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Browsing by discipline "Astronomy"

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  • Viitanen, Akke Esa Tapio (2017)
    Active galactic nuclei (AGN) are compact, luminous objects found in the central region of many galaxies. In the standard paradigm, the AGN is fueled by accretion of matter into a supermassive black hole (SMBH). In fact, the properties of many galaxies and their respective SMBHs are linked, which hints at the importance of AGN as factors in galaxy formation and evolution. The bulk of the matter in the Universe is some form of dark matter, which is still poorly understood. AGN are biased tracers of the underlying dark matter distribution. By comparing the clustering of AGN with that of the dark matter, the bias may be quantified and further, the bias can be linked to a characteristic mass of the dark matter halo hosting the AGN. The advent of high-resolution X-ray telescopes, namely Chandra and XMM-Newton, has made unprecedently large samples available for study. With detailed spectroscopic follow-up programs, the study of X-ray selected AGN clustering has received a major boost. The clustering measurements tell of the typical environments that are likely to host AGN and thus shed light on what actually triggers the AGN. In this thesis, the clustering of ∼ 600 X-ray selected AGN with z < 2.5 (z = 1.19) in the COS- MOS (Cosmic evolution survey) field surveyed with XMM-Newton (XMM-COSMOS) is studied. The full sample is split into subsamples based on the host galaxy stellar mass M∗ and the ratio between the X-ray luminosity and the stellar mass LX/M∗ which is a proxy for the Eddington ratio. For the full sample the bias is 3.61+0.37−0.40, which corresponds to a characteristic halo mass of log M halo /h−1 M⊙ = 13.52+0.12−0.16 , consistent with the overall picture of X-ray selected AGN residing in massive haloes with 12.5 < logMhalo/h−1M⊙ < 13.5. The low M∗ and high M∗ samples have biases 3.53+0.58−0.70 and 4.13+0.85−1.07, respectively and the data do not support a difference in the typical masses of the hosting haloes. For the LX/M∗ subsamples, there is marginal evidence that low L X /M∗ AGN (logM halo /h−1M⊙ = 13.52+0.22−0.37) reside in more massive haloes than high L X /M∗ AGN (logM halo /h−1M⊙ = 13.29+0.28−0.58). One possible explanation would be that the environment of the low LX /M∗ AGN reduces the amount of gas available for accretion and thus results in lower accretion rates.
  • Siltala, Lauri (2016)
    Estimates for asteroid masses are based on gravitational perturbations on the orbits of other objects such as Mars, spacecraft, or other asteroids and/or their satellites. In the case of asteroid-asteroid perturbations, this leads to a 13-dimensional inverse problem where the aim is to derive the mass of the perturbing asteroid and six orbital elements for both the perturbing asteroid and the test asteroid using astrometric observations. We have developed and implemented three different mass estimation algorithms utilizing asteroid-asteroid perturbations into the OpenOrb asteroid-orbit-computation software: the very rough 'marching' approximation, in which the asteroid orbits are fixed at a given epoch, reducing the problem to a one-dimensional estimation of the mass, an implementation of the Nelder-Mead simplex method, and most significantly, a Markov-Chain Monte Carlo (MCMC) approach. We introduce each of these algorithms with particular focus on the MCMC algorithm, and present example results for both synthetic and real data. Our results agree with the published mass estimates, but suggest that the published uncertainties may be misleading as a consequence of using linearized mass-estimation methods. Finally, we discuss remaining challenges with the algorithms as well as future plans.
  • Vesterinen, Henrik (2012)
    Astrobiology is an interdisciplinary research field which studies the origin of life. One of the great challenges of modern observational astronomy in this area is to find building blocks of life in interstellar molecular clouds. These so-called biomolecules are under study in this thesis. First I present some fundamentals of radio spectroscopy and molecular structure. Then emphasis is put on observations made with the SEST- and APEX-telescopes of the objects NGC 6334F and IRAS 16293-2422. These objects represent the so-called hot cores. They are concentrations of gas and dust inside a molecular cloud where a new star is being born. One of the objectives in studying these hot sources is to find glycine NH2CH2COOH. Glycine is the most simple amino acid which means it is also a building block of our DNA. It has been hypothesised that several reaction chains may lead to glycine, either in gas phase or solid phase. Molecules that are part of the reaction chains that lead to glycine, are called precursors. Possible precursos of glycine are, for example, acetic acid and formic acid. The objective of this thesis is to find some of these precursors or their isomers. I have endeavoured to identify all molecular lines in the observed rotation spectra. This is done with the GILDAS/CLASS software package and specifically with its new Weeds extension. This has required estimation of the column density and then modifying its value until Weeds' model fits the observations. A lot of organic molecules were found. Glycine was not found and of its precursors only formic acid and methyl formate were found. However, the most interesting result was the detection of aminoethanol (NH2CH2CH2OH), which is a precursor of amino acid alanine (CH3NH2CHCOOH). Although this is only a tentative detection, it justifies a thorough investigation of future observations. Many of the observed spectral lines are blended so better resolution is needed. Many lines are also weak and are lost amid all the noise. The new ALMA interferometer will prove to be an invaluable tool in searching for new biomolecules. ALMA has very high angular and spectral resolution, high sensitivity, and large bandwidth. These properties are needed if we are to confirm or refute this new detection of aminoethanol.
