Katja Poppenhaeger – Page 6 – Professor for Astrophysics in Potsdam/Berlin, Germany

New paper: X-ray line coincidence photopumping in a solar flare

2018-02-25 ktj

Energy level diagram for the transitions involved in this X-ray photopumping mechanism. This is actually the first time that one of my papers has an energy level diagram plot in it.

This is somewhat unusual research for me, but it was good fun – some recent work about identifying an emission line in the X-ray regime which is excited by photons from a different atomic species which just happens to have the correct wavelength for that. This can be used as an independent density diagnostics for plasma in flaring loops, for example. The paper has just been published, here is the title and abstract:

“X-ray line coincidence photopumping in a solar flare”

Line coincidence photopumping is a process where the electrons of an atomic or molecular species are radiatively excited through the absorption of line emission from another species at a coincident wavelength. There are many instances of line coincidence photopumping in astrophysical sources at optical and ultraviolet wavelengths, with the most famous example being Bowen fluorescence (pumping of O III 303.80 Å by He II), but none to our knowledge in X-rays. However, here we report on a scheme where a He-like line of Ne IX at 11.000 Å is photopumped by He-like Na X at 11.003 Å, which predicts significant intensity enhancement in the Ne IX 82.76 Å transition under physical conditions found in solar flare plasmas. A comparison of our theoretical models with published X-ray observations of a solar flare obtained during a rocket flight provides evidence for line enhancement, with the measured degree of enhancement being consistent with that expected from theory, a truly surprising result. Observations of this enhancement during flares on stars other than the Sun would provide a powerful new diagnostic tool for determining the sizes of flare loops in these distant, spatially unresolved, astronomical sources.

“X-ray line coincidence photopumping in a solar flare”, Keenan, F. P.; Poppenhaeger, K.; Mathioudakis, M.; Rose, S. J.; Flowerdew, J.; Hynes, D.; Christian, D. J.; Nilsen, J.; Johnson, W. R., Monthly Notices of the Royal Astronomical Society, Volume 474, Issue 3, p.3782-3786, 2018.

New paper and press release: Discovery of a monster planet

2017-10-31 ktj

Artist's impression of planet NGTS-1b with its neighbouring star (credit University of Warwick/Mark Garlick). — Artist’s impression of planet NGTS-1b with its neighbouring star (credit University of Warwick/Mark Garlick).

A timely discovery for Halloween: Our NGTS collaboration has discovered a “monster planet”, a giant planet around a very small star. This is very surprising, because barely any of those huge planets have been found close to tiny stars. We will have to re-think some of our planet formation theories.

A neat press release has been published by Queen’s University Belfast: Monster planet discovery challenges formation theory, which gives the key points about the discovery in layperson’s terms.

And here is the scientific information from the paper: We present the discovery of NGTS-1b, a hot-Jupiter transiting an early M-dwarf host in a P=2.674d orbit discovered as part of the Next Generation Transit Survey (NGTS). The planet has a mass of 0.812 Mjup, making it the most massive planet ever discovered transiting an M-dwarf. The radius of the planet is 1.33 Rjup. Since the transit is grazing, we determine this radius by modelling the data and placing a prior on the density from the population of known gas giant planets. NGTS-1b is the third transiting giant planet found around an M-dwarf, reinforcing the notion that close-in gas giants can form and migrate similar to the known population of hot Jupiters around solar type stars. The host star shows no signs of activity, and the kinematics hint at the star being from the thick disk population. With a deep (2.5%) transit around a K=11.9 host, NGTS-1b will be a strong candidate to probe giant planet composition around M-dwarfs via JWST transmission spectroscopy.

“NGTS-1b: A hot Jupiter transiting an M-dwarf”, Bayliss, Daniel; Gillen, Edward; Eigmuller, Philipp; McCormac, James; Alexander, Richard D.; Armstrong, David J.; Booth, Rachel S.; Bouchy, Francois; Burleigh, Matthew R.; Cabrera, Juan; Casewell, Sarah L.; Chaushev, Alexander; Chazelas, Bruno; Csizmadia, Szilard; Erikson, Anders; Faedi, Francesca; Foxell, Emma; Gansicke, Boris T.; Goad, Michael R.; Grange, Andrew; Gunther, Maximilian N.; Hodgkin, Simon T.; Jackman, James; Jenkins, James S.; Lambert, Gregory; Louden, Tom; Metrailler, Lionel; Moyano, Maximiliano; Pollacco, Don; Poppenhaeger, Katja; Queloz, Didier; Raddi, Roberto; Rauer, Heike; Raynard, Liam; Smith, Alexis M. S.; Soto, Maritza; Thompson, Andrew P. G.; Titz-Weider, Ruth; Udry, Stephane; Walker, Simon. R.; Watson, Christopher A.; West, Richard G.; Wheatley, Peter J.; accepted for publication by Monthly Notices of the Royal Astronomical Society (2017).

