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:
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.
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 🙂
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.
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 τ Boo A (F7 V) are anomalous, and we propose that this is due to the presence of the exoplanet.
The NGTS planet-search project in which I take part has detected a new planet in an interesting system:
“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.
I am happy to be part of the Kepler Object of Interest Network, a network of ground-based telescopes to observe transits of exoplanets discovered by the Kepler space telescope in order to figure out their masses through Transit Timing Variations.
The first paper about this project is now accepted:
“Kepler Object of Interest Network I. First results combining ground and space-based observations of Kepler systems with transit timing variations”
During its four years of photometric observations, the Kepler space telescope detected thousands of exoplanets and exoplanet candidates. One of Kepler’s greatest heritages has been the confirmation and characterization of hundreds of multi-planet systems via Transit Timing Variations (TTVs). However, there are many interesting candidate systems displaying TTVs on such long time scales that the existing Kepler observations are of insufficient length to confirm and characterize them by means of this technique. To continue with Kepler’s unique work we have organized the “Kepler Object of Interest Network” (KOINet). The goals of KOINet are, among others, to complete the TTV curves of systems where Kepler did not cover the interaction timescales well. KOINet has been operational since March, 2014. Here we show some promising first results obtained from analyzing seven primary transits of KOI-0410.01, KOI-0525.01, KOI-0760.01, and KOI-0902.01 in addition to Kepler data, acquired during the first and second observing seasons of KOINet. While carefully choosing the targets we set demanding constraints about timing precision (at least 1 minute) and photometric precision (as good as 1 part per thousand) that were achieved by means of our observing strategies and data analysis techniques. For KOI-0410.01, new transit data revealed a turn-over of its TTVs. We carried out an in-depth study of the system, that is identified in the NASA’s Data Validation Report as false positive. Among others, we investigated a gravitationally-bound hierarchical triple star system, and a planet-star system. While the simultaneous transit fitting of ground and space-based data allowed for a planet solution, we could not fully reject the three-star scenario. New data, already scheduled in the upcoming 2018 observing season, will set tighter constraints on the nature of the system.
As part of the Young Stellar Object VARiability project (YSOVAR), I am happy to report that we have published a new paper investigating the mid-infrared variability of young stellar objects in the star-forming region Serpens South. Here’s the title and abstract:
“YSOVAR: Mid-infrared Variability among YSOs in the Star Formation Region Serpens South”
We present a time-variability study of young stellar objects (YSOs) in the Serpens South cluster performed at 3.6 and 4.5 μm with the Spitzer Space Telescope; this study is part of the Young Stellar Object VARiability project. We have collected light curves for more than 1500 sources, including 85 cluster members, over 38 days. This includes 44 class I sources, 19 sources with flat spectral energy distributions (SEDs), 17 class II sources, and five diskless YSO candidates. We find a high variability fraction among embedded cluster members of ∼70%, whereas young stars without a detectable disk display no variability. We detect periodic variability for 32 sources with periods primarily in the range of 0.2–14 days and a subset of fast rotators thought to be field binaries. The timescale for brightness changes are shortest for stars with the most photospheric SEDs and longest for those with flat or rising SEDs. While most variable YSOs become redder when fainter, as would be expected from variable extinction, about 10% get bluer as they get fainter. One source, SSTYSV J183006.13‑020108.0, exhibits “cyclical” color changes.
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 ?>
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.
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).