Abstracts

Abstract. We have observed a magnitude-limited sample of 77 galaxies chosen from the Revised Shapley-Ames Catalogue with ISOCAM at 10 micron and with ISOPHOT at 60 micron, 100 micron, and 180 micron. We have complemented these data with images at JHK and with images for four galaxies at 850 micron. We will compare the normalized intensity and distribution of mid-infrared and far-infrared emission from these galaxies to investigate the correlation of infrared activity with other global galaxy properties. Our results show that the intensity and spatial distribution of star formation in galaxies does vary with morphology. Furthermore, we will investigate the spectral energy distribution in far-infrared and submillimeter wavelengths to better understand the temperature components of dust in these galaxies. Although the mid-infrared, far-infrared, and submillimeter images show emission from similar regions in these galaxies, a close comparison shows fundamental differences between the distribution of hot and cool dust.

Abstract. ISO observations at 200micron have modified our view of the dust component in spiral galaxies. For a sample of seven resolved spirals we have retrieved a mean temperature of 20K, about 10K lower than previous estimates based on IRAS data at shorter wavelengths. Because of the steep dependence of far-infrared emission on the dust temperature, the dust masses inferred from ISO fluxes are a factor of 10 higher than those derived from IRAS data only, leading to gas-to-dust ratios close to the value observed in the Galaxy. The scale-length of the 200micron emission is larger than for the IRAS 100micron emission, with colder dust at larger distances from the galactic centre, as expected if the interstellar radiation field is the main source of dust heating. The 200micron scale-length is also larger than the optical, for all the galaxies in the sample. This suggests that the dust distribution is more extended than that of the stars.
     A model of the dust heating is needed to derive the parameters of the dust distribution from the FIR emission. Therefore, we have adapted an existing radiative transfer code to deal with dust emission. Simulated maps of the temperature distribution within the dust disk and of the dust emission at any wavelength can be produced. The stellar spectral energy distribution is derived from observations in the ultraviolet, optical and near infrared. The parameters of the dust distribution (scale-lengths and optical depth) are chosen to reproduce the observed characteristics of the FIR emission, i.e. the shape of the spectrum, the flux and the spatial distribution. We describe the application of the model to one of the galaxies in the sample, NGC~6946.

Abstract. As a close companion of the Scd-type galaxy IC~342, UGCA~86 is influenced in it's development by the considerable gravitational interaction between the two galaxies. Signs for that have been found from HI as well as from optical observations. While the distribution of neutral hydrogen shows significant distortion at large scale, the optical data reveal regions of heavy star formation most probably induced by gas infall due to the gravitational interaction.
     In order to study the physical properties of the different star-forming regions in UGCA~86, we tried to analyse FIR data just looking for dust content and temperature of the individual regions. Therefore, ISOPHOT C100 and C200 observations have been performed at wavelengths of 60, 120, 160, and 200 micron. In addition, 12, 25, 60, and 100 micron maps were derived from reprocessed IRAS data (survey and pointed observations) by applying the maximum entropy method. This deconvoluting approach was required to achieve a sufficient resolution demanded by distances between the individual regions of only 3 arcminutes.
     The recent analysis of the combined set of ISO and IRAS data revealed further significant differences -- mainly in dust temperatures -- between the star-forming regions influenced (most probably induced) and not influenced by gas infall. The warmest dust is found in the southern star-forming region. This region is the only one connected with large Halpha filaments extending for more than 1 kpc.

Abstract. Oxygen is the most abundant element after hydrogen and helium in the Universe. It is therefore of key importance to know in which form oxygen is found in the different phases of the Interstellar Medium.
     We present low resolution (about 200) ISO-LWS observations of the [OI] (63 micron and 145 micron) lines towards the molecular cloud L1689N, which hosts the low-mass, Class 0 protostar IRAS16293-2422. From the observed ratio of the two [OI] lines, we deduce a mean gas temperature of 26 K, a molecular hydrogen density larger than about 3x10^4 cm^-3 and an [OI] column density larger than about 5x10^19 cm^-2. Combining these observations with previous CO observations, we obtain [OI]/[CO] = 50. This ratio implies that up to 98% of oxygen abundance is in atomic form in the gas phase. Furthermore, assuming all the gaseous carbon is locked into the CO, carbon has to be depleted by more than a factor 24.
     We also obtained high resolution (about 8000) observations with ISO-LWS towards the massive star formation W49N. Using a measured profile of the LWS FPs spectral response, we performed a decomposition of the detected signal, considering four distincts components: one associated with the compact HII region is seen in emission for the two [OI] lines, while the absorption part of the observed spectrum at 63 micron is due to three components associated with cold molecular clouds present in the line of sight. For the emission component, from the observed ratio of the two [OI] lines, we deduce a mean gas temperature of 42 K, a molecular hydrogen density larger than 3x10^4 cm^-3 and an [OI] column density larger than 10^20 cm^-2. For the cold molecular clouds, we compute the ``optical'' depth needed for each cloud to obtain the observed spectrum around 63 micron after convolution by the instrumental profile, assuming that OI and CO originate from the same region. From the [OI] 63 micron ``optical'' depths we derive [OI] column densities of 7x10^18 cm^-2, 7.7~10^18 cm^-2 and 2.2x10^19 cm^-2. Combining these observations with 13CO millimeter line emission observations, we obtain [OI]/[CO] about 194, 105 and 183, which also imply that in these cases a very large abundance (more than 99%) of atomic oxygen in the gas phase and a large depletion of CO.
     Therefore our observations strongly suggest that oxygen in cold molecular clouds is found mainly in the atomic form and that CO is more depleted than previously thought. This has important consequences on the thermal balance and chemical modeling of molecular clouds.

