I describe a method to transform a set of stellar evolution tracks onto a uniform basis and then interpolate within that basis to construct stellar isochrones. This method accommodates a broad range ...of stellar types, from substellar objects to high-mass stars, and phases of evolution, from the pre-main sequence to the white dwarf cooling sequence. I discuss situations in which stellar physics leads to departures from the otherwise monotonic relation between initial stellar mass and lifetime, and how these may be dealt with in isochrone construction. I close with convergence tests and recommendations for the number of points in the uniform basis and the mass between tracks in the original grid required to achieve a certain level accuracy in the resulting isochrones. The programs that implement these methods are free and open-source; they may be obtained from the project webpage.1
Stellar physics and evolution calculations enable a broad range of research in astrophysics. Modules for Experiments in Stellar Astrophysics (MESA) is a suite of open source, robust, efficient, ...thread-safe libraries for a wide range of applications in computational stellar astrophysics. A one-dimensional stellar evolution module, MESAstar, combines many of the numerical and physics modules for simulations of a wide range of stellar evolution scenarios ranging from very low mass to massive stars, including advanced evolutionary phases. MESAstar solves the fully coupled structure and composition equations simultaneously. It uses adaptive mesh refinement and sophisticated timestep controls, and supports shared memory parallelism based on OpenMP. State-of-the-art modules provide equation of state, opacity, nuclear reaction rates, element diffusion data, and atmosphere boundary conditions. Each module is constructed as a separate Fortran 95 library with its own explicitly defined public interface to facilitate independent development. Several detailed examples indicate the extensive verification and testing that is continuously performed and demonstrate the wide range of capabilities that MESA possesses. These examples include evolutionary tracks of very low mass stars, brown dwarfs, and gas giant planets to very old ages; the complete evolutionary track of a 1 M star from the pre-main sequence (PMS) to a cooling white dwarf; the solar sound speed profile; the evolution of intermediate-mass stars through the He-core burning phase and thermal pulses on the He-shell burning asymptotic giant branch phase; the interior structure of slowly pulsating B Stars and Beta Cepheids; the complete evolutionary tracks of massive stars from the PMS to the onset of core collapse; mass transfer from stars undergoing Roche lobe overflow; and the evolution of helium accretion onto a neutron star. MESA can be downloaded from the project Web site (http://mesa.sourceforge.net/).
ABSTRACT This is the first of a series of papers presenting the Modules for Experiments in Stellar Astrophysics (MESA) Isochrones and Stellar Tracks (MIST) project, a new comprehensive set of stellar ...evolutionary tracks and isochrones computed using MESA, a state-of-the-art open-source 1D stellar evolution package. In this work, we present models with solar-scaled abundance ratios covering a wide range of ages ( ), masses ( ), and metallicities ( ). The models are self-consistently and continuously evolved from the pre-main sequence (PMS) to the end of hydrogen burning, the white dwarf cooling sequence, or the end of carbon burning, depending on the initial mass. We also provide a grid of models evolved from the PMS to the end of core helium burning for . We showcase extensive comparisons with observational constraints as well as with some of the most widely used existing models in the literature. The evolutionary tracks and isochrones can be downloaded from the project website at http://waps.cfa.harvard.edu/MIST/.
Abstract
Recent work on metal-intermediate globular clusters (GCs) with Fe/H = −1.5 and −0.75 has illustrated the theoretical behavior of multiple populations in photometric diagrams obtained with ...the JWST. These results are confirmed by observations of multiple populations among the M dwarfs of 47 Tucanae. Here we explore multiple populations in metal-poor GCs with Fe/H = −2.3. We take advantage of synthetic spectra and isochrones that account for the chemical composition of multiple populations to identify photometric diagrams that separate the distinct stellar populations of GCs. We derive high-precision photometry and proper motion for main-sequence (MS) stars in the metal-poor GC M92 from JWST and Hubble Space Telescope images. We identify a first-generation (1G) and two main groups of second-generation (2G
A
and 2G
B
) stars and investigate their kinematics and chemical composition. We find isotropic motions with no differences among the distinct populations. The comparison between the observed colors of the M92 stars and the colors derived by synthetic spectra reveals that the helium abundances of 2G
A
and 2G
B
stars are higher than those of the 1G by Δ
Y
∼ 0.01 and 0.04, respectively. The
m
F090W
versus
m
F090W
−
m
F277W
color–magnitude diagram shows that below the knee MS stars exhibit a wide color broadening due to multiple populations. We constrain the amount of oxygen variation needed to reproduce the observed MS width, which is consistent with results on red giant branch stars. We conclude that multiple populations with masses of ∼0.1–0.8
M
⊙
share similar chemical compositions.
We update the capabilities of the open-knowledge software instrument Modules for Experiments in Stellar Astrophysics (MESA). RSP is a new functionality in MESAstar that models the nonlinear radial ...stellar pulsations that characterize RR Lyrae, Cepheids, and other classes of variable stars. We significantly enhance numerical energy conservation capabilities, including during mass changes. For example, this enables calculations through the He flash that conserve energy to better than 0.001%. To improve the modeling of rotating stars in MESA, we introduce a new approach to modifying the pressure and temperature equations of stellar structure, as well as a formulation of the projection effects of gravity darkening. A new scheme for tracking convective boundaries yields reliable values of the convective core mass and allows the natural emergence of adiabatic semiconvection regions during both core hydrogen- and helium-burning phases. We quantify the parallel performance of MESA on current-generation multicore architectures and demonstrate improvements in the computational efficiency of radiative levitation. We report updates to the equation of state and nuclear reaction physics modules. We briefly discuss the current treatment of fallback in core-collapse supernova models and the thermodynamic evolution of supernova explosions. We close by discussing the new MESA Testhub software infrastructure to enhance source code development.
Abstract
We update the capabilities of the open-knowledge software instrument Modules for Experiments in Stellar Astrophysics (
MESA
). The new
auto
_
diff
module implements automatic differentiation ...in
MESA
, an enabling capability that alleviates the need for hard-coded analytic expressions or finite-difference approximations. We significantly enhance the treatment of the growth and decay of convection in
MESA
with a new model for time-dependent convection, which is particularly important during late-stage nuclear burning in massive stars and electron-degenerate ignition events. We strengthen
MESA
’s implementation of the equation of state, and we quantify continued improvements to energy accounting and solver accuracy through a discussion of different energy equation features and enhancements. To improve the modeling of stars in
MESA
, we describe key updates to the treatment of stellar atmospheres, molecular opacities, Compton opacities, conductive opacities, element diffusion coefficients, and nuclear reaction rates. We introduce treatments of starspots, an important consideration for low-mass stars, and modifications for superadiabatic convection in radiation-dominated regions. We describe new approaches for increasing the efficiency of calculating monochromatic opacities and radiative levitation, and for increasing the efficiency of evolving the late stages of massive stars with a new operator-split nuclear burning mode. We close by discussing major updates to
MESA
’s software infrastructure that enhance source code development and community engagement.
We study the impact of mass-transfer physics on the observable properties of binary black hole populations that formed through isolated binary evolution. We used the
POSYDON
framework to combine ...detailed
MESA
binary simulations with the
COSMIC
population synthesis tool to obtain an accurate estimate of merging binary black hole observables with a specific focus on the spins of the black holes. We investigate the impact of mass-accretion efficiency onto compact objects and common-envelope efficiency on the observed distributions of the effective inspiral spin parameter
χ
eff
, chirp mass
M
chirp
, and binary mass ratio
q
. We find that low common envelope efficiency translates to tighter orbits following the common envelope and therefore more tidally spun up second-born black holes. However, these systems have short merger timescales and are only marginally detectable by current gravitational-wave detectors as they form and merge at high redshifts (
z
∼ 2), outside current detector horizons. Assuming Eddington-limited accretion efficiency and that the first-born black hole is formed with a negligible spin, we find that all non-zero
χ
eff
systems in the detectable population can come only from the common envelope channel as the stable mass-transfer channel cannot shrink the orbits enough for efficient tidal spin-up to take place. We find that the local rate density (
z
≃ 0.01) for the common envelope channel is in the range of ∼17–113 Gpc
−3
yr
−1
, considering a range of
α
CE
∈ 0.2, 5.0, while for the stable mass transfer channel the rate density is ∼25 Gpc
−3
yr
−1
. The latter drops by two orders of magnitude if the mass accretion onto the black hole is not Eddington limited because conservative mass transfer does not shrink the orbit as efficiently as non-conservative mass transfer does. Finally, using GWTC-2 events, we constrained the lower bound of branching fraction from other formation channels in the detected population to be ∼0.2. Assuming all remaining events to be formed through either stable mass transfer or common envelope channels, we find moderate to strong evidence in favour of models with inefficient common envelopes.
