University of Helsinki
Annual Report 1998
Observatory
University of Helsinki
Mailingaddress:
Observatory
P.O. Box 14
FIN{00014 University of Helsinki
FINLAND
Visiting address:
Observatory
Tahtitorninmaki
Helsinki
Phone number : +358{9{19122940
Fax number: +358{9{19122952
On the cover drawing of Observatory
This reportwas edited by
Jukka Piironen
Printed by
Diivari
Urho Kekkosenkatu 8
Helsinki
Helsinki 1999
This annual report is acompilationof the input from the dierent research
groupsatthe Observatory. Followingpeoplehaveprovidedtextandgures
for the report:
Jorma Harju and Kalevi Mattila: Interstellar medium and star formation.
Juhani Huovelin and Osmi Vilhu: High{energy astrophysics.
Karri Muinonen and Lauri Jetsu: Stellar{planetary astronomy
Kari Lumme: Planetary astronomy
Heikki Oja: University Almanac OÆce
The report covers the sta and its activities including also visits to the
Observatory during 1998. Also some continuing acitivities from 1997 have
been included to the report. At the end of the report, there is a reference
list of the publications during 1998.
Editor
Observatory
Sta
E-mailaddressesare:
Firstname.Lastname@gstar.astro.helsinki.
if not otherwise stated. To phone numbers
add +358{9{ in front of the number, when
callingfrom othercountries.
NOTE: Research group abbreviations in sta
listare:
HEA High{EnergyAstrophysics
ISM{SF InterstellarMediumandStarForma-
tion
PRG PlanetaryResearchGroup
SPA Stellar{PlanetaryAstronomy
Permanent andsemipermanent
sta
Haikala, Lauri, Dr.rer.nat., Docent, Assis-
tant,ISM{SF, onleave during1998 atESO,
substitutes T. Hackman(January{October)
andP.Harjunpaa(November{December), E{
mailLauri.Haikala@eso.org
Huovelin, Juhani, PhD, docent, Amanuen-
sis, on leave as Senior Research Fellow of
the Academy of Finland August{December
1998, HEA,phone 19122948
Isaksson, Eva,M.Sc.,Librarian,phone
19122940, E{mail Eva.Isaksson@helsinki.
Jetsu, Lauri, PhD, docent, Assistant, SPA,
phone19122946
Lind, Veikko,Janitor,phone19122949
Lumme, Kari,PhD,PersonalExtraordinary
ProfessorofAstronomy,DirectoroftheOb-
servatoryJanuary{September1998,PRG,
phone19122910
Mattila, Kalevi, PhD, Professor of Astron-
omy, Director of Observatoryfrom Septem-
ber 1998, ISM{SF, phone 19122947,E{mail
Mattila@cc.helsinki.,onleaveJanuary{June
1998, subsitutedbyO.Vilhu.
Muinonen, Karri, PhD, docent, Amanuen-
sis,onleaveasSeniorFellowoftheAcademy
of Finland, SPA, phone 19122941, substi-
Maisala(May{December).
Oja, Heikki, PhD, docent, Head of Univer-
sityAlmanacOÆce, phone19122942
E{mailHeikki.Oja@helsinki.
Palo, Anu,Secretary,19122940, E{mail
Anu.Palo@helsinki.
Toriseva,Mikko,Tech.Lic.,Amanuensis,ISM{
SF,phone 19122904
Vilhu,Osmi,PhD,docent,LaboratoryEngi-
neer,HEA,phone19122801,onleaveJanuary{
June1998, substitutedbyJ. Huovelin
Vacant: Observator, substituteT.Hackman
(November{December).
Externally FundedResearchSta
Donner, Karl Johan, PhD, docent,research
ongalactic and extragalactic astronomy
Hakala, Pasi,PhD,HEA, phone19123478
Harju,Jorma,PhD,ISM{SF,phone19122945
Heikkila,Arto,PhD,ISM{SF,phone19122945
E{mailArto@obs13.astro.helsinki.
Juvela,Mika,PhD,ISM{SF,phone19122909
Kaasalainen,Mikko,D.Phil.,SPA,phone19122802
Lehtinen,Kimmo,PhD,ISM{SF,phone19122909
Piironen, Jukka, PhD, on leave during1998
atEuropeanComissionJointResearch Cen-
ter,Ispra,Italy,PRGandSPA,phone19123718
PhD Students
Alha,Lauri,dipl.eng.,HEA,phone19122943,
E{mailLauri.Alha@lynx.astro.helsinki.
Hackman,Thomas,M.Sc.,SPA,phone19122946
Hannikainen,Diana, M.Sc.,HEA, phone
19122907,E{maildiana@carina.astro.helsinki.
Harjunpaa, Paivi, Phil.Lic., ISM{SF, phone
19122904
Keranen,Sanna,M.Sc.,PRG,phone19122940
Muhli, Panu,M.Sc. HEA, phone19122943
Nevalainen, Jukka, M.Sc., HEA,phone+1{
617{4967663, During 1998 on leave as Pre-
doctoral Student at theSmithsonianAstro-
physicalObservatory
E{mail jukka@head-cfa.harvard.edu
Palviainen, Asko, M.Sc., ISM{SF,phone
19122909
Vaisanen, Petri,MSc,ISM{SF, during1998
onleaveasPredoctoralStudentattheSmith-
sonianAstrophysical Observatory
M.Sc. Students
Kahanpaa, Jere, student,ISM{SF, phone
19122909
Laakso,Teemu,student,SPA,phone19122940
Maisala,Sami,student,HEA,phone19122907
Schultz,Juho,student,HEA,phone19122940
Torppa, Johanna,student,SPA,phone19122802,
E{mail jtpesone@gstar.astro.helsinki.
Vestama,Mikael,student,PRG,phone19122940
Virtanen,Jenni,student,SPA,phone19122940
Other sta
Latvala, Arja,Cand.Sc.,AlmanacSecretary,
UniversityAlmanacOÆce, phone191 22942
External Docents
Brandenburg, Axel, PhD, Professor,Univer-
sityof Newcastle uponTyne
Markkanen,Tapio,PhD, phone1912335
Moss, David, PhD, Mathemathical Depart-
ment,ManchesterUniversity,UK
Prusti, Timo, PhD, ESA Astrophysics Di-
vision,ISO ScienceCentre, VILSPA
Rahunen, Timo,PhD, Planetarium Sarkan-
niemiOy, Tampere, Finland
Tuominen, Ilkka, PhD, Professorof Astron-
omy,Universityof Oulu,phone08-5531930,
E{mailIlkka.Tuominen@oulu.
Urpo,Seppo,Professor,DirectorofMetsahovi
RadioResearch Station, HelsinkiUniversity
ofTechnology,phone 4512235
Valtonen,Mauri,Professor,DirectorofTuorla
Observatory,UniversityofTurku,Finland
Zinchenko,Igor,Dr.Sc.,HeadofRadiophysics
Department, Institute of Applied Physics,
RussianAcademyofSciences,(NizhnyNov-
gorod),asemi-permanentmemberofthein-
terstellarmediumgroup
Visiting Scientists 1998
TheISM{SFgrouphosted theOdinScience
TeamandAstronomyWorkingGroupmeet-
ings, held at the Observatory on May 25-
29, with ca. 30 participants from Canada,
France,and Sweden.
Dan Clemens, Associate Professor, Depart-
mentofAstronomy,BostonUniversity,U.S.A.,
June15 - 18.
Lev Pirogov, Radiophysics Department, In-
stituteofAppliedPhysics,RussianAcademy
ofSciences,NizhnyNovgorod,Russia,Novem-
ber11 - 30.
AndrejSobolev, PhD, UralUniversity,Eka-
terinburg, Russia,April 20 -25.
Shkuratov, Yu., PhD, Kharkov State Uni-
versity, 1998 June15-25.
D.Stankevych,PhD,KharkovStateUniver-
sity,1998 June15-25
EdwardTedesco,PhD,MissionResearchCor-
poration, USA, 1998 March 23-25
Igor Zinchenko, Dr. Sc., Head of Radio-
physics Department, Instituteof Applied
Physics,RussianAcademyofSciences,Nizhny
Novgorod, Russia, November11 - 30.
Research
Activities
Interstellar Medium and
Star Formation
The general goals of the research group can
beformulatedasfollows:
To investigate the physical and chemical
propetrties of interstellar molecular clouds,
especially the initial conditions for star for-
mation, i.e. thetemperature,density,radia-
tioneldandchemicalcomposition. Thera-
diospectroscopicalstudiesperformedbythe
grouphavebeendirectedtowardsthefollow-
ingthree mainelds:
1) Dynamicalprocesses and chemistryin
nearbylow-massstar forming regions
2) Physical properties and chemicalcompo-
sitionofgiantmolecularcloudcoresandtheir
variationasa functionof thegalactocentric
radius
3)Modelingofthestructureofdensemolec-
ular clouds with theaid of Monte Carlo ra-
diative transfer calculations of spectral line
prolesandthree{dimensionalcloudmodels
These three lines of investigation are inter-
related and are instrumental to the under-
standingoftheevolutionofmolecularclouds
and thestar formationprocess ingeneral.
