- ID:
- ivo://CDS.VizieR/J/AJ/158/243
- Title:
- A search for multiplanet systems with TESS
- Short Name:
- J/AJ/158/243
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Transiting exoplanets in multiplanet systems exhibit non-Keplerian orbits as a result of the gravitational influence from companions, which can cause the times and durations of transits to vary. The amplitude and periodicity of the transit time variations are characteristic of the perturbing planet's mass and orbit. The objects of interest from the Transiting Exoplanet Survey Satellite (TESS) are analyzed in a uniform way to search for transit timing variations (TTVs) with sectors 1-3 of data. Due to the volume of targets in the TESS candidate list, artificial intelligence is used to expedite the search for planets by vetting nontransit signals prior to characterizing the light-curve time series. The residuals of fitting a linear orbit ephemeris are used to search for TTVs. The significance of a perturbing planet is assessed by comparing the Bayesian evidence between a linear and nonlinear ephemeris, which is based on an N-body simulation. Nested sampling is used to derive posterior distributions for the N-body ephemeris and in order to expedite convergence, custom priors are designed using machine learning. A dual-input, multi-output convolutional neural network is designed to predict the parameters of a perturbing body given the known parameters and measured perturbation (O-C). There is evidence for three new multiplanet candidates (WASP-18, WASP-126, TOI 193) with nontransiting companions using the two-minute cadence observations from TESS. This approach can be used to identify stars in need of longer radial velocity and photometric follow-up than those already performed.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJS/234/9
- Title:
- A spectral approach to transit timing variations
- Short Name:
- J/ApJS/234/9
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The high planetary multiplicity revealed by Kepler implies that transit timing variations (TTVs) are intrinsically common. The usual procedure for detecting these TTVs is biased to long-period, deep transit planets, whereas most transiting planets have short periods and shallow transits. Here we introduce the Spectral Approach technique to TTVs that allows expanding the TTV catalog toward lower TTV amplitude, shorter orbital period, and shallower transit depth. In the spectral approach, we assume that a sinusoidal TTV exists in the data and then calculate the improvement to {chi}^2^ that this model allows over that of the linear-ephemeris model. This enables detection of TTVs even in cases where the transits are too shallow, so that individual transits cannot be timed. The spectral approach is more sensitive because it has fewer free parameters in its model. Using the spectral approach, we (a) detect 129 new periodic TTVs in Kepler data (an increase of ~2/3 over a previous TTV catalog); (b) constrain the TTV periods of 34 long-period TTVs and reduce amplitude errors of known TTVs; and (c) identify cases of multi-periodic TTVs, for which absolute planetary mass determination may be possible. We further extend our analysis by using perturbation theory assuming a small TTV amplitude at the detection stage, which greatly speeds up our detection (to a level of few seconds per star). Our extended TTV sample shows no deficit of short-period or low-amplitude transits, in contrast to previous surveys, in which the detection schemes were significantly biased against such systems.
- ID:
- ivo://CDS.VizieR/J/AJ/158/227
- Title:
- Asteroseismic parameters of RGB stars
- Short Name:
- J/AJ/158/227
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Every Sun-like star will eventually evolve into a red giant, a transition which can profoundly affect the evolution of a surrounding planetary system. The timescale of dynamical planet evolution and orbital decay has important implications for planetary habitability, as well as post-main-sequence star and planet interaction, evolution, and internal structure. Here, we investigate these effects by estimating planet occurrence around 2476 low-luminosity red giant branch (LLRGB) stars observed by the NASA K2 mission. We measure stellar masses and radii using asteroseismology, with median random uncertainties of 3.7% in mass and 2.2% in radius. We compare this planet population to the known population of planets around dwarf Sun-like stars, accounting for detection efficiency differences between the stellar populations. We find that 0.49%+/-0.28% of LLRGB stars host planets larger than Jupiter with orbital periods less than 10 days, tentatively higher than main-sequence stars hosting similar planets (0.15%+/-0.06%). Our results suggest that the effects of stellar evolution on the occurrence of close-in planets larger than Jupiter are not significant until stars have begun ascending substantially up the red giant branch (>~5-6 R_{sun}_).
