High resolution science with high redshift galaxies

We summarize the high-resolution science that has been done on high redshift galaxies with Adaptive Optics (AO) on the world’s largest ground-based facilities and with the Hubble Space Telescope (HST). These facilities complement each other. Ground-based AO provides better light gathering power and in principle better resolution than HST, giving it the edge in high spatial resolution imaging and high resolution spectroscopy. HST produces higher quality, more stable PSF’s over larger field-of-views in a much darker sky-background than ground-based AO, and yields deeper wide-field images and low-resolution spectra than the ground. Faint galaxies have steadily decreasing sizes at fainter fluxes and higher redshifts, reflecting the hierarchical formation of galaxies over cosmic time. HST has imaged this process in great structural detail to z  6, and ground-based AO and spectroscopy has provided measurements of their masses and other physical properties with cosmic time. Last, we review how the 6.5 m James Webb Space Telescope (JWST) will measure First Light, reionization, and galaxy assembly in the near–mid-IR after 2013.     

Science at the performance limits of the Hubble Space Telescope

As with any large telescope on the ground, HST will often be used at the limits of its performance capabilities. The actual performance will only be determined once HST is i n orbit, but detailed modeling based on mirror, structure, and control system characteristics gives a reasonable assessment of the expected performance. The purpose of this paper is to present (1) selected image characteristics expected for HST, (2) performance limits for selected instrument characteristics, and (3) examples of observations for which the performance limits are approached. Among the image features noted are point spread functions, encircled energy curves, and image diameters for selected wavelengths. Performance limits discussed include expected limiting magnitude and resolution of close point sources as a function of wavelength, each for selected camera focal ratios and pixel dimensions. Examples of observations discussed include a binary in which one component is faint and the detectability of a single luminous star at large distances.     

Physics of the impulsive phase of solar flares

The physics of the impulsive phase of solar flares is discussed in relation to high resolution microwave, hard X-ray and ultraviolet observations. High spatial resolution observations of the structure of microwave flaring loops and their interpretation in terms of arcades of loops as the sites of primary energy release are presented. Theoretical interpretation of the confinement of microwave producing energetic electrons in the coronal part of loops is discussed. High temporal and spatial resolution measurements in hard X-rays, as well as observations of the spectral evolution of the hard X-ray emission are presented. Observations of the relative locations of microwave and hard X-ray emitting regions are presented and their significance with respect to the energy release site and electron acceleration is discussed. The relative timing of the peaks of impulsive hard X-ray and microwave burst is discussed. The significance of ultraviolet measurements in obtaining the density of flaring regions is discussed. Possible diagnostics of impulsive phase onsets from cm-λ polarization data are presented, and the role of the emergence of new flux and of the current sheet formed between closed loops in producing impulsive energy release at centimeter wavelengths are analyzed. Decimeter and meter wave manifestations of preflash phase and millisecond pulsations at centimeter and decimeter wavelengths and the relevant physical processes involved are discussed.     

Far-infrared and submillimeter survey of the galactic center and nearby galactic plane

Maps are presented with 12′ resolution of the Galactic Center and adjacent galactic plane, from ?^II = 359° to ?^II = 5°. The data were obtained with the Steward Observatory cryogenically-cooled, balloon-borne telescope. The data are from channels filtered for a bandpass of 70 μm < γ < 110 μm and for a longpass of γ > 80 μm. For the typical effective temperature of 25 K of a galactic HII region at this spatial resolution, the effective wavelength of the channels are 93 μ and 145 μm. Continuous emission is mapped along the galactic plane in both wavelengths. There are two contrasts between the immediate vicinity of SgrA (?^π < 1°) and the galactic plane in general. Firstly, for ?^π > 1° the galactic plane narrows dramatically at 93 μm, while retaining its width at 145 μm. Secondly, the individual sources at ?^π > 1° (which we associate with HII regions) have greater peak brightness in the 145 μm channel than the 93 μm channel, while SgrA hasapproximately equal peak brightness in each. The maps demonstrate the importance of submillimeter wavelengths to galactic surveys.     