  • Willamo, Teemu (2017)
    This Master’s Thesis deals with stellar magnetic activity, both as it is seen in the Sun, our closest star, and in other, more extreme examples of stellar activity. For the Sun, much higher quality data is available, and for a much longer time, so it remains by far the best studied star, although stars, that are much more magnetically active, have been discovered. This thesis will review the most common forms of magnetic activity, as observed both in the Sun and in other stars. A special focus is given to BY Draconis -type stars. These are young stars, whose photometric brightness variations are caused by large, cool starspots, similar to the sunspots seen on the Sun. A particular BY Draconis -star, V889 Herculis, is analysed in detail, using spectroscopic and photometric methods. From spectroscopy, by the Doppler imaging method, a surface temperature map can be constructed for the star. From photometry, both short-term and long-term variations of the star can be studied. During the 20 years time span of the photometric data, the star seems to have gone through similar activity cycles as the well known 11 year solar cycle. The aim of this thesis is to compare solar and stellar activity in general, and specifically V889 Her to the Sun. Based on the analysis, the basic properties of V889 Her, seen in previous studies, are confirmed: a large polar spot is present on its surface, and there are clear changes in its activity. As the stellar parameters, like mass and surface temperature, of V889 Her are very similar to the Sun, and it is also a single star, the main difference is age. As a young star, V889 Her is still magnetically much more active than the Sun today, but probably it will continue to become more and more similar to the present Sun, losing its high activity with increasing age. Similarly, V889 Her shows us what the Sun most likely was like billions of years ago.
  • Lahén, Natalia (2015)
    Interactions and mergers play important roles in the evolution of galaxies. In this Master's thesis I have studied some basic properties of merging galaxies using numerical simulations. I have created initial conditions for equal-mass disk galaxy mergers and run the simulations using the numerical simulation codes GADGET-3 and its recently updated version SPHGal. In this Thesis I have also reviewed the basic physics modeled by GADGET-3 and the differences between the astrophysical subresolution models in the standard GADGET-3 and SPHGal versions of the code. The aim of the Thesis was to see how different initial conditions affect the mergers of disk galaxies, and how the updated astrophysics affect the properties of the mergers. The simulations were run on the supercomputer Sisu and the supercluster Taito at CSC, the Finnish IT Center for Science. From the results of the simulations I have studied the effect of having a dark matter halo with either an NFW density profile or a Hernquist density profile. Four observed mergers were succesfully reproduced with NFW profiles using position and velocity maps, and then compared to their Hernquist profile analogues. By comparing the results of the mergers between galaxies with the two types of haloes, I found that the steeper gravitational potentials of the NFW haloes produced more prominent tidal tails than the Hernquist haloes. The more compact morphology of the disks within the Hernquist haloes before the final coalescence enabled also faster coalescence times in the Hernquist halo mergers. As expected, the NFW halo mergers experienced slower orbital decay, were more violent, experienced higher star formation rates and produced thus 2-17% more new stars than the Hernquist halo mergers. In the Thesis I have also studied the effect of the updated subresolution models on the star formation process in the merging galaxies. The star formation in the standard GADGET-3 is self-regulated, whereas the star formation in SPHGal is regulated by detailed feedback processes. The star formation rates vary both spatially and on much shorter time scales in the SPHGal compared to the analogous simulations with the standard GADGET-3. I analyzed also the metal yields in the merger remnants of the Antennae galaxies, and found a metallicity gradient within the inner 2 kpc from the center of mass of the remnant. A gradient was also present in the oxygen abundance of the remnants, following the fact that the metallicity was dominated by the abundance of oxygen. Gradients in the inner regions of the merger remnants are to be expected, since star formation is most active in the central regions of the remnant.
