Of the more than 150,000 targets followed by the Kepler Mission, about 10% were selected as red giants. Due to their high scientific value, in particular for Galaxy population studies and stellar ...structure and evolution, their Kepler light curves were made public in late 2011. More than 13,000 (over 85%) of these stars show intrinsic flux variability caused by solar-like oscillations making them ideal for large-scale asteroseismic investigations. We automatically extracted individual frequencies and measured the period spacings of the dipole modes in nearly every red giant. These measurements naturally classify the stars into various populations, such as the red giant branch, the low-mass (M/M sub(middot in circle) <, ~ 1.8) helium-core-burning red clump, and the higher-mass (M/M sub(middot in circle) > ~ 1.8) secondary clump. The period spacings also reveal that a large fraction of the stars show rotationally induced frequency splittings. This sample of stars will undoubtedly provide an extremely valuable source for studying the stellar population in the direction of the Kepler field, in particular when combined with complementary spectroscopic surveys.
ABSTRACT
Asteroseismic scaling relations are often used to derive stellar masses and radii, particularly for stellar, exoplanet, and Galactic studies. It is therefore important that their precisions ...are known. Here we measure the intrinsic scatter of the underlying seismic scaling relations for Δν and νmax, using two sharp features that are formed in the H–R diagram (or related diagrams) by the red giant populations. These features are the edge near the zero-age core-helium-burning phase, and the strong clustering of stars at the so-called red giant branch bump. The broadening of those features is determined by factors including the intrinsic scatter of the scaling relations themselves, and therefore it is capable of imposing constraints on them. We modelled Kepler stars with a Galaxia synthetic population, upon which we applied the intrinsic scatter of the scaling relations to match the degree of sharpness seen in the observation. We found that the random errors from measuring Δν and νmax provide the dominating scatter that blurs the features. As a consequence, we conclude that the scaling relations have intrinsic scatter of $\sim 0.5$ (Δν), $\sim 1.1$ (νmax), $\sim 1.7$ (M), and $\sim 0.4{{\ \rm per\ cent}}$ (R), for the SYD pipeline measured Δν and νmax. This confirms that the scaling relations are very powerful tools. In addition, we show that standard evolution models fail to predict some of the structures in the observed population of both the HeB and RGB stars. Further stellar model improvements are needed to reproduce the exact distributions.
ABSTRACT We have detected a 12 M Jup planet orbiting in or near the habitable zone of a main-sequence A star via the pulsational phase shifts induced by orbital motion. The planet has an orbital ...period of 840 20 days and an eccentricity of 0.15. All known planets orbiting main-sequence A stars have been found via the transit method or by direct imaging. The absence of astrometric or radial velocity detections of planets around these hosts makes ours the first discovery using the orbital motion. It is also the first A star known to host a planet within 1 of the habitable zone. We find evidence for planets in a large fraction of the parameter space where we are able to detect them. This supports the idea that A stars harbor high-mass planets in wide orbits.
ABSTRACT
We have used NASA’s TESS mission to study catalogued δ Scuti stars. We examined TESS light curves for 434 stars, including many for which few previous observations exist. We found that 62 ...are not δ Scuti pulsators, with most instead showing variability from binarity. For the 372 δ Scuti stars, we provide a catalogue of the period and amplitude of the dominant pulsation mode. Using Gaia DR3 parallaxes, we place the stars in the period–luminosity (P–L) diagram and confirm previous findings that most stars lie on a ridge that corresponds to pulsation in the fundamental radial mode, and that many others fall on a second ridge that is a factor two shorter in period. This second ridge is seen more clearly than before, thanks to the revised periods and distances. We demonstrate the value of the P–L diagram in distinguishing δ Scuti stars from short-period RR Lyrae stars, and we find several new examples of high-frequency δ Scuti stars with regular sequences of overtone modes, including XX Pyx and 29 Cyg. Finally, we revisit the sample of δ Scuti stars observed by Kepler and show that they follow a tight period–density relation, with a pulsation constant for the fundamental mode of Q = 0.0315 d.
