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UVSTAR, UltraViolet Spectrograph Telescope for Astronomical Research, operates in the 500–1250 A wave-band at 1 to 3 A resolution. Here we report on the EUV and FUV observations of the B2 II star Adara, the brightest EUV source in the sky, obtained by UVSTAR during the STS 69 and STS 95 missions. The discussion concerns 1) wavelength and flux calibration, 2) short term time variability of selected spectral features, 3) comparison with previous measurements in the EUV band and 4) comparison with model atmospheres.

A low-mass, low-cost photon-counting scientific payload has been developed and launched on a commercial microsatellite in order to study the near-UV night-sky background emission with a telescope nicknamed “Notte” and the Aurora emission with “Alba”. AURORA, this is the name of the experiment, will determine, with the “Notte” channel, the overall night-side photon background in the 300–400 nm spectral range, together with a particular 2 + N 2 line ( λ c =337 nm). The “Alba” channel, on the other hand, will study the Aurora emissions in four different spectral bands (FWHM=8.4–9.6 nm) centered on: 367 nm (continuum evaluation), 391 nm (1 − N + 2 ), 535 nm (continuum evaluation), 560 nm (OI). The instrument has been launched on the 26 September, 2000 from the Baikonur cosmodrome on a modified SS18 Dnepr-1 “Satan” rocket. The satellite orbit is nearly circular ( h apogee =648 km, e =0.0022), and the inclination of the orbital plane is 64.56°. An overview of the techniques adopted is given in this paper.

UVSTAR is an EUV spectral imager intended as a facility instrument devoted to solar system astronomy and to astronomy. It covers the wavelength range of 500 to 1250A, with sufficient spectral resolution to separate atomic emission lines and to form spectrally resolved images of extended plasma sources. Targets include the Io plasma torus at Jupiter, hot stars, planetary nebulae and extragalactic sources. UVSTAR will make useful measurements of emissions from the Earth's atmosphere as well. UVSTAR consists of a pair of telescopes and concave-grating spectrographs that cover the overlapping spectral ranges of 500–900Aand 850–1250A. The telescopes use two 30 cm diameter off-axis paraboloids having a focal length of 1.4 m. An image of the target is formed at the entrance slits of two concave grating spectrographs. The gratings provide dispersion and re-image the slits at the detectors, intensified CCDs. The readout format of the detectors can be chosen by computer, and three slit widths are selectable to adapt the instrument to specific tasks. The spectrograph package has internal gimbals which allow rotation of ±3° about each of two axes. Dedicated finding and tracking telescopes will acquire and track the target after rough pointing is achieved by orienting the Orbiter. Responsibilities for the implementation and utilization of UVSTAR are shared by groups the U.S. and Italy. UVSTAR is scheduled for flight in early 1994.

The CARSO laboratory has recently built a calibration bench for electro-optical qualification of CCD sensors. For the CCD characterization the following measurements are operative: linearity, quantum efficiency, charge transfer efficiency, photon-transfer curve, dark charge and pixel-to-pixel sensitivity nonuniformity. The optical system is essentially made of two different optical paths: the first produces a spot of a few microns diameter, the second gives a uniform beam. For a 98% uniformity illumination, an integrating sphere is also available. There is a choice of two lamps, tungsten and xenon, to illuminate the optical path. The CCD sensor is positioned on a three axis assembly which can be displaced with a resolution of 1 μm on three degrees of freedom. It is set into a thermo-cryostatic vacuum chamber that can maintain the temperature between −140 and +80°C with a stability better than 0.1°C. The bench permits a quasi-automatic control of the various components and interfaces different types of CCDs of different sizes (up to 2048×2048 pixels). Some results of characterization measurements of a Thomson TH7863 CCD are presented.

We propose to use the IEH (International Ultraviolet Hitchhiker), a multidisciplinary facility (Astronomy, Solar System, Earth's atmosphere) to be mounted on the Shuttle pallet as a Hitchhiker flight opportunity, in order to obtain 2D images in the EUV-FUV ((400÷1300) A) of the optical phenomena occurring in the neighborhood of the TSS satellite. These peculiar phenomena, not detectable during the first TSS mission, are primarily due to the interaction of a high-potential conductive body with the surrounding ionospheric plasma.

