Background studies for acoustic neutrino detection at the South Pole

The detection of acoustic signals from ultra-high energy neutrino interactions is a promising method to measure the flux of cosmogenic neutrinos expected on Earth. The energy threshold for this process depends strongly on the absolute noise level in the target material. The South Pole Acoustic Test Setup (SPATS), deployed in the upper part of four boreholes of the IceCube Neutrino Observatory, has monitored the noise in Antarctic ice at the geographic South Pole for more than two years down to 500 m depth. The noise is very stable and Gaussian distributed. Lacking an in situ calibration up to now, laboratory measurements have been used to estimate the absolute noise level in the 10-50 kHz frequency range to be smaller than 20 mPa. Using a threshold trigger, sensors of the South Pole Acoustic Test Setup registered acoustic events in the IceCube detector volume and its vicinity. Acoustic signals from refreezing IceCube holes and from anthropogenic sources have been used to test the localization of acoustic events. An upper limit on the neutrino flux at energies E_ν > 10¹¹ GeV is derived from acoustic data taken over eight months.     

Muon density measurements with the KASCADE central detector

Frequency distributions of local muon densities in high-energy extensive air showers (EAS) are presented as signature of the primary cosmic ray energy spectrum in the knee region. Together with the gross shower variables like shower core position, angle of incidence, and the shower sizes, the KASCADE experiment is able to measure local muon densities for two different muon energy thresholds. The spectra have been reconstructed for various core distances, as well as for particular subsamples, classified on the basis of the shower size ratio N_μ/N_e. The measured density spectra of the total sample exhibit clear kinks reflecting the knee of the primary energy spectrum. While relatively sharp changes of the slopes are observed in the spectrum of EAS with small values of the shower size ratio, no such feature is detected at EAS of large N_μ/N_e ratio in the energy range of 1–10 PeV. Comparing the spectra for various thresholds and core distances with detailed Monte Carlo simulations the validity of EAS simulations is discussed.     

5@5 – a 5 GeV energy threshold array of imaging atmospheric Cherenkov telescopes at 5 km altitude

We discuss the concept and the performance of a powerful future ground-based astronomical instrument, 5@5 – a 5 GeV energy threshold stereoscopic array of several large imaging atmospheric Cherenkov telescopes (IACTs) installed at a very high mountain elevation of about 5 km a.s.l. – for the study of the γ-ray sky at energies from approximately 5 to 100 GeV, where the capabilities of both the current space-based and ground-based γ-ray projects are quite limited. With its potential to detect the “standard” EGRET γ-ray sources with spectra extending beyond several GeV in exposure times from 1 to 10³ s, such a detector may serve as an ideal “gamma-ray timing explorer” for the study of transient non-thermal phenomena like γ-radiation from AGN jets, synchrotron flares of microquasars, the high energy (GeV) counterparts of gamma ray bursts, etc. 5@5 also would allow detailed γ-ray spectroscopy of persistent nonthermal sources like pulsars, supernova remnants, plerions, radiogalaxies, and others, with unprecedented for γ-ray astronomy photon statistics. The existing technological achievements in the design and construction of multi(1000)-pixel, high resolution imagers, as well as of large, 20 m diameter class multi-mirror dishes with rather modest optical requirements, would allow the construction of such a detector in the foreseeable future, although in the longer terms from the point of view of ongoing projects of 100 GeV threshold IACT arrays like HESS which is in the build-up phase. An ideal site for such an instrument could be a high-altitude, 5 km a.s.l. or more, flat area with a linear scale of about 100 m in a very arid mountain region in the Atacama desert of Northern Chile.     

Number-magnitude count for galaxies at the South Galactic Pole

COSMOS measures on a deep UK Schmidt Telescope Plate have been used to obtain the number-magnitude count for galaxies in a field of 14.6 square degrees near the South Galactic Pole. The results are in excellent agreement with data for the North Galactic Pole for galaxies fainter thanB=18.0, indicating no large-scale differences between north and south. A deficiency in numbers is observed for galaxies withB16.0. This is comparable to the deficiency atB17.5 for counts at the North Galactic Pole and supports the suggested asymmetry of the bright galaxy distribution between north and south galactic poles.     

