Classical Be Stars: Rapidly Rotating B Stars with Viscous Keplerian
... symbiotic binaries, and compact planetary nebulae, partly discussed above. The nature of the fifth group, sometimes dubbed “unclassified B[e]” type stars, is not quite clear as of now, but in any case the forbidden lines and the dust-type infrared excess make them quite distinct from the classical B ...
... symbiotic binaries, and compact planetary nebulae, partly discussed above. The nature of the fifth group, sometimes dubbed “unclassified B[e]” type stars, is not quite clear as of now, but in any case the forbidden lines and the dust-type infrared excess make them quite distinct from the classical B ...
Giant Planet Formation, Evolution, and Internal Structure
... A modified Hill radius, within which gas does get accreted onto the planet, is found to be ∼ 0.25RH . Thus one can define an effective outer radius for the planet: Reff = ...
... A modified Hill radius, within which gas does get accreted onto the planet, is found to be ∼ 0.25RH . Thus one can define an effective outer radius for the planet: Reff = ...
γ Doradus pulsation in two pre-main sequence stars discovered by
... Sung et al. (1997) reported a cluster distance of 759 ± 83 pc, which corresponds to a distance modulus of 9.40 ± 0.25 mag. The age of NGC 2264 can only be determined with a relatively large error because its main sequence consists only of massive O and B stars and stars of later spectral types are s ...
... Sung et al. (1997) reported a cluster distance of 759 ± 83 pc, which corresponds to a distance modulus of 9.40 ± 0.25 mag. The age of NGC 2264 can only be determined with a relatively large error because its main sequence consists only of massive O and B stars and stars of later spectral types are s ...
Molecular Cloud Turbulence and Star Formation. Ballesteros
... interpreted as indicative of approximate virial equilibrium, and thus of general stability and longevity of the clouds (e.g., McKee et al., 1993; Blitz and Williams, 1999). In this picture, the fact that MCs have thermal pressures exceeding that of the general ISM by roughly one order of magnitude ( ...
... interpreted as indicative of approximate virial equilibrium, and thus of general stability and longevity of the clouds (e.g., McKee et al., 1993; Blitz and Williams, 1999). In this picture, the fact that MCs have thermal pressures exceeding that of the general ISM by roughly one order of magnitude ( ...
The Formation and Survival of Discs in a Lambda
... condenses within the dark matter haloes conserving its specific angular momentum (White & Rees 1978; Fall & Efstathiou 1980; Mo, Mao & White 1998). In these models, the final properties of discs are closely linked to those of their parent haloes: for example, disc sizes and stability properties depe ...
... condenses within the dark matter haloes conserving its specific angular momentum (White & Rees 1978; Fall & Efstathiou 1980; Mo, Mao & White 1998). In these models, the final properties of discs are closely linked to those of their parent haloes: for example, disc sizes and stability properties depe ...
What Gaia can reveal about the matter distribution in the Milky Way
... The satellite Gaia The 19th of December 2013, the astrometric satellite Gaia was launched from ESA’s launch site in Kourou, French Guyana. The goal of Gaia is to create a three-dimensional map of our homegalaxy, the Milky Way, by observing about a billion stars all over the Galaxy. That Gaia is an a ...
... The satellite Gaia The 19th of December 2013, the astrometric satellite Gaia was launched from ESA’s launch site in Kourou, French Guyana. The goal of Gaia is to create a three-dimensional map of our homegalaxy, the Milky Way, by observing about a billion stars all over the Galaxy. That Gaia is an a ...
GRB 130603B: No Compelling Evidence for Neutron Star Merger
... bursts. However, their proposed underlying mechanism—a spherical fireball produced by neutrino-antineutrino annihilation into electron positron pairs beyond the surface of the collapsing/merging star—turned out not to be powerful enough to produce GRBs observable at very large cosmological distances ...
... bursts. However, their proposed underlying mechanism—a spherical fireball produced by neutrino-antineutrino annihilation into electron positron pairs beyond the surface of the collapsing/merging star—turned out not to be powerful enough to produce GRBs observable at very large cosmological distances ...
