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 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 Lithium and Beryllium in Main Sequence Stars

1991 ◽  
Vol 145 ◽  
pp. 85-97 ◽  
Author(s):  
R. Rebolo
Keyword(s):  
Present State ◽  
Main Sequence ◽  
Open Cluster ◽  
Transport Processes ◽  
Stellar Atmospheres ◽  
Stellar Rotation ◽  
Main Sequence Stars ◽  
Halo Stars

Li and Be abundances in Main Sequence stars later than F0 are reviewed. Observations of Li in open cluster stars and metal-poor dwarf halo stars has promoted the development of a great variety of models invoking transport processes in the outermost layers of these stars. Although measurements in their present state do not allow to establish definitive conclusions on which process is the most important for each range of masses, they do manifest that metallicity and stellar rotation play an important role in controlling the processes which trigger disappearance of these elements from stellar atmospheres.

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 Evolution and appearance of Be stars in SMC clusters

2009 ◽  
Vol 5 (S266) ◽  
pp. 470-473
Author(s):  
C. Martayan ◽  
D. Baade ◽  
Y. Frémat ◽  
J. Zorec
Keyword(s):  
Main Sequence ◽  
Milky Way ◽  
Open Cluster ◽  
Central Star ◽  
Open Clusters ◽  
Be Stars ◽  
Ob Stars ◽  
Be Star ◽  
The Impact ◽  
Key Parameter

AbstractStar clusters are privileged laboratories for studying the evolution of massive stars (OB stars). One particularly interesting question concerns the phases during which the classical Be stars occur, which—unlike HAe/Be stars—are not pre-main-sequence objects, nor supergiants. Rather, they are extremely rapidly rotating B-type stars with a circumstellar decretion disk formed by episodic ejections of matter from the central star. To study the impact of mass, metallicity, and age on the Be phase, we observed Small Magellanic Cloud (SMC) open clusters with two different techniques: (i) with the ESO–WFI in slitless mode, which allowed us to find the brighter Be and other emission-line stars in 84 SMC open clusters, and (ii) with the VLT–FLAMES multifiber spectrograph to determine accurately the evolutionary phases of Be stars in the Be-star-rich SMC open cluster NGC 330. Based on a comparison to the Milky Way, a model of Be stellar evolution, appearance as a function of metallicity and mass, and spectral type is developed, involving the fractional critical rotation rate as a key parameter.

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.

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 Medium Resolution Spectroscopy at 1-2 Microns

1979 ◽  
Vol 47 ◽  
pp. 239-246
Author(s):  
J. R. Mould
Keyword(s):  
Fourier Transform ◽  
Main Sequence ◽  
Classification Criteria ◽  
Fourier Transform Spectrometer ◽  
Main Sequence Stars ◽  
Composite Spectra ◽  
Medium Resolution ◽  
M Stars

AbstractThe need for establishing classification criteria at long wavelengths is stressed. The usefulness of doing this is illustrated with a discussion of the composite spectra of FU Orionis stars. Spectra of these pre-main-sequence stars from 1.5-2.5μ were obtained with a Fourier Transform Spectrometer. Luminosity criteria in the l-2μ range are also discussed with application to M stars.

scholarly journals Cepheid distances from the Baade–Wesselink method

2012 ◽  
Vol 8 (S289) ◽  
pp. 138-144 ◽  
Author(s):  
Wolfgang Gieren ◽  
Jesper Storm ◽  
Nicolas Nardetto ◽  
Alexandre Gallenne ◽  
Grzegorz Pietrzyński ◽  
...  
Keyword(s):  
Excellent Agreement ◽  
Surface Brightness ◽  
Recent Progress ◽  
Main Sequence ◽  
Near Infrared ◽  
Open Cluster ◽  
Open Clusters ◽  
Distance Scale ◽  
Systematic Uncertainties ◽  
Classical Cepheids

AbstractRecent progress on Baade–Wesselink (BW)-type techniques to determine the distances to classical Cepheids is reviewed. Particular emphasis is placed on the near-infrared surface-brightness (IRSB) version of the BW method. Its most recent calibration is described and shown to be capable of yielding individual Cepheid distances accurate to 6%, including systematic uncertainties. Cepheid distances from the IRSB method are compared to those determined from open cluster zero-age main-sequence fitting for Cepheids located in Galactic open clusters, yielding excellent agreement between the IRSB and cluster Cepheid distance scales. Results for the Cepheid period–luminosity (PL) relation in near-infrared and optical bands based on IRSB distances and the question of the universality of the Cepheid PL relation are discussed. Results from other implementations of the BW method are compared to the IRSB distance scale and possible reasons for discrepancies are identified.

Stellar rotation in lower main-sequence stars measured from time variations in H and K emission-line fluxes. I - Initial results

1981 ◽  
Vol 250 ◽  
pp. 276 ◽  
Author(s):  
A. H. Vaughan ◽  
G. W. Preston ◽  
S. L. Baliunas ◽  
L. W. Hartmann ◽  
R. W. Noyes ◽  
...  
Keyword(s):  
Emission Line ◽  
Main Sequence ◽  
Stellar Rotation ◽  
Main Sequence Stars ◽  
Time Variations ◽  
Initial Results
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