The Absolute Reference Spectrograph at the VTT Precision Solar Spectroscopy with a Laser Frequency Comb H.-P. Doerr, T. J. Kentischer, M. Franz, W. Schmidt (KIS) T. Steinmetz, R. Probst, R. Holzwarth (MPQ, Garching) CASSDA & SOLARNET Meeting Freiburg, 19 February 2014
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Leibniz-Institut fuer Sonnenphysik (KIS): KIS · 2014. 11. 26. · Title: The Absolute Reference Spectrograph at the VTT - Precision Solar Spectroscopy with a Laser Frequency Comb
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The Absolute Reference Spectrograph at the VTTPrecision Solar Spectroscopy with a Laser Frequency Comb
H.-P. Doerr, T. J. Kentischer, M. Franz, W. Schmidt (KIS)T. Steinmetz, R. Probst, R. Holzwarth (MPQ, Garching)
CASSDA & SOLARNET MeetingFreiburg, 19 February 2014
Laser-Frequency-What?
Laser Frequency Combs (LFC)Optical frequency synthesizer with sub-Hz accuracyUltimate calibration sources for Astr. Spectrographs(Murphy et al. 2007, MNRAS 380)
First ever demonstration of an “Astro-Comb” at VTT in 2008(ESO/MPQ; Steinmetz et al. 2008, Sci 321)
Several groups working on astronomical applications(ESO/MPQ, MPQ/KIS, Harvard, Boulder)
LARS is an Absolute Reference SpectrographKIS received Leibniz grant to establish visible light LFCcalibrator at VTT in collaboration with MPQ, GarchingTarget instrument: VTT Echelle (R ≈ 106)Absolute wavelength calibration better than 1 m/s possible(Doerr et al. 2012, SPIE 8450)
Laser-Frequency-What?
Laser Frequency Combs (LFC)Optical frequency synthesizer with sub-Hz accuracyUltimate calibration sources for Astr. Spectrographs(Murphy et al. 2007, MNRAS 380)
First ever demonstration of an “Astro-Comb” at VTT in 2008(ESO/MPQ; Steinmetz et al. 2008, Sci 321)
Several groups working on astronomical applications(ESO/MPQ, MPQ/KIS, Harvard, Boulder)
LARS is an Absolute Reference SpectrographKIS received Leibniz grant to establish visible light LFCcalibrator at VTT in collaboration with MPQ, GarchingTarget instrument: VTT Echelle (R ≈ 106)Absolute wavelength calibration better than 1 m/s possible(Doerr et al. 2012, SPIE 8450)
Laser-Frequency-What?
Laser Frequency Combs (LFC)Optical frequency synthesizer with sub-Hz accuracyUltimate calibration sources for Astr. Spectrographs(Murphy et al. 2007, MNRAS 380)
First ever demonstration of an “Astro-Comb” at VTT in 2008(ESO/MPQ; Steinmetz et al. 2008, Sci 321)
Several groups working on astronomical applications(ESO/MPQ, MPQ/KIS, Harvard, Boulder)
LARS is an Absolute Reference SpectrographKIS received Leibniz grant to establish visible light LFCcalibrator at VTT in collaboration with MPQ, GarchingTarget instrument: VTT Echelle (R ≈ 106)Absolute wavelength calibration better than 1 m/s possible(Doerr et al. 2012, SPIE 8450)
short term: spectrograph seeing; ultra-short: vibrations?
VTT Spectrograph stability
-200
-100
0
100
200
300
400
500
600
700
800
0 1 2 3 4 5 6 7
759
760
761
762
763
764
Dri
ft (
m/s
)
Pre
ssure
(hPa
)
T - T0 = 06Mar2013 01:27 (Hours)
Spektrograph Drift vs air pressure (slit)
DriftPressure
long-term: air pressure (+temperature)
Instrument Characteristics
Single-mode fiber feed (SMFF; 1, 3, 10 arcsec FOV)Operating wavelength range ≈ 460 − 650 nmSpectral resolution ≈ 750 000Frequency solution accurate at ≈ 10 cm s−1 per exposure(Seeing limits repeatability; ≈ 1m/s, but averages out)Virtually no scattered lightPSF comes for free!“Real” flat-fields from continuum lamp; excellent fidelity
ApplicationsLarge-scale solar structures; Lab measurementsNot for: small-scale velocity fieldsBut: we can cross-calibrate co-observing instruments!
Instrument Characteristics
Single-mode fiber feed (SMFF; 1, 3, 10 arcsec FOV)Operating wavelength range ≈ 460 − 650 nmSpectral resolution ≈ 750 000Frequency solution accurate at ≈ 10 cm s−1 per exposure(Seeing limits repeatability; ≈ 1m/s, but averages out)Virtually no scattered lightPSF comes for free!“Real” flat-fields from continuum lamp; excellent fidelity
ApplicationsLarge-scale solar structures; Lab measurementsNot for: small-scale velocity fieldsBut: we can cross-calibrate co-observing instruments!
0
0.5
1
6300 6300.5 6301 6301.5 6302 6302.5 6303
Norm
aliz
ed
Inte
nsi
ty
Wavelength (A)
LARS fidelity in comparison
Kitt-Peak FTSLiegeLARS
0.95
1
6300 6300.5 6301
0.94
0.96
0.98
6301.8 6302
Instrument Characteristics
Single-mode fiber feed (SMFF; 1, 3, 10 arcsec FOV)Operating wavelength range ≈ 460 − 650 nmSpectral resolution ≈ 750 000Frequency solution accurate at ≈ 10 cm s−1 per exposure(Seeing limits repeatability; ≈ 1m/s, but averages out)Virtually no scattered lightPSF comes for free!“Real” flat-fields from continuum lamp; excellent fidelity
ApplicationsLarge-scale solar structures; Lab measurementsNot for: small-scale velocity fieldsBut: we can cross-calibrate co-observing instruments!
Example: Telluric O2 Wavelengths
1.30
1.32
1.34
1.36
1.38
1.40
1.42
1.44
1.46
1.48
1.50
1.52
02Aug12h
03Aug00h
03Aug12h
04Aug00h
04Aug12h
05Aug00h
05Aug12h
06Aug00h
1
1.2
1.4
1.6
1.8
2
2.2
Depart
ure
fro
m P
ierc
e B
reck
inri
dge (
mÅ
)
Air
mass
Date
LARS wavelengths of telluric O2 6298.5 Å line
wavelengthairmass
Example: Telluric O2 Wavelengths
-25
-20
-15
-10
-5
0
5
0 1 2 3 4 5 6 7
rela
tive lin
e c
ente
r sh
ift
(m/s
)
Time - 2013-12-03 9:44 UT (hours)
Relative shift, telluric O2 6298.46
Example: Telluric O2 Wavelengths
Pierce & Breckinridge (1973), LARS preliminary(!) (Aug 2013)