Abstract
We present a transit-timing variation (TTV) and planetary atmosphere analysis of the Neptune-mass planet HAT-P-26 b. We present a new set of 13 transit light curves from optical ground-based ...observations and combine them with light curves from the Wide Field Camera 3 on the Hubble Space Telescope, the Transiting Exoplanet Survey Satellite, and previously published ground-based data. We refine the planetary parameters of HAT-P-26 b and undertake a TTV analysis using 33 transits obtained over seven years. The TTV analysis shows an amplitude signal of 1.98 ± 0.05 minutes, which could result from the presence of an additional ∼0.02
M
Jup
planet at a 1:2 mean-motion resonance orbit. Using a combination of transit depths spanning optical to near-infrared wavelengths, we find that the atmosphere of HAT-P-26 b contains
2.4
−
1.6
+
2.9
% H
2
O with a derived temperature of
590
−
50
+
60
K.
ABSTRACT
Galactic microlensing datasets now comprise in excess of 104 events and, with the advent of next-generation microlensing surveys that may be undertaken with facilities such as the Rubin ...Observatory (formerly LSST) and Roman Space Telescope (formerly WFIRST), this number will increase significantly. So too will the fraction of events with measurable higher order information, such as finite-source effects and lens–source relative proper motion. Analysing such data requires a more sophisticated Galactic microlens modelling approach. We present a new second-generation Manchester–Besançon Microlensing Simulator (MaBμlS-2), which uses a version of the Besançon population synthesis Galactic model that provides good agreement with stellar kinematics observed by the Hubble Space Telescope (HST) towards the bulge. MaBμlS-2 provides high-fidelity signal-to-noise limited maps of the microlensing optical depth, rate and average time-scale towards a 400 deg2 region of the Galactic bulge in several optical to near-infrared pass-bands. The maps take full account of the unresolved stellar background, as well as limb-darkened source profiles. Comparing MaBμlS-2 with the efficiency-corrected OGLE-IV 8000 event sample shows a much improved agreement over the previous version of MaBμlS and succeeds in matching even small-scale structural features in the OGLE-IV event rate map. However, evidence remains for a small underprediction of the event rate per source and overprediction of the time-scale. MaBμlS-2 is available online (www.mabuls.net, Specht & Kerins) to provide on-the-fly maps for user-supplied cuts in survey magnitude, event time-scale and relative proper motion.
Abstract
Understanding of exoplanet atmospheres can be extracted from the transmission spectra using an important tool based on a retrieval technique. However, the traditional retrieval method (e.g. ...MCMC and nested sampling) consumes a lot of computational time. Therefore, this work aims to apply the random forest regression, one of the supervised machine learning technique, to retrieve exoplanet atmospheric parameters from the transmission spectra observed in the optical wavelength. We discovered that the random forest regressor had the best accuracy in predicting planetary radius (
R
F
i
t
2
= 0.999) as well as acceptable accuracy in predicting planetary mass, temperature, and metallicity of planetary atmosphere. Our results suggested that the random forest regression consumes significantly less computing time while gives the predicted results equivalent to those of the nested sampling PLATON retrieval.
Abstract
The Evanescent Wave Coronagraph, EvWaCo, is an in-development prototype coronagraph, designed for use on the 2.4m Thai National Telescope (TNT), in the R and I-band filters. This work ...examines the astronomical capabilities of EvWaCo using the results from Fourier-analysis simulations. Fourier optics simulations were applied to the EvWaCo prototype to analyse its performance, combining different sources of contrast degradation that will be present in the system. The simulations used for the main analysis assume a good night at the Thai National Observatory (TNO) and include the fitting error, aliasing, measurement noise and lag, providing a radially averaged contrast curve. From the contrast curve, the detection limit, as defined by a minimum signal to noise ratio of 5 for a typical observation time, can be calculated for different primary star magnitudes. The relative fluxes of various binary stars, with a range of spectral classes and separations, were modelled allowing comparison to the EvWaCo detection curves. The photon-noise limited detection curves provide a theoretical baseline for the performance that will be achieved with EvWaCo; they, therefore, give an indication of the types of objects EvWaCo can observe. Along with a broader discussion of observable objects, a number of known binary systems are suggested for observations on the TNT using EvWaCo.
Abstract
The evanescent wave coronagraph uses the principle of frustrated total internal reflection (FTIR) to suppress the light coming from the star and study its close environment. Its focal plane ...mask is composed of a lens and a prism placed in contact with each other to produce the coronagraphic effect. In this paper, we present the experimental results obtained using an upgraded focal plane mask of the Evanescent Wave Coronagraph (EvWaCo). These experimental results are also compared to the theoretical performance of the coronagraph obtained through simulations. Experimentally, we reach a raw contrast equal to a few 10
−4
at a distance equal to 3
λ
/
D
over the full
I
band (
λ
c
= 800 nm, Δ
λ
/
λ
≈ 20%) and equal to 4
λ
/
D
over the full
R
band (
λ
c
= 650 nm, Δ
λ
/
λ
≈ 23%) in unpolarized light. However, our simulations show a raw contrast close to 10
−4
over the full
I
band and
R
band at the same distance, thus confirming the theoretical achromatic advantage of the coronagraph. We also verify the stability of the mask through a series of contrast measurements over a period of 8 months. Furthermore, we measure the sensitivity of the coronagraph to the lateral and longitudinal misalignment of the focal plane mask and to the lateral misalignment of the Lyot stop.
Abstract
We perform transit timing variation (TTV) and transmission spectroscopy analyses of the planet HAT-P-37b, which is a hot Jupiter orbiting a G-type star. Nine new transit light curves are ...obtained and analyzed together with 21 published light curves from the literature. The updated physical parameters of HAT-P-37b are presented. The TTV analyses show a possibility that the system has an additional planet that induced the TTVs amplitude signal of 1.74 ± 0.17 minutes. If the body is located near the 1:2 mean-motion resonance orbit, the sinusoidal TTV signal could be caused by the gravitational interaction of a sub-Earth-mass planet with mass of 0.06
M
⊕
. From the analysis of an upper-mass limit for the second planet, a Saturn-mass planet with orbital period less than 6 days is excluded. The broadband transmission spectra of HAT-P-37b favors a cloudy atmospheric model with an outlier spectrum in the
B
filter.
ABSTRACT
HIP 41378 f is a temperate 9.2 ± 0.1 R⊕ planet with period of 542.08 d and an extremely low density of 0.09 ± 0.02 g cm−3. It transits the bright star HIP 41378 (V = 8.93), making it an ...exciting target for atmospheric characterization including transmission spectroscopy. HIP 41378 was monitored photometrically between the dates of 2019 November 19 and 28. We detected a transit of HIP 41378 f with NGTS, just the third transit ever detected for this planet, which confirms the orbital period. This is also the first ground-based detection of a transit of HIP 41378 f. Additional ground-based photometry was also obtained and used to constrain the time of the transit. The transit was measured to occur 1.50 h earlier than predicted. We use an analytic transit timing variation (TTV) model to show the observed TTV can be explained by interactions between HIP 41378 e and HIP 41378 f. Using our TTV model, we predict the epochs of future transits of HIP 41378 f, with derived transit centres of TC, 4 = $2459\,355.087^{+0.031}_{-0.022}$ (2021 May) and TC, 5 = $2459\,897.078^{+0.114}_{-0.060}$ (2022 November).
