Foreword
This year was the 50th anniversary year for Tuorla Observatory.
In 1952 Academician Yrjö Väisälä moved the
Turku University astronomical observatory from Iso-Heikkilä to
Tuorla. The observatory had operated at Iso-Heikkilä for
30 years, but the town had grown around it, so it was
not possible to observe there any more. At Tuorla the skies were
still dark, even though it is only 15 km from Turku.
The Väisälä Institute for Space Physics and Astronomy (VISPA)
was formed at the University of Turku in 2001, by joining the Space
Research Laboratory (SRL) in the Department of Physics and Tuorla
Obervatory. The two research units forming VISPA retained their previous
positions in the university administration, Tuorla as an independent
research institute, and SRL as one of the six laboratories of the
Department of Physics.
To celebrate the 50th anniversary the observatory organized an
international meeting ``High Energy Blazar Astronomy'' at Tuorla in June
17-21. The meeting brought together 70 astronomers around the world
to discuss the current status of blazar research. Emphasis in this
meeting was on the highest energies.
A lot of publicity was received by Esko Valtaoja, whose book
Kotona maailmankaikkeudessa ( At home in the universe, Ursa
2001) won the prestigious Finlandia award for nonfiction books. For a
while the book, discussing the possibility of life in the universe in
a witty style, was among the best-selling nonfiction books.
\pict{m109.ps}
The barred spiral galaxy Messier 109.
The image was taken in Tuorla with the Schmidt telescope on Dec 30, 2002.
(Katajainen and Lehto)
The 70 cm Schmidt-Väisälä telescope with a large field of view
has been used by Harry Lehto and Seppo Katajainen to take
public-relation CCD images of comets, asteroids and various nebulae,
as well as for scientific research.
\pict{comjuels.ps}
Comet Juels-Holvorcem, photographed in Tuorla with the Schmidt
telescope on Feb 13, 2003. (Lehto and Katajainen)}
Research activities
Telescopes and instrumentation
The MAGIC telescope.
In May 2002 Tuorla Observatory joined the MAGIC-telescope (Major
Atmospheric Gamma-ray Imaging Cherenkov telescope)
% http://hegra1.mppmu.mpg.de/MAGICWeb/)
collaboration as a full member. The MAGIC collaboration includes 14
mostly European institutes who are constructing a 17 meter
Cherenkov-telescope on La Palma, Canary Islands, Spain. First light
is expected in summer/fall 2003. This telescope will operate also in the
energy regime from 30 to 300 GeV, which has never before been
explored. Because of this new energy range and its much better
sensitivity compared with other Cherenkov telescopes, one expects MAGIC
to detect and observe a large number of new objects. So far
only 6 blazars have been detected with energies above 500 GeV.
The main contribution of Tuorla Observatory
to the collaboration is the use of the
60 cm optical KVA telescope on La Palma in connection with MAGIC
observations. This will allow simultaneous optical and gamma-ray
observations.
This collaboration organizes frequent meetings, last one was
held in W\"urzburg, Germany. Students E. Lindfors and M. Pasanen
together with researchers A. Sillanpää and L. Takalo
attended the meeting from Tuorla. Discussions during the meeting included
also preliminary observing proposals for MAGIC.
The SATU telescope.
M. Valtonen has spent much of the year at the St.Augustine-Tuorla
telescope (SATU) in Trinidad, in helping to get the telescope fully
operational, with assistance from H. Lehto. They have collaborated
with S. Haque-Copilah and other staff members of the Physics
Department of the University of the West Indies. The telescope is
meant for monitoring blazars and cataclysmic variables, especially in
summer time and when the object is close to the Sun in the sky. The
geographical latitude of the observatory (11 degrees N) allows for a
year around coverage in the monitoring programs, and minimises the
loss of data thanks to the short morning and evening twilight
periods. This is especially important during the upcoming campaign of
the blazar OJ287. OJ287 is expected to be in outburst from May 15 to
July 1 in 2006 and again from Sept 3 to Oct 15 in 2007. These are
difficult periods to cover from more northern observatories since the
Sun passes close to OJ287 in the sky in early August.
Dynamics
Chaos.
Violent relaxation induced by dynamical chaos in gravitating systems
is proposed by J.-Q.Zheng, M.Valtonen, A. Chernin, S.Wiren and L.Ossipkov
(St.Petersburg). The basic physics of violent relaxation, which is a nonlinear
collective process in many-body gravitating systems, is treated in terms of
few-body chaos which is due to the excitation of a few
high-amplitude collective modes that involve a considerable portion of the
mass of the system. Dynamical chaos can induce and drive most effectively
collective relaxation processes that lead eventually from the initial
Poincar\'e type chaos to the final Maxwell-Boltzmann chaos, in astronomical
gravitating systems like globular clusters, galaxies and galaxy clusters.
Resonances and fractality in three-body chaotic dynamics are
investigated by H. Lehto, P. Heinämäki, M. Valtonen, and A. Chernin
with the use of homology mapping. A general Newtonian three body
problem is calculated to follow the evolution of about 1 700 000 bound
three body systems which cover all the possible states where the
objects are initially at rest and have no angular momentum. The decay
time scales of the triple systems are determined and it is demonstrated
that the distribution of this parameter is fractal in appearance, in
homology map. The overall pattern is dominated by resonances.
The Contopoulos paradox is studied by A.Chernin, M.Valtonen, P.
Heinämäki and H. Lehto with the focus on the temporal
structure of evolving chaos in three-body dynamics. The fact that
the Lyapunov Characteristic Number, which is the major
quantitative measure of dynamical chaos, may be exactly zero for
some clear examples of chaotic behaviour is argued to point out
generic limits of chaos in a class of physical and astronomical
systems.