  • Kyyrö, Paula (2012)
    Filamentary structures appear to be very common in molecular clouds which are known to be the birth sites of stars. These interstellar filaments of gas and dust can have a dominant role in star formation. According to the current understanding of star formation, large-scale supersonic MHD turbulence present in the clouds tends to form these narrow elongated structures which are then broken into dense clumps through gravitational instability. The aim of my Master's thesis is to study the formation of stars by first reviewing the classical stability analysis of the most common self-gravitating structures subject to harmonic disturbances, having an emphasis on cylindrical symmetry which can be used to describe the behaviour of filamentary structures. Especially the density distribution, the critical line mass and the stability criterion (Jeans length) for self-gravitating isothermal cylinder are presented. Then the theory is applied to an individual target, a filament known as Taurus Molecular Cloud–1 (TMC–1). The goal is to investigate if the observed structures are in agreement with theoretical models and if stars can be formed in the filament through gravitational instability. By examining the properties of the cloud it is possible to find out when gravity (instead of external pressure) begins to dominate the evolution of the cloud. Important supportive forces, thermal pressure and turbulence, can be studied by observing standard molecular line tracers as ammonia. Ammonia NH3(1,1) and NH3(2,2) inversion lines are measured with the Effelsberg 100-m telescope in order to derive e.g. gas kinetic temperatures and non-thermal velocity dispersions along the TMC–1 filament. Furthermore, supplementing the molecular line data with the data from SCUBA 850 micron dust emission map of the cloud (Nutter et al., 2008) and assuming that the gas kinetic temperature equals to the dust temperature (Tkin = Tdust), hydrogen column densities can be calculated. Moreover, the cross-sectional column density profiles in several places along the filament can be fitted with the classical model of a hydrostatic isothermal cylinder by Stodolkiewicz (1963). The model fits roughly to the cross-sectional column density profiles. The fragment lengths or the projected clump separations along the ‘backbone’ of the filament (longitudinal profile) are derived from the intensity maxima seen in the SCUBA data. The observed fragment lengths along the filament are compared with the Jeans lengths and the fastest growing modes of disturbance predicted from Stodolkiewicz's model in order to investigate the star-forming potential of TMC-1. The observed clump separations are in a rough agreement with the local theoretical Jeans lengths. Moreover, the longitudinal SCUBA intensity profile is expanded into Fourier series, and the wavelengths corresponding to the dominating amplitudes are calculated. These wavelengths are compared with theoretical Jeans lengths in order to investigate if the perturbations travelling in the filament can cause collapse or if they are only ‘sound waves’. Two wavelengths, lambda = 0.23 pc and lambda = 0.30 pc, exceed the local theoretical Jeans length and hence may cause collapse within the filament and trigger star formation in the fragments.
  • Yli-Kankahila, Heidi (2012)
    In this Master's thesis, I have studied the properties of disk galaxy merger remnants formed in numerical simulations. I examined the star formation histories, black hole accretion, and the evolution of the total black hole mass during a 3 Gyr period in nine disk galaxy mergers with initially different galaxy progenitor masses, black hole masses and gas mass fractions. The simulations used in my analysis were performed by Johansson et al. (2009a) using the TreeSPH-code GADGET-2. My primary aim was to study the termination of star formation in the simulated mergers but I also examined the maximum rates of star formation and black hole accretion in these mergers and calculated the evolution of the galaxy colors during the merging process. I found the progenitor gas mass fraction to be the dominating effect in determining the star formation rate, black hole accretion rate, and the amount of black hole mass growth. A higher gas mass fraction systematically resulted in a higher star formation rate, black hole accretion rate, and larger final black hole mass. In the evolution of the galaxy colors, the dominating effects were the progenitor mass ratio and the progenitor gas mass fraction. Mergers with a higher gas mass fraction systematically resulted in redder remnants than corresponding mergers with a lower gas fraction. Mergers with a lower progenitor mass ratio resulted in redder remnants than mergers with the same black hole mass and gas fraction but a higher progenitor mass ratio. The redness of the low mass ratio mergers is due to the efficient black hole feedback which heats cold star-forming gas and drives it out of the galaxy. The color evolution of the simulated merger sample indicates that gas-rich disk galaxy mergers can, indeed, form red and dead remnants. This is in agreement with the merger scenario for early- type galaxy formation which states that star-forming gas-rich disk galaxies can result in red and non-star-forming ellipticals through merging.
