ABSTRACT Photometric completeness affects the photometry of stars in crowded regions such as the cores of star clusters. Some analysis such as deriving the structural parameters of star clusters ...using radial density profile is heavily affected by photometric completeness and the classical techniques to map this completeness in a given field are very expensive computationally. In most surveys, for example, the large quantity of data makes it impracticable to estimate the completeness using the traditional method for the whole sample due to time and computational requirements. In this work, we present a new method that is significantly faster and results in similar completeness curves and maps as the traditional approach, providing a great first-step completeness estimator for a large sample of data. Using the completeness corrected data for each cluster we built radial density profiles improving significantly the inner portion of the profile; we also fitted the King model to them, determining the clusters’ structural parameters based on a more realistic cluster profile. In this preliminary analysis, we derived structural parameters for nine selected clusters covering a range of core radii (5–40 arcesc) and tidal radii (40–180 arcesc) and discuss how the photometric completeness affects the determination of these parameters when we count stars to trace the radial profile of a star cluster.
Context. Open clusters are very useful targets for examining possible trends in galactocentric distance and age, especially when young and old open clusters are compared. Aims. We carried out a ...detailed spectroscopic analysis to derive the chemical composition of seven red giants in the young open cluster NGC 3114. Abundances of C, N, O, Li, Na, Mg, Al, Ca, Si, Ti, Ni, Cr, Y, Zr, La, Ce, and Nd were obtained, as well as the carbon isotopic ratio. Methods. The atmospheric parameters of the studied stars and their chemical abundances were determined using high-resolution optical spectroscopy. We employed the local-thermodynamic-equilibrium model atmospheres of Kurucz and the spectral analysis code MOOG. The abundances of the light elements were derived using the spectral synthesis technique. Results. We found that NGC 3114 has a mean metallicity of Fe/H = −0.01 ± 0.03. The isochrone fit yielded a turn-off mass of 4.2 M⊙. The N/C ratio is in good agreement with the models predicted by first dredge-up. We found that two stars, HD 87479 and HD 304864, have high rotational velocities of 15.0 km s-1 and 11.0 km s-1; HD 87526 is a halo star and is not a member of NGC 3114. Conclusions. The carbon and nitrogen abundance in NGC 3114 agree with the field and cluster giants. The oxygen abundance in NGC 3114 is lower compared to the field giants. The O/Fe ratio is similar to the giants in young clusters. We detected sodium enrichment in the analyzed cluster giants. As far as the other elements are concerned, their X/Fe ratios follow the same trend seen in giants with the same metallicity.
ABSTRACT
The structure of the Small Magellanic Cloud (SMC) outside of its main body is characterized by tidal branches resulting from its interactions mainly with the Large Magellanic Cloud (LMC). ...Characterizing the stellar populations in these tidal components helps to understand the dynamical history of this galaxy and of the Magellanic system in general. We provide full phase-space vector information for Southern Bridge clusters. We performed a photometric and spectroscopic analysis of twelve SMC clusters, doubling the number of SMC clusters with full phase-space vector information known to date. We reclassify the sample considering 3D distances and 3D velocities. We found that some of the clusters classified as Southern Bridge objects according to the projected 2D classification actually belong to the Main Body and Counter-Bridge in the background. The comparison of the kinematics of the genuine foreground Bridge clusters with those previously analysed in the same way reveals that Southern Bridge clusters are moving towards the LMC and share the kinematics of the Northern Bridge. Adding to our sample clusters from the literature with CaT metallicity determinations we compare the age–metallicity relation of the Southern Bridge with the one of the Northern Bridge. We reinforce the idea that both regions do not seem to have experienced the same chemical enrichment history and that there is a clear absence of clusters in the Northern Bridge older than 3 Gyr and more metal poor than −1.1, which would not seem to be due to a selection effect.
ABSTRACT
The structure of the Small Magellanic Cloud (SMC) is very complex, in particular in the periphery that suffers more from the interactions with the Large Magellanic Cloud (LMC). A wealth of ...observational evidence has been accumulated revealing tidal tails and bridges made up of gas, stars, and star clusters. Nevertheless, a full picture of the SMC outskirts is only recently starting to emerge with a 6D phase-space map plus age and metallicity using star clusters as tracers. In this work, we continue our analysis of another outer region of the SMC, the so-called West Halo, and combined it with the previously analysed Northern Bridge. We use both structures to define the Bridge and Counter-bridge trailing and leading tidal tails. These two structures are moving away from each other, roughly in the SMC–LMC direction. The West Halo form a ring around the SMC inner regions that goes up to the background of the Northern Bridge shaping an extended layer of the Counter-bridge. Four old Bridge clusters were identified at distances larger than 8 kpc from the SMC centre moving towards the LMC, which is consistent with the SMC–LMC closest distance of 7.5 kpc when the Magellanic Bridge was formed about 150Myr ago; this shows that the Magellanic Bridge was not formed only by pulled gas, but it also removed older stars from the SMC during its formation. We also found age and metallicity radial gradients using projected distances on sky, which are vanished when we use the real 3D distances.
