ISO INFO Newsletters: No. 14-Feb 1999


K. Leech

This issue of ISO Info describes some of the many changes that have taken place at Vilspa as we moved from the operational to the post-operational phase. One of the main changes is the opening of the ISO Data Archive, with which astronomers can access any public ISO data. More information on this can be read in the next section.

Also included is a short report on observing ISO from the ground, news of a forthcoming workshop at the ISO Data Centre and a snippet of some of the exciting science coming from the ISO data.

The ISO Data Archive

T. Prusti & M.F. Kessler

On December the 9th 1998 the ISO Data Archive was opened to the world via the new ISO Web Page. It allows astronomers around the world to query the ISO database of observations and obtain, via ftp or CD-ROM, any data they require. Accesses to the ISO Data Archive is via a user-friendly Java based tool (see figure 1). Users may query the database using either ISO specific information (e.g. instrument) or astronomical information (e.g. wavelength) to locate objects on the sky. Results of the query are presented in a similar manner, e.g. figure 2. The archive has been designed for everyone, from the casual user who wishes to determine if their particular objects have been observed by ISO and get a quick-look at the data, to the expert instrument user who wishes to get very specific information, e.g. to see if the dark currents of a detector change with phase of ISO's orbit.

Developing the ISO Data Archive has been a complex task stretching over almost two years. Planning for it started while the mission was still running, with the requirements being iterated between Vilspa and the several National Data Centres (NDCs) over several months. Programming was carried out mainly at Vilspa, with additional work being done at the NDCs and at IPAC. Several test versions of the archive were produced keeping an extensive army of beta testers on three continents busy. By this time the mission had ended and reprocessing of all the ISO data to a consistent level was taking place. This again involved new versions of the data reduction software. And we were changing our hardware with the end of the mission. Trying to tie all these pieces together seemed like a never ending puzzle, but it all came together on December the 9th.

Approximately 15% of ISO observations were publically available when the archive opened, with more being released all the time. All ISO observations are considered proprietary, that is belong only to the observer who requested them, for one year. This one year period starts after the observer has received his last observation from a programme processed with Off-Line Processing version 6. 95% of observations will be publically available by April 1999, with the very last observations public in August this year.

The interface to the ISO data archive will evolve further. The next additions are those requested by the experts, but the instrument specific query panels may be of interest to the general user. One important addition will be the possibility to request reprocessing of data with the latest software and calibration. The calibration efforts are translated into improvements in the off-line processing software which will be made available to all users through the archive. The first updates for CAM are planned to be available before summer. We are happy to hear suggestions from the community of useful additions to the ISO archive interface via our helpdesk (

Figure 1: The ISO Data Archive query panel
The ISO Data Archive query panel

Figure 2: The ISO Data Archive results screen showing results of a query and icons
The ISO Data Archive results screen

ISO Data Archive Browse Products

T. Prusti

During operations the ISO data products from the off-line processing were categorised into three levels: edited raw data (ERD), standard processed data (SPD) and auto analysis results (AAR). During the planning for the post-operations phase, it was realized that for the ISO data archive it would be useful to have browse products for an immediate visual impression of the observations and to aid the observer in deciding which observations may be of interest to retrieve for data reduction.

After several iterations and design reviews we converged to browse products in three levels: icons, postcards and survey products. These new browse products are produced from the AAR with some additional processing for LWS and SWS. The browse products themselves should not be used to draw scientific conclusions because they are automatically processed beyond the point at which an astronomers decision would have been needed (and the icons and postcards are generally too small to show important details). The survey products, however, may be used with care if one wishes to do statistical studies on a large sample of objects processed homogeneously.

The ISO Data Archive contains the three levels of browse products in different places. A query to the archive results in information on the resulting observations being displayed along with a small icon image displaying the data from that observation - three such icons are shown on the right of figure 2. If the user wants a closer look at the data, clicking on the icon will return a larger postcard in a separate window. This is a more advanced visual representation of the icon allowing the user to see the brightnesses in maps or wavelengths and flux levels in spectra and photometry. The postcard can be saved on local disk by the user for future reference, but postcards can be also requested through the data retrieval functionality in the ISO Data Archive. Icons and postcards are just pre-generated static images - if the user wants to manipulate the data to enhance features seen in them, they should download the FITS format survey products from the archive.

The future plans for the browse products include a survey product display tool integrated in the archive interface. This will give additional visualization possibilities not achievable with the static postcard image, such as zooming and scaling. The browse products can then be used to decide easily and quickly what data is of interest to the specific scientific problem at hand.

The ISO Post Operational Phase

M.F. Kessler

During its routine operational phase, ISO made around 30000 individual observations of all classes of astronomical objects at wavelengths from 2 - 240 $\,\mu $m with imaging, photometry and spectroscopy at a variety of spatial and spectral resolutions. The goal of the ISO post-operational phase is to maximise the scientific return of this vast trove of data by facilitating its effective and widespread exploitation.This will be accomplished by:

Near the end of the post-operations phase (end 2001), it is intended to make available a final archive of data, software and documentation, which will support continued exploitation of the ISO legacy by the astronomical community for at least the following 10 years.

