Photometric surveys such as Kepler have the precision to identify exoplanet and eclipsing binary candidates from only a single transit. K2, with its 75 d campaign duration, is ideally suited to ...detect significant numbers of single-eclipsing objects. Here we develop a Bayesian transit-fitting tool (‘Namaste: An Mcmc Analysis of Single Transit Exoplanets’) to extract orbital information from single transit events. We achieve favourable results testing this technique on known Kepler planets, and apply the technique to seven candidates identified from a targeted search of K2 campaigns 1, 2 and 3. We find EPIC203311200 to host an excellent exoplanet candidate with a period, assuming zero eccentricity, of
$540 ^{+410}_{-230}$
d and a radius of 0.51 ± 0.05R
Jup. We also find six further transit candidates for which more follow-up is required to determine a planetary origin. Such a technique could be used in the future with TESS, PLATO and ground-based photometric surveys such as NGTS, potentially allowing the detection of planets in reach of confirmation by Gaia.
We are entering an era of unprecedented quantities of data from current and planned survey telescopes. To maximize the potential of such surveys, automated data analysis techniques are required. Here ...we implement a new methodology for variable star classification, through the combination of Kohonen Self-Organizing Maps (SOMs, an unsupervised machine learning algorithm) and the more common Random Forest (RF) supervised machine learning technique. We apply this method to data from the K2 mission fields 0–4, finding 154 ab-type RR Lyraes (10 newly discovered), 377 δ Scuti pulsators, 133 γ Doradus pulsators, 183 detached eclipsing binaries, 290 semidetached or contact eclipsing binaries and 9399 other periodic (mostly spot-modulated) sources, once class significance cuts are taken into account. We present light-curve features for all K2 stellar targets, including their three strongest detected frequencies, which can be used to study stellar rotation periods where the observed variability arises from spot modulation. The resulting catalogue of variable stars, classes, and associated data features are made available online. We publish our SOM code in python as part of the open source pymvpa package, which in combination with already available RF modules can be easily used to recreate the method.
The LUX-ZEPLIN experiment is a dark matter detector centered on a dual-phase xenon time projection chamber operating at the Sanford Underground Research Facility in Lead, South Dakota, USA. This ...Letter reports results from LUX-ZEPLIN's first search for weakly interacting massive particles (WIMPs) with an exposure of 60 live days using a fiducial mass of 5.5 t. A profile-likelihood ratio analysis shows the data to be consistent with a background-only hypothesis, setting new limits on spin-independent WIMP-nucleon, spin-dependent WIMP-neutron, and spin-dependent WIMP-proton cross sections for WIMP masses above 9 GeV/c^{2}. The most stringent limit is set for spin-independent scattering at 36 GeV/c^{2}, rejecting cross sections above 9.2×10^{-48} cm at the 90% confidence level.
Since the start of the Wide-angle Search for Planets (WASP) program, more than 160 transiting exoplanets have been discovered in the WASP data. In the past, possible transit-like events identified by ...the WASP pipeline have been vetted by human inspection to eliminate false alarms and obvious false positives. The goal of this paper is to assess the effectiveness of machine learning as a fast, automated, and reliable means of performing the same functions on ground-based wide-field transit-survey data without human intervention. To this end, we have created training and test data sets made up of stellar light curves showing a variety of signal types including planetary transits, eclipsing binaries, variable stars, and non-periodic signals. We use a combination of machine-learning methods including Random Forest Classifiers (RFCs) and convolutional neural networks (CNNs) to distinguish between the different types of signals. The final algorithms correctly identify planets in the test data ∼90 per cent of the time, although each method on its own has a significant fraction of false positives. We find that in practice, a combination of different methods offers the best approach to identifying the most promising exoplanet transit candidates in data from WASP, and by extension similar transit surveys.
