Development of a three channel photometer for UPSO, Naini Tal

The design and performance of a portable three channel photometer installed at the Uttar Pradesh State Observatory (UPSO), Naini Tal is described. The photometer is modular and the whole unit can be disassembled as individual channels such that the system can also be used as a single channel or two channel photometer. The system also has provision to monitor a guide star. The instrument was put into operation since November 1999 on the 1m Sampurnanand telescope at UPSO, Naini Tal. Since then, it is used extensively for the ‘Survey of rapidly oscillating Ap (roAp) stars in the northern sky’ from UPSO. Observational results using this new photometer in its initial phase of operation are discussed. The advantage of having continuous sky measurement is demonstrated.     

Strongly-cooled ionizing plasma flows with application to venus

On the solar wind's penetration into an atmosphere of hydrogen or helium, symmetric charge exchange interactions give energy and momentum losses as the dominant source terms in the flow equations. One-dimensional, supersonic to subsonic solutions are available if the cooling is strong enough. In a model with transverse field and adiabatic (non-thermal) ions, a range of weakly-shocked solutions with upstream mach number less than 2.5 are discovered. As in the case of detonation waves, the shock strength is independent of downstream boundary conditions. The solutions may apply in the solar wind flow into the Venusian atmosphere.     

Observations of GRS 1915+105 from the USA Experiment on ARGOS

We present first results from a monitoring campaign of GRS 1915+105 undertaken with the USA X-ray timing experiment on the ARGOS satellite. A variety of behaviour has been observed, ranging from low, steady X-ray emission to rapid quasi-periodic flaring on timescales of approximately 10–120 seconds.     

Vesta,Vestoids, and the howardite,eucrite, diogenite group: Relationships and the origin of spectral differences

Abstract— Spectra of asteroid 4 Vesta and 21 small (estimated diameters less than 10 km) asteroids with Vesta‐like spectral properties (Vestoids) were measured at visible and near‐infrared wavelengths (～0.44 to ～1.65 μm). All of the measured small asteroids (except for 2579 Spartacus) have reflectance spectra consistent with surface compositions similar to eucrites and howardites and consistent with all being derived from Vesta. None of the observed asteroids have spectra similar to diogenites. We find no spectral distinction between the 15 objects tabulated as members of the Vesta dynamical family and 6 of the 7 sampled “non‐family” members that reside just outside the semi‐major axis (a), eccentricity (e), and inclination (i) region of the family. The spectral consistency and close orbital (a‐e‐i) match of these “non‐family” objects to Vesta and the Vesta family imply that the true bounds of the family extend beyond the subjective cut‐off for membership. Asteroid 2579 Spartacus has a spectrum consistent with a mixture of eucritic material and olivine. Spartacus could contain olivine‐rich material from Vesta's mantle or may be unrelated to Vesta altogether. Laboratory measurements of the spectra of eucrites show that samples having nearly identical compositions can display a wide range of spectral slopes. Finer particle sizes lead to an increase in the slope, which is usually referred to as reddening. This range of spectral variation for the best‐known meteoritic analogs to the Vestoids, regardless of whether they are actually related to each other, suggests that the extremely red spectral slopes for some Vestoids can be explained by very fine‐grained eucritic material on their surfaces.     

Chandra measurements of the distribution of mass in the luminous lensing cluster Abell 2390

We present spatially resolved X-ray spectroscopy of the luminous lensing cluster Abell 2390, using observations made with the Chandra observatory. The temperature of the X-ray gas rises with increasing radius within the central ∼ 200 kpc of the cluster, and then remains approximately isothermal, with kT =11.5_−1.6^+1.5 keV , out to the limits of the observations at r ∼1.0 Mpc . The total mass profile determined from the Chandra data has a form in good agreement with the predictions from numerical simulations. Using the parametrization of Navarro, Frenk and White, we measure a scale radius r _s∼0.8 Mpc and a concentration parameter c ∼3 . The best-fitting X-ray mass model is in good agreement with independent gravitational lensing results and optical measurements of the galaxy velocity dispersion in the cluster. The X-ray gas to total mass ratio rises with increasing radius with f _gas∼21 per cent at r =0.9 Mpc . The azimuthally averaged 0.3–7.0 keV surface brightness profile exhibits a small core radius and a clear 'break' at r ∼500 kpc , where the slope changes from S _X ∼^∝  r ^−1.5 to S _X ∼^∝  r ^−3.6 . The data for the central region of the cluster indicate the presence of a cooling flow with a mass deposition rate of 200–300 M_⊙ yr⁻¹ and an effective age of 2–3 Gyr .     

