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Last modified by Thomas Hackman on 2025/11/24 12:37
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1 The University of Helsinki astrophysics research group focuses on observations of stellar magnetic activity and its relation to exoplanets. The goal is to use these observations for a better general understanding of the magnetic activity of solar type stars, and in particular the Sun's activity. We also investigate the influence of a stars activity on the detectability and space climate of exoplanets. We use the following observations:
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3 * High resolution spectroscopy from e.g. the Nordic Optical Telescope (NOT) and telescopes of the European Southern Observatory (ESO)
4 * Spectropolarimetry from e.g. the NOT and ESO
5 * Ground based photometry from e.g. Automated Photometric Telescopes
6 * Space based high precision photometry from e.g. the Transiting Exoplanet Survey Satellite
7 * Ground-based Ca II H&K monitoring surveys
8 * Radiocarbon measurements from tree rings
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10 Methods we are using include Doppler imaging, Zeeman-Doppler imaging (ZDI) and time series analysis. Radiocarbon measurements are used to detect historical solar energetic particle events. An example of a **ZDI-map and the Stokes I&V LSD-profiles for V889 Her** (6/2021, publication in prep.) using **NOT observations** can be found here: **[[ZDI-map>>attach:V889Her_ZDI_2021.pdf]] and [[Stokes I&V profiles>>attach:V889Her_prof_2021.pdf]].**
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12 The research team consists of:
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14 * Thomas Hackman, PhD, University researcher
15 * András Haris-Kiss, MSc, Doctoral researcher
16 * Jyri Lehtinen, PhD, external member
17 * Emilia Rintamäki, Doctoral researcher
18 * Nora Routamo, MSc
19 * Mikko Tuomi, PhD, University researcher
20 * Teemu Willamo, PhD, external member
21 * Joonas Uusitalo, PhD, Postdoc researcher (Laboratory of Chronology, University of Helsinki)
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23 The group has extensive cooperation with a large number of national and international research institutes, e.g.: Aalto University (Maarit Korpi-Lagg), University of Oulu (Eija Tanskanen), Uppsala University (Oleg Kochukhov), AIP Potsdam (Ilya Ilyin), Konkoly Thege Miklós Astronomical Institute (Zsolt Kővári), Tennessee State University (Gregory Henry).
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25 **Recent presentations at seminars and scientific conferences**
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27 Posters at the 21st Cambridge Workshop: Cool Stars, Stellar Systems and the Sun in Toulouse 4-9 July, 2022:
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29 * V889 Her: abrupt changes in the magnetic field or differential rotation? [[Willamo_poster.pdf>>url:https://wiki.helsinki.fi/xwiki/bin/download/SOL/Stellar%20astrophysics%20group%20at%20University%20of%20Helsinki/SOLSTICE/WebHome/Willamo_poster.pdf?rev=1.1]]
30 * [[Investigating historical Solar eruptions>>url:https://wiki.helsinki.fi/xwiki/bin/download/SOL/Stellar%20astrophysics%20group%20at%20University%20of%20Helsinki/SOLSTICE/WebHome/Hackman_poster_CS21.pdf?rev=1.1]]
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32 **Recent publications by team members**
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34 Hackman, T., Kochukhov, O. , Viviani, M., Warnecke, J. , Korpi-Lagg, M.J., Lehtinen, J.J., 2024, "From convective stellar dynamo simulations to Zeeman-Doppler images", A&A 682, A156
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36 [[https:~~/~~/www.aanda.org/articles/aa/pdf/2024/02/aa47144-23.pdf>>https://www.aanda.org/articles/aa/pdf/2024/02/aa47144-23.pdf]]
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38 Haris, A., Tuomi, M., Hackman, T., 2024: "Homogeneous search for spot transits in Kepler and TESS photometry of K ﹣ M-type main-sequence stars", A&A, in press.
