Evolution of massive stars with new hydrodynamic wind models

Here we present evolutionary models for a set of massive stars, introducing a new prescription for the mass-loss rate obtained from hydrodynamical calculations in which the wind velocity profile, $v(r)$, and the line-acceleration, $g_\text{line}$, are obtained in a self consistently way. Replacing mass-loss rates at the Main Sequence stage from the standard Vink's formula by our new recipe, we generate a new set of evolutionary tracks for $M_\text{ZAMS}=25,40,70$ and $120\,M_\odot$ and metallicities $Z=0.014$ (Galactic), $Z=0.006$ (LMC), and $Z=0.002$ (SMC). Our new derived formula for mass-loss rate predicts a dependence $\dot M\propto Z^a$, where $a$ is not longer constant but dependent on the stellar mass: ranging from $a\sim0.53$ when $M_*\sim120\;M_\odot$, to $a\sim1.02$ when $M_*\sim25\;M_\odot$. We found that models adopting the new recipe for $\dot M$ retain more mass during their evolution, which is expressed in larger radii and consequently more luminous tracks over the Hertzsprung-Russell diagram. These differences are more prominent for the cases of $M_\text{ZAMS}=70$ and 120 $M_\odot$ at solar metallicity, where we found self-consistent tracks are $\sim0.1$ dex brighter and keep extra mass up to 20 $M_\odot$, compared with the classical models using the previous formulation for mass-loss rate. Moreover, we observed remarkable differences for the evolution of the radionuclide isotope $^{26}$Al in the core and the surface of the star. Since $\dot M_\text{sc}$ are weaker than the commonly adopted values for evolutionary tracks, self-consistent tracks predict a later modification in the abundance number of $^{26}$Al in the stellar winds. This new behaviour could provide useful information about the real contribution of this isotope from massive stars to the Galactic interstellar medium.Comment: Accepted for publication in Astronomy & Astrophysic

Analytical solutions for radiation-driven winds in massive stars - II: The δ-slow regime

Accurate mass-loss rates and terminal velocities from massive stars winds are essential to obtain synthetic spectra from radiative transfer calculations and to determine the evolutionary path of massive stars. From a theoretical point of view, analytical expressions for the wind parameters and velocity profile would have many advantages over numerical calculations that solve the complex non-linear set of hydrodynamic equations. In a previous work, we obtained an analytical description for the fast wind regime. Now, we propose an approximate expression for the line-force in terms of new parameters and obtain a velocity profile closed-form solution (in terms of the Lambert W function) for the δ-slow regime. Using this analytical velocity profile, we were able to obtain the mass-loss rates based on the m-CAK theory. Moreover, we established a relation between this new set of line-force parameters with the known stellar and m-CAK line-force parameters. To this purpose, we calculated a grid of numerical hydrodynamical models and performed a multivariate multiple regression. The numerical and our descriptions lead to good agreement between their values.Fil: Araya, I.. Universidad Mayor; ChileFil: Christen, A.. Universidad de Valparaíso; ChileFil: Cure, M.. Universidad de Valparaíso; ChileFil: Cidale, Lydia Sonia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; ArgentinaFil: Venero, Roberto Oscar José. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; ArgentinaFil: Arcos, C.. Universidad de Valparaíso; ChileFil: Gormaz Matamala, A.. Universidad de Valparaíso; Chile. Universidad Adolfo Ibañez; ChileFil: Haucke, Maximiliano. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; ArgentinaFil: Escarate, P.. Universidad Austral de Chile; ChileFil: Clavería, H.. Pontificia Universidad Católica de Valparaíso; Chil

Deriving metallicities from calcium triplet spectroscopy in combination with near-infrared photometry