Full text
Available for:
FMFMET, NUK, UL, UM, UPUK
The multiple stellar populations (MPs) of the ∼11-13 Gyr old globular clusters (GCs) in our Galaxy are characterized by the different content of several light elements. These elements describe ...well-defined patterns like the C-N and the Na-O anticorrelations and the He-N and Na-N correlations. The discovery of MPs in Magellanic Cloud GCs opened up new paths for the investigation of chemical anomalies in clusters with different ages and physical properties. In this context, we used Hubble Space Telescope photometry to investigate the MPs and constrain their chemical composition of four ∼6-11 Gyr extragalactic GCs, namely NGC 121, NGC 339, NGC 416, and Lindsay 1 in the Small Magellanic Cloud. The comparison of the stellar colors with synthetic spectra suggests that the second-population stars of NGC 121, NGC 339, and NGC 416 are slightly enhanced in helium by and 0.010 0.003, respectively, with respect to the first population, while we find no significant helium variation in Lindsay 1 . Moreover, the second-population stars of all the clusters are, on average, enhanced in nitrogen and depleted in carbon and oxygen, in close analogy with what we observe in Galactic GCs.
PAndAS' Progeny: Extending the M31 Dwarf Galaxy Cabal Richardson, Jenny C; J. Irwin, Mike; McConnachie, Alan W ...
Astrophysical journal/The Astrophysical journal,
05/2011, Volume:
732, Issue:
2
Journal Article
Peer reviewed
Open access
We present the discovery of five new dwarf galaxies, Andromeda XXIII-XXVII, located in the outer halo of M31. These galaxies were discovered during the second year of data from the Pan-Andromeda ...Archaeological Survey (PAndAS), a photometric survey of the M31/M33 subgroup conducted with the MegaPrime/MegaCam wide-field camera on the Canada-France-Hawaii Telescope. The current PAndAS survey now provides an almost complete panoramic view of the M31 halo out to an average projected radius of ~150 kpc. Here we present for the first time the metal-poor stellar density map for this whole region, not only as an illustration of the discovery space for satellite galaxies, but also as a birds-eye view of the ongoing assembly process of an L * disk galaxy. Four of the newly discovered satellites appear as well-defined spatial overdensities of stars lying on the expected locus of metal-poor (--2.5 < Fe/H < --1.3) red giant branch stars at the distance of M31. The fifth overdensity, And XXVII, is embedded in an extensive stream of such stars and is possibly the remnant of a strong tidal disruption event. Based on distance estimates from horizontal branch magnitudes, all five have metallicities typical of dwarf spheroidal galaxies ranging from Fe/H =--1.7 ? 0.2 to Fe/H =--1.9 ? 0.2 and absolute magnitudes ranging from MV = --7.1 ? 0.5 to MV = --10.2 ? 0.5. These five additional satellites bring the number of dwarf spheroidal galaxies in this region to 25 and continue the trend whereby the brighter dwarf spheroidal satellites of M31 generally have much larger half-light radii than their Milky Way counterparts. With an extended sample of M31 satellite galaxies, we also revisit the spatial distribution of this population and in particular we find that, within the current projected limits of the PAndAS survey, the surface density of satellites is essentially constant out to 150 kpc. This corresponds to a radial density distribution of satellites varying as r --1, a result seemingly in conflict with the predictions of cosmological simulations.
Abstract
Most massive stars are members of a binary or a higher-order stellar system, where the presence of a binary companion can decisively alter their evolution via binary interactions. ...Interacting binaries are also important astrophysical laboratories for the study of compact objects. Binary population synthesis studies have been used extensively over the last two decades to interpret observations of compact-object binaries and to decipher the physical processes that lead to their formation. Here, we present
POSYDON
, a novel, publicly available, binary population synthesis code that incorporates full stellar structure and binary-evolution modeling, using the
MESA
code, throughout the whole evolution of the binaries. The use of
POSYDON
enables the self-consistent treatment of physical processes in stellar and binary evolution, including: realistic mass-transfer calculations and assessment of stability, internal angular-momentum transport and tides, stellar core sizes, mass-transfer rates, and orbital periods. This paper describes the detailed methodology and implementation of
POSYDON
, including the assumed physics of stellar and binary evolution, the extensive grids of detailed single- and binary-star models, the postprocessing, classification, and interpolation methods we developed for use with the grids, and the treatment of evolutionary phases that are not based on precalculated grids. The first version of
POSYDON
targets binaries with massive primary stars (potential progenitors of neutron stars or black holes) at solar metallicity.
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