The seven centres involved in this effort, and their respective responsibilities, are:

All of these centres provide direct support to users and welcome visitors.

Please look at the post operations page for more information on the services the data centres will supply.

ISOCAM images of ultracompact HII regions in the LMC

P. Claes & F. Comerón

Between August and November 1997, ISOCAM imaged five fields at 15 $\,\mu $m in the Large Magellanic Cloud (LMC) suspected to contain ultracompact HII regions. The selection of fields was based on the existence of point sources observed by IRAS to have the far-infrared colours typical of galactic ultracompact HII regions, according to the widely used criterion of Wood & Churchwell 1989 (ApJ, 340, 265). Given the small linear size of these objects (< 0.1 pc), the IRAS beam included a high degree of contamination from nearby but unrelated LMC sources, making the colour selection criteria much less reliable than in our Galaxy. The dramatic improvement in angular resolution provided by ISOCAM has allowed us to identify some of the point sources, yielding important clues on their nature and morphology. Our findings are described in an Astronomy and Astrophysics Letter (Comerón & Claes, A&A 335, L13, 1998).

We identified three bright, unresolved sources in two of our ISOCAM fields (figure 3). These sources are projected on the HII region N159, near the 30 Doradus star forming complex. One of them, LI-LMC 1518, is identified with a known compact radio source, while for the other two, corresponding to the IRAS source LI-LMC 1501, no compact radio counterpart has been detected, at least down to the 6 mJy level at 2.4 GHz (Marx et al. 1997, A&AS, 126, 325). This seems to be indicative of an infrared to radio continuum flux much higher than in typical compact HII regions, especially taking into account that the lower metallicity of the LMC, and a consequently lower dust contents, should reduce that ratio with respect to typical values in our Galaxy.

Figure 3: ISOCAM 15 $\,\mu $m images of ultracompact HII regions in LMC
ISOCAM 15 micron images of ultracompact HII regions in LMC

The large ratio of infrared to radio continuum emission suggests that, unlike LI-LMC 1518, the two point sources of LI-LMC 1501 are true ultracompact HII regions. The lack of compact emission at 2.4 GHz can be explained by the high electron density of the emitting region that is characteristic of ultracompact HII regions, which produces turnover frequencies usually above 5 GHz. The non-detection of compact radio continuum sources at the position of the point sources of LI-LMC 1501, despite of their brightness at 15 $\mu$m, can thus be taken as an indication of them being optically thick at that frequency.

The angular resolution of the radio and infrared observations separately is insufficient to reliably pinpoint bona-fide ultracompact HII regions at the distance of the LMC. Nevertheless, our observations demonstrate how their combination can provide insight on the physical conditions of the emitting volume. In this way, we find evidence that makes the point sources of LI-LMC 1501 the best ultracompact HII region candidates identified so far in a galaxy different from ours. This provides a first sample of objects suitable for future studies of the early stages of massive star formation in an environment of much lower metallicity than that of our Galaxy.

The Observer's SWS

Interactive Analysis System OSIA

E. Wieprecht

The Observers SWS Interactive Analysis (OSIA) package has been released to the general user community. Before describing what the software can do, it is worthwhile to review briefly its origin.

For SWS the ISO data processing software can be split into five major parts:

the pipeline, composed of the instrument dependent pipeline (designed and developed by the SWS team),
the instrument-independent pipeline (designed and developed by ESA),
IA3, a software system used by the SWS teams to calibrate and analyse the performance of SWS and debug pipeline software,
the Infrared Spectroscopy Analysis Package (ISAP), a joint development by the LWS and SWS Instrument Teams and Data Centres,
the now released OSIA, a subset of IA3.

Parts 1 and 2 of the pipeline system, one written in FORTRAN, the other in IDL, do bulk processing without human interaction from raw satellite telemetry to the final calibrated spectrum (Auto Analysis Result - AAR) distributed to the observer.

The calibrated spectrum is the starting point for the Infrared Spectroscopy Analysis Package. This package is based on pure IDL and offers tools for further processing of the AAR data (e.g. bad data masking, averaging, or smoothing), and for a subsequent scientific analysis (e.g. line flux measurements, continuum fitting, synthetic photometry, etc.).

To make a clear separation between OSIA and ISAP, OSIA will only work at the Standard Processed Data (SPD) level, whereas ISAP will take all tasks from the AAR level. Special effort has been taken to make OSIA and ISAP work in one environment (one session), thus they are ideal partners for scientific data processing.

Some of the major design aspects were to keep OSIA simple, platform independent and easy to install. OSIA contains only pure IDL modules and FITS calibration files, and is strictly version controlled which allows referencing to specific software versions.

