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This Legacy journal article was published in Volume 1, May 1992, and has not been
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The HEASARC On-line Service
An Overview
K.L. Rhode
HEASARC
One of the primary objectives of the HEASARC is to provide a user-friendly,
multi-mission, multi-wavelength environment in which to access the data that it
archives. An On-line Service has been established to help accomplish that
objective. Users who log in to the Service can access data from orbiting
observatories (the list of which currently includes Cos-B, HEAO-1, Einstein,
EXOSAT, and Ginga) along with many well-known ground-based catalogs. The
database system and software within the On-line Service allow users to search
and locate data, and then to either analyze it remotely, or to export it to
their home computers for analysis there.
Introduction to the XOBSERVER environment
The HEASARC On-line Service resides on the NSSDC Data Archive and Distribution
Service, NDADS, a VAX cluster at GSFC. (For more information about the NSSDC,
see the article by Jim Green and Jeanne Behnke in this issue.) A captive
account called XRAY has been set up on the NDADSA VAX to provide secure remote
access to the database system and software. A program called XOBSERVER is run
when users log in to the XRAY account. XOBSERVER provides:
- automatic registration of users,
- a user directory where files can be stored and manipulated,
- TCP/IP, DECnet and PSI access (plus a gateway option),
- runtime execution of database access and analysis tasks, and
- tasks to transfer files to the user's computer.
A user logs in remotely to XOBSERVER and then runs database and analysis tasks
to search through astronomical catalogs, locate data files, and analyze or
transfer data. The XOBSERVER program originated from the EXOSAT Database
System, which was written by the European Space Agency's (ESA's) Space Science
Department between 1986 and 1990 to provide remote access to archival data
obtained by EXOSAT. Recently the HEASARC, the ESA, and the University of
Leicester, UK, have been jointly developing the system to provide a generic
environment for on-line astrophysics archival access and analysis. The system
has since been renamed XOBSERVER, in recognition of its multi-mission nature
and to distinguish the controlling environment from the analysis and database
tasks.
Logging in
Users can log in to the HEASARC On-line Service 24 hours a day via one of the
following methods (user entries are indicated in courier type):
NSI-DECnet:
NODE NAME: NDADSA
NODE NUMBER: 15761
DEC Example:
$ set host ndadsa
$ set host 15761
NSI-TCP/IP*:
NODE NAME: NDADSA.GSFC.NASA.GOV
NODE NUMBER: 128.183.36.17
DEC Example:
$ telnet ndadsa.gsfc.nasa.gov
$ telnet 128.183.36.17
GTE TELENET:
dial local TELENET phone number
@C NASA
*LOGON
ENTER USERID>**
ENTER PASSWORD>**
ENTER Service>**
DIRECT DIAL:
Dial autobaud phone number (301)286-9000
CALL, DISPLAY, MODIFY OR ENTER NUMBER?
CALL SISC
LOCAL> CONNECT NDADSA
*INTERnet users will be prompted for their local userid.
**Users must register a PSI address. Send a message to NDADSA::REQUEST or
15761::REQUEST.
Once the user has connected, NDADSA will signal its presence and ask for a
username. The user enters XRAY at the USERNAME prompt, and is logged in to the
On-line Service captive account. A new user, or one who is logging in from a
different location than usual, will be asked to type a HEASARC username. This
should be the user's first initial and last name, (e.g., INEWTON).
The HEASARC username forms part of the name of the top-level directory (e.g.,
user INEWTON's directory would be called OBSERVER:[INEWTON]) where the files
created during each session are written. The username ensures that the user
regains access to this directory during subsequent sessions. User directories
are not secure, and should be treated as scratch areas where data and files are
temporarily kept. The directories are periodically cleaned up, with scratch
files deleted and multiple versions purged.
Once the user has successfully logged in to the captive account, the
HEASARC> prompt appears; this indicates that HEASARC XOBSERVER is
ready to receive input. At this point there are a number of options available
to the user, including accessing the bulletin board or the databases, running
data analysis programs, or transferring files. On-line help can be accessed by
simply typing help at the HEASARC> prompt; this will call
up the XOBSERVER User's Guide, which contains information about all of
the programs in the XOBSERVER package.
