The Kepler Mission is in the development phase with launch planned for 2008. The mission goal is ... more The Kepler Mission is in the development phase with launch planned for 2008. The mission goal is to reliably detect a significant number of Earth-size and smaller planets in the habitable zone of solar-like stars. (see W. Borucki, et al, this meeting.) The mission design allows for exploring the diversity of planetary sizes and orbital periods for a wide variety
We have analyzed GHRS data of eight CTTS and one WTTS. The GHRS data consists of spectral ranges ... more We have analyzed GHRS data of eight CTTS and one WTTS. The GHRS data consists of spectral ranges 40Å wide centered on 1345, 1400, 1497, 1550, and 1900Å. These UV spectra show strong Si IV, and C IV emission, and large quantities of sharp (∼ 40 km s −1) H 2 lines. All the H 2 lines belong to the Lyman band and all the observed lines are single peaked and optically thin. The averages of all the H 2 lines centroids for each star are negative which may indicate that they come from an outflow. We interpret the emission in H 2 as being due to fluorescence, mostly by H Lyα and identify seven excitation routes within 4Å of that line. We obtain column densities (10 12 to 10 15 cm −2) and optical depths (∼ 1 or less) for each exciting transition. We conclude that the populations are far from being in thermal equilibrium. We do not observe any lines excited from the far blue wing of H Lyα , which implies that the molecular features are excited by an absorbed profile. Si IV and C IV (corrected for H 2 emission) have widths of ∼ 200 km s −1 , and an array of centroids (blueshifted lines, centered, redshifted). These characteristics are difficult to understand in the context of current models of the accretion shock. For DR Tau we observe transient strong blueshifted emission, perhaps the a result of reconnection events in the magnetosphere. We also see evidence of multiple emission regions for the hot lines. While C IV is optically thin in most stars in our sample, Si IV is not. However, C IV is a good predictor of Si IV and H 2 emission. We conclude that most of the flux in the hot lines may
Light curves of solar-like stars are known to show highly irregular variability. As a consequence... more Light curves of solar-like stars are known to show highly irregular variability. As a consequence, standard frequency analysis methods often fail to detect the correct rotation period. Recently, Shapiro et al. (2020) showed that the periods of such stars could still be measured by considering the Gradient of the Power Spectrum (GPS) instead of the power spectrum itself. In this study, the GPS method is applied to model light curves of solar-like stars covering all possible inclination angles and a large range of metallicities and observational noise levels. The model parameters are chosen such that they resemble those of many stars in the Kepler field. We show that the GPS method is able to detect the correct rotation period in ≈ 40% of all considered cases, which is more than ten times higher than the detection rate of standard techniques. Thus, we conclude that the GPS method is ideally suited to measure periods of those Kepler stars lacking such a measurement so far. We also show that the GPS method is significantly superior to auto-correlation methods when starspot lifetimes are shorter than a few rotation periods. GPS begins to yield rotation periods that are too short when dominant spot lifetimes are shorter than one rotation period. We conclude that new methods are generally needed to reliably detect rotation periods from sufficiently aperiodic time series-these periods will otherwise remain undetected.
We present a refined analysis of 15,038 Kepler main sequence light curves to determine the stella... more We present a refined analysis of 15,038 Kepler main sequence light curves to determine the stellar rotation periods. The initial period estimates come from an autocorrelation function, as has been done before. We then measure the duration of every intensity dip in the light curve, expressed as fractions of the initial rotation period estimate. These dip duration distributions are subdivided into several regions whose relation to each other helps determine which harmonic of the initial rotation period is most physically plausible. We compare our final rotation periods to those from McQuillan et al. (2014) and find that the great majority agree, but about 10% of their periods are doubtful (usually twice as long as is most plausible). We are still refining our method, and will later extend it to more stars to substantially increase the sample of reliable stellar rotation periods.
The IUE data on 36 late type close binary stars are presented. It is shown that the chromospheric... more The IUE data on 36 late type close binary stars are presented. It is shown that the chromospheric and TR line fluxes increase with decreasing stellar rotation period, though not as rapidly as does the X-ray flux. There is an increasing dependence upon rotation with increasing line temperature. The data are consistent with the hypothesis that there exists a critical rotation rate, which depends on temperature, below which the emission flux is independent of rotation and above which it increases linearly with increasing angular velocity omega.
