Transit Probability Research Articles

Exocomet orbital distribution around beta Pictoris

The $ sim 23$\,Myr young star beta \,Pictoris (beta \,Pic) is a laboratory for planet formation studies because of its observed debris disk, its directly imaged super-Jovian planets beta \,Pic\,b and c, and the evidence of extrasolar comets that regularly transit in front of the star. The most recent evidence of exocometary transits around beta \,Pic came from stellar photometric time series obtained with the TESS space mission. Previous analyses of these transits constrained the orbital distribution of the underlying exocomet population to a range between about 0.03 and 1.3\,AU assuming a fixed transit impact parameter. We examine the distribution of the observed transit durations Delta t$) to infer the orbital surface density distribution (delta ) of the underlying exocomet sample. The effect of the geometric transit probability for circular orbits was properly taken into account, but we assumed that the radius of the transiting comets and their possible clouds of evaporating material are much smaller than the stellar radius. We show that a narrow belt of exocomets around beta \,Pic, in which the transit impact parameters are randomized but the orbital semimajor axes are equal, results in a pile-up of long transit durations. This is in contrast to observations, which reveal a pile-up of short transit durations Delta t 0.1$\,d) and a tail of only a few transits with Delta t > 0.4$\,d. A flat density distribution of exocomets between about 0.03 and 2.5\,AU results in a better match between the resulting Delta t$ distribution and the observations, but the slope of the predicted $ Delta t$ histogram is not sufficiently steep. An even better match to the observations can be produced with a $ beta $ power law. Our modeling reveals a best fit between the observed and predicted $ Delta t$ distribution for $ A more reasonable scenario in which the exocometary trajectories are modeled as hyperbolic orbits can also reproduce the observed $ Delta t$ distribution to some extent. Future studies might reproduce the observed $ Delta t$ distribution with a full exploration of the four-dimensional parameter space of highly eccentric orbits, and they might need to relax our assumption that the transiting objects are smaller than the stellar disk. The number of observed exocometary transits around beta \,Pic is currently too small to validate the previously reported distinction of two distinct exocomet families, but this might be possible with future TESS observations of this star. Our results nevertheless imply that cometary material exists on highly eccentric orbits with a more extended range of semimajor axes than suggested by previous spectroscopic observations.

The frequency of transiting planetary systems around polluted white dwarfs

ABSTRACT This paper investigates the frequency of transiting planetary systems around metal-polluted white dwarfs using high-cadence photometry from ULTRACAM and ULTRASPEC on the ground and space-based observations with TESS. Within a sample of 313 metal-polluted white dwarfs with available TESS light curves, two systems known to have irregular transits are blindly recovered by box-least-squares and Lomb–Scargle analyses, with no new detections, yielding a transit fraction of $0.8_{-0.4}^{+0.6}$ per cent. Planet detection sensitivities are determined using simulated transit injection and recovery for all light curves, producing upper limit occurrences over radii from dwarf to Kronian planets, with periods from 1 h to 27 d. The dearth of short-period, transiting planets orbiting polluted white dwarfs is consistent with engulfment during the giant phases of stellar evolution, and modestly constrains dynamical re-injection of planets to the shortest orbital periods. Based on simple predictions of transit probability, where $(R_* + R_{\rm p})/a\simeq 0.01$, the findings here are nominally consistent with a model where 100 per cent of polluted white dwarfs have circumstellar debris near the Roche limit; however, the small sample size precludes statistical confidence in this result. Single transits are also ruled out in all light curves using a search for correlated outliers, providing weak constraints on the role of Oort-like comet clouds in white dwarf pollution.

Investigating the influence of sub-mesoscale current structures on Baltic Sea connectivity through a Lagrangian analysis

