Testing scaling relations for solar-like oscillations from the main sequence to red giants using kepler data (original) (raw)
Related papers
2010
We have studied solar-like oscillations in ∼ 800 red-giant stars using Kepler long-cadence photometry. The sample includes stars ranging in evolution from the lower part of the red-giant branch to the Helium main sequence. We investigate the relation between the large frequency separation (∆ν) and the frequency of maximum power (ν max ) and show that it is different for red giants than for mainsequence stars, which is consistent with evolutionary models and scaling relations. The distributions of ν max and ∆ν are in qualitative agreement with a simple stellar population model of the Kepler field, including the first evidence for a secondary clump population characterized by M 2 M ⊙ and ν max ≃ 40−110 µHz. We measured the small frequency separations δν 02 and δν 01 in over 400 stars and δν 03 in over 40. We present C-D diagrams for l = 1, 2 and 3 and show that the frequency separation ratios δν 02 /∆ν and δν 01 /∆ν have opposite trends as a function of ∆ν. The data show a narrowing of the l = 1 ridge towards lower ν max , in agreement with models predicting more efficient mode trapping in stars with higher luminosity. We investigate the offset ǫ in the asymptotic relation and find a clear correlation with ∆ν, demonstrating that it is related to fundamental stellar parameters. Finally, we present the first amplitude-ν max relation for Kepler red giants. We observe a lack of low-amplitude stars for ν max 110 µHz and find that, for a given ν max between 40 − 110 µHz, stars with lower ∆ν (and consequently higher mass) tend to show lower amplitudes than stars with higher ∆ν.
The Astrophysical Journal Letters
Scaling relations that link asteroseismic quantities to global stellar properties are important for gaining understanding of the intricate physics that underpins stellar pulsation. The common notion that all stars in an open cluster have essentially the same distance, age, and initial composition, implies that the stellar parameters can be measured to much higher precision than what is usually achievable for single stars. This makes clusters ideal for exploring the relation between the mode amplitude of solar-like oscillations and the global stellar properties. We have analyzed data obtained with NASA's Kepler space telescope to study solar-like oscillations in 100 red giant stars located in either of the three open clusters, NGC 6791, NGC 6819, and NGC 6811. By fitting the measured amplitudes to predictions from simple scaling relations that depend on luminosity, mass, and effective temperature, we find that the data cannot be described by any power of the luminosity-to-mass ra...
2015
Large-scale analyses of stellar samples comprised of cool, solar-like oscillators now commonly utilize the so-called asteroseismic scaling relations to estimate fundamental stellar properties. In this paper we present a test of the scaling relation for the global asteroseismic parameter ν_ max, the frequency at which a solar-like oscillator presents its strongest observed pulsation amplitude. The classic relation assumes that this characteristic frequency scales with a particular combination of surface gravity and effective temperature that also describes the dependence of the cut-off frequency for acoustic waves in an isothermal atmosphere, i.e., ν_ max∝ gT_ eff^-1/2. We test how well the oscillations of cool main-sequence and sub-giant stars adhere to this relation, using a sample of asteroseismic targets observed by the NASA Kepler Mission. Our results, which come from a grid-based analysis, rule out departures from the classic gT_ eff^-1/2 scaling dependence at the level of ≃ 1....
Monthly Notices of the Royal Astronomical Society, 2015
Large-scale analyses of stellar samples comprised of cool, solar-like oscillators now commonly utilize the so-called asteroseismic scaling relations to estimate fundamental stellar properties. In this paper, we present a test of the scaling relation for the global asteroseismic parameter ν max , the frequency at which a solar-like oscillator presents its strongest observed pulsation amplitude. The classic relation assumes that this characteristic frequency scales with a particular combination of surface gravity and effective temperature that also describes the dependence of the cutoff frequency for acoustic waves in an isothermal atmosphere, i.e. ν max ∝ gT −1/2 eff. We test how well the oscillations of cool main-sequence and subgiant stars adhere to this relation, using a sample of asteroseismic targets observed by the NASA Kepler Mission. Our results, which come from a grid-based analysis, rule out departures from the classic gT −1/2 eff scaling dependence at the level of 1.5 per cent over the full 1560 K range in T eff that we tested. There is some uncertainty over the absolute calibration of the scaling. However, any variation with T eff is evidently small, with limits similar to those above.
