ABSTRACT
Galactic spiral arms are traced using young objects as giant molecular clouds, H ii regions, OB stars, or young open/embedded clusters. To improve the knowledge of the Galactic structure in ...the second quadrant we selected, from more than 200 open clusters covered by the SDSS, a sample of 10 young stellar clusters to conduct a spectrophotometric study.
Photometric data were provided by SDSS and APASS in the optic bands and by 2MASS and WISE in the infrared. Spectroscopic information was obtained from observations acquired with GMOS/GEMINI complemented with data from the literature. For six of the 10 clusters, distances were also obtained with our astrometric Gaia data analysis. To perform all tasks we used a suite of tools developed by us.
Our results show that these open clusters are distributed along three spiral arms, covering distances from 1.8 to 8.0 kpc. We confirm, using our novel spectroscopic data, our previews photometric estimations regarding the Galactic location of the cluster Teutsch 45. We found that it is located beyond the ‘Outer Arm’ and probably belong to the more distant ‘New Arm’ extending its trace almost to the anticentre. Hence, it was possible to get a better picture of the structure of the outer regions of the Galaxy. For clusters with pre-main-sequence populations we also found traces of coeval star formation processes. Regarding spectroscopic data and most massive members of the clusters, we discovered seven B-type stars, all earlier than B4 and we also confirmed the spectral classification of one O8-8.5 type star.
Aims.
The purpose of this work is to study the properties of the spatial distribution of the young population in three nearby galaxies in order to better understand the first stages of star ...formation.
Methods.
We used ACS/HST photometry and the “path-linkage criterion” in order to obtain a catalog of young stellar groups (YSGs) in the galaxy NGC 2403. We studied the internal distribution of stars in these YSGs using the
Q
parameter. We extended these analyses to the YSGs detected in in NGC 300 and NGC 253 our previous works. We built the young stars’ density maps for these three galaxies. Through these maps, we were able to identify and study young stellar structures on larger scales.
Results.
We found 573 YSGs in the galaxy NGC 2403, for which we derived their individual sizes, densities, luminosity function, and other fundamental characteristics. We find that the vast majority of the YSGs in NGC 2403, NGC 300 and NGC 253 present inner clumpings, following the same hierarchical behavior that we observed in the young stellar structures on larger scales in these galaxies. We derived values of the fractal dimension for these structures between ∼1.5 and 1.6. These values are very similar to those obtained in other star forming galaxies and in the interstellar medium, suggesting that the star formation process is regulated by supersonic turbulence.
Aims.
Our main aims are to improve our understanding of the main properties of the radio source G316.8−0.1 (IRAS 14416−5937) where the DBS 89−90−91 embedded clusters are located, to identify the ...stellar population present in this region, and to study the interaction of these stars with the interstellar medium.
Methods.
We analyzed some characteristics of the G316.8−0.1 radio source, consulting the SUMSS to study the radio continuum emission at 843 MHz and the H I SGPS at 21 cm. We also used photometric data at the
JHK
bands in the region of DBS 89−90−91 clusters obtained from the VVV survey and supplemented with the 2MASS catalogue. Our investigation of possible stars associated with the H II region was complemented with an astrometric analysis using the
Gaia
Early Data Release 3. To study the young stellar objects (YSOs), we consulted the mid-infrared photometric information from WISE,
Spitzer
−GLIMPSE Surveys, and the MSX point source catalog.
Results.
The photometric and astrometric research carried out in the IRAS 14416−5937 region allowed us to improve our current understanding of the DBS 89−90−91 embedded clusters and their interaction with the interstellar medium. In the case of the cluster DBS 89, we identified 9 astrophotometric candidate members and 19 photometric candidate members, whereas for DBS 90−91 clusters we found 18 candidate photometric members. We obtained a distance value for DBS 89 linked to the radio source G316.8−0.1 of 2.9 ± 0.5 kpc. We also investigated 12 Class I YSO candidates, 35 Class II YSO candidates, 2 massive young stellar objects (MYSOs), and 1 compact ionized hydrogen (CHII) region distributed throughout the IRAS 14416−5937 region. Our analysis reveals that the G316.8−0.1 radio source is optically thin at frequencies ≥0.56 GHz. The H II regions G316.8−0.1−A and G316.8−0.1−B have similar radii and ionized hydrogen masses of ∼0.5 pc and ∼35
M
⊙
, respectively. The ionization parameter computed with the younger spectral types of adopted members of DBS 89 and DBS 90−91 clusters shows that they are able to generate the H II regions. The flux density of the H II region G316.8−0.1−B is lower than the flux density of the H II region G316.8−0.1−A.
Conclusions.
