scholarly journals Similarities of the intermediate-age SMC star cluster NGC 152 with inner disk clusters in the Milky Way

1991 ◽  
Vol 148 ◽  
pp. 198-199
Author(s):  
T. Richtler ◽  
Klaas S. De Boer ◽  
A. Vallenari ◽  
W. Seggewiss
Keyword(s):  
Globular Cluster ◽  
Milky Way ◽  
Star Clusters ◽  
Star Cluster ◽  
Horizontal Branch ◽  
Vertical Extension ◽  
Magnitude Diagram ◽  
The Mean ◽  
Normal Feature ◽  
Selection Of

A colour-magnitude diagram (CMD) of the region containing the intermediate-age SMC globular cluster NGC 152 was published recently (Melcher & Richtler 1989). A particularly interesting feature of this CMD is the “clump” of He-core burning stars, which are predominantly field stars. A selection of stars near the cluster centre leads to the CMD shown in Figure 1. The vertical extension of the clump (explainable by the evolution of stars younger than 1 Gyr) is replaced by a “tilted horizontal branch” (we use this expression for lack of a better one). The age of NGC 152 is about 1.3 Gyr and the reddening is small; the metallicity is unknown but less than −0.6 dex, which is the mean metallicity of the young SMC population. The tilted HB can be reproduced in CMD simulations using the method developed by Vallenari et al. (1990), and thus can be considered as a normal feature of star clusters like NGC 152. It is evident also in other intermediate-age MC clusters like Kron 3 (Rich et al. 1984).

Structural parameters for the globular-cluster-like objects in NGC 1052-DF2

2020 ◽  
Vol 496 (3) ◽  
pp. 3741-3754
Author(s):  
Jun Ma ◽  
Shoucheng Wang ◽  
Song Wang ◽  
Zhimin Zhou ◽  
Tianmeng Zhang ◽  
...  
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Surface Brightness ◽  
Milky Way ◽  
Hubble Space Telescope ◽  
Structural Parameters ◽  
Star Clusters ◽  
Star Cluster ◽  
Wilson Model ◽  
D 20

ABSTRACT Recently, van Dokkum et al. have found an ultra-diffuse galaxy NGC 1052-DF2 with little or no dark matter, based on a spectroscopic study of its 11 constituent globular-cluster-like objects. In this paper, we analyse these 11 objects using Hubble Space Telescope imaging. We derive the structural parameters for each object by fitting the surface brightness profiles to three different models. Our results indicate that these objects are better fitted by the Wilson model than by the King and Sérsic models. Using the distance of D = 20 Mpc to NGC 1052-DF2 obtained by van Dokkum et al., these 11 objects have half-light radii in the range from ∼11 to ∼16 pc. These values are much larger than for normal globular clusters in the Milky Way, and are comparable to the sizes of an extended star cluster and of a typical ultra-compact dwarf. The half-light radii obtained here are larger than those obtained by van Dokkum et al. and Trujillo et al. The offset of the differences between the half-light radii of van Dokkum et al. and ours is 6.17 pc, and the offset of the differences between the half-light radii of Trujillo et al. and ours is 4.99 pc. Our half-light radii are, on average, 11.74 pc, which corresponds to 53 and 43 per cent larger than those obtained by van Dokkum et al. and Trujillo et al., respectively. The Rh versus MV diagram shows that these objects occupy the same areas of extended star clusters and ultra-compact dwarfs. Using the distance of D = 13 Mpc obtained by Trujillo et al., there are still five objects that do not lie in the area of normal globular clusters in the Milky Way. So, we suggest that these globular-cluster-like objects in NGC 1052-DF2 are not normal globular clusters like those in the Milky Way.

scholarly journals From Young to Old: Spectral Models for Star Cluster Systems

2005 ◽  
Vol 13 ◽  
pp. 187-188
Author(s):  
Uta Fritze – v. Alvensleben ◽  
Peter Anders ◽  
Richard de Grijs
Keyword(s):  
Time Evolution ◽  
Globular Cluster ◽  
Milky Way ◽  
Star Clusters ◽  
Star Cluster ◽  
Cluster Systems ◽  
Luminosity Functions ◽  
Spectral Models ◽  
Model Star ◽  
Two Populations

