Multimission Archive at the Space Telescope Science Institute (MAST)
Annual Report for the Period October 1997-September 1998
OverviewThe Multimission Archive at the Space Telescope Science Institute (MAST), site of the Hubble Data Archive (HDA), was developed to support a variety of astronomical data archives, with the primary focus on scientifically related data sets in the optical, ultraviolet, and near-infrared parts of the spectrum. Initially set-up to hold, with the HDA, the International Ultraviolet Explorer (IUE) archive, MAST has evolved by holding, or providing links to, many other missions or projects. The data available through MAST, in addition to those in the HDA, include, as of October 1998:
Web-Based AccessAll archives are accessible via WWW pages which contain links for users to search the database, obtain help, retrieve data, and get access to on-line documentation and analysis software. All databases, apart from IUE and EUVE, are stored at MAST. HST and FIRST data are retrievable through the Data Archive and Distribution Service (DADS) at STScI. Copernicus, HUT, and WUPPE data are stored on magnetic disk, DSS data are stored on CD-ROMs, and UIT data are stored on DLT tapes. IUE data are currently accessible via links to the NASA Data Archive and Distribution Service (NDADS) system at the National Space Science Data Center(NSSDC), but will be made available directly from MAST in the coming months. EUVE data are physically stored at the High Energy Astrophysics Science Archive Research Center (HEASARC) at NASA GSFC, which also provides Web-based access. In the near future, most data will be stored at MAST (see below).
Catalog/Archive Cross-CorrelationsMAST staff has made it easier to look for data for particular classes of astronomical sources in the HST and other MAST archives. To take advantage of various archives at one site and enhance the potential of the single archives, we have in fact started a project which allows the cross-correlation of astronomical catalogs with the archives available at MAST. This interface, available at http://archive.stsci.edu/search/, enables at present the cross-correlation of an Active Galactic Nuclei (AGN) catalog, a galaxy cluster catalog, and a star catalog, plus a user-supplied list of positions, with the HST, IUE, EUVE, and other MAST archives.
Using this interface one can select AGN by class, redshift, magnitude, and 6 cm radio flux from a catalog heavily based on the Veron-Cetty & Veron (1996, ESO Scientific Report n. 17) catalog (see Padovani, Giommi & Fiore, 1997, Mem. Soc. Astron. It., 68, 147), and cross-correlate them with the HST and other MAST archives. For example, one can look for all radio-loud quasars at redshift > 4 observed by HST or all Seyfert galaxies brighter than 15th magnitude with IUE spectra. (For HST, one can select individual instruments, each with a different correlation radius.) Multiple missions can also be selected, with the option to show only those AGN that cross-correlate with every selected mission (so one can look for AGN that have been observed with both HST and IUE, or for AGN observed with either HST or IUE.) After the correlation is performed, the user can preview the images/spectra (at present only in the case of HST data), and retrieve the data.
The Abell catalog of rich clusters of galaxies (Abell, Corwin &
Olowin, 1989, ApJS, 70, 1), can also be cross-correlated with HST and other
MAST archives. The cluster selection can be done in terms of redshift,
richness, magnitude of the tenth brightest cluster member, and Galactic
coordinates. Users can also cross-correlate the Hipparcos catalog
(1997, ESA SP-1200), selecting stars on the basis of magnitude, B-V color,
parallax, spectral type, and coordinates, with the MAST archives to look
for objects with the relevant data.
User SupportMAST staff have handled many detailed questions and requests from astronomers in the US and abroad concerning MAST data sets, including data retrievals, processing, calibrations, software, data handling, and related analysis tools. Examples include: how to compute visual magnitudes from FES counts, possible problems in the crowded orders of IUE data, systematic effects in EUVE data, and help in reading the NEWSIPS FITS files with various software packages.
