arXiv subjects

K. Lehtinen

Publications and source records attributed to K. Lehtinen.

23 records · Page 2Linked to original sources

arXiv2003

Unidentified Infrared Bands in the Interstellar Medium across the Galaxy

We present a set of 6-12 micron ISOPHOT-S spectra of the general interstellar medium of the Milky Way. This part of the spectrum is dominated by a series of strong, wide emission features commonly called the Unidentified Infrared Bands. The sampled area covers the inner Milky Way from l = -60 degr to +60 degr with a ten-degree step in galactic longitude and nominal latitudes 0,+-1 degr. For each grid position the actual observed direction was selected from IRAS 100 micron maps to minimize contamination by point sources and molecular clouds. All spectra were found to display the same spectral features. Band ratios are independent of band strength and Galactic coordinates. A comparison of total observed flux in band features and IRAS 100 micron emission, a tracer for large interstellar dust grains, shows high correlation at large as well as small 1-arcmin scales. This implies a strong connection between large dust grains and the elusive band carriers; the evolutionary history and heating energy source of these populations must be strongly linked. The average mid-infrared spectrum of the Milky Way is found to be similar to the average spectrum of spiral galaxy NGC 891 and the spectra of other spirals. The common spectrum can therefore be used as a template for the 6-12 micron emission of late-type spiral galaxies. Finally, we show that interstellar extinction only weakly influences the observed features even at lambda = 10 microns, where the silicate absorption feature is strongest.

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arXiv2003

Centimetre continuum emission from young stellar objects in Cederblad 110

The low-mass star formation region associated with the reflection nebula Cederblad 110 in the Chamaeleon I cloud was mapped with the Australian Telescope Compact Array (ATCA) at 6 and 3.5cm. Altogether 11 sources were detected, three of which are previously known low mass young stellar objects associated with the nebula: the illuminating star IRS2 (Class III, Einstein X-ray source CHX7), the brightest far-infrared source IRS4 (Class I), and the weak X-ray source CHX10a (Class III). The other young stellar objects in the region, including the Class 0 protostar candidate Cha-MMS1, were not detected. The radio spectral index of IRS4 (alpha = 1.7 +/- 0.3) is consistent with optically thick free-free emission arising from a dense ionized region, probably a jet-induced shock occurring in the circumstellar material. As the only Class I protostar with a 'thermal jet' IRS4 is the strongest candidate for the central source of the molecular outflow found previously in the region. The emission from IRS2 has a flat spectrum (alpha = 0.05 +/- 0.05) but shows no sign of polarization, and therefore its origin is likely to be optically thin free-free emission either from ionized wind or a collimated jet. The strongest source detected in this survey is a new compact object with a steep negative spectral index (-1.1) and a weak linear polarization (about 2 %), which probably represents a background radio galaxy.

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arXiv2002

Far infrared observations of pre-protostellar sources in Lynds 183

Using ISOPHOT maps at 100 and 200um and raster scans at 100, 120, 150 and 200um we have detected four unresolved far-infrared sources in the high latitude molecular cloud L183. Two of the sources are identified with 1.3mm continuum sources found by Ward-Thompson et al. and are located near the temperature minimum and the coincident column density maximum of dust distribution. For these two sources, the ISO observations have enabled us to derive temperatures (about 8.3 K) and masses (about 1.4 and 2.4 solar masses). They are found to have masses greater than or comparable to their virial masses and are thus expected to undergo gravitational collapse. We classify them as pre-protostellar sources. The two new sources are good candidates for pre-protostellar sources or protostars within L183.

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arXiv2001

Far-infrared and molecular line observations of Lynds 183 - studies of cold gas and dust

We have mapped the dark cloud L183 in the far-infrared at 100um and 200um with the ISOPHOT photometer aboard the ISO satellite. The observations make it possible for the first time to study the properties of the large dust grains in L183 without confusion from smaller grains. The observations show clear colour temperature variations which are likely to be caused by changes in the emission properties of the dust particles. In the cloud core the far-infrared colour temperature drops below 12K. The data allow a new determination of the cloud mass and the mass distribution. The mass within a radius of 10 arcmin from the cloud centre is 25 Msun. We have mapped the cloud in several molecular lines including DCO+(2-1) and H13CO+(1-0). These species are believed to be tracers of cold and dense molecular material and we detect a strong anticorrelation between the DCO+ emission and the dust colour temperatures. In particular, the DCO+(2-1) emission is not detected towards the maximum of the 100um emission where the colour temperature rises above 15K. The H13CO+ emission follows the DCO+ distribution but CO isotopes show strong emission even towards the 100um peak. A comparison of the DCO+ and C18O maps shows sharp variations in the relative intensities of the species. Morphologically the 200um dust emission traces the distribution of dense molecular material as seen e.g. in C18O lines. A comparison with dust column density shows that C18O is depleted by a factor of 1.5 in the cloud core. We present results of R- and B-band starcounts. The extinction is much better correlated with the 200um than with the 100um emission. Based on the 200um correlation at low extinction values we deduce a value of ~17mag for the visual extinction towards the cloud centre.

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arXiv1998

Detection of widely distributed UIR band emission in the disk of NGC 891

The spectrum of the unidentified infrared (UIR) emission bands between 5.9 and 11.7 [micro]m has been observed for the first time in the disk of an external galaxy. We have used the low-resolution spectrometer of the ISOPHOT instrument aboard ISO. The UIR bands at 6.2, 7.7 and 11.3 [micro]m have absolute intensities which are similar to the values observed for the diffuse emission of our own Galaxy. The UIR bands between 5.9 and 11.7 [micro]m contribute ~9% of the total IR radiation of NGC 891. The intensity ratios and band widths in the NGC 891 disk emissions are similar to the diffuse emission of the Milky Way, pointing to a common carrier for the UIR bands in the two galaxies. However, there are some notable variations of the band ratios along the major axis of the galaxy.

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