Prsentation PowerPoint

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X-shooter DRS project
Paolo Goldoni, APC-SAp/CEA
VLT 2nd Generation Instruments Meeting - MPE
Munich 18/04/2007
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Call for proposals for 2nd Generation
VLT Instruments (http//www.eso.org/instruments/v
lt2ndgenins.html)
R 104 wide-band visible-NIR high-throughput
Spectrometer
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 mm) 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.
Goal of the instrument Single object
observations at the sky limit
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11 Institutes in 5 countriesstrong financial
contribution from
consortium
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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
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3 arms, single object spectrograph 1 IFU (1.8" x
4") reformatted into a 12 arcsec slit.
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Instrument characteristics

• Wavelength range 300 nm to 2.5 mm
• Prism cross-dispersed echelle (slit
  length12)
• Spectral resolution 6,000 to 12,000 for
  0.6 slit or IFU
• Calibration unit, AG unit, ADC for UVB and
  VIS arms
• Detectors 2Kx4K 15 mm CCDs (UVB and VIS
  arms) 2Kx1K segment of a 2K x 2K 18mm Hawaii2 RG
  MBE (NIR arm)
• Limiting magnitudes (1h, S/N10, slit
  width1)
• U21.9 B22.0 V21.7 R21.7 I21.3
  Z20.3
• J20.7 H20.9 K19 K18.9

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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.
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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
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Project Realisation
Written in C using wherever possible CPL
subroutines, on ESO CVS gt Fast Integration !!
Borrowing from UVES subroutines to speed up the
development standardize pipeline
Monthly progress teleconf with ESO (Instrument
Scientist, PI, DMD)
Intermediate Releases of the software
Time gain from standardization gt advanced
features
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X-shooter DRS Flowchart (staring)
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III
I
IV
V
See Goldoni et al. Proc. SPIE 2006
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Advanced Features I Physical Model
Highly precise wavelength calibration using
Physical Modelling. Projected accuracy of
Wavelength Calibration lt0.2 pix. Same method is
being used in CRIRES DRS
P. Ballester, M. Rosa Modeling Echelle
spectrographs (AAS 126, 563, 1997) Bristow,
Kerber, Rosa four papers in HST
Calibration Workshop, 2006 UVES,SINFONI,FOS,STIS
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Advanced Features II Single Frame Sky Subtraction
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.
Supersampling used in SDSS pipeline Kelson (2003)
PASP 115, 688
.

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Advanced Features III Single Frame Cosmic Rays
Subtraction
Used in HST/ACS images and in SDSS pipelines van
Dokkum (2001) PASP 113, 1420
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Advanced Features IV Optimal Extraction
Optimal Extraction using the method of Marsh
(1989) PASP 101, 1032 (similar method in
EspaDons/CFHT)
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Advanced Features V Improved Spectrophotometric
Calibration
Situationcurrent 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
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X-shooter Functional Scheme
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Integral Field Unit
Realised by GEPI-Observatoire de Paris (Girafe)
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IFU Image Reconstruction
Calibration across slices
Calibration along slices