scholarly journals Investigating surface correction relations for RGB stars

2020 ◽  
Vol 495 (4) ◽  
pp. 4965-4980 ◽  
Author(s):  
Andreas Christ Sølvsten Jørgensen ◽  
Josefina Montalbán ◽  
Andrea Miglio ◽  
Ben M Rendle ◽  
Guy R Davies ◽  
...  
Keyword(s):  
Surface Effect ◽  
Dynamical Evolution ◽  
Systematic Errors ◽  
Open Clusters ◽  
Eclipsing Binaries ◽  
Stellar Structure ◽  
Red Giants ◽  
Red Giant ◽  
Stellar Oscillation ◽  
Surface Correction

ABSTRACT State-of-the-art stellar structure and evolution codes fail to adequately describe turbulent convection. For stars with convective envelopes such as red giants, this leads to an incomplete depiction of the surface layers. As a result, the predicted stellar oscillation frequencies are haunted by systematic errors, the so-called surface effect. Different empirically and theoretically motivated correction relations have been proposed to deal with this issue. In this paper, we compare the performance of these surface correction relations for red giant branch stars. For this purpose, we apply the different surface correction relations in asteroseismic analyses of eclipsing binaries and open clusters. In accordance with previous studies of main-sequence stars, we find that the use of different surface correction relations biases the derived global stellar properties, including stellar age, mass, and distance estimates. We, furthermore, demonstrate that the different relations lead to the same systematic errors for two different open clusters. Our results overall discourage from the use of surface correction relations that rely on reference stars to calibrate free parameters. Due to the demonstrated systematic biasing of the results, the use of appropriate surface correction relations is imperative to any asteroseismic analysis of red giants. Accurate mass, age, and distance estimates for red giants are fundamental when addressing questions that deal with the chemo-dynamical evolution of the Milky Way galaxy. In this way, our results also have implications for fields such as galactic archaeology that draw on findings from stellar physics.

scholarly journals Extremely precise age and metallicity of the open cluster NGC 2506 using detached eclipsing binaries

2020 ◽  
Vol 499 (1) ◽  
pp. 1312-1339
Author(s):  
E Knudstrup ◽  
F Grundahl ◽  
K Brogaard ◽  
D Slumstrup ◽  
J A Orosz ◽  
...  
Keyword(s):  
Open Cluster ◽  
Age Determination ◽  
Open Clusters ◽  
Eclipsing Binaries ◽  
Stellar Structure ◽  
Red Giants ◽  
Effective Temperatures ◽  
Red Giant ◽  
The Masses ◽  
Giant Branch Stars

ABSTRACT Accurate stellar parameters of stars in open clusters can help constrain models of stellar structure and evolution. Here, we wish to determine the age and metallicity content of the open cluster NGC 2506. To this end, we investigated three detached eclipsing binaries (DEBs; V2032, V4, and V5) for which we determined their masses and radii, as well as four red giant branch stars for which we determined their effective temperatures, surface gravities, and metallicities. Three of the stars in the DEBs have masses close to the cluster turn-off mass, allowing for extremely precise age determination. Comparing the values for the masses and radii of the binaries to BaSTI (a Bag of Stellar Tracks and Isochrones) isochrones, we estimated a cluster age of 2.01 ± 0.10 Gyr. This does depend on the models used in the comparison, where we have found that the inclusion of convective core-overshooting is necessary to properly model the cluster. From red giant branch stars, we determined values for the effective temperatures, the surface gravities, and the metallicities. From these we find a cluster metallicity of −0.36 ± 0.10 dex. Using this value and the values for the effective temperatures, we determine the reddening to be E(b − y) = 0.057 ± 0.004 mag. Furthermore, we derived the distance to the cluster from Gaia parallaxes and found 3.101 ± 0.017 kpc, and we have performed a radial velocity membership determination for stars in the field of the cluster. Finally, we report on the detection of oscillation signals in γ Dor and δ Scuti members in data from the Transiting Exoplanet Survey Satellite (TESS) mission, including the possible detection of solar-like oscillations in two of the red giants.

scholarly journals Coupling 1D stellar evolution with 3D-hydrodynamical simulations on-the-fly II: stellar evolution and asteroseismic applications

