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Date	Action
Jan 2008	ARENA 2 paper writing
Feb 2008	Kick-off and presentation of goals and planning
Mar 2008	First iteration with industries / postponed due to lack of funding
Apr 2008	CHAPTER 1: WG Science advisers send a report on their field
May 2008	CHAPTER 3: Facilty vs. dedicated instrument ?
May 2008	CHAPTER 2: WG Site testing advisers send back their report
June 2008	Definition of a science case for a 12m-ALMA type antenna
June-Sep 2008	CHAPTER 3: Proposition for telescope designs with industries + instruments
Sep 2008	CHAPTER 5: Final iteration about logistics based on telescope proposition
Sep 2008	CHAPTER 4: Assessment of possible funding
Sep 2008	First report draft
Oct 2008	Meeting in Paris - 8/9th October
Dec 2008	Deliver progress report to ARENA

 

Download ARENA Working Group summary (pdf; 4 Mo)

 

An ARENA working group has been created to produce a document on the potential of Dome C for hosting a large telescope facilitiy that will operate in the far-infrared and submillimetre regime of the electromagnetic spectrum. The main goals of the Working Group are to specifically study the potential of a large single dish telescope AS WELL AS the possibility to deploy a FIR interferometer of 3 antennas.

 

Goals and guidelines

The ARENA CMC asks us to deliver a report in which the following issues are addressed in five CHAPTERS (CH) by order of priority. CH1 and 2 are the immediate priorities, CH3 will need interaction with industries, CH4 is a prospective work, and finally CH5 will be based on work achieved by ARENA NA4 and polar institutes.

 

CHAPTER1 - Science and Specifications:

WG members in Chapter 1: E. Daddi, L. Olmi, L. Spinoglio, F. Israel, C. Kramer, V. Minier

Contribution format: 2-3 pages + 1-2 figures + 1 synthetic table with sensitivities an observing parameters.

 

The main goals are to strenghen the scientific cases based on the Saclay workshop and ARENA-2 conference proceedings, and define the requirement in terms of atmosphere conditions (transmission, stability and skynoise) and instrumental characteristics (telescope specifications). Synergy with ALMA and Herschel science objective should be discussed.

Questions for a specific science driver:

- What are the BIG scientific questions that are likely to be addressed in the next decade or so?

- Which of them are likely to be partially or totally answered thanks to new instruments coming on-line
(Herschel, ALMA, South Pole Telescope)?

- What would the need be for a new ground-based FIR/submm telescope ?

- What type of telescopes (size; single dish or array) and instrument facilities (imagers; heterodyne receivers) are required ?

- Are the sensitivities (NEFD) in the table below sufficient to achieve science goals, else what should they be ?

- How much observing time (exclude overheads) is required based on the NEFD and telescope aperture required ?

- What can a 12-m class telescope achieve? Is this required as a pathfinder to a larger dish or should we propose instead a larger antenna to achieve the scientific goals mentioned above ?

- Would the inner 3-4m of the 12-m telescope designed for operating at 20-40µm strenghen the FIR/submm science case ?

- What are the requirements for calibrating the observations (planets, point sources ...) ?

 

Assumptions on sensitivities are the following:

For continuum with a filled bolometer array with 10,000 pixels of lambda/2D angular size, a range of NEFDs is given that corresponds to transmission deduced from two sets of PWV and airmass at an elevation of 50°. For instance radiosounding data analysis suggest that 25% PWV=0.23 mm, 50% PWV=0.33 mm, and 75% PWV=0.48 mm. The range of NEFDs is calculated using atmosphere transmission models (PWV=0.1-0.2 mm at 200 µm; 0.2-0.4 mm at 350 µm & 450 µm) + realistic telescope aperture efficiency (50% at 200 µm), optical transmission (50 to 80%), and bolometer absorption (80%). Please use both values in your mapping time estimate, the lower and upper limits. Modelled transmission can be found here.

