K. Mattila

University of Helsinki, Helsinki, Southern Finland Province, Finland

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Publications (173)334.75 Total impact

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    K. Lehtinen · K. Mattila
    [Show abstract] [Hide abstract] 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.
    Preview · Article · Nov 2012 · Astronomy and Astrophysics
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    M. G. Rawlings · M. Juvela · K. Lehtinen · K. Mattila · D. Lemke
    [Show abstract] [Hide abstract] 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.
    Preview · Article · Oct 2012 · Monthly Notices of the Royal Astronomical Society
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    [Show abstract] [Hide abstract] 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. Unit: We will use in this paper the abbreviation 1 cgs = 10−9erg s−1cm−2sr−1Å−1
    Preview · Article · Nov 2011 · Proceedings of the International Astronomical Union
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    K. Lehtinen · M. Juvela · K Mattila
    [Show abstract] [Hide abstract] 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.
    Preview · Article · May 2010 · Astronomy and Astrophysics
  • [Show abstract] [Hide abstract] 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).
    No preview · Article · Mar 2010
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    [Show abstract] [Hide abstract] 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.
    Full-text · Article · Jan 2010 · Monthly Notices of the Royal Astronomical Society
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    [Show abstract] [Hide abstract] ABSTRACT: Commission 21 consists of IAU members and consultants with expertise and interest in the study of the light of the night sky and its various diffuse components, at all accessible electromagnetic frequencies. In cosmic distance scales, the subjects of Commission 21 range from airglow and tropospheric scattering in Earth's atmosphere, through zodiacal light in the solar system, including thermal emission from interplanetary dust, integrated starlight in the Milky Way galaxy, diffuse galactic light due to dust scattering in the galactic diffuse interstellar medium, thermal emissions from interstellar dust and free free emission from ionized interstellar gas, to various diffuse extragalactic background sources, including the cosmologically important cosmic microwave background (CMB). Observations of the diffuse night sky brightness at any frequency typically include signals from several of these sources, and it has been the historic mandate of Commission 21 to foster the necessary collaboration of experts from the different astronomical sub-disciplines involved.
    Full-text · Article · Dec 2009 · Proceedings of the International Astronomical Union
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    K Mattila · R Renkonen
    [Show abstract] [Hide abstract] ABSTRACT: As birch pollen allergen enters epithelium of allergic patients via lipid rafts and caveola we began to analyse its putative amphiphilic and lipid ligands on atomic level using molecular modelling and computational ligand docking. We carry out 3D modelling docking with both experimentally verified Bet v 1 ligands as well as larger lipid molecules for which experimental affinity studies were not available. The results suggest that the hydrophobic cavity of Bet v 1 has different binding sites for different ligands and groups of ligand type-specific amino acids can be defined. Bet v 1 proteins may also be able to bind and transport more complex amphiphilic molecules like ceramides and sphingomyelins known to be enriched on caveolae/lipid rafts. Furthermore, the suggested binding mode, where the hydrophobic tail groups of lipids locate inside Bet v 1, while the polar head group may remain solvent accessible, would allow Bet v 1 to bind glycolipids, e.g. gangliosides, also rich on caveolae/lipid rafts. Taken together, this in silico work suggests that Bet v 1 bind to amphiphilic and lipid ligands present on the caveolae/lipid rafts and thus could provide a molecular mechanism for the pollen entry to epithelial tissue of allergic patients.
    Preview · Article · Sep 2009 · Scandinavian Journal of Immunology
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    M. Juvela · K Mattila · D. Lemke · U. Klaas · C. Leinert · Cs. Kiss
    [Show abstract] [Hide abstract] 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.
    Full-text · Article · May 2009 · Astronomy and Astrophysics
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    [Show abstract] [Hide abstract] ABSTRACT: (Brief Summary) What is the total radiative content of the Universe since the epoch of recombination? The extragalactic background light (EBL) spectrum captures the redshifted energy released from the first stellar objects, protogalaxies, and galaxies throughout cosmic history. Yet, we have not determined the brightness of the extragalactic sky from UV/optical to far-infrared wavelengths with sufficient accuracy to establish the radiative content of the Universe to better than an order of magnitude. Among many science topics, an accurate measurement of the EBL spectrum from optical to far-IR wavelengths, will address: What is the total energy released by stellar nucleosynthesis over cosmic history? Was significant energy released by non-stellar processes? Is there a diffuse component to the EBL anywhere from optical to sub-millimeter? When did first stars appear and how luminous was the reionization epoch? Absolute optical to mid-IR EBL spectrum to an astrophysically interesting accuracy can be established by wide field imagingat a distance of 5 AU or above the ecliptic plane where the zodiacal foreground is reduced by more than two orders of magnitude.
    Full-text · Article · Mar 2009
  • V.-M. Pelkonen · M. Juvela · P. Padoan · K. Mattila
    [Show abstract] [Hide abstract] 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.
    No preview · Article · Jan 2009
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    K. Mattila · M. Juvela · and K. Lehtinen
    [Show abstract] [Hide abstract] 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.
    Preview · Article · Dec 2008 · The Astrophysical Journal
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    K. Mattila
    [Show abstract] [Hide abstract] 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.
    Preview · Article · Dec 2008 · The Astrophysical Journal
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    [Show abstract] [Hide abstract] 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
    Full-text · Article · Feb 2008 · Astronomy and Astrophysics
  • Mika Juvela · Kalevi Mattila · Dietrich Lemke
    [Show abstract] [Hide abstract] 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%.
    No preview · Chapter · Jan 2008
  • [Show abstract] [Hide abstract] 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.
    No preview · Chapter · Jan 2008
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    M. Juvela · V. -M. Pelkonen · P. Padoan · K Mattila
    [Show abstract] [Hide abstract] 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
    Preview · Article · Aug 2007 · Astronomy and Astrophysics
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    K. Lehtinen · M. Juvela · K. Mattila · D. Lemke · D. Russeil
    [Show abstract] [Hide abstract] 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
    Preview · Article · May 2007 · Astronomy and Astrophysics
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    [Show abstract] [Hide abstract] 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.
    Full-text · Article · Nov 2006
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    K Mattila · M. Juvela · K. Lehtinen
    [Show abstract] [Hide abstract] 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.
    Preview · Article · Nov 2006

Publication Stats

2k Citations
334.75 Total Impact Points


  • 1970-2011
    • University of Helsinki
      • Department of Physics
      Helsinki, Southern Finland Province, Finland
  • 1998-2002
    • Max Planck Institute for Astronomy
      Heidelburg, Baden-Württemberg, Germany
  • 1987-1995
    • Ruhr-Universität Bochum
      Bochum, North Rhine-Westphalia, Germany