Context. When they are established with sufficient precision, the ages, metallicities and kinematics of Galactic globular clusters (GGCs) can shed much light on the dynamical and chemical evolution of the Galactic halo and bulge. While the most fundamental way of determining GC abundances is by means of high-resolution spectroscopy, in practice this method is limited to only the brighter stars in the nearest and less reddened objects. This restriction has, over the years, led to the development of a large number of techniques that measure the overall abundance indirectly from parameters that correlate with overall metallicity. One of the most efficient methods is measuring the equivalent width (EW) of the calcium II triplet (CaT) at λ ≈ 8500 Å in red giants, which are corrected for the luminosity and temperature effects using the V magnitude differences from the horizontal branch (HB). Aims. We establish a similar method in the near-infrared (NIR), by combining the power of the differential magnitudes technique with the advantages of NIR photometry to minimize differential reddening effects. Methods. We used the Ks magnitude difference between the star and the reddest part of the HB (RHB) or of the red clump (RC) to generate reduced equivalent widths (rEW) from previously presented datasets. Then we calibrated these rEW against three previously reported different metallicity scales; one of which we corrected using high-resolution spectroscopic metallicities. Results. We calculated the calibration relations for the two datasets and the three metallicity scales and found that they are approximately equivalent, with almost negligible differences. We compared our NIR calibrations with the corresponding optical ones, and found them to be equivalent, which shows that the luminosity-corrected rEW using the Ks magnitude is compatible with the one obtained from the V magnitude. We then used the metallicities obtained from the calibration to investigate the internal metallicity distributions of the GCs. Conclusions. We have established that the ([Fe/H]:rEW) relation is independent of the magnitude used for the luminosity correction and find that the calibration relations change only slightly for different metallicity scales. The CaT technique using NIR photometry is thus a powerful tool to derive metallicities. In particular, it can be used to study the internal metallicity spread of a GC. We confirm the presence of at least two metallicity populations in NGC 6656 and find that several other GCs present peculiar metallicity distributions

Analytical solutions for radiation-driven winds in massive stars II : The δ-slow regime

Accurate mass-loss rates and terminal velocities from massive stars winds are essential to obtain synthetic spectra from radiative transfer calculations and to determine the evolutionary path of massive stars. From a theoretical point of view, analytical expressions for the wind parameters and velocity profile would have many advantages over numerical calculations that solve the complex non-linear set of hydrodynamic equations. In a previous work, we obtained an analytical description for the fast wind regime. Now, we propose an approximate expression for the line-force in terms of new parameters and obtain a velocity profile closed-form solution (in terms of the Lambert W function) for the δ-slow regime. Using this analytical velocity profile, we were able to obtain the mass-loss rates based on the m-CAK theory. Moreover, we established a relation between this new set of line-force parameters with the known stellar and m-CAK line-force parameters. To this purpose, we calculated a grid of numerical hydrodynamical models and performed a multivariate multiple regression. The numerical and our descriptions lead to good agreement between their values.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat

Investigating potential planetary nebula/cluster pairs

Publisher's Version/PDFContext. Fundamental parameters characterizing the end-state of intermediate-mass stars may be constrained by discovering planetary nebulae (PNe) in open clusters (OCs). Cluster membership may be exploited to establish the distance, luminosity, age, and physical size for PNe, and the intrinsic luminosity and mass of its central star. Aims. Four potential PN-OC associations were investigated to assess the cluster membership for the PNe. Methods. Radial velocities were measured from intermediate-resolution optical spectra, complemented with previous estimates in the literature.When the radial velocity study supported the PN/OC association, we analyzed whether other parameters (e.g., age, distance, reddening, central star brightness) were consistent with this conclusion. Results. Our measurements imply that the PNe VBe 3 and HeFa 1 are not members of the OCs NGC5999 and NGC6067, respectively, and that they very likely belong to the background bulge population. Conversely, consistent radial velocities indicate that NGC2452/NGC 2453 could be associated, but our results are not conclusive so additional observations are warranted. Finally, we demonstrate that all the available information point to He 2-86 being a young, highly internally obscured PN member of NGC4463. New near-infrared photometry acquired via the Vista Variables in the Via Lactea ESO public survey was used in tandem with existing UBV photometry to measure the distance, reddening, and age of NGC4463, finding d = 1.55 ± 0.10 kpc, E(B − V) = 0.41 ± 0.02, and τ = 65 ± 10 Myr, respectively. The same values should be adopted for the PN if the proposed cluster membership is confirme

Deriving metallicities from calcium triplet spectroscopy\ud in combination with near-infrared photometry