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40 [[https:~~/~~/arxiv.org/abs/2502.18129>>https://arxiv.org/abs/2502.18129]]
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42 Kochukhov, O., Hackman, T., Lehtinen, J.J, 2023, Surface distribution of small-scale magnetic field on the active cool star LQ Hydrae, A&A 680, L17
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44 [[https:~~/~~/www.aanda.org/articles/aa/pdf/2023/12/aa47930-23.pdf>>https://www.aanda.org/articles/aa/pdf/2023/12/aa47930-23.pdf]]
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46 Lehtinen, J.J., Käpylä, M.J., Hackman, T., Kochukhov, O., Willamo, T., Marsden, S.C., Jeffers, S.V., Henry, G.W., Jetsu, L., 2022, ”Topological changes in the magnetic field of LQ Hya during an activity minimum”, A&A 660, A141
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48 [[https:~~/~~/www.aanda.org/articles/aa/pdf/2022/04/aa36780-19.pdf>>url:https://www.aanda.org/articles/aa/pdf/2022/04/aa36780-19.pdf]]
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50 Nikbakhsh, S., Tanskanen, E., Hackman, T., 2025, Magnetic evolution of complex solar active regions, A&A, subm.
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52 Tuomi, M , Lehtinen, J.,J., Henry, G.,W., Hackman, T., 2024, "Characterising the stellar differential rotation based on largest-spot statistics from ground-based photometry", A&A 689, A262
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54 [[https:~~/~~/doi.org/10.1051/0004-6361/202449861>>https://doi.org/10.1051/0004-6361/202449861]]
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56 Uusitalo, J, 2024, "Astronomical and terrestrial anomalies in high-latitude tree-rings", PhD thesis, University of Helsinki, Report series in astronomy 34
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58 [[https:~~/~~/helda.helsinki.fi/items/65e513f9-efec-400f-8ca4-5971f4bd80ff>>https://helda.helsinki.fi/items/65e513f9-efec-400f-8ca4-5971f4bd80ff]]
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60 Uusitalo, J, Arppe L., Helamaa, S. et al., 2022, "From lakes to ratios: ^^14^^C measurement process of the Finnish tree-ring research consortium", NIMPB 519, 37
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62 [[https:~~/~~/doi.org/10.1016/j.nimb.2022.03.013>>url:https://doi.org/10.1016/j.nimb.2022.03.013]]
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64 Uusitalo, J., Golubenko, K., Arppe, L., Brehm, N., Hackman, T., Hayakawa, H., Helama, S., Mizohata, K., Miyake, F., Mäkinen, H., Nöjd, Tanskanen, E., Tokanai, F., Rozanov, E., Wacker, L., Usoskin, Oinonen, M, 2024, "Transient Offset in 14C after the Carrington Event Recorded by Polar Tree Rings, Geophysical Research Letters 51, e2023GL106632
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66 [[https:~~/~~/doi.org/10.1029/2023GL106632>>https://doi.org/10.1029/2023GL106632]]
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68 Willamo, T., 2022, "Stellar activity : starspots, magnetic fields and activity cycles", PhD thesis, University of Helsinki, Report series in Astronomy 30
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70 [[https:~~/~~/helda.helsinki.fi/handle/10138/342285>>url:https://helda.helsinki.fi/handle/10138/342285]]
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72 Willamo, T., Hackman, T., Lehtinen, J.J., Korpi-Lagg, M., Kochukhov, Oleg, 2022, ”V889 Her: abrupt changes in the magnetic field or differential rotation?”, OJAp 5, 10
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74 [[https:~~/~~/arxiv.org/pdf/2203.13398v2.pdf>>url:https://arxiv.org/pdf/2203.13398v2.pdf]]
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76 Willamo, T., Lehtinen, J.J., Hackman, T., Käpylä, M. J., Kochukhov, O., Jeffers, S.V., Korhonen, H., Marsden, S.C, 2022, ”Zeeman-Doppler imaging of five young solar-type stars”, A&A 659, A71
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78 [[https:~~/~~/www.aanda.org/articles/aa/pdf/2022/03/aa41649-21.pdf>>url:https://www.aanda.org/articles/aa/pdf/2022/03/aa41649-21.pdf]]
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