The faint intergalactic-medium red-shifted emission balloon: future UV observations with EMCCDs

Abstract

We present the latest developments in our joint NASA/CNES suborbital project. This project is a balloon-borne UV multi-object spectrograph, which has been designed to detect faint emission from the circumgalactic medium (CGM) around low redshift galaxies. One major change from FIREBall-1 has been the use of a delta-doped Electron Multiplying CCD (EMCCD). EMCCDs can be used in photon-counting (PC) mode to achieve extremely low readout noise (¡ 1e − ). Our testing initially focused on reducing clock-induced-charge (CIC) through wave shaping and well depth optimisation with the CCD Controller for Counting Photons (CCCP) from Nüvü. This optimisation also includes methods for reducing dark current, via cooling and substrate voltage adjustment. We present result of laboratory noise measurements including dark current. Furthermore, we will briefly present some initial results from our first set of on-sky observations using a delta-doped EMCCD on the 200 inch telescope at Palomar using the Palomar Cosmic Web Imager (PCWI).

Delta-doped electron-multiplying CCDs for FIREBall-2

“…There is evidence for a lower limit to dark rate, where this rate plateaus at temperatures below −110°C. [14][15][16] We are continuing this work with the Nüvü V3 controller but our preliminary results show that detector noise through poor charge transfer efficiency (CTE) increases, at very low temperatures, making the dark rate more difficult to measure. This temperature effect will be discussed further in Sec.…”

“…Kyne et al have presented results of dark current testing in both an engineering-grade and delta-doped EMCCDs. 16 In summary, low dark current and CIC noise are achieved through wave shaping, well-depth optimization (to reduce the CIC), and device cooling (to reduce dark current). For FIREBall-2, the optimization of these devices using a Nüvü V2 controller has been performed using a dedicated test bed at Caltech.…”

“…3, where thermal, vacuum, noise, and QE characterization was performed. 16 The device is secured to both sides of the PCB. The device is fitted on one side with a goldplated copper cold-clamp and cooled down to operating temperatures with a CryoTel MT mechanical cryocooler (Sterling Engine) from Sunpower.…”

“…The thermal strap has a contact with a charcoal getter, which is used as a secondary pumping source in to the main vacuum pumping system (rough pump and turbopump system). The details of pressure and temperature monitoring achieved can be found in Kyne et al 16 Figure 4 describes the thermal chain, including the interface with the detector.…”

High-efficiency UV/optical/NIR detectors for large aperture telescopes and UV explorer missions: development of and field observations with delta-doped arrays

“…The first of these runs was in Nov. 2015, with follow up in spring and fall of 2016. 57 The detector was operated at -105° C, 10 MHz, initially with the NÜVÜ v.2 CCCP controller and the most recent run with the v.3. CWI is an integral field spectrograph (IFS) with 24 slices that cover a 60 x 40 arcsec 2 area with a resolution R~5000.…”