Arecibo radar observations of Rhea, Dione, Tethys, and Enceladus

We have measured the bulk radar reflectance properties of the mid-size saturnian satellites Rhea, Dione, Tethys, and Enceladus with the Arecibo Observatory's 13 cm wavelength radar system during the 2004 through 2007 oppositions of the Saturn system. Comparing to the better studied icy Galilean satellites, we find that the total reflectivities of Rhea and Tethys are most similar to Ganymede while Dione is most similar to Callisto. Enceladus' reflectivity falls between those of Ganymede and Europa. The mean circular polarization ratios of the saturnian satellites range from ∼0.8 to 1.2, and are on average lower than those of the icy Galilean satellites at this wavelength although still larger than expected for single reflections off the surface. The ratio for the trailing hemisphere of Enceladus may be the exception with a value ?0.56. The 13 cm wavelength radar albedos and polarization ratios may be systematically lower than similar results from the Cassini orbiter's RADAR instrument at 2.2 cm wavelength [Ostro, S.J., and 19 colleagues, 2006. Icarus 183, 479-490]. Overall, these reflectivities and polarization properties, together with the shapes of the echo spectra, suggest subsurface multiple scattering to be the dominant reflection mechanism although operating less efficiently than on the large icy moons of Jupiter. All these saturnian moons and icy jovian moons are atmosphere-less, low temperature water ice surfaces, and any differences in radar properties may be indicative of differences in composition or the effects of various processes that modify the regolith structure. The degree of variation in radar properties with wavelength on each satellite may constrain the thickness and efficiency of the scattering layer.     

The topside ionosphere above Arecibo at equinox during sunspot maximum

The coupled time-dependent O⁺ and H⁺ continuity and momentum equations and O⁺, H⁺ and electron heat balance equations are solved simultaneously within the L = 1.4 (Arecibo) magnetic flux tube between an altitude of 120 km and the equatorial plane. The results of the calculations are used in a study of the topside ionosphere above Arecibo at equinox during sunspot maximum. Magnetically quiet conditions are assumed.The results of the calculations show that the L = 1.4 magnetic flux tube becomes saturated from an arbitrary state within 2–3 days. During the day the ion content of the magnetic flux tube consists mainly of O⁺ whereas O⁺ and H⁺ are both important during the night. There is an altitude region in the topside ionosphere during the day where ion-counterstreaming occurs with H⁺ flowing downward and O⁺ flowing upward. The conditions causing this ion-counterstreaming are discussed. There is a net chemical gain of H⁺ at the higher altitudes. This H⁺ diffuses both upwards and downwards whilst O⁺ diffuses upwards from its solar e.u.v. production source which is most important at the lower altitudes. During the night the calculated O⁺ and H⁺ temperatures are very nearly equal whereas during the day there are occasions when the H⁺ temperature exceeds the O⁺ temperature by about 300 K.     

Arecibo observations of Parkes multibeam pulsars

The on-going Parkes multibeam survey has been astoundingly successful (Manchesteret al. 2001), and its discovery of over 600 pulsars has opened up new avenues for probing the Galaxy’s electron content and magnetic field. Here we report on recent observations made with the Arecibo 305-m telescope, where 80 distant, high dispersion measure pulsars (of which 35 are from the multibeam survey) were studied at multiple frequency bands in the range 0.4–2.4 GHz, in order to determine their scattering properties, rotation measures and spectral indices. The results will be used to meet a variety of science goals; viz., creating an improved model of the electron density, mapping out the Galactic magnetic field, and modeling the pulsar population.     

Arecibo radar observations of Phobos and Deimos

In November 2005, we observed the moons of Mars using the Arecibo 2380-MHz (13-cm) radar, obtaining a result for the OC radar albedo of Phobos (0.056±0.014) consistent with its previously reported radar albedo and implying an upper bound on its near-surface bulk density of . We detected Deimos by radar for the first time, finding its OC radar albedo to be 0.021±0.006, implying an upper bound on its near-surface density of , consistent with a high-porosity regolith. We briefly discuss reasons for these low radar albedos, Deimos' being possibly the lowest of any Solar System body yet observed by radar.     