2019 ◽  
Vol 491 (1) ◽  
pp. 1160-1173 ◽  
Author(s):  
Jakob Rørsted Mosumgaard ◽  
Andreas Christ Sølvsten Jørgensen ◽  
Achim Weiss ◽  
Víctor Silva Aguirre ◽  
Jørgen Christensen-Dalsgaard
Keyword(s):  
Stellar Evolution ◽  
Surface Effect ◽  
Stellar Structure ◽  
Red Giants ◽  
3D Simulations ◽  
Stellar Models ◽  
Red Giant ◽  
Hydrodynamical Simulations ◽  
Indispensable Tool ◽  
Oscillation Frequencies

ABSTRACT Models of stellar structure and evolution are an indispensable tool in astrophysics, yet they are known to incorrectly reproduce the outer convective layers of stars. In the first paper of this series, we presented a novel procedure to include the mean structure of 3D hydrodynamical simulations on-the-fly in stellar models, and found it to significantly improve the outer stratification and oscillation frequencies of a standard solar model. In this work, we extend the analysis of the method; specifically how the transition point between envelope and interior affects the models. We confirm the versatility of our method by successfully repeating the entire procedure for a different grid of 3D hydrosimulations. Furthermore, the applicability of the procedure was investigated across the HR diagram and an accuracy comparable to the solar case was found. Moreover, we explored the implications on stellar evolution and find that the red-giant branch is shifted about $40\, \mathrm{K}$ to higher effective temperatures. Finally, we present for the first time an asteroseismic analysis based on stellar models fully utilizing the stratification of 3D simulations on-the-fly. These new models significantly reduce the asteroseismic surface term for the two selected stars in the Kepler field. We extend the analysis to red giants and characterize the shape of the surface effect in this regime. Lastly, we stress that the interpolation required by our method would benefit from new 3D simulations, resulting in a finer sampling of the grid.

scholarly journals New light on the Gaia DR2 parallax zero-point: influence of the asteroseismic approach, in and beyond the Kepler field

2019 ◽  
Vol 628 ◽  
pp. A35 ◽  
Author(s):  
S. Khan ◽  
A. Miglio ◽  
B. Mosser ◽  
F. Arenou ◽  
K. Belkacem ◽  
...  
Keyword(s):  
Zero Point ◽  
Open Clusters ◽  
Eclipsing Binaries ◽  
Scaling Relations ◽  
Red Giants ◽  
The Third ◽  
Red Clump ◽  
Red Giant ◽  
Gaia Dr2 ◽  
Efficient Elimination

The importance of studying the Gaia DR2 parallax zero-point by external means was underlined by the articles that accompanied the release, and initiated by several works making use of Cepheids, eclipsing binaries, and asteroseismology. Despite a very efficient elimination of basic-angle variations, a small fluctuation remains and shows up as a small offset in the Gaia DR2 parallaxes. By combining astrometric, asteroseismic, spectroscopic, and photometric constraints, we undertake a new analysis of the Gaia parallax offset for nearly 3000 red-giant branch (RGB) and 2200 red clump (RC) stars observed by Kepler, as well as about 500 and 700 red giants (all either in the RGB or RC phase) selected by the K2 Galactic Archaeology Program in campaigns 3 and 6. Engaging in a thorough comparison of the astrometric and asteroseismic parallaxes, we are able to highlight the influence of the asteroseismic method, and measure parallax offsets in the Kepler field that are compatible with independent estimates from literature and open clusters. Moreover, adding the K2 fields to our investigation allows us to retrieve a clear illustration of the positional dependence of the zero-point, in general agreement with the information provided by quasars. Lastly, we initiate a two-step methodology to make progress in the simultaneous calibration of the asteroseismic scaling relations and of the Gaia DR2 parallax offset, which will greatly benefit from the gain in precision with the third data release of Gaia.

scholarly journals Non-linear seismic scaling relations

2018 ◽  
Vol 616 ◽  
pp. A104 ◽  
Author(s):  
T. Kallinger ◽  
P. G. Beck ◽  
D. Stello ◽  
R. A. Garcia
Keyword(s):  
Binary Systems ◽  
Open Clusters ◽  
Eclipsing Binaries ◽  
Probabilistic Methods ◽  
Frequency Separation ◽  
Scaling Relations ◽  
Distance Modulus ◽  
Red Giants ◽  
Eclipsing Binary ◽  
Non Linear

