Journal of Astrophysics and Astronomy最新文献

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.

We present photometric and kinematic analyses of an intermediate-age open cluster NGC 1027 using ({UBV(RI)}_c) and Gaia Early Data Release 3 (EDR3) data. Structural and fundamental parameters, such as cluster center, cluster extent, reddening, age and distance are estimated in this study. Cluster center is found about 4 arcmin away from the center reported earlier. Radius has been estimated to be about 8.00 arcmin (2.65 pc). Using proper motion Gaia EDR3 data, membership probabilities have been derived for the stars in the region of cluster radius. We found mean proper motion of the cluster to be (sim )(−0.84, 2.04) mas yr(^{-1}) in (RA, DEC). We found 217 most probable ((P_mu>) 70%) cluster members with mean parallax (0.892 pm 0.088) mas. Out of these, 160 members have counterparts in our optical observations. Few stars having (P_mu > 70)%, are found out of the cluster radius showing imprints of dynamical evolution. The color–color and color–magnitude diagrams for the cluster members found within 8.00 arcmin have been constructed using ({UBV(RI)}_c) photometry and Gaia EDR3 data. This yields a reddening (E(B-V) sim 0.36) mag, age (sim )130 Myr and distance (sim )1.14 kpc. The mass function slope in the cluster region is (Gamma sim -1.46 pm 0.15), which is similar to other Galactic open clusters. The dynamical study shows lack of faint stars in its inner region leading to mass segregation effect. A comparison of dynamical age with cluster age indicates that NGC 1027 is a dynamically relaxed cluster suggesting that mass segregation may be imprint of its dynamical relaxation.

Fragmentation is a key step in the process of transforming clouds (and their substructures, such as filaments, clumps and cores) into protostars. The thermal gas pressure and gravitational collapse are believed to be the primary agents governing this process, referred as thermal Jeans fragmentation. However, the contributions of other factors (such as magnetic fields and turbulence) to the fragmentation process remain less explored. In this work, we have tested possible fragmentation mechanisms by estimating the mean core mass and mean inter-core separation of the B213 filament. We have used the (sim )14(^circ ) resolution James Clerk Maxwell Telescope (JCMT) Submillimeter Common-User Bolometer Array 2 (SCUBA-2)/POL-2 850 (mu )m dust continuum map and combined it with a Planck 850 (mu )m map and Herschel data. We find that in addition to the thermal contribution, the presence of ordered magnetic fields could be important in the fragmentation of the B213 filament.

LDN1415-IRS, a low-mass young stellar object (YSO), went into an outburst between 2001 and 2006, illuminating a surrounding nebula, LDN1415-Neb. LDN1415-Neb was found to have brightened by (I=3.77) mag by April 2006. The optical light curve covering (sim )15.5 years, starting from October 2006 to January 2022, is presented in this study. The initial optical spectrum indicated the presence of winds in the system, but the subsequent spectra have no wind indicators. The declining light curve and the absence of the P-Cygni profile in later epoch spectra indicate that the star and nebula system is retrieving back from its outburst state. Two Herbig–Haro objects (HHOs) are positioned linearly with respect to the optical brightness peak of the nebula, probably indicating the circumstellar disk being viewed edge-on. Our recent deep near-infrared (NIR) imaging using TANSPEC has revealed the presence of a nearby star-like source, south of the LDN1415-IRS, at an angular distance of (sim !5.4'').

Protostellar jets are one of the primary signposts of star formation. A handful of protostellar objects exhibit radio emission from ionized jets, of which a few display negative spectral indices, indicating the presence of synchrotron emission. In this study, we characterize the radio spectra of HH80-81 jet with the help of a numerical model that we have developed earlier, which takes into account both thermal free–free and non-thermal synchrotron emission mechanisms. For modeling the HH80-81 jet, we consider jet emission towards the central region close to the driving source along with two Herbig-Haro objects, HH80 and HH81. We have obtained the best-fit parameters for each of these sources by fitting the model to radio observational data corresponding to two frequency windows taken across two epochs. Considering an electron number density in the range of (10^3)–(10^5) cm(^{-3}), we obtained the thickness of the jet edges and fraction of relativistic electrons that contribute to non-thermal emission in the range of (0.01^{circ })–(0.1^{circ }) and (10^{-7})–(10^{-4}), respectively. For the best-fit parameter sets, the model spectral indices lie in the range of − 0.15 to (+)0.11 within the observed frequency windows.

The Solar Mean Magnetic Field (SMMF) is the mean value of the line-of-sight (LOS) component of the solar vector magnetic field averaged over the visible hemisphere of the Sun. So far, the studies on SMMF have mostly been confined to the magnetic field measurements at the photosphere. In this study, we calculate and analyse the SMMF using magnetic field measurements at the chromosphere, in conjunction with that of photospheric measurements. For this purpose, we have used full-disk LOS magnetograms derived from spectropolarimetric observations carried out in Fe i 6301.5 Å and Ca ii 8542 Å by the Synoptic Optical Long-term Investigations of the Sun (SOLIS)/Vector Spectromagnetograph (VSM) instrument during 2010–2017. It is found from this study that the SMMF at the chromosphere is weaker by a factor of 0.60 compared to the SMMF at the upper-photosphere. The correlation analysis between them gives a Pearson correlation coefficient of 0.80. The similarity and reduced intensity of the chromospheric SMMF with respect to the photospheric SMMF corroborate the idea that it is the source of the Interplanetary Magnetic Field (IMF).

