Fast spectroscopy and imaging with the FORS2 HIT mode

TL;DR

The paper introduces the HIT mode of FORS2, enabling high time resolution imaging and spectroscopy on an 8m telescope, suitable for observing rapid astrophysical phenomena across various timescales.

Contribution

It presents a novel high time resolution mode for FORS2, combining imaging and spectroscopy with a unique CCD clocking pattern and flexible target selection.

Findings

Achieves up to 10 spectra per second in spectroscopy mode.

Enables high throughput imaging of pulsars and white dwarfs.

Provides flexible observation timescales with various 'wait' times.

Abstract

The HIgh-Time resolution (HIT) mode of FORS2 has 3 sub-modes that allow for imaging and spectroscopy over a range of timescales from milliseconds up to seconds. It is the only high time resolution spectroscopy mode available on an 8m class telescope. In imaging mode, it can be used to measure the pulse of pulsars and spinning white dwarfs in a variety of high throughput broad- and narrow-band filters. In spectroscopy mode it can take up to 10 spectra per second using a novel ''shift-and-wait'' clocking pattern for the CCD. It takes advantage of the user-designed masks which can be inserted into FORS2 to allow any two targets within the 6.8' x 6.8' field of view of FORS2 to be selected. A number of integration, or more precisely 'wait', times are available, which together with the high throughput GRISMs can observe the entire optical spectrum on a range of timescales.