This study explores the impact of sub-mesoscale structures and vertical advection on the connectivity properties of the Baltic Sea using a Lagrangian approach. High-resolution flow fields from the General Estuarine Transport Model (GETM) were employed to compute Lagrangian trajectories, focusing on the influence of fine-scale structures on connectivity estimates. Six river mouths in the Baltic Sea served as initial positions for numerical particles, and trajectories were generated using flow fields with varying horizontal resolutions: 3D trajectories with 250m resolution as well as 2D trajectories with 250m and 1km resolutions. Several Lagrangian indices, such as mean transit time, arrival depths, and probability density functions of transit times, were analyzed to unravel the complex circulation of the Baltic Sea and highlight the substantial impact of sub-mesoscale structures on numerical trajectories. Results indicate that in 2D simulations, particles exhibit faster movement on the eastern side of the Gotland Basin in high-resolution compared to coarse-resolution simulations. This difference is attributed to the stronger coastal current in high-resolution compared to coarse-resolution simulations. Additionally, the study investigates the influence of vertical advection on numerical particle motion within the Baltic Sea, considering the difference between 3D and 2D trajectories. Findings reveal that denser water in the eastern and south-eastern areas significantly affects particle dispersion in 3D simulations, resulting in increased transit times. Conversely, regions in the North-western part of the basin accelerate particle movement in 3D compared to the 2D simulations. Finally, we calculated the average residence time of numerical particles exiting the Baltic Sea through the Danish strait. Results show an average surface layer residence time of approximately 790 days over an eight-year integration period, highlighting the relatively slow water circulation in the semi-enclosed Baltic Sea basin. This prolonged residence time emphasizes the potential for the accumulation of pollutants. Overall, the study underscores the pivotal role of fine-scale structures in shaping the connectivity of the Baltic Sea, with implications for understanding and managing environmental challenges in this unique marine ecosystem.

In-depth Study on RTT-HC-MTT Relationship for Passenger Demand beyond Elevator Contract Capacity by Simulation

The traditional elevator system design practice is to calculate the round trip time (RTT) and associated parameters of pure incoming traffic during up-peak, followed by real-time computer simulation. Recent studies indicated that the normal traffic is much more complicated, consisting of a mixture of incoming, outgoing and interfloor patterns. The Universal RTT, under such complicated traffic patterns, was analytically developed eight years ago based on the concept of an appropriate origindestination matrix describing the passenger transit probability, and verified by Monte Carlo simulation. That model is based on the assumption that the total number of passengers demanding service within one round trip is limited to the elevator contract capacity, which is in line with the traditional up-peak incoming RTT formula. The idea of extending the consideration to beyond the contract capacity was initiated two years ago. In this article, an in-depth study on such consideration is carried out so that the performance such as RTT, handling capacity (HC) and mean transit time (MTT) etc. under different traffic patterns is evaluated and analyzed with the help of Monte Carlo simulation. This article may help designers optimally size an elevator system during the RTT calculation stage without oversizing it if the prevalent traffic patterns of the building are known.

The Potential of Detecting Nearby Terrestrial Planets in the HZ with Different Methods

Terrestrial planets in the habitable zone (hereafter HZ) around nearby stars are of great interest and provide a good sample to characterize their habitability. In this paper, we collect a nearby star catalog within 20 pc according to the Gaia Catalog of Nearby Stars, complete the physical parameters of the stars, and select stars that are not brown or white dwarfs. After selection, a sample of 2234 main-sequence stars is used to estimate the extended HZ. Then we inject Earth-like planets into the extended HZ around each star and calculate the signals with four methods, i.e., velocity amplitude for radial velocity, transit probability and depth for transit, stellar displacements for astrometry, and contrast and angular separation for imaging. Considering a typical noise model based on classic instruments, e.g., ESPRESSO, Kepler, Gaia, HabEx, and LIFE, we predict the highest possible detection number of Earth-like planets via different methods in the best-case hypothetical scenario. According to this, we conclude that both astrometry and imaging have the potential to detect nearby Earth-like planets around G-type stars, while radial velocity has the potential to detect 2% of nearby Earth-like planets around M stars with a precision of 0.2 m s−1. Our work also provides the precision requirements for future missions to reveal the nearby Earth-like planet in the HZ.

Exoplanet Nodal Precession Induced by Rapidly Rotating Stars: Impacts on Transit Probabilities and Biases

For the majority of short-period exoplanets transiting massive stars with radiative envelopes, the spin angular momentum of the host star is greater than the planetary orbital angular momentum. In this case, the orbits of the planets will undergo nodal precession, which can significantly impact the probability that the planets transit their parent star. In particular, for some combinations of the spin–orbit angle ψ and the inclination of the stellar spin i *, all such planets will eventually transit at some point over the duration of their precession period. Thus, as the time over which the sky has been monitored for transiting planets increases, the frequency of planets with detectable transits will increase, potentially leading to biased estimates of exoplanet occurrence rates, especially orbiting more-massive stars. Furthermore, due to the dependence of the precession period on orbital parameters such as spin–orbit misalignment, the observed distributions of such parameters may also be biased. We derive the transit probability of a given exoplanet in the presence of nodal precession induced by a rapidly spinning host star. We find that the effect of nodal precession has already started to become relevant for some short-period planets, i.e., hot Jupiters, orbiting massive stars, by increasing transit probabilities by order of a few percent for such systems within the original Kepler field. We additionally derive simple expressions to describe the time evolution of the impact parameter b for applicable systems, which should aid in future investigations of exoplanet nodal precession and spin–orbit alignment.