ABSTRACT
The rapidly increasing number of delta Scuti stars with regular patterns among their pulsation frequencies necessitates modelling tools to better understand the observations. Further, with a ...dozen identified modes per star, there is potential to make meaningful inferences on stellar structure using these young δ Sct stars. We compute and describe a grid of >200 000 stellar models from the early pre-main sequence (pre-MS) to roughly one-third of the MS lifetime, and calculate their pulsation frequencies. From these, we also calculate asteroseismic parameters and explore how those parameters change with mass, age, and metal mass fraction. We show that the large frequency separation, Δν, is insensitive to mass at the zero-age main sequence. In the frequency regime observed, the Δν we measure (from modes with n ∼ 5–9) differs from the solar scaling relation by ∼13 per cent. We find that the lowest radial order is often poorly modelled, perhaps indicating that the lower order pressure modes contain further untapped potential for revealing the physics of the stellar interior. We also show that different nuclear reaction networks available in mesa can affect the pulsation frequencies of young δ Sct stars by as much as 5 per cent. We apply the grid to five newly modelled stars, including two pre-MS stars each with 15+ modes identified, and we make the grid available as a community resource.
TESS asteroseismology of the Kepler red giants Stello, Dennis; Saunders, Nicholas; Grunblatt, Sam ...
Monthly notices of the Royal Astronomical Society,
03/2022, Letnik:
512, Številka:
2
Journal Article
Recenzirano
Odprti dostop
ABSTRACT
Red giant asteroseismology can provide valuable information for studying the Galaxy as demonstrated by space missions like CoRoT and Kepler. However, previous observations have been limited ...to small data sets and fields of view. The TESS mission provides far larger samples and, for the first time, the opportunity to perform asteroseimic inference from full-frame images full-sky, instead of narrow fields and pre-selected targets. Here, we seek to detect oscillations in TESS data of the red giants in the Kepler field using the 4-yr Kepler results as a benchmark. Because we use 1–2 sectors of observation, our results are representative of the typical scenario from TESS data. We detect clear oscillations in ∼3000 stars with another ∼1000 borderline (low S/N) cases. In comparison, best-case predictions suggest ∼4500 detectable oscillating giants. Of the clear detections, we measure Δν in 570 stars, meaning a ∼20 per cent Δν yield (14 per cent for one sector and 26 per cent for two sectors). These yields imply that typical (1–2 sector) TESS data will result in significant detection biases. Hence, to boost the number of stars, one might need to use only νmax as the seismic input for stellar property estimation. However, we find little bias in the seismic measurements and typical scatter is about 5–6 per cent in νmax and 2–3 per cent in Δν. These values, coupled with typical uncertainties in parallax, Teff, and Fe/H in a grid-based approach, would provide internal uncertainties of 3 per cent in inferred stellar radius, 6 per cent in mass, and 20 per cent in age for low-luminosity giant stars. Finally, we find red giant seismology is not significantly affected by seismic signal confusion from blending for stars with Tmag ≲ 12.5.
Abstract
51 Eri is well known for hosting a directly imaged giant planet and for its membership to the
β
Pictoris moving group. Using 2 minute cadence photometry from the Transiting Exoplanet Survey ...Satellite (TESS), we detect multiperiodic variability in 51 Eri that is consistent with pulsations of Gamma Doradus (
γ
Dor) stars. We identify the most significant pulsation modes (with frequencies between ∼0.5 and 3.9 cycles day
−1
and amplitudes ranging between ∼1 and 2 mmag) as dipole and quadrupole gravity modes, as well as Rossby modes, as previously observed in Kepler
γ
Dor stars. Our results demonstrate that previously reported variability attributed to stellar rotation is instead likely due to
γ
Dor pulsations. Using the mean frequency of the
ℓ
= 1 gravity modes, together with empirical trends of the Kepler
γ
Dor population, we estimate a plausible stellar core rotation period of
0.9
−
0.1
+
0.3
days for 51 Eri. We find no significant evidence for transiting companions around 51 Eri in the residual light curve. The detection of
γ
Dor pulsations presented here, together with follow-up observations and modeling, may enable the determination of an asteroseismic age for this benchmark system. Future TESS observations would allow a constraint on the stellar core rotation rate, which in turn traces the surface rotation rate, and thus would help clarify whether or not the stellar equatorial plane and orbit of 51 Eri b are coplanar.
