K. Mattila

University of Helsinki, Helsinki, Southern Finland Province, Finland

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Publications (166)313.3 Total impact

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    K. Lehtinen, K. Mattila
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    ABSTRACT: The optical surface brightness of dark nebulae is mainly due to scattering of integrated starlight by classical dust grains. It contains information on the impinging interstellar radiation field, cloud structure, and grain scattering properties. We have obtained spectra of the scattered light from 3500 to 9000 Angstrom in two globules, the Thumbprint Nebula and DC303.8-14.2. We use observations of the scattered light to study the impinging integrated starlight spectrum as well as the scattered H-alpha and other line emissions from all over the sky. We search also for the presence of other than scattered light in the two globules. We obtained long-slit spectra encompassing the whole globule plus adjacent sky in a one-slit setting, thus enabling efficient elimination of airglow and other foreground sky components. We calculated synthetic integrated starlight spectra for the solar neighbourhood using HIPPARCOS-based stellar distributions and the spectral library of Pickles. Spectra are presented separately for the bright rims and dark cores of the globules. The continuum spectral energy distributions and absorption line spectra can be well modelled with the synthetic integrated starlight spectra. Emission lines of H-alpha + NII, H-beta, and SII are detected and are interpreted in terms of scattered light plus an in situ warm ionized medium component behind the globules. We detected an excess of emission over the wavelength range 5200-8000 Angstrom in DC303.8-14.2 but the nature of this emission remains open.
    Astronomy and Astrophysics 11/2012; · 5.08 Impact Factor
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    ABSTRACT: We examine two positions, ON1 and ON2, within the Ophiuchus cloud LDN 1688 using observations made with the ISOPHOT instrument aboard the ISO satellite. The data include mid-IR spectra (~6-12{\mu}m) and several photometric bands up to 200{\mu}m. The data probe the emission from molecular PAH-type species, transiently-heated Very Small Grains (VSGs), and large classical dust grains. We compare the observations to earlier studies, especially those carried out towards an isolated translucent cloud in Chamaeleon (Paper I). The spectra towards the two LDN 1688 positions are very similar to each other, in spite of position ON1 having a larger column density and probably being subjected to a stronger radiation field. The ratios of the mid-IR features are similar to those found in other diffuse and translucent clouds. Compared to paper I, the 7.7/11.3{\mu}m band ratios are lower, ~2.0, at both LDN 1688 positions. A continuum is detected in the ~10{\mu}m region. This is stronger towards the position ON1 but still lower than on any of the sightlines in Paper I. The far-infrared opacities are higher than for diffuse medium. The value of the position ON2, {\tau}200/N(H) = 3.9 x 10^{-25} cm^2/H, is twice the value found for ON1. The radiation field of LDN 1688 is dominated by the two embedded B type double stars, {\rho} Oph AB and HD 147889, with an additional contribution from the Upper Sco OB association. The strong heating is reflected in the high colour temperature, ~24 K, of the large grain emission. Radiative transfer modelling confirms a high level of the radiation field and points to an increased abundance of PAH grains. However, when the hardening of the radiation field caused by the local B-stars is taken into account, the observations can be fitted with almost no change to the standard dust models. However, all the examined models underestimate the level of the mid-IR continuum.
    Monthly Notices of the Royal Astronomical Society 10/2012; 428(3). · 5.52 Impact Factor
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    ABSTRACT: The Extragalactic Background Light (EBL) at UV, optical and NIR wavelengths consists of the integrated light of all unresolved galaxies along the line of sight plus any contributions by intergalactic matter including hypothetical decaying relic particles. The measurement of the EBL has turned out to be a tedious problem. This is because of the foreground components of the night sky brightness, much larger than the EBL itself: the Zodiacal Light (ZL), Integrated Starlight (ISL), Diffuse Galactic Light (DGL) and, for ground-based observations, the Airglow (AGL) and the tropospheric scattered light. We have been developing a method for the EBL measurement which utilises the screening effect of a dark nebula on the EBL. A differential measurement in the direction of a high-latitude dark nebula and its surrounding area provides a signal that is due to two components only, i.e. the EBL and the diffusely scattered ISL from the cloud. We present a progress report of this method where we are now utilising intermediate resolution spectroscopy with ESO's VLT telescope. We detect and remove the scattered ISL component by using its characteristic Fraunhofer line spectral signature. In contrast to the ISL, in the EBL spectrum all spectral lines are washed out. We present a high quality spectrum representing the difference between an opaque position within our target cloud and several clear OFF positions around the cloud. We derive a preliminary EBL value at 400 nm and an upper limit to the EBL at 520 nm. These values are in the same range as the EBL lower limits derived from galaxy counts.
