(for references see the list of publications)
2.2.1 Deuterium fractionation and the degree of ionization in dense star-forming cores Most of the Galactic star formation takes place in clus-ters and smaller groups which are embedded in the dens-est parts of giant molecular clouds (GMCs). The frag-mentation of molecular clouds results in a dense struc-tures such as filaments and clumps which contain still denser cores. By studying the physical and chemical characteristics of these cores, one hopes to understand how fragmented clumps evolve and form stars. The 870 µm submillimetre dust continuum observations to-ward the Ori B9 cloud were carried out in 2007 Au-gust 4 with the 295 channel bolometer array LABOCA
Figure 1: N2H+(1−0) and N2D+(2−1) spectra toward the low-luminosity far-infrared source IRAS 05405-0117 within the clump in the central part of Ori B9.
(Large APEX Bolometer Camera) at the APEX. The N2H+(1−0) and N2D+(2−1) spectral line observa-tions toward the clump in the central part of Ori B9 have been performed with the IRAM 30 m telescope in Pico Veleta, Spain, in May 2007 (see Fig. 1). The total mass of gas and dust of the clump as derived from the dust continuum emission is ∼42 M⊙. Thus the clump has enough mass to form a small stellar group. This is also supported by the morphology of the clump, which is filamentary and fragmented into several cores. The relatively high degree of deuterium fractionation as de-rived from the N2D+ and N2H+ column density ratio, together with the physical properties of the cores within the clump indicate that they are low- to intermediate-mass star-forming cores. The ionization fraction in the cores, as derived using our previous H2D+ observations (Harju et al. 2006) together with the present observa-tions, is in the range of about ∼ 10−9 < x(e) < 10−7 and they appear to be evolving quasi-staticly through the process of ambipolar diffusion.
2.2.2 Density distribution in molecular clouds Theoretical star formation scenarios predict the radial density distribution for a molecular cloud at the initial stage of the collapse of a cloud. The form of the density distribution is linked to the rate at which a protostar
ac-cretes mass from the surrounding envelope and further to the timescale of the collapse. It is thus an essen-tial factor considering the process of star formation. We have exploited the near-infrared color excess technique to study the radial density distributions of two cloud cores: we determine the mass distribution of a core that has very recently formed a star, and a core which is re-garded to be quiescent, close to hydrostatic equilibrium and thus possibly close to the initial stage of star for-mation. This study is based on near-infrared data taken with the ISAAC instrument on ESO’s VLT (Very Large Telescope). The two cores have significantly different ra-dial density distributions; the core with star formation has a distribution well fitted with a single power-law, while the distribution of the core without star formation flattens at small radii. For the latter core, the distri-bution can be interpreted as the presence of significant additional support or very slow contraction.
2.2.3 Variations of far-infrared emissivity of dust particles
Recent observations have indicated that the far-IR emis-sivity (measured by the ratioτ(far-IR)/AV) of dust par-ticles in molecular clouds increases with decreasing tem-perature. Probable reasons for increased emissivity are coagulation of dust particles into large, fluffy aggregates and formation of ices on grain surfaces in dense regions.
We have combined ISO (Infrared Space Observatory) far-infrared observations with extinction measurements of the cloud L1642. We find that there is about a two-fold increase in emissivity when dust temperature de-creases from 19 K to 14 K. Our radiative transfer calcu-lations show that, in order to explain the observed de-crease of dust temperature towards the centre of L1642, an increase of emissivity of dust at far-IR is necessary.
This temperature decrease cannot be explained solely by the attenuation of interstellar radiation field.
2.2.4 High-latitude Hαclouds
Bright emission nebulae, or HII regions, around hot stars are readily seen in photographs. However, the all-pervasive faint Hαemission has only recently been de-tected and mapped over the whole sky. Mostly the Hα emission observed along a line of sight is produced by ionised gas in situ. There are, however, cases where all or most of the Hαradiation is due to scattering by elec-trons or dust particles which are illuminated by an Hα emitting source off the line of sight. We have shown that diffuse, translucent and dark dust clouds at high galactic latitudes are in many cases observed to have an excess of diffuse Hαsurface brightness, i.e. they are brighter than the surrounding sky. We have shown 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 Hαbackground radiation impinging on the dust clouds from all over the sky. (Mattila, Juvela and Lehtinen, 2007)
2.2.5 Scattered continuum radiation in inter-stellar and circuminter-stellar clouds and in galaxies
Near-infrared scattered light was observed towards sev-eral interstellar clouds using ESO/NTT and UKIRT tele-scopes. In Corona Australis, part of the molecular cloud filament was mapped in three near-infrared bands. In accordance with previous theoretical predictions (Juvela et al. 2006), the observed surface brightness could be explained by light scattering. The near-infrared surface brightness was found to be an accurate tracer of cloud mass distribution. Therefore, observations of scattered light could become an important new method in stud-ies of dense, qustud-iescent clouds (Juvela et al. 2008). The study resulted in the publication of an ESO press release (ESO 06/08).
