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Telluric Contamination effects, challenges, and solutions in the context of EPRV Sharon X. Wang, Jason T. Wright, Cullen Blake, Pedro Figueira, Nuno Santos, Peter Plavchan, Andreas Seifahrt, Claire Moutou, Franois Bouchy

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summary of current status Telluric lines have ~m/s level impact on RV precision (either optical or NIR). We can model most telluric lines to ~ 2%. (radiative transfer + atmospheric model + line list) Telluric lines are sources of contamination instead of wavelength calibrator for EPRV.

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telluric absorption in optical+NIR 500nm1m 2.6m Smette et al. (2015)

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pervasive micro lines in the optical Wavelength [ ] Cunha et al. (2014) 4430 4850 5040 5410 5750 line depth 0.2 -- 2%

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telluric: calibrator, contamination Griffin & Griffin (1973) suggested 10 m/s possible with O 2 (start of quest for PRVs?) Now 5-20 m/s in both optical and NIR using tellurics lines as calibrators (e.g. Barnes+2012, Blake+2010, Figueira+2010a). Studies in the optical show long-term stability at 10 m/s over 10 years with HARPS (Figueira+2010b) and that it is possible to improve upon this value using simple empirical models (e.g. Figueira+ 2012) EPRV definitely requires better calibrators and proper modeling of telluric lines (e.g. Bean+2010, upcoming instruments in NIR).

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optical (Th-Ar): alias induced by micro tellurics Cunha et al. (2014)

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Artigau et al., 2014, SPIE, 9149 Assumption : telluric absorption spectrum = sum of a finite number of chemical species that vary in relative strength = linear combination of individual absorbance with weight varying with airmass and weather. Library of individual absorbance (real telluric standards (hot stars) observed at a large variety of airmass and water column or TAPAS synthetic spectra) + principal component analysis to identify independently varying absorbers. Non-zero velocity of one absorber seen as an second component equal to the spectral derivative Science spectra = least-square fit of 1) absorption-free spectra + 2) linear combination of absorbance. Requirement = large spectral range + high resolution

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HARPS spectra restricted to 634 669 nm Without excluding telluric = 10.3 m/s RMS Excluding telluric (18% of the domain) = 3.6 m/s RMS PCA subtracted spectrum = 1.6 m/s RMS Artigau et al. (2014)

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optical (iodine): alias induced by micro tellurics clean telluric 0.4% absorption Wang et al. in prep simulation 2 chunk HD 185144

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NIR: modeling macro telluric lines Mauna Kea, PWV=3 mm, Airmass = 1 (from Gemini webpage) A different challenge: >>0.1 at many wavelengths Several different species (H2O, CH4, CO2)

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NIR: modeling macro telluric lines Seifahrt+2010 Bean+2010 Blake+2011

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NIR: modeling macro telluric lines Seifahrt+2010 Blake+2011 High optical depth - approximations that work at low optical depth not OK Detail line shape matters more, line mixing matters Water, water, everywhere! Multiple, overlapping species HITRAN errors mater more Good News? CO2, CH4 are well behaved, only small seasonal variations in concentration!

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modeling the telluric lines: approaches, codes available Physical: TAPAS (Bertaux et al. 2014, web) TelFit (Gullikson et al. 2014) Molecfit (Smette et al. 2015) TERRASPEC (Bender et al. 2012, cbender@psu.edu)cbender@psu.edu ATRAN (IR only, Lord 1992 + Gemini, web) Write your own using LBLTRM(Clough+2005)+HITRAN (Rothman+2012) Empirical: telluric standards (Vacca+2003) taking spectra at different airmass (Wallace+2011, solar atlas) PCA (Artigau et al. 2014)

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Empirical models Blake et al. (2010) FTS Template - >0.1, multiple species Forward modelling using FTS telluric template from Livingston & Wallace 1991

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challenges & pressing questions? How good are we? How well can we model telluric lines? o What are the current best codes? How well does each do? Do they agree? o What do we do about the challenging lines? o Whats the current limiting factor? Whats next? Empirical+physical? More physics? How well do we need to model them? o How well are we doing now? o Whats their impact on RV precision? o Whats the requirement for achieving 10cm/s?

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challenges & pressing questions? How good are they? How stable (in terms of RV) are the telluric lines? o The current knowledge? o What to be done? Different species? How stable do we need them to be or need to model? o Whats the RV limit for using them as calibrators? o Whats the requirement for achieving 10cm/s? o Include telluric RV as free parameter? Species?

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How well can we model telluric lines? o What are the current best codes? How well does each do? Do they agree? o What do we do about the challenging lines? o Whats the current limiting factor? Whats next? Empirical+physical? More physics? part 1/4

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How well can we model telluric lines? o What are the current best codes? How well does each do? Do they agree? Seifahrt et al. (2010) Cunha et al. (2014)

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How well can we model telluric lines? o What are the current best codes? How well does each do? Do they agree? o What do we do about the challenging lines? o Whats the current limiting factor? Whats next? Empirical+physical? More physics? Part 1/4

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Limitations of current modeling (roughly in order of impact) 1.First order problems in molecular databases (e.g. HITRAN) 1.Missing lines 2.Uncertainties/errors in line position, line strength, line shift and broadening parameters. Note: data quality in HITRAN is not homogeneous, neither for the same species nor for different species in a narrow wavelength range! 2.Limitations of current modeling codes (e.g. LBLRTM) from treatment of correct line profiles (i.e. speed dependence/line mixing effects, Dicke narrowing). Standard is Voigt profile, but would need Rautian or Galatry profile for certain species with strong line mixing. (see, e.g., Hartman et al. 2008) 3.Second order problems in molecular databases (e.g. HITRAN) 1.Missing data or approximate treatment of line coupling and mixing. Important e.g. for O2, CO2, N2, H2O, etc.