Soil moisture mapping over the Chinese Loess Plateau using ENVISAT/ASAR data

In this paper, we used the available algorithm for soil moisture estimation over LOPEX05 (the Loess Plateau land surface process Experiment (2005)) area. The available algorithm used ENVISAT/ASAR AP mode VV polarization observational data at a low incidence angle and ground measured soil moistures. The ground measurements were performed in the summer of the 2005 during the LOPEX05 field campaign. The validated results indicate that an average difference between the soil moistures estimated from the microwave remote sensing and ground measurements is less than 0.02 cm³/cm³, with a RMS error of 2.0%, and a maximum less than 0.04 cm³/cm³. The algorithm was applied to the surface soil moisture mapping later. The results show that this algorithm is suitable for monitoring soil moisture information of the agricultural fields over the Chinese Loess Plateau, when ground land cover situation and the resolution of imagery data are taken into account. However, we also find that there are large differences over the steep slope region, the edge of mesa. The results are not acceptable for surface soil moisture estimation in these regions. Thus, the surface soil moisture retrieval in the steep slope region of the Loess Plateau need to be further investigated in the future.     

A new window on the cosmos: The Stratospheric Observatory for Infrared Astronomy (SOFIA)

The Stratospheric Observatory for Infrared Astronomy (SOFIA) is a joint US/German Project to develop and operate a gyrostabilized 2.5-m telescope in a Boeing 747-SP. This observatory will allow astronomical observations from 0.3 μm to sub-millimeter wavelengths at stratospheric altitudes as high as 45,000 ft where the atmosphere is not only cloud-free, but largely transparent at infrared wavelengths. The dynamics and chemistry of interstellar matter, and the details of embedded star formation will be key science goals. In addition, SOFIA’s unique portability will enable large-telescope observations at sites required to observe transient phenomena and location specific events. SOFIA will offer the convenient accessibility of a ground-based telescope for servicing, maintenance, and regular technology upgrades, yet will also have many of the performance advantages of a space-based telescope. Initially, SOFIA will fly with nine first-generation focal plane instruments that include broad-band imagers, moderate resolution spectrographs that will resolve broad features from dust and large molecules, and high resolution spectrometers capable of studying the chemistry and detailed kinematics of molecular and atomic gas. First science flights will begin in 2010, leading to a full operations schedule of about 120 8–10 h flights per year by 2014. The next call for instrument development that can respond to scientifically exciting new technologies will be issued in 2010. We describe the SOFIA facility and outline the opportunities for observations by the general scientific community with cutting edge focal plane technology. We summarize the operational characteristics of the first-generation instruments and give specific examples of the types of fundamental scientific studies these instruments are expected to make.     

Simulation study for the determination of the lunar gravity field from PRARE-L tracking onboard the German LEO mission

A simulation study has been performed at GFZ Potsdam, which shows the anticipated improvement of the lunar gravity field model with respect to current (LP150Q model) or near-future (SELENE) knowledge in the framework of the planned German Lunar Explorations Orbiter (LEO) mission, based on PRARE-L (Precise Range And Range-rate Equipment – Lunar version) Satellite-to-Satellite (SST) and Satellite-Earth-Satellite (SEST) tracking observations. It is shown that the global mean error of the lunar gravity field can be reduced to less than 0.1 mGal at a spatial resolution of 50 km. In the spectral domain, this means a factor of 10 (long wavelengths) and some 100 (mid to short wavelengths) improvement as compared to predictions for SELENE or a factor of 1000 with respect to LP150Q. Furthermore, a higher spatial resolution of up to 28 km seems feasible and would correspond to a factor of 2–3 improvement of SELENE results. Moreover, PRARE-L is expected to derive the low-degree coefficients of the lunar gravity field with unprecedented accuracy. Considering long mission duration (at least 1 year is planned) this would allow for the first time a precise direct determination of the low-degree tidal Love numbers of the Moon and, in combination with high precision SEST, would provide an experimental basis to study relativistic effects such as the periselenium advance in the Earth–Moon system.     

Optical, X-ray and γ-ray observations of compact objects in globular clusters

In the past three years, a new era of study of globular clusters has begun with multiwavelength observations from the current generation of astronomical telescopes in space. We review the recent results obtained from our studies of compact binaries and x-ray sources in globulars with ROSAT and HST as well as our balloon-borne hard x-ray telescope EXITE and ground-based observations (CTIO). With ROSAT, we have obtained the most sensitive high resolution soft x-ray images of clusters which show multiple low luminosity sources in cluster cores that are likely indicative of the long-sought population of cataclysmic variables (CVs). We have obtained deep H images of two clusters with HST and found CV candidates for 3 of the ROSAT sources in the core of NGC 6397. New CTIO imaging and spectroscopy of two ‘dim source’ fields in ω-Cen are also described. With EXITE we carried out the first hard x-ray imaging observations of the cluster 47 Tuc; such studies can ultimately limit the populations of millisecond pulsars and pulsar emission mechanisms. A long ROSAT exposure on 47 Tuc also shows probable cluster diffuse emission, possibly due to hot gas from ablating millisecond pulsars. Multiwavelength studies of globular clusters may provide new constraints on problems as diverse as the origin of CVs and LMXBs and the origin of hot gas in globulars.     

