Katja Poppenhaeger

One of the major research questions in my group has reached a milestone – my PhD student Nikoleta Ilic led an investigation of the magnetic activity of planet-hosting stars that are located in wide multiple system with one or more other stars. Such systems allow us to test for an overactivity of the planet host star due to star-planet interaction (SPI) by using the other star(s) in the system as a negative, same-age control. Nikoleta found a significant correlation of…

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My group recently collaborated with the solar physics group and in particular Dr. Andrea Dierke for an investigation of solar H alpha emission. The paper is now published! Solar H alpha excess during Solar Cycle 24 from full-disk filtergrams of the Chromospheric Telescope Diercke, A.; Kuckein, C.; Cauley, P. W.; Poppenhäger, K.; Alvarado-Gómez, J. D.; Dineva, E.; Denker, C. The chromospheric H-alpha spectral line is a strong line in the spectrum of the Sun and other stars. In the stellar…

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During the first Covid lockdown I started what I call my little pandemic project. But then all the real-life consequences of living through a worldwide pandemic set in, and it took until early this year to wrap up my project. It is finally done! And it is the first single-author paper I have ever written. Here’s some information on the paper: Helium absorption in exoplanet atmospheres is connected to stellar coronal abundances Poppenhaeger, K. Transit observations in the helium triplet…

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My PhD student Ekaterina Ilin investigates stellar flares in various space-based observations, and has developed a flare-finding code names AltaiPony already a while ago. We used this in several of her papers, for example for the flare census in open clusters (Ilin et al. 2019, Ilin et al. 2021) and the high latitude flares on M dwarfs (Ilin et al. 2021, blog post). After having it available on github already for a good while, Ekaterina has now also published her…

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My PhD student Ekaterina Ilin has discovered a new method to localize flares on fast-rotating stars, using the rotational modulation of flares that last longer than the stellar rotation. With her new method she found that flares on fast-rotating M dwarfs occur close to the poles of the star, instead of neat to the equator like on our own Sun. This could be good news for exoplanets and their habitability, because particles expelled by the star during flares may miss…

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Our group’s first paper using data from the German-Russian eROSITA mission has been accepted for publication. My PhD student Grace Foster has investigated the X-ray irradiation and estimated the evaporation of exoplanets using data from eROSITA’s first and second all-sky scan. The paper is available here: Exoplanet X-ray irradiation and evaporation rates with eROSITA Foster, G. ; Poppenhaeger, K. ; Ilic, N. ; Schwope, A. High-energy irradiation is a driver for atmospheric evaporation and mass loss in exoplanets. This work…

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In a recent work by Prof. Carolina von Essen, with large contributions from our group from the side of Dr. Matthias Mallonn (and minor contributions from myself), we investigate the TESS phase curve and the dayside temperature of KELT-1b, which is a bit too heavy to still be called a planet and is therefore classified as a low-mass brown dwarf. From the abstract: We present the detection and analysis of the phase curve of KELT-1b at optical wavelengths, analyzing data…

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Ekaterina Ilin, a PhD student in my group, has recently published her work on stellar flares in three young and two middle-aged open clusters. From the abstract: “Drawing from the complete K2 archive, we searched 3435∼80 day long light curves of 2111 open cluster members for flares using the open-source software packages K2SC to remove instrumental and astrophysical variability from K2 light curves, and AltaiPony to search and characterize the flare candidates. We confirmed a total of 3844 flares on…

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Together with my PhD student Laura Ketzer and postdoc Matthias Mallonn, we have published a new paper on the atmospheric evaporation of the four very young planets around the star V1298 Tau. We measured the star’s X-ray spectrum by combining ROSAT and Chandra observations, and found that the star is highly active with an X-ray luminosity above 10^30 erg/s. Laura developed a numerical code to estimate the planetary evaporation as the star ages and becomes less X-ray bright. Depending on…

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