Journal of Astrophysics and Astronomy最新文献

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.

The study of protoplanetary disk formation and its connection with Solar system’s origin is considered to be one of the longest-standing problems in astronomy and astrophysics. To the current human understanding, planets are believed to be the hosts of life. Therefore, understanding the dynamic process affecting the formation of protoplanetary disk leads to predicting the origin of our Solar system. The fundamental question we raise here is how the properties of the surrounding gas and dust, which provide mass for the disk and central protostar formations, affect the properties of the protoplanetary disk. This paper investigates how the infalling core’s magnetic field, rotation and turbulence govern the protoplanetary disk formation. The theoretical model we have developed and the numerical results generated from the theoretical model show that a strongly magnetized and rotating core results in a relatively massive protoplanetary disk. Moreover, most of the disk’s angular momentum is removed outwards due to the infalling core’s magnetic field and its rotation speed.

In the interstellar medium (ISM), the complex organic molecules that contain the thiol group (–SH) play an important role in the polymerization of amino acids. We look for SH-bearing molecules in the chemically rich solar-type protostar IRAS 16293–2422. After extensive spectral analysis using the local thermodynamic equilibrium (LTE) model, we have detected the rotational emission lines of trans-isomer monothioformic acid (t-HC(O)SH) towards the IRAS 16293 B using the Atacama Large Millimeter/Submillimeter Array (ALMA). We did not observe any evidence of cis-isomer monothioformic acid (c-HC(O)SH) towards the IRAS 16293 B. The column density of t-HC(O)SH towards the IRAS 16293 B was ((1.02pm 0.6)times 10^{15}~hbox {cm}^{-2}) with an excitation temperature of (125pm 15) K. The fractional abundance of t-HC(O)SH with respect to (hbox {H}_{2}) towards the IRAS 16293 B is (8.50times 10^{-11}). The column density ratio of t-HC(O)SH/(hbox {CH}_{3}hbox {SH}) towards the IRAS 16293 B is 0.185. We compare our estimated abundance of t-HC(O)SH towards the IRAS 16293 B with the abundance of t-HC(O)SH towards the galactic center quiescent cloud G(+)0.693–0.027 and hot molecular core G31.41(+)0.31. After the comparison, we found that the abundance of t-HC(O)SH towards the IRAS 16293 B is several times of magnitude lower than G(+)0.693–0.027 and G31.41(+)0.31. We also discussed the possible formation mechanism of t-HC(O)SH in the ISM.

In the context of understanding star formation in the galactic plane, we present the results from the analysis of four young open clusters using archival data from Gaia Data Release 3, the Two-Micron All Sky Survey (2MASS) and Panoramic Survey Telescope and Rapid Response System (Pan-STARRS). The open clusters—[BDB2003]G085.25−00.02, [BDS2003]48, [BDS2003]65 and [FSR2007]0584 are situated close to the galactic plane between the galactic latitudes, (b = -0.23^{circ }) and (0.837^{circ }). The likely cluster members and mean proper motions were determined using a Gaussian likelihood model fit to the proper motion data provided by Gaia DR3. The cluster radii are estimated to be in the range of 2–3.3 arcmin. From the H–K vs. J–H color–color diagram, we identified probable young stellar objects. Using the J–H vs. J–K color–color diagram and PARSEC isochrones, we determined the line-of-sight interstellar reddening E(J–H) as (0.56pm 0.03) mag, (0.4pm 0.09) mag, (0.4pm 0.1) mag and (0.42pm 0.08) mag for [BDB2003]G085.25−00.02, [BDS2003]48, [BDS2003]65 and [FSR2007]0584, respectively. From the fit of isochrones to color–magnitude diagrams, we determined the distances and ages of the clusters. [BDB2003] G085.25−00.02 is located at a distance of (2.88pm 0.15) kpc, [BDS2003]48 is located at a distance of (4.78pm 0.18) kpc, [BDS2003]65 is located at a distance of (2.18pm 0.07) kpc and [FSR2007]0584 is located at a distance (3.31pm 0.14) kpc. We obtained the (log (textrm{age})) of [BDB2003] G085.25−00.02 as (6.85pm 0.2), the (log (textrm{age})) [BDS2003]48 as (6.2pm 0.5), the (log (textrm{age})) of [BDS2003]65 as (log (textrm{age})) of (6.7pm 0.16) and the (log (textrm{age})) of [FSR2007]0584 as (6.9pm 0.55). From the stellar masses predicted by the fitted isochrones for the cluster members, we obtained the present-day mass-functions of the clusters. The mass-function slopes are (-2.47pm 0.14) for [BDB2003]G085.25−00.02, (-2.1pm 0.25) for [BDS2003]48, (-2.61pm 0.22) for [BDS2003]65 and (-2.4pm 0.23) for [FSR2007]0584. Within the limits of error of a least-squares fit, the mass-function slopes are in fair agreement with the Salpeter slope of (-2.35).

The process of accretion through circumstellar disks in young stellar objects is an integral part of star formation and the (Halpha ) emission line is a prominent signature of accretion in low-mass stars. We present the detection and characterization of (Halpha ) emission line sources in the central region of a distant, low-metallicity young stellar cluster Dolidze 25 (at (sim ) 4.5 kpc) using medium-resolution optical spectra (4750–9350 Å) obtained with the multi-unit spectroscopic explorer (MUSE) at the VLT. We have identified 14 potential accreting sources within a rectangular region of ((2' times 1')) towards the center of the cluster based on the detection of strong and broad emissions in (Halpha ) as well as the presence of other emission lines, such as [OI] and (Hbeta ). Based on their positions in both photometric color–magnitude and color–color diagrams, we have also confirmed that these objects belong to the pre-main sequence phase of star formation. Our results were compared with the disk and diskless members of the cluster previously identified by Guarcello et al. (2021) using near-IR colors, and all sources they had identified as disks were confirmed to be accreting based on the spectroscopic characteristics.

We present the results from our deep optical photometric observations of Bochum 2 (Boc2) star cluster obtained using the 1.3-m Devasthal Fast Optical Telescope along with archival photometric data from Pan-STARRS2/2MASS/UKIDSS surveys. We also used high-quality parallax and proper motion data from the Gaia Data Release 3. We found that the Boc2 cluster has a small size ((sim )1.1 pc) and circular morphology. Using Gaia parallax of member stars and isochrone fitting method, the distance of this cluster is estimated as (3.8pm 0.4) kpc. We have found that this cluster holds young (({sim }5) Myr) and massive (O7–O9) stars as well as an older population of low mass stars. We found that the massive stars were formed in the inner region of the Boc2 cluster in a recent epoch of star formation. We have derived mass function slope ((Gamma )) in the cluster region as (-2.42pm 0.13) in the mass range of ({sim }0.72<M/M_{odot }<2.8). The tidal radius of the Boc2 cluster ((sim )7–9) is much more than its observed radius (({sim }1.1) pc). This suggests that most of the low-mass stars in this cluster are the remains of an older population of stars formed via an earlier epoch of star formation.