Journal of Astrophysics and Astronomy最新文献

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.

In the present paper, we performed the optical, astrometric and spectroscopic studies for the open star cluster NGC 6475 using Gaia DR3 data. Using the radial density profile, we estimated the radius of the cluster to be equal to 1.44°. It is located at a distance of 279 ± 17 pc and has a service life of 224 ± 26 Myr. The mean proper motions in RA are 268.50 ± 0.80 mas yr⁻¹ and in DEC, they are −34.83 ± 0.70 mas yr⁻¹. Using spectroscopic radial velocity data of Gaia DR3, the median radial velocity is −14.47 ± 1.92 km s⁻¹. We determined the physical parameters (T_eff, log g and V sin i) for 11 possible members of the B-type stars in the open cluster NGC 6475, using the Barbier–Chalonge–Divan (BCD) spectrophotometry system. We also determined the projected rotational velocity of the stars by matching them with the theoretical LTE model and located our studied stars over the HR diagram. From the 11 studied B-type stars, we found six members from them.

TIFR Near Infrared Imaging Camera-II (TIRCAM2) is being used at the 3.6-m Devasthal Optical Telescope (DOT) operated by Aryabhatta Research Institute of Observational Sciences (ARIES), Nainital, Uttarakhand, India. Earlier, the TIRCAM2 was used at the main port of the DOT on time-shared basis. It has now been installed at the side port of the telescope. Side port installation allows near simultaneous observations with the main port instrument as well as longer operating periods. Thus, the TIRCAM2 serves the astronomical community for a variety of observations ranging from lunar occultations, transient events and normal scheduled observations.

Herbig Ae/Be stars are intermediate-mass pre-main sequence stars undergoing accretion through their circumstellar disk. The optical and infrared (IR) spectra of HAeBe stars show Hi emission lines belonging to Balmer, Paschen and Brackett series. We used the archival X-Shooter spectra available for 109 HAeBe stars from Vioque et al. (2018) and analysed the various Hi lines present in them. We segregated the stars into different classes based on the presence of higher-order lines in different Hi series. We discussed the dependence of the appearance of higher-order lines on the stellar parameters. We found that most massive and younger stars show all the higher-order lines in emission. The stars showing only lower-order lines have (T_textrm{eff} < {12{,}000}) K and an age range of 5–10 Myr. We performed a case B line ratio analysis for a sub-sample of stars showing most of the Hi lines in emission. We noted that all but four stars belonging to the sub-sample show lower Hi line ratios than theoretical values, owing to the emitting medium being optically thick. The Hi line flux ratios do not depend on the star’s spectral type. Further, from the line ratios of lower-order lines and Paschen higher-order lines, we note that line ratios of most HAeBe stars match with electron density value in the range of (10^9)–(10^{11}) cm(^{-3}). The electron temperature, however, could not be ascertained with confidence using the line ratios studied in this work.

The nature of equation of state for the matter in the neutron star plays an important role in determining its maximal mass. In addition, it must comply with the condition of causality. Noting that the central density of a maximally massive neutron star is well above the nuclear saturation density, a deconfined quark core in the central region is motivated in this paper. We analyze this scenario by employing the MIT bag model to represent the core region and one of the unified equations of state for the region outside the core. Such a combination is found to solve the problem of causality violation. In each case of the combined equations of state, the radial profile of (rho r^2) displays a peak and the dominant contribution to the total mass of the star comes from the region around the peak value of (rho r^2), whereas the contribution is small from the regions near the center and the surface. This peak occurs in the region of hadronic matter for the combinations considered in this paper. Importantly, we find that the position of the peak in (rho r^2) is well-correlated with the maximal mass—the highest value of 1.98 (M_odot ) obtains for the case with the peak occurring farthest from the center. This gravitational threshold being obtained for a non-rotating neutron star, we expect the threshold to lie well above 2 (M_odot ) for a rapidly rotating neutron star, that may explain the existence of massive pulsars from recent astronomical observations.

We study the timing and spectral properties of the X-ray pulsar 2S 1553–542 using the NuSTAR and NICER during the outburst in January–February 2021. During the outburst, the spin period of the neutron star was (Psim 9.2822) s based on NuSTAR data. The pulse profiles are studied using different NICER observations, which implies that the profile is more or less sinusoidal with a single peak and the beaming patterns are dominated mainly by the pencil beam. The NICER spectra of the source are studied for different days of the outburst. They can be well described by a model consisting of a blackbody emission, power law and photoelectric absorption component. The variation of spectral parameters with luminosity is studied over the outburst. The photon index shows anti-correlation with luminosity below the critical luminosity, which implies that the source was accreting in the sub-critical accretion regime during the NICER observations. We also report the anti-correlation between pulsed fraction (PF) and luminosity of the 2S 1553–542 using NICER observations. The evolution of spin-up rate with luminosity is studied during the outburst, which implies that both are strongly correlated. The torque-luminosity model is applied to estimate the magnetic field at different spin-up rates. The magnetic field is estimated to be ({simeq }2.56 times 10^{12}) G from the torque-luminosity model using the source distance of 20 kpc. The magnetic field is also estimated using the critical luminosity, consistent with our findings.