90 research outputs found
Besançon Galactic model analysis of MOA-II microlensing: evidence for a mass deficit in the inner bulge
No full textInternational audienceGalactic bulge microlensing surveys provide a probe of Galactic structure. We present the first field-by-field comparison between microlensing observations and the Besançon population synthesis Galactic model. Using an updated version of the model we provide maps of optical depth, average event duration and event rate for resolved source populations and for difference imaging analysis (DIA) events. We also compare the predicted event time-scale distribution to that observed. The simulation follows the selection criteria of the MOA-II survey. We modify the Besançon model to include M dwarfs and brown dwarfs. Our best-fitting model requires a brown dwarf mass function slope of −0.4. The model provides good agreement with the observed average duration, and respectable consistency with the shape of the time-scale distribution (reduced χ2 ≃ 2.2). The DIA and resolved source limiting yields bracket the observed number of events by MOA-II (2.17 × and 0.83 × the number observed, respectively). We perform a two-dimensional fit to the event spatial distribution to predict the optical depth and event rate across the Galactic bulge. The most serious difficulty for the model is that it provides only ∼50 per cent of the measured optical depth and event rate per star at low Galactic latitude around the inner bulge (|b| < 3°). This discrepancy most likely is associated with known underestimated extinction and star counts in the innermost regions and therefore provides additional support for a missing inner stellar population
Circumbinary planet study around NSVS 14256825
No full textThe period variability of (O-C) diagram of an eclipsing binary, NSVS 14256825, which is composed of a hot subdwarf type OB star (sdOB) and a main-sequence low-mass type M star (dM) in close orbit with period P=0.110374 days, previously showed sinusoidal signal cause by the light travel time effects. This signal can be caused by the presence of third bodies. We re-examined (O-C) diagram of the system. We combined eclipse timings from published data and the data taken from ULTRASPEC at 2.4 m at Thai National Telescope on November 2018. From the fitting model, the parameters of the third body in NSVS 14256825 system are obtained
Besanccon Galactic model analysis of MOA-II microlensing: evidence for a mass deficit in the inner bulge
No full textEdge-Centric Quality Adaptation Scheme for Mobile Video Streaming
No full textThe proliferation of mobile video streaming necessitates efficient HTTP Adaptive Streaming (HAS) to optimize video quality and ensure equitable distribution among clients. Client-side ABR often degrades QoE and yields unfair bitrate allocation under mobile variability. We frame this challenge as a multi-objective optimization and propose EQAH, a Lyapunov-based, edge-assisted quality adaptation heuristic. Executed at the edge node, it optimizes video quality and fairness using a novel throughput estimator, Weighted Harmonic Exponential Averaging (WHEA), which improves robustness and accuracy under dynamic conditions. The algorithm runs once per segment in time (tens of s) with fresh buffer/throughput inputs, meeting real-time constraints. Evaluated on public 4G LTE and 5G traces, EQAH outperforms existing edge-assisted methods in both QoE and fairness across diverse mobility scenarios
A Robust Throughput Estimation in Edge-Assisted Adaptive Bitrate Streaming Networks
No full textDynamic Adaptive Streaming over HTTP (DASH) ensures continuous video transmission via Adaptive Bitrate (ABR) algorithms reliant on accurate throughput estimation. Existing methods often falter in unstable network conditions, impacting Quality of Experience (QoE). We address two intertwined issues in mobile HTTP video delivery. First, we present Weighted Harmonic–Exponential Averaging (WHEA), a lightweight hybrid estimator that reduces the next segment throughput prediction error compared to state-of-the-art baselines. Second, we embed WHEA within a new edge-executed adaptation framework, called Extended-EQAH, which leverages the cross-client view available at the edge to coordinate bitrate choices. Experiments on realistic LTE traces show that Extended-EQAH raises the mean quality by 10.74 % and Jain’s Fairness Index (JFI) by 10.98 % compared to its baseline schemes. In higher-variability settings using 5G traces, Extended-EQAH with WHEA yields substantially larger average relative gains about 27.73% in mean quality and 11.11% in JFI over representative baselines. These results demonstrate that combining accurate edge-side forecasting with joint buffer and throughput control is the key to robust video streaming in dynamic wireless networks
Exoplanetary atmosphere target selection in the era of comparative planetology
No full textThe large number of new planets expected from wide-area transit surveys means that follow-up transmission spectroscopy studies of their atmospheres will be limited by the availability of telescope assets. We argue that telescopes covering a broad range of apertures will be required, with even 1 m-class instruments providing a potentially important contribution. Survey strategies that employ automated target selection will enable robust population studies. As part of such a strategy, we propose a decision metric to pair the best target to the most suitable telescope, and demonstrate its effectiveness even when only primary transit observables are available. Transmission spectroscopy target selection need not therefore be impeded by the bottle-neck of requiring prior follow-up observations to determine the planet mass. The decision metric can be easily deployed within a distributed heterogeneous network of telescopes equipped to undertake either broad-band photometry or spectroscopy. We show how the metric can be used either to optimize the observing strategy for a given telescope (e.g. choice of filter) or to enable the selection of the best telescope to optimize the overall sample size. Our decision metric can also provide the basis for a selection function to help evaluate the statistical completeness of follow-up transmission spectroscopy data sets. Finally, we validate our metric by comparing its ranked set of targets against lists of planets that have had their atmospheres successfully probed, and against some existing prioritized exoplanet lists
Earth through the looking glass: how frequently are we detected by other civilizations through photometric microlensing?
