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We present multi-wavelength temporal and spectral characteristics of a magnetic cataclysmic variable (MCV) Swift J0503.7-2819, using far ultraviolet (FUV) and X-ray data from AstroSat, supplemented with optical data from the Southern African Large Telescope and X-ray data from the XMM-Newton and Swift observatories. The X-ray modulations at 4897.6657 s and 3932.0355 s are interpreted as the orbital ($P_{\Omega}$) and spin ($P_{\omega}$) period, respectively, and are consistent with prior reports. With a spin-orbit period ratio of 0.8 and $P_{\Omega}$ falling below the period gap (2-3 hrs) of CVs, Swift J0503.7-2819 would be the newest addition to the growing population of nearly synchronous MCVs, which we call EX Hya-like systems. Hard X-ray luminosity of $<$ $2.5\times10^{32} erg s^{-1}$, as measured with the Swift Burst Alert Telescope, identifies it to be a low-luminosity intermediate polar, similar to other EX Hya-like systems. The phenomenology of the light curves and the spectral characteristics rule out a purely disc-fed/stream-fed model and instead reveal the presence of complex accretion structures around the white dwarf. We propose a ring-like accretion flow, akin to EX Hya, using period ratio, stability arguments, and observational features. An attempt is made to differentiate between the asynchronous polar/nearly-synchronous intermediate polar nature of Swift J0503.7-2819. Further, we note that with the advent of sensitive surveys, a growing population of MCVs that exhibit characteristics of both polars and intermediate polars is beginning to be identified, likely forming a genealogical link between the two conventional classes of MCVs., Comment: Accepted for publication in MNRAS, 17 Pages, 13 Figures

We present our $AstroSat$ soft X-ray observations of a compact binary system, AR Sco, and analysis of its X-ray observations with $Chandra$ that were taken only about a week before the $AstroSat$ observations. An analysis of the soft X-ray ($0.3-2.0$ keV) data limits the modulation of the spin, orbital, or beat periods to less than 0.03 counts s$^{-1}$ or $<$10\% of the average count rate. The X-ray flux obtained from both observatories is found to be almost identical (within a few percent) in flux, and about 30\% lower than reported from the nine months older observations with $XMM-Newton$. A two-temperature thermal plasma model with the same spectral parameters fit $Chandra$ and $AstroSat$ data very well, and requires very little absorption in the line of sight to the source. The low-temperature component has the same temperature ($\sim$1 keV) as reported earlier, but the high-temperature component has a lower temperature of 5.0$^{+0.8}_{-0.7}$ keV as compared to 8.0 keV measured earlier, however, the difference is not statistically significant., Comment: 9 pages, 8 figures, to be published in the Journal of Astrophysics and Astronomy

Over the last 5 years, UVIT has completed observations of more than 500 proposals with ~ 800 unique pointings. In addition, regular planned monitoring observations have been made and from their analysis various key parameters related to in orbit performance of UVIT have been quantified. The sensitivities of the UV channels have remained steady indicating no effect of potential molecular contamination confirming the adequacy of all the protocols implemented for avoiding contamination. The quality of the PSF through the years confirms adequacy of thermal control measures. The early calibrations obtained during the Performance Verification (PV) phase have been further revised for more subtle effects. These include flat fields and detector distortions with greater precision. The operations of UVIT have also evolved through in orbit experience, e.g. tweaking of operational sequencing, protocol for recovery from bright object detection (BOD) shutdowns, parameters for BOD thresholds, etc. Finally, some effects of charged particle hits on electronics led to opimised strategy for regular resetting. The Near-UV channel was lost in one of such operations. All the above in-orbit experiences are presented here., Comment: Accepted for publication in Journal of Astrophysics & Astronomy, 11 pages, 10 figures, 1 table

