Characterization and correction of charge-induced pixel shifts in DECam

Interaction of charges in CCDs with the already accumulated charge distribution causes both a flux dependence of the point-spread function (an increase of observed size with flux, also known as the brighter/fatter effect) and pixel-to-pixel correlations of the Poissonian noise in flat fields. We describe these effects in the Dark Energy Camera (DECam) with charge dependent shifts of effective pixel borders, i.e. the Antilogus et al. (2014) model, which we fit to measurements of flat-field Poissonian noise correlations. The latter fall off approximately as a power-law r^-2.5 with pixel separation r, are isotropic except for an asymmetry in the direct neighbors along rows and columns, are stable in time, and are weakly dependent on wavelength. They show variations from chip to chip at the 20% level that correlate with the silicon resistivity. The charge shifts predicted by the model cause biased shape measurements, primarily due to their effect on bright stars, at levels exceeding weak lensing science requirements. We measure the flux dependence of star images and show that the effect can be mitigated by applying the reverse charge shifts at the pixel level during image processing. Differences in stellar size, however, remain significant due to residuals at larger distance from the centroid.Comment: typo and formatting fixes, matches version published in JINS

Precision Projector Laboratory: detector characterization with an astronomical emulation testbed

As astronomical observations from space benefit from improved sensitivity, the effectiveness of scientific programs is becoming limited by systematics that often originate in poorly understood image sensor behavior. Traditional, bottom-up detector characterization methods provide one way to model underlying detector physics and generate ever more faithful numerical simulations, but this approach is vulnerable to preconceptions and over-simplification. The alternative top-down approach is laboratory emulation, which enables observation, calibration, and analysis scenarios to be tested without relying on a complete understanding of the underlying physics. This complements detector characterization and simulation efforts by testing their validity. We describe a laboratory facility and experimental testbed that supports the emulation of a wide range of mission concepts such as gravitational weak lensing measurements by the Wide Field Infrared Survey Telescope and high precision spectrophotometry of transiting exoplanets by James Webb Space Telescope. An Offner relay projects readily customizable “scenes” (e.g., stars, galaxies, and spectra) with very low optical aberration over the full area of a typical optical or near-infrared image sensor. f  /  8 and slower focal ratios may be selected, spanning those of most proposed space missions and approximating the point spread function (PSF) size of seeing limited ground-based surveys. Diffraction limited PSFs are projected over a wide field of view and wavelength range to deliver highly predictable image patterns down to subpixel scales with stable intensity and fine motion control. The testbed enables realistic validation of detector performance on science-like images, which aids mission design and survey strategy as well as targeted investigations of various detector effects

Anti-Black racism workshop during the Vera C. Rubin Observatory virtual 2021 Project and Community Workshop

Systemic racism is a ubiquitous theme in societies worldwide and plays a central role in shaping our economic, social, and academic institutions. The Vera C. Rubin Observatory is a major US ground-based facility based in Chile with international participation. The Observatory is an example of excellence and will deliver the largest survey of the sky ever attempted. Rubin's full scientific and social potential can not be attained without addressing systemic racism and associated barriers to equity, diversity, and inclusion (EDI). During Rubin's 2021 virtual Project and Community Workshop (PCW), the annual Rubin community-based meeting, an anti-Black racism workshop took place, facilitated by 'The BIPOC Project' organization. About 60 members from different parts of the Rubin ecosystem participated. We describe the motivation, organization, challenges, outcomes, and near- and long-term goals of this workshop.Comment: Contribution to appear in 'An Astronomical Inclusion Revolution: Advancing Diversity, Equity, and Inclusion in Professional Astronomy and Astrophysics', to be published by IOP ebook

A General Framework for Removing Point Spread Function Additive Systematics in Cosmological Weak Lensing Analysis

Cosmological weak lensing measurements rely on a precise measurement of the shear two-point correlation function (2PCF) along with a deep understanding of systematics that affect it. In this work, we demonstrate a general framework for describing the impact of PSF systematics on the cosmic shear 2PCF, and mitigating its impact on cosmological analysis. Our framework can describe leakage and modeling error from all spin-2 quantities contributed by the PSF second and higher moments, rather than just the second moments. We interpret null tests using the HSC Year 3 (Y3) catalogs with this formalism, and find that leakage from the spin-2 combination of PSF fourth moments is the leading contributor to additive shear systematics, with total contamination that is an order of magnitude higher than that contributed by PSF second moments alone. We conducted a mock cosmic shear analysis for HSC Y3, and find that, if uncorrected, PSF systematics can bias the cosmological parameters $\Omega_m$ and $S_8$ by $\sim$0.3$\sigma$. The traditional second moment-based model can only correct for a 0.1$\sigma$ bias, leaving the contamination largely uncorrected. We conclude it is necessary to model both PSF second and fourth moment contamination for HSC Y3 cosmic shear analysis. We also reanalyze the HSC Y1 cosmic shear analysis with our updated systematics model, and identify a 0.07$\sigma$ bias on $\Omega_m$ when using the more restricted second moment model from the original analysis. We demonstrate how to self-consistently use the method in both real space and Fourier space, assess shear systematics in tomographic bins, and test for PSF model overfitting.Comment: 29 pages, 25 figures, submitted to MNRAS. Comments welcome

