scholarly journals On The Metal-poor non-Sagittarius Globular Cluster NGC 5053: Orbit, Mg, Al, and Si

2017 ◽  
Vol 13 (S334) ◽  
pp. 370-371
Author(s):  
Baitian Tang
Keyword(s):  
Radial Velocity ◽  
Globular Cluster ◽  
Globular Clusters ◽  
Near Infrared ◽  
Dwarf Galaxy ◽  
Optical Spectra ◽  
Spectral Lines ◽  
Multiple Populations ◽  
Multiple Population ◽  
Similar Location

AbstractMetal-poor globular clusters (GCs) show intriguing Al-Mg and Si-Al correlations, which are important clues to decipher the multiple population phenomenon. NGC 5053 is one of the most metal-poor GCs, and has been suggested to be associated with the Sagittarius dwarf galaxy (Sgr), due to its similar location and radial velocity with one of the Sgr arms. In this work, we simulate the orbit of NGC 5053, and argue against the connection between Sgr and NGC 5053. Meanwhile, Mg, Al, and Si spectral lines, which are difficult to detect in the optical spectra, have been detected in the near-infrared APOGEE spectra. We use three different sets of stellar parameters and codes to derive the Mg, Al, and Si abundances, and we always see a large Al variation, and a substantial Si enhancement. Comparing with other metal-poor GCs, we suggest metallicity may not be the only parameter that controls the multiple populations.

scholarly journals Chemical abundance analysis of red giant branch stars in the globular cluster E3

2018 ◽  
Vol 616 ◽  
pp. A181 ◽  
Author(s):  
L. Monaco ◽  
S. Villanova ◽  
G. Carraro ◽  
A. Mucciarelli ◽  
C. Moni Bidin
Keyword(s):  
Radial Velocity ◽  
Globular Cluster ◽  
Globular Clusters ◽  
Abundance Ratio ◽  
Chemical Abundance ◽  
Chemical Abundances ◽  
Multiple Populations ◽  
Red Giant ◽  
A Minor ◽  
Giant Branch Stars

Context. Globular clusters are known to host multiple stellar populations, which are a signature of their formation process. The globular cluster E3 is one of the few low-mass globulars that is thought not to host multiple populations. Aims. We investigate red giant branch stars in E3 with the aim of providing a first detailed chemical inventory for this cluster, we determine its radial velocity, and we provide additional insights into the possible presence of multiple populations in this cluster. Methods. We obtained high-resolution FLAMES-UVES/VLT spectra of four red giant branch stars likely members of E3. We performed a local thermodynamic equilibrium abundance analysis based on one-dimensional plane parallel ATLAS9 model atmospheres. Abundances were derived from line equivalent widths or spectrum synthesis. Results. We measured abundances of Na and of iron peak (Fe, V, Cr, Ni, Mn), α(Mg, Si, Ca, Ti), and neutron capture elements (Y, Ba, Eu). The mean cluster heliocentric radial velocity, metallicity, and sodium abundance ratio are νhelio = 12.6 ± 0.4 km s−1(σ = 0.6 ± 0.2 km s−1), [Fe/H] = −0.89 ± 0.08 dex, and [Na/Fe] = 0.18 ± 0.07 dex, respectively. The low Na abundance with no appreciable spread is suggestive of a cluster dominated by first-generation stars in agreement with results based on lower resolution spectroscopy. The low number of stars observed does not allow us to rule out a minor population of second-generation stars. The observed chemical abundances are compatible with the trends observed in Milky Way stars.

scholarly journals Central Dynamics of Globular Clusters: the Case for a Black Hole in ω Centauri

2007 ◽  
Vol 3 (S246) ◽  
pp. 341-345
Author(s):  
Eva Noyola ◽  
Karl Gebhardt ◽  
Marcel Bergmann
Keyword(s):  
Black Hole ◽  
Relaxation Time ◽  
Globular Cluster ◽  
Globular Clusters ◽  
Dwarf Galaxy ◽  
Kinematic Data ◽  
The Core ◽  
Galactic System ◽  
Interesting Candidate ◽  
Radial Anisotropy