We report here on unique post-perihelion (2.3 AU) measurements of Comet Hale-Bopp in the FUV-range (950–1250 A) by means of the UVSTAR spectrometer from the space shuttle with the main purpose of searching for argon and other FUV emitters. New methods for separating the strong airglow emission at shuttle altitudes are here discussed in detail. Due to our low resolution (15 A) and S/N ratio the possible rocket-borne detection of argon near perihelion (0.9 AU) could not be confirmed. New species as N2 are suspected but difficult to separate from the strong airglow emission at shuttle altitudes. From the Lyα brightness (1.30± 0.08 kRy) a water production rate Q = 5.9 ± 0.4 × 1029 molecules s−1 could be derived and compared with other post-perihelion observations.

A light photon-counting scientific payload, named AURORA, has been developed and launched on a commercial microsatellite in order to study the near-UV night-sky background emission (channel Notte) and the Aurora (Alba). AURORA is mapping, with the Notte channel, the night-side photon background in the 300-400 nm spectral range, together with a particular 2+ nitrogen line ((lambda) = 337nm). These measurements are required in the framework of the Extreme Universe Space Observatory (EUSO) experiment, approved by the European Space Agency (ESA) for the phase A and to be flown on the International Space Station (ISS) in 2009. The Alba channel studies the Aurora emissions in four different spectral bands centered on: 367nm, 391nm, 535nm, 560nm (OI). The instrument has been integrated on the MEGSAT-1 satellite and launched, on the September, 26th 2000, from the Baikonur cosmodrome. The nearly circular Low Earth Orbit (LEO), with inclination of 64.56 degrees, fully includes the ISS ground track envelope. The satellite overall mass is about 60 kg. An overview of the techniques adopted, including detectors, front-end electronics, Central Processor Unit (CPU), is given in this paper, together with a brief report on the mission status and plans.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

SD2000 is a new photon counting MCP based detector. It consists of a single MCP, coated with a suitable photocathode, closely coupled to a Silicon Drift Detector (SDD). The electron clouds generated by the MCP channels are accelerated by a strong electric field applied and proximity focussed on the SDD, that works as a position sensitive read-out detector. The SDD, developed by the INFN laboratories in Trieste, is a butterfly Silicon Drift Detector with no metal deposition on its cathodes. The absence of metallization in the sensitive zone of the chamber allows the electron clouds to penetrate uniformly into the active region of the detector and to be revealed. A suitable front-end amplifier, that works as a charge preamplifier and a bipolar shaper, has been developed starting from SPICE simulations and tested. A proto-type of the detector has been realized and tested and the first results have been achieved and compared with the expected best performances of the detector.

We present the relevant results from three UVSTAR missions on STS69, STS85 and STS95. In particular we discuss three hot sub-dwarf star and ɛ CMa (500–1250 A) observations.

The characteristics of the fine pointing and tracking system of UVISS, UltraViolet Italian Space Surveyor, which is proposed to fly as an external payload attached to the ISS (International Space Station) Express Pallet is presented. The system is derived from the pointing system of the UVSTAR telescope that has flown three times on the Shuttle. The electro-optical architecture of the tracking telescope, including the ICCD detector and the computational unit based on a DSP board with direct high speed interface to the camera and the on-board stellar catalog is described. The simulations performed to determine the instrument expected tracking precision and performances considering the dynamics of the ISS are reported. Finally the utilization of a high frequency tracking error correction based on the detection of the spectrographs zero-th order signal is considered as an independent tracking error measurement which provides information and corrections of possible residual tracking errors and could be used for alignment check as well.

