Full Resolution Images From The Mauritius Radio Telescope

The first set of full resolution images have been made using the Mauritius Radio Telescope (MRT) for the Right Ascension range 18:00 to 19:00 hours and the declination range -70^° to -10^°.This is a part of the southern sky survey at 151.5 MHz being carried out using the MRT. To minimise the effect of bandwidth decorrelation, the images are made from the visibilities recorded with four different delay settings. This paper discusses three key issues of data analysis for the survey: Selection of good data for the survey, detection and removal of interference in the images and, preliminary analysis of these images. This revised version was published online in July 2006 with corrections to the Cover Date.     

Imaging With The Mauritius Radio Telescope Challenges and Results

The Mauritius Radio Telescope (MRT) has been built with the main objective of surveying the southern sky at meter wavelengths. MRT is a Fourier synthesis, T-shaped non-coplanar array. It consists of a2048 m long East-West arm with 1024 fixed helices and a 880 m long South arm with 15 trolleys. Each trolley has four helices. A 512 channel, 2-bit 3-level complex correlation receiver is used to process the data from the EW and S group outputs. At least 60 days of observing are required for obtaining the Fourier components of the brightness distribution of the sky required to complete the survey. The MRT survey will be one of the most extensive survey at low frequencies providing a moderately deep radio catalog reaching a source density of about 2 × 10⁴ sr^-1 over most of the sky south of δ=-10^°with an angular resolution of 4' × 4.6' sec (δ) and a limiting flux density of 200 mJy (3 σ level) at 151 MHz. This paper will describe the telescope, the observations carried out so far, challenges of imaging with the data acquired over a period exceeding four years with a non-coplanar array, and summarises the results obtained so far. This revised version was published online in July 2006 with corrections to the Cover Date.     

Study of Extended Radio Galaxies at 151.6 MHz using the Mauritius Radio Telescope

The MRT survey will be by far one of the most extensive survey at low frequencies. This survey will provide a moderately deep radio catalog reaching a source density of about 2 × 10⁴ sr^-1over the southern sky with an angular resolution of 4' × 4' and a limiting flux density of 70 mJy (1 σ) at 151 MHz. The availability of zero spacing and short baselines in the MRT array will make it sensitive to the background temperature and to large scale features in the sky. In addition to this feature, the low frequency operation makes a study of continuum emission from large radio sources by MRT to have several interesting and important implications in the study of radio galaxies. This paper discusses the parameter space of radio galaxies which can be explored using the MRT. Images of a few extended radio galaxies are also presented. This revised version was published online in July 2006 with corrections to the Cover Date.     

The Bochum survey of the southern Galactic disk: I. Survey design and first results on 50 square degrees monitored in 2011

We are monitoring a 6° wide stripe along the southern Galactic disk simultaneously in the r and i bands, using a robotic 15‐cm twin telescope of the Universitätsternwarte Bochum near Cerro Armazones in Chile. Utilising the telescope's 2.7° field of view, the survey aims at observing a mosaic of 268 fields once per month and to monitor dedicated fields once per night. The survey reaches a sensitivity from 10^m down to 18^m (AB system), with a completeness limit of r ∼ 15.5^m and i ∼ 14.5^m which – due to the instrumental pixel size of 2.″4 – refers to stars separated by >3″. This brightness range is ideally suited to examine the intermediately bright stellar population supposed to be saturated in deep variability surveys with large telescopes. To connect to deep surveys or to explore faint long term variables, coadded images of several nights reach a depth of ∼ 20^m. The astrometric accuracy is better than 1″, as determined from the overlap of neighbouring fields. We describe the survey design, the data properties and our procedures to derive the light curves and to extract variable stars. We present a list of ∼2200 variable stars identified in 50 square degrees with 50‐80 observations between May and October 2011. For bright stars the variability amplitude A reaches down to A ∼ 0.05^m, while at the faint end variations of A > 1^m are detected. About 200 stars were known tobe variable, and their amplitudes and periods – as far as determinable from our six month monitoring – agree with literature values, demonstrating the performance of the Bochum Galactic Disk Survey (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The Rotational Parameters Of Hale–Bopp (C/1995 O1) From Observations Of The Dust Jets At Pic Du Midi Observatory

