OJ 287

Research report for 2000-2001
Research report for 2002

Recent research highlights

Polar hot spot in W Ser?

19th November 2005 · Detailed polarisation study provides intriguing evidence for a thick accretion disk around W Ser.

How far the neighbours?

14th September 2005 · Tuorlans and galaxy distance measuring methods

Little bangs on the Sun

14th September 2005 · Mini CMEs surprise astronomers

World's largest space mirror polished at Tuorla

19th April 2005 · Figuring of the Herschel telescope mirror completed

High redshift host spotted

1st March 2005 · European Southern Observatory's largest telescopes used to image distant galaxies

Venus' new "moon"

17th August 2004 · Venus has a quasi-satellite!

3C273 up close

10th August 2004 · Bright mutterings in the core of a quasar

Dust in Space

20th October 2004 · Polarised starlight up on high

The little telescope that could

5th July 2004 · Simultaneous optical and gamma ray observations

Dark energy

28th June 2004 · New cosmic force nearer than we think?

100 BL Lacs

2nd February 2004 · Galaxies show much of a muchness

Rise and rise of He

3rd March 2003 · Measuring the amount of Helium in the cosmos


Telescopes and Instrumentation

The Tuorla 1 m telescope was used for quasar monitoring on most clear nights. Nearly 1800 pictures were obtained. The 70 cm Schmidt telescope and the 60 cm reflector were used mainly for studies of variable stars.

The 70 cm Schmidt telescope was also used by Lehto and Katajainen for obtaining public-relation images of extended deepsky objects and comets.

MAGIC collaboration

The MAGIC telescope (Major Atmospheric Gamma-ray Imaging Cherenkov telescope; http://hegra1.mppmu.mpg.de/MAGICWeb/) is an atmospheric imaging Cherenkov telescope designed to detect cosmic gamma-ray photons (E = 30 GeV - 1 TeV). The 17-metre telescope is located on La Palma, Canary Islands, Spain and it is run by the MAGIC-collaboration that includes 18 (mostly European) institutes. The inauguration was held on La Palma on 10th October 2003 with Aimo Sillanpää representing Tuorla Observatory at the celebration. First light was obtained in June 2003. Since then the telescope has been in commissioning phase and has taken calibration data on the Crab nebula and also observed the blazar Markarian 421.

The main contribution of Tuorla Observatory to the MAGIC collaboration is the use of the 60 cm optical telescope on La Palma in connection with MAGIC observations. When MAGIC becomes fully operational we will be able to obtain for the first time truly simultaneous optical and gamma-ray observations. We have successfully been using the 60 cm telescope remotely from Tuorla since autumn 2003. Work on making the telescope fully automatic is in progress.

The MAGIC telescope at La Palma, which obtained "first-light" in late 2003. Tuorla is a full-member of the project, and will be providing simultaneous optical data with the Royal Swedish Academy's 60 cm telescope sited nearby.


Three-body problem

Mauri Valtonen has spent much of the year writing two textbooks: "Three-body Astrophysics" with Hannu Karttunen, and "Cosmology: Foundations and Frontiers" with Arthur Chernin and Gene Byrd (University of Alabama). Some of the research related to these books has also appeared or submitted to print. A study of the influence of the total angular momentum on the three-body break-up was completed with the St. Petersburg group (Victor Orlov and Alexei Rubinov) and Alexandre Mylläri. Some of the results were reported in an invited talk in the meeting on Order and Chaos in Stellar and Planetary Systems in St. Petersburg in August. The relevant distributions of the three-body break-up have been derived from the principle of chaoticity and have been confirmed by computer experiments. This confirms the conjecture of Henri Poincare from one hundred years ago that the three-body system is basically chaotic even though islands of order also appear.

One of the major applications of the three-body problem appears in the study of binary and triple stars, concerning their role in the evolution of star clusters. This work was reported in an invited talk in the meeting "Environment and Evolution of Binary and Multiple Stars" in Merida, Mexico, in February. The principle of chaoticity can be used to derive cross-sections in three-body scattering which then lead to evolutionary rates and properties of the binary population in star clusters.

Few-body problem

Seppo Mikkola has continued studies on the few-body problem applied mainly to the solar system. In collaboration with Wiegert, Innanen and Huang he has studied the dynamics of Pluto and the plutinos. Another application was the dynamics of selected interesting asteroids such as: the Neptune Trojan 2001 QR322 (paper MNRAS 347, 2004), a Venus quasi-satellite 2002 VE68 and an Earth quasi-satellite 2003 YN107 (papers submitted). This research was in collaboration with Brasser, Innanen, Wieger, Connors, Chodas and Huang.

Mikkola also studied spacecraft attitude dynamics (numerical methods) in collaboration with the Surrey Space Centre researchers Palmer and Hashida. New composite and energy-preserving-implicit, methods were invented.

Mikkola also gave an invited talk in JENAM20003 conference in Budapest on 'Co-orbitals of terrestrial planets'. He visited the Max Planck Institute fur Astronomy (MPIA) and the Astronomishes Recheninstitute (ARI), Heidelberg (for a week) giving several invited lectures on numerical few-body dynamics.

Extrasolar planets

Drs. Liyong Zhou, Harry Lehto and Jia-Qing Zheng in collaboration with Yi-Sui Sun from Nanjing University have carried studies on the extrasolar planetary system 55 Cancri. Three planets have been detected by other research groups in this system. The two inner planets appear to be trapped in a 3:1 mean motion resonance. By developing new theoretical and computational analysis tools Zhou et al. confirm the reality of such a resonance in this very system. The implication of this resonance to the stability of orbits of earth-like planets will be investigated in further studies.

The motion of the Venus quasi-satellite 2002 VE68 for the next 150 years. The coordinate system rotates with Venus. Orbits of Mercury, Venus and Earth are also (schematically) illustrated.