We present a feasibility study of a wide field UV imaging camera for the UV Italian Sky Surveyor (UVISS) under study by the Italian Space Agency as possible payload externally attached on an Express Pallet to the International Space Station. The camera will operate in the range 950 - 2700 angstrom, it will have a 1 square degree field of view with an expected angular resolution of about 3' at best. Two layouts are considered: the first is a camera based on the use of transmittance filters to select the bandpass of interest while the second one is based on the use of multilayers mirrors to define the bandpasses of the filters. In both options the detectors used will be intensified CCDs with an appropriate choice of photocathodes. Finally, we present some simulations to evaluate the performances of the camera.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The characteristics of the fine pointing and tracking system of UVISS, UltraViolet Italian Space Surveyor, which is proposed to fly as an external payload attached to the ISS (International Space Station) Express Pallet is presented. The system is derived from the pointing system of the UVSTAR telescope that has flown three times on the Shuttle. The electro-optical architecture of the tracking telescope, including the ICCD detector and the computational unit based on a DSP board with direct high speed interface to the camera and the on-board stellar catalog is described. The simulations performed to determine the instrument expected tracking precision and performances considering the dynamics of the ISS are reported. Finally the utilization of a high frequency tracking error correction based on the detection of the spectrographs zero-th order signal is considered as an independent tracking error measurement which provides information and corrections of possible residual tracking errors and could be used for alignment check as well.

A Mission into Hot Phenomena in the Universe is proposed by means of a small telescope of 50 cm aperture accommodated on the International Space Station. Two operating modes are envisaged: 3 angstrom dispersion imaging spectroscopy in the 90 - 320 nm range (1st priority) or wide field (1 degree) medium bandwidth imaging in the same range but Ly-(alpha) (2nd priority). It will use a pointing platform attached to an Express Pallet Adapter available to the Italian Space Agency (ASI) more than 4 - 6 months per year. During a life time of 6 yr focal plane instruments may be changed when on-ground refurbishment occurs. With reasonable exposure times hot thermal sources as faint as V equals 19 - 2 can be observed in the spectroscopy mode at 110 nm and active chromospheres on cool stars as faint as V equals 15 at 250 nm can be monitored. Assessment of FUV imaging is underway, possibly providing observations of hot sources as faint as V equals 21 - 22. Nominal uplift to ISS is set in Autumn 2005.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We present the characteristics of a star mapper, AMICA, which could be used for determining the pointing direction of external payloads mounted on the International Space Station. AMICA, which is complementary to the GPS attitude determination system provided by the ISS, is a stand alone system able to provide both the pointing direction in the inertial reference frame with arc-sec precision at a 1 Hz rate and the angular orientation of the stellar field with slightly lower precision. The star mapper is derived from the pointing system of the UVSTAR telescope that has flown three times on the Shuttle. We present a description of the AMICA optical and electronics architecture and its functionality. We also give a summary of the key pointing/tracking results obtained during the Shuttle missions. Finally we report on simulations performed to determine the instrument expected precision and performances, including the percentage of recognized stellar fields. AMICA is presently considered for flying in support ...

The discovery of the extreme energy cosmic rays (EERC) with energy greater than 1020 eV has opened a new research branch of astrophysics on both observational and interpretative point of views. Together with the EECR one has also to consider the neutrino component which, independently on its primary or secondary origin, can reach comparable energies. These particles can be detected through the giant showers (EAS) produced in the Earth atmosphere and the induced fluorescent molecular nitrogen emission. Observing the EECR 'signals' is very difficult; we need forefront technology or new developments. The main reason is that their flux is very weak, typically of the order of a few events/year/1000 km2 per EECR of E approximately equals 1020 eV. The proposed Airwatch mission, base don a single orbiting telescope which can measure both intensity and direction of the EAS, impose new concepts for the detectors; single photon sensitivity, fast response of the order of few microseconds with sampling times of tenths of nanoseconds, low noise and good S/N ratio, large area, adaptability to a curved surface. Fortunately the spatial resolution requirements are somehow relaxed. The peculiar characteristics of this application are such that no available detectors satisfies completely the requirements. Therefore the final detector has to be the result of a R and D program dedicated to the specific problem. In this paper we survey a number of possible detectors and identify their characteristics versus the Airwatch mission requirements.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

