Quick Start
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Choose a Payne model:
- 4most-hr — R≈20k. 3 windows: 3926-4355, 5160-5730, 6100-6790 Å. Δλ = 0.05 Å.
- 4most-lr — R≈7k. 1 window: 3700-9450 Å. Δλ = 0.25 Å.
- 80k — R≈80k; 3 windows: 3925-6800, 7700-7800 (for O 777 line), 9050-9130 (for some C I lines) Å. Δλ = 0.05 Å. When selected, a Resolution (R) field appears—enter your spectrum's resolving power to degrade Payne to the requested resolution (slower fitting though) or leave blank.
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Provide the observed spectrum:
- Either upload your own file, or choose a preset.
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Set fit parameters:
- - Good guess speeds convergence; tick Fit to include a parameter.
- - Min/Max default to the network's valid bounds—don't widen them (extrapolation is unsafe).
- - vmac/vsini/resolution convolutions slow down the fitting the most. Only turn on the ones you need or improve the guess/reduce fitting range.
- - RV cannot be fitted well, unless you set a larger Δλ. Small RV shifts will be fitted without any changes.
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Line masks:
- - 📝 opens the mask editor. One line per region: first column = λcenter, second = Δλ. Δλ automatically increases with vsini for indidual element fitting.
- - 📐 activates plot selection. Drag over a region and it's appended to the mask.
- - Stellar parameters (teff, logg, [Fe/H], vmic, broadening) share the same masks; element abundances are fitted with their own masks (individually).
- - Masks are not persistent, so please save them locally if you need to use them later.
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Run & iterate:
- - Click Run fitting. Results appear in Fitted with ±σ (including average systematic value; it may not be accurate).
- - ALL stellar parameters (teff, logg, [Fe/H], vmic, broadening) are fit together, by default using Fe, Mg and Ca lines (default for 4MOST-HR, add more if needed).
- - Default linemasks were selected based on the 4MOST-HR model.
- - Use the ← arrow to copy a fitted value back into Guess.
- - Inspect the plot; you can add masks via 📐 and re-run if needed.
- - NaN after the fit means either that the line failed to fit (e.g. no linemask within the wavelength range). Or the line is too weak (EW above the minimum bound is around 1-2 on average for all lines).
- - For low teff (less than 4200 K), the stellar parameters fitting will also fit C, Ti and O abundances to take into account molecular bands.
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Paper citation:
- Storm et al. 2025b subm. This is a beta version, please report any bugs, problems etc. Please wait until publication of the paper to use this tool for scientific results.
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Known issues:
- - loggf values are 0.31 dex too low for all diagnostic lines of Eu in the blue window. This means that all abundances are ~0.31 dex too high. We subtract 0.31 dex from your results, but in theory it only affects the lines in the blue window.
- - logg is typically ~0.3 dex underestimated. If you rely purely on the spectroscopic stellar parameters, I suggest to add 0.3 dex to logg after fitting, fix this parameter and refit everything else.
- - Too large files cannot be uploaded.
- - No solar difference abundance is applied. This is by choice, as 4MOST solar spectrum is not available yet.
- - No renormalisation is done during the fit.
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Date of last change to the code (keep track of it if you use this tool):
- 2026 March 26: Updated the fitting algorithm (no significant changes to the result), added more QoL features
- 2026 April 15: Added ability to upload 4MOST .fits files.
Running fit - please wait…