Context. In recent years the global seismic scaling relations for the frequency of maximum power, νmax ∝ g / √Teff, and for the large frequency separation, Δν ∝ √ρ¯, have drawn attention in various fields of astrophysics. This is because these relations can be used to estimate parameters, such as the mass and radius of stars that show solar-like oscillations. With the exquisite photometry of Kepler, the uncertainties in the seismic observables are small enough to estimate masses and radii with a precision of only a few per cent. Even though this seems to work quite well for main-sequence stars, there is empirical evidence, mainly from studies of eclipsing binary systems, that the seismic scaling relations systematically overestimate the mass and radius of red giants by about 15% and 5%, respectively. Various model-based corrections of the Δν-scaling reduce the problem but do not solve it. Aims. Our goal is to define revised seismic scaling relations that account for the known systematic mass and radius discrepancies in a completely model-independent way. Methods. We use probabilistic methods to analyse the seismic data and to derive non-linear scaling relations based on a sample of six red giant branch (RGB) stars that are members of eclipsing binary systems and about 60 red giants on the RGB as well as in the core-helium burning red clump (RC) in the two open clusters NGC 6791 and NGC 6819. Results. We re-examine the global oscillation parameters of the giants in the binary systems in order to determine their seismic fundamental parameters and we find them to agree with the dynamic parameters from the literature if we adopt non-linear scalings. We note that a curvature and glitch corrected Δνcor should be preferred over a local or average value of Δν. We then compare the observed seismic parameters of the cluster giants to those scaled from independent measurements and find the same non-linear behaviour as for the eclipsing binaries. Our final proposed scaling relations are based on both samples and cover a broad range of evolutionary stages from RGB to RC stars: g / √Teff = (νmax / νmax,⊙)1.0075±0.0021 and √ρ¯ = (Δνcor / Δνcor,⊙)[η − (0.0085 ± 0.0025) log2(Δνcor / Δνcor,⊙)]−1, where g, Teff, and ρ¯ are in solar units, νmax,⊙ = 3140 ± 5 μHz and Δνcor,⊙ = 135.08 ± 0.02 μHz, and η is equal to one in the case of RGB stars and 1.04 ± 0.01 for RC stars. Conclusions. A direct consequence of these new scaling relations is that the average mass of stars on the ascending giant branch reduces to 1.10 ± 0.03 M⊙ in NGC 6791 and 1.45 ± 0.06 M⊙ in NGC 6819, allowing us to revise the clusters’ distance modulus to 13.11 ± 0.03 and 11.91 ± 0.03 mag, respectively. We also find strong evidence that both clusters are significantly older than concluded from previous seismic investigations.

scholarly journals OCCASO – III. Iron peak and α elements of 18 open clusters. Comparison with chemical evolution models and field stars

2019 ◽  
Vol 490 (2) ◽  
pp. 1821-1842 ◽  
Author(s):  
L Casamiquela ◽  
S Blanco-Cuaresma ◽  
R Carrera ◽  
L Balaguer-Núñez ◽  
C Jordi ◽  
...  
Keyword(s):  
Chemical Evolution ◽  
Open Cluster ◽  
Dynamical Evolution ◽  
Open Clusters ◽  
Chemical Abundances ◽  
Homogeneous Sample ◽  
Giant Stars ◽  
Stellar Nucleosynthesis ◽  
Solar Abundances ◽  
Red Giant

ABSTRACT The study of open-cluster chemical abundances provides insights on stellar nucleosynthesis processes and on Galactic chemo-dynamical evolution. In this paper we present an extended abundance analysis of 10 species (Fe, Ni, Cr, V, Sc, Si, Ca, Ti, Mg, O) for red giant stars in 18 OCCASO clusters. This represents a homogeneous sample regarding the instrument features, method, line list and solar abundances from confirmed member stars. We perform an extensive comparison with previous results in the literature, and in particular with the Gaia FGK Benchmark stars Arcturus and $\mu$-Leo. We investigate the dependence of [X/Fe] with metallicity, Galactocentric radius (6.5 kpc < RGC < 11 kpc), age (0.3 Gyr < Age < 10 Gyr), and height above the plane (|z| < 1000 pc). We discuss the observational results in the chemo-dynamical framework, and the radial migration impact when comparing with chemical evolution models. We also use APOGEE DR14 data to investigate the differences between the abundance trends in RGC and |z| obtained for clusters and for field stars.

scholarly journals Systematic search for stellar pulsators in the eclipsing binaries observed by Kepler

2019 ◽  
Vol 630 ◽  
pp. A106 ◽  
Author(s):  
Patrick Gaulme ◽  
Joyce A. Guzik
Keyword(s):  
Stellar Evolution ◽  
Percent Level ◽  
Eclipsing Binaries ◽  
Light Curves ◽  
Systematic Search ◽  
Red Giants ◽  
Low Mass Stars ◽  
Orbital Periods ◽  
Red Giant ◽  
Stellar Properties

