Properties of massive stars in four clusters of the VVV survey (original) (raw)
Related papers
Astronomy & Astrophysics, 2015
Context. The ESO public survey VISTA Variables in the Vía Láctea (VVV) has contributed with deep multi-epoch photometry of the Galactic bulge and the adjacent part of the disk over 526 sq. deg. More than a hundred cluster candidates have been reported thanks to this survey. Aims. We present the fifth article in a series of papers focused on young and massive clusters discovered in the VVV survey. In this paper, we present the physical characterization of five clusters with a spectroscopically confirmed OB-type stellar population. Methods. To characterize the clusters, we used near-infrared photometry (J, H, and K S) from the VVV survey and near-infrared K-band spectroscopy from ISAAC at VLT, following the methodology presented in the previous articles of the series. Results. All clusters in our sample are very young (ages between 1-20 Myr), and their total mass are between (1.07 +0.40 −0.30) × 10 2 M and (4.17 +4.15 −2.08) × 10 3 M. We observed a relation between the clusters total mass M ecl and the mass of their most massive stellar member m max , for clusters with an age <10 Myr.
Massive open star clusters using the VVV survey
Astronomy & Astrophysics, 2012
Context. The ESO Public Survey "VISTA Variables in the Vía Láctea" (VVV) provides deep multi-epoch infrared observations for an unprecedented 562 sq. degrees of the Galactic bulge, and adjacent regions of the disk. In this survey nearly 150 new open clusters and cluster candidates have been discovered. Aims. This is the second in a series of papers about young, massive open clusters observed using the VVV survey. We present the first study of six recently discovered clusters. These clusters contain at least one newly discovered Wolf-Rayet (WR) star. Methods. Following the methodology presented in the first paper of the series, wide-field, deep JHK s VVV observations, combined with new infrared spectroscopy, are employed to constrain fundamental parameters for a subset of clusters. Results. We affirm that the six studied stellar groups are real young (2-7 Myr) and massive (between 0.8 and 2.2 10 3 M ⊙ ) clusters. They are highly obscured (A V ∼ 5 − 24 mag) and compact (1-2 pc). In addition to WR stars, two of the six clusters also contain at least one red supergiant star. We claim the discovery of 8 new WR stars, and 3 stars showing WR-like emission lines which could be classified WR or OIf. Preliminary analysis provides initial masses of ∼30-50 M ⊙ for the WR stars. Finally, we discuss the spiral structure of the Galaxy using as tracers the six new clusters together with the previously studied VVV clusters.
Young Stellar Clusters Containing Massive Young Stellar Objects in the VVV Survey
The Astronomical Journal, 2016
The purpose of this research is to study the connections of the global properties of eight young stellar clusters projected in the Vista Variables in the Via Lactea (VVV) ESO Large Public Survey disk area and their young stellar object (YSO) populations. The analysis is based on the combination of spectroscopic parallax-based reddening and distance determinations with main-sequence and pre-main-sequence ishochrone fitting to determine the basic parameters (reddening, age, distance) of the sample clusters. The lower mass limit estimations show that all clusters are low or intermediate mass (between 110 and 1800M e), the slope Γ of the obtained present-day mass functions of the clusters is close to the Kroupa initial mass function. The YSOs in the cluster's surrounding fields are classified using low resolution spectra, spectral energy distribution fits with theoretical predictions, and variability, taking advantage of multi-epoch VVV observations. All spectroscopically confirmed YSOs (except one) are found to be massive (more than 8 M e). Using VVV and GLIMPSE color-color cuts we have selected a large number of new YSO candidates, which are checked for variability and 57% are found to show at least lowamplitude variations. In few cases it was possible to distinguish between YSO and AGB classifications on the basis of light curves.