    Proceedings of the International Astronomical Union 11/2011;
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    K. Lehtinen, M. Juvela, K Mattila
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    ABSTRACT: We study an undocumented large translucent cloud, detected by means of its enhanced radiation on the SHASSA (Southern H-Alpha Sky Survey Atlas) survey. We consider whether its excess surface brightness can be explained by light scattered off the dust grains in the cloud, or whether emission from in situ ionized gas is required. In addition, we aim to determine the temperature of dust, the mass of the cloud, and its possible star formation activity. We compare the observed H-alpha surface brightness of the cloud with predictions of a radiative transfer model. We use the WHAM (Wisconsin H-Alpha Mapper) survey as a source for the Galactic H-alpha interstellar radiation field illuminating the cloud. Visual extinction through the cloud is derived using 2MASS J, H, and K band photometry. We use far-IR ISOSS (ISO Serendipitous Survey), IRAS, and DIRBE data to study the thermal emission of dust. The LAB (The Leiden/Argentine/Bonn Galactic HI Survey) is used to study 21cm HI emission associated with the cloud. Radiative transfer calculations of the Galactic diffuse H-alpha radiation indicate that the surface brightness of the cloud can be explained solely by radiation scattered off dust particles in the cloud. The maximum visual extinction through the cloud is about 1.2mag. The cloud is found to be associated with 21cm HI emission at a velocity of about -9 km/s. The total mass of the cloud is about 550-1000 solar masses. There is no sign of star formation in this cloud. The distance of the cloud is estimated from the Hipparcos data to be about 100 pc.
    Astronomy and Astrophysics 05/2010; · 5.08 Impact Factor
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    ABSTRACT: Table A.2 lists the full photometric catalog of the ISOPHOT EBL project North Galactic Pole fields acquired with the Nordic Optical Telescope, using the ALFOSC (in R and I band) and NOTCAM (in K band) instruments. The photometry is performed with SExtractor and both "total" and aperture magnitudes are given using the AUTO and APER (with 2.7" diameter) magnitudes, as well as the star/galaxy CLASS parameter. The photometry is matched with the SDSS and the ugriz magnitudes are also given. All objects falling within 60" of a given ISOPHOT far-IR source are indicated - these areas are analysed in the Paper. (2 data files).
    VizieR Online Data Catalog. 03/2010;
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    ABSTRACT: We present follow-up observations of the far-infrared (FIR) sources at 90, 150 and 180 μm detected as part of the ISOPHOT EBL project, which has recently measured the absolute surface brightness of the cosmic infrared background (CIRB) radiation for the first time independently from COBE data. We have observed the fields at the North Galactic Pole region in the optical and near-IR, and complement these data with Sloan Digital Sky Survey photometry, and spectroscopy where available, and present identifications of the 25 FIR sources which reach down to ∼150 mJy in all three ISOPHOT bands. Identifications are done by means of full spectral energy density fitting to all sources in the FIR error circle areas. Approximately 80 per cent are identified as star-forming or star-bursting galaxies at z < 0.3. We also find that more than half of the counterparts have disturbed morphologies, with signs of past or present interactions. However, only 20 per cent of all the sources are uniquely matched with a single galaxy –40 per cent are blends of two or more of these nearby star-forming galaxies, while another 20 per cent are likely blends of nearby and fainter galaxies. The final 20 per cent are likely to be more luminous IR galaxies at higher redshifts. The blended sources have an effect on the FIR source counts. In particular, taking into account realistic confusion or blending of sources, the differential FIR counts move down by a factor of ∼1.5 and steepen in the 100 to 400 mJy range.