Chapter 1
... ratios are higher than a cooler nebula. This is because to produce [O iii] λ4363 an electron needs to be excited to 5.3 eV, which requires more energy than for 4959/5007 which result from decay from 1 D2 level, 2.5 eV above the ground-state (see Figure 2.2). Therefore, these ratios can be used to co ...
... ratios are higher than a cooler nebula. This is because to produce [O iii] λ4363 an electron needs to be excited to 5.3 eV, which requires more energy than for 4959/5007 which result from decay from 1 D2 level, 2.5 eV above the ground-state (see Figure 2.2). Therefore, these ratios can be used to co ...
Recent star formation in local, morphologically disturbed
... galaxy formation paradigm. Following the seminal work of Toomre (1977), numerical simulations have consistently demonstrated that galaxy collisions end in rapid merging – a fundamental feature of the standard model – and typically produce spheroidal remnants (e.g. Barnes & Hernquist 1992) in cases w ...
... galaxy formation paradigm. Following the seminal work of Toomre (1977), numerical simulations have consistently demonstrated that galaxy collisions end in rapid merging – a fundamental feature of the standard model – and typically produce spheroidal remnants (e.g. Barnes & Hernquist 1992) in cases w ...
Stellar Mass Loss in Globular - Jodrell Bank Centre for Astrophysics
... 47 Tucanae and ω Centauri, finding 47 Tuc V1 (and possibly V18) and ω Cen V6 surrounded by circumstellar silicate dust. ω Cen V42 may also be surrounded by carbon-rich dust. Much of this work is devoted to finding the threshold for dust production and the mass-loss rates from cluster stars with both c ...
... 47 Tucanae and ω Centauri, finding 47 Tuc V1 (and possibly V18) and ω Cen V6 surrounded by circumstellar silicate dust. ω Cen V42 may also be surrounded by carbon-rich dust. Much of this work is devoted to finding the threshold for dust production and the mass-loss rates from cluster stars with both c ...
Multi-dimensional structure of accreting young stars
... to the radial grid close to the surface. In the 1D model, the surface is defined using the Eddington approximation, with the surface corresponding to the photosphere at an optical depth τ = 2/3 and a surface temperature T surf equal to the effective temperature T eff (see e.g. Chabrier & Baraffe 199 ...
... to the radial grid close to the surface. In the 1D model, the surface is defined using the Eddington approximation, with the surface corresponding to the photosphere at an optical depth τ = 2/3 and a surface temperature T surf equal to the effective temperature T eff (see e.g. Chabrier & Baraffe 199 ...
Background Information on Galaxy Classification
... The Milky Way is a large spiral galaxy, but there are galaxies that are ten times its size, and many that are thousands of times smaller. In fact, astronomers now think that tiny, faint galaxies, called dwarf galaxies, may be the most plentiful galaxies in the universe. Indeed, there are probably so ...
... The Milky Way is a large spiral galaxy, but there are galaxies that are ten times its size, and many that are thousands of times smaller. In fact, astronomers now think that tiny, faint galaxies, called dwarf galaxies, may be the most plentiful galaxies in the universe. Indeed, there are probably so ...
Equations of state and structure of neutron stars
... and are concentrated in two connected fields related to structure of the neutron (strange) stars and their external gravitational field. The first one is oriented on testing of equation of state for dense nuclear matter by astrophysical observations. We used set of parameterizations that has been fo ...
... and are concentrated in two connected fields related to structure of the neutron (strange) stars and their external gravitational field. The first one is oriented on testing of equation of state for dense nuclear matter by astrophysical observations. We used set of parameterizations that has been fo ...
THE DYNAMICAL STRUCTURE AND EVOLUTION OF GIANT
... does not apply to unbound clumps in GMCs, which can have lower column densities 5], nor to the OB star{forming clumps studied by Plume et al 87], which have N!H22 60. There are several other characteristics of GMCs that we must take note of. First, GMCs appear to have magnetic elds that are dynam ...
... does not apply to unbound clumps in GMCs, which can have lower column densities 5], nor to the OB star{forming clumps studied by Plume et al 87], which have N!H22 60. There are several other characteristics of GMCs that we must take note of. First, GMCs appear to have magnetic elds that are dynam ...
