• Volume 40, Issue 2

      April 2019

    • Optical detection of a GMRT-detected candidate high-redshift radio galaxy with 3.6-m Devasthal optical telescope


      More Details Abstract Fulltext PDF

      We report optical observations of TGSS J1054 $+$ 5832, a candidate high-redshift ($z = 4.8 \pm 2$) steep-spectrum radio galaxy, in $r$ and $i$ bands, using the faint object spectrograph and camera mounted on 3.6-m Devasthal Optical Telescope (DOT). The source previously detected at 150 MHz from Giant Meterwave Radio Telescope (GMRT) and at 1420 MHz from Very Large Array has a known counterpart in near-infrared bands with $K$-band magnitude of AB 22. The source is detected in $i$-band with AB24.3 $\pm$ 0.2 magnitude in theDOT images presented here. The source remains undetected in the $r$-band image at a 2.5$\sigma$ depth of AB 24.4 mag over an $1.2^{\prime\prime}\times 1.2^{\prime\prime}$ aperture. An upper limit to $i−K$ color is estimated to be $\sim$2.3, suggesting youthfulness of the galaxy with active star formation. These observations highlight the importance and potential of the 3.6-mDOT for detections of faint galaxies.

    • Transfer of radiation in the formic acid: A precursor for amino acids


      More Details Abstract Fulltext PDF

      Formic acid (HCOOH), a simplest carboxylic acid, has great importance as it is a precursor for amino acids (constituents of life). It has two rotameric isomers: trans-HCOOH and cis-HCOOH, each of which lies in a plane due to the delocalization of $\pi$-electrons over the heavy atom chain. In each of the isomers, the electric dipole moment is aligned such that there are both $a$ and $b$ type rotational transitions. Further, the energy levels in each type of transitions can be classified into two groups. Thus, there are 8 groups in which the rotational transitions of formic acid may be classified. The trans-HCOOH is detected in Sgr B2, cold dark cloud L134N, Sgr A, comet Hale-Bopp, Orion KL, W51, IRAS 16293-2422 through its $a$-type transitions. Because of very small value of $b$-component of electric dipole moment, the $b$-type transitions of trans-HCOOH may not be detected. To our knowledge, no transitions of cis-HCOOH are yet detected in the interstellar medium, though $a$ and $b$ components of its electric dipole moment are quite large. Using spectroscopic data of trans-HCOOH and cis-HCOOH, we have calculated energies of 100 rotational levels for each of the 8 groups, and the radiative transition probabilities (Einstein $A$ and $B$ coefficients) for radiative transitions between the levels. Since the rate coefficients for collisional transitions between the levels are not available, by using the scaled values for them along with the radiative transition probabilities, we have solved a set of 100 statistical equilibrium equationscoupled with the equations of radiative transfer for each group.We have investigated intensities of 16 observed $a$-type transitions and 12 $b$-type transitions of trans-HCOOH. We have also found six transitions, $1_{10} − 1_{11}$ (1.405 GHz), $2_{12} − 3_{03}$ (7.545 GHz), $3_{12} − 3_{03}$ (79.744 GHz), $3_{21} − 3_{12}$ (222.287 GHz), $1_{11} − 2_{02}$ (30.843 GHz) and $4_{13}−4_{04}$ (82.740 GHz) of cis-HCOOH showing anomalous absorption and nine transitions $4_{14}−3_{13}$ (85.042 GHz), $5_{15} −4_{14}$ (106.266 GHz), $3_{03} −2_{02}$ (65.840 GHz), $4_{04} −3_{03}$ (87.694 GHz), $5_{05} −4_{04}$ (109.470 GHz), $5_{05}−4_{14}$ (40.778 GHz), $7_{07}−6_{16}$ (90.910 GHz), $4_{04}−3_{13}$ (16.350 GHz) and $6_{06}−5_{15}$ (65.661 GHz) of cis-HCOOH showing emission feature. These transitions of cis-HCOOH in addition to those of trans-HCOOH may help in the identification of HCOOH in a cosmic object.