Motion of the temporary Earth quasi-satellite 2003 YN107 in geocentric coordinates. This asteroid became orbitally trapped near the Earth about 8 years ago and will stay in such an orbit for about four more years. The tiny circle represents Moon's orbit around the Earth. Larger image


Local Hubble flow

In the area of cosmology, Valtonen was involved in the study of the very local Hubble flow and its consequences to the models of the Universe. Here the collaboration is with the groups from the Special astrophysical observatory in South Russia (Igor Karachentsev and Dimitri Makarov) and from Moscow University (Valentin Dolgachev and Ludmila Domozhilova) as well as with Arthur Chernin. This work follows from an attempt to secure a European Union grant for the detection of dark energy of the Universe in local measurements. The application failed, probably because the concept of dark energy was not familiar among European astronomers at the time. Anyhow, the work went on with a smaller research team and more slowly than intended, and it has now provided the third, independent, verification of the dark energy, in addition to the American WMAP satellite data and the results of the two (Anglo-Australian and American) supernova teams. It was also demonstrated that the concept of Little Bang, an initial chaotic state of the Local group of galaxies, is quite relevant in the dark energy cosmologies. This concept was introduced by Valtonen and colleages about ten years ago.

Large scale structure of the Universe

During 2003 Pekka Heinämäki and his collaborators from Tartu Observatory cosmology group; Jaan Einasto, Enn Saar, Maret Einasto, Mirt Gramann, Gert Huts, Ivan Suhhonenko, continued their studies with large scale structure of the universe and cosmological N-body simulations.

In the recent papers (2003) they calculated and used the density field of the Las Campanas Redshift Survey (LCRS) and Sloan Digital Sky Survey (LDSS) to find clusters and superclusters of galaxies and investigate their properties. Using previous surveys and numerical N-body simulations they studied also the mass function of the loose groups of galaxies and environmental enhancement of loose groups around rich cluster of galaxies. Physical interpretation of the results found in previous papers needs theoretical studies and numerical simulations and it is planned to address these issues in more detail in forthcoming papers.

Using the MLAPM (Multi Level Adaptive Particle Mesh), development of the so called light-cone simulations was started. While recent and forthcoming observations extend deeper and deeper (e.g. SDSS, 2dF, DEEP2) forthcoming influence of the evolutionary effects are more prominent in surveys. Light cone simulations are needed to mimic such observational data. This subject is computational challenge and there were several methodological questions which have to be solved. Very few such simulations are done in cosmology before. Methodological questions related to the light-cone simulations have now been solved and calculations started.

This work complements also the Planck related work of the group. Last summer 2003 in working group 5 (Clusters distribution, Evolution, and Motion: Large-Scale Structure Simulations) meeting, the group announced that developing MLAPM (Multi Level Adaptive Particle Mesh) light-cone simulations (mock catalogs) would be one of their contributions to the Planck project.

One of the plans for the year 2003 was to have a post-doctoral fellow from the Tartu Observatory to the Tuorla Observatory. This was realised, when Ph.D. Ivan Suhhonenko started his work (in the cosmology group) in Tuorla Observatory at the beginning of November 2003.

Simulation of large scale structure in the cosmos. Credit, Pekka Heinämäki .

Active galaxies

Multifrequency studies of blazars

The blazar research group consists of Elina Lindfors, Kari Nilsson, Mikko Pasanen, Tuomas Savolainen, Aimo Sillanpää, Leo Takalo, and Kai Wiik.
The ENIGMA network
The ENIGMA network is a blazar research network funded through the European Union Training and Mobility through Research (TMR) program. The network that started its operations in November 2002 includes 8 European institutes doing blazar related research. Two network meetings were held in 2003: Maysschoss, Germany; 11-14 May and Portovenere, Italy; 11-15 October.

The first multifrequency campaigns were organized in autumn 2003 together with the WEBT collaboration ( http://www.to.astro.it/blazars/webt/). The targeted blazars were 3C 66A (with the RXTE satellite joining the campaign), AO 0235+164 (XMM satellite) and S5 0716+714 (INTEGRAL satellite). Simultaneous radio, optical and X-ray lightcurves were obtained during the campaign periods. The data are currently being assembled together and analyzed.

During these campaigns we obtained VLBA monitoring observations of all three targets and optical lightcurves using the 60 cm telescope on La Palma and the Tuorla 1 m telescope. The 60 cm telescope has the rather rare capacity to also measure the polarization of the source, which we used to monitor the polarization state of the two brighter objects (3C 66A and S5 0716+714). Preliminary lightcurves can be seen at http://users.utu.fi/kani/1m/index.html. Preliminary campaign results can be accessed from the WEBT home page.

Optical monitoring of the TeV blazars
We have continued our optical monitoring of the potential TeV blazars from the Costamante & Ghisellini A&A, 384, 56 list using the Tuorla 1m telescope and the 60 cm telescope on La Palma (see http://users.utu.fi/kani/1m/index.html for most recent lightcurves). For many of the selected targets no previous optical photometry exists. The aim is to measure their variability properties and select possible interesting targets for followup studies, possibly involving also TeV observations. We are also working on establishing calibration sequences for several of the fields.


Mauri Valtonen has studied the highly variable quasar OJ287. The currently favoured model for OJ287 is the precessing binary black hole model of Lehto and Valtonen (1996) which evolved from the binary model of Sillanpää et al. (1988). Since these models were put forward, Hudec et al. (2001) discovered an outburst of OJ287 in the historical light curve of OJ287 in 1956 which is the second or third strongest ever recorded in this quasar. Because this outburst is well off the mean 12 year cycle, it puts strong constraints on the possible models. In the framework of the precessing black hole model, it fixes the one remaining free parameter, related to the properties of the accretion disk of the primary black hole.

One of the consequences of this discovery is that the time of the next outburst becomes very well determined. It should begin on 11 March 2006, add or take a few days. This is important, and also the original motivation of this work, because several groups are interested in the study of this outburst, both from the ground and from satellites, and time allocations have to be specific.

In this connection, the setting up and functioning of the Trinidad telescope for monitoring quasars has been one of Valtonen's activities in 2003. He has spent several weeks of his work time (and even more of his free time) on the St.Augustine campus of the University of the West Indies. Even though small, the telescope has advantages in the monitoring work due to its low latitude, especially during the summer and the evening and morning twilights.

In the theoretical study of OJ287, the precession of the accretion disk was calculated. It has the same cycle as the relativistic precession of the major axis of the black hole binary. The assumption that the jet of the quasar is always perpendicular to the accretion disk leads to the precession of the jet of OJ287, and to the variation of brightness due to relativistic beaming. It was demonstrated that the observed brightess variations in OJ287 in the 60 year cycle are well explained by this idea.