Open clusters are very useful examples to explain the constraint of the nucleosynthesis process with the luminosities of stars because the distances of the clusters are better known than those of ...field stars. We carried out a detailed spectroscopic analysis to derive the chemical composition of two red giants in the young open cluster NGC 5822, NGC 5822-2, and NGC 5822-201. We obtained abundances of C, N, O, Na, Mg, Al, Ca, Si, Ti, Ni, Cr, Y, Zr, La, Ce, and Nd. The atmospheric parameters of the studied stars and their chemical abundances were determined using high-resolution optical spectroscopy. We employed the local thermodynamic equilibrium model atmospheres of Kurucz and the spectral analysis code MOOG. The abundances of the light elements were derived using the spectral synthesis technique. We found that NGC 5822-2 and-201 have, respectively, a mean overabundance of the elements created by the s-process, "s," with the notation s/Fe of 0.77 + or - 0.12 and 0.83 + or - 0.05. These values are higher than those for field giants of similar metallicity. We also found that NGC 5822-2 and -201 have, respectively, luminosities of 140 Lodot and 76 Lodot, which are much lower than the luminosity of an asymptotic giant branch star. We conclude that NGC 5822-2 and NGC 5822-201 are two new barium stars first identified in the open cluster NGC 5822. The mass transfer hypothesis is the best scenario to explain the observed overabundances.
The VISCACHA survey Saroon, S.; Dias, B.; Tsujimoto, T. ...
Astronomy and astrophysics (Berlin),
09/2023, Letnik:
677
Journal Article
Recenzirano
Odprti dostop
The chemical evolution history of the Small Magellanic Cloud (SMC) has been a matter of debate for decades. The challenges in understanding the SMC chemical evolution are related to a very slow star ...formation rate (SFR) combined with bursts triggered by the multiple interactions between the SMC and the Large Magellanic Cloud, a significant (∼0.5 dex) metallicity dispersion for the SMC cluster population younger than about 7.5 Gyr, and multiple chemical evolution models tracing very different paths through the observed age–metallicity relation of the SMC. There is no doubt that these processes were complex. Therefore, a step-by-step strategy is required in order to better understand the SMC chemical evolution. We adopted an existing framework to split the SMC into regions on the sky, and we focus on the west halo in this work, which contains the oldest and most metal-poor stellar populations and is moving away from the SMC, that is, in an opposite motion with respect to the Magellanic Bridge. We present a sample containing ∼60% of all west halo clusters to represent the region well, and we identify a clear age–metallicity relation with a tight dispersion that exhibits a 0.5 dex metallicity dip about 6 Gyr ago. We ran chemical evolution models and discuss possible scenarios to explain this metallicity dip, the most likely being a major merger accelerating the SFR after the event. This merger should be combined with inefficient internal gas mixing within the SMC and different SFRs in different SMC regions because the same metallicity dip is not seen in the AMR of the SMC combining clusters from all regions. We try to explain the scenario to better understand the SMC chemo-dynamical history.
Abstract
Single stars in open clusters with known distances are important targets in constraining the nucleosynthesis process since their ages and luminosities are also known. In this work, we ...analyze a sample of 29 single red giants of the open clusters NGC 2360, NGC 3680, and NGC 5822 using high-resolution spectroscopy. We obtained atmospheric parameters, abundances of the elements C, N, O, Na, Mg, Al, Ca, Si, Ti, Ni, Cr, Y, Zr, La, Ce, and Nd, as well as radial and rotational velocities. We employed the local thermodynamic equilibrium atmospheric models of Kurucz and the spectral analysis code
moog
. Rotational velocities and light-element abundances were derived using spectral synthesis. Based on our analysis of the single red giants in these three open clusters, we could compare, for the first time, their abundance pattern with that of the binary stars of the same clusters previously studied. Our results show that the abundances of both single and binary stars of the open clusters NGC 2360, NGC 3680, and NGC 5822 do not have significant differences. For the elements created by the s-process, we observed that the open clusters NGC 2360, NGC 3680, and NGC 5822 also follow the trend already raised in the literature that young clusters have higher s-process element abundances than older clusters. Finally, we observed that the three clusters of our sample exhibit a trend in the Y/Mg-age relation, which may indicate the ability of the Y/Mg ratio to be used as a clock for the giants.
