First paper of the PEPSI Exoplanet Transit Survey (PETS) publication series ?>

First paper of the PEPSI Exoplanet Transit Survey (PETS) publication series

Non-detection of ionized calcium aroung the rocky planet 55 Cnc e (from Keles et al. 2022).

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 55 Cnc e

Keles, Engin; Mallonn, Matthias; Kitzmann, Daniel; Poppenhaeger, Katja; Hoeijmakers, H. Jens; Ilyin, Ilya; Alexoudi, Xanthippi; Carroll, Thorsten A.; Alvarado-Gomez, Julian; Ketzer, Laura; Bonomo, Aldo S.; Borsa, Francesco; Gaudi, B. Scott; Henning, Thomas; Malavolta, Luca; Molaverdikhani, Karan; Nascimbeni, Valerio; Patience, Jennifer; Pino, Lorenzo; Scandariato, Gaetano; Schlawin, Everett; Shkolnik, Evgenya; Sicilia, Daniela; Sozzetti, Alessandro; Foster, Mary G.; Veillet, Christian; Wang, Ji; Yan, Fei; Strassmeier, Klaus G.

The study of exoplanets and especially their atmospheres can reveal key insights on their evolution by identifying specific atmospheric species. For such atmospheric investigations, high-resolution transmission spectroscopy has shown great success, especially for Jupiter-type planets. Towards the atmospheric characterization of smaller planets, the super-Earth exoplanet 55 Cnc e is one of the most promising terrestrial exoplanets studied to date. Here, we present a high-resolution spectroscopic transit observation of this planet, acquired with the PEPSI instrument at the Large Binocular Telescope. Assuming the presence of Earth-like crust species on the surface of 55 Cnc e, from which a possible silicate-vapor atmosphere could have originated, we search in its transmission spectrum for absorption of various atomic and ionized species such as Fe , Fe +, Ca , Ca +, Mg, and K , among others. Not finding absorption for any of the investigated species, we are able to set absorption limits with a median value of 1.9 × RP. In conclusion, we do not find evidence of a widely extended silicate envelope on this super-Earth reaching several planetary radii.

Monthly Notices of the Royal Astronomical Society, Volume 513, Issue 1, pp.1544-1556, June 2022

Paper on tidal star-planet interaction ?>

Paper on tidal star-planet interaction

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 excess stellar activity with the expected tidal interaction strength between a star and its planet. This has been very difficult to show unambiguously in previous studies because of the various biases from planet detection methods which can cause a similar trend in activity levels if not corrected for. So I am very happy that this bias-controlled sample actually shows significant SPI effects!

The activity difference of planet-hosting stars relative to their same-age stellar companions correlates with the tidal interaction strength between planet and star. (Ilic et al. 2022)

Tidal star-planet interaction and its observed impact on stellar activity in planet-hosting wide binary systems

Ilic, N.; Poppenhaeger, K.; Hosseini, S. Marzieh

Tidal interaction between an exoplanet and its host star is a possible pathway to transfer angular momentum between the planetary orbit and the stellar spin. In cases where the planetary orbital period is shorter than the stellar rotation period, this may lead to angular momentum being transferred into the star’s rotation, possibly counteracting the intrinsic stellar spin-down induced by magnetic braking. Observationally, detecting altered rotational states of single, cool field stars is challenging, as precise ages for such stars are rarely available. Here we present an empirical investigation of the rotation and magnetic activity of a sample of planet-hosting stars that are accompanied by wide stellar companions. Without needing knowledge about the absolute ages of the stars, we test for relative differences in activity and rotation of the planet hosts and their co-eval companions, using X-ray observations to measure the stellar activity levels. Employing three different tidal interaction models, we find that host stars with planets that are expected to tidally interact display elevated activity levels compared to their companion stars. We also find that those activity levels agree with the observed rotational periods for the host stars along the usual rotation-activity relationships, implying that the effect is indeed caused by a tidal interaction and not a purely magnetic interaction which would be expected to affect the stellar activity, but not necessarily the rotation. We conclude that massive, close-in planets have an impact on the stellar rotational evolution, while the smaller, more distant planets do not have a significant influence.

Monthly Notices of the Royal Astronomical Society, Advance Access, April 2022

Paper on AU Mic’s space weather ?>

Paper on AU Mic’s space weather

The Alfvén surface of AU Mic (double-lobed shadow) encloses the orbits of the two innermost planets in this simulation (Alvarado-Gomez et al. 2022).

A new study by our Schwarzschild Fellow Dr. Julián Alvarado-Gomez shows that the space weather of AU Mic makes the survival of exoplanet atmospheres very challenging.