Two long AstroSat Soft X-ray Telescope observations were taken of the third recorded outburst of the Symbiotic Recurrent Nova, V3890 Sgr. The first observing run, 8.1-9.9 days after the outburst, initially showed a stable intensity level with a hard X-ray spectrum that we attribute to shocks between the nova ejecta and the pre-existing stellar companion. On day 8.57, the first, weak, signs appeared of Super Soft Source (SSS) emission powered by residual burning on the surface of the White Dwarf. The SSS emission was observed to be highly variable on time scales of hours. After day 8.9, the SSS component was more stable and brighter. In the second observing run, on days 15.9-19.6 after the outburst, the SSS component was even brighter but still highly variable. The SSS emission was observed to fade significantly during days 16.8-17.8 followed by re-brightening. Meanwhile the shock component was stable leading to increase in hardness ratio during the period of fading. AstroSat and XMM-Newton observations have been used to study the spectral properties of V3890 Sgr to draw quantitative conclusions even if their drawback is model-dependence. We used the xspec to fit spectral models of plasma emission, and the best fits are consistent with the elemental abundances being lower during the second observing run compared to the first for spectra >1 keV. The SSS emission is well fit by non-local thermal equilibrium model atmosphere used for white dwarfs. The resulting spectral parameters, however, are subject to systematic uncertainties such as completeness of atomic data., Comment: 15 pages, 10 figures, Accepted for publication in the Monthly Notices of the Royal Astronomical Society

Results of the initial calibration of the Ultra-Violet Imaging Telescope (UVIT) were reported earlier by Tandon et al. (2017). The results reported earlier were based on the ground calibration as well as the first observations in orbit. Some additional data from the ground calibration and data from more in-orbit observations have been used to improve the results. In particular, extensive new data from in-orbit observations have been used to obtain (a) new photometric calibration which includes (i) zero-points (ii) flat fields (iii) saturation, (b) sensitivity variations (c) spectral calibration for the near Ultra Violet (NUV; 2000 - 3000 Angstroms) and far Ultra-Violet (FUV; 1300 - 1800 Angstroms) gratings, (d) point spread function and (e) astrometric calibration which included distortion. Data acquired over the last three years show continued good performance of UVIT with no reduction in sensitivity in both the UV channels., Comment: 15 pages, 8 figures, Accepted for publication in Astronomical Journal

HD 219134 hosts several planets, with seven candidates reported, and the two shortest period planets are rocky (4-5 $M_{\oplus}$) and transit the star. Here we present contemporaneous multi-wavelength observations of the star HD 219134. We observed HD 219134 with the Narval spectropolarimeter at the Observatoire du Pic du Midi, and used Zeeman Doppler Imaging to characterise its large-scale stellar magnetic field. We found a weak poloidal magnetic field with an average unsigned strength of 2.5 G. From these data we confidently confirm the rotation period of 42 days, measure a stellar inclination of 77$\pm$8 degrees, and find evidence for differential rotation. The projected obliquity of the two transiting super-Earths is therefore between 0 and 20 degrees. We employed HST STIS observations of the Ly$\alpha$ line to derive a stellar wind mass-loss rate of half the solar value ($10^{-14} M_{\odot} {\rm yr}^{-1}$). We further collected photometric transit observations of the closest planet at near-UV wavelengths centred on the Mg II h&k lines with AstroSat. We found no detectable absorption, setting an upper limit on the transit depth of about 3%, which rules out the presence of a giant magnesium cloud larger than 9 planet radii. Finally, we estimated the high-energy flux distribution of HD 219134 as seen by planets b and c. These results present a detailed contemporaneous characterisation of HD 219134, and provide the ingredients necessary for accurately modelling the high-energy stellar flux, the stellar wind, and their impact on the two shortest-period planets, which will be presented in the second paper of this series., Comment: Accepted for publication in MNRAS. This paper is the first of a pair, the second is: Characterisation of the HD 219134 multi-planet system II. Stellar-wind sputtered exospheres in rocky planets b & c. 11 pages 5 figures

