Ground-based Program Research Articles

Characterization of Structural Defects in (Cd,Zn)Te Crystals Grown by the Travelling Heater Method

Structural defects and compositional uniformity remain the major problems affecting the performance of (Cd, Zn)Te (CZT) based detector devices. Understanding the mechanism of growth and defect formation is therefore fundamental to improving the crystal quality. In this frame, space experiments for the growth of CZT by the Travelling Heater Method (THM) under microgravity are scheduled. A detailed ground-based program was performed to determine experimental parameters and three CZT crystals were grown by the THM. The structural defects, compositional homogeneity and resistivity of these ground-based crystals were investigated. A ZnTe content variation was observed at the growth interface and a high degree of stress associated with extensive dislocation networks was induced, which propagated into the grown crystal region according to the birefringence and X-ray White Beam Topography (XWBT) results. By adjusting the growth parameters, the ZnTe variations and the resulting stress were efficiently reduced. In addition, it was revealed that large inclusions and grain boundaries can generate a high degree of stress, leading to the formation of dislocation slip bands and subgrain boundaries. The dominant defects, including grain boundaries, dislocation networks and cracks in the interior of crystals, led to the resistivity variation in the crystals. The bulk resistivity of the as-grown crystals ranged from 109 Ωcm to 1010 Ωcm.

Analysis of Te Inclusion Striations in (Cd,Zn)Te Crystals Grown by Traveling Heater Method

The growth of (Cd,Zn)Te (CZT) crystals and the improvement of the crystal quality are part of a research project towards experiments under microgravity using the Traveling Heater Method (THM). In order to determine the experimental parameters, we performed a detailed ground-based program. Three CZT crystals with a nominal Zn content of 10% were grown using THM from a Te-rich solution. The size and distribution of the Te inclusions were evaluated by transmission infrared microscopy (IR). From the three-dimensional mapping of the inclusions, we observed striation-like patterns in all of the crystals. The correlation between the growth parameters and the formation of these striations was explored and discussed. We found that the inclusion striations are related to periodic temperature variations.

Untangling Optical Emissions of the Jet and Accretion Disk in the Flat-spectrum Radio Quasar 3C 273 with Reverberation Mapping Data

Abstract 3C 273 is an intensively monitored flat-spectrum radio quasar with both a beamed jet and blue bump together with broad emission lines. The coexistence of the comparably prominent jet and accretion disk leads to complicated variability properties. Recent reverberation mapping monitoring for 3C 273 revealed that the optical continuum shows a distinct long-term trend that does not have a corresponding echo in the Hβ fluxes. We compile multiwavelength monitoring data from the Swift archive and other ground-based programs and clearly find two components of emissions at optical wavelength. One component stems from the accretion disk itself, and the other component can be ascribed to the jet contribution, which also naturally accounts for the nonechoed trend in reverberation mapping data. We develop an approach to decouple the optical emissions from the jet and accretion disk in 3C 273 with the aid of multiwavelength monitoring data. By assuming that the disk emission has a negligible polarization in consideration of the low inclination of the jet, the results show that the jet contributes a fraction of ∼10% at the minimum and up to ∼40% at the maximum to the total optical emissions. This is the first time to provide a physical interpretation of the “detrending” manipulation conventionally adopted in reverberation mapping analysis. Our work also illustrates the importance of appropriately analyzing variability properties in cases of coexisting jets and accretion disks.

