Monitoring a high--amplitude Delta Sct star for 152 days: discovery of 12 additional modes and modulation effects in the light curve of CoRoT 101155310
Ennio Poretti, Monica Rainer, Werner W. Weiss, Zsofia Bognar, Andy Moya, Ewa Niemczura, Juan Carlos Suarez, Michel Auvergne, Annie Baglin, Frederic Baudin, Jozs… 展开作者
Ennio Poretti, Monica Rainer, Werner W. Weiss, Zsofia Bognar, Andy Moya, Ewa Niemczura, Juan Carlos Suarez, Michel Auvergne, Annie Baglin, Frederic Baudin, Jozsef M. Benko, Jonas Debosscher, Rafa Garrido, Luciano Mantegazza, Margit Paparo
备注：
10 pages, 6 figures, Tables 1 and 2 available at CDS after publication. Accepted for publication in Astronomy and Astrophysics
The detection of small-amplitude nonradial modes in high-amplitude Delta Sct (HADS) variables has been very elusive until at least five of them were detected in the light curve of V974 Oph obtained from ground-based observations. The combination of radial and nonradial modes has a high asteroseismic potential, thanks to the strong constraints we can put in the modelling. The continuous monitoring of ASAS 192647-0030.0=CoRoT 101155310 (P=0.1258 d, V=13.4) ensured from space by the CoRoT (Convection, Rotation and planetary Transits) mission constitutes a unique opportunity to exploit such potential. The 22270 CoRoT measurements were performed in the chromatic mode. They span 152 d and cover 1208 consecutive cycles. After the correction for one jump and the long-term drift, the level of the noise turned out to be 29 micromag. The phase shifts and amplitude ratios of the coloured CoRoT data, the HARPS spectra, and the period-luminosity relation were used to determine a self-consistent physical model. In turn, it allowed us to model the oscillation spectrum, also giving feedback on the internal structure of the star. In addition to the fundamental radial mode f1=7.949 c/d with harmonics up to 10f1, we detected 12 independent terms. Linear combinations were also found and the light curve was solved by means of 61 frequencies (smallest amplitude 0.10 mmag). The newest result is the detection of a periodic modulation of the f1 mode (triplets at +/-0.193 c/d centred on f1 and 2f1), discussed as a rotational effect or as an extension of the Blazhko effect to HADS stars. The physical model suggests that CoRoT 101155310 is an evolved star, with a slight subsolar metallic abundance, close to the terminal age main sequence. All the 12 additional terms are identified with mixed modes in the predicted overstable region.
A systematic search for gamma Dor and gamma Dor - delta Scuti hybrid pulsators was conducted on the CoRoT LRa01 Exo-archive yielding a total of 418 gamma Dor and 274 hybrid candidates. After an automatic jump correction 194 and 167 respectively, show no more obvious jumps and were investigated in more detail. For about 25\% of these candidates classification spectra from the Anglo-Australian Observatory (AAO) are available. The detailed frequency analysis and a check for combination frequencies together with spectroscopic information allowed us to identify I) 34 gamma Dor stars which show very…
It has been suggested that the detection of a wealth of very low amplitude modes in Delta Sct stars was only a matter of signal--to--noise ratio. Access to this treasure, impossible from the ground, is one of the scientific aims of the space mission CoRoT, developed and operated by CNES. This work presents the results obtained on HD 50844: the 140,016 datapoints allowed us to reach the level of 10^{-5} mag in the amplitude spectra. The frequency analysis of the CoRoT timeseries revealed hundreds of terms in the frequency range 0--30 d^{-1}. The initial guess that Delta Sct stars have a very ri…
Several Delta Sct stars were photometrically monitored with the satellite CoRoT and observed in high-resolution spectroscopy from ground. We present here the preliminary analysis of the abundance analysis of several potential CoRoT targets. Moreover, new insights are given about the problem of the huge number of detected frequencies by comparing Delta Sct stars with normal A-stars.
