New Astronomy最新文献

In the present paper, the expansion of Locally Rotational Symmetric (LRS) Bianchi type - I cosmological model have been investigated with Bulk Viscous matter in the context of $f\left(T\right)$ theory of gravity, where $T$ signifies the torsion scalar. The power model, exponential model and linear functional model of the universe have been discussed for choices of $f\left(T\right)$with utilization of the special form of time dependent varying deceleration parameter. The discussion involves the examination of the dynamical behaviour of these models using some dynamical parameters and its graphical representation.

We identify a point-symmetric morphology of the supernova remnant (SNR) Cassiopeia A compatible with shaping by at least two, and more likely more than four, pairs of opposite jets, as expected in the jittering jets explosion mechanism (JJEM) of core-collapse supernovae. Using an old Spitzer Telescope infrared map of argon, we identify seven pairs of opposite morphological features that we connect with lines that cross each other at the same point on the plane of the sky. The opposite morphological features include protrusions, clumps, filaments, and funnels in the main SNR shell. In addition to these seven symmetry axes, we find two tentative symmetry axes (lines). These lines form a point-symmetric wind-rose. We place this point-symmetric wind-rose on a new JWST and X-ray images of Cassiopeia A. We find other morphological features and one more symmetry axis that strengthen the identified point-symmetric morphology. Not all symmetry axes correspond to jets; e.g., some clumps are formed by the compression of ejecta between two jet-inflated lobes (bubbles). The robust point-symmetric morphology in the iconic Cassiopeia A SNR strongly supports the JJEM and poses a severe challenge to the neutrino-driven explosion mechanism.

Using observations with XMM-Newton, we study the characteristics of a flare emanating from a solar analogous V895 Tau. At the peak of the flare, its luminosity reached $3.3\times 10^{30}$ $\mathrm{erg}{s}^{-1}$, which is $\sim$ 600 times more energetic than the X10 class flare on the Sun. The quiescent state corona of V895 Tau is depicted by a two-temperature plasma model with temperatures of 3.9 and 11 MK. The flare’s evolution was carefully scrutinized through time-resolved X-ray spectroscopy, unveiling the variations in temperature, emission measure, abundance and luminosity during the flare. The temperature peaked at 36.1 MK, which is approximately four times higher than the pre-flare temperature. Employing a hydrodynamic loop model, we have estimated the half length of the flaring loop to be $5.9\times 10^{10}$ cm. Using the loop scaling laws, other loop parameters like density, pressure, volume, and minimum magnetic field are also estimated, and are found to be similar to those of other flares from similar type of stars.

The mass–radius relationship of white dwarfs (WDs) is one of their defining characteristics, largely derived from electron degeneracy pressure. We present a model-independent study of the observed mass–radius relationship in WD binaries of Parsons et al. (2017), listing data over a broad temperature range up to about 60,000 K (5 eV). The data show an appreciable temperature sensitivity with pronounced intrinsic scatter (beyond measurement uncertainty) for the canonical He-models with proton$-$to$-$neutron ratio 1:1. We characterize temperature sensitivity by a temperature scale $T_0$ in model-agnostic power-law relations with temperature normalized radius. For low-mass WDs, the results identify a remarkably modest $T_0=1\sim 2$  eV. We comment on a potential interpretation for atmospheres insulating super-Eddington temperature cores from the sub-Eddington photospheres of low-mass WDs.

The decrease rate of dust mass due to strong shock waves ($v_s\ge 150$ km s⁻¹) from supernovae (SNe) estimated for the Milky Way interstellar medium significantly exceeds the overall production rate by both asymptotic giant branch stars and core collapse SNe. The interplay between the production and destruction rates is critically important for evaluation of the net dust outcome from SNe at different conditions. In light of this, we study the dynamics of initially polydisperse dust grains pre-existing in an ambient medium swept up the SN shock front depending on magnitude of inhomogeneity (clumpiness) in the medium. We find that dust destruction inside the bubble is inhibited in more inhomogeneous medium: the larger amount of dust survives for the higher dispersion of density. This trend is set by the interrelation between radiative gas cooling and dust sputtering in different environment. After several radiative times the mass fraction of the survived dust saturates at the level almost independent on the gas mean density. We note that for more clumpy medium the distributions of dust over thermal phases of a gas inside the bubble and over sizes are smoother and flatter in comparison with those in a nearly homogeneous medium.

In this paper, we present an analytical solution for the interacting generalized holographic dark energy model, assuming a linear interaction rate between dark energy and dark matter. We determine the equation of state parameter, the generalized holographic Ricci dark energy density, the matter density, and the deceleration parameter. By analyzing the behavior of these cosmological parameters, we demonstrate that our model aligns with recent observations and reproduces the late-time accelerated expansion of the Universe. To compare our model with the $\Lambda$CDM model, we use various diagnostic tools including statefinder, $Om\left(z\right)$-diagnostic, statefinder hierarchy, growth rate analysis, and ${\omega }_H$-${\omega }_H^{\prime }$ plane. We also analyze the stability of the model by examining the speed of sound. These methods show that the dynamics of the Universe remain very close to that of the standard cosmological model.

We have analyzed the light curves of three $\delta$ Scuti stars that were observed by the Kepler Space Telescope. Data collected by the Kepler space telescope, as well as analysis of the light curve of each star and the use of online databases, have been utilized to achieve the objectives of this project. Data has been collected through Kepler's main mission. We compare both data that we get from the Lightkurve package of Python and the KASOC online data centre to verify the data. We select the necessary data like flux, observation date, and the spectral type of the stars. By investigating various types of pulsating variable stars, three Delta Scuti stars have been selected due to their flux, pulsating type, etc. It is observed that most of these stars are pulsating in the p-modes. However, the selected stars pulsate in both p-modes and (possibly) g-modes. We select these stars, due to the lack of articles about them. Furthermore, some physical properties of these stars are deduced from their light curves. In summary, the results of this study indicate that the stars KIC3429637 and KIC10451090 are pulsating only in p-modes, while KIC2987660 is pulsating both in p-modes and g-modes.

We present the first combined photometric and spectroscopic solution of the bright southern contact binary S Ant based on the Transiting Exoplanet Survey Satellite (TESS) light curve and the radial velocities from the David Dunlap Observatory survey. S Ant is a W UMa type binary in deep contact, with a mass ratio of 0.34 and a relatively massive and hot F-type primary. Beside the standard modeling of the phase-binned light curve, we also perform “seasonal modeling” where we treat each of the 83 orbital cycles present in the TESS data as a separate light curve. The resulting ensemble of solutions shows evidence of quasi-periodic migration of a long-lived, dark, polar spot. The migration is confirmed independently by eclipse time variations which display remarkably strong correlation with the spot location.