Proceedings Article | 27 August 2024
Edgar Marrufo Villalpando, Alex Drlica-Wagner, Brandon Roach, Marco Bonati, Abhishek Bakshi, Julia Campa, Gustavo Cancelo, Braulio Cancino, Claudio Chavez, Fernando Chierchie, Jaun Estrada, Guillermo Fernandez Moroni, Luciano Fraga, Manuel Gaido, Stephen Holland, Rachel Hur, Michelle Jonas, Peter Moore, Eduardo Paolini, Andrés Plazas Malagón, Leandro Stefanazzi, Javier Tiffenberg, Ken Treptou, Sho Uemura, Neal Wilcer
KEYWORDS: Charge-coupled devices, Signal to noise ratio, Stars, CCD image sensors, Quantum reading, Interference (communication), Sensors, Electrons, Astronomy, Aluminium phosphide
We present the first on-sky results from an ultra-low-readout-noise Skipper CCD focal plane prototype for the SOAR Integral Field Spectrograph (SIFS). The Skipper CCD focal plane consists of four 6k×1k, 15μm pixel, fully-depleted, p-channel devices that have been thinned to ∼250μm, backside processed, and treated with an anti-reflective coating. These Skipper CCDs were configured for astronomical spectroscopy, i.e., a single-sample readout noise <4.3 e− rms/pixel, the ability to achieve multi-sample readout noise ≪ 1 e− rms/pixel, full-well capacities ∼40,000 to 65,000 e−, low dark current and charge transfer inefficiency (∼2×10−4 e−/pixel/s and 3.44×10−7, respectively), and an absolute quantum efficiency of ≳80% between 450nm and 980nm (≳90% between 600nm and 900nm). We optimized the readout sequence timing to achieve sub-electron noise (∼ 0.5 e− rms/pixel) in a region of 2k×4k pixels and photon-counting noise (∼0.22 e− rms/pixel) in a region of 220×4k pixels, each with a readout time of ≲17 min. We observed two Lyman-α emitting quasars (HB89 1159+123 and QSOJ1621–0042) at redshift z∼3.5, two moderate redshift galaxy clusters (CL J1001+0220 and SPT-CL J2040−4451), an emission line galaxy at z=0.3239, a candidate member star of the Boötes II ultra-faint dwarf galaxy, and five CALSPEC spectrophotometric standard stars (HD074000, HD60753, HD106252, HD101452, HD200654). We present charge-quantized, photon-counting observation of the quasar HB89 1159+123 and show the detector sensitivity increase for faint spectral features. We demonstrate signal-to-noise performance improvements for SIFS observations in the low-background, readout-noise-dominated regime. We outline future scientific studies that will leverage these SIFS-Skipper CCD data, as well as new detector architectures that utilize the Skipper floating gate amplifier with faster readout times.