  • Rantala, Antti (2014)
    In this Master's thesis, I have reviewed the theory of galaxy formation and evolution from primordial fluctuations to present-day galaxies. I have also examined the procedure for creating initial conditions for cosmological Zoom-in simulations. The main aim of this thesis was to perform groundwork in the field of Zoom-in simulations at the Department of Physics of the University of Helsinki for my future PhD studies. I have prepared a total number of 10 high-resolution multi-mass Zoom-in initial conditions, five of which contains dark matter and baryons and the rest consisting of dark matter only. The Zoom-in initial conditions were calculated using the P-GenIC N-body initial conditions code using the Alcyone cluster at the Department of Physics in July and August 2013. The computation of the Zoom-in initial conditions took approximately 41 days in wall-clock time using 24 processors. The ten Zoom-in simulations were run on the supercomputer Sisu at CSC, the Finnish IT Center for Science in September and October 2013 using the N-body simulation code GADGET-3. The code calculated the Newtonian gravitational force using the TreePM method. The gas dynamics was computed with the SPH algorithm and the properties of the interstellar medium and star formation were modeled using a statistical subgrid model. The simulation runs took approximately from one hour to one week of wall-clock time using 64 processors. The ten simulated galaxies were searched for contamination from low-resolution particles. The high-resolution regions of the galaxies were not contaminated, validating the preparation method of the Zoom-in initial conditions. The basic properties of the galaxies at z=0 were analyzed, including virial radii and virial masses, circular rotation curves and density profiles. Finally, star formation histories and colors of the simulated galaxies were extracted. The properties of the simulated galaxies were consistent with previous studies in the field of Zoom-in simulations (Naab et al. 2007, Johansson et al. 2012). Thus, I conclude that the aims set for this Master's thesis were successfully completed. After the groundwork has been conducted, it is convenient to move to future studies in the field of cosmological structure formation simulations. The focus of the future work will be in improving the simulation codes and in developing more realistic astrophysical feedback models. Increased spatial resolution and improved feedback models of the simulations can lead to significant progress on the most demanding challenges in the field of cosmological structure formation simulations.
  • Saajasto, Mika Markus (2014)
    Recent studies suggest a population of dust grains exceeding the classical maximum grain size of 0.25 µm to be present in the denser regions of the interstellar medium. In this study, we examine the possibility of using scattered near- and mid-infrared light as an instrument to determine the properties of interstellar dust grains. We will be utilizing observations of the filament TMC-1N located in the Taurus molecular cloud complex with a wavelength coverage from 1.25 µm to 8.0 µm. The observations were made with the United Kingdom infrared telescopes (UKIRT) wide-field infrared camera (WFCAM), and with Spitzer space telescopes IRAC instrument. We have also used the COBE satellites DIRBE instrument, and observations from the WISE satellite to determine the strength of the background intensity towards our source. To analyse the observations, we use radiative-transfer calculations and Markov chain Monte Carlo computations on several different dust models with varying grain-size distributions and chemical compositions. The optical properties of the dust grains are based on the computations made by Li and Draine (The Astrophysical Journal, vol. 554, p. 778, 2001). The parameters we are studying are the maximum grain size of the dust grains, the size distribution of the grains, the strength of the radiation field towards the Taurus molecular cloud complex, and the optical depth of the TMC-1N filament. Comparing our simulations with the observations, a dust grain population with maximum grain sizes exceeding the classical 0.25 µm seems most probable. Our simulations also indicate that the grain size distribution favours smaller grains over the large ones, although the larger grains contribute a significant portion of the total dust mass. These changes in the grain population should also be seen in the observed thermal emission. Thus, for further studies on the topic, we would suggest methods that combine information gathered from infrared light scattering and emission studies.
  • Nikbakhsh, Shabnam (2014)
    This dissertation develops and introduces a new interplanetary (IP) shock database. The database includes currently IP shocks and their related parameters for four years: 1998, 2000, 2003 and 2008 identified using the data provided by the Advance Composition Explorer(ACE) spacecraft. IP shocks have a crucial role in space weather as they are responsible for the most effective particle acceleration in the solar corona and solar wind. These particles are hazardous for satellites and space-embedded technology. Thus, studying of IP shocks has received considerable attention in recent decades and to date various lists and databases have been developed and introduced to study IP shocks. This database provides an important opportunity to advance the understanding of IP shocks. In the future the database will be extended to have a comprehensive coverage of observations from the spacecraft that have been monitoring the solar wind (e.g. Wind, ACE, STEREO) it brings users a new system for quick analysis of IP shock properties. One can filter IP shocks from the database by date and several key shock parameters, e.g., shock type, magnetosonic speed, etc. This thesis will introduce theory behind IP shocks, the structure of the database and how IP shock candidates were selected. In addition, a statical analysis of ACE IP shocks for 1998, 2000, 2003 and 2008 are performed.