Data EvaluationMAST staff have evaluated data characteristics of the recent "NEWSIPS" processing of IUE data. These activities have led to two studies. The first evaluation is of the apparent radial velocities of high-dispersion spectra among the three cameras as a function of relevant parameters such as time and entrance apertures. Results from IUE spectra were compared by standard cross-correlation techniques between IUE spectra of hot star standards as well as between the IUE and other missions, such as Copernicus and the Orbiting and Retrievable Far and Extreme Ultraviolet Spectrometers (ORFEUS). Although residual zero-point errors still exist for NEWSIPS Short Wavelength Prime (SWP) camera data, both respect to apparent radial velocities from images from the long wavelength LWP and LWR cameras and with respect to radial velocities determined from optical data, most NEWSIPS-processed SWP images are to be greatly preferred over IUESIPS-processed data because of they have much less sensitivity to spurious time-dependent calibration effects. Differences in apparent velocity between large- and small-aperture data arise for all three cameras for bright stars exist because of systematic centering errors. Small systematic velocity shifts occur among the three cameras, with the SWP camera giving results in between those of the two long wavelength cameras.
One of the most interesting systematics found in the radial velocity study is a wavelength-dependent errors in NEWSIPS SWP images with respect to IUESIPS processings and Copernicus archive data. This systematic is likely to arise from the 1990 revision of laboratory wavelengths of the PtNe calibration source commissioned by NASA for HST/GHRS wavelength calibrations and used in the IUE NEWSIPS (but not IUESIPS) processings. This study was presented as a poster paper at the January 1998 AAS meeting and is available on the Web at http://archive.stsci.edu/iue/newsips/radvel.
A second study was done to evaluate NEWSIPS data arose from a report that
the background fluxes of high-dispersion SWP images from the standard star
Tau Scorpii exhibit a time-dependent level relative to a local zero, e.g.
as determined from the core of the saturated Lyman alpha line. Our study
confirms this dependence, but shows that it is actually a symptom of a
much larger problem affecting IUE data with time. A study of the fluxes
of "null image" surfaces with time shows that they decrease in a highly
nonuniform way such that over time they change first and most rapidly near
the corner of the image where the Lyman alpha and other short-wavelength
orders fall on the SWP camera image. These changes cause a change with
time in the morphology of the functional fit to raw fluxes extracted through
an SWP image and therefore time-dependent errors in the results. Although
changes to the SWP null surface occurred continually through the IUE-mission
lifetime, both they and a degradation in camera sensitivity accelerated
in 1990-1991. We speculate this acceleration could be due to an aging of
the phosphor detector from particle storms during in the last solar maximum.
This study has been written up in a paper entitled "A Study of the Time-Dependent
Background Flux Levels in IUE High-Dispersion SWP Images" which will soon
be submitted to the Publications of the Astronomical Society of the Pacific.
Dissemination of InformationMAST publishes a newsletter, which is distributed electronically via a mailing list, to provide information about its activities. Users can subscribe by sending e-mail to email@example.com; put the single word SUBSCRIBE in the body of the message. The newsletter can also be read on the WWW at http://archive.stsci.edu/archive_news/. Various articles about MAST have also been published in the AAS and STScI Newsletters.
Interaction with Other Data Centers and ServicesMAST has been interacting with other NASA centers to maximize accessibility to optical/UV data and at the same time minimize duplication of efforts, within the broader objectives of the Space Science Data System (SSDS) concepts of interoperability and interdisciplinary access to data. An example of this sort of approach has been the inclusion of Extreme Ultraviolet Explorer (EUVE) data into MAST. EUVE has been managed, from the design and construction to the scientific mission and data archive, by the Center for Extreme Ultraviolet Astrophysics (CEA) of the University of California, Berkeley (http://www.cea.berkeley.edu). Due to reduced resources, CEA is now terminating support to the EUVE archive. As a result of a collaborative effort between CEA and STScI, the National Space Science Data Center (NSSDC), and the High Energy Astrophysics Science Archive Research Center (HEASARC), the latter three centers have agreed to take responsibility of the EUVE archive. Namely, the science archive data (images and event files) are now available both through STScI (http://archive.stsci.edu/euve) and HEASARC (http://euve.gsfc.nasa.gov/). This is in keeping with the nature of EUVE data, which is complementary to both optical/UV and X-ray research, and with the fact that the optical/UV and X-ray communities will benefit from using interfaces with which they are already familiar. The data are currently held for network access at HEASARC (with links to them from STScI and NSSDC). STScI will support the IRAF-based EUVE software. NSSDC, on the other hand, will provide a permanent archive of the science and the telemetry (raw) archive data (http://nssdc.gsfc.nasa.gov).
