A Novel Method to Automatically Detect and Measure the Ages of Star Clusters in Nearby Galaxies: Application to the Large Magellanic Cloud

Bitsakis, T.; Bonfini, P.; González-Lópezlira, Rosa A.; Ramirez-Siordia, V. H.; Bruzual, G.; Charlot, S.; Maravelias, G.; Zaritsky, Dennis

doi:10.3847/1538-4357/aa8090

Cited by 18 publications

(34 citation statements)

References 55 publications

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“…These authors consider SL 482-IR1 as a member of the young stellar cluster SL 482 (also named as LMC 1015) with a cluster age of log t = 7.2±0.24 (van Loon et al 2005). Other authors estimated different values for the cluster age ranging from log t = 7.6 to 8.0 (Glatt et al 2010;Ko et al 2013;Bitsakis et al 2017). Comparing the position of LHA 120-S 35 in the Hertzsprung-Russell diagram to the evolutionary track of a massive star with ∼22 M ⊙ (Ekström et al 2012), we corroborated that an isochrone of log t = 7.0 can reconcile the cluster age derived by van Loon et al (2005) with the position of a post-RSG object (see Fig.…”

Section: Discussionmentioning

confidence: 99%

“…Therefore, if we consider the classification of SL 482-IR1 as a B[e]SG and the age inferred by van Loon et al (2005), LHA 120-S 35 would be the third B[e]SG known up to now belonging to a young stellar cluster. Recently, the LHA 120-S 35 membership to the cluster SL 482 has been discussed by Bitsakis et al (2017), who were able to determine the members of the star cluster using a robust decontamination technique, providing a probability of more than 92% that LHA 120-S 35 is member of the cluster. The previously reported B[e]SGs associated to open clusters are: LHA 120-S 111, which belongs to the compact cluster NGC 1994 of the LMC (Melgarejo et al 2001;Lortet & Testor 1988) and Wd1-9, which is a member of the massive Galactic stellar cluster Westerlund 1 (Clark et al 2013b;Fenech et al 2017).…”

Section: Discussionmentioning

confidence: 99%

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Resolving the clumpy circumstellar environment of the B[e] supergiant LHA 120-S 35

Torres

Cidale

Kraus

et al. 2018

A&A

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Context. B[e] supergiants are massive post-main-sequence stars, surrounded by a complex circumstellar environment where molecules and dust can survive. The shape in which the material is distributed around these objects and its dynamics as well as the mechanisms that give rise to these structures are not well understood. Aims. The aim of this work is to deepen our knowledge of the structure and kinematics of the circumstellar disc of the B[e] supergiant LHA 120-S 35. Methods. High-resolution optical spectra were obtained in three different years. Forbidden emission lines, that contribute to trace the disc at different distances from the star, are modelled in order to determine the kinematical properties of their line-forming regions, assuming Keplerian rotation. In addition, we used low-resolution near-infrared spectra to explore the variability of molecular emission. Results. LHA 120-S 35 displays an evident spectral variability in both optical and infrared regions. The P-Cygni line profiles of H i, as well as those of Fe ii and O i, suggest the presence of a strong bipolar clumped wind. We distinguish density enhancements in the P-Cygni absorption component of the first Balmer lines, which show variations in both velocity and strength. The P-Cygni profile emission component is double-peaked, indicating the presence of a rotating circumstellar disc surrounding the star. We also observe line-profile variations in the permitted and forbidden features of Fe ii and O i. In the infrared, we detect variations in the intensity of the H i emission lines as well as in the emission of the CO band-heads. Moreover, we find that the profiles of each [Ca ii] and [O i] emission lines contain contributions from spatially different (complete or partial) rings. Globally, we find evidence of detached multiring structures, revealing density variations along the disc. We identify an inner ring, with sharp edge, where [Ca ii] and [O i] lines share their forming region with the CO molecular bands. The outermost regions show a complex structure, outlined by fragmented clumps or partial-ring features of Ca ii and O i. Additionally, we observe variations in the profiles of the only visible absorption features, the He i lines. Conclusions. We suggest that LHA 120-S 35 has passed through the red-supergiant (RSG) phase and evolves back bluewards in the Hertzsprung-Russell diagram. In this scenario, the formation of the complex circumstellar structure could be the result of the windwind interactions of the post-RSG wind with the previously ejected material from the RSG. The accumulation of material in the circumstellar environment could be attributed to enhanced mass-loss, probably triggered by stellar pulsations. However, the presence of a binary companion can not be excluded. Finally, we find that LHA 120-S 35 is the third B[e] supergiant belonging to a young stellar cluster.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Resolving the clumpy circumstellar environment of the B[e] supergiant LHA 120-S 35

Torres

Cidale

Kraus

et al. 2018

A&A

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“…The code we used here to automatically detect and estimate the ages of the SMC star clusters was analytically described in Bitsakis et al (2017). Summarizing, the code makes use of the star counts method (see Schmeja 2011 and references therein), which estimates the density of stars in a given region of interest and finds overdensities above some local background thresholds (Zaritsky et al 2002), which was also surveyed by our code.…”