The work on OJ287 is a collabration with astronomers from Czech Republic (Rene Hudec and Milan Basta), from Trinidad (Shirin Haque), from Helsinki University of Technology (Harri Teräsranta) and from Turku (Harry Lehto, Aimo Sillanpää and Esko Valtaoja). The first results were presented in the Sixth Caribbean Conference on Fluid Dynamics in Trinidad, January 2004.

The cosmic evolution of quasar host galaxies

In collaboration with R. Falomo (Padova), C. Pagani and A. Treves (Como) and R. Scarpa (ESO), Jari Kotilainen has studied the host galaxies of quasars at redshifts 1 < z < 2, using near-infrared images obtained at the ESO VLT UT1 under excellent seeing conditions (~0.4 arcsec). The sample includes radio-loud (RLQ) and radio-quiet (RQQ) quasars with similar distribution of redshift and optical luminosity. For all quasars the global properties of the host galaxy were derived. The host galaxies of both types of quasars follow the expected trend in luminosity of massive ellipticals undergoing simple passive evolution, but RLQ hosts are systematically more luminous than RQQ hosts by a factor ~2. Comparison with quasar hosts at similar and lower redshift indicates that the difference in the host luminosity between RLQs and RQQs remains the same from z = 2 to the present epoch. No significant correlation is found between the nuclear and the host luminosities. Assuming that the host luminosity is proportional to the black hole mass, as observed in nearby massive spheroids, these quasars emit at very different levels with respect to their Eddington luminosity and with the same distribution for RLQs and RQQs. Apart from the difference in luminosity, the hosts of RLQs and RQQs appear to follow the same cosmic evolution as massive inactive spheroids. The results support a view where nuclear activity can occur in all luminous ellipticals without producing a significant change in their global properties and evolution. Quasar hosts appear to be already well formed at z~2, in disagreement with models for the joint formation and evolution of galaxies and active nuclei based on the hierarchical structure formation scenario.

Black hole masses and the fundamental plane of BL Lacertae objects

J. Kotilainen, R. Falomo (Padova), N. Carangelo and A. Treves (Como) have measured the stellar velocity dispersion (sigma) from the optical spectra of the host galaxies of BL Lac objects. Together with the previously derived photometric and structural properties, these data are used to construct the fundamental plane (FP) of the BL Lac hosts. The BL Lac objects follow the same FP as low redshift radio galaxies and inactive luminous elliptical galaxies. This indicates that the photometric, structural, and kinematical properties of the host galaxies of BL Lac objects are indistinguishable from those of inactive massive elliptical galaxies. Using the correlation between black hole mass (MBH) and sigma in nearby elliptical galaxies, the masses of the central black hole are derived in BL Lac objects. These masses, in the range from 60 to 900 million solar masses, are consistent with the values derived from the bulge luminosity and appear to be linearly correlated with the mass of the galaxies.

Near-infrared spectroscopy of nearby Seyfert galaxies

J. Reunanen, J. Kotilainen and A. Prieto (Heidelberg) obtained near-infrared long-slit spectra of nearby Seyfert galaxies, both parallel and perpendicular to the ionization cone, and studied the spatial extent of the line emission, the integrated masses of excited molecular gas and the excitation mechanisms of interstellar gas. Large nuclear concentrations of molecular gas (H2) were found, regardless of the Seyfert type. The spatial extent of the H2 emission is usually larger perpendicular to the cone than parallel to it, in agreement with the unified models of AGN. The size of the nuclear H2 emission is larger than the predicted size for molecular torus (1-100 pc). Thus the emission probably arises from material surrounding the torus rather than directly from the torus. Broad Br gamma was detected in nearly half of the optically classified Seyfert 2 galaxies, including two objects with no evidence for a hidden polarized broad line region. This high detection rate stresses the importance of extinction effects as the main cause for the Seyfert dichotomy. Nuclear [Fe II] emission is generally blueshifted which, together with the high Br gamma/[Fe II] ratios, suggests shocks as the dominant excitation mechanism in Seyfert galaxies. Bright coronal emission lines [SiVI] and [Si VII] are detected in ~60 % of the galaxies. In three galaxies the coronal lines are extended only parallel to the cone. This could be explained by a strongly collimated radiation field or, most plausibly, by shock excitation due to the jet or superwind interacting with the interstellar medium.

Seyfert - starburst connection in radio continuum

The connection of circumnuclear starburst rings to Seyfert nuclei is a controversial subject. Does nuclear activity have an impact on the properties of the ring, or vice versa, what is the role of the ring in regulating or even triggering nuclear activity? Arcsecond resolution VLA radio continuum observations, obtained by J. Kotilainen and J. Reunanen in collaboration with S. Laine (Caltech), S. Ryder (AAO), R. Norris (ATNF) and R. Beck (MPIfR), show clearly the morphology of circumnuclear emission. Careful analysis of the radio continuum morphology and flux levels, together with spectral index information, is crucial for investigating the interplay (or lack thereof) between the nucleus and the circumnuclear ring. Search has been made for radio jets which could trigger star formation in the circumnuclear ring of gas, and for differences in the ring properties between Seyfert and starburst galaxies. Preliminary results suggest that there is no obvious direct connection between nuclear activity and star formation in the circumnuclear rings.

A recent optical light curve for the BL Lac object Mkn 421. Optical monitoring of the potential TeV blazars from the Costamante & Ghisellini (Astronomy and Astrophysics, 384, 56) list using the Tuorla 1m telescope and the 60 cm telescope on La Palma see http://users.utu.fi/kani/1m/index.html for most recent lightcurves). For many of the selected targets no previous optical photometry exists. Credit: Kari Nilsson.


Far-infrared galaxies in the ISOPHOT Cosmic Infrared Background Project

The ISOPHOT Cosmic Infrared Background (CIRB) project detected 55 far-infrared sources at multiple wavelengths between 90 and 180 microns. These sources produce up to 20% of the CIRB detected by COBE, and the high source counts require models with extreme evolution or unknown populations. It is thus important to learn their nature to understand the star formation history of the universe and the early build-up of galaxies. J. Kotilainen, P. Väisänen (Univ. Chile), M. Juvela, K. Mattila and J. Kahanpää (Helsinki) are conducting an optical, near-infrared and radio imaging and spectroscopy follow-up to identify these sources. Initial classification based on optical and near-infrared colours, interaction properties and photometric redshifts, confirms previous indications that a large fraction of these far-infrared sources are local star forming galaxies, while the rest are galaxy clusters, or dusty star forming galaxies or obscured AGN at higher redshifts (z = 1-2).