One of the most challenging tissues in Astroparticle Physics is represented today by the observation of the energy spectrum of the Extreme Energy Cosmic Radiation. The very existence of particles with energy above 1020 eV and of neutrinos of comparable energy raises fundamental scientific questions in connection with their origin and propagation in the interstellar/intergalactic space. These particles can be detected through the gain showers produced in the Earth Atmosphere. The shower development is accompanied by emission of fluorescence in the atmosphere, in particular that induced in Nitrogen with characteristics spectral lines in the UV. Following a first suggestion by J. Linsley in the early 1980's, taken over by Y/ Takahashi, the fluorescence observation can be advantageously carried out by space. By using wide angel optics with large collecting surface, we can monitor a target area of atmosphere of the order of millions square kilometers x sr and corresponding mass above 1013 tons, allowing the detection of the very small flux values typical of the EECR and making possible the search of the elusive high energy neutrinos. AIRWATCH follows this approach. We describe the main scientific goals for the investigation of the EECR, High Energy neutrinos and of the Gamma Ray Bursts, together with the relevant connections to the problem of their origin. The experimental framework is outlined and a description is given of the space mission and of the observational strategy.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

UVSTAR, UV Spectrograph Telescope for Astronomical Research operates in the 500-1200 angstrom waveband; it has capability for long slit spectral imaging of extended cosmic sources. UVSTAR has recently flown as a Hitchhiker-M payload on the STS 85 mission of the SHuttle Discovery. UVSTAR is a joint collaboration between the University of Arizona and the University of Trieste. The instrument consists of a movable platform and an optical system The platform provides fine pointing within +/- 3 degrees from the nominal view direction, which is near the shuttle +Y axis, i.e. perpendicular to the long axis of the Shuttle and in the plane of the wings. The optical system has two channels, each formed of a telescope and Rowland concave-grating spectrograph with intensified CCD detector. The first channel, FUV, operates in the 850-1250 angstrom spectral range, the second, EUV, has covered the 500-900 angstrom region. UVSTAR includes capabilities for independent target acquisition and tracking. Here we report FUV observations, obtained in August 1997, of the sdO star BD +28 degrees 4211 which is a secondary flux standard and of the central star of the planetary nebula NGC 246, a hot degenerate star which shows strong OVI lines in the optical region. The UVSTAR spectrum of NGC 246 displays remarkable P Cygni profiles indicating a very fast stellar wind.

UVSTAR is an EUV spectral imager intended as a facility instrument devoted to solar system and astronomy studies. It covers the wavelength range of 500 to 1250 angstrom, with sufficient spectral resolution to separate emission lines and to form spectrally resolved images of extended plasma sources. Targets include the Io plasma torus at Jupiter, hot stars, planetary nebulae and bright galaxies. UVSTAR consists of a pair of telescopes and concave grating spectrographs that cover the overlapping spectral ranges of 500 - 900 and 850 - 1250 angstrom. The telescopes use two 30 cm diameter off-axis paraboloids having a focal length of 1.5 m. An image of the target is formed at the entrance slits of the two concave grating spectrographs. The gratings provide dispersion and re-image the slits at the detectors, intensified CCDs. The readout format of the detectors can be chosen by computer, and three slit widths are selectable to adapt the instrument to specific tasks. UVSTAR has internal gimbals which allow rotation of +/- 3 degree(s) about each of two axes. Dedicated finding and tracking telescopes will acquire and track the target after rough pointing is achieved by orienting the orbiter. Responsibilities for implementation and utilization of UVSTAR are shared by groups in Italy and the U.S. The first of the five approved UVSTAR flights is scheduled for May 1995.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

