Performance of the Southern Astrophysical Research Telescope Speckle Instrument

TL;DR

This study evaluates the performance of the HRCam speckle imager at the 4.1 m SOAR telescope, analyzing its sensitivity, noise characteristics, and potential improvements to guide future observations.

Contribution

It provides a detailed performance analysis of HRCam, including the effects of detector noise and exposure time, and suggests enhancements with CMOS detectors for better sensitivity.

Findings

Limiting magnitude ranges from 11.5 to 14 mag depending on seeing conditions.

Increasing exposure beyond 30 ms does not improve limiting magnitude.

Replacing CCD with CMOS could gain at least one magnitude in sensitivity.

Abstract

The High Resolution Camera (HRCam) speckle imager at the 4.1 m Southern Astrophysical Research telescope is a highly productive instrument that has accumulated about 40K observations to date. Its performance (detected flux, level of the speckle signal, signal-to-noise ratio, and limiting magnitude) is studied here using both the actual data and realistic simulations, including the detector noise. In the calculation of the speckle power spectrum, signal clipping is essential to reduce the noise impact and maximize the sensitivity. Increasing exposure time of individual frames beyond 30 ms does not improve the limiting magnitude, which ranges from 11.5 to 14 mag under a seeing from 1.6" to 0.6" in the wide-band I filter. A gain of at least one magnitude is expected if the current electron multiplication CCD is replaced by a high-end CMOS detector with a sub-electron readout noise. This study will help in planning, executing, and automating future speckle observations with HRCam and other speckle imagers.