Doppler¶
Introduction¶
Doppler [1] is a general-purpose stellar radial velocity determination software. It uses a forward-modeling approach, convolving a model spectrum to the resolution or Line Spread Function (LSF) of the observed spectrum. Doppler can be used with a high-resolution model of the The Cannon (Casey et al. 2016) and also of The Payne (Ting et al. 2019), both machine-learning approaches to modeling stellar spectra. Doppler can determine the radial velocity (RV) and stellar parameters for a spectrum of any wavelength (3000-18000A) and resolution (R<20,000 at the blue end and 120,000 at the red end) with minimal setup.
The current set of three Cannon models cover temperatures of 3,500K to 60,000K with 3-parameter (Teff, logg, [Fe/H]) and radial velocity. The current Payne model covers temperatures of 3,500K to 6,000K with 33 labels (Teff, logg, Vmicro, [C/H], [N/H], [O/H], [Na/H], [Mg/H], [Al/H], [Si/H], [P/H], [S/H], [K/H], [Ca/H], [Ti/H], [V/H], [Cr/H], [Mn/H], [Fe/H], [Co/H], [Ni/H], [Cu/H], [Ni/H], [Cu/H], [Ge/H], [Ce/H], [Nd/H], [Ba/H], [Eu/H], [La/H], [Y/H], [Sc/H], [Zr/H], [Pr/H], [Yb/H]) as well as radial velocity, rotational velocity and macrotubulence.
Doppler also has the ability to simultaneously fit (“jointfit”) multiple spectra of a star, with a single set of stellar parameters and elemental abundances and separate radial velocities for each spectrum.
Description¶
Doppler fits spectra using a multi-step approach to zero-in on the best solution.
The default, multi-step approach using the Cannon is:
Get initial RV using cross-correlation with rough sampling of Teff/logg/[Fe/H] parameter space.
Get improved Cannon stellar parameters using initial RV.
Improved RV using better Cannon template.
Improved Cannon stellar parameters.
Full least-squares fitting of all stellar parameters and RV.
Run fine-grid in RV using template from previous step
Run MCMC (if requested).
The approach with the Payne is:
Get initial RV using cross-correlation with rough sampling of Teff/logg/[Fe/H]/[alpha/Fe] parameter space.
Least-squares fitting of all desired Payne labels and RV, using best-fit of previous step as initial guess.
Run fine-grid in RV using best-fit template from previous step.
Run MCMC (if requested).
When jointfit is used,
Run regular Doppler fit on each spectrum separately.
Find weighted mean of all labels and Vhelio.
Fit all spectra simultaneously determining one set of labels and a separate RV for each spectrum.
Doppler can be called from python directly or the command-line script doppler can be used.
Examples¶
Doppler¶
Here are the various input arguments for command-line script doppler:
usage: doppler [-h] [--outfile OUTFILE] [--payne] [--fitpars FITPARS]
[--fixpars FIXPARS] [--figfile FIGFILE] [-d OUTDIR] [-l] [-j]
[--snrcut SNRCUT] [-p] [-c] [-m] [-r READER] [-v]
[-nth NTHREADS] [--notweak] [--tpoly] [--tpolyorder TPOLYORDER]
files [files ...]
Run Doppler fitting on spectra
positional arguments:
files Spectrum FITS files or list
optional arguments:
-h, --help show this help message and exit
--outfile OUTFILE Output filename
--payne Fit a Payne model
--fitpars FITPARS Payne labels to fit (e.g. TEFF,LOGG,FE_H
--fixpars FIXPARS Payne labels to hold fixed (e.g. TEFF:5500,LOGG:2.3
--figfile FIGFILE Figure filename
-d OUTDIR, --outdir OUTDIR
Output directory
-l, --list Input is a list of FITS files
-j, --joint Joint fit all the spectra
--snrcut SNRCUT S/N threshold to fit spectrum separately
-p, --plot Save the plots
-c, --corner Make corner plot with MCMC results
-m, --mcmc Run MCMC when fitting spectra individually
-r READER, --reader READER
The spectral reader to use
-v, --verbose Verbose output
-nth NTHREADS, --nthreads NTHREADS
Number of threads to use
--notweak Do not tweak the continuum using the model
--tpoly Use low-order polynomial for tweaking
--tpolyorder TPOLYORDER
Polynomial order to use for tweaking
Index¶
Footnotes