Abstract. We will discuss the results of a series of photometric and spectroscopic observations using ISOCAM, the LWS and PHOT on two nearby, fully evolved planetary nebulae, the Helix nebula (NGC 7293) and the Dumbbell nebula (NGC6853). The ISO data allow the study of the neutral envelopes of these nebulae through the pure rotational lines of molecular hydrogen and the major atomic lines, providing a quite complete view of the photo-dissociation region associated with these objects.

Abstract. FIRBACK is a one of the deepest survey performed at 170 micron with ISOPHOT onboard ISO, and is aimed at the study of the cosmic far infrared background. Three low foreground contamination fields have been observed, covering four square degrees in total. About 300 extragalactic sources between 75 mJy and 1 Jy are detected. Source counts present a strong slope of 2.2 in the integral "logN-logS" plot, which cannot be due to the effect of the K-correction if no cosmological evolution is present. These sources account for less that 10% of the Cosmic Infrared Backgound at 170 micron, and their nature is still unknown, even if most of them are expected to be dust-enshrouded galaxies, and some of them above-redshift-1 sources.
     We will present a phenomenological model, based on FIRBACK and ISOCAM source counts, which constrain the galaxy luminosity function (LF) evolution with the redshift. We show that an strong evolution of a galaxy population with L_FIR = 10^11 Lsun between redshifts 0 and 1.4 (in account with the values derived from the CIB spectrum) reproduces the observed counts.
     The detection of the Cosmic Infrared Backgroud fluctuations will also be discussed. We extract point sources from the maps using a proper PHOT footprint at 170 micron, and make an analysis based on the decomposition of galactic and extragalactic components in the map's power spectrum.

Abstract. We searched for far-infrared (60 micron) extended emission, in the form of circumstellar dust disks, in the maps of seven main-sequence stars. Direct detection of circumstellar disks in these systems can advance our understanding of the Vega phenomenon and the nature of protoplanetary disk candidates.
     We obtained 60 micron maps with the PHOT C-100 3x3-pixel far-infrared camera on-board ISO, in the P32 microscanning dedicated mapping mode. The maps span 6'15''x5'45'' (RAxdecl), at a spatial resolution of about 30''. The maps presented here were obtained with integration times of 128 seconds at each spacecraft raster position. These integration times are 4 times larger than in previous similar maps of Vega-type stars obtained by Fajardo-Acosta, Stencel, and Backman (1997, ApJ, 487, L151; 1998, ApJ, 503, L193, hereafter FSB). Our goal was to increase S/N in the newer maps by a factor of 2 with respect to the previous ones.
     The stars we observed are gamma Oph (A0 V), alpha PsA (A3 V), gamma Tri (A1 Vnn), 61 Cyg A (K5 V), tau1 Eri (F5-6 V), tau Cet (G8 V), and eps Eri (K2 V). These systems are nearby, within 30 pc from us, and are suspected to harbor Vega-like circumstellar dust disks (Backman and Paresce 1993, Protostars and Planets III, ed. Levy and Lunine, 1253). We compared the maps of these systems with similar maps of the stars alpha Boo and alpha Aql, which do not possess circumstellar dust. We discuss techniques to model point-spread functions (PSFs) from the latter, and their subtraction from our Vega-type stellar maps.
     We did not spatially resolve extended emission in the maps of gamma Tri, 61 Cyg A, and tau Cet, upon comparison with our modeled PSFs. We could only marginally detect a ring of 60 micron emitting dust around eps Eri, previously reported by Fajardo-Acosta, Stencel, and Backman (1998, BAAS, 193, 69.07). This detection remains tentative.
     The maps of gamma Oph, alpha PsA, and tau1 Eri definitely show extended emission when compared with model PSFs. We confirmed the previous detection in alpha PsA by FSB, but now can detect extended emission as far as about 700 AU from the star, as opposed to about 500 AU in the previous observations. The detection in gamma Oph was only hinted at by FSB. The detection of extended emission around tau1 Eri is reported for the first time here.

Abstract. The ISOPHOT Interactive Analysis (PIA) contains several map coadding algorithms and flat-fielding techniques. They should help to optimize the results obtained with ISOPHOT raster data. They are embedded in an environment combining a large flexibility with a very high user friendliness.
     The many different ways of performing raster observations with ISOPHOT makes an assessment of the reliability of the obtained results somewhat difficult. A map simulator has been developed under the PIA framework, for addressing different questions like the validity of theoretical / experimental beam profiles; detection limits and confusion levels; optimization of the use of the mapping algorithms by the different raster configurations.