Eclipsing binaries (EBs) are unique targets for measuring precise stellar properties and can be used to constrain stellar evolution models. In particular, it is possible to measure masses and radii of both components of a double-lined spectroscopic EB at the percent level. Since the advent of high-precision photometric space missions (MOST, CoRoT, Kepler, BRITE, TESS), the use of stellar pulsation properties to infer stellar interiors and dynamics constitutes a revolution for studies of low-mass stars. The Kepler mission has led to the discovery of thousands of classical pulsators such as δ Scuti and solar-like oscillators (main sequence and evolved), but also almost 3000 EBs with orbital periods shorter than 1100 days. We report the first systematic search for stellar pulsators in the entire Kepler EB catalog. The focus is mainly aimed at discovering δ Scuti, γ Doradus, red giant, and tidally excited pulsators. We developed a data inspection tool (DIT) that automatically produces a series of plots from the Kepler light curves that allows us to visually identify whether stellar oscillations are present in a given time series. We applied the DIT to the whole Kepler EB database and identified 303 systems whose light curves display oscillations, including 163 new discoveries. A total of 149 stars are flagged as δ Scuti (100 from this paper), 115 as γ Doradus (69 new), 85 as red giants (27 new), and 59 as tidally excited oscillators (29 new). There is some overlap among these groups, as some display several types of oscillations. Despite the likelihood that many of these systems are false positives, for example, when an EB light curve is blended with a pulsator, this catalog gathers a vast sample of systems that are valuable for a better understanding of stellar evolution.

scholarly journals Orbit circularization time in binary stellar systems

1984 ◽  
Vol 105 ◽  
pp. 411-414 ◽  
Author(s):  
M. Mayor ◽  
J.-C. Mermilliod
Keyword(s):  
Time Scale ◽  
Dynamical Evolution ◽  
Open Clusters ◽  
Spectroscopic Binaries ◽  
Stellar Systems ◽  
Orbital Parameters ◽  
Short Period ◽  
Red Giant

We have analyzed the orbital parameters of 33 red dwarf and 17 red giant spectroscopic binaries belonging to open clusters to deduce the time-scale for orbital circularization. The dynamical evolution of BD +23°635, a short period binary member of the Hyades, should result in the formation either of a cataclysmic binary or a WUMa system.

scholarly journals The Aarhus red giants challenge

2020 ◽  
Vol 635 ◽  
pp. A164 ◽  
Author(s):  
V. Silva Aguirre ◽  
J. Christensen-Dalsgaard ◽  
S. Cassisi ◽  
M. Miller Bertolami ◽  
A. Serenelli ◽  
...  
Keyword(s):  
Stellar Evolution ◽  
Main Sequence ◽  
Energy Generation ◽  
Abundance Ratio ◽  
Solar Radius ◽  
Stellar Mass ◽  
Stellar Structure ◽  
Red Giants ◽  
Numerical Implementation ◽  
Red Giant

Context. With the advent of space-based asteroseismology, determining accurate properties of red-giant stars using their observed oscillations has become the focus of many investigations due to their implications in a variety of fields in astrophysics. Stellar models are fundamental in predicting quantities such as stellar age, and their reliability critically depends on the numerical implementation of the physics at play in this evolutionary phase. Aims. We introduce the Aarhus red giants challenge, a series of detailed comparisons between widely used stellar evolution and oscillation codes that aim to establish the minimum level of uncertainties in properties of red giants arising solely from numerical implementations. We present the first set of results focusing on stellar evolution tracks and structures in the red-giant-branch (RGB) phase. Methods. Using nine state-of-the-art stellar evolution codes, we defined a set of input physics and physical constants for our calculations and calibrated the convective efficiency to a specific point on the main sequence. We produced evolutionary tracks and stellar structure models at a fixed radius along the red-giant branch for masses of 1.0 M⊙, 1.5 M⊙, 2.0 M⊙, and 2.5 M⊙, and compared the predicted stellar properties. Results. Once models have been calibrated on the main sequence, we find a residual spread in the predicted effective temperatures across all codes of ∼20 K at solar radius and ∼30–40 K in the RGB regardless of the considered stellar mass. The predicted ages show variations of 2–5% (increasing with stellar mass), which we attribute to differences in the numerical implementation of energy generation. The luminosity of the RGB-bump shows a spread of about 10% for the considered codes, which translates into magnitude differences of ∼0.1 mag in the optical V-band. We also compare the predicted [C/N] abundance ratio and find a spread of 0.1 dex or more for all considered masses. Conclusions. Our comparisons show that differences at the level of a few percent still remain in evolutionary calculations of red giants branch stars despite the use of the same input physics. These are mostly due to differences in the energy generation routines and interpolation across opacities, and they call for further investigation on these matters in the context of using properties of red giants as benchmarks for astrophysical studies.

