Improved Spectrophotometric Calibration of the SDSS-III BOSS Quasar Sample

TL;DR

This paper develops a model to correct spectrophotometric calibration errors in SDSS-III BOSS quasar observations, improving the accuracy of flux measurements crucial for cosmological studies.

Contribution

It introduces a new correction procedure for calibration errors caused by atmospheric effects and guiding offsets in BOSS quasar data.

Findings

Calibration errors cause flux overestimation at 3600 Å and underestimation at 10,000 Å.

The correction model reduces systematic flux errors in BOSS quasar spectra.

Corrected flux measurements are publicly available for improved scientific analysis.

Abstract

We present a model for spectrophotometric calibration errors in observations of quasars from the third generation of the Sloan Digital Sky Survey (SDSS-III) Baryon Oscillation Spectroscopic Survey (BOSS) and describe the correction procedure we have developed and applied to this sample. Calibration errors are primarily due to atmospheric differential refraction and guiding offsets during each exposure. The corrections potentially reduce the systematics for any studies of BOSS quasars, including the measurement of baryon acoustic oscillations using the Lyman-$\alpha$ forest. Our model suggests that, on average, the observed quasar flux in BOSS is overestimated by $\sim 19\%$ at 3600 \AA\ and underestimated by $\sim 24\%$ at 10,000 \AA. Our corrections for the entire BOSS quasar sample are publicly available.