Stephan Hotzel

The kinetic temperature of Barnard 68

We have observed the nearby isolated globule Barnard 68 (B68) in the (J,K) = (1,1) and (2,2) inversion lines of ammonia. The gas kinetic temperature derived from these is T = 10 ± 1.2 K. The observed line-widths are almost thermal: ∆V = 0.181 ± 0.003 kms −1 (∆Vtherm = 0.164 ± 0.010 kms −1 ), supporting the earlier hypothesis that B68 is in hydrostatic equi- librium. The kinetic temperature is an input parameter to the physical cloud model put forward recently, and we discuss the impact of the new value in this context.

Dense gas and cold dust in the dark core B217

The Barnard object B217 was observed in the infrared and radio region. The 170 m continuum was detected with ISOPHOT, the ammonia 1.3 cm radio lines with the Eelsberg 100 m-telescope. Mapping B217SW in (J;K )=( 1; 1) and (2; 2) inversion lines revealed the temperature and density distribution of the gas and made it possible to investigate the dynamical state of this dense core inside B217. The ISOPHOT Serendipity Survey (ISOSS) detected the cold dust emission of B217 in all of 3 slews crossing the region. Combining ISOSS with IRAS data, we derive the core parameters of the dust from FIR emission and compare them with the NH3 data, which sample the densest region of the core. This study shows the power of combining ISOSS 170 mw ith IRAS/HIRES data in order to study the dust characteristics in nearby star forming regions on small spatial scales. The (170m/100m) dust colour temperature is 11 K{12 K in the dense cores and 12 K{14 K in the other regions of B217. The low dust temperatures cannot be explained by attenuation of the interstellar radiation eld alone and may reflect a change in the optical properties of the dust as compared to diuse clouds. In B217SW, molecular depletion through freeze-out onto grains is suggested by the comparison of our FIR and NH3 data with previous C 18 O observations. On the basis of our ammonia data investigation, we nd in B217SW dense gas with kinetic temperatures between 9 K and 12 K, increasing outwards. Using near-infrared extinction and NH3 collisional excitation calculations, the fractional ammonia abundance (N(NH3)=N (H2)) is found to be 3{5 10 8 , and the comparison of gas and dust observations supports this range. Knowing the ammonia abundance, we calculate the thermal, turbulent and gravitational energies of the dense core, which appears to be close to hydrostatic equilibrium. Our results are compatible with B217SW being now on the verge of collapse or in an early collapse phase.

Solar system objects in the ISOPHOT 170

The ISOPHOT Serendipity Survey (ISOSS) covered approximately 15% of the sky at a wavelength of 170m while the ISO satellite was slewing from one target to the next. By chance, ISOSS slews went over many solar system objects (SSOs). We identied the comets, asteroids and planets in the slews through a fast and eective search procedure based on N-body ephemeris and flux estimates. The detections were analysed from a calibration and scientic point of view. Through the measurements of the well-known asteroids Ceres, Pallas, Juno and Vesta and the planets Uranus and Neptune it was possible to improve the photometric calibration of ISOSS and to extend it to higher flux regimes. We were also able to establish calibration schemes for the important slew end data. For the other asteroids we derived radiometric diameters and albedos through a recent thermophysical model. The scientic results are discussed in the context of our current knowledge of size, shape and albedos, derived from IRAS observations, occultation measurements and lightcurve inversion techniques. In all cases where IRAS observations were available we conrm the derived diameters and albedos. For the ve asteroids without IRAS detections only one was clearly detected and the radiometric results agreed with sizes given by occultation and HST observations. Four dierent comets have clearly been detected at 170 ma nd two have marginal detections. The observational results are presented to be used by thermal comet models in the future. The nine ISOSS slews over Hale-Bopp revealed extended and asymmetric structures related to the dust tail. We attribute the enhanced emission in post-perihelion observations to large particles around the nucleus. The signal patterns are indicative of a concentration of the particles in the trail direction.