Distances to galaxies

Pekka Teerikorpi has continued studies on the extragalactic distance scale, the separate class of quasars as a cosmological probe, and the theory and applications of multifluid Friedmann cosmological models.

In collaboration with G. Paturel (Lyon) he has performed numerical simulations on the new extragalactic Cepheid distance bias which they discovered in 2002. The simulations show that the bias, for which the amplitude of Cepheid variations are important, behaves qualitatively and quantitatively similarly as the bias pattern in the observations. The identification of this bias may significantly influence the cosmic distance scale, increasing the distances to calibrator galaxies and decreasing the inferred value of the Hubble constant. The work on the actual effect on the distance scale is going on. A paper by P.T. on the separate class of luminous quasars in the Hubble diagram showed that the class is as well or even better visible within the current Lambda dominated cosmologies than within the previously used Einstein-de Sitter model. This study utilized the cosmological Malmquist bias approach.

In collaboration with A. Gromov and Yu. Baryshev (St.Petersburg), Teerikorpi has studied on a phenomenological level multifluid Friedmann models with different matter and dark energy compositions with and without interaction and with different equations of state, both stationary and non-stationary. A useful classification of cosmological models based on interaction and equations of state was proposed. In a paper by these authors a special case of models with interaction, coherent models, were studied. Interestingly, a model was found which has almost the same Hubble relation (luminosity distance vs. redshift) as the current standard flat model that well explains the Hubble diagram of high-redshift supernovae of type Ia.

In collaboration with Yu. Baryshev, Teerikorpi continued writing the monograph on fundamental questions of practical cosmology, planned to be completed during 2004.

Distances to galaxies in the extended local group

Rami Rekola has obtained observations of dwarf elliptical and irregular galaxies of the extended local group using the NOT. Distances to the galaxies are being determined via the surface brightness fluctuation method (with Helmut Jerjen, Mount Stromlo Observatory ). Cepheid based distances for IC 342, a large, starburst spiral galaxy, are being determined, using observations with the NOT over a long baseline (5 years). Planetary nebulae have been used to make a distance determination to NGC 253 (using imaging data from the ESO 3.6 metre).  This is part of a longer term program to assemble reliable masses and distances for the extended local group galaxies with a view to simulating their dynamics. Many of these galaxies are at distances where the effects of "dark energy" on the Hubble flow are first noticable; accurate distances to the galaxies are therefore of particular interest.

Part of the giant spiral galaxy IC 342. It lies just beyond our own Local Group of Galaxies in another group called Maffei Group or IC342/Maffei Group. The image above is a combination of images taken with BVRI filters (roughly blue, visual = green, red, and infrared) by Rami Rekola and Kari Nilsson at the Nordic Optical Telescope.

Very long baseline interferometry

In 2003, Tuorla VLBI group (Wiik, Savolainen and Valtaoja) carried out several large observing campaigns using the NRAO's Very Long Baseline Array (VLBA) - a 10-element highly efficient instrument dedicated to very long baseline interferometry.

45 hours of observing time was used for multi-frequency polarimetric monitoring of the pc-scale jet of the nearest quasar 3C 273, which was also a target for the INTEGRAL gamma-ray satellite. The data obtained with the VLBA are of excellent quality and the multi-frequency approach is providing interesting results of the spectral evolution of the jet's emission regions. From the VLBA data it is also possible to deduce limits for several physical parameters (e.g. the Lorentz factor and the Doppler factor), which will be used for the interpretation of the INTEGRAL observations.

The group also participated in two other INTEGRAL-related projects besides 3C 273. 3C 279 was observed twice with the VLBA during 2003 and one more observation will take place in early 2004. This blazar was clearly in a low state of activity during last year, but INTEGRAL still managed to obtain a detection of it. As a large multi-wavelength campaign was organized for this source, it was possible to reconstruct the spectral energy distribution of the quiet state of a blazar. Interpretation of these results will be interesting and the obtained VLBI data are utilized in a similar way as with 3C 273.

A highly active intra-day variable blazar 0716+714 went through a major outburst in late 2003 and it was observed with the INTEGRAL for 500 ksec. At the time, the source was also a target for intensive radio-optical monitoring performed with the Whole Earth Blazar Telescope (WEBT). The Tuorla VLBI group proposed target-of-opportunity observations with the VLBA and they were granted with 10 hours of observing time, which was executed immediately. Also the proposed follow-up project was approved by the VLBA scheduling committee and thus the group will continue to monitor 0716+714 in 2004.

Another source which experienced a major flare in 2003, was 0420-014. The group managed to get exploratory time from the VLBA to image the source during the outburst. The analysis of the data is in progress.

In addition to activities described above, the group also participated in two WEBT-related observing campaigns, which are still running. 72 hours of observing time was obtained from the VLBA to carry out a multi-frequency polarimetric monitoring of an intermediate BL Lac object 3C 66A together with the WEBT, the RXTE-satellite and ground based Cherenkov telescopes. A total of 135 hours of observing time was granted to a similar project targeted to a BL Lac object AO 0235+164, a source which is possibly showing a 5-year period in its optical light curve. The monitoring will continue in 2004 and it will hopefully see the predicted outburst.

The group finished the reduction of the data from its gigahertz-peaked spectrum sources project, which was done in collaboration with the Metsähovi radio observatory. The results are to published in 2004.

VLBA image of 3C454.3 at 4 cm. This source was used as a calibrator in the Tuorla-Metsähovi Gigahertz Peaked Spectrum (GPS) project. Although only 10 minutes of the granted 18 hours of total observing time was spent for this particular source, it was possible to make this rather high quality image during the preliminary inspection of the dataset. Credit: Kaj Wiik.
Dark Matter

Dark Matter as black holes

Jyrki Hänninen and Chris Flynn completed a numerical study of the orbits of stars in the disk of the Galaxy by masive black holes (dark matter) and giant molecular clouds. The work is a follow up of a study of the effect of such dark matter and clouds on stars in the Solar Neighbourhood. In the new work, the effect of these gravitational perturbers has been studied for disk stars from the inner to the outer disk, and the results compared to observations of the velocity dispersion of disk K giants over a wide range of Galactocentric radius. We conclude that black holes can be coaxed into reproducing the observed velocities of the disk giants from the inner to the outer disk; in other words they remain a possible but somewhat unlikely source of disk heating. The figure shows a patch of the Galactic disk, seen close to edge-on, and surrounded by massive balck holes.