Abstract
The orbital parameters of binaries at intermediate periods (102–103 d) are difficult to measure with conventional methods and are very incomplete. We have undertaken a new survey, applying ...our pulsation timing method to Kepler light curves of 2224 main-sequence A/F stars and found 341 non-eclipsing binaries. We calculate the orbital parameters for 317 PB1 systems (single-pulsator binaries) and 24 PB2s (double-pulsators), tripling the number of intermediate-mass binaries with full orbital solutions. The method reaches down to small mass ratios q ≈ 0.02 and yields a highly homogeneous sample. We parametrize the mass-ratio distribution using both inversion and Markov-Chain Monte Carlo forward-modelling techniques, and find it to be skewed towards low-mass companions, peaking at q ≈ 0.2. While solar-type primaries exhibit a brown dwarf desert across short and intermediate periods, we find a small but statistically significant (2.6σ) population of extreme-mass-ratio companions (q < 0.1) to our intermediate-mass primaries. Across periods of 100–1500 d and at q > 0.1, we measure the binary fraction of current A/F primaries to be 15.4 per cent ± 1.4 per cent, though we find that a large fraction of the companions (21 per cent ± 6 per cent) are white dwarfs in post-mass-transfer systems with primaries that are now blue stragglers, some of which are the progenitors of Type Ia supernovae, barium stars, symbiotics, and related phenomena. Excluding these white dwarfs, we determine the binary fraction of original A/F primaries to be 13.9 per cent ± 2.1 per cent over the same parameter space. Combining our measurements with those in the literature, we find the binary fraction across these periods is a constant 5 per cent for primaries M1 < 0.8 M⊙, but then increases linearly with log M1, demonstrating that natal discs around more massive protostars M1 ≳ 1 M⊙ become increasingly more prone to fragmentation. Finally, we find the eccentricity distribution of the main-sequence pairs to be much less eccentric than the thermal distribution.
There are many Slowly Pulsating B (SPB) stars and γ Dor stars in the Kepler mission data set. The light curves of these pulsating stars have been classified phenomenologically into stars with ...symmetric light curves and with asymmetric light curves. In the same effective temperature ranges as the γ Dor and SPB stars, there are variable stars with downward light curves that have been conjectured to be caused by spots. Among these phenomenological classes of stars, some show ‘frequency groups’ in their amplitude spectra that have not previously been understood. While it has been recognized that non-linear pulsation gives rise to combination frequencies in a Fourier description of the light curves of these stars, such combination frequencies have been considered to be a only a minor constituent of the amplitude spectra. In this paper, we unify the Fourier description of the light curves of these groups of stars, showing that many of them can be understood in terms of only a few base frequencies, which we attribute to g-mode pulsations, and combination frequencies, where sometimes a very large number of combination frequencies dominate the amplitude spectra. The frequency groups seen in these stars are thus tremendously simplified. We show observationally that the combination frequencies can have amplitudes greater than the base frequency amplitudes, and we show theoretically how this arises. Thus for some γ Dor and SPB stars, combination frequencies can have the highest observed amplitudes. Among the B stars are pulsating Be stars that show emission lines in their spectra from occasional ejection of material into a circumstellar disc. Our analysis gives strong support to the understanding of these pulsating Be stars as rapidly rotating SPB stars, explained entirely by g-mode pulsations.
ABSTRACT
In asteroseismology, the surface effect refers to a disparity between the observed and the modelled frequencies in stars with solar-like oscillations. It originates from improper modelling ...of the surface layers. Correcting the surface effect usually requires using functions with free parameters, which are conventionally fitted to the observed frequencies. On the basis that the correction should vary smoothly across the H–R diagram, we parameterize it as a simple function of surface gravity, effective temperature, and metallicity. We determine this function by fitting a wide range of stars. The absolute amount of the surface correction decreases with luminosity, but the ratio between it and νmax increases, suggesting the surface effect is more important for red giants than dwarfs. Applying the prescription can eliminate unrealistic surface correction, which improves parameter estimations with stellar modelling. Using two open clusters, we found a reduction of scatter in the model-derived ages for each star in the same cluster. As an important application, we provide a new revision for the Δν scaling relation that, for the first time, accounts for the surface correction. The values of the correction factor, fΔν, are up to 2 per cent smaller than those determined without the surface effect considered, suggesting decreases of up to 4 per cent in radii and up to 8 per cent in masses when using the asteroseismic scaling relations. This revision brings the asteroseismic properties into an agreement with those determined from eclipsing binaries. The new correction factor and the stellar models with the corrected frequencies are available at https://www.github.com/parallelpro/surface.
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