AbstractThe globular cluster ω Centauri is one of the largest and most massive members of the Galactic system. Its classification as a globular cluster has been challenged making it a candidate for being the stripped core of an accreted dwarf galaxy; this and the fact that it has one of the largest velocity dispersions for star clusters in our galaxy makes it an interesting candidate for harboring an intermediate mass black hole. We measure the surface brightness profile from integrated light on an HST/ACS image, and find a central power-law cusp of logarithmic slope -0.08. We also analyze Gemini GMOS-IFU kinematic data for a 5”x5” field centered on the nucleus of the cluster, as well as for a field 14″ away. We detect a clear rise in the velocity dispersion from 18.6 kms−1 at 14″ to 23 kms−1 in the center. Given the very large core in ω Cen (2.58'), an increase in the dispersion in the central 10″ is difficult to attribute to stellar remnants, since it requires too many dark remnants and the implied configuration would dissolve quickly given the relaxation time in the core. However, the increase could be consistent with the existence of a central black hole. Assuming a constant M/L for the stars within the core, the dispersion profile from these data and data at larger radii implies a black hole mass of 4.0+0.75−1.0×104M⊙. We have also run flattened, orbit-based models and find a similar mass. In addition, the no black hole case for the orbit model requires an extreme amount of radial anisotropy, which is difficult to preserve given the short relaxation time of the cluster.

scholarly journals Narrow-Band Photometry of Red Variables in Globular Clusters

1973 ◽  
Vol 21 ◽  
pp. 164-177
Author(s):  
Robert F. Wing
Keyword(s):  
Radial Velocity ◽  
Globular Clusters ◽  
Near Infrared ◽  
Narrow Band ◽  
Small Range ◽  
Mira Variables ◽  
Color System ◽  
Red Giant ◽  
M Stars

AbstractFourteen red variables in the southern globular clusters 47 Tuc, ω Cen, and NGC 362 have been observed on an eight-color system of narrow-band photometry in the near infrared. Temperatures are derived from blackbody fits to the calibrated fluxes, and spectral types are given for the M stars. The types observed for the three Mira variables in 47 Tuc range from M3.1 to M7.5; two small-range variables in the same cluster are later than M4. The variables in ω Cen are mostly earlier than K5, but spectra of types M3 and MO were also encountered among radial-velocity members. In both the metal-rich 47 Tuc and the metal-poor ω Cen, the relation between TiO band strength and temperature is approximately normal. Several of these stars fall well above or below the red giant branches of their clusters in diagrams of infrared magnitude against temperature. Comparisons are made with recent results obtained at Radcliffe Observatory on some of the same stars.

scholarly journals IC 4499 revised: Spectro-photometric evidence of small light-element variations

2018 ◽  
Vol 618 ◽  
pp. A131 ◽  
Author(s):  
E. Dalessandro ◽  
C. Lardo ◽  
M. Cadelano ◽  
S. Saracino ◽  
N. Bastian ◽  
...  
Keyword(s):  
Globular Clusters ◽  
Milky Way ◽  
Dwarf Galaxy ◽  
Light Element ◽  
High Resolution Spectroscopy ◽  
Multiple Populations ◽  
Number Ratio ◽  
Red Giant ◽  
Good Agreement

