Contrast the old definition of constellation with the
... As the Earth orbits (revolves around) the Sun during the year, the Sun appears to move from west to east against the celestial sphere and its constellations. If the Sun is out, then its light prevents us from seeing other stars. ...
... As the Earth orbits (revolves around) the Sun during the year, the Sun appears to move from west to east against the celestial sphere and its constellations. If the Sun is out, then its light prevents us from seeing other stars. ...
THE N/O RATIO IN EARLY B-TYPE MAIN SEQUENCE STARS AS
... logC , logN , and logO for MS B-stars found in Ref. 14, together with recent estimates of the abundances of C, N, and O for the sun [15,16]. The latter were obtained using nonstationary hydrodynamic 3D models of the solar atmosphere. We note that the elemental abundances here and in the ...
... logC , logN , and logO for MS B-stars found in Ref. 14, together with recent estimates of the abundances of C, N, and O for the sun [15,16]. The latter were obtained using nonstationary hydrodynamic 3D models of the solar atmosphere. We note that the elemental abundances here and in the ...
FIRST LIGHT IN THE UNIVERSE
... • In practice, these samples are contaminated by foreground stars, z~2 galaxies etc to an extent which remains controversial. We are unlikely to resolve this definitively with spectroscopy until era of ELTs. • Comoving SF rate declines from z~3 to z~6 (and probably beyond) suggesting insufficient 6< ...
... • In practice, these samples are contaminated by foreground stars, z~2 galaxies etc to an extent which remains controversial. We are unlikely to resolve this definitively with spectroscopy until era of ELTs. • Comoving SF rate declines from z~3 to z~6 (and probably beyond) suggesting insufficient 6< ...
low surface brightness galaxies
... When this infall happens, we assume that the galaxy is stripped of its hot gas reservoir so it is no longer able to accrete fresh material for star formation. The galaxy then rapidly consumes its cold gas moving towards the red sequence. ...
... When this infall happens, we assume that the galaxy is stripped of its hot gas reservoir so it is no longer able to accrete fresh material for star formation. The galaxy then rapidly consumes its cold gas moving towards the red sequence. ...
Chapter 20. Galaxies
... star light from the galaxy. It is further characterized by sometimes extreme variability that reflects variations in the accretion rate. The time scale for the variations can be as short as minutes, hours, days or months. When variable galaxies on these time scales were first discovered it was hard ...
... star light from the galaxy. It is further characterized by sometimes extreme variability that reflects variations in the accretion rate. The time scale for the variations can be as short as minutes, hours, days or months. When variable galaxies on these time scales were first discovered it was hard ...
The Dark Age of the Universe
... Tvir ⬵ 2000 K and mass ⬃106 MJ; at lower temperatures, the rotational transitions of H2 do not provide sufficient cooling for the gas to dissipate its energy. The slow cooling in these first objects leads to the formation of a central core with a mass of 100 to 1000 MJ of gas cooled to ⬃200 K, and t ...
... Tvir ⬵ 2000 K and mass ⬃106 MJ; at lower temperatures, the rotational transitions of H2 do not provide sufficient cooling for the gas to dissipate its energy. The slow cooling in these first objects leads to the formation of a central core with a mass of 100 to 1000 MJ of gas cooled to ⬃200 K, and t ...
numerical exercises
... So ~1011 M is derived for the mass of the Galaxy internal to the Sun. If the orbital velocity curve is flat to ~16 kpc from the Galactic centre, then one can redo the calculations to find that ~21011 M is derived for the mass of the Galaxy internal to ~16 kpc from the centre. Where did the extra ...
... So ~1011 M is derived for the mass of the Galaxy internal to the Sun. If the orbital velocity curve is flat to ~16 kpc from the Galactic centre, then one can redo the calculations to find that ~21011 M is derived for the mass of the Galaxy internal to ~16 kpc from the centre. Where did the extra ...
Winds of Main-Sequence Stars - Harvard
... The solar wind mass los rate • The sphere-averaged “M” isn’t usually considered by solar physicists! • Wang (1998, CS10) used empirical relationships between B-field, wind speed, and density to reconstruct M over two solar cycles. ...
... The solar wind mass los rate • The sphere-averaged “M” isn’t usually considered by solar physicists! • Wang (1998, CS10) used empirical relationships between B-field, wind speed, and density to reconstruct M over two solar cycles. ...
Age patterns in a sample of spiral galaxies
... relate Hα emission or UV flux of a source to its current star formation rate (SFR), are based on simple SF models that neglect environmental factors affecting stellar evolution [14, 19]. Such factors include SF driven by tidal forces instead of bars, and flocculent (as opposed to dominant) spiral ar ...
... relate Hα emission or UV flux of a source to its current star formation rate (SFR), are based on simple SF models that neglect environmental factors affecting stellar evolution [14, 19]. Such factors include SF driven by tidal forces instead of bars, and flocculent (as opposed to dominant) spiral ar ...
http://www.lanl.gov/orgs/adtsc/publications/science_highlights_2013/docs/Pg24_25.pdf
... Despite the large amounts of data, the information we can derive about the progenitor stars from all of these observations is limited because for most of these SNe we have only lightcurve data, while for some we have spectra as well. Even in the extremely rare cases where the progenitor stars of nea ...
... Despite the large amounts of data, the information we can derive about the progenitor stars from all of these observations is limited because for most of these SNe we have only lightcurve data, while for some we have spectra as well. Even in the extremely rare cases where the progenitor stars of nea ...
Think about the universe
... sequence. The rarer types are stars passing relatively quickly through later stages of development on the way to extinction as their nuclear fuel runs out. ...
... sequence. The rarer types are stars passing relatively quickly through later stages of development on the way to extinction as their nuclear fuel runs out. ...
Lecture 8
... It is related to the so-called “strong CP-problem” in particle physics. We shall not go into the details of this, but note that it can be phrased as the question “why is the neutron electric dipole moment so small?”. (It is zero to the accuracy of measurement, the upper limit being dn < 0.63 × 10−25 ...
... It is related to the so-called “strong CP-problem” in particle physics. We shall not go into the details of this, but note that it can be phrased as the question “why is the neutron electric dipole moment so small?”. (It is zero to the accuracy of measurement, the upper limit being dn < 0.63 × 10−25 ...
The effects of red supergiant mass loss on
... lower than the escape velocity from the stellar photosphere, v esc ∼ 100 km s−1 . He assessed the possibility that radiation pressure on the circumstellar ions (and atoms) could drive the wind until the local escape velocity would have dropped below the wind speed, but the values for the achieved ac ...
... lower than the escape velocity from the stellar photosphere, v esc ∼ 100 km s−1 . He assessed the possibility that radiation pressure on the circumstellar ions (and atoms) could drive the wind until the local escape velocity would have dropped below the wind speed, but the values for the achieved ac ...
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.