Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userPrecision Analysis of Evolved Stars
252
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Evolved stars dominate galactic spectra, enrich the galactic medium, expand to change their planetary systems, eject winds of a complex nature, produce spectacular nebulae and illuminate them, and transfer material between binary companions. While doing this, they fill the HR diagram with diagnostic loops that write the story of late stellar evolution. Evolved stars sometimes release unfathomable amounts of energy in neutrinos, light, kinetic flow, and gravitational waves. During these late-life times, stars evolve complexly, with expansion, convection, mixing, pulsation, mass loss. Some processes have virtually no spatial symmetries, and are poorly addressed with low-resolution measurements and analysis. Even a simple question as how to model mass loss resists solution. However, new methods offer increasingly diagnostic tools. Astrometry reveals populations and groupings. Pulsations/oscillations support study of stellar interiors. Optical/radio interferometry enable 2-3d imagery of atmospheres and shells. Bright stars with rich molecular spectra and velocity fields are a ripe opportunity for imaging with high spatial and spectral resolution, giving insight into the physics and modeling of later stellar evolution.
rate research
Read More
A new two dimensional non-perturbative code to compute accurate oscillation modes of rapidly rotating stars is presented. The 2D calculations fully take into account the centrifugal distorsion of the star while the non perturbative method includes the full influence of the Coriolis acceleration. This 2D non-perturbative code is used to study pulsational spectra of highly distorted evolved models of stars. 2D models of stars are obtained by a self consistent method which distorts spherically averaged stellar models a posteriori. We are also able to compute gravito-acoustic modes for the first time in rapidly rotating stars. We present the dynamics of pulsation modes in such models, and show regularities in their frequency spectra.
Long-slit spectroscopy with the Southern African Large Telescope (SALT) of central stars of mid-infrared nebulae detected with the Spitzer Space Telescope and Wide-field Infrared Survey Explorer (WISE) led to the discovery of numerous candidate luminous blue variables (cLBVs) and other rare evolved massive stars. With the recent advent of the SALT fibre-fed high-resolution echelle spectrograph (HRS), a new perspective for the study of these interesting objects is appeared. Using the HRS we obtained spectra of a dozen newly identified massive stars. Some results on the recently identified cLBV Hen 3-729 are presented.
High resolution maps of maser emission provide very detailed information on processes occurring in circumstellar envelopes of late-type stars. A particularly detailed picture of the innermost shells around AGB stars is provided by SiO masers. Considerable progress is being made to provide astrometrically aligned multi-transition simultaneous observations of these masers, which are needed to better constrain the models. In view of the large amount of high quality data available, models should now be developed to fully explain all maser characteristics together (spatial distribution, variability, etc). New generation instruments (VERA, VSOP-2), new observational techniques (frequency-phase transfer), and new models promise important improvements of our knowledge on this topic.
About 10% of hot stars host a fossil magnetic field on the pre-main sequence and main sequence. However, the first magnetic evolved hot stars have been discovered only recently. An observing program has been set up to find more such objects. This will allow us to test how fossil fields evolve, and the impact of magnetism on stellar evolution. Already 7 evolved magnetic hot stars are now known and the rate of magnetic discoveries in the survey suggests that they host dynamo fields in addition to fossil fields. Finally, the weakness of the measured fields is compatible at first order with simple magnetic flux conservation, although the current statistics cannot exclude intrinsic decay or enhancement during stellar evolution.
This chapter reviews some of the expected contributions of the ngVLA to the understanding of the late evolutionary stages of low-to-intermediate mass stars, including asymptotic giant branch (AGB) stars, post-AGB stars, and pre-planetary nebulae. Such objects represent the ultimate fate of stars like the Sun, and the stellar matter they lose to their immediate vicinity contributes significantly to the chemical enrichment of galaxies. Topics addressed in this chapter include continuum imaging of radio photospheres, studies of circumstellar envelopes in both thermal and nonthermal lines, and the investigation of the transition stages from the AGB to planetary nebulae using radio wavelength diagnostics. The authors gratefully acknowledge contributions to the content of this chapter from members of the evolved star community.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
