ESA Science & Technology - Publication Archive

We have carried out a high spectral resolution (lambda/Deltalambda ~ 6800-9700) line survey towards the Orion Kleinmann-Low (KL) cluster from 44 to 188 micron. The observations were taken with the Long Wavelength Spectrometer (LWS) in Fabry-Pérot mode, on board the Infrared Space Observatory (ISO). A total of 152 lines are clearly detected and a further 34 features are present as possible detections. The spectrum is dominated by the molecular species H₂O, OH and CO, along with [OI] and [CII] lines from photodissociation region (PDR) or shocked gas and [O III] and [NIII] lines from the foreground M42 HII region. Several isotopic species, as well as NH₃, are also detected. HDO and H₃O+ are tentatively detected for the first time in the far-infrared (FIR) range towards Orion KL. A basic analysis of the line observations is carried out, by comparing with previous measurements and published models and deriving rotational temperatures and column densities in the case of the molecular species.

As part of the first far-IR line survey toward Orion KL, we present the detection of seven new rotationally excited OH Lambda-doublets (at ~48, ~65, ~71, ~79, ~98, and ~115 mum). Observations were performed with the Long Wavelength Spectrometer Fabry-Pérot on board the Infrared Space Observatory. In total, more than 20 resolved OH rotational lines, with upper energy levels up to ~620 K, have been detected at angular and velocity resolutions of ~80" and ~33 km/s, respectively. The OH line profiles show a complex behavior evolving from pure absorption, P Cygni type, to pure emission. We also present a large-scale, 6' declination raster in the OH ²Pi_3/2 J=5/2⁺-3/2^- and ²Pi_3/2 J=7/2^--5/2⁺ lines (at 119.441 and 84.597 mum) revealing a decrease of excitation outside the core of the cloud. From the observed profiles, mean intrinsic line widths, and velocity offsets between emission and absorption line peaks, we conclude that most of the excited OH arises from Orion outflow(s), that is, the "plateau" spectral component. We determine an averaged OH abundance relative to H₂of chi(OH)=(0.5-1.0)×10^-6, a kinetic temperature of more than ~100 K, and a density of n(H₂)~=5×10⁵ cm^-3. Even with these conditions, the OH excitation is heavily coupled with the strong dust continuum emission from the inner "hot core" regions and from the expanding flow itself. Based on observations with ISO, an ESA project with instruments funded by ESA member states (especially the PI countries: France, Germany, the Netherlands, and the UK) and with the participation of ISAS and NASA.

Stars are born and die in clouds of gas and dust, opaque to most types of radiation, but transparent in the infrared. Requiring complex detectors, space missions and cooled telescopes, infrared astronomy is the last branch of this discipline to come of age. After a very successful sky survey performed in the eighties by the IRAS satellite, the Infrared Space Observatory, in the nineties, brought spectacular advances in the understanding of the processes giving rise to powerful infrared emission by a great variety of celestial sources.

Outstanding results have been obtained on the bright comet Hale-Bopp, and in particular of its water spectrum, as well as on the formation, chemistry and dynamics of planetary objects in the solar system. Ideas on the early stages of stellar formation and on the stellar initial mass function have been clarified.

ISO is the first facility in space able to provide a systematic diagnosis of the physical phenomena and the chemistry in the close environment of pre-main sequence stars, in the interstellar medium, and in the final stages of stellar life, using, among other indicators, molecular hydrogen, ubiquitous crystalline silicates, water and ices.

ISO has dramatically increased our ability to investigate the power production, excitation and fuelling mechanism of galaxies of every type, and has discovered a new very cold dust component in galaxies.

ISO has demonstrated that luminous infrared galaxies were brighter and much more numerous in the past, and that they played a dominant role in shaping present day galaxies and in producing the cosmic infrared background.

We report the discovery of two very cold and massive molecular cloud cores in the region ISOSS J18364-0221. The object has been identified by a systematic search for very early evolutionary stages of high-mass stars using the 170 micron ISOPHOT Serendipity Survey (ISOSS). Submillimeter continuum and molecular line measurements reveal two compact cores within this region. The first core has a temperature of 16.5 K, shows signs of ongoing infall and outflows, has no near- or mid-infrared counterpart, and is massive enough (M~75 M_solar) to form at least one O star with an associated cluster. It is therefore considered a candidate for a genuine high-mass protostar and a high-mass analog to the Class 0 objects. The second core has an average gas and dust temperature of only ~12 K and a mass of M~280 M_solar. Its temperature and level of turbulence are below the values found for massive cores so far, and we suggest that this represents the initial conditions from which high-mass star formation occurs.

Markarian (Mkn) 297 is a complex system comprised of two interacting galaxies that has been modelled with a variety of scenarios. Observations of this system were made with the Infrared Space Observatory (ISO) using the ISOCAM, ISOPHOT and LWS instruments.

Observations of four WR galaxies (NGC 5430, NGC 6764, Mrk 309 and VII Zw 19) using the Infrared Space Observatory are presented here. ISOCAM maps of NGC 5430, Mrk 309 and NGC 6764 revealed the location of star formation regions in each of these galaxies. ISOPHOT spectral observations from 4 to 12 microns detected the ubiquitous PAH bands in the nuclei of the targets and several of the disk star forming regions, while LWS spectroscopy detected [OI] and [CII] emission lines from two galaxies, NGC 5430 and NGC 6764.

Using a combination of ISO and IRAS flux densities, a dust model based on the sum of modified blackbody components was successfully fitted to the available data. These models were then used to calculate new values for the total IR luminosities for each galaxy, the size of the various dust populations, and the global SFR.

The derived flux ratios, the SFRs, the high L(PAH)/L(40-120 microns) and F(PAH 7.7 microns)/F(7.7 microns continuum) values suggest that most of these galaxies are home to only a compact burst of star formation. The exception is NGC 6764, whose F(PAH 7.7 microns)/F(7.7 microns continuum) value of 1.22 is consistent with the presence of an AGN, yet the L(PAH)/L(40-120 microns) is more in line with a starburst, a finding in line with a compact low-luminosity AGN dominated by the starburst.

We explore the possibilities of TIMMI2 N-band observations of improving our knowledge on the physics of the short transition phase which precedes the formation of a planetary nebula. Both imaging and spectroscopic capabilities of TIMMI2 are shown to be extremely powerful and suitable to study the hidden evolution of AGB stars in their way to become planetary nebulae. These data are complementary to previously obtained ISO SWS spectra corresponding to sources at different evolutionary stages covering the whole path from the start of the AGB to the formation of a new planetary nebula. Both TIMMI2 and ISO SWS spectra are used to classify the sources as carbon-rich or oxygen-rich and to propose a tentative evolutionary sequence of spectral characteristics based on the detailed analysis of the gas phase and solid state features detected in the mid-infrared range.

Starting with nearby galaxy clusters like Virgo and Coma, and continuing out to the furthest galaxy clusters for which ISO results have yet been published (z=0.56), we discuss the development of knowledge of the infrared and associated physical properties of galaxy clusters from early IRAS observations, through the "ISO-era" to the present, in order to explore the status of ISO's contribution to this field. Relevant IRAS and ISO programmes are reviewed, addressing both the cluster galaxies and the still-very-limited evidence for an infrared-emitting intra-cluster medium. ISO made important advances in knowledge of both nearby and distant galaxy clusters, such as the discovery of a major cold dust component in Virgo and Coma cluster galaxies, the elaboration of the correlation between dust emission and Hubble-type, and the detection of numerous Luminous Infrared Galaxies (LIRGs) in several distant clusters. These and consequent achievements are underlined and described. We recall that, due to observing time constraints, ISO's coverage of higher-redshift galaxy clusters to the depths required to detect and study statistically significant samples of cluster galaxies over a range of morphological types could not be comprehensive and systematic, and such systematic coverage of distant clusters will be an important achievement of the Spitzer Observatory.

