Recent measurements of rotation periods ( ) in the benchmark open clusters Praesepe (670 Myr), NG... more Recent measurements of rotation periods ( ) in the benchmark open clusters Praesepe (670 Myr), NGC 6811 (1 Gyr), and NGC 752 (1.4 Gyr) demonstrate that, after converging onto a tight sequence of slowly rotating stars in mass–period space, stars temporarily stop spinning down. These data also show that the duration of this epoch of stalled spin-down increases toward lower masses. To determine when stalled stars resume spinning down, we use data from the K2 mission and the Palomar Transient Factory to measure for 58 dwarf members of the 2.7 Gyr old cluster Ruprecht 147, 39 of which satisfy our criteria designed to remove short-period or near-equal-mass binaries. Combined with the Kepler data for the approximately coeval cluster NGC 6819 (30 stars with M ⋆ > 0.85 ), our new measurements more than double the number of ≈2.5 Gyr benchmark rotators and extend this sample down to ≈0.55 . The slowly rotating sequence for this joint sample appears relatively flat (22 ± 2 days) compared to...
The ages of the most common stars--low-mass (cool) stars like the Sun, and smaller--are difficult... more The ages of the most common stars--low-mass (cool) stars like the Sun, and smaller--are difficult to derive because traditional dating methods use stellar properties that either change little as the stars age or are hard to measure. The rotation rates of all cool stars decrease substantially with time as the stars steadily lose their angular momenta. If properly calibrated, rotation therefore can act as a reliable determinant of their ages based on the method of gyrochronology. To calibrate gyrochronology, the relationship between rotation period and age must be determined for cool stars of different masses, which is best accomplished with rotation period measurements for stars in clusters with well-known ages. Hitherto, such measurements have been possible only in clusters with ages of less than about one billion years, and gyrochronology ages for older stars have been inferred from model predictions. Here we report rotation period measurements for 30 cool stars in the 2.5-billion-...
We present a study of spectra obtained with the Hectchelle spectrograph on the MMT for late-type ... more We present a study of spectra obtained with the Hectchelle spectrograph on the MMT for late-type stars in the open clusters M67 and NGC6811. We have tested and further developed codes for reducing and classifying Hectochelle spectra. We determine the effective temperature, surface gravity, metallicity, and projected rotational velocity from Hectochelle spectra via cross-correlation with synthetic template spectra. From analysis
We report magnetic field measurements for Kappa1 Cet, a proxy of the young Sun when life arose on... more We report magnetic field measurements for Kappa1 Cet, a proxy of the young Sun when life arose on Earth. We carry out an analysis of the magnetic properties determined from spectropolarimetric observations and reconstruct its large-scale surface magnetic field to derive the magnetic environment, stellar winds and particle flux permeating the interplanetary medium around Kappa1 Cet. Our results show a closer magnetosphere and mass-loss rate of Mdot = 9.7 x 10^-13 Msol/yr, i.e., a factor 50 times larger than the current solar wind mass-loss rate, resulting in a larger interaction via space weather disturbances between the stellar wind and a hypothetical young-Earth analogue, potentially affecting the planet's habitability. Interaction of the wind from the young Sun with the planetary ancient magnetic field may have affected the young Earth and its life conditions
Recent measurements of rotation periods ( ) in the benchmark open clusters Praesepe (670 Myr), NG... more Recent measurements of rotation periods ( ) in the benchmark open clusters Praesepe (670 Myr), NGC 6811 (1 Gyr), and NGC 752 (1.4 Gyr) demonstrate that, after converging onto a tight sequence of slowly rotating stars in mass–period space, stars temporarily stop spinning down. These data also show that the duration of this epoch of stalled spin-down increases toward lower masses. To determine when stalled stars resume spinning down, we use data from the K2 mission and the Palomar Transient Factory to measure for 58 dwarf members of the 2.7 Gyr old cluster Ruprecht 147, 39 of which satisfy our criteria designed to remove short-period or near-equal-mass binaries. Combined with the Kepler data for the approximately coeval cluster NGC 6819 (30 stars with M ⋆ > 0.85 ), our new measurements more than double the number of ≈2.5 Gyr benchmark rotators and extend this sample down to ≈0.55 . The slowly rotating sequence for this joint sample appears relatively flat (22 ± 2 days) compared to...
The ages of the most common stars--low-mass (cool) stars like the Sun, and smaller--are difficult... more The ages of the most common stars--low-mass (cool) stars like the Sun, and smaller--are difficult to derive because traditional dating methods use stellar properties that either change little as the stars age or are hard to measure. The rotation rates of all cool stars decrease substantially with time as the stars steadily lose their angular momenta. If properly calibrated, rotation therefore can act as a reliable determinant of their ages based on the method of gyrochronology. To calibrate gyrochronology, the relationship between rotation period and age must be determined for cool stars of different masses, which is best accomplished with rotation period measurements for stars in clusters with well-known ages. Hitherto, such measurements have been possible only in clusters with ages of less than about one billion years, and gyrochronology ages for older stars have been inferred from model predictions. Here we report rotation period measurements for 30 cool stars in the 2.5-billion-...
We present a study of spectra obtained with the Hectchelle spectrograph on the MMT for late-type ... more We present a study of spectra obtained with the Hectchelle spectrograph on the MMT for late-type stars in the open clusters M67 and NGC6811. We have tested and further developed codes for reducing and classifying Hectochelle spectra. We determine the effective temperature, surface gravity, metallicity, and projected rotational velocity from Hectochelle spectra via cross-correlation with synthetic template spectra. From analysis
We report magnetic field measurements for Kappa1 Cet, a proxy of the young Sun when life arose on... more We report magnetic field measurements for Kappa1 Cet, a proxy of the young Sun when life arose on Earth. We carry out an analysis of the magnetic properties determined from spectropolarimetric observations and reconstruct its large-scale surface magnetic field to derive the magnetic environment, stellar winds and particle flux permeating the interplanetary medium around Kappa1 Cet. Our results show a closer magnetosphere and mass-loss rate of Mdot = 9.7 x 10^-13 Msol/yr, i.e., a factor 50 times larger than the current solar wind mass-loss rate, resulting in a larger interaction via space weather disturbances between the stellar wind and a hypothetical young-Earth analogue, potentially affecting the planet's habitability. Interaction of the wind from the young Sun with the planetary ancient magnetic field may have affected the young Earth and its life conditions
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