It has also been suggested that the detection of a wealth of very low amplitude modes in Delta Sct stars was only a matter of signal--to--noise ratio. Access to this treasure, impossible from the ground, is one of the scientific aims of the space mission CoRoT, a space mission developed and operated by CNES. This work presents the results obtained on HD 50844: the 140,016 datapoints were analysed using independent approaches and several checks performed. A level of 10^{-5} mag was reached in the amplitude spectra of the CoRoT timeseries. The frequency analysis of the CoRoT timeseries revealed …
We present the results obtained with the CoRoT satellite for HD 50870, a Delta Sct star which was observed for 114.4 d. The 307,570 CoRoT datapoints were analysed with different techniques. The photometric observations were complemented over 15 nights of high-resolution spectroscopy with HARPS on a baseline of 25 d. Some uvby photometric observations were also obtained to better characterize the pulsation modes. HD 50870 proved to be a low-amplitude, long-period spectroscopic binary system seen almost pole-on (i~21 deg. The brighter component, which also has the higher rotational velocity (v s…
Searching for magnetic fields in pulsating A-type stars: the discovery of a strong field in the probable delta Sct star HD340577 and a null result for the gamma Dor star HR8799
We present the analysis of the time series observations of CoRoT\,102699796 obtained by the CoRoT satellite that show the presence of five independent oscillation frequencies in the range 3.6-5 c/d. Using spectra acquired with FLAMES@VLT, we derive the following stellar parameters: spectral type F1V, T$_{\rm eff}$=7000$\pm$200 K, log(g)=$3.8\pm0.4$, [M/H]=$-1.1\pm0.2$, $v$sin$i$=$50\pm5$ km/s, L/L$_{\odot}$=21$^{+21}_{-11}$. Thus, for the first time we report the existence of a metal poor, intermediate-mass PMS pulsating star. Ground-based and satellite data are used to derive the spectral ene…
Ground-based spectroscopic follow-up observations of the pulsating stars observed by the Kepler satellite mission are needed for their asteroseismic modelling. We aim to derive the fundamental parameters for a sample of 26 Gamma Doradus candidate stars observed by the Kepler satellite mission to accomplish one of the required preconditions for their asteroseismic modelling and to compare our results with the types of pulsators expected from the existing light curve analysis. We use the spectrum synthesis method to derive the fundamental parameters like Teff, logg, [M/H], and vsini from newly o…
Delta Sct - gamma Dor hybrids pulsate simultaneously in p- and g-modes, which carry information on the structure of the envelope as well as to the core. Hence they are key objects for investigating A and F type stars with asteroseismic techniques. An important requirement for seismic modeling are small errors in temperature, gravity and chemical composition. Furthermore, we want to investigate the existence of an abundance indicator typical for hybrids, something that is well established for the roAp stars. Previous to the present investigation, the abundance pattern of only one hybrid and ano…
The results of our six year systematic observational survey on candidate eclipsing binaries with a delta Sct component are briefly presented. A new catalogue for this kind of systems as well as the properties of their delta Sct members are also presented. The comparison between the components-pulsators and the single delta Sct stars shows that both the evolution and the pulsating properties differ significantly. Finally, we introduce the new era of studying stellar pulsations using high accuracy data from Kepler mission and emphasizing the great opportunities that are now opened for a deep kno…
We study the frequency distributions of Delta Scuti stars observed by the Kepler satellite in short-cadence mode. To minimize errors in the estimated stellar parameters, we divided the instability strip into ten regions and determined the mean frequency distribution in each region. We confirm that the presence of low frequencies is a property of all Delta Scuti stars, rendering meaningless the concept of Delta Sct/Gamma Dor hybrids. We obtained the true distribution of equatorial rotational velocities in each region and calculated the frequency distributions predicted by pulsation models, taki…
The Kepler space mission provided a wealth of δ Sct-γ Dor hybrid candidates. While some may be genuine hybrids, others might be misclassified due to the presence of a binary companion or to rotational modulation caused by magnetism and related surface inhomogeneities. In particular, the Kepler δ Sct-γ Dor hybrid candidate HD 188774 shows a few low frequencies in its light and radial velocity curves, whose origin is unclear. In this work, we check for the presence of a magnetic field in HD 188774. We obtained two spectropolarimetric measurements with ESPaDOnS at CFHT. The data were analysed wit…