The uniqueness of Antarctica for the study of AGB stars
... Bolometric Variability (ISO) Bolometric variability……… How is this generated ? 1. Shock waves caused by dynamic events in the photosphere? 2. Magneto-hydrodynamical modes (and magnetic storms)? ...
... Bolometric Variability (ISO) Bolometric variability……… How is this generated ? 1. Shock waves caused by dynamic events in the photosphere? 2. Magneto-hydrodynamical modes (and magnetic storms)? ...
The First Galaxies: Assembly under Radiative Feedback from the
... The most massive of the simulated MW dark matter subhalos have progenitors with masses 108 − 1010 M⊙ at z & 6 (e.g., Boylan-Kolchin et al. 2012). This suggests an intimate relation with the first dwarf galaxies, and renders investigations into these objects a promising tool to understand the origin ...
... The most massive of the simulated MW dark matter subhalos have progenitors with masses 108 − 1010 M⊙ at z & 6 (e.g., Boylan-Kolchin et al. 2012). This suggests an intimate relation with the first dwarf galaxies, and renders investigations into these objects a promising tool to understand the origin ...
A systematic study of X-ray variability in the ROSAT all
... analysis. All these sources turned out to be very weak and for such sources at a distance of less than about 15 degrees of the ecliptical poles there is another problem illustrated in Fig. 3. Sources with an average count rate of less than ∼0.5 photons per second show a typical curvature that increa ...
... analysis. All these sources turned out to be very weak and for such sources at a distance of less than about 15 degrees of the ecliptical poles there is another problem illustrated in Fig. 3. Sources with an average count rate of less than ∼0.5 photons per second show a typical curvature that increa ...
The magnetic field and wind confinement of b Cephei: new clues for
... From figs 1 and 4 of Pigulski & Boratyn (1992), we obtain that these observations were recorded when b Cep was very close to periastron and thus that the orbital period of the system is 85 ^ 1 yr, slightly shorter than (though still roughly compatible with) the value of 91:6 ^ 3:7 derived by Pigulsk ...
... From figs 1 and 4 of Pigulski & Boratyn (1992), we obtain that these observations were recorded when b Cep was very close to periastron and thus that the orbital period of the system is 85 ^ 1 yr, slightly shorter than (though still roughly compatible with) the value of 91:6 ^ 3:7 derived by Pigulsk ...
Five Planets and an Independent Confirmation of
... are used to model the wavelength scale and the instrumental profile of the telescope and spectrometer optics for each observation (Marcy & Butler 1992; Butler et al. 1996) The iodine cell at Lick Observatory has not been changed over the entire duration of the planet search project, helping to prese ...
... are used to model the wavelength scale and the instrumental profile of the telescope and spectrometer optics for each observation (Marcy & Butler 1992; Butler et al. 1996) The iodine cell at Lick Observatory has not been changed over the entire duration of the planet search project, helping to prese ...
Galactic Evolution - Harvard-Smithsonian Center for Astrophysics
... massive than the combination of stars, gas, and dust within the luminous parts of galaxies, is non-baryonic. Furthermore, roughly spherical accumulations of dark matter likely helped initiate galaxy formation by gravitationally trapping H gas, which is then further concentrated by dissipative intera ...
... massive than the combination of stars, gas, and dust within the luminous parts of galaxies, is non-baryonic. Furthermore, roughly spherical accumulations of dark matter likely helped initiate galaxy formation by gravitationally trapping H gas, which is then further concentrated by dissipative intera ...
Phase-resolved high-resolution spectrophotometry of the eclipsing
... By means of Doppler tomography their origin could be located unequivocally (a) on the secondary star, (b) the ballistic part of the accretion stream (horizontal stream), and (c) the magnetically funnelled part of the stream (vertical stream). For the first time we were able to derive a (near-)comple ...
... By means of Doppler tomography their origin could be located unequivocally (a) on the secondary star, (b) the ballistic part of the accretion stream (horizontal stream), and (c) the magnetically funnelled part of the stream (vertical stream). For the first time we were able to derive a (near-)comple ...