Bioverse: A Comprehensive Assessment of the Capabilities of Extremely Large Telescopes to Probe Earth-like O2 Levels in Nearby Transiting Habitable-zone Exoplanets

Molecular oxygen is a strong indicator of life on Earth and may indicate biological processes on exoplanets too. Recent studies proposed that Earth-like O2 levels might be detectable on nearby exoplanets using high-resolution spectrographs on future extremely large telescopes (ELTs). However, these studies did not consider constraints like relative velocities, planet occurrence rates, and target observability. We expanded on past studies by creating a homogeneous catalog of 286,391 main-sequence stars within 120 pc using Gaia DR3 and used the Bioverse framework to simulate the likelihood of finding nearby transiting Earth analogs. We also simulated a survey of M dwarfs within 20 pc accounting for η ⊕ estimates, transit probabilities, relative velocities, and target observability to determine how long ELTs and theoretical 50–100 m ground-based telescopes need to observe to probe for Earth-like O2 levels with an R = 100,000 spectrograph. This would only be possible within 50 yr for up to ∼21% of nearby M-dwarf systems if a suitable transiting habitable-zone Earth analog was discovered, assuming signals from every observable partial transit from each ELT can be combined. If so, Earth-like O2 levels could be detectable on TRAPPIST-1 d–g within 16–55 yr, respectively, and about half that time with an R = 500,000 spectrograph. These results have important implications for whether ELTs can survey nearby habitable-zone Earth analogs for O2 via transmission spectroscopy. Our work provides the most comprehensive assessment to date of the ground-based capabilities to search for life beyond the solar system.

Occurrence rate of hot Jupiters orbiting red giant stars

Context. Hot Jupiters form an enigmatic class of object whose formation pathways are not yet clear. Determining their occurrence rates as a function of orbit, planet and stellar mass, and system age can be an important ingredient for understanding how they form. To date, various hot Jupiters have been discovered orbiting red giant stars, and deriving their incidence would be highly interesting. Aims. In this study our aim is to determine the number of hot Jupiters in a well-defined sample of red giants, estimate their occurrence rate, and compare it with that for A-, F-, and G-type stars. Methods. A sample of 14474 red giant stars, with estimated radii between 2 and 5 R⊙, was selected using Gaia to coincide with observations by the NASA TESS mission. Subsequently, the TESS light curves were searched for transits from hot Jupiters. The detection efficiency was determined using injected signals, and the results further corrected for the geometric transit probability to estimate the occurrence rate. Results. Three previously confirmed hot Jupiters were found in the TESS data, in addition to one other TESS object of interest, and two M-dwarf companions. This results in an occurrence rate of 0.37−0.09+0.29%. Due to the still large uncertainties, this cannot be distinguished from that of A-, F-, and G-type stars. We argue that it is unlikely that planet engulfment in expanding red giants plays an important role in this sample.

Null transit detections of 68 radial-velocity exoplanets observed by TESS

In recent years, the number of exoplanets has grown considerably. The most successful techniques in these detections are the radial velocity (RV) and planetary transits techniques, the latter of which has been significantly advanced by the Kepler, K2 and, more recently, the Transiting Exoplanet Survey Satellite (TESS) missions. The detection of exoplanets by means of both transits and RVs is of importance because this allows the characterization of their bulk densities and internal compositions. The TESS survey offers a unique possibility to search for transits of extrasolar planets detected using RVs. In this work, we present the results of our search for transits of RV-detected planets using the photometry of the TESS space mission. We focus on systems with super-Earth- and Neptune-sized planets on orbits with periods of shorter than 30 days. This cut is intended to keep objects with a relatively high transit probability, and is also consistent with the duration of TESS observations on a single sector. Given the summed geometric transit probabilities, the expected number of transiting planets is 3.4 ± 1.8. The sample contains two known transiting planets. We report null results for the remaining 66 out of 68 planets studied, and we exclude in all cases planets larger than 2.4 R⊕ under the assumption of central transits. The remaining two planets orbit HD 136352 and were recently announced.

