SPEAR-1: An experiment to measure current collection in the ionosphere by high voltage biased conductors

An experiment is described in which a high electrical potential difference, up to 45 kV, was applied between deployed conducting spheres and a sounding rocket in the ionosphere. Measurements were made of the applied voltage and the resulting currents for each of 24 applications of different high potentials. In addition, diagnostic measurements of optical emissions in the vicinity of the spheres, energetic particle flow to the sounding rocket, dc electric field and wave data were made. The ambient plasma and neutral environments were measured by a Langmuir probe and a cold cathode neutral ionization gauge, respectively. The payload is described and examples of the measured current and voltage characteristics are presented. The characteristics of the measured currents are discussed in terms of the diagnostic measurements and the in-situ measurements of the vehicle environment. In general, it was found that the currents observed were at a level typical of magnetically limited currents from the ionospheric plasma for potentials less than 12 kV, and slightly higher for larger potentials. However, due to the failure to expose the plasma contactor, the vehicle sheath modified the sphere sheaths and made comparisons with the analytic models of Langmuir-Blodgett and Parker-Murphy less meaningful. Examples of localized enhancements of ambient gas density resulting from the operation of the attitude control system thrusters (cold nitrogen) were obtained. Current measurements and optical data indicated localized discharges due to enhanced gas density that reduced the vehicle-ionosphere impedance

A high-resolution late Holocene lake isotope record from Turkey and links to North Atlantic and monsoon climate

A high resolution proxy record of precipitation and evaporation variability through the past 1700 yr from δ18O analysis of a varved lake sequence from central Turkey shows rapid shifts between dry periods (AD 300–500 and AD 1400–1950) and wetter intervals (AD 560–750 and AD 1000–1350). Changes are consistent with changes in instrumental and proxy records of the Indian monsoon, dry summers in the Eastern Mediterranean being associated with periods of enhanced monsoon rainfall. In addition major shifts in the record are coherent with changes in North Atlantic winter climate with cold, wet periods in the Alps occurring at times of dry Turkish climate

The effects of surface structure mutations in <i>Arabidopsis thaliana</i> on the polarization of reflections from virus-infected leaves

<div><p>The way in which light is polarized when reflected from leaves can be affected by infection with plant viruses. This has the potential to influence viral transmission by insect vectors due to altered visual attractiveness of infected plants. The optical and topological properties of cuticular waxes and trichomes are important determinants of how light is polarized upon reflection. Changes in expression of genes involved in the formation of surface structures have also been reported following viral infection. This paper investigates the role of altered surface structures in virus-induced changes to polarization reflection from leaves. The percentage polarization of reflections from <i>Arabidopsis thaliana cer5</i>, <i>cer6</i> and <i>cer8</i> wax synthesis mutants, and the <i>gl1</i> leaf hair mutant, was compared to those from wild-type (WT) leaves. The <i>cer5</i> mutant leaves were less polarizing than WT on the adaxial and abaxial surfaces; <i>gl1</i> leaves were more polarizing than WT on the adaxial surfaces. The <i>cer6</i> and <i>cer8</i> mutations did not significantly affect polarization reflection. The impacts of <i>Turnip vein clearing virus</i> (TVCV) infection on the polarization of reflected light were significantly affected by <i>cer5</i> mutation, with the reflections from <i>cer5</i> mutants being higher than those from WT leaves, suggesting that changes in <i>CER5</i> expression following infection could influence the polarization of the reflections. There was, however, no significant effect of the <i>gl1</i> mutation on polarization following TVCV infection. The <i>cer5</i> and <i>gl1</i> mutations did not affect the changes in polarization following <i>Cucumber mosaic virus</i> (CMV) infection. The accumulation of TVCV and CMV did not differ significantly between mutant and WT leaves, suggesting that altered expression of surface structure genes does not significantly affect viral titres, raising the possibility that if such regulatory changes have any adaptive value it may possibly be through impacts on viral transmission.</p></div

A New Method for Characterizing Very Low-Mass Companions with Low-Resolution Near-Infrared Spectroscopy