New paper: Next Generation Transit Survey (2)

2017-10-30 ktj

The twelve 20 cm telescopes of the NGTS facility at Cerro Paranal, Chile (Wheatley et al. 2017).

The mission paper about the Next Generation Transit Survey (NGTS), a ground-based telescope network to search for transiting exoplanets, has just been published. I’m happy to be part of this project, which is a collaboration between several universities in the UK, Germany, Chile, and Switzerland – lots of exciting discoveries to come soon!

Here’s some more info about the paper: We describe the Next Generation Transit Survey (NGTS), which is a ground-based project searching for transiting exoplanets orbiting bright stars. NGTS builds on the legacy of previous surveys, most notably WASP, and is designed to achieve higher photometric precision and hence find smaller planets than have previously been detected from the ground. It also operates in red light, maximising sensitivity to late K and early M dwarf stars. The survey specifications call for photometric precision of 0.1 per cent in red light over an instantaneous field of view of 100 square degrees, enabling the detection of Neptune-sized exoplanets around Sun-like stars and super-Earths around M dwarfs. The survey is carried out with a purpose-built facility at Cerro Paranal, Chile, which is the premier site of the European Southern Observatory (ESO). An array of twelve 20cm f/2.8 telescopes fitted with back-illuminated deep-depletion CCD cameras are used to survey fields intensively at intermediate Galactic latitudes. The instrument is also ideally suited to ground-based photometric follow-up of exoplanet candidates from space telescopes such as TESS, Gaia and PLATO. We present observations that combine precise autoguiding and the superb observing conditions at Paranal to provide routine photometric precision of 0.1 per cent in 1 hour for stars with I-band magnitudes brighter than 13. We describe the instrument and data analysis methods as well as the status of the survey, which achieved first light in 2015 and began full survey operations in 2016. NGTS data will be made publicly available through the ESO archive.

“The Next Generation Transit Survey (NGTS)”, Wheatley, Peter J.; West, Richard G.; Goad, Michael R.; Jenkins, James S.; Pollacco, Don L.; Queloz, Didier; Rauer, Heike; Udry, Stephane; Watson, Christopher A.; Chazelas, Bruno; Eigmuller, Philipp; Lambert, Gregory; Genolet, Ludovic; McCormac, James; Walker, Simon; Armstrong, David J.; Bayliss, Daniel; Bento, Joao; Bouchy, Francois; Burleigh, Matthew R.; Cabrera, Juan; Casewell, Sarah L.; Chaushev, Alexander; Chote, Paul; Csizmadia, Szilard; Erikson, Anders; Faedi, Francesca; Foxell, Emma; Gansicke, Boris T.; Gillen, Edward; Grange, Andrew; Gunther, Maximilian N.; Hodgkin, Simon T.; Jackman, James; Jordan, Andres; Louden, Tom; Metrailler, Lionel; Moyano, Maximiliano; Nielsen, Louise D.; Osborn, Hugh P.; Poppenhaeger, Katja; Raddi, Roberto; Raynard, Liam; Smith, Alexis M. S.; Soto, Maritza; Titz-Weider, Ruth; accepted for publication by Monthly Notices of the Royal Astronomical Society (2017).

Musings on scientific discoveries, luck, and being prepared

2017-10-21 ktj

I’ve been thinking about the relationship between luck and good preparation lately. We have published a paper on the discovery of three plus one small planets around a small star recently, and we basically did the work for that in one day. The way that worked out got me thinking.

From the outside, what happened was this: Data from the latest Kepler-K2 campaign was publicly released. My student Rob Wells looked through some light curves and found something that looked like a triple-planet system. We started writing a paper about it, and had it finished after a bit more than one day of full-steam-ahead work. We submitted it to the journal (MNRAS Letters), and the arXiv, in the early evening. Got some helpful and thorough comments from the reviewer, edited the paper draft, got it accepted, done. From the outside, I imagine that this looks like being quite lucky.

