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VEGA and CHARA Denis Mourard Observatoire de la Côte d’Azur, Dépt GEMINI Proposal for a V isible sp E ctro G raph and pol A rimeter on CHARA. Outline. General presentation of VEGA Characteristics and expected performances Summary of the science cases Technical proposition
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VEGA and CHARA Denis Mourard Observatoire de la Côte d’Azur, Dépt GEMINI Proposal for a Visible spEctroGraph and polArimeter on CHARA
Outline • General presentation of VEGA • Characteristics and expected performances • Summary of the science cases • Technical proposition • Organisation, schedule, budget
General presentation of VEGA (1) • GI2T is closed now and we propose to move and adapt the spectrograph REGAIN on CHARA. • VEGA intends to offer access to the visible band (0.45 to 0.9µm), with spectroscopic (spectral resolution from 1500 to 30000) and polarimetric capabilities. • VEGA will combine 2 to 4 telescopes in a dispersed fringes mode.
General presentation of VEGA (2) We already have: - a spectrograph with its calibration sources, - 2 new generation photon counting detectors, - a global control system and a data reduction pipeline. We will have to modify: - the magnification of the cameras of the spectrograph - the injection of the calibration sources. We will have to: - develop the interface optic system, - adapt the control system in the CHARA framework - upgrade the software control for the 3/4 telescopes mode and the dedicated data reduction pipeline. Our current plan is to install VEGA at Mt Wilson by the end of 2007 and to begin operation at the beginning of 2008: Immediate science with two telescopes. Qualification and tests of the 3T/4T mode.
Multimode interferometry Image plane, 2D analysis, photon noise limitation Bério et al., 1999, 2001 • Large field of view for science … and for alignment! • Cophasing has no sense in multimode! • Coherencing with and accuracy of Lcoh/NSpCh • Mlim (fringe tracking) Nph/speckle/frame, independent of D • SNR increases as • Differential Interferometry approach • Increased limiting magnitude and SNR
Accuracy in visible multimode interferometryMourard et al., 2002 • Vega observed in June 2001 • different nights (seeing) • different baselines • no reference star • V2 estimations • selection of correctly guided images • Dl=9nm @ 645 nm • correction of centroiding effects • correction for the photon bias • instrumental corrections (flux ratio, pupil geometry) • Simultaneous adjustment of Vinstr and q* V2inst = 0.367 ± 0.005 and q = 3.07 ± 0.06
1 D b=2D 2 +D/l -d 4 b/l -D/l +d 3 VEGA, a 4 beams dispersed fringes combiner 1-3 1-3 1-3 1-4 2-3 1-4 2-3 2-3 2-4 1-2 2-4 4-3 1-2 4-3 Pupil plane Modulation Transfer Function
// ┴ // ┴ b UMa (A1V), 650-680nm GI2T/REGAIN SPIN Natural light SPIN experiment K. Perraut, J.B. Le Bouquin, D. Mourard Instrumental polarization A&A 2006, in press.
New Generation Photon Counting Detectors (OCA/CRAL) • Sensitivity : x 5 • Rate : x 2 (Algol) x 5 (CPNG) • Volume : / 5 • Price : / 2,5
Expected performances Hypothesis for calculations: • For a V=0 star, the number of photons received is equal to N0=1000 ph/s/cm²/A • Transmission in the visible QTotal=0.15% assuming • QCHARA = 0.03 (…) • QInstrument = 0.15 (13 mirrors @ 0.98 + 1 grating 0.6 + the slit 0.3) • QDetector = 0.3 • Exposure time t0=20ms, integration time=1800s • Instrumental visibility of CHARA 0.8 • r0 estimations (for 650 nm) @ Mt Wilson. These informations have been extracted from the Nils Turner presentation in 2005: • Median conditions, r0=8.0*(650/500)6/5=11.0 cm (seeing=1.25’’) • Excellent conditions, r0=15.0*(650/500)6/5=20.6 cm (seeing 0.7’’)
Limiting magnitude 30mn of integration. l=650nm. SNR=10 on |Vl1. Vl2| with Dl1= 50 nm (40, 6.7) and Dl2= 0.4 nm (0.13, 0.02)
Signal to noise ratio The calculations are made for a seeing of 1.25’’ and 30mn of integration time
Summary of performances(preliminary estimations) Dispersed fringe mode (4 telescopes) • Highest spectral resolution: 35000 • 180 spectral channelsof0.02nm • SNR=10 in 1800s, Mlimbetween 5.5 and 6.5 depending on seeing conditions. • Lowest spectral resolution: 1500 • 180 spectral channels of 0.4 nm • SNR=10 in 1800s, Mlimbetween 8.5 and 9.5 depending on seeing conditions. • Simultaneous polarizations measurement
