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Gravitational redshifts, and other wavelength shifts in stellar spectra
Dainis Dravins – Lund Observatory
www.astro.lu.se/~dainis
KVA
Exactly 100 years ago
A.Einstein, Annalen der Physik 340, 848 (1911)
Predicted effects by gravity on light
Foreground galaxy cluster manually retouched away
STRONG LENSING WEAK LENSING MICROLENSING
Already long before Einstein…
John Mitchell (1784)
Predicting gravitational effects on light
Predicting gravitational effects on light
John Mitchell (1784)
Predicting gravitational effects on light
John Mitchell (1784)
Predicting gravitational effects on light
Pierre-Simon Laplace (1796)
Verifying Einstein ?
Klaus Hentschel: Erwin Finlay Freundlich and Testing Einstein’s Theory of Relativity, Archive for History of Exact Sciences 47, 243 (1994)
Freundlich’s attempts to verify relativity theory (I)
Erwin Finlay Freundlich (1885-1964) worked to experimentally verify the predictions from Einstein’s theory of relativity and the effects of gravity on light.
Freundlich’s attempts to verify relativity theory (II)
Klaus Hentschel: Erwin Finlay Freundlich and Testing Einstein’s Theory of Relativity, Archive for History of Exact Sciences 47, 243 (1994)
Einsteinturm, Potsdam-Telegrafenberg
Nature 306, 727 (1983)
Unethical falsifications in astronomy ?
QJRAS 26, 279 (1985)
Controversial interpretations of history
Actual gravitational redshift in white dwarfs
X-ray spectra for early (top), and late phases of the bursts from neutron stars.
Red: Absorption lines from the circumstellar medium
Blue: Photospheric absorption lines at redshift Z = 0.35
J.Cottam, F.Paerels, M.Mendez: Gravitationally redshifted absorption lines in the X-ray burst spectra of a neutron star, Nature 420, 51
Gravitational redshift in neutron stars
Gravitational redshift in the laboratory
R.V.Pound & G.A.Rebka: Gravitational Red-Shift in Nuclear Resonance, Phys.Rev.Lett. 3, 439 (1959)
Robert Pound
Glen Rebka
Stellar spectroscopy
EFFECTS ON SPECTRAL LINES
L.Lindegren & D.Dravins: The fundamental definition of “radial velocity, A&A 401, 1185
Mechanisms causing wavelength shifts
The process includes: motion of the object; its emission of an electromagnetic signal; its propagation through space; motion of the observer; and the reception of the signal.
R.F.Griffin: Spectroscopic Binaries near the North Galactic Pole. Paper 6: BD 33° 2206, J.Astrophys.Astron. 3, 383 (1982)
Expected gravitational redshifts
Expected gravitational redshifts
D. Dravins
IAU Symp. 210
Radial velocities without spectroscopy
Astrometric radial velocities I
Dravins, Lindegren & Madsen, A&A 348, 1040
Astrometric radial velocities II
Dravins, Lindegren & Madsen, A&A 348, 1040
Astrometric radial
velocities from
perspective acceleration
Dravins, Lindegren & Madsen, A&A
348, 1040
Astrometric radial velocities III
Dravins, Lindegren & Madsen, A&A 348, 1040
STARPATHS (200,000 y)
Madsen, Dravins & Lindegren, A&A 381, 446
Pleiades from Hipparcos Proper motions over 120,000 years
Hyades from Hipparcos D. Dravins, IAU Symp. 215 (2004)
Hyades lineshifts Madsen, Dravins & Lindegren, A&A 381, 446
S.Madsen, D.Dravins, H.-G.Ludwig, L.Lindegren: Intrinsic spectral blueshifts in rapidly rotating stars?, A&A 411, 581
Apparent radial velocity vs. rotation?
Differential velocities within open clusters
B.Nordström, J.Andersen, M.I.Andersen: Critical tests of stellar evolution in open clusters II. Membership, duplicity, and stellar and
dynamical evolution in NGC 3680, Astron. Astrophys. 322, 460
Different “velocities” ─ giants vs. dwarfs?
Dean Jacobsen, astrophoto.net
M 67
L.Pasquini, C.Melo, C.Chavero, D.Dravins, H.-G.Ludwig, P.Bonifacio, R.De La Reza:
Gravitational redshifts in main-sequence and giant stars, A&A 526, A127 (2011)
Searching for gravitational redshifts in M67
M67 (NGC 2682) open cluster in Cancer contains some 500 stars;
age about 2,6 Gy, distance 850 pc.