KIC 8569819 is an eclipsing binary star with an early F primary and G secondary in a 20.85-d eccentric orbit. The primary is a delta Sct - gamma Dor star pulsating in both p modes and g modes. Using 4 years of Kepler Mission photometric data we independently model the light curve using the traditional technique with the modelling code PHOEBE, and we study the orbital characteristics using the new frequency modulation (FM) technique. We show that both methods provide the equivalent orbital period, eccentricity and argument of periastron, thus illustrating and validating the FM technique. In the…
The light curves of 2768 stars with effective temperatures and surface gravities placing them near the gamma Doradus/delta Scuti instability region were observed as part of the Kepler Guest Observer program from Cycles 1 through 5. The light curves were analyzed in a uniform manner to search for gamma Doradus, delta Scuti, and hybrid star pulsations. The gamma Doradus, delta Scuti, and hybrid star pulsations extend asteroseismology to stars slightly more massive (1.4 to 2.5 solar masses) than our Sun. We find 207 gamma Doradus, 84 delta Scuti, and 32 hybrid candidate stars. Many of these stars…
In this work, we have gone one step further from the study presented in the first CoRoT symposium. Our analysis consists on constructing a model database covering the entire uncertainty box of the $δ$ Sct star HD174966, derived from the usual observables ($\mathrm{T}_{\mathrm{eff}}$, $\log g$ and [Fe/H]), and constraining the models representative of the star. To do that, we use the value of the periodicity (related to $Δν_{\ell}$) found in its CoRoT pulsating spectrum.
KIC 10661783 is an eclipsing binary that shows Delta Sct-like oscillations. More than 60 pulsation frequencies have been detected in its light curve as observed by the Kepler satellite. We want to determine the fundamental stellar and system parameters of the eclipsing binary as a precondition for asteroseismic modelling of the pulsating component and to establish whether the star is a semi-detached Algol-type system. We measured the radial velocities of both components from new high-resolution spectra using TODCOR and compute the orbit using PHOEBE. We used the KOREL program to decompose the …
Delta Scuti (delta Sct) stars are opacity-driven pulsators with masses of 1.5-2.5M$_{\odot}$, their pulsations resulting from the varying ionization of helium. In less massive stars such as the Sun, convection transports mass and energy through the outer 30 per cent of the star and excites a rich spectrum of resonant acoustic modes. Based on the solar example, with no firm theoretical basis, models predict that the convective envelope in delta Sct stars extends only about 1 per cent of the radius, but with sufficient energy to excite solar-like oscillations. This was not observed before the Ke…
More than 40 years of ground-based photometric observations of the delta Sct star 4CVn revealed 18 independent oscillation frequencies, including radial as well as non-radial p-modes of low spherical degree l<=2. From 2008 to 2011, more than 2000 spectra were obtained at the 2.1-m Otto-Struve telescope at the McDonald Observatory. We present the analysis of the line-profile variations, based on the Fourier-parameter fit method, detected in the absorption lines of 4CVn, which carry clear signatures of the pulsations. From a non-sinusoidal, periodic variation of the radial velocities, we discove…
Observations of the pulsations of stars can be used to infer their interior structure and test theoretical models. The main sequence $γ$ Doradus (Dor) and $δ$ Scuti (Sct) stars with masses 1.2-2.5 $M_{\sun}$ are particularly useful for these studies. The $γ$ Dor stars pulsate in high-order $g$ modes with periods of order 1 day, driven by convective blocking at the base of their envelope convection zone. The $δ$ Sct stars pulsate in low-order $g$ and $p$ modes with periods of order 2 hours, driven by the $κ$ mechanism operating in the Heii ionization zone. Theory predicts an overlap region in t…
Among A-type main-sequence variables, pulsations of $δ$ Sct and $γ$ Dor variables are driven in the He II ionization zone, while H-ionization zone and strong magnetic fields seem to play roles in the excitation of high-order p-modes in rapidly oscillating Ap (roAp) stars. Pulsations in B-type variables, $β$ Cephei and slowly pulsating B (SPB) stars are excited by the $κ$-mechanism at the Fe-opacity bump at $T\approx 2\times10^5$K. In addition, the strange-mode instability seems responsible for the excitation of pulsations in luminous AB-supergiants ($α$ Cygni variables). We discuss excitation …
