Spectroscopic and Photometric Training Data

SALTShaker input files use SNANA format, which allows easy synergy between model training and SN simulations, light-curve fitting, and systematic uncertainty estimation. The SNANA-formatted data necessary for training includes photometry, spectroscopy, and filter functions/photometric system information.

For photometry and spectroscopy, a number of light curves and spectra are provided in the examples/SALT3TRAIN_K21_PUBLIC/ directory for training. Light curves and spectra are combined into a single file. The training data themselves are described in Kenworthy et al., 2021.

For the photometric information, so-called “kcor” files - which confusingly contain no k-corrections - are given in the examples/SALT3TRAIN_K21_PUBLIC/kcor directory. These FITS-formatted files define the photometric system associated with each survey that comprises the training sample. The SNANA function kcor.exe will create these files from the .input files in the same directory if anything needs to be adjusted. “kcor” files contain filter transmission functions, AB, BD17, or Vega spectra depending on the photometric system of the data, zeropoint offsets, and optional shifts to the central wavelength of each filter.

Photometry and Spectroscopy Format

SNANA file format consists of a number of header keys giving information about each SN, followed by photometry and spectroscopy.

An example of the minimum required header is below:

SURVEY: FOUNDATION
SNID: ASASSN-15bc
RA: 61.5609874
DEC: -8.8856098
MWEBV: 0.037 # Schlafly & Finkbeiner MW E(B-V)

Below the header, the photometry is included in the following format:

NOBS: 64
NVAR:   7
VARLIST:  MJD  FLT FIELD   FLUXCAL   FLUXCALERR    MAG     MAGERR
OBS: 57422.54 g VOID  21576.285 214.793 16.665 0.011
OBS: 57428.47 g VOID  30454.989 229.733 16.291 0.008
OBS: 57436.55 g VOID  26053.054 253.839 16.460 0.011
OBS: 57449.46 g VOID  11357.888 158.107 17.362 0.015
...
END_PHOTOMETRY:

The SALT3 training code only reads the MJD, FLT (filter), FLUXCAL, and FLUXCALERR values. FLUXCAL and FLUXCALERR use a zeropoint of 27.5 mag.

The beginning of the spectroscopy section is identified by the following header lines:

NVAR_SPEC: 3
VARNAMES_SPEC: LAMAVG  FLAM  FLAMERR

Where the columns are wavelength (angstrom), flux (erg/cm^2/s/A), and flux uncertainty (not currently used). Each spectrum has the following format:

SPECTRUM_ID:       1
SPECTRUM_MJD:      54998.378  # Tobs =  -13.832
SPECTRUM_TEXPOSE:  100000.000  # seconds
SPECTRUM_NLAM:     352 (of 352)  # Number of valid wavelength bins
SPEC:  4200.00  4209.35  -2.068e-10   5.701e-10
SPEC:  4209.35  4218.76  -2.704e-10   6.359e-10    2.557e-10  23.25
SPEC:  4218.76  4228.23  -2.725e-10   6.312e-10    2.543e-10  23.26
SPEC:  4228.23  4237.76  -4.588e-11   6.232e-10    2.538e-10  23.25
SPEC:  4237.76  4247.35  -8.320e-10   6.152e-10    2.541e-10  23.25
...
END_SPECTRUM: