scholarly journals Extended main sequence turnoffs in open clusters as seen by Gaia – I. NGC 2818 and the role of stellar rotation

2018 ◽  
Vol 480 (3) ◽  
pp. 3739-3746 ◽  
Author(s):  
N Bastian ◽  
S Kamann ◽  
I Cabrera-Ziri ◽  
C Georgy ◽  
S Ekström ◽  
...  
Keyword(s):  
Main Sequence ◽  
Open Clusters ◽  
Stellar Rotation

scholarly journals Extended main sequence turnoffs in open clusters as seen by Gaia – II. The enigma of NGC 2509

2019 ◽  
Vol 491 (2) ◽  
pp. 2129-2136 ◽  
Author(s):  
M de Juan Ovelar ◽  
S Gossage ◽  
S Kamann ◽  
N Bastian ◽  
C Usher ◽  
...  
Keyword(s):  
Stellar Evolution ◽  
Main Sequence ◽  
Narrow Range ◽  
Open Cluster ◽  
Open Clusters ◽  
Stellar Rotation ◽  
Rotation Rates ◽  
Magnitude Diagram ◽  
Stellar Density

ABSTRACT We investigate the morphology of the colour–magnitude diagram (CMD) of the open cluster NGC 2509 in comparison with other Galactic open clusters of similar age using Gaia photometry. At ${\sim}900\,\rm {Myr}$ Galactic open clusters in our sample all show an extended main sequence turnoff (eMSTO) with the exception of NGC 2509, which presents an exceptionally narrow CMD. Our analysis of the Gaia data rules out differential extinction, stellar density, and binaries as a cause for the singular MSTO morphology in this cluster. We interpret this feature as a consequence of the stellar rotation distribution within the cluster and present the analysis with mesa Isochrones and Stellar Tracks (MIST) stellar evolution models that include the effect of stellar rotation on which we based our conclusion. In particular, these models point to an unusually narrow range of stellar rotation rates (Ω/Ωcrit, ZAMS = [0.4, 0.6]) within the cluster as the cause of this singular feature in the CMD of NGC 2509. Interestingly, models that do not include rotation are not as good at reproducing the morphology of the observed CMD in this cluster.

scholarly journals Clusters and stellar angular-momentum evolution

2009 ◽  
Vol 5 (S266) ◽  
pp. 510-510
Author(s):  
M. H. Pinsonneault ◽  
D. M. Terndrup ◽  
P. Denisenkov
Keyword(s):  
Angular Momentum ◽  
Empirical Support ◽  
Open Clusters ◽  
Data Sets ◽  
Stellar Rotation ◽  
Origin And Evolution ◽  
Rotation Rates ◽  
Wide Range ◽  
Internal Transport

AbstractThe origin and evolution of stellar rotation has proven to be both important and challenging. Data obtained in star clusters has already provided key constraints on the role of protostellar disks and the timescales for angular-momentum loss and internal transport. Recent data sets also provide empirical support for the idea that a wide range of rotation rates converge on the main sequence. We evaluate the prospects for rotation–mass–age relationships and the role of open clusters in calibrating them.

scholarly journals Properties of abundance gradient along the Galactic disk and the role of LAMOST

2013 ◽  
Vol 9 (S298) ◽  
pp. 304-309
Author(s):  
J.L. Hou ◽  
L. Chen ◽  
J.C. Yu ◽  
J. Sellwood ◽  
C. Pryor
Keyword(s):  
Radial Velocity ◽  
Main Sequence ◽  
Milky Way ◽  
Galactic Disk ◽  
Open Cluster ◽  
Dynamical Evolution ◽  
Open Clusters ◽  
Main Sequence Stars ◽  
Abundance Gradient

AbstractIn this paper, we present our recent work on the evolution of abundance gradients along the Milky Way disk based on the Geneva Copenhagen Survey (GCS) and Radial Velocity Experiment (RAVE) data. We will also discuss the role of the LAMOST Milky Way disk survey in clarifying the properties of metallicity breaks observed through open clusters and young tracers along the Milky Way disk. It is believed that the Galactic disk forms inside-out, in which the stellar population at increasing radii is younger and more metal poor. This picture is consistent with most Galactic Chemical Evolution (GCE) models which also predict a tight correlation between the metallicity and age of stars at a given radius. However, it is only a result of “steady state" and no dynamical evolution effects were taken into account. We have selected two stellar samples from GCS and RAVE, each sample contains about 10,000 local thin-disk, main-sequence stars. We use the guiding radius which is determined by the conservation of z-direction angular momentum, to eliminate the blurring effects. And also use the effective temperature of the main sequence stars as a proxy of stellar age. It is shown that the metallicity gradient flattens as the age increases. This is not consistent with our previous GCE prediction, but can be explained by radial mixing effects. In order to further demonstrate the abundance breaks observed in the Galactic disk we have proposed, and have been carrying out, an open cluster survey project based on LAMOST. We plan to observe at least 400 open clusters in the northern Galactic sky. From the observations, we will get uniform parameters for those clusters with radial velocity and metallicities. We anticipate that this uniform open cluster sample could clarify the observed abundance break around the Milky Way disk corotation radius and also give a more robust result concerning the evolution of the abundance gradient.