We present a new and computationally efficient method for characterizing very low-mass companions using low-resolution (R ∼ 30), near-infrared (YJH) spectra from high-contrast imaging campaigns with integral field spectrograph (IFS) units. We conduct a detailed quantitative comparison of the efficacy of this method through tests on simulated data comparable in spectral coverage and resolution to the currently operating direct-imaging systems around the world. In particular, we simulate Project 1640 data as an example of the use, accuracy, and precision of this technique. We present results from comparing simulated spectra of M, L, and T dwarfs with a large and finely sampled grid of synthetic spectra using Markov-chain Monte Carlo techniques. We determine the precision and accuracy of effective temperature and surface gravity inferred from fits to PHOENIX dusty and cond, which we find reproduce the low-resolution spectra of all objects within the adopted flux uncertainties. Uncertainties in effective temperature decrease from ± 100–500 K for M dwarfs to as small as ± 30 K for some L and T spectral types. Surface gravity is constrained to within 0.2–0.4 dex for mid-L through T dwarfs, but uncertainties are as large as 1.0 dex or more for M dwarfs. Results for effective temperature from low-resolution YJH spectra generally match predictions from published spectral type-temperature relationships except for L–T transition objects and young objects. Single-band spectra (i.e., narrower wavelength coverage) result in larger uncertainties and often discrepant results, suggesting that high-contrast IFS observing campaigns can compensate for low spectral resolution by expanding the wavelength coverage for reliable characterization of detected companions. We find that S/N ∼ 10 is sufficient to characterize temperature and gravity as well as possible given the model grid. Most relevant for direct-imaging campaigns targeting young primary stars is our finding that low-resolution near-infrared spectra of known young objects, compared to field objects of the same spectral type, result in similar best-fit surface gravities but lower effective temperatures, highlighting the need for better observational and theoretical understanding of the entangled effects of temperature, gravity, and dust on near-infrared spectra in cool low-gravity atmospheres

A new approach for luminescence dating glaciofluvial deposits - High precision optical dating of cobbles

In recent years luminescence dating has increasingly been applied to date glaciofluvial sediments, but uncertainties about the degree of bleaching of the luminescence signal at deposition make dating of such sediments challenging. Here we test a new approach for luminescence dating of glaciofluvial sediments, based on the analysis of rock cores drilled from granite cobbles, and compare the luminescence ages generated against independent age control. Luminescence measurements from rock slices in cobble-sized clasts can be used to reconstruct the extent of bleaching, thereby giving greater confidence in the ages produced. This study illustrates that another important advantage of using cobbles is that at depths of 2 mm or more below the cobble surface >90% of the total dose rate arises from the cobble itself, making the dose rate insensitive to the water content of the sediment matrix. Ordinarily, uncertainties in estimating water content during burial are one of the largest sources of uncertainty in luminescence dating methods, and hence reducing the reliance upon the dose rate could be particularly advantageous for glacial deposits, where water contents can potentially be large and highly variable. Measurements of cobbles from Orrisdale Head, Isle of Man, demonstrate that the luminescence signal was completely bleached to depths of up to 12 mm into the cobble. Sampling of orientated cobbles from lithofacies diagnostic of bar-top environments was used to maximise the chances of exposure to sunlight. The upper-faces of these orientated cobble surfaces appear to be bleached to a greater depth than the lowermost faces. Data from 45 rock slices from these cobbles were tightly clustered, yielding a mean age of 20.7 ± 0.3 ka that is in agreement with independent age control. One of the well-bleached cobbles shows evidence of two discrete exposure events, potentially recording both the advance at 26.2 ± 0.8 ka, and retreat at 20.7 ± 0.3 ka, of the Irish Sea Ice Stream

Constraining mass ratio and extinction in the FU Orionis binary system with infrared integral field spectroscopy

We report low resolution near infrared spectroscopic observations of the eruptive star FU Orionis using the Integral Field Spectrograph Project 1640 installed at the Palomar Hale telescope. This work focuses on elucidating the nature of the faint source, located 0.5" south of FU Ori, and identified in 2003 as FU Ori S. We first use our observations in conjunction with published data to demonstrate that the two stars are indeed physically associated and form a true binary pair. We then proceed to extract J and H band spectro-photometry using the damped LOCI algorithm, a reduction method tailored for high contrast science with IFS. This is the first communication reporting the high accuracy of this technique, pioneered by the Project 1640 team, on a faint astronomical source. We use our low resolution near infrared spectrum in conjunction with 10.2 micron interferometric data to constrain the infrared excess of FU Ori S. We then focus on estimating the bulk physical properties of FU Ori S. Our models lead to estimates of an object heavily reddened, A_V =8-12, with an effective temperature of ~ 4000-6500 K . Finally we put these results in the context of the FU Ori N-S system and argue that our analysis provides evidence that FU Ori S might be the more massive component of this binary syste