    Monthly Notices of the Royal Astronomical Society 01/2010; 401(3):1587 - 1601. · 5.52 Impact Factor
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    ABSTRACT: The cosmic infrared background (CIRB) consists mainly of the integrated light of distant galaxies. In the far-infrared the current estimates of its surface brightness are based on the measurements of the COBE satellite. Independent confirmation of these results is still needed from other instruments. In this paper we derive estimates of the far-infrared CIRB using measurements made with the ISOPHOT instrument aboard the ISO satellite. The results are used to seek further confirmation of the CIRB levels that have been derived by various groups using the COBE data. We study three regions of very low cirrus emission. The surface brightness observed with the ISOPHOT instrument at 90, 150, and 180 um is correlated with hydrogen 21 cm line data from the Effelsberg radio telescope. Extrapolation to zero hydrogen column density gives an estimate for the sum of extragalactic signal plus zodiacal light. The zodiacal light is subtracted using ISOPHOT data at shorter wavelengths. Thus, the resulting estimate of the far-infrared CIRB is based on ISO measurements alone. In the range 150 to 180 um, we obtain a CIRB value of 1.08+-0.32+-0.30 MJy/sr quoting statistical and systematic errors separately. In the 90 um band, we obtain a 2-sigma upper limit of 2.3 MJy/sr. The estimates derived from ISOPHOT far-infrared maps are consistent with the earlier COBE results.
    Astronomy and Astrophysics 05/2009; · 5.08 Impact Factor
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    ABSTRACT: In the first part, we present some results of our ongoing modelling of the polarized thermal dust emission from cloud cores. In our radiative transfer calculations we record the direction-dependence of the incoming radiation, thus allowing us to calculate the anisotropy of the radiation, which should play a major part in the efficiency of the radiative torques. Radiative torque mechanism is widely considered to be a quite promising explanation for the grain alignment in clouds. In addition to the anisotropy, we show the derived polarization map and compare our results with previous studies. In the second part, we discuss the use of near-infrared diffuse surface brightness maps, arising from scattered light, as a tracer of dust column density in clouds with AV in the range 1, 15^m. We present our SOFI NTT -observations of a quiescent filament in the Corona Australis molecular cloud, and compare the derived dust column densities to the result derived from the extinction of the background stars.
    01/2009;
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    K. Mattila
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    ABSTRACT: A critical discussion is presented of the data analysis applied by Bernstein, Freedman, & Madore in 2002 to their measurement of the extragalactic background light. There are questionable assumptions in the analysis of the ground-based observations of the zodiacal light. The modeling of the diffuse Galactic light is based on an underestimated value of the dust column density along the line of sight. Comparison with the previously presented results from the same observations reveals a puzzling situation: in spite of a large difference in the atmospheric scattered-light corrections, the derived extragalactic background light values are exactly the same. The claim of the paper of a "detection of the extragalactic background light" appears premature.
    The Astrophysical Journal 12/2008; 591(1):119. · 6.73 Impact Factor
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    K. Mattila, M. Juvela, and K. Lehtinen
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    ABSTRACT: Bright emission nebulae, or H II regions, around hot stars are readily seen in Hα light. However, the all-pervasive faint Hα emission has only recently been detected and mapped over the whole sky. Mostly the Hα emission observed along a line of sight is produced by ionized gas in situ. There are, however, cases where all or most of the Hα radiation is due to scattering by electrons or dust particles that are illuminated by an Hα-emitting source off the line of sight. Here we demonstrate that diffuse, translucent, and dark dust clouds at high Galactic latitudes are in many cases observed to have an excess of diffuse Hα surface brightness; i.e., they are brighter than the surrounding sky. We show that the majority of this excess surface brightness can be understood as light scattered off the interstellar dust grains. The source of incident photons is the general Galactic Hα background radiation impinging on the dust clouds from all over the sky.