Arecibo timing and single-pulse observations of 17 pulsars

We have analysed the soft X-ray emission in a wide area of the Sculptor supercluster by using overlapping ROSAT Position Sensitive Proportional Counter pointings. After subtraction of the point sources, we have found evidence for extended, diffuse soft X-ray emission. We have investigated the nature of such extended emission through the cross-correlation with the density of galaxies as inferred from the Münster Redshift Survey. In particular, we have analysed the correlation as a function of the temperature of the X-ray emitting gas. We have found a significant correlation of the galaxy distribution only with the softest X-ray emission (0.1 – 0.3 keV) and only for gas temperatures   kT < 0.5 keV  . We have excluded the fact that this soft X-ray diffuse emission, and its correlation with the galaxy distribution, is significantly contributed by unresolved active galactic nuclei, groups of galaxies or individual galaxies. The most likely explanation is that the soft, diffuse X-ray emission is tracing warm–hot intergalactic medium, with temperatures below 0.5 keV, associated with the large-scale structures in the Sculptor supercluster.     

Discovery of 10 pulsars in an Arecibo drift-scan survey

We present the results of a 430-MHz survey for pulsars conducted during the upgrade to the 305-m Arecibo radio telescope. Our survey covered a total of 1147 deg² of sky using a drift-scan technique. We detected 33 pulsars, 10 of which were not known prior to the survey observations. The highlight of the new discoveries is PSR J0407+1607, which has a spin period of 25.7 ms, a characteristic age of 1.5 Gyr and is in a 1.8-yr orbit about a low-mass  (>0.2 M_⊙)  companion. The long orbital period and small eccentricity  ( e = 0.0009)  make the binary system an important new addition to the ensemble of binary pulsars suitable to test for violations of the strong equivalence principle. We also report on our initially unsuccessful attempts to detect optically the companion to J0407+1607, which imply that its absolute visual magnitude is >12.1. If, as expected on evolutionary grounds, the companion is an He white dwarf, our non-detection implies a cooling age of least 1 Gyr.     

The Meteoritical Bulletin,No. 77, 1994 November*

Abstract— This Meteoritical Bulletin is again dominated by meteorite finds from hot and cold deserts: 99 from the Nullarbor, 12 from the Sahara, and 35 from Antarctica. Besides 161 ordinary chondrites, it lists 5 irons (Cotton, Hidden Valley, Miles, Tagounite, Tres Castillos), 2 ureilites (FRO90168, Hughes 009), 1 howardite (ALH 88135), 1 CV3 (Axtell), 1 CK4 (Sleeper Camp 006), and 2 enstatite chondrites (ALH 88070, Forrest 033). Three of the meteorites are falls.     

The Meteoritical Bulletin,No. 78, 1995 November*

Abstract— This Meteoritical Bulletin lists 53 meteorites, of which 16 are from the Nullarbor, Australia, and 12 from Roosevelt County, New Mexico. Besides ordinary chondrites, there are five irons and one howardite (Mundrabilla 018). Four of the meteorites are falls (Baszkówka, Campos Salos, Neagari, and New Halfa).     

The mm wave outbursts of November 1 and 2, 1968

On November 1 and 2, 1968 two flares of importance 2b associated with the active region = S15°, L = 173° presented particular activity in the mm band. The outburst of November 1 in the mm wavelength band was of the gradual rise and fall type, while 24 hours later, the outburst of November 2 was of the sudden increase type with flux increase of the order of 4000 units. In the cm band the flare of November 1 produced a flux increase greater than in the mm band, while on November 2 the flare produced a series of outbursts with gradually increasing maxima, but much lower than the mm flux increase. It is reported that generally the peak flux decreases with increasing wavelength. The outburst of November 2 follows this rule but it is exactly the opposite for the sudden increase outburst produced by the November 1 flare. As to whether an increased brightness produces a higher mm or cm flux increase, available observations are not sufficient to make a firm statement.     

