Design study for electronic system for Jupiter Orbit Probe (JOP)

The conceptual design of the Jupiter probe spectrometer is presented. Block and circuit diagrams are presented along with tabulated parts lists. Problem areas are considered to be (1) the schedule, (2) weight limitations for the electronic systems, and (3) radiation hardness of the electronic devices

Advanced Langmuir Probe (LP)

The dynamic response of the MK-2 version of the Langmuir probe amplifier was studied. The settling time of the step response is increased by: (1) stray node-to-ground capacitance at series connections between high value feedback resistors; and (2) input capacitance due to the input cable, FET switches, and input source follower. The stray node-to-ground capacitances can be reduced to tolerable levels by elevating the string of feedback resistors above the printing board. A new feedback network was considered, with promising results. The design uses resistances having much lower nominal values, thereby minimizing the effect of stray capacitances. Faster settling times can be achieved by using an operational amplifier having a higher gain-bandwidth product

The HI environment of the Sculptor dwarf spheroidal galaxy

New observations of the neutral hydrogen (HI) in and around the line of sight of the Sculptor dwarf spheroidal (dSph) are presented. The data obtained with the single-dish Parkes telescope cover a large area of 7\degr x 7\degr in the direction of the dwarf, and have resolutions of 15\farcm x 1.12 km/s. The Australia Telescope Compact Array (ATCA) was used to map a smaller area of 2\degr x 2\degr centered on the direction of the dwarf with higher resolutions (350\arcsec x 140\arcsec x 1.65 km/s). Many HI structures having velocities outside the range of the normal Galactic disk velocities were detected, including the two Sculptor clouds (northeast and southwest) of Carignan et al. (1998, C98). The present study shows the total extent of the C98 clouds. We derived heliocentric radial velocities for the NE and SW clouds of 100.2\pm 0.9 km/s and 105.1\pm 0.3 km/s, respectively. The intensity-weighted mean HI velocity for both clouds is 104.1\pm 0.4 km/s. The mass of each cloud is (4.1\pm 0.2) x 10^4 M_\odot (NE cloud) and (1.93\pm 0.02) x 10^5 M_\odot (SW cloud) at the Sculptor dSph distance (79 kpc).Comment: 21 pages, 7 figures, to be published in A

Gas Rich Dwarf Spheroidals

We present evidence that nearly half of the dwarf spheroidal galaxies (dSph and dSph/dIrr) in the Local Group are associated with large reservoirs of atomic gas, in some cases larger than the stellar mass. The gas is sometimes found at large distance (~10 kpc) from the center of a galaxy and is not necessarily centered on it. Similarly large quantities of ionized gas could be hidden in these systems as well. The properties of some of the gas reservoirs are similar to the median properties of the High-Velocity Clouds (HVCs); two of the HI reservoirs are catalogued HVCs. The association of the HI with the dwarf spheroidals might thus provide a link between the HVCs and stars. We show that the HI content of the Local Group dSphs and dIrrs exhibits a sharp decline if the galaxy is within 250 kpc of either the Milky Way or M31. This can be explained if both galaxies have a sufficiently massive x-ray emitting halo that produces ram-pressure stripping if a dwarf ventures too close to either giant spiral. We also investigate tidal stripping of the dwarf galaxies and find that although it may play a role, it cannot explain the apparent total absence of neutral gas in most dSph galaxies at distances less than 250 kpc. For the derived mean density of the hot gas, n_0 = 2.5e-5 cm^-2, ram-pressure stripping is found to be more than an order of magnitude more effective in removing the gas from the dSph galaxies. The hot halo, with an inferred mass of 1e10 solar masses, may represent a reservoir of ~1000 destroyed dwarf systems, either HVCs or true dwarf galaxies similar to those we observe now.Comment: AASTex preprint style, 27 pages including 12 figures. Submitted to ApJ. See also http://astro.berkeley.edu/~robisha

Report from upper atmospheric science

Most of the understanding of the thermosphere resulted from the analysis of data accrued through the Atmosphere Explorer satellites, the Dynamics Explorer 2 satellite, and observations from rockets, balloons, and ground based instruments. However, new questions were posed by the data that have not yet been answered. The mesosphere and lower thermosphere have been less thoroughly studied because of the difficulty of accessibility on a global scale, and many rather fundamental characteristics of these regions are not well understood. A wide variety of measurement platforms can be used to implement various parts of a measurement strategy, but the major thrusts of the International Solar Terrestrial Physics Program would require Explorer-class missions. A remote sensing mission to explore the mesosphere and lower thermosphere and one and two Explorer-type spacecraft to enable a mission into the thermosphere itself would provide the essential components of a productive program of exploration of this important region of the upper atomsphere. Theoretical mission options are explored

