A B S T R A C TWe present high-angular-resolution, far-infrared images of the Small Magellanic Cloud (SMC). The images were reconstructed from data obtained with the Infrared Astronomical Satellite (IRAS), using the Pyramid Maximum Entropy algorithm. The angular resolutions of the images are 1 arcmin at 12, 25 and 60 mm, and 1.7 arcmin at 100 mm, which provides an excellent complement to the recent neutral hydrogen (H i) survey from the Australia Telescope Compact Array, which has a resolution of 1.6 arcmin. We use the 60-and 100-mm data, together with a standard dust model, to derive a temperature map and a dust column density distribution. Dust temperatures range from 23 to 45 K, which is, on average, warmer than for the Galaxy, although there is a deficit of warm, very small dust grains in the SMC. The total amount of cool dust in the SMC is 1X8 1X3 20X2 Â 10 4 M ( X There is a significant variation of the observed dust-to-gas ratio across the SMC. This may be caused by corresponding variations in metallicity, but this explanation is not supported by the limited available data in the literature. Alternatively, there may be a large amount of molecular hydrogen (H 2 ) in the SMC, , 8 Â 10 8 M ( Y and/or a large amount (,10 6 M ( ) of cold dust (#15 K) not seen by IRAS or COBE/DIRBE. The average dust-to-atomic gas ratio is, by mass, 8X2 Â 10 25 Y which is a factor of ,30 below the Galactic value. The spatial power spectrum of the dust column density image can be approximated by P d k G k 23X1 Y which shows that, as with the H i power spectrum, there is no preferred scale size for dust clouds. A spatial coherence analysis shows that, over a wide range of spatial scales (*50 pc), H i and dust are well correlated (.60 per cent).

We report accurate new wavelengths for 29 mid-infrared ionic Ðne-structure lines, based on observations with the Short Wavelength Spectrometer (SWS) on board the Infrared Space Observatory (ISO). Our results originate from observations of NGC 7027, NGC 6543, NGC 6302, the Circinus galaxy, Sgr A West, and W51 IRS 2. The obtained accuracies (j/*j) range from 3 ] 104 to 1 ] 105, depending on instrumental mode and uncertainty in radial velocities.

Abstract. We have examined forty-two carbon stars which show excess emission at 60 and/or 100 #m by applying maximum-entropy image reconstruction techniques to the IRAS 60 #m survey data. Thirteen stars are found to be extended in the reconstructed images. Four of them show a detached ring centered on the stellar position. In particular, U Ant may have a double detached dust shell. The implications of our results are discussed concerning the variation of mass loss on the AGB evolution.

Aims. Previous studies by the satellites SWAS and Odin provided stringent upper limits on the gas phase water abundance of dark clouds (x(H 2 O) < 7 × 10 −9 ). We investigate the chemistry of water vapor in starless cores beyond the previous upper limits using the highly improved angular resolution and sensitivity of Herschel and measure the abundance of water vapor during evolutionary stages just preceding star formation. Results. The RMS in the brightness temperature measured for the B68 and L1544 spectra is 2.0 and 2.2 mK, respectively, in a velocity bin of 0.59 km s −1 . The continuum level is 3.5 ± 0.2 mK in B68 and 11.4 ± 0.4 mK in L1544. No significant feature is detected in B68 and the 3σ upper limit is consistent with a column density of o-H 2 O N(o-H 2 O) < 2.5 × 10 13 cm −2 , or a fractional abundance x(o-H 2 O) < 1.3 × 10 −9 , more than an order of magnitude lower than the SWAS upper limit on this source. The L1544 spectrum shows an absorption feature at a 5σ level from which we obtain the first value of the o-H 2 O column density ever measured in dark clouds: N(o-H 2 O) = (8 ± 4) × 10 12 cm −2 . The corresponding fractional abundance is x(o-H 2 O) 5 × 10 −9 at radii >7000 AU and 2 × 10 −10 toward the center. The radiative transfer analysis shows that this is consistent with a x(o-H 2 O) profile peaking at 10 −8 , 0.1 pc away from the core center, where both freeze-out and photodissociation are negligible. Conclusions. Herschel has provided the first measurement of water vapor in dark regions. Column densities of o-H 2 O are low, but prestellar cores such as L1544 (with their high central densities, strong continuum, and large envelopes) appear to be very promising tools to finally shed light on the solid/vapor balance of water in molecular clouds and oxygen chemistry in the earliest stages of star formation.

Abstract. We present an atlas of near-infrared spectra (2.36 µm-4.1 µm) of ∼300 stars at moderate resolution (λ/δ λ ≈ 1500-2000). The spectra were recorded using the Short-Wavelength Spectrometer aboard the Infrared Space Observatory (ISO-SWS). The bulk of the observations were performed during a dedicated observation campaign after the liquid helium depletion of the ISO satellite, the so-called post-helium programme. This programme was aimed at extending the MK-classification to the nearinfrared. Therefore the programme covers a large range of spectral types and luminosity classes. The 2.36 µm-4.05 µm region is a valuable spectral probe for both hot and cool stars. H I lines (Bracket, Pfund and Humphreys series), He I and He II lines, atomic lines and molecular lines (CO, H 2 O, NH, OH, SiO, HCN, C 2 H 2 , ...) are sensitive to temperature, gravity and/or the nature of the outer layers of the stellar atmosphere (outflows, hot circumstellar discs, etc.). Another objective of the programme was to construct a homogeneous dataset of near-infrared stellar spectra that can be used for population synthesis studies of galaxies. At near-infrared wavelengths these objects emit the integrated light of all stars in the system. In this paper we present the dataset of post-helium spectra completed with observations obtained during the nominal operations of the ISO-SWS. We discuss the calibration of the SWS data obtained after the liquid helium boil-off and the data reduction. We also give a first qualitative overview of how the spectral features in this wavelength range change with spectral type. The dataset is scrutinised in two papers on the quantitative classification of near-infrared spectra of early-type stars (Lenorzer et al. 2002) and late-type stars (Vandenbussche et al., in prep).