Cataclysmic variables in a white dwarf survey at the South Galactic Pole

During a photometric and spectrophotometric survey of 200 white dwarf candidates with m_pg<15^m.0 in a field around the South Galactic Pole two new cataclysmic variables have been identified and new observations of one already known object have been accumulated. Observations in the visible and UV-region show variability and differences in spectral type. If compared to the numbers of cataclysmic variables/white dwarfs as computed by Ritter and Burkert (1985) there is a shortage of a factor of 5.Paper presented at the IAU Colloquium No. 93 on Cataclysmic Variables. Recent Multi-Frequency Observations and Theoretical Developments, held at Dr. Remeis-Sternwarte Bamberg, F.R.G., 16–19 June, 1986.     

SPIREX-near infrared astronomy from the South Pole

Over the next several years we will deploy a series of spectrometers, imagers, and telescopes at the South Pole as part of a project named SPIREX-for South Pole Infrared Explorer. Our goal is to survey a substantial area of the sky to study the origins of galaxies and stars.From space, the zodiacal light is the limiting source of noise over a wide range of wavelengths. It has a minimum in the near infrared: the reflected sunlight is diminishing with wavelength and reradiated thermal emission from the warm dust is on the rise. For this and other reasons, the near infrared is potentially the best window in which to carry out deep surveys of galaxies.On the ground, the sensitivity of observations in the near infrared is limited by the Poisson noise of the large background flux from the atmosphere and telescope. Within a restricted wavelength range, this background depends only on two parameters: their temperature and emissivity. By building very low emissivity telescopes and operating them in the bitter cold of the Antarctic winter we expect to make observations that will rival in sensitivity those attainable from cooled space-based telescopes.     

A sample of galaxies near the South Celestial Pole

This paper reports the results of a modest redshift survey carried out, at generally low Galactic latitudes, in the vicinity of the South Celestial Pole. Target galaxies were selected as a 'representative' sample of underlying large-scale structures. Dimensions, approximate magnitudes and radial velocity measurements, are reported for 336 galaxies. Two obvious Seyfert 1 galaxies, one probably Seyfert 1 and three Seyfert 2 galaxies have been discovered. The redshifts are used to supplement existing data and serve to map southern voids and features out to 25 000 km s⁻¹ in the region  270° < l < 330°, 0° > b > −45°  . Three distinct superclusters and twenty apparent voids are tentatively identified. One Void, at   l = 300°, b =−20°, cz = 16 000 km s⁻¹  , with a diameter of 6000 km s⁻¹, is as large as any yet mapped. It appears as part of a general underdense region.     

Characteristics of the dust-plasma interaction near Enceladus’ South Pole

We present RPWS Langmuir probe data from the third Enceladus flyby (E3) showing the presence of dusty plasma near Enceladus’ South Pole. There is a sharp rise in both the electron and ion number densities when the spacecraft traverses through Enceladus plume. The ion density near Enceladus is found to increase abruptly from about 10² cm⁻³ before the closest approach to 10⁵ cm⁻³ just 30 s after the closest approach, an amount two orders of magnitude higher than the electron density. Assuming that the inconsistency between the electron and ion number densities is due to the presence of dust particles that are collecting the missing electron charges, we present dusty plasma characteristics down to sub-micron particle sizes. By assuming a differential dust number density for a range in dust sizes and by making use of Langmuir probe data, the dust densities for certain lower limits in dust size distribution were estimated. In order to achieve the dust densities of micrometer and larger sized grains comparable to the ones reported in the literature, we show that the power law size distribution must hold down to at least 0.03 μm such that the total differential number density is dominated by the smallest sub-micron sized grains. The total dust number density in Enceladus’ plume is of the order of 10² cm⁻³ reducing to 1 cm⁻³ in the E-ring. The dust density for micrometer and larger sized grains is estimated to be about 10⁻⁴ cm⁻³ in the plume while it is about 10⁻⁶-10⁻⁷ cm⁻³ in the E-ring. Dust charge for micron sized grains is estimated to be about eight thousand electron charges reducing to below one hundred electron charges for 0.03 μm sized grains. The effective dusty plasma Debye length is estimated and compared with inter-grain distance as well as the electron Debye length. The maximum dust charging time of 1.4 h is found for 0.03 μm sized grains just 1 min before the closest approach. The charging time decreases substantially in the plume where it is only a fraction of a second for 1 μm sized grains, 1 s for 0.1 μm sized grains and about 10 s for 0.03 μm sized grains.     