The bulletin board
The HEASARC bulletin board contains the latest news concerning the HEASARC and
the On-line Service. Announcements are posted there on topics such as new or
revised databases, new software, procedural or structural changes to the
Service itself, and occasionally even job announcements. In addition, ROSAT
and CGRO status reports are posted on the bulletin board as soon as they are
released. To access the bulletin board, the user simply types
HEASARC> bulletin
(Note that all commands throughout the XOBSERVER system can be abbreviated to
the least number of characters which make them unique; e.g., bull for
"bulletin".)
Commands within the bulletin board program are logical: DIR displays a
bulletin directory, and READ followed by a bulletin number displays a
particular bulletin. Other commands are BACK, NEXT, and EXIT. HELP will
invoke the bulletin board help facility.
The BROWSE databases
Typically, a user will begin an XOBSERVER session by running the database
access program, BROWSE, to search through and display the available data and
catalogs. BROWSE is a command-driven program that uses a database management
system to select data from tables of information and results, and access any
associated data product files. The analysis tasks available within the
XOBSERVER environment can be executed from within BROWSE, or outside of it,
whichever the user prefers.
BROWSE is started by typing
HEASARC> browse [dbname]
The optional parameter dbname specifies the name of the database to be
accessed; if no dbname is given, BROWSE will prompt for a database
name. Typing a ? or carriage return will display a list of all
available HEASARC databases. Once a user chooses a database to "browse", that
database is loaded as the current database, and the user enters commands to
manipulate the database entries. Users can sort, search, display and plot
entries in the database, and can also cross-correlate the data with entries in
other databases. In addition, the data can be passed to other programs for
spectral, timing, and image analysis, and interactive plotting and fitting.
Note that here the word "database" simply means a collection of information or
results which has been organized into a table. The rows in the table are
called "entries", and the columns are "parameters". HEASARC databases
typically contain observation logs, astronomical catalogs, bibliographies, file
names and locations, and/or data analysis results. In the case of an
observation log, the database may contain one entry for each observation, with
the associated parameters being the observation date, time, and duration,
pointing coordinates, and instrument used. Catalog databases often are
organized with one entry (or row) for each source, and parameters (or columns)
such as source names, coordinates, count rates, magnitudes, and
classifications.
At present, there are more than 50 HEASARC databases on line. A complete
listing of the available databases appears in Table 1. Some databases contain
data from missions like Einstein, EXOSAT, Ginga, and ROSAT, while others
contain well-known ground-based catalogs, such as the HST Guide Star, SAO, and
HD catalogs. The databases can be accessed separately, or cross-correlated
with one another to find matches in common parameter fields. For example,
celestial coordinates can be used to find all matching sources in two
databases, based on positional coincidences within a specified radius.
Table 1: HEASARC On-line Service Available Databases
4UHURU Catalog: 4th Uhuru X-ray
IRAS Catalog: IRAS
VSTARS Catalog: Variable Stars 4th ed
VSTARSUSP Catalog: Suspected Variables
3ARIEL Catalog: 3A (Ariel-V)
PULSAR Catalog: Lyne Pulsar
GSC Catalog: HST guide stars
VERON Catalog: AGN Veron and Veron
RITTER Catalog: Ritter CVs & LMXRBs
HD Catalog: Henry Draper
SAO Catalog: SAO stars
TD1 Catalog: Stellar UV Fluxes
MCKSION Catalog: McCook & Sion WD's
QSO Catalog: Hewitt & Burbidge QSO
WOOLLEY Catalog: Stars <25 pc from Sun
MRC Catalog: Molonglo Radio Srcs
6CMNORTH Catalog: 6cm radio
ABELL Catalog: Abell Clusters
20CMNORTH Catalog: 20cm radio
DOCUMENTS Documents: HEASARC
LE EXOSAT CMA (central 6 arc min)
CMA EXOSAT CMA Database
CMAIMAGE EXOSAT CMA Images
GS EXOSAT GS database
ME EXOSAT ME database
TGS EXOSAT TGS L and R orders
TGS2 EXOSAT Transmission Grating
EXOPUBS EXOSAT bibliography
EXOLOG EXOSAT observation log
IPC Einstein IPC Source List
SSS Einstein SSS database
EINLOG Einstein observation log
SSSHME Einstein SSS dbase-IBM listing
HRIIMAGE Einstein HRI Image Database
HRICFA Einstein HRI CFA Source List
HRIEXO Einstein HRI EXO source list
IPCIMAGE Einstein IPC Image Database
EMSS Einstein EMSS catalog
GINGALOG Ginga LAC Log Catalog
GINGAMODE Ginga LAC Mode Catalog
A4 HEAO 1 A4 X-ray catalog
A2PIC HEAO 1 A2 Piccinotti Catalog
A1 HEAO 1 A1 X-ray Catalog
A2POINT HEAO 1 A2 Point Catalog
A2LED HEAO 1 A2 LED Sky Catalog
A3 HEAO 1 MC LASS Catalog
IUE IUE ULDA database
X-RAY Master Catalog: X-ray
XCOLL Master Catalog: X-ray Collim.
RADIO Master Catalog: radio
ZZDB Metabase
ROSTL2 ROSAT AO2 long-term timeline
ROSTL1 ROSAT AO1 long-term timeline
ROSAO ROSAT accepted AO proposals
ROSATLOG ROSAT log of observations
ROSOBS ROSAT observations status
ROSSTL ROSAT short-term timeline
SMMGRS SMM GRS [[gamma]]-Ray Burst D'base
The databases called X-RAY and OPTICAL contain master catalogs, which are
created by merging the common parameters from several individual catalogs.
X-RAY combines data from six separate X-ray source catalogs (A2PIC, A3, EMSS,
HRICFA, IPC and IPCSLEW), while OPTICAL combines information from about a dozen
optical catalogs (including VSTARS, QSO, RITTER, SAO and ABELL). The master
catalogs allow users to obtain general information about astronomical objects
without having to access separate databases one by one.
Some of the BROWSE databases contain data products. The IPCIMAGE and HRIIMAGE
databases provide access to the Einstein IPC and HRI FITS images which have
been distributed by SAO. The SSS database contains spectral and lightcurve
data products from the Einstein SSS, plus the associated MPC spectra. These
spectra are currently in XSPEC format, and will be available soon in FITS
format as well.
The section of this article called XOBSERVER examples illustrates some
commonly-used BROWSE commands, including commands to search the databases and
extract data products. Also, examples and on-line help documentation can be
displayed from within BROWSE by typing the help or dbhelp
commands. Help will display general BROWSE information, while
dbhelp displays information about the currently-loaded database,
including a description of each parameter, the available data products, and the
name of a contact person.
File transfer options
Files that are created during an XOBSERVER session are stored in the user's
directory, including any extracted data products, and log and history files
created by the XOBSERVER programs. (A complete record of all output from a
user's BROWSE session or XOBSERVER session is written to log files called
BROWSE.LOG or XOBSERVER.LOG.) These files can be transferred from the user's
directory to his or her home computer. The transfer can be made either from
the XRAY account using the mail, send or FTP
commands, or from the user's computer using the VMS copy command. The
file transfer method used depends on whether the file is ASCII or binary, and
whether it is a VMS to VMS or VMS to UNIX transfer.
Help documentation, which describes what each file transfer command is suitable
for, is contained in the XOBSERVER User's Guide. Type help at
the HEASARC> prompt to access the guide.
Spectral analysis
The spectral fitting package available within the XOBSERVER environment is
XSPEC, which is part of the XANADU analysis package that originated at the
Institute of Astronomy, Cambridge, UK. XSPEC was written by R.A. Shafer and is
currently maintained jointly by the EXOSAT Observatory, the HEASARC, and MSFC.