Dark Matter as white dwarfs in a Galactic "shroud"

Part of the solution to this so-called "dark matter problem" would be that there are a lot of very dim stars out there which we have yet to detect with our telescopes. A very thick disk of stars , "shrouding" the galaxy's disk, has been proposed as a solution to the problem. 

If such a shroud of stars actually envelopes the Galaxy, then the stars must be very faint in order never to have been seen before; the best candidate for these stars are the so-called "white dwarfs", stars which have run out of fuel and are slowly cooling away to near invisibility. Whether the proposed shroud could be made of such stars has now been addressed by Janne Holopainen and Chris Flynn at Tuorla Observatory by creating a model of the distribution of the low-mass stars around the Sun, including the colours, luminosities and space motions of the stars. They compared their model to two very large surveys of the fastest moving and faintest detectible stars on the sky. The team concluded that, although a few quite interesting stars have turned up in these two surveys, practically all the observations are well understood in terms of our present knowledge of the Milky Way. Furthermore, they were able to put strong constraints on how bright the putative white dwarfs could be before significant numbers of them would have been detected in the surveys; the results indicate that the white dwarfs must be very faint indeed to have avoided detection. But there is still hope forwhite dwarfs; they need only be a bit dimmer than the limits of the existing surveys to have been missed. New large surveys are being planned and may yet find them, if they are there.

Disk surface mass density determination

The thickness of the Milky Way's disk is a balance between the total gravity of all the stars in it, and how fast they are individually moving. A given star, moving with a certain speed near the Sun, will rise upwards through the surrounding disk stars until the total gravity of all the stars below it pulls it back down again.

To measure the amount of matter above and below the Sun in the Galactic disk, Chris Flynn of Tuorla Observatory and Johan Holmberg of Lund Observatory have used data from the European Space Agency's Hipparcos satellite on so-called K giant stars. These stars are cooler but much brighter than the Sun; indeed, the Sun is expected to become a K giant itself some 5 billion years from now.

The Hipparcos satellite measures very accurately the distances and speeds of nearby K giant stars; the research team have applied these measurements to much more distant K giants directly 'above' the Sun (i.e. perpendicular to the Milky Way disk) in order to determine accurate distances to these stars too. The data they used was first collected in the mid-1980's using a 100 year old brass and clockwork 5 inch telescope on Mount Stromlo Observatory, the Oddie Telescope (sadly destroyed along with all the other telescopes in the bushfire which swept over Mount Stromlo in January 2003). It wasn't until now that the results of the Hipparcos satellite could be utilised to measure the distances to the stars with real precision.

Their new results confirmed their analysis from almost 20 years ago: the thickness of the disk is exactly what is expected if only the visible matter contributes to the Galactic potential. There is no need to invoke putative dark matter in the Galactic disk.

Disk dark matter. Distribution of red giants perpendicular to the Milky Way disk. The plot shows the number of K giant stars above the Sun seen in a survey taken with telescopes at Mount Stromlo Observatory. The curve shows the expected number of stars based on a theoretical computation using the gravitational attraction of all the known stars around the Sun; it is a very good match to the data.

White dwarfs 'with molecular spectral features'

Using the ALFOSC 'in spectropolarimetric mode' on the Nordic Optical Telescope, Svetlana Berdyugina (Astronomy Division, University of Oulu, Finland), Andrei Berdyugin and Vilppu Piirola (Tuorla Observatory) have studied a sample of very cool, helium-rich white dwarfs whose atmospheres are enriched with carbon. Optical spectra of these stars are dominated by broad bands of molecular carbon C2. One of the stars, G99-37, is known to be a unique white dwarf which in addition to the C2 bands shows the strong CH band. Previous spectropolarimetric observations obtained with very low spectral resolution revealed that the star possesses a strong magnetic field, of the order of 1 MG. The new observations with the ALFOSC confirmed the remarkable circular polarization signal in the CH band with much higher spectral resolution. In addition, the violet CN band was identified for the first time in a white dwarf. In contrast to the C2 bands and similar to the CH band, the CN band shows significant circular polarization. The discovery of the CN band in a white dwarf implies that a significant amount of nitrogen was brought to the surface from the stellar core. This may provide an estimate of the mass of a progenitor star. Also, up to now the CN molecule was not observed at magnetic field strengths of 1 MG, and this presents a serious interpretive challenge for molecular physics.

Interstellar polarization at high galactic latitudes from distant stars

In collaboration with V. Piirola and P. Teerikorpi, Berdyugin compiled a detailed map of interstellar polarization for the South Galactic Pole (b < -70 degrees). The map is based on new polarization measurements of 183 stars of spectral classes from A to K at distances up to 500 pc. These stars were observed with with the 2.6 m Nordic Optical Telescope (La Palma), the 60 cm KVA telescope (La Palma) and the 2.15 m Jorge Sahade telescope (CASLEO Observatory, El Leoncito, Argentina) in 2001-2003. We use polarization data to investigate the distribution of dust and to map the Galactic magnetic field at high southern galactic latitudes and make a comparison with the opposite northern polar zone. In general, the magnetic field is smoother in the south and aligned with the global pattern. There are no such extended dusty structures here as Markkanen's cloud in the north. Another interesting finding is the indication for larger extent of the dust layer in the South Galactic Pole direction.

Interacting binary W Serpentis

Berdyugin, Piirola and Mikkola have studied the active interacting binary W Ser. Polarimetric and photometric monitoring of the star carried out in June-July 2001 revealed phase-locked variations of polarization with the amplitude of about 0.8 % accompanied by large (more than 50 degrees) variations in polarization angle. The following observations, obtained in August 2002, revealed the noticeable changes in amplitude and shape of the variability curve. Moreover, as we found, the latest ephemeris published in literature is not valid any more. Due to very high mass exchange rate the orbital period is changing. Combining new photometric data with the data published for the last 80 years, we have derived a new improved ephemeris. In June 2003 we have conducted a polarimetric monitoring of W Ser primary eclipse on the NOT with the Turpol. We detected the rapid change of the polarization angle seen through the phase range -0.15 - 0.15. It happens due to eclipse of the accretion disk and primary star by secondary component. Detailed modelling of this eclipse will allow to estimate the size of the disk as well as the size of the components.