No full textInternational audienceMicrolensing is proving to be one of the best techniques to detect distant, low-mass planets around the most common stars in the Galaxy. In principle, Earth's microlensing signal could offer the chance for other technological civilizations to find the Earth across Galactic distances. We consider the photometric microlensing signal of Earth to other potential technological civilizations and dub the regions of our Galaxy from which Earth's photometric microlensing signal is most readily observable as the 'Earth microlensing zone' (EMZ). The EMZ can be thought of as the microlensing analogue of the Earth Transit Zone (ETZ) from where observers see Earth transit the Sun. Just as for the ETZ, the EMZ could represent a game-theoretic Schelling point for targeted searches for extra-terrestrial intelligence (SETI). To compute the EMZ, we use the Gaia DR2 catalogue with magnitude G < 20 to generate Earth microlensing probability and detection rate maps to other observers. While our Solar system is a multiplanet system, we show that Earth's photometric microlensing signature is almost always well approximated by a binary lens assumption. We then show that the Earth is in fact well hidden to observers with technology comparable to our own. Specifically, even if observers are located around every Gaia DR2 star with G < 20, we expect photometric microlensing signatures from the Earth to be observable on average only tens per year by any of them. In addition, the EMZs overlap with the ETZ near the Galactic Centres which could be the main areas for future SETI searches
Euclid-Roman joint microlensing survey: early mass measurement, free floating planets and exomoons
No full textFunding: EB gratefully acknowledge support from NASA grant 80NSSC19K0291. The work of DS is funded by a UK Science and Technology Facilities Council (STFC) PhD studentship. EK also acknowledges support from the STFC. EB, JPB and CR’s work was carried out within the framework of the ANR project COLD-WORLDS supported by the French National Agency for Research with the reference ANR-18-CE31-0002. JPB was supported by the University of Tasmania through the UTAS Foundation, ARC grant DP200101909 and the endowed Warren Chair in Astronomy. JR was supported by NASA ROSES grant 12-EUCLID12-0004, the Nancy Grace Roman Telescope, and JPL, which is run by Caltech under a contract for NASA. RP was supported by the Polish National Agency for Academic Exchange via Polish Returns 2019 grant. DM acknowledges support by the European Research Council (ERC) under the European Union’s FP7 Programme, Grant No. 833031.As the Kepler mission has done for hot exoplanets, the ESA Euclid and NASA Roman missions have the potential to create a breakthrough in our understanding of the demographics of cool exoplanets, including unbound, or "free-floating", planets (FFPs). In this study, we demonstrate the complementarity of the two missions and propose two joint-surveys to better constrain the mass and distance of microlensing events. We first demonstrate that an early brief Euclid survey (7 h) of the Roman microlensing fields will allow the measurement of a large fraction of events relative proper motions and lens magnitudes. Then, we study the potential of simultaneous observations by Roman and Euclid to enable the measurement of the microlensing parallax for the shortest microlensing events. Using detailed simulations of the joint detection yield we show that within one year Roman-Euclid observations will be at least an order of magnitude more sensitive than current ground-based measurements. Depending on the exact distribution of FFP, a joint Roman-Euclid campaign should detect around 130 FFP events within a year, including 110 with measured parallax that strongly constrain the FFP mass, and around 30 FFP events with direct mass and distance measurements. The ability of the joint survey to completely break the microlens mass-distance-velocity degeneracy for a significant subset of events provides a unique opportunity to verify unambiguously the FFP hypothesis or else place abundance limits for FFPs between Earth and Jupiter masses that are up to two orders of magnitude stronger than provided by ground-based surveys. Finally, we study the capabilities of the joint survey to enhance the detection and charcterization of exomoons, and found that it could lead to the detection of the first exomoon.Peer reviewe
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