AWG Evaluation of F2/F3 Proposals

In priority order the AWG places NGST top, followed by Eddington/COROT. At a very different financial level but nevertheless with highly ranked science, the AWG recommends a modest ESA participation in VSOP-2. Finally, in the context of the scientific utilisation of the International Space Station, the AWG recommends accommodation studies for two proposals, EUSO and LOBSTER. Considerations regarding the remaining 11 proposals are given in the Appendix attached.

NGST Proposal

Fully consistent with its previous reviews, the most recent being at the Capodimonte meeting in September 1999, the AWG unanimously confirms the NGST science to be of the highest merit, and ranked it top of those proposals it received. The NGST will provide access to unique areas of study covering an extremely broad range of astrophysics. As a facility NGST will become one of the central pillars of world astronomy in the second decade of this century. A significant level of guaranteed access to the ESA community via participation in the NGST project is therefore crucial.

The AWG recommends as its highest priority ESA's participation in this mission, at the level of an F-mission as proposed. The AWG reiterates its view regarding ESA's contribution to the core instrument payload, as formulated in AWG recommendation ASTRO(2000)3.

Eddington / COROT proposals

Understanding the structure and evolution of stars lies at the very core of astrophysics, but we are still far from having the complete picture. Asteroseismology, the study of resonant oscillation frequencies of stars, is an exciting new and potentially powerful technique to probe internal stellar structure, inaccessible by other means. Such research builds on the solid foundations provided by SOHO data in terms of the sun, and would strengthen and broaden this as a field of European excellence. It transpires that techniques deployed in asteroseismology are similar to those required for planet finding. This is an area that has now emerged as a major subject in mainstream astronomy, with implications for the formation of planetary systems, and the eventual prospect of making a profound cultural impact.

The F proposal called Eddington, after the pioneer of stellar evolution theory, addresses both asteroseismology and planet finding as two of its central science themes. Via asteroseismology Eddington would measure 50K stars, and provide data needed to study mixing processes, which determine the radial composition needed to determine the age, and ultimate fate of stars. Furthermore, by means of extremely accurate photometry Eddington will be sensitive to transits across a stellar disc of terrestrial-size planets, and will measure 700K stars during the mission lifetime.

The Eddington proposal is techically mature in that it builds on the previous Phase A industrial study carried out for Stars (a candidate for M3). The AWG rates Eddington as its highest priority after the NGST, and recommends that a study be carried out, focusing on those mission elements which need up-dating from the previous related studies.

In the broader sense Eddington should be considered as contributing to a coherent overall strategy within the theme of extra-solar planets, leading to future missions such as Darwin.

In the same context, COROT will provide early scientific return in both asteroseismology and planet finding. The AWG recommends that ESA seek involvement in COROT. This should be by means of ESA representation on COROT teams as Associate Scientists from each member state, who would receive early access to catalogues and other survey data. ESA should also have appropriate representation on the Scientific Council of COROT, which defines its observing programme.

ESA's involvement in Eddington and COROT should be viewed as building on an existing strength (solar studies with SOHO), and extending this into a new domain. The costs to ESA of both missions could be incorporated within an F-mission envelope.

Space VLBI proposal

Space VLBI provides uniquely high spatial resolution not achievable by any other technique in the foreseeable future. The VSOP-2 will be a Japanese led mission with a planned launch in 2007, following the heritage of the HALCA (VSOP-1) space VLBI mission.

The science aims are to study structures on scales of down to 25 micro-arcsec. (2500 times greater than that provided by the HST). Areas of interest include regions close to massive black holes i.e. the structure and variability of radio jets, masers and megamasers, and gravitational lense systems.

The AWG noted the strong participation by European astronomers in the HALCA science programme and ground support segment, together with the high level of interest from this community in such mission proposals, eg. QUASAT (M1 candidate) and IVS (M2 candidate). VSOP-2 is the next logical step in SpaceVLBI, and based on the science return, the AWG considers that an ESA contribution to this mission is clearly justified.

A modest investment to VSOP-2 in the range 10-15Meuros in such areas as ground station tracking and data processing, would ensure continuation of European scientific leadership in this field.

Accommodation on the ISS; EUSO and LOBSTER proposals

EUSO - Extreme Universe Space Observatory, is a collaborative proposal involving Europe, the U.S. and Japan. It is concerned with astroparticles, and how these can be used to answer basic questions in Cosmology and Fundamental Physics. Its clever approach is to use the Earth's nighttime atmosphere as a detector. Extremely energetic particles produce a short duration flash of light via fluorescence as well as by directional Cherenkov radiation.

The aims are to understand extreme energy cosmic ray production. Are they produced in known objects eg. BL Lacs, Gamma Ray Bursts, or alternatively via exotic processes such as the decay of Topological Defects. EUSO is proposed as a free flyer, but in a modified form it could be a candidate for accommodation on the ISS.

