scholarly journals On the origin of the bimodal rotational velocity distribution in stellar clusters: rotation on the pre-main sequence

2020 ◽  
Vol 495 (2) ◽  
pp. 1978-1983
Author(s):  
Nate Bastian ◽  
Sebastian Kamann ◽  
Louis Amard ◽  
Corinne Charbonnel ◽  
Lionel Haemmerlé ◽  
...  
Keyword(s):  
Main Sequence ◽  
Rotational Velocity ◽  
Open Clusters ◽  
Observational Constraints ◽  
Stellar Clusters ◽  
Period Distribution ◽  
Low Mass ◽  
Rotational Distribution ◽  
Set Up ◽  
Pms Stars

ABSTRACT We address the origin of the observed bimodal rotational distribution of stars in massive young and intermediate age stellar clusters. This bimodality is seen as split main sequences at young ages and also has been recently directly observed in the Vsini distribution of stars within massive young and intermediate age clusters. Previous models have invoked binary interactions as the origin of this bimodality, although these models are unable to reproduce all of the observational constraints on the problem. Here, we suggest that such a bimodal rotational distribution is set-up early within a cluster’s life, i.e. within the first few Myr. Observations show that the period distribution of low-mass ($\lesssim\! 2 \, \mathrm{M}_\odot$) pre-main-sequence (PMS) stars is bimodal in many young open clusters, and we present a series of models to show that if such a bimodality exists for stars on the PMS that it is expected to manifest as a bimodal rotational velocity (at fixed mass/luminosity) on the main sequence for stars with masses in excess of ∼1.5 M⊙. Such a bimodal period distribution of PMS stars may be caused by whether stars have lost (rapid rotators) or been able to retain (slow rotators) their circumstellar discs throughout their PMS lifetimes. We conclude with a series of predictions for observables based on our model.

scholarly journals Measurements of the Ca ii infrared triplet emission lines of pre-main-sequence stars

2020 ◽  
Vol 72 (5) ◽  
Author(s):  
Mai Yamashita ◽  
Yoichi Itoh ◽  
Yuhei Takagi
Keyword(s):  
Main Sequence ◽  
Open Clusters ◽  
Emission Lines ◽  
Main Sequence Stars ◽  
Low Mass Stars ◽  
Chromospheric Activity ◽  
Low Mass ◽  
Pms Stars ◽  
Infrared Triplet ◽  
Narrow Emission

Abstract We investigated the chromospheric activity of 60 pre-main-sequence (PMS) stars in four molecular clouds and five moving groups. It is considered that strong chromospheric activity is driven by the dynamo processes generated by stellar rotation. In contrast, several researchers have pointed out that the chromospheres of PMS stars are activated by mass accretion from their protoplanetary disks. In this study, the Ca ii infrared triplet (IRT) emission lines were investigated utilizing medium- and high-resolution spectroscopy. The observations were conducted with Nayuta/MALLS and Subaru/HDS. Additionally, archive data obtained by Keck/HIRES, VLT/UVES, and VLT/X-Shooter were used. The small ratios of the equivalent widths indicate that Ca ii IRT emission lines arise primarily in dense chromospheric regions. Seven PMS stars show broad emission lines. Among them, four PMS stars have more than one order of magnitude brighter emission line fluxes compared to the low-mass stars in young open clusters. The four PMS stars have a high mass accretion rate, which indicates that the broad and strong emission results from a large mass accretion. However, most PMS stars exhibit narrow emission lines. No significant correlation was found between the accretion rate and flux of the emission line. The ratios of the surface flux of the Ca ii IRT lines to the stellar bolometric luminosity, $R^{\prime }_{\rm IRT}$, of the PMS stars with narrow emission lines are as large as the largest $R^{\prime }_{\rm IRT}$ of the low-mass stars in the young open clusters. This result indicates that most PMS stars, even in the classical T Tauri star stage, have chromospheric activity similar to zero-age main-sequence stars.

scholarly journals Rotational Evolution of Intermediate and Low Mass Main Sequence Stars

2004 ◽  
Vol 215 ◽  
pp. 127-135
Author(s):  
John R. Stauffer
Keyword(s):  
Main Sequence ◽  
Massive Stars ◽  
Rotational Velocity ◽  
Open Cluster ◽  
Open Clusters ◽  
Solar Mass ◽  
Low Mass Stars ◽  
Cluster Data ◽  
Rotational Evolution ◽  
Low Mass