CoRoT ID 105733033 is an excellent example of hybrid pulsators as it shows g- and p-modes with almost similar amplitudes in two clearly distinct frequency domains. Classical Fourier analysis allows the dectection of frequencies with an amplitude as small as 0.1 mmag up to 50c/d. The frequency spectrum of CoRoT ID 105733033 clearly consists of two distinct ranges, which are typical of gamma Doradus and delta Scuti pulsation. Focus was placed on the identification of linear combinations and frequencies due to the coupling between gamma Doradus and delta Scuti modes. We detect 198 gamma Doradus t…
The primary target in the seismo-field of CoRoT, HD 49434, known to be a bona fide hybrid gamma Doradus/delta Scuti, shows excited intermediate-order g modes. Time-Dependent Convection models, however, predict a range in frequency that is stable to pulsations, between the simultaneously excited high-order g modes (gamma Dor) and low-order p and g modes (delta Sct). Furthermore, theoretical studies based on model computations of delta Sct stars suggest that stochastically excited modes are likely to be observed. A pertinent question would then be to ask: Might those observed intermediate-order …
The star HD 51844 was observed in CoRoT LRa02 as a Seismo target which turned out to be an SB2 system. The 117 days long light curve revealed delta Scuti pulsation in the range of 6 to 15 d^{-1} where four frequencies have amplitudes larger than 1.4 mmag and a rich frequency spectrum with amplitudes lower than 0.6 mmag. Additionally, the light curve exhibits a brightening event recurring every 33.5 days with a maximum of 3 mmag and a duration of about 5 days. Thus, this star can be considered as a heartbeat candidate. The radial velocities from spectroscopy confirmed an eccentric binary system…
We present the largest collection of delta Scuti-type stars in the Milky Way. Together with the recently published OGLE collection of delta Sct variables in the inner Galactic bulge, our sample consists of 24 488 objects distributed along the Milky Way plane, over galactic longitudes ranging from about -170 deg to +60 deg. The collection data include the I- and V-band time-series photometry collected since 1997 during the OGLE-II, OGLE-III, and OGLE-IV surveys. We show the on-sky distribution of delta Sct stars in the Galactic bulge and disk, discuss their period, luminosity and amplitude dist…
From TESS photometry, 493 mid- to late-B stars with high frequencies (Maia variables) have been identified. The distribution of projected rotational velocities shows that the rotation rates of Maia variables are no different from those of SPB stars. Moreover, many Maia stars pulsate with frequencies exceeding 60 c/d. Rapid rotation is ruled out as a possible factor in understanding the Maia variables. There is clearly a serious problem with current pulsational models. Not only are the models unable to account for the Maia stars, but they also fail to account for the fact that SPB and gamma Dor…
We present Kepler photometry and ground based spectroscopy of KIC 4544587, a short-period eccentric eclipsing binary system with self-excited pressure and gravity modes, tidally excited modes, tidally influenced p modes, and rapid apsidal motion of 182 y per cycle. The primary and secondary components of KIC 4544587 reside within the delta Scuti and gamma Dor instability region of the Hurtzsprung-Russell diagram, respectively. By applying the binary modelling software PHOEBE to prewhitened Kepler photometric data and radial velocity data obtained using the William Herschel Telescope and 4-m Ma…
The Kepler spacecraft is providing time series of photometric data with micromagnitude precision for hundreds of A-F type stars. We present a first general characterization of the pulsational behaviour of A-F type stars as observed in the Kepler light curves of a sample of 750 candidate A-F type stars. We propose three main groups to describe the observed variety in pulsating A-F type stars: gamma Dor, delta Sct, and hybrid stars. We assign 63% of our sample to one of the three groups, and identify the remaining part as rotationally modulated/active stars, binaries, stars of different spectral…
In our 2013 Astronomical Review article, we discussed the statistics of variability for 633 faint spectral type A-F stars observed by the Kepler spacecraft during Quarters 6-13. We found six stars that showed no variability with amplitude 20 ppm or greater in the range 0.2 to 24.4 cycles/day, but whose positions in the log g--Teff diagram place them in the delta Sct or gamma Dor pulsation instability regions established from pre-Kepler ground-based observations. Here we present results for 2137 additional stars observed during Quarters 14-17, and find 34 stars that lie within the instability r…
We concentrate on an asteroseismological study of HD 261711, a rather hot delta Scuti type pulsating member of the young open cluster NGC 2264 located at the blue border of the instability region. HD 261711 was discovered to be a pre-main sequence delta Scuti star using the time series photometry obtained by the MOST satellite in 2006. High-precision, time-series photometry of HD 261711 was obtained by the MOST and CoRoT satellites in 4 separate new observing runs that are put into context with the star's fundamental atmospheric parameters obtained from spectroscopy. With the new MOST data set…
The high accuracy of space data increased the number of the periodicities determined for pulsating variable stars, but the mode identification is still a critical point in the non-asymptotic regime. We use regularities in frequency spacings for identifying the pulsation modes of the recently discovered delta Sct star ID 102749568. In addition to analysing CoRoT light curves (15252 datapoints spanning 131 days), we obtained and analysed both spectroscopic and extended multi-colour photometric data. We applied standard tools (MUFRAN, Period04, SigSpec, and FAMIAS) for time-series analysis. A sat…
Based on regularities in rotational splittings, we seek possible multiplets for the observed frequencies of CoRoT 102749568. Twenty-one sets of multiplets are identified, including four sets of multiplets with $l=1$, nine sets of multiplets with $l=2$, and eight sets of multiplets with $l=3$. In particular, there are three complete triplets ($f_{10}$, $f_{12}$, $f_{14}$), ($f_{31}$, $f_{34}$, $f_{35}$), and ($f_{41}$, $f_{43}$, $f_{44}$). The rotational period of CoRoT 102749568 is estimated to be $1.34^{+0.04}_{-0.05}$ days. When doing model fittings, three $l=1$ modes ($f_{12}$, $f_{34}$, an…
We report the discovery of 19 variable stars and two blue-stragglers in the field of the open cluster NGC6866. Three of the variable stars we classify as delta Sct, two, as gamma Dor, four, as WUMa, two, as ellipsoidal variables, and one, as an eclipsing binary. Seven stars show irregular variability. Two of the pulsators, a delta Sct star NGC 6866-29 and a gamma Dor star NGC6866-21, are multiperiodic. From an analysis of proper motions, we conclude that the delta Sct stars, one of the gamma Dor stars and both blue-stragglers are very probable members of the cluster. The position on the color-…
Rich regular frequency patterns were found in the Fourier spectra of low-amplitude delta Scuti stars observed by CoRoT satellite (see Paparó et al. 2016a,b). The CoRoT observations are, however, influenced by the disturbing effect of the South Atlantic Anomaly. The effect is marginal for high amplitude variable stars but it could be critical in the case of low amplitude variables, especially if the frequency range of the intrinsic variation overlaps the interval of the instrumental frequencies. Some tests were carried out both on synthetic and real data for distinguishing technical and stars' …
Delta Scuti ($δ$ Sct) stars are intermediate-mass pulsators, whose intrinsic oscillations have been studied for decades. However, modelling their pulsations remains a real theoretical challenge, thereby even hampering the precise determination of global stellar parameters. In this work, we used space photometry observations of eclipsing binaries with a $δ$ Sct component to obtain reliable physical parameters and oscillation frequencies. Using that information, we derived an observational scaling relation between the stellar mean density and a frequency pattern in the oscillation spectrum. This…
The Praesepe cluster contains a number of Delta Sct and Gamma Dor pulsators. Asteroseismology of cluster stars is simplified by the common distance, age and stellar abundances. Since asteroseismology requires a large number of known frequencies, the small pulsation amplitudes of these stars require space satellite campaigns. The present study utilizes photometric MOST satellite measurements in order to determine the pulsation frequencies of two evolved (EP Cnc, BT Cnc) and two main-sequence (BS Cnc, HD 73872) Delta Sct stars in the Praesepe cluster. The frequency analysis of the 2008 and 2009 …
Among the known groups of pulsating stars, $δ$ Sct stars are one of the least understood. Theoretical models do not predict the oscillation frequencies that observations reveal. Complete asteroseismic studies are necessary to improve these models and better understand the internal structure of these targets. We study the $δ$ Sct star HD 41641 with the ultimate goal of understanding its oscillation pattern. The target was simultaneously observed by the CoRoT space telescope and the HARPS high-resolution spectrograph. The photometric data set was analyzed with the software package PERIOD04, whil…
Eclipsing binary systems with pulsating components allow the determination of several physical parameters of the stars, such as mass and radius, that, when combined with the pulsation properties, can be used to constrain the modeling of stellar interiors and evolution. Hereby, we present the results of the study of CoRoT 105906206, an eclipsing binary system with a pulsating component located in the CoRoT LRc02 field. The analysis of the CoRoT light curve was complemented by high-resolution spectra from the Sandiford at McDonald Observatory and FEROS at ESO spectrographs, which revealed a doub…
The presence of g- and p-modes allows testing stellar models from the core to the envelope. Moreover, binarity in an eclipsing system constrains the physical parameters of the pulsating star. CoRot ID 100866999 is a relatively large-amplitude hybrid gDor - dSct star with two clearly distinct frequency domains. The large number of detected frequencies allows a detailed study of the interaction between them. In addition, we can derive the fundamental parameters of both components from the study of the eclipsing light curve. After removing the eclipsing phases, we analyzed the data with the Perio…
Observations during the first long run (~150 days) in the exo-planet field of CoRoT increase the number of G-K giant stars for which solar-like oscillations are observed by a factor of 100. This opens the possibility to study the characteristics of their oscillations in a statistical sense. We aim to understand the statistical distribution of the frequencies of maximum oscillation power (nu_max) in red giants and to search for a possible correlation between nu_max and the large separation (delta_nu). The nu_max distribution shows a pronounced peak between 20 - 40 microHz. For about half of the…
We report the discovery of a new eclipsing EL CVn-type binary, consisting of a $δ$ Sct-type pulsator and a thermally bloated low-mass pre-He white dwarf (WD). Spectroscopy and time-series $BV$ photometry of V1224 Cas were carried out. The spectroscopy reveals a spectral type of A3 for the star. Light-curve modelling indicate that V1224 Cas is a short-period detached system containing a possible low-mass WD with an effective temperature of about 9516 K. Based on the effective temperature and the surface gravity of the A-type primary star from the spectroscopic results, the absolute parameters o…
We present a collection of 10 111 genuine delta Sct-type pulsating variable stars detected in the OGLE-IV Galactic bulge fields. In this sample, 9835 variables are new discoveries. For most of the stars photometric data cover the whole decade 2010-2019. We illustrate a huge variety of light curve shapes of delta Sct variables. Long-term observations have allowed us to spot objects with evident period, amplitude, and mean brightness variations. Our analysis indicates that about 28% of the stars are single-mode pulsators. Fourteen delta Sct stars show additional eclipsing or ellipsoidal binary m…
We present the results of a spectroscopic follow-up of various puzzling variable objects detected in the OGLE-III Galactic disk and bulge fields. The sample includes mainly short-period multi-mode pulsating stars that could not have been unambiguously classified as either delta Sct or beta Cep type stars based on photometric data only, also stars with irregular fluctuations mimicking cataclysmic variables and stars with dusty shells, and periodic variables displaying brightenings in their light curves that last for more than half of the period. The obtained low-resolution spectra show that all…
Asteroseismology is witnessing a revolution thanks to high-precise asteroseismic space data (MOST, CoRoT, Kepler, BRITE), and their large ground-based follow-up programs. Those instruments have provided an unprecedented large amount of information, which allows us to scrutinize its statistical properties in the quest for hidden relations among pulsational and/or physical observables. This approach might be particularly useful for stars whose pulsation content is difficult to interpret. This is the case of intermediate-mass classical pulsating stars (i.e. gamma Dor, delta Scuti, hybrids) for wh…