To investigate the origin of the features discovered in the exoplanet population, the knowledge of exoplanets' mass and radius with a good precision (≲10%) is essential. To achieve this purpose the ...discovery of transiting exoplanets around bright stars is of prime interest. In this paper, we report the discovery of three transiting exoplanets by the SuperWASP survey and the SOPHIE spectrograph with mass and radius determined with a precision better than 15%. WASP-151b and WASP-153b are two hot Saturns with masses, radii, densities and equilibrium temperatures of 0.31−0.03+0.04 MJ$0.31_{-0.03}^{+0.04}\,{M_{\textrm{J}}}$0.31−0.03+0.04 MJ, 1.13−0.03+0.03 RJ$1.13_{-0.03}^{+0.03}\,{R_{\textrm{J}}}$1.13−0.03+0.03 RJ, 0.22−0.02+0.03 ρJ$0.22_{-0.02}^{+0.03}\,\rho_{\mathrm{J}}$0.22−0.02+0.03 ρJ and 1290−10+20 K$1290_{-10}^{+20}~\mathrm{K}$1290−10+20 K, and 0.39−0.02+0.02 MJ$0.39_{-0.02}^{+0.02}\,{M_{\textrm{J}}}$0.39−0.02+0.02 MJ, 1.55−0.08+0.10 RJ$1.55_{-0.08}^{+0.10}\,{R_{\textrm{J}}}$1.55−0.08+0.10 RJ, 0.11−0.02+0.02 ρJ$0.11_{-0.02}^{+0.02}\,\rho_{\mathrm{J}}$0.11−0.02+0.02 ρJ and 1700−0.40+0.40 K$1700_{-40}^{+40}~\mathrm{K}$1700−40+40 K, respectively. Their host stars are early G type stars (with mag V ~ 13) and their orbital periods are 4.53 and 3.33 days, respectively. WASP-156b is a super-Neptune orbiting a K type star (mag V = 11.6). It has a mass of $0.128_{-0.009}^{+0.010}\,{M_{\rm J}}$0.128−0.009+0.010 MJ0.128-0.009+0.010MJ, a radius of $0.51_{-0.02}^{+0.02}\,{R_{\rm J}}$0.51−0.02+0.02 RJ0.51-0.02+0.02RJ, a density of 1.0−0.1+0.1 ρJ$1.0_{-0.1}^{+0.1}\,\rho_{\mathrm{J}}$1.0−0.1+0.1 ρJ, an equilibrium temperature of 970−20+30 K$970_{-20}^{+30}~\mathrm{K}$970−20+30 K and an orbital period of 3.83 days. The radius of WASP-151b appears to be only slightly inflated, while WASP-153b presents a significant radius anomaly compared to a recently published model. WASP-156b, being one of the few well characterized super-Neptunes, will help to constrain the still debated formation of Neptune size planets and the transition between gas and ice giants. The estimates of the age of these three stars confirms an already observed tendency for some stars to have gyrochronological ages significantly lower than their isochronal ages. We propose that high eccentricity migration could partially explain this behavior for stars hosting a short period planet. Finally, these three planets also lie close to (WASP-151b and WASP-153b) or below (WASP-156b) the upper boundary of the Neptunian desert. Their characteristics support that the ultra-violet irradiation plays an important role in this depletion of planets observed in the exoplanet population.
On the abundance of circumbinary planets Armstrong, D. J; Osborn, H. P; Brown, D. J. A ...
Monthly notices of the Royal Astronomical Society,
10/2014, Letnik:
444, Številka:
2
Journal Article
Recenzirano
Odprti dostop
We present here the first observationally based determination of the rate of occurrence of circumbinary planets. This is derived from the publicly available Kepler data, using an automated search ...algorithm and debiasing process to produce occurrence rates implied by the seven systems already known. These rates depend critically on the planetary inclination distribution: if circumbinary planets are preferentially coplanar with their host binaries, as has been suggested, then the rate of occurrence of planets with Rp
> 6R⊕ orbiting with P
p
< 300 d is
$10.0 ^{+18}_{-6.5}$
per cent (95 per cent confidence limits), higher than but consistent with single star rates. If on the other hand the underlying planetary inclination distribution is isotropic, then this occurrence rate rises dramatically, to give a lower limit of 47 per cent. This implies that formation and subsequent dynamical evolution in circumbinary discs must either lead to largely coplanar planets, or proceed with significantly greater ease than in circumstellar discs. As a result of this investigation, we also show that giant planets ( > 10R⊕) are significantly less common in circumbinary orbits than their smaller siblings, and confirm that the proposed shortfall of circumbinary planets orbiting the shorter period binaries in the Kepler sample is a real effect.
The detection of low-mass transiting exoplanets in multiple systems brings new constraints to planetary formation and evolution processes and challenges the current planet formation theories. ...Nevertheless, only a mere fraction of the small planets detected by Kepler and K2 have precise mass measurements, which are mandatory to constrain their composition. We aim to characterise the planets that orbit the relatively bright star K2-138. This system is dynamically particular as it presents the longest chain known to date of planets close to the 3:2 resonance. We obtained 215 HARPS spectra from which we derived the radial-velocity variations of K2-138. Via a joint Bayesian analysis of both the K2 photometry and HARPS radial-velocities (RVs), we constrained the parameters of the six planets in orbit. The masses of the four inner planets, from b to e, are 3.1, 6.3, 7.9, and 13.0 M⊕ with a precision of 34, 20, 18, and 15%, respectively. The bulk densities are 4.9, 2.8, 3.2, and 1.8 g cm−3, ranging from Earth to Neptune-like values. For planets f and g, we report upper limits. Finally, we predict transit timing variations of the order two to six minutes from the masses derived. Given its peculiar dynamics, K2-138 is an ideal target for transit timing variation (TTV) measurements from space with the upcoming CHaracterizing ExOPlanet Satellite (CHEOPS) to study this highly-packed system and compare TTV and RV masses.