Planets, candidates, and binaries from the CoRoT/Exoplanet programme

The CoRoT space mission observed 163 665 stars over 26 stellar fields in the faint star channel. The exoplanet teams detected a total of 4123 transit-like features in the 177 454 light curves. We present the complete re-analysis of all these detections carried out with the same softwares so that to ensure their homogeneous analysis. Although the vetting process involves some human evaluation, it also involves a simple binary flag system over basic tests: detection significance, presence of a secondary, difference between odd and even depths, colour dependence, V-shape transit, and duration of the transit. We also gathered the information from the large accompanying ground-based programme carried out on the planet candidates and checked how useful the flag system could have been at the vetting stage of the candidates. From the initial list of transit-like features, we identified and separated 824 false alarms of various kind, 2269 eclipsing binaries among which 616 are contact binaries and 1653 are detached ones, 37 planets and brown dwarfs, and 557 planet candidates. We provide the catalogue of all these transit-like features, including false alarms. For the planet candidates, the catalogue gives not only their transit parameters but also the products of their light curve modelling: reduced radius, reduced semi-major axis, and impact parameter, together with a summary of the outcome of follow-up observations when carried out and their current status. For the detached eclipsing binaries, the catalogue provides, in addition to their transit parameters, a simple visual classification. Among the planet candidates whose nature remains unresolved, we estimate that eight (within an error of three) planets are still to be identified. After correcting for geometric and sensitivity biases, we derived planet and brown dwarf occurrences and confirm disagreements with Kepler estimates, as previously reported by other authors from the analysis of the first runs: small-size planets with orbital period less than ten days are underabundant by a factor of three in the CoRoT fields whereas giant planets are overabundant by a factor of two. These preliminary results would however deserve further investigations using the recently released CoRoT light curves that are corrected of the various instrumental effects and a homogeneous analysis of the stellar populations observed by the two missions.

A Catalog of Cool Dwarf Targets for the Transiting Exoplanet Survey Satellite

Abstract We present a catalog of cool dwarf targets ( , T eff ≲ 4000 K) and their stellar properties for the upcoming Transiting Exoplanet Survey Satellite (TESS), for the purpose of determining which cool dwarfs should be observed using two minute observations. TESS has the opportunity to search tens of thousands of nearby, cool, late K- and M-type dwarfs for transiting exoplanets, an order of magnitude more than current or previous transiting exoplanet surveys, such as Kepler, K2, and ground-based programs. This necessitates a new approach to choosing cool dwarf targets. Cool dwarfs are chosen by collating parallax and proper motion catalogs from the literature and subjecting them to a variety of selection criteria. We calculate stellar parameters and TESS magnitudes using the best possible relations from the literature while maintaining uniformity of methods for the sake of reproducibility. We estimate the expected planet yield from TESS observations using statistical results from the Kepler mission, and use these results to choose the best targets for two minute observations, optimizing for small planets for which masses can conceivably be measured using follow-up Doppler spectroscopy by current and future Doppler spectrometers. The catalog is available in machine readable format and is incorporated into the TESS Input Catalog and TESS Candidate Target List until a more complete and accurate cool dwarf catalog identified by ESA’s Gaia mission can be incorporated.

The SpaceInn SISMA archive

The Spectroscopic Indicators in a SeisMic Archive (SISMA) has been built in the framework of the FP7 SpaceInn project to contain the 7013 HARPS spectra observed during the CoRoT asteroseismic groundbased program, along with their variability and asteroseismic indicators. The spectra pertain to 261 stars spread around the whole Herztsprung-Russell diagram: 72 of them were CoRoT targets while the others were observed in order to better characterize their variability classes. The Legacy Data lightcurves of the CoRoT targets are also stored in the archive.

The gaia survey contribution to EChO target selection and characterization

The scientific output of the proposed EChO mission (in terms of spectroscopic characterization of the atmospheres of transiting extrasolar planets) will be maximized by a careful selection of targets and by a detailed characterization of the main physical parameters (such as masses and radii) of both the planets and their stellar hosts. To achieve this aim, the availability of high-quality data from other space-borne and ground-based programs will play a crucial role. Here we identify and discuss the elements of the Gaia catalogue that will be of utmost relevance for the selection and characterization of transiting planet systems to be observed by the proposed EChO mission.

