The spectrum of Mars in the LWS wavelength range showing many water
vapour absorption lines.
The data from all ten detectors have been
scaled so as to show a continuous spectrum (Sidher et al. 1999)
This issue of ISO Info is being printed just as all the science data from
the ISO mission enters the public domain. Any of the 30000 science
observations may be retrieved from the ISO Data Archive, details of which
appear later.
Also included is a summary of a Solar System Object workshop held at Vilspa and notification of a spectroscopy conference to be held here in the near future.
Mars was intensively observed with the spectrometers aboard ISO during July and August 1997, the only period during which this planet was not hidden behind the Sun or the Earth constraint. Numerous rotational and ro-vibrational transitions of water appeared prominently in its spectrum, as can be seen above. Comparing their strength as measured by the SWS with predictions from atmospheric models calculated for different mixing ratios of H2O it was possible to derive the global column density of water vapour in the Martian atmosphere, and it was found that condensation of the observed vapor would have formed a layer of liquid H2O with a thickness of 15 µm over the planet (Encrenaz et. al., ESA SP-427, 1999, p.173). In particular, at the time of the ISO observations the atmosphere at a height of 10 km was saturated with water, a result important for an understanding of the cloud formation and hence the water transport on Mars. Around the same time the Imager for Mars Pathfinder (IMP) found somewhat lower values both for the column density and for the saturation level; the difference was probably caused by the different local hour at which IMP and ISO made their observations, since saturation is expected to be maximum at sunrise and sunset.
The line strengths in the LWS wavelength range were predicted from the vertical distribution of water in the atmosphere. The only unknown was the surface emissivity, which could be derived from the measured line to continuum ratios. An average value close to 1 was found between 50 and 180 µm. Because Mars is widely used as a standard for flux calibration in the far infrared, e.g. by LWS, an accurate determination of the emissivity is important. As line-to-continuum ratios can be measured much more accurately than absolute flux levels, the LWS was therefore used to improve its own calibration standard!
It was even possible with ISO to detect directly the rotational modulation in the Martian continuum flux. These diurnal variations amount only to a few percent, but they were found to be in good agreement with a model that had been advanced by Don Rudy 12 years ago, thus proving the excellent reproducibility of the LWS measurements (Sidher et. al., ESA SP-427, 1999, p189).
With a reliable model for the continuum flux of Mars and for the various lines and bands in its atmosphere it is possible to characterise the solid-state absorption features that were detected with the SWS (Lellouch et. al., ESA SP-427, 1999, p125; Morris et. al., in preparation). Particularly interesting are spectral features that seem to coincide with the vibrational modes of certain carbonates. CO2-containing compounds in Mars' dust have been the object of intense, but essentially unsuccessful, searches since they could shed light on important questions about Mars history. This is because carbonates would probably have formed by precipitating gas from a dense CO 2 atmosphere, a mechanism that requires the presence of water lakes and would have had big consequences on the Martian climate. Other minerals, however, exhibit similar features in the SWS wavelength range, hence further efforts at modelling the surface spectrum are needed for a definite identification.
The ISO archive is now fully public. The proprietary period of one year was
linked to data products being shipped to users, and as the last data CDs were
sent to observers in August 1998, everything is now public.
The number of available observations in the archive exceeds 100000, consisting of, approximately, 30000 standard, more than 6000 scientific non-standard, 60000 parallel/serendipitous and 17000 engineering observations. And these numbers are not yet final. As the data processing advances, new products are being added. The next addition is LWS parallel and serendipitous data which is currently being extracted from the raw data.
All data becoming public allows us to enhance our services. The internet explosion can be seen in the ever increasing number of cross links between astronomical archives. Other archives will be able to directly access the postcards from our archive, one category of the ISO browse products. This way another archive can add a quick-look link to the ISO data without the need to invoke our interface which is tuned to ISO specific queries and retrievals.
Frequent archive users will have noticed that since the opening of the ISO archive in December last year, there have been regular upgrades of the archive software. These were not only bug fixes, but every release enhanced the functionality to access the ISO data. A very important release was version 1.3 on 19 May, introducing ``On-the-fly reprocessing'' (OFRP), making the most recent knowledge of ISO calibration available to the community. In the archive interface this is hidden under a very innocent button ``Latest processing'' (by default on). By accepting this the user automatically triggers the latest off-line processing for the data requested. At present there is new software available for CAM, PHT and SWS. The LWS update is to follow later this year and further improvements for all instruments will go live during 2000.
In addition to the OFRP there have been other enhancements to the archive during this year, with Version 2.0 released on 20 July. This was a major upgrade tuned mainly to the expert user. Many of the enhancements are therefore not easy to notice as they appear in the database which you need to access with direct SQL. Some additions, however, are very visible. There are more choices to select on the spacecraft pointing and raster parameters. On the instrument side there are new instrument specific panels, of use to the more experienced users. The improved observational detail section (accessed from the query results page by pushing the ``Details''-button) is very informative to everyone.
The next planned version 3.0 is for the general user. Currently there is easy access to the static postcards showing the archive users quickly what kind of data are in the observations. The postcard is extracted from the survey product, which is in FITS format. We are currently working in collaboration with ST-ECF on a survey product display tool. This tool will be integrated into the archive interface and will allow the archive users to browse the survey products to a greater detail than is possible with the postcard. The basic functionality will include zooming and colour table manipulations. This way the users can focus on desired spectral region or intensity level on spectra and images respectively.
Another service to be provided through the ISO archive interface is an easy access to the IRAS data. This effort is done in collaboration with IPAC. The principle is to give access to the IRAS maps of the region surrounding the selected ISO observation. Direct access to IRAS point source information will be provided through this facility.