    The Astrophysical Journal 12/2008; 654(2):L131. · 6.73 Impact Factor
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    ABSTRACT: Cold cores in interstellar molecular clouds represent the very first phase in star formation. The physical conditions of these objects are studied in order to understand how molecular clouds evolve and how stellar masses are determined. The purpose of this study is to probe conditions in the dense, starless clump Ophichus D (Oph D). The ground-state (1(10)-1(11)) rotational transition of ortho-H2D+ was observed with APEX towards the density peak of Oph D. The width of the H2D+ line indicates that the kinetic temperature in the core is about 6 K. So far, this is the most direct evidence of such cold gas in molecular clouds. The observed H2D+ spectrum can be reproduced with a hydrostatic model with the temperature increasing from about 6 K in the centre to almost 10 K at the surface. The model is unstable against any increase in the external pressure, and the core is likely to form a low-mass star. The results suggest that an equilibrium configuration is a feasible intermediate stage of star formation even if the larger scale structure of the cloud is thought to be determined by turbulent fragmentation. In comparison with the isothermal case, the inward decrease in the temperature makes smaller, i.e. less massive, cores susceptible to externally triggered collapse. Comment: 7 pages, 5 figures, accepted for Astronomy and Astrophysics
    Astronomy and Astrophysics 02/2008; · 5.08 Impact Factor
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    ABSTRACT: We present results of a far-infrared molecular cloud mapping program which utilizes the PHT-P photometer and PHT-C cameras of the ISOPHOT instrument. ISO has enabled us to study the emission of very cold dust, Td < 15 K. The multi-wavelength observations between 3.6–200 μm allow to discern emission of different grain components, and to construct spectral energy distributions for embedded young stellar objects at far-IR wavelengths where their emission is at maximum. The extension up to 200 μm and the multi-filter coverage of the 60–200 μm wavelength range are essential improvements for study of physical properties of young stellar objects.
    01/2008: pages 317-324;
  • Mika Juvela, Kalevi Mattila, Dietrich Lemke
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    ABSTRACT: Far-infrared maps obtained with ISOPHOT have been searched for point-like sources. The majority of the 55 sources is believed to be extragalactic and in most cases no previously known sources can be associated with them. Based on the far-infrared spectral energy distributions it is likely that dust-enshrouded, distant galaxies form a significant fraction of the sources. We estimate the number densities of extragalactic sources at 90μm, 150μm and 180μm wavelengths and at flux density levels down to ∼100 mJy. The counts are compared with models of galaxy evolution. The counts exceed the predictions of current models, even those with strong evolution, and no-evolution models are rejected at a high confidence level. Comparison with recent results from COBE mission indicates that at 90μm the detected sources correspond to ≳20% of the extragalactic background light. At longer wavelengths the corresponding fraction is 10%.
    01/2008: pages 88-95;
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    ABSTRACT: With current near-infrared (NIR) instruments the near-infrared light scattered from interstellar clouds can be mapped over large areas. The surface brightness carries information on the line-of-sight dust column density. Therefore, scattered light could provide an important tool to study mass distribution in quiescent interstellar clouds at a high, even sub-arcsecond resolution. We wish to confirm the assumption that light scattering dominates the surface brightness in all NIR bands. Furthermore, we want to show that scattered light can be used for an accurate estimation of dust column densities in clouds with Av in the range 1-15mag. We have obtained NIR images of a quiescent filament in the Corona Australis molecular cloud. The observations provide maps of diffuse surface brightness in J, H, and Ks bands. Using the assumption that signal is caused by scattered light we convert surface brightness data into a map of dust column density. The same observations provide colour excesses for a large number of background stars. These data are used to derive an extinction map of the cloud. The two, largely independent tracers of the cloud structure are compared. Results. In regions below Av=15m both diffuse surface brightness and background stars lead to similar column density estimates. The existing differences can be explained as a result of normal observational errors and bias in the sampling of extinctions provided by the background stars. There is no indication that thermal dust emission would have a significant contribution even in the Ks band. The results show that, below Av=15mag, scattered light does provide a reliable way to map cloud structure. Compared with the use of background stars it can also in practice provide a significantly higher spatial resolution. Comment: 14 pages, 15 figures, accepted to A&A, the version includes small changes in the text and an added appendix