Toinvestigatethepropertiesandcomposi-
tion of interstellar dust grains in dense and
diuseclouds,especiallybymeansofthein-
frared emissionand scattered radiation.
Tomeasuretheintensityoftheextragalac-
tic background radiation at optical and in-
frared wavelengths. This is connected with
the development of methods for separating
theextragalacticcomponentfromthegalac-
ticcirrusand otherforeground components.
The group has utilized a multi-wavelength
approach where radio, infrared, and optical
telescopeshavebeenused. Theobservational
facilitiesmost important forthe grouphave
been the Swedish-ESO Submillimetre Tele-
scope (SEST), the Infrared Space Observa-
tory(ISO),and starting1999 theOdinsub-
millimetre satellite. Considerable eort has
beeninvested intothedevelopmentofmeth-
ods and, especially for space-born observa-
tions, into the preparation of extensive ob-
Section 'Instruments and Facilities' of this
report.
Thegroupcollaboratedin1998 mainlywith
the following foreign institutes: the Max-
Planck-InstituteforAstronomy(Heidelberg,
Germany, especially the ISOPHOT Team),
Stockholm Observatory, Onsala Space Ob-
servatory (Sweden),InstituteofApplied
Physics(NizhnyNovgorod,Russia),andAs-
tronomicalObservatoryandTheoreticalAs-
trophysics Centre, Copenhagen.
LehtinendefendedonJune16thhisPhDthe-
sis\Studiesofdustandstarformationinglob-
ules". The oÆcial opponent was Professor
Dan Clemens of Boston University and the
CustosProfessor KaleviMattila.
Infraredstudies withISO: Mid-
infrared emission of Unidenti-
ed Infrared (UIR) Bands
.
Theobjective of thisprogramis to measure
the intensities of the Unidentied Infrared
(UIR) emission features, and to determine
the distribution of their carriers in dier-
entcomponentsoftheinterstellarmediumin
theMilkyWayGalaxyandanotherSbspiral
NGC891. TheUIRfeaturesaresuspectedto
becausedbyPolycyclicAromaticHydrocar-
bons(PAH)whichareaconstituentbetween
thelargestinterstellarmoleculesidentiedso
far and the classical interstellar grains (ca.
0.05 to 0.3 m insize). Priorto ISO, these
features (with the exception of 3.3 and 6.2
m) had been detected only in very bright
nebulae, and it has not been clear whether
they are present also in the normal diuse
interstellarmedium.
Thesecondobjectiveistomeasuretheemis-
sion spectra by small and large dust grains
along the same lines of sight in the galactic
diskastheUIRspectra. Usingthecombined
data base the connections and correlations
betweenthe three (or possiblymore) dier-
ent dust components will be studied in the
galactic scale.
ThediuseemissionoftheinnerGalaxybe-
tween 5.8 and 11.6 m has been observed
using the ISO low-resolution spectrometer
PHOT-S in an ISOPHOT GTproject with
Mattilaas PI.The UIR features at 6.2, 7.7,
8.6,and11.3mweredetectedineachspec-
45 Æ
). Therstresultsofthisstudywerepub-
lishedinthespecialissueofAstronomyand
Astrophysics devoted to ISO results (Mat-
tila et al.,1996, AA,315, L353). In order to
correlatethegalacticdistributionoftheUIR
bandcarrierswiththemoleculargas 13
CO(1
- 0) spectra have been observed withSEST
at the ISO positions (Kahanpaa and Mat-
tila).
Mattila, Lehtinen and Liljestromtogether
with Lemke and Herbstmeier (Heidelberg),
Laureijs (ESA, VILSPA), and Leger (Paris)
havedetectedtheunidentiedinfrared(UIR)
emission bands at 7.7 and 11.3 m in the
emission ofan isolatedcirruscloudin
Chamaeleon(G300.2-16.8),externallyheated
bythetypical interstellarradiationeld
(ISRF) of the solarneighbourhood. For the
observations the ISOPHOT-S spectrometer
wasused. ThedetectedUIRbandshaveab-
solute intensities 1/1000th of the values
typically observed in planetary and reec-
tionnebulae. Theintensityratio11.3 to 7.7
misatthehigherendoftherangeobserved
for reection nebulae, planetaries, HII re-
gions,orforthediuseemissionoftheinner
Galaxy. Theobservationspresentedgivefur-
therevidence thattheUIR featuresseemto
beubiquitousthroughoutthegalaxy. Thisis
insupportofthePAHsascarriersofthefea-
turesand, moreover, askey agentsin trans-
forming the stellar UV into infrared radia-
tion (Lemke etal. 1998).
Mattila and Lehtinen together with Lemke
(Heidelberg) have observed the spectrum of
theUIRemissionbandsbetween5.9and11.7
m for the rst time in the disk of an ex-
ternal galaxy (NGC 891). They have used
the low-resolution spectrometer ISOPHOT-
S. The UIR bands at 6.2, 7.7, 8.6, and 11.3
mhave absolute intensitieswhich are sim-
ilar to the values observed for the diuse
emissionofourownGalaxy. TheUIRbands
between 5.9 and 11.7 m contribute 9%
of the total IR radiation of NGC 891. The
intensityratiosandbandwidthsintheNGC
891 disk emission are similar to the diuse
emission of the Milky Way, pointing to a
commoncarrierfortheUIRbandsinthetwo
galaxies. However, there are some notable
variations of the band ratios along the ma-
joraxisof thegalaxy (Mattila et al. 1999).
5 6 7 8 9 101112 Wavelength [ µ m]
0 10 20 30 40 50 60
F λ [10 -10 W cm -2 µ m -1 sr -1 ]
-240 -216 -192 -168 -144 -120 -96 -72 -48 -24 0 24 48 72 96 120 144 168 192 216
Position ["]
Figure On the left PHT-SL spectra along
themajoraxisofNGC891. Ontherightop-
ticalBbandimageofNGC891fromtheDig-
ital Sky Survey with the observed 24"24"
areassuperposed(Mattila,LehtinenandLemke
1999)
Infrared studies with ISO: Far
Infraredemission of galacticstar
formingregions, molecular clouds
and cirrus.
The purpose of these ISO programs is to
studythedistributionandpropertiesofdust
in nearby molecular and cirrus clouds. Es-
peciallycondensations ofvery colddustand
veryearlyphasesofnewly-born(proto)stars
are being searched. The connection of dust
distributionanddustpropertiestothepres-
enceof newly-formedstarsis studied.
Lehtinen, Mattila andHaikalatogetherwith
Lemke (Heidelberg) have observed a quies-
cent smallglobule,theThumbprint Nebula,
with the ISOPHOT far-infrared camera at
100 and 200 m. The observed emission
is opticallythinthermalemission from dust
at a temperature of 14-16K. The energy
budget of the cloud is studied by consider-
ing the energy input (interstellar radiation
eld), and outputs (scattered and emitted
radiation). ItisfoundthattheISRFissuÆ-
cienttobetheonlyheatingsourceofdustin
the cloud. The authors have derived values
of absorption cross sections of dust at 100
and 200 m, and foundthem to be ingood
agreement with current dust models(Lehti-
nen et al. 1998).
100µm
12 h 42 m 40 -78° 35′
30 25
a)
200µm
12 h 44 m 42 40 -78° 40′
35 30
b)
13.0
100µm
12 h 42 m 40 -78° 35′
30 25
13.0
c)
39
200µm
12 h 44 m 42 40 -78° 40′
35 30
39
d)
ESO/SRC red plate
12 h 42 m 40 Right Ascension (1950) -78° 35′
30 25
e)
Declination (1950)
13 CO
12 h 44 m 42 40
-78° 35′
30
f)
Figure Greyscale and contour plots of the
surfacebrightnessof theThumbprint Nebula
at100m(a,c)and200m(b,d). Thecon-
tour levelsarefrom12to14by 0.5MJysr 1
at 100m, and from33 to 48by 3MJysr 1
at200m. In paneleisshown thegrayscale
image of the surface brightness at R-band
(ESO/SRCredSkySurveyPlate),andinthe
panel f is shown the 13
CO(J=1{0) column
density contour map
-7 -6 -5 -4 -3
log( λ ) [m]
-8.0 -7.5 -7.0 -6.5 -6.0
log( λ F λ ) [W m -2 sr -1 ]
0.1 1 λ [ 10 µ m] 100 1000
ISRF
I scat
_____
I emit
_____
Figure The spectral energy distribution of
the emitted radiation I
emit
and the scattered
radiation I
scat
for the Thumbprint Nebula.