Regions of stable motions are analyzed around a periodic
Eight-like orbit in the general three-body problem by V.Orlov,
A.Rubinov (St.Petersburg) and A.Chernin. The fractal structure of
the regions is recognized in three-dimensional scans, and the
fractal dimension is estimated to be between 2 and 3.
Three-body problem.
M. Valtonen and H. Karttunen have worked on a text book
"Three-body Astrophysics" which is nearly completed. It gives the
basic theories of the General Three-body problem, using both
statistical and perturbation approaches at a level which is aimed at
advanced undergraduate students. It also has a thorough introduction
to classical celestial mechanics, and a discussion of applications to
the scattering problems in the Solar System and in stellar systems.
It is hoped that the book will be in print in 2004.
In connection with the above work, M. Valtonen has derived several new
results in the General Three-body problem. The parabolic passage of a
third body past a circular binary was studied by using
millions of numerical orbits as well as a second order perturbation
theory. The orbits were calculated by the highly efficient
Aarseth/Mikkola chain regularisation code which solves one orbit per
second in a personal computer. The solution is given in an analytic
form as a function of the masses, the relative orbit inclination, the
pericentre distance of the unperturbed orbit, and the phase angle of
the binary at the pericentre time. This result may be applied, among
other things, to the study of the long term stability of triple stars.
Together with A. Mylläri (Tuorla), V. Orlov and Rubinov (St.\
Petersburg State University), M. Valtonen has studied the statistical
outcomes of three-body experiments in initially strongly bound
systems. A modified Monaghan/Heggie theory has been compared with
100 000 numerically calculated orbits. Special emphasis was given to
escape directions and to the spin relations after the system broke up
into a binary and a third escaping body. The previously known strong
concentration of escapers in the fundamental plane was confirmed, and
an analytic expression for the distribution as a function of the
relative total angular momentum was derived. This is relevant, for
example, to black holes escaping from galactic nuclei via the
slingshot mechanism which is generally thought to be an important
consequence of multiple mergers of galaxies.
In collaboration with L.-Y. Zhou, Y.-S. Sun, J.-L. Zhou (Nanjing
University) and J.-Q. Zheng (Tuorla), M. Valtonen has studied what
effect planet migration has on Kuiper belt objects. The new feature of
this study is the stochastic way in which the migration should
happen. Numerical integrations of small body orbits show that
stochasticity has a major effect on the resulting structure of the
Kuiper belt. Stochastic effects excite the orbital eccentricities and
inclinations in the non-resonant regions. They lead to a good match of
orbital distributions in the Kuiper belt, and possibly explain the
sources of the classical and scattered Kuiper belt objects.
The scattering theory in the General three-body problem has been
applied to the evolution of the population of stellar binaries in star
clusters and in the general Galactic field. It has been known since
1924 that the distribution of binary semimajor-axes, or alternatively,
of their periods is flat in a logarithmic scale over the range of six
orders of magnitude. This rather surprising result, known as öpik's
law after its discoverer or as scale free property of binary periods,
has been without a generally accepted explanation. M. Valtonen has shown
that Heggie's hardening law for binaries in clusters together with a
distribution of observed star cluster ages leads quite naturally to
the öpik's law of Galactic binaries. Some initial form of scale free
distribution may also be justified among cluster binaries, using the
statistical three-body theory, even though it should be applicable
only over a more limited range of periods.
In collaboration with S. Laine (Hubble Space Telescope Institute)
and J.-Q. Zheng (Tuorla), M. Valtonen has studied the dynamical
structure of the Coma cluster of galaxies under various assumptions of
its mass distribution. The starting point of these models is the
double gravitational well (massive binary galaxy) at the
cluster centre. Such a model is strongly supported by recent X-ray
maps of the cluster centre as well as previous studies of number density
and radial velocity distributions around the two dominant cluster
members. The effect of the binary on the rest of the cluster
population depends on the length of time of the three-body action but
generally it causes some of the cluster members to escape. If we carry
out mass estimates of the cluster by standard methods and are unaware
of this, the mass estimates become too high by as much as a factor of
two. This has significance in the evaluation of the baryonic mass of
the Universe since the Coma cluster is one of the best studied and most
quoted examples of clusters with a large amount of dark matter.
Few-body problem.
S. Mikkola has continued development of numerical integration
methods for the few-body problem and artificial satellite motion.
This work has been conducted in collaboration with P. Wiegert
(Canada), P. Palmer (UK), S. Aarseth (UK) and
K. Innanen (Canada).
As a participant in an international team, Mikkola has investigated
the motion of interesting asteroids, such as 2002 AA29, which moves
in a very tight horseshoe orbit co-orbiting with the Earth.
Mikkola has supervised his graduate student R. Brasser in studies
of various aspects of the Solar System and three-body dynamics.
Among other things, the role of secular resonances in the motions
of asteroids, co-orbital with the planets, has been investigated
both numerically and theoretically.
Solar sail orbital dynamics.
V. Koblik has continued the study of solar sails.
In previous studies, the numerical simulations were used to
examine the flight duration of some selected sail missions and to
investigate the evolution of the osculating elliptical orbits. A
point-like solar radiation pressure force model has been assumed
throughout and sail thermal estimations were applied in their simplest
form when the sail is taken as an ideal mirror. Both the planar
(ecliptic) and the three-dimensional transfer cases were examined with
an upper limit on the admissible sail temperature being considered as
the basic restriction. The ``instantaneously'' local-optimal control
law of the sail orientation angle was chosen in such a way that the
rate of decrease of the orbital focal parameter (semi-latus rectum)
reached its maximal value. In the three-dimensional case, the
requirement of maximization of the orbital plane rotation rate was
added to the model. The numerical results confirmed the great
potential and unique performances of a solar sail as a space thruster,
especially in near-Sun regions.