Bob Kraft (1967) showed that there is a break in the mean rotational velocity of stars at about spectral type F5, with more massive stars generally being rapid rotators and less massive stars generally being slow rotators. He also showed that in the late F spectral range at least, there is an evolution with time on the main sequence, with younger F stars being more rapidly rotating. Kraft's observational database extended only to about one solar mass due to the sensitivy limitations of photographic plates. Modern observations of low mass stars in open clusters, extending down in mass to nearly the hydrogen burning mass limit in a few clusters, have since been used to show that rotational spindown is the common feature of stars less massive than the sun but that there is a wide spread in rotational velocities when stars arrive on the ZAMS. I will review what is known empirically concerning the rotational velocities of intermediate and low mass field stars, using the open cluster data to place the field star observations in context.

scholarly journals Stellar models and isochrones from low-mass to massive stars including pre-main sequence phase with accretion

2019 ◽  
Vol 624 ◽  
pp. A137 ◽  
Author(s):  
L. Haemmerlé ◽  
P. Eggenberger ◽  
S. Ekström ◽  
C. Georgy ◽  
G. Meynet ◽  
...  
Keyword(s):  
Star Formation ◽  
Stellar Evolution ◽  
Main Sequence ◽  
Massive Stars ◽  
Mass Range ◽  
Stellar Clusters ◽  
Solar Metallicity ◽  
Low Mass ◽  
Stellar Models ◽  
Young Clusters

Grids of stellar models are useful tools to derive the properties of stellar clusters, in particular young clusters hosting massive stars, and to provide information on the star formation process in various mass ranges. Because of their short evolutionary timescale, massive stars end their life while their low-mass siblings are still on the pre-main sequence (pre-MS) phase. Thus the study of young clusters requires consistent consideration of all the phases of stellar evolution. But despite the large number of grids that are available in the literature, a grid accounting for the evolution from the pre-MS accretion phase to the post-MS phase in the whole stellar mass range is still lacking. We build a grid of stellar models at solar metallicity with masses from 0.8 M⊙ to 120 M⊙, including pre-MS phase with accretion. We use the GENEC code to run stellar models on this mass range. The accretion law is chosen to match the observations of pre-MS objects on the Hertzsprung-Russell diagram. We describe the evolutionary tracks and isochrones of our models. The grid is connected to previous MS and post-MS grids computed with the same numerical method and physical assumptions, which provides the widest grid in mass and age to date.

scholarly journals Observations of low mass stars in clusters: Some constraints and puzzles for stellar evolution theory

1984 ◽  
Vol 105 ◽  
pp. 123-138
Author(s):  
R.D. Cannon
Keyword(s):  
Globular Clusters ◽  
Main Sequence ◽  
Star Clusters ◽  
Variable Stars ◽  
Open Clusters ◽  
Low Mass Stars ◽  
Theory Of Evolution ◽  
Theoretical Predictions ◽  
Low Mass ◽  
Red Giant

This review will attempt to do two things: (i) discuss some of the data which are available for testing the theory of evolution of low mass stars, and (ii) point out some problem areas where observations and theory do not seem to agree very well. This is of course too vast a field of research to be covered in one brief review, so I shall concentrate on one particular aspect, namely the study of star clusters and especially their colour-magnitude (CM) diagrams. Star clusters provide large samples of stars at the same distance and with the same age, and the CM diagram gives the easiest way of comparing theoretical predictions with observations, although crucial evidence is also provided by spectroscopic abundance analyses and studies of variable stars. Since this is primarily a review of observational data it is natural to divide it into two parts: (i) galactic globular clusters, and (ii) old and intermediate-age open clusters. Some additional evidence comes from Local Group galaxies, especially now that CM diagrams which reach the old main sequence are becoming available. For each class of cluster I shall consider successive stages of evolution from the main sequence, up the hydrogen-burning red giant branch, and through the helium-burning giant phase.

scholarly journals Rotation of Pre-Main Sequence Stars from High S/N Spectroscopy

1988 ◽  
Vol 132 ◽  
pp. 95-98
Author(s):  
J. Bouvier
Keyword(s):  
Stellar Evolution ◽  
Main Sequence ◽  
Spectroscopic Studies ◽  
Main Sequence Stars ◽  
Rotation Rates ◽  
Large Samples ◽  
Stellar Formation ◽  
Low Mass ◽  
Pms Stars ◽  
Large Telescopes

Until 1980, only a handful of low-mass, active pre-main sequence (pms) stars had known rotation velocities (vsini) /1/. Since then, increasingly sensitive detectors coupled to large telescopes led to high–resolution (a few 104) spectroscopic studies of these faint stars (mv = 10–13), with S/N ratio of the order of 100. The measurement of vsini for large samples of pms stars that resulted brought new insights on various pressing questions related to stellar formation and early stellar evolution : how do the rotation rates of pms stars compare with those expected from models of stellar formation ? how does the stellar angular momentum change during pms evolution ? is pms activity linked with rotation as would be expected if activity were triggered by magnetic processes ?

scholarly journals The rotation period distribution of the rich Pleiades-age southern open cluster NGC 2516