  • Järvelä, Emilia (2014)
    High-energy γ-rays produced by powerful relativistic jets are usually associated with blazars and radio galaxies. Recently Fermi/LAT detected γ-rays from a few Narrow-Line Seyfert 1 galaxies and thus confirmed the presence of relativistic jets in those sources. In the current AGN paradigm powerful relativistic jets are almost exclusively launched from massive elliptical galaxies. Since NLSy1s are young evolving AGN they offer a unique opportunity to study the production of relativistic jets in late-type galaxies. In this study our aim is to determine via which processes and where different kinds of radiation are produced in NLSy1s. We compiled the so far largest multiwavelength database of NLSy1s which allowed us to explore correlations between different wavebands. We did this separately for radio loud and radio quiet sources. Multiwavelength correlations indicate that radio loud sources host a jet whereas radio quiet sources do not or the jet is very weak. Kolmogorov-Smirnov test suggests also that radio quiet and radio loud sources have different parent populations in redshift, luminosity and black hole mass. Open questions aroused also by this study are e.g. the origin of the infrared emission in NLSy1s and the differences between radio quiet and radio loud sources. In the future the large multiwavelength database of NLSy1s will permit us to easily identify and compare properties of new γ-ray NLSy1s to be detected by Fermi or other facilities.
  • Luoma, Antton (2018)
    The visual structure of galaxies, their morphologies, reveal a lot of information about the ongoing physical processes in galaxies. Galaxies interact gravitationally with each other, so the effects of the environment can be studied via galaxy structure. Galaxy structure can be studied by fitting analytical light profile functions to the observed images. The fitting is based on an assumption that the shape of the galaxy can be described by certain analytical forms. This kind of parametric studies can be done using the GALFIT software. As a result, these fitted models give values for the fundamental parameters describing galaxy size, shape and brightness. In this Master's thesis I introduce GALFIT as a tool for structural studies and morphological classifications of galaxies. I have gathered a sample of group member spiral galaxies in multiwavelength Hubble Space Telescope CANDELS survey data. I have completed detailed multicomponent and multiwavelength fits for 9 galaxies from the sample of 73 galaxies. The results are used to study stellar mass-to-light ratios and star formation using galaxy colors. Also a variety of asymmetry measurements are calculated for a subsample of these 9 galaxies. The results imply that the fitting process should be unified to measure similar comparable parameters for the entire sample. I have used my knowledge in GALFIT in a study of galaxies in the infalling groups observed in LoCuSS survey by completing bulge-to-disk decomposition fitting for a sample of several hundred galaxies. The sample galaxies are classified based on the Sérsic indices from my fits and tests verify the classification. The results imply that the effect of mass-quenching is negligible in the infalling galaxy groups. The results also imply that the star-forming galaxies are more elongated than the passive ones, and that the bulge luminosity of the star-forming galaxies rise towards the center of the cluster, however with a low statistical significance. GALFIT is capable of producing images based on the initial input parameter values if it's not used to fit existing data. I have applied this feature to simulate mock observational data of fields covered in galaxies for the Euclid mission. The images accompanied with catalogs of coordinates, magnitudes and position angles of the objects are used by the Euclid group in Helsinki as independent test data for developing validation tools for Euclid data simulations.
  • Mäkelä, Veikko (2015)
    We studied an RS Canum Venacorum type star BD Ceti. It is a chromospherically active binary (CAB). The primary component is a giant star, but shows solar type activity. With the orbital period of 35.1 days, it belongs into the long period group of RS CVn stars. The tidal interaction between the binary components has accelerated the rotation of the active component so that orbital and rotational period are almost the same. This fast rotation maintains magnetic and chromospheric activity. We applied the Continuous Period Search (CPS) method to 20 years automated V-band photometry. Modelling gave us mean magnitudes, amplitudes, periods, and primary and secondary minima of the light curve, as well as their error estimates. We studied both long and short term variations of the star. We found a possible 17.9 years activity cycle in the minimum starspot coverage. Because this cycle covers 90 % of the time span of our data, we could not confirm if this is a real phenomenon. From the period changes, we got the differential rotation coeffient |k| > 0.14, if the activity is present from the equator to the poles. We compared our result with latitudinal spot activity of the Sun and another RS CVn star Sigma Geminorum. BD Ceti has a higher differential rotation rate. We compared our result also to other published relations for estatimating differential rotation. We found that our results agree with the predictions by Collier Cameron (2007) and Küker &amp; Rüdiger (2011) and Reinhold et al. (2013). Our relatively high differential rotation estimate is consistent to published results where slower rotating stars have higher differential rotation. We found two active longitudes located almost at the opposite sides of the star. The primary active longitude existed through entire 20 years observing period. The second active longituge existed only occasionally. No evidence of occasional activity switch, so called ‘flip-flops’, between these longitudes was not found. We got a period of 34.6 ± 0.1 days for those longitudes, which is close to orbital period of the binary system. This active longitude structure may be an evidence of azimuthal magnetic dynamo rotating slightly faster than the star.