In 2002 the investigation, focused on planar (ecliptic) solar sailing
toward the Sun, was studied in combination with gravity-assisted (GA)
flyby manoeuvres at the Earth, Venus, and Mercury in sequence
(multiplanet flybys). The orbit dynamics for these cases were
simulated under the assumption of a strong thermal restriction on the
sail surface temperature. Atmospheric correction was taken into
account. The numerical results, obtained in this study, confirmed
that only GA flybys of Venus change the orbit sufficiently, because
Mercury is too small. GA usually increases the orbital eccentricity
and may be used for transfers to destination orbits with large
eccentricity.
The proposed studies have a considerable importance in both
theoretical and practical perspectives. From the theoretical
perspective, the present project aims at investigating a new class of
trajectories for a space probe with an ecological pure solar sail
thrust with different control laws, at exploring their principal
properties and, in general, at expanding our knowledge about the
application of a solar sail as an unique thrust for a space probe.
The practical aspect of the project involves formulation of the
specific recommendations for possible use of the solar sail thrust for
reaching various types of orbits (trajectories) and for avoiding
asteroid hazard for the Earth.
Cosmology
A framework is suggested by A.Chernin in which the energy
integrals of the Friedmann cosmology are identified as genuine
time-independent physical characteristics for both vacuum and
non-vacuum forms of cosmic energy. The integrals are found to be
numerically coincident within two orders of magnitude. It is
assumed that this coincidence reveals a symmetry that relates
vacuum to non-vacuum forms of cosmic energy at fundamental level.
A simple kinematic model of cosmological freeze out is used to
examine how - at least, in principle - the electroweak scale
physics might explain the nature of the symmetry between vacuum
and non-vacuum cosmic energies and determine the value of the
energy integrals in terms of the fundamental energy scales. It is
demonstrated that the symmetry relation between vacuum and matter
is basically behind the observed phenomenon of parabolic or near
parabolic cosmological expansion with the flat or near flat
three-dimensional space. A concept of large macroscopic extra
dimensions is also used to show that, in the case of two extra
dimensions, the Friedmann integrals are expressed in terms of the
fundamental electroweak energy M* ~ 1 TeV and the size
R* ~ 10-3 cm of extra dimensions.
The correct value of the
cosmic vacuum density proves to be ~ R*-4.
A.Chernin, S.Starikova and D.Nagirner (St.Petersburg) found
a new exact explicit analytical solution for the growth rate
of cosmological perturbations against the cosmic vacuum background.
In terms of the Newtonian mechanics, the solution describes the
evolution of weak linear protogalactic perturbations of arbitrary
shape and strong nonlinear perturbations in the Zeldovich flow of
plane symmetry. Perturbations develop
under the action of gravitational instability during the matter
domination epoch, and the instability is terminated when
cosmic vacuum with its antigravity starts to dominate.
A.Chernin, Yu.Baryshev (St.Petersburg) and P.Teerikorpi addressed the
question: Why is the Hubble flow so quiet? Recent original
observations in the Local Volume are used together with other data to
estimate the velocity dispersion and matter nonuniformity in the
Hubble local flow. A dynamical role of cosmic vacuum is demonstrated
to be dominant at distances 2-10 Mpc.
A. Chernin, I. Karachentsev (SAO), M. Valtonen, V. Dolgachev and
L. Domozhilova (Moscow) discussed a newly discovered phenomenon of
the Hubble very local (< 3 Mpc) flow on the basis of original
data obtained with the Hubble Space Telescope. A set of computer
simulations is performed to trace the trajectories of the flow
galaxies back in time to the epoch of the formation of the Local
Group. It is found that the `initial conditions' of the flow were
drastically different from the linear velocity-distance relation
and can adequately be treated within the conjecture of The Little
Bang developed earlier by M.Valtonen et al. The simulations enable
to recognize the major trend of the flow evolution and to identify
the anti-gravity of cosmic vacuum as its driving force.
A.Chernin, D.Santiago and A.Silbergleit (Stanford) studied the
interplay between gravity and quintessence with the use of a set
of new exact analytical General Relativity solutions. It is found
that cosmic vacuum and other forms of dark energy with large
negative pressure can produce both nonuniform static and uniform
nonstatic configuration where the antigravity of large negative
pressure plays a key role. In particular, a configuration is found
with a spatial singularity in which antigravity is infinitely
strong. The work attracted interest of the media; United Press
International: "A team of U.S. and Russian physicists has proposed
important new solutions to Einstein's famous gravity equations
that suggest an entirely new object - a kind of anti-black hole
with infinitely strong anti-, or repulsive gravity", etc.
A new kind of bias in the extragalactic Cepheid distance indicator was
identified by Teerikorpi, in collaboration with G. Paturel (Lyon).
This may explain the high value of H0 obtained by the HST key
project, via biased Cepheid distance values in their calibrations.
Using the cosmological Malmquist bias approach Teerikorpi showed that
the evidence for the separate class of the most luminous quasars does
not depend on the previously used cosmological model. In fact, the
class appears best within the presently favoured flat Lambda-model.