AbstractEvolutionary synthesis models for star clusters of various metallicities, including gaseous emission during the lifetime of the ionizing stars, are used to model star cluster systems comprising two populations: an old metal-poor globular cluster (GC) population similar to that of the Milky Way halo, and a second GC population of arbitrary metallicity. We investigate the time evolution of color distributions and luminosity functions for the two GC populations and compare with observations of E/SO galaxies. We show that multi-passband data for GC populations give clues to the relative ages and metallicities of the two subpopulations, and help constrain formation scenarios for their parent galaxies.

scholarly journals The Variable Stars in NGC 6723

1973 ◽  
Vol 21 ◽  
pp. 178-179
Author(s):  
John Menzies
Keyword(s):  
Southern Hemisphere ◽  
Globular Cluster ◽  
Variable Stars ◽  
Horizontal Branch ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
Horizontal Branch Stars ◽  
Magnitude Diagram ◽  
The Mean ◽  
Lyrae Stars

Abstract*.A study has been made of the variables in the Southern Hemisphere globular cluster NGC 6723, which is suspected of being relatively metal-rich on the basis of its colour-magnitude diagram and of its integrated spectral type of G3. Seven new RR Lyrae stars and two bright red, probably semiregular, variables have been found and the suspected variable of Fourcade and Laborde has been confirmed. The complement of RR Lyrae stars is now 27, consisting of 4 c-type and 23 ab-type variables, the mean periods being Pc = 0.d292 and Pab = 0.d537. On the basis of the two-colour diagram of the horizontal branch stars the cluster is considered to be virtually un-reddened. Applying Christy’s models to the data from this study we find the following parameters for the variables: Mv= 1.m10, mass = 0.42 M⊙, and Y=0.4.

scholarly journals Strömgren metallicities for intermediate-age and old star clusters

2020 ◽  
Vol 642 ◽  
pp. A114 ◽  
Author(s):  
Andrés E. Piatti
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Star Clusters ◽  
Star Cluster ◽  
Small Magellanic Cloud ◽  
Similar Comparison ◽  
Age Dependent ◽  
Similar Range ◽  
Red Giant ◽  
Selection Of

We report results that show that the straightforward star cluster metallicities obtained from Strömgren vby photometry are age-dependent and need to be corrected for further use. This outcome arises from the comparison of [Fe/H] values derived from Strömgren photometry with those metallicities published in the literature for 26 Large and Small Magellanic Cloud star clusters, whose ages range from ∼1 Gyr up to the oldest-known globular cluster ages in these galaxies. While deriving mean star cluster metallicities, we carried out a thorough selection of red giant branch candidates to comply with the Strömgren metallicity calibration validity regime. We paid attention to the effect of contamination by field stars, particularly those that lie inside the star clusters’ radii, that are distributed along the star cluster red giant branches and that have [Fe/H] values covering a similar range as that for the selected stars. We find that the measured Strömgren metallicities are systematically more metal-poor than the published ones and that a quadratically age-varying function reproduces the relative metallicity values with an overall uncertainty of ∼0.05 dex. We finally performed a similar comparison relying on a fully independent approach, which consisted in using theoretical red giant branches of old globular clusters spanning [Fe/H] values from −2.0 up to 0.0 dex as standards. We then superimposed onto them the red giant branches of star clusters with ages in the range 1.0−12.5 Gyr and estimated their associated metallicities by interpolation. The derived theoretical relative metallicities follow a similar trend as a function of the star clusters’ ages as what has been found from observations of star clusters.

scholarly journals A preliminary color-magnitude diagram for late-type stars in the solar neighborhood

1959 ◽  
Vol 10 ◽  
pp. 39-40
Author(s):  
O. C. Wilson
Keyword(s):  
Main Sequence ◽  
Star Clusters ◽  
Solar Neighborhood ◽  
Late Type ◽  
Main Sequence Stars ◽  
Individual Values ◽  
Magnitude Diagram ◽  
Trigonometric Parallaxes ◽  
Nearby Stars ◽  
The Mean