We observed comet Hale-Bopp (C/1995 O1) at Pic du Midi Observatory in 1997 from February 2.24 UT to March 31.89 UT with the 1.05-m telescope equipped with a CCD camera and broad- and narrow-band IHW filters. A total of 30000 images were acquired both during night- and day-time. The images were automatically reduced and all the images obtained within 10 min. were co-added to give a set of ∼1000 images used during the analysis. We can identify two jets on the images. The position angle of the brightest jet from February 2.24 UT to March 5.22 UT is measured using an automatic routine which searches for the averaged position angle of the maximum of brightness at a projected distance of 3200–6100 km from the optocenter. A preliminary model of nucleus rotation is used to fit the data and retrieve the rotational parameters of the nucleus. The best fit is found for a source located at a latitude of 64 ± 3°, a sidereal rotation period of 11.35 ± 0.04 h and a right ascension and declination of the North pole of 275 ± 10° and -57 ± 10°. This preliminary analysis shows no evidence for a precession. Grains with velocities of 450–600 m s⁻¹ and radii <;∼ 1 μm dominate the optical scattering cross section in the jets. This revised version was published online in July 2006 with corrections to the Cover Date.     

The Hα Luminosity Functions of Nearby Clusters of Galaxies

We present a deep wide field Hα imaging survey of the central regions of the two nearby clusters of galaxies Coma and Abell 1367, taken with the WFC at the INT 2.5m telescope. We determine for the first time the Schechter parameters of the Hα luminosity function (LF) of cluster galaxies. The Hα LFs of Abell 1367 and Coma are compared with each other. Typical parameters of φ ≈ 10^0.00±0.07 Mpc^-3, L ^*≈ 10^41.25±0.05 erg sec^-1 and α ≈ -0.70±0.10 are found for both clusters. This revised version was published online in September 2006 with corrections to the Cover Date.     

On the latitude migration of polar faculae in the solar activity cycle period: 1970–1978

Coordinates of polar faculae have been measured and processed using daily photoheliograms of the Kislovodsk Station of the Pulkovo observatory with the final goal of studying their latitude distribution during the solar cycles 20–21. The results obtained are as follows:

1. The first polar faculae emerge immediately after the polarity inversion of the solar magnetic field at the latitudes from 40° to 70° with the average ?-55°.
2. The zone of the emergence of polar faculae migrates poleward during the period between the neighbouring polarity inversions of the solar magnetic field. This migration is about 20° for 8 years, which corresponds to a velocity of 0.5 m s^-1.
3. The maximum number of polar faculae was reached at the activity minimum (1975–1976).
4. The last polar faculae were observed in the second half of 1978 at the latitudes from 70° to 80°.

     

Time Analysis of the CO+ COMA OF COMET P/HALLEY BY IMAGE PROCESSING TECHNIQUES

Photographic and photoelectric observations of comet P/Halley's ion gas coma from CO⁺ at 4250 ? were part of the Bochum Halley Monitoring Program, conducted from 1986 February 17, to April 17 at the European Southern Observatory on La Silla (Chile). In this spectral range it is possible to watch the continuous formation, motion and expansion of plasma structures. To observe the morphology of these structures 32CO⁺ photos (glass plates) from P/Halley's comet have been analysed. They have a field of view of 28°.6× 28°.6 and were obtained from 1986 March 29, to April 17 with exposure times between 20 and120 minutes. All photos were digitized with a PDS 2020 GM (Photometric Data System) microdensitometer at the Astronomisches Institut derWestf?lischen Wilhelms-Universit?t in Münster (one pixel= 25 μm × 25 μm ≈ 46′.88×46′.88). After digitization the data were reduced to relative intensities, and the part with proper calibrations were also converted to absolute intensities, expressed in terms of column densities using the image data systems MIDAS (Munich Image Data Analysis System; ESO – Image Processing Group, 1988) and IHAP (Image Handling And Processing; Middleburg, 1983). With the help of the Stellingwerf-Theta-Minimum-Method (Stellingwerf, 1978) a period of (2.22 ± 0.09) days results from analysis of structures in the plasma-coma by subtracting subsequent images. This method is also compared with the Fourier method. There may be a second cycle with a period of about 3.6 days. The idea behind subtracting subsequent images is that rotation effects are only 10% phenomena on gas distribution. Difference images are than used to suppress the static component of the gas cloud. This revised version was published online in July 2006 with corrections to the Cover Date.     