Synthèse des impacts écologiques des feux et des coupes forestières sur les lacs de l'écozone boréale au Québec

Cet article présente une première synthèse comparative des impacts des feux et des coupes forestières sur la qualité des eaux et les communautés aquatiques des lacs de l'écozone boréale de l'est du Canada. La recherche a été réalisée de 1996 à 1998 dans le cadre d'un projet du Réseau de centre d'excellence sur la gestion durable des forêts (RCE-GDF) et porte sur 38 lacs du Bouclier Canadien du Québec. Les changements dans la qualité de l'eau ainsi que dans la diversité, la biomasse et la structure des communautés de plancton et de poissons ont été suivis pendant trois ans dans 20 lacs dont les bassins versants étaient non perturbés, dans 9 lacs qui avaient subit des coupes forestières et dans 9 lacs qui avaient subit des feux de forêt.Notre étude montre que les feux et les coupes ont des impacts significatifs qui diffèrent selon le type de perturbation. En général, les lacs affectés par les coupes et les feux ont des concentrations de phosphore 2 à 3 fois plus élevées que les lacs de référence. Toutefois, les lacs affectés par les feux montrent des concentrations en nitrates beaucoup plus élevées tandis que les lacs affectés par les coupes sont moins transparents et ont des eaux plus colorées, très riches en carbone organique dissous. Les feux et les coupes affectent aussi de façon différente la minéralisation des eaux et les concentrations des ions majeurs. Les feux et les coupes n'ont pas d'effet sur la biodiversité des communautés planctoniques, sauf dans les lacs ayant un grand bassin versant et plus de 40 % de perturbation. Aucune différence n'a été observée entre les lacs de référence et les lacs perturbés au niveau de l'occurrence, l'abondance et la croissance des espèces de poissons. En revanche, les feux et les coupes affectent la production et la structure des communautés aquatiques. Dans les lacs affectés par les feux, l'enrichissement en azote et phosphore provoque une hausse de la concentration en chlorophylle a, et de la biomasse du phytoplancton et du limnoplancton (seston > 53 µm), en particulier des diatomées, des rotifères et des gros crustacés, pendant deux à trois années après les feux. En revanche, dans les lacs affectés par les coupes, l'enrichissement en phosphore n'entraîne qu'une augmentation très faible et limitée à un an de la biomasse des algues et pas de changement dans les biomasses du limnoplancton, en raison de la forte couleur et de la transparence réduite des eaux, qui limite la production biologique. Les coupes ont un impact négatif sur les copépodes calanoïdes, un groupe de zooplancton caractéristique des lacs oligotrophes et transparents. Une diminution significative de la proportion des individus de petite taille a été observée chez les populations de perchaude et de meunier noir des lacs perturbés (lacs de coupe et de feux formant un seul groupe). Les impacts observés dans la qualité des eaux et la production du plancton augmentent avec l'importance relative des perturbations au niveau du bassin versant. Cependant, la variabilité dans les caractéristiques des bassins versants et des lacs, en particulier le rapport de drainage et le temps de résidence des eaux, a des effets confondants sur les réponses des écosystèmes lacustres aux perturbations par les feux et les coupes.This paper presents a comparative review on ecological impacts of wildfires and harvesting on water quality and aquatic community attributes of boreal lakes in eastern Canada. This project was carried out from 1996 to 1998, as part of the research program of the Sustainable Forest Management Network Centre of Excellence (NCE-SFM), on 38 lakes of the Boreal Canadian Shield (Québec, Canada). Changes in water quality, and in diversity, biomass and community structure of pelagic plankton and fish populations were monitored for 3 years in 20 reference lakes, 9 cut lakes and 9 burnt lakes.Our study shows that wildfires and logging have significant impacts on water quality as well as primary and secondary producers in boreal lakes. However, fire and logging does not have similar impacts. In general, cut and burnt lakes showed higher concentrations of total phosphorus (TP: 2-3 folds) than reference lakes. However nitrates concentrations (NO3-) were higher in burnt lakes than in reference and cut lakes, whereas dissolved organic carbon (DOC), light extinction coefficient (e PAR) and water colour were higher in cut lakes than in reference lakes, burnt lakes showing intermediate values. Wildfire and logging also affect ionic composition of lake water. Both burnt and cut lakes had higher concentrations of potassium (K+), chloride (Cl-) and calcium (Ca2+) than reference lakes, while sulphates (SO42-) and magnesium (Mg2+) increased only in burnt lakes. The observed increases in organic and mineral elements reflect their export from the watershed and were related to the drainage ratio. As mobile ions are rapidly flushed from the perturbed watersheds, ionic water composition returned to normal levels within three years after the perturbation. In contrast, some changes in water quality (P and N enrichment in perturbed lakes; DOC increase in cut lakes) seems to be on longer term and might have a more important effect on limnological features of lakes such as thermal stratification, mixed and euphotic depth, plankton biomass and bioaccumulation of mercury in zooplankton and fish.Wildfires and logging do not have significant impacts on species richness of planktonic communities, except for lakes with large drainage basins and those where the perturbation was higher than 40% of the watershed area. However, wildfires and logging affect biomass of plankton communities. In burnt lakes, the nutrient enrichment induced important increases in Chl. a concentration and phytoplankton biomass, and a small increase in limnoplankton biomass (seston > 53 µm). Diatoms, rotifers and large crustaceans showed significant increases. In burnt lakes, increases in phytoplankton were observed during the three years of the survey and were highest in the first 2 years after fires. Limnoplankton increases lasted only 2 years and were highest the second year after fires. In cut lakes, nutrient enrichment was not reflected in a proportional increase in plankton production due to increase in DOC concentrations and lake water colour that reduced water transparency. Phytoplankton slightly increased only the first year after logging and no increase was observed for limnoplankton and zooplankton. Logging negatively affect calanoids, a zooplankton group characteristic of clear and oligotrophic lakes. No significant differences were observed in the occurrence, abundance and growth of fish populations among reference and perturbed lakes. However, the proportion of small yellow perch and white sucker were significantly lower in populations of impacted lakes (burned and logged lakes pooled). In most cases, impacts on water quality and plankton communities were related to the intensity of fire or logging, when expressed as the percent area of watershed harvested or burnt divided by the lake surface or volume. Simple models may then be developed and help to predict the effect of harvesting practices on lake ecosystems. However, environmental variation in watershed and lakes characteristics, especially drainage ratio and lake water residence time, are important confounding factors in the responses of lakes to watershed perturbations by fire or logging. Lakes with drainage ratio > 4 and with more of 30% of their watershed perturbed are the most sensitive to fire and logging. These factors should be considered when developing lake management models in the boreal forest impacted by fire and logging

