Cool Stars 20.5 ?>

Cool Stars 20.5

Because Zenodo sometimes give a too-many-requests error during the conference, here’s a backup of my conference poster:

Katja’s Cool Stars 20.5 poster on stellar coronal abundances and helium observations of exoplanet atmospheres

Paper on stellar winds blowing around our nearest exoplanet neighbour ?>

Paper on stellar winds blowing around our nearest exoplanet neighbour

A recent work led by our Schwarzschild-Fellow Dr. Julián Alvarado-Gómez shows through numerical simulations that our nearest exoplanetary neighbour experiences a space weather environment similar to our own Earth. The planet is Proxima Centauri c, a planet a few times the size of the Earth, which orbits our nearest stellar neighbour Proxima Centauri in a roughly 5-year orbit.

Simulated stellar wind enviroment of the exoplanet Proxima Centauri c during a magnetic activity minimum of its host star, from Alvarado-Gómez et al. (2020).

From the abstract:

A new planet has been recently discovered around Proxima Centauri. With an orbital separation of ∼1.44 au and a minimum mass of about 7M , Proxima c is a prime direct imaging target for atmospheric characterization. The latter can only be performed with a good understanding of the space environment of the planet, as multiple processes can have profound effects on the atmospheric structure and evolution. Here, we take one step in this direction by generating physically realistic numerical simulations of Proxima’s stellar wind, coupled to a magnetosphere and ionosphere model around Proxima c. We evaluate their expected variation due to the magnetic cycle of the host star, as well as for plausible inclination angles for the exoplanet orbit. Our results indicate stellar wind dynamic pressures comparable to present-day Earth, with a slight increase (by a factor of 2) during high-activity periods of the star. A relatively weak interplanetary magnetic field at the distance of Proxima c leads to negligible stellar wind Joule heating of the upper atmosphere (about 10% of the solar wind contribution on Earth) for an Earth-like planetary magnetic field (0.3 G). Finally, we provide an assessment of the likely extreme conditions experienced by the exoplanet candidate Proxima d, tentatively located at 0.029 au with a minimum mass of 0.29 M.

“An Earth-like Stellar Wind Environment for Proxima Centauri c”, Alvarado-Gómez, Julián D.; Drake, Jeremy J.; Garraffo, Cecilia; Cohen, Ofer; Poppenhaeger, Katja; Yadav, Rakesh K.; Moschou, Sofia P., The Astrophysical Journal Letters, Volume 902, Issue 1, id.L9, 7 pp. (2020).

Also featured in a Science Update by the Harvard-Smithsonian Center for Astrophysics.



Paper on stellar flares in open clusters ?>

Paper on stellar flares in open clusters

Median fraction of stellar luminosity in flares plotted as a function of cluster age, from Ilin et al. (2020).

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 high probability open cluster members with ages from zero age main sequence(Pleiades) to 3.6 Gyr (M67). We extended the mass range probed in the first study of this series to span from Sun-like stars to mid-Mdwarfs. We added the Hyades (690 Myr) to the sample as a comparison cluster to Praesepe (750 Myr), the 2.6 Gyr old Ruprecht 147, and several hundred light curves from the late K2 Campaigns in the remaining clusters. We found that the flare energy distribution was similar in the entire parameter space, following a power law relation with exponent a=1.84−2.39. We confirmed that flaring rates declined with age, and declined faster for higher mass stars. Our results are in good agreement with most previous statistical flare studies. We found evidence that a rapid decline in flaring activity occurred in M1-M2 dwarfs around Hyades/Praesepe age, when these stars spun down to rotation periods of about 10 d, while higher mass stars had already transitioned to lower flaring rates, and lower mass stars still resided in the saturated activity regime. We conclude that somediscrepancies between our results and flare studies that used rotation periods for their age estimates could be explained by sample selection bias toward more active stars, but others may hint at limitations of using rotation as an age indicator without additional constraints from stellar activity.”

Flares in Open Clusters with K2. II. Pleiades, Hyades, Praesepe, Ruprecht 147, and M67“, Ilin, Ekaterina; Schmidt, Sarah J.; Poppenhäger, Katja; Davenport, James R. A.; Kristiansen, Martti H.; Omohundro, Mark, accepted by A&A, 2020.

Welcome to new group members ?>

Welcome to new group members

Two new group members are starting their research here in fall 2020: Judy Chebly is a new PhD student who works with Julián Alvarado-Gómez and myself on simulations of coronal mass ejections in stars-planet systems, and Dr. Eliana Amazo-Gomez is a new postdoc who works on stellar rotation and activity. We’re very happy to have them on board!

Conference: Exoplanets III ?>

Conference: Exoplanets III

Exoplanets III conference background image
This week the Exoplanets III is taking place – it has been moved from Heidelberg into a virtual format because of the Covid-19 pandemic. I’m really excited about this particular conference, because it looks like a really well thought-out way to do an online conference, with all talks being available as videos for non-synchronous viewing, interactive online posters, and active discussion on Slack. Several of our group members are presenting their work:

PhD students:
Laura Ketzer: Poster “Using PLATYPOS to estimate the atmospheric mass loss of V1298 Tau’s four young planets”
Vada Xanthippi Alexoudi: Poster “On the degeneracy of the planetary spectral slope with orbital parameters”
Engin Keles: poster “Probing the atmosphere of HD189733b with the Na-I and K-I lines”

Matthias Mallonn: poster “Challenging the weather forecast: the observational study of day side clouds”
myself: talk “Connecting the exoplanet radius gap with stellar activity evolution”

plus a few more are attending (Grace Foster, Nikoleta Ilic).

