CADC Observation Search

JCMT Archive Help: Overview

The JCMT Science Archive is the official distribution site for observational data obtained with the James Clerk Maxwell Telescope on Mauna Kea, Hawaii, and is a collaboration between the Canadian Astronomy Data Centre (CADC), Victoria and the James Clerk Maxwell Telescope (JCMT), Hilo.

System Requirements: Users should enable Java and Javascript in their web browsers to experience all of the features of the JCMT Science Archive. Especially, the download manager requires that Javascript be enabled. The JCMT Archive makes use of the Centre de Donnees astronomiques de Strasbourg's Aladin Java applet for previews so you will also receive a security warning when you first launch a preview.

Archive Help: This menu provides information to get you started. The "Form Help" page contains instructions on how to fill the forms, including the formats used to select dates, ranges of values, and coordinate search boxes. In most cases descriptions of each field in a form can also be retrieved by clicking on the link attached to the field's label.

Introduction:The "home" page for the JCMT Archive allows the user to search immediately for processed JCMT data. These include spectral datacubes produced by ACSIS as well as images and IQU polarization datacubes taken with the SCUBA camera. Images from the SCUBA2 camera will be added when they come available.

Each product contains fully calibrated data in FITS format with a full set of world coordinate system headers. Depending on the grouping algorithm, each product is the average of raw observations grouped by project, object name, filter/frequency, observing mode and date. For a more complete discussion of the processing procedure for ACSIS and SCUBA-2 products see Standard Pipeline Processing, and for the older SCUBA products see SCUBA Data processing: Calibration and Associations. Note that ACSIS and SCUBA-2 products remain proprietary as long as the raw data from which they were derived remains proprietary.

Other options on the "JCMT Queries" menu allow astronomers to find raw data from the ACSIS, SCUBA-2, SCUBA and SCAN catalogues using observational criteria like the object name, project ID, and instrument configuration. Observations using the ACSIS spectrometer will be proprietary until they pass the release date assigned by the JCMT. Users authorized to access these data should log in using their CADC username and password, after which they will be able to search for and download proprietary data from all JCMT projects of which they are members. The SCUBA catalogue includes all observations made with the SCUBA camera, a continuum bolometer array that worked at submillimetre wavelengths. The JCMT SCAN catalogue includes all observations taken with the JCMT in semester 05B or before except those in the SCUBA catalogue. Most of these observations were taken with heterodyne receivers, but they also include data taken with the older continuum detectors like UKT14 and CBE.

All public JCMT data can be downloaded freely from the CADC. Raw SCUBA, ACSIS and SCUBA2 data are provided in the Starlink Data Format (SDF) and raw SCAN data in the uncommon GSD format. Software for processing these data is available from the JCMT and the interested user is referred to the JCMT web page for more details.

NOMENCLATURE

New instruments at the JCMT and steady development of tools for the virtual observatory project, have lead to some new nomenclature for the archive.