Proxima Centauri is known as the closest star to the Sun. Recently, radial velocity (RV) observations revealed the existence of an Earth-mass planet around it. With an orbital period of ∼11 days, ...Proxima Centauri b is probably in the habitable zone of its host star. We undertook a photometric monitoring campaign to search for its transit, using the Bright Star Survey Telescope at the Zhongshan Station in Antarctica. A transit-like signal appearing on 2016 September 8 has been tentatively identified. Its midtime, TC = 2,457,640.1990 0.0017 HJD, is consistent with the predicted ephemeris based on the RV orbit in a 1 confidence interval. Time-correlated noise is pronounced in the light curve of Proxima Centauri, affecting the detection of transits. We develop a technique, in a Gaussian process framework, to gauge the statistical significance of a potential transit detection. The tentative transit signal reported here has a confidence level of 2.5 . Further detection of its periodic signals is necessary to confirm the planetary transit of Proxima Centauri b. We plan to monitor Proxima Centauri in the next polar night at Dome A in Antarctica, taking advantage of continuous darkness. Kipping et al. reported two tentative transit-like signals of Proxima Centauri b observed by the Microvariability and Oscillation of Stars space telescope in 2014 and 2015. The midtransit time of our detection is 138 minutes later than that predicted by their transit ephemeris. If all of the signals are real transits, the misalignment of the epochs plausibly suggests transit timing variations of Proxima Centauri b induced by an outer planet in this system.
Today the search for and study of exoplanets is one of the most interesting areas of modern astronomy. Over the last two decades, the number of detected exoplanets continues to increase. At present, ...over 3,300 exoplanets have been discovered. This thesis presents high precision studies based on the transit and microlensing methods which are used to detect hot and cool exoplanets, respectively. In this thesis, the effects of intrinsic stellar noise to the detectability of an exomoon orbiting a transiting exoplanet are investigated using transit timing variation and transit duration variation. The effects of intrinsic stellar variation of an M-dwarf reduce the detectability correlation coefficient by 0.0-0.2 with 0.1 median reduction. The transit timing variation and transmission spectroscopy observations and analyses of a hot-Neptune, GJ3470b, from telescopes at Thai National Observatory, and the 0.6-metre PROMPT-8 telescope in Chile are presented, in order to investigate the possibility of a third body in the system and to study its atmosphere. From the transit timing variation analyses, the presence of a hot Jupiter with a period of less than 10 days or a planet with an orbital period between 2.5 and 4.0 days in GJ3470 system are excluded. From transmission spectroscopy analyses, combined optical and near-infrared transmission spectroscopy favour a H/He dominated haze (mean molecular weight 1.08 \pm 0.20) with methane in the atmosphere of GJ3470b. With the microlensing technique, real-time online simulations of microlensing properties based on the Besancon Galactic model, called Manchester-Besancon Microlensing Simulator (MaBulS), are presented. We also apply it to the recent MOA-II survey results. This analysis provides the best comparison of Galactic structure between a simulated Galactic model and microlensing observations. The best-fitting model between Besancon and MOA-II data provides a brown dwarf mass function slope of -0.4. The Besancon model provides only 50 per cent of the measured optical depth and event rate per star at low Galactic latitude around the inner bulge. However, the revised MOA-II data are consistent the Besancon model without any missing inner bulge population.
We present the discovery of KELT-24 b, a massive hot Jupiter orbiting a bright (V = 8.3 mag, K = 7.2 mag) young F-star with a period of 5.6 days. The host star, KELT-24 (HD 93148), has a Teff = K, a ...mass of M* = M , a radius of R* = 1.506 0.022 R , and an age of Gyr. Its planetary companion (KELT-24 b) has a radius of RP = 1.272 0.021 RJ and a mass of MP = MJ, and from Doppler tomographic observations, we find that the planet's orbit is well-aligned to its host star's projected spin axis ( ). The young age estimated for KELT-24 suggests that it only recently started to evolve from the zero-age main sequence. KELT-24 is the brightest star known to host a transiting giant planet with a period between 5 and 10 days. Although the circularization timescale is much longer than the age of the system, we do not detect a large eccentricity or significant misalignment that is expected from dynamical migration. The brightness of its host star and its moderate surface gravity make KELT-24b an intriguing target for detailed atmospheric characterization through spectroscopic emission measurements since it would bridge the current literature results that have primarily focused on lower mass hot Jupiters and a few brown dwarfs.
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