Monitoring of cataclysmic variables

Lehto and Katajainen have continued their monitoring campaing on cataclysmic variables (CV). They have used the Tuorla Observatory 0.7 m Schmidt telescope with a ST-8 CCD. The aim of the monitoring, which began in 2002, is to cover long term variability of magnetic cataclysmic variables (mCVs), polars and intermediate polars. The long term variations, i.e. high and low states, occur unfrequently and unpredictable. The different states are related to the thermal balance of the secondary star and the refilling of the Roche lobe, but the detailed physics behind these phenomena are still largely unknown. Long term monitoring of mCVs are needed also to measure accurately the ephemeris of the WD spin (to an accuracy of 10-9 days or better) and of the orbital period. To do this we need light curves spread over several years. About 20 polars and intermediate polars are monitored regularly.

Lehto and Katajainen also collaborate in CV studies with Dr. Andy Norton at the Open University (Milton Keynes, UK), and with Dr. P. Hakala (Observatory, University of Helsinki).

X-ray binaries

Lehto and Dr. Emilios Harlaftis, from Athens, Greece have been studying X-ray binaries. Regular monitoring of 28 X-ray binaries with the Nancay decimetric radiotelescope began in February 2003, and has continued since on a weekly basis. The analysis of the 2003 data is in progress and is carried out in collaboration with Mr. Sakari Nummila. This is now the largest database of radio variability of a sample of X-binary sources containing a black hole or a neutron star. It is by itself a very unique and useful data set and can be used to bridge the connection between radio emission and other properties of these systems, eg. type of primary, and type of variability observed in other electromagnetic bands. These observations were initiated in support of the forthcoming EVN observations which are done in collaboration with Dr. Anthonis Polatidis, Bonn. The primary aim of these studies is to understand the kick recieved by the X-ray binary during the SN I explosion of the primary component and to compare the spatial velocity distribution of X-ray binaries to X-ray pulsars.

Lehto and Harlaftis in collaboration with Drs. Pierre Colon, Eric Gerard and Jean-Michel Martin from Paris Observatory, Meudon, and Nancay Radio Observatory have studied GRS1915+105 in a large international ToO campaign. High level of variability was observed. The analysis of this data combined with other radio data from RATAN, MERLIN and Ryle telescope data is in progress.

Lehto, Katajainen in collaboration with Dr. Boris Gäsicke from Southampton, UK have been monitoring several new possible magnetic variables. Lightcurves were obtained in white light with the 70 cm Schmidt Camera of Tuorla Observatory.

K dwarfs

Kotoneva has been working in collaboration with the scientists at York University, Toronto. The main interest has concerned "Kapteyn's star". This star is one of our most interesting stellar neighbourhood, e.g. its proper motion is very large and it is one of the few stars with retrograde stellar orbit. We have observed the IR-spectrum of the star in order to compare it with the synthetic spectra (so called NextGen models). Also theoretical Galactic simulations have been run to explain reasons for its peculiar spectrum as well as its strange orbit.

In 2002 Eira Kotoneva completed a study of the metal composition of a large uniform set of K dwarf stars in the European Space Agency's Hipparcos satellite in order to make a very precise measurement to be made of the distribution of ``heavy'' elements (i.e. elements heavier than Helium) in a representative sample of stars near the Sun. This is a major constraint on models of the evolution of galaxies, and can be used inderectly to constrain the density of matter (dark or otherwise) near the Sun. The work has been extended to spectral analysis of many of the stars in a collaboration with National Astronomical Observatories of China, part of the Chinese Academy of Sciences; high resolution spectra were obtained by Kotoneva; effective temperatures, surface gravities and abundances for a wide range of elements are currently being computed. These data will probe the nature of chemical enrichment in the Galaxy using K dwarfs for the first time; accurate abundances for K dwarfs will also be very useful for constraining the production of Helium over successive stellar generations (as described below).

Production of Helium

Chris Flynn, in collaboration with Raul Jimenez of the University of Pennsylvania; James MacDonald of the University of Delaware and Brad Gibson of Swinburne University of Technology have used data from the European Space Agency  Hipparcos satellite and so-called K dwarf stars to measure the production of Helium in the cosmos. These stars are cooler and fainter than the Sun and are essentially stellar fossils. They have changed very little of their initial supply of hydrogen into helium during their long lives; in other words the hydrogen, helium and heavy elements we see in them today is they same as when they were born. We can follow the production of helium and heavy metals with a set of these stars. The Hipparcos satellite measures very accurately the real energy output of these stars. The research team have used computer calculations to predict how brightly such stars should shine depending on how much hydrogen, helium and heavier elements they contain. Measuring the amount of heavier elements using telescopes can be done very easily -- it is the amount of helium in stars which has been very difficult to measure. Now, the comparison of the model computations with the real stars reveals, indirectly, the amount of helium they contain.

The team have found that over the billions of years since the Universe was born, stars have produced just about exactly twice as much helium as everything else. Stars are primarily helium factories!   

We are now intensively following this work up at Tuorla Observatory. PhD student Luca Casagrande will obtain phtometry for a carefully selected set of K dwarfs with accurate metallicities; straightforward observations will triple the size of the basic sample and lead to an improved measure of the Helium production rate.

Light curve of the polar GG Leo (V=17-18) over one 79.7 min orbital cycle (from phase 0.5 to 1.5) observed in Tuorla 2003. Larger image  










The Goldilocks effect. K dwarf stars have been used to measure the amount of Helium which has been produced via fusion in stellar cores over cosmic time-scales.

The Sun

Solar activity

N.B. More on the latest work of the solar group can be found here.

The study of solar variations from solar minimum to maximum continued by analysis of energetic particle fluxes of 1996-2001. The study included listing of solar energetic particle events, analysis of anomalous cosmic rays, and comparison of energetic particle fluxes vs. sunspot number and number of flares. The results show that the current solar cycle (cycle23) is less active in energetic particle production than cycles 21 and 22. Also the minimum of solar energetic particle fluxes in 1996-97 was deeper and longer than the minimum of sunspot number, but the activity increased in 1998 faster. In 1999 the increase in particle fluxes stopped, but the sunspot number increased continuously. All forms of solar activity reached their maximum during the years 2000-01. Due to the improved instruments it was for the first time possible to study anomalous cosmic rays at 1 AU from solar minimum till the maximum. The studies showed a rather smooth decrease of intensities during 1996-2001.

