WSO–UV project Mikhail Sachkova,∗, Boris Shustova , and Ana Ines G´omez de Castrob a
b
Institute of Astronomy RAS, 48 Pyatnitskaya str., 119017 Moscow, Russia AEGORA, Fac. of Mathematics, Universidad Complutense de Madrid, Plaza de Ciencias 3, 28040 Madrid, Spain
Abstract During last three decades, astronomers have enjoyed continuous access to the 100–300 nm ultraviolet (UV) spectral range where the resonance transitions of the most abundant atoms and ions (at temperatures between 3 000 and 300 000 K) reside. This UV range is not accessible from ground-based facilities. The successful International Ultraviolet Explorer (IUE) observatory, the Russian ASTRON mission and successor instruments such as the Galaxy Evolution Explorer (GALEX) mission or the COS and STIS spectrographs on-board the Hubble Space Telescope (HST) prove the major impact of observations in the UV wavelength range in modern astronomy. Future access to space-based observatories is expected to be very limited. For the next decade, the post–HST era, the World Space Observatory – Ultraviolet (WSO–UV) will be the only 2-m class UV telescope with capabilities similar to the HST. WSO–UV will be equipped with instruments for imaging and spectroscopy and it will be a facility dedicated, full-time, to UV astronomy. In this article, we briefly outline the current status of the WSO–UV mission and the science management plan. Keywords: instrumentation: spectrographs, space vehicles: instruments, ultraviolet: general 1. Introduction The World Space Observatory – Ultraviolet is the solution to the problem of future access to UV spectroscopy. WSO–UV is ideally placed in time, ∗
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Preprint submitted to Advances in Space Research
December 9, 2013
and essential, to provide follow-up studies of the large number of UV sources observed by the GALEX sky survey. The WSO–UV is a Russian led mission with important Spanish participation both in instrumentation (ISSIS) and in the ground segment. The project has entered Phase C with a planned launch in 2017. In this article we describe the WSO–UV key science issues, the WSO–UV project with its general objectives and main features, the details and status of instrumentation, WSO–UV ground segment and science management plan. 2. WSO–UV Key Science Issues As agreed by the Agencies funding the project, the science drivers of the WSO–UV observatory are: • The determination of the diffuse baryonic content in the Universe and its chemical evolution. The main topics will be the investigation of baryonic content in warm and hot Inter Galactic Matter, of damped Lyman-α systems, the role of starburts and the formation of galaxies. • The physics of accretion and outflows: stars, black holes, and all those objects dominated by accretion mechanisms. The efficiency and time scales of the phenomena will be studied, together with the role of the radiation pressure and the disk instabilities. • The study of the formation and evolution of the Milky Way. The Milky Way history could be tracked through observations complementary to those obtained by the GAIA mission. • The investigation of the extrasolar planetary atmospheres and astrochemistry in presence of strong UV radiation fields. See G´omez de Castro et al. (2009) for more details. 3. WSO–UV mission WSO–UV consists of a 1.7 m aperture telescope equipped with instrumentation to carry out high resolution spectroscopy, long-slit low resolution spectroscopy and direct sky imaging. Spain and Russia develop jointly the WSO–UV Ground Segment (GS). Both countries will control the Mission 2
and will provide the project with the satellite tracking stations. The project launch date is 2017. The nominal lifetime is 5 years with an expected extension up to 10 years. The ground segment architecture is to be based on a modular approach, relying on a common framework able to run different subsystems developed by different agencies and institutions. These modules can be upgraded over several years (Sachkov, 2007). The T-170M telescope (see Fig. 1) is designed as a powerful radiation collector for spectroscopy and direct images at 115–310 nm (Sachkov et al., 2009). It is a Ritchey-Chr´etien reflective optical design with a focal length of 17 m. The telescope provides an accessible field of view of 30 arcmin on the telescope focal surface (Shustov et al., 2009, 2011). The telescope passed its vibration tests in 2012 (Fig. 2). The T-170M telescope has inherited the successful experience gained during the Soviet ASTRON project. The telescope is under responsibility of Russia.
Figure 1: The T-170M telescope scheme
WSO–UV will use the Russian NAVIGATOR platform which was designed in Lavochkin Science & Technology Association (Russia) as a unified unit for several missions including Radioastron (successfully launched 2011) and 3
Figure 2: The T-170M telescope model for vibration tests at the Lavochkin Science & Technology Association
Spektrum-Roentgen-Gamma (launch scheduled 2014) and WSO–UV. The platform is also used for commercial satellites, which have successfully proved the concept. The platform weighs 1300 kg and has a payload mass of 1600 kg. With assistance through the fine guidance system the pointing stabilization is about 0.03 arcseconds. The bus provides 300 W power for all instruments and a data download rate of up to 4 Mbit/s. WSO–UV will be launched from Baikonur (Kazakhstan) with a Proton rocket. The factor of 2 difference in collecting surface between HST and WSO– UV is compensated by the much more efficient geosynchronous orbit which has an inclination of 51.o 6. Earth occultation periods will be short and the orbital period will allow long term monitoring and rapid access to targets of opportunity. Geosynchronous orbit was chosen based mainly on launcher capabilities, residence time in the Earth Radiation Belts, continuous visibility zones, minimum duration of the Earth shadow periods, stability of the orbit and available technical equipment of the Space and Ground Segments for radio communication. WSO–UV has been developed as a multipurpose, observatory-type mission (Shustov et al., 2011) carrying instrumentation for UV imaging and spectroscopy (Fig. 3).
