Calibration

Magnitude Systems

Magnitude systems are stored under the mag_sys directory. In there, the user can find the magnitude_systems.txt file that contains the names of the magnitude systems (first column) and their respective files (second column), which contain the zero-points of these magnitude systems:

#magnitude_system       file
AB                      ab_sys_zps.dat
BD17                    bd17_sys_zps.dat
VEGA                    vega_sys_zps.dat
AB_B12                  ab_b12_sys_zps.dat
AB_SDSS                 ab_sdss_sys_zps.dat
BD17_JLA                bd17_jla_sys_zps.dat
BD17_SNLS3              bd17_snls3_sys_zps.dat
BD17_SWOPE              bd17_swope_sys_zps.dat
CSP_BD17                csp_sys_bd17.dat
CSP_VEGA                csp_sys_vega.dat

The magnitude system files (e.g. bd17_sys_zps.dat) must contain a line which tells PISCOLA which standard SED to use and the standard magnitudes for each filter. For example:

standard_sed: bd_17d4708_stisnic_005.dat

# Start filters for VERSION = PS1s_CFA1_JRK07_DS16
Bessell_U       9.724
Bessell_B       9.907
Bessell_V       9.464
Bessell_R       9.166
Bessell_I       8.846

# Start filters for VERSION = PS1s_CFA3_4SHOOTER2_DS17
4Shooter2_U     9.6930
4Shooter2_B     9.87400-0.0345
4Shooter2_V     9.47900-0.0087
4Shooter2_R     9.15500-0.021
4Shooter2_I     8.85100-0.0136

Everything else in the files is ignored (considered as comments). If you want to add another magnitude system, just follow the same structure.

Standard Stars

Standard stars are found in the standards directory (e.g., alpha_lyr_stis_005.dat, bd_17d4708_stisnic_005.dat). If the user wants to use an AB SED, simply set standard_sed: AB (or ab). The available standard stars are: \(BD +17.4708\), Vega (\(\alpha Lyr.\)) and AB. The latter is defined as:

c = 2.99792458e18  # speed of light in [Å/s]
sed_wave = np.arange(1000, 250000, 1)  # in [Å]
sed_flux = 3631e-23 * c / sed_wave**2  # in [erg s^-1 cm^-2 Å^-1]

Zero-points

The zero-point for a given magnitude system, e.g. Vega. is calculated as follows:

\(ZP_{Vega} = m_{Vega} + 2.5*log_{10}(f_{Vega})\)

where \(m_{Vega}\) is the tabulated standard magnitude of Vega in a given filter (taken from the files mentioned above) and \(f_{Vega}\) the integrated flux through the same given filter (using the standard star SED).