Context. When they are established with sufficient precision, the ages, metallicities and kinematics of Galactic globular clusters\ud (GGCs) can shed much light on the dynamical and chemical evolution of the Galactic halo and bulge.While the most fundamental\ud way of determining GC abundances is by means of high-resolution spectroscopy, in practice this method is limited to only the brighter\ud stars in the nearest and less reddened objects. This restriction has, over the years, led to the development of a large number of techniques\ud that measure the overall abundance indirectly from parameters that correlate with overall metallicity. One of the most efficient\ud methods is measuring the equivalent width (EW) of the calcium II triplet (CaT) at λ ≈ 8500 Å in red giants, which are corrected for\ud the luminosity and temperature effects using the V magnitude differences from the horizontal branch (HB).\ud Aims. We establish a similar method in the near-infrared (NIR), by combining the power of the differential magnitudes technique with\ud the advantages of NIR photometry to minimize differential reddening effects.\ud Methods. We used the Ks magnitude difference between the star and the reddest part of the HB (RHB) or of the red clump (RC) to\ud generate reduced equivalent widths (rEW) from previously presented datasets. Then we calibrated these rEWagainst three previously\ud reported different metallicity scales; one of which we corrected using high-resolution spectroscopic metallicities.\ud Results. We calculated the calibration relations for the two datasets and the three metallicity scales and found that they are approximately\ud equivalent, with almost negligible differences. We compared our NIR calibrations with the corresponding optical ones, and\ud found them to be equivalent, which shows that the luminosity-corrected rEW using the Ks magnitude is compatible with the one\ud obtained from the V magnitude. We then used the metallicities obtained from the calibration to investigate the internal metallicity\ud distributions of the GCs.\ud Conclusions. We have established that the ([Fe/H]:rEW) relation is independent of the magnitude used for the luminosity correction\ud and find that the calibration relations change only slightly for different metallicity scales. The CaT technique using NIR photometry is\ud thus a powerful tool to derive metallicities. In particular, it can be used to study the internal metallicity spread of a GC.We confirm the\ud presence of at least two metallicity populations in NGC6656 and find that several other GCs present peculiar metallicity distributionsFONDECYT - project 3140177GEMINI-CONICYT 3210008GEMINI-CONICYT 32110005Chilean BASAL Centro de Excelencia en Astrofísica y Tecnologías Afines (CATA) - PFB 06/200

Investigating potential planetary nebula/cluster pairs

Fundamental parameters characterizing the end-state of intermediate-mass stars may be constrained by discovering planetary nebulae (PNe) in open clusters (OCs). Cluster membership may be exploited to establish the distance, luminosity, age, and physical size for PNe, and the intrinsic luminosity and mass of its central star. Four potential PN-OC associations were investigated, to assess the cluster membership for the PNe. Radial velocities were measured from intermediate-resolution optical spectra, complemented with previous estimates in the literature. When the radial velocity study supported the PN/OC association, we analyzed if other parameters (e.g., age, distance, reddening, central star brightness) were consistent with this conclusion. Our measurements imply that the PNe VBe3 and HeFa1 are not members of the OCs NGC5999 and NGC6067, respectively, and likely belong to the background bulge population. Conversely, consistent radial velocities indicate that NGC2452/NGC2453 could be associated, but our results are not conclusive and additional observations are warranted. Finally, we demonstrate that all the available information point to He2-86 being a young, highly internally obscured PN member of NGC4463. New near-infrared photometry acquired via the Vista Variables in the Via Lactea ESO public survey was used in tandem with existing UBV photometry to measure the distance, reddening, and age of NGC4463, finding d=1.55+-0.10 kpc, E(B-V)=0.41+-0.02, and tau=65+-10 Myr, respectively. The same values should be adopted for the PN if the proposed cluster membership will be confirmed.Comment: Accepted for publication in A&

Evolution of rotating massive stars with new hydrodynamic wind models

Context. Mass loss due to radiatively line-driven winds is central to our understanding of the evolution of massive stars in both single and multiple systems. This mass loss plays a key role in modulating the stellar evolution at different metallicities, particularly in the case of massive stars with M* ≥ 25 M⊙. Aims. We extend the evolution models introduced in Paper I, where the mass-loss recipe is based on the simultaneous calculation of the wind hydrodynamics and the line acceleration, by incorporating the effects of stellar rotation. Methods. As in Paper I, we introduce a grid of self-consistent line-force parameters (k, α, δ) for a set of standard evolutionary tracks using GENE

Results Of The Spectroscopic Analysis Of WR6 Using CMFGEN

Using ESPaDOnS optical spectra of WR6, we search variations on the stellar wind parameters during the different phases of the spectral variations. We use the radiative transfer code CMFGEN (Hillier & Miller 1998) to determine the wind parameters. Our work gives mean parameters for WR6, Teff = 55 kK, M = 2.7 × 10^-5 M⊙/yr and v∞ =1700 km/s. Furthermore the line profiles variations at different phases are the consequence of a variation of mass loss rate and temperature un the winds. Effective temperature reaches 59 kK at the highest intensity, whereas the mass-loss rate decreases to 2.5 × 10^-5 M⊙/yr in that case. On the other hand, effective temperature decreases to 52.5 kK and the mass-loss rate increases to 3 × 10^-5 M/⊙yr when the line profile reach its minimum intensity. Results confirm the variable nature of the stellar wind, presented in this case on two of its fundamental parameters: temperature and mass-loss; which could be used to constrain the nature of the instability at the basis of the wind