We report the discovery of K2-287b, a Saturn mass planet orbiting a G-dwarf with a period of P 15 days. First uncovered as a candidate using K2 campaign 15 data, follow-up photometry and spectroscopy ...were used to determine a mass , radius , period days, and eccentricity . The host star is a metal-rich V = 11.410 0.129 mag G-dwarf for which we estimate a mass , radius , metallicity Fe/H = 0.20 0.05, and K. This warm eccentric planet with a time-averaged equilibrium temperature of K adds to the small sample of giant planets orbiting nearby stars whose structure is not expected to be affected by stellar irradiation. Follow-up studies on the K2-287 system could help constrain theories of planet migration in close-in orbits.
Abstract
We describe the Zonal Atmospheric Stellar Parameters Estimator (zaspe), a new algorithm, and its associated code, for determining precise stellar atmospheric parameters and their ...uncertainties from high-resolution echelle spectra of FGK-type stars. zaspe estimates stellar atmospheric parameters by comparing the observed spectrum against a grid of synthetic spectra only in the most sensitive spectral zones to changes in the atmospheric parameters. Realistic uncertainties in the parameters are computed from the data itself, by taking into account the systematic mismatches between the observed spectrum and the best-fitting synthetic one. The covariances between the parameters are also estimated in the process. zaspe can in principle use any pre-calculated grid of synthetic spectra, but unbiased grids are required to obtain accurate parameters. We tested the performance of two existing libraries, and we concluded that neither is suitable for computing precise atmospheric parameters. We describe a process to synthesize a new library of synthetic spectra that was found to generate consistent results when compared with parameters obtained with different methods (interferometry, asteroseismology, equivalent widths).
ABSTRACT
Current space-based missions, such as the Transiting Exoplanet Survey Satellite (TESS), provide a large database of light curves that must be analysed efficiently and systematically. In ...recent years, deep learning (DL) methods, particularly convolutional neural networks (CNN), have been used to classify transit signals of candidate exoplanets automatically. However, CNNs have some drawbacks; for example, they require many layers to capture dependencies on sequential data, such as light curves, making the network so large that it eventually becomes impractical. The self-attention mechanism is a DL technique that attempts to mimic the action of selectively focusing on some relevant things while ignoring others. Models, such as the Transformer architecture, were recently proposed for sequential data with successful results. Based on these successful models, we present a new architecture for the automatic classification of transit signals. Our proposed architecture is designed to capture the most significant features of a transit signal and stellar parameters through the self-attention mechanism. In addition to model prediction, we take advantage of attention map inspection, obtaining a more interpretable DL approach. Thus, we can identify the relevance of each element to differentiate a transit signal from false positives, simplifying the manual examination of candidates. We show that our architecture achieves competitive results concerning the CNNs applied for recognizing exoplanetary transit signals in data from the TESS telescope. Based on these results, we demonstrate that applying this state-of-the-art DL model to light curves can be a powerful technique for transit signal detection while offering a level of interpretability.
We report on 13 new high-precision measurements of stellar diameters for low-mass dwarfs obtained by means of near-infrared long-baseline interferometry with PIONIER at the Very Large Telescope ...Interferometer. Together with accurate parallaxes from Gaia DR2, these measurements provide precise estimates for their linear radii, effective temperatures, masses, and luminosities. This allows us to refine the effective temperature scale, in particular towards the coolest M-dwarfs. We measure for late-type stars with enhanced metallicity slightly inflated radii, whereas for stars with decreased metallicity we measure smaller radii. We further show that Gaia DR2 effective temperatures for M-dwarfs are underestimated by ∼8.2 per cent and give an empirical MG-Teff relation that is better suited for M-dwarfs with Teff between 2600 and 4000 K. Most importantly, we are able to observationally identify a discontinuity in the Teff-radius plane, which is likely due to the transition from partially convective M-dwarfs to the fully convective regime. We found this transition to happen between 3200 and 3340 K, or equivalently for stars with masses {≈ } 0.23 M_{\odot }. We find that in this transition region the stellar radii are in the range from 0.18 to 0.42 R\odot for similar stellar effective temperatures.
