Abstract
We report the discovery of K2-232 b using photometric data of the Kepler K2 satellite coupled with ground-based spectroscopic observations. K2-232 b has a mass of MP = 0.397 ± 0.037 MJ, a ...radius of RP = 1.00 ± 0.020 RJ, and a moderately low equilibrium temperature of Teq = 1030 ± 15 K due to its relatively large star–planet separation of a = 0.1036 au. K2-232 b orbits its bright (V = 9.9) late F-type host star in an eccentric orbit (e = 0.258 ± 0.025) every 11.2 d, and is one of only four well-characterized warm Jupiters having host stars brighter than V = 10. We estimate a heavy element content of 20 ± 7 M⊕ for K2-232 b, which is consistent with standard models of giant planet formation. The bright host star of K2-232 b makes this system a well-suited target for detailed follow-up observations that will aid in the study of the atmospheres and orbital evolution of giant planets at moderate separations from their host stars.
Abstract
We report an intrinsically precise relation of the barium-to-iron enrichment as a function of age for a local, volume-complete (N = 30) sample of ancient Population II (τ ≥ 12 Gyr) and ...intermediate-disc stars (τ ≃ 10 Gyr), which suggests a common, r-process-dominated nucleosynthesis site for both elements in the early stages of the Milky Way. Deviants from this empirical relation are to a large extent identified as formerly known or new blue straggler stars. We report in particular the striking case of the Population II star HD 159062, whose barium overabundance is difficult to explain without wind accretion of s-process material from a former asymptotic giant branch (AGB) primary that very likely survived as a white dwarf companion. The weak but significant barium enhancement that we measure for HR 3578 and 104 Tau also suggests that both may be accompanied by faint degenerate companions. If confirmed through precision astrometry or direct imaging observations, this would mean a very efficient method to uncover ancient stellar remnant companions around solar-type stars.
With the present and soon-to-be breakthrough of optical interferometry, countless objects shall be within reach of interferometers; yet, most of them are expected to remain only marginally resolved ...with hectometric baselines. In this paper, we tackle the problem of deriving the properties of a marginally resolved object from its optical visibilities. We show that they depend on the moments of flux distribution of the object: centre, mean angular size, asymmetry, and curtosis. We also point out that the visibility amplitude is a second-order phenomenon, whereas the phase is a combination of a first-order term, giving the location of the photocentre, and a third-order term, more difficult to detect than the visibility amplitude, giving an asymmetry coefficient of the object. We then demonstrate that optical visibilities are not a good model constraint while the object stays marginally resolved, unless observations are carried out at different wavelengths. Finally, we show an application of this formalism to circumstellar discs.
Evidence for very nearby hidden white dwarfs Fuhrmann, K; Chini, R; Kaderhandt, L ...
Monthly notices of the Royal Astronomical Society,
06/2016, Volume:
459, Issue:
2
Journal Article
Peer reviewed
Open access
We report the discovery of a tertiary component to the prominent and nearby (d = 14 pc) visual binary α Fornacis. The new invisible component is part of a 4-d short-period Ba-Bb subsystem, whose ...K-type α For Ba primary shows a striking Ba/Fe = +0.26 dex overabundance, at variance with a close to solar Ba/Fe = +0.04 dex abundance for its distant visual companion α For A. For the even nearer (d = 8 pc) multiple star ξ Ursae Majoris and its alike 4-d Ba-Bb subsystem, we similarly find Ba/Fe = +0.37 dex for its G-type ξ UMa Ba primary, compared to a significantly lower Ba/Fe = +0.12 dex for the visual companion ξ UMa A. In both cases, the differential barium enrichment is direct evidence for short-period white dwarf systems and the creation of blue straggler stars through mass transfer and wind accretion, for their close and distant companions, respectively. These findings also imply that conventional stellar age datings for both α For and ξ UMa are likely not reliable.
ABSTRACT
We report the discovery of two hot Jupiters orbiting the stars K2-237 and K2-238. We used photometric data from Campaigns 11 and 12 of the Kepler K2 mission and radial velocity data obtained ...using the HARPS, FEROS, and CORALIE spectrographs. K2-237 b and K2-238 b have masses of $1.60^{+0.11}_{-0.11}$ and $0.86^{+0.13}_{-0.12}\,M_\mathrm{Jup}$, radii of $1.65^{+0.07}_{-0.08}$ and $1.30^{+0.15}_{-0.14}\,R_\mathrm{Jup}$, and are orbiting their host stars in 2.18- and 3.20-d orbits, respectively. The large radius of K2-237 b leads us to conclude that this candidate corresponds to a highly inflated hot Jupiter. K2-238 b has a radius consistent with theoretical models, considering the high incident flux falling on the planet. We consider K2-237 b to be an excellent system for follow-up studies, since not only is it very inflated, but it also orbits a relatively bright star (V = 11.6).
COSMOGRAIL Bonvin, V.; Millon, M.; Chan, J. H.-H. ...
