highest-resolution spectroscopy at the largest telescopes ?
DESCRIPTION
Highest-Resolution Spectroscopy at the Largest Telescopes ? Dainis Dravins – Lund Observatory , Sweden www.astro.lu.se /~ dainis. But why ? Changing paradigms…. Stellar atmosphere theory classics… Unsöld (1938, 1968); Mihalas (1969, 1978). CHANGING STELLAR PARADIGMS. - PowerPoint PPT PresentationTRANSCRIPT
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Highest-Resolution Spectroscopyat the Largest Telescopes ?
Dainis Dravins – Lund Observatory, Swedenwww.astro.lu.se/~dainis
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But why ?
Changing paradigms…
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Stellar atmosphere theory classics…
Unsöld (1938, 1968); Mihalas (1969, 1978)
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CHANGING STELLAR PARADIGMS
PAST: ”Inversion” of line profiles; “any part of a profile corresponds to some height of formation”
NOW: Stellar line profiles reflect distribution of lateral inhomogeneities across stellar surfaces
Not possible, not even in principle, to ”invert” observed profiles into atmospheric parameters
Confrontation with theory through ”forward modeling” – computations versus observables
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Spatially resolved line profiles of the Fe I 608.27 nm line in a 3-D solar simulation.Thick red line is the spatially averaged profile.
Steeper temperature gradients in upflows tend to make their blue-shifted lines stronger M.Asplund: New Light on Stellar Abundance Analyses: Departures from LTE and Homogeneity , Ann.Rev.Astron.Astrophys. 43, 481
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Limits to information
content of stellar spectra ?
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“ULTIMATE” INFORMATION CONTENT OF STELLAR SPECTRA ?
3-D models predict detailed line shapes and shifts
… but …their predictions may not be verifiable due to: Absence of relevant stellar lines Blends with stellar or telluric lines Uncertain laboratory wavelengths Data noisy, low resolution, poor wavelengths Line-broadening: rotation, oscillations
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Spectral complexity
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Individual bisectors (red), overplotted on line profiles, for Fe II lines in UVES Paranal spectra of 68 Eri (F2 V), θ Scl (F5 V), and ν Phe (F9 V).
Bisector scale (top) is expanded a factor of 10. Dravins, A&A 492, 199 (2008)
Limits of ‘unblended’ lines ?
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Fe II bisectors at solar disk center, and of integrated sunlight, on an absolute wavelength scale. Thin curves are individual bisectors; thick dashed is their
average.Dravins, A&A 492, 199 (2008)
Limits to line statistics ?
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Finite spectral resolution
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Different line profiles in different recordings of solar spectra.Solar disk center (Jungfraujoch & Hamburg); Integrated sunlight (Kitt Peak); Moonlight (UVES).
Dravins, A&A 492, 199 (2008)
Limits to spectral fidelity ?
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Theoretical bisectors of 522.84 nm Fe I line for V sin i = 0 and 2 km/s, at R= infinite, R = 210,000, and R = 160,000I.Ramírez, C. Allende Prieto, L. Koesterke, D. L. Lambert, M. AsplundGranulation in K-type dwarf stars. II. Hydrodynamic simulations and 3D spectrum synthesisAstron. Astrophys. 501, 1087 (2009)
Theoretical bisectors in K-type dwarfs,“observed” at R=160,000 & R=200,000
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Fe I-line bisectors
in Sun and Procyon(F5 IV-V)
Bisectors for Fe I lines of different strength, produced from a time-dependent 3-D model
C.Allende Prieto, M.Asplund, R.J.García López, D.L.Lambert: Signatures of Convection in the Spectrum of Procyon: Fundamental Parameters and Iron Abundance, Astrophys.J. 567, 544
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Fe II bisectors in Procyon, measured with successively higher spectral resolution. Left: R = 80,000; Middle: R = 160,000; Right: R = 200,000.
Dravins, A&A 492, 199 (2008)
Limits to spectral resolution ?
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Absorption in the Earth’s
atmosphere
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Wavelength noise
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MODELING SPECTRA (not only single lines)
Hans-Günter Ludwig
LTE solar 3-D spectra, assuming [O]=8.86 for two different van der Waals damping constant (black lines). Blue line: observed disk center FTS spectrum by Neckel (“Hamburg photosphere”), slightly blueshifted.
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O I LINE PROFILES & SHIFTS
Hans-Günter Ludwig
LTE solar 3-D hydrodynamic spectra, assuming [O]=8.86, for two different damping constants (black lines). Blue line: observed disk-center FTS spectrum, slightly blueshifted.
O I 777.19 777.41 777.53
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Ti II bisectors at solar disk center from the Jungfraujoch grating spectrometer, and as recorded with the Kitt Peak FTS . Bisectors have similar shapes but differ in
average lineshift, and scatter about their average. Dravins, A&A 492, 199 (2008)
Limits from wavelength noise ?
