Activity III: Calibrating Images
... Suppose you have images of the same region of the sky taken on two different nights. The region contains two stars. One is your target star, the star you have chosen to study. It may be a Cepheid variable star or a star that has just gone supernova or any other star for which you wish to measure bri ...
... Suppose you have images of the same region of the sky taken on two different nights. The region contains two stars. One is your target star, the star you have chosen to study. It may be a Cepheid variable star or a star that has just gone supernova or any other star for which you wish to measure bri ...
Thermohaline mixing and the photospheric composition of low
... the hydrogen burning shell (HBS) encounters the chemical discontinuity left behind by the first dredge-up. We also find that the thermohaline unstable region, which initially appears on the exterior wing of the HBS, is unable to reach the outer convective envelope, with the consequence that no mixin ...
... the hydrogen burning shell (HBS) encounters the chemical discontinuity left behind by the first dredge-up. We also find that the thermohaline unstable region, which initially appears on the exterior wing of the HBS, is unable to reach the outer convective envelope, with the consequence that no mixin ...
arXiv 2011 Feroci
... are also observed during type I X-ray bursts, which are mostly the result of thermally unstable helium ignition in the accreted envelope of a neutron star. This generates a thermonuclear explosion that is observed as an X-ray burst with a rapid rise (∼1 s) followed by a slower decay (∼10–100 s). X-r ...
... are also observed during type I X-ray bursts, which are mostly the result of thermally unstable helium ignition in the accreted envelope of a neutron star. This generates a thermonuclear explosion that is observed as an X-ray burst with a rapid rise (∼1 s) followed by a slower decay (∼10–100 s). X-r ...
radioactive 26a1 in the galaxy: observations versus theory
... larger than what was obtained from supernova models in the early 80ies. Based on galactic chemical evolution arguments, Clayton [27] pointed out that supernovae, the main producers of the stable isotope *‘Al in the Galaxy, could not be at the origin of such an intense 26A1 emission, because in that ...
... larger than what was obtained from supernova models in the early 80ies. Based on galactic chemical evolution arguments, Clayton [27] pointed out that supernovae, the main producers of the stable isotope *‘Al in the Galaxy, could not be at the origin of such an intense 26A1 emission, because in that ...
The First Galaxies: Assembly under Radiative Feedback from the
... heats the gas inside the first halos and the intergalactic medium (IGM). The associated increase in pressure drives the gas outside halos with virial temperatures . 104 K, suppressing star formation in both minihalos and the first atomic cooling halos (e.g., Thoul & Weinberg 1996; Barkana & Loeb 199 ...
... heats the gas inside the first halos and the intergalactic medium (IGM). The associated increase in pressure drives the gas outside halos with virial temperatures . 104 K, suppressing star formation in both minihalos and the first atomic cooling halos (e.g., Thoul & Weinberg 1996; Barkana & Loeb 199 ...
YELLOW SUPERGIANTS IN THE ANDROMEDA GALAXY (M31)
... through the yellow supergiant region as stars evolve from the OB main-sequence stage (off the plot to the left) over to the RSG region on the right. However, in some cases, such as the evolutionary track that includes rotation (solid curve) for 25 M at Galactic metallicity (z = 0.020) the star then ...
... through the yellow supergiant region as stars evolve from the OB main-sequence stage (off the plot to the left) over to the RSG region on the right. However, in some cases, such as the evolutionary track that includes rotation (solid curve) for 25 M at Galactic metallicity (z = 0.020) the star then ...
A self-consistent empirical model atmosphere, abundance and
... Context. Chemically peculiar (CP) stars are unique natural laboratories for the investigation of the microscopic diffusion processes of chemical elements. The element segregation under the influence of gravity and radiation pressure leads to the appearance of strong abundance gradients in the atmosph ...
... Context. Chemically peculiar (CP) stars are unique natural laboratories for the investigation of the microscopic diffusion processes of chemical elements. The element segregation under the influence of gravity and radiation pressure leads to the appearance of strong abundance gradients in the atmosph ...
stochastic star formation and a (nearly) uniform stellar
... approaches the theoretical upper end mmax,∗ of the IMF. At low SFRs instead, due to the smaller number of stars that are formed, the probability of finding massive stars decreases. The IMF is not fully sampled, and mmax mmax,∗ . In this regime, stochastic effects become important to describe the o ...
... approaches the theoretical upper end mmax,∗ of the IMF. At low SFRs instead, due to the smaller number of stars that are formed, the probability of finding massive stars decreases. The IMF is not fully sampled, and mmax mmax,∗ . In this regime, stochastic effects become important to describe the o ...
Searching for Planets During Predicted Mesolensing Events: II
... have not deterred astronomers, with their familiarity of the universe of possible lenses and background sources, from predicting specific lensing events. In 1966, Feibelman suggested that the star 40 Eridani-a, a member of a triple which also contains a white dwarf, would pass close enough to a back ...
... have not deterred astronomers, with their familiarity of the universe of possible lenses and background sources, from predicting specific lensing events. In 1966, Feibelman suggested that the star 40 Eridani-a, a member of a triple which also contains a white dwarf, would pass close enough to a back ...
The dual nature of the Milky Way stellar halo
... bulge,the disk and the stellar halo. The galactic disk is indeed surrounded by a spheroid halo of old stars and globular clusters, of which 90% lie within 30 kpc, suggesting a stellar halo diameter of 60 kpc. The observed rotation of the stars and gas clouds indicates that the visible matter is surr ...
... bulge,the disk and the stellar halo. The galactic disk is indeed surrounded by a spheroid halo of old stars and globular clusters, of which 90% lie within 30 kpc, suggesting a stellar halo diameter of 60 kpc. The observed rotation of the stars and gas clouds indicates that the visible matter is surr ...
Rotation, activity, and stellar obliquities in a large uniform sample of
... during its activity cycle significantly overlaps the range seen in solar-like stars in the open cluster M67, which is similar to the Sun in both age and metallicity, while Önehag et al. (2011) performed a differential spectroscopic analysis of a solar analog in the same cluster and found it to be ne ...
... during its activity cycle significantly overlaps the range seen in solar-like stars in the open cluster M67, which is similar to the Sun in both age and metallicity, while Önehag et al. (2011) performed a differential spectroscopic analysis of a solar analog in the same cluster and found it to be ne ...
part iv - the war medal 1939-45
... troops of the Army who have taken part in airborne operations will qualify subject to the completion of two months in a fully operational unit. (b) Qualifying service between the 8th May 1945 and the 2nd September 1945, must have been rendered in operations in specified zones in the area bounded on ...
... troops of the Army who have taken part in airborne operations will qualify subject to the completion of two months in a fully operational unit. (b) Qualifying service between the 8th May 1945 and the 2nd September 1945, must have been rendered in operations in specified zones in the area bounded on ...
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.