Galactic 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.
Abstract
Studying the chemical compositions of exoplanetary atmospheres provides valuable information about the conditions and characteristics of those atmospheres, which could help search for signs ...of extraterrestrial life. To date, over 3,000 exoplanets have been discovered using the transit method. The transmission spectroscopy technique, which studies exoplanetary atmospheres during their transits, is widely used to study the atmosphere of transiting exoplanets. Wide Field Camera 3 (WFC3), an instrument on the Hubble Space Telescope (HST), use the transmission spectroscopy technique by observing the spectrum of light curves of transiting exoplanets in optical and infrared wavelengths, which could reveal some molecular absorption in the exoplanetary atmosphere. In this work, we study the atmospheres of 20 transiting exoplanets that are Jovian planets. Light curves of these exoplanets observed by the WFC3 are used to analyze their physical properties using the Iraclis package and transit depth using the TransitFit package, a python exoplanetary fitting package based on nested sampling algorithms. Our physical parameters from TransitFit are approximately the same as those in previous literature. Finally, TauREx 3, a fully Bayesian spectral retrieval code, analyzes the transit depth per wavelength channel and reveals atmospheric compositions of these exoplanetary atmospheres. One notable finding from our analysis is the detection of
5
−
3
+
8
%
H
2
O abundance in the atmosphere of WASP-63 b.
In this paper, the detectability of habitable exomoons orbiting around giant planets in M-dwarf systems using transit timing variations (TTVs) and transit duration variations (TDVs) with Kepler-class ...photometry is investigated. Light curves of systems with various configurations were simulated around M-dwarf hosts of mass 0.5 M and radius 0.55 R. Jupiter-like giant planets which offer the best potential for hosting habitable exomoons were considered with rocky super-Earth-mass moons. The detectability is measured by using the phase-correlation between TTV and TDV signals. Since the TDV signal is typically weaker than the TTV signal, confirmation of an exomoon detection will depend on being able to detect a TDV signal. We find that exomoons around planets orbiting within the habitable zone of an M-dwarf host star can produce both detectable TTV and TDV signatures with Kepler-class photometry. While aliasing between the planet period and moon period may hinder exomoon detection, we also find some strong correlation signatures in our simulation (e.g. correlation: >0.7) which would provide convincing exomoon signatures. With the addition of red noise stellar variability, correlations generally weaken. However simulated examples with planet masses less than around 25 M⊕, moons of mass 8-10 M⊕ and specific values of planet and moon periods still yield detectable correlation in 25-50 per cent of cases. Our simulation indicates that Kepler provides one of the best available opportunities for exomoon detection.
Hot spring environments encompass broad physicochemical ranges, in which temperature and pH account for crucial factors shaping hot spring microbial community and diversity. However, the presence of ...photosynthetic microbial mats adjacent to boiling hot spring vents, where fluid temperatures extend beyond photosynthetic capability, questions the microbial profiles and the actual temperatures of such adjacent mats. Therefore, this study aims to characterize thermophilic microbial communities at Pong Dueat Pa Pae hot spring using next-generation sequencing, including investigating hot spring mineralogy. Results suggest that Pong Dueat Pa Pae hot spring precipitates comprise mainly silica which also acts as the main preservative medium for microbial permineralization. Molecular results revealed the presence of cyanobacterial and Chloroflexi species in the thick, orange and green subaerial mats surrounding the vents, suggesting the mats would be at least 30 °C cooler than source vents despite constantly receiving geyser splashes. Bacterial abundance was considerably higher than archaeal (97.9% versus 2.1%). Cyanobacterial (mainly
Synechococcus
and
Leptolygbya
) and Chloroflexi species (mainly
Roseiflexus
) accounted for almost half (40.04%) of the bacterial community, while DHVEG-6 and Thaumarchaeota comprised dominant members (> 90%) of the archaeal fraction. This study updates and provides insights into thermophilic microbial community composition and mineralogy of hot springs in Thailand.
