge). The range of action of the sudden explosion-like gas-dynamic surge of the Kolka glacier on September 20, 2002, was certainly not limited only by the reservoir of the Kolka glacier or the Kolka cirque, as it is sometimes supposed, but captured the vast territory of the Kolka and Genaldon gorges and was limited (and even then not completely) only by the insurmountable mechanical barrier of the Skalisty (Rocky Ridge). Aim. In terms of the comparison with explosion-like directional gas-dynamic surges of glaciers, the article considers an issue of the history of study of directional volcanic explosions determined half a century earlier. Methods. The analysis of the available data and the existing approaches for their assessments was carried out. Results. The results of the work show the enormous power of explosion-like directed gas-dynamic surges of the Kolka glacier, which are quite comparable in this respect with large directed volcanic explosions.

Transition of the initial mass function in the metal-poor environments

We study star cluster formation in a low-metallicity environment using three dimensional hydrodynamic simulations. Starting from a turbulent cloud core, we follow the formation and growth of protostellar systems with different metallicities ranging from 10−6 to 0.1 Z⊙. The cooling induced by dust grains promotes fragmentation at small scales and the formation of low-mass stars with M* ∼ 0.01–0.1 M⊙ While the number of low-mass stars increases with metallicity, when Z/Z⊙ ≳ 10−5. the stellar mass distribution is still top-heavy for Z/Z⊙ ≲ 10−2 compared to the Chabrier initial mass function (IMF). In these cases, star formation begins after the turbulent motion decays and a single massive cloud core monolithically collapses to form a central massive stellar system. The circumstellar disk preferentially feeds the mass to the central massive stars, making the mass distribution top-heavy. When Z/Z⊙ = 0.1, collisions of the turbulent flows promote the onset of the star formation and a highly filamentary structure develops owing to efficient fine-structure line cooling. In this case, the mass supply to the massive stars is limited by the local gas reservoir and the mass is shared among the stars, leading to a Chabrier-like IMF. We conclude that cooling at the scales of the turbulent motion promotes the development of the filamentary structure and works as an important factor leading to the present-day IMF.