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Last modified by Thomas Hackman on 2025/11/24 12:37
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Thomas Hackman 31.2 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:
hackman@helsinki_fi 1.1 2
Thomas Hackman 5.1 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
Thomas Hackman 4.1 9
Thomas Hackman 31.1 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]].**
Thomas Hackman 6.1 11
12 The research team consists of:
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14 * Thomas Hackman, PhD, University researcher
Thomas Hackman 11.1 15 * András Haris-Kiss, MSc, Doctoral researcher
Thomas Hackman 17.2 16 * Jyri Lehtinen, PhD, external member
Thomas Hackman 33.1 17 * Emilia Rintamäki, Doctoral researcher
Thomas Hackman 31.3 18 * Nora Routamo, MSc
Thomas Hackman 6.1 19 * Mikko Tuomi, PhD, University researcher
Thomas Hackman 17.2 20 * Teemu Willamo, PhD, external member
Thomas Hackman 19.1 21 * Joonas Uusitalo, PhD, Postdoc researcher (Laboratory of Chronology, University of Helsinki)
Thomas Hackman 6.1 22
Thomas Hackman 31.4 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).
Thomas Hackman 13.2 24
Thomas Hackman 6.1 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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Thomas Hackman 10.1 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]]
Thomas Hackman 6.1 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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Thomas Hackman 9.2 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
Thomas Hackman 6.1 35
Thomas Hackman 9.2 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]]
Thomas Hackman 6.1 37
Thomas Hackman 31.4 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.
Thomas Hackman 19.1 39
Thomas Hackman 31.4 40 [[https:~~/~~/arxiv.org/abs/2502.18129>>https://arxiv.org/abs/2502.18129]]
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Thomas Hackman 6.2 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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Thomas Hackman 6.1 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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Thomas Hackman 31.6 50 Nikbakhsh, S., Tanskanen, E., Hackman, T., 2025, Magnetic evolution of complex solar active regions, A&A, subm.
Thomas Hackman 31.5 51
Thomas Hackman 16.1 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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Thomas Hackman 17.2 56 Uusitalo, J, 2024, "Astronomical and terrestrial anomalies in high-latitude tree-rings", PhD thesis, University of Helsinki, Report series in astronomy 34
Thomas Hackman 16.2 57
Thomas Hackman 18.1 58 [[https:~~/~~/helda.helsinki.fi/items/65e513f9-efec-400f-8ca4-5971f4bd80ff>>https://helda.helsinki.fi/items/65e513f9-efec-400f-8ca4-5971f4bd80ff]]
Thomas Hackman 17.2 59
Thomas Hackman 6.1 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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Thomas Hackman 20.1 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
Thomas Hackman 9.2 65
Thomas Hackman 13.1 66 [[https:~~/~~/doi.org/10.1029/2023GL106632>>https://doi.org/10.1029/2023GL106632]]
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Thomas Hackman 6.1 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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