# Browsing by Subject "stars: variables: delta scuti"

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Item Discovery Of Binarity, Spectroscopic Frequency Analysis, And Mode Identification Of The Delta Scuti Star 4 CVn(2014-10) Schmid, V. S.; Themessl, N.; Breger, M.; Degroote, P.; Aerts, C.; Beck, P. G.; Tkachenko, A.; Van Reeth, T.; Bloemen, S.; Debosscher, J.; Castanheira, B. G.; McArthur, B. E.; Papics, P. I.; Fritz, V.; Falcon, R. E.; Castanheira, B. G.; McArthur, B. E.; Falcon, R. E.Show more More than 40 years of ground-based photometric observations of the delta Sct star 4 CVn has 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 2.1m 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 4 CVn, which carry clear signatures of the pulsations. From a non-sinusoidal, periodic variation of the radial velocities, we discover that 4 CVn is an eccentric binary system with an orbital period P-orb = 124.44 +/- 0.03 d and an eccentricity e = 0.311 +/- 0.003. We detect 20 oscillation frequencies, 9 of which previously unseen in photometric data; attempt mode identification for the two dominant modes, f(1) = 7.3764 d(-1) and f(2) = 5.8496 d(-1); and determine the prograde or retrograde nature of 7 of the modes. The projected rotational velocity of the star, v(eq) sin i similar or equal to 106.7 km s(-1), translates to a rotation rate of v(eq)/v(crit) >= 33%. This relatively high rotation rate hampers unique mode identification, since higher order effects of rotation are not included in the current methodology. We conclude that, in order to achieve unambiguous mode identification for 4CVn, a complete description of rotation and the use of blended lines have to be included in mode-identification techniques.Show more Item Evidence Of Resonant Mode Coupling And The Relationship Between Low And High Frequencies In A Rapidly Rotating A Star(2014-03) Breger, Michel; Montgomery, Michael H.; Breger, Michel; Montgomery, Michael H.Show more In the theory of resonant mode coupling, the parent and child modes are directly related in frequency and phase. The oscillations present in the fast rotating delta Sct star KIC 8054146 allow us to test the most general and generic aspects of such a theory. The only direct way to separate the parent and coupled (child) modes is to examine the correlations in amplitude variability between the different frequencies. For the dominant family of related frequencies, only a single mode and a triplet are the origins of nine dominant frequency peaks ranging from 2.93 to 66.30 cycles day(-1) (as well as dozens of small-amplitude combination modes and a predicted and detected third high-frequency triplet). The mode-coupling model correctly predicts the large amplitude variations of the coupled modes as a product of the amplitudes of the parent modes, while the phase changes are also correctly modeled. This differs from the behavior of " (n)ormal" combination frequencies in that the amplitudes are three orders of magnitude larger and may exceed even the amplitudes of the parent modes. We show that two dominant low frequencies at 5.86 and 2.93 cycles day(-1) in the gravity-mode region are not harmonics of each other, and their properties follow those of the almost equidistant high-frequency triplet. We note that the previously puzzling situation of finding two strong peaks in the low-frequency region related by nearly a factor of two in frequency has been seen in other delta Sct stars as well.Show more Item The Kepler Characterization Of The Variability Among A- And F-Type Stars I. General Overview(2011-10) Uytterhoeven, K.; Moya, A.; Grigahcene, A.; Guzik, J. A.; Gutierrez-Soto, J.; Smalley, B.; Handler, G.; Balona, L. A.; Niemczura, E.; Machado, L. F.; Benatti, S.; Chapellier, E.; Tkachenko, A.; Szabo, R.; Suarez, J. C.; Ripepi, V.; Pascual, J.; Mathias, P.; Martin-Ruiz, S.; Lehmann, H.; Jackiewicz, J.; Hekker, S.; Gruberbauer, M.; Garcia, R. A.; Dumusque, X.; Diaz-Fraile, D.; Bradley, P.; Antoci, V.; Roth, M.; Leroy, B.; Murphy, S. J.; De Cat, P.; Cuypers, J.; Kjeldsen, H.; Christensen-Dalsgaard, J.; Breger, M.; Pigulski, A.; Kiss, L. L.; Still, M.; Thompson, S. E.; Van Cleve, J.; Breger, MShow more Context. The Kepler spacecraft is providing time series of photometric data with micromagnitude precision for hundreds of A-F type stars. Aims. 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, and observationally investigate the relation between gamma Doradus (gamma Dor), delta Scuti (delta Sct), and hybrid stars. Methods. We compile a database of physical parameters for the sample stars from the literature and new ground-based observations. We analyse the Kepler light curve of each star and extract the pulsational frequencies using different frequency analysis methods. We construct two new observables, >energy> and >efficiency>, related to the driving energy of the pulsation mode and the convective efficiency of the outer convective zone, respectively. Results. 