We present ISOPHOT observations at 120 and 200 µm of a 31 × 57 arcmin² region, with optical extinction AV ranging between ~ 0.5 and 11 mag, that encloses the Taurus molecular cloud TMC-2. The far-infrared emission is separated into a warm and a cold component using the ISOPHOT data and IRAS measurements at 60 and 100 µm. This separation is based on the very different morphologies of the 60 and 200 µm emission maps.

Using the Long Wavelength Spectrometer on board the Infrared Space Observatory, we have observed thermal water vapor emission from a roughly circular field of view approximately 750 in diameter centered on the Orion BN-KL region. The Fabry-Perot line strengths, line widths, and spectral line shifts observed in eight transitions between 71 and 125 mm show good agreement with models of thermal emission arising from a molecular cloud subjected to a magnetohydrodynamic C-type shock. Both the breadth and the relative strengths of the observed lines argue for emission from a shock rather than from warm quiescent gas in the Orion core. Although one of the eight transitions appears anomalously strong and may be subject to the effects of radiative pumping, the other seven indicate an H₂O/H₂ abundance ratio on the order of and a 5x10^-4 corresponding gas-phase oxygen-to-hydrogen abundance ratio on the order of 4x10^-4. Given current estimates of the interstellar, gas-phase, oxygen and carbon abundances in the solar vicinity, this value is consistent with theoretical shock models that predict the conversion into water of all the gas-phase oxygen that is not bound as CO. The overall cooling provided by rotational transitions of H₂O in this region appears to be comparable to the cooling through rotational lines of CO but is an order of magnitude lower than cooling through H₂ emission. However, the model that best fits our observations shows cooling by H₂O and CO dominant in that portion of the postshock region where temperatures are below ~800 K and neither vibrational nor rotational radiative cooling by H is appreciable.

The massive cluster of galaxies Abell 2219 (z=0.228) with two spectacular gravitational lensing arcs was observed at 14.3mu (hereafter 15mu) with the Infrared Space Observatory and results were published by Barvainis et al.(1999). These observations have been reanalyzed using a method specifically designed for the detection of faint sources that had been applied to other clusters.

Five new sources were detected and the resulting cumulative total of ten sources all have optical counterparts. The mid-infrared sources are identified with three cluster members, three foreground galaxies, an Extremely Red Object, a star and two galaxies of unknown redshift. The spectral energy distributions (SEDs) of the galaxies are fit with models from a selection, using the program GRASIL. Best-fits are obtained, in general, with models of galaxies with ongoing star formation. Infrared luminosities and star formation rates are obtained for six sources_ the cluster members and the foreground galaxies. For the three cluster members the infrared luminosities derived from the model SEDs are between 5.7x10e10 L_sol and 1.4x10e11 L_sol, corresponding to infrared star formation rates between 10 and 24 M_sol/yr. The two cluster galaxies that have optical classifications are in the Butcher-Oemler region of the colour-magnitude diagramme. The three foreground galaxies have infrared luminosities between 1.5x10E10 L_sol and 9.4x10e10 L_sol, yielding infrared star formation rates between 3 and 16 M_sol/yr. Two of the foreground galaxies are located in two foreground galaxy enhancements (Boschin et al.2004). Including Abell 2219, six distant clusters of galaxies have been mapped with ISOCAM and luminous infrared galaxies (LIRGs) have been found in three of them. The presence of LIRGs in Abell 2219 strengthens the association between luminous infrared galaxies in clusters and recent or ongoing cluster merger activity.

In keeping with ISO's role as an observatory, the majority of its observing time will be available to the astronomical community. The traditional route of Calls for Observing Proposals, followed by peer review, is being used. There has been one Call prior to launch and a single Supplemental Call is foreseen post-launch. The expected high sensitivity of the ISO instruments will lead to observations of relatively short duration, typically tens of minutes to a few hours. This, in turn, means that many thousands of observations using the four highly sophisticated instruments with multiple operating modes will be carried out in ISO's limited lifetime of 18 months. Thus, as many as possible of the processes, from proposal submission to sending specific commands to the satellite to carry out a particular observation, have been automated. In addition, all details of the desired observations have to be specified by the observer in advance of the observation being executed to allow the complex observing programmes to be established.