Section: The Cluster Detection and Age Estimation Methodsmentioning

confidence: 99%

“…In Section 2, we describe the data set we use in the current study. Section 3 contains a brief description of the cluster detection and age estimation codes (a more analytic description along with statistical tests can be found in Bitsakis et al 2017). The results are presented in Section 4, while in Section 5 we make a comparison of the SMC-LMC star cluster age distributions and derive useful conclusions about their interaction history.…”

Section: Introductionmentioning

confidence: 99%

“…Despite the plethora of studies of the star clusters in the Magellanic Clouds, the lack of a statistically robust detection method that creates uniform and complete samples (as opposed to the visual identification methods that are usually applied) has posed significant limitations for the systematic study of the star cluster formation history of both galaxies. In Bitsakis et al (2017), we presented a new fully automated method to robustly detect and estimate the ages of star clusters in nearby galaxies. Using statistical analysis on high-resolution maps of the LMC, we obtained a large, uniform sample of star clusters (in the central 49 deg…”

Section: Introductionmentioning

confidence: 99%

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The Distribution and Ages of Star Clusters in the Small Magellanic Cloud: Constraints on the Interaction History of the Magellanic Clouds

Bitsakis

González-Lópezlira

Bonfini

et al. 2018

ApJ

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We present a new study of the spatial distribution and ages of the star clusters in the Small Magellanic Cloud (SMC). To detect and estimate the ages of the star clusters we rely on the new fully automated method developed by Bitsakis et al. Our code detects 1319 star clusters in the central 18 deg 2 of the SMC we surveyed (1108 of which have never been reported before). The age distribution of those clusters suggests enhanced cluster formation around 240 Myr ago. It also implies significant differences in the cluster distribution of the bar with respect to the rest of the galaxy, with the younger clusters being predominantly located in the bar. Having used the same setup, and data from the same surveys as for our previous study of the LMC, we are able to robustly compare the cluster properties between the two galaxies. Our results suggest that the bulk of the clusters in both galaxies were formed approximately 300 Myr ago, probably during a direct collision between the two galaxies. On the other hand, the locations of the young (50 Myr) clusters in both Magellanic Clouds, found where their bars join the H I arms, suggest that cluster formation in those regions is a result of internal dynamical processes. Finally, we discuss the potential causes of the apparent outside-in quenching of cluster formation that we observe in the SMC. Our findings are consistent with an evolutionary scheme where the interactions between the Magellanic Clouds constitute the major mechanism driving their overall evolution.

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Evolved massive stars at low-metallicity

Yang

Bonanos

Jiang

et al. 2021

A&A

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We present a clean, magnitude-limited (IRAC1 or WISE1 ≤ 15.0 mag) multiwavelength source catalog for the Large Magellanic Cloud (LMC). The catalog was built by crossmatching (1″) and deblending (3″) between the source list of Spitzer Enhanced Imaging Products and Gaia Data Release 2, with strict constraints on the Gaia astrometric solution in order to remove the foreground contamination. It is estimated that about 99.5% of the targets in our catalog are most likely genuine members of the LMC. The catalog contains 197 004 targets in 52 different bands, including two ultraviolet, 21 optical, and 29 infrared bands. Additional information about radial velocities and spectral and photometric classifications were collected from the literature. We compare our sample with the sample from Gaia Collaboration (2018, A&A, 616, A12), indicating that the bright end of our sample is mostly comprised of blue helium-burning stars (BHeBs) and red HeBs with inevitable contamination of main sequence stars at the blue end. After applying modified magnitude and color cuts based on previous studies, we identified and ranked 2974 red supergiant, 508 yellow supergiant, and 4786 blue supergiant candidates in the LMC in six color-magnitude diagrams (CMDs). The comparison between the CMDs from the two catalogs of the LMC and Small Magellanic Cloud (SMC) indicates that the most distinct difference appears at the bright red end of the optical and near-infrared CMDs, where the cool evolved stars (e.g., red supergiant stars (RSGs), asymptotic giant branch stars, and red giant stars) are located, which is likely due to the effect of metallicity and star formation history. A further quantitative comparison of colors of massive star candidates in equal absolute magnitude bins suggests that there is essentially no difference for the BSG candidates, but a large discrepancy for the RSG candidates since LMC targets are redder than the SMC ones, which may be due to the combined effect of metallicity on both spectral type and mass-loss rate as well as the age effect. The effective temperatures (Teff) of massive star populations are also derived from reddening-free color of (J − KS)0. The Teff ranges are 3500 < Teff < 5000 K for an RSG population, 5000 < Teff < 8000 K for a YSG population, and Teff > 8000 K for a BSG population, with larger uncertainties toward the hotter stars.

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A Novel Method to Automatically Detect and Measure the Ages of Star Clusters in Nearby Galaxies: Application to the Large Magellanic Cloud

Cited by 18 publications

References 55 publications

Resolving the clumpy circumstellar environment of the B[e] supergiant LHA 120-S 35

Resolving the clumpy circumstellar environment of the B[e] supergiant LHA 120-S 35

The Distribution and Ages of Star Clusters in the Small Magellanic Cloud: Constraints on the Interaction History of the Magellanic Clouds

Evolved massive stars at low-metallicity

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