In this paper, we present the first results of spectral and timing properties of the atoll source 4U 1705-44 using $\sim$ 100 ks data obtained with Large Area X-ray Proportional Counter (LAXPC) onboard {\it AstroSat}. The source was in the high-soft state during our observations and traced out a {\it banana track} in the Hardness Intensity Diagram (HID). We study {\bf the} evolution of the Power Density Spectra (PDS) and the energy spectra along the HID. PDS show presence of a broad Lorentzian feature (Peaked Noise or PN) centered at $1-13$ Hz and a very low frequency noise (VLFN). The energy spectra can be described by sum of a thermal Comptonized component, a power-law and a broad iron line. The hard tail seen in the energy spectra is variable and contribute $4-30$\% of the total flux. The iron line seen in this source is broad (FWHM $\sim$ 2 keV) and strong (EW $\sim$ $369-512$ eV). Only relativistic smearing in the accretion disc can not explain the origin of this feature and requires other mechanism such as broadening by Comptonization process in the external part of the `Comptonized Corona'. A subtle and systematic evolution of the spectral parameters (optical depth, electron temperature etc.) is seen as the source moves along the HID. We study the correlation between frequency of the PN and the spectral parameters. PN frequency seems to be correlated with the strength of the corona. We discuss the implication of the results in the paper., Comment: 10 pages, 8 figures, accepted in MNRAS

We present the UV photometry of the globular cluster NGC 1851 using images acquired with the Ultra-violet Imaging Telescope (UVIT) onboard the ASTROSAT satellite. PSF-fitting photometric data derived from images in two far-UV (FUV) filters and one near-UV (NUV) filter are used to construct color-magnitude diagrams (CMD), in combination with HST and ground-based optical photometry. In the FUV, we detect only the bluest part of the cluster horizontal branch (HB); in the NUV, we detect the full extent of the HB, including the red HB, blue HB and a small number of RR Lyrae stars. UV variability was detected in 18 RR Lyrae stars, and 3 new variables were also detected in the central region. The UV/optical CMDs are then compared with isochrones of different age and metallicity (generated using Padova and BaSTI models) and synthetic HB (using helium enhanced $Y^2$ models). We are able to identify two populations among the HB stars, which are found to have either an age range of 10-12~Gyr, or a range in Y$_{ini}$ of 0.23 - 0.28, for a metallicity of [Fe/H] =$-$1.2 to $-$1.3. These estimations from the UV CMDs are consistent with those from optical studies. The almost complete sample of the HB stars tend to show a marginal difference in spatial/azimuthal distribution among the blue and red HB stars. This study thus show cases the capability of UVIT, with its excellent resolution and large field of view, to study the hot stellar population in Galactic globular clusters., Comment: 46 pages, 19 figures, accepted for publication in Astronomical Journal

The Ultra-Violet Imaging Telescope (UVIT) is one of the payloads in ASTROSAT, the first Indian Space Observatory. The UVIT instrument has two 375mm telescopes: one for the far-ultraviolet (FUV) channel (1300--1800\AA), and the other for the near-ultraviolet (NUV) channel (2000--3000\AA) and the visible (VIS) channel (3200--5500\AA). UVIT is primarily designed for simultaneous imaging in the two ultraviolet channels with spatial resolution better than 1.8 arcsec, along with provision for slit-less spectroscopy in the NUV and FUV channels.The results of in-orbit calibrations of UVIT are presented in this paper., Comment: Accepted to appear in AJ

Ultraviolet Imaging Telescope (UVIT) is one of the payloads onboard AstroSat, India's first multi-wavelength Astronomy mission. UVIT is primarily designed to make high resolution images in wide field, in three wavelength channels simultaneously: FUV (130 - 180 nm), NUV (200 - 300 nm) and VIS (320 - 550 nm). The intensified imagers used in UVIT suffer from distortions, and a correction is necessary for these to achieve good astrometry. In this article we describe the methodology and calculations used to estimate the distortions in ground calibrations., Comment: 16 pages, 12 figures, Accepted for publication in Experimental Astronomy

The performance of the ultraviolet telescope (UVIT) on-board ASTROSAT is reported. The performance in orbit is also compared with estimates made from the calibrations done on the ground. The sensitivity is found to be within ~15% of the estimates, and the spatial resolution in the NUV is found to exceed significantly the design value of 1.8 arcsec and it is marginally better in the FUV. Images obtained from UVIT are presented to illustrate the details revealed by the high spatial resolution. The potential of multi-band observations in the ultraviolet with high spatial resolution is illustrated by some results., Comment: Comment: Accepted for publication in JAA on December 1, 2016

