To improve our comprehension of the beta Cephei stars, we set up a photometric multi-site campaign on the open cluster NGC 884 (Chi Persei). Thirteen telescopes joined the 2005-2007 campaign which resulted in almost 78000 CCD frames. We present an up-to-date status of the analysis of these data, in which several interesting oscillating stars are pointed out. We end with the future prospects.
Asteroseismology has been proven to be a successful tool to unravel details of the internal structure for different types of stars in various stages of their main sequence and post-main sequence evolution. Recently, we found a relation between the detected pulsation properties in a sample of 34 pre-main sequence (pre-MS) delta Scuti stars and the relative phase in their pre-MS evolution. With this we are able to demonstrate that asteroseismology is similarly powerful if applied to stars in the earliest stages of evolution before the onset of hydrogen core burning.
Asteroseismology offers the possibility of probing stellar interiors and testing evolutionary and seismic models. Precise photometry and spectroscopy obtained during multi-site campaigns on young open clusters allows discovering rich samples of pulsating stars and using them in a simultaneous seismic modelling called ensemble asteroseismology. The aim of this study is to obtain the age of the open cluster NGC 6910 by means of ensemble asteroseismology of the early-type pulsating members, to derive their stellar parameters, and to classify the excited modes. We used time-series analysis, perfor…
We present an asteroseismological study on the two high-gravity pulsating PG1159 (GW Vir or DOV) stars, PG 2131+066 and PG 1707+427, and on the pulsating [WCE] star NGC 1501. We compute adiabatic $g$-mode pulsation periods on PG1159 evolutionary models with stellar masses ranging from 0.530 to 0.741 Msun. These models take into account the complete evolution of progenitor stars, through the thermally pulsing AGB phase, and born-again episode. We constrain the stellar mass of PG 2131+066, PG 1707+427 and NGC 1501 by comparing the observed period spacing with the asymptotic period spacing and wi…
Precise parameter determination of the open cluster NGC 1647 via asteroseismology of p-mode pulsators
Beijing Normal University（北京师范大学）；Xinjiang Astronomical Observatory, Chinese Academy of Sciences（中国科学院新疆天文台）；INAF – Osservatorio Astrofisico di Catania（意大利国家天体物理研究所卡塔尼亚天文台）
The successful launches of the CoRoT and Kepler space missions have led to the detections of solar-like oscillations in large samples of red-giant stars. The large numbers of red giants with observed oscillations make it possible to investigate the properties of the sample as a whole: ensemble asteroseismology. In this article we summarise ensemble asteroseismology results obtained from data released by the Kepler Science Team (~150,000 field stars) as presented by Hekker et al. (2011b) and for the clusters NGC 6791, NGC 6811 and NGC 6819 (Hekker et al. 2011a) and we discuss the importance of …
This is a progress report on the ongoing project dealing with ensemble asteroseismology of B-type stars in young open clusters. The project is aimed at searches for B-type pulsating stars in open clusters, determination of atmospheric parameters for some members and seismic modeling of B-type pulsators. Some results for NGC 457, IC 1805, IC 4996, NGC 6910 and alpha Per open clusters are presented. For the last cluster, BRITE data for five members were used.
