Major prospects of exoplanet astronomy with the World Space Observatory–UltraViolet mission

The success of the International Ultraviolet Explorer (IUE) first and then of the STIS and COS spectrographs on-board the Hubble Space Telescope (HST) demonstrate the impact that observations at UV wavelengths had and are having on modern astronomy. Several discoveries in the exoplanet field have been done at UV wavelengths. Nevertheless, the amount of data collected in this band is still limited both in terms of observed targets and time spent on each of them. For the next decade, the post-HST era, the only large (2-m class) space telescope capable of UV observations will be the World Space Observatory–UltraViolet (WSO–UV). In its characteristics, the WSO–UV mission is similar to that of HST, but all observing time will be dedicated to UV astronomy. In this work, we briefly outline the major prospects of the WSO–UV mission in terms of exoplanet studies. To the limits of the data and tools currently available, here we also compare the quality of key exoplanet data obtained in the far-UV and near-UV with HST (STIS and COS) to that expected to obtain with WSO–UV.     

The VOISE algorithm: a versatile tool for automatic segmentation of astronomical images

The auroras on Jupiter and Saturn can be studied with a high sensitivity and resolution by the Hubble Space Telescope ( HST ) ultraviolet (UV) and far-ultraviolet Space Telescope Imaging Spectrograph (STIS) and Advanced Camera for Surveys (ACS) instruments. We present results of automatic detection and segmentation of Jupiter's auroral emissions as observed by the HST ACS instrument with the VOronoi Image SEgmentation (VOISE). VOISE is a dynamic algorithm for partitioning the underlying pixel grid of an image into regions according to a prescribed homogeneity criterion. The algorithm consists of an iterative procedure that dynamically constructs a tessellation of the image plane based on a Voronoi diagram, until the intensity of the underlying image within each region is classified as homogeneous. The computed tessellations allow the extraction of quantitative information about the auroral features, such as mean intensity, latitudinal and longitudinal extents and length-scales. These outputs thus represent a more automated and objective method of characterizing auroral emissions than manual inspection.     

The cosmic origins spectrograph: capabilities and prelaunch performance

The Cosmic Origins Spectrograph (COS) is an ultraviolet spectrograph scheduled for installation in the Hubble Space Telescope (HST) during HST Servicing Mission 4, currently planned to occur in August 2008. COS was designed to maximize sensitivity to faint point sources, and will provide limiting sensitivities at moderate spectral resolutions (R～20,000) that are a factor of 2 to >10 times better than those provided by previous ultraviolet spectrographs on HST. Here, we present an overview of the some of the science areas that will be addressed by COS observations and provide a summary of the capabilities of COS and the expected on-orbit performance.     

Ultraviolet observations of comet Hale-Bopp

Ultraviolet spectroscopy and imaging of comet Hale-Bopp (C/1995 O1) were obtained from a variety of space platforms from shortly after the discovery of the comet through perihelion passage. Observations with the International Ultraviolet Explorer (IUE) and the Hubble Space Telescope (HST) spanned the range of 6.8 to 2.7 AU pre-perihelion, but IUE was decommissioned in September 1996 and HST was precluded from near-perihelion observations because of its solar avoidance constraint. In September 1996, observations were made by the Extreme Ultraviolet Explorer (EUVE) that showed the presence of soft X-rays offset from the optical center of the coma and provided a sensitive spectroscopic upper limit to the Ne/O abundance ratio. During the perihelion period NASA mounted a successful campaign of four sounding rockets that were launched at the White Sands Missile Range, New Mexico, between March 25 and April 8, 1997. The payloads included long-slit spectroscopy and ultraviolet imaging polarimetry. In addition, Hale-Bopp was observed near perihelion by ultraviolet instruments on orbiting spacecraft that were designed for solar or terrestrial observations. Observations with HST, using the Space Telescope Imaging Spectrograph (STIS), installed during the February 1997 servicing mission, resumed in August 1997. Intercomparison of the ultraviolet observations and comparison with the results on gas composition and activity from ground-based visible, infrared and radio observations may permit the resolution of many discrepant results present in the literature. This revised version was published online in July 2006 with corrections to the Cover Date.     

Early science results from the Cosmic Origins Spectrograph

The Cosmic Origins Spectrograph (COS) is an ultraviolet spectrograph installed on the Hubble Space Telescope during Servicing Mission Four. COS covers 1150–3200 Å at spectral resolutions up to R～18,000. COS is the most sensitive UV spectrograph to have flown on HST. In this paper, I present science results from the first nine months of COS science operations, focusing on how COS has enabled probes of cosmic origins, from star and planet formation to the large scale structure of the modern universe.     

Monitoring the scale factor of the PICARD SODISM instrument

The SODISM Telescope of the PICARD Space mission will perform diameter measurements by directly imaging the Sun on a CCD camera. An internal calibration system allows us to follow scale factor variations induced by instrument deformations resulting from temperature fluctuations on orbit or from others causes. We present this calibration system in this paper as well as some simulations on how to correct observations. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Cassini UVIS observations of Jupiter's auroral variability

The Cassini spacecraft Ultraviolet Imaging Spectrograph (UVIS) obtained observations of Jupiter's auroral emissions in H₂ band systems and H Lyman-α from day 275 of 2000 (October 1), to day 81 of 2001 (March 22). Much of the globally integrated auroral variability measured with UVIS can be explained simply in terms of the rotation of Jupiter's main auroral arcs with the planet. These arcs were also imaged by the Space Telescope Imaging Spectrograph (STIS) on Hubble Space Telescope (HST). However, several brightening events were seen by UVIS in which the global auroral output increased by a factor of 2-4. These events persisted over a number of hours and in one case can clearly be tied to a large solar coronal mass ejection event. The auroral UV emissions from these bursts also correspond to hectometric radio emission (0.5-16 MHz) increases reported by the Galileo Plasma Wave Spectrometer (PWS) and Cassini Radio and Plasma Wave Spectrometer (RPWS) experiments. In general, the hectometric radio data vary differently with longitude than the UV data because of radio wave beaming effects. The 2 largest events in the UVIS data were on 2000 day 280 (October 6) and on 2000 days 325-326 (November 20-21). The global brightening events on November 20-21 are compared with corresponding data on the interplanetary magnetic field, solar wind conditions, and energetic particle environment. ACE (Advanced Composition Explorer) solar wind data was numerically propagated from the Earth to Jupiter with an MHD code and compared to the observed event. A second class of brief auroral brightening events seen in HST (and probably UVIS) data that last for ∼2 min is associated with auroral flares inside the main auroral ovals. On January 8, 2001, from 18:45-19:35 UT UVIS H₂ band emissions from the north polar region varied quasiperiodically. The varying emissions, probably due to auroral flares inside the main auroral oval, are correlated with low-frequency quasiperiodic radio bursts in the 0.6-5 kHz Galileo PWS data.     

Doppler Tomography of X‐ray binaries

The Space Telescope Imaging Spectrograph (STIS) on HST provides the first ultraviolet data that are of sufficient spectral and temporal resolution to generate Doppler tomograms of X‐ray binaries.We show both optical and ultraviolet maps constructed for the intermediate mass system Hercules X‐1/HZ Her and the massive wind‐fed system SMC X‐1/SK160. We have used the maps and corresponding lightcurves as diagnostics with which to test the validity of published models for Hercules X‐1. We find that although the models are mostly able to explain the light curves they are not consistent with the full phase maps. We present simulations of Doppler maps of X‐ray lines that will be possible with the spectral and temporal resolution and substantial effective area of the next major X‐ray mission, Con‐X. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Two new systems with enhanced UV line flux ratios as indication of the evolution of cataclysmic variables

We present ultraviolet spectra of 62 cataclysmic variables observed with Hubble Space Telescope Space Telescope Imaging Spectrograph & Faint Object Spectrograph (HST STIS FOS) to diagnose cataclysmic variables with enhanced NV/C IV line flux ratios. We concentrated on calculating the line flux ratios of the above mentioned sample. We found that a number of cataclysmic variables reveal enhanced NV/C IV line flux ratios in agreement with the previous studies (de Martino and Gänsicke, 2009, Gänsicke et al., 2003). Also we found that two new systems (U SCO, V1974 CYG) reveal enhanced NV/C IV line flux ratios. Such anomalous line flux ratios confirmed that these CVs went through a phase of thermal timescale mass transfer (TTSMT) and now accrete CNO processed material from a companion stripped of its external layers (Gänsicke et al., 2003, Gänsicke, 2004, de Martino and Gänsicke, 2009).     

The European HST science data archive

The design of the Data Management Facility (DMF), the system to handle the data from HST, has been based on the concepts of modularity and flexibility, so that changes inevitably due to occur during the long lifetime of the project could be gracefully accomodated. At the Space Telescope European Coordinating Facility (ST-ECF), new constraints have led the archive group to evolve the system, so to allow a more efficient ingesting of the data imported from the Space Telescope Science Institute (STScI), an easier browsing of the HST catalogue of observations, and a more efficient servicing of archive researchers' retrieval requests. In this paper, the European Science Data Archive of HST data is described, with particular reference to dataflow, hardware and software system structure, operations, differences with DMF, and foreseen developments.Affiliated with the Astrophysics Division, Space Science Dept., ESAThe observations of the NASA/ESA Hubble Space Telescope are obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555.     

