Opacities (cross sections per unit mass) are fundamental for analysing the spectra of the atmospheres of exoplanets. They are a key ingredient in radiative transfer and atmospheric retrieval models. As we move into the era of precision exo-atmospheric spectroscopy, there is an urgent need to benchmark and compare the opacities used in different calculations by different individuals/groups.
The DACE opacity database was created in 2020 to address this need of the exoplanet community. Input from various spectroscopic databases ExoMol, HITEMP, HITRAN, Kurucz, NIST, VALD3, etc is used with the open-source HELIOS-K opacity calculator to compute opacities for a wide variety of atoms and molecules. The original sources of the opacities have been properly acknowledged. The DACE opacity database offers the capability of versioning the opacities as the various spectroscopic databases report updates.
There are three major aspects of the DACE opacity database. Users may visualise and compare opacities from different species and/or different temperatures and pressures. Figures of these opacity comparisons may be generated by the user interface. The original, high-resolution opacity files (resolution: 0.01 cm^-1) are available for download in binary format. There is also the option to interpolate the high-resolution files to obtain opacities with arbitrary spacings in temperature and pressure, as well as to choose the desired range in wavenumber or wavelength. These interpolated opacity files are available in HDF5 format.
In the future, we would like to offer users the ability to archive their own calculations of opacities in order to facilitate a transparent comparison of different implements of opacities by different individuals/groups.
The *e3b folders contain binary files with a wavenumber resolution of 0.01 cm^-1. The files contain only the opacities [cm^2/g] in a 32 bit floating point binary format. The corresponding wavenumbers can be calculated by using the resolution and the running index of the opacity entry.
The *_0DAT folders contain text files with a wavenumber resolution of 1 cm^-1 The files contain two columns: wavenumbers [cm^-1] and opacities [cm^2/g].
The *_cbin folders contain the corresponding k-coefficients
The file size will be around {{fileSizeInfo}}. This will take a few minutes.
Temperatures are calculated at the following values:
- Attention, the spacing is not equal!
- For some species the maximum temperature is lower.
- Some species are calculated also for higher temperatures.
Pressure points are calculated at the following values in atmosphere units:
The file names contain the following information:
lower wavenumber limit in cm^-1, upper wavenumber limit in cm^-1, temperature in K, pressure exponent * 100 in bar.
a 'n' means negative exponents, a 'p' means positive exponents
So, e.g, Out_00000_49000_00050_n200.bin would be numin = 0 cm^-1, numax = 49000 cm^-1, T = 50K, and P = 10^(-2.00) bars = 0.01 bars
or Out_00000_49000_00050_p266.bin would be numin = 0 cm^-1, numax = 49000 cm^-1, T = 50K, P = 10^(+2.66) bars = 457.088 bars = 458.08 atm
The *.ref files contain the references for each species
HELIOS-K calculator:
https://github.com/exoclime/HELIOS-K
Grimm & Heng (2015):
https://ui.adsabs.harvard.edu/abs/2015ApJ...808..182G/abstract
Grimm et al. (2021):
https://ui.adsabs.harvard.edu/abs/2021ApJS..253...30G/abstract