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Figure 3: WSO–UV Instrument Compartment
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Figure 4: WSO-UV Spectrographs (WUVS)
4. WUVS: WSO–UV Spectrographs The WSO–UV spectrographs (WUVS) consists of a set of three instruments (Fig. 4): – far UV high resolution spectrograph (VUVES) that will carry out echell´e spectroscopy with resolution about 50 000 in the 115–176 nm range. – near UV high resolution spectrograph (UVES) to carry out echell´e spectroscopy with resolution about 50 000 in the 174–310 nm range. – Long Slit Spectrograph (LSS) that will provide low resolution (R=1000), long slit spectroscopy in the 115–310 range. The spatial resolution will be 0.5 arcsec. Since 2012, the development of WUVS has been fully under the responsibility of Russia (see Kappelmann et al., 2006; Reutlinger et al., 2011). All spectrographs will be equipped with CCD detectors. Their characteristics will allow detailed spectral observations and analysis of objects up to V = 17m (Klochkova et al., 2009), see Fig. 5 and Fig. 6 for their radiometric 6
Figure 5: WUVS efficiency
performance. The prospects of WSO–UV for stellar spectroscopic studies are described in Sachkov (2010). 5. ISSIS: Imaging and Slitless Spectroscopy Instrument for Surveys The WSO–UV Imaging and Slitless Spectroscopy Instrument for Surveys (ISSIS) is a multipurpose instrument with a mode selector wheel that allows imaging and slitless spectroscopy in the 115–320 nm spectral range. The instrument is equipped with two MCP detectors, with CsI and CsTe photocathods for FUV and NUV observations, respectively. The resolution in the slitless spectroscopy mode is about 500 and the spatial resolution is less than 0.1 arcsec, relying in the telescope pointing accuracy (see Section 4). ISSIS will be the first UV imager located in such a high altitude orbit. This has the advantage of being above the geocoronal emission and thus dimishing the UV background significantly. The current design was approved in the Preliminary Design Review (PDR) in June 2012 (Fig. 7). Construction of the ISSIS Instrument is the responsibility of Spain (G´omez de Castro et al., 2011, 2013). 7
Figure 6: Comparison of the expected effective area of the WSO–UV Spectrographs, UVES and VUVES, and HST/COS and HST/STIS
6. WSO–UV Science Management Plan WSO–UV will work as a targeted space observatory with a core program, an open program for scientific projects from the world-wide community and national (funding bodies) programs for the project partners (Malkov et al., 2011). For the core and open programs the projects will be selected on the basis of their scientific excellence by a Time Allocation Committee (TAC), appointed by the Agencies funding the project The Core Program (CP) of scientific observations with the WSO–UV is defined to carry out high impact or legacy projects that require large amounts of observing time. The Open Program (OP) consists of astronomical observations obtained with the WSO–UV by astronomers who may or may not belong to the WSO– UV international consortium. Guaranteed time to the WSO-UV project Funding Bodies (FB) is managed through the FB Program . The membership of the OP TAC will be renewed every two years. The CP TAC will be the same as the OP TAC selected for the first two years of 8
Figure 7: WSO-UV Imagers (ISSIS)
Figure 8: The ISSIS Structural Thermal Model
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the WSO–UV mission. National TACs will select the scientific programs for the FB Programs. The time for astronomical observations will be distributed according to the following scheme: during the first and second years: 50% of the total time will be granted to the CP, 48% to the FBP and 2% to the Director Discretionary Time (DDT). CP shall be completed within the first 2 years of the mission. For the following years: 58% of the observing time will go to the FBP, 40% OT, 2% DDT. 7. WSO–UV Ground Segment The WSO–UV Ground Segment (GS) is composed of all the infrastructure and facilities involved in the preparation and execution of the WSO–UV mission operations, which typically encompass real-time monitoring and control of the spacecraft, telescope and instruments as well as reception, processing and storage of the scientific data. There will be two complete GS systems: the Russian one will be located in Moscow (Lavochkin Science & Technology Association and Institute of Astronomy of the RAS), and the Spanish one will be sited at Madrid. The satellite operations will be shared between both Ground Control Centers, transferring the mission control from one center to the other on a regular basis. The science operations system and a fraction of the mission operations system are part of the Spanish contribution to the WSO–UV. The Remote Proposal System, the Science Data Processing System, the Science Archive and the Scheduling systems are defined by the international science team composed of Spanish and Russian Science Support Teams based at the Universidad Complutense de Madrid (UCM) and Institute of Astronomy of the Russian Academy of Science (INASAN). The Science Team is part of the man power of the GS, and is responsible of laying the foundation of and supervising all the operations related to the mission primary users: the scientists. At mission level, the Science Team constitutes the core of the future WSO–UV international observatory. One of the main challenges of GS development is the management of shared information between both centers and the alignment of all the operational data (telemetry, telecommand and planning) according to the operational shifts (see Lozano et al., 2010; G´omez de Castro et al., 2013).