It has been suggested that IC 4499 is one of the very few old globulars to not host multiple populations with light-element variations. To follow-up on this very interesting result, here we have made use of accurate HST photometry and FLAMES at VLT high-resolution spectroscopy to investigate in more detail the stellar population properties of this system. We find that the red giant branch of the cluster is clearly bimodal in near-UV-optical colour-magnitude diagrams, thus suggesting that IC 4499 is actually composed by two sub-populations of stars with different nitrogen abundances. This represents the first detection of multiple populations in IC 4499. Consistently, we also find that one star out of six is Na-rich to some extent, while we do not detect any evidence of intrinsic spread in both Mg and O. The number ratio between stars with normal and enriched nitrogen is in good agreement with the number ratio – mass trend observed in Galactic globular clusters. Also, as typically found in other systems, nitrogen rich stars are more centrally concentrated than normal stars, although this result cannot be considered conclusive because of the limited field of view covered by our observations (∼1rh). On the contrary, we observe that both the RGB UV colour spread, which is a proxy of N variations, and Na abundance variations, are significantly smaller than those observed in Milky Way globular clusters with mass and metallicity comparable to IC 4499. The modest N and Na spreads observed in this system can be tentatively connected to the fact that IC 4499 likely formed in a disrupted dwarf galaxy orbiting the Milky Way, as previously proposed based on its orbit.

scholarly journals The Formation and Evolution of Star Clusters and Galaxies

2005 ◽  
Vol 13 ◽  
pp. 347-349
Author(s):  
Stephen E. Zepf
Keyword(s):  
Galaxy Formation ◽  
Globular Cluster ◽  
Globular Clusters ◽  
Near Infrared ◽  
Cluster Formation ◽  
Star Clusters ◽  
Elliptical Galaxies ◽  
Cluster Systems ◽  
Important Observation ◽  
Formation And Evolution

AbstractThis paper addresses the questions of what we have learned about how and when dense star clusters form, and what studies of star clusters have revealed about galaxy formation and evolution. One important observation is that globular clusters are observed to form in galaxy mergers and starbursts in the local universe, which both provides constraints on models of globular cluster formation, and suggests that similar physical conditions existed when most early-type galaxies and their globular clusters formed in the past. A second important observation is that globular cluster systems typically have bimodal color distributions. This was predicted by merger models, and indicates an episodic formation history for elliptical galaxies. A third and very recent result is the discovery of large populations of intermediate age globular clusters in several elliptical galaxies through the use of optical to near-infrared colors. These provide an important link between young cluster systems observed in starbursts and mergers and old cluster systems. This continuum of ages of the metal-rich globular cluster systems also indicates that there is no special age or epoch for the formation of the metal-rich globular clusters, which comprise about half of the cluster population. The paper concludes with a brief discussion of recent results on the globular cluster – low-mass X-ray binary connection.

scholarly journals New CCD Survey of Globular Clusters in M31

2002 ◽  
Vol 207 ◽  
pp. 46-51 ◽  
Author(s):  
Myung Gyoon Lee ◽  
Sang Chul Kim ◽  
Doug Geisler ◽  
Juan Seguel ◽  
Ata Sarajedini ◽  
...  
Keyword(s):  
Radial Velocity ◽  
Globular Cluster ◽  
Globular Clusters ◽  
Progress Report ◽  
Wide Field

We present a progress report of our wide field CCD survey of globular clusters in M31. We have covered a 3 deg × 3 deg area centered on M31, using the KPNO 0.9m and Washington CMT1 filters. Our survey is much deeper and more sensitive than previous surveys. We have found several hundred new globular cluster candidates in M31 in addition to confirming previously known globular clusters, and also have found a number of interlopers among previous globular cluster catalogs. We have also obtained spectra of about 500 objects among these candidates using HYDRA at the WIYN 3.5m telescope, which are used for classification and measuring the radial velocity of the candidate objects. When completed, a new master catalog of globular clusters in M31 will be made, combining the new globular clusters with the known globular clusters.

scholarly journals Discovery of a nitrogen-enhanced mildly metal-poor binary system: Possible evidence for pollution from an extinct AGB star