Edge-of-the-Multis: Evidence for a Transition in the Outer Architectures of Compact Multiplanet Systems

Although the architectures of compact multiple-planet systems are well characterized, there has been little examination of their “outer edges,” or the locations of their outermost planets. Here we present evidence that the observed high-multiplicity Kepler systems truncate at smaller orbital periods than can be explained by geometric and detection biases alone. To show this, we considered the existence of hypothetical planets orbiting beyond the observed transiting planets with properties dictated by the “peas-in-a-pod” patterns of intrasystem radius and period ratio uniformity. We evaluated the detectability of these hypothetical planets using (1) a novel approach for estimating the mutual inclination dispersion of multitransiting systems based on transit chord length ratios, and (2) a model of transit probability and detection efficiency that accounts for the impacts of planet multiplicity on completeness. Under the assumption that the “peas-in-a-pod” patterns continue to larger orbital separations than observed, we find that ≳35% of Kepler compact multis should possess additional detected planets beyond the known planets, constituting a ∼7σ discrepancy with the lack of such detections. These results indicate that the outer (∼100–300 days) regions of compact multis experience a truncation (i.e., an “edge-of-the-multis”) or a significant breakdown of the “peas-in-a-pod” patterns, in the form of systematically smaller radii or larger period ratios. We outline future observations that can distinguish these possibilities, and we discuss implications for planet formation theories.

A study on universal round trip time analysis for passenger demand beyond elevator contract capacity by Monte Carlo simulation

The traditional elevator system design practice is to calculate the round trip time (RTT) and associated parameters of pure incoming traffic during up-peak, followed by real-time computer simulation. Recent studies indicated that the normal traffic is much more complicated, consisting of a mixture of incoming, outgoing and interfloor patterns. A major breakthrough to analytically calculate the Universal RTT, under such complicated traffic patterns, emerged 6 years ago based on an appropriate origin-destination matrix describing the passenger transit probability. That genesis model played safe by assuming that the total number of passengers demanding service within one round trip is limited elevator contract capacity, which is in line with the traditional up-peak incoming RTT formulae. In this article, such assumption is removed and the study is based on Monte Carlo simulation. It is found that there is room for enhancing the handling capacity, up to two times the contract capacity, by not sacrificing the RTT and average passenger transit time by too much. This phenomenon, that is, total passenger demand beyond contract capacity, is only valid under the existence of multiple entrance floors and/or mixed traffic conditions. This approach may prevent oversizing the design which could be more realistic. Practical applications: Elevator system designers, according to ISO 8100:32:2020 and CIBSE Guide D: 2020, are recommended to carry out calculation of the RTT and related parameters before any real-time computer simulation. This practice has been adopted by the elevator industry for decades. However, conventional RTT evaluation is mainly on pure incoming traffic during up-peak. The Universal RTT calculation method developed in 2014–15 extended RTT evaluation to cover dominant and complicated traffic patterns of modern buildings, but the assumed number of passengers to be handled within one round trip was limited to the contract capacity of the elevator. This article further removes this limitation to evaluate the limit of handling capacity with reasonable RTT and average passenger transit time. Then, the Universal RTT method could be more realistic and rolled out, and prevent oversizing the system design.

On the Detection of Exomoons Transiting Isolated Planetary-mass Objects

Abstract All-sky imaging surveys have identified several dozen isolated planetary-mass objects (IPMOs) far away from any star. Here we examine the prospects for detecting transiting moons around these objects. We expect transiting moons to be common, occurring around 10%–15% of IPMOs, given that close-orbiting moons have a high geometric transit probability and are expected to be a common outcome of giant planet formation. The IPMOs offer an advantage over other directly imaged planets in that high-contrast imaging is not necessary to detect the photometric transit signal. For at least 30 (>50%) of the currently known IPMOs, observations of a single transit with the James Webb Space Telescope would have low enough forecast noise levels to allow for the detection of an Io- or Titan-like moon. The intrinsic variability of the IPMOs will be an obstacle. Using archival time-series photometry of IPMOs with the Spitzer Space Telescope as a proof of concept, we found evidence for a fading event of 2MASS J1119–1137 AB that might have been caused by intrinsic variability but is also consistent with a single transit of a habitable-zone 1.7 R ⊕ exomoon. Although the interpretation of this particular event is inconclusive, the characteristics of the data and the candidate signal suggest that Earth-sized habitable-zone exomoons around IPMOs are detectable with existing instrumentation.