M67 color–magnitude diagram with well-developed giant branch.
Filled squares denote single stars.
Dean Jacobsen, astrophoto.net
L.Pasquini, C.Melo, C.Chavero, D.Dravins, H.-G.Ludwig, P.Bonifacio, R.De La Reza:
Gravitational redshifts in main-sequence and giant stars, A&A 526, A127 (2011)
Searching for gravitational redshifts in M67
Radial velocities in M67 with a superposed Gaussian centered on
Vr = 33.73, σ = 0.83 km s−1
Radial velocities in M67: No difference seen between giants (red)
and dwarfs (dashed)
Real line formation
Solar disk
June 12, 2009
GONG/Teide
AN ”IDEAL” STAR ?
Granulation near the limb (towards the top) at 488 nm; Swedish 1-m solar telescope, La Palma
A REAL STAR
Solar Optical Telescope on board HINODE (Solar-B) G-band (430nm) & Ca II H (397nm) movies
Spectral scan
across the solar surface.
Left: H-alpha line
Right: Slit-jaw image
Big Bear Solar Observatory
“Wiggly” spectral lines
of solar granulation
“Wiggly" spectral lines in the solar photosphere
inside and outside a region of activity, reflecting
rising and sinking motions in granulation (wavelength increases to the right).
The central part crosses a magnetically active region
with reduced velocity amplitudes. (W.Mattig)
“Wiggly” spectral lines
of stellar granulation
(modeled)
Disk-center Fe I profiles from 3-D hydrodynamic model of the metal-poor star HD 140283 in NLTE and LTE.
Top: Synthetic “wiggly-line” spectra across stellar surface. Curves show equivalent widths W along the slit.
Bottom: Spatially resolved profiles; average is red-dotted.
N.G.Shchukina, J.Trujillo Bueno, M.Asplund, Astrophys.J. 618, 939 (2005)
Spatially resolved line profiles of the Fe I 608.27 nm line (exc = 2.22 eV) in a 3-D solar simulation.
The thick red line denotes the spatially averaged profile.
The steeper temperature structures in upflows tend to make their lines stronger (blue-shifted components).
M.Asplund: New Light on Stellar Abundance Analyses: Departures from LTE and Homogeneity, Ann.Rev.Astron.Astrophys. 43, 481
Solar-type granulation causes
convective lineshifts on order 300 m/s
”INVERTED” GRANULATION & CONVECTIVE REDSHIFTS ?
Simulated (top) and observed (Dutch Open Telescope) solar images in continuum (left) and
Ca II H wing (right).
(Leenaarts & Wedemeyer-Böhm, Astron.Astrophys. 431, 687, 2005)
Other stars
A.S.Brun, A.Palacios: Numerical Simulations of a Rotating Red Giant Star. I. Three-dimensional Models of Turbulent Convection and
Associated Mean Flows, ApJ 702, 1078
3-D modeling of stellar hydrodynamics
Cool supergiant (”Betelgeuse”)
Bernd Freytag (Uppsala)
STELLAR CONVECTION – White dwarf vs. Red giant
Snapshots of emergent intensity during granular evolution on a 12,000 K white dwarf (left) and a 3,800 K red giant. Horizontal areas differ by dozen orders of magnitude: 7x7 km2
for the white dwarf, and 23x23 RSun2 for the giant. (H.-G. Ludwig)
CORRUGATED STELLAR
SURFACES ?
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 positions
towards the limb
D.Dravins & Å.Nordlund
Stellar Granulation IV.
Line Formation in
Inhomogeneous
Stellar Photospheres
A&A 228, 84
Fe I-line bisectors in Sun and Procyon
(F5 IV-V) Average 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
Bisectors of the same
spectral line in different
stars Adapted from
Dravins & Nordlund, A&A 228, 203
From left:
Procyon (F5 IV-V),
Beta Hyi (G2 IV),
Alpha Cen A (G2 V),
Alpha Cen B (K1 V).
Velocity [m/s]
Non-LTE effects on spectral line wavelength
shifts
Adapted from
Dravins & Nordlund, A&A 228, 184
L.Pasquini, C.Melo, C.Chavero, D.Dravins, H.-G.Ludwig, P.Bonifacio, R.De La Reza:
Gravitational redshifts in main-sequence and giant stars, A&A 526, A127 (2011)
Searching for gravitational redshifts in M67
Gravitational redshift predictions vs. mass/radius ratio (M/R) (dashed red)
do not agree with observations.