UVSTAR is an EUV spectral imager intended as a facility instrument devoted to solar system and astronomy studies. It covers the wavelength range of 500 to 1250 angstrom, with sufficient spectral resolution to separate emission lines and to form spectrally resolved images of extended plasma sources. Targets include the Io plasma torus at Jupiter, hot stars, planetary nebulae and bright galaxies. UVSTAR consists of a pair of telescopes and concave grating spectrographs that cover the overlapping spectral ranges of 500-900 and 850-1250 angstrom. The telescopes use two 30 cm diameter off-axis paraboloids having focal length of 1.5 m. An image of the target is formed at the entrance slits of the two concave grating spectrographs. The gratings provide dispersion and re-image the slits at the detectors, intensified CCDs. The readout format of the detectors can be chosen by computer, and three slit widths are selectable to adapt the instrument to specific tasks. UVSTAR has internal gimbals which allow rotation of +/- 3 degree(s) about each of two axes. Dedicated finding and tracking telescopes will acquire and track the target after rough pointing is achieved by orienting the Orbiter. Responsibilities for implementation and utilization of UVSTAR are shared by groups in Italy and the U.S. The first of the five approved UVSTAR flights is scheduled on May 1995.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

This paper describes one of the research projects currently in progress at C.A.R.S.O. The goal is to develop space qualified Intensified CCD detectors for applications in different wavelength bands, from the visual to the UV and EUV, and the related control electronics. The required performances, high sensitivity and flexibility, allow to obtain spectral images of faint extended sources and to operate, simultaneously, multiple detectors, in order to respond to different scientific and operational tasks.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

SANTA MARIA is a program of international scope, being a collaboration between scientific groups in Italy, Spain and the United States. The experiment consists of a cooperative space project with the objective of designing, developing, launching, data processing and scientific exploitation of an astronomical satellite under the name of SANTA MARIA.

The concept of a new bidimensional photon-counting, MCPbased detector is presented together with estimates of imaging and dynamic range performances. The first results of tests on the position readout system, a silicon drift chamber, are also presented.

Software for star field identification and star pointing and tracking is described. The software will be implemented in the guiding system of UVSTAR, a spectrograph/telescope system for UV astronomy and planetary physics that will operate as a Hitchhiker payload on the Shuttle. The software work with the wide-field CCD camera and an on-board stellar catalog. It is capable of (1) providing high accuracy (better than 2 arcsec) attitude determination from coarse (± 3 deg) initial knowledge of the pointing direction and (2) pointing toward the target. It is capable of tracking at the same high accuracy with a processing time of less than a few hundredths of a second. Simulation of observations and various types of tests are also discussed.

UVSTAR (Ultraviolet Spectrograph Telescope for Astronomical Research) is an EUV spectral imager intended as a facility instrument devoted to solar system and stellar astronomy. It covers the wavelength range of 500 to 1250 A, with sufficient spectral resolution to separate atomic emission lines and to form spectrally resolved images of extended plasma sources. Targets include the lo plasma torus at Jupiter, hot stars, and planetary nebulae. UVSTAR will make useful measurements of emissions from Earth's atmosphere as well. UVSTAR consists of a pair of telescopes and concave-grating spectrographs that cover the overlapping spectral ranges of 500 to 900 and 850 to 1250 A. The telescopes use two 30-cm-diam off-axis paraboloids having a focal length of 1.4 m. An image of the target is formed at the entrance slits of two concave grating spectrographs. The gratings provide dispersion and reimage the slits at the detectors, intensified CCDs. The readout format of the detectors can be chosen by computer, and three slit widths are selectable to adapt the instrument to specific tasks. The spectrograph package has internal gimbals, which allow rotation of ±3 deg about each of two axes. Dedicated finding and tracking telescopes will acquire and track the target after rough pointing is achieved by orienting the Orbiter. Responsibilities for the implementation and utilization of UVSTAR are shared by groups in Italy and the United States. UVSTAR is scheduled for flight in early 1995, timed for an opportunity to observe the Jovian system.