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 type, or stars that show no clear periodic variability. 23% of the stars (171 stars) are hybrid stars, which is a much higher fraction than what has been observed before. We characterize for the first time a large number of A-F type stars (475 stars) in terms of number of detected frequencies, frequency range, and typical pulsation amplitudes. The majority of hybrid stars show frequencies with all kinds of periodicities within the gamma Dor and delta Sct range, also between 5 and 10 d(-1), which is a challenge for the current models. We find indications for the existence of delta Sct and gamma Dor stars beyond the edges of the current observational instability strips. The hybrid stars occupy the entire region within the delta Sct and gamma Dor instability strips and beyond. Non-variable stars seem to exist within the instability strips. The location of gamma Dor and delta Sct classes in the (T-eff, log g)-diagram has been extended. We investigate two newly constructed variables, >efficiency> and >energy>, as a means to explore the relation between gamma Dor and delta Sct stars. Conclusions. Our results suggest a revision of the current observational instability strips of delta Sct and gamma Dor stars and imply an investigation of pulsation mechanisms to supplement the kappa mechanism and convective blocking effect to drive hybrid pulsations. Accurate physical parameters for all stars are needed to confirm these findings.Show more Item Refining The Asteroseismic Model For The Young Delta Scuti Star HD 144277 Using HARPS Spectroscopy(2014-07) Zwintz, K.; Ryabchikova, T.; Lenz, P.; Pamyatnykh, A. A.; Fossati, L.; Sitnova, T.; Breger, M.; Poretti, E.; Rainer, M.; Hareter, M.; Mantegazza, L.; Breger, M.Show more Context. HD 144277 was previously discovered by Microvariability and Oscillations of Stars (MOST) space photometry to be a young and hot delta Scuti star showing regular groups of pulsation frequencies. The first asteroseismic models required lower than solar metallicity to fit the observed frequency range based on a purely photometric analysis. Aims. The aim of the present paper is to determine, by means of high-resolution spectroscopy, fundamental stellar parameters required for the asteroseismic model of HD 144277, and subsequently, to refine it. Methods. High-resolution, high signal-to-noise spectroscopic data obtained with the HARPS spectrograph were used to determine the fundamental parameters and chemical abundances of HD 144277. These values were put into context alongside the results from asteroseismic models. Results. The effective temperature, T-eff, of HD 144277 was determined as 8640(-100)(+300) K, log g is 4.14 +/- 0.15 and the projected rotational velocity, v sin i, is 62.0 +/- 2.0 km s(-1). As the v sin i value is significantly larger than previously assumed, we refined the first asteroseimic model accordingly. The overall metallicity Z was determined to be 0.011 where the light elements He, C, O, Na, and S show solar chemical composition, but the heavier elements are significantly underabundant. In addition, the radius of HD 144277 was determined to be 1.55 +/- 0.65 R-circle dot from spectral energy distribution fitting, based on photometric data taken from the literature. Conclusions. From the spectroscopic observations, we could confirm our previous assumption from asteroseismic models that HD 144277 has less than solar metallicity. The fundamental parameters derived from asteroseismology, T-eff, log g, L/L-circle dot and R/R-circle dot agree within one sigma to the values found from spectroscopic analysis. As the v sin i value is significantly higher than assumed in the first analysis, near-degeneracies and rotational mode coupling were taken into account in the new models. These suggest that HD 144277 has an equatorial rotational velocity of about 80 km s(-1) and is seen equator-on. The observed frequencies are identified as prograde modes.Show more Item Regular Frequency Patterns In The Young Delta Scuti Star HD 261711 Observed By The CoRoT And MOST Satellites(2013-04) Zwintz, K.; Fossati, L.; Guenther, D. B.; Ryabchikova, T.; Baglin, A.; Themessl, N.; Barnes, T. G.; Matthews, J. M.; Auvergne, M.; Bohlender, D.; Chaintreuil, S.; Kuschnig, R.; Moffat, A. F. J.; Rowe, J. F.; Rucinski, S. M.; Sasselov, D.; Weiss, W. W.; Barnes, T. G.Show more Context. The internal structure of pre-main-sequence (PMS) stars is poorly constrained at present. This could change significantly through high-quality asteroseismological observations of a sample of such stars. Aims. We concentrate on an asteroseismological study of HD261711, a rather hot delta Scuti-type pulsating member of the young open cluster NGC 2264 located at the blue border of the instability region. HD261711 was discovered to be a PMS delta Scuti star using the time series photometry obtained by the MOST satellite in 2006. Methods. High-precision, time-series photometry of HD261711 was obtained by the