Astronomy Letters-A Journal of Astronomy and Space Astrophysics最新文献

A mechanism is proposed for synchronizing core-collapse supernova with a recent loss of a red supergiant (RSG) envelope in the common envelope regime. A prerequisite for the synchronization is a moderate RSG expansion during final decade. This scenario is based on the phenomenon of preSN II dense shell formed at the final stage of 10–20 yr as a result of powerfull mass loss. The energy deposition into the RSG envelope that powers the enormous mass loss rate is able to expand the RSG. The moderate expansion is sufficient for the close secondary component to plunge into the common envelope with a subsequent explosion of stripped helium core. Superluminous SN 2006gy is suggested to be the outcome of this scenario.

We consider the optimization of the attitude control strategy for orbital telescopes in the vicinity of the Sun–Earth libration point L2 to minimize the propellant consumption of the motion control system. We analyze the changes in the mission profile that lead to a growth of the requirements for correcting maneuvers and propose the methods of their reduction by choosing an optimal space observatory positioning scenario. Our attention is focused on finding a balance between the reaction-wheel offloading of the attitude control system, the reduction of fuel consumption, and the fulfilment of the requirements for scientific observations. We show that applying the proposed approach allows one to increase the stability of the orbit and to prolong the active lifetime of the telescopes by reducing the frequency of corrections and rationally using the control impulses.

The influence of the dust component of a magnetocentrifugal disk wind on the circumstellar extinction and the infrared thermal radiation of T Tauri stars is investigated. The wind models from Safier’s papers, which are analytical approximations of the solutions for a magnetocentrifugal dusty disk wind, are taken as a basis. An accretion spot whose luminosity is scaled in accordance with the accretion rate and stellar parameters is added to the stellar spectrum. The radiative transfer in the wind and the circumstellar disk has been simulated by the Monte Carlo method using the RADMC3D code. The results of our simulations are applied to T Tauri stars with UX Ori-type variability. We show that when such stars are observed at a small angle to the disk plane, an increase in the accretion rate can cause an optical fading of the stars and, simultaneously, an enhancement of their infrared radiation. We also show that the results of our simulations are sensitive to the magnetic field topology in the disk in the wind formation zone. The results of our calculations are discussed in connection with the observations of deep minima in the T Tauri stars V1184 Tau and RW Aur accompanied by an enhancement of their radiation in the near-infrared spectral range. In the Conclusions we briefly discuss alternative mechanisms for the uplift of dust above the disk capable of causing an enhancement of the infrared radiation from young stars.

Based on optical and infrared survey data spanning (approx 20) years of observations, the long-term variability of the polar V379 Vir with a brown dwarf secondary has been studied. By modeling the spectral energy distribution, we constrain the white dwarf’s mass to (M_{1}=0.61pm 0.05;M_{odot}) and its effective temperature to (T_{textrm{eff}}=10,930pm 350text{ K}). Near-infrared photometry yields a donor radius of (R_{2}=0.095pm 0.018;R_{odot}) and temperature (T_{textrm{eff}}=1600pm 180text{ K}). Modeling of the cyclotron emission from the accretion spot, detected with the Spitzer infrared telescope, gives an accretion rate of (dot{M}approx 3times 10^{-13};M_{odot}/textrm{yr}). This rate is consistent with polars in a low accretion state, but significantly higher than expected from wind-driven mass transfer.

We present new (UBV) photometric observations (2009–2024) of the carbon-rich post-AGB star IRAS 22272+5435 (V354 Lac), combined with our data spanning over 30 years (1991–2024). The star shows pulsations with two closely spaced periods, 127 and 132 d, which cause brightness variations of variable amplitude. We also detect low-amplitude oscillations with a 661-day period, of uncertain origin. Color analysis reveals both temperature variations during pulsations and spectral anomalies. For the first time, we analyze long-term (JHKLM) photometry (1994–2024), showing increased (KLM)-band brightness from 1996 to 2004—likely due to dust emission following a sudden mass ejection. The absence of strong optical variability suggests either a large angle between the ejection direction and the line of sight or a low optical depth of the ejected material. We discuss possible mechanisms and observational signatures of this dust-formation event.