Modern photoelectric techniques yield magnitudes and colors of stars with accuracies of the order of a few thousandths and a few hundredths of a magnitude respectively. Hence for star clusters it is possible to derive highly accurate color-magnitude arrays since all of the members of a cluster may be considered to be at the same distance from the observer. It is much more difficult to do this for the nearby stars where all of the objects concerned are at different, and often poorly determined, distances. If one depends upon trigonometric parallaxes, the bulk of the reliable individual values will refer to main sequence stars, and while the mean luminosities of brighter stars are given reasonably well by this method, the scatter introduced into a color-magnitude array by using individual trigonometrically determined luminosities could obscure important features. Somewhat similar objections could be raised against the use of the usual spectroscopic parallaxes which also should be quite good for the main sequence but undoubtedly exhibit appreciable scatter for some, at least, of the brighter stars.

scholarly journals Globular cluster candidates in the Galactic bulge: Gaia and VVV view of the latest discoveries

2019 ◽  
Vol 628 ◽  
pp. A45 ◽  
Author(s):  
F. Gran ◽  
M. Zoccali ◽  
R. Contreras Ramos ◽  
E. Valenti ◽  
A. Rojas-Arriagada ◽  
...  
Keyword(s):  
Main Sequence ◽  
Star Clusters ◽  
Forthcoming Paper ◽  
Variable Stars ◽  
Star Cluster ◽  
Proper Motions ◽  
Magnitude Diagram ◽  
Spatial Coordinates ◽  
Red Giant ◽  
Moving Groups

Context. Thanks to the recent wide-area photometric surveys, the number of star cluster candidates have risen exponentially in the last few years. Most detections, however, are based only on the presence of an overdensity of stars in a given region or an overdensity of variable stars, regardless of their distance. As candidates, their detection has not been dynamically confirmed. Therefore, it is currently unknown how many and which of the published candidates are true clusters and which are chance alignments. Aims. We present a method to detect and confirm star clusters based on the spatial distribution, coherence in motion, and appearance on the color-magnitude diagram. We explain and apply this approach to one new star cluster and several candidate star clusters published in the literature. Methods. The presented method is based on data from the second data release of Gaia complemented with data from the VISTA Variables in the Vía Láctea survey for the innermost bulge regions. This method consists of a nearest neighbors algorithm applied simultaneously over spatial coordinates, star color, and proper motions to detect groups of stars that are close in the sky, move coherently, and define narrow sequences in the color-magnitude diagram, such as a young main sequence or a red giant branch. Results. When tested in the bulge area (−10 <  ℓ (deg) <  +10; −10 <  b (deg) <  +10) the method successfully recovered several known young and old star clusters. We report in this work the detection of one new, likely old star cluster, while deferring the others to a forthcoming paper. Additionally, the code has been applied to the position of 93 candidate star clusters published in the literature. As a result, only two of these clusters are confirmed as coherently moving groups of stars at their nominal positions.

scholarly journals Short Period Variables in the Magellanic Cloud Cluster NGC 1466

1973 ◽  
Vol 21 ◽  
pp. 113-119 ◽  
Author(s):  
M. V. Norris
Keyword(s):  
Globular Cluster ◽  
Metal Content ◽  
Globular Clusters ◽  
Magellanic Clouds ◽  
Horizontal Branch ◽  
A Value ◽  
Short Period ◽  
Magnitude Diagram ◽  
The Galaxy ◽  
Metal Abundance

NGC 1466 (α1950 = 3h44.m6, δ1950= -71°45’) is a globular cluster which appears to be situated between the two Magellanic Clouds. Previous estimates (Gascoigne, 1966) put it at roughly the same distance from us as the LMC, so it is regarded as a member of the Cloud system. It is globular in appearance, and its colour-magnitude diagram confirms this classification. It has a fairly well-developed horizontal branch, and was found by Wesselink (1970) to be quite rich in variables. The metallicity index, Q, (van den Bergh, 1967) has a value of -0.36 for NGC 1466 (Andrews and Lloyd Evans, 1971). This would rank it with M5 and NGC 6171 as a cluster of intermediate metal content. This comparison is consistent with the value of Δ V for the cluster, which, at 2.m6, is representative of the Δ V values of globular clusters of intermediate metal abundance in the Galaxy.

scholarly journals Detailed study of the Milky Way globular cluster Laevens 3

2019 ◽  
Vol 490 (2) ◽  
pp. 1498-1508
Author(s):  
Nicolas Longeard ◽  
Nicolas Martin ◽  
Rodrigo A Ibata ◽  
Michelle L M Collins ◽  
Benjamin P M Laevens ◽  
...  
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Milky Way ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
Magnitude Diagram ◽  
Mass Segregation ◽  
Stellar Properties ◽  
Lyrae Stars ◽  
Gaia Dr2