MOST and CoRoT satellites in four separate new observing runs that are put into context with the star's fundamental atmospheric parameters obtained from spectroscopy. Frequency Analysis was performed using Period04. The spectral analysis was performed using equivalent widths and spectral synthesis. Results. With the new MOST data set from 2011/12 and the two CoRoT light curves from 2008 and 2011/12, the delta Scuti variability was confirmed and regular groups of frequencies were discovered. The two pulsation frequencies identified in the data from the first MOST observing run in 2006 are confirmed and 23 new delta Scuti-type frequencies were discovered using the CoRoT data. Weighted average frequencies for each group were determined and are related to l = 0 and l = 1 p-modes. Evidence for amplitude modulation of the frequencies in two groups is seen. The effective temperature (T-eff) was derived to be 8600 +/- 200K, log g is 4.1 +/- 0.2, and the projected rotational velocity (upsilon sin i) is 53 +/- 1 km s(-1). Using our T-eff value and the radius of 1.8 +/- 0.5 R-circle dot derived from spectral energy distribution (SED) fitting, we get a luminosity log L/L-circle dot of 1.20 +/- 0.14 which agrees well to the seismologically determined values of 1.65 R-circle dot and, hence, a log L/L-circle dot of 1.13. The radial velocity of 14 +/- 2 km s(-1) we derived for HD261711, confirms the star's membership to NGC 2264. Conclusions. Our asteroseismic models suggest that HD261711 is a delta Scuti-type star close to the zero-age main sequence (ZAMS) with a mass of 1.8 to 1.9 M-circle dot. With an age of about 10 million years derived from asteroseismology, the star is either a young ZAMS star or a late PMS star just before the onset of hydrogen-core burning. The observed splittings about the l = 0 and 1 parent modes may be an artifact of the Fourier derived spectrum of frequencies with varying amplitudes.Show more Item Regular Frequency Patterns In The Young Delta Scuti Star HD 261711 Observed By The CoRoT And MOST Satellites(2013-04) Zwintz, K.; Fossati, L.; Guenther, D. B.; Ryabchikova, T.; Baglin, A.; Themessl, N.; Barnes, T. G.; Matthews, J. M.; Auvergne, M.; Bohlender, D.; Chaintreuil, S.; Kuschnig, R.; Moffat, A. F. J.; Rowe, J. F.; Rucinski, S. M.; Sasselov, D.; Weiss, W. W.; Barnes, T. G.Show more Context. The internal structure of pre-main-sequence (PMS) stars is poorly constrained at present. This could change significantly through high-quality asteroseismological observations of a sample of such stars. Aims. We concentrate on an asteroseismological study of HD261711, a rather hot delta Scuti-type pulsating member of the young open cluster NGC 2264 located at the blue border of the instability region. HD261711 was discovered to be a PMS delta Scuti star using the time series photometry obtained by the MOST satellite in 2006. Methods. High-precision, time-series photometry of HD261711 was obtained by the MOST and CoRoT satellites in four separate new observing runs that are put into context with the star's fundamental atmospheric parameters obtained from spectroscopy. Frequency Analysis was performed using Period04. The spectral analysis was performed using equivalent widths and spectral synthesis. Results. With the new MOST data set from 2011/12 and the two CoRoT light curves from 2008 and 2011/12, the delta Scuti variability was confirmed and regular groups of frequencies were discovered. The two pulsation frequencies identified in the data from the first MOST observing run in 2006 are confirmed and 23 new delta Scuti-type frequencies were discovered using the CoRoT data. Weighted average frequencies for each group were determined and are related to l = 0 and l = 1 p-modes. Evidence for amplitude modulation of the frequencies in two groups is seen. The effective temperature (T-eff) was derived to be 8600 +/- 200K, log g is 4.1 +/- 0.2, and the projected rotational velocity (upsilon sin i) is 53 +/- 1 km s(-1). Using our T-eff value and the radius of 1.8 +/- 0.5 R-circle dot derived from spectral energy distribution (SED) fitting, we get a luminosity log L/L-circle dot of 1.20 +/- 0.14 which agrees well to the seismologically determined values of 1.65 R-circle dot and, hence, a log L/L-circle dot of 1.13. The radial velocity of 14 +/- 2 km s(-1) we derived for HD261711, confirms the star's membership to NGC 2264. Conclusions. Our asteroseismic models suggest that HD261711 is a delta Scuti-type star close to the zero-age main sequence (ZAMS) with a mass of 1.8 to 1.9 M-circle dot. With an age of about 10 million years derived from asteroseismology, the star is either a young ZAMS star or a late PMS star just before the onset of hydrogen-core burning. The observed splittings about the l = 0 and 1 parent modes may be an artifact of the Fourier derived spectrum of frequencies with varying amplitudes.Show more Item Regular Frequency Patterns In The Young Delta Scuti Star HD 261711 Observed By The CoRoT And