A New Component in the Radio Continua of PNe

A byproduct of experiments designed to map the CMB is the recent detection of a new component of foreground galactic emission. The anomalous foreground at 10–30 GHz, unexplained by traditional emission mechanisms, correlates with 100 mum dust emission, and is thus presumably due to dust.Is the anomalous foreground ubiquitous in the Galaxy? I will present evidence obtained with the CBI and SIMBA+SEST supporting the existence of the new component in the ISM at large, and in specific objects, in the form of a 31 GHz excess over free-free emission in PNe

Molecular abundances in carbon-rich circumstellar envelopes

Wetensch. publicatieFaculteit der Wiskunde en Natuurwetenschappe

Molecular excitation in the Eagle nebula's fingers

Context: The M16 nebula is a relatively nearby Hii region, powered by O stars from the open cluster NGC 6611, which borders to a Giant Molecular Cloud. Radiation from these hot stars has sculpted columns of dense obscuring material on a few arcmin scales. The interface between these pillars and the hot ionised medium provides a textbook example of a Photodissociation Region (PDR). Aims: To constrain the physical conditions of the atomic and molecular material with submillimeter spectroscopic observations. Methods: We used the APEX submillimeter telescope to map a ~3'x3' region in the CO J=3-2, 4-3 and 7-6 rotational lines, and a subregion in atomic carbon lines. We also observed C18O(3-2) and CO(7-6) with longer integrations on five peaks found in the CO(3-2) map. The large scale structure of the pillars is derived from the molecular lines' emission distribution. We estimate the magnitude of the velocity gradient at the tips of the pillars and use LVG modelling to constrain their densities and temperatures. Excitation temperatures and carbon column densities are derived from the atomic carbon lines. Results: The atomic carbon lines are optically thin and excitation temperatures are of order 60 K to 100 K, well consistent with observations of other Hii region-molecular cloud interfaces. We derive somewhat lower temperatures from the CO line ratios, of order 40 K. The Ci/CO ratio is around 0.1 at the fingers tips.Comment: 4 pages, APEX A&A special issue, accepte

Physical properties of Southern infrared dark clouds

It is commonly assumed that cold and dense Infrared Dark Clouds (IRDCs) likely represent the birth sites massive stars. Therefore, this class of objects gets increasing attention. To enlarge the sample of well-characterised IRDCs in the southern hemisphere, we have set up a program to study the gas and dust of southern IRDCs. The present paper aims at characterizing the continuuum properties of this sample of objects. We cross-correlated 1.2 mm continuum data from SIMBA@SEST with Spitzer/GLIMPSE images to establish the connection between emission sources at millimeter wavelengths and the IRDCs we see at 8 $\mu$m in absorption against the bright PAH background. Analysing the dust emission and extinction leads to a determination of masses and column densities, which are important quantities in characterizing the initial conditions of massive star formation. The total masses of the IRDCs were found to range from 150 to 1150 $\rm M_\odot$ (emission data) and from 300 to 1750 $\rm M_\odot$ (extinction data). We derived peak column densities between 0.9 and 4.6 $\times 10^{22}$ cm$^{-2}$ (emission data) and 2.1 and 5.4 $\times 10^{22}$ cm$^{-2}$ (extinction data). We demonstrate that the extinction method fails for very high extinction values (and column densities) beyond A$_{\rm V}$ values of roughly 75 mag according to the Weingartner & Draine (2001) extinction relation $R_{\rm V} = 5.5$ model B. The derived column densities, taking into account the spatial resolution effects, are beyond the column density threshold of 3.0 $\times 10^{23}$ cm$^{-2}$ required by theoretical considerations for massive star formation. We conclude that the values for column densities derived for the selected IRDC sample make these objects excellent candidates for objects in the earliest stages of massive star formation.Comment: Accepted for publication in Astronomy & Astrophysic

Submillimeter spectroscopy of southern hot cores: NGC6334(I) and G327.3-0.6

High-mass star-forming regions are known to have a rich molecular spectrum from many species. Some of the very highly excited lines are emitted from very hot and dense gas close to the central object(s). The physics and chemistry of the inner cores of two high mass star forming regions, NGC6334(I) and G327.3-0.6, shall be characterized. Submillimeter line surveys with the APEX telescope provide spectra which sample many molecular lines at high excitation stages. Partial spectral surveys were obtained, the lines were identified, physical parameters were determined through fitting of the spectra. Both sources show similar spectra that are comparable to that of the only other high mass star forming region ever surveyed in this frequency range}, Orion-KL, but with an even higher line density. Evidence for very compact, very hot sources is found.Comment: APEX A&A special issue, accepte

Looking for the S-Z Effect towards Distant ROSAT Clusters of Galaxies

We report on observations of the Sunyaev-Zeldovich effect towards X-ray ROSAT clusters taken with a double channel (1.2 and 2 mm) photometer installed at the focus of the 15m SEST antenna in Chile. This paper describes the first results obtained for the high-z clusters S1077, A2744 and S295. Marginal detections were found for A2744 and at 1 mm for S1077. We discuss these data in terms of contamination of sources along the line of sight and give a constraint on the amplitude of the kinematic effect.Comment: 17 pg Latex file (using aasms4.sty) gzip'd tar'd uuencoded file including 1 ps figure, ApJ Letter in pres

Circumstellar masers in the Magellanic Clouds

We have searched for 22 GHz H2O and 43/86/129 GHz SiO masers in bright IRAS point sources in the SMC and LMC, to test whether the kinematics of the mass loss from these stars depends on metallicity. H2O masers were detected in the red supergiants IRAS04553-6825 and IRAS05280-6910, and tentatively in the luminous IR object IRAS05216-6753 and the AGB star IRAS05329-6708. SiO masers were detected in IRAS04553-6825. The outflow velocity increases between the H2O masing zone near the dust-formation region and the more distant OH masing zone from 18 to 26 km/s for IRAS04553-6825 and from 6 to 17 km/s for IRAS05280-6910. The total sample of LMC targets is analysed in comparison with circumstellar masers in the Galactic Centre. The photon fluxes of circumstellar masers in the LMC are very similar to those in the Galactic Centre. The expansion velocities in the LMC appear to be 20% lower than for similarly bright OH masers in the Galactic Centre, but the data are consistent with no difference in expansion velocity. OH/IR stars in the LMC appear to have slower accelerating envelopes than OH/IR stars in the Galactic Centre. Masers in the LMC have blue-asymmetric emission profiles. This may be due to the amplification of stellar and/or free-free radiation, rather than the amplification of dust emission, and may be more pronounced in low metallicity envelopes. SiO maser strength increases with the photometric amplitude at 2.2 micron but is independent of the photometric amplitude at 10 micron. This suggests a strong connection between shocks in the dust-free SiO masing zone and the dust formation process. Appendices describe H2O maser emission from R Dor in the Milky Way, optical echelle spectroscopy of IRAS04553-6825, and the properties of masers in the Galactic Centre (Abridged).Comment: 19 pages, 17 figures. Accepted for publication in Astronomy & Astrophysics Main Journa