KAT-7 Science Verification: Using HI Observations of NGC 3109 to Understand its Kinematics and Mass Distribution

HI observations of the Magellanic-type spiral NGC 3109, obtained with the seven dish Karoo Array Telescope (KAT-7), are used to analyze its mass distribution. Our results are compared to what is obtained using VLA data. KAT-7 is the precursor of the SKA pathfinder MeerKAT, which is under construction. The short baselines and low system temperature of the telescope make it sensitive to large scale low surface brightness emission. The new observations with KAT-7 allow the measurement of the rotation curve of NGC 3109 out to 32', doubling the angular extent of existing measurements. A total HI mass of 4.6 x 10^8 Msol is derived, 40% more than what was detected by the VLA observations. The observationally motivated pseudo-isothermal dark matter (DM) halo model can reproduce very well the observed rotation curve but the cosmologically motivated NFW DM model gives a much poorer fit to the data. While having a more accurate gas distribution has reduced the discrepancy between the observed RC and the MOdified Newtonian Dynamics (MOND) models, this is done at the expense of having to use unrealistic mass-to-light ratios for the stellar disk and/or very large values for the MOND universal constant a0. Different distances or HI contents cannot reconcile MOND with the observed kinematics, in view of the small errors on those two quantities. As for many slowly rotating gas-rich galaxies studied recently, the present result for NGC 3109 continues to pose a serious challenge to the MOND theory.Comment: 25 pages, 20 figures, accepted for publication in Astronomical Journa