Solar-like oscillations in low-luminosity red giants: first results from Kepler
2010
We have measured solar-like oscillations in red giants using time-series photometry from the first 34 days of science operations of the Kepler Mission. The light curves, obtained with 30-minute sampling, reveal clear oscillations in a large sample of G and K giants, extending in luminosity from the red clump down to the bottom of the giant branch. We confirm a strong correlation between the large separation of the oscillations (∆ν) and the frequency of maximum power (ν max ). We focus on a sample of 50 low-luminosity stars (ν max > 100 µHz, L 30 L ⊙ ) having high signal-to-noise ratios and showing the unambiguous signature of solar-like oscillations. These are H-shell-burning stars, whose oscillations should be valuable for testing models of stellar evolution and for constraining the star-formation rate in the local disk. We use a new technique to compare stars on a singleéchelle diagram by scaling their frequencies and find well-defined ridges corresponding to radial and non-radial oscillations, including clear evidence for modes with angular degree l = 3. Measuring the small separation between l = 0 and l = 2 allows us to plot the so-called C-D diagram of δν 02 versus ∆ν. The small separation δν 01 of l = 1 from the midpoint of adjacent l = 0 modes is negative, contrary to the Sun and solar-type stars. The ridge for l = 1 is notably broadened, which we attribute to mixed modes, confirming theoretical predictions for low-luminosity giants. Overall, the results demonstrate the tremendous potential of Kepler data for asteroseismology of red giants.
2010
Context. The length of the asteroseismic timeseries obtained from the Kepler satellite analysed here span 19 months. Kepler provides the longest continuous timeseries currently available, which calls for a study of the influence of the increased timespan on the accuracy and precision of the obtained results. Aims. We aim to investigate how the increased timespan influences the detectability of the oscillation modes, and the absolute values and uncertainties of the global oscillation parameters, i.e., frequency of maximum oscillation power, ν max , and large frequency separation between modes of the same degree and consecutive orders, ∆ν . Methods. We use published methods to derive ν max and ∆ν for timeseries ranging from 50 to 600 days and compare these results as a function of method, timespan and ∆ν . Results. We find that in general a minimum of the order of 400 day long timeseries are necessary to obtain reliable results for the global oscillation parameters in more than 95% of the stars, but this does depend on ∆ν . In a statistical sense the quoted uncertainties seem to provide a reasonable indication of the precision of the obtained results in short (50-day) runs, they do however seem to be overestimated for results of longer runs. Furthermore, the different definitions of the global parameters used in the different methods have non-negligible effects on the obtained values. Additionally, we show that there is a correlation between ν max and the flux variance. Conclusions. We conclude that longer timeseries improve the likelihood to detect oscillations with automated codes (from ∼60% in 50 day runs to > 95% in 400 day runs with a slight method dependence) and the precision of the obtained global oscillation parameters. The trends suggest that the improvement will continue for even longer timeseries than the 600 days considered here, with a reduction in the median absolute deviation of more than a factor of 10 for an increase in timespan from 50 to 2000 days (the currently foreseen length of the mission). This work shows that global parameters determined with high precision -thus from long datasetsusing different definitions can be used to identify the evolutionary state of the stars.
Period-luminosity relations in evolved red giants explained by solar-like oscillations
Astronomy & Astrophysics, 2013
Context. Solar-like oscillations in red giants have been investigated with the space-borne missions CoRoT and Kepler, while pulsations in more evolved M giants have been studied with ground-based microlensing surveys. After 3.1 years of observation with Kepler, it is now possible to link these different observations of semi-regular variables. Aims. We aim to identify period-luminosity sequences in evolved red giants identified as semi-regular variables and to interpret them in terms of solar-like oscillations. Then, we investigate the consequences of the comparison of groundbased and space-borne observations. Methods. We first measured global oscillation parameters of evolved red giants observed with Kepler with the envelope autocorrelation function method. We then used an extended form of the universal red giant oscillation pattern, extrapolated to very low frequency, to fully identify their oscillations. The comparison with ground-based results was then used to express the period-luminosity relation as a relation between the large frequency separation and the stellar luminosity. Results. From the link between red giant oscillations observed by Kepler and period-luminosity sequences, we have identified these relations in evolved red giants as radial and non-radial solar-like oscillations. We were able to expand scaling relations at very low frequency (periods as long as 100 days and large frequency separation less than 0.05 µHz). This helped us identify the different sequences of period-luminosity relations, and allowed us to propose a calibration of the K magnitude with the observed large frequency separation. Conclusions. Interpreting period-luminosity relations in red giants in terms of solar-like oscillations allows us to investigate the time series obtained from ground-based microlensing surveys with a firm physical basis. This can be done with an analytical expression that describes the low-frequency oscillation spectra. The different behavior of oscillations at low frequency, with frequency separations scaling only approximately with the square root of the mean stellar density, can be used to precisely address the physics of the semi-regular variables. This will allow improved distance measurements and opens the way to extragalactic asteroseismology with the observations of M giants in the Magellanic Clouds.