scholarly journals Binary-driven stellar rotation evolution at the main-sequence turn-off in star clusters

2021 ◽  
Vol 502 (3) ◽  
pp. 4350-4358
Author(s):  
Weijia Sun ◽  
Richard de Grijs ◽  
Licai Deng ◽  
Michael D Albrow
Keyword(s):  
Main Sequence ◽  
Open Cluster ◽  
Open Clusters ◽  
Stellar Rotation ◽  
Main Sequence Stars ◽  
Number Ratio ◽  
Medium Resolution ◽  
Novel Method ◽  
Tight Correlation ◽  
The Impact

ABSTRACT The impact of stellar rotation on the morphology of star cluster colour–magnitude diagrams is widely acknowledged. However, the physics driving the distribution of the equatorial rotation velocities of main-sequence turn-off stars is as yet poorly understood. Using Gaia Data Release 2 photometry and new Southern African Large Telescope medium-resolution spectroscopy, we analyse the intermediate-age ($\sim 1\text{-}{\rm Gyr}$-old) Galactic open clusters NGC 3960, NGC 6134, and IC 4756 and develop a novel method to derive their stellar rotation distributions based on SYCLIST stellar rotation models. Combined with literature data for the open clusters NGC 5822 and NGC 2818, we find a tight correlation between the number ratio of slow rotators and the clusters’ binary fractions. The blue-main-sequence stars in at least two of our clusters are more centrally concentrated than their red-main-sequence counterparts. The origin of the equatorial stellar rotation distribution and its evolution remains as yet unidentified. However, the observed correlation in our open cluster sample suggests a binary-driven formation mechanism.

scholarly journals The role of rotation in stellar evolution

1984 ◽  
Vol 105 ◽  
pp. 475-489
Author(s):  
Jean-Louis Tassoul
Keyword(s):  
Stellar Evolution ◽  
Main Sequence ◽  
Direct Consequence ◽  
Axial Rotation ◽  
Stellar Structure ◽  
Spherically Symmetric ◽  
Stellar Rotation ◽  
Solar Differential Rotation ◽  
Effects Of Rotation

During the seventeenth century, in the wake of the discovery of the solar differential rotation, some scientists argued that stellar variability was a direct consequence of axial rotation, the spinning body showing alternately its bright (unspotted) and dark (spotted) hemispheres to the observer (Brunet 1931). Although this idea did not withstand the passage of time, it is nevertheless an interesting one because it is clearly indicative of the kind of fascination stellar rotation has aroused since its inception. And yet, at this writing there is no longer any doubt that spherically symmetric models do explain the major observed properties of stars. Moreover, if one excepts the very early and very late moments of a star's lifetime, the effects of rotation on stellar structure are apparently dynamically unimportant (e.g., Tassoul 1978, hereafter T.R.S.; Moss and Smith 1981, and references therein). What is the purpose, then, to discuss the role of rotation on the main-sequence and post-main-sequence phases of stellar evolution?

scholarly journals Extended Main-sequence Turnoffs in the Double Cluster h and χ Persei: The Complex Role of Stellar Rotation

2019 ◽  
Vol 876 (1) ◽  
pp. 65 ◽  
Author(s):  
Chengyuan Li ◽  
Weijia Sun ◽  
Richard de Grijs ◽  
Licai Deng ◽  
Kun Wang ◽  
...  
Keyword(s):  
Main Sequence ◽  
Stellar Rotation ◽  
Double Cluster

scholarly journals Helium, [Fe/H] Abundances and the HR (Log TEFF, MBol) Diagram With Hipparcos Data of The Four Nearest Open Clusters: Hyades, Coma Berenices, The Pleiades and Praesepe

1998 ◽  
Vol 11 (1) ◽  
pp. 565-565
Author(s):  
G. Cayrel de Strobel ◽  
R. Cayrel ◽  
Y. Lebreton
Keyword(s):  
Main Sequence ◽  
Open Clusters ◽  
Main Sequence Stars ◽  
Spectroscopic Analyses ◽  
Solar Metallicity ◽  
Metal Abundances ◽  
The Mean ◽  
The Moment ◽  
The One ◽  
Best Fit