- ID:
- ivo://CDS.VizieR/J/AJ/161/78
- Title:
- Astrometry for 14 debris disk stars with SPHERE
- Short Name:
- J/AJ/161/78
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Debris disk stars are good targets for high-contrast imaging searches for planetary systems, since debris disks have been shown to have a tentative correlation with giant planets. We selected 20 stars identified as debris disk hosts by the WISE mission, with particularly high levels of warm dust. We observed these with the VLT/SPHERE high-contrast imaging instrument with the goal of finding planets and imaging the disks in scattered light. Our survey reaches a median 5{sigma} sensitivity of 10.4MJ at 25au and 5.9MJ at 100au. We identified three new stellar companions (HD18378B, HD19257B, and HD133778B): two are mid-M-type stars and one is a late-K or early-M star. Three additional stars have very widely separated stellar companions (all at >2000au) identified in the Gaia catalog. The stars hosting the three SPHERE-identified companions are all older (>~700Myr), with one having recently left the main sequence and one a giant star. We infer that the high volumes of dust observed around these stars has been caused by a recent collision between the planets and planetesimal belts in the system, although for the most evolved star, mass loss could also be responsible for the infrared excess. Future mid-infrared spectroscopy or polarimetric imaging may allow the positions and spatial extent of these dust belts to be constrained, thereby providing evidence as to the true cause of the elevated levels of dust around these old systems. None of the disks in this survey is resolved in scattered light.
- ID:
- ivo://CDS.VizieR/J/A+A/659/L7
- Title:
- AU Mic b and c transits with CHEOPS
- Short Name:
- J/A+A/659/L7
- Date:
- 10 Mar 2022 07:19:39
- Publisher:
- CDS
- Description:
- Here we report large-amplitude transit timing variations (TTVs) for AU Microcopii b and c as detected in combined TESS (2018, 2020) and CHEOPS (2020, 2021) transit observations. AU Mic is a young planetary system with a debris disk and two transiting warm Neptunes. A TTV on the order of several minutes was previously reported for AU Mic b, which was suggested to be an outcome of mutual perturbations between the planets in the system. In 2021, we observed AU Mic b (five transits) and c (three transits) with the CHEOPS space telescope to follow-up the TTV of AU Mic b and possibly detect a TTV for AU Mic c. When analyzing TESS and CHEOPS 2020-2021 measurements together, we find that a prominent TTV emerges with a full span of >=23 minutes between the two TTV extrema. Assuming that the period change results from a periodic process - such as mutual perturbations - we demonstrate that the times of transits in the summer of 2022 are expected to be 30-85 minutes later than predicted by the available linear ephemeris.
- ID:
- ivo://CDS.VizieR/J/AJ/158/25
- Title:
- Automated triage and vetting of TESS candidates
- Short Name:
- J/AJ/158/25
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- NASA's Transiting Exoplanet Survey Satellite (TESS) presents us with an unprecedented volume of space-based photometric observations that must be analyzed in an efficient and unbiased manner. With at least ~1000000 new light curves generated every month from full-frame images alone, automated planet candidate identification has become an attractive alternative to human vetting. Here we present a deep learning model capable of performing triage and vetting on TESS candidates. Our model is modified from an existing neural network designed to automatically classify Kepler candidates, and is the first neural network to be trained and tested on real TESS data. In triage mode, our model can distinguish transit-like signals (planet candidates and eclipsing binaries) from stellar variability and instrumental noise with an average precision (the weighted mean of precisions over all classification thresholds) of 97.0% and an accuracy of 97.4%. In vetting mode, the model is trained to identify only planet candidates with the help of newly added scientific domain knowledge, and achieves an average precision of 69.3% and an accuracy of 97.8%. We apply our model on new data from Sector 6, and present 288 new signals that received the highest scores in triage and vetting and were also identified as planet candidates by human vetters. We also provide a homogeneously classified set of TESS candidates suitable for future training.
- ID:
- ivo://CDS.VizieR/J/AJ/158/58
- Title:
- Autoregressive planet search for Kepler stars
- Short Name:
- J/AJ/158/58
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The 4 yr light curves of 156717 stars observed with NASA's Kepler mission are analyzed using the autoregressive planet search (ARPS) methodology described by Caceres et al. (2019AJ....158...57C). The three stages of processing are maximum-likelihood ARIMA modeling of the light curves to reduce stellar brightness variations, constructing the transit comb filter periodogram to identify transit-like periodic dips in the ARIMA residuals, and Random Forest classification trained on Kepler team confirmed planets using several dozen features from the analysis. Orbital periods between 0.2 and 100 days are examined. The result is a recovery of 76% of confirmed planets, 97% when period and transit depth constraints are added. The classifier is then applied to the full Kepler data set; 1004 previously noticed and 97 new stars have light-curve criteria consistent with the confirmed planets, after subjective vetting removes clear false alarms and false positive cases. The 97 Kepler ARPS candidate transits mostly have periods of P<10 days; many are ultrashort period hot planets with radii <1% of the host star. Extensive tabular and graphical output from the ARPS time series analysis is provided to assist in other research relating to the Kepler sample.