New variable stars discovered in the fields of three Galactic open clusters using the VVV survey
New Astronomy, 2016
This project is a massive near-infrared (NIR) search for variable stars in highly reddened and obscured open cluster (OC) fields projected on regions of the Galactic bulge and disk. The search is performed using photometric NIR data in the J-, Hand K s-bands obtained from the Vista Variables in the Vía Láctea (VVV) Survey. We performed in each cluster field a variability search using Stetson's variability statistics to select the variable candidates. Later, those candidates were subjected to a frequency analysis using the Generalized Lomb-Scargle and the Phase Dispersion Minimization algorithms. The number of independent observations range between 63 and 73. The newly discovered variables in this study,
The evolution of massive stars and their spectra
Astronomy & Astrophysics, 2014
For the first time, the interior and spectroscopic evolution of a massive star is analyzed from the zero-age main sequence (ZAMS) to the pre-supernova (SN) stage. For this purpose, we combined stellar evolution models using the Geneva code and stellar atmospheric/wind models using CMFGEN. With our approach, we were able to produce observables, such as a synthetic high-resolution spectrum and photometry, thereby aiding the comparison between evolution models and observed data. Here we analyze the evolution of a nonrotating 60 M star and its spectrum throughout its lifetime. Interestingly, the star has a supergiant appearance (luminosity class I) even at the ZAMS. We find the following evolutionary sequence of spectral types: O3 I (at the ZAMS), O4 I (middle of the H-core burning phase), B supergiant (BSG), B hypergiant (BHG), hot luminous blue variable (LBV; end of H-core burning), cool LBV (Hshell burning through the beginning of the He-core burning phase), rapid evolution through late WN and early WN, early WC (middle of He-core burning), and WO (end of He-core burning until core collapse). We find the following spectroscopic phase lifetimes: 3.22 × 10 6 yr for the O-type, 0.34 × 10 5 yr (BSG), 0.79 × 10 5 yr (BHG), 2.35 × 10 5 yr (LBV), 1.05 × 10 5 yr (WN), 2.57 × 10 5 yr (WC), and 3.80 × 10 4 yr (WO). Compared to previous studies, we find a much longer (shorter) duration for the early WN (late WN) phase, as well as a long-lived LBV phase. We show that LBVs arise naturally in single-star evolution models at the end of the MS when the mass-loss rate increases as a consequence of crossing the bistability limit. We discuss the evolution of the spectra, magnitudes, colors, and ionizing flux across the star's lifetime, and the way they are related to the evolution of the interior. We find that the absolute magnitude of the star typically changes by ∼ 6 mag in optical filters across the evolution, with the star becoming significantly fainter in optical filters at the end of the evolution, when it becomes a WO just a few 10 4 years before the SN explosion. We also discuss the origin of the different spectroscopic phases (i.e., O-type, LBV, WR) and how they are related to evolutionary phases (H-core burning, H-shell burning, He-core burning).
New Galactic star clusters discovered in the VVV survey
Astronomy & Astrophysics, 2011
Context. VISTA Variables in the Vía Láctea (VVV) is one of the six ESO Public Surveys operating on the new 4-meter Visible and Infrared Survey Telescope for Astronomy (VISTA). VVV is scanning the Milky Way bulge and an adjacent section of the disk, where star formation activity is high. One of the principal goals of the VVV Survey is to find new star clusters of different ages. Aims. In order to trace the early epochs of star cluster formation we concentrated our search in the directions to those of known star formation regions, masers, radio, and infrared sources. Methods. The disk area covered by VVV was visually inspected using the pipeline processed and calibrated KS-band tile images for stellar overdensities. Subsequently, we examined the composite JHKS and ZJKS color images of each candidate. PSF photometry of 15 × 15 arcmin fields centered on the candidates was then performed on the Cambridge Astronomy Survey Unit reduced images. After statistical field-star decontamination, color-magnitude and color-color diagrams were constructed and analyzed. Results. We report the discovery of 96 new infrared open clusters and stellar groups. Most of the new cluster candidates are faint and compact (with small angular sizes), highly reddened, and younger than 5 Myr. For relatively well populated cluster candidates we derived their fundamental parameters such as reddening, distance, and age by fitting the solarmetallicity Padova isochrones to the color-magnitude diagrams.
The VLT-FLAMES survey of massive stars
Arxiv preprint arXiv: …, 2008
The VLT0FLAMES Survey of Massive Stars was an ESO Large Programme to understand rotational mixing and stellar mass0loss in different metallicity environments, in order to better constrain massive star evolution. We gathered high0quality spectra of over 800 stars in the Galaxy ...
