Santiago Serrano

The Dark Energy Survey and operations: Year 1

The Dark Energy Survey (DES) is a next generation optical survey aimed at understanding the accelerating expansion of the universe using four complementary methods: weak gravitational lensing, galaxy cluster counts, baryon acoustic oscillations, and Type Ia supernovae. To perform the 5000 sq-degree wide field and 30 sq-degree supernova surveys, the DES Collaboration built the Dark Energy Camera (DECam), a 3 square-degree, 570-Megapixel CCD camera that was installed at the prime focus of the Blanco 4-meter telescope at the Cerro Tololo Inter-American Observatory (CTIO). DES started its first observing season on August 31, 2013 and observed for 105 nights through mid-February 2014. This paper describes DES “Year 1” (Y1), the strategy and goals for the first years data, provides an outline of the operations procedures, lists the efficiency of survey operations and the causes of lost observing time, provides details about the quality of the first years data, and hints at the “Year 2” plan and outlook.

The PAU camera and the PAU survey at the William Herschel Telescope

The Physics of the Accelerating Universe (PAU) is a project whose main goal is the study of dark energy. For this purpose, a new large field of view camera (the PAU Camera, PAUCam) is being built. PAUCam is designed to carry out a wide area imaging survey with narrow and broad band filters spanning the optical wavelength range. The PAU Camera is now at an advance stage of construction. PAUCam will be mounted at the prime focus of the William Herschel Telescope. With the current WHT corrector, it will cover a 1 degree diameter field of view. PAUCam mounts eighteen 2k×4k Hamamatsu fully depleted CCDs, with high quantum efficiency up to 1 μm. Filter trays are placed in front of the CCDs with a technologically challenging system of moving filter trays inside the cryostat. The PAU Camera will use a new set of 42 narrow band filters ranging from ~4400 to ~8600 angstroms complemented with six standard broad-band filters, ugrizY. With PAUCam at the WHT we will carry out a cosmological imaging survey in both narrow and broad band filters that will perform as a low resolution spectroscopic survey. With the current survey strategy, we will obtain accurate photometric redshifts for galaxies down to iAB~22.5 detecting also galaxies down to iAB~24 with less precision in redshift. With this data set we will obtain competitive constraints in cosmological parameters using both weak lensing and galaxy clustering as main observational probes.

The Readout and Control System of the Dark Energy Camera

The Dark Energy Camera (DECam) is a new 520 Mega Pixel CCD camera with a 3 square degree field of view designed for the Dark Energy Survey (DES). DES is a high precision, multi-bandpass, photometric survey of 5000 square degrees of the southern sky. DECam is currently being installed at the prime focus of the Blanco 4-m telescope at the Cerro- Tololo International Observatory (CTIO). In this paper we describe SISPI, the data acquisition and control system of the Dark Energy Camera. SISPI is implemented as a distributed multi-processor system with a software architecture based on the Client-Server and Publish-Subscribe design patterns. The underlying message passing protocol is based on PYRO, a powerful distributed object technology system written entirely in Python. A distributed shared variable system was added to support exchange of telemetry data and other information between different components of the system. We discuss the SISPI infrastructure software, the image pipeline, the observer console and user interface architecture, image quality monitoring, the instrument control system, and the observation strategy tool.

The DECam Data Acquisition and Control System

In this paper we describe the data acquisition and control system of the Dark Energy Camera (DECam), which will be the primary instrument used in the Dark Energy Survey (DES). DES is a high precision multibandpath wide area survey of 5000 square degrees of the southern sky. DECam currently under construction at Fermilab will be a 3 square degree mosaic camera mounted at the prime focus of the Blanco 4m telescope at the Cerro-Tololo International Observatory (CTIO). The DECam data acquisition system (SISPI) is implemented as a distributed multi-processor system with a software architecture built on the Client-Server and Publish-Subscribe design patterns. The underlying message passing protocol is based on PYRO, a powerful distributed object technology system written entirely in Python. A distributed shared variable system was added to support exchange of telemetry data and other information between different components of the system. In this paper we discuss the SISPI infrastructure software, the image pipeline, the observer interface and quality monitoring system, and the instrument control system.

ProtoDESI: First On-Sky Technology Demonstration for the Dark Energy Spectroscopic Instrument

The Dark Energy Spectroscopic Instrument (DESI) is under construction to measure the expansion history of the universe using the baryon acoustic oscillations technique. The spectra of 35 million galaxies and quasars over 14,000 square degrees will be measured during a 5-year survey. A new prime focus corrector for the Mayall telescope at Kitt Peak National Observatory will deliver light to 5,000 individually targeted fiber-fed robotic positioners. The fibers in turn feed ten broadband multi-object spectrographs. We describe the ProtoDESI experiment, that was installed and commissioned on the 4-m Mayall telescope from August 14 to September 30, 2016. ProtoDESI was an on-sky technology demonstration with the goal to reduce technical risks associated with aligning optical fibers with targets using robotic fiber positioners and maintaining the stability required to operate DESI. The ProtoDESI prime focus instrument, consisting of three fiber positioners, illuminated fiducials, and a guide camera, was installed behind the existing Mosaic corrector on the Mayall telescope. A Fiber View Camera was mounted in the Cassegrain cage of the telescope and provided feedback metrology for positioning the fibers. ProtoDESI also provided a platform for early integration of hardware with the DESI Instrument Control System that controls the subsystems, provides communication with the Telescope Control System, and collects instrument telemetry data. Lacking a spectrograph, ProtoDESI monitored the output of the fibers using a Fiber Photometry Camera mounted on the prime focus instrument. ProtoDESI was successful in acquiring targets with the robotically positioned fibers and demonstrated that the DESI guiding requirements can be met.