The Solar-System-Scale Disk Around AB Aurigae

The young star AB Aurigae is surrounded by a complex combination of gas-rich and dust dominated structures. The inner disk which has not been studied previously at sufficient resolution and imaging dynamic range seems to contain very little gas inside a radius of least 130 astronomical units (AU) from the star. Using adaptive-optics coronagraphy and polarimetry we have imaged the dust in an annulus between 43 and 302 AU from the star, a region never seen before. An azimuthal gap in an annulus of dust at a radius of 102 AU, along with a clearing at closer radii inside this annulus, suggests the formation of at least one small body at an orbital distance of about 100 AU. This structure seems consistent with crude models of mean motion resonances, or accumulation of material at two of the Lagrange points relative to the putative object and the star. We also report a low significance detection of a point source in this outer annulus of dust. This source may be an overdensity in the disk due to dust accreting onto an unseen companion. An alternate interpretation suggests that the object's mass is between 5 and 37 times the mass of Jupiter. The results have implications for circumstellar disk dynamics and planet formation.Comment: 11 pages, 5 figures, accepted for publication in Astrophysical Journal, V. 680, June 10, 200

Interpreting lake isotope records of Holocene environmental change in the Eastern Mediterranean

Oxygen isotope records from lake sediment archives are becoming an increasingly common tool for palaeoenvironmental reconstruction. We discuss their interpretation in the Eastern Mediterranean region with particular reference to three records, Zeribar, Van and Eski Acıgöl during the Holocene. The latter two records have been interpreted as controlled by changes in the precipitation to evaporation ratio, and the first due to changes in precipitation seasonality. In light of recent isotope work in the region and comparison with other proxy data from the same lakes, we show both of these initial interpretations to be oversimplified. Careful interpretations of complex lake isotope systems are therefore required in order that palaeoclimatic inferences are drawn correctly

Seasonality of Holocene hydroclimate in the Eastern Mediterranean reconstructed using the oxygen isotope composition of carbonates and diatoms from Lake Nar, central Turkey

A positive shift in the oxygen isotope composition (δ18O) of lake carbonates in the Eastern Mediterranean from the early to late Holocene is usually interpreted as a change to drier (reduced P/E) conditions. However, it has also been suggested that changes in the seasonality of precipitation could explain these trends. Here, Holocene records of δ18O from both carbonates and diatom silica, from Lake Nar in central Turkey, provide insights into palaeoseasonality. We show how Δδ18Olakewater (the difference between spring and summer reconstructed δ18Olakewater) was minimal in the early Holocene and for most of the last millennium, but was greater at other times. For example, between ~4,100-1,600 years BP we suggest that increased Δδ18Olakewater could have been the result of relatively more spring/summer evaporation, amplified by a decline in lake level. In terms of change in annual mean δ18O, isotope mass balance modelling shows that this can be influenced by changes in seasonal P/E as well as inter-annual P/E, but lake level falls inferred from other proxies confirm there was a mid Holocene transition to drier climatic conditions in central Turkey

Proxy reconstruction of ultraviolet-B irradiance at the Earth’s surface, and its relationship with solar activity and ozone thickness

Solar ultraviolet-B (UV-B) irradiance that reaches the Earth’s surface acts as a biotic stressor and has the potential to modify ecological and environmental functioning. The challenges of reconstructing ultraviolent (UV) irradiance prior to the satellite era mean that there is uncertainty over long-term surface UV-B patterns, especially in relation to variations in solar activity over centennial and millennial timescales. Here, we reconstruct surface UV-B irradiance over the last 650 years using a novel UV-B proxy based on the chemical signature of pollen grains. We demonstrate a statistically significant positive relationship between the abundance of UV-B absorbing compounds in Pinus pollen and modelled solar UV-B irradiance. These results show that trends in surface UV-B follow the overall solar activity pattern over centennial timescales, and that variations in solar output are the dominant control on surface level UV-B flux, rather than solar modulated changes in ozone thickness. The Pinus biochemical response demonstrated here confirms the potential for solar activity driven surface UV-B variations to impact upon terrestrial biotas and environments over long timescales