    • Determination of short-period terms of total solar irradiance


      More Details Abstract Fulltext PDF

      In addition to the evident 11-year periodic changes, Total solar irradiance (TSI) also has some short-period processes. We carried out the wavelet analysis for TSI observational series and its inter-annual time series that is filtered out components less than 2 years and more than 8 years . Whether the wavelet graph or the global wavelet power spectrum, the results significantly show that there is a short period about 5.3 years, and its length and intensity both vary with time. Specifically, the strength of this period varies with the 11-year cyclechange, showing pronounced characteristics of peak strength and valley weakness. Moreover, the amplitude of these low-frequency fraction results indicates different TSI variation properties. Under each solar cycle, thesum of the power spectrum density of the 3–6 year period terms reflects that the energy value of the short period is concentrated in that range. When the 11-year cycle is intensive, the 3–6 year period also becomes intensive in TSI. And the total spectral intensity of TSI will be concentrated in that short-period terms.

    • Nonlinear power spectrum in clustering and smooth dark energy models beyond the BAO scale


      More Details Abstract Fulltext PDF

      We study the nonlinear effects of the clustering and smooth quintessence. We present numerical and also approximate semi-analytical expressions of nonlinear power spectrum both for clustering and smooth dark energy models beyond the Baryon Acoustic Oscillations (BAO) scale. This approximation is motivated by the extension of the resummation method of Anselmi and Pietroni (J Cosmol Astro-Part Phys 12:13, 2012.arXiv:1205.2235) for the dark energy models with evolving equation of state. The results of this scheme allowus for the prediction of the nonlinear power spectrum in the mildly nonlinear regime up to few percentage accuracies compared to the other available tools to compute the nonlinear power spectrum for the evolving dark energy models.

    • A modified holographic Ricci dark energy model in $f(R, T)$ theory of gravity


      More Details Abstract Fulltext PDF

      In the present paper,we studied the Bianchi type-V cosmological model in the presence of $f (R, T)$ Theory of Gravity using modified Holographic Ricci Dark Energy. To compute dynamical cosmological parameters, we used the relation between pressure and energy density $p_{\Lambda} = ω_{\Lambda} ρ_{\Lambda}$. We have also discussed the physical and geometrical properties of the model in detail.

    • Analytical study of Whistler mode waves for relativistic plasma with AC electric field in inner magnetosphere of Saturn


      More Details Abstract Fulltext PDF

      The population of plasma present in the rotationally dominated inner magnetosphere of Saturn is identified by the observed plasma waves in the magnetosphere. Whistler mode emissions along with electrostatic cyclotron emissions often with harmonics are a common feature of Saturnian inner magnetosphere. We present the outcomes of a study of very large amplitude Whistler mode waves characteristics inside the magnetosphere of radial distance of less than 15R$_s$. Whistler mode waves with temperature anisotropy in the magnetosphere of Saturn have been studied in the present work. Observations of Whistler mode emissions from Cassini Radio and Plasma Wave Science instruments have been obtained. Whistler mode waves were investigated using the method of characteristic solution by kinetic approach, in the presence of AC field. The observations made by space probes Voyager 1 and 2 and Cassini, launched by NASA, showed that charged particles are trapped in planet’s magnetic field lines. In 2004, the Cassini encounter with Saturn revealed that magnetosphere of Saturn exhibitsMaxwellian distribution. So, the dispersion relation, real frequency and growth rate were evaluated using ring distribution function. Effect of AC frequency, temperature anisotropy, energy and number density of particles was found. Temperature anisotropies greater than one (T$_{\perp}$/T$_{\parallel} > 1$) and pancake-like distribution can generate Whistler mode emissions of the warmer plasma population. The study also extended to oblique propagation of Whistler mode waves in presence of AC electric field. However, when relativistic factor $\beta =\sqrt{1-\frac{v^2}{c^2}}$ increases, growth rate decreases. Through comprehensive mathematical analysis, it was found that when Whistler modewaves propagate parallel to the intrinsic magnetic field of Saturn, its growth is enhanced more than in the case of oblique propagation. Results are also discussed while computing the rate with which the wave grows for a particular wavenumber.