Abstract. COBE observations reveal an offset in the center of symmetry of the zodiacal cloud from the Sun. If the zodiacal cloud were symmetric about the Sun, the maximum and minimum average of the North (N) and South (S) polar brightnesses, (N + S)/2, of the cloud would occur at perihelion and aphelion, respectively. However, the minimum of the COBE curve is displaced from aphelion showing that the cloud is offset from the Sun. The variation in average polar brightness is an annual variation. COBE was only a nine month long mission, so ISO data was taken to supplement the missing three months of data. The variation of the average polar brightness was small, less than 2 MJy/sr throughout the year. In the 25 micron waveband, we show the ISO PHOT data (PHT3 and PHT5), which has some rather large errors associated with it, for the variation in (N + S)/2 with Ecliptic Longitude of Earth in comparison with the COBE data.

This research was funded in part by a NASA GSRP grant.

Abstract. We have studied the spectrum of the galactic cirrus in low surface brightness regions using ISOPHOT raster maps made at wavelengths 90, 150, and 180 micron.
     We will first discuss the calibration of the observations. The ISOPHOT surface brightness values have been compared with DIRBE data and the methods used in this comparison are described. A good correspondence is found at 90 micron while at longer wavelengths the DIRBE surface brightness values tend to be higher.
     Surface brightness variations caused by cirrus fluctuations make it possible to determine the spectrum of the emission. Cirrus spectra have been derived for several regions with average surface brightness values between 2 and 8 MJy/sr. Some results from this study will be shown.

Abstract. Thermal infra-red images of comets Hale-Bopp, 126P/IRAS, 103P/Hartley 2, 22P/Kopff, 133P/Elst-Pizarro, 55P/Tempel-Tuttle and 46P/Wirtanen have been acquired in 1996 and 1998 with ISOCAM using its highest spatial resolution of 1.5 arcsec/pixel and several filters centered at 7-15 micron. After correction from the instrumental response (dark current, flat-field, glitches and transient), the images are fitted by the sum of the coma and nucleus contribution, convolved by the PSF to photometrically discriminate the signal of the nucleus from that of the coma. This technique is also used to interpret HST images of comets (Lamy et al., A&A 337, 945, 1998). The thermal emission from the nucleus of comet Hale-Bopp and of four short-period comets is successfully detected. The thermal spectrum of Hale-Bopp exhibits the silicate feature at 10 micron, the first time that it is detected on a cometary nucleus, and helps to constain its thermal model and finally its size. In three cases, Hale-Bopp, 22P/Kopff and 55P/Tempel-Tuttle, independent optical observations with the HST allow to determine the albedo and therefore the size with limited assumptions. For the other comets, and in the absence of optical data, the Standard Thermal Model is applied to estimate the size of their nucleus. Preliminary results on the thermal properties of the dust coma of Hale-Bopp will also be shown, the maps of the temperature distribution and the strength of the silicate feature.
     Upper limits are derived for the other comets P/Kopff and P/IRAS. We will propose a preliminary interpretation of these fluxes in terms of the nuclei properties.

Abstract. We have measured the spectral energy distribution of infrared cirrus using 9 filterbands in the 60--200 micron wavelength range with ISO. The spectrum is obtained by correlating the same spatial structures at different wavelengths. We have accurately determined the peak in the spectral energy distribution from which we can derive the temperature of the large dust particles assuming a fixed value for the power beta in the emissivity: 17.0 K for beta =2 and 20.5 K for beta =1. The observations were centred on an IRAS point source which was classified as a ``cirrus'' source only detected by IRAS at 100 micron. With ISO we have been able to resolve the source and we confirm that the far-infrared colours of the source for lambda > 100 micron are indeed indistinguishable from the cirrus background. At 60 micron the emission is relatively higher than the background suggesting a higher abundance of very small grains. Because of the small size of the source (of order 3'), we derive a moderately high density of n(H)>10^3 cm^-2 which suggests that the IRAS source must be a significant density enhancement. The mass of the source is not sufficient to make the cloudlet gravitationally bound but is only a few times below the critical mass. Our results suggest that a fraction of the 100 micron ``cirrus'' point source detections by IRAS could contain cloudlets that are diffuse/translucent but also gravitationally bound.

Abstract. With ISOPHOT we have obtained maps in 2 bands, 60 and 90 micron, of 18 fields at proximity of red giants (however one of the maps, at 60 micron, is incomplete). The data were acquired with C100 and the fields were covered with 3x3 rasters (AOT: PHT22).
     The data show gradients of emission towards the positions of the red giants. (In all cases the red giant has been kept out of the observed field.) In general, emission from an extended circumstellar shell is seen, but we have no evidence for detached shells. In half of the cases we detect isolated sources of emission, probably due to blobs of interstellar matter heated to about 25-40 K by the nearby (<= 2 pc) red giant. We will detail a few examples and characterize these blobs.
     We have encountered difficulties mainly with flat-fielding, especially when the gradient of emission covers the whole field, and with the absolute photometric calibration. Preliminary results of our study have been presented in [1], [2] and [3].