Energetic solar particles

Solar cosmic-ray studies remain as the main field of research at the Space Research Laboratory (SRL). The ERNE (Energetic and Relativistic Nuclei and Electron) experiment on the SOHO spacecraft continued trustworthly to provide observations of solar energetic particles (SEPs) associated with solar flares and coronal mass ejections (CMEs). Within the Väisälä Institute of Space Physics and Astronomy (VISPA) co-operation with Tuorla Observatory to advance common research of current problems in astrophysics and space science has continued during 2002-2003.

Recently improved anisotropy measurements of high-energy protons with ERNE have allowed a discovery of a kind of interplanetary "highway" for solar energetic particles. The ERNE has measured the proton flux anisotropy during the 2-3 May 1998 SEP event, when SOHO was inside a magnetic cloud associated with a previous CME. During most of the first four hours of the SEP event the proton intensity parallel to the magnetic field was ~1000 times higher than in the perpendicular direction. The ERNE observations indicate that the magnetic flux-rope structure of the CME provides a "highway" for transport of solar energetic protons with a parallel mean free path of at least 10 AU. The SEP anisotropy observed in the solar wind at 1 AU may be related to processes of the solar wind acceleration, because those processes also load the solar wind with the turbulence that scatters SEPs. There is increasing evidence that acceleration of the normal solar wind is a result of the reconnection of open magnetic flux with coronal loops. If so, our observations may indicate that the closed flux of the magnetic rope has experienced much fewer reconnections than the open flux of normal solar wind, and for this reason there are fewer small-scale irregularities within CMEs from which to scatter high-energy protons.

SEP observations of the ERNE instrument enable measurements of the isotope 3He in the high-energy range >15 MeV/nucleon, with a good statistical resolution. We have surveyed the ERNE observations for the period from 8 February 1999 to 7 December 2000. A histogram of the daily 3He/4He abundance ratio revealed a common overabundance of 3He. We consider the 3He overabundance as a signature of impulsive processes, which seem unavoidable during the development of the SEP-productive solar eruptions comprising CMEs and flares. The ERNE registered also less frequent 3He-rich events with super high enhancements of 3He/4He. These high-energy 3He-rich events make up a new kind of hybrid events, possessing the impulsive-type composition and the gradual-type time-profiles. This group of solar particle events has not been identified in earlier observations. We have developed the first theoretical model of interplanetary reacceleration of 3He that explains main properties of the new group of solar particle events. Our numerical simulations suggest that appearance of 3He in the unusually high energy range can be caused by a reacceleration of ~1 MeV solar ions in oblique shocks or compressions driven by not very fast CMEs associated with those events.

The study of solar variations from solar minimum to maximum continued by analysis of energetic particle fluxes of 1996-2000. The study included listing of solar energetic particle events, analysis of anomalous cosmic rays, and comparison of energetic particle fluxes vs. sunspot number and number of flares. The results show that the minimum of solar energetic particle fluxes in 1996-97 was deeper and longer than the minimum of sunspot number, but the activity increased in 1998 faster. Also in 1999 the increase in particle fluxes stopped but continued in sunspot number.

Theoretical research at SRL included the experiment-oriented modelling of the SEP acceleration in solar corona and subsequent propagation in the interplanetary medium to 1 AU. We have performed the first modelling of SEP events inside corotating compression regions (CIRs). A trap-like structure of the interplanetary magnetic field modifies the SEP intensity-time profiles, energy spectra, and anisotropy. The numerical model forms a basis on which to interpret SEP observations made by present and future spacecrafts at the longitude-dependent speed of solar wind. The modelling results are similar to the patterns observed with the ERNE in August 1996. In the high-energy proton anisotropy data, we have revealed a signature of the CIR-associated magnetic mirror, which is already formed at 1 AU and can locally accelerate low energy ions typically observed inside CIRs, in contrast to the previously assumed acceleration exclusively at > 2 AU from the Sun.

The energetic particle observations can give valuable constraints on the models of coronal heating and acceleration of solar wind by plasma waves. This is because precisely the same waves that heat and accelerate the solar wind plasma, also influence the propagation of energetic particles through the corona and interplanetary medium. The group has initiated separate studies on solar wind heating in parallel with the energetic particle studies. On the other hand, the modelling of the cyclotron wave heating and acceleration of the solar wind allows to compute the mean free path profiles of solar energetic particles, which can be used for modelling the diffusive shock acceleration near the Sun. The first theoretical results indicate, however, that more efforts are needed to bring consistency between the SEP observations and the models of solar wind. For this purpose, the SRL group turned its attention to turbulent cascading of the wave energy, which has such capabilities. It was found that the interplanetary transport could be brought closer to the observed one, while the acceleration would still be possible in the corona. Currently, a more consistent description of the cascade is under development. These studies have been conducted in co-operation with Ruhr-Universität Bochum, Germany, under the Academy of Finland and Deutscher Akademischer Austausch Dienst (DAAD) -funded project "Collective Processes in Astrophysical Plasmas: Waves, Heating, and Accelerated Particles".

The SRL participated in the Space Weather for Antares Program (SWAP), funded by the ANTARES programme of the Academy of Finland. The goal of the program was to improve the understanding of space weather effects and their predictability. SRL participated in the research by studying the energetic particle production and transport related to the potentially geoeffective CMEs, using both observations from ERNE and other space-borne instruments, and theoretical considerations.

The primary goal was to seek connection between the strength of the potentially resulting geomagnetic storm, and the energetic particle signatures of the solar-terrestrial events, those being SEPs, accelerated at the Sun, and the energetic storm particles (ESPs), accelerated locally at the CME-driven shock front. It was found that the time-difference of the onsets of these two features, representative of the CME transit time, correlates well with the storm strength. As the ESP onset occurs typically around 5 hours before the shock arrival to the observing spacecraft, the ESP can be used as an early warning mechanism of a geoeffective event.

