Photometric

Photometric is an adjective related to photometry, the measurement of light intensity. In astronomy and related fields, photometric measurements quantify the flux or brightness of objects within defined wavelength bands, often expressed as magnitudes or calibrated fluxes. Photometry depends on well-characterized detectors, standard filter systems, and careful corrections for instrumental response and atmospheric effects.

Photometric systems use sets of filters to sample an object’s spectral energy distribution. Observed signals are translated into physical fluxes using zero points derived from standard stars. Color terms describe differences between the instrument and the standard system. Common techniques include aperture photometry, which sums light within a defined aperture, and PSF-fitting photometry, which models the point-spread function to extract flux in crowded fields. Differential photometry compares a target to nearby non-variable stars to mitigate atmospheric variability.

Applications of photometric data include monitoring variable stars and supernovae, detecting and characterizing exoplanet transits, and constructing photometric redshifts for distant galaxies using color information. Photometry underpins the calibration and cross-matching of large surveys, enabling studies of stellar populations, galaxy structure, and cosmology. It is often used in conjunction with spectroscopy, but generally provides broad-band information with higher signal-to-noise for faint sources.

Limitations include degeneracies among temperature, metallicity, and interstellar reddening, and the lower spectral resolution relative to spectroscopy. Photometric results rely on accurate calibration, atmospheric models, and consistent data reduction pipelines to ensure comparability across observations and instruments.