The Kepler Mission is in the development phase with launch planned for 2008. The mission goal is ... more The Kepler Mission is in the development phase with launch planned for 2008. The mission goal is to reliably detect a significant number of Earth-size and smaller planets in the habitable zone of solar-like stars. (see W. Borucki, et al, this meeting.) The mission design allows for exploring the diversity of planetary sizes and orbital periods for a wide variety
We have analyzed GHRS data of eight CTTS and one WTTS. The GHRS data consists of spectral ranges ... more We have analyzed GHRS data of eight CTTS and one WTTS. The GHRS data consists of spectral ranges 40Å wide centered on 1345, 1400, 1497, 1550, and 1900Å. These UV spectra show strong Si IV, and C IV emission, and large quantities of sharp (∼ 40 km s −1) H 2 lines. All the H 2 lines belong to the Lyman band and all the observed lines are single peaked and optically thin. The averages of all the H 2 lines centroids for each star are negative which may indicate that they come from an outflow. We interpret the emission in H 2 as being due to fluorescence, mostly by H Lyα and identify seven excitation routes within 4Å of that line. We obtain column densities (10 12 to 10 15 cm −2) and optical depths (∼ 1 or less) for each exciting transition. We conclude that the populations are far from being in thermal equilibrium. We do not observe any lines excited from the far blue wing of H Lyα , which implies that the molecular features are excited by an absorbed profile. Si IV and C IV (corrected for H 2 emission) have widths of ∼ 200 km s −1 , and an array of centroids (blueshifted lines, centered, redshifted). These characteristics are difficult to understand in the context of current models of the accretion shock. For DR Tau we observe transient strong blueshifted emission, perhaps the a result of reconnection events in the magnetosphere. We also see evidence of multiple emission regions for the hot lines. While C IV is optically thin in most stars in our sample, Si IV is not. However, C IV is a good predictor of Si IV and H 2 emission. We conclude that most of the flux in the hot lines may
Light curves of solar-like stars are known to show highly irregular variability. As a consequence... more Light curves of solar-like stars are known to show highly irregular variability. As a consequence, standard frequency analysis methods often fail to detect the correct rotation period. Recently, Shapiro et al. (2020) showed that the periods of such stars could still be measured by considering the Gradient of the Power Spectrum (GPS) instead of the power spectrum itself. In this study, the GPS method is applied to model light curves of solar-like stars covering all possible inclination angles and a large range of metallicities and observational noise levels. The model parameters are chosen such that they resemble those of many stars in the Kepler field. We show that the GPS method is able to detect the correct rotation period in ≈ 40% of all considered cases, which is more than ten times higher than the detection rate of standard techniques. Thus, we conclude that the GPS method is ideally suited to measure periods of those Kepler stars lacking such a measurement so far. We also show that the GPS method is significantly superior to auto-correlation methods when starspot lifetimes are shorter than a few rotation periods. GPS begins to yield rotation periods that are too short when dominant spot lifetimes are shorter than one rotation period. We conclude that new methods are generally needed to reliably detect rotation periods from sufficiently aperiodic time series-these periods will otherwise remain undetected.
We present a refined analysis of 15,038 Kepler main sequence light curves to determine the stella... more We present a refined analysis of 15,038 Kepler main sequence light curves to determine the stellar rotation periods. The initial period estimates come from an autocorrelation function, as has been done before. We then measure the duration of every intensity dip in the light curve, expressed as fractions of the initial rotation period estimate. These dip duration distributions are subdivided into several regions whose relation to each other helps determine which harmonic of the initial rotation period is most physically plausible. We compare our final rotation periods to those from McQuillan et al. (2014) and find that the great majority agree, but about 10% of their periods are doubtful (usually twice as long as is most plausible). We are still refining our method, and will later extend it to more stars to substantially increase the sample of reliable stellar rotation periods.
The IUE data on 36 late type close binary stars are presented. It is shown that the chromospheric... more The IUE data on 36 late type close binary stars are presented. It is shown that the chromospheric and TR line fluxes increase with decreasing stellar rotation period, though not as rapidly as does the X-ray flux. There is an increasing dependence upon rotation with increasing line temperature. The data are consistent with the hypothesis that there exists a critical rotation rate, which depends on temperature, below which the emission flux is independent of rotation and above which it increases linearly with increasing angular velocity omega.
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Papers by Gibor Basri