2020 ◽  
Vol 641 ◽  
pp. A51 ◽  
Author(s):  
D. J. Fritzewski ◽  
S. A. Barnes ◽  
D. J. James ◽  
K. G. Strassmeier
Keyword(s):  
Time Series ◽  
Open Cluster ◽  
Rotation Period ◽  
Open Clusters ◽  
Ccd Photometry ◽  
Activity Diagram ◽  
Cool Star ◽  
Period Distribution ◽  
Rotational Distribution ◽  
Star Rotation

Aims. We wish to measure the cool star rotation period distribution for the Pleiades-age rich open cluster NGC 2516 and use it to determine whether cluster-to-cluster variations exist in otherwise identical open clusters. Methods. We obtained 42 d-long time-series CCD photometry of NGC 2516 in the V and Ic filters using the Yale 1 m telescope at CTIO and performed a number of related analyses, including PSF-based time-series photometry. Our data are complemented with additional information from several photometric datasets, literature radial velocities, and Gaia DR2 astrometry. All available data are used to construct an integrated membership list for NGC 2516, containing 844 stars in our ≈1° field of view. Results. We derived 308 rotation periods for late-F to mid-M cluster members from our photometry. We identified an additional 247 periodic M dwarf stars from a prior study as cluster members, and used these to construct a 555-star rotation period distribution for NGC 2516. The colour-period diagram (in multiple colours) has almost no outliers and exhibits the anticipated triangular shape, with a diagonal slow rotator sequence that is preferentially occupied by the warmer stars along with a flat fast rotator sequence that is preferentially populated by the cooler cluster members. We also find a group of extremely slowly rotating M dwarfs (10 d ≲ Prot ≲ 23 d), forming a branch in the colour-period diagram which we call the “extended slow rotator sequence”. This, and other features of the rotational distribution can also be found in the Pleiades, making the colour-period diagrams of the two clusters nearly indistinguishable. A comparison with the well-studied (and similarly aged) open cluster M 35 indicates that the cluster’s rotational distribution is also similarly indistinguishable from that of NGC 2516. Those for the open clusters M 50 and Blanco 1 are similar, but data issues for those clusters make the comparisons somewhat more ambiguous. Nevertheless, we demonstrate the existence of a representative zero-age main sequence rotational distribution and provide a simple colour-independent way to represent it. We perform a detailed comparison of the NGC 2516 rotation period data with a number of recent rotational evolution models. Using X-ray data from the literature, we also construct the first rotation-activity diagram for solar-type stars in NGC 2516, one that we find is essentially indistinguishable from those for the Pleiades and Blanco 1. Conclusions. The two clusters NGC 2516 and Pleiades can be considered twins in terms of stellar rotation and related properties (and M 35, M 50, and Blanco 1 are similar), suggesting that otherwise identical open clusters also have intrinsically similar cool star rotation and activity distributions.

scholarly journals The Effects of Magnetic Activity on Lithium-Inferred Ages of Stars

2013 ◽  
Vol 9 (S302) ◽  
pp. 100-101
Author(s):  
Aaron J. Juarez ◽  
Phillip A. Cargile ◽  
David J. James ◽  
Keivan G. Stassun
Keyword(s):  
Pilot Study ◽  
Main Sequence ◽  
Open Cluster ◽  
Star Clusters ◽  
Magnetic Activity ◽  
Lithium Abundance ◽  
Stellar Radius ◽  
Low Mass ◽  
Stellar Properties ◽  
Pms Stars

AbstractIn this project, we investigate the effects of magnetic activity on the Lithium Depletion Boundary (LDB) to recalibrate the measured ages for star clusters, using the open cluster Blanco 1 as a pilot study. We apply the LDB technique on low-mass Pre-Main-Sequence (PMS) stars to derive an accurate age for Blanco 1, and we consider the effect of magnetic activity on this inferred age. Although observations have shown that magnetic activity directly affects stellar radius and temperature, most PMS models do not include the effects of magnetic activity on stellar properties. Since the lithium abundance of a star depends on its radius and temperature, we expect that LDB ages are affected by magnetic activity. After empirically accounting for the effects of magnetic activity, we find the age of Blanco 1 to be ~100 Myr, which is ~30 Myr younger than the standard LDB age of ~130 Myr.

scholarly journals Main Sequence Abundances, Mass Loss and Meridional Circulation

1988 ◽  
Vol 108 ◽  
pp. 3-12
Author(s):  
Georges Michaud
Keyword(s):  
Mass Loss ◽  
Loss Rate ◽  
Main Sequence ◽  
Meridional Circulation ◽  
Mass Loss Rate ◽  
Rotational Velocity ◽  
Open Clusters ◽  
Halo Stars ◽  
Abundance Anomalies ◽  
F Stars