The Hinode X-Ray Telescope (XRT): Camera Design, Performance and Operations

The X-ray Telescope (XRT) aboard the Hinode satellite is a grazing incidence X-ray imager equipped with a 2048×2048 CCD. The XRT has 1 arcsec pixels with a wide field of view of 34×34 arcmin. It is sensitive to plasmas with a wide temperature range from < 1 to 30 MK, allowing us to obtain TRACE-like low-temperature images as well as Yohkoh/SXT-like high-temperature images. The spacecraft Mission Data Processor (MDP) controls the XRT through sequence tables with versatile autonomous functions such as exposure control, region-of-interest tracking, flare detection, and flare location identification. Data are compressed either with DPCM or JPEG, depending on the purpose. This results in higher cadence and/or wider field of view for a given telemetry bandwidth. With a focus adjust mechanism, a higher resolution of Gaussian focus may be available on-axis. This paper follows the first instrument paper for the XRT (Golub et al., Solar Phys. 243, 63, 2007) and discusses the design and measured performance of the X-ray CCD camera for the XRT and its control system with the MDP.     

The effects of density gradients on the convective amplification of upper hybrid waves in the magnetosphere

Intense (? 10 mVm^?1) electrostatic plasma waves near the upper hybrid frequency have been observed between ± 50° magnetic latitude during spacecraft plasmapause crossings. We present wave growth rate and three-dimensional convective amplification calculations which suggest how intense upper hybrid (IUH) events can occur over such a wide range of latitudes. The effects of wave refraction are shown to be crucial to the proper calculation of convective amplification.We first calculate upper hybrid wave growth for an IUH event at 10° MLAT during which a complete electron distribution function with a loss cone feature was measured simultaneously with the waves. We show that a parallel density gradient may be necessary to account for the observed amplification. Without such a density gradient, the dipole magnetic field gradient would quickly refract the wave vector component parallel to the local field lines out of the unstable region in wave vector space. Upon mapping the distribution function observed at 10° MLAT to other latitudes by conserving the electrons' magnetic moments, we then find that the mapped distribution could produce large amplification at higher latitudes only if there is an appropriate parallel density gradient. At the equator, the long magnetic field gradient scale length enables large amplitudes to be attained without a density gradient.The results of our UH ray tracing analysis are related to theories and observations of magnetospheric continuum radiation.     

High Angular Resolution Study of the Ion and Neutral Spectra as a Probe of the Magnetic Field Structure

We present the observations and analysis of the spectral linewidths of neutral and ion species across the DR21(OH) core to investigate the cyclotron interaction as a probe of magnetic fields. It has been suggested that under average interstellar field strengths the cyclotron interaction between ions and magnetic fields is strong enough to narrow the linewidth and suppress the line wings in the ion spectra. We have obtained high spatial resolution spectral line images of H¹³CN and H¹³CO⁺ at 3 mm in DR21(OH) with the Millimeter Array of the Owens Valley Radio Observatory. Our results show that in the eastern parts of the DR21(OH) core the spectral linewidth of the ions is narrower than that of the neutrals. We use our results, along with the existing Zeeman and dust/CO polarization data on small scales, to derive the 3D magnetic field structure. We obtain a field strength of 0.44 ± 0.12 mG with inclination of 36° to the line of sight, directed toward the observer, and a position angle of ?75° in the plane of the sky.     

Near-IR imaging of Asteroid 4 Vesta

The Keck Observatory's adaptive optics (AO) system has been used to observe Asteroid 4 Vesta during its 2003 closest approach to Earth. Broadband K^′- and L^′-band images, centered at 2.1 and 3.6 μm, respectively, are presented here. The sharpness of the images was improved by applying a deconvolution algorithm, MISTRAL, to the images. The K^′- and L^′-band images at spatial resolutions of 53 km (^0.055″) and 88 km (^0.085″), respectively, display albedo features on the surface of the asteroid that can also be seen in the HST images (673 nm) presented by Thomas et al. [1997. Impact excavation on Asteroid 4 Vesta: Hubble Space Telescope results. Science 277, 1492-1495] and Binzel et al. [1997. Geologic mapping of Vesta from 1994 Hubble Space Telescope images. Icarus 128, 95-103] at the same latitudes and longitudes. While we cannot determine the morphology of these features, we can speculate that some of the albedo features may be impact craters filled with dark material. Spectra, centered at 1.65 and 2.1 μm, were also obtained. Spectra were corrected for the solar flux and are similar to those published by Gaffey [1997. Surface lithologic heterogeneity of Asteroid 4 Vesta. Icarus 127, 130-157], along the same wavelength range.     

