Feedback from γ Cassiopeiae: Large Expanding Cavity, Accelerating Cometary Globules, and Peculiar X-Ray Emission

We present wide-field multiwavelength observations of γ Cassiopeiae (or γ Cas for short) in order to study its feedback toward the interstellar environment. A large expanding cavity is discovered toward γ Cas in the neutral hydrogen (H i) images at a systemic velocity of about −10 km s−1. The measured dimension of the cavity is roughly 2.°0 × 1.°4 (or 6.0 pc × 4.2 pc at a distance of 168 pc), while the expansion velocity is ∼5.0 ± 0.5 km s−1. The CO observations reveal systematic velocity gradients in IC 63 (∼20 km s−1 pc−1) and IC 59 (∼30 km s−1 pc−1), two cometary globules illuminated by γ Cas, proving fast acceleration of the globules under stellar radiation pressure. The gas kinematics indicate that the cavity is opened by strong stellar wind, which has high potential to lead to the peculiar X-ray emission observed in γ Cas. Our result favors a new scenario that emphasizes the roles of stellar wind and binarity in the X-ray emission of the γ Cas stars.

INTERPRETATION OF OPTICAL AND IR LIGHT CURVES FOR TRANSITIONAL DISK CANDIDATES IN NGC 2264 USING THE EXTINCTED STELLAR RADIATION AND THE EMISSION OF OPTICALLY THIN DUST INSIDE THE HOLE

In the stellar forming region NGC 2264 there are objects catalogued as hosting a transitional disk according to spectrum modeling. Four members of this set have optical and infrared light curves coming from the CoRoT and Spitzer telescopes. In this work, we try to simultaneously explain the light curves using the extinction of the stellar radiation and the emission of the dust inside the hole of a transitional disk. For the object Mon-296, we were successful. However, for Mon-314, and Mon-433 our evidence suggests that they host a pre-transitional disk. For Mon-1308 a new spectrum fitting using the 3D radiative transfer code Hyperion allows us to conclude that this object hosts a full disk instead of a transitional disk. This is in accord to previous work on Mon-1308 and with the fact that we cannot find a fit for the light curves using only the contribution of the dust inside the hole of a transitional disk.

A target list for observing habitable exomoons

<p>There is no confirmed exomoon discovery up to date, and a possible explanation for this is the lower probability of stable moon orbits around close-in planets which are often easier to observe (Barnes & O'Brien 2002). We provide a target list for observations listing known exoplanets which might host habitable moons on stable orbits. For this, we investigate the habitability of hypothethical moons that are on stable orbits around known exoplanets. To determine their habitability, we calculate the incident stellar radiation and the tidal heat flux that might arise in moons depending on their orbital and physical parameters. Our target list contains interesting observation targets which might help in detecting the first habitable exomoon.</p>

Modelling H2 and its effects on star formation using a joint implementation of gadget-3 and KROME

ABSTRACT We present p-gadget3-k, an updated version of gadget-3, that incorporates the chemistry package krome. p-gadget3-k follows the hydrodynamical and chemical evolution of cosmic structures, incorporating the chemistry and cooling of H2 and metal cooling in non-equilibrium. We performed different runs of the same ICs to assess the impact of various physical parameters and prescriptions, namely gas metallicity, molecular hydrogen formation on dust, star formation recipes including or not H2 dependence, and the effects of numerical resolution. We find that the characteristics of the simulated systems, both globally and at kpc-scales, are in good agreement with several observable properties of molecular gas in star-forming galaxies. The surface density profiles of star formation rate (SFR) and H2 are found to vary with the clumping factor and resolution. In agreement with previous results, the chemical enrichment of the gas component is found to be a key ingredient to model the formation and distribution of H2 as a function of gas density and temperature. A star formation algorithm that takes into account the H2 fraction together with a treatment for the local stellar radiation field improves the agreement with observed H2 abundances over a wide range of gas densities and with the molecular Kennicutt–Schmidt law, implying a more realistic modelling of the star formation process.