A sequence search method was developed to search regular frequency spacing in delta Scuti stars by visual inspection and algorithmic search. We searched for sequences of quasi-equally spaced frequencies, containing at least four members per sequence, in 90 delta Scuti stars observed by CoRoT. We found an unexpectedly large number of independent series of regular frequency spacing in 77 delta Scuti stars (from 1 to 8 sequences) in the non-asymptotic regime. We introduce the sequence search method presenting the sequences and echelle diagram of CoRoT 102675756 and the structure of the algorithmi…
Since CoRoT observations unveiled the very low amplitude modes that form a flat plateau in the power spectrum structure of delta Scuti stars, the nature of this phenomenon, including the possibility of spurious signals due to the light curve analysis, has been a matter of long-standing scientific debate. We contribute to this debate by finding the structural parameters of a sample of four delta Scuti stars, CID 546, CID 3619, CID 8669, and KIC 5892969, and looking for a possible relation between these stars' structural parameters and their power spectrum structure. For the purposes of characte…
A sequence search method was developed for searching for regular frequency spacing in delta Scuti stars by visual inspection and algorithmic search. The sample contains 90 delta Scuti stars observed by CoRoT. An example is given to represent the visual inspection. The algorithm (SSA) is described in detail. The data treatment of the CoRoT light curves, the criteria for frequency filtering and the spacings derived by two methods (three approaches: VI, SSA and FT) are given for each target. Echelle diagrams are presented for 77 targets, for which at least one sequence of regular spacing was iden…
We report the classification of 24 puzzling short-period variable stars located in OGLE-IV Galactic bulge fields. The stars are low-amplitude (<0.05 mag) multi-periodic objects with dominant periods between 22 and 54 min whose type could not have been unambiguously established based on photometry only. A low-resolution spectroscopic follow-up has shown that all the objects are main sequence A/F-type stars. Thus, all the variables are delta Sct-type pulsators. We have added them to the OGLE-IV Collection of Variable Stars.
We present the results of a search for pulsating stars in the 7.12 deg^2 OGLE-III Galactic disk area in the direction tangent to the Centaurus Arm. We report the identification of 20 Classical Cepheids, 45 RR Lyr type stars, 31 Long-Period Variables, such as Miras and Semi-Regular Variables, one pulsating white dwarf, and 58 very likely delta Sct type stars. Based on asteroseismic models constructed for one quadruple-mode and six triple-mode delta Sct type pulsators, we estimated masses, metallicities, ages, and distance moduli to these objects. The modeled stars have masses in the range 0.9-2…
We consider the high mode density reported in the delta Scuti star HD 50844 observed by CoRoT. Using simulations, we find that extracting frequencies down to a given false alarm probability by means of successive prewhitening leads to a gross over-estimate of the number of frequencies in a star. This is due to blending of the peaks in the periodogram due to the finite duration of the time series. Prewhitening is equivalent to adding a frequency to the data which is carefully chosen to interfere destructively with a given frequency in the data. Since the frequency extracted from a blended peak …
Gamma Doradus are F-type stars pulsating with high order g-modes. Their instability strip (IS) overlaps the red edge of the delta Scuti one. This observation has led to search for objects in this region of the HR diagram showing p and g-modes simultaneously. The existence of such hybrid pulsators has recently been confirmed (Handler 2009) and the number of candidates is increasing (Matthews 2007). From a theoretical point of view, non-adiabatic computations including a time-dependent treatment of convection (TDC) predict the existence of gamma Dor/delta Sct hybrid pulsators (Dupret et al. 2004…
High-resolution spectroscopy is a powerful tool to study the dynamical structure of pulsating stars atmosphere. We aim at comparing the line asymmetry and velocity of the two delta Sct stars rho Pup and DX Cet with previous spectroscopic data obtained on classical Cepheids and beta Cep stars. We obtained, analysed and discuss HARPS high-resolution spectra of rho Pup and DX Cet. We derived the same physical quantities as used in previous studies, which are the first-moment radial velocities and the bi-Gaussian spectral line asymmetries. The identification of f=7.098 (1/d) as a fundamental radia…