The role of ultraviolet imaging in studies of resolved and unresolved young stellar populations. M31 and M33

We discuss the relevance of UV data in the detection and characterization of hot massive stars and young stellar populations in galaxies. We show results from recent extensive surveys in M31 and M33 with Hubble Space Telescope (HST) multi-wavelength data including UV filters, which imaged several regions at a linear resolution (projected) of less than half a pc in these galaxies, and from GALEX far-UV and near-UV wide-field, low-resolution imaging of the entire galaxies. Both datasets allow us to study the hierarchical structure of star formation: the youngest stellar groups are the most compact, and are often arranged within broader, sparser structures. The derived recent star-formation rates are rather similar for the two galaxies, when scaled for the respective areas. We show how uncertainties in metallicity and type of selective extinction for the internal reddening may affect the results, and how an appropriate complement of UV filters could reduce such uncertainties, and significantly alleviate some parameter degeneracies.     

Balloon-borne far-infrared spectrophotometry of the galactic center region

Far-infrared observations of the Galactic Center have been carried through with the MPE Im balloon-borne telescope “Golden Dragon”. The measurements are composed of photometric scanning (33–95 μm) of the inner 4′×4′ and low resolution spectroscopy (δ^ν = 10 cm^?1) of the center and of a position approximately 1.5′ to the north. A Mars spectrum has been obtained for calibration. The spatial resolution of the photometry map is increased using the Maximum Entropy Method and the resulting map is compared to other observations in the same and other spectral regions. A clear asymmetry in the ring-like structure around the center indicates the presence of noncircular motions. The shape of the spectra is fairly smooth with at least no prominent dust features. A simple modelling shows a drastic increase of column density within 2 pc from the center and a modest drop over the next 3 pc to the north.     

A reflectance spectra-based approach to mapping salt fields using PCA-fused Landsat TM data

In this paper a method based on in situ measured reflectance spectra was developed for accurately mapping salt fields in the Taibei Salt Farm in Lianyungang City of East China. After radiometric correction and geometric rectification, six multispectral ETM+ bands were fused with the panchromatic band via principal components analysis (PCA). The fused data were used to map salt fields in the farm. Salt fields were mapped 91.95% correctly in comparison with ground statistics from raw multispectral bands. This accuracy level rose to 96.4% with the use of the panchromatic band (15 m resolution). However, PCA-fused data produced the highest accuracy of 98.8%. At the zone level, coarse resolution data resulted in an accuracy of 98.93% for crystallization ponds, but only 82.68% for condensation ponds. Use of the panchromatic band alone improved the accuracy for condensation ponds but decreased the accuracy for crystallization and evaporation ponds. Results derived from PCA-fused data are highly consistent with the ground statistics at a discrepancy between 0.35% for evaporation zone and 1.80% for condensation zone. It is concluded that a fine spectral resolution is important to separation of ponds of a varying salt content while a fine spatial resolution is important to their mapped area. Ponds of a lower salt content can be mapped more accurately from fused data than from raw spectral bands.     

Where does the heliospheric modulation of galactic cosmic rays start?

The long outstanding question of where the heliospheric (solar) modulation of galactic cosmic rays actually begins, in terms of spatial position, as well as at what high kinetic energy, can now be answered. Both answers are possible by using the results of an advanced numerical model, together with appropriate observations. Voyager 1 has been exploring the outskirts of the heliosphere and is presently entering what can be called the very local interstellar medium. It has been generally expected, and accepted, that once the heliopause is crossed, the local interstellar spectrum (LIS) should be measured in situ by the Voyager spacecraft. However, we show that this may not be the case and that modulation effects on galactic cosmic rays can persist well beyond the heliopause. For example, proton observations at 100 MeV close to the heliopause can be lower by ∼$\sim$25% to 40% than the LIS, depending on solar modulation conditions. It is also illustrated quantitatively that significant solar modulation diminishes above ∼$\sim$50 GeV at Earth. It is found that cosmic ray observations above this energy contain less that 5%$5\%$ solar modulation effects and should therefore reflect the LIS for galactic cosmic rays. Input spectra, in other words the very LIS, for solar modulation models are now constrained by in situ observations and can therefore not any longer be treated arbitrarily. It is also possible for the first time to determine the lower limit of the very LIS from a few MeV/nuc to very high energies.     