The VISCACHA survey – I. Overview and first results Maia, Francisco F S; Dias, Bruno; Santos, João F C ...
Monthly notices of the Royal Astronomical Society,
04/2019, Letnik:
484, Številka:
4
Journal Article
Recenzirano
Odprti dostop
ABSTRACT
The VISCACHA (VIsible Soar photometry of star Clusters in tApii and Coxi HuguA) Survey is an ongoing project based on deep photometric observations of Magellanic Cloud star clusters, ...collected using the SOuthern Astrophysical Research (SOAR) telescope together with the SOAR Adaptive Module Imager. Since 2015 more than 200 h of telescope time were used to observe about 130 stellar clusters, most of them with low mass (M < 104 M⊙) and/or located in the outermost regions of the Large Magellanic Cloud and the Small Magellanic Cloud. With this high-quality data set, we homogeneously determine physical properties from statistical analysis of colour–magnitude diagrams, radial density profiles, luminosity functions, and mass functions. Ages, metallicities, reddening, distances, present-day masses, mass function slopes, and structural parameters for these clusters are derived and used as a proxy to investigate the interplay between the environment in the Magellanic Clouds and the evolution of such systems. In this first paper we present the VISCACHA Survey and its initial results, concerning the SMC clusters AM3, K37, HW20, and NGC 796 and the LMC ones KMHK228, OHSC3, SL576, SL61, and SL897, chosen to compose a representative subset of our cluster sample. The project’s long-term goals and legacy to the community are also addressed.
ABSTRACT
The formation scenario of the Magellanic Bridge during an encounter between the Large and Small Magellanic Clouds ∼200 Myr ago, as proposed by N-body models, would be imprinted in the ...chemical enrichment and kinematics of its stars and sites of ongoing star formation along its extension. We present an analysis of 33 Bridge star clusters using photometry obtained with the SOAR 4-m telescope equipped with adaptive optics for the VISCACHA survey. We performed a membership selection and derived self-consistent ages, metallicities, distances, and reddening values via statistical isochrone fitting, as well as tidal radii and integrated masses from structure analysis. Two groups are clearly detected: 13 well-studied clusters older than the Bridge, with 0.5–6.8 Gyr and $\hbox{Fe/H} < -0.6$ dex; and 15 clusters with <200 Myr and $\rm {Fe/H} > -0.5$ dex, probably formed in situ. The old clusters follow the overall age and metallicity gradients of the SMC, whereas the younger ones are uniformly distributed along the Bridge. The main results are as follows: (i) we derive ages and metallicities for the first time for 9 and 18 clusters, respectively; (ii) we detect two metallicity dips in the age-metallicity relation of the Bridge at ∼200 Myr and 1.5 Gyr ago for the first time, possibly chemical signatures of the formation of the Bridge and Magellanic Stream; (iii) we estimate a minimum stellar mass for the Bridge of 3–5 × 105 M⊙; (iv) we confirm that all the young Bridge clusters at ${\rm RA} < 3^h$ are metal-rich with $\rm {Fe/H} \sim -0.4$ dex.
Binary stars in open clusters are very useful targets in constraining the nucleosynthesis process. The luminosities of the stars are known because the distances of the clusters are also known, so ...chemical peculiarities can be linked directly to the evolutionary status of a star. We carried out a detailed spectroscopic analysis to derive the atmospheric parameters for 16 red giants in binary systems and the chemical composition of 11 of them in the open clusters NGC 2360, NGC 3680, and NGC 5822. We obtained abundances of C, N, O, Na, Mg, Al, Ca, Si, Ti, Ni, Cr, Y, Zr, La, Ce, and Nd. The atmospheric parameters of the studied stars and their chemical abundances were determined using high-resolution optical spectroscopy. We employ the local thermodynamic equilibrium model atmospheres of Kurucz and the spectral analysis code moog. The abundances of the light elements were derived using the spectral synthesis technique. Finally, rotational velocities were also determined and their values were compared with those already determined for field giant stars.
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