ARTICLE High-resolution spectroscopy of giant stars in the open clusters IC 4651 and IC 4725 1
Open clusters are important astrophysical laboratories to study the stellar formation and evolution and to verify the disk structure of the Milky Way. We present calculations of stellar atmospheric parameters and s-process abundances for nine giant stars in the galactic open clusters IC 4651 and IC 4725. These objects have their memberships confirmed from dynamic studies and chemical analysis. The high-resolution spectra are available in the FEROS ESO archive. We have applied a line by line analysis relative to Juno solar spectrum to determine the stellar atmospheric parameters and chemical abundances of Y II, Zr I, La II, Ce II, and Nd II under the local thermal equilibrium hypothesis. The obtained results were compared to the literature values. The derived s-process abundance pattern agrees with the most recent behaviors reported for giant stars in galactic open clusters. Résumé : Les amas ouverts constituent d'importants laboratoires pour étudier la formation et l'évolution stellaire et pour vérifier la structure en disque de la Voie lactée. Nous présentons des calculs des paramètres atmosphériques stellaires et d'abondances obtenues du processus s pour neuf étoiles géantes dans les amas ouverts galactiques IC 4651 et IC 4725. Ces objets ont vu leur nature confirmée par des études dynamiques et des analyses chimiques. Les spectres de haute résolution sont disponibles dans les archives de FEROS ESO. Nous appliquons une analyse relative raie par raie au spectre solaire de Juno pour déterminer les paramètres de l'atmosphère stellaire et les abondances stellaires en Y II, Zr I, Ce II et Nd II sous l'hypothèse de l'équilibre thermodynamique local (ETL/LTE). Les résultats obtenus sont comparés a ` ceux trouvés dans la littérature. Le patron d'abondance dérivé du processus s agrée avec les comportements les plus récents rapportés pour les étoiles géantes dans les amas ouverts de la galaxie. [Traduit par la Rédaction] Mots-clés : évolution stellaire, abondances stellaires, amas ouverts et associations stellaires, paramètres fondamentaux stellaires, atmosphère stellaire.
High-resolution spectroscopy of giant stars in the open clusters IC 4651 and IC 4725
Canadian Journal of Physics
Open clusters are important astrophysical laboratories to study the stellar formation and evolution and to verify the disk structure of the Milky Way. We present calculations of stellar atmospheric parameters and s-process abundances for nine giant stars in the galactic open clusters IC 4651 and IC 4725. These objects have their memberships confirmed from dynamic studies and chemical analysis. The high-resolution spectra are available in the FEROS ESO archive. We have applied a line by line analysis relative to Juno solar spectrum to determine the stellar atmospheric parameters and chemical abundances of Y II, Zr I, La II, Ce II, and Nd II under the local thermal equilibrium hypothesis. The obtained results were compared to the literature values. The derived s-process abundance pattern agrees with the most recent behaviors reported for giant stars in galactic open clusters.
A search for variable stars in the four open star clusters
Journal of Astrophysics and Astronomy, 2020
We present a CCD photometric survey for the search of variable stars in four open clusters namely Berkeley 69, King 5, King 7, and Berkeley 20. The time series observations were carried out for 1 and/or 2 nights for each of the clusters in the year 1998, which have led to identify nineteen variable stars in these clusters. Out of these 19 variable stars, five stars show δ Scuti like variability and two stars show W UMa type variability. In other stars, we could not find the periods and hence the type of variability due to the lack of sufficient data. The periods of δ Scuti type stars are found to be in the range of 0.13 to 0.21 days, whereas the two stars in the cluster Berkeley 20, which showed W UMa type variability have orbital periods of 0.396 and 0.418 days, respectively. Using the Gaia data, the basic parameters of the clusters Berkeley 69, King 7 and King 5 are also revised. The age and reddening are estimated to be 0.79 ± 0.09 Gyr and 0.68 ± 0.03 mag for Berkeley 69, 0.79 ± 0.09 Gyr and 1.22 ± 0.03 mag for the cluster King 7 and 1.59 ± 0.19 Gyr and 0.63 ± 0.02 mag for the cluster King 5, respectively. Signature of mass segregation is found in the clusters King 7 and King 5.