Context. The multi-planetary system HD 106315 was recently found in K2 data. The planets have periods of Pb ~ 9.55 and Pc ~ 21.06 days, and radii of rb = 2.44 ± 0.17 R⊕ and rc = 4.35 ± 0.23 R⊕ . The ...brightness of the host star (V = 9.0 mag) makes it an excellent target for transmission spectroscopy. However, to interpret transmission spectra it is crucial to measure the planetary masses. Aims. We obtained high precision radial velocities for HD 106315 to determine the mass of the two transiting planets discovered with Kepler K2. Our successful observation strategy was carefully tailored to mitigate the effect of stellar variability. Methods. We modelled the new radial velocity data together with the K2 transit photometry and a new ground-based partial transit of HD 106315c to derive system parameters. Results. We estimate the mass of HD 106315b to be 12.6 ± 3.2 M⊕ and the density to be 4.7 ± 1.7 g cm-3, while for HD 106315c we estimate a mass of 15.2 ± 3.7 M⊕ and a density of 1.01 ± 0.29 g cm-3. Hence, despite planet c having a radius almost twice as large as planet b, their masses are consistent with one another. Conclusions. We conclude that HD 106315c has a thick hydrogen-helium gaseous envelope. A detailed investigation of HD 106315b using a planetary interior model constrains the core mass fraction to be 5–29%, and the water mass fraction to be 10–50%. An alternative, not considered by our model, is that HD 106315b is composed of a large rocky core with a thick H–He envelope. Transmission spectroscopy of these planets will give insight into their atmospheric compositions and also help constrain their core compositions.
K2-265 b: a transiting rocky super-Earth Lam, K. W. F.; Santerne, A.; Sousa, S. G. ...
Astronomy and astrophysics (Berlin),
12/2018, Letnik:
620
Journal Article
Recenzirano
Odprti dostop
We report the discovery of the super-Earth K2-265 b detected with K2 photometry. The planet orbits a bright (Vmag = 11.1) star of spectral type G8V with a period of 2.37 days. We obtained ...high-precision follow-up radial velocity measurements from HARPS, and the joint Bayesian analysis showed that K2-265 b has a radius of 1.71 ± 0.11 R⊕ and a mass of 6.54 ± 0.84 M⊕, corresponding to a bulk density of 7.1 ± 1.8 g cm−3. Composition analysis of the planet reveals an Earth-like, rocky interior; this object has a rock mass fraction of ~80%. The short orbital period and small radius of the planet puts it below the lower limit of the photoevaporation gap, where the envelope of the planet could have eroded owing to strong stellar irradiation, leaving behind an exposed core. Knowledge of the planet core composition allows us to infer the possible formation and evolution mechanism responsible for its current physical parameters.
ABSTRACT We report the discovery of EPIC 201702477b, a transiting brown dwarf in a long period (40.73691 0.00037 day) and eccentric (e = 0.2281 0.0026) orbit. This system was initially reported as a ...planetary candidate based on two transit events seen in K2 Campaign 1 photometry and later validated as an exoplanet candidate. We confirm the transit and refine the ephemeris with two subsequent ground-based detections of the transit using the Las Cumbres Observatory Global Telescope 1 m telescope network. We rule out any transit timing variations above the level of ∼30 s. Using high precision radial velocity measurements from HARPS and SOPHIE we identify the transiting companion as a brown dwarf with a mass, radius, and bulk density of 66.9 1.7 MJ, 0.757 0.065 RJ, and 191 51 g cm−3 respectively. EPIC 201702477b is the smallest radius brown dwarf yet discovered, with a mass just below the H-burning limit. It has the highest density of any planet, substellar mass object, or main-sequence star discovered so far. We find evidence in the set of known transiting brown dwarfs for two populations of objects-high mass brown dwarfs and low mass brown dwarfs. The higher-mass population have radii in very close agreement to theoretical models, and show a lower-mass limit around 60 MJ. This may be the signature of mass-dependent ejection of systems during the formation process.
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