    • Holographic dark energy models in LTB inhomogeneous universe


      More Details Abstract Fulltext PDF

      The holographic principle is investigated for the generalized Lemaitre–Tolman–Bondi (LTB) model of an inhomogeneous and an isotropic dark energy. The inhomogeneity is considered as spherically symmetric and locally flat overdense of dark energy with a few Gpc in size and has a core size on the scale of apparent horizon. Two particular forms of refined parabolic arbitrary scale function $R(r, t)$ are used in the LTB metric and some cosmological functions are calculated and plotted with the cosmological time and the distance fromthe center of the inhomogeneity. By choosing specific values of some numerical parameters of the models, we showed that some of these functions are in agreement with recent observations and have behavior similar to that of the cosmological constant dark energy universe.

    • A study of four low-latitude ($|l|$ < 10$^{\circ}$) far-infrared cavities


      More Details Abstract Fulltext PDF

      We present dust color temperature, dustmass, planck function and visual extinction distributions in the four low-latitude ($|l|$ < 10$^{\circ}$) far-infrared cavities namely FIC01$+$55, FIC05$+$28, FIC06$−$05 and FIC06$−$01which are found to be located within 0.5$^{\circ}$ far-infrared loops G128$−$03, G182$+$00, G212$−$11 and G214$−$01, respectively. These cavities are located within 3$^{\circ}$ of AGB stars ABG01$+$55, AGB05$+$28, AGB06$−$05 and PAGB181, respectively. The dust color temperature of the core region is found to lie in the range $18.4\pm 1.2$ to $26.2 \pm 1.7$ K. The product of dust color temperature and visual extinction is found to be consistent. The contour maps showed that the low temperature region have greater mass density. The distribution of planck function along major and minor diameters is found to be sinusoidal, suggesting oscillation in the grain temperaturedistribution.

    • Study of diffuse emission in cluster MACSJ0417.5-1154 from 76 MHz to 18 GHz


      More Details Abstract Fulltext PDF

      We present new radio observations of the massive and X-ray luminous galaxy cluster MACS J0417.5–1154, at 1.387 GHz and 18 GHz, from the Giant Metrewave Radio Telescope (GMRT) and the Australia Telescope Compact Array (ATCA) respectively.We estimate diffuse emission in the central region ofthe cluster at 1.387 GHz and 18 GHz. We combine these data with previously published results and present the spectrum of diffuse emission from 76 MHz to 18 GHz. This is possibly a unique study of the radio halo emission in galaxy cluster over this wide range of frequencies. Such studies lay the prospects of future studies with radio telescopes with wide-range of frequencies like the Square Kilometre Array (SKA). Our 1.387 GHz data, with 2$^{\prime\prime}$ angular resolution, provides a better estimate of point source emission than previous L-band observations, which is crucial, given the claim of sharp steepening of the radio halo spectrum at 0.61 GHz reported earlier. We find that the spectrum of the radio halo has a spectral index fit up to 18 GHz, and yields a spectral indexbetween 76 MHz and 18 GHz that fits the available data better than earlier L-band observations. We discuss possible reasons for the peculiar spectral characteristics of the diffuse emission.

    • Parameterization of non-canonical model of the exponential harmonic field


      More Details Abstract Fulltext PDF

      In this work we have proposed a non-canonical model of exponential harmonic field as dark energy in FRW universe. In this context, we have studied the inflationnary parameters in presence of power law potential. The analysis showed that observational data have been confirmed for quadratic and cubic potentials. In addition, deceleration parameter have been examined by associating to that dark energy, gas of Chaplygin as dark matter; three types of parametrisation have been considered in this case. The behaviors of deceleration parameter show transition from positive values to negative values, which would show that recent accelerated phase of the universe was preceded by a deceleration phase.

  • Journal of Astrophysics and Astronomy | News

    • 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

      Click here for Editorial Note on CAP Mode

© 2017-2019 Indian Academy of Sciences, Bengaluru.