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The ISOPHOT Serendipity Survey utilizes the slew time between ISOs pointed observations with strip scanning measurements of the sky in the far-IR at 170 micrometers . The slews contain information about two fundamentally different types of objects, namely unresolved galactic and extragalactic far-IR sources as well as extended regions of galactic cirrus emission. Since the structure of the obtained data is almost unique, the development of dedicated software to extract astrophysically interesting parameters for the crossed sources is mandatory. Data analysis is currently in its early stages and concentrates on the detection of point sources. First results from an investigation of a high galactic latitude field near the North Galactic Pole indicate that the detection completeness with respect to previously known IRAS sources will be almost 100 percent for sources with f(subscript 100micrometers > 2 Jy, dropping below approximately equals 50 percent for f(subscript 100micrometers < 1.5 Jy. Nevertheless, even faint sources down to a level of f(subscript 170micrometers approximately equals 1 Jy can be detected. Since the majority of the detected point sources are galaxies, the Serendipity Survey will result in a large database of approximately equals 2000 galaxies.

m serendipity survey

Chemical reactions in starless molecular clouds are heavily dependent on interactions between gas phase material and solid phase dust and ices. We have observed the abundance and distribution of molecular gases in the cold, starless core DC 000.4?19.5 (SL42) in Corona Australis using data from the Swedish ESO Submillimeter Telescope. We present column density maps determined from measurements of C18O (J = 2-1, 1-0) and N2H+ (J = 1-0) emission features. Herschel data of the same region allow a direct comparison to the dust component of the cloud core and provide evidence for gas phase depletion of CO at the highest extinctions. The dust color temperature in the core calculated from Herschel maps ranges from roughly 10.7 to 14.0?K. This range agrees with the previous determinations from Infrared Space Observatory and Planck observations. The column density profile of the core can be fitted with a Plummer-like density distribution approaching n(r) ~ r ?2 at large distances. The core structure deviates clearly from a critical Bonnor-Ebert sphere. Instead, the core appears to be gravitationally bound and to lack thermal and turbulent support against the pressure of the surrounding low-density material: it may therefore be in the process of slow contraction. We test two chemical models and find that a steady-state depletion model agrees with the observed C18O column density profile and the observed N(C18O) versus AV relationship.

ISOPHOT far-infrared serendipity sky survey

Small isolated clouds were discovered by the ISOPHOT 170 m Serendipity Survey (ISOSS) as faint I170 < 13 MJy sr 1 FIR sources. One of them is ISOSS J20246+6540, a cold (Td 14:5 K) pointlike ISOSS source without an IRAS pointsource counterpart. In the Digitized Sky Survey B band it is seen as a 3 0 size bipolar nebulosity with an average excess DSS blue band surface brightness of 8% of the backgrounds photographical density. The CO column density distribution determined by multi-isotopic, multi-level CO measurements with the IRAM-30 m telescope agrees well with the optical appearance. An av- erage hydrogen column density of10 21 cm 2 was derived from both the FIR and CO data. Using a kinematic distance estimate of 400 pc the NLTE modelling of the CO, HCO + , and CS measurements gives a peak density of10 4 cm 3 . The multiwave- length data characterise ISOSS 20246+6540 as a representative of a class of globules which has not been discovered so far due to their small angular size and low 100m brightness. A significant overabundance of 13 CO is found X( 13 CO) 150X(C 18 O).

