The ALHAMBRA photometric system

TL;DR

This paper characterizes the ALHAMBRA photometric system's optical response, standard stars, and calibration methods, enabling accurate transformation and zero point calculations for astronomical observations.

Contribution

It provides a detailed response curve, standard star set, and transformation equations linking ALHAMBRA with SDSS, along with a calibration strategy.

Findings

Response curve characterized from 3500A to 9700A.

Transformation equations between SDSS and ALHAMBRA established.

Calibration strategy for zero points discussed.

Abstract

This paper presents the characterization of the optical range of the ALHAMBRA photometric system, a 20 contiguous, equal-width, medium-band CCD system with wavelength coverage from 3500A to 9700A. The photometric description of the system is done by presenting the full response curve as a product of the filters, CCD and atmospheric transmission curves, and using some first and second order moments of this response function. We also introduce the set of standard stars that defines the system, formed by 31 classic spectrophotometric standard stars which have been used in the calibration of other known photometric systems, and 288 stars, flux calibrated homogeneously, from the Next Generation Spectral Library (NGSL). Based on the NGSL, we determine the transformation equations between Sloan Digital Sky Survey (SDSS) ugriz photometry and the ALHAMBRA photometric system, in order to establish some relations between both systems. Finally we develop and discuss a strategy to calculate the photometric zero points of the different pointings in the ALHAMBRA project.