New paper: a small planet in the temperate zone of K2-133 ?>

New paper: a small planet in the temperate zone of K2-133

A new paper by my PhD student Rob Wells is now accepted for publication:

Validation of a temperate fourth planet in the K2-133 multiplanet system“, Wells, R.; Poppenhaeger, K.; Watson, C. A.

Phase-folded light curve of the fourth planet in the K2-133 system, with best-fitting model (Wells et a. 2019).

Abstract: We present follow-up observations of the K2-133 multiplanet system. Previously, we announced that K2-133 contained three super-Earths orbiting an M1.5V host star – with tentative evidence of a fourth outer-planet orbiting at the edge of the temperate zone. Here, we report on the validation of the presence of the fourth planet, determining a radius of 1.73 R⊕. The four planets span the radius gap of the exoplanet population, meaning further follow-up would be worthwhile to obtain masses and test theories of the origin of the gap. In particular, the trend of increasing planetary radius with decreasing incident flux in the K2-133 system supports the claim that the gap is caused by photo-evaporation of exoplanet atmospheres. Finally, we note that K2-133 e orbits on the edge of the star’s temperate zone, and that our radius measurement allows for the possibility that this is a rocky world. Additional mass measurements are required to confirm or refute this scenario.

Monthly Notices of the Royal Astronomical Society, Volume 487, Issue 2, p.1865-1873, 2019.

Review on star-planet systems ?>

Review on star-planet systems

My review talk on interactions in star-planet systems I gave at the XMM-Newton science workshop in summer 2018 is now published in a peer-reviewed article:

How stars and planets interact: A look through the high-energy window“, Poppenhaeger, Katja

Montage of a close-in Hot Jupiter orbiting a cool star with the solar corona as background, all object sizes and distances to scale (taking the values of the WASP-12 exoplanet system as an example). Some exoplanets are close enough to their host stars to orbit within the outer structures of the stellar corona. Solar corona image by K. van Gorm, montage by K. Poppenhaeger.

Abstract: The architecture of exoplanetary systems is often different from the solar system, with some exoplanets being in close orbits around their host stars and having orbital periods of only a few days. In analogy to interactions between stars in close binary systems, one may expect interactions between the star and the exoplanet as well. From theoretical considerations, effects on the host star through tidal and magnetic interaction with the exoplanet are possible; for the exoplanet, some interesting implications are the evaporation of the planetary atmosphere and potential effects on the planetary magnetism. In this review, several possible interaction pathways and their observational prospects and existing evidence are discussed. A particular emphasis is put on observational opportunities for these kinds of effects in the high-energy regime.

Astronomische Nachrichten, Volume 340, Issue 4, pp. 329-333, 2019.

New papers: exoplanets and stellar results from NGTS ?>

New papers: exoplanets and stellar results from NGTS

Explanetary radii versus their equilibrium temperature, NGTS-2b is indicated as one of the known inflated exoplanets, from Raynard et al. (2018).
The Next Generation Transit Survey has had some new discoveries over the past few months which I was happy to contribute to. We’ve discovered a new exoplanet (an inflated hot Jupiter), a fully-convective eclipsing binary system, and a giant flare with pulsations on a pre-main sequence M star. The papers are:

“NGTS-2b: an inflated hot-Jupiter transiting a bright F-dwarf”, L. Raynard and 44 co-authors including K. Poppenhaeger, Monthly Notices of the Royal Astronomical Society, Volume 481, Issue 4, p.4960-4970 (2018)

“A low-mass eclipsing binary within the fully convective zone from the Next Generation Transit Survey”, S. Casewell and 24 co-authors including K. Poppenhaeger, Monthly Notices of the Royal Astronomical Society, Volume 481, Issue 2, p.1897-1907 (2018)

“Detection of a giant flare displaying quasi-periodic pulsations from a pre-main-sequence M star by the Next Generation Transit Survey”, J. Jackman and 20 co-authors including K. Poppenhaeger, Monthly Notices of the Royal Astronomical Society, Volume 482, Issue 4, p.5553-5566 (2019)

Home colloquium at AIP ?>

Home colloquium at AIP

Title slide of my talk today.

Today I gave the colloquium talk at my new home institution, the AIP. I chose a quite relatable title with “A field trip to the exoplanet zoo”, and I was blown away by how many people showed up. We actually had to open the second half of the lecture hall, which is usually only done for conferences – quite flattering! It was good fun and my colleagues from the AIP and the university had a bunch of interesting questions. Looking forward to all the science I’ll do here from now on.