From the inside of our group, there was actually much more work involved. My student had spent a lot of time over the past half year to get a data crunching pipeline working, which did quite a number of things (detrending the telescope data, doing a rough search for transits fully automatically, producing image files that allow the human user to quickly browse through stuff and sort for things that look like interesting systems). I had previously worked on spectral energy distributions of stars for another project (the YSOVAR project and my paper in the project series), and had some experience with proper MCMC fitting of transits from yet another project (my work on X-ray transits). All this preparation meant that we could directly jump into the relevant analysis for the paper and write it up with a collaborative online latex editor really quickly. We had to determine the stellar spectral type, produce proper transit fits (which eventually revealed the fourth planet candidate), and perform a stability analysis for the spectrum (in which our colleague Chris already had some experience, so he got that up and running really quickly). A lot of this came down to having all of the necessary experience in our small team. It would have been even better if we had all of the necessary tools and code somewhere easily accessible in one place – that’s what we have done now with a shared code repository for our group, so that other discoveries should be publishable quite quickly from now on. I’m really happy about this.

Another thing I like about how all of this worked out: My student came to me with his interesting dataset on a Friday afternoon. We did some of the work for the paper on that Friday afternoon, then all went home for a work-free weekend, and came back on Monday to put a full 8 hours of work into the project. Submitted to arXiv just before the daily deadline (18:00 in our time zone). And everybody got to go home on time. I was a little bit worried that maybe lots of other teams would be working through the weekend to publish interesting results from that K2 data release. But it turned out that we were the first people to publish anything from that campaign at all, and the next papers (about different star systems) came out more than 2 weeks after ours. This means that, even in the exoplanet field, one can do one’s work during normal work hours, Monday to Friday, and not be scooped left and right. This makes me much happier about recommending the pursuit of an academic career to my students.

New paper: Discovery of three (plus one) small planets around a small star

2017-10-21 ktj

Phase-folded transit light curves of the three detected planets (b, c, d) and the planet candidate (e); from Wells, Poppenhaeger & Watson (2017).

Happy to report that we have discovered three small planets, plus one additional candidate planet, around a small cool star. This is some very nice work by my PhD student Rob Wells. The planets were discovered using data from the Kepler K2 space telescope. The planets are in fairly close orbits around their host star; the candidate planet, for which we need some more data to be certain it is really a planet, might be in the habitable zone of the star. Here’s some more info about the paper:

We report on the detection of three transiting small planets around the low-mass star LP 358-499 (K2-133), using photometric data from the Kepler-K2 mission. Using multiband photometry, we determine the host star to be an early M dwarf with an age likely older than a Gigayear. The three detected planets K2-133 b, c, and d have orbital periods of ca. 3, 4.9 and 11 days and transit depths of ca. 700, 1000 and 2000 ppm, respectively. We also report a planetary candidate in the system (EPIC 247887989.01) with a period of 26.6 days and a depth of ca. 1000 ppm, which may be at the inner edge of the stellar habitable zone, depending on the specific host star properties. Using the transit parameters and the stellar properties, we estimate that the innermost planet may be rocky. The system is suited for follow-up observations to measure planetary masses and JWST transmission spectra of planetary atmospheres.

“Three small transiting planets around the M dwarf host star LP 358-499”, Wells, R.; Poppenhaeger, K.; Watson, C. A., accepted for publication by MNRAS Letters (2017).

Conference: “Ages^2 – Taking stellar ages to the next power”

2017-09-28 ktj

Poster and coffee session at the conference.

I spent some time at a fantastic conference, “Ages^2 – Taking stellar ages to the next power” on Elba, Italy. It was a great meeting, with people from very different areas of astronomy coming together to share progress on measuring how old different kinds of stars are, which is a very fundamental and very difficult to solve question. I gave an invited talk on the topic of “Precise stellar ages as the key to exoplanet evolution”, and my PhD student Rachel Booth gave a contributed plenary (!) talk on “Activity of cool stars older than a gigayear”. Part of the success of the meeting was that the organizers had chosen a venue that catered to all our needs for food, caffeine, and sunshine – we were able to have the poster sessions outdoors with an ocean view, in late September! I think this was actually the most scientifically productive meeting I’ve attended so far, I already have ideas for two new papers…

Press release: Are we being watched? Tens of other worlds could spot the Solar System

2017-09-08 ktj

Image showing where transits of our Solar System planets can be observed. Each line represents where one of the planets could be seen to transit, with the blue line representing Earth; an observer located here could detect us. Credit: 2MASS / A. Mellinger / R. Wells.

