Gamma-Ray Line Emission from Radioactive Isotopes in Stars and
... and difficulties. We discuss their nature briefly, addressing a few of the physical aspects involved. The treatment of convection, and its implications, constitute one problem area common to several source types. The convective coupling between mass zones in both the oxygen-neon and hydrogen shell-b ...
... and difficulties. We discuss their nature briefly, addressing a few of the physical aspects involved. The treatment of convection, and its implications, constitute one problem area common to several source types. The convective coupling between mass zones in both the oxygen-neon and hydrogen shell-b ...
nuclear
... is set primarily by the accretion rate, which we infer from the persistent X-ray flux • The accretion rate cannot (much) exceed the Eddington limit, at which point the radiation pressure balances gravitational attraction, preventing further accretion • Many LMXBs are transients, that is they undergo ...
... is set primarily by the accretion rate, which we infer from the persistent X-ray flux • The accretion rate cannot (much) exceed the Eddington limit, at which point the radiation pressure balances gravitational attraction, preventing further accretion • Many LMXBs are transients, that is they undergo ...
The Physics of Star Formation: Understanding the Youngest Protostars
... an evolutionary sequence from highly embedded protostars still accreting mass (Class I SED) to young stars surrounded by substantial accretion disks (Class II SED) to revealed young stars which have dissipated their disks and may have completed their planet formation (Class III SED). Although we hav ...
... an evolutionary sequence from highly embedded protostars still accreting mass (Class I SED) to young stars surrounded by substantial accretion disks (Class II SED) to revealed young stars which have dissipated their disks and may have completed their planet formation (Class III SED). Although we hav ...
Astronomy Astrophysics - Utrecht University Repository
... is the observed minimum brightness of the EROS II light curve over the 5 years of observations. The size of the symbols corresponds to the RE -band amplitude of variability during the period of EROS II observations. The figure shows that the stars are distributed on an increasingly wider range of ∆R ...
... is the observed minimum brightness of the EROS II light curve over the 5 years of observations. The size of the symbols corresponds to the RE -band amplitude of variability during the period of EROS II observations. The figure shows that the stars are distributed on an increasingly wider range of ∆R ...
Behaviour of elements from lithium to europium in stars with and
... In order to identify either the presence or the absence of a possible relation between chemical abundances and mechanisms of planetary formation, various studies have been performed to examine the chemical peculiarities of planet-hosting stars (e.g. Meléndez et al. 2009; Ramı́rez, Meléndez & Asplu ...
... In order to identify either the presence or the absence of a possible relation between chemical abundances and mechanisms of planetary formation, various studies have been performed to examine the chemical peculiarities of planet-hosting stars (e.g. Meléndez et al. 2009; Ramı́rez, Meléndez & Asplu ...
What powers luminous infrared galaxies?
... of the line emission we show that three key representatives of this class, Arp 220, NGC 6240 and NGC 3256 are likely powered mainly by recently formed, massive stars. While an active nucleus may well be present in anyone of these sources, ratios of fine structure lines in different stages of ionizat ...
... of the line emission we show that three key representatives of this class, Arp 220, NGC 6240 and NGC 3256 are likely powered mainly by recently formed, massive stars. While an active nucleus may well be present in anyone of these sources, ratios of fine structure lines in different stages of ionizat ...
The physics of star formation
... of their high opacity, the rate at which they are heated by external radiation is low; the result is that molecular clouds are very cold and have typical temperatures of only about 10–20 K. Higher temperatures of up to 100 K or more may exist locally in regions heated by luminous newly formed stars. ...
... of their high opacity, the rate at which they are heated by external radiation is low; the result is that molecular clouds are very cold and have typical temperatures of only about 10–20 K. Higher temperatures of up to 100 K or more may exist locally in regions heated by luminous newly formed stars. ...
Mode Identification
... ▸ Theoretical amplitude ratios and phase differences depend on the stellar flux. ▸ The stellar flux is determined by the metallicity, the effective temperature, the mass and the radius, or equivalently, by the gravity, of the star. ▸ Parameters are often not well known; their errors propagate into t ...
... ▸ Theoretical amplitude ratios and phase differences depend on the stellar flux. ▸ The stellar flux is determined by the metallicity, the effective temperature, the mass and the radius, or equivalently, by the gravity, of the star. ▸ Parameters are often not well known; their errors propagate into t ...
2_ISM - UCT Astronomy Department
... •Reminder: Extinction caused by both scattering and absorption • Absorption: radiant energy transformed into heat, re-radiated at IR wavelengths corresponding to temperatures of dust particles reduced intensity and reddening of colour • Scattering: the direction of light changed as f(λ), leading t ...
... •Reminder: Extinction caused by both scattering and absorption • Absorption: radiant energy transformed into heat, re-radiated at IR wavelengths corresponding to temperatures of dust particles reduced intensity and reddening of colour • Scattering: the direction of light changed as f(λ), leading t ...
The Formation and Evolution of the Milky Way
... blobs of gas. How the universe made the Milky Way from such simple beginnings is not altogether clear. The task of unraveling this mystery has been cast to astronomers, such as myself, who attempt to construct models of the Galaxy’s evolution based on its present appearance. These models need to acc ...