Large ground and space-based surveys in optical and near-infrared (NIR) wavelengths will revolutionize astronomy in the coming decade. Unfortunately, no ultraviolet (UV) facilities are planned to complement these surveys, which is crucial for studying the most active phase of the Universe that includes star formation in galaxies, active galactic nuclei (AGN), galaxy clusters, etc. A dedicated UV mission, the Indian Spectroscopic and Imaging Space Telescope (INSIST), is proposed to observe the UV sky. The compelling science objectives defined a set of high-level mission requirements. According to which, the INSIST is to have a wide field-of-view ((textrm{FoV} approx 0.25) square degree) comparable to India’s Ultraviolet Imaging Telescope (UVIT) and about two orders of magnitude larger than that of the Hubble Space Telescope, simultaneous imaging of the FoV in UV (150–300 nm), u (300–400 nm) and g (400–550 nm) bands, a Multi-Object-Slit medium resolution spectroscopy in a narrow FoV in UV and a simultaneous slitless spectroscopic capability in UV and u bands. To achieve these requirements, several optical design configurations were explored. Here, we present an optical design trade study conducted on various optical design configurations to achieve a sensitivity limit of (m_{textrm{AB}}> 26) mag, in the UV band and a spatial resolution better than 0.2(^{prime prime }), using a 1-m size telescope aperture. We also present results from our fabrication and alignment tolerance analysis of the selected optical designs, and the design performance that meets the design requirements. Critical parameters like the encircled energy concentration, point spread function (its stability over the field), effects of the spiders supporting the secondary, etc., are explored during the design phase. Based on the trade study conducted in reference to various performance matrices, we down-selected the most optimal optical design for the INSIST.

We present an estimation and analysis of Near Infrared (NIR) background for the astronomical site at Mount Abu. Mount Abu Observatory is situated at Gurushikhar, Rajasthan, India, operated by the Physical Research Laboratory. Data obtained from the NIR observations of various sources using the Near Infrared Camera/Spectrograph (NICS) on the 1.2-m telescope are used to derive the NIR background estimates. We notice seasonal variations in these values, with the summer months showing brighter background compared to the winter. We also present a comparison of synthetic atmospheric transmission at Mount Abu with other Indian observatories at various altitudes. We identify the plausible contributors to the NIR background in our observations and discuss the potential ones that can contribute to the noticed seasonal variations. Overall, we found that the NIR background does not show any systematic variation over the period of observations from 2010 to 2019. The results reported here are specific to the NICS instrument on the 1.2-m telescope.

The hosts of OH megamaser (OHM) are luminous infrared galaxies (LIRGs), in fact 1/3 of them are ultra-luminous infrared galaxies (ULIRGs), which imply that OHM phenomena should be related to the infrared radiation field. In this paper, we investigate the far infrared (FIR) properties of OHM host galaxies, through detailed infrared data covering broad bands. All known OHM sources and one control sample of (U)LIRGs without maser detections (non-OHM sources) are cross-identified with AKARI and Herschel photometric catalogs. Comparative analysis on the spectral energy distribution (SED) with broad coverage from J to 350 (mu )m (taken from 2MASS, WISE, Spitzer, and AKARI and Herschel archive data) shows that the OHM sources tend to have higher FIR luminosities than those of the non-OHM sources, which are more pronounced in the SED range covered by the AKARI. These are consistent with our statistical results of the FIR luminosities distribution of both the samples, which show that the OHM sources tend to have higher FIR luminosities, especially, at short FIR wavelength (i.e., the 65 and 90 (mu )m). However, the non-OHM sources tend to have much stronger emission than those of OHM sources at both the near infrared (NIR) and middle infrared (MIR) bands. The statistic analysis of the color–color properties at MIR and FIR bands shows that the OHM sources have much cooler MIR and warmer FIR colors than non-OHM sources. These clues could help us to choose OHM candidates for future OHM surveys with the Five-hundred-meter Aperture Spherical radio Telescope (FAST), where the OHM detection rate may exceed 40%. Further, one significant correlation of (L_textrm{OH} propto L_{T_textrm{FIR}}^{1.18pm 0.11}) can be found between the maser luminosity and total FIR luminosity of OHM LIRGs. Combined with previous studies, we suggest that the OHM is dominantly pumped by the FIR, instead of NIR and MIR radiation fields.

TIFR Near Infrared Imaging Camera-II (TIRCAM2) is being used at the Devasthal Optical Telescope (DOT) operated by Aryabhatta Research Institute of Observational Sciences (ARIES), Nainital, Uttarakhand, India. In addition to the normal full frame observations, there has been a requirement for high speed sub-array observations for applications, such as lunar occultation and star speckle observations. Fast sub-array modes have been implemented in TIRCAM2 with suitable changes in the camera software at the computer and controller DSP code level. Successful observations have been carried out with the fast sub-array mode of observation.