 

12-m class telescope
Wavelengths	NEFD (mJy/beam)	Beam (arcsec)	Total FOV (arcmin)
200 µm	500-1000	3.4 (l/D)	2.8x2.8
350 µm	100-200	6.0 (l/D)	5.0x5.0
450 µm	100-200	7.8 (l/D)	6.5x6.5

 

To scale a mapping time for a different telescope aperture at a given lambda and site (transmission), we may use the simple reasoning:

Mapping time = [NEFD/Flux]² x AREA/FOV  proportional to NEP²/[D.exp(-tau).Flux.lambda]²

where Flux is the source flux or the required sensitivities; NEP depends on lambda (the wavelength), the bandwidth, the optics transmission and the aperture efficiency; FOV is proportional to (lambda/2D)²; AREA is the area to be mapped;  tau is the atmosphere opacity at zenith;  D is the telescope diameter.

 

For a 25m telescope, NEFD and FOV are divided by (25/12)², hence mapping time is 4 times less.

 

We could also assume on-the-fly mapping, but it will require more elaborated performance estimates.

 

For spectral line:

Use APEX-2A interface with appropriate opacity for Dome C. Modelled transmission can be found here.

 

CHAPTER2 - Site characteristics:

WG members in Chapter 2: L. Valenziano (coord.), N. Schneider, G. Durand ...

The main goals are to summarise the current knowledge of Dome C in terms of atmospheric transmission, frost formation, thermal gradients and turbulences, and phase stability for interferometry; it will be based on meteo data and PWV derivation, direct measurement and modelling of the transmission, current understanding of turbulence and thermal gradients in the 45-m layer above ground. Future site testing experiments will be proposed. Transmission in the 200, 350 and 450 µm bands should be measured/estimated. Comparisons with Chajnantor sites (up to 5800 m) and South Pole.

 

CHAPTER3 - Telescope design:

WG members in Chapter 3: Luca Olmi (coord.), Gianpietro Marchiori, Luigi Spinoglio, Alberto Franceschini, Vincent Minier, Gilles Durand, Nick Tohill

The main goals are to propose instrumental concepts (telescope, front-end receivers, focal plane imagers...) that could be used to define a future funding proposal (Design Study), and the international consortium that will realise this study (including industries).

Today the construction of the ALMA antennas is an opportunity to obtain a 12m antenna at Dome C, after necessary upgrade to "antarctize" this telescope. You all can up with potential science cases for a 12m dish or more generally for FIR/THz/submm astronomy. Nonetheless given the very remote location of Dome C and the quasi-impossibility to maintain a telescope there by wintertime, we may whether we shall aim for an international telescope facility (with many front-end instruments) or a telescope dedicated to one BIG science case (with only a couple of imager and/or receiver) ?
 

General questions:

- Facility vs. PI/dedicated telescope ?

- A 12-m ALMA-like telescope with possibilities to observe in the mid-IR (e.g. ASO project) ?

- A 25-m class telescope ?

- A FIR/THz interferometer ?

- A dedicated imager ?

- Heterodyne receivers ?

 

Specific technical problems to be solved in collaboration with EIE and Thales Alenia Space:

-Materials and joints at T<-70 C
-Constraint imposed by vertical temperature gradients

-Use of active primary mirror (pointing device, mirror actuators qualified for Antarctic conditions)
-Wind and ice formation (warming up of the back-up structure? => deformations of the surface + power consumption)
-Increased surface accuracy to work at 200 micron (maintain current ALMA panel design?)
-Subarcsec pointing/tracking accuracy (use optical/IR auxiliary telescope?)
-Is a wobbling secondary required? (=> struts & antenna structure)
-Space requirements and constraints in the receiver cabin
-Power & cryogenic requirements
-Shipping constraints and assembling of the antenna components
-Operations and maintenance w. minimum personnel

 

CHAPTER4 - Funding:

WG members in Chapter 4: all

The main goals are to evaluate an estimate of the cost, to prospect sources of funding (National agencies, International agenies, ...), and evaluate risks.

 

CHAPTER5 - Logistics:

WG members in Chapter 5: NA4  

The main goals are to propose a planning for the building and installation (time-scales, pre-study, design, transportation and assembling phases) of the telescope taken into account the logistics issues (with Polar Institutes); to study the impact of the telescope operation on logistics, operation of Concordia and Antarctic environment including energy supply.