INTENSITY MAPPING OF Lyα EMISSION DURING THE EPOCH OF REIONIZATION

We calculate the absolute intensity and anisotropies of the Lyman-alpha radiation field present during the epoch of reionization. We consider emission from both galaxies and the intergalactic medium (IGM) and take into account the main contributions to the production of Lyman-alpha photons: recombinations, collisions, continuum emission from galaxies and scattering of Lyman-n photons in the IGM. We find that the emission from individual galaxies dominates over the IGM with a total Lyman-alpha intensity (times frequency) of about (1.43-3.57)x10^{-8} erg s^{-1} cm^{-2} sr^{-1} at a redshift of 7. This intensity level is low so it is unlikely that the Lyman-\alpha background during reionization can be established by an experiment aiming at an absolute background light measurement. Instead we consider Lyman-\alpha intensity mapping with the aim of measuring the anisotropy power spectrum which has rms fluctuations at the level of 1 x 10^{-16} [erg s^[-1} cm^{-2} sr^{-1}]^2 at a few Mpc scales. These anisotropies could be measured with a spectrometer at near-IR wavelengths from 0.9 to 1.4 \mu m with fields in the order of 0.5 to 1 sq. degrees. We recommend that existing ground-based programs using narrow band filters also pursue intensity fluctuations to study statistics on the spatial distribution of faint Lyman-\alpha emitters. We also discuss the cross-correlation signal with 21 cm experiments that probe HI in the IGM during reionization. A dedicated sub-orbital or space-based Lyman-\alpha intensity mapping experiment could provide a viable complimentary approach to probe reionization, when compared to 21 cm experiments, and is likely within experimental reach.

Calibration of solid state nuclear track detectors at high energy ion beams for cosmic radiation measurements: HAMLET results

The MATROSHKA experiments and the related HAMLET project funded by the European Commission aimed to study the dose burden of the crew working on the International Space Station (ISS). During these experiments a human phantom equipped with several thousands of radiation detectors was exposed to cosmic rays inside and outside the ISS. Besides the measurements realized in Earth orbit, the HAMLET project included also a ground-based program of calibration and intercomparison of the different detectors applied by the participating groups using high-energy ion beams. The Space Dosimetry Group of the Centre for Energy Research (formerly Atomic Energy Research Institute) participated in these experiments with passive solid state nuclear track detectors (SSNTDs). The paper presents the results of the calibration experiments performed in the years 2008–2011 at the Heavy Ion Medical Accelerator (HIMAC) of the National Institute of Radiological Sciences (NIRS), Chiba, Japan. The data obtained serve as update and improvement for the previous calibration curves which are necessary for the evaluation of the SSNTDs exposed in unknown space radiation fields.

Comparison of the response of various TLDs to cosmic radiation and ion beams: Current results of the HAMLET project

HAMLET is an European Commission research project aiming at optimal scientific exploitation of the data produced within the space experiment MATROSHKA. During phase 1 of this experiment a human phantom equipped with several thousands of radiation detectors (mainly TLDs) was exposed outside the International Space Station for 1.5 years. Besides the measurements realized in Earth orbit, the HAMLET project includes also a ground-based program of intercomparison of detector response to high-energy ion beams. Within the paper, the relative response of main glow-curve peaks of various TLDs (mostly based on LiF) used in frame of the MATROSHKA experiment by three laboratories (DLR Cologne, ATI Vienna and IFJ Krakow) for radiation in space and several ion beams, has been compared. For LiF:Mg,Ti detectors a very good agreement between results obtained by the three laboratories was observed, both for space and accelerator-based exposures. This should be considered a remarkable result, taking into account that the studied TLDs originated from six different batches, manufactured by two producers exploiting different production techniques and were processed by three laboratories, using significantly different protocols (annealing, readout, calibration, glow-curve analysis). Another type of TL detectors, LiF:Mg,Cu,P, was found to show response to cosmic radiation lower than that of LiF:Mg,Ti by 5%e18%.