2019 ◽  
Vol 631 ◽  
pp. A97 ◽  
Author(s):  
José G. Fernández-Trincado ◽  
Ronald Mennickent ◽  
Mauricio Cabezas ◽  
Olga Zamora ◽  
Sarah L. Martell ◽  
...  
Keyword(s):  
Binary System ◽  
Radial Velocity ◽  
Globular Clusters ◽  
Near Infrared ◽  
Asymptotic Giant Branch ◽  
Main Element ◽  
Large Variability ◽  
Asymptotic Giant Branch Star ◽  
Red Giant ◽  
Branch Star

We report the serendipitous discovery of a nitrogen-rich, mildly metal-poor ([Fe/H] = −1.08) giant star in a single-lined spectroscopic binary system found in the SDSS-IV Apache Point Observatory Galactic Evolution Experiment (APOGEE-2) survey, Data Release 14 (DR14). Previous work has assumed that two percent of halo giants with unusual elemental abundances have been evaporated from globular clusters, but other origins for their abundance signatures, including binary mass transfer, must also be explored. We present the results of an abundance reanalysis of the APOGEE-2 high-resolution near-infrared spectrum of 2M12451043+1217401 with the Brussels Automatic Stellar Parameter (BACCHUS) automated spectral analysis code. We manually re-derive the main element families, namely light elements (C, N), elements (O, Mg, Si), the iron-peak element (Fe), s-process element (Ce), and light odd-Z element (Al). Our analysis confirms the N-rich nature of 2M12451043+1217401, which has a [N/Fe] ratio of +0.69, and shows that the abundances of C and Al are slightly discrepant from those of a typical mildly metal-poor red giant branch star, but exhibit Mg, Si, O and s-process abundances (Ce) of typical field stars. We also detect a particularly large variability in the radial velocity of this star over the period of the APOGEE-2 observations; the most likely orbit fit to the radial velocity data has a period of 730.89  ±  106.86 days, a velocity semi-amplitude of 9.92  ±  0.14 km s−1, and an eccentricity of ∼0.1276  ±  0.1174. These data support the hypothesis of a binary companion, which has probably been polluted by a now-extinct asymptotic giant branch star.

scholarly journals The s-process enriched star HD 55496: origin from a globular cluster or from the tidal disruption of a dwarf galaxy?

2019 ◽  
Vol 488 (1) ◽  
pp. 482-494 ◽  
Author(s):  
C B Pereira ◽  
N A Drake ◽  
F Roig
Keyword(s):  
Globular Cluster ◽  
Binary Stars ◽  
Globular Clusters ◽  
Dwarf Galaxy ◽  
Dynamical Analysis ◽  
Element Abundance ◽  
Tidal Disruption ◽  
Abundance Pattern ◽  
Retrograde Motion ◽  
Process Elements

Abstract We present a new abundance analysis of HD 55496, previously known as a metal-poor barium star. We found that HD 55496 has a metallicity [Fe/H]  = −1.55 and is s-process enriched. We find that HD 55496 presents four chemical peculiarities: (i) a Na–O abundance anticorrelation; (ii) it is aluminium rich; (iii) it is carbon poor for an s-process enriched star, and (iv) the heavy second s-process peak elements, such as Ba, La, Ce, and Nd, present smaller abundances than the light s-process elements, such as Sr, Y, and Zr, which is not usually observed among the chemically peculiar binary stars at this metallicity. The heavy-element abundance pattern suggests that the main source of the neutrons is the 22Ne(α,n)25Mg reaction. Taking all these abundance evidences together into consideration strongly suggests that HD 55496 is a ‘second-generation of globular cluster stars’ formed from gas already strongly enriched in s-process elements and now is a field halo object. Our dynamical analysis, however, indicates that the past encounter probabilities with the known globular clusters are very low ($\le \!6{{\ \rm per\ cent}}$). This evidence, together with the retrograde motion, points to a halo intruder possibly originated from the tidal disruption of a dwarf galaxy.

scholarly journals The pristine dwarf-galaxy survey – III. Revealing the nature of the Milky Way globular cluster Sagittarius II