In the longer term we are considering possibilities to include links to articles based on ISO data. Ideally we would like to provide a link from each published observation to the respective article. However, this may be difficult as already it is not easy to trace back precisely which observations were used in some ISO articles. Another interesting possibility is to allow users to return reduced data back to the archive for others to retrieve. In this area we still need to consider the technical aspects such as allowed formats. We are happy to hear any suggestions from the ISO archive users for possible further facilities to the archive - please don't hesitate to let us know about them by writing to the ISO helpdesk (helpdesk@iso.vilspa.esa.es).
The user documents are undergoing a major update prior to being released in the final archive form. The ISO Instruments, Data Archive products, processing steps and final accuracies are currently described in the 5 Data Users Manuals (ISO, CAM, LWS, PHT, SWS). These form the basis for the future ISO Handbook, which will be the definitive stand-alone reference document for the ISO mission and the ISO data products.
At the moment, the transition from the ``Data User Manuals'' to the individual volumes (version 1.0) of the ISO Handbook is taking place. There will be six Handbook Volumes covering the following topics: I. The ISO Mission; II. The ISO satellite and Cross-calibration; III. ISOCAM; IV. ISOLWS; V. ISOPHT; and VI. ISOSWS. These will be available at the ISO Handbook, with the CAM Handbook already available
The first volume will include an overview of the observatory mission, its scientific programme and some important historic events. The instrument volumes will contain a complete instrument overview, the observing modes, in-orbit performance, OLP processing of data, calibration and accuracy, caveats and a guide to the data products.
In the course of the next two years, after every major OLP update a new version of the applicable instrument Handbook will be issued. The final version (2.0) is planned to be issued in May 2001, when the legacy archive will be available. This version will also be published in a hardcopy form. Intermediate versions will be available on the WWW and may be published as an ISO preprint upon request.
In the meantime, check the ISO Explanatory Library for new documents, technical notes on calibration, data reduction and data products, together with Interactive Analysis recipes.
Between the 10th and 12th of May 1999 an ISO workshop on Solar System Objects (SSOs) was held at the ISO Data Centre in Villafranca. The workshop brought together ISO observers working on solar system programmes with experts in instrument calibration and data reduction. Bearing in mind the specific data reduction needs of ISO's solar system observations, our main objective for this workshop was 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 (Ithaca, New York); and Division of Planetary Sciences meeting in October (Padova, Italy).
The first day of the workshop was dedicated to science topics, including planets, satellites, asteroids and comets, observations and modeling. During the second and third day the technical PHT and CAM presentations and the ``hands-on'' sessions took place. PHT03/PHT22 (multi-filter photometry), PHT40 (spectroscopy) and CAM01 (single pointing and raster scans) were treated in detail. The technical outcome of the workshop in form of ``CAM and PHT Interactive Analysis Recipes for SSOs'' is available on the ISO Web
As a supplement to the Interactive Analysis cookbooks/recipes, the solar system pages now include overviews of all performed programmes and lists of observed solar system objects. Since pointing and tracking of ISO was based on a priori knowledge of object ephemeris, it is advisable to make a cross check between the ISO centric positions of an object and the ISO pointing during the observation. In particular, comet ephemeris were not always perfectly known at the time of the observation planning. A small package of IDL routines, including the ISO Orbit file and detailed instructions on how to evaluate possible offsets, is available on the these Web-pages. The ``independent methods to estimate the background'' are not only of interest for SSO experts, but driven by their needs to verify or to establish a background flux in cases of failed, unusable or unreliable background measurements.
Highlights from the scientific presentations were well recognized by the Spanish press. Alan Harris (DLR-Germany), Therese Encrenaz (Meudon-France) and Athena Coustenis (Meudon-France) participated together with Martin Kessler and Thomas Mueller in a press conference with representatives of newspapers, radio and television stations.
Focusing on data reduction and finalization of SSO programmes, no workshop proceedings have been produced (apart from the Web pages). Most of the scientific results can be found in the near future in proceedings of the ACM and DPS conferences and in specialized SSO literature. The new webpages will facilitate analysis of all SSO observations with ISO.
The second ISO workshop on analytical spectroscopy, ``ISO Beyond the Peaks'', will take place between the 2nd and the 4th of February 2000 at the ISO Data Centre, Villafranca del Castillo, Madrid.
The scientific programme of the workshop is aimed at highlighting theoretical and empirical methods impacting the detailed analyses and interpretation of ISO spectra, and assessing the data quality and calibrations. One aim of the workshop will be to review the ISO spectroscopy heritage. This will not only encourage further scientific work on the ISO data themselves but will also benefit the preparation of future missions such as SIRTF, FIRST, SOFIA, NGST, etc. Another aim of the workshop is to assist in establishing the final goals for the ISO archive phase and in defining the end products.
Without specific orientation of programme topics towards object class, a broad range of observational and theoretical branches relevant to ISO will be covered through interaction on the availability and application of analytical tools, reference data, laboratory studies, and spectral identifications. Topics may include, but are not limited to: planetary models; hot and cool stellar atmosphere and wind models, and grids of models; photoionization, spectral synthesis; circumstellar and interstellar dust features; dust in planetary environments; the diffuse ISM; optical depth effects and estimation; laboratory studies and line lists; ices and unidentified IR features; PDRs; molecular line modeling and data interpretation; and data reduction techniques for optimizing scientific output from standard data products.
Particular emphasis will be given on the cross-calibration between ISO spectrometers and other facilities, referring to continuum issues as well as line ratios, beam size corrections, etc.
If you are interested in participating in the workshop, or would like more information, please look at our web page
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
Telefax: International +34-91-813-1308
e-mail: `kleech@iso.vilspa.esa.es'
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