The reddenings caused by dark haloes around galaxies at intermediate
redshifts were studied by Teerikorpi. Radio-loud quasars with narrow
absorption line systems in their spectra were used as probes which now
revealed for the first time a clear correlation with the reddening and
the number of absorption systems. The effect corresponds to an
intrinsic B-absorption of about 0.2 mag in a dusty halo.
Blazars
K. Nilsson, T. Pursimo, L. Takalo and A. Sillanpää have continued the blazar
monitoring program. They have been monitoring the TeV BL Lacs using
the 1.03 m telescope at Tuorla and BVR-bands since fall 2002. The
monitoring list includes 24 objects, selected from the paper by
Costamante \& Ghisellini (A\&A, 384, 56, 2002), and listed there as
TeV sources or TeV candidate sources. For many of the objects no
previous monitoring data can be found in the literature. The aim is to
characterize their variability and calibrate suitable comparison stars
in their vicinity to facilitate future observations. These
observations will provide ``ground work'' for the MAGIC observations,
since these objects are possible targets for MAGIC.
Host galaxies of RGB BL Lacertae objects.
BL Lacertae objects are a subgroup of active galactic nuclei whose
defining characteristics are rapid flux variations over the whole
electromagnetic spectrum, high polarization and almost total lack of
optical emission lines. Recent imaging studies have shown that they
reside almost exclusively in the nuclei of luminous elliptical
galaxies. There is also growing evidence showing that they are
actually low-luminosity radio galaxies with a relativistic jet
pointing nearly towards us.
Studying the host galaxies can reveal important clues to the origin of
the activity of BL Lacertae objects. For instance, the role of the
galactic environment in triggering and maintaining the nuclear
activity is still unknown. Since the properties of the host galaxy
do not depend on the orientation, they also provide a way to study
the parent population of BL Lacs.
An imaging study of the RGB sample of BL Lacs was carried out using
the NOT. The RGB sample consists of 127 objects, all of which are
X-ray and radio emitters. During the study R-band images of 100
objects wewre obtained and the host galaxies analyzed using a
two-dimensional surface brightness fitting procedure that separates
the nuclear emission from the host galaxy emission.
The host galaxy could be resolved in 62 cases and 37 new host galaxies
were found. The hosts were found to be luminous and large elliptical
galaxies, whose basic properties were very similar to those of
inactive large ellipticals. This indicates that the galactic
environment has little effect on the nuclear activity and possibly
every galaxy is capable of entering an active phase at some stage
during their evolution. Contrary to some previous studies, not a
single clear example of a disk-dominated (i.e. spiral) galaxy was
found, although in a few cases the galaxies clearly possessed embedded
disk components. Also a dozen optically weak nuclei were found
supporting the view that the BL Lac sequence continues to lower
luminosities than previously thought.
\pict{nilsson.ps}
BL Lac object RGB1532+302 (the large elliptical
galaxy in the upper right corner). The host galaxy of this nearby BL
Lac (z = 0.064) has an R-band luminosity of MR= -23.1 and effective
radius reff = 8.5 kpc, and it is surrounded by a small group of
spiral galaxies. The nucleus is relatively weak, only ~ 5 % of
the total light of the system comes from it.
Galaxies
Multi-component kinematics of the interstellar medium around rich OB
associations and triggering star formation were studied by T. Lozinskaya
(Moscow) and A. Chernin with the use of the original observations of
the kinematics of the ISM around stellar associations Cyg OB1, Cyg
OB3. The data indicate that a rich OB association can produce a set
of expanding shells, and the most massive of them is swept first by
the stellar winds. A gasdynamical model is worked out in which new
shells are produced due to the activity of WR stars and supernova
explosions. These secondary shells expand rapidly and reach the first
one. The collisions of the shells provide favorable physical
conditions for triggering star formation, under which two basic
mechanisms - gravitational fragmentation and shock compression - act
together, enhancing each other.
V. Arkhipova, R. Noskova (Moscow) and A.Chernin studied the
phenomenon of Markarian activity in interacting galaxies with the
use of observational data collected in an extended new edition of
The Catalogue of Interacting Galaxies (Vorontsov-Vel'yaminov et al.\
2001). The total number of interacting systems in the catalogue is
2014, and about 10 % of them are found to be Markarian galaxies.
The morphological and dynamical systematics of the galaxies with
interaction induced activity are analyzed and an interpretation of
the mechanism of nucleus activity is discussed on the basis of the
models proposed earlier by M.Valtonen and G.Byrd.
Systematics in the location of brightest OB/HII complexes in the major
spiral arms of M 51 is discussed by A.Chernin
with the use of recently published far-UV and H\alpha data.
It is demonstrated that the objects occupy predominantly the areas
around the corners of the polygonal arm pattern of this galaxy.
This is treated as evidence that the
physical conditions in these specific areas can enhance massive
star formation. A possible gas dynamical explanation is suggested for
the phenomenon.
A.Chernin, V. Dolgachev and L.Domozhilova developed two classes of
computer models for wide triplets of galaxies, one with individual
galaxy dark matter halos, and the other with the common dark
matter halo of a system as a whole. It is argued that X-ray
observations of these systems can provide a critical test for the
models and may also give new direct cosmological constraints by
establishing whether ongoing clustering and hierarchical evolution
are still occurring on the mass scale of ~ 1013 Msun and
space scale ~ 1 Mpc or the systems on these scales are in the
quasi-steady-state virial equilibrium.
Distances to galaxies in the extended local group.
R. 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 H. 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 are being used for a
distance determination to NGC 253 (using imaging data from the ESO 3.6
meter). Mass determinations for a small set of low surface brightness
disk galaxies (with a view to determining their dark matter content)
are also underway. 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.