THE PROPER MOTION OF THE MAGELLANIC CLOUDS. II. NEW RESULTS FOR FIVE SMALL MAGELLANIC CLOUD FIELDS

We present new results from a ground-based program to determine the proper motion of the Magellanic Clouds (MCs) relative to background quasars (QSOs), being carried out with the Ir?ne? du Pont 2.5?m telescope at Las Campanas Observatory, Chile. The data were secured over a time base of seven years and with eight epochs of observation As measured (field) proper motions were obtained for five QSO fields in the Small Magellanic Cloud (SMC): QJ0033?7028, QJ0035?7201, QJ0047?7530, QJ0102?7546, and QJ0111?7249. Assuming that the SMC has a disklike central structure, but that it does not rotate, we determined a center-of-mass (CM) proper motion for the SMC from two of these fields, QJ0033?7028 and QJ0035?7201, located to the northwest and west of the main body of the SMC, respectively. Combining these latter proper motions with the CM proper motion presented by Costa et?al. (hereafter CMP09) for the SMC (from the field QJ0036?7227, located to the west of the main body of the SMC), we obtain a weighted mean of ?? cos ? = +0.93 ? 0.14?mas?yr?1 and ?? = ?1.25 ? 0.11?mas?yr?1. This CM proper motion is in good agreement with recent results by Piatek et?al. and Vieira et?al., and we are confident that it is a good representation of the bulk transverse motion of the SMC. On the contrary, the results we obtain from the fields QJ0047?7530 and QJ0102?7546, located to the south of the main body of the SMC, and the field QJ0111?7249, located to the east of its main body, seem to be affected by streaming motions. For this reason, we have not used the latter to determine the SMC CM proper motion. These streaming motions could be evidence that the SMC was tidally disrupted in a close encounter with the Large Magellanic Cloud (LMC). Complementing the SMC CM proper motions given here and in CMP09, with the currently accepted radial velocity of its center, we have derived its galactocentric (gc) velocity components, obtaining a weighted mean of V gc,t = +289 ? 25?km?s?1 and V gc,r = +14 ? 24?km?s?1. These velocities, together with the galactocentric velocity components given for the LMC in CMP09, imply a relative velocity between the LMC and SMC of 67 ? 42?km?s?1 for V rot,LMC = 50?km?s?1 and of 98 ? 48?km?s?1 for V rot,LMC = 120?km?s?1. Despite our large errors, these values are consistent with the standard assumption that the MCs are gravitationally bound to each other.

New Chains of Space Weather Monitoring Stations in China

To develop an understanding of near-Earth space’s response to solar activities and to eventually enhance the success of space weather predictions, it is crucial to make synergetic observations of the entire environment from the Sun to the Earth as a system. Since the beginning of the space era, direct observations by satellites have become a much needed means toward this end. However, ground-based observations also have advantages and serve as a counterpart to those made in space. For example, instruments on the ground are much less expensive and easier to repair than those on satellites. Groundbased observations provide continuous highresolution data not subject to the limitation of the downlink data rate from satellites to ground receiving stations. Also, because some observations have been made from Earth for hundreds of years, society has long and continuous records of quantities such as geomagnetic field variations, measurements of relative ionospheric opacity, and sunspot observations. Data from spacecraft, on the other hand, go back only a few decades. China has a total land area of about 9,600,000 square kilometers, with geomagnetic locations covering middle to low latitudes. The first geomagnetic observatory in China was constructed in Beijing in 1870 by Russians, but it ceased working in 1882. China briefly participated in the International Geophysical Year (1957–1958) and started to explore the upper atmosphere using rockets and balloons in the 1960s. Though research at government institutions and universities picked up in the late twentieth century, the ability to monitor the geospace environment and capture the evolution and characteristics of the weather in geospace above China is still insufficient today. Not only is China’s large population increasingly reliant on space-based technologies, but there are also not enough locations across the country where space weather conditions are monitored. This limits Chinese scientists’ understanding of the basic physical processes in geospace and their ability to make accurate predictions of adverse space weather for their country’s citizens. To acknowledge the needs of both basic science and useful space weather operations, a ground-based program to monitor China’s geospace environment is currently under way. Called the Meridian Space Weather Monitoring Project (or Chinese Meridian Project), the effort consists of a chain of 15 ground-based observatories located roughly along 120°E longitude and 30°N latitude. Each observatory is equipped with multiple instruments to measure key parameters such as the baseline and timevarying geomagnetic field, as well as the middle and upper atmosphere and ionosphere from about 20 to 1000 kilometers. Starting in 2011, the project will collect data for at least 11 years, providing the wide-range, continuous, and multiparameter data sets needed to guide model developments, which in turn will better describe and predict the characteristics and dynamics of the geospace environment.