The SOPHIE search for northern extrasolar planets

Context.Due to their low transit probability, the long-period planets are, as a population, only partially probed by transit surveys. Radial velocity surveys thus have a key role to play, in particular for giant planets. Cold Jupiters induce a typical radial velocity semi-amplitude of 10 m s−1, which is well within the reach of multiple instruments that have now been in operation for more than a decade.Aims.We take advantage of the ongoing radial velocity survey with the SOPHIEhigh-resolution spectrograph, which continues the search started by its predecessor ELODIEto further characterize the cold Jupiter population.Methods.Analyzing the radial velocity data from six bright solar-like stars taken over a period of up to 15 yr, we attempt the detection and confirmation of Keplerian signals.Results.We announce the discovery of six planets, one per system, with minimum masses in the range 4.8–8.3Mjupand orbital periods between 200 days and 10 yr. The data do not provide enough evidence to support the presence of additional planets in any of these systems. The analysis of stellar activity indicators confirms the planetary nature of the detected signals.Conclusions.These six planets belong to the cold and massive Jupiter population, and four of them populate its eccentric tail. In this respect, HD 80869 b stands out as having one of the most eccentric orbits, with an eccentricity of 0.862−0.018+0.028. These planets can thus help to better constrain the migration and evolution processes at play in the gas giant population. Furthermore, recent works presenting the correlation between small planets and cold Jupiters indicate that these systems are good candidates to search for small inner planets.

Exploring the effect of the built environment, weather condition and departure time of travel on mode choice decision for different travel purposes: Evidence from Isfahan, Iran

A growing number of researchers have investigated the role of key factors that affect transport mode choice. Scant studies, however, have tried to incorporate the built environment factors at origin and destination, weather condition, departure time, and different trip purposes into mode choice models. To address these shortcomings, we developed four multinomial logit (MNL) models to analyze travel mode choice decision for different purposes in the context of a developing country, Iran. Travel data drawn from household travel survey conducted by Isfahan Municipality in 2015 and weather parameters were retrieved from five stations located inside the city. The results of models reveal some important insights. While entropy index and average block size stronglyinfluence transport mode decisions, other built environment factors have weak associations with transport modes. Further, low temperature and low relative humidity decrease the probability of transit, motorcycle and bicycle usage over automobile. The impact of weather condition on discretionary trips is stronger than that of work trips. Apart from mentioned variables, socio-demographic characteristics and departure time of travel are other important variables. Findings of this paper indicate that nonphysical strategies in tandem with land use policies should be considered based on local condition.

HD 76920 b pinned down: A detailed analysis of the most eccentric planetary system around an evolved star

Abstract We present 63 new multi-site radial velocity (RV) measurements of the K1III giant HD 76920, which was recently reported to host the most eccentric planet known to orbit an evolved star. We focused our observational efforts on the time around the predicted periastron passage and achieved near-continuous phase coverage of the corresponding RV peak. By combining our RV measurements from four different instruments with previously published ones, we confirm the highly eccentric nature of the system and find an even higher eccentricity of $e=0.8782 \pm 0.0025$ , an orbital period of $415.891^{+0.043}_{-0.039}\,\textrm{d}$ , and a minimum mass of $3.13^{+0.41}_{-0.43}\,\textrm{M}_{\textrm{J}}$ for the planet. The uncertainties in the orbital elements are greatly reduced, especially for the period and eccentricity. We also performed a detailed spectroscopic analysis to derive atmospheric stellar parameters, and thus the fundamental stellar parameters ( $M_*, R_*, L_*$ ), taking into account the parallax from Gaia DR2, and independently determined the stellar mass and radius using asteroseismology. Intriguingly, at periastron, the planet comes to within 2.4 stellar radii of its host star’s surface. However, we find that the planet is not currently experiencing any significant orbital decay and will not be engulfed by the stellar envelope for at least another 50–80 Myr. Finally, while we calculate a relatively high transit probability of 16%, we did not detect a transit in the TESS photometry.

A statistical model of secondary ion emission and attenuation clarifies disparities in quasi-simultaneous arrival coefficients measured with secondary ion mass spectrometry.