The OSIA functionalities can be grouped as follows:

I/O modules
Tools to access SWS data products
Pipeline modules
These modules run the automatic pipeline steps between SPD and AAR separately or together. E.g. Dark subtraction.
Interactive pipeline steps
Modules which fulfil the task of the pipeline, but can be used in a highly interactive manner to achieve a better result
Scan table tools
These give an overview of the observation
Tools to treat status and flags
Decoding etc. of status and flag words
Header modules
Modules to extract data product header information
Masking tools
Visualise the SPD data product and remove invalid data points
Calfile selection tools
These tools allow a flexible calibration file usage
Selecting & Combining
A very extensive tool to flatfield SWS spectrum
Standard sigma clipping tool with a lot of options
A very extensive tool to rebin SWS spectrum
Standard plotting of all relevant data products, SWS aperture on the sky and internal checks
Calibration G files
Common tools
Various tools to support data reduction
Installation modules
Modules which are necessary to install the system

OSIA was released with a user manual describing its functionalities. Similar information is provided by an expanded IDL help system. It may be downloaded by following the ISO Data Analysis Software link on the main ISO homepage or from: or

User are able to report problems via the WEB interface at Such reports will be reviewed and, if necessary, changes made to the software. At this site it is possible to subscribe to a list to stay informed about ongoing OSIA development and releases.

The World Wide Web

J. Matagne

Since it was started in 1995 our Web server has been growing at an amazing pace. From just a few pages of information on ISO the web server now holds more than 4100 individual HTML pages, containing slightly less than 1 Gbyte of images and documents (this does not include the voluminous documents which are linked and served from our ftp site). On average it is visited from around 1500 different sites each week. Figure 4 shows the number of external accesses to our site per week. The number of accesses was fairly constant before summer, increased rapidly around the time of the Paris ISO conference, dropped back to more normal levels and then has been increasing since the ISO Data Archive opened (except around Christmas).

Figure 4: Access to the public ISO web pages per week from machines external to ESA.
Access to the public ISO web pages per week

Just before the mission ended, the server for web site moved from ESTEC to Vilspa, Spain with the new URL most users will probably not have noticed this as calls to the old address are automatically forwarded to the new. Users are recommended to change their bookmarks to the new server however.

To meet the new requirements of the ISO users and community during the ISO Post-Mission, the decision was taken this summer to investigate new technology and restructure the site. Therefore in early December a totally new Homepage was released. While the old site was oriented towards keeping observers informed as to the progress of their observations, the new one is orientated towards informing users of how to use the ISO data and allowing observers to access the archive of all observations to download any useful data.

The new site has four main sections:

Data Archive. Here users can access the ISO Data Archive and obtain the data analysis packages.

Users Information. This links to the explanatory documentation on the satellite and instruments, the repository for ISO information. It also links to information on what services the IDC offers observers and how to get to Vilspa.

Science. This contains our gallery of science images, a list of ISO publications, list of meetings concerning ISO science and links to other science sites of interest to ISO users.

Outreach. A compilation of ISO facts, press releases, background articles (including ISO Info!) and images and movies of ISO.

ISO Workshop on Solar System Objects

T. Müller

The ISO Data Centre team in Vilspa intends to hold a workshop on Solar System Objects (SSOs) at ESA's satellite tracking station near Madrid (Spain) in May 1999. Bearing in mind the specific needs in data reduction of ISO's Solar System observations, our initial objective for this workshop is to support the finalisation of data reduction of individual observing programmes for presentations at the two major conferences on solar system objects this year: Asteroids, Comets, Meteors meeting in July and the Division of Planetary Sciences meeting in October. Also, one should not forget that by August 1999 all ISO data will have become public.

This workshop would bring together the ISO observers working on Solar System programmes with the experts in instrument calibration and data reduction for an exchange on latest calibration updates, advanced data processing techniques and also latest results on Solar System studies. In addition, the IDC has a number of facilities which can be used to reduce and fine tune SSO data with support from the staff at the Data Centre.

Possible topics will include: pointing, tracking and their impact on observations using small apertures; parallax; solar system observations with PHT; analysis of asteroid data and thermal modelling; modelling planet emission; beam-tracking effects on SWS data analysis. However, this list is not exhaustive and you may have other specific topics you would like to see discussed.

For more information on this conference see the ISO web site.

ISO Mailing List

ISO INFO is edited by:
Kieron Leech ISO Resident Astronomer
Villafranca del Castillo,
Satellite Tracking Station,
P.O. Box 50727, 28080 Madrid, Spain
Telephone: International +34-91-813-1254
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ISO Observed!

M. Busch & R. Kresken

Remarkably enough, ISO can be observed from the ground using a fairly small telescope. Figure 5 shows an image the Infrared Space Observatory satellite (95062A) observed when approx. 63,800 km from Earth on the 16th of December 1998 from the Starkenburg Observatory, Heppenheim, Germany. North is to the left. ISO is the trailed object in the upper right of the image.

The instrument used was the Mühleis Telescope (450 mm, f/4.4, Newton) with a CCD Camera (768x512 pixels in 2x2 binning mode, 12x8 arcmin fov).

Figure 5: ISO Observed from the ground

In all five images were taken, and an animation generated from these can be seen at the main (ISO web site) or at the Starkenburg Observatory site