XSPEC can be run either stand-alone from the main HEASARC> prompt,
or from within BROWSE. In the latter case, BROWSE will provide the required
spectral files, while in the former the user must extract them or create them
manually.
To run XSPEC from within BROWSE, the user must first ensure that the database
being "browsed" contains spectral products (the xp/summary command
displays a summary of available data products). Next, the user searches the
database for the entries containing the spectra to be analyzed. Then the user
types xspec on the BROWSE command line; this invokes an interface to
XSPEC which locates the required files and creates the necessary response
matrices and background files. Thus most of the complexity of the program is
hidden from the user.
To run XSPEC as a stand-alone procedure, independent of BROWSE, the user should
first extract the chosen spectral file using BROWSE, and then exit BROWSE. If
necessary, the user next runs the VIMAT program to create a response matrix and
background files. Finally, the user types xspec at the
HEASARC> prompt.
On-line help documentation on XSPEC can be accessed from a number of places.
Users can type help when inside XSPEC for descriptions of commands.
Also, both the BROWSE and the XOBSERVER on-line documentation contain
information about XSPEC and examples of how to use it; the former can be
accessed by typing help within BROWSE, and the latter by typing
help at the HEASARC> prompt.
For users who wish to copy spectral files back to their home computers to
analyze them, XSPEC and its associated programs are available for local
installation. Both the VAX/VMS and Sun-UNIX versions can be obtained by
sending e-mail to ndadsa@request.gsfc.nasa.gov, or Karen
Smale at ksmale@heasarc.gsfc.nasa.gov.
Timing analysis
The timing analysis package available in the XOBSERVER environment is called
XRONOS. XRONOS is made up of a collection of programs, each dedicated to one
task, which can be run from within BROWSE, as stand-alone routines, or from a
XRONOS command-driven environment. There are XRONOS tasks for:
- plotting light curves,
- plotting hardness ratio and color-color diagrams,
- epoch folding,
- power spectrum analysis,
- auto-correlation, cross-correlation and time skewness analysis, and
- statistical analysis.
If the XRONOS tasks are run from within BROWSE, then the command-driven
interface is used; that is, applications are run by entering a command string
followed by qualifiers and arguments. For example, a user selects data with
BROWSE, and then plots the data by simply typing the name of the XRONOS task,
e.g., lc1. On the other hand, to run XRONOS in stand-alone mode, the
user should first type the BROWSE command xp/li to extract the data
product file. After exiting BROWSE, the user would then run individual XRONOS
tasks on the extracted files.
Each of the XRONOS tasks is explained in the on-line help documentation within
the program itself; the documentation is accessed by typing help at
the XRONOS> prompt, or replying help to any question asked
by a XRONOS application. Information about XRONOS can be found in the on-line
help for BROWSE and XOBSERVER as well.
At present, XRONOS is available for remote installation on VAX/VMS machines,
and will soon be available in Sun-UNIX and HP-UX versions as well. Information
can be obtained from Lorella Angelini at angelini@heasrc.gsfc.nasa.gov.
Image analysis
XIMAGE is the program used in the XOBSERVER environment to provide an on-line
image display and analysis capability. Like the other analysis packages,
XIMAGE can be run either from within the BROWSE program, or in stand-alone mode
starting from the HEASARC> prompt.
Before running XIMAGE, users should first access a database with BROWSE, and
then type the command xp/summary or pp/summary to see whether
images are available for that database. Next the user searches the database
and selects the data to be analyzed.
At this point, users can run XIMAGE from within BROWSE by simply typing a
command that looks like
> ximage[/qualifiers] entry_number
where entry_number is the database entry number of the image the user
wishes to analyze. Qualifiers, such as /smooth, /threshold,
and /rebin, can be used to control features of the image display.
