Katja Poppenhaeger

My PhD student Nikoleta Ilic has investigated a really interesting object, the close M dwarf / brown dwarf pair NLTT 41135, which forms a hierarchical wide triple system with the M dwarf NLTT 41136. Nikoleta found an elevated activity of about an order of magnitude in X-rays that is most likely caused by tidal interaction between the brown dwarf and the M dwarf. Nikoleta was able to quantify this with the help of other wide M dwarf systems from the…

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Laura Ketzer, one of my PhD students, recently published a detailed study on the fate of small exoplanets – super-Earths and mini-Neptunes – under different time evolutions of the magnetic activity of the host star. The so-called radius gap manisfests itself differently for stars that experience an early versus a late spin-down. Also in samples of mixed stellar spin-down histories the features of the gap as a whole change with age, so that uniform age samples, such as open stellar…

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My PhD student Nikoleta Ilic has published a project we have been working on for the past two years: the identification of tidal star-planet interaction in a sample of planet-hosting stars. The tidal interaction leads to a spin-up of the host stars, which we identified through comparisons with co-eval companion stars in wide orbits around the star-planet systems. The paper was also featured in a joint press release of the AIP and the Harvard-Smithsonian Center for Astrophysics: https://chandra.harvard.edu/press/22_releases/press_110222.html Ilic, N….

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The second paper of the PEPSI Exoplanet Transit Survey (PETS) performs a search for possible atomic and molecular species that may drive the thermal inversion in the atmospheres of ultrahot Jupiters, and it rules out several species in the case of KELT-20 b/MASCARA-2 b: Title: “The PEPSI-LBT Exoplanet Transit Survey (PETS). II. A Deep Search for Thermal Inversion Agents in KELT-20 b/MASCARA-2 b with Emission and Transmission Spectroscopy” Johnson, Marshall C.; Wang, Ji; Pai Asnodkar, Anusha; Bonomo, Aldo S.; Gaudi,…

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One possible manifestation of (magnetic) star-planet interactions is flare triggering by a planet passing by some active region of the star and disturbing the magnetic field structure of the active region enough that a flare is triggered earlier than it usually would have occurred. My PhD student Ekaterina Ilin recently studied the many TESS-observed flares of the young planet-hosting star AU Mic to test whether there is any significant correlation of flare timing with the orbit of the exoplanet or…

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Our group is in a collaboration with other groups from Germany, Italy and the US to perform the PEPSI Exoplanet Transit Survey (PETS), which investigates exoplanet atmospheres in transmission and reflection observations. The first paper of the paper series is now published, and it’s an investigation of the nature of 55 Cnc e, a small rocky exoplanet, performed by my postdoc Engin Keles. The PEPSI exoplanet transit survey (PETS) I: investigating the presence of a silicate atmosphere on the super-earth…

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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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