precision doppler spectroscopy guillem anglada-escude school of physics and astronomy queen mary,...
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Precision Doppler spectroscopy
Guillem Anglada-EscudeSchool of Physics and AstronomyQueen Mary, University of London
Institute for AstrophysicsGeorg-August-Universität Göttingen
2nd CARMENES science meeting
Precision Doppler spectroscopy as a detection method
Indirect methods
Kinematic
Doppler spectroscopy
Astrometry Timing
Photometric
Gravitationalmicro-lensing
Transit
Dynamic
Orbital perturbations
Disk-planet interactions
Star-planet interactions
Width of a typical solar line is 15
km/s
Spectroscopic binary K=30 km/s
Hot jupiterK=300 m/s
Precision Doppler spectroscopy as a detection method
Tau Ceti G8.5VO
rder
Pixel
6900 A
3800 A
HARPS-ESOSpectral format
Precision Doppler spectroscopy as a detection method
Precision Doppler spectroscopy : (quick & unfair) historical overview
+ Perforated binary mask (CORAVELs)
Digital CCF (ELODIE)Hot jupiters
Tellurics
HF cell (CFHT)
Iodine cell - (M. Hamilton)Warm Jupiters
50 m/s
25 m/s
5 m/s
Echelle spectrograph
CCDComputers
Stabilized spectrographs
300 m/s
10 m/s
Absorption cells
4 m/sNextGen CCDs
3 m/sDedicated ultra-stable(HARPS-ESO)
Sub-Neptune
Large telescopes(HIRES-Keck)
Sub-Neptune
2 m/s
1 m/s
<1 m/sG, K
dwarfs
Software, Pipelining + calibration Few Earth masses
Dedicated semi-stabilized(PFS-Magellan)
Few Earth masses
High incident angle Grating
Prism
Many interference orders overlapped
Orders separated
Absorption cell
Absorption cell
Stabilized spectrograph
High incident angle Grating
Prism
Many interference orders overlaping
Orders separated
High incident angle Grating
Prism
Many interference orders overlaping
Orders separated
Fiber – light transport + scrambling
Stabilized spectrograph
au
earth
aM
mscmK
1/ 10
*
au
jup
aM
msmK
1 / 30
*
G dwarfHZ @ 1 AU
M dwarfHZ @ 0.1 AU
30 m/s 950 m/s
0.1 m/s 3.1 m/s
Exo-Jupiter formula
Exo-Earth formula
500+ planetsELODIE, Hamilton, HIRES/Keck, CORALIE, HARPS, UVES/VLT, AAT …
Happening now…HARPS, PFS/Magellan, HIRES/Keck
Precision Doppler spectroscopy : (quick & unfair) historical overview
Precision Doppler spectroscopy : (quick & unfair) historical overview
High resolution – Large telescopes (CRIRES)
Absorption cells 6 m/s
50 m/s
New large format arrays, nIR cross dispersion, stabilized cryogenic optics…
Tellurics
HF cell (CFHT)
Iodine cell - (M. Hamilton)Warm Jupiters
Large telescopes(HIRES-Keck)
Sub-Neptune
Dedicated semi-stabilized(PFS-Magellan)
Few Earth masses
50 m/s
25 m/s
5 m/s
4 m/s
2 m/s
Absorption cells
Infrared (~2000)
First high-res spectrographs(CSHELL-IRTF, 256x256 pixels)
Echelle – low resolution(Tellurics-NIRSPEC)
100 m/s
Bean et al. ApJ 2010Proxima Cen, CRIRES/VLT with Ammonia
RMS 5.4 m/s
Proxima Cen, HARPS/3.5m RMS 2.3 m/s
M-dwarfs : Radial velocities in the near infrared?
Requires an absorption cell External calibration source (ThAr)
But (some) HARPS data is public!
Absorption cell technique Stabilized spectrograph
Precision limited by PSF Stabilized PSF
Works on any spectrograph Specialized spectrograph
No-cell templates are critical High SNR templates
Available on several instruments Built only by Geneva group
Very complex software. Private data reduction pipelines
Proprietary instruments & Data reduction pipelines …
Absorption cell (optical and nIR) vs Stabilized spectrographs (optical)
& CARMENES!
