New Astronomy最新文献

We present the discovery of 269 pulsating variable stars of $\delta$ Scuti, $\gamma$ Doradus, and Maia types in the vicinity of the open cluster NGC 6871, using data from the Transiting Exoplanet Survey Satellite (TESS). Our small-scale regional survey centered on the $\delta$ Scuti star V1821 Cyg in the open cluster NGC 6871, covering a radius of one degree. The results include a remarkable total of 1512 newly classified variable stars, comprising the following categories: 105 $\delta$ Scuti stars, 121 $\gamma$ Doradus stars, 50 Maia variables, 198 eclipsing binary systems, with 12 exhibiting pulsating or rotating components, 500+ rotating variable stars, and dozens of other types. Out of 1512 newly discovered variable stars, 108 are confirmed members of NGC 6871 with a membership probability exceeding 50%. Notably, dedicated Fourier analyses were applied to eight representative stars from the newly discovered variables. Among these, one star exhibits a rich and complex pulsation spectrum characterized by amplitude variations in dominant pulsations. To contextualize the new pulsators, we plotted them in the Hertzsprung–Russell diagrams alongside the largest known group of class member stars. Surprisingly, both $\delta$ Scuti and $\gamma$ Doradus stars occupy nearly the same region in the diagrams, hinting at a potential unified pulsation mechanism. This study contributes valuable insights into the variability census of NGC 6871 and sheds light on the pulsation behavior of different stellar types. Further investigations into the physical properties and evolutionary status of these stars are warranted.

The paper examines out-of-plane equilibrium points (OEPs) of the restricted three-body problem with variable masses and shape. The bigger primary varies it shape as the lengths of the semi-axes vary with time. For the autonomized system, two pair of OEPs $L_{6,7\kappa }$ and $L_{8,9\kappa }$, are obtained and differ from those of the non-autonomous system due to time $t$. The stability of OEPs of both systems is found to be unstable. Further, numerical illustrations is provided when variations in shape of the bigger primary is, a triaxial prolate, a sphere and a triaxial oblate shape. The positions, stability and zero velocity curves (ZVC) of the particle around the OEPs are explored. It is seen that when the bigger primary is a triaxial prolate body, the OEPs $L_{8,9\kappa }$ are closer to the primaries than $L_{6,7\kappa }$. However, the converse happens when it is a triaxial oblate body. Also, when the bigger primary is a triaxial oblate body, the OEPs are farther away from the primaries than when it is a triaxial prolate. In the case of the ZVC, it is seen that when the bigger primary is a triaxial prolate body, there is a petal around it, and region of allowed motion of the particle increases, while the region reduces when the bigger primary evolves from a sphere to a triaxial oblate body. This study can be used to describe motion of a dust grain in the vicinity of Betelgeuse, a red giant star whose mass and shape changes with time and its stellar companion.

Dark energy, one of the mysterious and impactful forms of energy in the cosmos has a crucial role in propelling the rapid expansion of the cosmos. As a result it is highly likely that dark energy interacts with astrophysical objects in some direct or indirect way. The present paper introduces a simplified method to simulate the interaction between energy and conspicuous baryonic matter. It is accomplished by using a dense pulsar named PSRJ1614-2230 as a representative model star. The study involves solving Einsteins field equations within the stars interior using the Kuchowicz spacetime framework. The solutions obtained are then analyzed across physical as well as geometrical parameters such as metric potentials, pressure, density and energy conditions. Based on this analysis, it is suggested that the formation of the star embraced with dark energy equation of state exhibits stability. Importantly the proposed stellar model does not have any singularities, meets the stability criteria. Additionally, numerical results for the adiabatic and abreu index indicate that the model star displays stiffness and resilience against radial adiabatic perturbations.

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.