The upper limits of the IRAS 12, 25 and
60memissionat2levelareindicatedwith
an arrow. The mean intensity of the inter-
stellarradiationeld(ISRF)between0.0912{
8.0m is shown for comparison. The ISRF
plottedwithadottedlineistheportionofthe
ISRF that suers extinction in the cloud
Lehtinen and Mattila together with Lemke
(Heidelberg) have analyzed the far-infrared
GTobservationsofthedarkcloudDC303.8-
14.2 made with the ISOPHOT instrument
at 60, 100, and 200 m. An IRAS source
is located in the centre of the cloud. This
is a deeply embedded young stellar object
(YSO). The purpose of this research is to
studythepropertiesofcolddustinthecloud,
and to derive more reliable estimates of the
evolutionarystageoftheYSO.Thedusttem-
peraturedecreasestowards thecentreof the
cloud, where it is about 14 K. The circum-
stellar mass of the YSO is estimated to be
about0.2M
. TheauthorsclassifytheYSO
tobebetweentheClass0andClassIevolu-
tionarystages. Theyhavealsocomparedthe
cloud DC 303.8-14.2 with the Thumbprint
Nebula,amorphologicallysimilarcloudwhich
has no signs of star formation (Lehtinen et
al. 1999).
Lehtinen, HaikalaandMattilatogether with
Lemke (Heidelberg) have analyzed the 70,
100, 150, and 200 m GT and OT obser-
vations of theCederblad 110 star formation
regioninChamaeleonI.Analysisofthelarge
70-200mmapscoveringthewholecentral
and southern parts of Cha I is in progress,
aswellasthecomparisonofthesemapswith
theextensiveC OmapsobtainedwithSEST.
Mattila,Lehtinen,andHaikalatogetherwith
Lemke (Heidelberg) have analysed the 100
and 200 m maps and 3 { 200 m spec-
trophotometryofL183,averyopaque(A
V
>
20mag)darkcloudabovethegalacticplane.
Preliminaryresultshave beengiven inMat-
tila et al., 1997, Astron.Ges. Abstracts Ser.
13, 128. For the purpose of comparing the
colddustandmoleculargasdistributionsthe
cloudcore hasbeenmappedat SESTinthe
J=1- 0linesof 13
CO,C 18
O, H 13
CO +
,and
theJ=2 - 1lineof DCO +
(Juvela).
MattilahascollaboratedwithHerbstmeieret
al. (Heidelberg)andLaureijs(ESA/VILSPA)
in a study of the small-scale structures in
thefar-infrared background. At 180 mthe
small-scaleuctuationswerestudied forthe
rsttimebyacoldspacetelescopewitharc-
minute-resolution. Forcirruscloudsthespa-
tial frequency spectrum in the far-infrared
hasasimilarshapeasthatderivedfrom21cm
line observations of the interstellar neutral
hydrogen. In faint regions the uctuations
arecausedpresumablybyrandomlydistributed
extragalacticsources(Herbstmeieretal. 1998).
Radio spectroscopic studies of
nearby low-mass star forming
regions
Anderson, Caselli, Haikala and Harju have
investigated with the SEST the deuterium
and13-carbonfractionationinHCO +
towards
the nearby R Coronae Australis molecular
cloudcore. Thepurposeofthisstudywasto
test chemistry modelsand inparticular the
predicted temperature dependence of deu-
teriumfractionation,andtoestimatethede-
gree of ionization in this star-forming core.
TheH 13
CO +
/HC 18
O +
abundanceratiowas
foundtovarylittlefrom10withinthemapped
region,inexcellent agreement with the
13
CO/C 18
O abundance ratios derived ear-
lier towards the cloud. This corroborates
the close relationship between HCO +
and
COpredictedbytheion-moleculechemistry.
The variation of the DCO +
/HCO +
abun-
danceratiowithinthecorewasshowntobe
duetotheriseofthekinetictemperature(as
derived frommethylacetyleneobservations)
neartheclusterof newlybornstars.
FigureChemicalfractionationintheRCoro-
naeAustralismolecularcloudcore. The 13
C-
andDvariantsofHCO +
showdierentspa-
tialdistributions. DCO +
thrives inthecold-
est dense clumps. The maps are from the
work Anderson, Caselli, Haikala and Harju
(1999).
Firstly, the reaction H
2 D
+
!H +
3
becomes
faster; and secondly, an intensied desorp-
tion from grain surfaces makes the abun-
dance of neutral atoms and molecules in-
creaseinthegasphase,whichleadstoanef-
fectivedestructionoftheH +
3
andH
2 D
+
ions.
Both processes decrease the DCO +
/HCO +
ratio. Far from the active region around
IRS 7thederived abundancesof neutral
species indicate the presence of depletion.
The observations suggest furthermore that
thefractionalelectronabundancerisesalong
with the distance from IRS 7. This is also
connectedwiththehighdegree ofgas phase
depletioninthedense,quiescentgas(Ander-
sonetal. 1999).
Harju,WinnbergandWouterloothavestud-
iedthedistributionoftheOHradicalinTau-
rus MolecularCloud-1, withthe purposeto
predict the distribution of O
2
which would
serve as guidance for the coming observa-
tions with the Odin satellite. Further mo-
tivationwasto ndoutther^oleofdepletion
onto the grain surfaces in the well-known
chemicalgradientinthecloud,whichislikely
to be reectedintheOHabundance. It was
shown that the cyanopolyyne peak in the
southern part of TMC-1 corresponds to a
distinctOHmaximum. Thismaximummay
represent theso called'radical peak',which
according to some chemistry modelsoccurs
whendepletionstartstodominate thecloud
chemistry. The OH observations thus sup-
porttherecentlypresentedideathattheex-
istence ofcomplexmolecules notnecessarily
require chemical youth but may also indi-
cate a high degree of depletion. On the ba-
sisofcomparisonbetweenOHandearlierSO
data the authors suggest that in the north-
ern part of TMC-1 OH has been converted
to O
2
. Thissuggestion willbetestedduring
theOdinmission(Harju etal. 1999).
Garay,Kohnenkamp,Bourke,Rodriguezand
Lehtinenhave observedwiththeSESTrota-
tional transitions of SiO, CS, CH
3
OH and
HCO +
towards the highly collimated bipo-
lar outow BHR 71. Broad wing emission
wasdetected towardtheoutowlobesinall
the observed molecular lines. The shapes
of the proles are strikingly dierent from
molecule to molecule. The integrated wing
emission is extended and shows well-sepa-
rated blueshifted and redshifted lobes. The
abundanceofmethanolandsiliconmonoxide
intheoutowlobesisfoundtobeenhanced
withrespectto thatoftheambientcloudby
factorsofupto40and350,respectively
Radio spectroscopy of giant
molecular cloud cores
Harju, Lehtinen,Boothand Zinchenkohave
conductedasurveyofthermalSiOlineemis-
sion towards galactic giant molecular cloud
coresinorder to studythecharacteristicsof
shocksassociatedwithmolecularlinemasers
andembeddedfar-infraredsources. Gaseous
SiO is not assumed to exist under normal
conditions in dense interstellar clouds. For
thissurveywhichcontained369objectsthey
used the 15-m SEST and the 20-m Onsala
radiotelescopes. It was foundthat for ux
and luminositylimited samples the SiOde-
tectionrateishigherintheinner7kpcfrom
thegalacticcentrethanelsewhere. Thissug-
gests that dense cores belonging to the so
called \molecular ring"provide particularly
favourable conditions for the production of
SiO.Althoughthelineshapesingeneralagree
withamodelwheretheemissionarisesfrom
turbulent wakes behind bow-shocks, there
are a large number of cores with symmet-
ric,relativelynarrowproles. Thisindicates
a contribution from the quiescent gas com-
ponent, which cannotbe wellunderstood in
termsofcurrentchemistrymodels. Insubse-
quentstudiespresentlyunderwaythegroup
uses theobtainedSiOdatabase forcorrela-
tionwithvariousmaserand thermallinesto
understand better wherethe masers are ex-
cited, and for search for 'Orionlike', strong
SiOmaser sources(Harju et al. 1998).