Proper Motions of Local Group Dwarf Spheroidal Galaxies I: First Ground-Based Results for Fornax11Based on observations made with ESO Telescopes at the La Silla Observatory under program ID 060.A-9701, 065.N-0472, 066.B.0276, 074.B-0456, 076.B-0528, 079.B-0379, 080.B-0144, 081.B-0534, and 082.B-0034.

ABSTRACTIn this article we present in detail the methodology and the first results of a ground-based program to determine the absolute proper motion of the Fornax dwarf spheroidal galaxy. The proper motion was determined using bona fide Fornax star members measured with respect to a fiducial at-rest background spectroscopically confirmed quasar, QSO J0240-3434B. Our homogeneous measurements, based on this one quasar gives a value of (μα cos δ,μδ) = (0.64 ± 0.08,-0.01 ± 0.11) mas yr-1. There are only two other (astrometric) determinations for the transverse motion of Fornax: one based on a combination of plates and HST data, and another (of higher internal precision) based on HST data. We show that our proper motion errors are similar to those derived from HST measurements on individual QSOs. We provide evidence that, as far as we can determine it, our motion is not affected by magnitude, color, or other potential systematic effects. Last epoch measurements and reductions are underway for other four quasar fields of this galaxy, which, when combined, should yield proper motions with a weighted mean error of ∼50 μas yr-1, allowing us to place important constraints on the orbit of Fornax.

Sample Return Missions from Minor Bodies: Achievements, Future Plan and Observational Support

We are entering in a new era of space exploration signed by sample return missions. Since the Apollo and Luna Program, the study of extraterrestrial samples in laboratory is gathering an increased interest of the scientific community so that nowadays exploration program of the Solar System is characterized by swelling sample return missions. Beside lunar samples, the NASA Stardust mission was the first successful space mission that on 15 January 2006 brought to Earth solid extraterrestrial samples collected from comet 81P/Wild 2 coma. Grains were collected during cometary fly-by into aerogel and once on Earth have been extracted for laboratory analyses. In the coming two decades many space missions on going or under study will harvest samples from minor bodies. Measurements required for detailed analysis that cannot be performed from a robotic spacecraft, will be carried out on Earth laboratories with the highest analytical accuracy attainable so far. An intriguing objective for the next sample return missions is to understand the nature of organic compounds. Organic compounds found in Stardust grains even if processed to large extend during aerogel capturing are here reported. Major objectives of Marco Polo mission are reported. Various ground-based observational programs within the framework of general characterizations of families and classes, cometary–asteroid transition objects and NEOs with cometary albedo are discussed and linked to sample return mission.