- ID:
- ivo://CDS.VizieR/J/AJ/158/59
- Title:
- Autoregressive planet search: irregular time series
- Short Name:
- J/AJ/158/59
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Sensitive signal processing methods are needed to detect transiting planets from ground-based photometric surveys. Caceres et al. (2019AJ....158...58C) show that the autoregressive planet search (ARPS) method - a combination of autoregressive integrated moving average (ARIMA) parametric modeling, a new transit comb filter (TCF) periodogram, and machine learning classification - is effective when applied to evenly spaced light curves from space-based missions. We investigate here whether ARIMA and TCF will be effective for ground-based survey light curves that are often sparsely sampled with high noise levels from atmospheric and instrumental conditions. The ARPS procedure is applied to selected light curves with strong planetary signals from the Kepler mission that have been altered to simulate the conditions of ground-based exoplanet surveys. Typical irregular cadence patterns are used from the Hungarian-made Automated Telescope Network-South (HATSouth) survey. We also evaluate recovery of known planets from HATSouth. Simulations test transit signal recovery as a function of cadence pattern and duration, stellar magnitude, planet orbital period, and transit depth. Detection rates improve for shorter periods and deeper transits. The study predicts that the ARPS methodology will detect planets with >~0.1% transit depth and periods ~<40 days in HATSouth stars brighter than ~15 mag. ARPS methodology is therefore promising for planet discovery from ground-based exoplanet surveys with sufficiently dense cadence patterns.
- ID:
- ivo://CDS.VizieR/J/MNRAS/474/2129
- Title:
- Barium dwarfs with white dwarf companions
- Short Name:
- J/MNRAS/474/2129
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report three new barium (Ba) dwarfs lying in Sirius-like systems. They provide direct evidence that Ba dwarfs are companions to white dwarfs (WDs). Atmospheric parameters, stellar masses and the chemical abundances of 25 elements, including light, {alpha}, Fe-peak and s-process elements, are derived from high-resolution and high S/N spectra. The enhancement of s-process elements with [s/Fe] ratios between 0.4 and 0.6 confirm them as mild barium stars. The estimated metallicities (-0.31, -0.06 and 0.13) of BD+68 1027, RE J0702+129 and BD+80 670 are in the range of known Ba dwarfs and giants. As expected, the observed indices [hs/ls], [s/Fe] and [C/Fe] show an anti-correlation with metallicity. Asymptotic giant branch (AGB) progenitor masses are estimated for the WD companions of RE J0702+129 (1.47M_{sun}_) and BD+80 670 (3.59M_{sun}_). These confirm the predicted range of progenitor AGB masses (1.5-4M_{sun}_) for unseen WDs around Ba dwarfs. The surface abundances of s-process elements in RE J0702+129 and BD+80 670 are compared with AGB models and they are in close agreement, within the predicted accretion efficiencies and pollution factors for Ba stars. These results support that the origin of s-process overabundances in Ba dwarfs is similar to those of Ba giants via the McClure hypothesis in which Ba stars accumulate s-process elements through mass transfer from their host companions during the AGB phase.
- ID:
- ivo://CDS.VizieR/J/A+A/646/A164
- Title:
- BEAST sample properties
- Short Name:
- J/A+A/646/A164
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- While the occurrence rate of wide giant planets appears to increase with stellar mass at least up through the A-type regime, B-type stars have so far not been systematically studied in large scale surveys. It therefore remains unclear up to what stellar mass this occurrence trend continues. The B-star Exoplanet Abundance Study (BEAST) is a direct imaging survey with the Extreme Adaptive Optics instrument SPHERE, targeting 85 B-type stars in the young Scorpius-Centaurus (Sco-Cen) region with the aim of detecting giant planets at wide separations and constraining their occurrence rate and physical properties. The statistical outcome of the survey will help determining if and where an upper stellar mass limit for planet formation occurs. Here, we describe the selection and characterization of the BEAST target sample.
