Strong magnetic fields in chemically peculiar A-type (Ap) stars typically
suppress low-overtone pressure modes (p modes) but allow high-overtone p modes
to be driven. KIC 11296437 is the first star ...to show both. We obtained and
analysed a Subaru spectrum, from which we show that KIC 11296437 has abundances
similar to other magnetic Ap stars, and we estimate a mean magnetic field
modulus of $2.8\pm0.5$ kG. The same spectrum rules out a double-lined
spectroscopic binary, and we use other techniques to rule out binarity over a
wide parameter space, so the two pulsation types originate in one $\delta$
Sct--roAp hybrid pulsator. We construct stellar models depleted in helium and
demonstrate that helium settling is second to magnetic damping in suppressing
low-overtone p modes in Ap stars. We compute the magnetic damping effect for
selected p and g modes, and find that modes with frequencies similar to the
fundamental mode are driven for polar field strengths $\lesssim4$ kG, while
other low-overtone p modes are driven for polar field strengths up to $\sim$1.5
kG. We find that the high-order g modes commonly observed in $\gamma$ Dor stars
are heavily damped by polar fields stronger than 1--4 kG, with the damping
being stronger for higher radial orders. We therefore explain the observation
that no magnetic Ap stars have been observed as $\gamma$ Dor stars. We use our
helium-depleted models to calculate the $\delta$ Sct instability strip for
metallic-lined A (Am) stars, and find that driving from a Rosseland mean
opacity bump at $\sim$$5\times10^4$ K caused by the discontinuous H-ionization
edge in bound-free opacity explains the observation of $\delta$ Sct pulsations
in Am stars.
Mutual gravitation between a pulsating star and an orbital companion leads to a time-dependent variation in path length for starlight traveling to Earth. These variations can be used for coherently ...pulsating stars, such as the {\delta} Scuti variables, to constrain the masses and orbits of their companions. Observing these variations for {\delta} Scuti stars has previously relied on subdividing the light curve and measuring the average pulsation phase in equally sized subdivisions, which leads to under-sampling near periapsis. We introduce a new approach that simultaneously forward-models each sample in the light curve and show that this method improves upon current sensitivity limits - especially in the case of highly eccentric and short-period binaries. We find that this approach is sensitive enough to observe Jupiter mass planets around {\delta} Scuti stars under ideal conditions, and use gravity-mode pulsations in the subdwarf B star KIC 7668647 to detect its companion without radial velocity data. We further provide robust detection limits as a function of the SNR of the pulsation mode and determine that the minimum detectable light travel time amplitude for a typical Kepler {\delta} Scuti is around 2 s. This new method significantly enhances the application of light travel time variations to detecting short period binaries with pulsating components, and pulsating A-type exoplanet host stars, especially as a tool for eliminating false positives.
We perform a search for rapidly oscillating Ap stars in the Kepler long-cadence data, where true oscillations above the Nyquist limit of 283.21 {\mu}Hz can be reliably distinguished from aliases as a ...consequence of the barycentric time corrections applied to the Kepler data. We find evidence for rapid oscillations in six stars: KIC 6631188, KIC 7018170, KIC 10685175, KIC 11031749, KIC 11296437 and KIC 11409673, and identify each star as chemically peculiar through either pre-existing classifications or spectroscopic measurements. For each star, we identify the principal pulsation mode, and are able to observe several additional pulsation modes in KIC 7018170. We find that KIC 7018170 and KIC 11409673 both oscillate above their theoretical acoustic cutoff frequency, whilst KIC 11031749 oscillates at the cutoff frequency within uncertainty. All but KIC 11031749 exhibit strong amplitude modulation consistent with the oblique pulsator model, confirming their mode geometry and periods of rotation.