Resolving the planetesimal belt of HR 8799 with ALMA Booth, Mark; Jordán, Andrés; Casassus, Simon ...
Monthly notices of the Royal Astronomical Society. Letters,
07/2016, Letnik:
460, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The star HR 8799 hosts one of the largest known debris discs and at least four giant planets. Previous observations have found evidence for a warm belt within the orbits of the planets, a cold ...planetesimal belt beyond their orbits and a halo of small grains. With the infrared data, it is hard to distinguish the planetesimal belt emission from that of the grains in the halo. With this in mind, the system has been observed with ALMA in band 6 (1.34 mm) using a compact array format. These observations allow the inner edge of the planetesimal belt to be resolved for the first time. A radial distribution of dust grains is fitted to the data using an MCMC method. The disc is best fitted by a broad ring between
$145^{+12}_{-12}$
au and
$429^{+37}_{-32}$
au at an inclination of
$40^{+5}_{-6}{^{\circ }}$
and a position angle of
$51^{+8}_{-8}{^{\circ }}$
. A disc edge at ∼145 au is too far out to be explained simply by interactions with planet b, requiring either a more complicated dynamical history or an extra planet beyond the orbit of planet b.
ABSTRACT
When a planet is only observed to transit once, direct measurement of its period is impossible. It is possible, however, to constrain the periods of single transiters, and this is desirable ...as they are likely to represent the cold and far extremes of the planet population observed by any particular survey. Improving the accuracy with which the period of single transiters can be constrained is therefore critical to enhance the long-period planet yield of surveys. Here, we combine Gaia parallaxes with stellar models and broad-band photometry to estimate the stellar densities of K2 planet host stars, then use that stellar density information to model individual planet transits and infer the posterior period distribution. We show that the densities we infer are reliable by comparing with densities derived through asteroseismology, and apply our method to 27 validation planets of known (directly measured) period, treating each transit as if it were the only one, as well as to 12 true single transiters. When we treat eccentricity as a free parameter, we achieve a fractional period uncertainty over the true single transits of $94^{+87}_{-58}{{\ \rm per\ cent}}$, and when we fix e = 0, we achieve fractional period uncertainty $15^{+30}_{-6}{{\ \rm per\ cent}}$, a roughly threefold improvement over typical period uncertainties of previous studies.
CERES Brahm, Rafael; Jordán, Andrés; Espinoza, Néstor
Publications of the Astronomical Society of the Pacific,
03/2017, Letnik:
129, Številka:
973
Journal Article
Recenzirano
We present the Collection of Elemental Routines for Echelle Spectra (CERES). These routines were developed for the construction of automated pipelines for the reduction, extraction, and analysis of ...spectra acquired with different instruments, allowing the obtention of homogeneous and standardized results. This modular code includes tools for handling the different steps of the processing: CCD image reductions; identification and tracing of the echelle orders; optimal and rectangular extraction; computation of the wavelength solution; estimation of radial velocities; and rough and fast estimation of the atmospheric parameters. Currently, CERES has been used to develop automated pipelines for 13 different spectrographs, namely CORALIE, FEROS, HARPS, ESPaDOnS, FIES, PUCHEROS, FIDEOS, CAFE, DuPont/Echelle, Magellan/Mike, Keck/HIRES, Magellan/PFS, and APO/ARCES, but the routines can be easily used to deal with data coming from other spectrographs. We show the high precision in radial velocity that CERES achieves for some of these instruments, and we briefly summarize some results that have already been obtained using the CERES pipelines.
A spectral survey of WASP-19b with ESPRESSO Sedaghati, Elyar; MacDonald, Ryan J; Casasayas-Barris, Núria ...