We carried out a photometric and astrometric study, looking for members of the DBS 89−90−91 embedded clusters. We were able to identify the earliest stars of the clusters as the main exciting sources of the G316.8−0.1 radio source and have also estimated the main physical parameters of this source. We improve the current knowledge of the stellar components present in the Sagittarius-Carina arm of our Galaxy and its interaction with the interstellar medium.
A new X-ray, UBVRIc, and JHKs study of the young cluster Westerlund 2 was undertaken to resolve discrepancies tied to the cluster’s distance. Existing spectroscopic observations for bright cluster ...members and new multi-band photometry imply a reddening relation toward Westerlund 2 described by EU − B/EB − V = 0.63 + 0.02EB − V. Variable-extinction analyses for Westerlund 2 and nearby IC 2581 based upon spectroscopic distance moduli and ZAMS fitting yield values of RV = AV/EB − V = 3.88 ± 0.18 and 3.77 ± 0.19, respectively, and confirm prior assertions that anomalous interstellar extinction is widespread throughout Carina. The results were confirmed by applying the color-difference method to UBVRIcJHKs data for 19 spectroscopically observed cluster members, yielding RV = 3.85 ± 0.07. The derived distance to Westerlund 2 of d = 2.85 ± 0.43 kpc places the cluster on the far side of the Carina spiral arm. The cluster’s age is no more than τ ~ 2 × 106 yr as inferred from the cluster’s brightest stars and an X-ray (Chandra) cleaned analysis of its pre-main-sequence demographic. Four Wolf-Rayet stars in the cluster core and surrounding corona (WR20a, WR20b, WR20c, and WR20aa) are very likely cluster members, and their inferred luminosities are consistent with those of other late-WN stars in open clusters. The color–magnitude diagram for Westerlund 2 also displays a gap at spectral type B0.5 V with associated color spread at higher and lower absolute magnitudes that might be linked to close binary mergers. These features, in conjunction with the evidence for mass loss from the WR stars, may help to explain the high flux of γ-rays, cosmic rays, and X-rays from the direction toward Westerlund 2.
ABSTRACT
The Cygnus region harbours a vast diversity of rich stellar complexes. Hence, it is ideal for studying recently formed stellar clusters, and investigate how the feedback effect and radiation ...emitted by its massive stars modifies the interstellar medium giving place to induced star forming processes. This is the case of the small and poorly studied cluster DB2001-22. We focus our attention at analysing the cluster and its encompassing region, to distinguish different stellar populations and study their relationship with the surrounding environment. We gleaned literature and data bases for optical and IR photometry, astrometry provided by Gaia eDR3 and spectroscopy, and obtained new infrared Gemini spectra of three young stellar objects candidates (cYSOs). Furthermore, we detected two new massive stars: O7 V and B3 V, in the LAMOST data base, pointing out that DB2001–22 belongs to a much larger complex that involves an entire bubble structure and houses a richer massive population at a distance of 3.0 kpc. In this sense, DB2001–22 and the H ii region G82.6+0.4 are clearly related. Some observed gas and dust structures seem to have been sculpted by these massive stars. Infrared emission is compatible with a hot ionized gas mixed with warm dust surrounded by a structured photo-dissociation region (PDR) scenario. We found nine Class I and 56 Class II cYSOs, whose distribution along the PDR and the tips of pillar structures suggests that their formation may have been induced by the action of the earliest stars in the cluster on to their environment.
Aims. The purpose of this work is to understand the global characteristics of the stellar populations in NGC 300. In particular, we focused our attention on searching young star groups and study ...their hierarchical organization. The proximity and orientation of this Sculptor Group galaxy make it an ideal candidate for this study. Methods. The research was conducted using archival point spread function (PSF) fitting photometry measured from images in multiple bands obtained with the Advanced Camera for Surveys of the Hubble Space Telescope (ACS/HST). Using the path linkage criterion (PLC), we cataloged young star groups and analyzed them from the observation of individual stars in the galaxy NGC 300. We also built stellar density maps from the bluest stars and applied the SExtractor code to identify overdensities. This method provided an additional tool for the detection of young stellar structures. By plotting isocontours over the density maps and comparing the two methods, we could infer and delineate the hierarchical structure of the blue population in the galaxy. For each region of a detected young star group, we estimated the size and derived the radial surface density profiles for stellar populations of different color (blue and red). A statistical decontamination of field stars was performed for each region. In this way it was possible to build the color–magnitude diagrams (CMD) and compare them with theoretical evolutionary models. We also constrained the present-day mass function (PDMF) per group by estimating a value for its slope. Results. The blue population distribution in NGC 300 clearly follows the spiral arms of the galaxy, showing a hierarchical behavior in which the larger and loosely distributed structures split into more compact and denser ones over several density levels. We created a catalog of 1147 young star groups in six fields of the galaxy NGC 300, in which we present their fundamental characteristics. The mean and the mode radius values obtained from the size distribution are both 25 pc, in agreement with the value for the Local Group and nearby galaxies. Additionally, we found an average PDMF slope that is compatible with the Salpeter value.
