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 present a new homogeneous sample of 32 spectroscopic binary orbits in the young (∼ 150 Myr) ma... more We present a new homogeneous sample of 32 spectroscopic binary orbits in the young (∼ 150 Myr) main-sequence open cluster M35. The distribution of orbital eccentricity vs. orbital period (e -log(P )) displays a distinct transition from eccentric to circular orbits at an orbital period of ∼ 10 days. The transition is due to tidal circularization of the closest binaries. The population of binary orbits in M35 provide a significantly improved constraint on the rate of tidal circularization at an age of 150 Myr. We propose a new and more robust diagnostic of the degree of tidal circularization in a binary population based on a functional fit to the e -log(P ) distribution. We call this new measure the tidal circularization period. The tidal circularization period of a binary population represents the orbital period at which a binary orbit with the most frequent initial orbital eccentricity circularizes (defined as e = 0.01) at the age of the population. We determine the tidal circularization period for M35 as well as for 7 additional binary populations spanning ages from the pre main-sequence (∼ 3 Myr) to late main-sequence (∼ 10 Gyr), and use Monte Carlo error analysis to determine the uncertainties on the derived circularization periods. We conclude that current theories of tidal circularization cannot account for the distribution of tidal circularization periods with population age.
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
A new sample of solar analogs and twin candidates have been constructed and studied, with particu... more A new sample of solar analogs and twin candidates have been constructed and studied, with particular attention to their light curves from NASA's Kepler mission. This letter aims to assess the evolutionary status, derive their rotation and ages and identify those solar analogs or solar twin candidates. We separate out the subgiants that compose a large fraction of the asteroseismic sample, and which show an increase in the average rotation period as the stars ascend the subgiant branch. The rotation periods of the dwarfs, ranging from 6 to 30 days, and averaged 19d, allow us to assess their individual evolutionary states on the main sequence, and to derive their ages using gyrochronology. These ages are found to be in agreement with a correlation coefficient of r = 0.79 with the independent asteroseismic ages, where available. As a result of this investigation, we are able to identify 34 stars as solar analogs and 22 of them as solar twin candidates.
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 present a new homogeneous sample of 32 spectroscopic binary orbits in the young (∼ 150 Myr) ma... more We present a new homogeneous sample of 32 spectroscopic binary orbits in the young (∼ 150 Myr) main-sequence open cluster M35. The distribution of orbital eccentricity vs. orbital period (e -log(P )) displays a distinct transition from eccentric to circular orbits at an orbital period of ∼ 10 days. The transition is due to tidal circularization of the closest binaries. The population of binary orbits in M35 provide a significantly improved constraint on the rate of tidal circularization at an age of 150 Myr. We propose a new and more robust diagnostic of the degree of tidal circularization in a binary population based on a functional fit to the e -log(P ) distribution. We call this new measure the tidal circularization period. The tidal circularization period of a binary population represents the orbital period at which a binary orbit with the most frequent initial orbital eccentricity circularizes (defined as e = 0.01) at the age of the population. We determine the tidal circularization period for M35 as well as for 7 additional binary populations spanning ages from the pre main-sequence (∼ 3 Myr) to late main-sequence (∼ 10 Gyr), and use Monte Carlo error analysis to determine the uncertainties on the derived circularization periods. We conclude that current theories of tidal circularization cannot account for the distribution of tidal circularization periods with population age.
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
A new sample of solar analogs and twin candidates have been constructed and studied, with particu... more A new sample of solar analogs and twin candidates have been constructed and studied, with particular attention to their light curves from NASA's Kepler mission. This letter aims to assess the evolutionary status, derive their rotation and ages and identify those solar analogs or solar twin candidates. We separate out the subgiants that compose a large fraction of the asteroseismic sample, and which show an increase in the average rotation period as the stars ascend the subgiant branch. The rotation periods of the dwarfs, ranging from 6 to 30 days, and averaged 19d, allow us to assess their individual evolutionary states on the main sequence, and to derive their ages using gyrochronology. These ages are found to be in agreement with a correlation coefficient of r = 0.79 with the independent asteroseismic ages, where available. As a result of this investigation, we are able to identify 34 stars as solar analogs and 22 of them as solar twin candidates.
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Papers by S. Meibom