Zhinchenko,Pirogov,andTorisevasurveyed
55 northern non-stellar H
2
O masers in the
CS(J = 2 1) line with the 20-m Onsala
radiotelescope. They detected 47 CS cores
associated probably with 50 masers. From
the CS maps and optically thin C 34
S emis-
sion they derive the basic physical parame-
tersofthecores: size,LTEmass,meanden-
sity, virialmass. Combiningthe present re-
sultswith the previousSEST datathey ob-
tain statistical distributions of the core pa-
rametersandanalyzethedependenceonthe
galactocentric distance R . The mean den-
sityof the cores drops with increasing R in
the interval R 7 14 kpc. It is consis-
tent with an exponential law with a scale
length of about 3 kpc. The IR luminosity
to mass ratio changes probably in a similar
way. ThecoresizeincreaseswithRinaccor-
dancewiththedensitydecreaseandconstant
Molecular gas in the Magel-
lanic Clouds
HeikkilahasobservedlineemissionfromCS,
SOandH
2
Sinasample ofmolecularclouds
in the Large Magellanic Cloud (LMC) and
theSmallMagellanic Cloud(SMC).The re-
sultingaverage SO/CScolumndensityratio
isabout1,fallinginbetweenthatofGalactic
diuse clouds (typical ratio >1) and dense
clouds(typical ratio<1),respectively. Con-
sideringdense clouds,thehigherSO/CS ra-
tiointheLMCandtheSMCascomparedto
theGalaxycouldbeduetoahigheroxygen-
to-carbon (O/C) ratio; although then the
apparentlackof dierenceintheSO/CSra-
tio between the LMC and the SMC is un-
expected. Since thevariationof the SO/CS
ratio from cloud to cloud is small, the ra-
tiodoesnotseemto dependstronglyon the
cloud age. An alternative production path
for SO, via gas-phase ion-neutral reactions,
was briey investigated. This involves the
reaction SO +
+H
2
!HSO +
+H. Using a re-
centestimationoftheformationheatofHSO +
,
thereactionquotedabove isfoundto been-
dothermicbyabout172kJ/mole(20700K)
and,accordingly,doesnotappearto beable
tocompetewithknownneutral-neutralreac-
tions, exceptpossiblyin gaswhich is highly
energeticandwhereatomicsulphurisalmost
exclusively in the form of S +
, e.g. the hot
partofaphoton-dominatedregion(PDR),a
strongshock, orahotmolecular core. Since
spectroscopic data forrotational transitions
arenotavailableforHSO +
,atthemomentit
isnotpossibletoobservationallytestwhether
this ion is important in interstellar sulphur
chemistry(Heikkila 1999).
Radiativetransfer modelling of
dense molecular clouds
Juvela analysed CS and C 34
S spectra ob-
served towards southern massive star form-
ing cores with the aid of radiative transfer
calculationsperformedwiththeMonteCarlo
methodusingthreedimensionalclumpycloud
models. The densitydistributionsof the
modelcloudsareeitherfractalorconsistofa
formodelsthatwouldsimultaneouslyrepro-
duceall theobserved CS and C 34
S spectra.
Inmostcasessatisfactorytscouldbefound
withmodelshavingconstantkinetictemper-
atures. The models tend to have very low
volume lling factors, typically < 0:2. The
radial density dependences of the original
models were n r
with 1:0. Al-
though thisprovided ingeneral a good cor-
respondence withtheobservations,emission
fromthe highrotationaltransition
CS(J = 7 6) was underestimated. Bet-
ter ts were obtained with models having
steeperradialdensitydistributionsand with
models with kinetic temperature increasing
inwards (Juvela1998).
FigureAnexampleofthethree-dimensional
density distributions used in the modelling
of interstellar clouds. The density distri-
butions were created with dierent methods
(e.g. fractalalgorithms)andaradiativetrans-
fer program was used to calculate molecular
line spectra that could be compared with ob-
servations. The density distribution of the
gure is based on the structure tree method.
(Juvela1997)
FigureSpectracalculatedfromathree-dimen-
sionalcloudmodel(continuouslines)together
withspectraobservedtowardsasouthernmas-
sivestarformingcore(histograms). Average
spectrawerecalculated forfourCSandC 34
S
transitions atdistances =0, 20and40arc
seconds from the core centre and the model
parameters (e.g. density and temperature)
were adjusted in order to obtain a good t.
(Juvela 1998)
Padoan,Juvela,BallyandNordlundstudied
the dynamics of molecular clouds by using
numericalsolutionsof thethree-dimensional
compressiblemagnetohydrodynamic(MHD)
equations in a regime of highly supersonic
randommotions. The non-LTEradiative
transfer calculations are performed through
the complex density and velocity elds ob-
tained as solutions of the MHD equations,
andmorethan510 5
spectraof 12
CO, 13
CO,
andCSareobtained. Inthiswaytheybuild
synthetic molecular clouds of 5 and 20 pc
diameter, evolved for about one dynamical
time from their initial conguration. They
use a numerical, super-Alfvenic ow with-
out gravity or external forcing. The syn-
thetic maps and spectra bear a remarkable
resemblance to the corresponding observa-
tions of real clouds and are therefore more
realistic thanprevious calculations(Padoan
et al 1998).
Padoan, Bally, Billawala, Juvela and Nord-
lund have compared the predictions of the
MHD modelswith observationsof interstel-
lar clouds. The calculated spectra have en-
abled direct comparison of the models with
e.g. theextensive 13
CO(1{0)mappingmade
ofthePerseusmolecularcloudcomplex. The
withtheobservationsandthisdemonstrates
thatthethree-dimensionalstructureanddy-
namics of the region can be adequately de-
scribedbyrandomsuper-AlfvenicMHDows
(Padoan et al. 1999a)
Padoan, Juvela, Bally and Nordlund have
usedthe MHD modelsand the spectra pro-
ducedwithradiativetransfercalculationsto
testmethodsthatarecommonlyusedto an-
alyzemolecularlineobservations. Thestudy
has shown that LTE analysis of 12
CO and
13
COspectrausuallyunderestimatesthetrue
13
CO column density and in extreme cases
thiserror can be more than a factor of ve
(Padoan et al. 1999b).
Jimenez, Padoan, Juvela et al. have com-
putedspectralenergydistributionsofproto-
galacticstarburstsathighredshift. Thecal-
culationsinclude the modelling of synthetic
stellarpopulations,thechemicalevolutionof
the interstellar medium and the changes in
the star formation rates. In addition to es-
timates of the visibleand infrared emission
predictionsarecalculated formolecular line
radiationofe.g.
12
COandO
2
. Theobtained
COluminosityof 10 8
L
for a proto-galaxy
of 10 10
M
is in agreement with current
CO detections at high redshift (Jimenez et
al. 1999).
Polarisation, extinction andthe
CO/H
2
ratio in dark clouds
Juvelapresentssimulatedextinctionmeasure-
mentsusingdierentthree-dimensionalmod-
els for the density structure of interstellar
clouds. It is shown that the observed small
scaleextinction variationsare very eective
in limitingthe free parameters of the cloud
models. On the other hand, all the tested
models(i.e. fractal and structure-tree mod-
els) are able to reproduce the observed ex-
tinctionvariationswithsomeparameterval-
ues. This is found to be true even for a
modelconsistingofrandomlyplacedclumps
ofconstantdensity. Theextinctionmeasure-
ments can, however, be used to get crude
estimates of the volume llingfactor of the
clouds. Comparisonbetweenthemodelsand
the observations of the cloud IC 5146 indi-
catesavolumellingfactorintherange0.1-
0.2(Juvela 1998).
Gahm(Stockholm)hascarriedoutdeepCCD
polarimetry in the I band in selected elds
in three lamentary, molecular clouds, the
L1400 complex, L204, and MBM25. I mag-
nitudesandthedegreeanddirectionoflinear
polarizationweremeasuredwithsatisfactory
accuracies for 387 stars down to I = 19:5.
Themeasurementsshowthatthepatternsof
polarizationareremarkablysmoothoverthe
eldsstudied,particularlyintheL1400com-
plex. There is no indication of any statisti-
callysignicantdierenceinpolarizationan-
gle and degree between obscured and non-
obscured regions. The method opens the
possibilityto studysmall-scaleirregularities
inthepolarizationpatternonangularscales
down to a few arc seconds. Comparing the
extinctionA
V
andP=A
V
intheeldobserved
inthe H and Kbands theauthors ndthat
P=A
V
can attain high values (close to the
P = 3A
V
relation) only for small values of
A
V
. (Harjunpaa etal. 1999).
Harjunpaa hasinvestigatedtheratio ofcar-
bon monoxide column density to colour ex-
cessE(J-K)andH
2
columndensityinthedi-
rectionofbackgroundeldstarsinthreedif-
ferentglobules: B133, B335 and L466. This
is a continuationof thestudy of Harjunpaa
and Mattila (1996) of the same relations in
thedirectionofthreenearbymolecularclouds,
Cha I, RCrAand Coalsack. The N(CO)to
E(J-K) ratio was found to vary from cloud
to cloud: itis largerintheactive star form-
ingglobuleB335thaninthemore quiescent
globulesB133and L466. Theresultscan be
understood in two alternative ways, either
the N(CO)/N(H
2
) ratio is higher in active
star forming regions (B335) than inregions
withoutstar formation(B133, L466), orthe
ratioN(H
2
)=E(J K)changesfromcloudto
cloudandishigherinactivestarformingre-
gions than in quiescent clouds. (Harjunpaa
1998).
Infrared studies of external
galaxies and clusters of galax-
ies.