Groups of galaxies.
P. Heinämäki finished his 2.5 year post-doc period in Tartu
Observatory in July 2002. During 2002 Heinämäki continued his
work with Las Campanas Loose Groups (LCLG), the mass function of
loose groups of galaxies and environmental enhancement of loose
groups around rich clusters of galaxies. Owing to the poor number of
determinations of observational mass function available in the
literature, in particular for less massive systems, the study of the
mass function of loose groups of galaxies is particularly
relevant. Furthermore, the amplitude and shape of the mass function
reflect the underlying cosmology and value of the normalization
parameter, \sigma8. In this work theoretical mass functions found
in numerical simulations (such as the Virgo Consortium and own
simulations) of structure evolution were compared with the empirical
mass function. Results prefer a \LambdaCDM model with
\Omegam = 0.3, \Omega\Lambda = 0.7,
h = 0.65 and \sigma8 = 0.78-0.87.
It was found that the sample of LCLG is almost complete
for masses in the interval M ~ 1012 Msun to
1015 Msun.
The work has been continued with new deep galaxy samples, Sloan
Digital Sky Survey (SDSS), and our intention among the ongoing
analysis of the survey is to compare SDSS with numerical simulations.
The aim of the simulations is to find a cosmological model explaining
the CMB anisotropies and observed large scale-structure on scales of
clusters of galaxies and superclusters. Theoretical research and
modelling in this field is especially important now before the
PLANCK-satellite mission. We have joined the PLANCK-satellite project
and now are a member of a working group of the large scale structure
simulations. During the year 2002 the collaboration between Tartu and
Tuorla observatories will be further developed.
The Milky Way.
A. Berdyugin and P. Teerikorpi continued the study of interstellar
polarization at high galactic latitudes from distant stars, using both
the NOT telescope and the KVA telescope at La Palma. An extended
polarization map for the northern polar cap was interpreted as showing
structural features connected with the local spiral arm.
Very long baseline interferometry
\pict{3c454.eps}
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.
Tuorla AGN VLBI group (Wiik, Savolainen and Valtaoja) was granted a grand
total of 102 hours of observing time from the 10 VLBA telescopes for
multi frequency observations with the INTEGRAL gamma-ray satellite.
VLBA is commissioning its 3 mm capability and therefore the success of
routine monitoring observations at this frequency can not yet be
guaranteed. However, the group agreed to observe also at 3 mm which
enables them to get the highest resolution possible and interesting
spectral information of the sources at the millimetre regime.
Also, a joint project with Metsähovi Radio Observatory was started in
order to study a selection of gigahertz-peaked spectrum (GPS) radio
sources with extremely high peak frequencies. A total of 18 hours of
Very Long Baseline Array (VLBA) observing time was used to produce
high resolution radio images at six frequencies of four selected sources.
Total flux density variations in 27 gamma-ray blazars were compared
with structural changes in their parsec-scale jets using multi-epoch
VLBA observations at 22 and 43 GHz together with data from the
Metsähovi quasar monitoring program at 22 and 37 GHz. There is a clear
connection between total flux density outbursts and VLBI components
emerging into the jet. For essentially every new moving VLBI component,
there is a coincident total flux density flare, with evolution
similar to that of the component. A large fraction of the shocks
grow and decay within the innermost few tenths of a milliarcsecond and
therefore we see them only as ``core flares'' in the VLBI images.
High energy connection.
Lähteenmäki and Valtaoja showed that comparisons with the EGRET
data indicate that gamma-ray flares originate in the shocks located
downstream the jet rather than near the central engine. At the time of
an EGRET flare, the shock is typically already over a parsec downstream
from the radio core, beyond the accretion disk and/or the broad line
region (BLR) photon fields. Thus, present models for gamma-ray
production are inadequate, since they typically model the gamma-ray
inverse Compton flux as coming these external photon fields near the
central engine (Valtaoja et al. 2002).
Lindfors and Valtaoja modelled the inverse-Compton flux produced in the
shock by synchrotron self-Compton (SSC) process. Also the quiet level
gamma-ray production was included in the model as a constant jet
component. The high frequency spectrum cannot be explained exclusively
by the first-order SSC-process (Lindfors, M.Sc. thesis, completed in
March 2003) and further modelling is to be done.
Dark Matter
C. Flynn has led the DARKSTAR project, ``Space Based Studies of Dark
Matter'', which is funded under the ANTARES program of the Academy of
Finland and TEKES. DARKSTAR achieved its first year of operation in
2002 and continues until early 2004. Flynn spent the entire year 2002
on sabbatical leave (supported by the Academy of Finland) at the
Astrophysics and Supercomputing Centre of Swinburne University of
Technology in Melbourne, Australia. Most of the time was spent
analysing dwarf stars measured by the the European Space Agency's
Hipparcos satellite. These studies have lead to two spin-off results
and are presently being utilised to constrain the amount of visible
matter in the Galaxy's ``normal'' (i.e.\ stellar) halo, for comparison
with studies which seek to constrain the luminosity of the ``dark
halo''. The second spin-off was the development of a rather
precise (indirect) means to measure the cosmic production of helium
since the Big Bang.
\pict{bh.ps}
The Galactic disk, seen edge-on, surrounded by massive black holes.}
\pict{opp.ps}
The diagram shows comparison between a large proper motion survey
and one of the simulations.}
Dark Matter as black holes.