ISO, the Infrared Space Observatory, will provide astronomer's with an unprecedented opportunity - and the only one for the next 10 years - to make scientific observations of weak infrared radiation sources. The development of the Observatory proved to be a challenging task: there was little available experience with the advanced technologies required for such a new infrared-astronomy mission. The scientific instruments were developed by groups of scientific institutes and industry under national funding. The satellite was developed, manufactured, integrated and tested by an industrial consortium made up of 32 companies, mostly from Europe. ESA is performing the flight operations. The USA and Japan are also contributing to the mission in return for observation time.

he payload of ESA's Infrared Space Observatory (ISO) consists of four scientific instruments: a camera (ISOCAM), an imaging photo-polarimeter (ISOPHOT), a long-wavelength spectrometer (LWS), and a short-wavelength spectrometer (SWS). Each of these instruments was built by an international consortium of scientific institutes using national funding. ESA was responsible for their subsequent integration into the ISO spacecraft and will carry out the in-orbit operations.

ESA's Infrared Space Observatory (ISO) consists of two modules: the Payload module, which includes the telescope and the scientific instruments, and the Service Module, which houses the instruments electronics, the hydrazine propellant tank and all other classical spacecraft subsystems. To ensure that the telescope is kept near absolute zero and thus is the least disturbed by the effects of the infrared emissions from other elements of the system, the telescope is enclosed in a helium-cooled cryostat. The cryostat in turn is shaded by a Sun-shield to protect it from the heat of the direct Sun. The shield has a covering of solar cells that provide the electrical power needed for the mission.

The Infrared Space Observatory (ISO) satellite will be the world's first true astronomical observatory in space operating at infrared wavelengths. Astronomers will be able to choose specific targets in the sky and point ISO towards them for up to ten hours at a time to make observations with versatile instruments of unprecedented sensitivity. During its lifetime of 18 months, ISO will be used to observe all classes of astronomical objects ranging from planets and comets in our own solar system, right out to the most distant galaxies.

ESA's Infrared Space Observatory (ISO) was successfully launched from the Guiana Space Centre in Kourou on 17 November 1995. Its requirements in terms of ground-segment preparation were particularly demanding due to the limited mission lifetime, which calls for highly efficient operations, the very fast pace of the ISO observations, some lasting just a few minutes, the severe pointing requirements which demand sophisticated planning, and the real-time commanding of the highly sophisticated payload of four instruments with multiple operating modes from a computer- generated, automatically executing file. It was recognised that, given these demanding constraints, a well thought out approach to overall ground-segment integration, testing and validation would be required to ensure success. The approach that was chosen, based on the concept of end-to-end testing supported by sophisticated instrument simulators, proved highly effective. As a result, the ISO ground segment was ready to support all of the mission's operational phases in time for the spacecraft's launch.

This article gives a summary of the early in-orbit performance of the Agency's recently launched Infrared Space Observatory (ISO) spacecraft and its instruments and presents some of the initial scientific results.

The Infrared Space Observatory (ISO), the world's first true orbiting infrared observatory, was switched off in May 1998, long after the expiry date foreseen in the specifications for the mission. Instead of the required 18 months, the highly-successful in-orbit operations of this excellent satellite continued for more than 28 months leading to an extensive database of observations which will be providing astronomical surprises for years to come. This article looks back at the way operations were conducted.

Water, the basic substance essential for life, has been detected by the Infrared Space Observatory (ISO) in many places throughout the Universe, including our planetary neighbours in the Solar System, clouds circling or pouring out of stars, the vast spaces between stars, and distant galaxies. We show here how these observations enable us to reconstruct the cosmic cycling of water, and its relevance to the presence of water on the Earth.