ABSTRACT
One of the principal bottlenecks to atmosphere characterization in the era of all-sky surveys is the availability of fast, autonomous, and robust atmospheric retrieval methods. We present a ...new approach using unsupervised machine learning to generate informed priors for retrieval of exoplanetary atmosphere parameters from transmission spectra. We use principal component analysis (PCA) to efficiently compress the information content of a library of transmission spectra forward models generated using the platon package. We then apply a k-means clustering algorithm in PCA space to segregate the library into discrete classes. We show that our classifier is almost always able to instantaneously place a previously unseen spectrum into the correct class, for low-to-moderate spectral resolutions, R, in the range R = 30−300 and noise levels up to 10 per cent of the peak-to-trough spectrum amplitude. The distribution of physical parameters for all members of the class therefore provides an informed prior for standard retrieval methods such as nested sampling. We benchmark our informed-prior approach against a standard uniform-prior nested sampler, finding that our approach is up to a factor of 2 faster, with negligible reduction in accuracy. We demonstrate the application of this method to existing and near-future observatories, and show that it is suitable for real-world application. Our general approach is not specific to transmission spectroscopy and should be more widely applicable to cases that involve the repetitive fitting of trusted high-dimensional models to large data catalogues, including beyond exoplanetary science.
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).
Roman
will dedicate part of its core survey program to the detection of cool exoplanets via microlensing, while
Euclid
may undertake a microlensing program as an ancillary science goal. 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 at least 30% of the events’ relative proper motions
µ
rel
and 42% of the lens magnitudes. This survey would place strong constraints on the mass and distance on thousands of microlensing events observed by
Roman
just after the first year of observation. 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 and, ultimately, obtain a direct measurement of the masses, distances, and transverse motions of FFPs. 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. The recent tentative detection of an excess of short-duration events by the OGLE survey is consistent with a scenario of up to ten Earth-mass FFPs per Galactic star. For such a scenario 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 characterization of exomoons, and find that it could lead to the detection of the first exomoon.
Abstract During the last 25 yr, hundreds of binary stars and planets have been discovered toward the Galactic bulge by microlensing surveys. Thanks to a new generation of large-sky surveys, it is now ...possible to regularly detect microlensing events across the entire sky. The OMEGA Key Projet at the Las Cumbres Observatory carries out automated follow-up observations of microlensing events alerted by these surveys with the aim of identifying and characterizing exoplanets as well as stellar remnants. In this study, we present the analysis of the binary lens event Gaia20bof. By automatically requesting additional observations, the OMEGA Key Project obtained dense time coverage of an anomaly near the peak of the event, allowing characterization of the lensing system. The observed anomaly in the lightcurve is due to a binary lens. However, several models can explain the observations. Spectroscopic observations indicate that the source is located at ≤2.0 kpc, in agreement with the parallax measurements from Gaia. While the models are currently degenerate, future observations, especially the Gaia astrometric time series as well as high-resolution imaging, will provide extra constraints to distinguish between them.
Abstract
Nowadays, more than 4,000 exoplanets have been discovered, including a hundred of circumbinary planets. In the following work, the orbital variations of 67 S-type circumbinary planets have ...been studied. Their orbital evolutions for a thousand years are simulated using the REBOUND package. The published physical and orbital parameters of the systems are used to computed the systems’ orbital instability limits: Roche limit and Hill’s sphere. From 67 systems, there are two unstable circumbinary systems: Kepler-420 and GJ 86. Kepler-420 Ab orbit passes into the system’s Roche limit due to its high orbital eccentricity. For GJ 86 Ab, the planet orbits outside its Hill’s sphere. The instability of GJ 86 Ab might be caused by an inaccurate measurement of GJ 86 A physical parameters. Using the GJ 86 A mass obtained from Farihi et al., the planet orbits in the stable orbit zone.
ABSTRACT
Microlensing 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.
GJ3470b is a hot Neptune exoplanet orbiting an M dwarf and the first sub-Jovian planet to exhibit Rayleigh scattering. We present transit timing variation (TTV) and transmission spectroscopy analyses ...of multiwavelength optical photometry from 2.4-m and 0.5-m telescopes at the Thai National Observatory, and the 0.6-m PROMPT-8 telescope in Chile. Our TTV analysis allows us to place an upper mass limit for a second planet in the system. The presence of a hot Jupiter with a period of less than 10 d or a planet with an orbital period between 2.5 and 4.0 d are excluded. Combined optical and near-infrared transmission spectroscopy favour an H/He-dominated haze (mean molecular weight 1.08 plus or minus 0.20) with high particle abundance at high altitude. We also argue that previous near-infrared data favour the presence of methane in the atmosphere of GJ3470b.
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