Photoelectron flux variations observed from the FAST satellite

This paper examines high resolution (ΔE/E = 0.15) photoelectron energy spectra from 10 eV to 1 keV, created by solar irradiances between 1.2 and 120 nm. The observations were made from the FAST satellite at ∼3000 km, equatorward of the auroral oval for the July–August, 2002 solar rotation. These data are compared with the solar irradiance observed by the Solar EUV Experiment (SEE) on the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite and fluxes calculated using the Field Line Interhemispheric Plasma (FLIP) code. The 41 eV photoelectron flux, which corresponds to solar EUV fluxes near 20 nm, shows a clear solar rotation variation in very good agreement with the EUV flux measurements. This offers the possibility that the 41 eV photoelectron flux could be used as a check on measured solar EUV fluxes near 20 nm. Because of unexpected noise, the solar rotation signal is not evident in the integral photoelectron flux between 156 and 1000 eV corresponding to EUV wavelengths between 0.1 and 7 nm measured by the SEE instrument. Examination of daily averaged photoelectron fluxes at energies between 25 and 500 eV show significant changes in the photoelectron spectra in response X and M class flares. The intensity of photoelectrons produced in this energy region is primarily due to two very narrow EUV wavelength regions at 2.3 and 3 nm driving Auger photoionization in O at 500 eV and N₂ at ∼360 eV. Comparison of calculated and daily averaged electron fluxes shows that the HEUVAC model solar spectrum used in the FLIP code does not reproduce the observed variations in photoelectron intensity. In principle, the 21 discrete photoelectron energy channels could be used to improve the reliability of the solar EUV fluxes at 2.3 and 3 nm inferred from broad band observations. In practice, orbital biases in the way the data were accumulated and/or noise signals arising from natural and anthropogenic longitudinally restricted sources of ionization complicate the application of this technique.     

Synergetic retrieval of terrestrial AOD from MODIS images of twin satellites Terra and Aqua

Aerosol optical depth (AOD) is one of the most important indicators of atmospheric pollution. It can be retrieved from satellite imagery using several established methods, such as the dark dense vegetation method and the deep blue algorithm. All of these methods require estimation of surface reflectance prior to retrieval, and are applicable to a certain pre-designated type of surface cover. Such limitations can be overcome by using a synergetic method of retrieval proposed in this study. This innovative method is based on the fact that the ratio K of surface reflectance at different angles/geometries is independent of wavelength as reported by Flowerdew and Haigh (1995). An atmospheric radiative transfer model was then established and resolved with the assistance of the ratio K obtained from two Moderate Resolution Imaging Spectroradiometer (MODIS) spectral bands acquired from the twin satellites of Terra and Aqua whose overpass is separated by three hours. This synergetic method of retrieval was tested with 20 pairs of MODIS images. The retrieved AOD was validated against the ground observed AOD at the Taihu station of the AErosol RObotic NETwork (AERONET). It is found that they are correlated with the observations at a coefficient of 0.828 at 0.47 μm and 0.921 at 0.66 μm wavelengths. The retrieved AOD has a mean relative error of 25.47% at 0.47 μm and 24.3% at 0.66 μm. Of the 20 samples, 15 and 17 fall within two standard error of the line based observed AOD data on the ground at the 0.47 μm and 0.66 μm, respectively. These results indicate that this synergetic method can be used to reliably retrieve AOD from the twin satellites MODIS images, namely Terra and Aqua. It is not necessary to determine surface reflectance first.     

Hard X-ray and metric/decimetric spatially resolvedobservations of the 10 April 2002 solar flare

The GOES M8.2 flare on 10 April 2002 at 1230 UT was observed at X-ray wavelengths by RHESSI and atmetric/decimetric wavelengths by the Nançay Radioheliograph (NRH). We discuss the temporal evolution of X-ray sources together with the evolution of the radio emission sites observed at different coronal heights by the NRH. While the first strong HXR peak at energies above 50 keV arises from energy release in compact magnetic structures (with spatial scales of a few 10⁴ km) and is not associated with strong radio emission, the second one leads to energy release in magnetic structures with scales larger than 10⁵ km and is associated with intense decimetric/metric and dekametric emissions. We discuss these observations in the context of the acceleration sites of energetic electrons interacting at the Sun and of escaping ones.     