We present the in-orbit performance and the first results from the ultra-violet Imaging telescope (UVIT) on ASTROSAT. UVIT consists of two identical 38cm coaligned telescopes, one for the FUV channel (130-180nm) and the other for the NUV (200-300nm) and VIS (320-550nm) channels, with a field of view of 28 $arcmin$. The FUV and the NUV detectors are operated in the high gain photon counting mode whereas the VIS detector is operated in the low gain integration mode. The FUV and NUV channels have filters and gratings, whereas the VIS channel has filters. The ASTROSAT was launched on 28th September 2015. The performance verification of UVIT was carried out after the opening of the UVIT doors on 30th November 2015, till the end of March 2016 within the allotted time of 50 days for calibration. All the on-board systems were found to be working satisfactorily. During the PV phase, the UVIT observed several calibration sources to characterise the instrument and a few objects to demonstrate the capability of the UVIT. The resolution of the UVIT was found to be about 1.4 - 1.7 $arcsec$ in the FUV and NUV. The sensitivity in various filters were calibrated using standard stars (white dwarfs), to estimate the zero-point magnitudes as well as the flux conversion factor. The gratings were also calibrated to estimate their resolution as well as effective area. The sensitivity of the filters were found to be reduced up to 15\% with respect to the ground calibrations. The sensitivity variation is monitored on a monthly basis. UVIT is all set to roll out science results with its imaging capability with good resolution and large field of view, capability to sample the UV spectral region using different filters and capability to perform variability studies in the UV., Comment: 10 pages, To appear in SPIE conference proceedings, SPIE conference paper, 2016

We present analysis of archival X-ray data obtained with the XMM-Newton and Suzaku for a new Intermediate Polar identified as a counterpart of an INTEGRAL discovered gamma-ray source, IGR J17195-4100. We report a new period of 1053.7\pm12.2 s in X-rays. A new binary orbital period of 3.52+1.43-0.80 h is strongly indicated in the power spectrum of the time series. An ephemeris of the new period proposed as the spin period of the system has also been obtained. The various peaks detected in the power spectrum suggest a probable disc-less accretion system. The soft X-rays (<3 keV) dominate the variability seen in the X-ray light curves. The spin modulation shows energy dependence suggesting the possibility of a variable partial covering accretion column. The averaged spectral data obtained with XMM-Newton EPIC cameras show a multi temperature spectra with a soft excess. The latter can be attributed to the varying coverage of accretion curtains., Comment: LaTeX 10 pages, 7 figures and 4 tables, accepted publication in MNRAS

In this paper we present a high-resolution spectroscopic analysis of the chemically peculiar star HD207561. During a survey programme to search for new roAp stars in the Northern hemisphere, Joshi et al. (2006) observed significant photometric variability on two consecutive nights in the year 2000. The amplitude spectra of the light curves obtained on these two nights showed oscillations with a frequency of 2.79 mHz [P~6-min]. However, subsequent follow-up observations could not confirm any rapid variability. In order to determine the spectroscopic nature of HD207561, high-resolution spectroscopic and spectro-polarimetric observations were carried out. A reasonable fit of the calculated Hbeta line profile to the observed one yields the effective temperature (Teff) and surface gravity (log g) as 7300 K and 3.7 dex, respectively. The derived projected rotational velocity (vsin i) for HD207561 is 74 km/sec indicative of a relatively fast rotator. The position of HD207561 in the H-R diagram implies that this is slightly evolved from the main-sequence and located well within the delta-Scuti instability strip. The abundance analysis indicates the star has slight under-abundances of Ca and Sc and mild over-abundances of iron-peak elements. The spectro-polarimetric study of HD207561 shows that the effective magnetic field is within the observational error of 100 gauss (G). The spectroscopic analysis revealed that the star has most of the characteristics similar to an Am star, rather than an Ap star, and that it lies in the delta-Scuti instability strip; hence roAp pulsations are not expected in HD207561, but low-overtone modes might be excited., Comment: 8 pages, 7 figures, 3 tables. Accepted for pubblication in MNRAS

