“Call for proposals for 2nd Generation VLT Instruments” ( http://www.eso.org/instruments/vlt2ndgenins.html ) The main goal is to get maximum detectivity on stellar or small emission-line objects, while covering the largest possible wavelength range (ideally 0.32 to 2.4 m) in a single observation, presumably leading to a multiple arm ("x-shooter") system. A particularly important requirement is the ability to get spectrographic data on unpredictable/fast varying objects like supernova explosions or gamma ray burst optical counterparts, for the latter if possible in a matter of minutes…. R~ 10 4 wide-band visible-NIR high-throughput Spectrometer Goal of the instrument: Single object observations at the sky limit
11 Institutes in 5 countries:strong financial contribution from consortium
Consortium and Schedule ESO approval 12/2003 PDR 13/12/2004 FDR 07/07/2006 PAE 04/2008 PAC 04/2009 X-shooter will be released to the community in April 2009 ESO-Coordination -Instrument Assembly PI: S. D ’ Odorico DMK-Backbone unit - UVB spectrograph PI: P. Kjaergaard NLDNIR spectrograph Support to DRS (NIR) PI:L. Kaper ITA VIS Spectrograph Observing Software PI: R. Pallavicini FRAIFU (GEPI) Data Reduction Software (APC/GEPI) PI: F. Hammer Co PI: P. Binetruy
3 arms, single object spectrograph 1 IFU (1.8" x 4") reformatted into a 12 arcsec slit.
Instrument characteristics Wavelength range: 300 nm to 2.5 m Prism cross-dispersed echelle (slit length12”) Spectral resolution: 6,000 to 12,000 for 0.6” slit or IFU Calibration unit, A&G unit, ADC for UVB and VIS arms Detectors: 2Kx4K 15 m CCDs (UVB and VIS arms); 2Kx1K segment of a 2K x 2K 18 m Hawaii2 RG MBE (NIR arm) Limiting magnitudes (1h, S/N=10, slit width=1”): U=21.9 B=22.0 V=21.7 R=21.7 I=21.3 Z=20.3 J=20.7 H=20.9 K ’ =19 K=18.9
Simulated image, VIS arm Difficulties: Spectral range, Curved orders, tilted lines (e.g. need a new method for optimal extraction). Moreover Staring mode preferred in UVB, ON/OFF (or dithering) required in NIR.
X-shooter DRS Project Products The DRS for X-shooter shall produce a wavelength calibrated, sky subtracted, flux calibrated, merged, 1D spectrum of the observed target both in the slit and IFU modes of the instrument for the three separated arms, together with the corresponding sky and noise spectra. 1D mode: optimal extraction of the sky-subtracted spectrum of the stellar like targets. The 2D (the second dimension being the coordinated along the slit) extracted and wavelength calibrated spectra shall also be made available. IFU Mode: The DRS product shall be the wavelength calibrated spectra in a reconstructed 3D data cube ( x,y coordinates on the sky and wavelength) Team: P. Goldoni (APC/CEA), M. Horrobin (UvA), F. Royer (OPM), G. Blanc (APC), L. Guglielmi (APC), R. Haigron (OPM) + ESO P. Bristow, A. Modigliani, J.M. Larsen
Project Realisation Written in C using wherever possible CPL subroutines, on ESO CVS ==> Fast Integration !! Borrowing from UVES subroutines to speed up the development & standardize pipeline Intermediate Releases of the software Monthly progress teleconf with ESO (Instrument Scientist, PI, DMD) Time gain from standardization ==> advanced features
X-shooter DRS Flowchart (staring) II III IV V See Goldoni et al. Proc. SPIE 2006 I
Advanced Features I: Physical Model Highly precise wavelength calibration using Physical Modelling. Projected accuracy of Wavelength Calibration : <0.2 pix. Same method is being used in CRIRES DRS P. Ballester, M. Rosa: Modeling Echelle spectrographs (A&AS 126, 563, 1997) Bristow, Kerber, Rosa: four papers in HST Calibration Workshop, 2006 UVES,SINFONI,FOS,STIS
Advanced Features II: Single Frame Sky Subtraction Supersampling used in SDSS pipeline Kelson (2003) PASP 115, 688. Because of the tilt, each pixel samples a slightly different part of the wavelength space, on the left a single row of data, on the right a sampling of all data rows.
Advanced Features III: Single Frame Cosmic Rays Subtraction Used in HST/ACS images and in SDSS pipelines van Dokkum (2001) PASP 113, 1420
Advanced Features IV: Optimal Extraction Optimal Extraction using the method of Marsh (1989) PASP 101, 1032 (similar method in EspaDons/CFHT)
Advanced Features V: Improved Spectrophotometric Calibration Situation:current methods for spectro-photometric calibration in the NIR no more precise than 20-30% because a proper set of NIR spectro-photometric standards simply does not exist at the moment. Extend the wavelength coverage of the well established UV/Optical spectro-photometric standards (Oke 1990, Hamuy et al. 1992,1994) into the near-IR with SINFONI observations. Rely on the 2 HST Primary Standards(WD): –robust reference: flux measured outside the atmosphere between 115 and 1800 nm (accuracy better than 1%, Bohlin 2007) –Interpolate between flux measurement windows using state-of-the-art stellar atmosphere models (TMAP) and derive and absolute flux table for each Secondary Standard across the whole wavelength range Proposal being carried out, first data being analyzed. See Vernet et al. Proc. Cal2007