• Volume 40, Issue 4

August 2019

• A near-infrared camera for iRobo-AO on the IUCAA 2-m telescope

The effect of atmospheric turbulence is gentler at infrared wavelengths than in visible regime. Hence adaptive optics (AO) delivers better performance in the infrared regime. Robotic Adaptive Optics (Robo-AO) is an AO system for medium-sized telescopes jointly built by Caltech, USA and IUCAA, India. It works with minimal overheads and provides good sky coverage in both visible and infrared regime. The ﬁrst version of Robo-AO does not have a high-quality NIR camera. For the second version called iRobo-AO, an NIR camera was developed at IUCAA to accommodate AO-corrected 1.0$^{\prime}$ ﬁeld-of-view in near-infrared bands. It can be used as a science camera as well as a tip-tilt camera. Here we describe the salient features of the NIR camera like optics, optomechanical design, detector control system etc.

• Temporal variations of the solar EUV network properties

The chromospheric network extended to the transition region as the solar EUV network disperses at the coronal level. The EUV emission lines from the transition region give information about different atmospheric heights. The network properties have been obtained from the daily spectroscopic data from theCoronal Diagnostic Spectrometer (CDS) on board the Solar and Heliospheric Observatory (SOHO) in two lines He I 584.5 Å and O v 630 Å. The synoptic changes in the line intensity, skewness of intensity distribution, meancontrast and network index with respect to the sunspot cycle were studied for a period of 11 years from 1996 to 2006. We have obtained the cross correlation of the monthly average of these quantities with the monthly sunspot number. The mean intensity and skewness of the two lines generally show a positive correlation with the sunspot cycle. The network contrast and network index of the He I shows a definite negative correlation with the sunspot cycle. The negative correlations shown by the He I line are unexpected which could be due toits anomalous behaviour. There are differences in the behaviour of the two lines regarding the time lag with the sunspot cycle and the magnitude of the correlation which is always higher for the He I line. The results haveimplications to the studies of solar irradiance, magnetic flux transfer and solar atmospheric dynamics.

• Rotational fatigue analysis on Shanghai 65-m fully-steerable antenna structure during its normal operation

Structural fatigue property of Shanghai 65-m fully-steerable antenna structure is analysed. According to the active fully-steerable working pattern, the typical fatigue stress piece is put forward based on simple sampling and decomposed by real-time rain flow counting algorithms. Subsequently, the fatigue lives of pitchmechanism bearings were computed by miner linear accumulative damage criterion. What’s more, in a complete cycle of dynamic observation, the shear force and axial force of high strength friction grip bolts for all of the supporting nodes are extracted and counted aiming at each pitching angle. As a result, fatigue analysis is carried out on the supporting nodes of the back-frame structure connected with the pitching mechanism. Last but notthe least, finite element refinement model is conducted for the contact part between antenna wheels and the rail. Based on contact fatigue curve spectrum, the contact fatigue existing between the antenna structure roller andthe track is analysed. The results show that the fatigue life of the whole antenna structure can meet the safety requirements in the design reference period which is intended to be 30 years. This systematic fatigue analysis procedure, method and results can provide valuable references for design, construction and maintenance of such similar fully-steerable antenna structures in future.

• Dynamics of tilted Bianchi type-III cosmological model in $f (R, T)$ gravity

Tilted Bianchi type-III cosmological model filled with perfect fluid is investigated in $f (R, T)$ theory of gravity, where $R$ is the Ricci scalar and $T$ is the trace of stress energy momentum tensor. Here we study the class of $f (R, T) = R+2 f (T)$. To decipher the solutions of field equations, we used time power-law form of a metric potential $C$, i.e. $C = t^{m}$, where $m$ is a positive constant, which yields constant decelerationparameter. The solution of field equations represent an expanding model of the Universe. The physical behavior of the model are discussed by using some physical parameters.

• Quark novae: An alternative channel for the formation of isolated millisecond pulsars

Isolated millisecond pulsars (IMSPs) are a topic of academic contention. There are various models to explain their formation. We explore the formation of IMSP via quark novae (QN). During this formation process, low-mass X-ray binaries (LMXBs) are disrupted when the mass of the neutron star (NS) reaches1.8$M_{\odot}$. Using population synthesis, this work estimates that the galactic birthrate of QN-produced IMSPs lies between $\sim 9.5 \times 10^{−6}$ and $\sim 1.7 \times 10^{−4}$ yr$^{−1}$. The uncertainties shown in our experiment model is due to the QN’s kick velocity. Furthermore, our findings not only show that QN-produced IMSPs are statistically more significant than those produced by mergers, but also that millisecond pulsar binaries with a high eccentricity may originate from LMXBs that have been involved in, yet not disrupted by, a QN.

