| 1. |
- Bonifacio, P., et al.
(författare)
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Using CO5BOLD models to predict the effects of granulation on colours .
- 2017
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Ingår i: MEMORIE della Società Astronomica Italiana. - 0037-8720 .- 1824-016X. ; 88
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Abstract.In order to investigate the effects of granulation on fluxes and colours, we computedthe emerging fluxes from the models in theCO5BOLDgrid with metallicities [M/H]=0.0,–1.0,–2.0 and –3.0. These fluxes have been used to compute colours in different photometric systems.We explain here how our computations have been performed and provide some results.Key words.Convection – Hydrodynamics - Stars: atmosphere
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| 2. |
- Chugai, N. N., et al.
(författare)
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Type II supernovae at high redshifts.
- 2000
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Ingår i: Memorie della Società Astronomica Italiana. - 1824-016X. ; 71, s. 383-388
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Tidskriftsartikel (refereegranskat)abstract
- A hydro code coupled with radiation transfer was applied to produce monochromatic light curves of two models of type II supernovae (SN II) simulating SN II-P and SN IIb (SN 1993J-like). The authors then used these template light curves to evaluate the possibility of detecting SNe II at different redshifts. With a 5 hour exposure at VLT/FORS the SN II-P model may be detected at z = 1. However, since the model of SN II-P is underluminous at early phase (t < 10 days) by ≍1.5 mag a detection at z = 2 is quiet plausible. SN IIb can be detected as far as at z = 4. For 100% detection efficiency up to z = 2 one expects to find roughly 1 SN II yr-1arcmin-2.
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| 3. |
- Davies, M. B.
(författare)
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Blue straggler stars : Formation channels
- 2016
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Ingår i: Memorie della Societa Astronomica Italiana - Journal of the Italian Astronomical Society. - 1824-016X. ; 87:4, s. 479-482
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Konferensbidrag (refereegranskat)abstract
- I review formation channels for blue stragglers. I consider how they may be produced via collisions between two single main-sequence stars, or via collisions during encounters involving binary stars. Further, I discuss how blue stragglers may be produced via the evolution of isolated binaries. Observations of globular clusters suggest that both mechanisms are contributing.
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| 4. |
- Freytag, Bernd
(författare)
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Boundary conditions in CO5BOLD
- 2017
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Ingår i: MEMORIE della Società Astronomica Italiana. - 0037-8720 .- 1824-016X. ; 88, s. 12-21
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The declaration of boundary conditions is a crucial step in the setup of a CO5BOLD simulation (and many others) due to the physical nature of the problem, that is reflected in the mathematical description by partial differential equations, discrete versions of which are integrated by the numerical solver(s). While parameters controlling the flux of energy through the computational box are most important for all simulations of convective flows, the detailed specifications describing the behavior of energy, gas and dust densities, velocities, and magnetic fields at or just beyond the boundaries influence the flow, dynamics, and stratification within the box. Recent refinements of the treatment of boundary conditions in CO5BOLD resulted in reliably working implementations of open and closed versions for top, bottom, and ``inner'' boundaries even under conditions with strong velocity fields (waves, shocks, or downdrafts). They are implemented and available in the current version of CO5BOLD - but have to be activated properly with parameters adapted to the type of the star under consideration (by defining for instance the depth of the damping layers for the closed-bottom boundary or by specifying the damping constants for the open-bottom boundary).
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| 5. |
- Justtanont, Kay, 1965, et al.
(författare)
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Mass loss from an extreme OH/IR star: OH 26.5+0.6
- 2017
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Ingår i: Memorie della Societa Astronomica Italiana - Journal of the Italian Astronomical Society. - 1824-016X. ; 88:3, s. 342-345
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Konferensbidrag (refereegranskat)abstract
- Observations of H 2 O isotopologues of the extreme OH/IR star OH 26.5+0.6 show that the star has an initial mass consistent with it being an intermediate-mass star. The Herschel-HIFI spectra show clear detection of H 162 O and H 172 O while H 182 O is missing, consistent with the prediction of hot bottom burning which occurs in stars with an initial mass ≥ 5 M ʘ . The star is currently losing mass at a high rate of a few 10 -4 M ʘ yr −1 which is thought to commence in the past ∼ 200 years. We present new ALMA CO J=3-2 image which show that this high mass loss (superwind) region is compact, surrounded by extended shells of lower mass loss.