A spectroscopic survey of the youngest field stars in the solar neighbourhood

We present the first results of a ground-based programme conducted on 1-4m class telescopes. Our sample consists of 1097 active and presumably young stars, all of them being optical counterparts of RASS X-ray sources in the northern hemisphere. We concentrate on the 704 optically brightest (V_Ticho<=9.5 mag) candidates. We acquired high-res spectroscopy in the Halpha/Li spectral regions for 426 of such stars without relevant literature data. We describe the sample and the observations and we start to discuss its physical properties. We used a cross-correlation technique and other tools to derive accurate radial/rotational velocities and to perform a spectral classification for both single and SB2 stars. The spectral subtraction technique was used to derive chromospheric activity levels and Li abundances. We estimated the fraction of young single stars and multiple systems in stellar soft X-ray surveys and the contamination by more evolved systems, like RS CVn's. We classified stars on the basis of Li abundance and give a glimpse of their sky distribution. The sample appears to be a mixture of young Pleiades-/Hyades- like stars plus an older Li-poor population (~1-2 Gyr). 7 stars with Li abundance compatible with the age of IC 2602 (~30 Myr) or younger were detected as well, although 2 appear to be Li-rich giants. The discovery of a large number of Li-rich giants is another outcome of this survey. The contamination of soft X-ray surveys by old systems in which the activity level is enhanced by tidal synchronisation is not negligible, especially for K-type stars. 5 stars with Li content close to the primordial abundance are probably associated with known moving groups in the solar neighbourhood. Some of them are PTTS candidates according to their positions in the HR diagram.

THE PROPER MOTION OF THE MAGELLANIC CLOUDS. I. FIRST RESULTS AND DESCRIPTION OF THE PROGRAM

We present the first results of a ground-based program to determine the proper motion of the Magellanic Clouds (MCs) relative to background quasars (QSO), being carried out using the Iréneé du Pont 2.5 m telescope at Las Campanas Observatory, Chile. Eleven QSO fields have been targeted in the Small Magellanic Cloud (SMC) over a time base of six years, and with seven epochs of observation. One quasar field was targeted in the Large Magellanic Cloud (LMC), over a time base of five years, and with six epochs of observation. The shorter time base in the case of the LMC is compensated by the much larger amount of high-quality astrometry frames that could be secured for the LMC quasar field (124 frames), compared to the SMC fields (an average of roughly 45 frames). In this paper, we present final results for field Q0557−6713 in the LMC and field Q0036−7227 in the SMC. From field Q0557−6713, we have obtained a measured proper motion of μαcos δ = +1.95 ± 0.13 mas yr−1, μδ = +0.43 ± 0.18 mas yr−1 for the LMC. From field Q0036−7227, we have obtained a measured proper motion of μα cosδ = +0.95 ± 0.29 mas yr−1, μδ = −1.14 ± 0.18 mas yr−1 for the SMC. Although we went through the full procedure for another SMC field (QJ0036−7225), on account of unsolvable astrometric difficulties caused by blending of the QSO image, it was impossible to derive a reliable proper motion. Current model rotation curves for the plane of the LMC indicate that the rotational velocity (Vrot) at the position of LMC field Q0557−6713 can be as low as 50 km s−1, or as high as 120 km s−1. A correction for perspective and rotation effects leads to a center of mass proper motion for the LMC of μα cosδ = +1.82 ± 0.13 mas yr−1, μδ = +0.39 ± 0.15 mas yr−1 (Vrot = 50 km s−1), and to μα cosδ = +1.61 ± 0.13 mas yr−1, μδ = +0.60 ± 0.15 mas yr−1 (Vrot = 120 km s−1). Assuming that the SMC has a disk-like central structure, but that it does not rotate, we obtain a center of mass proper motion for the SMC of μα cosδ = +1.03 ± 0.29 mas yr−1, μδ = −1.09 ± 0.18 mas yr−1. Our results are in reasonable agreement with most previous determinations of the proper motion of the MCs, including recent Hubble Space Telescope measurements. Complemented with published values of the radial velocity of the centers of the LMC and SMC, we have used our proper motions to derive the galactocentric (gc) velocity components of the MCs. For the LMC, we obtain Vgc,t = +315 ± 20 km s−1, Vgc,r = +86 ± 17 km s−1 (Vrot = 50 km s−1), and Vgc,t = +280 ± 24 km s−1, Vgc,r = +94 ± 17 km s−1 (Vrot = 120 km s−1). For the SMC, we obtain Vgc,t = +258 ± 50 km s−1, Vgc,r = +20 ± 44 km s−1. These velocities imply a relative velocity between the LMC and SMC of 84 ± 50 km s−1, for Vrot,LMC = 50 km s−1, and 62 ± 63 km s−1 for Vrot,LMC = 120 km s−1. Albeit our large errors, these values are not inconsistent with the standard assumption that the MCs are gravitationally bound to each other.