The research was continued with studies of the ESP events by comparing the properties of the ESP time profiles to the theoretical predictions, in order to obtain further information of the approaching CME. In particular, it was of interest to see whether the state of the ambient background plasma, the solar wind, could be used with the ESP observations in estimating the CME properties. The preliminary results show correlation between the storm strength and the deviation of the observed properties from a simple theoretical model. The refinement of the observations and the theoretical considerations is underway.

The work with building the Alpha Magnetic Spectrometer (AMS) phase II detector continued at the Space Research Laboratory. Since the AMS-I test flight in 1998, the main emphasis at SRL has been the co-ordination of the Finnish industry activities for AMS-II construction. The flight design of AMS-II phase detector was fixed during 2003 and the detector is planned to have a three-year flight on International Space Station starting on late 2005.

Collective processes in astrophysical plasmas

The "Collective Processes in Astrophysical Plasmas: Waves, Heating and Accelerated Particles" (COPAP) project continued for the second year in 2003. The project is a collaboration between researchers in VISPA (R. Vainio, T. Laitinen, J. Virtanen, and E. Valtaoja) and Ruhr-Universität Bochum, Germany, and it is aimed at the modelling of the solar wind and of particle acceleration at the Sun, and transferring this knowledge to the modelling of relativistic jets.

Vainio, Laitinen and Fichtner (2003) studied wave-wave interactions in the solar wind. They developed a simple analytical model that describes the erosion of the wave spectrum as a result of these interactions during the wave propagation outwards from the Sun. The model was shown to have potential use in the modelling of coronal heating and solar wind acceleration. In addition, Laitinen and Vainio (2003) applied the model to calculate the mean free path of solar energetic particles from the solar corona out to the interplanetary medium, and applied this mean free path to the modelling of particle acceleration in a coronal shock wave. They demonstrated that these scattering conditions yield efficient particle acceleration at shocks propagating quasi-perpendicular to the mean field.

Vainio, Virtanen and Schlickeiser (2003) studied the transmission of Alfven waves through relativistic shock fronts, and demonstrated that this process can lead to extremely efficient acceleration of particles in relativistic jets: electron spectral indices close to unity, corresponding to flat synchrotron spectra can be obtained at jets with large Alfven speeds and magnetic fields nearly aligned with the shock normal upstream of the shock front (in shock frame). This result may allow us explain, e.g., the emission from flat-spectrum radio sources as synchrotron emission of shock accelerated electrons.

Solar eruptions

Solar flare and coronal mass ejection studies were continued in collaboration with the Paris Observatory in Meudon, France (S. Pohjolainen and N. Lehtinen at VISPA, N. Vilmer, L. van Driel-Gesztelyi and P. Demoulin at LESIA) and several other institutes that provide solar eruption data or take part in the analyses. The funding agencies included Väisälä Foundation, CIMO, and EGIDE (France). J.I. Khan took part in the project during his visiting Academy Fellow post in 2002-2003 at VISPA. The project aims at understanding eruption mechanisms, which can be analysed in detail using multi-wavelength flux and imaging data especially in radio, EUV, H-alpha, and X-rays.

Enhanced temperature regions

Alexandr Riehokainen in collaboration with Esko Valtaoja and Silja Pohjolainen made a comparison between the CaII(k3), H(alpha), SOHO/MDI and radio enhanced temperature regions of the Sun. It was found that the radio maximum coincides either with the brightest CaII(k3)/H(alpha) and strongest magnetic field structures within the ETR area, or with a density enhancement of the less bright CaII (k3)/H(alpha) and less strong magnetic field structures. Thus it was shown that ETRs are connected with the chromospheres structures. Role of the coronal hole for ETRs existence is still unknown.

Some session of solar radio observations were carried out on the Metsähovi radio telescope at 37 GHz during July - October 2003. Using data obtained from these observations it is possible to study some important characteristics of the weak radio enhanced temperature regions such as lifetime, brightness and flux variations. Another goal of this study is investigating of the solar coronal holes at millimetre radio waves.

Solar oscillations

In November 2003 a new study devoted to the solar oscillations was started. The first result of the group (article in preparation) showed that the power of the 3 minutes oscillations variates with solar cycle. This result was obtained using Nobeyama radio heliograph data from 1992 - 2002.

Development of the directional proton intensity in the energy range 17-22 MeV observed with ERNE/HED in successive 20-minute subintervals on 2 May 1998. The ERNE instrument axis is in a frame centre. The Sun is shown as a white circle with dot. WIND/MFI magnetic field direction is indicated by a white crossed red circle. Directions perpendicular to the magnetic field are mapped as gray curve. Larger image

Scatter plot of 3He intensity vs. 4He intensity on 3He event days (in the energy channel 15-30 MeV/n) and the corresponding day-number distribution over the abundance ratio 3He/4He. The vertical line in the left panel represents the minimum limit above which all 4He enhancements are associated with 3He. The fitted curve in the right panel reveals a main peak and a high-abundance tail in 3He/4He. Larger image

Yohkoh soft X-ray images of a region that produced repeated flaring in radio and X-rays. The analysis of EUV, H-alpha, radio, and X-ray images together with magnetic field information indicated that the flaring was due to loop-loop interactions. Credit : S. Pohjolainen. Larger image


The first Finnish astrobiology meeting "Astrobiology in Finland" was organized by Harry Lehto and Kirsi Lehto (Biology and Plantphysiology Laboratory, Department of Biology, University of Turku). About 15 invited scientists and 55 others scientists and students attended the two day meeting held in May 2003 at University of Turku. This was also the founding meeting of the Finnish Astrobiology Network (FAN) set up to promote collaboration between scientists involved in astrobiology. Students are also encouraged to join FAN. Seven FAN newsletters were issued during the year. In November 2003, Finland joined the European Astrobiology Network Association (EANA) with FAN representing Finnish astrobiologists and Harry Lehto as the national representative in EANA.

Theses obtained in 2003

Doctoral dissertations

Alexandr Riehokainen: Weak Radio Enhanced Temperature Regions at High and Low Solar Latitudes

Viatcheslav Koblik: Solar Sail Motion in near-sun Regions

Timo Laitinen: Energetic Particle Acceleration and Transport in Wave-Heated Solar Wind

Ramon Brasser: Aspects of Solar System and Three-body Dynamics

Tero Sahla: Analysis of Directional Distributions of Solar Energetic Particles Detected by SOHO/ERNE

Master's theses

Mikko Ranta