# Browsing by Subject "praesepe cluster"

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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