Journal of Astrophysics and Astronomy最新文献

The planetary conjunctions have always procured a very prominent place in astronomy texts from India. The calculations aim at the determination of exact instant of conjunction by method of iteration and prediction of the possibility of occultation, grazing or otherwise. We discuss details of the procedure from a text of 17th century and offer two examples from texts of 16th century devoted to worked examples based on different methods. One of them gives an angular separation of 1′, which would have been a challenge to observe. The possible sources of error in the estimates of longitude and speed are discussed. We also infer that the approximations in the estimation of angular diameter and node led to errors in the prediction of type of occultation.

Age distribution of the open cluster system is a key piece of information to decipher the star-formation history of the milky way disk. Recently, a remarkable earlier drop of its older end was found, which caught our attention. Precisely, we analysed in detail the population of open clusters older than 1 Gyr located inside a circle of 2.0 kpc from the Sun contained in the milky way star-cluster catalog, using the data release 3.0 of the Gaia survey, and found that it contains a slightly larger old open-cluster population with respect to that witnessing the earlier drop age distribution. However, there are still some aspects that deserve further attention to undoubtedly handle a statistically complete cluster sample, that allows us to comprehensively know the older end of the open-cluster age-distribution function. We discuss some reasons that affect such a completeness, among them, the photometric depth of the database employed, the performance of machine-learning techniques used to recognize open clusters, the cleaning of cluster color–magnitude diagrams from field star contamination, etc.

We have investigated the five-dimensional Bianchi type-III string cosmological models with dark energy using the Saez–Ballester scalar-tensor theory of gravitation. To solve the field equations, we applied the laws of volumetric expansions and assumed a scaling relation between the shear scalar (sigma ) and the expansion scalar (theta ), which leads to a relationship between the metric potentials, i.e., ( D=C^{r} ) (where r is a non-zero constant). We have considered both power-law model and exponential model and have discussed the physical and kinematical parameters of these models.

Understanding the evolution and dissipation of protoplanetary disks are crucial in star and planet formation studies. We report the protoplanetary disk population in the nearby young (sigma ) Orionis cluster ((dsim 408) pc; (textrm{age}sim 1.8) Myr) and analyse the disk properties, such as dependence on stellar mass and disk evolution. We utilize the comprehensive census of 170 spectroscopic members of the region refined using astrometry from Gaia DR3 for a wide mass range of (sim )19–0.004 (M_odot ). Using the near-infrared (2MASS) and mid-infrared (WISE) photometries, we classify the sources based on the spectral index, into class I, class II, flat spectrum and class III young stellar objects. The frequency of sources hosting a disk with stellar mass <2 (M_odot ) in this region is (41pm 7)%, which is consistent with the disk fraction estimated in previous studies. We see that there is no significant dependence of disk fraction on stellar mass among T Tauri stars (<2 (M_odot )), but we propose rapid disk depletion around higher mass stars (>2 (M_odot )). Furthermore, we found the lowest mass of a disk-bearing object to be (sim )20 (M_{textrm{Jup}}) and the pronounced disk-fraction among the brown dwarf population hints at the formation scenario that brown dwarfs form similar to low-mass stars.

Using multi-wavelength data sets, we studied the star-formation activity in H ii region Sh 2-61 (hereafter S61). We identified a clustering in the region and estimated the membership using the Gaia proper motion data. The physical environment of S61 is inspected using infrared to radio wavelength images. We also determined the Lyman continuum flux associated with the H ii region and found that the H ii region is formed by at least two massive stars (S1 and S2). We also analyzed the (^{12})CO ((J =3)–2) JCMT data of S61, and a shell structure accompanying three molecular clumps are observed towards S61. We found that the ionized gas in S61 is surrounded by dust and a molecular shell. Many young stellar objects and three molecular clumps are observed at the interface of the ionized gas and surrounding gas. The pressure at the interface is higher than in a typical cool molecular cloud.

Classical T Tauri stars (TTS) are low-mass pre-main sequence stars with an active circumstellar environment. In this work, we present the identification and study of 260 classical TTS using LAMOST Data Release 6, among which 104 stars are newly identified. We distinguish classical TTS from giants and main-sequence dwarfs based on the (log {g}) values, and the presence of H(alpha ) emission line and infrared excess that arises from the circumstellar accretion disk. We estimated the mass and age of 210 stars using the Gaia color–magnitude diagram. The age is from 0.1 to 20 Myr, where 90% of the stars have age <10 Myr and the mass ranges between 0.11 and 1.9 (M_{odot }). From the measured H(alpha ) equivalent widths, we homogeneously estimated the mass accretion rates for 172 stars, with most values ranging from (10^{-7}) to (10^{-10}) (M_{odot }) yr(^{-1}). The mass accretion rates are found to follow a power law distribution with the mass of the star, having a relation of the form (dot{M}_textrm{acc}propto M_{*} ^ {1.43 pm 0.26}), in agreement with previous studies.

