A5037717341- Stellar, planetary, and galactic studies
- Astro and Planetary Science
- Astrophysics and Star Formation Studies
- Astronomy and Astrophysical Research
- Astronomical Observations and Instrumentation
- Solar and Space Plasma Dynamics
- Calibration and Measurement Techniques
- Geomagnetism and Paleomagnetism Studies
- Geophysics and Gravity Measurements
- Gamma-ray bursts and supernovae
- Adaptive optics and wavefront sensing
- Astrophysical Phenomena and Observations
- Solar Radiation and Photovoltaics
- Economic Zones and Regional Development
- Climate variability and models
- Classical Antiquity Studies
- Craniofacial Disorders and Treatments
- Oceanographic and Atmospheric Processes
- Historical and Contemporary Political Dynamics
- Atmospheric Ozone and Climate
- Galician and Iberian cultural studies
- Vietnamese History and Culture Studies
- Atmospheric and Environmental Gas Dynamics
- Geology and Paleoclimatology Research
- Methane Hydrates and Related Phenomena
University of Helsinki
2015-2024
Helsinki Institute of Physics
2009-2023
University of Turku
2010-2022
Turku Centre for Computer Science
2010-2022
Aalto University
2022
Max Planck Institute for Solar System Research
2022
Uppsala University
2022
Dalhousie University
2006
Izaak Walton Killam Health Centre
2006
Global magnetic fields of active solar-like stars are, nowadays, routinely detected with spectropolarimetric measurements and are mapped Zeeman Doppler imaging (ZDI). However, due to the cancellation opposite field polarities, polarimetry only captures a tiny fraction flux cannot assess overall stellar surface if it is dominated by small-scale component. The analysis broadening in high-resolution intensity spectra can reveal these hidden complex fields. Historically, there were very few...
Aims. The goal of this work is to study the magnetic fields six young solar-analogue stars both individually, and collectively, search for possible field trends with age. If such are found, they can be used understand magnetism in context stellar evolution solar-like past Sun solar system. This also important atmospheric inner planets, Earth particular.
Abstract Recently, a rapid increase in radiocarbon ( 14 C) was observed Japanese tree rings at AD 774/775. Various explanations for the anomaly have been offered, such as supernova, γ-ray burst, cometary impact, or an exceptionally large Solar Particle Event (SPE). However, evidence of origin and exact timing event remains incomplete. In particular, key issue latitudinal dependence C intensity has not addressed yet. Here, we show that most likely caused by Sun occurred during spring 774....
The dynamo processes in cool active stars generate complex magnetic fields responsible for prominent surface stellar activity and variability at different time scales. For a small number of field topologies were reconstructed from the series spectropolarimetric observations using Zeeman Doppler imaging (ZDI) method. In this study we follow long-term evolution topology RS CVn binary star II Peg. We collected high-resolution circular polarisation Peg SOFIN spectropolarimeter Nordic Optical...
FK Comae is a rapidly rotating magnetically active star, the light curve of which modulated by cool spots on its surface. It was first star where "flip-flop" phenomenon discovered. Since then, flip-flops in spot activity have been reported many other stars. Therefore, it interest to perform more thorough study evolution Com. In this study, we analyse 15 years photometric observations with two different time series analysis methods, special emphasis detecting flip-flop type events from data....
We study the generation of large-scale vortices in rotating turbulent convection by means Cartesian direct numerical simulations. find that for sufficiently rapid rotation, cyclonic structures on a scale large comparison to convective eddies emerge, provided fluid Reynolds number exceeds critical value. For slower cool are preferred, whereas warm anti-cyclonic favored. In some runs intermediate regime both types cyclones coexist thousands turnover times. The temperature contrast between and...
We study a sample of 21 young and active solar-type stars with spectral types ranging from late F to mid K characterize the behaviour their activity. apply continuous period search (CPS) time series analysis method on 16 27 years photometry estimate surface differential rotation determine existence longitudes activity cycles stars. supplement results by calculating new $\log{R'_{\rm HK}}$ emission indices for high resolution spectroscopy. The photometric variations reveal positive...
Nearby, active stars with relatively rapid rotation and large starspot structures offer the opportunity to compare interferometric, spectroscopic, photometric imaging techniques. In this paper, we image a spotted star three different methods for first time. The giant primary of RS Canum Venaticorum binary $\sigma$ Geminorum ($\sigma$ Gem) was imaged two epochs high-resolution observations. light curves from reconstructions show good agreement observed curves, supported by...
Abstract The Carrington event of 1859 has been the strongest solar flare in observational history. It plays a crucial role shedding light on frequency and impacts past future Solar Energetic Particle (SEP) events human societies. We address impact by measuring tree‐ring 14 C with multiple replications from high‐latitude locations around comparing them mid‐latitude measurements. A transient offset following is observed high statistical significance. Our state‐of‐the‐art production transport...
