(for references see the list of publications)
1.2.1 Magnetic activity in stars and circumstellar discs We have successfully continued the investigation of the mag-netic field structure, especially the polarity of the field in spots of two active longitudes, in active late-type stars (detected earlier on by the group using surface temperature maps and named as ”active star Hale rule”). Spectroscopic
observa-tions, based on which surface temperature maps have been inverted, were started in 1991 with the high resolution spec-trograph SOFIN at the Nordic Optical Telescope, La Palma.
The time series collected since is one of the few most exten-sive and complete existing data sets to study long-term vari-ability (cycles) in active late-type stars. An important devel-opment is the magnetic inversions based on new spectropo-larimetic data with upgraded spectropolarimeter and reduc-tion software, giving the first observareduc-tional proof for the the-oretical prediction of the magnetic field polarity. The work is done in collaboration with astronomers in Uppsala, Sweden, and Potsdam, Germany, most of the collaborators originally having worked in Helsinki Observatory and/or Oulu Univer-sity. We have also continued the research on the behaviour of solar activity using sunspot data over 400 years, from the Maunder minimum to the present one. This is also gener-ally important because the solar activity has now been in very long minimum and solar irradiance to Earth’s atmospere has decreased.
Simultaneously to the observations, local and global MHD models (PENCIL-CODE, MEFISTO;Korpi,K¨apyl¨a, Lilje-str¨om, Lindborg, Snellman) have been developed and uti-lized, to be able to investigate the transformation from solar-like dynamo activity to the activity seen in the active rapid ro-tators. Numerical modeling has yielded new results in a vari-ety of systems: local turbulence models have been utilized to study the turbulent transport of angular momentum (Snellman et al. 2009, Korpi et al. 2009 in press), and numerical studies of convection have, for the first time, revealed a large-scale dynamo (K¨apyl¨a et al. 2009a,b,c). The latter project was ac-cepted to the DEISA-DECI programme (CONVDYN PId by Korpi), from which 900 000 CPU hours of computing time was granted and used during the year 2009. An international conference on the topic of Astrophysical Magnetohydrody-namics was organised by the MHD-group in Kiljava, Nurmi-jarvi, Finland, during 6.–10. of April 2009, with roughly 50 participants from 13 different countries.
1.2.2 Interstellar clouds
Molecular line and NIR study of cometary clouds.Cometary shape is common in the interstellar space. The objects range from tiny globulettes embedded in HII regions to parsec sized cometary globules and to cometary shaped star forming re-gions like Corona Australis. We are using molecular line ob-servations and NIR imaging to study the properties of these sources (size, mass, density, dynamics, star formation) to gain insight to their formation mechanism.
Even though Cometary globule 12 (CG 12) has been clas-sified as a cometary globule it is in fact a medium- and low mass star forming region 210 pc above the Galactic plane.
To complement our earlier molecular line studies (Haikala et.
al 2006 and Haikala and Olberg 2007) NIR J, H, and Ks imaging obtained with SOFI at the La Silla NTT telescope
was used to analyse the stellar content and the structure of CG 12. A color coded SOFI image of CG 12 is shown in 1.
Several new members and member candidates of the CG 12 stellar cluster were found. The new members include in par-ticular a highly embedded source with a circumstellar disk or shell. The central source of the known collimated molecu-lar outflow in CG 12 and an associated “hourglass”-shaped object due to reflected light from the source were also de-tected. HIRES-enhanced IRAS images were used together with SOFIJHKs imaging to study the two associated IRAS point sources. Two new 12µm sources coinciding with NIR excess stars were detected in the direction of IRAS 13546–
3941. The IRAS 13547–3944 emission at 12 and 25µm orig-inates in the Herbig AeBe star h4636n and the 60 and 100µm emission from an adjacent cold source. The study will appear in A&A (Haikala and Reipurth 2009, in press).
Cometary Globule 1 is the archetype cometary globule in the Gum nebula. NTT SOFI NIR Js, H, and Ks imag-ing and stellar photometry is used to analyse the structure of CG 1 and the extinction of stars in its direction (Haikala and M¨akel¨a). Preliminary results include an embedded, pre-viously unknown protostar in the globule head. The observed maximum extinction in the cloud is∼10 magnitudes in vi-sual. Like in the case of CG 12 HIRES enhanced IRAS im-ages were used together with SOFIJHKs imaging to study the associated IRAS point source, 07178-4430. This point source resolves into two separate sources. The 12 and 25µm emis-sion comes from the Herbig AeBe star NX Puppis and the 60 and 100µm emission from the adjacent, newly detected protostar.
Scattered Hαfrom interstellar clouds. Lehtinen, Ju-vela & Mattila have identified an undocumented large translu-cent cloud, detected by means of its enhanced radiation on the SHASSA (Southern H-Alpha Sky Survey Atlas) survey.