  • Parikka, Anna (Helsingin yliopistoHelsingfors universitetUniversity of Helsinki, 2012)
    In this study, I have investigated interstellar molecular clouds and specifically three fields mapped with the Planck satellite and Herschel Space Observatory at radio and sub-millimeter wavelengths: G131.65+9.75, G108.28+16.68, and G161.55-9.30. In these fields, four cloud cores were selected for closer investigation. The molecular line observations at 13CO, C18O, and N2H+ were made with the 20-m radio telescope in Onsala Space Observatory, Sweden. Also, data from Herschel Space Observatory was used. The molecular line observations were used for the study of cloud morphology and kinematics. The hydrogen column densities were estimated from both the molecular line and the dust continuum observations. Radiative transfer models were created for both the continuum and line data. The molecular line emission maxima were approximately where the dust continuum emission maxima were. The molecular line observations indicate that the studied cores are quite stable and show low turbulence. No clear detections of outflows were found in any of the cores. The column densities estimated from the dust continuum observations were 1 - 5 times the column densities derived from the molecular line observations. The column densities derived from the molecular line observations were also considerably lower than what is expected for protostellar cores. When comparing the masses estimated from the molecular line observations to virial and Bonnor-Ebert masses, the mass estimates were considerably lower and it seems that the cores are not on the verge of collapsing. The column density estimates derived from dust emission, however, are in line with the ones expected from prestellar cores and even in the light of the molecular line observations, there is no reason to doubt these data. Clearly, some more research in this area is needed to confirm, for example, the molecular depletion as an explanation of the apparent discrepancy between the continuum and line data
  • Martikainen, Julia (2016)
    Understanding light scattering on meteorite surfaces is difficult. Multiple factors affect the reflectance spectra of meteorites, such as space weathering, terrestrial weathering, and shocks. The main focus of this thesis was to investigate how shock induced iron changes meteorite spectra. The reflectance spectra of 30 meteorite pieces were measured with the University of Helsinki spectrometer in the wavelength range of 300 to 2500 nm. A principal component analysis (PCA) was performed on the spectra and the results were compared with previous studies carried out by Pentikäinen et al. (JQSRT, 146, 2014) and Gaffey (NASA PDS, 2001). The analyses show that HED meteorites can be separated from chondrites. However, more HED measurements are needed to verify the validity of the results. The effects of shock induced iron on meteorite spectra were modeled with the SIRIS3 (Muinonen et al., 2009) light-scattering program. Three different spectra of the Chelyabinsk meteorite were modeled, each of them having experienced a different degree of shock, and thus representing a different lithology: light-colored lithology was modeled as 10% air particles in olivine, dark-colored lithology as 10% iron particles in olivine, and impact-melt lithology as 5% air particles and 5% iron particles in olivine. The modeled spectra were then compared with the spectral measurements of the three lithologies of the Chelyabinsk meteorite. The compability of the measured and the modeled spectra was fair. In general, a higher iron occurrence makes the spectra darker and more flat. The differences between the modeled and the measured spectral shapes of the impact-melt and light-colored lithologies are caused by the absence of pyroxene in the simulations, whereas the modeled and the measured spectral shapes of the dark-colored lithology are different because the occurrence of iron in the measured spectrum is probably higher.