Substellar Objects in Nearby Young Clusters (SONYC) VI: The
... good conditions. The pre-images were reduced and calibrated using 2MASS photometry. Aperture magnitudes were measured for all our candidates, to complement and verify the available photometry. These pre-images are used to define the masks for the spectroscopy run, which was carried out in the night ...
... good conditions. The pre-images were reduced and calibrated using 2MASS photometry. Aperture magnitudes were measured for all our candidates, to complement and verify the available photometry. These pre-images are used to define the masks for the spectroscopy run, which was carried out in the night ...
Edmund C. Stoner and the discovery of the maximum mass of white
... equilibrium would ensue, even at zero temperature, due to the “degeneracy” pressure of the electrons caused by the exclusion principle. Fowler, however, did not attempt to determine the equilibrium properties of such a star which he regarded as “strictly analogous to one giant molecule in the groun ...
... equilibrium would ensue, even at zero temperature, due to the “degeneracy” pressure of the electrons caused by the exclusion principle. Fowler, however, did not attempt to determine the equilibrium properties of such a star which he regarded as “strictly analogous to one giant molecule in the groun ...
Analysis of cool DO-type white dwarfs from the Sloan Digital Sky
... Key words. stars: abundances – stars: evolution – stars: AGB and post-AGB – white dwarfs ...
... Key words. stars: abundances – stars: evolution – stars: AGB and post-AGB – white dwarfs ...
The 8190-A sodium doublet in cataclysmic variables
... variations of instrumental response with wavelength and for largescale sensitivity variations by multiplying by a calibration spectrum produced from the FIGARO tables of the Oke & Gunn standards. There were no comparison stars on the same slit for any of our objects, so absolute fluxes are not avail ...
... variations of instrumental response with wavelength and for largescale sensitivity variations by multiplying by a calibration spectrum produced from the FIGARO tables of the Oke & Gunn standards. There were no comparison stars on the same slit for any of our objects, so absolute fluxes are not avail ...
Main sequence
In astronomy, the main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Hertzsprung and Henry Norris Russell. Stars on this band are known as main-sequence stars or ""dwarf"" stars.After a star has formed, it generates thermal energy in the dense core region through the nuclear fusion of hydrogen atoms into helium. During this stage of the star's lifetime, it is located along the main sequence at a position determined primarily by its mass, but also based upon its chemical composition and other factors. All main-sequence stars are in hydrostatic equilibrium, where outward thermal pressure from the hot core is balanced by the inward pressure of gravitational collapse from the overlying layers. The strong dependence of the rate of energy generation in the core on the temperature and pressure helps to sustain this balance. Energy generated at the core makes its way to the surface and is radiated away at the photosphere. The energy is carried by either radiation or convection, with the latter occurring in regions with steeper temperature gradients, higher opacity or both.The main sequence is sometimes divided into upper and lower parts, based on the dominant process that a star uses to generate energy. Stars below about 1.5 times the mass of the Sun (or 1.5 solar masses (M☉)) primarily fuse hydrogen atoms together in a series of stages to form helium, a sequence called the proton–proton chain. Above this mass, in the upper main sequence, the nuclear fusion process mainly uses atoms of carbon, nitrogen and oxygen as intermediaries in the CNO cycle that produces helium from hydrogen atoms. Main-sequence stars with more than two solar masses undergo convection in their core regions, which acts to stir up the newly created helium and maintain the proportion of fuel needed for fusion to occur. Below this mass, stars have cores that are entirely radiative with convective zones near the surface. With decreasing stellar mass, the proportion of the star forming a convective envelope steadily increases, whereas main-sequence stars below 0.4 M☉ undergo convection throughout their mass. When core convection does not occur, a helium-rich core develops surrounded by an outer layer of hydrogen.In general, the more massive a star is, the shorter its lifespan on the main sequence. After the hydrogen fuel at the core has been consumed, the star evolves away from the main sequence on the HR diagram. The behavior of a star now depends on its mass, with stars below 0.23 M☉ becoming white dwarfs directly, whereas stars with up to ten solar masses pass through a red giant stage. More massive stars can explode as a supernova, or collapse directly into a black hole.