Scientific Goals

WSO-UV is a multipurpose observatory. It will provide observations that are of exceptional importance for the study of many astrophysical problems.

The mission has four key scientific objectives:

•          The determination of the diffuse baryonic content in the Universe and its chemical evolution.

•          The formation and evolution of the Milky Way.

•          The physics of accretion and outflows: the astronomical engines.

•          Extrasolar planetary atmospheres and astrochemistry in presence of strong UV radiation fields.

Therefore, major scientific aims of “WSO-UV” Project are:

  • The Universe evolution exploration (including universe reionization study, universe chemical evolution study, search of hidden diffusive baryon substance in universe).

  • Nature of active processes on stars exploration.

  • Stars like Sun and protoplanetary disks early evolution study.

  • Chemical composition of planetary atmospheres in solar system and outside it physical- exploration.

WSO-UV is not going to duplicate any existing or foreseen mission or ground based project, even when the expected launch date will take advantage of the previous GALEX survey mission and the COS instrument on board the HST.

The high resolution provided by the WSO-UV at R 50000, as well as its capability to evaluate the spectrum of Quasi-Stellar Object (QSO) at low resolution (R 1000) will constitute a powerful tool for the study of the metal enrichment history of the content of the Universe at redshifts less than z approx. 2 (this z contains nearly most of the volume of the Universe and 80% of the cosmic time). The basic enrichment of the primary material from which the current star formation is drawn is a multifaceted problem in which the Inter Galactic Medium (IGM) plays a fundamental role, and only limited studies have been performed in order to clarify the nature of the metallicity of the IGM at those redshifts. The high resolution of the WSO-UV and superior Supernova Remnant (SNR) for absorption lines associated with the Lyman alpha and Lyman Limit systems will permit the exploration of the full range of the ionised and neutral gas out of z=2 (the resolution is a critical parameter since it must be sufficient to assure that no component mixing occur).

Similarly to QSO, white dwarfs can act as background sources for the study of the local interstellar medium (LISM) A comparison of the LISM Deuterium/Hydrogen (D/H) ratio with the D/H observations in metal poor Lyman alpha clouds toward high redshift QSOs provides a powerful constraint on Galactic chemical evolution models. The WSO-UV will contribute by measuring the D/H ratio within the LISM and define its variation and map the 3D structure of the LISM and determine its composition and ionisation state.

Another field where the WSO-UV will be targeted will be the definition of the evolutionary history of the hot white dwarfs stars through detailed modelling of their photospheric composition and structure, and the study of the pattern of circumstellar material surrounding the white dwarfs and their interaction with the ISM. Understanding the effects of the, ass-loss in the form of weak winds, ejecting material in the local ISM and direct accretion of material from ISM is an essential question and the WSO-UV will allow these issues to be addressed simultaneously through its high resolution and easy modes of operation which will allow the acquisition of data on a very significant sample of some 300 white dwarfs.

Another key issue where the role of WSO-UV will be important is the physic of accretion, which applies to the formation of the Solar System, some planetary nebulae (bipolar ones), Cataclysmic Variables, microquasars, Seyfert galaxies and quasars. A large amount of secondary (or reprocessed) radiation is emitted here in form of UV as the plasma is heated up 105 K, and the high resolution and sensitivity of the WSO-UV will provide some insight here.

Scientific programs with the WSO-UV

The project observing time is planned to be distributed as:

  • Core Program (CP).
  • National Programs (NP).
  • Open Time for the International Community (OT).

The Core Program will be designed by a Core Program Team and should be carried out during the first 2 years of the project. The time for Funding Bodies Programs is allocated by a national panel for each of the countries involved in the implementation process of WSO-UV. The observing time granted for each country will be proportional to its contribution to the project. There will be a large fraction (up to 40 percent) of Open Time for the International Community. First call for proposals for national and open times will be one year before launch.

The observatory will provide unique opprotunities for study of the "cosmic web" (as illustrated in the figure), search for dark baryonic matter, study of thermal and chemical evolution of the Universe as well as for study of "standard candles" used in cosmology - type Ia supernovae.

 

 

WSO-UV is a powerful tool for stellar physics, study of accretion discs and of other manifestations of activity of stars and compact objects.

The overwhelming majority of stars are binaries. Of special interest is the physics of close binaries. At a certain stage of its evolution, one of the components expands and fills its critical volume (the Roche lobe). In this case, mass exchange begins between the components - the matter of the expanded component forms a jet flow and produces an accretion disk surrounding the second component. Complex processes of interaction between the accretion disk and the central star determine the development of powerful stellar flares (explosions) and other energetic processes accompanied by strong UV radiation.

The WSO-UV optical and UV imagers will allow unprecedented detailed investigation of resolved stellar populations in the Milky Way, star clusters and nearby galaxies. On the leftt the Andromeda galaxy, as imaged in the optical from the ground, shows the old stellar population, while on the right the UV image of the same galaxy (from the small UV GALEX telescope) shows spiral arms, star forming regions, and exotic hot stellar objects (binaries, LXRS, pulsars). WSO-UV diffraction limited images will be used to derive proper motions in crowded environments: WSO-UV is complementary to GAIA in this respect.

Studies of outer layers of planetary atmospheres are also planned. These observations will contribute to better understanding of terrestrial atmospheric features. This image (from HST archive) demonstrates the auroral activity at Saturn.

Study with WSO-UV of extrasolar planet transits will provide important information on the planetary atmospheres and their interaction with the parent star.

The figure below is an artist's impression of atmosphere evaporation in a young planet orbiting very close to its parent star (courtesy Alfred Vidal-Madjar).