The presence in the far-UV spectra of early-type stars of spectral lines of superionized atoms is argument of controversial debate among astronomers. Presently there is agreement on the non-radiative origin of these ions but not on the proposed mechanisms for their production nor on the proposed locations in the stellar atmosphere where they are abundant. Cassinelli et al. (1978) suggest that the Auger mechanism is operative in a cool wind blowing above a narrow corona to produce these ions; Lucy and White (1980) introduce radiative instabilities growing into hot blobs distributed across the stellar wind; Doazan and Thomas (1982) make these ions to be formed in both pre- and post-coronal, high temperature regions at low and high velocity respectively.

The ESA “Ultraviolet Bright Star Spectrophotometric Catalogue” (Jamar et al. 1976) and the “Catalogue of 0.2 A Resolution Far-ultraviolet Stellar Spectra Measured with Copernicus” (Snow and Jenkins 1976) have been used to try to separate, by means of simple diagrams, O-type stars belonging to different luminosity classes and having different temperatures. The ESA catalogue gives absolute fluxes for 43 O-type stars, mostly reddened, with a spectral resolution of 35–40 A, depending on the channel, in the wavelength range 1350–2550 A. The Copernicus catalogue gives spectra between 1000 and 1450 A for 17 O-type stars, with low reddening, at 0.2 A resolution.

This is a progress report on a study of the far-UV spectra of hot stars observed with the Voyager ultraviolet spectrometers (UVS); we discuss UV flux distribution and variability of a set of early type high luminosity stars.

In order to discuss the impact of IUE observations on studies of Be star phenomena, we must first address the question of what a Be star is. The fact that this is required says something significant about the field: Be stars represent an assortment of complex phenomena for which there is still no comprehensive theoretical understanding. If there were, we might have less trouble saying just what a Be star is.

The ESA “Ultraviolet Bright Star Spectrophotometric Catalogue” (Jamar et al. 1976) and the “Catalogue of 0.2 A Resolution Far-ultravio-let Stellar Spectra Measured with Copernicus” (Snow and Jenkins 1976) have been used to try to separate, by means of simple diagrams, O-type stars belonging to different luminosity classes and having different temperatures. The ESA catalogue gives absolute fluxes for 43 O-type stars, mostly reddened, with a spectral resolution of 35–40 A, depending on the channel, in the wavelength range 1350–2550 A. The Copernicus catalogue gives spectra between 1000 and 1450 A for 17 O-type stars, with low reddening, at 0.2 A resolution.

We propose an instrument to look for Extensive Air Showers (EAS) produced by Extremely High Energy Cosmic Rays (EHECR, E>1020 eV) from space (Airwatch concept) by observing nitrogen fluorescence radiation.

Collaboration de l'universite d'Arizona et de l'observatoire et universite de Trieste pour des observations astronomiques et planetaires entre 400 et 1300 A

The initial results of a program to investigate the far-UV (500-1700 A) spectra of Be stars using the Voyager ultraviolet spectrometers axe presented. Observations of eleven Be stars, with spectral types from B0 through B7, obtained between March 1979 and July 1984 are discussed. The Voyager resolution (∼15 A) allows only limited spectroscopic studies; shortward of 1150 A C III λ977 and LyJβ λ1025 are the most prominent spectral features. Two stars, γ Cas and 59 Cyg, showed enhanced C III λ977 absorption. The flux distributions of the Be stars were intercompared with those of reference stars with low projected rotational velocities and, in a parallel study, to predictions from rotating star models. The model calculations suggest that the observable effects of a high rotational velocity (V≳ 0.9 of critical velocity) on the flux distribution are small except in the FUV (λ < 1150A). The Voyager flux distributions were found to be indistinguishable from those of the low v sin i reference stars. No evidence was found for critical rotation in Be stars. All observations were consistent with Be stars rotating at less than 0.85 of critical velocity.

Low-dispersion 500-3200-A spectra of 20 OB stars are used to derive three individual extinction curves in the wavelength range 912-1200 A. The dependence of the intrinsic UV fluxes of OB stars on both spectral type and luminosity is demonstrated. UV color indices are proposed. The results confirm the previous finding that O star spectra are not significantly bluer than the spectrum of the B0 main-sequence star Upsilon Ori.