Simulating the Space Weather in the AU Mic System: Stellar Winds and Extreme Coronal Mass Ejections

Alvarado-Gómez, Julián D.; Cohen, Ofer; Drake, Jeremy J.; Fraschetti, Federico; Poppenhaeger, Katja; Garraffo, Cecilia; Chebly, Judy; Ilin, Ekaterina; Harbach, Laura; Kochukhov, Oleg

Two close-in planets have been recently found around the M-dwarf flare star AU Microscopii (AU Mic). These Neptune-sized planets (AU Mic b and c) seem to be located very close to the so-called “evaporation valley” in the exoplanet population, making this system an important target for studying atmospheric loss on exoplanets. This process, while mainly driven by high-energy stellar radiation, will be strongly mediated by the space environment surrounding the planets. Here we present an investigation of this last area, performing 3D numerical modeling of the quiescent stellar wind from AU Mic, as well as time-dependent simulations describing the evolution of a highly energetic coronal mass ejection (CME) event in this system. Observational constraints on the stellar magnetic field and properties of the eruption are incorporated in our models. We carry out qualitative and quantitative characterizations of the stellar wind, the emerging CMEs, as well as the expected steady and transient conditions along the orbit of both exoplanets. Our results predict extreme space weather for AU Mic and its planets. This includes sub-Alfvénic regions for the large majority of the exoplanet orbits, very high dynamic and magnetic pressure values in quiescence (varying within 102-105 times the dynamic pressure experienced by Earth), and an even harsher environment during the passage of any escaping CME associated with the frequent flaring observed in AU Mic. These space weather conditions alone pose an immense challenge for the survival of exoplanetary atmospheres (if any) in this system.

The Astrophysical Journal, Volume 928, Issue 2, id.147, 12 pp., April 2022

Paper on solar H alpha emission ?>

Paper on solar H alpha emission

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!

ChroTel Hα filtergram of the Sun on 2013 April 13
(top left) and the corresponding mask for bright
(bottom left) and dark features (bottom right).
For comparison, we display the corresponding
continuum map from HMI/SDO (top right). (Dierke et al. 2022)

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 regime, this spectral line is already used as a powerful tracer of stellar activity. For the Sun, other tracers (i.e, CaII K) are typically used to monitor solar activity. We used observations of full-disk H-alpha filtergrams of the Chromospheric Telescope (ChroTel) to extract the imaging H-alpha excess and deficit, which are related to bright features (plage regions) and dark absorption features (filaments and sunspots), respectively. The aim of this study is to introduce the imaging H-alpha excess and deficit as tracers of solar activity and compare them to other established indicators: the relative sunspot number, the F10.7cm radio flux, and the MgII index. The H-alpha excess and deficit follow the behavior of the solar activity over the course of the cycle, whereby the peak of the H-alpha deficit is shortly after the solar maximum. The H-alpha excess is closely correlated to the chromospheric MgII index. The highest correlation of the H-alpha deficit is found with the F10.7cm radio flux. The H-alpha deficit reflects the cyclic behavior of polar crown filaments and their disappearance shortly before the solar maximum. We investigated the mean intensity distribution for H-alpha excess regions for solar minimum and maximum, whereby the shape of the distributions is very similar, but with different amplitudes. Furthermore, we investigate whether the area coverage fraction or the changing H-alpha excess in the active regions dominates temporal variability in solar H-alpha observations. The area coverage fraction and the H-alpha excess are strongly correlated, whereas the weak correlation between the area coverage fraction and mean intensity leaves us pessimistic that the degeneracy between these two quantities can be broken for the modeling of unresolved stellar surfaces.

eprint arXiv:2203.04357, accepted for publication in Astronomy & Astrophysics, March 2022

Paper on helium transits of exoplanets ?>

Paper on helium transits of exoplanets

Stellar coronae with different iron abundance cause different levels of helium ionization which is important for observing helium transits of exoplanets. (From Poppenhaeger 2022)

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 around 10 830 Angstrom are a successful tool to study exoplanetary atmospheres and their mass loss. Forming those lines requires ionization and recombination of helium in the exoplanetary atmosphere. This ionization is caused by stellar photons at extreme ultraviolet (EUV) wavelengths; however, no currently active telescopes can observe this part of the stellar spectrum. The relevant part of the stellar EUV spectrum consists of individual emission lines, many of them being formed by iron at coronal temperatures. The stellar iron abundance in the corona is often observed to be depleted for high-activity low-mass stars due to the first ionization potential (FIP) effect. I show that stars with high versus low coronal iron abundances follow different scaling laws that tie together their X-ray emission and the narrow-band EUV flux that causes helium ionization. I also show that the stellar iron to oxygen abundance ratio in the corona can be measured reasonably well from X-ray CCD spectra, yielding similar results to high-resolution X-ray observations. Taking coronal iron abundance into account, the currently observed large scatter in the relationship of EUV irradiation with exoplanetary helium transit depths can be reduced, improving the target selection criteria for exoplanet transmission spectroscopy. In particular, previously puzzling non-detections of helium for Neptunic exoplanets are now in line with expectations from the revised scaling laws.

Monthly Notices of the Royal Astronomical Society, Volume 512, Issue 2, pp.1751-1764, May 2022

Code published: AltaiPony ?>

Code published: AltaiPony

The AltaiPony flare-finder on github (Ilin et al. 2022).

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 code in the peer-reviewed Journal for Open Source Software and it is linked in the Astrophysical Source Code Library. It is pip-installable and a very useful tool!