SMC in space and time: a project to study the evolution of the prototype interacting late-type dwarf galaxy

AbstractWe introduce the SMC in space and time, a large coordinated space and ground-based program to study star formation processes and history, as well as variable stars, structure, kinematics and chemical evolution of the whole SMC. Here, we present the Colour-Magnitude Diagrams (CMDs) resulting from HST/ACS photometry, aimed at deriving the star formation history (SFH) in six fields of the SMC. The fields are located in the central regions, in the stellar halo, and in the wing toward the LMC. The CMDs are very deep, well beyond the oldest Main Sequence Turn-Off, and will allow us to derive the SFH over the entire Hubble time.

New mechanisms for international coordination of large observing projects

AbstractProgress on many fronts in the study of the Milky Way requires major new imaging and/or spectroscopic surveys as well as coordinated ground-based programmes in support of space missions. The present uncoordinated planning and operation of the 2-4m (and some of the larger) telescopes across the world are an impediment to the efficient conduct of such programmes and the overall cost-effectiveness of the investments in astronomy. We briefly report on recent initiatives to improve the situation, notably the part played by the ASTRONET consortium in setting up a comprehensive long-term plan for the development of European astronomy.

The THEMIS Mission

The Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission is the fifth NASA Medium-class Explorer (MIDEX), launched on February 17, 2007 to determine the trigger and large-scale evolution of substorms. The mission employs five identical micro-satellites (hereafter termed “probes”) which line up along the Earth’s magnetotail to track the motion of particles, plasma and waves from one point to another and for the first time resolve space–time ambiguities in key regions of the magnetosphere on a global scale. The probes are equipped with comprehensive in-situ particles and fields instruments that measure the thermal and super-thermal ions and electrons, and electromagnetic fields from DC to beyond the electron cyclotron frequency in the regions of interest. The primary goal of THEMIS, which drove the mission design, is to elucidate which magnetotail process is responsible for substorm onset at the region where substorm auroras map (∼10 RE): (i) a local disruption of the plasma sheet current (current disruption) or (ii) the interaction of the current sheet with the rapid influx of plasma emanating from reconnection at ∼25 RE. However, the probes also traverse the radiation belts and the dayside magnetosphere, allowing THEMIS to address additional baseline objectives, namely: how the radiation belts are energized on time scales of 2–4 hours during the recovery phase of storms, and how the pristine solar wind’s interaction with upstream beams, waves and the bow shock affects Sun–Earth coupling. THEMIS’s open data policy, platform-independent dataset, open-source analysis software, automated plotting and dissemination of data within hours of receipt, dedicated ground-based observatory network and strong links to ancillary space-based and ground-based programs. promote a grass-roots integration of relevant NASA, NSF and international assets in the context of an international Heliophysics Observatory over the next decade. The mission has demonstrated spacecraft and mission design strategies ideal for Constellation-class missions and its science is complementary to Cluster and MMS. THEMIS, the first NASA micro-satellite constellation, is a technological pathfinder for future Sun-Earth Connections missions and a stepping stone towards understanding Space Weather.

Overview of the HST Contamination Engineering Program at 15 Years: A Cleanliness Metric for Success with Optical Satellites

Over the past two decades, the Hubble Space Telescope (HST) contamination control program has evolved from a ground-based integration program to a space-based science-sustaining program. On-orbit, the primary contamination requirement for the telescope was maintaining a low contamination flux in the optical path of the instrument. In addition, to maintain the scientific capability of the telescope, the contamination requirements and specific contamination controls from the second- and third-generation scientific instruments and orbital replacement units were captured within the HST contamination control program. Contamination controls involving the Orbiter, astronauts, and mission were developed for on-orbit operations and four servicing missions. Long-term on-orbit scientific data has shown that these contamination controls successfully protected the HST from contamination.