    Astronomy and Astrophysics 08/2007; · 5.08 Impact Factor
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    ABSTRACT: Aims:Our aim is to compare the infrared properties of big, "classical" dust grains with visual extinction in the cloud L1642. In particular, we study the differences in grain emissivity between diffuse and dense regions in the cloud. Methods: The far-infrared properties of dust are based on large-scale 100 mum and 200 mum maps. Extinction through the cloud was derived by using the star count method in the B- and I-bands, and colour excess method in the J, H, and Ks bands. Radiative transfer calculations were used to study the effects of increasing absorption cross-section on the far-infrared emission and dust temperature. Results: Dust emissivity, measured by the ratio of far-infrared optical depth to visual extinction, tau(far-IR)/A_V, increases with decreasing dust temperature in L1642. There is about a two-fold increase in emissivity over the dust temperature range of 19 K-14 K. Radiative transfer calculations show that, in order to explain the observed decrease of dust temperature towards the centre of L1642, an increase of absorption cross-section of dust at far-IR is necessary. This temperature decrease cannot be explained solely by the attenuation of interstellar radiation field. Increased absorption cross-section also manifests itself as an increased emissivity. We find that, due to temperature effects, the apparent value of optical depth tau_app(far-IR), derived from 100 mum and 200 mum intensities, is always lower than the true optical depth. Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, The Netherlands, and the UK) and with the participation of ISAS and NASA. Appendices A-D are only available in electronic form at http://www.aanda.org
    Astronomy and Astrophysics 01/2007; 466(3):969-976. · 5.08 Impact Factor
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    ABSTRACT: We present results from an on-going follow-up campaign of far-infrared sources detected as part of our ISOPHOT Cosmic IR Background project. Fields have been imaged in the optical and near-infrared, and we find at least a third of the FIR targets areas to contain a bright and nearby star-forming galaxy. We also explore the largely neglected possibility that instead of individual galaxies some of the fainter FIR sources are confused sums of several sources - or even whole cores of galaxy clusters at redshifts of z \sim 0.4-0.8. We look for correlations in the FIR positions with extremely red objects (EROs) and significant peaks in the galaxy surface density and peaks in cluster red sequence signal. Several matches are found and we have set out to study cluster candidates spectroscopically. The campaign is producing an interesting base to study IR-luminous, strongly star-forming galaxies in potential cluster environments.
    11/2006;
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    K Mattila, M. Juvela, K. Lehtinen
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    ABSTRACT: Bright emission nebulae, or HII regions, around hot stars are readily seen in H-alpha light. However, the all-pervasive faint H-alpha emission has only recently been detected and mapped over the whole sky. Mostly the H-alpha emission observed along a line of sight is produced by ionised gas in situ. There are, however, cases where all or most of the H-alpha radiation is due to scattering by electrons or dust particles which are illuminated by an H-alpha emitting source off the line of sight. Here we demonstrate that diffuse, translucent and dark dust clouds at high galactic latitudes are in many cases observed to have an excess of diffuse H-alpha surface brightness, i.e. they are brighter than the surrounding sky. We show that the majority of this excess surface brightness can be understood as light scattered off the interstellar dust grains. The source of incident photons is the general Galactic H-alpha background radiation impinging on the dust clouds from all over the sky.
