Glossary of terms used at ESO

Calibration Frame
A frame used in the process of data reduction to remove instrument signature from observations
Calibration product (also called master calibration)
A pipeline-processed frame made of an input set of raw calibration frames. It typically provides instrument signature (like detector read noise level, fixed-pattern noise, dispersion relation etc.).

Storage media in use by the computer industry to store data and programs. The CD-ROM and DVD-ROM support directory based file systems and structure.

Data Interface
Set of definitions that describe the contents of data products (see section 2 of the ESO Data Interface Control Document (DICD) for a detailed discussion).

(VLT) Data Flow System
The system that handles the flow of scientific data and information for the ESO VLT. It includes subsystems for proposal handling, observation handling, science archiving, data pipeline and quality control (see the DFS overview for more information).

Data Preview
A highly compressed view of an observation, mostly obtained by reducing observation frames via a suitable pipeline procedure.

Data File
This term describes all data files resulting from the execution of ESO observing programmes or files created by pipeline processing. Data files include: raw observation frames, processed (by the pipeline) observation frames, observatory calibrations.

Flexible Image Transport System (FITS)
A standard data format widely used in the astronomical community. FITS descriptions and documents are available from the NASA FITS support Office. A FITS file consists of one or more Header + Data Units (HDUs), where the first HDU is called Primary HDU or Primary Array. The primary array contains an N-dimensional array of pixels, e.g. as a 1-D spectrum, a 2-D image or a 3-D data cube. Any number of additional HDUs may follow the primary array, these additional HDUs are called FITS extensions. Three types of extensions are currently defined by the FITS standard: images (N-dimensional data arrays), binary or ASCII tables. Each HDU consists of a ASCII header unit and an (optional) data unit. The header part consists of keyword = value records that describe each parameter. The FITS header describes the structure of the data part and includes, in ESO data products, also the description of the observation performed. The headers of ESO FITS files deviate from the FITS standard beacuse of using hierarchical keywords.

FITS Keyword
A string consisting of groups of maximum 8 alphanumeric characters, separated by blanks, used in FITS headers to encode parameter information related to the data formatted in the FITS file.

Graphical User Interface (GUI)
A user interface based on the presentation of data and command options via graphical panels and user selection via mouse and keyboard data entry.

Log File
A computer readable file containing log records. Log files are written by handlers that receive log requests from distributed applications running in the on-line environment. Typically, log handlers will record major normal operations as well as unforeseen events and errors. The format of log files is defined in DICD, section 5.1.

Observation Block
The smallest schedulable observational unit for the ESO VLT. An observation block contains a sequence of high level operations, called templates that need to be performed sequentially and without interruption in order to ensure the scientific usefulness of an observation. Observation blocks may include only one target acquisition.

Observation (raw) Frame
The data product containing the result of an observation. In general, different instrument modes produce different observation frames.

Observing Programme
A list of observation descriptions and targets to be observed to achieve a scientific aim. Observing programmes are proposed by PI and are granted observing time by a time allocation committee (e.g. the ESO OPC). For the VLT, observing programmes are formulated during Phase 2 Proposal Preparation in terms of Observation Blocks. Observation Programme may consist of one or more Observing Runs.

Observing Run
Observation or set of observations, performed in unique telescope/instrument configuration, constituting a logical unit item of the observing programme, as specified by the proposer.

Phase 2 Proposal Preparation
Detailed preparation of observations. This phase is used by astronomers who have been granted observing time in order to give detailed observation setup for each target within their Observing Programme.

The software system used to process VLT raw data into calibration or science products. Pipelines consist of recipes which typically process a certain type of raw data. Pipelines require infrastructure for classification, grouping and association of data. They are running in on-line mode on Paranal, and in off-line mode at the Data Flow Operations group in Garching. The main purpose of pipelines are the extraction of instrument quality information, and the extraction (calibration data) or removal (science data) of instrument signature.

Quality Control
The VLT Quality Control process comprises the following tasks: visual checks of observed science and calibration data, checks of ambient conditions for science observations against user-specified constraints, checking the formal correctness of the data files, creating master calibration data, extracting quality parameters for quality assessment of data files and of the instrument status, populating the master calibration archive and performing instrument trend analysis.

Quality Control (QC) Level 0
Quality control during or immediately after the execution of the observation. Involves monitoring of ambient parameters (e.g. seeing, humidity) against user constraints, and checking of flux levels. QC level 0 is typically done on-site.

Quality Control (QC) Level 1
Off-line quality control using the pipeline. Involves extraction of QC1 parameters (e.g. read noise, grating position, zero points) and comparison to reference and historical data (trending). QC level 1 is typically done by Data Flow Operations Quality Control Group.

Processed Frame
The result of data reduction applied to either raw or calibration frames.

Setup File
A computer readable file containing configuration information for either telescope, instrument, detector, etc.

High level VLT operation. Templates provide the means to group commonly used procedures in a well defined and standardised unit. Templates have input parameters described by a template signature, and produce results that can serve as input to other templates. As an example, an Acquisition Template takes target coordinates and produces through an interactive procedure the precise positions used later, e.g. to place the slit.

Translation/Alias Table
A table containing alternative names for ESO standard keywords. This table is used by data delivery tools or control software to translate short names into ESO standard parameter keywords. The Science Archive can deliver FITS files with non-ESO keyword headers by translating the ESO standard into an external specification defined through a translation table.

VLT Control Software (VCS)
The software tools and systems that are directly involved in the control of VLT instruments, telescopes and related hardware. It enables and performs the acquisition of scientific data (see the VCS web site for more information).

Selected abbreviations and acronyms used at ESO

ADASS Astronomical Data Analysis Software and Systems
ASCII American Standard Code for Information Interchange
ASU Astronomical Server URL
ASTO Archive Storage System
CADC Canadian Astronomy Data Centre
CCD Charge Coupling Device
CDS Centre des Donnees Astronomique des Strasbourg
CD-R Compact Disk - Recordable
CD-ROM Compact Disk - Read-Only Memory
DEC Declination
DBCM (ESO) DataBase Content Management team
DFS (VLT) Data Flow System
DICB (ESO) Data Interface Control Board
DID Data Interface Dictionary
DMD (ESO) Data Management Division
DLT Digital Linear Tape
DTD (XML) Document Type Definition
DSS Digital Sky Survey
DVD-R Digital Versatile Disk - Recordable
DVD-RAM Digital Versatile Disk - Random Access Memory
EIS ESO Imaging Survey
ESO European Southern Observatory
FITS Flexible Image Transport System
FHT File Handling Tool
GSC Guide Star Catalogue
GUI Graphical User Interface
HST Hubble Space Telescope
HDF Hubble Deep Field
HTML Hyper-Text Markup Language
IDC Instrument Definition and Calibration database
IDD Instrument Definition Database
IOT Instrument Observing Template
JIPA Java Image Preview Application
LCU (VCS) Local Control Unit
LSO La Silla Operations
NTT (ESO) New Technology Telescope
OB Observing Block
OLAS On-Line Archive System
OTF On-the-Fly re-calibration
OPC Observing Programmes Committee
PI/CO-I Principal/Co-Investigator
QC1 Quality Control Level 1
RA Right Ascension
SAO Science Archive Operations
SAS Science Archive System
SQL Structured Query Language
STSDAS Space Telescope Standard Data Analysis Software
SV Science Verification
URL Unified Resource Locator
UTC Universal Time Coordinated
VCS VLT Control Software
VLT (ESO) Very Large Telescope
WFI Wide-Field Imager on the ESO 2.2m telescope
WCS World Coordinate System
XML Extensible Markup Language