The study of planet occurrence as a function of stellar mass is important for a better understanding of planet formation. Estimating stellar mass, especially in the red giant regime, is difficult. In ...particular, stellar masses of a sample of evolved planet-hosting stars based on spectroscopy and grid-based modelling have been put to question over the past decade with claims they were overestimated. Although efforts have been made in the past to reconcile this dispute using asteroseismology, results were inconclusive. In an attempt to resolve this controversy, we study four more evolved planet-hosting stars in this paper using asteroseismology, and we revisit previous results to make an informed study of the whole ensemble in a self-consistent way. For the four new stars, we measure their masses by locating their characteristic oscillation frequency, \(\mathrm{\nu}_{\mathrm{max}}\), from their radial velocity time series observed by SONG. For two stars, we are also able to measure the large frequency separation, \(\mathrm{\Delta\nu}\), helped by extended SONG single-site and dual-site observations and new TESS observations. We establish the robustness of the \(\mathrm{\nu}_{\mathrm{max}}\)-only-based results by determining the stellar mass from \(\mathrm{\Delta\nu}\), and from both \(\mathrm{\Delta\nu}\) and \(\mathrm{\nu}_{\mathrm{max}}\). We then compare the seismic masses of the full ensemble of 16 stars with the spectroscopic masses from three different literature sources. We find an offset between the seismic and spectroscopic mass scales that is mass-dependent, suggesting that the previously claimed overestimation of spectroscopic masses only affects stars more massive than about 1.6 M\(_\mathrm{\odot}\).
We have examined the period-luminosity (P-L) relation for delta Scuti stars using Gaia DR2 parallaxes. We included 228 stars from the catalogue of Rodriguez et al. (2000), as well as 1124 stars ...observed in the four-year Kepler mission. For each star we considered the dominant pulsation period, and used DR2 parallaxes and extinction corrections to determine absolute V magnitudes. Many stars fall along a sequence in the P-L relation coinciding with fundamental-mode pulsation, while others pulsate in shorter-period overtones. The latter stars tend to have higher effective temperatures, consistent with theoretical calculations. Surprisingly, we find an excess of stars lying on a ridge with periods half that of the fundamental. We suggest this may be due to a 2:1 resonance between the third or fourth overtone and the fundamental mode.
"exoplanet" is a toolkit for probabilistic modeling of astronomical time series data, with a focus on observations of exoplanets, using PyMC3 (Salvatier et al., 2016). PyMC3 is a flexible and ...high-performance model-building language and inference engine that scales well to problems with a large number of parameters. "exoplanet" extends PyMC3's modeling language to support many of the custom functions and probability distributions required when fitting exoplanet datasets or other astronomical time series. While it has been used for other applications, such as the study of stellar variability, the primary purpose of "exoplanet" is the characterization of exoplanets or multiple star systems using time-series photometry, astrometry, and/or radial velocity. In particular, the typical use case would be to use one or more of these datasets to place constraints on the physical and orbital parameters of the system, such as planet mass or orbital period, while simultaneously taking into account the effects of stellar variability.
Detached eclipsing binaries allow stellar masses and radii to be measured with unrivalled accuracy. While inspecting light curves obtained with the Transiting Exoplanet Survey Satellite (TESS), we ...noticed that the A0 III star \(\alpha\) Dra shows clear and well-separated primary and secondary eclipses. This star is known to be a single-lined spectroscopic binary, with a period of 51.5 d and an eccentricity of 0.43. The currently available TESS observations cover two 27-d sectors and the light curve shows a primary eclipse (depth 9%) and a secondary eclipse (depth 2%), separated in time by 38.5 days. Additional TESS observations of \(\alpha\) Dra will come from TESS Sectors 16, 21 and 22, and we predict that an eclipse will be visible in each of these. With a \(V\) magnitude of 3.68, \(\alpha\) Dra is one of the brightest known detached eclipsing binaries.