MattilahascollaboratedwithHaasetal. (Hei-
delberg)in a complete175 m(ISOPHOT)
mappingoftheAndromedagalaxy(M31)at
1 arcmin resolution. The bulk of the dust
has a temperature of only 16 K, consider-
ferred from the IRAS data and also colder
thanthe19 KfoundfortheMilkyWay. For
thecold dust component themasswasesti-
mated from its emission yielding 3 10 7
M
,
a dust mass about a factor of ten higher
thaninferredfromtheIRAS60/100mdata
alone. Thenewcolddustmass-ifevenlydis-
tributedin the plane of the galaxy - would
be suÆcient to make the diskof M31 mod-
erately opaque in the optical (Haas et al.
1998).
Mattila and Haikala have collaborated with
Stickel etal. (Heidelberg) in a studyof the
far-infrared emission of intracluster dust in
the Coma galaxy cluster. The ISOPHOT
C200 has been used to detect the extended
farinfrared emissionfrom the Comacluster
ofgalaxies. A conservative value fortheex-
cesssurfacebrightnessat120micronsis 0.1
MJy/sr,corresponding to a total netuxof
0.7Jy. The detectedexcess emission rep-
resentstherstdirectevidenceforintraclus-
ter dust in a galaxy cluster. Since dust is
destroyed eectively by the hot intracluster
medium, thedust detected may result from
galaxystrippingduringtheongoingmerging
process inComa. (Stickel et al. 1998).
Vaisanen, while continuing his predoctoral
studentship period at the Smithsonian As-
trophysical Observatory (SAO), has taken
partin theELAIS collaboration asmember
of the Helsinki Observatory team. He has
done, together with EricTollestrup (SAO),
NIRfollowupobservationswiththeMt. Hop-
kins1.2-mtelescopeequippedwiththeSTER-
LIRCam array camera, and with the 3-m
IRTF telescope at Mauna Kea. The NIR
surveyhasconcentratedintheELAISelds
N1 and N2 where there are data in opti-
cal, sub-mm, and radio bands, in addition
to the ISO mid- and FIR-bands. In addi-
tiontothesciencecomingoutfromthecom-
bined eort of the ELAIS consortium, the
NIR data have been used to study the J-
and K-band galaxy counts. These will be
the rst published wide-eld, medium-deep
J-bandgalaxy counts.
Theextragalactic infraredand
opticalbackground light (EBL)
Thecosmicinfraredbackgroundradiationcar-
ries information from the otherwise unob-
servable"darkages"oftheUniversebetween
the redshifts 4 and 1000, during which e.g.
Alsohereinterstellardustgrains,formeddur-
ing the rst phasesof galaxy evolution, are
the "elementary" emitting particles for far-
IR. For the disentanglement of the dier-
ent foreground components, ISOPHOT of-
ferssomeadvantagesandcomplimentaryfea-
turesascomparedwithCOBE/DIRBE.The
150 and 180 m maps of some very dark
patches of the sky near the North Galactic
Pole, belonging to an ISOPHOT EBL pro-
gram (PI Mattila), have been preliminarily
analysed in 1998. The analysis shows that
ISOPHOTissensitiveand stableenoughfor
this type of extremely demanding measure-
ment.
JuvelaandMattilaincollaborationwithLemke
etal. (Heidelberg)havebeensearchingpoint
sources in far infrared maps observed with
the ISOPHOT C200 and C100 cameras in
several very dark areas of the sky, mapped
for the ISOPHOT EBL project and some
other projects. Majorityofthe detected
sources can be assumed to be extragalactic.
In many cases no previously known sources
can be associatedwith thedetected objects.
It isprobable thatdust-enshrouded, distant
galaxiesformasignicantfractionofthede-
tected sources. The number counts of the
detectedsources arecompatible withstrong
evolution models and exclude no-evolution
modelsat a highcondence level. Theinte-
grated surface brightness contribution from
the detected sources forms 5 - 10 % of the
cosmic far infrared background if the value
announcedbytheDIRBEteam is adopted.
Vaisanen andTollestrup (SAO)(1998)have
presented a reviewof the faint and lowsur-
face brightness galaxy contributions to the
extragalactic optical background radiation.
This is an extension of the previously pub-
lishedresults(Vaisanen,P.,1996,A&A315,
21). The review also presented work on a
uctuationmethodwhichcanbeusedtostudy
faint galaxy populations by complementing
EBL results and direct source counts. This
hasbeenappliedto SIRTFdeepsurveypre-
dictionsand confusionlimitdeterminations.
Optical and infrared night sky
brightness
Mattila and Haikala have collaborated with
Leinert and twelve further colleagues from
France,Germany,andU.S.A.inthecompila-
tionofan extensivereviewpaperon thedif-
materialintabularandgraphicalform,with
theaim toallowthenon-specialistto obtain
a realistic estimate of the diuse night sky
brightnessovera widerange of wavelengths
fromthefarUV longwardofLyto thefar-
infrared. At the same time the data are to
providea reference for cases in which back-
ground brightness has to be discussed, in-
cluding the planning for space observations
and the issue of protection of observatory
sites(Leinert et al. 1998).
Instruments and facilities
The use of SEST has been made possible
through an agreement of the Academy of
Finland and the Swedish Science Research
Council,according to whichFinnishastron-
omers can use a 10 % share of the Swedish
observingtimeatSEST.Sincethebeginning
of the SEST operation in1987 The Univer-
sity of Helsinki group has been responsible
for utilizingca. half of the Finnish time at
SEST.
Members of the group have frequentlyused
the Onsala 20-m and the Eelsberg 100-m
telescopes. ThegrouphasusedtheMetsahovi
14-m radiotelescope of the Helsinki Univer-
sity of Technology since 1979. It has been
responsiblefortheconstructionandrunning
of the spectrometre system. At present the
group uses the telescope mainlyfor student
training.
The research goals of the group have moti-
vatedastronginvolvementininfraredobser-
vations, 2to 200 m. Mattila wasinvitedto
become co{investigator in the ISOPHOT
consortium and he has also had the task of
thecoordinatoroftheISOPHOTinterstellar
medium research program.Members of the
grouphaveparticipatedinthepreparationof
the Guaranteed Time (GT) program of the
ISOPHOTteam. The group hasleadership
in three extensive GT programs. In addi-
tion,sixopenordiscretionarytimeprojects
weregrantedobservingtime.
Odin is a small Swedish satelliteunder de-
velopmentforsub-millimeterheterodynespec-
troscopyofinterstellarcloudsandtheEarth's
atmosphere. LaunchisscheduledforDecem-
ber1999. Thegrouphasco{investigatorsta-
tusinOdinandisresponsiblefortheFinnish
share of its astronomical research program.
Harju has beenappointed asan OdinLead
international eorts to set up a well coor-
dinated observing program for dark clouds.
Mattila has been member of the Odin Sci-
enceTeam.
Commitments
Harju continuedasmemberof the
Onsala/SEST Programme Committee until
June1998.
Lehtinen was electedto chairman ofthe
Finnish Astronomical Society, starting au-
tumn 1998
Mattila continued (until spring 1998) as a
memberoftheBoardofDirectorsofAstron-
omy and Astrophysics (A European Jour-
nal),asco{investigatoroftheISOPHOTCon-
sortium, as member of the ODIN Science
Team, as external team member of the EU
fundedELAISproject(EuropeanLargeArea
InfraredSurvey),asmemberoftheScientic
Organising Committee of IAU Colloquium
No. 171 \The Low Surface BrightnessUni-
verse"andtheRingbergConferenceon\ISO
surveysofadustyUniverse",andasreviewer
of funding applications of the Swedish Na-
tional Space Board. He continued as mem-
ber of the Finnish Academy of Science and
Letters, as memberof the FinnishNational
Committees of IAU, URSI, and COSPAR.
He was Co-ordinatorofthe EU/INTAS
Project \Dense cores in interstellar molec-
ular clouds". He was appointed a member
oftheFinnishMinistryofEducationad hoc
WorkingGrouponLargefacilitiesinAstron-
omy, anda memberof theOrganisingCom-
mittee of the Finnish Graduate School for
Astronomyand SpacePhysics.
Observations
SEST:
Harju 25.{28.2. and 6.{8.10.; Harjunpaa 4{
20.8.;Heikkila10.{17.12.;Juvela28.1.{13.2.;
Kahanpaa10{12.10.
Mt. Hopkins1.2{m infraredtelescope:
Vaisanen3.{8.4
MaunaKea 3{mIRTF:
Vaisanen11.{15.6
Harjuparticipated(with poster)intheZer-
mattconferenceonPhysicsandchemistryof
theinterstellarmedium22.{25.9.
Harjunpaa accomplishedseveral visits to
Stockholm Observatoryinthe framework of
collaborationwihtprofessorG. Gahn.