Calculated convective wavelength shifts for Fe I lines in dwarf (red crosses)
and giant models (squares).
Spatially resolved stellar spectroscopy
Solar granulation near the limb (upward on the image)
Filtergram at 488 nm; Swedish 1-m Solar Telescope on La Palma (G.Scharmer & M.G.Löfdahl)
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
Exoplanet transits
EFFECT OF TRANSIT GEOMETRY ON THE ROSSITER EFFECT FOR HD209458
Left: Geometry of the crossing for 3 cases
Right: Radial- velocity anomalies for these cases, for different stellar rotation Vsini
D.Queloz, A.Eggenberger, M.Mayor, C.Perrier, J.L.Beuzit, D.Naef, J.P.Sivan & S.Udry
Detection of a spectroscopic transit by the planet orbiting the star HD 209458
Astron.Astrophys. 359, L13
RADIAL-VELOCITY
RESIDUALS FOR
THE STAR HD209458
TOP:
Outside planetary transit,
residuals are random errors.
BOTTOM:
During transit
(dashed line),
Rossiter effect appears.
ELODIE observations
D.Queloz, A.Eggenberger, M.Mayor,
C.Perrier, J.L.Beuzit, D.Naef
J.P.Sivan & S.Udry
Detection of a spectroscopic transit by
the planet orbiting the star HD 209458
Astron.Astrophys. 359, L13
Exoplanet transits (Rossiter-McLaughlin effect)
When an exoplanet transits a stellar disk,
successive center-to-limb contributions
to the integrated line profile are occulted,
with different effects for stars of different
rotational velocities.
Hiva Pazira (Lund Observatory)
Spatially resolved stellar spectroscopy
Synthetic line profiles
across stellar disks
Examples of synthetic line profiles from
hydrodynamic simulations of a solar-type star.
Curves are time-averaged line profiles, at
different positions and angles on the stellar disk.
Black curve is line profile at disk-center;
gradually lower intensities of blue, green, and
red curves reflect the limb darkening.
Solar model; Fe I, 620 nm, 1 eV.
Disk locations µ=1, 0.87, 0.59, 0.21;
azimuthal angles 0, 90, 180, 270°
Simulation by Hans-Günter Ludwig (Landessternwarte Heidelberg)
Spatially resolved stellar spectroscopy
Doppler imaging
DOPPLER
IMAGING
OF
STELLAR
SURFACES
S.S.Vogt, G.D.Penrod,
PASP 95, 565
Doppler imaging of stellar surfaces
For a star with a dark spot close to
the equator, spectral line profiles
are affected throughout their whole
Width, as the spot is carried around
the star by rotation.
(Jean-François Donati)
Doppler imaging of stellar surfaces
If the spot is located close to the pole,
spectral lines are only affected in their
core regions; the difference with the
previous case enables one to recover
information on both latitude and longitude
of starspots.
(Jean-François Donati)
Spectroscopy at very & extremely large telescopes
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 84,000 110,000 120,000 160,000 320,000
Wavelengths [µm] 0.37– 0.89 0.3 – 1.0 0.3 – 1.1 0.39 – 1.1 0.3 – 1.0 0.38 – 0.91
Potsdam Echelle Polarimetric and Spectroscopic Instrument @ Large Binocular Telescope
2080 cm R4 echelle grating for
PEPSI
HE 1523−0901: A strongly r-process-enhanced metal-poor star, [Fe/H] = − 2.95 , with detected uranium
(Figure by Klaus Strassmeier)
At B=12.1, PEPSI @ LBT needs 9 hours to reach S/N=850 at R=300,000
Resolving power and
spectral range of proposed
E-ELT spectrographs
Pasquini et al.: CODEX: the high resolution visual spectrograph for the E-ELT
Proc. SPIE 7014, 70141I (2008)
Optical arrangement of multi-camera CODEX design
40-m
European
Extremely
Large
Telescope
E-ELT on Cerro Armazones (artist’s impression)
Hiva Pazira (Lund Observatory)
Spatially resolved spectroscopy with ELTs
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..
Grand challenge: Design an efficient
R = 1,000,000 high-fidelity
spectrometer for E-ELT !