“Spektr-UF” project

The “Spektr-UF” project is intended for the design and development of a large space observatory operating in the ultraviolet (UV) band of the spectrum inaccessible for survey from the surface of the Earth. The main observatory instrument is a space telescope T-170M with a primary mirror 1.7 m in diameter; it will be equipped with high and low resolution spectrographs and cameras for high-quality UV imaging. In respect of capabilities, the project is similar to the American Hubble Space Telescope (HST), and exceeds the latter in some parameters. The project is included in the Russian Federal Space Program for the period 2006–2015. The launch is planned for 2016. The project is under development by the Lavochkin Association in cooperation with the Institute of Astronomy, Russian Academy of Sciences.     

Prospects for astrometry with the Hubble Space Telescope

The Hubble Space Telescope (HST), a large optical telescope having an aperture of 2.4 meters and a length of 8.8 meters, is being developed by the National Aeronautics and Space Administration. This telescope will be placed into earth orbit by the space shuttle. Astrometric observations with the HST are made using a Fine Guidance Sensor which is capable of measuring the position of one object relative to another with an accuracy of ±0.002 arcseconds. The astrometric user of HST will be provided with an Astrometric Data Reduction Software package (ADRS). The variety of astrometric problems to be investigated with HST is discussed.     

Hubble Space Telescope observations of SV Cam – I. The importance of unresolved star-spot distributions in light-curve fitting

We have used maximum entropy eclipse-mapping to recover images of the visual surface brightness distribution of the primary component of the RS CVn eclipsing binary SV Cam, using high-precision photometry data obtained during three primary eclipses with Space Telescope Imaging Spectrograph aboard the Hubble Space Telescope ( HST ). These were augmented by contemporaneous ground-based photometry secured around the rest of the orbit. The goal of these observations was to determine the filling factor and size distribution of star-spots too small to be resolved by Doppler imaging. The information content of the final image and the fit to the data were optimized with respect to various system parameters using the χ² landscape method, using an eclipse-mapping code that solves for large-scale spot coverage. It is only with the unprecedented photometric precision of the HST data (0.000 15 mag) that it is possible to see strong discontinuities at the four contact points in the residuals of the fit to the light curve. These features can only be removed from the residual light curve by the reduction of the photospheric temperature, to synthesize high unresolvable spot coverage, and the inclusion of a polar spot. We show that this spottedness of the stellar surface can have a significant impact on the determination of the stellar binary parameters and the fit to the light curve by reducing the secondary radius from  0.794 ± 0.009  to  0.727 ± 0.009 R_⊙  . This new technique can also be applied to other binary systems with high-precision spectrophotometric observations.     

Io's dayside SO2 atmosphere

An extensive set of HI Lyman-α images obtained with the Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph (STIS) from 1997-2001 has been analyzed to provide information about the spatial and temporal character of Io's SO₂ atmosphere. An atmospheric distribution map derived from the observations reveals that the sunlit SO₂ atmosphere is temporally stable on a global scale, with only small local changes. An anti-/sub-jovian asymmetry in the SO₂ distribution is present in all 5 years of the observations. The average daytime atmosphere is densest on the anti-jovian hemisphere in the equatorial regions, with a maximum equatorial column density of 5.0×¹⁰¹⁶ cm−2 at 140° longitude. The SO₂ atmosphere also has greater latitudinal extent on the anti-jovian hemisphere as compared to the sub-jovian. The atmospheric distribution appears to be best correlated with the location of hot spots and known volcanic plumes, although small number statistics for the plumes limits the correlation.     

High resolution spectroscopy in the far UV: Observations of the interstellar medium by IMAPS on ORFEUS-SPAS

The Interstellar Medium Absorption Profile Spectrograph (IMAPS) is an objectivegrating, echelle spectrograph built to observe the spectra of bright, hot stars over the spectral region 950–1150Å, below the wavelength coverage of HST. This instrument has a high wavelength resolving power, making it especially well suited for studies of interstellar absorption lines. Following a series of sounding rocket flights in the 1980's, IMAPS flew on its first Shuttle-launched orbital mission in September 1993, as a partner in the ORFEUS-SPAS program sponsored by the US and German Space Agencies, NASA and DARA.On ORFEUS-SPAS, IMAPS spent one day of orbital time observing the spectra of 10 O- and early B-type stars. In addition to outlining how IMAPS works, we document some special problems that had an influence on the data, and we explain the specific steps in data reduction that were employed to overcome them. This discussion serves as a basic source of information for people who may use archival data from this flight, as well as those who are interested in some specific properties of the data that will be presented in forthcoming research papers.IMAPS is scheduled to fly once again on ORFEUS-SPAS in late 1996. On this flight, 50% of the observing time available for IMAPS and two other spectrographs on the mission will be available to guest observers.     