... blobs of gas. How the universe made the Milky Way from such simple beginnings is not altogether clear. The task of unraveling this mystery has been cast to astronomers, such as myself, who attempt to construct models of the Galaxy’s evolution based on its present appearance. These models need to acc ...
1 Pau Amaro Seoane - modest 15-s
... We present an expression of the external gravitational field of a general ring-like object with the axial and plane symmetries such as annular disks or oval toroids with an arbitrary density distribution. The main term is that of an infinitely thin ring (Fukushima, 2010, Celest. Mech. Dyn. Astron., ...
... We present an expression of the external gravitational field of a general ring-like object with the axial and plane symmetries such as annular disks or oval toroids with an arbitrary density distribution. The main term is that of an infinitely thin ring (Fukushima, 2010, Celest. Mech. Dyn. Astron., ...
Age dating stellar populations in the near infrared
... versus the J−H (F110W–F160W) colour for the inner (top panel) and outer (bottom panel) fields of M83 (Bastian et al. 2011, 2012). These colours have not been dereddened. The solid red curve displays our theoretically calculated colour evolution using Geneva evolutionary tracks and colours calculated ...
... versus the J−H (F110W–F160W) colour for the inner (top panel) and outer (bottom panel) fields of M83 (Bastian et al. 2011, 2012). These colours have not been dereddened. The solid red curve displays our theoretically calculated colour evolution using Geneva evolutionary tracks and colours calculated ...
The Be/X-ray transient V0332153: evidence for a tilt between the
... for a review). Both the emission lines and the characteristic strong infrared excess when compared to normal stars of the same spectral types are attributed to the presence of a circumstellar disc. Most Be/X-ray binaries have relatively eccentric orbits, and the neutron star companion is normally fa ...
... for a review). Both the emission lines and the characteristic strong infrared excess when compared to normal stars of the same spectral types are attributed to the presence of a circumstellar disc. Most Be/X-ray binaries have relatively eccentric orbits, and the neutron star companion is normally fa ...
Rotation Periods of Wide Binaries in the Kepler Field
... and Barnes, et al. (2016) have derived periods for some of the cluster stars. However, all of these clusters are relatively distant, so cluster stars later than early K spectral type are too faint for Kepler. Angus, et al. (2015) used rotation periods of Kepler stars as well as cluster stars and oth ...
... and Barnes, et al. (2016) have derived periods for some of the cluster stars. However, all of these clusters are relatively distant, so cluster stars later than early K spectral type are too faint for Kepler. Angus, et al. (2015) used rotation periods of Kepler stars as well as cluster stars and oth ...
Confronting Dark Matter Powered Stars with Recent Results from
... Explaining the nature of the non-luminous matter component, called dark matter (DM), is most crucial to both scienti c elds. This study combines considerations about the nature of the dark matter particle and fundamental questions concerning the nature of the rst stars forming in the history of th ...
... Explaining the nature of the non-luminous matter component, called dark matter (DM), is most crucial to both scienti c elds. This study combines considerations about the nature of the dark matter particle and fundamental questions concerning the nature of the rst stars forming in the history of th ...
Stellar evolution
Stellar evolution is the process by which a star changes during its lifetime. Depending on the mass of the star, this lifetime ranges from a few million years for the most massive to trillions of years for the least massive, which is considerably longer than the age of the universe. The table shows the lifetimes of stars as a function of their masses. All stars are born from collapsing clouds of gas and dust, often called nebulae or molecular clouds. Over the course of millions of years, these protostars settle down into a state of equilibrium, becoming what is known as a main-sequence star.Nuclear fusion powers a star for most of its life. Initially the energy is generated by the fusion of hydrogen atoms at the core of the main-sequence star. Later, as the preponderance of atoms at the core becomes helium, stars like the Sun begin to fuse hydrogen along a spherical shell surrounding the core. This process causes the star to gradually grow in size, passing through the subgiant stage until it reaches the red giant phase. Stars with at least half the mass of the Sun can also begin to generate energy through the fusion of helium at their core, whereas more-massive stars can fuse heavier elements along a series of concentric shells. Once a star like the Sun has exhausted its nuclear fuel, its core collapses into a dense white dwarf and the outer layers are expelled as a planetary nebula. Stars with around ten or more times the mass of the Sun can explode in a supernova as their inert iron cores collapse into an extremely dense neutron star or black hole. Although the universe is not old enough for any of the smallest red dwarfs to have reached the end of their lives, stellar models suggest they will slowly become brighter and hotter before running out of hydrogen fuel and becoming low-mass white dwarfs.Stellar evolution is not studied by observing the life of a single star, as most stellar changes occur too slowly to be detected, even over many centuries. Instead, astrophysicists come to understand how stars evolve by observing numerous stars at various points in their lifetime, and by simulating stellar structure using computer models.In June 2015, astronomers reported evidence for Population III stars in the Cosmos Redshift 7 galaxy at z = 6.60. Such stars are likely to have existed in the very early universe (i.e., at high redshift), and may have started the production of chemical elements heavier than hydrogen that are needed for the later formation of planets and life as we know it.