We studied solar-like oscillations in 115 red giants in the three open clusters NGC 6791, NGC 6811, and NGC 6819, based on photometric data covering more than 19 months with NASA's Kepler space telescope. We present the asteroseismic diagrams of the asymptotic parameters δν_02, δν_01 and ε, which show clear correlation with fundamental stellar parameters such as mass and radius. When the stellar populations from the clusters are compared, we see evidence for a difference in mass of the red giant branch stars, and possibly a difference in structure of the red clump stars, from our measurements …
We perform an asteroseismic investigation of giant stars in the field of NGC 6791 with previous indications of atypical evolution. The analysis makes use of observations from Kepler and Gaia in combination with ground-based photometry, a literature radial-velocity study, and measurements of eclipsing binaries in the cluster. We derive mass, radius, effective temperature, evolutionary stage and apparent distance modulus of each target. Among the investigated cluster giants we find clear evidence of overmassive and undermassive members, and non-members with strong hints of potential past members…
Recent progress in the seismic interpretation of field beta Cep stars has resulted in improvements of the physics in the stellar structure and evolution models of massive stars. Further asteroseismic constraints can be obtained from studying ensembles of stars in a young open cluster, which all have similar age, distance and chemical composition. We present an observational asteroseismology study based on the discovery of numerous multi-periodic and mono-periodic B-stars in the open cluster NGC 884. We describe a thorough investigation of the pulsational properties of all B-type stars in the c…
We present an asteroseismic analysis of the Kepler light curve of KIC 8263801, a red-giant star in the open cluster NGC 6866 that has previously been reported to be a helium-burning red-clump star. We extracted the frequencies of the radial and quadrupole modes from its frequency power spectrum and determined its properties using a grid of evolutionary models constructed with MESA. The oscillation frequencies were calculated using the GYRE code and the surface term was corrected using the Ball & Gizon(2014) prescription. We find that the star has a mass of $M/M_{\odot} = 1.793\pm 0.072$, age $…
As a result of the variability survey in Chi Persei and NGC6910, the number of Beta Cep stars that are members of these two open clusters is increased to twenty stars, nine in NGC6910 and eleven in Chi Persei. We compare pulsational properties, in particular the frequency spectra, of Beta Cep stars in both clusters and explain the differences in terms of the global parameters of the clusters. We also indicate that the more complicated pattern of the variability among B type stars in Chi Persei is very likely caused by higher rotational velocities of stars in this cluster. We conclude that the …
In this paper, we present a detailed asteroseismological analysis of six GW Vir stars including the observations collected by the TESS mission. We processed and analyzed TESS observations of RX J2117+3412, HS 2324+3944, NGC 6905, NGC 1501, NGC 2371, and K 1-16. We carried out a detailed asteroseismological analysis of these stars on the basis of PG 1159 evolutionary models that take into account the complete evolution of the progenitor stars. In total, we extracted 58 periodicities from the TESS light curves using a standard pre-whitening procedure to derive the potential pulsation frequencies…
Mass loss of red giant branch (RGB) stars is still poorly determined, despite its crucial role in the chemical enrichment of galaxies. Thanks to the recent detection of solar-like oscillations in G-K giants in open clusters with Kepler, we can now directly determine stellar masses for a statistically significant sample of stars in the old open clusters NGC6791 and NGC6819. The aim of this work is to constrain the integrated RGB mass loss by comparing the average mass of stars in the red clump (RC) with that of stars in the low-luminosity portion of the RGB (i.e. stars with L <~ L(RC)). Stellar…
Space photometric time series of the most massive members of the young open cluster NGC 2264 allow us to study their different sources of variability down to the millimagnitude level and permits a search for Slowly Pulsating B (SPB) type pulsation among objects that are only a few million years old. Our goal is to conduct a homogeneous study of young B type stars in the cluster NGC 2264 using photometric time series from space in combination with high-resolution spectroscopy and spectropolarimetry obtained from the ground. The latter will be presented in a separate follow-up article. We perfor…
The current status of asteroseismic studies is here reviewed and the adequate techniques of analysis available today for the study of the oscillation frequencies are presented. Comments on prospects for future investigations through the possibility of getting ever more precise asteroseismic observations from ground and space are given.
The Mount Wilson Ca II index log$(R'_{\rm HK})$ is the accepted standard metric of calibration for the chromospheric activity versus age relation of FGK stars. Recent results claim its inability to discern activity levels, and thus ages, for stars older than $\sim$2 Gyr, which would severely hamper its application to date disk stars older than the Sun. We present a new activity-age calibration of the Mt. Wilson index explicitly taking into account mass and $[$Fe/H$]$ biases, implicit in samples of stars selected to have precise ages, that have so far gone unappreciated. We show that these sele…
Studying stellar pulsations in open clusters offers the possibility to perform ensemble asteroseismology. The reasonable assumption that the cluster members have the same age, distance, and overall metallicity aids in the seismic modelling process and tightly constrains it. Therefore it is important to identify open clusters with many pulsators. New pulsating stars of the Beta Cephei type were searched for among the members of the open cluster NGC 637. Thirty-one hours of time resolved V filter CCD photometry were obtained. The measurements confirmed two previously known variables, and reveale…
Pulsating hydrogen-deficient white dwarfs and pre-white dwarfs observed with TESS VI. Asteroseismology of the GW Vir-type central star of the Planetary Nebula NGC 246
Our goal is to perform in-depth ensemble asteroseismology of the young open cluster NGC2244 with the 2-wheel Kepler mission. While the nominal Kepler mission already implied a revolution in stellar physics for solar-type stars and red giants, it was not possible to perform asteroseismic studies of massive OB stars because such targets were carefully avoided in the FoV in order not to disturb the exoplanet hunting. Now is an excellent time to fill this hole in mission capacity and to focus on the metal factories of the Universe, for which stellar evolution theory is least adequate. Our white pa…
The NASA space telescope Kepler has provided unprecedented time-series observations which have revolutionised the field of asteroseismology, i.e. the use of stellar oscillations to probe the interior of stars. The Kepler-data include observations of stars in open clusters, which are particularly interesting for asteroseismology. One of the clusters observed with Kepler is NGC 6811, which is the target of the present paper. However, apart from high-precision time-series observations, sounding the interiors of stars in open clusters by means of asteroseismology also requires accurate and precise…
We present the analysis of an eccentric, partially eclipsing long-period ($P=19.23$ d) binary system KIC 9777062 that contains main sequence stars near the turnoff of the intermediate age open cluster NGC 6811. The primary is a metal-lined Am star with a possible convective blueshift to its radial velocities, and one star (probably the secondary) is likely to be a $γ$ Dor pulsator. The component masses are $1.603\pm0.006$(stat.)$\pm0.016$(sys.) and $1.419\pm0.003\pm0.008 M_\odot$, and the radii are $1.744\pm0.004\pm0.002$ and $1.544\pm0.002\pm0.002 R_\odot$. The isochrone ages of the stars are…
We briefly review the current status of the study of tidally excited oscillations (TEOs) in heartbeat binary stars. Particular attention is paid to correctly extracting the TEOs when the Fourier spectrum also contains other types of pulsations and variabilities. We then focus on the theoretical modeling of the TEO amplitudes and phases. Pulsation amplitude can be modeled by a statistical approach, and pulsation phases can help to identify the azimuthal number m of pulsation modes. We verify the results by an ensemble study of ten systems. We discuss some future prospects, including the secular…
Asteroseismology has the capability of precisely determining stellar properties which would otherwise be inaccessible, such as radii, masses and thus ages of stars. When coupling this information with classical determinations of stellar parameters, such as metallicities, effective temperatures and angular diameters, powerful new diagnostics for Galactic studies can be obtained. The ongoing Stroemgren survey for Asteroseismology and Galactic Archaeology (SAGA) has the goal of transforming the Kepler field into a new benchmark for Galactic studies, similarly to the solar neighborhood. Here we pr…
Isochrone-cloud fitting and asteroseismology of the Kepler open cluster NGC6866
Institute of Astronomy, KU Leuven（KU鲁汶大学天文学研究所）；Centre for Astrophysics, University of Southern Queensland（南昆士兰大学天体物理中心）；Department of Astrophysics, IMAPP, Radboud University Nijmegen（拉特罗布大学IMAPP天体物理学系）；Max Planck Institut für Astronomie（马克斯·普朗克天文学研究所）
Recent progress in the seismic interpretation of field β Cep stars has resulted in improvements of the physical description in the stellar structure and evolution model computations of massive stars. Further asteroseismic constraints can be obtained from studying ensembles of stars in a young open cluster, which all have similar age, distance and chemical composition. We present an observational asteroseismic study based on the discovery of numerous multi-periodic and mono-periodic B-stars in the open cluster NGC 884. Our study illustrates the current status of ensemble asteroseismology of a y…
We provide a status report on the determination of stellar ages from asteroseismology for stars of various masses and evolutionary stages. The ability to deduce the ages of stars with a relative precision of typically 10 to 20% is a unique opportunity for stellar evolution and also of great value for both galactic and exoplanet studies. Further, a major uncalibrated ingredient that makes stellar evolution models uncertain, is the stellar interior rotation frequency $Ω(r)$ and its evolution during stellar life. We summarize the recent achievements in the derivation of $Ω(r)$ for different types…
We present detailed chemical compositions of 10 red giant star members of the Galactic (open) cluster NGC 752, derived from high-resolution (R $\approx$ 60,000), high signal-to-noise ($S/N$ $\geq$ 140) spectra. We confirmed cluster memberships by measuring the stellar radial velocities, and by deriving model atmosphere parameters ($T_{eff}$, logg, [Fe/H] and $ξ_{t}$) from equivalent widths of Fe I, Fe II, Ti I, and Ti II lines. The metallicity we obtained for NGC 752 ([Fe/H]=$-$0.02$\pm$0.05) is in good agreement with previous studies. We derived abundances of $α$ (Mg, Si, Ca), light odd-Z (Na…
Asteroseismology is a very useful tool for exploring the stellar interiors and evolutionary status and for determining stellar fundamental parameters, such as stellar mass, radius, surface gravity, and the stellar mean density. In the present work, we use it to preliminarily analyze the 14 new-type pulsating stars: Blue Large-Amplitude Pulsators (BLAPs) which is observed by OGLE project, to roughly analyze their evolutionary status. We adopt the theory of single star evolution and artificially set the mass loss rate of $\dot{M}=-2\times10^{-4}~{\rm M_{\odot}/year}$ and mass loss beginning at t…
Studying star clusters offers significant advances in stellar astrophysics due to the combined power of having many stars with essentially the same distance, age, and initial composition. This makes clusters excellent test benches for verification of stellar evolution theory. To fully exploit this potential, it is vital that the star sample is uncontaminated by stars that are not members of the cluster. Techniques for determining cluster membership therefore play a key role in the investigation of clusters. We present results on three clusters in the Kepler field of view based on a newly estab…
Asteroseismology of stars in clusters has been a long-sought goal because the assumption of a common age, distance and initial chemical composition allows strong tests of the theory of stellar evolution. We report results from the first 34 days of science data from the Kepler Mission for the open cluster NGC 6819 -- one of four clusters in the field of view. We obtain the first clear detections of solar-like oscillations in the cluster red giants and are able to measure the large frequency separation and the frequency of maximum oscillation power. We find that the asteroseismic parameters allo…
We present the study of dynamical status of the globular cluster NGC 1851. A combination of multiwavelength space and ground-based data sets are used for the present analysis. In order to select the genuine cluster members, we used the astro-photometric data available from HST and GAIA-DR2 catalogs. The BSS radial distribution of the cluster is plotted from the center of the cluster to the outskirts. The radial distribution of BSS shows a central peak, followed by a dip at the intermediate radii (rmin ~ 90'') and a rising trend in the outskirts. We also estimated A+rh parameter as 0.391 +/- 0.…
Models of stellar structure and evolution can be constrained by measuring accurate parameters of detached eclipsing binaries in open clusters. Multiple binary stars provide the means to determine helium abundances in these old stellar systems, and in turn, to improve estimates of their age. In the first paper of this series, we demonstrated how measurements of multiple eclipsing binaries in the old open cluster NGC6791 sets tighter constraints on the properties of stellar models than has previously been possible, thereby potentially improving both the accuracy and precision of the cluster age.…
Today, asteroseismology is entering in its golden age thanks to the observations provided by the CoRoT and Kepler space missions. In particular, we will make significant progresses in the understanding of the structure and evolution of solar-like oscillating stars. These stars have acoustic modes stochastically excited by the near-surface convection. Thanks to the observations already provided by these two missions, we have detected several hundred of stars showing solar-like oscillations in the main sequence and several thousands in the red- giant branch. Here, I give an overview of the prese…
We present the current state of the WOCS radial-velocity (RV) survey for the rich open cluster NGC 6819 (2.5 Gyr) including 93 spectroscopic binary orbits with periods ranging from 1.5 to 8,000 days. These results are the product of our ongoing RV survey of NGC 6819 using the Hydra Multi-Object Spectrograph on the WIYN 3.5 m telescope. We also include a detailed analysis of multiple prior sets of optical photometry for NGC 6819. Within a 1-degree field of view, our stellar sample includes the giant branch, the red clump, and blue straggler candidates, and extends to almost 2 mag below the main…
I discuss and consider the status of observational determinations of the rotation velocities of white dwarf stars via asteroseismology and spectroscopy. While these observations have important implications on our understanding of the angular momentum evolution of stars in their late stages of evolution, more direct methods are sorely needed to disentangle ambiguities.
Context. The availability of asteroseismic constraints for a large sample of red giant stars from the CoRoT and Kepler missions paves the way for various statistical studies of the seismic properties of stellar populations. Aims. We use the first detailed spectroscopic study of 19 CoRoT red-giant stars (Morel et al 2014) to compare theoretical stellar evolution models to observations of the open cluster NGC 6633 and field stars. Methods. In order to explore the effects of rotation-induced mixing and thermohaline instability, we compare surface abundances of carbon isotopic ratio and lithium wi…
Stellar mass $M$, radius $R$, and gravity $g$ are important basic parameters in stellar physics. Accurate values for these parameters can be obtained from the gravitational interaction between stars in multiple systems or from asteroseismology. Stars in a cluster are thought to be formed coevally from the same interstellar cloud of gas and dust. The cluster members are therefore expected to have some properties in common. These common properties strengthen our ability to constrain stellar models and asteroseismically derived $M$, $R$ and $g$ when tested against an ensemble of cluster stars. He…
Hybrid $δ$ Scuti-$γ$ Doradus pulsating stars show acoustic ($p$) oscillation modes typical of $δ$ Scuti variable stars, and gravity ($g$) pulsation modes characteristic of $γ$ Doradus variable stars simultaneously excited. Observations from space missions like MOST, CoRoT, and \emph{Kepler} have revealed a large number of hybrid $δ$ Scuti-$γ$ Doradus pulsators, thus paving the way for a exciting new channel for asteroseismic studies. We perform a detailed asteroseismological modeling of five hybrid $δ$ Scuti-$γ$ Doradus stars. We employ a grid-based modeling approach to sound the internal stru…
The helium abundance of stars is a strong driver of evolutionary timescales, however it is difficult to measure in cool stars. We conduct an asteroseismic analysis of NGC 6791, an old, metal rich open cluster that previous studies have indicated also has a high helium abundance. The cluster was observed by Kepler and has unprecedented lightcurves for many of the red giant branch stars in the cluster. Previous asteroseismic studies with Kepler data have constrained the age through grid based modeling of the global asteroseismic parameters ($Δν$ and $ν_{\mathrm{max}}$). However, with the precisi…
We present the high resolution (R $\approx$ 60000), high signal-to-noise (S/N $\simeq$ 120) spectroscopic analysis of 12 red giant members of the Galactic open cluster NGC 6940. We applied Yonsei-Yale isochrones to the color-magnitude diagram, which suggested an age of 1.1 Gyr for the cluster with a turn-off mass of 2 M$_{\odot}$. Atmospheric parameters ($T_{\rm eff}$, $log~{\it g}$, [Fe/H] and $ξ_{t}$) were determined via equivalent widths of Fe I, Fe II, Ti I, and Ti II lines. Calculated mean metallicity of the cluster is $\langle {\rm [Fe/H]} \rangle = 0.04\pm0.02$. We derived abundances of…
We present dynamical status of the Galactic globular cluster NGC 6656 using spatial distribution of Blue Straggler Stars (BSSs). A combination of multi-wavelength high-resolution space and ground-based data are used to cover a large cluster region. We determine the centre of gravity ($C_{grav}$) and construct the projected density profile of the cluster using the probable cluster members selected from HST and Gaia DR2 proper motion data sets. The projected density profile in the investigated region is nicely reproduced by a single mass King model, with core ($r_{c}$) and tidal ($r_{t}$) radius…
Asteroseismic analysis of solar-like stars allows us to determine physical parameters such as stellar mass, with a higher precision compared to most other methods. Even in a well-studied cluster such as the Hyades, the masses of the red giant stars are not well known, and previous mass estimates are based on model calculations (isochrones). The four known red giants in the Hyades are assumed to be clump (core-helium-burning) stars based on their positions in colour-magnitude diagrams, however asteroseismology offers an opportunity to test this assumption. Using asteroseismic techniques combine…
$Context.$ Pulsating stars are windows to the physics of stars enabling us to see glimpses of their interior. Not all stars pulsate, however. On the main sequence, pulsating stars form an almost continuous sequence in brightness, except for a magnitude range between $δ$ Scuti and slowly pulsating B stars. Against all expectations, 36 periodic variables were discovered in 2013 in this luminosity range in the open cluster NGC 3766, the origins of which was a mystery. $Aims.$ We investigate the properties of those new variability class candidates in relation to their stellar rotation rates and st…
Aims. The magnetic star HD148937 is the only Galactic Of?p star surrounded by a nebula. The structure of this nebula is particularly complex and is composed, from the center out outwards, of a close bipolar ejecta nebula (NGC6164/5), an ellipsoidal wind-blown shell, and a spherically symmetric Stromgren sphere. The exact formation process of this nebula and its precise relation to the star's evolution remain unknown. Methods. We analyzed infrared Spitzer IRS and far-infrared Herschel/PACS observations of the NGC6164/5 nebula. The Herschel imaging allowed us to constrain the global morphology o…
Protostellar evolution, following the formation of the protostar is becoming reasonably well characterized, but the evolution from a prestellar core to a protostar is not well known, although the first hydrostatic core (FHSC) must be a pivotal step. NGC 1333 IRAS 4C is a potentially very young object, that we directly compare with the nearby Class 0 IRAS 4A and IRAS 4B. Observational constraints are provided by spectral imaging from the JCMT Spectral Legacy Survey (330-373 GHz) and continuum and line observations from CARMA. We present integrated intensity and velocity maps of several species,…
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 w…
Extended main-sequence turn-offs (eMSTO) are a commonly observed property of young clusters. A global theoretical interpretation for the eMSTOs is still lacking, but stellar rotation is considered a necessary ingredient to explain the eMSTO. We aim to assess the importance of core-boundary and envelope mixing in stellar interiors for the interpretation of eMSTOs in terms of one coeval population. We construct isochrone-clouds based on interior mixing profiles of stars with a convective core calibrated from asteroseismology of isolated galactic field stars. We fit these isochrone-clouds to the …
We report novel observational evidence on the evolutionary status of lithium-rich giant stars by combining asteroseismic and lithium abundance data. Comparing observations and models of the asteroseismic gravity-mode period spacing $ΔΠ_{1}$, we find that super-Li-rich giants (SLR, A(Li)~$> 3.2$~dex) are almost exclusively young red-clump (RC) stars. Depending on the exact phase of evolution, which requires more data to refine, SLR stars are either (i) less than $\sim 2$~Myr or (ii) less than $\sim40$~Myr past the main core helium flash (CHeF). Our observations set a strong upper limit for the …
A Li-rich red giant star (2M19411367+4003382) recently discovered in the direction of NGC 6819 belongs to the rare subset of Li-rich stars that have not yet evolved to the luminosity bump, an evolutionary stage where models predict Li can be replenished. The currently favored model to explain Li enhancement in first-ascent red giants like 2M19411367+4003382 requires deep mixing into the stellar interior. Testing this model requires a measurement of 12C/13C, which is possible to obtain from APOGEE spectra. However, the Li-rich star also has abnormal asteroseismic properties that call into quest…
In this paper we analyse the evolutionary status of three open clusters: NGC 1817, NGC 2141, and Berkeley 81. They are all of intermediate age, two are located in the Galactic anti-centre direction while the third one is located in the Galactic centre direction. All of them were observed with LBC@LBT using the Bessel B, V, and I filters. The cluster parameters have been obtained using the synthetic colour-magnitude diagram (CMD) method, i.e. the direct comparison of the observational CMDs with a library of synthetic CMDs generated with different evolutionary sets (Padova, FRANEC, and FST). Thi…
Existing photometry for NGC 2264 tied to the Johnson and Morgan (1953) UBV system is reexamined and, in the case of the original observations by Walker (1956), reanalyzed in order to generate a homogeneous data set for cluster stars. Color terms and a Balmer discontinuity effect in Walker's observations were detected and corrected, and the homogenized data were used in a new assessment of the cluster reddening, distance, and age. Average values of E(B-V)=0.075+-0.003 s.e. and Vo-Mv=9.45+-0.03 s.e. (d=777+-12 pc) are obtained, in conjunction with an inferred cluster age of ~5.5x10^6 yr from pre…
Based on a set of over 100 medium- to high-resolution optical spectra collected from 2003 to 2009, we investigate the properties of the O-type star population in NGC6611 in the core of the Eagle Nebula (M16). Using a much more extended data set than previously available, we revise the spectral classification and multiplicity status of the nine O-type stars in our sample. We confirm two suspected binaries and derive the first SB2 orbital solutions for two systems. We further report that two other objects are displaying a composite spectrum, suggesting possible long-period binaries. Our analysis…
In an optical color-magnitude diagram sub-subgiants (SSGs) lie red of the main sequence and fainter than the base of the red giant branch in a region not easily populated by standard stellar-evolution pathways. In this paper, we present multi-epoch radial velocities for five SSG candidates in the old and metal-rich open cluster NGC 6791 (8 Gyr, [Fe/H] = +0.30). From these data we are able to make three-dimensional kinematic membership determinations and confirm four SSG candidates to be likely cluster members. We also identify three member SSGs as short-period binary systems and present their …
Asteroseismology is a powerful tool to infer the evolutionary status and chemical stratification of white dwarf (WD) stars, and to explore the physical processes that lead to their formation. This is particularly true for the variable H-rich atmosphere (DA) WDs, known as DAV or ZZ Ceti stars. We present a new grid of DA WD models that take into account the last advances in the modeling and input physics of both the progenitor and the WD stars, thus avoiding and improving several shortcomings present in the set of DA WD models employed in the asteroseismological analyses of ZZ Ceti stars we car…