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8. Conclusions The World Space Observatory–Ultraviolet (WSO–UV) is an international space mission born as a response to the need for UV facilities by the astronomical community. WSO–UV will be the only 2-meter class UV mission after the end of HST operations, and will guarantee access to UV wavelength domain. The project is managed by an international consortium led by the Federal Space Agency (ROSCOSMOS, Russia). Current information on the WSO–UV project can be found at the official web site: http://wso-uv.org. 9. Acknowledgements The Spanish participation in the WSO-UV project is being funded by the Ministry of Industry, Energy and Tourism of Spain. The science team acknowledges the support of the Ministry of Economy and Competitivity through grants AYA2008-06423-C03-01 and AYA2011-29754-C03-C01. G´omez de Castro, A. I., Pagano, I., Sachkov, M., et al., Science with the World Space Observatory - Ultraviolet, in: Chavez, M., Bertone, E., RosaGonzalez, D., Rodrigez-Merino, L. H. New Quests in Stellar Astrophysics. II. Ultraviolet Properties of Evolved Stellar Populations Springer, Berlin, p.319 - 327, 2009. G´omez de Castro, A. I., Ma´ız, J., Rodrigez, P., et al., The imaging and slitless spectroscopy instrument for surveys (ISSIS) for the world space observatory - ultraviolet (WSO-UV), Ap&SS 335, 283 - 289, 2011. G´omez de Castro, A. I., Sestito, P., Sanchez Doreste, N., et al., Status update of the WSO-UV project in 2012: The Spanish participation in WSO-UV, in: Guirado, J. C., Lara, L. M., Quilis, V., & Gorgas, J. (eds.) Highlights of Spanish Astrophysics VII, Proceedings of the X Scientific Meeting of the Spanish Astronomical Society (SEA), held in Valencia, July 9 - 13, 2012, p.820 - 831, 2013. Kappelmann, N., Barnstedt, J., Gringel, W., et al., HIRDES UV spectrographs, in: Turner, M., Hasinger, G. (eds.) Space Telescopes and Instrumentation II: Ultraviolet to Gamma Ray. Proc. of the SPIE 6266, 62660X, 2006.
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Klochkova, V., Panchuk, V., Sachkov, M., & Yushkin, M., Efficiency of Selected UV Space Based Spectrometers, in: Chavez, M., Bertone, E., RosaGonzalez, D., Rodrigez-Merino, L. H. New Quests in Stellar Astrophysics. II. Ultraviolet Properties of Evolved Stellar Populations Springer, Berlin, p.337 - 340, 2009. Lozano, J. M., Molina, M. A., G´omez de Castro, A.I., et al., Shared operations within the WSO-UV observatory, Space Optics, 213993, 693 - 703, 2010. Malkov, O., Sachkov, M., Shustov, B., et al., Scientific program construction principles and time allocation scheme for the World Space Observatory Ultraviolet mission, Ap&SS 335, 323 - 327, 2011. Reutlinger, A., Sachkov, M., G´al, C., et al., Using the CeSiC material for the WSO-UV spectrographs, Ap&SS 335, 311 - 316, 2011. Sachkov, M., World Space Observatory-Ultraviolet: International Mission for UV Spectroscopy and Imaging, AIP Conf. Proc. 938, 148 - 155, 2007. Sachkov, M., G´omez de Castro, A. I., Pagano, I., et al., World Space Observatory - UltraViolet: International Space Mission for the Nearest Future, in: Chavez, M., Bertone, E., Rosa-Gonzalez, D., Rodrigez-Merino, L. H. New Quests in Stellar Astrophysics. II. Ultraviolet Properties of Evolved Stellar Populations Springer, Berlin, p.301 - 308, 2009. Sachkov, M., UV observations of sdB stars and prospects of WSO-UV mission for such studies, Ap&SS 329, 261 - 266, 2010. Shustov, B., Sachkov, M., G´omez de Castro, A.I., et al., WSO-UVultraviolet mission for the next decade, Ap&SS 320, 187 - 190, 2009. Shustov, B., Sachkov, M., G´omez de Castro, A.I., et al., World space observatory-ultraviolet among UV missions of the coming years, Ap&SS 335, 273 - 282, 2011.
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