Secondary ion mass spectrometry data collected using electron multiplier detectors are subject to a correction for the quasi-simultaneous arrival (QSA) effect. Published Poisson statistical models indicate that the QSA coefficients, β, should have an invariant value of 0.5, whereas, with one exception, published experimental determinations vary between 0.6 and 1.0, with a mean value of 0.75. We developed a more complex model, combining both ion emission and attenuation, that predicts the observed range in measured β and elucidates the mechanism of secondary ion formation. For a given aperture setting, any secondary ion has an equal probability of successful transit to the electron multiplier. Binomial statistics can model pass-fail aperture attenuation but require probability distributions of the quasi-simultaneously emitted (QSE) ion tally, per primary ion, as input. Assuming (a) that each primary ion impact results in 0, 1, 2,… secondary ion emissions, randomly, with an average Ks and (b) that there is finite probability (P2) of a further emission process dependent on Ks , the required QSE probability distributions were generated via a combined Poisson-binomial statistical model. The value of β was output as a function of Ks and P2. For values of P2 > 0 and any value of Ks , β always exceeds 0.5. As P2 → 0, β → 0.5; for values of increasing P2 > 0.5 and decreasing Ks < 0.5, β → >1. Were the emission of one ion not to influence the probability of the formation of a second (i.e. model output for P2 = 0), β should always be 0.5. Yet measurements have never reported this value. Consequently, assuming that published β values are correct, emissions of QSE secondary ions do not occur independently, and it may be inferred that there are linked mechanisms of secondary ion formation as shown here.

Hidden Worlds: Dynamical Architecture Predictions of Undetected Planets in Multi-planet Systems and Applications to TESS Systems

Abstract Multi-planet systems produce a wealth of information for exoplanet science, but our understanding of planetary architectures is incomplete. Probing these systems further will provide insight into orbital architectures and formation pathways. Here we present a model to predict previously undetected planets in these systems via population statistics. The model considers both transiting and non-transiting planets, and can test the addition of more than one planet. Our tests show the model’s orbital period predictions are robust to perturbations in system architectures on the order of a few percent, much larger than current uncertainties. Applying it to the multi-planet systems from the Transiting Exoplanet Survey Satellite (TESS) provides a prioritized list of targets, based on predicted transit depth and probability, for archival searches and for guiding ground-based follow-up observations hunting for hidden planets.

Erwinia carotovora Quorum Sensing System Regulates Host-Specific Virulence Factors and Development Delay in Drosophila melanogaster.

Multihost bacteria have to rapidly adapt to drastic environmental changes, relying on a fine integration of multiple stimuli for an optimal genetic response. Erwinia carotovora spp. are phytopathogens that cause soft-rot disease. Strain Ecc15 in particular is a model for bacterial oral-route infection in Drosophila melanogaster as it harbors a unique gene, evf, that encodes the Erwinia virulence factor (Evf), which is a major determinant for infection of the D. melanogaster gut. However, the factors involved in the regulation of evf expression are poorly understood. We investigated whether evf could be controlled by quorum sensing as, in the Erwinia genus, quorum sensing regulates pectolytic enzymes, the major virulence factors needed to infect plants. Here, we show that transcription of evf is positively regulated by quorum sensing in Ecc15 via acyl-homoserine lactone (AHL) signal synthase ExpI and AHL receptors ExpR1 and ExpR2. We also show that the load of Ecc15 in the gut depends upon the quorum sensing-mediated regulation of evf Furthermore, we demonstrate that larvae infected with Ecc15 suffer a developmental delay as a direct consequence of the regulation of evf via quorum sensing. Finally, we demonstrate that evf is coexpressed with plant cell wall-degrading enzymes (PCWDE) during plant infection in a quorum sensing-dependent manner. Overall, our results show that Ecc15 relies on quorum sensing to control production of both pectolytic enzymes and Evf. This regulation influences the interaction of Ecc15 with its two known hosts, indicating that quorum sensing signaling may impact bacterial dissemination via insect vectors that feed on rotting plants.IMPORTANCE Integration of genetic networks allows bacteria to rapidly adapt to changing environments. This is particularly important in bacteria that interact with multiple hosts. Erwinia carotovora is a plant pathogen that uses Drosophila melanogaster as a vector. To interact with these two hosts, Ecc15 uses different sets of virulence factors: plant cell wall-degrading enzymes to infect plants and the Erwinia virulence factor (evf) to infect Drosophila Our work shows that, despite the virulence factors being specific for each host, both sets are coactivated by homoserine lactone quorum sensing and by the two-component GacS/A system in infected plants. This regulation is essential for Ecc15 loads in the gut of Drosophila and minimizes the developmental delay caused by the bacteria with respect to the insect vector. Our findings provide evidence that coactivation of the host-specific factors in the plant may function as a predictive mechanism to maximize the probability of transit of the bacteria between hosts.