In order to run XIMAGE as a stand-alone procedure, a user must first use BROWSE
to select and extract the images. The BROWSE xp command will extract
the images in their original format, while xfits extracts them in FITS
format. After exiting BROWSE, the user types XIMAGE at the
HEASARC> prompt to start the program. The extracted files can be
read into XIMAGE using one of the read commands in conjunction with
the necessary qualifiers.
Detailed help documentation for XIMAGE can be accessed from within the program
by typing help. Information on XIMAGE and associated image analysis
routines is also contained in the XOBSERVER help and in the BROWSE help.
XIMAGE can be installed locally on the user's computer. Currently, only a
VAX-VMS version is available; Sun-UNIX and HP-UX versions are under
development. Contact Lorella Angelini at angelini@heasarc.gsfc.nasa.gov for more information.
QDP/PLT
The plotting and function-fitting package that is used within the XOBSERVER
environment is called QDP. The program operates on ASCII files which contain
both the data and the commands that control the display. QDP can also be used
in an interactive mode to customize the plot and perform simple analysis tasks
on the data.
The QDP package is used by the BROWSE, XSPEC and XRONOS programs to plot light
curves and spectra. From each of these programs, a QDP file can be generated,
and later input to QDP for plotting and fitting. Users can also generate QDP
files in the XRAY account, and then transfer them to their home computer, where
they can replot and manipulate them locally.
Like XSPEC, QDP originated as part of the XANADU EXOSAT analysis package at the
Institute of Astronomy, Cambridge, UK. It was written by Allyn Tennant, and is
now maintained by him at MSFC. Users who wish to install a copy of QDP on
their home computers can contact the HEASARC. QDP is available in VMS, UNIX and MS-DOS versions.
A full help facility is available within QDP. There is also information about
QDP in the on-line documentation for XOBSERVER and BROWSE.
Obtaining user's guides and information
This article describes only a fraction of the tasks that can be performed and
the information that can be accessed within the HEASARC On-line Service. In
addition to the extensive on-line help in the XRAY account, a variety of
documentation is available from the HEASARC. User's guides for XOBSERVER, the
BROWSE databases, XSPEC, XRONOS and XIMAGE are among the documents available; a
complete list is contained in the BROWSE database called DOCUMENTS. Requests
for documentation should be sent to request@ndadsa.gsfc.nasa.gov.
User questions or problems with any of the XOBSERVER software or the database
system should also be reported to requests@ndadsa.gsfc.nasa.gov. Comments and suggestions are welcome, and will be implemented when possible.
XOBSERVER Examples
Below are examples of the database access and analysis tasks which can
be run within the XOBSERVER environment.
HEASARC> help ! Display the XOBSERVER help documentation
HEASARC> bulletin ! Access the HEASARC bulletin board
Search the ROSAT and EXOSAT observation logs, using the "sc", "sn",
and "sp" commands:
HEASARC> browse ROSATLOG ! Browse the ROSAT pointing log
ROSATLOG_TOTAL_DEC> keywords ! Display a list of BROWSE command keywords
ROSATLOG_TOTAL_DEC> search ! List all of the search commands
ROSATLOG_TOTAL_DEC> dbhelp ! Display a description of the contents
! of the ROSATLOG database
ROSATLOG_TOTAL_DEC > sn cygx-1 ! Search for entries with target name "CYGX-1"
ROSATLOG_TOTAL_NAM 3> dall 1-** ! Display all of the information in
! the three found entries
ROSATLOG_TOTAL_NAM 3> sp pi mushotzky ! Search for all observations with
! Mushotzky as PI
ROSATLOG_TOTAL_NAM 20> dall 1-** ! Display all the parameters in the
! twenty found entries
ROSATLOG_TOTAL_NAM 20> cdb exolog ! Change to the EXOSAT observation log
EXOLOG_TOTAL_DEC > sc ! Search by coordinates
R.A. (1950 d/f= 20 h 47 m 58.20sec): 18 20! RA = 18 20
Dec (1950 d/f=-52 deg 31 m 4.42sec): -30 ! Dec = -30
Radius in arcmin. (d/f= 60.00): ! Cone radius = 60 arc min
EXOLOG_TOTAL_DEC 15> dsam ! Redisplay the found entries
Search ROSOBS, the ROSAT observations status database, for all entries
beginning "LMC". Then use the filtering and sorting commands:
EXOLOG_TOTAL_DEC 15> cdb rosobs ! Change to the ROSOBS database
ROSOBS_TOTAL_DEC > sn lmc* ! Search for names starting "LMC"
ROSOBS_TOTAL_NAM 13> sif country US ! Set an inclusive filter on the
! COUNTRY parameter. Include only
! the entries where the COUNTRY
! parameter is "US"
ROSOBS_TOTAL_NAM 13:11> dsam ! Display the remaining entries
ROSOBS_TOTAL_NAM 13:11> sort done ! Sort on the DONE TIME parameter
ROSOBS_TOTAL_NAM 13:11> dsam ! Display the sorted entries
ROSOBS_TOTAL_NAM 13:11> sef done ! Set an exclusive filter.