Astronomy and astrophysics (Berlin),
09/2019, Volume:
629
Journal Article
Peer reviewed
Open access
We present new measurements of the time delays of WFI2033−4723. The data sets used in this work include 14 years of data taken at the 1.2 m Leonhard Euler Swiss telescope, 13 years of data from the ...SMARTS 1.3 m telescope at Las Campanas Observatory and a single year of high-cadence and high-precision monitoring at the MPIA 2.2 m telescope. The time delays measured from these different data sets, all taken in the R-band, are in good agreement with each other and with previous measurements from the literature. Combining all the time-delay estimates from our data sets results in ΔtAB = 36.2+0.7−0.8 Δ t AB = 36 . 2 − 0.8 + 0.7 $ \Delta t_{\mathrm{AB}} = 36.2_{-0.8}^{+0.7} $ days (2.1% precision), ΔtAC = −23.3+1.2−1.4 Δ t AC = − 23 . 3 − 1.4 + 1.2 $ \Delta t_{\mathrm{AC}} = -23.3_{-1.4}^{+1.2} $ days (5.6%) and ΔtBC = −59.4+1.3−1.3 Δ t BC = − 59 . 4 − 1.3 + 1.3 $ \Delta t_{\mathrm{BC}} = -59.4_{-1.3}^{+1.3} $ days (2.2%). In addition, the close image pair A1-A2 of the lensed quasars can be resolved in the MPIA 2.2 m data. We measure a time delay consistent with zero in this pair of images. We also explore the prior distributions of microlensing time-delay potentially affecting the cosmological time-delay measurements of WFI2033−4723. Our time-delay measurements are not precise enough to conclude that microlensing time delay is present or absent from the data. This work is part of a H0LiCOW series focusing on measuring the Hubble constant from WFI2033−4723.
In long-baseline interferometry, bandwidth smearing of an extended source occurs at finite bandwidth when its different components produce interference packets that only partially overlap. In this ...case, traditional model fitting or image reconstruction using standard formulas and tools lead to biased results. In this paper, we propose and implement a method to overcome this effect by calculating analytically a corrective term for the conventional interferometric observables: the visibility amplitude and closure phase. For that purpose, we model the interferogram taking into account the finite bandwidth and the instrumental differential phase. We obtain generic expressions for the visibility and closure phase in the case of temporally modulated interferograms, either processed using Fourier analysis or with the ABCD method. The expressions can be used to fit arbitrary models to the data. We then apply our results to the search and charactrization of stellar companions with the Precision Integrated-Optics Near-infrared Imaging ExpeRiment at the Very Large Telescope Interferometer, assessing the bias on observables and model-fitted parameters of a binary star. Finally, we consider the role of the atmosphere, first with an analytic model to identify the main contributions to bias and, secondly, by confirming the model with a numerical simulation of the atmospheric turbulence. In addition to the analytic expressions, the main results of our study are as follows: (i) the chromatic dispersion in the beam transport in the instrument has a strong impact on the closure phase and introduces additional biases even at separations where smearing is not expected to play an important role; (ii) the atmospheric turbulence introduces additional biases when smearing is present, but the impact is important only at very low spectral resolution; (iii) the bias on the observables strongly depends on the recombination scheme and data processing; (iv) the goodness of model fits is improved by modelling a Gaussian bandpass as long as the smearing is moderate.
Recent developments have unlocked the main issues arising from the combination of III-V and silicon and have opened a new way to fabricate tandem solar cells. In this study we provide a detailed ...analysis of III-V/epi-SiGe tandem devices performance using opto-electrical models and parameters acquired from previous experimental realizations of single junction devices. At first, we present the validation of our top and bottom cells models by comparison with previously published solar cells. The analysis of the current matching and the impact of the Al content in AlGaAs absorber on the open circuit voltage is performed on a very wide range of thickness and Al content. The optimal configurations for tandems with thin film absorbers are found with an empirical expression. This expression relates the required bottom absorber thickness to the Al content for current matching in a flat tandem device. Low-temperature epitaxial SiGe growth on III-V materials is an inverted growth technique, meaning that the last material grown is the Si(Ge) bottom cell. We can thus easily texture the back of the bottom cell for higher photon absorption. The proposed nanostructurization of the back reflector shows that, to reach the same efficiency, only half of the thickness is required if a 2D grating is combined with a silver reflector. The detailed influence of the bulk and interface electrical quality in the epi-SiGe bottom cell is also assessed. Finally, the prediction of the tandem device performance according to different realistic scenarios is presented.
•Opto-electrical modeling and optimization of III-V/Si(Ge) tandem cells performance.•Assessed the electronic quality of epi-Si(Ge) absorbers for use in bottom cells.•Retrieved the effective diffusion length parameter from fabricated cells.•Determined empirical relations for current matching of thin film sub cells.•Reducing bottom cell thickness by half by enhanced light trapping.
PDF