Gravity field of Mars from Mariner 9 tracking data

Further reduction of Doppler tracking data from Mariner 9 confirms our earlier conclusion that the gravity field of Mars is considerably rougher than the fields of either the Earth or the Moon. The largest positive gravity anomaly uncovered is in the Tharsis region which is also topographically high and geologically unusual. The best determined coefficients of the harmonic expansion of the gravitational potential are: J₂ = (1.96 ± 10.01) × 10^?3 ; C₂₂ = ?(5.1 ± 0.2) × 10^?5; and S₂₂ = (3.4 ± 0.2) × 10^?5. The other coefficients have not been well determined on an individual basis, but the ensemble yields a useful model for the gravity field for all longitudes in the vicinity of 23° South latitude which corresponds to the periapse position for the orbiter.The value obtained for the inverse mass of Mars (3 098 720 ± 70 M⊙^?1) is in good agreement with prior determinations from Mariner flyby trajectories. The direction found for the rotational pole of Mars, referred to the mean equinox and equator of 1950.0, is characterized by α = 317°.3 ± 0°.2, δ = 52°.7 ± 0°.2. This result is in excellent agreement with Sinclair's recent value, determined from earth-based observations of Mars' satellites, but differs by about 0°.5 from the previously accepted value. Other important physical constants that have either been refined or confirmed by the Mariner 9 data include: (i) the dynamical flattening, f = (5.24 ± 0.02) × 10^?3; (ii) the maximum principal moment of inertia, C = (0.375 ± 0.006) MR²; and (iii) the period of precession of Mars' pole, P ? (1.73 ± 0.03) × 10⁵ yr, corresponding to a rate of 7.4 sec of arc per yr.     

The Distribution of Craters Within Craters

Photometric correction is a necessary step in planetary image pre-processing since the images of planetary surfaces are acquired by orbiting spacecraft at various observational geometries. In this study, visible (748 nm) and near-infrared (948 nm) bands of Hyper Spectral Imager (HySI) onboard Chandrayaan-1 have been used to derive a preliminary photometric correction for lunar data. The purpose of the proposed photometric correction for HySI is to convert observations taken at solar incidence (i), sensor emission (e), and the solar phase angles (α) to a fixed geometry by applying i?=?α?=?30° and e?=?0° to each image. The Lommel–Seeliger function was used to model the lunar limb darkening effect, while topography data from the merged Digital Elevation Model of Lunar Reconnaissance Orbiter—Lunar Orbiter Laser Altimeter (LRO-LOLA) and SELENE Terrain Camera (TC) was used to correct local topographic effects. Data from Moon Mineralogy Mapper (M³), SELENE Multiband Imager (MI) and Clementine Ultraviolet and Visible Camera (UV/VIS) were also used to compare radiance, reflectance and phase functions derived from HySI. Our analysis reveals that HySI is darker than M³ primarily due to low surface radiance conditions observed by HySI. The derived phase functions for the two HySI bands indicate a good correlation between the derived reflectance and phase angle as well as with the phase functions derived for the empirically corrected M³ data. This approach led to the derivation of a photometric correction for maria regions. Finally, it is expected that the proposed correction would be applicable to all HySI images covering the lunar mare region.

     

STEREO SECCHI COR1-A/B Intercalibration at 180° Separation

The twin Solar Terrestrial Relations Observatory (STEREO) spacecraft reached a separation angle of 180° on 6 February 2011. This provided a unique opportunity to test the intercalibration between the Sun–Earth Connection Coronal and Heliospheric Investigation (SECCHI) telescopes on both spacecraft for areas above the limb. So long as the corona is optically thin, at 180° separation each spacecraft sees the same corona from opposite directions. Thus, the data should appear as mirror images of each other. We report here on the results of the comparison of the images taken by the inner coronagraph (COR1) on the STEREO-Ahead and -Behind spacecraft in the hours when the separation was close to 180°. We find that the intensity values seen by the two telescopes agree with each other to a high degree of accuracy. This validates both the radiometric intercalibration between the COR1 telescopes, and the method used to remove instrumental background from the images. The relative error between COR1-A and COR1-B is found to be less than 10⁻⁹ B/B _⊙ over most of the field-of-view, growing to a few ×10⁻⁹ B/B _⊙ for the brighter pixels near the edge of the occulter. The primary source of error is the background determination. We also report on the analysis of star observations which show that the absolute radiometric calibration of either COR1 telescope has not changed significantly since launch.     