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Spectroscopy at Very & Extremely Large Telescopes
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Visual high-resolution spectrometers at 8-10 m telescopes
Telescope SALT Keck I VLT Kueyen
HET Subaru LBT
Diameter [m] 10 10 8.2 9.2 8.2 2 8.4
Spectrometer HRS HIRES UVES HRS HDS PEPSI
Maximum R 65,000 84,000 110,000 120,000 160,000 300,000
Wavelengths [µm] 0.37– 0.89 0.3 – 1.0 0.3 – 1.1 0.39 – 1.1 0.3 – 1.0 0.39 – 1.05
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PotsdamEchellePolarimetricandSpectroscopic Instrument
@ Large Binocular Telescope
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2080 cm R4 echelle grating for
PEPSI
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Pasquini et al.: CODEX: the high resolution visual spectrograph for the E-ELTProc. SPIE 7014, 70141I (2008)
Optical arrangement of multi-camera CODEX design
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Resolving power and spectral range of proposed
42-m E-ELT spectrograp
hs
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Beyond CODEX:Spatially resolved
stellar spectroscopyVLT image of Betelgeuse in near-IR
Kervella et al.:The close circumstellar environment of Betelgeuse. Adaptive optics spectro-imaging in the near-IR with VLT/NACO A&A, in press (2009)
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Corrugatedstellar surfaces ?
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Simulated intensities
approaching the solar
limb
Mats Carlsson, Oslo; in
Å.Nordlund, R.F.Stein, M.Asplund:
Solar Surface Convection,
Living Reviews in Solar Physics, 2009
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Granulation on stars
Synthetic images [negative] of
granulation in four stellar models
From top: Procyon (F5 IV-V),
Alpha Cen A (G2 V),Beta Hyi (G2 IV), &Alpha Cen B (K1 V).
Disk center (=1), and two positionstowards the limb.
D.Dravins & Å.NordlundStellar Granulation IV. Line Formation in InhomogeneousStellar PhotospheresA&A 228, 84
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Same spectral line in
different stars
Adapted from Dravins & Nordlund,
A&A 228, 203
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Lineshifts change on order 300 m/s
across stellar disks
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( Jean-Pierre Maillard, Institut d’Astrophysique de Paris )
A visible imaging FTS for E-ELTwith XAO & integral-field-unit covering a stellar disk ?
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Common fallacy:Belief that high optical efficiency is crucial to
scientific discovery
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Still … A grand challenge:
Design an efficient R = 1,000,000high-fidelity
spectrometer for ELTs !
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…
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Blended lines
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Pr II HYPERFINE STRUCTURE
Pr II 422.29 nm hyperfine multiplet; 11 components; Hans-Günter Ludwig (2003)
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Limits from telluric absorption ?
Spectrum of Sirius (A1 V) from space (R.Kurucz; Hubble Space Telescope), and from the ground (E.Griffin; Mt.Wilson), showing atmospheric ozone absorption in near-UV
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R. Pallavicini, F. M. Zerbi, P. Spano, P. Conconi, R. Mazzoleni, E. Molinari, K. G. StrassmeierThe ICE spectrograph for PEPSI at the LBT: Preliminary optical design, Proc. SPIE, 4841, 1345 (2003)
PEPSI spectropolarimeter at the Large Binocular Telescope
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(Figure courtesy of Klaus Strassmeier)
At B=12.1, PEPSI @ LBT needs 9 hours to reach S/N=850 at R=300,000
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Spanò et al.: Challenges in optics for Extremely Large Telescope instrumentation Astron. Nachr. 327, 649 (2006)
Possible CODEX layout: 4x1 R4 echelle mosaic of length 1.7 m
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Solar granulation near the limb (upward)Filtergram at 488 nm; Swedish 1-m Solar Telescope on La Palma (G.Scharmer & M.G.Löfdahl)
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Center-to-limb line-
profile changes
in Procyon
Evolution of spatially averaged line profiles and bisectors in
the Procyon model, leading to the global averages.
Time variability increases toward the limb, and the limb effect has opposite sign from
that on the Sun.
D.Dravins & Å.NordlundStellar Granulation IV. Line Formation in InhomogeneousStellar PhotospheresA&A 228, 84
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1-meter FTS; R = 3,000,000National Solar Observatory, Kitt Peak
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Really high resolution:Special grating spectrometers
(R 1,000,000)Heterodyne IR lasers
(R 10,000,000)
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Line asymmetry in the halo star HD 74000, for the mean of five Fe I lines having a stratification and a strength similar to the components of the doublet of the Li resonance line. Red open circles represent the observed asymmetric profile. Green open circles represent the mirrored blue wing of the asymmetric profile. The difference between the green and the red points defines the size of the asymmetry. The effect of a Li blend corresponding to a Li/Li of 4.4 per cent (value of the Asplund et al. Li plateau) is shown as the green signal. Black solid line shows the sum of the green symmetric wing and the depression due to 0.044 Li signal. It is always within ±1 sigma of the asymmetric (red circles) wing, demonstrating that the two effects (convection/line blend) are observationally indistinguishable. The red dots indicate the bisector of the asymmetric profile. (R.Cayrel, M.Steffen, H.Chand, P.Bonifacio, M.Spite, F.Spite, P.Petitjean, H.-G.Ludwig, E.Caffau: Line shift, line asymmetry and the Li/Li isotopic ratio determination. Astron. Astrophys. 473 (2007), L37
The asymmetry of the Li lines casts doubton previous determinations of the isotopic ratio
6Li/7Li
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