scholarly journals Exploring the nature and synchronicity of early cluster formation in the Large Magellanic Cloud – IV. Evidence for multiple populations in Hodge 11 and NGC 2210

2019 ◽  
Vol 486 (4) ◽  
pp. 5581-5599 ◽  
Author(s):  
Christina K Gilligan ◽  
Brian Chaboyer ◽  
Jeffrey D Cummings ◽  
Dougal Mackey ◽  
Roger E Cohen ◽  
...  
Keyword(s):  
Globular Clusters ◽  
Main Sequence ◽  
Hubble Space Telescope ◽  
Cluster Formation ◽  
Stellar Populations ◽  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
Wide Field ◽  
Horizontal Branch ◽  
Advanced Camera For Surveys

Abstract We present a multiple population search in two old Large Magellanic Cloud (LMC) Globular clusters, Hodge 11 and NGC 2210. This work uses data from the Advanced Camera for Surveys and Wide Field Camera 3 on the Hubble Space Telescope from programme GO-14164 in Cycle 23. Both of these clusters exhibit a broadened main sequence with the second population representing (20 ± ∼5) per cent for NGC 2210 and (30 ± ∼5) per cent for Hodge 11. In both clusters, the smaller population is redder than the primary population, suggesting CNO variations. Hodge 11 also displays a bluer second population in the horizontal branch, which is evidence for helium enhancement. However, even though NGC 2210 shows similarities to Hodge 11 in the main sequence, there does not appear to be a second population on NGC 2210’s horizontal branch. This is the first photometric evidence that ancient LMC Globular clusters exhibit multiple stellar populations.

scholarly journals Exploring the nature and synchronicity of early cluster formation in the Large Magellanic Cloud – V. Multiple populations in ancient globular clusters

2020 ◽  
Vol 494 (2) ◽  
pp. 1946-1955
Author(s):  
Christina K Gilligan ◽  
Brian Chaboyer ◽  
Jeffrey D Cummings ◽  
Dougal Mackey ◽  
Roger E Cohen ◽  
...  
Keyword(s):  
Globular Clusters ◽  
Main Sequence ◽  
Hubble Space Telescope ◽  
Cluster Formation ◽  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
Wide Field ◽  
Multiple Populations ◽  
Show Evidence ◽  
Advanced Camera For Surveys

ABSTRACT We examine four ancient Large Magellanic Cloud (LMC) globular clusters (GCs) for evidence of multiple stellar populations using the Advanced Camera for Surveys and Wide Field Camera 3 on the Hubble Space Telescope Programme GO-14164. NGC 1466, NGC 1841, and NGC 2257 all show evidence for a redder, secondary population along the main sequence. Reticulum does not show evidence for the presence of a redder population, but this GC has the least number of stars and Monte Carlo simulations indicate that the sample of main-sequence stars is too small to robustly infer whether a redder population exists in this cluster. The second, redder, population of the other three clusters constitutes $\sim 30-40{{\ \rm per\ cent}}$ of the total population along the main sequence. This brings the total number of ancient LMC GCs with known split or broadened main sequences to five. However, unlike for Hodge 11 and NGC 2210 (see Gilligan et al. (2019)), none of the clusters shows evidence for multiple populations in the horizontal branch. We also do not find evidence of a second population along the red giant branch.

scholarly journals The HST survey of Magellanic-Cloud clusters and of their stellar populations

2015 ◽  
Vol 12 (S316) ◽  
pp. 275-280 ◽  
Author(s):  
A. P. Milone
Keyword(s):  
Globular Clusters ◽  
Main Sequence ◽  
Milky Way ◽  
Hubble Space Telescope ◽  
Stellar Populations ◽  
Magellanic Cloud ◽  
Stellar Rotation ◽  
Cloud Clusters ◽  
Magnitude Diagram ◽  
Red Clump

AbstractA large number of intermediate-age (~1-2-Gyr old) globular clusters (GCs) in the Large and the Small Magellanic Cloud (MC) exhibit either bimodal or extended main-sequence (MS) turn off and dual red clump (RC). Moreover, recent papers have shown that the MS of the young clusters NGC 1844 and NGC 1856 is either broadened or split. These features of the color-magnitude diagram (CMD) are not consistent with a single isochrone and suggest that star clusters in MCs have experienced a prolonged star formation, in close analogy with Milky-Way GCs with multiple stellar populations. As an alternative, stellar rotation or interacting binaries can be responsible of the CMD morphology. In the following I will summarize the observational scenario and provide constraints on the nature of the complex CMD of young and intermediate-age MC clusters from our ongoing photometric survey with the Hubble Space Telescope (HST).