J. Hänninen completed a numerical study of the orbits of stars in
the disk of the Galaxy affected by massive black holes (dark matter) and giant
molecular clouds, for comparison with data also obtained from the
Hipparcos satellite. The conclusion was that black holes remain a
possible but unlikely source of disk heating. These simulations are
presently being extended to the rest of the Galactic disk, not just
the region near the Sun. The intention is to combining the code with
the Galaxy formation models being developed at Swinburne by Fenner and
Gibson.
Dark Matter as white dwarfs.
J. Holopainen is nearing the completion of his master's thesis. He
studied white dwarfs as dark matter candidates, utilising recent space
and ground based data. He concluded that claims in the literature that
(part of) the dark matter have been found in the form of ancient white
dwarfs are premature. The dark matter might be in this form, but there
is little direct evidence for it yet.
Stars
Ongoing work on K dwarf stars.
E. Kotoneva completed her Ph.D. thesis in January 2002. She
computed the chemical composition of a large uniform set of K dwarf
stars in the European Space Agency's Hipparcos satellite. The sample
allows 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
indirectly to constrain the density of matter (dark or otherwise) near
the Sun.
Kotoneva has also used archival Hipparcos data to demonstrate a simple
and elegant relation between the stellar position in the lower main
sequence (stars less massive than the Sun) and metallicity. The
relationship that was uncovered is really remarkably tight - so clear
and with such little scatter, that it leads to metallicities for stars
which are as accurate as doing detailed spectroscopic work. The
relationship was predicted by stellar theory, but until now had not
been empirically demonstrated.
The technique leads to a new, independent distance estimator. It is
very useful because it can be applied to existing Hubble Space
Telescope data to constrain the density of dwarf stars in the Galactic
halo, with very much more accurate distance measurements than all
work previously. This is a useful quantity for comparison with studies
of the dark matter content of the Galactic halo in low mass stars.
Variable stars.
H. Lehto and S. Katajainen have started a long term campaign of
monitoring cataclysmic variables (CVs) using the Tuorla 70 cm
(f2.5) Schmidt-Väisälä telescope equipped with an ST8 CCD. The CCD was
installed in November 2002, and since then CVs have been observed.
Most of the CV-targets are magnetic cataclysmic variables (mCVs), but
also some dwarf novae, low-mass X-ray binaries and symbiotic stars
are included in the sample. Due to the high latitude of the
observatory (60o 25') and long boreal nights,
very long times series
can be obtained for intermediate polar (IP) objects such as YY Dra,
PQ Gem, V709 Cas, HT Cam, and V405 Aur, and polars
(i.e.\ AM Herculis stars) such as GG Leo, EV UMa, RX J0719.2+6557.
Also some new CV candidates are being monitored.
This large amount of CV data helps in studying the accretion
geometry of each individual object and variability from one orbital
period to the next one and over several nights.
A second aim of the program is the (re)determination of ill-known mCV
ephemerides. Even many well studied IP-systems have ephemerides which have
been determined a long time ago (10 years or so), and due to unaccuracy
of the original ephemerides, the orbital phases calculated with those
ephemeris will now include quite large errors. By monitoring
intensively objects in our sample it is possible to calculate new
and more accurately determined ephemerides. The long monitoring (in time
scales of years) is able to reveal also if some of the IPs have
different spin rates than originally was expected/calculated, because the
determination of spin period in IPs is not very straightforward in
some IPs due to different sideband frequencies in their
power spectrum. In this IP-project we are collaborating with A. Norton
et al.\ in the Open University (Milton Keynes, UK)
In collaboration with the 40 cm SATU telescope at the University of West
Indies, Trinidad and Tobago, a long term monitoring program was begun to
determine the relative and absolute lengths of times the mCVs spend in high
and low states. The low states of mCV-systems are poorly understood, because to
cover well the frequency of low states, monitoring in times scales of years
is needed. In the low states the light emitted in the system is mainly from
the cool secondary star (K or M dwarf), and to understand how this
secondary adjusts thermally and refills its Roche lobe again, long
term monitoring is essential.
In 2002 Katajainen and Lehto have also studied polars (AM Her star)
V1309 Ori (MNRAS paper in press), and GG Leo and EV UMa in
collaboration with V. Piirola (Tuorla), P. Hakala (Helsinki
University), F. Scaltriti (Turin) and G. Ramsay and M. Cropper
(Mullard Space Science Laboratory, Surrey, UK).
\pict{wga.ps}
Circular polarization of the intermediate polar WGA J1958+3232 in
the R-band. Observed at the NOT on March 1, 2001.}
Lehto and Katajainen are also collaborating with Dr. Laurits Leedjärv
(Tartu Observatory, Estonia) and V. Piirola (Tuorla) in studies of
symbiotic stars. They had one observing run at the NOT
in September 2002. The data is being analyzed together with
previous data from the NOT. The scientific aim is to find
differences between the polarization characteristics of normal symbiotic
stars and of symbiotic stars that show high-velocity bipolar jets and/or
rapid light variations. The results will help to constrain possible models
of those peculiar symbiotic stars. In a wider context it is aimed to
contribute to explanation of the jet ejection mechanism in general, which
is important also for understanding the AGN, X-ray binaries etc.
Lehto and K. Mäkinen collaborate with D. Johnsson (UK) in
studies of the symbiotic star R Aqr. The analysis of radio data is in
progress with a new jet model being formulated.
Lehto has in collaboration with E. Harlaftis (National
observatory of Athens, Greece) begun a work to determine the
spatial velocity distribution of X-ray binaries with VLBI techniques. For
these VLBI observations a weekly monitoring campaign of about 30 sources
started in Feb 2003 at the Nan\c cay radio telescope.