  • Kiiveri, Kimmo (2016)
    Havaittavaan maailmankaikkeuteen lähes tasaisesti jakaantunut ja noin 380 000 vuotta sitten syntynyt kosminen mikroaaltotaustasäteily on merkittävin yksittäinen havaittavan kosmologian tiedonlähde. Tämä taustasäteily on matkannut sen syntyhetkestä lähtien halki maailmankaikkeuden laajenemishistorian aina herkkiin mittalaitteisiimme saakka, ja täten se on sekä suora havaintoikkuna nuoreen maailmankaikkeuteen, että tärkeä havaintoaineisto maailmankaikkeuden laajenemishistoriasta. Vuonna 1992 NASA lähetti matkaan ensimmäisen taustasäteilyn epäisotropioita kartoittavan COBE-satelliitin, jonka mittaustulosten ja tätä seuranneiden satelliittimissioiden, WMAPin ja Planckin, ansiosta nykykosmologiasta on tullut täsmätiedettä. Vuonna 2009 laukaistun Planck-satelliitin perintö kosmologialle tulee olemaan unohtumaton. Jotta sen tarkat mittaustulokset saadaan luotettaviksi, tulee satelliitin havaintokeilat tuntea hyvin, sillä keiloista aiheutuvat efektit ovat suuria systemaattisten virheiden lähteitä. Havaintokeiloilla tarkoitetaan satelliitin yksittäisen detektorin, tai vaihtoehtoisesti useampien detektorien, spatiaalista vastetta, johon on huomioitu satelliitin skannausstrategiasta, datan käsittelystä, detektorista ja optiikasta aiheutuvat efektit. Tavallisesti nämä havaintokeilat on tapana esittää harmonisessa avaruudessa, mitatun tai simuloidun datan jatkoanalyysiä varten, jolloin niistä käytetään nimitystä skalaari-ikkunafunktio. Näiden skalaari-ikkunafunktioiden on todettu sisältävän ylimääräisiä systemaattisia efektejä, erityisesti lämpötila- ja polarisaatiosignaalin välistä vuotoa, joiden oletetaan olevan seurausta satelliitin samaan syöttötorveen kytkettyjen kahden detektorin välisten havaintokeilojen eroista. Tässä työssä esitetään uudenlainen malli, jolla voidaan vähentää kosmisen mikroaaltotaustasäteilyn epäisotropioita kartoittavan satelliitin instrumenteista ja skannausstrategiasta aiheutuvia ylimääräisiä efektejä, erityisesti signaalivuotoa lämpötilan ja polarisaation välillä. Vaikka tätä mallia on esitelty tässä tutkielmassa erityisesti Planck-satelliitin matalan taajuuden instrumenttien (engl. Low Frequency Instrument, LFI) taustasäteilyä koskevan signaalivuodon eristämiseen, soveltuu se käytettäväksi niin Planckin korkean taajuuden instrumenteille kuin myös signaalivuodon eristämiseen etualan säteilystä. Tästä mallista käytetään nimitystä matriisi-ikkunafunktio, ja se on vuonna 2015 kehitetty Helsingin yliopiston Planck-tutkimusryhmän yhteistyönä. Tässä tutkielmassa tarkastellaan CMB Monte Carlo —simulaatioiden avulla, miten havaintokeilojen erilainen muoto eri detektorien välillä vaikuttaa vuotokomponenttien suuruuteen. Erityisesti matriisi-ikkunafunktiomallin simulaatioilla näytetään, miten nämä signaalivuodot saadaan tehokkaasti eristettyä omiksi komponenteikseen, ja miten matriisi-ikkunafunktiota voidaan hyödyntää todenmukaisen taivaan lämpötilan ja polarisaation kulmatehospektrien rekonstruoimiseen. Näistä rekonstruoiduista taivaan kulmatehospektreistä voidaan puolestaan selvittää nykykosmologialle merkittävät kosmologiset parametrit, jotka karakterisoivat maailmankaikkeuden rakennetta, syntyä ja kehitystä.
  • Nikula, Petter (2016)
    This thesis investigates the automated near real time science analysis performed at the INTEGRAL Science Data Centre. The structure of the Quick-Look Analysis pipeline and individual analysis stages are detailed. The stage performing pattern recognition for two-dimensional coordinate lists, i.e. source identification, is tested in-depth. The lists contain sources located in a randomly selected 9ÌŠ by 9ÌŠ area of the sky. Using the current live version and default parameters; a simulated new source was correctly identified 98% of the time, fields with no new sources produced false detections 8% of the time. The testing reveals two separate flaws; a code error and a methodological error. The sensitivity of recognizing that a new source has been detected is reduced because of the code error. The methodological error causes the algorithm to report the detection of previously unknown sources where none exists. A possible solution is presented. New source detection was improved to well above 99% and false detections reduced below 2% with the new solution. A second methodological error causes the algorithm used to correct for the pointing error of the instrument to produce unreliable results. Fortuitously this problem is serious only for small pointing errors where the source matching algorithm is able to compensate for it.