The unusual anisotropic solar particle event of November 18, 1968

The ground level event of November 18, 1968, was unusual in that pronounced anisotropy persisted essentially until the cessation of the arrival at the earth of relativistic protons. Real and significant differences were observed in the intensity profiles at different neutron monitor stations. By a method of successive approximations, the geographical coordinates of the axis of symmetry were determined as: latitude = - 25° ± 10° and longitude = -35° ± 10°. The exponent in a power law spectral representation over the narrow range covered by the nucleonic intensity measurements was 5.The onset times of the GLE were related to the angular differences between the mean directions of viewing and the axis of symmetry. The event differed markedly from earlier isotropic events that were well described by diffusion theory, but was compatible with the predictions of a model envisaging diffusion only in the vicinity of the Sun (radius R of solar envelope 34 solar radii). The diffusion coefficient D 3 × 10²¹ cm²/s is consistent with that deduced for earlier isotropic events, but the values of other parameters are smaller than those derived for the only previously observed event to which the model of diffusion in an inhomogeneous medium was applicable (May 4, 1960).It is concluded that the observed one hundred percent anisotropy was a direct consequence of the propagation mechanism rather than other postulated causes. Furthermore, the observed large pitchangle distribution was produced by scattering from small scale field irregularities.This research was sponsored by the National Science Foundation and Air Force Cambridge Research Laboratories, Office of Aerospace Research, under Contract No. F19628-70-C-0190, but the report does not necessarily reflect endorsement by the sponsor.     

Arecibo ALFA Array Observations in Search of Lunar Meteoroid-Strike EMPs

Earth, Moon, and Planets - We present the preliminary results of a search for transient Electromagnetic Pulses (EMP) associated with the impact of meteoroids on the lunar surface as observed with...     

Composition and temperatures of the topside ionosphere over Arecibo

Results of analysis of about 150 autocorrelation functions are presented for the period from about 2300 hr on 5 October to about 1200 hr on 7 October 1967. A large percentage concentration of helium ions are observed. It reaches a value as high as 50 per cent with a maximum at around 800 km. Downward heat fluxes deduced from the temperature variations yield a value of about 2–2.5 × 10⁹ eV cm^?2 sec^?1 during the period 1200–1600 hr and a value of about 1.5 × 10⁸ eV cm^?2 sec^?1 during the period 0100–0400 hr at night. These agree well with other measurements. The O⁺ ions are found not to be in diffusive equilibrium, and from the O⁺ fluxes and the electron density profiles, the O⁺ drift velocity has been estimated. It is found that the speed can be as high as 1–5 × 10³ cm sec^?1 even at altitudes as high as 700 km.     

The magnetic configuration of the November 18, 1968 loop prominence system

Computed current-free magnetic fields are compared to the loop prominence associated with the west limb proton flare of 18 November 1968. Successive sets of fitting fieldlines closely resemble the loop prominence system throughout its growth and lifetime. The successive position bases of the fieldlines reproduce the drift rate of spreading two-ribbon flares.     

Deep analyses of nulling in Arecibo pulsars reveal further periodic behaviour

Numerous studies of conal pulsars, e.g. B1133+16, have revealed fluctuation features and a steady null fraction. Sensitive Arecibo observations provide an unprecedented ability to detect nulls and confirm previously found fluctuation features. By replacing each pulse with a scaled version of the average profile, we were able to quench all subpulse modulation, dubbed pulse-modulation quelling (PMQ). It was surprising to note that the low-frequency feature observed in the natural longitude resolved fluctuation spectra (LRF) persisted in the PMQ LRFs. It appears that we can conclude, then, that in the natural pulse sequence the nulls themselves reflect whatever underlying periodicity is responsible for the low-frequency feature. Conversely, the aggregate fluctuation power of the low-frequency feature changes little whether the pulse modulation is quelled or not, implying that the feature fluctuations are produced by the nulls!     