This is a week full of press releases: my other PhD student, Rob Wells, just published a paper in MNRAS about transit zones (places in the sky where an extraterrestrial observer could detect our solar system planets through transits). There are about 70 currently known exoplanet systems that are located in the solar system’s transit zones. None of those have any known habitable zone planets, but prospects of finding a habitable system with mutual transit visibility are good: the Kepler-K2 mission looks at exactly the right locations in the sky (namely the ecliptic) to find them. The Royal Astronomical Society did a really neat press release about our work today: https://www.ras.org.uk/news-and-press/3042-are-we-being-watched-tens-of-other-worlds-could-spot-the-earth.

“Transit Visibility Zones of the Solar System Planets“, Wells, R.; Poppenhaeger, K.; Watson, C. A.; Heller, R., accepted for publication by MNRAS (2017).

Press release: X-rays Reveal Temperament of Possible Planet-Hosting Stars

2017-09-07 ktj

gj176_nasa — Artist’s illustration of an old star with a coronal hole. Credits: X-ray: NASA/CXC/Queens Univ. of Belfast/R. Booth, et al.; Illustration: NASA/CXC/M. Weiss

My PhD student Rachel Booth has been working on X-ray data from several space telescopes and has published our findings in MNRAS recently: X-ray emission from stars quiets down with age much more dramatically than thought before (see here for more details about the paper). Now NASA has published a press release on Rachel’s research, here is the link: https://www.nasa.gov/mission_pages/chandra/news/x-rays-reveal-temperament-of-possible-planet-hosting-stars.html. Some really nice results, and hopefully we’ll be able to collect more data soon and study this in even more detail!

“An Improved Age-Activity Relationship for Cool Stars older than a Gigayear”, R. S. Booth, K. Poppenhaeger, C. A. Watson, V. Silva Aguirre, S. J. Wolk, MNRAS vol. 471, issue 1, pp. 1012-1025 (2017).

New paper: Transit visibility zones of the solar system planets

2017-09-07 ktj

The shadow projected outward by a planet orbiting its star is the "Transit Visibility Zone", i.e. the area in the universe where the planet can be detected by its transit (Wells, Poppenhaeger et al. 2017). — The shadow projected outward by a planet orbiting its star is the “Transit Visibility Zone”, i.e. the area in the universe where the planet can be detected by its transit (Wells, Poppenhaeger et al. 2017).

New paper by my PhD student Rob Wells:

The detection of thousands of extrasolar planets by the transit method naturally raises the question of whether potential extrasolar observers could detect the transits of the Solar System planets. We present a comprehensive analysis of the regions in the sky from where transit events of the Solar System planets can be detected. We specify how many different Solar System planets can be observed from any given point in the sky, and find the maximum number to be three. We report the probabilities of a randomly positioned external observer to be able to observe single and multiple Solar System planet transits; specifically, we find a probability of 2.518% to be able to observe at least one transiting planet, 0.229% for at least two transiting planets, and 0.027% for three transiting planets. We identify 68 known exoplanets that have a favourable geometric perspective to allow transit detections in the Solar System and we show how the ongoing K2 mission will extend this list. We use occurrence rates of exoplanets to estimate that there are ca. 3 and 7 temperate Earth-sized planets orbiting GK and M dwarf stars brighter than $V=13$ and $V=16$ respectively, that are located in the Earth’s transit zone.

“Transit Visibility Zones of the Solar System Planets”, Wells, R.; Poppenhaeger, K.; Watson, C. A.; Heller, R., accepted for publication by Monthly Notices of the Royal Astronomical Society (2017).

Arcus, a new high-resolution X-ray spectrometer in space

2017-08-29 ktj

Artist im pression of the Arcus space telscope. Image credit: SAO/Orbital ATK

Very good news: the Arcus mission – a high-resolution X-ray spectrograph onboard a small space telescope – has received funding from NASA for a concept study! I am part of the proposal team as an international collaborator, our PI is Randall Smith from the Harvard-Smithsonian Center for Astrophysics. We just received 2 million US$ funding through NASA’s MIDEX mission call for phase A, and we will be working frantically on Arcus for the next year to demonstrate it can actually do the things we want it to do.

Here’s some more coverage: Arcus press release.