Juvela participated in the ISOPHOT Con-
sortiummeetinginHeidelberg22{23.6. (with
atalk),participated(withposter)intheZer-
matt conference on Physics and chemistry
of the interstellar medium 22.{25.9 the 7th
COSPAR-meetingofFinnishspacescientists,
14{15.9., inKiljavanranta (poster).
KahanpaaparticipatedintheESO-OHPSum-
mer School14{25.7.
LehtinenparticipatedintheISOPHOTCon-
sortiummeeting inHeidelberg22-23.6.(with
a talk),attended theESAConference \The
UniverseasseenbyISO",20{23.10. inParis
(poster),the7thCOSPAR-meetingofFinnish
space scientists, 14{15.9. in Kiljavanranta
(poster), the Conference \Solid state inter-
stellar matter- the ISO revolution", 1.{8.2,
inLesHouches,France(poster),participated
(with poster) in the Zermatt conference on
Physics and chemistryofthe interstellar
medium22.{25.9.
Mattila attended the ESAConference \The
UniverseasseenbyISO",20{23.10. inParis
(poster), theAnnualmeeting of theFinnish
PhysicalSociety,19{20.3. inTampere(poster),
the 7th COSPAR-meeting of Finnish space
scientists,14{15.9. inKiljavanranta (review
talk),andtheNordicconference\Astrophys-
ics with NOT", 12-14.8. in Turku. He par-
ticipatedintheISOPHOTConsortiummeet-
ing22{23.6. inHeidelberg,theOdinScience
team meetings on 11.2. and 26{27.11. in
Stockholm, andthe LSAConsortiumBoard
meeting on12.11. inBonn.
Vaisanen participated in IAU Colloquium
No. 171 \LowSurface BrightnessUniverse"
6{10.7. inCardi(invitedtalk).
Activities in space instrument
projects
TheHighEnergyAstrophysicsteamhasbeen
working ontheSiliconX-RayArray(SIXA)
for the Spectrum-X-Gamma satellite (esti-
mated launch during2001-2002). The team
alsoparticipatedinthesciencedataanalysis
software development of the X-ray monitor
JEM-XonboardINTEGRAL(launch2001)
and initiated planning for the X-ray Solar
Monitor (XSM) for the SMART 1 mission
(launch 2001).
0 0 1 1
0 0 1 1
SMART-1
XSM detector locations (tentative) ion or plasma thruster
Figure SMART{1 spacecraft
These project activities were directed byO.
Vilhu (PrincipalInvestigator forSIXA, and
Co-I forJEM-X and XSM)and J. Huovelin
(Principal Investigator for XSM, and Co-I
for SIXA and JEM-X). In all these space
instrument projects, the Finnish company
Metorex International Inc. is the manufac-
turer of the detectors. There is also collab-
orationwiththeX-rayphysicslaboratory of
ourUniversityintheSIXAandXSMprojects.
The Technology Development Centre
(TEKES)and theAcademyof Finlandpro-
vided funding for these instrument-related
projects.
science
VilhuandNevalainen,usingRXTEobserva-
tions, discovered a peculiar X-ray variabil-
ity in the superluminal jet-source ('micro-
quasar')GRS1915+105,seenasaring{shaped
patterninthetwo-color diagram(ApJ,508,
L85, see Fig.4). The rings are thought to
exhibit phenomena close to the black hole
horizonundersuper-Eddingtonaccretion.
Huovelin,Vilhu,Pohjolainen(fromtheMetsa-
hovi Radio Research Station) and J. Virta-
nenstarted detailedstudy ofthe
SOHO/SUMERobservationsof theX-ray
brightpoints(XRBP's)oftheSunconducted
inOctober 1996 byVilhu(see Fig. 5). The
observations show a fairly detailed spatial
shape(1arcsec/715kmresolution)andshort
termevolution(about1hourtimespanwith
4 minutes time resolution) of the XRBP's.
Among other interestingresults, the spatial
intensity distribution of the observed emis-
sion reveals the fact that the transition re-
gion heating on the Sunis notstrictly con-
ned in the XRBP's. This may be a sign
of rapid heat diusion in the atmosphere,
or sub-arcsecond spatial structures of small
magneticloopsontheSun,causinglocalised
temperatureenhancementswhicharenotre-
solvedbyourobservations(MNRAS,inprepa-
ration).
Hakalaconcentratedonfurtherdevelopment
and application of forward foldinginversion
techniques in astronomy (especially genetic
algorithms). His contributions to this eld
have included the construction of the rst
ever map of the magnetic white dwarf sur-
face and modelling the eclipse prole light
curves of polars (MNRAS 297, 1261; MN-
RAS302, 362).
Hakala and Muhli developed a geometrical
3D modellingcode to t the light curves of
X-raybinaries. Theircodecanbeusedtode-
rive crucialparameters of X-ray binarysys-
tems,includinginclinationoftheorbitalplane,
massratioofthebinarycomponentsandver-
tical structure of the accretion disk around
the compact star. Hakala and Muhli used
theircode tot themulticolorlightcurveof
theblackholebinarycandidate4U1957+115,
obtainedearlier at the Nordic OpticalTele-
scope (NOT). The system has shown evi-
dence of dramatically evolving optical light
curvesontimescalesofyears,eventhoughno
signicant variations have been observed in
tingresultsgaveproofofanon-axisymmetric
accretiondiskwithsubstantialverticalthick-
ness in its outer rim. Evolving shape of the
outerrimissuspectedtocausethepronounced
variationsinthelightcurves.
HannikainenandcollaboratorsatthePhysics
DepartmentoftheUniversityofSydney,Aus-
tralia, explored links between radio and X-
ray emission from Galactic radio-jet X-ray
binaries,especiallytheirbehaviorduringjet
ejection episodes. Primarily three sources
werestudied: GX339{4,GRS1915+105and
GROJ1655{40. The rst two areblackhole
candidates, whereasthethirdisconjectured
to be a black hole based on optical radial
velocity measurements. GRS1915+105 and
GROJ1655{40areknowntoexhibitjetswith
velocities 0.92c, while GX339{4 is not a
conrmedjetsource. GROJ1655{40hashad
one major multiple jet ejection episode ac-
companiedbyaringstatesinboththeradio
andtheX-rays(in1994),whileGRS1915+105
hasundergoneseveralsuchepisodes(oncein
1994andagainin1997). D.Hannikainenre-
duced and analyzed Molonglo Observatory
Synthesis Telescope (MOST) and Australia
TelescopeCompactArray(ATCA)data. The
principal resultsto emerge from these stud-
ieswasthediscoveryofasignicant amount
oflinearlypolarizedradiouxduringthejet
ejections and radioaringepisodesin
GROJ1655{40, and the discovery of a ar-
ingepisodewhichoccurredsimultaneouslyin
theradio, soft andhard X-rays in GX339{4
which strongly suggested the outowing of
matter fromthe system.
Figure The MOST 843 MHz,RXTE/ASM
2-12keV,andBATSE20-100keVlightcurves
of GX 339-4, showing the aring episode in
all threewavelength regimes on TJD50300.
sityof Oxford and IAC, Tenerife, examined
optical data, obtained earlierat the Nordic
Optical Telescope (NOT), of an enigmatic
radio source, GT2318+620. Earlier radio
imageshaverevealedjet-likefeaturesaround
anunresolved core. Basedon radioobserva-
tions and a very limited set of optical data
previousauthorshaveclassiedthesourceas
a Low Mass X-Ray Binary. However, NOT
imagesuncoveredaveryred,extendedsource
instead of a stellar point source suggesting
thatthesourcemightbeanactiveradiogalaxy.
On the other hand, NOT spectroscopy ex-
hibitedONLYinterstellarlinesinabsorption
which does not favor the active galaxy sce-
nario. Furtheroptical and infrared observa-
tionsweretakenbytheIACcollaboratorsin
late1998 to unveilthe mysteryof
GT2318+620.
MuhliandHakalapreparedtwoapplications
forobservingtimewiththeNOTinorderto
study three X-ray binaries with high speed
photometryand spectroscopy. Bothpropos-
als were granted observing time, 10 nights
in total, for 1999. One of the targets, 4U
0614+09,aneutronstarbinarywithunknown
orbitalperiodhasexhibitedperiodicitiesbe-
tween 15-30 mins in earlier observations. If
conrmedbytheforthcomingNOTobserva-
tionsasanorbitalperiodtheshortperiodic-
ity would give proof of a double degenerate
system, crucial for understanding interact-
ingbinaryevolution. Thetwoother targets,
4U 1957+115 and MS 1603+2600, are both
potentialblackhole binariesandshow dras-
tically evolving optical light curves. How-
ever, as the overall luminosity of both sys-
temsremainsroughly unchanged, thevaria-
tionscannot beduetochangingmassaccre-
tion rate. UsingNOT observations and the
3D disk modelling code Muhli and Hakala
intendtostudyvariationsinthegeometrical
structureof thesystems.