Instrument Classification	Data in the archive is better classified by the backend that created the data files than by the frontend that detected the signal from the sky.
	ACSIS "Auto-Correlation Spectrometer and Imaging System" is a versatile multichannel spectrometer can be used for both deep integration on single points and for large-scale spectral line mapping. SCUBA-2 The successor to the original SCUBA camera, SCUBA-2 is designed for large-area continuum mapping and photometry at submm wavelengths. SCUBA The original Submm Common User Bolometer Array (SCUBA), retired in 2005, was the first large-format continuum camera for mapping and photometry at submm wavelengths. SCAN For semesters 05B and earlier, all JCMT observations that did not use SCUBA are collectively referred to as SCAN data. The majority of these are spectral line observations taken with the DAS and AOSC backends and with one of the suite of spectral line receivers (RXA, RXB, etc.). However, they also include continuum observations taken with UKT14, calibration observations (pointing, focus, etc.) that were taken with the Continuum Back End (CBE), and a miscellaneous collection of special-purpose observations with other combinations of receivers and backends.
Data Reduction	Files are grouped in the archive primarily by the way they are handled in the data reduction system.
	PRODUCT The ORAC-DR data reduction pipeline can be used to transform raw data files into a number of different kinds of reduced data products, such as images and IQU polarization datacubes for SCUBA, or spectral datacubes for ACSIS. GROUPING ALGORITHMS and ASSOCIATIONs Raw data can be grouped in a variety of useful ways: obs : one observation at a time night : all observations of a source for a particular project, wavelength and observing mode on a given night project : all observations of a source for a particular project, wavelength and observing mode in a semester public : all public observations of a source for a particular wavelength and observing mode For ACSIS, the obs, night and project products will be generated as the data arrives in the archive and will be available to authorized project members along with the raw data during the proprietary period. The obs and night products are primarily intended to allow project members to assess the quality of newly available data, but are intended to be of publication quality by themselves if no further observations are made of that source. For SCUBA, only the project products have been generated, because these correspond most closely to the products previously available from the archive. OBSERVATION At the JCMT, an observation is the fundamental unit of data collection and in times past would result in a single raw data file being stored on the disk. ACSIS and SCUBA2 will produce too much raw data for every observation to be contained in a single file, but the JCMT Archive will preserve the observation as the fundamental organizational unit for astronomical data. For use with the tools of the virtual observatory, an observation is generalized to be a set of data files derived from a particular set of photons collected at the telescope. For example, a raw SCUBA file together with its "obs" products would comprise a simple observation. An observation in this sense does not necessarily include raw data. Large images, for example, are normally built up from many smaller images. Similarly, deep integrations average together many shorter integrations to achieve better sensitivity. These composite observations share the raw data from the simple observations that comprise their membership. The night and project products will be examples of composite observations. PLANE Within an observation, files are grouped into "planes" where each plane is a different view of the same set of photons. The raw data files comprise the "raw" plane. Fully calibrated images produced by the standard pipeline comprise the "reduced" plane. Other planes may contain previews, or catalogs derived from the images in the reduced plane. To keep files within a manageable size, large images or datacubes may be broken into tiles that are guaranteed not to share more than a trivial set of photons along the edges of the tiles. Because ACSIS subsystems can be configured to overlap in frequency, the raw data for different ACSIS subsystems are always stored in different planes.
Proprietary Data	Most JCMT data is proprietary to the members of the project group for a period after the data is taken.
	RELEASE DATE Each observation is part of a project and is assigned a release date by the JCMT. Prior to the release date the observation is proprietary and is accessible only by members of the project group. An observation that has passed its release date is public and can be accessed by anyone. Calibration observations become public immediately. PROJECT GROUP Each observing project at the JCMT has a "project group" of people who are authorized to access the project's proprietary data before the release date. The membership in the project group always includes the PI and Co-Is from the original application, provided they have registered their CADC userids with the JAC. ADMINISTRATION GROUP In addition to the project group, each observing project at the JCMT has an "administration group" whose members are authorized to add and remove members of the project group beyond the original PI and Co-Is. PIs are always members of the administration groups for their projects (provided that they have registered their CADC userid with the JAC). The JAC staff can add additional administrators on the request of the PI (see Proprietary Access Control under "Archive Help").
Queries	There are three steps needed to find and download a set of data
	SEARCH : In the UI, the search page is used to set constraints on the kinds of observations to be sought. For example, the user might request only observations from a particular project, or of a particular object like M31 or OriA. For SCUBA products, if "Group Type" = "Observation", the query will only search for simple observations, or if "Group Members" > 1, the query will only search for composite observations with 2 or more members. A typical query for ACSIS raw data might specify a project ID and a range of UT dates. RESULTS : The result of a query will be shown on the "Search results" page, listing all of the planes that satisfied the search constraints. Note that the planes can contain more that just the files selected in the original search. For example, searching for 450 micron processed SCUBA data will return observations that contain both 850 and 450 micron images in their "intensity" planes. For SCAN and SCUBA raw data searches, the Search Results will list all of the "raw" planes from simple observations that satisfy the constraints. The "Download Marked Files" button for processed data proceeds to the downloadManager page. DOWNLOAD : The user will be prompted for a location to store the files in the planes selected for download, and possibly for authorization to fetch proprietary data. DownloadManager allows the user to increase the number of download threads for better performance, and to cancel the download of files that have not yet been completed.