Prediction of uniaxial compression PFC3D model micro‐properties using artificial neural networks

Artificial neural networks are used to predict the micro‐properties of particle flow code in three dimensions (PFC3D) models needed to reproduce macro‐properties of cylindrical rock samples in uniaxial compression tests. Data for the training and verification of the networks were obtained by running a large number of PFC3D models and observing the resulting macro‐properties. Four artificial networks based on two different architectures were used. The networks used different numbers of input parameters to predict the micro‐properties. Multi‐layer perceptron networks using Young's modulus, Poisson's ratio, uniaxial compressive strength, model particle resolution and the maximum‐to‐minimum particle ratio showed excellent performance in both training and verification. Adding one more variable—namely, minimum particle radius—showed degrading performance. Copyright © 2009 John Wiley & Sons, Ltd.     

A Direct Image of the Inner Torus of NGC 1068

We present the first VLBI observations of the compact source S1 in the radio jet of NGC 1068. Roughly 1 pc in length and 0.2 pc wide, S1 resolves into clumps aligned perpendicular to the local radio jet axis. The radio continuum emission arises from a hot (Te ~ 106 K), dense (ne ~ 106 cm-3) plasma, and the source of the radio emission is either thermal free-free emission or Thomson-reflected synchrotron emission. The clouds comprising S1 are opaque to soft X-radiation, and we therefore propose that S1 is the inner, ionized region, or ‘hot zone,’ of the obscuring medium surrounding the active nucleus. The covering fraction of the hot zone is small, Cf ⋦ 10%. Since the covering fraction of the dusty, obscuring medium is probably much larger, the obscuring disk must either flare or warp outside of the hot zone. That the radio jet and hot zone axes are perpendicular also suggests that the hot zone may be considered to trace the outermost extent of the accretion disk. This revised version was published online in July 2006 with corrections to the Cover Date.     

TWO COMPONENTS OF COSMIC-RAY MODULATION

The long-term modulation of galactic cosmic rays is investigated from 1957 up to 1992 analysing the dynamic and the quasi-stationary components, separately. It has been found that the dynamic component is characterized by the presence of two peaks at the maximum phase of each solar activity cycle. We infer that the time interval between the two peaks corresponds to a period (well-related to the polar heliomagnetic reversal) in which somewhat decreased activity occurs for intense and long-lasting solar events. In fact, a contemporary dip in the magnetic energy released from the Sun was observed, in agreement with the suggested double maximum displayed by the basic features of the 11-year solar-activity cycle (Gnevyshev, 1977, and references therein). Moreover, the dynamic component of cosmic-ray modulation often shows a multi-structured profile in both peaks of activity, fairly well-connected with the pattern of the green corona brightness. On the other hand, analysing the quasi-stationary long-term trend of cosmic-ray intensity we pick out a good relationship between periods of enhanced cosmic-ray modulation and the area expansion of coronal intensity levels. The relevance of our results for solar-terrestrial forecasting is underlined.     

Spatial Distribution of Accreting Isolated Neutron Stars in the Galaxy

In the last few years, the spatial distribution of old, isolated neutron stars has become of great interest (see, for example, Treves and Colpi (1991)). Several sources of this size have been observed by ROSAT. We present here a computer model of the distribution of the luminosity produced by old, isolated neutron stars accreting from the interstellar medium.We use direct calculations of trajectories in the Galaxy potential, taken in the form given by Paczynski (1990). The system of differential equations was solved numerically. We made calculations on a grid with cell size 100 pc in the R direction and 10 pc in the Z direction (centered at R=50 pc, Z=5 pc and so on). Stars were born in the Galactic plane with a specified velocity distribution corresponding to non-symmetrical supernova explosions.In our model, we assumed that the birth rate of neutron stars is proportional to the square of the local density. The local density was calculated using the data and formulas of Bochkarev (1993) and Zane et al. (1995). We then calculated the luminosity using the Bondi formula (in the inner kiloparsec our results are only a rough estimate).We show that for various mean velocities for the old isolated neutron stars, the distribution of the luminosity has a torus-like structure, with the maximum at 5kpc. Since we made very general assumptions, we argue that this type of distribution is not unique to our Galaxy, and all spiral galaxies should have such a distribution of the luminosity density, associated with accreting old, isolated neutron stars.