We report two anti-reflection (AR) coatings that give better quantum efficiency (QE) than the existing AR coating on the Gaia astrometric field (AF) charged coupled devices (CCDs). Light being the core of optical astronomy is extremely important for such missions, therefore, the QE of the devices that are used to capture it should be substantially high. To reduce the losses due to the reflection of light from the surface of the CCDs, AR coatings can be applied. Currently, the main component of the Gaia satellite, the AF CCDs use hafnium dioxide (HfO₂) AR coating. In this paper, the ATLAS module of the SILVACO software has been employed for simulating and studying the AF CCD pixel structure and several AR coatings. Our findings suggest that zirconium dioxide (ZrO₂) and tantalum pentoxide (Ta₂O₅) will prove to be better AR coatings for broadband astronomical CCDs in the future and will open new avenues to understand the evolution of the milky way.

The dispersion relation and Landau damping rate of dust-acoustic waves (DAWs) are studied by the incorporation of Poison–Vlasov model of the kinetic theory of plasmas. The real and imaginary frequencies of DAWs are obtained in a three-component plasma i.e., electrons, ions and dust grains. The electrons are taken as hybrid non-thermal Vasyliunas–Cairns distributed and in limiting cases as kappa and Cairns distributed as well, while the ions and dust are kept Maxwellian. The findings reveal that the simultaneous presence of two non-thermality parameters (i.e., (alpha ) and (kappa )) have a remarkable impact on the dispersion and damping rates of DAWs as compared to the sole presence of any non-thermality parameter and also in the case of thermal electrons. It is also presented that the real and imaginary frequencies of DAWs are significantly influenced by the other important parameters, such as electron to ion temperature and density ratios. This work has notable significance in the understanding of important constituents of space plasmas i.e., thermal and non-thermal dusty plasmas in various environments of space plasmas, where the mixed particle distributions are observed.

Secondary cosmic rays are produced from the interaction of primary cosmic rays, which are high-energy ((sim )GeV) particles originating from outer space, primarily, protons ((sim )89%) and alpha particles ((sim )10%) with atoms (mainly nitrogen and hydrogen) present in our Earth’s atmosphere. Such rays are dependent on solar activity and geomagnetic latitude through magnetic rigidity and are found to be modulated by these factors. For analysis of secondary cosmic ray data, we use the Indian Centre for Space Physics’s data obtained through small stratospheric balloon-borne experiments. In the present paper, we have measured the secondary cosmic ray intensity at low geomagnetic latitude of (sim )14.50(^circ )N in the low energy range of 25–60 keV from the ground to 30 km altitude for different detectors used in various balloon missions because such missions are almost detecting the X-ray sources above 30 km till 42 km. We also calculated background flux of the detector with the help of some justifiable physical assumptions, secondary cosmic gamma-ray component measurements, and assumed internal background functions. Finally, using our data of 2012–2019, which falls in the 24th solar cycle, we have shown that there is a clear anti-correlation between cosmic ray intensity at Regener–Pfotzer maximum and the solar activity.

We present the dynamical evolution of 10 open clusters, which were part of our previous studies. These clusters include both young and intermediate-age open clusters with ages ranging from (25 pm 19) Myr to (1.78pm 0.20) Gyr. The total mass of these clusters ranges from (356.18pm 142.90) to (1811.75pm ~901.03) (M_{odot }). The Galactocentric distances to the clusters are in the range of (8.91pm 0.02)–(11.74pm 0.18) kpc. The study is based on the ground-based UBVRI data supplemented by the astrometric data from the Gaia archive. We studied the minimum spanning tree of the member stars for these clusters. The mass segregation in these clusters was quantified by mass segregation ratios calculated from the mean edge length obtained through the minimum spanning tree. The clusters NGC 2360, NGC 1960, IC 1442, King 21 and SAI 35 have (Gamma _textrm{MSR}) to be (1.65pm 0.18), (1.94pm 0.22), (2.21pm 0.20), (1.84pm 0.23) and (1.96pm 0.25), respectively, which indicate moderate mass segregation in these clusters. The remaining five clusters are found to exhibit weak or no mass segregation. We used the ratio of half mass radius to the tidal radius i.e., (R_{h}/R_{t}) to investigate the effect of the tidal interactions on the cluster structure and dynamics. The ratios of half mass radii to tidal radii are found to be positively correlated with the Galactocentric distances with a linear slope of (0.06pm 0.01) having linear regression coefficient r-square (=) 0.93 for the clusters.