They compared the observed Hα surface brightness of the cloud with predictions of a radiative transfer model, by us-ing the WHAM (Wisconsin H-Alpha Mapper) survey as a source for the Galacticα interstellar radiation field illumi-nating the cloud. Visual extinction through the cloud is de-rived from 2MASSJ,HandKband photometry. Far-infrared ISOSS (ISO Serendipitous Survey), IRAS and DIRBE data was used to study the thermal emission of dust, and LAB (The Leiden/Argentine/Bonn Galactic HI Survey) was used to study 21 cm HI emission associated with the cloud. Radia-tive transfer calculations of the Galactic diffuse Hαradiation indicated that the surface brightness of the cloud can be ex-plained solely by radiation scattered offdust particles in the cloud. The maximum visual extinction through the cloud is about 1.4 mag. The cloud is found to be associated with 21 cm HI emission at a velocity∼ −9 km s−1. The total molecular mass of the cloud is about 310–460 solar masses. There was no sign of star formation in this cloud. The distance of the cloud is from the Hipparcos data estimated to be∼ 75 pc, making it one of the closest translucent molecular clouds.
Figure 1: Colour coded SOFI image of CG 12. TheJ,H, andKs bands are coded in blue, green and red, respectively. Square root scaling has been used to better bring out the faint surface brightness structures.
Magnetic fields in interstellar clouds.Studies were com-pleted of the polarized sub-millimeter emission from dust grains in interstellar clouds. In a magnetic field, dust grains remain aligned as long as their rotation speed is significantly larger than their thermal rotation speed. The grains are believed to be spinned up mainly by radiative torques. The efficiency of radiative torques was investigated using magnetohydrody-namic cloud simulations and detailed radiative transfer mod-elling (Pelkonen et al. 2009). Results indicate large spatial variations in the polarization efficiency. In particular, in dense clouds, the dust emission is not likely to probe magnetic fields deeper than a few magnitudes inAV.
Through Zeeman effect, magnetic fields cause splitting of some radio lines. Because the split components have opposite circular polarization, the line-of-sight component of the mag-netic field can be estimated from the Stokes I and V spectra.
With radiative transfer modelling, three-dimensional magne-tohydrodynamic simulations could be compared with existing measurements of the Zeeman effect in cloud cores (Lunttila et al. 2009). Good agreement was found between models of super-Alfv´enic turbulence, combined with self-gravity, and available observations of OH molecule lines. This suggests that the average magnetic field of molecular clouds may be low and supports the idea of turbulence as a central factor behind the formation of self-gravitating cloud cores.
1.2.3 Prestellar cores and star formation
Infrared dark clouds as precursors to high-mass stars and star clusters. The so-called infrared dark clouds (IRDCs), which are identified as extinction features against the bright mid-infrared (MIR) Galactic background radiation, are likely to represent very early stages of high-mass star/star cluster formation. In particular, some of the IRDCs may harbour high-mass starless cores (HMSCs), which provide the best targets to study the initial conditions of high-mass star forma-tion. We have mapped the IRDC G304.75+01.32 in the 870 µm dust continuum emission with the LABOCA bolometer on APEX. The obtained LABOCA map is presented in Fig. 2 (Miettinen & Harju 2009, submitted). Twelve clumps were identified from the 870µm map. Star formation has already started in the cloud as four of the clumps are associated with infrared (MSX and/or IRAS) point sources. The remaining eight clumps are MIR dark. The masses of these MIR dark clumps,∼40−200 M¯, are sufficiently large to enable high-mass star formation. Thus, some of them could be candidates of being/harbouring HMSCs. The submillimetre map of the cloud also enabled us to study the clump mass and spatial distributions. The clump masses in G304.74 were compared with the clump mass spectra from more extensive surveys of IRDCs. It was found that the clump mass distributions in G304.74 and in several other IRDCs probably represent the subsamples of the same parent distribution. Also clump sep-arations in different IRDCs are comparable to each other, and
also to the corresponding random distributions. This suggests that the fragmentation length-scale does not vary much from cloud to cloud. The results of this study support the scenario that the origin of IRDCs, and their further fragmentation into smaller subunits is caused by supersonic turbulence in accor-dance with results from giant molecular clouds.
Chemical modelling of prestellar cores. Taking advan-tage of recently published chemical rate coefficients for the H+3 +H2reacting system (Hugo et al. 2009, J. Chem. Phys., 130, 164302), we have developed chemical models to calcu-late chemical abundances in prestellar cores. Chemical evo-lution in the cores affects, among other things, the observ-able emission radiation from these objects, and thus chemical models can be used to constrain the properties of the cores by comparing model predictions with observations.
One such comparison is presented in Fig. 3. In the Fig-ure, an observation by Harju et al. (2008) of line emission produced in the H2D+ 110 - 111 transition is plotted against the model prediction of Sipil¨a et al. (2009, in press). The agreement between the observation and the model prediction is good, even though the chemical model in this case includes only the lightest elements. This result is consistent with the depletion of heavy substances toward the centers of prestellar cores, as has been widely discussed in the literature.