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Limitations of current modeling (roughly in order of impact) - cont. 4.Limited knowledge of atmospheric conditions 1.Standard atmospheric profiles probably fine for well mixed species, but absolute column densities for, e.g., CH4, or CO2 need to be adjusted. 2.Water vapor is problematic in standard atmospheric profiles due to high absolute variability and variable vertical distribution (different temperature, pressure broadening effects etc.). -> Water vapor spectrum for same PWV column can look different depending on vertical distribution. 5.Wind-induced line-shifts 1.Can be substantial, especially for observatories under jet stream with light path into the jet stream (i.e., azimut and airmass dependent). See Figuera et al. (2010)

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Improvements to current modeling 1.Invest manpower and/or money into codes and (more importantly) groups providing data for HITRAN database -> unlikely to happen. 2.Build a simplified (and unphysical) astro-HITRAN with line data retrieved from fitting high-SNR, high-resolution stellar spectra from instruments with stable and/or well known LSFs (e.g. HARPS, or gas-cell aided spectrographs). Need to be done over large number of spectra taken under different conditions to disentangle stellar and telluric features. Successful example: CRIRES program of Bean et al. 2010. 3.Improve knowledge of local conditions of the atmosphere. Particularly important for H2O and for wind-speed issues. -> Launch weather balloons every night? -> Potential use of LIDAR techniques for remote retrieval? What about GPS or microwave radiometers?

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How well do we need to model them? o How well are we doing now? o Whats their impact on RV precision? o Whats the requirement for achieving 10cm/s? Part 2/4

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How stable (in terms of RV) are the telluric lines? o The current knowledge? o What to be done? Different species? Part 3/4

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How stable (in terms of RV) are the telluric lines? o The current knowledge? o What to be done? Different species? Figueira et al. (2010) O2 lines in HARPS data HARPS - Telluric O2 line RVs relative to star: ~2 m/s with simple model over years, 5 m/s out of the box

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How stable (in terms of RV) are the telluric lines? o The current knowledge? o What to be done? Different species? Balthasar+1982 - Telluric O2 lines can be modeled to 3 m/s Caccin+1985 - Pressure-induced asymmetries+winds < 5 m/s Smith 1982 - ~5 m/s on Arcturus using O2 lines What about H2O lines?

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How stable do we need them to be or need to model? o Whats the RV limit for using them as calibrators? o Whats the requirement for achieving 10cm/s? o Include telluric RV as free parameter? Species? Part 4/4

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Bibliography (to be completed) http://bit.ly/eprv_telluric_references Stay tuned for summary of the session!

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extra slides feel free to add. be sure to give citations and add notes!

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optical (iodine): micro telluric lines everywhere! using TERRASPEC

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optical (iodine): alias induced by micro tellurics

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Recipe: How to clean your deconvolved stellar template Ingredients: high SNR stellar template spectra (taken with no iodine), bracketing telluric standard observations through nearby B star (optional but desirable), bracketing nearby B star spectra through iodine cell (to provide spectral PSF). Prepare: telluric model generator which can generate models under different atmospheric conditions (e.g. varying water vapor), tuned to your observatory. Your favorite deconvolution algorithm. Cook: 1. Fit the B star telluric standards to get atmosphere model. 2. Fit the B star + iodine spectra with iodine atlas + telluric model to get the correct PSF. 3. Deconvolve the stellar template spectra with PSF. 4. Divide out telluric model from deconvolved stellar template (note: first solve for absolute stellar RV!).

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How well can we model telluric lines? o What are the current best codes? How well does each do? Do they agree? Gullikson et al. (2014) correction with TelFit modelingcorrection with telluric standards 3-5%

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How well can we model telluric lines? o What are the current best codes? How well does each do? Do they agree? Smette et al. (2015) 2%

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NIR: modeling macro telluric lines Bean et al. (2010)

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Theoretical Telluric Spectrum Terraspec: Chad Bender

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Frequency Optical Depth Telluric Line RV Shifts Pressure Shifts: RV< 20 m/s Winds: RV< 20 m/s Telluric Lines are Asymmetric!

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Atmospheric Pressure ~0.01 1% Pressure Change is RV=3 m/s at 1 micron Depends on Zenith Angle : 1 Variation in Pressure Pressure with Altitude For H 2 0, CO 2, CH 4, O 2 P/P Altitude (km)

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Atmospheric Winds East-West North-South Vertical East Average Jet Stream Average Winds Radial Wind Speed Alt=5 Km Alt=20 Km January March JuneSeptember

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Monte Carlo Simulations 100 night atmosphere models over 12 months Models for mountain site in New Mexico 10 random sight lines each night, AM