LOBSTER - is a proposal for an all sky monitor in the soft X-ray band (0.1-3.0 keV). It uses a novel arrangement of MCPs to provide the extremely wide field of view. LOBSTER would generate a confusion limited catalogue of about 250,000 sources every two months, with a spatial resolution of a few arcminutes. For the first time it would provide us with a complete census of X-ray source properties in the forth dimension - time. All classes of compact X-ray source are variable. The LOBSTERobservations would impact many areas eg. accretion disk physics in both binary systems and active galaxies, afterglows of GRBs, stellar transients and coronal activity.

The AWG rated the science goals of both these missions highly, and was particularly impressed by the synergy between the astronomy and astroparticle areas obvious in the EUSO proposal.

Given their high scientific return and the broad, in the case of EUSO cross community, interest in these missions, the AWG recommends studies to define the scientific and technical trade-offs for their accommodation on the ISS.

Appendix - Consideration of Other Proposals

In addition to the proposals mentioned specifically in the preceding recommendations, the AWG fully considered the 11 mission proposals listed below in alphabetical order.

CMB
The objective of this proposal is to observe the Cosmic Microwave Background at extremely high angular resolution, using the Sun as a gravitational lens. Whilst an intriguing idea, the AWG did not consider this proposal as sufficiently mature both in terms of the discussion of technical matters, and in terms of its scientific rationale.

Compton Cube
The aim of Compton Cube is to provide the first all-sky survey in the low-energy gamma-ray region (150 keV to 1.5 MeV), using 12 independent cameras, two on each side of a cube. The data analysis would be very challenging, particularly so in the context of the ISS option. In view of the sensitivity and the source location accuracy, it was considered that it would be difficult to achieve the stated goals.

Epicurus
This proposal envisages 36 free-flying satellites each with 30 cm aperture, over a baseline of 200 M. Such a facility would provide angular resolutions of about 0.5 milli-arcsec., and could be used to study a wide range of phenomena from planet transits to active galactic nuclei. The necessary technology is very challenging, and will require demonstration. As proposed this mission was considered likely to lie outside of a Flexi budget envelope.

EXTRA
A proposal to follow-on from the RXTE, EXTRA would perform sensitive X-ray timing studies from 1-50 keV. Also included in the payload is an all sky monitor, and a hard X-ray monitor up to 200 keV. Concern was expressed on the technological maturity of parts of the main instrument, and on the evaluation of the background.

H2EX
This proposal would build on the success of ISO, and proposes mapping of warm molecular hydrogen via its lowest rotational lines which occur in the mid-infrared. Although of considerable importance, the science area was not thought to be as broad as those of some other proposals. Whilst generally complementary to the NGST, some of the aims of H2EX will be studied using the NGST, if it has a mid-infrared capability.

MAX
Using crystal diffraction techniques MAX would observe soft gamma ray lines in the energy range 200 - 850 keV, and hence study supernovae, and other compact high energy sources. Concerns were raised on technical issues related to the use of the Bragg lens, and on estimates of the background.

MEGA
MEGA would perform an all-sky survey in the gamma-ray domain, from 0.5-50 MeV, following on from and complementing missions such as COMPTEL, EGRET and in the future INTEGRAL. Whereas the science area is certainly of interest, the advance in sensitivity over previous and approved missions was not considered to be as great as that for some proposals in other areas.

Panoram-X
Using a wide-field X-ray telescope, Panoram-X would perform a sensitive X-ray all-sky survey at energies up to 10 keV. This would complement the previous soft band X-ray survey carried out by ROSAT. Parts of the science programme proposed for Panoram-X, may be realized after a few years of operation by XMM-Newton (serendipitous source survey).

Treasure
Treasure proposes a novel technique to detect planet transits across the discs of nearby stars, using a compact assembly of 30 x 15 cm lenses in a fly-eye configuration. In addition, Treasure would also perform astroseismology studies. Problems were identified in the technical and managerial areas. The main objectives of this proposal have considerable overlap with those of the Eddington proposal.

XRASE
Following on from the current Chandra and XMM-Newton missions, XRASE would use calorimeter arrays to provide efficient high resolution X-ray spectroscopy. (Note: the recent loss of the Japanese mission Astro-E, which was to have demonstrated this technique). In addition, XRASE would include other instruments to provide multi- frequency observations. The AWG noted concern on a number of technical issues, and a significant overall programmatic risk.

Galactic Dune
The aim of Galactic Dune is to characterize the properties of interstellar dust. Although submitted to the SSWG for evaluation, the AWG was asked to comment from the astronomy perspective. The AWG rated the science as good, but considered it as somewhat narrow in comparison with other competing mission proposals.