Dainis Dravins Lund Observatory Sweden wwwastroluse dainis KVA Towards the science case for EELT HIRES Cambridge UK September 2012 STELLAR SURFACES where starlight and stellar spectra originate ID: 546125
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Slide1
LINE PROFILES & WAVELENGTHS ACROSS STELLAR SURFACES
Dainis
Dravins
– Lund
Observatory
, Sweden
www.astro.lu.se
/~
dainis
KVA
Towards the science case for E-ELT
HIRES
, Cambridge UK, September 2012Slide2
STELLAR SURFACES… where starlight and stellar spectra originate
Simulations feasible for widely different stars
But … any precise physical conclusion
depends on the reliability of modeling
(
metallicity
, magnetic activity,
gravitational redshift, center-to-limb wavelength changes).
How does one verify/falsify 3-D simulations
(except for the spatially resolved Sun) ?
High-resolution spectroscopy acrossspatially resolved stellar disks !Granulation on a 12,000 K white dwarf (top) and a 3,800 K red giant. Areas differ by enormous factors: 7x7 km2 for the white dwarf, and 23x23 RSun2 for the giant.
(H.-G. Ludwig, Heidelberg)Slide3
LINE PROFILES FROM 3-D HYDRODYNAMIC SIMULATIONS
Model predictions insensitive to modest spatial smearing
(Models by Hans-Günter Ludwig,
Landessternwarte
Heidelberg
)
Spatially averagedline profiles from20 timesteps, andtemporal averages.
= 620 nm = 3 eV5 line strengthsGIANT STAR
Teff= 5000 Klog g [cgs] = 2.5(approx. K0 III)
Stellar disk center;µ = cos = 1.0Slide4
Figure by
Hiva
Pazira (Lund Observatory)
(1) Spatially
resolved spectroscopy with
E-ELT
Requires adaptive optics with integral-field unit
Left:
Hydrodynamic
simulation of the supergiant Betelgeuse (B.Freytag
)Right: Betelgeuse imaged with ESO’s 8.2 m VLT (Kervella et al., A&A, 504, 115)Top right: 40-m E-ELT diffraction limits at 550 nm & 1.04 μm.Slide5
(2) Selecting portions of stellar disk during exoplanet transits
Requires very high S/N in high-resolution spectrometers
Figure by
Hiva
Pazira
(Lund Observatory)Slide6
WAVELENGTH SHIFTS OF INTERGALACTIC ABSORPTION LINES
Dainis
Dravins
– Lund
Observatory
, Sweden
www.astro.lu.se
/~
dainis
KVA
Towards the science case for E-ELT
HIRES
, Cambridge UK, September 2012
HIRES quasar spectrum (
A.S.Cowie
,
Univ.of
Hawaii)Slide7
WHENEVER SPECTRAL LINES DO NOT ORIGINATE IN ISOTROPIC TURBULENCE, WAVELENGTH SHIFTS RESULT
SOLAR MODEL
Synthetic line profiles showing convective wavelength shifts originating in granulation
= 620
nm;
= 1, 3, 5
eV; 5 line strengths
Teff= 5700 K; log g [
cgs] = 4.4; G2 V
Solar disk center; µ = cos = 1.0
(Models by Hans-Günter Ludwig, Landessternwarte Heidelberg) Observed solar granulation (Swedish Solar Telescope on La Palma; G.Scharmer
& M.G.Löfdahl
)Slide8
WHENEVER SPECTRAL LINES DO NOT ORIGINATE IN ISOTROPIC TURBULENCE, WAVELENGTH SHIFTS RESULT
… AND THE SAME MUST APPLY TO ALSO INTERGALACTIC CONVECTION, DRIVEN BY HEATING BY
AGNs
NEAR CLUSTER CENTERS
(
Even if
timescales
might be 100 Myr,
rather than solar 10
minutes)
Perseus cluster core in X-rays (Chandra), overlaid with Hα (WYIN). Arc-shaped H
α filaments suggest vortex-like
flows.
Density slices
at
three
times. Viscosity
stabilizes the bubble, allowing a flattened buoyant “cap” to form
. X-ray
brightness and inferred velocity field in Per-A can be reproduced
.
(Reynolds et al.: Buoyant radio-lobes in a viscous
intracluster
medium, MNRAS
357
, 242, 2005
)Slide9
INTERGALACTIC LINE ASYMMETRIES AND SHIFTS:
Plausible amount: 1
% of “general” line broadening
= 0.5 –
1 km/s
?
Mapping 3-D structure from different shifts in different lines
!
Need line synthesis from 3-D hydrodynamic models
!Lines closer to cluster centers gravitationally more
redshiftedMapping depth structure from multiple line components ?Probably useful to have resolving power approaching 1,000,000 ??Resolving lateral structure from secular time changes ???
ANALOGIES
AND
DIFFERENCES
TO
STELLAR
CONVECTION
: