X-shooter DRS projectPaolo Goldoni, APC-SAp/CEA

VLT 2nd Generation Instruments Meeting - MPE Munich 18/04/2007

“Call for proposals for 2nd Generation VLTInstruments” (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~ 104 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 2009X-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

NLD NIR spectrograph

Support to DRS (NIR)

PI:L. Kaper

ITA VIS Spectrograph

Observing Software

PI: R. Pallavicini

FRA IFU (GEPI)

Data Reduction Software (APC/GEPI)

PI: F. Hammer

Co PI: P. Binetruy

3 arms, single object spectrograph1 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 18m 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 foroptimal 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 andIFU 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 liketargets. The 2D (the second dimension being the coordinated along theslit) extracted and wavelength calibrated spectra shall also be made available .

IFU Mode: The DRS product shall be the wavelength calibrated spectra in areconstructed 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 wavelengthcalibration using PhysicalModelling. Projectedaccuracy of WavelengthCalibration : <0.2 pix.Same method is beingused in CRIRES DRS

P. Ballester, M. Rosa: ModelingEchelle spectrographs (A&AS126, 563, 1997)Bristow, Kerber, Rosa: fourpapers in HST CalibrationWorkshop, 2006UVES,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 nomore 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/Opticalspectro-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 and1800 nm (accuracy better than 1%, Bohlin 2007)–Interpolate between flux measurement windows using state-of-the-art stellaratmosphere models (TMAP) and derive and absolute flux table for each SecondaryStandard across the whole wavelength range

Proposal being carried out, first data being analyzed.

See Vernet et al. Proc. Cal2007

X-shooter Functional Scheme

Integral Field Unit

Realised by GEPI-Observatoire de Paris (Girafe):

IFU Image Reconstruction

Calibration along slices

Calibration across slices