Climatología del viento sobre la Península Ibérica: observaciones y modelos

Ponencia presentada en: IX Congreso de la Asociación Española de Climatología celebrado en Almería entre el 28 y el 30 de octubre de 2014.[ES]En este trabajo se presenta la climatología del viento en la Península Ibérica (PI) obtenida a partir de datos de más de 500 estaciones con registros horarios para el periodo 1999-2007. Se describen distintos aspectos; rosa de los vientos, funciones de distribución de probabilidad, ciclo anual y respuesta a distintos tipos de circulación del campo de vientos a escala regional (20 regiones). Las regiones fueron obtenidas a partir de un análisis clúster imponiendo máxima similitud temporal entre las series observacionales.[EN]In this work the wind climatology of the Iberian Peninsula is presented. It has been obtained using more tan 500 weather stations with hourly records for the period 1999-2007. Wind Roses, annual cycles and probability distribution functions as well as the response of the wind field to circulation types are characterized at regional scale. Regions are obtained using a a cluster analysis, grouping places with similar temporal variability.Este trabajo ha sido financiado por el Gobierno de España y el Fondo Europeo de Desarrollo Regional (FEDER) por medio de los proyectos MINIEOLICA (PSE.120000.2007.14), CORWES (CGL210-22158) y SPEQ-TRES (CGL2011-29672-C02-02)

Photometry, Centroid and Point-Spread Function Measurements in the LSST Camera Focal Plane Using Artificial Stars

The Vera C. Rubin Observatory's LSST Camera pixel response has been characterized using laboratory measurements with a grid of artificial stars. We quantify the contributions to photometry, centroid, point-spread function size, and shape measurement errors due to small anomalies in the LSSTCam CCDs. The main sources of those anomalies are quantum efficiency variations and pixel area variations induced by the amplifier segmentation boundaries and "tree-rings" -- circular variations in silicon doping concentration. We studied the effects using artificial stars projected on the sensors and find that the resulting measurement uncertainties pass the ten-year LSST survey science requirements. In addition, we verify that the tree-ring effects can be corrected using flat-field images if needed, because the astronomic shifts and shape measurement errors they induce correlate well with the flat-field signal. Nevertheless, further sensor anomaly studies with on-sky data should probe possible temporal and wavelength-dependent effects.Comment: Submitted to PAS

Influencia de los forzamientos externos en los tipos de circulación sobre la Península Ibérica en el último milenio

Ponencia presentada en: VIII Congreso de la Asociación Española de Climatología celebrado en Salamanca entre el 25 y el 28 de septiembre de 2012.[ES]Nuestro estudio analiza la evolución de la frecuencia de los principales TCs obtenidos para invierno y verano, mediante una simulación paleoclimática llevada a cabo para el último milenio con una versión climática del modelo MM5 sobre Europa y la Penísula Ibérica (PI). La simulación incluye tres forzamientos externos diferentes: Gases de Efecto Invernadero (período industrial), actividad volcánica (máximo entorno a 1810) y radiación solar (mínimo hacia 1700). Para la caracterización de los TCs se utilizaron datos diarios de Presión a Nivel del Mar y Geopotencial a 500 hPa sobre una ventana que cubre la PI.[EN]This study analyses the behavior in the frequency of the main CTs obtained for winter and summer from a paleosimulation performed for Europe and the Iberian Peninsula for the last millennium (1001- 1990) using a climate version of MM5. The simulation includes three kind of external forcings: Greenhouse Gases (industrial period), volcanic activity (maximun near 1810) and solar activity (minimun around 1700). For the characterization of the CTs were employed daily data of Sea Level Pressure (SLP) and Geopotential Height at 500 hPa Level of a window that covers the Iberian Peninsula (IP)

Design of a Skipper CCD Focal Plane for the SOAR Integral Field Spectrograph

We present the development of a Skipper Charge-Coupled Device (CCD) focal plane prototype for the SOAR Telescope Integral Field Spectrograph (SIFS). This mosaic focal plane consists of four 6k $\times$ 1k, 15 $\mu$m pixel Skipper CCDs mounted inside a vacuum dewar. We describe the process of packaging the CCDs so that they can be easily tested, transported, and installed in a mosaic focal plane. We characterize the performance of $\sim 650 \mu$m thick, fully-depleted engineering-grade Skipper CCDs in preparation for performing similar characterization tests on science-grade Skipper CCDs which will be thinned to 250$\mu$m and backside processed with an antireflective coating. We achieve a single-sample readout noise of $4.5 e^{-} rms/pix$ for the best performing amplifiers and sub-electron resolution (photon counting capabilities) with readout noise $\sigma \sim 0.16 e^{-} rms/pix$ from 800 measurements of the charge in each pixel. We describe the design and construction of the Skipper CCD focal plane and provide details about the synchronized readout electronics system that will be implemented to simultaneously read 16 amplifiers from the four Skipper CCDs (4-amplifiers per detector). Finally, we outline future plans for laboratory testing, installation, commissioning, and science verification of our Skipper CCD focal plane