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 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 Main-sequence broadening, Be stars, and stellar rotation inhand χ Persei

1994 ◽  
Vol 162 ◽  
pp. 151-152
Author(s):  
J. Denoyelle ◽  
C. Aerts ◽  
C. Waelkens
Keyword(s):  
Main Sequence ◽  
Large Fraction ◽  
Variable Stars ◽  
Theoretical Studies ◽  
Be Stars ◽  
Stellar Rotation ◽  
B Stars ◽  
Fundamental Parameters ◽  
Magnitude Diagram ◽  
Double Cluster

The double cluster h andxPersei is one of the richest clusters containing early-B stars, and therefore is important for observational and theoretical studies on the fundamental parameters of massive stars. The colour-magnitude diagram of the double cluster shows an important scatter (see Figure 1). It has long been known thathandxPersei are extremely rich in Be stars (Slettebak 1968). Our previous contention (Waelkens et al. 1990) that the large-amplitude variable stars we discovered are also Be stars, could be confirmed for a few objects. Rotation velocities for stars inhandxPersei are usually high, which is not surprising in view of the large fraction of Be stars.

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 OCAAT: automated analysis of star cluster colour-magnitude diagrams for gauging the local distance scale

2014 ◽  
Vol 10 (S306) ◽  
pp. 298-300
Author(s):  
Gabriel I. Perren ◽  
Ruben A. Vázquez ◽  
Andrés E. Piatti ◽  
André Moitinho
Keyword(s):  
Main Sequence ◽  
Star Clusters ◽  
Automated Analysis ◽  
Star Cluster ◽  
Magellanic Clouds ◽  
Distance Scale ◽  
Analysis Tool ◽  
Large Set ◽  
Uncertainty Estimates ◽  
Local Distance

AbstractStar clusters are among the fundamental astrophysical objects used in setting the local distance scale. Despite its crucial importance, the accurate determination of the distances to the Magellanic Clouds (SMC/LMC) remains a fuzzy step in the cosmological distance ladder. The exquisite astrometry of the recently launched ESA Gaia mission is expected to deliver extremely accurate statistical parallaxes, and thus distances, to the SMC/LMC. However, an independent SMC/LMC distance determination via main sequence fitting of star clusters provides an important validation check point for the Gaia distances. This has been a valuable lesson learnt from the famous Hipparcos Pleiades distance discrepancy problem. Current observations will allow hundreds of LMC/SMC clusters to be analyzed in this light.Today, the most common approach for star cluster main sequence fitting is still by eye. The process is intrinsically subjective and affected by large uncertainties, especially when applied to poorly populated clusters. It is also, clearly, not an efficient route for addressing the analysis of hundreds, or thousands, of star clusters. These concerns, together with a new attitude towards advanced statistical techniques in astronomy and the availability of powerful computers, have led to the emergence of software packages designed for analyzing star cluster photometry. With a few rare exceptions, those packages are not publicly available.Here we present OCAAT (Open Cluster Automated Analysis Tool), a suite of publicly available open source tools that fully automatises cluster isochrone fitting. The code will be applied to a large set of hundreds of open clusters observed in the Washington system, located in the Milky Way and the Magellanic Clouds. This will allow us to generate an objective and homogeneous catalog of distances up to ~ 60 kpc along with its associated reddening, ages and metallicities and uncertainty estimates.

scholarly journals Red Variable Stars in Metal Rich Globular Clusters

1973 ◽  
Vol 21 ◽  
pp. 151-163
Author(s):  
T. Lloyd Evans ◽  
J. W. Menzies
Keyword(s):  
Systematic Study ◽  
Globular Clusters ◽  
Variable Stars ◽  
Large Numbers ◽  
Magnitude Diagram ◽  
Metal Abundance ◽  
The Mean ◽  
Red Giant ◽  
Photoelectric Observations ◽  
Considerable Range

The globular clusters contain sufficiently large numbers of stars to permit a systematic study of the intrinsically rare variable stars which lie near the tip of the red giant branch. The position of the smaller amplitude stars in the colour magnitude diagram is of particular interest. Eggen (1972) has published photoelectric observations of such stars in several globular clusters, most of intermediate or low metal abundance. The mean colour of 14 stars in 5 clusters is (V-IK) = 1.40, with a spread from 1.60 to 1.12 (or 0.75 if V8 in M22 is of this type) which Eggen regards as indicating a range of temperature. The red variable stars in the metal rich globular cluster 47 Tucanae are much redder and show a considerable range of colour.