• CCD $UBV(RI)_{\rm KC}$ photometry of NGC 2323 and NGC 2539 open clusters

The open clusters NGC 2323 and NGC 2539 have been analysed using CCD $UBV(RI)_{KC}$ photometric data, observed at the San Pedro Mártir Observatory. Cluster memberships have been determined with the proper motion and parallax measures from the GaiaDR2 astrometric data release. Photometric metal and heavy element abundances have been obtained as $([M/H], Z) = (−0.10, 0.012)$ (NGC 2323) and ($−$0.31, 0.007) (NGC 2539) from the $\delta (U–B)$ technique in the two-colour diagrams, which are used to select the appropriate PARSEC isochrones. The estimated reddening of NGC 2323 is $E(B − V) = 0.23 \pm 0.04$ using 11 early type stars. For NGC 2539, we find $E(B − V) = 0.02 \pm 0.06$. For $(B − V)$ colour, distance moduli and distances for NGC 2323 and NGC 2539 are derived as $(V_0 − M_V , d ({\rm pc})) = (10.00 \pm 0.10, 1000 \pm 50)$ and$(V_0 − M_V , d ({\rm pc})) = (10.00\pm 0.04, 1000\pm 20)$, respectively. The median GaiaDR2 distance $d = 1000\pm 140$ pc ($\varpi = 0.998\pm 0.136$ mas) for the likely members of NGC 2323 is in concordance with its four-colour photometric distances 910–1000 pc. For NGC 2539, its GaiaDR2 distance $d = 1330\pm 250$ pc ($\varpi = 0.751\pm 0.139$ mas) is close to its four-colour photometric distances, 1000 pc. Fitting the PARSEC isochrones to the colourmagnitude diagrams (CMDs) gives an old age, $890\pm 110$ Myr, for NGC 2539. Whereas NGC 2323 has an intermediate age, $200\pm 50$ Myr. One red clump/red giant candidate (BD-12 2380) in the CMDs of NGC 2539 has been confirmed as a member in terms of the distances $d_I = 950 \pm 50$ pc and $d_V = 910 \pm 90$ pc of $V I$ filters within the uncertainties, as compared to the distance $1000 \pm 20$ pc of NGC 2539. This giant’s GaiaDR2 distance ($d = 1200 \pm 70$ pc) is not close to these photometric distances.

• Stability of gluonic systems with multiple soft interactions

In this paper,we investigate the stability properties of soft gluons in SIBYLL 2.1with reference to its original version 1.7 that corresponds to hadronic hard interactions. In order to investigate the stability structures, we classify the regions of the gluon density fluctuations in its double leading logarithmic approximation and its equivalent description as the fractional power law. In the parameter space of initial transverse momentum $Q$ and QCD renormalization scale $L$ that correspond to extensive air showers of cosmic rays, we have categorized the surface of parameters over which the proton is stable. We further discuss the nature of local and global correlations and stability properties where the concerning statistical basis yields a stable system or undergoes a geometric phase transition. Finally, we give a phenomenological understanding towards the stability of soft interactions, pomeron particle productions in mini-jet model, string fragmentation and verify our result corresponding to the experiments – CDF, P238, UAS, GEUS and UA4 collaborations.

• Tracing the outer disk of NGC 300: An ultraviolet view

We present an ultra-violet (UV) study of the galaxy NGC 300 using GALEX far-UV (FUV) and near-UV (NUV) observations. We studied the nature of UV emission in the galaxy and correlated it with optical, H I and mid-infrared (3.6 $\mu$m) wavelengths. Our study identified extended features in the outer disk, with the UV disk extending up to a radius of 12 kpc ($>2R_{25}$). We estimated the FUV and NUV disk scale-length as $3.05 \pm 0.27$ kpc and $2.66 \pm 0.20$ kpc respectively. The scale-length in FUV is 2.3 times larger than that at 3.6 $\mu$m, and we also find the disk to gradually become flatter from longer to shorter wavelengths. We performed a statistical source subtraction to eliminate the background contaminants and identified 261 unresolved UV sources between the radii 5.3 kpc and 10 kpc ($1 \sim 2R_{25}$). The identified UV sources show an age range between 1–300 Myr with a peak at 25 Myr and a mass range between 10$^{3} M_{\odot}$ to 10$^{6}M_{\odot}$, estimated using Starburst 99 models. The north-eastern spiral arm is found to be populated by young low mass sources suggesting that the star formation in this spiral arm is a recent phenomenon. The UV emission beyond the $R_{25}$ radius has contribution from these low mass sources and is extended up to $\sim 2R_{25}$ radius. We conclude that NGC 300 has an extended UV disk, mainly populated by young low mass sources. The star formation rate is measured to be $\sim 0.46 M_{\odot}$/yr which is comparable to its near optical twin M33.

• A revised catalogue of 294 Galactic supernova remnants

A revised catalogue of Galactic supernova remnants (SNRs) is presented, along with some simple statistics of their properties. Six new SNRs have been added to the catalogue since the previous published version from 2014, and six entries have been removed, as they have been identified as H II regions, leaving the number of entries in the catalogue at 294. Some simple statistics of the remnants in the catalogue, and the selection effects that apply, are discussed, along with some recently proposed Galactic SNR candidates.

• # Journal of Astrophysics and Astronomy

Current Issue
Volume 40 | Issue 5
October 2019

• # Continuous Article Publication

Posted on January 27, 2016

Since January 2016, the Journal of Astrophysics and Astronomy has moved to Continuous Article Publishing (CAP) mode. This means that each accepted article is being published immediately online with DOI and article citation ID with starting page number 1. Articles are also visible in Web of Science immediately. All these have helped shorten the publication time and have improved the visibility of the articles.

• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019