Doppler measurement
𝑅𝑖= 𝑓 𝑖−F (𝑘 𝜆𝑖 )Most simple case : Only Doppler offset
𝑅𝑖=𝑎0 𝑓 𝑖−F (𝑘 𝜆𝑖 )A bit better: Doppler offset +
flux scaling
Doppler measurement
𝑅𝑖= 𝑓 𝑖−F (𝑘 𝜆𝑖 )Most simple case : Only Doppler offset
𝑅𝑖=(𝑎0+𝑎1 𝜆𝑖+…𝑎𝑛𝜆𝑖) 𝑓 𝑖−F (𝑘 𝜆𝑖 )Even better : Polynomial flux correction
n
Doppler measurement
𝜕 𝜒 2
𝜕𝑎0
=0
𝜕 𝜒 2
𝜕𝑎𝑛=0
𝜕 𝜒 2
𝜕𝑘=0
Preferred solver (and interpolator)
𝜒2min
𝑘=1−𝑣𝑐
Doppler measurement : and what about cross-correlation methods?
𝑅𝑖= 𝑓 𝑖−𝐹 (𝑘 𝜆𝑖 )
𝜒2=∑𝑖
( 𝑓 𝑖−𝐹 (𝑘 𝜆𝑖 ))❑2
𝜒2=∑𝑖
𝑓 𝑖+𝐹 (𝑘 𝜆𝑖 )−2 𝑓 𝑖𝐹 (𝑘 𝜆𝑖 )2 2
Doppler measurement : and what about cross-correlation methods?
2 2
Doppler measurement : and what about cross-correlation methods?
𝜕𝜕𝑘
𝜒 2=𝜕𝜕𝑘∑𝑖 𝑓 𝑖+
𝜕𝜕𝑘∑𝑖 𝐹 (𝑘 𝜆𝑖 )−2
𝜕𝜕𝑘∑𝑖 𝑓 𝑖𝐹 (𝑘 𝜆𝑖 )
𝜕𝜕𝑘
𝜒 2=𝜕𝜕𝑘∑𝑖 𝑓 𝑖+
𝜕𝜕𝑘∑𝑖 𝐹 (𝑘 𝜆𝑖 )−2
𝜕𝜕𝑘∑𝑖 𝑓 𝑖𝐹 (𝑘 𝜆𝑖 )
2 2
Doppler measurement : and what about cross-correlation methods?
Cross Correlation Function (CCF)D. Queloz, Proc. IAU Symposium 1995
l0
1
30 RV offset (km/s)
10 0 20 -10 -30 -20
CCF
Cross-correlation with binary mask (weighted)
Proxima Cen
Some M-dwarfs are more stable than G and K dwarfs!
2.6%
Perspective acceleration effectZechmeister et al. 2009 A&A
Some M-dwarfs are more stable than G and K dwarfs!
2.6%
Perspective acceleration effectZechmeister et al. 2009 A&A
Now we are surfing the photon noise!
Toolbox : periodograms
Δ 𝑙𝑛𝐿=𝑙𝑛𝐿− 𝑙𝑛𝐿P null
𝐿=∏𝑖
1
√2𝜋 (𝜎2+𝑠2)𝑒𝑥𝑝[− 1
2
(𝑣 𝑖−𝑣 (𝑡𝑖 ;𝜃 ))𝜎 2+𝑠2 ]
𝑙𝑛𝐿=−𝑁2
ln (2𝜋 )− 12∑𝑖 ln (𝜎 2+𝑠2 )− 1
2∑𝑖 𝜒2
2
i i
i
More detailed/correct discussion see: Baluev 2009 & 2012(his codes are public!)
Multiplanet system!
GJ 676A, M0V2 gas giants+1 hot Neptune+1 very hot super-Earth
Anglada-Escude & Tuomi, 2012 A&A
0.041 AU
0.187 AU1.8 AU 5.2 AU
𝐿∝𝐸𝑋𝑃 [− 12𝜒2]
Likelihood function
Period
Mas
s
Provides optimal sampling in highly dimensional spaces
N = 3 + 5 x Nplanets
Run a few million steps and you are done!
Toolbox : Bayesian MCMC
Periodograms + Bayesian + dynamics + priors + attempts to model red noise
b
c
d
ef
g
Applying dynamical stability prior
Take home message
Understand your instrument AND YOUR DATA
Learn how to design your model optimization scheme
Get trained into basic data analysis techniques. Take a course if necessary
Think further : • Bayesian RV measuring algorithm?• How can I measure line shapes? (e.g. bisector-like indices)• How to incorporate activity information into the Doppler model?
• Find collaborators to take care of thinks you don’t have time to learn (e.g. dynamics!) or do (TRANSIT SEARCHES, anybody in charge???)
Be skeptic of black-boxes. If you can code it, you master it.