Andrei Berdyugin has continued the study of interstellar polarization
at high galactic latitudes (b > 70o) using the NOT and KVA on
La Palma. With the new data obtained in December with the Casleo
telescope (Argentina), now 3/4 of the area around South Galactic Pole
is covered. Polarization observations of the interacting early-type
binaries with the KVA telescope have been continued. Dependence of
the polarization with the orbital phase has been detected and studied
for CX Dra and W Ser. CX Dra shows typical double-wave pattern, which
a small (0.1-0.2 %) amplitude and shape variation in the time scale
of several months. Polarization variability in W Ser seems very
peculiar: it shows large (> 1 %) amplitude with unusually strong
first harmonic of the orbital period. Shape of the variability curve
varies strongly between different orbital cycles.
The Sun
Radio observations.
The solar group at the Tuorla Observatory (Valtaoja, Pohjolainen,
Riehokainen, Khan) was originally established to analyse solar radio
data from the Metsähovi Radio Observatory (a Helsinki University of
Technology facility) and to make comparisons with other ground-based
observations. Emphasis was first on investigating quiet Sun features
at centimeter and millimeter wavelengths. A PhD thesis on radio bright
regions at high solar latitudes was being prepared by A. Riehokainen.
The scientific interests of the group now extend to solar
flare and coronal mass ejection (CME) research, using X-ray and EUV
data together with imaging and spectral observations at various radio
wavelengths. The research subjects include, e.g., formation and
signatures of shock waves, flare and CME precursors, sources of
homologous flaring, and evolution of solar bright points. Most of the
work was done in collaboration with science teams abroad and in
Finland. Dr. J.I. Khan, coming from the Yohkoh satellite science team
at ISAS, Japan, joined the group in August 2002, on a one-year Academy
of Finland visiting scientist fellowship.
\pict{silja.ps}
{A 2-meter solar radio telescope has been built on the observatory
hill at Tuorla, and first tests at 12 GHz were performed in April
2002. The antenna was also used in student exercises: the lecturer
S. Pohjolainen and antenna constructor V. Khaikin explain here for
the students how the system works. The students were also lucky
in observing a solar flare during the exercise week!
The new Multibeam Solar Radio Telescope (MSRT), developed in
cooperation with the New Radio Telescope Technologies Lab.
(Special Astrophysical Observatory/St. Petersburg Technical University),
was brought into use in 2002. The first observations at the 12 GHz
test frequency were performed in April, and MSRT observed two flares,
on April 10 and April 22, 2002. The antenna was also used for student
exercises for the first time. The development and building of the final
multi-beam receiver was continued.
Enhanced temperature region at high and low solar latitudes.
A. Riehokainen investigated
enhanced temperature regions (ETR) at mm radio wavelengths
at Tuorla observatory during 1996-2003. Data for
this study were obtained from the Metsähovi Radio Telescope at 37 GHz and
87 GHz and also from the Nobeayma Radioheliograph at 17 GHz. Radio data
were compared with different optical data such as SOHO/EIT/MDI, white
light polar faculae, CaII(k3) and H\alpha spectral line
observations.
Results obtained showed that ETRs are connected with two different types
of bright structures seen in CaII (k3) and H\alpha spectral line
observations. The differential rotation of the Sun was obtained using
the radio data. In addition, existence of torsional oscillations at
chromospheric and possible low coronal height was established.
Connection between latitude time distribution of the ETRs at high
solar latitudes with the latitude time distribution of the polar
faculae was obtained.
Association between ETRs and coronal holes is one of the main goals in
this study.
Importance of the eruption history to the SEP acceleration.
Production of solar energetic particles (SEPs) in the high-energy
range, 10-100 MeV/nucleon, has been studied with the data of the
electromagnetic-wave and particle telescopes - EIT, LASCO, SUMER, and
ERNE/HED, onboard SOHO. Coronal mass ejections (CME) and near-surface
phenomena, including flares, were carefully studied for the time
periods of the SEP events registered with ERNE. A recent series of the
investigations comprises the case studies, a statistical
analysis, and their perception. A SEP-producing eruption
typically consists of both flare and CME. Based on the
multi-wavelength studies, the importance of the eruption history to
the production of solar energetic particles has been emphasized. It
often happens that in the SEP-producing eruptions an impulsive-CME liftoff
triggers in corona the local flares and the global waves that start
the particle acceleration, which continues later at interplanetary
shocks driven by CMEs. This finding suggests that a forecasting of the
high-energy particle fluxes at 1 AU requires the broad-band data from
a set of the spaceborne telescopes, like those on SOHO.
Discovery of the high-energy 3He-rich events.
Energetic particle observations of the ERNE instrument onboard SOHO
enable measurements of 3He and 4He fluxes beyond 10 MeV/nucleon with a
good statistical resolution. The survey of the ERNE data for 1999-2000
has revealed a new group of SEP events with 3He/4He > 0.2, which
was apparently missed in the previous observations.
In the event of October 29, 2000, a very strong 3He enhancement
persists over the high-energy range up to 50 MeV/nucleon. This is the
first time that the 3He/4He > 1 has been recorded at above 10
MeV/nucleon. The ERNE has enabled the first ever measurement of the
3He energy spectrum in such an event. The particle event was
associated with an impulsive flare and interplanetary shock wave.
Type II radio burst was observed with the WAVES experiment onboard the
Wind spacecraft before and then simultaneously with the 3He-rich event
registered with ERNE.
The analysis shows that the high-energy 3He-rich events refer to the
flare material reaccelerated at the flank of interplanetary coronal
mass ejection (CME). Onsets of the high-energy 3He-rich events were
observed in the far upstream regions, when the CME-driven shocks were
at about 0.3 AU from the Sun. A numerical modeling of the 3He
re-acceleration in oblique shock driven by CME supports this
interpretation.