UsingNOT and ROSAT, Hakala and Vilhu
collaboratedwiththeGermangroupanddis-
covered a new polarRX J1015.5+0904near
thelowerperiodlimit80min(Burwitzetal.
AA,331,262). Hakala, MuhliandVilhucol-
laborated withD.H. Chaytorand S.L. Mor-
risandnisheda long termprogramof
MS1603+2600(usingNOTandROSAT)and
concludedthat thisshort periodbinary can
be a new soft X-ray transient in quiescence
(X-raynova) neverseen inoutburst.
Nevalainenhasundertakenhisdoctoralthe-
sisresearchworkinHarvard-SmithsonianCen-
terforAstrophysics,Cambridge, USA, with
September 1997. The work has included-
generating software to t spatially resolved
ASCAX-raytemperaturedata,combinedwith
ROSAT X-ray imaging data of clusters of
galaxies withhydrostatic mass models. The
aim is to nd out dark and baryonic mat-
ter distributions in clusters. The data of
theA401andA3571 clustershave beensuc-
cessfully t using this software, and ts for
clustersA85,A539andAWM4arecurrently
being run. The essential result is that the
ASCAspectroscopyrevealsthatinmostclus-
terstheintraclustergastemperaturedeclines
with increasing radius, contrary to earlier
isothermalassumptions,andthatthemasses
derivedareconsequentlysignicantlysmaller
than what was thought before. This im-
pliesthatthevalueofthecosmologicalmat-
terdensityparameterwouldbesmallerthan
whattheclusteranalysisgavepriortoASCA
data, instrongconictwithEinstein-deSit-
ter universe.
Nevalainen and Roos from the Physics De-
partmentof theUniversityofHelsinkistud-
ied the metallicityeect of LMC calibrated
Period-Luminosityrelation of Cepheidvari-
able stars. Combiningall theavailabledata
(mainly Hubble Telescope measurements of
galaxyandsupernovamagnitudes,galaxyve-
locitiesand galaxy metallicities) Nevalainen
andRoosdeterminedthevalueofthemetal-
licitycoeÆcient,whichdescribesquantitavely
how the Cepheid metallicity aects the ob-
served galaxy distances. With thismethod,
previously very discrepant Hubble constant
values were brought into agreement (A&A
339, 7).
Vilhu,Muhli,Huovelin,Hakala,S.M.Rucin-
ski and A. Collier Cameron(AJ 115, 1610)
usedthe HubbleSpace Telescopeand found
bimodallineprolesofthetransition region
CIV 1549 line in quiescence (indicative of
microaring)and detectedseveralimpulsive
ares intheyoungstar AB Doradus.
Vilhuand Huovelincollaborated withthe
french-USgroup(Durouchoux,Grindlay,Bally
etal.) andconductedamultiwavelengthstudy
(includingSEST)ofthenewblackholecan-
didateEXS1737.9-2952andcarefullymapped
its surroundings (Durouchoux et al. ApJ
507, 781).
Vilhuwasaco-editor(withN.J.Westergaard
and R. Svensson) of the proceedings of the
NordicConferenceinHighEnergyTheoreti-
calAstrophysics(PhysicaScriptaT77,1998)
can be found.
Observing runs
Hakalavisited theNordicOpticalTelescope
twice (March and June). Four dierent ob-
servingprogramswerecarriedoutduringthese
visits.
Hannikainen and S. Corbel (CEA, Saclay,
France)visitedtheSwedish-ESOSubmillime-
tre Telescope (SEST) inFebruary 1998 and
conductedtwoobservingruns,mappingmolec-
ular clouds associated with Galactic X-ray
andgamma-raysources.
Huovelin, Vilhu, etal. obtained BeppoSAX
X-ray satellite observations (30000 seconds
ofobservingtime)ofthegamma/X-raytran-
sientEXS1737.9-2952neartheGalacticCen-
tre in April, 1998. Preliminary studies of
theseobservationsrevealedpreviouslyundis-
covered distribution of X-ray emission en-
hancements inthe observed eld,whichare
currently under more detailedstudy by the
team (A&A,inpreparation).
HuovelinandPh. Durouchoux(CEA,Saclay,
France)visitedtheSESTinMarch1998,and
conductedmappingofe.g. theSS433region
at 115 GHz and230 GHz (CO-lines).
Muhli continued his long-term program for
photometricmonitoring of theopticalcoun-
terpartsof X-ray binariesat Metsahovi Ob-
servatory,Kirkkonummi,attainingatotalof
seven nightsin1998.
Conferences and other visits
Hakalavisited theOxfordUniversity,the
Mullard Space Science Laboratory and Le-
icesterUniversityforatwo-weekvisittodis-
cussscientic projects inJune1998. Hakala
attendedthe Annapolismagnetic CV work-
shopinJuly,theXMMworkshopatESTEC
in September, and the NOT-OPC meeting
onLa PalmainDecember.
HakalaandMuhlivisitedtheircollaborators
attheUniversityofOxfordinNovemberfor
ascientic colloquium.
Hannikainen gave a talk at the 2nd Galac-
tic Sources withRelativistic Jets Workshop
hostedbytheOpenUniversity,MiltonKeynes,
inApril1998,attendedtheworkshoponHigh
Energy Processes in Accreting Black Holes,
ber participated both at the Second Work-
shoponRelativisticJetSourcesintheGalaxy
andthe19thTexasSymposiumonRelativis-
ticAstrophysicsandCosmology,bothinParis,
France.
Hannikainenvisitedhercollaboratorsatthe
UniversityofSydneyinAugust 1998to con-
tinuethereductionandanalysisofradiodata.
HuovelinandAlhaparticipatedintheCOSPAR
meeting of the Finnish Space Scientists in
Kiljava,14thSeptember1998,whereHuovelin
presentedatalkonHighenergyAstrophysics
at theUniversityof Helsinki.
Hannikainen and Muhli attended the 19th
TexasSymposiumonRelativisticAstrophysics
and Cosmology,Paris, France.
Vilhugave talksintheAASmeeting inMay
(SanDiego),AccretingBlackHoleworkshop
inSweden(July)andRelativisticJetsources
workshop in December (Paris) and partici-
pated with a posterin the3rd INTEGRAL
workshop in September (Tormina). He also
actedasamemberintheorganizingcommit-
tees of the IAU Commission No. 42 'Close
Binaries' and DivisionXI 'High Energy As-
trophysicsand SpaceAstronomy', aswellas
intheNORDITAAstrophysicssubeldcom-
mittee.
Theplanetaryresearchgroup(PRG)hascon-
tinuedresearch work in its two main elds:
light scattering and radiative transfer. In
bothcasesthePRGhasbeenstudingspecic
applications and possibilitiesforgeneraliza-
tion of the existing methods. One impor-
tant question has beento explain two long-
standing observational ubiquitous phenom-
ena in planetary photometry. Atmosphere-
less bodies (moons, asteroids and comets)
and the Zodiacal light all show a nonlinear
rapidincreasein brightnesstowards theex-
act backscattering geometry i.e. the plan-
etary opposition. Also, linear polarization
of these objects alwaysshows thesame pat-
tern being negative at small phase angles,
changingsignatabout20degreesandreach-
ingmaximum closeto90 degrees. Although
thesephenomenahavebeenknownfordecades
no quantitative and physicallyplausible ex-
planation has been been oered. Our sys-
tematicalstudyonlightscatteringhasshown
that both solid irregularly shaped particles
andtightlypackedaggregatescanalmostau-
tomatically producethese phenomena. Our
light scattering code carries out these com-
putationsincompactand versatile way.
Interestinglyenoughexactlythesamemeth-
ods can be used for various technologically
importantmundaneproblems. ThePRGhas
actively participated in paint and paper in-
dustry research. With ourexisting code we
can, among other things, explainhowsmall
pigmentsshouldbedistributedinpaintsand
how thebest paperquality can be achieved
witha properselection ofcoating pigments.
Radiative transfer approach is a fundamen-
tal tool in studing reection properties of
planetary bodies. Once properobservations
existthedatacan beinverted toyieldphys-
ical informaton on the structure of the re-
golith,i.e. theloosedust layercovering the
surfacesofmostsolidatmospherelessobjects.
The PRG has been able to generalize the
classicaltheoryofradiativetransferintothe
case where the interface of the layer is a
stochastically roughsurface.
Lumme participatesintheMars
Express{spaceprojectataCo.I-status. His
taskwillbetousethestate-of-the-art meth-
odsof light scattering in order to derive in-
formation on the Martian dust and clouds.