MAST staff also collaborated with the GSFC National Space Science Data Center (NSSDC) and the GSFC Astrophysics Data Facility (ADF) during the past year. ADF provided associated documentation and information about the instruments that were part of the Astro Observatory: the Ultraviolet Imaging Telescope (UIT), the Wisconsin Ultraviolet Photo-Polarimeter Experiment (WUPPE), and the Hopkins Ultraviolet Telescope (HUT). ADF staff answered numerous questions about problems associated with the data. NSSDC has provided copies of EUVE data as they arrived from the project. ADF has provided facilities and some software for the MAST staff to create copies and indexes of the IUE, UIT, WUPPE and HUT archives on DLT tape that will be used for the permanent archive. While creating copies of these archives, MAST staff made copies of the data on DLT for ADF usage. During the past year, while MAST has been developing plans for archiving the IUE data, users of the MAST IUE search pages have been able to retrieve the data from the NSSDC near-line archive NDADS. In addition, the MAST has been pointing to the browse files developed by the ADF staff to provide preview information to users of the MAST search pages for the IUE and UIT datasets.
MAST staff worked with Dr. George Sonneborn of GSFC's Laboratory for Astronomy and Solar Physics (LASP), who with his collaborators had created a new version of the Copernicus archive funded by an ADP grant. The data files and web pages developed under this grant were received and installed on-line. Updates resulting from this ADP grant continue to be installed as they are completed.
MAST staff has also developed working relationships with staff from several of the missions including EUVE, WUPPE, HUT, and all three of the instrument teams from the ORFEUS Project. The projects have provided further documentation and insight into the data acquired with their instruments. The ORFEUS instrument teams will provide data and documentation directly to MAST. In addition to receiving information from the projects, MAST staff members have made suggestions concerning the FITS formats for the WUPPE and ORFEUS Extreme Ultraviolet Spectrograph (EUVS) datasets.
Finally, MAST has participated actively in the creation of the Astrophysics
Data Centers Coordination Council (ADCCC). This body includes representatives
from all NASA archive centers who convene to discuss issues such as improving
the interoperabilty and increasing the interconnectedness of their data
Plans for the Coming YearMAST plans to incorporate additional ultraviolet and optical data sets in the future, including data from the Orbiting and Retrievable Far and Extreme Ultraviolet Spectrometers (ORFEUS) and the Far Ultraviolet Spectroscopic Explorer (FUSE), currently scheduled for launch in February 1999. MAST will further enhance the scientific value of its data holdings by archiving Mosaic Imager data from the National Optical Astronomy Observatories. The Mosaic Imager is a CCD camera consisting of 8 4Kx2K CCDs placed together to span a large continuous field. Mosaic will be used on the KPNO 4m telescope in prime focus and covers a field of 36' x 36'. Mosaic can also be used at the Cassegrain focus of the 0.9m covering 59' x 59'. Mosaic will perform sub-arcsec imaging of large fields of view and perform surveys in standard photometric bands. Each raw mosaic image is about 128 Mbytes and Mosaic will produce about 6 GB of observations per night. NOAO will be calibrating the raw data and MAST will only be receiving the calibrated data. Mosaic Imager data currently has an 18 month proprietary period and initial demand on the archive will be low. This will give MAST time to build up a substantial dataset. Mosaic begin routine operations in the fall of 1998. The cost of Mosaic archiving and data distribution is borne fully by funds provided by NOAO.
In collaboration with the GSFC ADF and NSSDC, MAST has acquired the following archives on DLT tape or via FTP: IUE Final Archive, UIT, HUT (Astro 1), and UIT. Copernicus data were acquired from collaborators from GSFC's LASP who developed new data products under an ADP grant. MAST staff is currently distributing data from the Copernicus, UIT, HUT (Astro 1) and WUPPE missions. These data are being distributed from copies that are on-line or read from the DLT tape. Plans to store on CD-ROMs all data acquired from GSFC (ADF, NSSDC, and LASP) and the ORFEUS instrument teams are well advanced.
MAST will continue to work in the context of the Space Science Data
System to improve the level of interoperability with the other astrophysics
data services and with planetary science (Planetary
Data System) and space physics data services. For example, we
plan to implement additional cross-correlation capabilities by providing
transparent links to the on-line catalog search services of the Astronomy
Data Center at GSFC. We will also work with new astrophysics
mission projects (e.g., the GALEX SMEX project) to assure access to these
data sets via MAST and to help them develop plans for data delivery and
long-term data access.