ABSTRACT
We present a study of the internal structure of 82 star clusters located at the outer regions of the Large Magellanic Cloud and the Small Magellanic Cloud using data of the VISCACHA Survey. ...Through the construction of the minimum spanning tree, which analyses the relative position of stars within a given cluster, it was possible to characterize the internal structure and explore the fractal or subclustered distribution for each cluster. We computed the parameters $\overline{m}$ (which is the average length of the connected segments normalized by the area), $\overline{s}$ (which is the mean points separation in units of cluster radius), and Q (the ratio of these components). These parameters are useful to distinguish between radial, homogeneous, and substructured distributions of stars. The dependence of these parameters with the different characteristics of the clusters, such as their ages and spatial distribution, was also studied. We found that most of the studied clusters present a homogeneous stellar distribution or a distribution with a radial concentration. Our results are consistent with the models, suggesting that more dynamically evolved clusters seem to have larger Q values, confirming previous results from numerical simulations. There also seems to be a correlation between the internal structure of the clusters and their galactocentric distances, in the sense that for both galaxies, the more distant clusters have larger Q values. We also paid particular attention to the effects of contamination by non-member field stars and its consequences finding that field star decontamination is crucial for these kinds of studies.
Context. Previous studies of the Carina region have revealed its complexity and richness as well as a significant number of early-type stars. However, in many cases, these studies only concentrated ...on the central region (Trumpler 14/16) or were not homogeneous. This latter aspect, in particular, is crucial because very different ages and distances for key clusters have been claimed in recent years. Aims. The aim of this work is to study in detail an area of the Galactic plane in Carina, eastward eta Carina. We analyze the properties of different stellar populations and focus on a sample of open clusters and their population of young stellar objects and highly reddened early stars. We also studied the stellar mass distribution in these clusters and the possible scenario of their formation. Finally, we outline the Galactic spiral structure in this direction. Methods. We obtained deep and homogeneous photometric data (UBVI sub(KC)) for six young open clusters: NGC 3752, Trumpler 18, NGC 3590, Hogg 10, 11, and 12, located in Carina at l~ 291degrees, and their adjacent stellar fields, which we complemented with spectroscopic observations of a few selected targets. We also culled additional information from the literature, which includes stellar spectral classifications and near-infrared photometry from 2MASS. We finally developed a numerical code that allowed us to perform a homogeneous and systematic analysis of the data. Our results provide more reliable estimates of distances, color excesses, masses, and ages of the stellar populations in this direction. Results. We estimate the basic parameters of the studied clusters and find that they identify two overdensities of young stellar populations located at about 1.8 kpc and 2.8 kpc, with E sub(B- V)~ 0.1 - 0.6. We find evidence of pre-main-sequence populations inside them, with an apparent coeval stellar formation in the most conspicuous clusters. We also discuss apparent age and distance gradients in the direction NW-SE. We study the mass distributions of the covered clusters and several others in the region (which we took form the literature). They consistently show a canonical IMF slope (the Salpeter one). We discover and characterise an abnormally reddened massive stellar population, scattered between 6.6 and 11 kpc. Spectroscopic observations of ten stars of this latter population show that all selected targets were massive OB stars. Their location is consistent with the position of the Carina-Sagittarius spiral arm.
ABSTRACT
By using six newly determined mid‐eclipse times together with those collected from the literature, we have found that the observed minus calculated (O−C) curve of RR Cae shows a cyclic ...change with a period of 11.9 yr and an amplitude of 14.3 s while it undergoes an upward parabolic variation revealing a long‐term period increase at a rate of . The cyclic change was analysed for the light‐travel‐time effect that arises from the gravitational influence of a third companion. The mass of the third body was determined to be M3sin i′= 4.2(± 0.4) MJup, suggesting that it is a circumbinary giant planet when its orbital inclination is larger than 176. The orbital separation of the circumbinary planet from the central eclipsing binary is about 5.3(± 0.6) au. The period increase is opposite to the changes caused by angular momentum loss via magnetic braking or/and gravitational radiation; and it cannot be explained by the mass transfer between both components because of its detached configuration. These indicate that the observed upward parabolic change is only a part of a long‐period (longer than 26.3 yr) cyclic variation, which may reveal the presence of another giant circumbinary planet in a wide orbit.
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