We report the discovery of a warm sub-Saturn, TOI-257b (HD 19916b), based on data from NASA's Transiting Exoplanet Survey Satellite (TESS). The transit signal was detected by TESS and confirmed to be ...of planetary origin based on radial velocity observations. An analysis of the TESS photometry, the Minerva-Australis, FEROS, and HARPS radial velocities, and the asteroseismic data of the stellar oscillations reveals that TOI-257b has a mass of \(M_P=0.138\pm0.023\)\,\(\rm{M_J}\) (\(43.9\pm7.3\)\,\(M_{\rm \oplus}\)), a radius of \(R_P=0.639\pm0.013\)\,\(\rm{R_J}\) (\(7.16\pm0.15\)\,\(R_{\rm \oplus}\)), bulk density of \(0.65^{+0.12}_{-0.11}\) (cgs), and period \(18.38818^{+0.00085}_{-0.00084}\)\,\(\rm{days}\). TOI-257b orbits a bright (\(\mathrm{V}=7.612\)\,mag) somewhat evolved late F-type star with \(M_*=1.390\pm0.046\)\,\(\rm{M_{\odot}}\), \(R_*=1.888\pm0.033\)\,\(\rm{R_{\odot}}\), \(T_{\rm eff}=6075\pm90\)\,\(\rm{K}\), and \(v\sin{i}=11.3\pm0.5\)\,km\,s\(^{-1}\). Additionally, we find hints for a second non-transiting sub-Saturn mass planet on a \(\sim71\)\,day orbit using the radial velocity data. This system joins the ranks of a small number of exoplanet host stars (\(\sim100\)) that have been characterized with asteroseismology. Warm sub-Saturns are rare in the known sample of exoplanets, and thus the discovery of TOI-257b is important in the context of future work studying the formation and migration history of similar planetary systems.
In this paper we present a catalog of 4584 eclipsing binaries observed during the first two years (26 sectors) of the TESS survey. We discuss selection criteria for eclipsing binary candidates, ...detection of hither-to unknown eclipsing systems, determination of the ephemerides, the validation and triage process, and the derivation of heuristic estimates for the ephemerides. Instead of keeping to the widely used discrete classes, we propose a binary star morphology classification based on a dimensionality reduction algorithm. Finally, we present statistical properties of the sample, we qualitatively estimate completeness, and discuss the results. The work presented here is organized and performed within the TESS Eclipsing Binary Working Group, an open group of professional and citizen scientists; we conclude by describing ongoing work and future goals for the group. The catalog is available from http://tessEBs.villanova.edu and from MAST.
To assess the accuracy of principal investigators' (PIs) predictions about three events for their own clinical trials: positivity on trial primary outcomes, successful recruitment and timely trial ...completion.
A short, electronic survey was used to elicit subjective probabilities within seven months of trial registration. When trial results became available, prediction skill was calculated using Brier scores (BS) and compared against uninformative prediction (i.e. predicting 50% all of the time).
740 PIs returned surveys (16.7% response rate). Predictions on all three events tended to exceed observed event frequency. Averaged PI skill did not surpass uninformative predictions (e.g., BS = 0.25) for primary outcomes (BS = 0.25, 95% CI 0.20, 0.30) and were significantly worse for recruitment and timeline predictions (BS 0.38, 95% CI 0.33, 0.42; BS = 0.52, 95% CI 0.50, 0.55, respectively). PIs showed poor calibration for primary outcome, recruitment, and timelines (calibration index = 0.064, 0.150 and 0.406, respectively), modest discrimination in primary outcome predictions (AUC = 0.76, 95% CI 0.65, 0.85) but minimal discrimination in the other two outcomes (AUC = 0.64, 95% CI 0.57, 0.70; and 0.55, 95% CI 0.47, 0.62, respectively).
PIs showed overconfidence in favorable outcomes and exhibited limited skill in predicting scientific or operational outcomes for their own trials. They nevertheless showed modest ability to discriminate between positive and non-positive trial outcomes. Low survey response rates may limit generalizability.
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