ABSTRACT We present a photometric and spectroscopic study of the Milky Way satellite Laevens 3. Using MegaCam/Canada–France–Hawaii Telescope $g$ and $i$ photometry and Keck II/DEIMOS multi-object spectroscopy, we refine the structural and stellar properties of the system. The Laevens 3 colour–magnitude diagram shows that it is quite metal-poor, old ($13.0 \pm 1.0$ Gyr), and at a distance of $61.4 \pm 1.0$ kpc, partly based on two RR Lyrae stars. The system is faint ($M_V = -2.8^{+0.2}_{-0.3}$ mag) and compact ($r_h = 11.4 \pm 1.0$ pc). From the spectroscopy, we constrain the systemic metallicity (${\rm [Fe/H]}_\mathrm{spectro} = -1.8 \pm 0.1$ dex) but the metallicity and velocity dispersions are both unresolved. Using Gaia DR2, we infer a mean proper motion of $(\mu _\alpha ^*,\mu _\delta)=(0.51 \pm 0.28,-0.83 \pm 0.27)$ mas yr−1, which, combined with the system’s radial velocity ($\langle v_r\rangle = -70.2 \pm 0.5 {\rm \, km \,\, s^{-1}}$), translates into a halo orbit with a pericenter and apocenter of $40.7 ^{+5.6}_{-14.7}$ and $85.6^{+17.2}_{-5.9}$ kpc, respectively. Overall, Laevens 3 shares the typical properties of the Milky Way’s outer halo globular clusters. Furthermore, we find that this system shows signs of mass segregation that strengthens our conclusion that Laevens 3 is a globular cluster.

scholarly journals The Influence of Gas Expulsion on the Evolution of Star Clusters

2007 ◽  
Vol 3 (S246) ◽  
pp. 36-40
Author(s):  
H. Baumgardt ◽  
P. Kroupa
Keyword(s):  
Globular Clusters ◽  
Milky Way ◽  
Three Dimensional ◽  
Star Clusters ◽  
Dynamical Evolution ◽  
Mass Function ◽  
Star Cluster ◽  
Dissolution Mechanism ◽  
Large Set ◽  
Cluster Systems

AbstractWe present new results on the dynamical evolution and dissolution of star clusters due to residual gas expulsion and the effect this has on the mass function and other properties of star cluster systems. To this end, we have carried out a large set of N-body simulations, varying the star formation efficiency, gas expulsion time scale and strength of the external tidal field, obtaining a three-dimensional grid of models which can be used to predict the evolution of individual star clusters or whole star cluster systems by interpolating between our runs. When applied to the Milky Way globular cluster system, we find that gas expulsion is the main dissolution mechanism for star clusters, destroying about 80% of all clusters within a few 10s of Myers. Together with later dynamical evolution, it seems possible to turn an initial power-law mass function into a log-normal one with properties similar to what has been observed for the Milky Way globular clusters.

scholarly journals An Update on the ACS Virgo and Fornax Cluster Surveys

2007 ◽  
Vol 3 (S246) ◽  
pp. 377-386 ◽  
Author(s):  
Patrick Côté ◽  
Laura Ferrarese ◽  
Andrés Jordán ◽  
John P. Blakeslee ◽  
Chin-Wei Chen ◽  
...  
Keyword(s):  
Globular Clusters ◽  
Milky Way ◽  
Dwarf Galaxies ◽  
Hubble Space Telescope ◽  
Structural Parameters ◽  
Star Clusters ◽  
Early Type ◽  
Space Telescope ◽  
Fornax Cluster ◽  
Selection Of

AbstractWe present a brief update on the ACS Virgo and Fornax Cluster Surveys —Hubble Space Telescopeprograms to obtainACSimaging for 143 early-type galaxies in the two galaxy clusters nearest to the Milky Way. We summarize a selection of science highlights from the surveys as including new results on the central structure of early-type galaxies, the apparent continuity of photometric and structural parameters between dwarf and giant galaxies, and the properties of globular clusters, diffuse star clusters and ultra-compact dwarf galaxies.

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