New UVIS and IR Photometric Zeropoint Tables Available

IR

UVIS

Photometric Systems:

• VEGAmag : SYNPHOT standard magnitude system, for which Vega by definition has magnitude 0 at all wavelengths. The vega magnitude of a star with flux F is -2.5 log10 (F/F_vega) where F_vega is the calibrated spectrum of Vega in Synphot.
• STmag and ABmag: both systems define an equivalent flux density for a source, corresponding to the flux density of a source of predefined spectral shape that would produce the observed count rate, and convert this equivalent flux to a magnitude. The conversion is chosen so that the magnitude in V corresponds roughly to that in the Johnson system. In the STmag system, the flux density is expressed per unit wavelength, and the reference spectrum is flat in F_lam , while in the ABmag system, the flux density is expressed per unit frequency , and the reference spectrum is flat in F_nu. The definitions are:
  • STmag = -2.5 Log F_lam -21.10
  • ABmag = -2.5 Log F_nu - 48.6
  where F_nu is expressed in erg cm^-2 s^-1 Hz^-1, and F_lam in erg cm^-2 s^-1 Ang^-1. Another way to express these zeropoints is to say that an object with F_nu = 3.63 x 10^-20 erg cm^-2 s^-1 Hz^-1 will have magnitude AB =0 in every filter, and an object with F_lam = 3.63 x 10^-9 erg cm^-2 s^-1 Ang^-1 will have magnitude ST=0 in every filter.

• PHOTMODE: Observation configuration for photometric calibration.
• PHOTFLAM: inverse sensitivity (erg cm^-2 s^-1 Ang^-1).
• PHOTZPT: ST magnitude zeropopint (= 21.10).
• PHOTPLAM: pivot wavelength.

• STMAG_ZEROPOINT = -2.5 Log (PHOTFLAM) - PHOTZPT = -2.5 Log (PHOTFLAM) - 21.10
• ABMAG_ZEROPOINT = -2.5 Log (PHOTFLAM) - 21.10 - 5 Log (PHOTPLAM) + 18.6921