Aims. We study the spot activity of II Peg during years 2004-2010 to determine long- and short-term changes in magnetic activity. In a previous study, we detected persistent active longitude, as well major configuration occurring on timescale shorter than year. The main objective this is whether same phenomena persist star these six spectroscopic monitoring. Methods. observations were collected with high-resolution SOFIN spectrograph at Nordic Optical Telescope. temperature maps calculated...
We present surface temperature maps for the FK Comae-type star HD 199178 (V1794 Cygni) calculated from high resolution spectra obtained in 1994 and 1995. The spot pattern evolves, but all reveal a large cool remaining nearly at same latitude. main is 1200-1600 K cooler than mean temperature. observed slightly flat bottomed absorption lines would usually be interpreted as evidence polar spot. argue that antisolar differential rotation offers better explanation box like shape of line profiles....
Aims.We investigate the spot evolution and surface differential rotation of single late-type giant FK Com.
<i>Aims. <i/>We gathered about 100 high-resolution spectra of three typical HgMn (mercury-manganese) stars, HD 11753, 53244, and 221507, to search for slowly pulsating B-like pulsations surface inhomogeneous distribution various chemical elements. <i>Methods. <i/>Classical frequency analysis methods were used detect line profile variability determine the variation period. Doppler imaging reconstruction was performed obtain abundance maps elements on stellar surface. <i>Results. <i/>For which...
Aims. We publish 16 Doppler imaging temperature maps for the years 1994–2002 of active RS CVn star II Peg. The six from 1999-2002 are based on previously unpublished observations. Through we want to study spot evolution and in particular compare this with previous results showing a cyclic behaviour persistent, longitudes.
We investigate the spot activity of young chromospherically active main sequence star LQ Hya. Our aims are to identify possible longitudes, estimate differential rotation and study long short term changes in activity. analysis is based on 24 years Johnson V-band photometry. use previously published Continuous Period Search (CPS) method model evolution light curve The CPS fits a Fourier series overlapping subsets data. This enables us monitor configuration with higher time resolution. find...
Aims: Time series of high-resolution spectra the late B-type star HD 11753 exhibiting HgMn chemical peculiarity are used to study surface distribution different elements and their temporal evolution. Methods: High-resolution high signal-to-noise ratio were obtained using CORALIE spectrograph at La Silla in 2000, 2009, 2010. Surface maps YII, SrII, TiII, CrII calculated Doppler imaging technique. The results also compared equivalent width measurements. evolution spots both on short long time...
The detection of exoplanets using any method is prone to confusion due the intrinsic variability host star. We investigate effect cool starspots on detectability around solar-like stars radial velocity method. For investigating this activity-caused "jitter" we calculate synthetic spectra radiative transfer, known stellar atomic and molecular lines, different surface spot configurations, an added planetary signal. Here, methods are described in detail, tested compared previously published...
Context. By studying young magnetically active late-type stars, i.e. analogues to the Sun, we can draw conclusions on evolution of solar dynamo.
In this study, we present simultaneous low-resolution longitudinal magnetic field measurements and high-resolution spectroscopic observations of the cool single giant FK Com. The variation over rotational period 2.4 d is compared with star-spot location obtained using Doppler imaging techniques, V-band photometry V−I colours. chromospheric activity studied simultaneously photospheric Hα, Hβ Hγ line profiles. Both maximum (272 ± 24 G) minimum (60 17 in mean field, 〈Bz〉, are detected close to...
We formulate an improved time series analysis method for the of photometry active stars. This new Continuous Period Search (CPS) is applied to 12 years V band young solar analogue HD 116956 (NQ UMa). The developed from previous Three Stage Analysis (TSPA) method. Our improvements are use a sliding window in choosing modelled datasets, criterion select best model each dataset and computation scale change light curve. test performance CPS with simulated real data. has much resolution which...
Aims. Previous studies have related surface temperature maps, obtained with the Doppler imaging (DI) technique, of LQ Hya long-term photometry. Here, we compare magnetic field Zeeman (ZDI) contemporaneous photometry, aim quantifying star’s cycle characteristics. Methods. We inverted Stokes IV spectropolarimetry, HARPSpol and ESPaDOnS instruments, into brightness maps using a tomographic inversion code that models high signal-to-noise ratio mean line profiles produced by least squares...
Aims. According to previously published Doppler images of the magnetically active primary giant component RS CVn binary II Peg, surface star was dominated by one single longitude that clearly drifting in rotational frame system during 1994-2002; later imaging for 2004–2010, however, showed decreased and chaotic spot activity, with no signs drift pattern. Here we set out investigate from a more extensive photometric dataset whether this is persistent phenomenon, which case it could be caused...
Aims. Our aim is to examine the solar cycle variability of magnetically simple and complex active region. Methods. We studied ($\alpha$ $\beta$) ($\beta\gamma$ $\beta\gamma\delta$) regions based on Mount Wilson magnetic classification by applying our newly developed daily approach. analyzed number (SARs) compared that abundance (CARs) over entire 23 24 until December 2018. Results. show CARs evolve differently from SARs. The time evolution SARs different hemispheres also shows differences,...