AbstractConstraints that abundance anomalies observed on main sequence stars put on turbulence, meridional circulation and mass loss are reviewed. The emphasis is on recent observations of Li abundances.Upper limits to turbulence are obtained from the Be abundance in the Sun and from underabundances of Ca and Sc in FmAm stars. The Li abundance in G type stars suggests the presence of turbulence below convection zones.The abundance anomalies, both over and underabundances, observed in FmAm and λ Booti stars can be explained by diffusion in the presence of mass loss. A mass loss rate of 10−15 Mo yr−1 is required to explain the FmAm stars while a mass loss rate of 10−13 Mo yr−1 is required by the λ Booti stars.The position and width of the Li abundance gap observed in Hyades and other open clusters is explained by diffusion. A detailed reproduction of the Li(Teff) curve seems to require a mass loss rate of slightly more than 10−15 Mo yr−1, of the same order as the mass loss rate required by the FmAm stars. In the presence of such a mass loss only small overabundances of heavy elements are expected. The observed variations in the Li abundance as a function of the age of clusters suggests that the Li abundance observed in old halo stars does not represent the cosmological abundance.Detailed two dimensional calculations of diffusion in presence of meridional circulation for HgMn and FmAm stars lead to a cut-off of about 100 km s−1 for the maximum equatorial rotational velocity at which abundance anomalies are expected in these objects. This agrees with observations. A similar calculation for the F stars of the Hyades where Li underabundances are observed leads to a contradiction, unless meridional circulation patterns are modified by the presence of convection zones once they become as large as in late F stars. There remains a possibility that meridional circulation would be responsible for some of the reduction of the Li abundance as observed in the Hyades and UMa. Further observations are suggested to distinguish the effects of settling and nuclear destruction.

scholarly journals Planetary tidal interactions and the rotational evolution of low-mass stars

2018 ◽  
Vol 619 ◽  
pp. A80 ◽  
Author(s):  
F. Gallet ◽  
E. Bolmont ◽  
J. Bouvier ◽  
S. Mathis ◽  
C. Charbonnel
Keyword(s):  
Angular Momentum ◽  
Main Sequence ◽  
Open Cluster ◽  
Rotation Period ◽  
Rotational Period ◽  
Low Mass Stars ◽  
General Behaviour ◽  
Period Distribution ◽  
Rotational Evolution ◽  
Low Mass

Context. The surface angular velocity evolution of low-mass stars is now globally understood and the main physical mechanisms involved in it are observationally quite constrained. However, while the general behaviour of these mechanisms is grasped, their theoretical description is still under ongoing work. This is the case, for instance, about the description of the physical process that extracts angular momentum from the radiative core, which could be described by several theoretical candidates. Additionally, recent observations showed anomalies in the rotation period distribution of open cluster, main sequence, early K-type stars that cannot be reproduced by current angular momentum evolution models. Aims. In this work, we study the parameter space of star-planet system’s configurations to investigate if including the tidal star-planet interaction in angular momentum evolution models could reproduce the anomalies of this rotation period distribution. Methods. To study this effect, we use a parametric angular momentum evolution model that allows for core-envelope decoupling and angular momentum extraction by magnetized stellar wind that we coupled to an orbital evolution code where we take into account the torque due to the tides raised on the star by the planet. We explore different stellar and planetary configurations (stellar mass from 0.5 to 1.0 M⊙ and planetary mass from 10 M⊕ to 13 Mjup) to study their effect on the planetary orbital and stellar rotational evolution. Results. The stellar angular momentum is the most impacted by the star-planet interaction when the planet is engulfed during the early main sequence phase. Thus, if a close-in Jupiter-mass planet is initially located at around 50% of the stellar corotation radius, a kink in the rotational period distribution opens around late and early K-type stars during the early main sequence phase. Conclusions. Tidal star-planet interactions can create a kink in the rotation period distribution of low-mass stars, which could possibly account for unexpected scatter seen in the rotational period distribution of young stellar clusters.

scholarly journals Magnetic Activity of T Tauri Stars

1992 ◽  
Vol 9 ◽  
pp. 653-654
Author(s):  
T. Montmerle
Keyword(s):  
Solar Activity ◽  
Main Sequence ◽  
Magnetic Activity ◽  
T Tauri Stars ◽  
X Rays ◽  
General Review ◽  
Near Ir ◽  
T Tauri ◽  
Low Mass ◽  
Pms Stars

T Tauri stars (TTS) are low-mass (M ≲ 1M⊙) pre-main sequence (PMS) stars (for a general review, see Bertout 1989). They have long been known to be variable from near-TIV to near-IR wavelengths, on timescales ranging from a few minutes to a few decades. They are observed to flare in many wavenlength rages, from X-rays to the radio, and all the existing evidence is consistent with a very strong magnetic activity, in many ways analogous to solar activity (for a review, see, e.g., Montmerle et al. 1991).

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