Observations of the Galilean satellites of Jupiter from Earth orbit

In April 1972 OAO-2 obtained broadband filter measurements of the Galilean satellites from 2100 to 4300 Å. All four bodies were shown to have low albedos declining towards shorter wavelengths, thus constraining the proportions of their surfaces that could be covered by reflective frosts. Although the vast data return from Voyager spacecraft has for the first time permitted a detailed comparison of Galilean satellites with terrestrial planets, it has not removed the need for continuing long time-base observations of the former. Since January 1978, IUE has repeatedly obtained Galilean spectra within the range 1150 to 3200 Å. Observations of Io have placed an upper limit on the global abundance of SO₂ in its atmosphere. Spectral variations with phase have allowed spatial mapping of surface reflectance in the case of Io, and may enable volcanic activity to be monitored.     

Assimilation of Mars Global Surveyor meteorological data

The Mars Global Surveyor (MGS) Mission is more than just a return to Mars. It represents a qualitatively new type of planetary mission. This is true not only because of the capable instrumentation aboard the spacecraft and the choice of orbit and data rate, but also because of a major beneficial change in our understanding of the interplay between observation and modeling. The Thermal Emission Spectrometer (TES), for example, is capable of taking thousands of infrared spectra per day. The 15 micrometer carbon dioxide band in these spectra can be inverted to obtain atmospheric temperature profiles, amounting to some 15,000–25,000 separate measurements each day. In addition, radio occultations produce fewer, but much higher resolution, temperature and pressure profiles. How is such a quantity of data to be handled? Clearly not in the old-fashioned manner in which a single profile is studied at great length and detail. The quantity of data does not allow this; and the quality of the data does not support it. (A single atmospheric profile is bound to contain small-scale spatial and temporal variation—e.g., gravity waves—that cannot be removed unambiguously, as well as possible errors due to noise in the observations or non-uniqueness of the inversions). Furthermore, much of the atmospheric science of interest (winds, for example) depends on quantities like horizontal temperature gradients that are not directly observed. Instead, the data should be examined collectively with the aid of a model that incorporates our knowledge of the governing physics. Described here are the first results of such a data assimilation exercise with TES observations during the aerobraking hiatus period at L_s ≈ 200.     

SPOT 4 VEGETATION system: Association with high resolution data for multiscale studies

The SPOT 4 VEGETATION system is a joint program of the European Commission, France, Sweden, Belgium and Italy, to be launched in 1997. It will provide global and frequent measurements adapted to biosphere studies, especially for monitoring of the biophysical processes of the vegetation canopies. Information derived from its measurements will allow operational and long term studies related either to the production of agricultural areas or to the functioning of ecosystems, to their interaction with the atmosphere and climatic changes. The design of the entire system, from the instrument to the ground segment, was aimed at providing direct capability for multitemporal analysis of surface reflectance measurements at medium spatial resolution as well as for association with high spatial resolution data sets available from the SPOT High Resolution instrument or from other systems. Nature and quality of products delivered by the system were especially tailored taking into account the development of research done on previous systems and the needs for characterizing the temporal dynamic aspects of biosphere processes and relating regional or ecosystems' parameters to local parameters less affected by spatial heterogeneity.     

Equatorial cloud properties on Venus from pioneer orbiter infrared observations

Infrared observations of Venus from the Pioneer Orbiter have been used to study the limb darkening properties of the cloud tops at wavelengths and spatial resolutions not previously attained. The preliminary results show evidence for an extensive haze feature over the equatorial morning terminator and for small amounts of a far-infrared absorber concentrated near local noon, also near the equator. The evidence for these features is reviewed and their possible origins briefly discussed.     

Goddard Robotic Telescope – Optical follow-up of GRBs and coordinated observations of AGNs

Since it is not possible to predict when a Gamma-Ray Burst (GRB) will occur or when Active Galactic Nucleus (AGN) flaring activity starts, follow-up/monitoring ground telescopes must be located as uniformly as possible all over the world in order to collect data simultaneously with Fermi and Swift detections. However, there is a distinct gap in follow-up coverage of telescopes in the eastern U.S. region based on the operations of Swift. Motivated by this fact, we have constructed a 14″ fully automated optical robotic telescope, Goddard Robotic Telescope (GRT), at the Goddard Geophysical and Astronomical Observatory. The aims of our robotic telescope are (1) to follow-up Swift/Fermi GRBs and (2) to perform the coordinated optical observations of Fermi Large Area Telescope (LAT) AGN. Our telescope system consists of off-the-shelf hardware. With the focal reducer, we are able to match the field of view of Swift narrow instruments (20′ × 20′). We started scientific observations in mid-November 2008 and GRT has been fully remotely operated since August 2009. The 3σ upper limit in a 30 s exposure in the R filter is ∼15.4 mag; however, we can reach to ∼18 mag in a 600 s exposures. Due to the weather condition at the telescope site, our observing efficiency is 30–40% on average.