Exomoons are the natural satellites of planets orbiting stars outside our solar system, of which there are currently no confirmed examples. We present new observations of a candidate exomoon ...associated with Kepler-1625b using the Hubble Space Telescope to validate or refute the moon's presence. We find evidence in favor of the moon hypothesis, based on timing deviations and a flux decrement from the star consistent with a large transiting exomoon. Self-consistent photodynamical modeling suggests that the planet is likely several Jupiter masses, while the exomoon has a mass and radius similar to Neptune. Since our inference is dominated by a single but highly precise Hubble epoch, we advocate for future monitoring of the system to check model predictions and confirm repetition of the moon-like signal.
Abstract
The claim of an exomoon candidate in the Kepler-1625b system has generated substantial discussion regarding possible alternative explanations for the purported signal. In this work, we ...examine these possibilities in detail. First, the effect of more flexible trend models is explored, and we show that sufficiently flexible models are capable of attenuating the signal—although this is an expected byproduct of invoking such models. We also explore trend models using
x-
and
y-
centroid positions, and show that there is no data-driven impetus to adopt such models over temporal ones. We quantify the probability that the 500 ppm moon-like dip could be caused by a Neptune-sized transiting planet to be <0.75%. We show that neither autocorrelation, Gaussian processes, nor a Lomb–Scargle periodogram are able to recover a stellar rotation period, demonstrating that K1625 is a quiet star with periodic behavior <200 ppm. Through injection and recovery tests, we find that the star does not exhibit a tendency to introduce false-positive dip-like features above that of pure Gaussian noise. Finally, we address a recent reanalysis by Kreidberg et al. and show that the difference in conclusions is not from differing systematics models but rather the reduction itself. We show that their reduction exhibits, in comparison to the original analysis: (i) slightly higher intraorbit and post-fit residual scatter, (ii) ≃900 ppm larger flux offset at the visit change, (iii) ≃2 times larger
y
-centroid variations, and (iv) ≃3.5 times stronger flux-centroid correlation coefficient. These points could be explained by larger systematics in their reduction, potentially impacting their conclusions.
ABSTRACT
The so-called ‘exomoon corridor’ is a potentially powerful new tool for identifying possible exomoon hosts, enabled by the observation that fully half of all planets hosting an exomoon will ...exhibit transit timing variation (TTV) periodicities of 2–4 epochs. One key outstanding problem in the search for exomoons, however, is the question of how well the methods we have developed under the single moon assumption extend to systems with multiple moons. In this work, we use N-body simulations to examine the exomoon corridor effect in the more general case of N ≥ 1 moons, generating realistic TTVs produced by satellite systems more akin to those seen in the outer Solar System. We find that indeed the relationship does hold for systems with up to 5 moons in both resonant and non-resonant chain configurations. Our results suggest an observational bias against finding systems with large numbers of massive moons; as the number of moons increases, total satellite mass ratios are generally required to be significantly lower in order to maintain stability, or architectures must be more finely tuned to survive. Moons produced in impact or capture scenarios may therefore dominate early detections. Finally, we examine the distribution of TTV periods measured for a large number of Kepler objects of interest (KOIs) and find the same characteristic exomoon corridor distribution in several cases. This could be dynamical evidence for an abundance of moons in the field, though we caution against strong inferences based on this result.
ABSTRACT
The search for exomoons in time-domain photometric data has to-date generally consisted of fitting transit models that are comprised of a planet hosting a single moon. This simple model has ...its advantages, but it may not be particularly representative, as most of the major moons in our Solar system are found in multimoon satellite systems. It is critical that we investigate, then, the impact of applying a single-moon model to systems containing multiple moons, as there is the possibility that utilizing an inaccurate or incomplete model could lead to erroneous conclusions about the system. To that end, in this work we produce a variety of realistic multimoon light curves, perform standard single-moon model selection, and analyse the impacts that this model choice may have on the search for exomoons. We find that the number of moons in a system fit with a single-moon model generally has little impact on whether we find evidence for a moon in that system, and other system attributes are individually not especially predictive. However, the model parameter solutions for the moon frequently do not match any real moon in the system, instead painting a picture of a ‘phantom’ moon. We find no evidence that multimoon systems yield corresponding multimodal posteriors. We also find a systematic tendency to overestimate planetary impact parameter and eccentricity, to derive unphysical moon densities, and to infer potentially unphysical limb darkening coefficients. These results will be important to keep in mind in future exomoon search programmes.
Abstract Discovering and characterizing exoplanets at the outer edge of the transit method’s sensitivity has proven challenging owing to geometric biases and the practical difficulties associated ...with acquiring long observational baselines. Nonetheless, a sample of giant exoplanets on orbits longer than 100 days has been identified by transit hunting missions. We present long-term Doppler spectroscopy for 11 such systems with observation baselines spanning a few years to a decade. We model these radial velocity observations jointly with transit photometry to provide initial characterizations of these objects and the systems in which they exist. Specifically, we make new precise mass measurements for four long-period giant exoplanets (Kepler-111 c, Kepler-553 c, Kepler-849 b, and PH-2 b), we place new upper limits on mass for four others (Kepler-421 b, KOI-1431.01, Kepler-1513 b, and Kepler-952 b), and we show that several confirmed planets are in fact not planetary at all. We present these findings to complement similar efforts focused on closer-in short-period giant planets, and with the hope of inspiring future dedicated studies of cool giant exoplanets.