After having studied in great detail the observational HR diagram (log Teff, Mbol) composed by 40 main sequence stars of the Hyades (Perryman et al.,1997, A&A., in press), we have tried to apply the same method to the observational main sequences of the three next nearest open clusters: Coma Berenices, the Pleiades, and Praesepe. This method consists in comparing the observational main sequence of the clusters with a grid of theoretical ZAMSs. The stars composing the observational main sequences had to have reliable absolute bolometric magnitudes, coming all from individual Hipparcos parallaxes, precise bolometric corrections, effective temperatures and metal abundances from high resolution detailed spectroscopic analyses. If we assume, following the work by Fernandez et al. (1996, A&A,311,127), that the mixing-lenth parameter is solar, the position of a theoretical ZAMS, in the (log Teff, Mbol) plane, computed with given input physics, only depends on two free parameters: the He content Y by mass, and the metallicity Z by mass. If effective temperature and metallicity of the constituting stars of the 4 clusters are previously known by means of detailed analyses, one can deduce their helium abundances by means of an appropriate grid of theoretical ZAMS’s. The comparison between the empirical (log Teff, Mbol) main sequence of the Hyades and the computed ZAMS corresponding to the observed metallicity Z of the Hyades (Z= 0.0240 ± 0.0085) gives a He abundance for the Hyades, Y= 0.26 ± 0.02. Our interpretation, concerning the observational position of the main sequence of the three nearest clusters after the Hyades, is still under way and appears to be greatly more difficult than for the Hyades. For the moment we can say that: ‒ The 15 dwarfs analysed in detailed in Coma have a solar metallicity: [Fe/H] = -0.05 ± 0.06. However, their observational main sequence fit better with the Hyades ZAMS. ‒ The mean metallicity of 13 Pleiades dwarfs analysed in detail is solar. A metal deficient and He normal ZAMS would fit better. But, a warning for absorption in the Pleiades has to be recalled. ‒ The upper main sequence of Praesepe, (the more distant cluster: 180 pc) composed by 11 stars, analysed in detail, is the one which has the best fit with the Hyades ZAMS. The deduced ‘turnoff age’ of the cluster is slightly higher than that of the Hyades: 0.8 Gyr instead of 0.63 Gyr.

The Main Sequence of Human Optokinetic Afternystagmus (OKAN)

2009 ◽  
Vol 101 (6) ◽  
pp. 2889-2897 ◽  
Author(s):  
Andre Kaminiarz ◽  
Kerstin Königs ◽  
Frank Bremmer
Keyword(s):  
Neural Networks ◽  
Eye Movements ◽  
Main Sequence ◽  
Critical Role ◽  
Saccade Target ◽  
Control Mechanisms ◽  
Visually Guided ◽  
Background Characteristics ◽  
Optokinetic Afternystagmus

Different types of fast eye movements, including saccades and fast phases of optokinetic nystagmus (OKN) and optokinetic afternystagmus (OKAN), are coded by only partially overlapping neural networks. This is a likely cause for the differences that have been reported for the dynamic parameters of fast eye movements. The dependence of two of these parameters—peak velocity and duration—on saccadic amplitude has been termed “main sequence.” The main sequence of OKAN fast phases has not yet been analyzed. These eye movements are unique in that they are generated by purely subcortical control mechanisms and that they occur in complete darkness. In this study, we recorded fast phases of OKAN and OKN as well as visually guided and spontaneous saccades under identical background conditions because background characteristics have been reported to influence the main sequence of saccades. Our data clearly show that fast phases of OKAN and OKN differ with respect to their main sequence. OKAN fast phases were characterized by their lower peak velocities and longer durations compared with those of OKN fast phases. Furthermore we found that the main sequence of spontaneous saccades depends heavily on background characteristics, with saccades in darkness being slower and lasting longer. On the contrary, the main sequence of visually guided saccades depended on background characteristics only very slightly. This implies that the existence of a visual saccade target largely cancels out the effect of background luminance. Our data underline the critical role of environmental conditions (light vs. darkness), behavioral tasks (e.g., spontaneous vs. visually guided), and the underlying neural networks for the exact spatiotemporal characteristics of fast eye movements.

scholarly journals The Problem ofHipparcosDistances to Open Clusters. I. Constraints from Multicolor Main‐Sequence Fitting

1998 ◽  
Vol 504 (1) ◽  
pp. 170-191 ◽  
Author(s):  
Marc H. Pinsonneault ◽  
John Stauffer ◽  
David R. Soderblom ◽  
Jeremy R. King ◽  
Robert B. Hanson
Keyword(s):  
Main Sequence ◽  
Open Clusters
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