1.2.4 The Planck and Herschel satellite projects
The Planck and Herschel satellites were launched success-fully in May 2009. By the end of 2009, the first data were received from both satellites.
We participate in several science projects within the Planck Surveyor satellite consortium. The main emphasis is on stud-ies of dense interstellar clouds and especially their cold and compact cloud cores. The population of cold cores (Tdust <
12 K) is still poorly known. Planck is the first space borne mission that has the sensitivity and the resolution necessary for the study of the cold core population over the whole sky.
At the end of 2009, Planck has already scanned a significant fraction of the whole sky and the preliminary analysis of the observations has resulted in the detection of hundreds of new cold cores.
We are coordinating a Herschel Open Time Key Programme, where a sample of the Planck-detected cores are investigated in more detail using the Herschel PACS and SPIRE instru-ments. Herschel can observe wavelengths close to the peak of dust emission,λ ∼ 100−500µm. Compared to Planck, Herschel has much higher spatial resolution. This makes it possible to study the internal structure of the selected cores and to determine their evolutionary stages and their relation to future star formation. The key programme was awarded
∼151 hours of observing time on the Herschel satellite. The main observations are expected to start at the end of 2010.
However, a few cores were already mapped as part of the Herschel Science Demonstration Phase and the initial results
Figure 2: LABOCA map of the 870µm dust continuum emission from the IRDC G304.74. The green and black plus signs mark the positions of the IRAS and MSX point sources, respectively.
Figure 3: Model predictions for the line emission produced in the ground-state transitions of ortho-H2D+(372 GHz, top) and para-D2H+ (692 GHz, bottom) from the prestellar core Oph D as observed with APEX (Sipil¨a et al. 2009, in press).
The H2D+line is plotted against the observed profile (dotted curve, Harju et al. 2008). Both transitions are potential tools of prestellar core studies with ALMA.
were presented in a workshop in December 2009.
We participate in several other Planck science projects, including the study of nearby galaxies. We are also involved in the Herschel key programme HiGal that is going to map a large fraction of the plane of our Galaxy.
1.2.5 Extragalactic Background Light
Search for the optical Extragalactic Background Light.
Using our understanding of the light scattering in dense in-terstellar 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 photometric EBL observing program we have developed a spectroscopic analogy for it. This new tech-nique utilizes the difference between the spectra of the dif-fuse galactic scattered light (absorption line spectrum) and the EBL (pure continuum spectrum with possible discontinu-ities). For the spectroscopic observing program we (Mattila, Lehtinen, V¨ais¨anen) earlier received 20 hours observing time at ESO VLT telescope and FORS instrument. For the ESO Period 82, 18.5 hours were again allocated but only a few hours were realised in 2008/09.
The modelling of the FORS spectra requires knowledge of the spectrum of the Local Interstellar Radiation Field (ISRF).
A new population synthetic spectral model is being devel-oped along the lines of an earlier model by Mattila based on the high-resolution stellar spectrum library STELIB (Borgne et al. 2003, A&A 4002, 433) and on stellar distribution pa-rameters derived from HIPPARCOS and other recent data by Flynn et al. (MNRAS 372, 1149, 2006). An excellent fit is found between the ISRF spectrum thus derived and the observed scattered light spectrum of the dark nebula Lynds 1642, our target for the VLT FORS spectroscopy.
Far-infrared Extragalactic Background Light. Using data from the ISOPHOT instrument of the ISO satellite, we have completed a study of the extragalactic far-infrared back-ground light at 90, 150 and 180µm (Juvela, Mattila et al.
2009, the ISOPHOT EBL project). The signal represents a significant fraction of the cosmic energy output from stars that has been reprocessed by interstellar dust and is redshifted to far-infrared wavelengths. Our study is the first independent measurement of the absolute surface brightness of the cos-mic infrared background radiation (CIRB) obtained since the COBE result some ten years earlier. Our values are in agree-ment with the published COBE results, confirming the inten-sity of this extragalactic component at a level of∼1 MJy sr−1 at wavelengths∼150–180µm.
Identification of far-infrared sources at the North Galac-tic Pole.As a follow-up of the far-infrared extragalactic back-ground light (ISOPHOT EBL) project V¨ais¨anen (SALT, South Africa), Juvela, Mattila et al.(2009) have performed observa-tions of the far-infrared (FIR) sources detected as part of that project. 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 SDSS photometry, and spectroscopy where available, and present identifications of the 25 FIR sources which reach down to 150 mJy in all three ISOPHOT bands at 90, 150 and 180µm. 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 redshifts z<0.3. We also found that more than half of the counterparts have disturbed morphologies, and some 40 per cent are blends of two or more nearby star-forming galaxies.
The blended sources have an effect on the FIR source counts.
In particular, taking into account realistic confusion or blend-ing of sources, the differential FIR counts move down by a factor of 1.5 and steepen in the 100 to 400 mJy range.