We study the (f(Q,C)) gravity model by finding a power-law solution for the Hubble parameter (H(z)=H_{0}(1+z)^{{3}/{2n}}) and examine its consequences using a variety of cosmological datasets. Our approach involves the fitting of the model parameters to datasets from Hubble, BAO and Phantom that are in good agreement with observations. Upon analyzing the energy density (rho(z)), we discover that it provides evidence for a dynamic dark energy theory. The (Om(z)) diagnostic and the statefinder parameters (r) and (s) show the behaviours that is compatible with quintessence models. According to our findings, the (f(Q,C)) gravity model offers a feasible substitute for the conventional (Lambda)CDM model and offer a valuable understanding into the dynamic characteristics of dark energy and cosmic expansion.

We study the origin of the soft X-ray precursors that arise before the impulsive phase of a flare and testify to the rapid heating of the footpoints of flaring magnetic loops to temperatures of 10–15 MK. We show that the precursor heating rate at an observed duration ({sim})10 s must exceed the quasi-steady-state coronal heating rate at comparable electric currents by three orders of magnitude. We suggest that the preflare heating is associated with a sharp increase in the longitudinal electric current as the Rayleigh-Taylor instability develops at the chromospheric footpoints of the flaring loops. We show that if the pulse current exceeds (10^{11}{-}10^{12}) A, then the plasma Joule heating leads the ionization. In this case, a relatively large fraction of neutrals, (n_{a}/n=10^{-5}), which significantly exceeds the fraction of neutrals in a quasi-steady-state corona, is retained in the precursor plasma during the heating process. This ensures the rapid heating of the precursor region through an increase in the current dissipation rate under the Cowling resistivity associated with ion-atom collisions.

The method for estimating the spatial period of energy release in solar flares based on the application of a Fourier analysis to the difference images of flare arcades in the far ultraviolet is applied to the observations of the large solar flare on November 4, 2003. The flare occurred at the solar limb; the flare arcade extending along the solar limb was imaged in detail in the ultraviolet 195 Å channel of the TRACE satellite. The Fourier analysis of its difference images has shown the presence of a series of harmonics in the spatial distribution of the regions of flare energy release with characteristic periods lying in the range from 3.3 to 18.6 Mm. Such periodization may result from the decay of the preflare current layer accumulating the solar flare energy in coronal magnetic fields due to some instability of thermal, plasma, or other nature.

Using the Mikhail Pavlinsky ART-XC onboard the SRG observatory we have detected, for the first time, X-ray pulsations with a period of (simeq 106) s from the poorly-studied high-mass X-ray binary RX J0535.0-6700 located in the Large Magellanic Cloud (LMC), thus proving that the accretor is a neutron star with stong magnetic field. Pulsations with similar period were also found in archival archival data from Chandra and XMM-Newton telescopes. Using photometry from WISE we shown that the source demonstrate significant variability in IR during the last twenty years, which could be caused by a secular evolution of the decretion disk. This discovery makes RX J0535.0-6700 another member of the large family of X-ray pulsars with Be-type companions in the LMC.

It is shown for the first time that the stripped helium stars with masses (2–7) (M_{odot}) which are formed in close binary systems in the so-called case B of mass-exchange and retained low-mass hydrogen-helium envelopes, experience nonlinear radial pulsations. Pulsations are excited by the (kappa)-mechanism due to helium ionization. The region of pulsational instability extends over the Hertzsprung–Russell diagram from the red giant branch to the region of effective temperatures (4.5lesssimlog T_{textrm{eff}}lesssim 4.7). Stellar luminosity variations must be observed mostly in the ultraviolet. The amplitudes of pulsations of the studied models reach (Delta(M_{textrm{bol}})=0.8) and increase as the stellar radii (R) decrease. The pulsation periods of stars with (log T_{textrm{eff}}>4) range from 0.17 to 3.9 days and decrease with decreasing (R). The stars have substantially larger (T_{textrm{eff}}) than their companions, which could be Be stars. They are the components of relatively wide binaries with orbital periods up to several years. The number of pulsating moderate-mass stripped helium stars in the Galaxy is ({simeq}1000).