scholarly journals Effects of mass loss on the formation of planetary nebulae

1981 ◽  
Vol 59 ◽  
pp. 347-351 ◽  
Author(s):  
Sun Kwok
Keyword(s):  
Mass Loss ◽  
Planetary Nebulae ◽  
Open Clusters ◽  
Dominant Factor ◽  
Red Giants ◽  
Late Type ◽  
Solar Mass ◽  
Late Evolution ◽  
Nuclear Burning ◽  
Red Giant

The idea that planetary nebulae (PN) originated from outer layers of red giants goes back to Shlovskii (1956). This hypothesis was supported by Abell and Goldreich (1966) who argued convincingly that red giants are the most likely progenitors of PN. Although this is generally accepted today, the details of the transition from red giants to PN remain in controversy. It was pointed out by Paczyński (1971 a) that PN progenitors must have similar luminosities to central stars of PN, and therefore are likely to be late-type supergiants undergoing double-shell burning. The advent of infrared astronomy led to the discovery that most, if not all, late-type giants and supergiants are losing mass at rates of 10-6 - 10-5 Mʘyr-1 (Gehrz and Woolf 1971). Such mass loss rates greatly exceed the nuclear burning rate (6 x 10-8 - 5 x 10-7 Mʘyr-1 for stars with core masses between 0.6 and 1.2 Mʘ) and must be the dominant factor in the late evolution of intermediate mass stars. The observation of white dwarfs in open clusters implies that up to 6 Mʘ can be lost during the red-giant phase (Romanishin and Angel 1980). Since the observed masses of PN are no more than a few tenths of a solar mass, the existence of massive circumstellar envelopes formed by steady mass loss must have an effect on the formation of PN.

scholarly journals Metallicity effect on stellar granulation detected from oscillating red giants in open clusters

2017 ◽  
Vol 605 ◽  
pp. A3 ◽  
Author(s):  
E. Corsaro ◽  
S. Mathur ◽  
R. A. García ◽  
P. Gaulme ◽  
M. Pinsonneault ◽  
...  
Keyword(s):  
Time Scales ◽  
Model Comparison ◽  
Open Clusters ◽  
Stellar Atmospheres ◽  
Surface Gravity ◽  
Scaling Relations ◽  
Red Giants ◽  
Giant Stars ◽  
Red Giant Stars ◽  
Red Giant

Context. The effect of metallicity on the granulation activity in stars, and hence on the convective motions in general, is still poorly understood. Available spectroscopic parameters from the updated APOGEE-Kepler catalog, coupled with high-precision photometric observations from NASA’s Kepler mission spanning more than four years of observation, make oscillating red giant stars in open clusters crucial testbeds. Aims. We aim to determine the role of metallicity on the stellar granulation activity by discriminating its effect from that of different stellar properties such as surface gravity, mass, and temperature. We analyze 60 known red giant stars belonging to the open clusters NGC 6791, NGC 6819, and NGC 6811, spanning a metallicity range from [Fe/H] ≃ − 0.09 to 0.32. The parameters describing the granulation activity of these stars and their frequency of maximum oscillation power, νmax, are studied while taking into account different masses, metallicities, and stellar evolutionary stages. We derive new scaling relations for the granulation activity, re-calibrate existing ones, and identify the best scaling relations from the available set of observations. Methods. We adopted the Bayesian code Diamonds for the analysis of the background signal in the Fourier spectra of the stars. We performed a Bayesian parameter estimation and model comparison to test the different model hypotheses proposed in this work and in the literature. Results. Metallicity causes a statistically significant change in the amplitude of the granulation activity, with a dependency stronger than that induced by both stellar mass and surface gravity. We also find that the metallicity has a significant impact on the corresponding time scales of the phenomenon. The effect of metallicity on the time scale is stronger than that of mass. Conclusions. A higher metallicity increases the amplitude of granulation and meso-granulation signals and slows down their characteristic time scales toward longer periods. The trend in amplitude is in qualitative agreement with predictions from existing 3D hydrodynamical simulations of stellar atmospheres from main sequence to red giant stars. We confirm that the granulation activity is not sensitive to changes in the stellar core and that it only depends on the atmospheric parameters of stars.

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