scholarly journals Synthetic spectroscopic indices for identifying multiple stellar populations in globular clusters

2020 ◽  
Vol 493 (2) ◽  
pp. 2195-2206
Author(s):  
Emanuele Bertone ◽  
Miguel Chávez ◽  
J César Mendoza
Keyword(s):  
Globular Clusters ◽  
Main Sequence ◽  
Stellar Populations ◽  
Stellar Model ◽  
Chemical Compositions ◽  
Horizontal Branch ◽  
Atmospheric Parameters ◽  
Data Set ◽  
Spectral Diagnostics ◽  
Red Giant

ABSTRACT We present an investigation of synthetic spectroscopic indices that can plausibly help in identifying the presence of multiple stellar populations in globular clusters. The study is based on a new grid of stellar model atmospheres and high-resolution (R  = 500 000) synthetic spectra, that consider chemical partitions that have been singled out in Galactic globular clusters. The data base is composed of 3472 model atmospheres and theoretical spectra calculated with the collection of Fortran codes DFSYNTHE, ATLAS9 and SYNTHE, developed by Robert L. Kurucz. They cover a range of effective temperature from 4300 to 7000 K, surface gravity from 2.0 to 5.0 dex and four different chemical compositions. A set of 19 spectroscopic indices were calculated from a degraded version (R  = 2500) of the theoretical spectra data set. The set includes five indices previously used in the context of globular clusters analyses and 14 indices that we have newly defined by maximizing the capability of differentiating the chemical compositions. We explored the effects of atmospheric parameters on the index values and identified the optimal spectral diagnostics that allow to trace the signatures of objects of different stellar populations, located in the main sequence, the red giant branch and the horizontal branch. We found a suitable set of indices, that mostly involve molecular bands (in particular NH, but also CH and CN), that are very promising for spectroscopically identifying multiple stellar populations in globular clusters.

scholarly journals Chromosome maps of young LMC clusters: an additional case of coeval multiple populations

2020 ◽  
Vol 493 (4) ◽  
pp. 6060-6070 ◽  
Author(s):  
S Saracino ◽  
S Martocchia ◽  
N Bastian ◽  
V Kozhurina-Platais ◽  
W Chantereau ◽  
...  
Keyword(s):  
Globular Clusters ◽  
Hubble Space Telescope ◽  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
Host Galaxy ◽  
Clear Correlation ◽  
Age Difference ◽  
Multiple Star ◽  
Multiple Populations ◽  
Red Giant

ABSTRACT Recent studies have revealed that the multiple populations (MPs) phenomenon does not occur only in ancient and massive Galactic globular clusters (GCs), but it is also observed in external galaxies, where GCs sample a wide age range with respect to the Milky Way. However, for a long time, it was unclear whether we were looking at the same phenomenon in different environments or not. The first evidence that the MPs phenomenon is the same regardless of cluster age and host galaxy came out recently, when an intermediate-age cluster from the Small Magellanic Cloud, Lindsay 1, and a Galactic GC have been directly compared. By complementing those data with new images from the Hubble Space Telescope (HST), we extend the comparison to two clusters of different ages: NGC 2121 (∼2.5 Gyr) and NGC 1783 (∼1.5 Gyr), from the Large Magellanic Cloud. We find a clear correlation between the RGB (red giant branch) width in the pseudo-colour CF275W, F343N, F438W and the age of the cluster itself, with the older cluster having larger σ(CF275W, F343N, F438W)RGB and vice versa. Unfortunately, the σ values cannot be directly linked to the N-abundance variations within the clusters before properly taking account the effect of the first dredge-up. Such HST data also allow us to explore whether multiple star formation episodes occurred within NGC 2121. The two populations are indistinguishable, with an age difference of only 6 ± 12 Myr and an initial helium spread of 0.02 or lower. This confirms our previous results, putting serious constraints on any model proposed to explain the origin of the chemical anomalies in GCs.

scholarly journals The sub-solar initial mass function in the Large Magellanic Cloud

2008 ◽  
Vol 4 (S256) ◽  
pp. 250-255
Author(s):  
Dimitrios A. Gouliermis
Keyword(s):  
Star Formation ◽  
Hubble Space Telescope ◽  
Mass Function ◽  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
Magellanic Clouds ◽  
Initial Mass Function ◽  
Initial Mass ◽  
Star Forming ◽  
Advanced Camera For Surveys