Properties of flux tubes and the relation with solar irradiance variability

At the solar surface the magnetic field is bundled into discrete elements of concentrated flux, often referred to as magnetic flux tubes, which cover only a small fraction of the solar surface. Flux tubes span a whole spectrum of sizes, ranging from sunspots to features well below the best currently obtainable spatial resolution. Whereas sunspots have been well studied, our knowledge of the true brightness of small-scale magnetic features is hampered by the insufficient spatial resolution of the observations. A better understanding of the thermal and magnetic properties of these small-scale features, however, is crucial for an understanding of (climate-relevant) long-term solar irradiance variations.     

Historical variation in the meteor flux as found in Chinese and Japanese chronicles

Numbers of meteors recorded in Chinese and Japanese histories are counted. Two distinct maxima in Chinese records are found in the 11th and 15th centuries, and the latter is also recorded in Japan. Of those records, numbers of bright meteors with sound and great fireballs that appeared in the daytime are also investigated.Correlations between the meteor numbers and the apparitions of naked-eye comet likely to be found, and seasonal variations in the meteor flux recorded during nineteen centuries show two maxima in July–August and October–November, the latter may be related to the Taurid complex.     

Measurement of the meteoroid flux at Mars

In the fall of 2005, a dedicated meteor observing campaign was carried out by the Panoramic Camera (Pancam) onboard the Mars Exploration Rover (MER) Spirit to determine the viability of using MER cameras as meteor detectors and to obtain the first experimental estimate of the meteoroid flux at Mars. Our observing targets included both the sporadic meteoroid background and two predicted martian meteor showers: one associated with 1P/Halley and a potential stream associated with 2001/R1 LONEOS. A total of 353 images covering 2.7 h of net exposure time were analyzed with no conclusive meteor detections. From these data, an upper limit to the background meteoroid flux at Mars is estimated to be for meteoroids with mass larger than 4 g. For comparison, the estimated flux to this mass limit at the Earth is [Grün, E., Zook, H.A., Fechtig, H., Giese, R.H., 1985. Icarus 62, 244-272]. This result is qualitatively consistent, within error bounds, with theoretical models predicting martian fluxes of ∼50% that at Earth for meteoroids of mass ¹⁰⁻³-¹⁰¹ g [Adolfsson, L.G., Gustafson, B.A.S., Murray, C.D., 1996. Icarus 119, 144-152]. The MER cameras, even using the most sensitive mode of operation, should expect to see on average only one coincident meteor on of order 40-150 h of total exposure time based on these same theoretical martian flux estimates. To more meaningfully constrain these flux models, a longer total integrated exposure time or more sensitive camera is needed. Our analysis also suggests that the event reported as the first martian meteor [Selsis, F., Lemmon, M.T., Vaubaillon, J., Bell, J.F., 2005. Nature 435, 581] is more likely a grazing cosmic ray impact, which we show to be a major source of confusion with potential meteors in all Pancam images.     

The sensitivity of the next generation of lunar Cherenkov observations to UHE neutrinos and cosmic rays

We present simulation results for the detection of ultra-high energy (UHE) cosmic ray (CR) and neutrino interactions in the Moon by radio-telescopes. We simulate the expected radio signal at Earth from such interactions, expanding on previous work to include interactions in the sub-regolith layer for single dish and multiple telescope systems. For previous experiments at Parkes, Goldstone (GLUE), and Kalyazin we recalculate the sensitivity to an isotropic flux of UHE neutrinos. We find the published sensitivity for the GLUE experiment to be too high (too optimistic) by an order of magnitude, and consequently the GLUE limit to be too low by an order of magnitude. Our predicted sensitivity for future experiments using the Australia Telescope Compact Array (ATCA) and the Australian SKA Pathfinder (ASKAP) indicate these instruments will be able to detect the more optimistic UHE neutrino flux predictions, while the square kilometre array (SKA) will also be sensitive to all bar one prediction of a diffuse ‘cosmogenic’, or ‘GZK’, neutrino flux.Outstanding theoretical uncertainties at both high-frequency and low-frequency limits currently prevent a reliable estimate of the sensitivity of the lunar Cherenkov technique for UHE cosmic ray (CR) astronomy. Here, we place limits on the effects of large-scale surface roughness on UHE CR detection, and find that when near-surface ‘formation-zone’ effects are ignored, the proposed SKA low-frequency aperture array could detect CR events above 56 EeV at a rate between 15 and 40 times that of the current Pierre Auger Observatory. Should further work indicate that formation-zone effects have little impact on UHE CR sensitivity, observations of the Moon with the SKA would allow directional analysis of UHE cosmic rays, and investigation of correlations with putative cosmic ray source populations, to be conducted with very high statistics.     