2021 ◽  
Vol 503 (2) ◽  
pp. 2754-2762
Author(s):  
Nicolas Longeard ◽  
Nicolas Martin ◽  
Rodrigo A Ibata ◽  
Else Starkenburg ◽  
Pascale Jablonka ◽  
...  
Keyword(s):  
Globular Cluster ◽  
Confidence Limit ◽  
Globular Clusters ◽  
Milky Way ◽  
Velocity Dispersion ◽  
Dwarf Galaxy ◽  
Low Velocity ◽  
Data Set ◽  
Large Size ◽  
Additional Member

ABSTRACT We present a new spectroscopic study of the faint Milky Way satellite Sagittarius II. Using multiobject spectroscopy from the Fibre Large Array Multi-Element Spectrograph, we supplement the data set of Longeard et al. with 47 newly observed stars, 19 of which are identified as members of the satellite. These additional member stars are used to put tighter constraints on the dynamics and the metallicity properties of the system. We find a low velocity dispersion of $\sigma _\mathrm{v}^\mathrm{SgrII} = 1.7 \pm 0.5$ km s−1, in agreement with the dispersion of Milky Way globular clusters of similar luminosity. We confirm the very metal-poor nature of the satellite ([Fe/H]$_\mathrm{spectro}^\mathrm{SgrII} = -2.23 \pm 0.07$) and find that the metallicity dispersion of Sgr II is not resolved, reaching only 0.20 at the 95 per cent confidence limit. No star with a metallicity below −2.5 is confidently detected. Therefore, despite the unusually large size of the system (r$_h = 35.5 ^{+1.4}_{-1.2}$ pc), we conclude that Sgr II is an old and metal-poor globular cluster of the Milky Way.

scholarly journals A stellar census in globular clusters with MUSE: multiple populations chemistry in NGC 2808

2019 ◽  
Vol 631 ◽  
pp. A14 ◽  
Author(s):  
M. Latour ◽  
T.-O. Husser ◽  
B. Giesers ◽  
S. Kamann ◽  
F. Göttgens ◽  
...  
Keyword(s):  
Globular Clusters ◽  
Signal To Noise Ratio ◽  
Spectral Lines ◽  
High Resolution Spectroscopy ◽  
High Signal ◽  
Multiple Populations ◽  
Synthetic Populations ◽  
Central Regions ◽  
Chromosome Maps ◽  
Red Giant

Context. Galactic globular clusters (GCs) are now known to host multiple populations displaying particular abundance variations. The different populations within a GC can be well distinguished following their position in the pseudo two-colors diagrams, also referred to as “chromosome maps”. These maps are constructed using optical and near-UV photometry available from the Hubble Space Telescope (HST) UV survey of GCs. However, the chemical tagging of the various populations in the chromosome maps is hampered by the fact that HST photometry and elemental abundances are both only available for a limited number of stars. Aims. The spectra collected as part of the MUSE survey of globular clusters provide a spectroscopic counterpart to the HST photometric catalogs covering the central regions of GCs. In this paper, we use the MUSE spectra of 1115 red giant branch (RGB) stars in NGC 2808 to characterize the abundance variations seen in the multiple populations of this cluster. Methods. We used the chromosome map of NGC 2808 to divide the RGB stars into their respective populations. We then combined the spectra of all stars belonging to a given population, resulting in one high signal-to-noise ratio spectrum representative of each population. Results. Variations in the spectral lines of O, Na, Mg, and Al are clearly detected among four of the populations. In order to quantify these variations, we measured equivalent width differences and created synthetic populations spectra that were used to determine abundance variations with respect to the primordial population of the cluster. Our results are in good agreement with the values expected from previous studies based on high-resolution spectroscopy. We do not see any significant variations in the spectral lines of Ca, K, and Ba. We also do not detect abundance variations among the stars belonging to the primordial population of NGC 2808. Conclusions. We demonstrate that in spite of their low resolution, the MUSE spectra can be used to investigate abundance variations in the context of multiple populations.

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