Paper on the atmospheric evaporation of four very young exoplanets ?>

Paper on the atmospheric evaporation of four very young exoplanets

The four young planets of V1298 Tau lose different fractions of their atmospheres, depending on the star’s spin-down behaviour (from Poppenhaeger et al. 2020).
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 the masses of the planetary cores and the age at which the star will start spinning down, some of the planets may lose their complete atmosphere by the time the star reaches the age of our Sun.

This paper was also featured in a press release of our institute:

For a read, go here: “X-ray irradiation and evaporation of the four young planets around V1298 Tau”, Poppenhaeger, K.; Ketzer, L.; Mallonn, M., Monthly Notices of the Royal Astronomical Society, Advance Access, May 2020

Paper on the magnetic activity of old sunlike stars ?>

Paper on the magnetic activity of old sunlike stars

Chromospheric activity of old sun-like stars as a function of age, with sample stars of spectral type G (green) and late-F (blue), with hotter stars (red) as a comparison. Data from clusters is shown as black symbols. No “coasting” type of behavior, i.e. a stopping of the decay of stellar activity, is seen in this sample.

My freshly graduated PhD student, Dr. Rachel Booth, has published the final paper from her PhD thesis together with me and a few coworkers. We have analysed how the magnetic activity of sun-like stars decays as they age, and have used a sample of stars that all have well-determined asteroseismic ages. We find that even at old stellar ages on the main sequence the spin down and therefore the decay of stellar activity continues.

For a read go here: “Chromospheric emission of solar-type stars with asteroseismic ages“, Booth, R. S.; Poppenhaeger, K.; Watson, C. A.; Silva Aguirre, V.; Stello, D.; Bruntt, H., Monthly Notices of the Royal Astronomical Society, Volume 491, Issue 1, p.455-467, 2020. (arXiv link).

Paper on alkali metals in an exoplanet’s atmosphere ?>

Paper on alkali metals in an exoplanet’s atmosphere

Artist’s impression of the hot Jupiter (right) and its cool host star. Credit: AIP/Kristin Riebe

Together with my colleagues at AIP, and led by Engin Keles, a PhD student in my Star-Planet Systems group, we have published a paper on the detection of potassium in the atmosphere of a Hot Jupiter using high-resolution transmission spectroscopy.

The potassium absorption on HD189733b and HD209458b, Keles, E.; Mallonn, M.; von Essen, C.; Carroll, T. A.; Alexoudi, X.; Pino, L.; Ilyin, I.; Poppenhäger, K.; Kitzmann, D.; Nascimbeni, V.; Turner, J. D.; Strassmeier, K. G.

The Large Binocular Telescope (LBT) was used with the PEPSI spectrograph in this work; both the LBT and our institute published press releases about the result (LBT press release; AIP press release). This is an exciting result because not all Hot Jupiters have potassium detected in their atmospheres, even when they have detections of the similar element sodium. The data will be used to gain more insight into the atmospheric chemistry of Hot Jupiters.

Monthly Notices of the Royal Astronomical Society: Letters, Volume 489, Issue 1, p.L37-L41 (2019).

White paper on X-ray interferometry ?>

White paper on X-ray interferometry

From Uttley et al. (2019).

Together with many colleagues, I have contributed to a White Paper on a possible X-ray Interferometry mission. This project is led by Phil Uttley from the University of Amsterdam, and we hope to be considered for ESA’s Vision 2050 mission slot. X-ray interferometry can yield amazing spatial resolution for bright X-ray sources, even though there is still quite some technology to be developed. For stars and exoplanets, we could spatially resolve transits in front of the stellar corona – see the conceptual image I made for the White Paper.

“The high energy universe at ultra-high resolution: the power and promise of X-ray interferometry “, P. Uttley and 26 co-authors including K. Poppenhaeger, A White Paper submitted in response to ESA’s Voyage 2050 call, arXiv 1908.03144 (2019).

Exostar19 research program in Santa Barbara ?>

Exostar19 research program in Santa Barbara

This summer I organized a 3-month research program called Exostar19 ( at the Kavli Institute for Theoretical Physics (KITP) in Santa Barbara, together with Bekki Dawson, Dan Huber, and Jim Fuller. Victor Silva Aguirre was the one who brought us all together with his idea to come up with a program that focuses on all the new insights that the stellar and planetary field can gain from TESS and Gaia data. It’s now the last week of the program, and it’s been a blast! My office has a view onto a little slice of the ocean, just behind the palm trees:

Beachside office view

and I’ve worked on a bunch of cool new projects with new collaborators – stellar rotation and activity, X-ray and UV observations of exoplanets, some work on transits in the infrared helium lines, plus a near wrap-up of a project on an ultrahot Jupiter. We’ve held a conference in the middle of the program, which went really well I think ( I really liked the KITP policy that all of their conferences have one third of questions time. So every talk was 20 minutes plus 10 minutes questions, and that led a really lively and interesting discussions, and just just by the same few people that always ask questions at other conferences.

This is us organizers:

Left to right: Jim Fuller, Dan Huber, Katja Poppenhaeger, and Bekki Dawson.

I brought my family along, and we stayed in the KITP residence, which has very good spaces for people with kids. We had a lot of great barbecues with the other program participants, and also managed to spend a bit of time at the beach.