Invited colloquium at API Amsterdam ?>

Invited colloquium at API Amsterdam

Neighbourhood of my hotel in Amsterdam.

Last week I was a guest at the Anton Pannekoek Intitute at the University of Amsterdam for two days and gave an invited colloquium. Also learned a lot about the research going on at Amsterdam, especially in the exoplanet groups of Birkby and Desert. Title and abstract of my talk:

Strange beasts in the exoplanet zoo

Almost all exoplanets known today are orbiting around cool stars. This is caused by certain biases in our planet detection methods, but nevertheless it means that almost all exoplanets we can study today live in a system where the host star displays magnetic activity, which is ubiquitous amongst cool stars. As exoplaneteers, we care about stellar activity due to a variety of reasons: stellar activity can drive mass loss of planets; it likely influences the habitability of a planet; and it can make the detection of planets much more difficult, depending on the stellar properties and the techniques used. I will talk about several interesting projects going on in my group, concerning the field of cool stars and exoplanets – there will be news about magnetic activity in close star-planet systems, the decline of stellar activity in cool stars, and strange transit signatures around young and active stars.

Arrival at my new institute in Potsdam ?>

Arrival at my new institute in Potsdam

Me on my way to work, looking cool.

I’m a tenured full professor now! I’ve started my new position, a joint professorship at the Leibniz Institute for Astrophysics Potsdam (AIP) and the University of Potsdam, this autumn. I had a very good time in Belfast, but it’s really nice to be back in my home country and have continued access to European funding, whatever will happen with Brexit. Fortunately my two PhD students in Belfast are both in their final year now, so I can supervise them from afar as they’re pretty independent now.

My new office is in one of the historical observatory buildings at AIP, which is quite fancy. Also, the new position comes with a good chunk of funding, plus I am very happy that I was awarded a large grant by the Leibniz Association (similar to an ERC starting grant). So there will be lots of hiring over the next year! I did my PhD in a very large group, and I was always hoping that I would be able to build such a large research group myself – looks like that is actually happening now 🙂

Cool Stars 20 conference in Boston ?>

Cool Stars 20 conference in Boston

Giving my invited talk on how planets affect cool stars at the Cool Stars 20 conference.

This summer the Cambridge Workshop on Cool Stars, Stellar Systems and the Sun had its 20th anniversary, and took place in Boston. This is my favourite conference series, and this year I was really excited because I had the honour of being an invited speaker. I gave a talk on “How planets affect cool stars”, and had a lot of good interactions with people about the science of stars and exoplanets. This was the first time I’ve given an invited talk wearing a “My little pony” T-shirt. Also, this was the first time for me to introduce my PhD students to the Cool Stars community, which was a neat thing I hadn’t had the chance to do before.

It was a fantastic meeting, with lots of scientific input, and it was wonderful to see all my friends and colleagues from the Harvard-Smithsonian Center for Astrophysics again.

The proceedings can be found here:, and my contribution is here:

New paper: X-ray emission line spectra of main-sequence stars ?>

New paper: X-ray emission line spectra of main-sequence stars

Part of the X-ray emission line spectra of AB Dor A and alpha Cen B analyzed in this study (Wood et al. 2018).
We investigated the X-ray emission line spectra of cool main-sequence stars in order to construct their emission measure distributions and compare them to the Sun:

“A Chandra/LETGS Survey of Main-sequence Stars”

We analyze the X-ray spectra of 19 main-sequence stars observed by Chandra using its LETGS configuration. Emission measure (EM) distributions are computed based on emission line measurements, an analysis that also yields evaluations of coronal abundances. The use of newer atomic physics data results in significant changes compared to past published analyses. The stellar EM distributions correlate with surface X-ray flux (FX) in a predictable way, regardless of spectral type. Thus, we provide EM distributions as a function of FX, which can be used to estimate the EM distribution of any main-sequence star with a measured broadband X-ray luminosity. Comparisons are made with solar EM distributions, both full-disk distributions and spatially resolved ones from active regions (ARs), flares, and the quiet Sun. For moderately active stars, the slopes and magnitudes of the EM distributions are in excellent agreement with those of solar ARs for logT< 6.6, suggesting that such stars have surfaces completely filled with solar-like ARs. A stellar surface covered with solar X-class flares yields a reasonable approximation for the EM distributions of the most active stars. Unlike the EM distributions, coronal abundances are strongly dependent on spectral type, and we provide relations with surface temperature for both relative and absolute abundances. Finally, the coronal abundances of the exoplanet host star Ď„ Boo A (F7 V) are anomalous, and we propose that this is due to the presence of the exoplanet.