A Bayesian approach to scaling relations for amplitudes of solar-like oscillations in Kepler stars
Monthly Notices of the Royal Astronomical Society, 2013
We investigate different amplitude scaling relations adopted for the asteroseismology of stars that show solar-like oscillations. Amplitudes are among the most challenging asteroseismic quantities to handle because of the large uncertainties that arise in measuring the background level in the star's power spectrum. We present results computed by means of a Bayesian inference on a sample of 1640 stars observed with Kepler, spanning from main sequence to red giant stars, for 12 models used for amplitude predictions and exploiting recently wellcalibrated effective temperatures from Sloan Digital Sky Survey photometry. We test the candidate amplitude scaling relations by means of a Bayesian model comparison. We find the model having a separate dependence upon the mass of the stars to be largely the most favoured one. The differences among models and the differences seen in their free parameters from early to late phases of stellar evolution are also highlighted.
Characterization of the power excess of solar-like oscillations in red giants withKepler
Astronomy & Astrophysics, 2011
Context. The space mission Kepler provides us with long and uninterrupted photometric time series of red giants. This allows us to examine their seismic global properties and to compare these with theoretical predictions. Aims. We aim to describe the oscillation power excess observed in red giant oscillation spectra with global seismic parameters, and to investigate empirical scaling relations governing these parameters. From these scalings relations, we derive new physical properties of red giant oscillations. Methods. Various different methods were compared in order to validate the processes and to derive reliable output values. For consistency, a single method was then used to determine scaling relations for the relevant global asteroseismic parameters: mean mode height, mean height of the background signal superimposed on the oscillation power excess, width of the power excess, bolometric amplitude of the radial modes and visibility of non-radial modes. A method for deriving oscillation amplitudes is proposed, which relies on the complete identification of the red giant oscillation spectrum. Results. The comparison of the different methods has shown the important role of the way the background is modelled. The convergence reached by the collaborative work enables us to derive significant results concerning the oscillation power excess. We obtain several scaling relations, and identify the influence of the stellar mass and the evolutionary status. The effect of helium burning on the red giant interior structure is confirmed: it yields a strong mass-radius relation for clump stars. We find that none of the amplitude scaling relations motivated by physical considerations predict the observed mode amplitudes of red giant stars. In parallel, the degreedependent mode visibility exhibits important variations. Both effects seem related to the significant influence of the high mode mass of non-radial mixed modes. A family of red giants with very weak dipole modes is identified, and its properties are analyzed. Conclusions. The clear correlation between the power densities of the background signal and of the stellar oscillation induces important consequences to be considered for deriving a reliable theoretical relation of the mode amplitude. As a by-product of this work, we have verified that red giant asteroseismology delivers new insights for stellar and Galactic physics, given the evidence for mass loss at the tip of the red giant branch.
A search for red giant solar-like oscillations in all Kepler data
Monthly Notices of the Royal Astronomical Society, 2019
The recently published Kepler mission Data Release 25 (DR25) reported on ∼197 000 targets observed during the mission. Despite this, no wide search for red giants showing solar-like oscillations have been made across all stars observed in Kepler’s long-cadence mode. In this work, we perform this task using custom apertures on the Kepler pixel files and detect oscillations in 21 914 stars, representing the largest sample of solar-like oscillating stars to date. We measure their frequency at maximum power, νmax, down to numathrmmaxsimeq4,mu\nu _{\mathrm{max}}\simeq 4\, \munumathrmmaxsimeq4,muHz and obtain log (g) estimates with a typical uncertainty below 0.05 dex, which is superior to typical measurements from spectroscopy. Additionally, the νmax distribution of our detections show good agreement with results from a simulated model of the Milky Way, with a ratio of observed to predicted stars of 0.992 for stars with 10ltnumathrmmaxlt270,mu10 \lt \nu _{\mathrm{max}}\lt 270\, \mu10ltnumathrmmaxlt270,muHz. Among our red giant detections, we find 909 to be dwarf/subgi...