  • Pentikäinen, Hanna (2013)
    The interpretation of asteroid spectra is closely tied to surface structure and composition. Asteroid surfaces are usually assumed to be covered with a regolith, which is a mixture of mineral grains ranging from micrometers to centimeters in size. The inverse problem of deducing the characteristics of the grains from the scattering of light (e.g., using photometric and polarimetric observations) is difficult. Meteorite spectroscopy can be a valuable alternative source of information considering that unweathered meteoritic 'falls' are almost pristine samples of their parent bodies. Reflectance spectra of 18 different meteorites were measured with the Finnish Geodetic Institute Field Goniospectrometer (FIGIFIGO) covering a wavelength range of 350-2500 nm and a zenith angle of reflection range of ± 60 degrees (Suomalainen et al., Sensors 9, 3891, 2009). Principal Component Analysis (PCA) performed on the spectra tends to separate the undifferentiated ordinary chondrites and the differentiated achondrites. The measurements expand the database of reflectance spectra obtained by Paton et al. (JQSRT 112, 1803, 2012) and Gaffey (NASA PDS, 2001). The spectra of meteorites found in all the data sets are consistent. For the FIGIFIGO measurements, the principal components suggest a discrimination between the spectra from ordinary chondrites of petrologic grades 5 and 6. The distinction is not present when the data are supplemented with the spectra from the two other data sets obtained with differing measuring techniques. Single-scattering albedos for meteoritic fundamental scatterers were derived with a Monte Carlo radiative-transfer model. In the derivation, realistic scattering phase functions were utilized. The functions were obtained by fitting triple Henyey-Greenstein functions to the scattering matrix elements of olivine powder for two different size distributions (Muñoz et al., A&A 360, 777, 2000; JQSRT 113, 565, 2012). The simulated reflectances for different scattering phase functions were fitted to the measured meteorite spectra. The single-scattering albedos for the analyzed ordinary chondrites range from 0.65 to 0.9, which is in line with the largest single-particle albedo values of 0.50 ± 0.25 for the ordinary chondrite Bjurböle measured by Piironen et al. (PSS 46, 937, 1998). Based on the analysis, meteorites with higher petrologic grades have higher single-scattering albedos across the wavelength range. Using the larger single scatterer results in a lower albedo but a wider range in albedo values.
  • Fedorets, Grigori (2013)
    The investigation of rotation of asteroids is an important means to deriving information about their physical properties and processes using ground-based instrumentation. The rotation rate distribution imply the significance of non-gravitational forces depending on the size of the asteroid. The absence of certain rotation rates in the asteroid population poses constraints on the inner structure of asteroids of different sizes. The majority of rotation periods of asteroids solved from photometric lightcurves belong to fast rotators. The observation time required for obtaining an accurate period estimate is substantially longer for a slowly rotating asteroid than for a rapidly rotating asteroid. Therefore, lightcurve surveys with limited observation time which allocate the same amount of time for all asteroids, are expected to only produce accurate periods for asteroids with short rotation periods. This thesis concentrates on various aspects of asteroid rotation. Methods used to obtain asteroid rotation periods and shape models are discussed. Also, physical mechanisms affecting the rotation of asteroids are considered. The focus is on the main-belt objects and slowly rotating bodies. The Thousand Asteroid Lightcurve Survey (Masiero et al. 2009) carried out with the Canada-France-Hawaii Telescope was one of the first systematic asteroid lightcurve surveys. One of the objects selected for follow-up was Hungaria asteroid (39420) 2084 T-2. Masiero et al. (2009) quoted a rotation period of 105 ± 21 h which is a relatively inaccurate solution, especially compared to the solutions for the fast rotators. In this work we present an updated period fit as well as a possible convex shape solution (Kaasalainen \& Torppa 2001, Kaasalainen et al. 2001) for the asteroid. The possibility that the investigated asteroid is a close binary or a non-principal-axis rotator is also discussed.
  • Kupri, Artem (2014)
    In this Master's thesis, I present for the first time the consideration of the effect of uncertainty associated with the astrophysical modeling of lens systems on the derived value of Omega_Lambda. I show that strong gravitational lensing, in the Universe described by the LCDM model, can be used for determination of a value of the vacuum energy density. The models used in this work are based on differences between the observed stellar velocity dispersions and the actual stellar velocity dispersions of elliptical and lenticular galaxies, which play a role of lenses in lensing systems. It will be shown that the accuracy of observations is very important in such kind of calculations. I present an own derivation of the formulas used in this work for determination of Omega_Lambda, which was never done in a reference work [Schwab et al., 2010]. Moreover, in difference from [Schwab et al., 2010], I will represent these formulas in the correct form. In this work, I use 30 lensing systems, observed by the Sloan Digital Sky Survey and the Hubble Space Telescope. I calculate the angular diameter distances of lensing and background galaxies and combine them with the stellar velocity dispersion measurements, taking into account the total mass density, the luminosity density and the anisotropy of the lensing galaxy. Finally, I have performed chi-squared test to identify the acceptable model. The value of the vacuum energy density determined in this thesis, by using a restricted sample (26 galaxy lensing systems), has realistic confidence intervals, much larger than previously published. I show that the strong constraints on the value of Omega_Lambda determined in some other similar works ([Schwab et al., 2010] and [Cao et al., 2012]) depend on inclusion of systems that are not described by the model.