STAGES: the Space Telescope A901/2 Galaxy Evolution Survey

We present an overview of the Space Telescope A901/2 Galaxy Evolution Survey (STAGES). STAGES is a multiwavelength project designed to probe physical drivers of galaxy evolution across a wide range of environments and luminosity. A complex multicluster system at   z ∼ 0.165  has been the subject of an 80-orbit F606W Hubble Space Telescope (HST) /Advanced Camera for Surveys (ACS) mosaic covering the full     span of the supercluster. Extensive multiwavelength observations with XMM–Newton , GALEX, Spitzer , 2dF, Giant Metrewave Radio Telescope and the 17-band COMBO-17 photometric redshift survey complement the HST imaging. Our survey goals include simultaneously linking galaxy morphology with other observables such as age, star formation rate, nuclear activity and stellar mass. In addition, with the multiwavelength data set and new high-resolution mass maps from gravitational lensing, we are able to disentangle the large-scale structure of the system. By examining all aspects of an environment we will be able to evaluate the relative importance of the dark matter haloes, the local galaxy density and the hot X-ray gas in driving galaxy transformation. This paper describes the HST imaging, data reduction and creation of a master catalogue. We perform the Sérsic fitting on the HST images and conduct associated simulations to quantify completeness. In addition, we present the COMBO-17 photometric redshift catalogue and estimates of stellar masses and star formation rates for this field. We define galaxy and cluster sample selection criteria, which will be the basis for forthcoming science analyses, and present a compilation of notable objects in the field. Finally, we describe the further multiwavelength observations and announce public access to the data and catalogues.     

The James Webb Space Telescope and its Infrared Detectors

The James Webb Space Telescope (JWST) was conceived as the scientific successor to the Hubble Space Telescope (HST) and Spitzer Space Telescope. The instrument suite provides broad wavelength coverage and capabilities aimed at four key science themes: 1) The end of the dark ages: first light and reionization, 2) The assembly of galaxies, 3) The birth of stars and protoplanetary systems, and 4) Planetary systems and the origins of life. To accomplish these ambitious goals, JWST's detectors provide state-of-the-art performance spanning the λ = 0.6–28 μm wavelength range. In this paper, we describe JWST with an emphasis on its infrared detectors.     

Heating of the intergalactic medium as a result of structure formation

We report observations of the dwarf star ε Eri (K2 V) made with the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope . The high sensitivity of the STIS instrument has allowed us to detect the magnetic dipole transitions of Fe  xii at 1242.00 and 1349.38 Å for the first time in a star other than the Sun. The width of the stronger line at 1242.00 Å has also been measured; such measurements are not possible for the permitted lines of Fe  xii in the extreme-ultraviolet. To within the accuracy of the measurements, the N  v and the Fe  xii lines occur at their rest wavelengths. Electron densities and linewidths have been measured from other transition region lines. Together, these can be used to investigate the non-thermal energy flux in the lower and upper transition regions, which is useful in constraining possible heating processes. The Fe  xii lines are also present in archival STIS spectra of other G/K-type dwarfs.     

World space observatory-ultraviolet among UV missions of the coming years

Continuous access to the UV domain has been considered of importance to astrophysicists and planetary scientists since the mid-sixties. However, the future of UV missions for the post-HST era is believed by a significant part of astronomical community to be less encouraging. We argue that key science problems of the coming years will require further development of UV observational technologies. Among these hot astrophysical issues are: the search for missing baryons, revealing the nature of astronomical engines, properties of atmospheres of exoplanets as well as of the planets of the Solar System etc. We give a brief review of UV-missions both in the past and in the future. We conclude that UV astronomy has a great future but the epoch of very large and efficient space UV facilities seems to be a prospect for the next decades. As to the current state of the UV instrumentation we think that this decade will be dominated by the HST and coming World Space Observatory-Ultraviolet (WSO-UV) with a 1.7 m UV-telescope onboard. The international WSO-UV mission is briefly described. It will allow high resolution/high sensitivity imaging and high/low resolution spectroscopy from the middle of the decade.