The Late Gradual Phase of Large Flares: The Case of November 3, 2003

The hard X-ray time profiles of most solar eruptive events begin with an impulsive phase that may be followed by a late gradual phase. In a recent article (Aurass et al. in Astron. Astrophys. 555, A40, 2013), we analyzed the impulsive phase of the solar eruptive event on November 3, 2003 in radio and X-ray emission. We found evidence of magnetic breakout reconnection using the radio diagnostic of the common effect of the flare current sheet and, at heights of ±0.4 R_⊙, of a coronal breakout current sheet (a source site that we called X). In this article we investigate the radio emission during the late gradual phase of this event. The work is based on 40?–?400 MHz dynamic spectra (Radio Spectrograph, Observatorium Tremsdorf, Leibniz Institut für Astrophysik Potsdam, AIP) combined with radio images obtained by the French Nançay Multifrequency Radio Heliograph (NRH) of the Observatoire de Paris-Meudon. Additionally, we use Ramaty High Energy Solar Spectroscopic Imager (RHESSI) hard X-ray (HXR) flux records, and Solar and Heliospheric Observatory (SOHO) Large Angle and Spectrometric Coronagraph (LASCO) and Extreme ultraviolet Imaging Telescope (EIT) images. The analysis shows that the late gradual phase is subdivided into two distinct stages. Stage 1 (lasting five minutes in this case) is restricted to reoccurring radio emission at source site X. We observe plasma emission and an azimuthally moving source (from X toward the NE; speed≈1200 km?s^?1) at levels radially ordered against the undisturbed coronal density gradient. These radio sources mark the lower boundary of an overdense region with a huge azimuthal extent. By the end of its motion, the source decays and reappears at point X. This is the onset of stage 2 traced here during its first 13 minutes. By this time, NRH sources observed at frequencies≤236.6 MHz radially lift off with a speed of ≈?400 km?s^?1 (one third of the front speed of the coronal mass ejection (CME)) as one slowly decaying broadband source. This speed is still observable in SOHO/LASCO C3 difference frames in the wake of the CME four hours later. In stage 2, the radio sources at higher frequencies appear directly above the active region with growing intensity. We interpret the observations as the transit of the lower boundary of the CME body through the height range of the coronal breakout current sheet. The relaxing global coronal field reconnects with the magnetic surroundings of the current sheets that still connect the CME in its wake with the Sun. The accelerated particles locally excite plasma emission, but can also escape toward the active region, the CME, and the large-scale solar magnetic field. The breakout relaxation process may be a source of reconnection- and acceleration rate modulations. In this view, the late gradual phase is a certain stage of the coronal breakout relaxation after the release of the CME. This article is, to our best knowledge, the first observational report of the coronal breakout recovery. Our interpretation of the radio observations agrees with some predictions of magnetic breakout simulations (e.g. Lynch et al. in Astrophys. J. 683, 1192, 2008). Again, combined spectral and imaging radio observations give a unique access to dynamic coronal processes that are invisible in other spectral ranges.     

Radio and Meteor Science Outcomes From Comparisons of Meteor Radar Observations at AMISR Poker Flat, Sondrestrom, and Arecibo

Radio science and meteor physics issues regarding meteor “head-echo” observations with high power, large aperture (HPLA) radars, include the frequency and latitude dependency of the observed meteor altitude, speed, and deceleration distributions. We address these issues via the first ever use and analysis of meteor observations from the Poker Flat AMISR (PFISR: 449.3 MHz), Sondrestrom (SRF: 1,290 MHz), and Arecibo (AO: 430 MHz) radars. The PFISR and SRF radars are located near the Arctic Circle while AO is in the tropics. The meteors observed at each radar were detected and analyzed using the same automated FFT periodic micrometeor searching algorithm. Meteor parameters (event altitude, velocity, and deceleration distributions) from all three facilities are compared revealing a clearly defined altitude “ceiling effect” in the 1,290 MHz results relative to the 430/449.3 MHz results. This effect is even more striking in that the Arecibo and PFISR distributions are similar even though the two radars are over 2,000 times different in sensitivity and at very different latitudes, thus providing the first statistical evidence that HPLA meteor radar observations are dominated by the incident wavelength, regardless of the other radar parameters. We also offer insights into the meteoroid fragmentation and “terminal” process.     

The growth of electric current in the eruptive prominence of June 8, 1974

The observed twisting of bright threads during the eruption of a limb prominence is described in terms of the transfer of energy from the large-scale to the small-scale magnetic field. Modeling the process by means of an inductive circuit, the time constant for the growth of current along the bundle of threads appears to be consistent with the observed rate of twisting.Visiting astronomer on leave from the Department of Astro-Geophysics, University of Colorado, Boulder, Colorado 80309, U.S.A.