Near-infrared observations and the role of dust scat-tering was investigated also in connection with exter-nal galaxies. Numerical simulations indicated large un-certainty in the mass and mass spectrum of clouds de-tected with near-infrared observations (Kainulainen et al. 2007).
A separate study was conducted on the dust enve-lope of the carbon star IRC+10216, leading to new con-straints on the properties of the dust formed in stellar envelopes (Lunttila & Juvela 2007).
2.2.6 MHD phenomena: observations and mod-elling
We have successfully continued the investigation of the magnetic field structure, especially the polarity of the field in spots of two active longitudes, in active late-type stars (detected earlier by the group using surface tem-perature maps) and named on the basis of numerical modelling as ”active star Hale rule”. Spectroscopic ob-servations were started in 1991 with the high resolution spectrograph SOFIN at the Nordic Optical Telescope, La Palma. The time series collected since is one of the few most extensive and complete existing data sets to study long-term variability (cycles) in active late-type stars.
An important recent development is the magnetic inver-sions based on new spectropolarimetric data with up-graded spectropolarimeter and reduction software, giv-ing the first observational proof for the theoretical pre-diction of magnetic field polarity.
The work is done in collaboration with astronomers in Potsdam, Germany and earlier with Uppsala, Swe-den, most of the collaborators originally having worked
in Helsinki Observatory and/or Oulu University.
Simultaneously to the observations, local and global MHD models (PENCIL-CODE, MEFISTO; Korpi, K¨apyl¨a, Lindborg) have been developed and utilized, to be able to investigate the transformation from solar-like dynamo activity to the activity seen in the active rapid rotators. This includes participation in a solar dynamo benchmark project which is likely to be helpful in the development and validation of dynamo codes (Jouve et al. in press). Local turbulence models have been uti-lized to study the turbulent transport of angular momen-tum (K¨apyl¨a & Brandenburg 2007), and the importance of magnetic helicity conservation in laboratory (Bran-denburg & K¨apyl¨a 2007) and astrophysical settings have been studied (Brandenburg et al. 2007).
2.2.7 The Planck-satellite project
We participate in several science projects within the Planck Surveyor satellite project. The main emphasis is on studies of dense and cold parts of molecular clouds.
Simulations were carried out of the polarized emission of dust grains aligned in a magnetic field. The efficiency of radiative torques was investigated using magnetohydro-dynamic cloud simulations and radiative transfer mod-elling. Predictions were made for future Planck obser-vations (Pelkonen et al. 2007). Preparations were made to study Galactic cold and compact cloud cores using Planck data. The population of cold cores (Tdust<12 K) is still poorly known and Planck will be the first space borne mission that will be sensitive to their radiation.
Methods were developed for the detection of cold cores and for the analysis of their dust emission. We partici-pate also in other Planck science projects, including one where Planck observations will be used for the study of nearby galaxies.
We coordinated a successful open time key program proposal for the Herschel satellite. The aim of that project is to use Herschel satellite for follow-up obser-vations of a number of cold cloud cores detected in the Planck survey. The higher resolution of the Herschel in-struments will be used to measure the internal structure of selected cores and to determine their relation with future star formation.
2.2.8 Extragalactic background light
Using our understanding of the light scattering in dense interstellar clouds of dust, we have been developing a method for the detection of the optical extragalactic background light. This is the so-called “shadow of a dark cloud method”. Based on our previous photomet-ric EBL observing program we have developed a spec-troscopic analogy for it. This new technique utilizes the
difference between the spectra of the diffuse galactic scat-tered light (absorption line spectrum) and the EBL (pure continuum spectrum with possible discontinuities). For the spectroscopic observing program we have received 20 hours observing time at the ESO VLT/UT4 telescope, and the reductions and analysis of these data have been performed by Mattila and Lehtinen largely during 2007.