Collective Processes in Astrophysical Plasmas: Waves, Heating and
Accelerated Particles (COPAP).
In 2002, VISPA researchers started a three-year COPAP project with the
Ruhr-Universität Bochum to study collective plasma phenomena relevant to
the solar corona and solar wind, as well as to the jets of active
galactic nuclei (AGN). The project is co-funded by the Academy of
Finland and Deutscher Akademischer Austauschdienst for travel and
accomodation costs of researcher exchange between the institutes.
The VISPA team participating in the project consists of four researches,
R. Vainio (team leader, SRL), E. Valtaoja (Tuorla),
T. Laitinen (SRL) and J. Virtanen (Tuorla). The team in
Ruhr-Universität Bochum, lead by R. Schlickeiser, likewise
consists of four researchers participating in the collaboration. Several
researcher visits between the groups were conducted during the first
year of the project.
During the first year of the project, energetic particles transport and
acceleration in a wave-heated solar wind was studied. A numerical model
capable of computing the Alfv\'en-wave frequency spectrum consistently
with the solar wind plasma parameters resulting from wave heating was
constructed and used to study the acceleration of solar energetic
particles in the self-consistently modeled solar wind. The results gave
important clues on both the mechanisms of solar wind heating and the
mechanisms of solar energetic particle accleleration.
The AGN modeling within the project during the first year concentrated
on explaining gamma-rays up to TeV energies observed from several AGN.
The model developed for this employs hadronic emission from a dense
blast wave moving relativistically into the ambient interstellar medium.
Research was done also on electron acceleration in relativistic shock
waves, studying especially the effect of the structure of the shock
wave on the acceleration process.
Earth's radiation environment and space weather
Energetic particle production in coronal mass ejection (CME) driven
shocks has been studied. Energetic particle observations provide
information on the lift-off and coronal evolution of potentially
geoeffective interplanetary CMEs and thus are important for
understanding the global scenario of the solar-terrestrial events.
In order to obtain the parameters essential for the coronal energetic
particle acceleration, a novel approach for modeling the solar wind
wave heating in parallel with the energetic particles has been applied.
As the essential processes in both domains are related with the
plasma wave power, a scenario where both solar wind and energetic
particle models are consistent with observations, would produce
realistic parameters for coronal energetic particle acceleration.
A solar wind wave heating model has been created and presented by
T. Laitinen et al. The model was used to study the coronal
energetic particle acceleration and interplanetary transport. The
resulting interplanetary transport was found to be orders of magnitude
too slow, compared to observations. However, the coronal energetic
particle acceleration was found efficient.
The energetic particle model was improved by incorporating nonlinear
wave-wave -interactions, which reduce the wave power significantly.
As a result, more reasonable interplanetary transport was obtained,
already consistent with some observed energetic particle events.
The coronal energetic particle acceleration efficiency, however,
was somewhat reduced. Within the model, the effect of CME-driven
shock geometry and waves generated by the energetic particle beams
have also been studied.
As the next step, wave-wave -interactions will be implemented in
the solar wind model. The model will then be used for studying the
energetic particle acceleration and transport with different ambient
solar wind and CME characteristics.
The solar wind and energetic particle modeling has been conducted
in co-operation with Ruhr-Universität Bochum under project
COPAP, as mentioned in the previous section.
Experimental investigation by using data from the SOHO spacecraft
and from international data archives concentrated in deducing
signatures from energetic particle observations, which could be
used for predicting geoeffectivity of CMEs. Encouraging results have
been obtained based on the analysis of data from the rising phase
of the present solar cycle.
The feasibility of energetic particle observations as an additional
source of information in predicting occurrence of geomagnetic storms
has been demonstrated. A proxy for the CME transit time from the
Sun to the Earth has been derived. Analyses have shown that the
time difference between the onsets of a primary particle event and a
particle shock peak in interplanetary space correlates strongly with
the strength of the observed geomagnetic storm.
Analysis of experimental data from the declining phase of the present
solar cycle will be continued. The solar wind/energetic particle model
will be applied in studying the energetic storm particles, observed as
an intensity peak (shock peak), when a CME is passing the observing
spacecraft. Using the solar wind and energetic particle observations
and models, a detailed investigation of the relation between the
particle peak properties and the geomagnetic storm strength will be
carried out.
Solar system physics
Most rough surfaces exhibit an opposition effect, strong brightening
as the phase angle (the angle light source - target - observer) goes
to zero. Although there are several theories and empirical models
describing this behaviour, the true cause is not yet completely
understood.
H. Karttunen has worked together with the Helsinki Observatory
group, mainly S. Kaasalainen and J. Piironen, studying light
scattering from solar system objects and laboratory samples. Recently
the work has concentrated on scattering properties of snow and ice,
the results constituting a major part of Kaasalainen's Ph.D. thesis,
accepted in 2002. Although the measurement procedure is simple in
principle, there are some practical problems, which may explain why
only very few results have been published. One problem is the heat
radiating from the devices and the observer; the heat tends to melt
the sample and change its crystal structure.
Contaminated snow seems to produce a stronger opposition
effect than pure snow. The effect of the crystal size still needs
more detailed measurements. The work will be continued next winter.
Studies
Doctoral Theses
Eira Kotoneva
Kaj Wiik
Master's Theses
Tiina Schafeitel
Carita Siponen
Kati Rautakorpi-Salmio
Joni Virtanen
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