Exclude
Enter minimum number: -100 ! entries with DONE TIME between
Enter maximum number: 0.01 ! -100 and 0.01 ksecs
ROSOBS_TOTAL_NAM 13:11:2> dsam ! Display the remaining 2 entries
ROSOBS_TOTAL_NAM 13:11:2> rlf ! Remove the last filter that was set
ROSOBS_TOTAL_NAM 13:11> cdb cma ! Change to the EXOSAT CMA catalog
Search the EXOSAT CMA catalog for all entries of 3C382, and then plot
the count rates from different filters against each other:
CMA_SOURCES_DEC >sn 3c382 ! Search for name 3c382
CMA_SOURCES_NAM 16> sc ! Search by coordinates, to be sure
R.A. (1950 d/f= 18 h 33 m 11.75sec): ! all entries are found
Dec (1950 d/f= 32deg 39 m 17.93sec):
Radius in arcmin. (d/f= 30.00):
CMA_SOURCES_DEC 47> sif filter 7 ! Keep only filter 7 data (thin lexan)
CMA_SOURCES_DEC 47:26> dsam ! Display the remaining entries
CMA_SOURCES_DEC 47:26> cpd /te ! Change plot device to Tektronix
CMA_SOURCES_DEC 47:26> psam/plt time count ! Plot TIME vs. COUNT RATE
! The "/plt" qualifier leaves the user
! in QDP/PLT for interactive changes to
! the plot
CMA (time vs. count rate)
PLT> hard 3c382_lex.ps/ps ! To have a hard copy of the plot,
! write it to a postscript file
PLT> exit ! Exit from PLT mode
CMA_SOURCES_DEC 47:26> rsam ! Now, reset the sample to include
! all entries
Plot an image of Cas A and extract it in FITS format. Also plot,
extract and fit Cas A spectra using XSPEC:
CMA_SOURCES_DEC > sn casa ! Search for all Cas A entries
CMA_SOURCES_DEC 11> cpd /gterm ! Change plot device to GTERM
CMA_SOURCES_DEC 11> ximage 1 ! Plot the entry #1 image
CasA Image
CMA_SOURCES_DEC 11> xfits/im 1 ! Extract the image in FITS format
CMA_SOURCES_DEC 11> cdb me ! Change to the EXOSAT ME database
ME_TOTAL_DEC > sc/default ! Search using the default coordinates
! from the previous search
ME_TOTAL_DEC 5> pp/sp 1 ! Plot the spectral product for
! the first entry
Spectrum 1
ME_TOTAL_DEC 5> xp/sp 1-** ! Extract all the spectral products
ME_TOTAL_DEC 5> xspec/int 1 ! Run XSPEC interactively on the
! spectrum from entry #1
ME_TOTAL_DEC 5> exit
HEASARC> mail 3c382_lex.ps ! Mail the 3C382 postscript plot
file and the
HEASARC> mail browse.log ! BROWSE log file to the user's
home computer
HEASARC> lo ! End the XOBSERVER session
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