H i kinematics, mass distribution and star formation threshold in NGC 6822, using the SKA pathfinder KAT-7

We present high sensitivity H I observations of NGC 6822, obtained with the Karoo Array Telescope (KAT-7). We study the kinematics, the mass distribution and the star formation thresholds. The KAT-7 short baselines and low system temperature make it sensitive to large-scale, low surface brightness emission. The observations detected ∼ 23 per cent more flux than previous Australian Telescope Compact Array observations. We fit a tilted ring model to the H I velocity field to derive the rotation curve (RC). The KAT-7 observations allow the measurement of the rotation curve of NGC 6822 out to 5.8 kpc, ∼1 kpc further than existing measurements. NGC 6822 is seen to be dark matter dominated at all radii. The observationally motivated pseudo-isothermal dark matter (DM) halo model reproduces well the observed RC while the Navarro Frank-White DM model gives a poor fit to the data. We find the best-fitting mass-to-light ratio (M/L) of 0.12 ± 0.01 which is consistent with the literature. The modified Newtonian dynamics gives a poor fit to our data. We derive the star formation threshold in NGC 6822 using the H I and H α data. The critical gas densities were calculated for gravitational instabilities using the Toomre-Q criterion and the cloud-growth criterion. We found that in regions of star formation, the cloud-growth criterion explains star formation better than the Toomre-Q criterion. This shows that the local shear rate could be a key player in cloud formation for irregular galaxies such as NGC 6822

Solar extreme ultraviolet sensor and advanced langmuir probe

For more than two decades, the staff of the Space Physics Research Laboratory (SPRL) has collaborated with the Goddard Space Flight Center (GSFC) in the design and implementation of Langmuir probes (LP). This program of probe development under the direction of Larry Brace of GSFC has evolved methodically with innovations to: improve measurement precision, increase the speed of measurement, and reduce the weight, size, power consumption and data rate of the instrument. Under contract NAG5-419 these improvements were implemented and are what characterize the Advanced Langmuir Probe (ALP). Using data from the Langmuir Probe on the Pioneer Venus Orbiter, Brace and Walter Hoegy of GSFC demonstrated a novel method of monitoring the solar extreme ultraviolet (EUV) flux. This led to the idea of developing a sensor similar to a Langmuir probe specifically designed to measure solar EUV (SEUV) that uses a similar electronics package. Under this contract, a combined instrument package of the ALP and SEUV sensor was to be designed, constructed, and laboratory tested. Finally the instrument was to be flight tested as part of sounding rocket experiment to acquire the necessary data to validate this method for possible use in future earth and planetary aeronomy missions. The primary purpose of this contract was to develop the electronics hardware and software for this instrument, since the actual sensors were suppied by GSFC. Due to budget constraints, only a flight model was constructed. These electronics were tested and calibrated in the laboratory, and then the instrument was integrated into the rocket payload at Wallops Flight Facility where it underwent environmental testing. After instrument recalibration at SPRL, the payload was reintegrated and launched from the Poker Flat Research Range near Fairbanks Alaska. The payload was successfully recovered and after refurbishment underwent further testing and developing to improve its performance for future use

HI Detection in two Dwarf S0 Galaxies in Nearby Groups: ESO384-016 and NGC 59

An \hi survey of 10 dE/dS0 galaxies in the nearby Sculptor and Centaurus A groups was made using the Australia Telescope Compact Array (ATCA). The observed galaxies have accurate distances derived by Jerjen et al (1998; 2000b) using the surface brightness fluctuation technique. Their absolute magnitudes are in the range $-9.5 > M_B > -15.3$. Only two of the ten galaxies were detected at our detection limit ($\sim 1.0 \times 10^6$ \msol for the Centaurus group and $\sim 5.3 \times 10^5$ \msol for the Sculptor group), the two dS0 galaxies ESO384-016 in the Centaurus A Group and NGC 59 in the Sculptor Group, with \hi masses of $6.0 \pm 0.5 \times 10^6$ \msol and $1.4 \pm 0.1 \times 10^7$ \msol respectively. Those two detections were confirmed using the Green Bank Telescope. These small \hi reservoirs could fuel future generations of low level star formation and could explain the bluer colors seen at the center of the detected galaxies. Similarly to what is seen with the Virgo dEs, the two objects with \hi appear to be on the outskirt of the groups.Comment: 25 pages (11 figures), accepted by A