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| 6. |
- Lemasle, B., et al.
(författare)
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Abundance gradients to trace galaxy formationand evolution : the Galactic disk
- 2022
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Ingår i: MEMORIE della Società Astronomica Italiana. - : Italian Astronomical Society (SAIt). - 0037-8720 .- 1824-016X. ; 93:4
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Tidskriftsartikel (refereegranskat)abstract
- Abundance gradients are one of the few observables constraining the chemo-dynamical models of the Milky Way disk. Here, we review recent improvements regarding the determination of chemical abundances of young stellar systems, Cepheids, and RGB stars, that are used to trace abundance gradients, before focusing on the oxygen gradient.
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| 7. |
- Maldonado, R. F., et al.
(författare)
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Dynamical evolution of two planet systems into the white dwarf phase
- 2019. - 4
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Ingår i: Memorie della Societa Astronomica Italiana. - 1824-016X. ; 90, s. 675-677
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Konferensbidrag (refereegranskat)abstract
- In this contribution we present some preliminary results on the dynamical evolution of two planet systems around stellar hosts evolving from the main sequence to the white dwarf phase. The aim is to study the instabilities triggered by stellar evolution that may bring planets onto the stellar surface or produce planetary scale collisions (hence debris) that could explain the metallic atmospheric pollution observed in white dwarfs.
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| 8. |
- Traven, G., et al.
(författare)
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Machine learning techniques meet binaries
- 2019
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Ingår i: Memorie della Societa Astronomica Italiana - Journal of the Italian Astronomical Society. - 1824-016X. ; 90:3, s. 327-339
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Tidskriftsartikel (refereegranskat)abstract
- We briefly review the various machine learning methods and discuss how they can be used in efficient identification and analysis of spectroscopic binary stars. They can be treated as complementary to conventional methods, and we argue that some amount of human oversight is always needed and in fact highly beneficial when employing machine learning. We propose that a general dimensionality reduction technique can serve to diagnose and classify a given data set, and in case of GALAH spectra, our method quite effectively reveals a population of SB2 and SB3 systems. Once identified, the binary spectra can be analysed with the help of generative models, which can be constructed using machine learning techniques such as The Cannon and The Payne. Furthermore, in the case of spectroscopically unresolved multiple stars, we can recover the multiple contributions to an observed spectrum by reversing the process and proceeding from analysis to identification.
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| 9. |
- Tremblay, P. -E, et al.
(författare)
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Convective overshoot and metal accretion onto white dwarfs.
- 2017
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Ingår i: MEMORIE della Società Astronomica Italiana. - 0037-8720 .- 1824-016X. ; 88, s. 104-
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- A large fraction of white dwarfs host evolved planetary systems and show evidence of accretion from planetary debris. The accretion-diffusion model is the preferred method to understand the metal pollution in these otherwise hydrogen- and helium-rich white dwarf atmospheres. In this scenario, the accreted material first settles on the atmosphere. If the outer stellar layers are unstable to convection, the metals are then rapidly mixed up within the convection zone. In the classical 1D approach, it is generally assumed that the convection zone has a sharp bottom boundary, below which microscopic diffusion is unhampered and slowly removes metals from the visible layers. More realistic 3D radiation-hydrodynamics simulations of white dwarfs with CO5BOLD demonstrate, however, that the bottom of the convection zone does not have a sharp boundary, and that velocities decay exponentially below the unstable convective layers with a velocity scale height of the order of one pressure scale height. This has a potentially dramatic effect on the inferred mass of accreted materiel, hence on the chemical composition and size of planetary debris around white dwarfs.
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