CHEMICAL AND PHYSICAL CONDITIONS IN MOLECULAR CLOUD CORE DC 000.4–19.5 (SL42) IN CORONA AUSTRALIS*

The ISOPHOT C200 stressed Ge:Ga array aboard the Infrared Space Observatory was used to carry out scientific observations while the telescope was moved from one target to the next. These strip scanning measurements of the sky in the far-infrared (FIR) at 170 μm comprise the ISOPHOT Serendipity Survey, the first slew survey designed as an integral part of a space observatory mission. The ISOPHOT Serendipity Survey is the only large scale sky survey in the unexplored wavelength region beyond the IRAS 100 μm limit to date. Within nearly 550 hours more than 12000 slew measurements with a total slew length of more than 150000 degrees were collected, corresponding to a sky coverage of about 15%. The slew data analysis has been focused on the detection of compact sources, which required the development of special algorithms. A severe problem at 170 μm is the confusion of genuine compact sources with foreground galactic cirrus knots and ridges. The selection and identification of objects therefore necessarily requires a multi-wavelengths approach, which makes use of a broad variety of additional data from databases and other surveys. Known galaxies were identified by cross-correlating the Serendipity Survey source positions with galaxy entries in the NED and Simbad databases and a subsequent cross-check of optical images from the Digital Sky Survey. A large catalogue with 170 μm fluxes for ≈2000 galaxies is being complied. The particularly interesting rare galaxies with very cold dust and very large dust masses further require additional FIR data from the IRAS survey as well as measured redshifts. A large fraction of the compact galactic structures are prestellar cores inside cold star forming regions. Early stages of medium and high mass star forming regions are identified by combining compact bright and cold Serendipity Survey sources with the near-infrared 2MASS and MSX surveys, the combination of which indicates large dust masses in conjunction with embedded young stars of early spectral types. In all the studied samples of different object classes the 170 μm flux provides the crucial data point for a complete characterization of the FIR spectral energy distributions and the derivation of total dust masses. Follow-up observations are underway to study selected objects in more detail.

Extending the limits of globule detection - ISOPHOT Serendipity Survey observations of interstellar clouds II

ISOPHOT Serendipity Survey (ISOSS) observations of the nearby interstellar medium towards Chamaeleon have revealeda number of cold cloud cores. Far-infraredcolours have been studiedusing ISOSS and IRAS data. 10 very cold cores with colour temperatures Tdust≲13 K have been foundin an 11° x 8° sized region. Comparing the FIR data with radio measurements, all of the very cold cores have high gas column densities, N(H2) > 1021 cm-2, and 7 out of 10 have low gas temperatures as indicated by Tex(C18O) ≈ 8 K.

Multi-Wavelength Data Mining of the ISOPHOT Serendipity Sky Survey

The higher spatial resolution and sensitivity of ISO allowed several extragalactic surveys to be extended to greater depth than obtained with IRAS. With the extended wavelength range deep surveys were performed for the first time at wavelengths up to rv 200 uu». They favour galaxy models with strong evolution. With ISOs new capabilities the spectral energy distributions of larger samples of ULIRGs in the local universe and those of quasars and radio galaxies were determined. These data are applicable as templates to the more distant universe. Foreground components from zodiacal light and cirrus to the intracluster dust emission were studied in connection with their separation from the extragalactic background radiation.

Chamaeleon’s Cold Cloud Cores

The ISOPHOT Serendipity Survey utilized the slew time between ISO’s pointedobserv ations with strip scanning measurements of the sky in the far-infrared at 170 μm. From the slew data with low (I100μm ≤ 15 MJy/sr) cirrus background, 115 well-observedsources with a high signal-to-noise ratio in all four detector pixels having a galaxy association were extracted. The integral 170 μm fluxes measured from the Serendipity slews have been put on an absolute flux level by using a number of calibrator sources observedwith ISOPHOT’s photometric mapping mode. For all but a few galaxies, the 170 μm fluxes are determined for the first time, which represents a significant increase in the number of galaxies with measuredFIR fluxes beyondthe IRAS 100 μm limit. The vast majority of the galaxies are morphologically classifiedas spirals. The large fraction of sources with a high F170μm/F100μm flux ratio indicates that a very cold (T < 20 K) dust component is present in many galaxies. The typical mass of the coldest dust component is MDust = 107.5±0.5 M⊙, a factor 2 – 10 larger than that derived from IRAS fluxes alone. As a consequence, the gas-to-dust ratios are much closer to the canonical value of ≈ 160 for the Milky Way. By relaxing the selection criteria, it is expectedthat the Serendipity survey will eventually leadto a catalogue of 170 μm fluxes for ≈ 1000 galaxies.