ABSTRACT
Targeted observations of possible exomoon host systems will remain difficult to obtain and time-consuming to analyse in the foreseeable future. As such, time-domain surveys such as Kepler, ...K2, and TESS will continue to play a critical role as the first step in identifying candidate exomoon systems, which may then be followed up with premier ground- or space-based telescopes. In this work, we train an ensemble of convolutional neural networks (CNNs) to identify candidate exomoon signals in single-transit events observed by Kepler. Our training set consists of ∼27 000 examples of synthetic, planet-only, and planet + moon single transits, injected into Kepler light curves. We achieve up to 88 per cent classification accuracy with individual CNN architectures and 97 per cent precision in identifying the moons in the validation set when the CNN ensemble is in total agreement. We then apply the CNN ensemble to light curves from 1880 Kepler Objects of Interest with periods >10 d (∼57 000 individual transits), and further test the accuracy of the CNN classifier by injecting planet transits into each light curve, thus quantifying the extent to which residual stellar activity may result in false positive classifications. We find a small fraction of these transits contain moon-like signals, though we caution against strong inferences of the exomoon occurrence rate from this result. We conclude by discussing some ongoing challenges to utilizing neural networks for the exomoon search.
A cloaking device for transiting planets Kipping, David M; Teachey, Alex
Monthly notices of the Royal Astronomical Society,
06/2016, Letnik:
459, Številka:
2
Journal Article
Recenzirano
Odprti dostop
The transit method is presently the most successful planet discovery and characterization tool at our disposal. Other advanced civilizations would surely be aware of this technique and appreciate ...that their home planet's existence and habitability is essentially broadcast to all stars lying along their ecliptic plane. We suggest that advanced civilizations could cloak their presence, or deliberately broadcast it, through controlled laser emission. Such emission could distort the apparent shape of their transit light curves with relatively little energy, due to the collimated beam and relatively infrequent nature of transits. We estimate that humanity could cloak the Earth from Kepler-like broad-band surveys using an optical monochromatic laser array emitting a peak power of ∼30 MW for ∼10 hours per year. A chromatic cloak, effective at all wavelengths, is more challenging requiring a large array of tunable lasers with a total power of ∼250 MW. Alternatively, a civilization could cloak only the atmospheric signatures associated with biological activity on their world, such as oxygen, which is achievable with a peak laser power of just ∼160 kW per transit. Finally, we suggest that the time of transit for optical Search for Extraterrestrial Intelligence (SETI) is analogous to the water-hole in radio SETI, providing a clear window in which observers may expect to communicate. Accordingly, we propose that a civilization may deliberately broadcast their technological capabilities by distorting their transit to an artificial shape, which serves as both a SETI beacon and a medium for data transmission. Such signatures could be readily searched in the archival data of transit surveys.
ABSTRACT
We present the discovery of a pair of transiting giant planets using four sectors of TESS photometry. TOI-216 is a 0.87 M⊙ dwarf orbited by two transiters with radii of 8.2 and 11.3 R⊕, and ...periods of 17.01 and 34.57 d, respectively. Anticorrelated TTVs are clearly evident indicating that the transiters orbit the same star and interact via a near 2:1 mean motion resonance. By fitting the TTVs with a dynamical model, we infer masses of $30_{-14}^{+20}$ and $200_{-100}^{+170}$ M⊕, establishing that the objects are planetary in nature and have likely sub-Kronian and Kronian densities. TOI-216 lies close to the southern ecliptic pole and thus will be observed by TESS throughout the first year, providing an opportunity for continuous dynamical monitoring and considerable refinement of the dynamical masses presented here. TOI-216 closely resembles Kepler-9 in architecture, and we hypothesize that in such systems these Saturn analogues failed to fully open a gap and thus migrated far deeper into the system before becoming trapped into resonance, which would imply that future detections of new analogues may also have sub-Jupiter masses.
ABSTRACT Diffuse gamma-ray emission from interstellar clouds results largely from cosmic ray (CR) proton collisions with ambient gas, regardless of the gas state, temperature, or dust properties of ...the cloud. The interstellar medium is predominantly transparent to both CRs and gamma-rays, so GeV emission is a unique probe of the total gas column density. The gamma-ray emissivity of a cloud of known column density is then a measure of the impinging CR population and may be used to map the k-scale CR distribution in the Galaxy. To this end, we test a number of commonly used column density tracers to evaluate their effectiveness in modeling the GeV emission from the relatively quiescent, nearby Ophiuchi molecular cloud. We confirm that both H i and an appropriate tracer are required to reproduce the total gas column densities probed by diffuse gamma-ray emisison. We find that the optical depth at 353 GHz ( ) from Planck best reproduces the gamma-ray data overall, based on the test statistic across the entire region of interest, but near-infrared stellar extinction also performs very well, with smaller spatial residuals in the densest parts of the cloud.
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