The Radiation Monitor (RADOM) payload is a miniature dosimeter-spectrometer onboard Chandrayaan-1 mission for monitoring the local radiation environment in near-Earth space and in lunar space. RADOM measured the total absorbed dose and spectrum of the deposited energy from high energy particles in near-Earth space, en-route and in lunar orbit. RADOM was the first experiment to be switched on soon after the launch of Chandrayaan-1 and was operational till the end of the mission. This paper summarizes the observations carried out by RADOM during the entire life time of the Chandrayaan-1 mission and some the salient results., Comment: Accepted for publication in Advances in Geosciences

Imaging in hard X-rays of any astrophysical source with high angular resolution is a challenging job. Shadow-casting technique is one of the most viable options for imaging in hard X-rays. We have used two different types of shadow-casters, namely, Coded Aperture Mask (CAM) and Fresnel Zone Plate (FZP) pair and two types of pixellated solid-state detectors, namely, CZT and CMOS in RT-2/CZT payload, the hard X-ray imaging instrument onboard the CORONAS-PHOTON satellite. In this paper, we present the results of simulations with different combinations of coders (CAM & FZP) and detectors that are employed in the RT-2/CZT payload. We discuss the possibility of detecting transient Solar flares with good angular resolution for various combinations. Simulated results are compared with laboratory experiments to verify the consistency of the designed configuration., Comment: 27 pages, 16 figures, Accepted for publication in Experimental Astronomy (in press)

We present the results of simulations of shadows cast by a zone plate telescope which may have one to four pairs of zone plates. From the shadows we reconstruct the images under various circumstances. We discuss physical basis of the resolution of the telescope and demonstrate this by our simulations. We allow the source to be at a finite distance (diverging beam) as well as at an infinite distance (parallel beam) and show that the resolution is worsened when the source is nearby. By reconstructing the zone plates in a way that both the zone plates subtend the same solid angles at the source, we obtain back high resolution even for sources at a finite distance. We present simulated results for the observation of the galactic center and show that the sources of varying intensities may be reconstructed with accuracy. Results of these simulations would be of immense use in interpreting the X-ray images from recently launched CORONAS-PHOTON satellite., Comment: 17 pages, 36 figures, Published in Experimental Astronomy

We present the results of high resolution spectroscopy of the prototype polar AM Herculis observed with Chandra High Energy Transmission Grating. The X-ray spectrum contains hydrogen-like and helium-like lines of Fe, S, Si, Mg, Ne and O with several Fe L-shell emission lines. The forbidden lines in the spectrum are generally weak whereas the hydrogen-like lines are stronger suggesting that emission from a multi-temperature, collisionally ionized plasma dominates. The helium-like line flux ratios yield a plasma temperature of 2 MK and a plasma density 1 - 9 x10^12 cm^-3, whereas the line flux ratio of Fe XXVI to Fe XXV gives an ionization temperature of 12.4 +1.1 -1.4 keV. We present the differential emission measure distribution of AM Her whose shape is consistent with the volume emission measure obtained by multi-temperature APEC model. The multi-temperature plasma model fit to the average X-ray spectrum indicates the mass of the white dwarf to be ~1.15 M_sun. From phase resolved spectroscopy, we find the line centers of Mg XII, S XVI, resonance line of Fe XXV, and Fe XXVI emission modulated by a few hundred to 1000 km/s from the theoretically expected values indicating bulk motion of ionized matter in the accretion column of AM Her. The observed velocities of Fe XXVI ions are close to the expected shock velocity for a 0.6 M_sun white dwarf. The observed velocity modulation is consistent with that expected from a single pole accreting binary system., Comment: 6 figures, AASTEX style, accepted for publication in ApJ