AltaiPony: Flare finder for Kepler, K2, and TESS light curves


Ilin, Ekaterina; Schmidt, Sarah J.; Poppenhäger, Katja; Davenport, James R. A.; Kristiansen, Martti H.; Omohundro, Mark

AltaiPony de-trend light curves from Kepler, K2, and TESS missions, and searches them for flares. The code also injects and recovers synthetic flares to account for de-trending and noise loss in flare energy and determines energy-dependent recovery probability for every flare candidate. AltaiPony uses K2SC (ascl:1605.012), AstroPy (ascl:1304.002) and lightkurve (ascl:1812.013) in addition to other common codes, and extensive documentation and tutorials are provided for the software.

Astrophysics Source Code Library, record ascl:2201.009, January 2022

New group members and completed Master’s theses ?>

New group members and completed Master’s theses

We have two new group members who joined us this fall: Prachi Rahate, who is a Master student and works with Dr. Eliana Amazo-Gomez on stellar rotation, and Dr. Andy Gallagher, who is a postdoc and works with Dr. Matthias Steffen on 3D NLTE stellar atmospheres. Welcome!

We also had two students successfully complete their Master theses over the summer: Marzie Hosseini completed her thesis on “Transits in the young system PTFO 8-8695, is there a planet?”, as well as Alexandre Gillet, who completed his thesis on the topic “Are there clouds on Ultra Hot Jupiters?”. We were able to have a socially distanced outdoors picnic to celebrate Marzie’s and Alex’s completion of the Master’s degree – it was really nice seeing (almost) the whole group together in person again.

Paper on polar flares on fast-rotating M dwarfs ?>

Paper on polar flares on fast-rotating M dwarfs

Small stars flare actively and expel particles that can alter and evaporate the atmospheres of planets that orbit them. New findings suggest that large superflares prefer to occur at high latitudes, sparing planets that orbit around the stellar equator. Credit: AIP/ J. Fohlmeister

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 the planets and harm their atmospheres less.

The AIP published a press release about Ekaterina’s paper.

Giant white-light flares on fully convective stars occur at high latitudes

Ilin, Ekaterina; Poppenhaeger, Katja; Schmidt, Sarah J.; Järvinen, Silva P.; Newton, Elisabeth R.; Alvarado-Gómez, Julián D.; Pineda, J. Sebastian; Davenport, James R. A.; Oshagh, Mahmoudreza; Ilyin, Ilya

White-light flares are magnetically driven localized brightenings on the surfaces of stars. Their temporal, spectral, and statistical properties present a treasury of physical information about stellar magnetic fields. The spatial distributions of magnetic spots and associated flaring regions help constrain dynamo theories. Moreover, flares are thought to crucially affect the habitability of exoplanets that orbit these stars. Measuring the location of flares on stars other than the Sun is challenging due to the lack of spatial resolution. Here we present four fully convective stars observed with the Transiting Exoplanet Survey Satellite that displayed large, long-duration flares in white-light which were modulated in brightness by the stars’ fast rotation. This allowed us to determine the loci of these flares directly from the light curves. All four flares occurred at latitudes between 55° and 81°, far higher than typical solar flare latitudes. Our findings are evidence that strong magnetic fields tend to emerge close to the stellar rotational poles for fully convective stars, and suggest that the impact of flares on the habitability of exoplanets around small stars could be weaker than previously thought.

Monthly Notices of the Royal Astronomical Society, Volume 507, Issue 2, pp.1723-1745 (2021)

Paper on the X-ray irradiation and evaporation of exoplanets ?>

Paper on the X-ray irradiation and evaporation of exoplanets

Exoplanets host stars detected on the German half of the eROSITA X-ray sky, shown as pink dots, other exoplanet host stars shown as small grey dots. Credit: AIP/K. Poppenhaeger

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 is based on data from eROSITA, the soft X-ray instrument aboard SRG (Spectrum Roentgen Gamma) mission, as well as archival data from other missions, we aim to characterise the high-energy environment of known exoplanets and estimate their mass loss rates. We use X-ray source catalogues from eROSITA, XMM-Newton, Chandra and ROSAT to derive X-ray luminosities of exoplanet host stars in the 0.2-2 keV energy band with an underlying coronal, i.e. optically thin thermal spectrum. We present a catalogue of stellar X-ray and EUV luminosities, exoplanetary X-ray and EUV irradiation fluxes and estimated mass loss rates for a total of 287 exoplanets, 96 among them being characterised for the first time from new eROSITA detections. We identify 14 first time X-ray detections of transiting exoplanets that are subject to irradiation levels known to cause observable evaporation signatures in other exoplanets, which makes them suitable targets for follow-up observations.

eprint arXiv:2106.14550, accepted by A&A (2021)

XMM-Newton Workshop on exoplanets and their environments ?>

XMM-Newton Workshop on exoplanets and their environments

This week I am organizing the XMM-Newton 2021 virtual workshop on the topic of “A high-energy view of exoplanets and their environments” as the chair of the Scientific Organizing Committee. We have over 350 participants, which is fantastic! The program and workshop website is here:

The conference proceedings will be peer-reviewed and published in Astronomische Nachrichten/Astronomical Notes.