КОМПОНЕНТ ТЕМНОЇ МАТЕРІЇ І СОНЦЕ

Some consequences from the hypothesis of the origin of particles of one of the components of dark matter are presented. The reason for the hypothesis was the observational data of stellar radiation, considered through the prism of the relationship of all phenomena in Nature and the law of conservation of energy. It is argued that a part of the stellar electromagnetic radiation, which does not participate in the interaction with baryonic matter, will not wander forever in space. This radiation will interact with a subtle level of matter, continuously giving it its energy, shifting to the microwave region. In this frequency region, two quanta of close energies can form a neutral boson of spin 0, or spin 2, on opposite “courses”. Based on the observed spectrum of cosmic microwave radiation, it is assumed that these Bose particles have a continuous mass spectrum. These light nonrelativistic bosons are precisely the component of the thin medium that interacts with stellar radiation, taking energy from it. Bose particles participate in gravitational interactions. This means that in addition to the distribution of dark matter around galaxies, an increased concentration of particles in the form of large clouds can be observed in it. If an internal shock wave appears in such a cloud, located far from galactic streams of baryon particles, it will destroy the particles of the cloud, creating “strange radio circles” visible exclusively in the radio range. The gravitational interaction causes dark particles to drift towards large clusters of visible matter. The process of their drift to massive objects will be accompanied by resistance from the outgoing stellar radiation. Therefore, near the surface of a burning star, these particles themselves will resist the outgoing radiation, shifting it towards longer wavelengths. The plasma ejected by the star, with sufficient energy of its particles, is capable of destroying the particles of the dark component, creating pairs of photons and providing itself with "seed" quanta for bremsstrahlung. Free quanta remaining from the decay of dark particles will give microwave radiation. Therefore, burning stars should exhibit a redshift in the emission spectra and microwave radiation. Taking a certain model in the distribution of the dark component of matter near the Sun, it is possible to predict the nature of the redshift in the spectra of its radiation as the observation point moves along the solar disk from its center to the limb. A similar conclusion is made regarding the intensity of microwave radiation near the surface of the star. The galactic movement of the Sun should lead to some temperature effects associated with a denser counter flow of dark particles to the corresponding area of the solar surface. Knowing the direction of motion of the Sun in the Galaxy, based on the results of the temperature deviation on the surface of the star, one can determine the local speed and direction of movement of the cloud of the dark component of matter.

Measurement of Urban Expansion and Spatial Correlation of Central Yunnan Urban Agglomeration Using Nighttime Light Data

The Central Yunnan Urban Agglomeration (CYUA) is an important zone of western development in China. The clarification of the spatial structure and changing trends in CYUA could help promote the coordinated development of the CYUA and enhance the overall competitiveness of the region. Based on data from the Yunnan Statistical Yearbook and the nighttime light data, this paper extracts the urban built-up area of the CYUA and analyzes the urban expansion and urban spatial connection intensity of the CYUA from 2000 to 2018 by using the urban gravity center model and the gravity model. The results show the following: (1) From 2000 to 2018, the urban built-up area of the CYUA expanded rapidly, and the urban built-up area increased by 369.35%, with Kunming accounting for 45.41% of the increased area. Kunming was the main contributor to the increase in the urban built-up area in the CYUA. From 2000 to 2018, the urban built-up areas of the CYUA were scattered in various mountain basins. (2) Overall, the urban gravity center of the CYUA has moved to Kunming, and the distance of the urban gravity center has increased since 2005, indicating that urban expansion has accelerated since 2005. (3) The development of the CYUA is extremely unbalanced. The urban spatial connection intensity between Kunming city, Yuxi city, and Qujing city, and Yi Autonomous Prefecture of Chuxiong is relatively strong, while the urban spatial connection intensity among cities other than Kunming is weak. Overall, the CYUA is characterized by stellar radiation with Kunming city as the core and Yuxi city as the secondary core.

Line-drag damping of Alfvén waves in radiatively driven winds of magnetic massive stars

ABSTRACT Line-driven stellar winds from massive (OB) stars are subject to a strong line-deshadowing instability. Recently, spectropolarimetric surveys have collected ample evidence that a subset of Galactic massive stars hosts strong surface magnetic fields. We investigate here the propagation and stability of magnetoradiative waves in such a magnetized, line-driven wind. Our analytic, linear stability analysis includes line-scattering from the stellar radiation, and accounts for both radial and non-radial perturbations. We establish a bridging law for arbitrary perturbation wavelength after which we analyse separately the long- and short-wavelength limits. While long-wavelength radiative and magnetic waves are found to be completely decoupled, a key result is that short-wavelength, radially propagating Alfvén waves couple to the scattered radiation field and are strongly damped due to the line-drag effect. This damping of magnetic waves in a scattering-line-driven flow could have important effects on regulating the non-linear wind dynamics, and so might also have strong influence on observational diagnostics of the wind structure and clumping of magnetic line-driven winds.