Toward Complete Characterization: Prospects for Directly Imaging Transiting Exoplanets

Abstract High-contrast direct imaging of exoplanets can provide many important observables, including measurements of the orbit, spectra that probe the lower layers of the atmosphere, and phase variations of the planet, but cannot directly measure planet radius or mass. Our future understanding of directly imaged exoplanets will therefore rely on extrapolated models of planetary atmospheres and bulk composition, which need robust calibration. We estimate the population of extrasolar planets that could serve as calibrators for these models. Critically, this population of “standard planets” must be accessible to both direct imaging and the transit method, allowing for radius measurement. We show that the search volume of a direct imaging mission eventually overcomes the transit probability falloff with semimajor axis, so that as long as cold planets are not exceedingly rare, the population of transiting planets and directly imageable planets overlaps. Using current extrapolations of Kepler occurrence rates, we estimate that ∼8 standard planets could be characterized shortward of 800 nm with an ambitious future direct imaging mission like LUVOIR-A and several dozen could be detected at the V band. We show the design space that would expand the sample size and discuss the extent to which ground- and space-based surveys could detect this small but crucial population of planets.

Mass distribution of exoplanets considering some observation selection effects in the transit detection technique

While the radial velocity technique (RV) allows to determine only the product m·sin i of the mass m of one exoplanet by sin i (i, angle of inclination of orbital pole to the observer), when it is applied to a planet already detected while transiting its host star, the true mass m is determined, since angle i is near 90° and sin i ~ 1. Therefore, the mass distribution of transiting exoplanets discovered by photometric observations is of particular interest. However, there are some selection effects that distort the true (original) mass distribution into the observed mass distribution. We have studied the whole observed mass distribution of transiting exoplanets that were discovered from space-borne and ground-based surveys (NASA Exoplanet Archive 2019) and corrected them from some selection effects to retrieve a de-biased true mass distribution. For this, we take into account two factors: the probability of mass determination and the probability of transit configurations. The first factor is a bias introduced by a number of effects inherent to the RV method. The bias factor could be estimated by computing the fraction of transiting planets for which the mass was determined from the RV or TTV (Transit Timing Variations) methods. Photometric surveys for transit detection allow determining the planetary radii, and the bias factor was estimated for various bins of planetary sizes. The second factor is the transit probability, a geometrical factor which is precisely known for each detected transiting planet and therefore easy to account for. The mass distribution of exoplanets corrected for the first factor (de-biased) was analyzed, and it is found that this distribution can be well approximated by a power law: dN/dm ∝ m−2. When both factors of observation selection are taken into account, a flat statistically significant area (plateau) in the mass interval of 0.3–2 mJ appears on the mass distribution. The mass distributions derived from transiting planets is preliminary and can be updated after the RV follow-up of K2 planets will be more complete and the number of Kepler11https://www.nasa.gov/mission_pages/kepler/main/index.html confirmed planets definitive. The significances of the local minima (plateau) in the retrieved mass distribution have been estimated by the Kolmogorov-Smirnov test.Our de-biased mass distribution was compared to the theoretical model of Mordasini (2018). The slopes are similar, but a plateau present in the model in the range 0.1–5 Jupiter mass is appearing in the data if one considers the probability of transit configuration and considers the lower sensitivity of transit method (with follow-up mass measurement by RV) to planets with long periods and large orbits. In fact, Mordasini (2018) included exoplanets on all orbits. The Gaia22https://sci.esa.int/web/gaia astrometric method should be able to clarify this discrepancy.Radial velocity surveys are more complete than transits for long period planets. And though the sin i effect is present, its amplitude is indeed not strongly relevant from a statistical point of view (and can actually be taken into account). However RV-database is formed by surveys with substantially different durations, sensitivities, and other sources of inhomogeneities. Some examples of regularization of RV data are shown by e.g. (Mordasini, 2018; Ananyeva et al., 2019; Tuomi et al., 2019), but it is hoped that more biases/inhomogeneities may be dealt with in the future.