Journal of Astrophysics and Astronomy最新文献

Impact of p-capture reactions on the abundances of neon and magnesium considering the nuclear reaction chain, Neon–Sodium–Magnesium–Aluminum (hereafter extended Ne–Al) for stellar conditions of temperature range of (0.02times 10^{9})–(0.10times 10^{9}) K and typical density of 100 g cc({}^{-1}) has been studied. Then, we have estimated abundances of Ne and Mg, which are of a little special importance. The estimated abundances of these aforesaid elements are then compared with their counterparts, which have been observed in some B-type stars. For those B-type stars, we have discovered a significant agreement in the abundances between the estimated and observed values with a correlation coefficient >0.8.

In this paper, we report the results of the detailed temporal and spectral studies of the BeXRB J21347(+)4737 based on the data from the nuclear spectroscopic telescope array (NuSTAR) and Swift/XRT in a wide energy range of 0.5–50 keV. Coherent pulsation with a period of (322.738pm 0.018) s was found in the light curve, implying the source pulsation has spun down by 0.341 s yr(^{-1}) when compared with the coherent pulsation estimated from XMM Newton >7 years ago. The pulse profile of the source demonstrates energy dependence and has evolved with time. The pulse fraction of the source observed by NuSTAR initially decreases with energy up to (sim )15 keV, followed by a non-monotonic increasing trend above 15 keV. The source spectrum can be well approximated by an absorbed power-law model with modification by an exponential cutoff at high energies. The absorbed flux of the source is (4times 10^{-11}) erg cm(^{-2}) s(^{-1}) and its corresponding luminosity is (3.5times 10^{35}) erg s(^{-1}). The study of pulse-phase resolved spectroscopy shows a strong variation of spectral parameters on the phase. No additional emission or absorption features in the form of Fe line or cyclotron lines were observed both in the phase-averaged and phase-resolved spectra of IGR J21347(+)4737.

We considered a modified gravity theory through a special kind of ghost-free bimetric gravity, where one massive spin-2 field interacts with a massless spin-2 field. In this bimetric gravity, the late-time cosmic acceleration is achievable. Alongside the background expansion of the Universe, we also studied the first-order cosmological perturbations and probe the signature of the bimetric gravity on large cosmological scales. One possible probe is to study the observational signatures of the bimetric gravity through the post-reionization 21-cm power spectrum. We considered upcoming SKA1-mid antenna telescope specifications to show the prospects of the detectability of the ghost-free bimetric gravity through the post-reionization 21-cm power spectrum. Depending on the values of the model parameter, there is a possibility to distinguish the ghost-free bimetric gravity from the standard (Lambda )CDM model with the upcoming SKA1-mid telescope specifications.

Optical spectroscopy offers the most direct view of the stellar properties and the accretion indicators. Standard accretion tracers, such as H(beta ), H(alpha ) and Ca II triplet lines, and most photospheric features fall in the optical wavelengths. However, these tracers are not readily observable from deeply embedded protostars because of the large line of sight extinction ((A_v sim 50)–100 mag) toward them. In some cases, however, it is possible to observe protostars at optical wavelengths if the outflow cavity is aligned along the line-of-sight that allows observations of the photosphere, or the envelope is very tenuous and thin, such that the extinction is low. In such cases, we not only detect these protostars at optical wavelengths, but also follow up spectroscopically. We have used the HOPS catalog (Furlan et al. in 2016) of protostars in Orion to search for optical counterparts for protostars in the Gaia DR3 survey. Out of the 330 protostars in the HOPS sample, an optical counterpart within 2('') is detected for 62 of the protostars. For 17 out of 62 optically detected protostars, we obtained optical spectra (between 5500 and 8900 Å) using nt Object Spectrograph and Camera (ADFOSC) on the 3.6-m Devasthal Optical Telescope (DOT) and Hanle Faint Object Spectrograph Camera (HFOSC) on 2-m Himalayan Chandra Telescope (HCT). We detect strong photospheric features, such as the TiO bands in the spectra (of 4 protostars), hinting that photospheres can form early in the star-formation process. We further determined the spectral types of protostars, which show photospheres similar to a late M-type. Mass accretion rates derived for the protostars are similar to those found for T-Tauri stars, in the range of 10(^{-7})–10(^{-8}) (M_odot ) yr(^{-1}).