P Cygni on GI2T (1994) X-l MR Vakili et al., A&A 323, 1997 P Cygni V=5 hGI2T94=0.3% Ti=180s, Vinstr=0.5 Dl2=5nm, Dl1=0.3nm
Summary of the science cases • Fundamental stellar parameters • Stellar activity: spots and Doppler Imaging • Differential rotation and stellar inclination • Asteroseismology • Cepheids: distance scale and pulsating atmospheres • Mira stars and related objects • Active hot stars • Hot emission-line stars in binaries • Wolf Rayet stars …see detailed presentation by Philippe on Thursday…
CHARA DETECTOR NEUTRAL DENSITIES PICKING OPTICS SPECTROGRAPH INTERFACE OPTICS CAMERA OPTICS DISPERSIVE OPTICS BEAM COMPRESSION POLARIZATION MODULE COLLIMATING OPTICS BEAM CONFIGURATION ANAMORPHOSIS OPTICS CALIBRATION /ALIGNMENT UNIT FOCUSING OPTICS SLIT MODULE CHARA/SOURCES SELECTION Functional analysis of VEGA
Preliminary design of the picking optic Note: will certainly be considered as an element of CHARA
Design of the Interface optics Side view Top view Sources
Remarks • The 4 cat’s eye have been designed in order to minimize the difference of longitudinal pupil distances (M2 of BCP) and to match the ZOPD plan of CHARA (longitudinal position of cat’s eye). • We do not need a longitudinal dispersion correction.
Chromatic Optical Path Difference • We take the pessimistic hypothesis of L=100 m due to the differential air path in the delay lines. • The chromatic optical path difference Dis given by D = L(nl1- nl2) = L(1-nl1/nl2) • The contrast loss due to this chromatic OPD is given by DC = 1 - sin(pD/lc)/ (pD/lc) where lc represents the coherence length: lc = l²/dl = R.l • In the case of VEGA, the lowest spectral resolution is R = 1700. At l=0.6 µm, it means that the bandwidth of each spectral channel is about dl=0.35 nm. So, the chromatic OPD inside a spectral channel is only D=0.4 µm. • The contrast loss due to the chromatic OPD is then negligible and the use of a chromatic OPD compensator can be avoided.
7) Detector output 6) Camera M2s 4) Grating 1) Entrance optic 2) Slit module 3) Collimator optic 5) Camera M1s 8) Slit viewer The spectrograph
Provisional schedule 2006 2007
Costs and manpower • Equipment = 110k€ • Additional manpower = 2 men.year • (1.5 software, 0.5 mechanical) • but mechanic ok • and a solution is searched for the software • Mission: certainly overestimated • Already obtained this year: 35k€ • In 2006: request from ANR for 3 years (deadline 20th march) • This table includes the additional manpower required and corresponds to the 2 years of development. • This does not include the CHARA participation, that has to be defined if the project is accepted.
Participants Université de Nice, LUAN, Nice Armando Domiciano (Science) Slobodan Jankov (Science) Romain Petrov (Science) Observatoire de Paris, LESIA, Paris Vincent Coudé du Foresto (Science) Pierre Kervella (Science) Antoine Mérand (Science) Chantal Stehlé (Science) Max Planck Institute, Bonn Karl-Heinz Hoffmann (Science) Dieter Schertl (Science) Gerd Weigelt (Science) Observatoire de Ondrejov, Prague Petr Harmanec (Science) Pavel Koubsky (Science) Observatoire de la Côte d’Azur GEMINI, Grasse Alain Blazit (Science, Detector) Daniel Bonneau(Science, System) Sandra Bosio (Mechanic) Yves Bresson (Optic) Olivier Chesneau (Science) Jean-Michel Clausse(Software) François Hénault (Managem., System) Yves Hughes (Mechanic) Stéphane Lagarde(System) Aurélie Marcotto(Optic) Philippe Mathias (Science) Guy Merlin (Software, Electronic) Denis Mourard(Science, System) Nicolas Nardetto (Science) Alain Roussel (Mechanic) Philippe Stee(Science) Observatoire de Grenoble, LAOG, Grenoble Karine Rousselet-Perraut (Sci., Sys.) Jean-Baptiste LeBouquin (Sci., Syst.) Observatoire de Lyon, CRAL Lyon Paul Berlioz-Arthaud (Science) Renaud Foy (Science) Isabelle Tallon-Bosc (Science, System) Michel Tallon (Science, System) Eric Thiébaut (Science, Detector) Our wish is also to develop, through this project, a partnership with the CHARA group (and others also if wished and possible) for the scientific exploitation.