scholarly journals Infrared modeling of the starburst clone NGC 3603

1999 ◽  
Vol 193 ◽  
pp. 478-479
Author(s):  
Daniel Devost ◽  
Claus Leitherer
Keyword(s):  
Stellar Population ◽  
Main Sequence ◽  
Star Cluster ◽  
Radial Profiles ◽  
Magnitude Diagram

We present results of an HST archive study of the star cluster NGC 3603. The color-magnitude diagram (CMD) and the radial profiles have been derived using HST-nicmos F110W and F171M images. As expected, the CMD shows that the cluster is very young (< 3 Myr) and that a significant portion of the stellar population (M < 4M⊙) is on the pre-main sequence phase. From the radial profiles, we derive a similar half-light radius for both wavebands of 0.17 pc.

scholarly journals CCD Photometry in the Globular Cluster M4

1995 ◽  
Vol 164 ◽  
pp. 411-411
Author(s):  
W.K. Griffiths ◽  
I.N. Kanatas ◽  
R.J. Dickens ◽  
A.J. Penny
Keyword(s):  
Globular Cluster ◽  
Main Sequence ◽  
Ccd Photometry ◽  
Magnitude Diagram ◽  
Red Giant

A V, B- V composite colour-magnitude diagram, based upon CCD photometry from V~ 12 on the red giant branch to V~ 25 on the main-sequence has been derived for the globular cluster M4. A distance to the cluster of (m – M)v = 12.84 ± 0.19 is determined and the best match to theoretical isochrones is for the case [Fe/H]=−1.27 and an age of 16±1 Gyr. A differential age comparison with NGC 362 shows that M4 is approximately 1.7 Gyr older.

scholarly journals The extended main-sequence turn-off of the Milky Way open cluster Collinder 347

2019 ◽  
Vol 490 (2) ◽  
pp. 2414-2420 ◽  
Author(s):  
Andrés E Piatti ◽  
Charles Bonatto
Keyword(s):  
Main Sequence ◽  
Milky Way ◽  
Open Cluster ◽  
Age Difference ◽  
Proper Motions ◽  
Gaussian Distributions ◽  
Young Object ◽  
Magnitude Diagram ◽  
Chemical Content ◽  
Gaia Dr2

ABSTRACT We made use of the Gaia DR2 archive to comprehensively study the Milky Way open cluster Collinder 347, known until now as a very young object of solar metal content. However, the G versus GBP − GRP colour–magnitude diagram (CMD) of bonafide probable cluster members, selected on the basis of individual stellar proper motions, their spatial distribution, and placement in the CMD, reveals the existence of a Hyades-like age open cluster (log(t /yr) = 8.8) of moderately metal-poor chemical content ([Fe/H]  = −0.4 dex), with a present-day mass of 3.3 × 103 M⊙. The cluster exhibits an extended main-sequence turn-off (eMSTO) of nearly 500 Myr, while that computed assuming Gaussian distributions from photometric errors, stellar binarity, rotation, and metallicity spread yields an eMSTO of ∼340 Myr. Such an age difference points to the existence within the cluster of stellar populations with different ages.

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).

scholarly journals Observational hints of a real age spread in the young LMC star cluster NGC 1971

2017 ◽  
Vol 470 (1) ◽  
pp. L77-L81 ◽  
Author(s):  
Andrés E. Piatti ◽  
Andrew Cole
Keyword(s):  
Main Sequence ◽  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
Star Cluster ◽  
Stellar Rotation ◽  
Cloud Cluster ◽  
Magnitude Diagram ◽  
Observational Errors ◽  
Age Range

Abstract We report that the serendipitous young Large Magellanic Cloud cluster NGC 1971 exhibits an extended main-sequence turn-off (eMSTO) possibly originated mostly by a real age spread. We used CT1 Washington photometry to produce a colour–magnitude diagram (CMD) with the fiducial cluster features. From its eMSTO, we estimated an age spread of ∼170 Myr (observed age range 100–280 Myr), once observational errors, stellar binarity, overall metallicity variations and stellar rotation effects were subtracted in quadrature from the observed age width.

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