AbstractThe Magellanic Clouds offer a unique variety of star forming regions seen as bright nebulae of ionized gas, related to bright young stellar associations. Nowadays, observations with the high resolving efficiency of the Hubble Space Telescope allow the detection of the faintest infant stars, and a more complete picture of clustered star formation in our dwarf neighbors has emerged. I present results from our studies of the Magellanic Clouds, with emphasis in the young low-mass pre-main sequence populations. Our data include imaging with the Advanced Camera for Surveys of the association LH 95 in the Large Magellanic Cloud, the deepest observations ever taken with HST of this galaxy. I discuss our findings in terms of the initial mass function, which we constructed with an unprecedented completeness down to the sub-solar regime, as the outcome of star formation in the low-metallicity environment of the LMC.

scholarly journals The predicted properties of helium-enriched globular cluster progenitors at high redshift

2020 ◽  
Vol 496 (3) ◽  
pp. 3222-3234
Author(s):  
David M Nataf ◽  
Shunsaku Horiuchi ◽  
Guglielmo Costa ◽  
Rosemary F G Wyse ◽  
Yuan-Sen Ting ◽  
...  
Keyword(s):  
Adaptive Optics ◽  
Globular Cluster ◽  
Globular Clusters ◽  
Hubble Space Telescope ◽  
High Redshift ◽  
Cluster Formation ◽  
Stellar Populations ◽  
Space Telescope ◽  
James Webb Space Telescope ◽  
Galactic Astronomy

ABSTRACT Globular cluster progenitors may have been detected by Hubble Space Telescope, and are predicted to be observable with James Webb Space Telescope (JWST) and ground-based extremely large telescopes with adaptive optics. This has the potential to elucidate the issue of globular cluster formation and the origins of significantly helium-enriched subpopulations, a problem in Galactic astronomy with no satisfactory theoretical solution. Given this context, we use model stellar tracks and isochrones to investigate the predicted observational properties of helium-enriched stellar populations in globular cluster progenitors. We find that, relative to helium-normal populations, helium-enriched (ΔY = +0.12) stellar populations similar to those inferred in the most massive globular clusters, are expected, modulo some rapid fluctuations in the first ∼30 Myr, to be brighter and redder in the rest frame. At fixed age, stellar mass, and metallicity, a helium-enriched population is predicted to converge to being ∼0.40 mag brighter at $\lambda \approx 2.0\, {\mu \rm m}$, and to be 0.30-mag redder in the JWST–NIRCam colour (F070W − F200W), and to actually be fainter for $\lambda \lesssim 0.50 \, {\mu \rm m}$. Separately, we find that the time-integrated shift in ionizing radiation is a negligible $\sim \!5{{\ \rm per\ cent}}$, though we show that the Lyman-α escape fraction could end up higher for helium-enriched stars.

New Proper Motions of the Small Magellanic Cloud Using HST and Implications for Milky Way Mass

2017 ◽  
Vol 13 (S334) ◽  
pp. 394-395
Author(s):  
P. Zivick ◽  
N. Kallivayalil ◽  
S. Linden ◽  
T. Fritz ◽  
G. Besla ◽  
...  
Keyword(s):  
Milky Way ◽  
Hubble Space Telescope ◽  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
Wide Field ◽  
Small Magellanic Cloud ◽  
Proper Motions ◽  
Exact Mass ◽  
History Of ◽  
Magellanic Stream

AbstractAs new work on the proper motions (PMs) of the Large Magellanic Cloud (LMC) has come out, our view of the history of the Magellanic Clouds has evolved. We now believe they are on their first infall into the Milky Way (MW), having been tidally bound at the start of infall (though not necessarily now). Combining these observations with initial PMs of the Small Magellanic Cloud (SMC) suggests a new formation mechanism of the Magellanic Stream through the stripping of material from the SMC. However, large uncertainties remain in the exact mass of the LMC. We present a measurement of the systemic proper motions of the SMC from astrometry with the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST), covering a ~3 year baseline of 30 fields with background QSOs. We find these motions to be μW = −0.82 ± 0.06 mas/yr and μN = −1.23 ± 0.07 mas/yr. Combining these measurements with previous efforts in studying the Clouds will help constrain their interactions with each other and the MW, including the mass of the LMC and the MW, as well as provide new insight into the internal dynamics of the SMC.

scholarly journals Exploring the nature and synchronicity of early cluster formation in the Large Magellanic Cloud – III. Horizontal branch morphology

2017 ◽  
Vol 474 (4) ◽  
pp. 4358-4365 ◽  
Author(s):  
R Wagner-Kaiser ◽  
Dougal Mackey ◽  
Ata Sarajedini ◽  
Roger E Cohen ◽  
Doug Geisler ◽  
...  
Keyword(s):  
Cluster Formation ◽  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
Horizontal Branch ◽  
Branch Morphology
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