Theseproblemsarealsocloselyconnectedto
various green house and Sahara sand ques-
tions.
teninternational experts who participate in
thelightscatteringexperimentundermicro-
gravityonboardtheInternationalSpaceSta-
tion(ISS). To support thisexperiment and
the ongoing basic research in light scatter-
ing and radiative transfer work the PRG is
currentlycarryingout afeasibilitystudyon
buildingbothagoniometerandascatterom-
eterforfurthertestingofthetheories. These
instrumentswouldbetheonlyexistingones
inwhole Scandinavia and could also benet
industrialresearch intheeld.
PiironendefendedhisPhDDissertation'Pho-
tometry of asteroids at small phase angles
withrelatedlaboratorymeasurements',Pro-
fessor Lumme acted as custos and Dr. Al-
berto Cellino, Osservatorio Astronomico di
Torino, as opponent. Keranen nishes her
MScdegree .
Visits and observing runs
Piironen acted the whole year 1998 as an
detachednational expertinEuropeanCom-
missionsSpace Application Institute, Ispra,
Italy. He worked asa group leaderof Euro-
pean Goniometric Facility (EGO). Keranen
visitedEGOtoprovidephotoklinometricdata
ofdierentroughsurfaceswithvaryinggaus-
sianstatistics.
Astronomy Group
NumerousNEOs(Near{EarthObjects),near{
Earthasteroidsandcomets, orbittheSunin
the neighborhood of the Earth. The vast
majorityoftheseobjectsareunknowntous.
Thesecelestialbodiescanberemnantsofthe
early solar system material,from which the
Earth and the other planets were formed,
andsomecanbeeitheractive,coma{covered
ordormant asteroidal comets.
NEOs are an important research topic be-
cause of several reasons. They can provide
usessentialinformationabouttheoriginand
early evolution of the solar system. Know-
ing the NEO population is of utmost im-
portancewheninterpretingthecrateredsur-
facesoftheEarth andtheMoon. NEOsim-
pose a signicant impact hazard upon the
Earth; the Jupiter{impact by Comet Shoe-
maker Levy 9 in summer 1994 proved that
cosmicimpactstakeplaceinthepresentevo-
lutionary phaseof theplanetarysystem.
NEOs can be important future resources of
ore minerals, and they are excellent targets
for space missions: Rosetta, one of ESA's
(European Space Agency) cornerstone mis-
sions, willbe launchedtostudy Comet
P/Wirtanen, which is a near{Earth comet
on ahighly chaoticorbit.
Near{Earth asteroids and comets are small
bodies of the planetary system with orbital
perihelialessthan1.3AUfromtheSun(AU
isthedistancebetweentheSunandtheEarth).
Onaverage, one 1kmcomet passesbetween
the Earth and the Moon per century, and
one impacts the Earth or the Moon every
few hundred thousandyears. Several 100 m
{1kmasteroidspassbetweentheEarthand
theMoon every year.
The youngstellar-planetaryastronomy
-project (SPA) started its activities in the
beginning of 1998. The overall goal of the
SPA is to gain new insights into the phe-
nomenaandcollectivepropertiesoflate-type
starsandplanetarysystems. Currently,SPA
coversawidespectrumofresearchareasthat,
to name afew,consists of
theoretical and experimental physical
studies of electromagnetic scattering
bysmallparticles and mediathereof,
photopolarimetricobservations and
lightcurve analyses of near-Earthand
main-beltasteroids,
ability analyses of near-Earth aster-
oids,
Hamiltoniandynamics of n-bodysys-
tems,timeseriesanalysesappliedtoa
multitudeofscientic problems,
surfaceimagingoflate-type stars
SeemoredetailedinformationfromtheSPA
pageintheserver:
http://albedo.astro.helsinki.fi/.
Muinonen(1998)publishedtherstapplica-
tionoftheso-calledGaussianrandomsphere
to the modeling of the shapes of asteroids
andcometary nuclei. TheGaussian random
spherewasreviewedindetail,andexemplary
lightcurveswerecomputedforsampleGaus-
sian asteroids. Intriguingly ne lightcurve
detailsshowed up in the computations that
partlyexplainedtheincreaseof theasteroid
lightcurve amplitudes with increasing solar
phaseangle.
FigureSample Gaussian sphere
NousiainenandMuinonen(1999)appliedthe
Gaussian random sphere to model the ir-
regular shapes of oscillating raindrops and,
indeed, were the rst to study light scat-
tering by oscillating raindrops in the visi-
bledomainoftheelectromagneticspectrum.
Muinonen and Saarinen (1999) established
dom cylinder, completing their earlier work
(MuinonenandSaarinen1996),andpublished
theray optics approximation forcomputing
light scatteringbysuch cylinders.
Lamberg(article underpreparation with
Muinonenandothers) providedamaximum
likelihood estimator for solving the inverse
problem of deriving the statistical param-
eters of the Gaussian random sphere from
sample shapes. By making use of existing
three-dimensionalshape modelsof asteroids
and planetary satellites and extending the
workbyLambergetal.,MuinonenandLager-
ros(1998)succeededindescribingtheshapes
of small solar system bodies with a small
numberof statistical parameters. Theirsta-
tistical modelpromises to be applied innu-
merous simulations of the physics of small
solar system bodies (see back page of this
annualreport).
Battaglia etal. (1999) computed light scat-
teringbyGaussianparticlesintheRayleigh-
ellipsoid approximation. They developed a
new method for describingthe shapesof ir-
regularparticleswithellipsoids: theso-called
best-t ellipsoid is the one that maximizes
the common volume of the particle and the
ellipsoid. Extensive light scattering simu-
lations were carried out, and the Rayleigh-
ellipsoidapproximationturnedeÆcientinthe
computationof scatteringbyelongatedpar-
ticles.
At an international meeting on Light Scat-
tering by Nonspherical Particles, Muinonen
(1998) gave an invited presentationon light
scatteringbystochasticallyshaped particles
and, subsequently, wrote a review chapter
forabooksoontobepublishedbyAcademic
Press.
Piironenetal.,(1998)publishedsingle-particle
albedomeasurementsofseveraltypesofme-
teorite particles. The measurements were
carriedoutattheInstituteofTechnicalTher-
modynamics(DLR,Stuttgart)bymakinguse
of novel technique based on electrodynamic
levitationofsmallparticles(techniquepaten-
ted in Germany with Muinonen and Piiro-
nen among participants). Piironen et al.
(1999) published the rst experimental re-
sultsontheoppositioneectofvarioussnow
samples. It appears thatcoherent backscat-
tering(Muinonen1994,andreferencestherein)
can explaintheobserved narrowpeaksclose
to thebackscatteringdirection.
Shkuratovetal.(1998)publishedapaperon
the diagnostic senseof the oppositioneect
cent snow measurements by Piironen et al.
(1999). In order to study shadow-hiding in
porous particulate media, Muinonen (1999)
extendedtherayopticscomputationstoclus-
ters ofGaussianrandomparticles. The rst
resultsshowed the gradual strengtheningof
shadow-hidingeectwithincreasingnumber
ofmemberparticles in clusters. Stankevych
etal. (1999)completedanextensivestudyof
the shadow-hiding eect in inhomogeneous
layered particulate media. The results oer
importantinsightintounderstandingtheop-
positioneectof airlesssolarsystembodies.
Muinonen participated in the ESA Topical
Team on Interactions in Cosmicand Atmo-
spheric Particle Systems that designed ex-
tensiveexperimentsaboardthefutureInter-
national Space Station (Blum et al. 1998).
Worms et al. (1999) worked on lidar imag-
ingofsmallto medium-sizedspace debrisin
low-Earth orbit.
Forhis invitedtalkon thediscovery of
Tunguska{sizedbodiesintheSpaceguardSur-
veyofnear-EarthobjectsattheInternational
Workshop Tunguska'96inBologna, Italy,
Muinonen (1998) carried out discovery and
follow-upsimulationsforsmallEarth-crossing
asteroids, down to the diameter of 10 m,
reaching substantial conclusions about the
discovery biases for various classes of near-
Earth objects. These simulations will help
designeÆcientgroundbasedand spaceborne
search programs for near-Earth objects in
the visible and infrared regime of the elec-
tromagnetic spectrum.
Thenear-Earthasteroid1997XF
11
madethe
newsmediaheadlinesinspring1998asitwas
suggested that a collisionwith the Earth in
October2028couldnotberuledoutwiththe
existingastrometric data. Muinonen (1999)
participated in the vivid discussion about
thecollisionprobability(with interviewsby
Science and Nature scientic journals) and
showed, using rigorous statistical methods,
that the collision probability was, in fact,
vanishingly small. The aforedescribed arti-
cle culminated from two invited lectures by
Muinonen on near-Earth asteroid searches
and orbit determination at an international
AdvancedStudy InstituteinJuly1997
(Maratea,Italy). Intheresultingvolumeen-
titled TheDynamics of Small Bodies in the
SolarSystem(KluwerAcademicPublishers),
MuinonenandMilani(1999)coordinatedan
important Sectionon near-Earthobjects.