Monthly notices of the Royal Astronomical Society,
07/2021, Letnik:
505, Številka:
1
Journal Article
Recenzirano
Odprti dostop
ABSTRACT
High-resolution precision spectroscopy provides a multitude of robust techniques for probing exoplanetary atmospheres. We present multiple VLT/ESPRESSO transit observations of the ...hot-Jupiter exoplanet WASP-19b with previously published but disputed atmospheric features from low resolution studies. Through spectral synthesis and modelling of the Rossiter–McLaughlin (RM) effect we calculate stellar, orbital and physical parameters for the system. From narrow-band spectroscopy we do not detect any of H i, Fe i, Mg i, Ca i, Na i, and K i neutral species, placing upper limits on their line contrasts. Through cross-correlation analyses with atmospheric models, we do not detect Fe i and place a 3σ upper limit of $\log \, (X_{\textrm {Fe}}/X_\odot) \approx -1.83\, \pm \, 0.11$ on its mass fraction, from injection and retrieval. We show the inability to detect the presence of H2O for known abundances, owing to lack of strong absorption bands, as well as relatively low S/N ratio. We detect a barely significant peak (3.02 ± 0.15 σ) in the cross-correlation map for TiO, consistent with the sub-solar abundance previously reported. This is merely a hint for the presence of TiO and does not constitute a confirmation. However, we do confirm the presence of previously observed enhanced scattering towards blue wavelengths, through chromatic RM measurements, pointing to a hazy atmosphere. We finally present a reanalysis of low-resolution transmission spectra of this exoplanet, concluding that unocculted starspots alone cannot explain previously detected features. Our reanalysis of the FORS2 spectra of WASP-19b finds a ∼100× sub-solar TiO abundance, precisely constrained to $\log \, X_{\textrm {TiO}} \approx -7.52 \pm 0.38$, consistent with the TiO hint from ESPRESSO. We present plausible paths to reconciliation with other seemingly contradicting results.
ABSTRACT We present 197 planet candidates discovered using data from the first year of the NASA K2 mission (Campaigns 0-4), along with the results of an intensive program of photometric analyses, ...stellar spectroscopy, high-resolution imaging, and statistical validation. We distill these candidates into sets of 104 validated planets (57 in multi-planet systems), false positives, and 63 remaining candidates. Our validated systems span a range of properties, with median values of RP = , P = days, = K, and Kp = mag. Stellar spectroscopy provides precise stellar and planetary parameters for most of these systems. We show that K2 has increased by 30% the number of small planets known to orbit moderately bright stars (1-4 R⊕, Kp = 9-13 mag). Of particular interest are planets smaller than 2 R⊕, orbiting stars brighter than Kp = 11.5 mag, 5 receiving Earth-like irradiation levels, and several multi-planet systems-including 4 planets orbiting the M dwarf K2-72 near mean-motion resonances. By quantifying the likelihood that each candidate is a planet we demonstrate that our candidate sample has an overall false positive rate of 15%-30%, with rates substantially lower for small candidates ( ) and larger for candidates with radii and/or with . Extrapolation of the current planetary yield suggests that K2 will discover between 500 and 1000 planets in its planned four-year mission, assuming sufficient follow-up resources are available. Efficient observing and analysis, together with an organized and coherent follow-up strategy, are essential for maximizing the efficacy of planet-validation efforts for K2, TESS, and future large-scale surveys.
ABSTRACT We present early high-resolution spectroscopic observations of the nova V1369 Cen. We have detected an absorption feature at 6695.6 that we have identified as blueshifted 7Li i λ6708 . The ...absorption line, moving at −550 km s−1, was observed in five high-resolution spectra of the nova obtained at different epochs. Based on the intensity of this absorption line, we infer that a single nova outburst can inject in the Galaxy = 0.3-4.8 × 10−10 . Given the current estimates of the Galactic nova rate, this amount is sufficient to explain the puzzling origin of the overabundance of lithium observed in young star populations.
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