The bulk motion of flat galaxies on scales of 100 Mpc in the quadrupole and octupole approximations

The peculiarities of non-Hubble bulk motions of galaxies are studied by analyzing a sample of 1271 thin edge-on spirals with distances determined using a multiparametric Tully-Fisher relation that includes the amplitude of the galaxy rotation, the blue and red diameters, surface brightness, and morphological type. In the purely dipole approximation, the bulk motion of galaxies relative to the cosmic microwave background frame can be described by the velocity of 336±96 km s^?1 in the direction l=321°, b=?1° within radius R _max =10000 km s^?1. An analysis of more complex velocity field models shows that the anisotropy of the Hubble expansion described by the quadrupole term is equal to ～5% on scale lengths R _max=6000–10000 km s^?1. The amplitude within the Local Supercluster (R _max=3000 km s^?1) is as high as ～20%. The inclusion of the octupole component reduces the dipole amplitude to 134±111 km s^?1 on scale lengths of ～8000 km s^?1. The most remarkable feature of the galaxy velocity field within R _max=8000 km s^?1 is the zone of minimum centered on l=80°, b=0° (the constellation of Cygnus) whose amplitude reaches 18% of the mean Hubble velocity.     

Faint Features of Interacting Galaxies Revealed by the Digital Coaddition of 13 Tech-Pan Films of the Virgo Cluster

We have digitally coadded APM scans of 13 Kodak TechPan films of the SE region of the Virgo Cluster of galaxies. The ≈6.2°×6.2°field of the R-band films combined with the resolution of ≈2 arcsec pixel^- results in data-file sizes of about 222 MBytes. The 13 scanned films have been aligned, coadded, corrected for vignetting effects and cleaned of stellar features. To illustrate the astrophysical uses of this technique, we present high-contrast images of a sample of interacting galaxies in the field. Several very faint features (but very clearly seen in the coadded array) – such as the interaction between IC 3481,IC 3481A and IC 3483, and NGC 4410A and B and IC 790 – have been presented with clarity for the first time. This revised version was published online in July 2006 with corrections to the Cover Date.     

The angular distribution of cosmic rays at the boundary of the heliosphere

Measurements of the sidereal daily variation of the muon intensity at a depth of 60 m.w.e. have been carried out in London using telescopes inclined at 70° to the zenith for the period 1972 to the present. The direction of maximum sensitivity for these telescopes lies in the Earth's equatorial plane and the asymptotic directions of look at the boundary of the heliosphere have been determined by integrating the equation of motion of the primary particles in a model interplanetary magnetic field. In this way the measured sidereal variation can be related to the cosmic ray intensity distribution in interstellar space. It is shown that the observational data are consistent with an axially symmetric intensity distribution of the form ΔI = 0.09 (1 + cosα) % where ΔI is the direction from the mean intensity and α is measured from the direction of maximum intensity which lies at 1^Π = 250° b^Π = ?60°. The most likely interpretation of this result is that the axis of this distribution corresponds to the local direction of the interstellar magnetic field and that the cosmic rays have a bulk streaming motion of 65±15 km s^?1 along the field direction.     

Photometric observations of Earth‐impacting asteroid 2008 TC3

Abstract– A calibrated lightcurve is presented of the near‐Earth asteroid 2008 TC₃, obtained before it impacted Earth on October 7, 2008. The asteroid was observed in unfiltered images from the end of astronomical twilight until the object entered Earth’s shadow about 2 h later. The observations covered a wide range of phase angles from 14.79° to 2.93°, during which the asteroid ranged from 82,000 km to 29,000 km distance from the observer. A method is presented for obtaining photometrically filtered brightness values for the asteroid using unfiltered imaging techniques. Over 1,700 images of the asteroid produce a lightcurve with a peak‐to‐peak variation in V of 0.76 magnitude. Analysis of the lightcurve yields values for H = 30.86 ± 0.01 and G = 0.33 ± 0.03. Combined with other constraints on the kinetic energy and diameter of the asteroid, which suggest a low 1.8 g cm^?3 density and albedo 0.05 ± 0.01, the value of H implies an asteroid of about 4.1 m in diameter, 28 m³ in volume, and 51,000 kg in mass. The determined value of G is out of range for normal, larger asteroids of albedo 0.05–0.15.