MOST Satellites(2013-04) Zwintz, K.; Fossati, L.; Guenther, D. B.; Ryabchikova, T.; Baglin, A.; Themessl, N.; Barnes, T. G.; Matthews, J. M.; Auvergne, M.; Bohlender, D.; Chaintreuil, S.; Kuschnig, R.; Moffat, A. F. J.; Rowe, J. F.; Rucinski, S. M.; Sasselov, D.; Weiss, W. W.; Barnes, T. G.Show more Context. The internal structure of pre-main-sequence (PMS) stars is poorly constrained at present. This could change significantly through high-quality asteroseismological observations of a sample of such stars. Aims. We concentrate on an asteroseismological study of HD261711, a rather hot delta Scuti-type pulsating member of the young open cluster NGC 2264 located at the blue border of the instability region. HD261711 was discovered to be a PMS delta Scuti star using the time series photometry obtained by the MOST satellite in 2006. Methods. High-precision, time-series photometry of HD261711 was obtained by the MOST and CoRoT satellites in four separate new observing runs that are put into context with the star's fundamental atmospheric parameters obtained from spectroscopy. Frequency Analysis was performed using Period04. The spectral analysis was performed using equivalent widths and spectral synthesis. Results. With the new MOST data set from 2011/12 and the two CoRoT light curves from 2008 and 2011/12, the delta Scuti variability was confirmed and regular groups of frequencies were discovered. The two pulsation frequencies identified in the data from the first MOST observing run in 2006 are confirmed and 23 new delta Scuti-type frequencies were discovered using the CoRoT data. Weighted average frequencies for each group were determined and are related to l = 0 and l = 1 p-modes. Evidence for amplitude modulation of the frequencies in two groups is seen. The effective temperature (T-eff) was derived to be 8600 +/- 200K, log g is 4.1 +/- 0.2, and the projected rotational velocity (upsilon sin i) is 53 +/- 1 km s(-1). Using our T-eff value and the radius of 1.8 +/- 0.5 R-circle dot derived from spectral energy distribution (SED) fitting, we get a luminosity log L/L-circle dot of 1.20 +/- 0.14 which agrees well to the seismologically determined values of 1.65 R-circle dot and, hence, a log L/L-circle dot of 1.13. The radial velocity of 14 +/- 2 km s(-1) we derived for HD261711, confirms the star's membership to NGC 2264. Conclusions. Our asteroseismic models suggest that HD261711 is a delta Scuti-type star close to the zero-age main sequence (ZAMS) with a mass of 1.8 to 1.9 M-circle dot. With an age of about 10 million years derived from asteroseismology, the star is either a young ZAMS star or a late PMS star just before the onset of hydrogen-core burning. The observed splittings about the l = 0 and 1 parent modes may be an artifact of the Fourier derived spectrum of frequencies with varying amplitudes.Show more Item Relationship Between Low And High Frequencies In Delta Scuti Stars: Photometric Kepler And Spectroscopic Analyses Of The Rapid Rotator KIC 8054146(2012-11) Breger, Michel; Fossati, L.; Balona, L.; Kurtz, D. W.; Robertson, Paul; Bohlender, D.; Lenz, P.; Mueller, I.; Lueftinger, T.; Clarke, B. D.; Hall, Jennifer R.; Ibrahim, Khadeejah A.; Breger, Michel; P. RobertsonShow more Two years of Kepler data of KIC 8054146 (delta Sct/gamma Dor hybrid) revealed 349 statistically significant frequencies between 0.54 and 191.36 cycles day(-1) (6.3 mu Hz to 2.21 mHz). The 117 low frequencies cluster in specific frequency bands, but do not show the equidistant period spacings predicted for gravity modes of successive radial order, n, and reported for at least one other hybrid pulsator. The four dominant low frequencies in the 2.8-3.0 cycles day(-1) (32-35 mu Hz) range show strong amplitude variability with timescales of months and years. These four low frequencies also determine the spacing of the higher frequencies in and beyond the delta Sct pressure-mode frequency domain. In fact, most of the higher frequencies belong to one of three families with spacings linked to a specific dominant low frequency. In the Fourier spectrum, these family regularities show up as triplets, high-frequency sequences with absolutely equidistant frequency spacings, side lobes (amplitude modulations), and other regularities in frequency spacings. Furthermore, within two families the amplitude variations between the low and high frequencies are related. We conclude that the low frequencies (gravity modes, rotation) and observed high frequencies (mostly pressure modes) are physically connected. This unusual behavior may be related to the very rapid rotation of the star: from a combination of high-and low-resolution spectroscopy we determined that KIC 8054146 is a very fast rotator (upsilon sin i = 300 +/- 20 km s(-1)) with an effective temperature of 7600 +/- 200 K and a surface gravity log g of 3.9 +/- 0.3. Several astrophysical ideas explaining the origin of the relationship between the low and high frequencies are explored.Show more