Water in the upper martian surface at mid- and low-latitudes: presence, state, and consequences

Sublimation of water ice is more effective than evaporation of sorption water at the same temperature. Therefore, water in the form of ice must, over geologic time-scales, have left the upper martian surface (m-scale) at mid- and low-latitudes, leaving sorption water as a possible physical form of stable subsurface water. Adsorption water is “liquid-like” at these temperatures (in the sense of a 2D-liquid). This property is the reason for the specific importance of physisorbed water under martian conditions. It is shown that unfrozen adsorption water can cause numerous physical, chemical, and possibly also biological processes in the upper martian surface and may be responsible for a number of its properties.     

Sublimation of the Martian CO2 Seasonal South Polar Cap

The polar condensation/sublimation of CO₂, that involve about one fourth of the atmosphere mass, is the major Martian climatic cycle. Early observations in visible and thermal infrared have shown that the sublimation of the Seasonal South Polar Cap (SSPC) is not symmetric around the geographic South Pole.Here we use observations by OMEGA/Mars Express in the near-infrared to detect unambiguously the presence of CO₂ at the surface, and to estimate albedo. Second, we estimate the sublimation of CO₂ released in the atmosphere and show that there is a two-step process. From Ls=180° to 220°, the sublimation is nearly symmetric with a slight advantage for the cryptic region. After Ls=220° the anti-cryptic region sublimation is stronger. Those two phases are not balanced such that there is 22% ± 9 more mass the anti-cryptic region, arguing for more snow precipitation. We compare those results with the MOLA height measurements. Finally we discuss implications for the Martian atmosphere about general circulation and gas tracers, e.g. Ar.     

Comparison of the atmosphere above the South Pole, Dome C and Dome A: first attempt

The atmospheric properties above three sites (Dome C, Dome A and the South Pole) on the Internal Antarctic Plateau are investigated for astronomical applications using the monthly median of the analyses from ECMWF (the European Centre for Medium-Range Weather Forecasts). Radiosoundings extended on a yearly time-scale at the South Pole and Dome C are used to quantify the reliability of the ECMWF analyses in the free atmosphere as well as in the boundary and surface layers, and to characterize the median wind speed in the first 100 m above the two sites. Thermodynamic instability properties in the free atmosphere above the three sites are quantified with monthly median values of the Richardson number. We find that the probability to trigger thermodynamic instabilities above 100 m is smaller on the Internal Antarctic Plateau than on mid-latitude sites. In spite of the generally more stable atmospheric conditions of the Antarctic sites compared to mid-latitude sites, Dome C shows worse thermodynamic instability conditions than those predicted above the South Pole and Dome A above 100 m. A rank of the Antarctic sites done with respect to the strength of the wind speed in the free atmosphere (ECMWF analyses) as well as the wind shear in the surface layer (radiosoundings) is presented.     

Source, sea level and circulation effects on the sediment flux to the deep ocean over the past 15 ka off eastern New Zealand

