The ORCA-TWIN qCMOS Project I. Commissioning at Calar Alto Observatory

TL;DR

The paper advocates a fast, low-noise qCMOS approach for time-domain astronomy and introduces the ORCA-TWIN pilot, which uses two synchronized qCMOS cameras at distant sites to enable high-cadence observations and parallax-based measurements. Through numerical simulations, commissioning at CAHA, and initial on-sky tests, it demonstrates that qCMOS can outperform traditional CCDs for short-exposure, high-cadence work on 1 m-class telescopes, while EMCCDs remain competitive only in very short exposure regimes. The results validate the feasibility of rapid deployment and synchronized observations, with key applications including solar system object triangulation, precise stellar photometry, and speckle-imaging-like techniques. The work lays the groundwork for expanded multi-site time-domain campaigns and detector-lab development, with plans to commission a second camera at STELLA and publish subsequent performance results.

Abstract

Aims. We describe a pilot study to explore a new generation of fast and low noise CMOS image sensors for time domain astronomy, using two remote telescopes with a baseline of 1800 km. Methods. Direct imaging with novel qCMOS image sensor technology that combines fast readout with low readout noise. Synchronized observations from two remote telescope sites will be used to explore new approaches for measuring solar system bodies, precision stellar photometry, and speckle imaging. Results. A fast-track installation of an ORCA-Quest 2 camera at the Calar Alto Observatory (CAHA) 1.23m telescope has demonstrated the potential of the qCMOS technology for time domain astronomy. Conclusions. qCMOS technology generally outperforms classical CCDs for high-cadence imaging on 1-m telescopes, although EMCCDs remain competitive, and in some cases slightly superior, for very short exposures and faint sources.

Figures (12)

• Figure 1: Simultaneous observations of asteroid 4179 Toutatis, left: WFI La Silla, right: FORS1 Paranal. Credit: ESO
• Figure 2: Left: triangulation of asteroid 4179 Toutatis with 513 km baseline between ESO observatories at Paranal and La Silla. Right: 1800 km baseline of ORCA-TWIN sites on mainland Spain and Tenerife. Credit: ESO, OpenStreetMap Wiki.
• Figure 3: CMOS pixel layout, including the floating transfer gate detail. Legend: pixel (80), thick low-doped p-type silicon substrate (82), transistors (83), (84), (86), (88), buried oxide insulator layer (90), photodetector area (82), polysilicon gates defining photodetector (94), deep depletion region for photo electron collection (98), reset transistor (84), buffer transistor (86), row selection transistor (88), transfer gate transistor (83), floating sense node (96). Reproduced from US Patent No. US 6,380,572 B1.
• Figure 4: Simulated images of a star for qCMOS (left) and CCD sensor (right), respectively, within a window of approx. $10\times10$ arcsec$^2$ width. The concentric circles indicate the aperture and the sky annulus for DAOPHOT photometry that is applied to the images to measure photon flux and its uncertainty.
• Figure 5: Simulated images in the V band for qCMOS (left) and CCD sensor (right), showing a sequence of decreasing exposure times 10 s, 1.0 s, and 0.1 s.