    11/2006;
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    ABSTRACT: Cometary globule CG 12 lies at the distance of 630 pc more than 200 pc above the Galactic plane. The cloud's structure could be due to the passage of a supernova blast wave. Curiously, the cometary tail points at the galactic plane which would put the putative supernova even farther above the Galactic plane than the globule. The globule contains a low/intermediate mass stellar cluster with at least 9 members (Williams et al. 1977). The head of CG 12 has been observed using NIR imaging (NTT SOFI), mm continuum (SEST SIMBA) and sub mm (APEX) and mm (SEST) spectroscopy (Haikala & Olberg 2006, Haikala et al.). The molecular material is distributed in a North-South 10' long elongated lane with two compact maxima separated by 3'. Strong C18O (3-2), (2-1) and (1-0) emission is detected in both maxima and both have an associated compact 1.2 mm continuum source. The Northern core, CG 12 N, is cold and is possibly still pre-stellar. A dense and compact core is observed in DCO+ and CS emission in the direction of the Southern core, CG 12 S. A remarkable C18O hot spot was detected in CG 12 S. This is the first detection of such a compact, warm object in a low mass star forming region. The hot spot can be modelled with a 60″ to 80″ diameter (~0.2 pc) hot (80 K Tex 100 K) 1.6 solar mass clump (Haikala et al. 2006). The hot spot lies at the edge of a dense cloud core and on the axis of a highly collimated bipolar molecular outflow (White 1993). The driving source of the outflow is most probably embedded in the dense core. NIR imaging reveals a bright cone like feature with a faint counter cone in the centre of CG 12 S. The size of the CG 12 compact head, 1.1 pc by 1.8 pc, and the C18O mass larger than 100 solar masses are comparable to those of other nearby low/intermediate mass star formation regions.
    Proceedings of the International Astronomical Union 07/2006; 2:420 - 420.
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    ABSTRACT: Aims. The purpose of this study is to examine the prediction that the deuterated H3+ ion, H2D+, can be found exclusively in the coldest regions of molecular cloud cores. This is also a feasibility study for the detection of the ground-state line of ortho-H2D+ at 372 GHz with APEX. Methods. The 1(10)-1(11) transition of H2D+ at 372 GHz was searched towards selected positions in the massive star forming cloud OriB9, in the dark cloud L183, and in the low- to intermediate mass star-forming cloud R CrA. Results. The line was detected in cold, prestellar cores in the regions of OriB9 and L183, but only upper limits were obtained towards other locations which either have elevated temperatures or contain a newly born star. The H2D+ detection towards OriB9 is the first one in a massive star-forming region. The fractional ortho-H2D+ abundances (relative to H2) are estimated to be about 1.0E-10 in two cold cores in OriB9, and 3.0E-10 in the cold core of L183. Conclusions. The H2D+ detection in OriB9 shows that also massive star forming regions contain very cold prestellar cores which probably have reached matured chemical composition characterized, e.g., by a high degree of deuterium fractionation. Besides as a tracer of the interior parts of prestellar cores, H2D+ may therefore be used to put contraints on the timescales related to massive star formation. Comment: 5 pages, 1 figure, accepted for publication in Astronomy and Astrophysics
    Astronomy and Astrophysics 06/2006; · 5.08 Impact Factor
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    ABSTRACT: The feasibility of observing the C18O (3-2) spectral line in cold clouds with the APEX telescope has been tested. As the line at 329.330 GHz lies in the wing of a strong atmospheric H2O absorption it can be observed only at high altitude observatories. Using the three lowest rotational levels instead of only two helps to narrow down the physical properties of dark clouds and globules. The centres of two C18O maxima in the high latitude low mass star forming region CG 12 were mapped in C18O (3-2) and the data were analyzed together with spectral line data from the SEST. The T_MB(3-2)/T_MB(2-1) ratio in the northern C18O maximum, CG 12 N, is 0.8, and in the southern maximum, CG 12 S, ~2. CG 12 N is modelled as a 120'' diameter (0.4pc) cold core with a mass of 27 Msun. A small size maximum with a narrow, 0.8 kms-1, C18O (3-2) spectral line with a peak temperature of T_MB ~11 K was detected in CG 12 S. This maximum is modelled as a 60'' to 80'' diameter (~0.2pc) hot (80 K < Tex < 200 K) ~1.6 Msun clump. The source lies on the axis of a highly collimated bipolar molecular outflow near its driving source. This is the first detection of such a compact, warm object in a low mass star forming region. Comment: APEX A&A special issue, accepted
    Astronomy and Astrophysics 06/2006; · 5.08 Impact Factor