The last post-glacial transgression and present highstand of sea level were accompanied by a reduction in the terrigenous flux to the deep ocean bordering the active convergent margin off the eastern North Island of New Zealand. Although in accord with long-established models of highstand shelf deposition, new data from giant piston core MD97 2121 (2314 m depth) reveal that the flux also varied with terrigenous supply and palaeocirculation. Between 15 and 9.5 ka, the flux reduced from 33 to 20 g/cm²/ka as supply declined with an expanding vegetation cover, and mud depocentres became established on the continental shelf. An increase from 20 to 27 g/cm²/ka during 9.5–3.5 ka coincided with a strengthened East Cape Current which probably introduced sediment from fluvial and shelf sources in the north. The flux profile shows no immediate response to the establishment of modern sea level 7 ka. However, accumulation decreased from 3.5 to 1 ka as more sediments were retained on the shelf, possibly under wind-strengthened, along-shelf currents. Over the last 1 ka, the flux decline halted under increased terrigenous supply during anthropogenic development of the land.Despite the proximity of the North Island's Central Volcanic Region, major eruptions caused only brief increases (centuries duration) in the terrigenous flux through direct deposition of airfall and possibly fluvial redistribution of onshore volcanic deposits. Frequent earthquakes also had little short-term effect on accumulation although such events, along with volcanism, probably contribute to the long-term high flux of the region.The other measured flux component, biogenic carbonate, reached maxima of 6 g/cm²/ka between 11 and 8.5 ka when nutrient-bearing waters of the East Cape Current dominated the palaeoceanography. After these peaks, carbonate accumulation declined gradually to modern levels of 3 g/cm²/ka.     

Response of peak electron densities in the martian ionosphere to day-to-day changes in solar flux due to solar rotation

Photochemical Chapman theory predicts that the square of peak electron density, N_m, in the dayside ionosphere of Mars is proportional to the cosine of solar zenith angle. We use Mars Global Surveyor Radio Science profiles of electron density to demonstrate that this relationship is generally satisfied and that positive or negative residuals between observed and predicted values of are caused by periods of relatively high or low solar flux, respectively.Understanding the response of the martian ionosphere to changes in solar flux requires simultaneous observations of the martian ionosphere and of solar flux at Mars, but solar flux measurements are only available at Earth. Since the Sun's output varies both in time and with solar latitude and longitude, solar flux at Mars is not simply related to solar flux at Earth by an inverse-square law. We hypothesize that, when corrected for differing distances from the Sun, solar fluxes at Mars and Earth are identical when shifted in time by the interval necessary for the Sun to rotate through the Earth–Sun–Mars angle.We perform four case studies that quantitatively compare time series of N_m at Mars to time series of solar flux at Earth and find that our hypothesis is satisfied in the three of them that used ionospheric data from the northern hemisphere. We define a solar flux proxy at Mars based upon the E_10.7 proxy for solar flux at Earth and use our best case study to derive an equation that relates N_m to this proxy. We discuss how the ionosphere of Mars can be used to infer the presence of solar active regions not facing the Earth.Our fourth case study uses ionospheric observations from the southern hemisphere at latitudes where there are strong crustal magnetic anomalies. These profiles do not have Chapman-like shapes, unlike those of the other three case studies. We split this set of measurements into two subsets, corresponding to whether or not they were made at longitudes with strong crustal magnetic anomalies. Neither subset shows N_m responding to changes in solar flux in the manner that we observe in the three other case studies.We find many similarities in ionospheric responses to short-term and long-term changes in solar flux for Venus, Earth, and Mars. We consider the implications of our results for different parametric equations that have been published describing this response.     

Sediment flux sensitivity to climate change: A case study in the Longchuanjiang catchment of the upper Yangtze River, China

Climate change may affect the sediment generation and transportation processes and the consequent sediment flux in a river. The sensitivity of suspended sediment flux to climate change in the Longchuanjiang catchment is investigated with Artificial Neural Networks (ANNs). ANNs were calibrated and validated using sediment flux data from 1960 to 1990 during which the influence from human activities was relatively stable. The established ANN is used to predict the responses of sediment flux to 25 hypothetical climate scenarios, which were generated by adjusting the baseline temperature up to − 1, 1, 2 and 3 °C and by scaling the baseline precipitation by +/− 10% and +/− 20%. The results indicated when temperature remains unchanged, an increase in rainfall will lead to a rise in sediment flux; when rainfall level remains unchanged, an increase in temperature is likely to result in a decrease in sediment flux. Same percentage of changes in rainfall and temperature are likely to trigger higher responses in wetter months than in drier months. However, it is the combination of the change in temperature and rainfall that determines the change of sediment flux in a river. Higher sediment flux is expected to appear under wetter and warmer climate, when higher transport capacity is accompanied by higher erosion rate.