A Chandra/LETGS Survey of Main-sequence Stars, Wood, Brian E.; Laming, J. Martin; Warren, Harry P.; Poppenhaeger, Katja, The Astrophysical Journal, Volume 862, Issue 1, article id. 66, 24 pp. (2018).

XMM-Newton Conference in Madrid ?>

XMM-Newton Conference in Madrid

Poster of the XMM Science Workshop 2018.

I was invited to give a talk on “How Stars and Planets Interact: a Look Through the High-Energy Window” at the XMM-Newton 2018 Science Workshop with a focus on X-ray time-domain astronomy. As always, had some very nice interactions with the colleagues at ESAC in Madrid. It’s interesting to hear what’s new in all the other subfields being probed by soft X-rays.

New paper: Unmasking a hot Jupiter in an unresolved binary system ?>

New paper: Unmasking a hot Jupiter in an unresolved binary system

The NGTS planet-search project in which I take part has detected a new planet in an interesting system:

Transit light curve of the newly discovered Hot Jupiter NGTS-3Ab, from GĂĽnther et al. (2018).
Transit light curve of the newly discovered Hot Jupiter NGTS-3Ab, from GĂĽnther et al. (2018).

“Unmasking the hidden NGTS-3Ab: a hot Jupiter in an unresolved binary system”

We present the discovery of NGTS-3Ab, a hot Jupiter found transiting the primary star of an unresolved binary system. We develop a joint analysis of multi-colour photometry, centroids, radial velocity (RV) cross-correlation function (CCF) profiles and their bisector inverse slopes (BIS) to disentangle this three-body system. Data from the Next Generation Transit Survey (NGTS), SPECULOOS and HARPS are analysed and modelled with our new BLENDFITTER software. We find that the binary consists of NGTS-3A (G6V-dwarf) and NGTS-3B (K1V-dwarf) at <1" separation. NGTS-3Ab orbits every 1.675 days. The planet radius and mass are Rplanet=1.48 ± 0.37 RJand Mplanet=2.38 ± 0.26 MJ, suggesting it is potentially inflated. We emphasise that only combining all the information from multi-colour photometry, centroids and RV CCF profiles can resolve systems like NGTS-3. Such systems cannot be disentangled from single-colour photometry and RV measurements alone. Importantly, the presence of a BIS correlation indicates a blend scenario, but is not sufficient to determine which star is orbited by the third body. Moreover, even if no BIS correlation is detected, a blend scenario cannot be ruled out without further information. The choice of methodology for calculating the BIS can influence the measured significance of its correlation. The presented findings are crucial to consider for wide-field transit surveys, which require wide CCD pixels (>5″) and are prone to contamination by blended objects. With TESS on the horizon, it is pivotal for the candidate vetting to incorporate all available follow-up information from multi-colour photometry and RV CCF profiles.

Unmasking the hidden NGTS-3Ab: a hot Jupiter in an unresolved binary system, Günther, Maximilian N.; Queloz, Didier; Gillen, Edward; Delrez, Laetitia; Bouchy, François; McCormac, James; Smalley, Barry; Almleaky, Yaseen; Armstrong, David J.; Bayliss, Daniel; Burdanov, Artem; Burleigh, Matthew; Cabrera, Juan; Casewell, Sarah L.; Cooke, Benjamin F.; Csizmadia, Szilárd; Ducrot, Elsa; Eigmüller, Philipp; Erikson, Anders; Gänsicke, Boris T.; Gibson, Neale P.; Gillon, Michaël; Goad, Michael R.; Jehin, Emmanuël; Jenkins, James S.; Louden, Tom; Moyano, Maximiliano; Murray, Catriona; Pollacco, Don; Poppenhaeger, Katja; Rauer, Heike; Raynard, Liam; Smith, Alexis M. S.; Sohy, Sandrine; Thompson, Samantha J.; Udry, Stéphane; Watson, Christopher A.; West, Richard G.; Wheatley, Peter J., accepted for publication by Monthly Notices of the Royal Astronomical Society, 2018.