The AB and ST magnitude systems are two different ways of measuring the brightness of astronomical objects. The AB system is based on the energy received from the object, while the ST system is based on the number of photons received from the object.
The AB magnitude system is more commonly used in modern astronomy. It is the standard system used by most telescopes and is considered to be more accurate and consistent.
The zero point of the AB system is defined by a hypothetical object with a specific energy flux, while the zero point of the ST system is defined by a specific number of photons received. This means that the zero points of the two systems are not equivalent.
Yes, it is possible to convert magnitudes from the AB system to the ST system and vice versa. However, this conversion is not a simple mathematical formula and requires knowledge of the spectral energy distribution of the object being measured.
The AB system is more suitable for measuring objects with a broad range of spectral energy distributions, such as galaxies and quasars. The ST system is more suitable for measuring objects with a specific spectral energy distribution, such as stars.