To search photometric variability in chemically peculiar A type stars in the northern hemisphere. High-speed photometric observations of Ap and Am star candidates have been carried out from ARIES (Manora Peak, Nainital) using a three-channel fast photometer attached to the ARIES 104-cm Sampurnanand telescope. This paper presents three new variables: HD 113878, HD 118660 and HD 207561. During the time span of the survey (1999 December to 2004 January) pulsations of the $\delta$ Sct type were also found for the two evolved Am stars HD 102480 and HD 98851, as reported in Joshi et al. (2002, 2003). Additionally, we present 140 null results of the survey for this time span. The star HD 113878 pulsates with a period of 2.31 hr, which is typical of $\delta$ Sct stars. HD 118660 exhibits multi-periodic variability with a prominent period of nearly 1 hr. These periods need to be investigated and make HD 118660 a particularly interesting target for further observations. For HD 207561, a star classified as Am, a probable pulsation with a period of 6 min was found in the light curves obtained on two consecutive nights. Both HD 102480 and HD 98851 exhibit unusual alternating high and low amplitude maxima, with a period ratio of 2:1. The analysis of the null results confirms the photometric quality of the Nainital, Comment: 14 pages, 13 figures, Accepted for publication in A&A

NainiTal-Cape Survey is a survey started with the aim of searching for new rapidly oscillating Ap stars in the northern hemisphere and has discovered one mono-periodic roAp star HD 12098. The frequency separation of HD 12098 suggests a rotation period of 5.5 day for the star. The discovery of roAp oscillations in HD 12098 and the results of the multi-site observation campaign organized to resolve the ambiguity in the determination of the rotation period of HD 12098 is presented. The results of non oscillating Ap stars discovered in the survey and two promising roAp candidates HD 17431 and HD 207561 are also presented. If confirmed, the variability in HD 207561 will make it the first Am star showing roAp type rapid variability., Comment: 10 pages, 10 figures, JAA sty, To appear in the proceedings of ARIES international workshop on Asteroseismology

The chemically peculiar (CP) stars HD 98851 and HD 102480 have been discovered to be unusual pulsators during the ``Naini Tal Cape Survey'' programme to search for pulsational variability in CP stars. Time series photometric and spectroscopic observations of these newly discovered stars are reported here. Fourier analyses of the time series photometry reveal that HD 98851 is pulsating mainly with frequencies 0.208 mHz and 0.103 mHz, and HD 102480 is pulsating with frequencies 0.107 mHz, 0.156 mHz and 0.198 mHz. The frequency identifications are all subject to 1 d$^{-1}$ cycle count ambiguities. We have matched the observed low resolution spectra of HD 98851 and HD 102480 in the range 3500-7400 \AA with theoretical synthetic spectra using Kurucz models with solar metallicity and a micro-turbulent velocity 2 km s$^{-1}$. These yield $T_{eff}=7000\pm250$ K, log $g=3.5 \pm 0.5$ for HD 98851 and $T_{eff} = 6750 \pm 250$ K, log $g = 3.0 \pm 0.5$ for HD 102480. We determined the equivalent H-line spectral class of these stars to be F1 IV and F3 III/IV, respectively. A comparison of the location of HD 98851 and HD 102480 in the HR diagram with theoretical stellar evolutionary tracks indicates that both stars are about 1-Gyr-old, 2-$M_{\odot}$ stars that lie towards the red edge of the $\delta$ Sct instability strip. We conclude that HD 98851 and HD 102480 are cool, evolved Am pulsators. The light curves of these pulsating stars have alternating high and low amplitudes, nearly harmonic (or sub-harmonic) period ratios, high pulsational overtones and Am spectral types. This is unusual for both Am and $\delta$ Sct pulsators, making these stars interesting objects., Comment: 9 pages, 6 Figures, Accepted for publication in MNRAS

We present the analysis of 65 hours of high speed photometric observations of HD 12098 taken from State Observatory, Naini Tal and Gurushikhar Observatory, Mt.Abu on sixteen nights spanning from November 1999 to November 2000. HD 12098 is the first rapidly oscillating Ap star discovered from the `Naini Tal-Cape survey for northern hemisphere roAp stars'. It is the 32nd in the complete list. HD 12098 exhibits one predominant mode of oscillation at nu_1 = 2.1738 mHz. The second-most significant frequency in our data is at nu_2 = 2.1641 mHz with a 1 cycle/day alias ambiguity. We argue that nu_2 is a rotational sidelobe of nu_1, rather than an independent pulsation mode. Evidence for the presence of two other frequencies at 2.1807 and 2.3056 mHz is also presented., Comment: 6 pages, 4 eps figures, A&A style, Accepted for publication in A&A