The DECam DAQ System: Lessons learned after one year of operations

The Dark Energy Camera (DECam) is a new 520 Mega Pixel CCD camera with a 3 square degree field of view built for the Dark Energy Survey (DES). DECam is mounted at the prime focus of the Blanco 4-m telescope at the Cerro-Tololo International Observatory (CTIO). DES is a 5-year, high precision, multi-bandpass, photometric survey of 5000 square degrees of the southern sky that started August 2013. In this paper we briefly review SISPI, the data acquisition and control system of the Dark Energy Camera and follow with a discussion of our experience with the system and the lessons learned after one year of survey operations.

CosmoHub and SciPIC: Massive cosmological data analysis, distribution and generation using a Big Data platform

Galaxy surveys require support from massive datasets in order to achieve precise estimations of cosmological parameters. The CosmoHub platform (https://cosmohub.pic.es), a web portal to perform interactive analysis of massive cosmological data, and the SciPIC pipeline have been developed at the Port dInformacio Cientifica (PIC) to provide this support, achieving nearly interactive performance in the processing of multi-terabyte datasets. Cosmology projects currently supported include European Space Agency Euclid space mission, the Dark Energy Survey (DES), the Physics of the Accelerating Universe (PAU) survey and the Marenostrum Institut de Ciencies de lEspai Simulations (MICE). Support for additional projects can be added as needed. CosmoHub enables users to interactively explore and distribute data without any SQL knowledge. It is built on top of Apache Hive, part of the Apache Hadoop ecosystem, which facilitates reading, writing, and managing large datasets. More than 50 billion objects, from public and private data, as well as observed and simulated data, are available. Over 500 registered scientists have produced about 2000 custom catalogs occupying 10TiB in compressed format over the last three years. All those datasets can be interactively explored using an integrated visualization tool. The current implementation allows an interactive analysis of 1.1 billion object datasets to complete in 45 seconds. The SciPIC scientific pipeline has been developed to efficiently generate mock galaxy catalogs using as input a dark matter halo population. It runs on top of the Hadoop platform using Apache Spark, which is an open-source cluster-computing framework. The pipeline is currently being calibrated to populate the full sky Flagship dark matter halo catalog produced by the University of Zurich, which contains about 44 billion dark matter haloes in a box size of 3.78 Gpc/h. The resulting mock galaxy catalog is directly stored in the CosmoHub platform.

The DESI instrument control system

The Dark Energy Spectroscopic Instrument (DESI) , a new instrument currently under construction for the Mayall 4m telescope at Kitt Peak National Observatory, will consist of a wide-field optical corrector with a 3.2 degree diameter field of view, a focal plane with 5,000 robotically controlled fiber positioners and 10 fiber fed broadband spectrographs. This article describes the design of the DESI instrument control system (ICS). The ICS coordinates fiber positioner operations, interfaces to the Mayall telescope control system, monitors operating conditions, reads out the 30 spectrograph CCDs and provides observer support and data quality monitoring.

PAUCam filter interchange system

The Physics of the Accelerating Universe (PAU) is a new project whose main goal is to study dark energy surveying the galaxy distribution. For that purpose we need to determine the galaxy redshifts. The most accurate way to determine the redshift of a galaxy and measure its spectral energy distribution (SED) is achieved with spectrographs. The PAU collaboration is building an instrument (PAUCam) devoted to perform a large area survey for cosmological studies using an alternative approach. SEDs are sampled and redshifts determined using narrow band filter photometry. For efficiency and manufacturability considerations, the filters need to be placed close to the CCD detector surfaces on segmented filter trays. The most innovative element of PAUCam is a set of 16 different exchangeable trays to support the filters arranged in a jukebox-like changing mechanism inside the cryostat. The device is designed to operate within the range of temperatures from 150K to 300K at the absolute pressure of 10-8mbar, being class-100 compliant.

The DESI instrument control systems: status and early testing

The Dark Energy Spectroscopic Instrument (DESI) is a new instrument currently under construction for the Mayall 4-m telescope at Kitt Peak National Observatory. It will consist of a wide-field optical corrector with a 3.2 degree diameter field of view, a focal plane with 5,000 robotically controlled fiber positioners and 10 fiber-fed broad-band spectrographs. The DESI Instrument Control System (ICS) coordinates fiber positioner operations, interfaces to the Mayall telescope control system, monitors operating conditions, reads out the 30 spectrograph CCDs and provides observer support and data quality monitoring. In this article, we summarize the ICS design, review the current status of the project and present results from a multi-stage test plan that was developed to ensure the system is fully operational by the time the instrument arrives at the observatory in 2019.