Mass of stars

Thus the mass of stars and that of the whole system steadily increase while z soon approaches 1 and the stellar metallicity distribution is very narrow (see Fig. 8.24). The accretion rate is constant in time if the star formation rate is any fixed function of the mass of gas. Other models in which the accretion rate is constant, but less than in the extreme model, have been quite often considered in the older literature (e.g. Twarog 1980), but are less popular now because they are not well motivated from a dynamical point of view, there is an upper limit to the present inflow rate into the whole Galaxy of about 1 M0yr 1 from X-ray data (Cox Smith 1976) and they do not provide a very good fit to the observed metallicity distribution function. 

Fig. 8.39. Chemo-spectrophotometric evolution of the solar neighbourhood (left) and the whole Milky Way (right) as a function of time. Panels aA show the oxygen and iron abundances, bB the mass of stars and gas and the star formation rate, cC the extinction in B, V and K bands along a line of sight normal to the plane, dD the luminosity in solar units (taking extinction into account), eE the colour indices and fF the supernova rates. Note that panels aA are in linear units (see Fig. 8.16), while the others are all logarithmic. After Boissier and Prantzos (1999).

Fig. 11.17. Metallicities of stars and gas as a function of the total mass of stars in an elliptical galaxy growing by mergers, assuming a true yield of 0.02. The trend is for stellar Z to increase approximately as A/1/2 for small masses, flattening to Af1/4 for larger ones. Filled circles show the point beyond which there will be little star formation in mergers because the gas cannot cool sufficiently between collisions arrows indicate possible outcomes of further mergers without star formation. After Tinsley and Larson (1979).

Suppose that, at any time t, the mass of stars within a fixed mass coordinate m is s(m, t) and that the gas is confined within a decreasing mass coordinate ma(t). We make the simplifying but reasonable assumption that, within ma t), the radial distributions of stars and of the star formation rate are the same. Furthermore, we assume the Ansatz... 

The mass of stars within the sphere m having metallicity less than z is then given by... 

The mass function, which is a pure combination of observables, is a lower limit to the possible mass of star 2 if the orbit is other than edge-on (that is, if % < 90°) or the observed star has mi > 0, then m2 > / Thus, observation of one star constrains the mass of the other star. Note, incidentally, that in a neutron star binary system with a high-mass companion (mi m2), / is low... 

The total mass of the Galaxy is about 10 Mq. Of this 10(X) billion solar masses, only about one-tenth is actually visible. This is what is implied by the Galaxy s rotation curve, i.e. the graph of its rotation speed at different distances from the centre. All other matter is therefore classed as dark matter. The mass of stars is thus about 100 billion solar masses, and the mass of interstellar material a few billion more. 

However, during the past few years the situation has dramatically changed. The theory of radiation driven winds has been strongly improved and very detailed and complex multi-level NLTE calculations for stellar winds have become available. The purpose of this paper therefore is to convince that on the basis of this new framework stellar wind lines provide a powerful quantitative diagnostic tool to determine independently radii, luminosities and masses of stars. 

The orbits of double stars, where the sizes of the orbits have been determined, provide the only information we have about the masses of stars other than the Sun. Close doublestars will become decidedly non-spherical because of tidal distortion and/or rapid rotation, which produces effects analogous to those described above for close artificial planetary satellites. Also, such stars often have gas streaming from their tidal and equatorial bulges, which can transfer mass from one star to the other, or can even eject it completely out of the system. Such effects are suspected to be present in close doublestars where their period of revolution is found to be changing. 

The evidence on which this theory of stellar evolution is based comes not only from known nuclear reactions and the relativistic equivalence of mass and energy, but also from the spectroscopic analysis of the light reaching us from the stars. This leads to the spectral classification of stars, which is the cornerstone of modem experimental astrophysics. The spectroscopic analysis of starlight reveals much information about the... 

Oscillations of black holes. Non-radial oscillations of black holes can be excited when a mass is captured by the black hole. The so called quasinormal modes have eigenfrequencies and damping times which are characteristic of black holes, and very different of eigenfrequencies and damping times of quasi normal modes of stars having the same mass. Also the eigenmodes being different for a star and a black hole, the associated gw will also exhibit characteristic features. 

Unlike prisms, in this class of bodies uniqueness requires knowledge of the density. This theorem was proved by P. Novikov. The simplest example of starshaped bodies is a spherical mass. Of course, prisms are also star-shaped bodies but due to their special form, that causes field singularities at corners, the inverse problem is unique even without knowledge of the density. It is obvious that these two classes of bodies include a wide range of density distributions besides it is very possible that there are other classes of bodies for which the solution of the inverse problem is unique. It seems that this information is already sufficient to think that non-uniqueness is not obvious but rather a paradox. 

The darkness associated with dense interstellar clouds is caused by dust particles of size =0.1 microns, which are a common ingredient in interstellar and circum-stellar space, taking up perhaps 1% of the mass of interstellar clouds with a fractional number density of 10-12. These particles both scatter and absorb external visible and ultraviolet radiation from stars, protecting molecules in dense clouds from direct photodissociation via external starlight. They are rather less protective in the infrared, and are quite transparent in the microwave.6 The chemical nature of the dust particles is not easy to ascertain compared with the chemical nature of the interstellar gas broad spectral features in the infrared have been interpreted in terms of core-mantle particles, with the cores consisting of two populations, one of silicates and one of carbonaceous, possibly graphitic material. The mantles, which appear to be restricted to dense clouds, are probably a mixture of ices such as water, carbon monoxide, and methanol.7... 

The formation of stars in the interiors of dense interstellar clouds affects the chemistry of the immediate environment in a variety of ways depending on many factors such as the stage in the evolution of star formation, the mass of the star or protostar, and the density and temperature of the surrounding material. In general, the dynamics of the material in the vicinity of a newly forming star are complex and show many manifestations. Table 3 contains a list of some of the better studied such manifestations, which tend to have distinctive chemistries. These are discussed individually below. 

These reactions take place in the inner zone of stars heavier than 15 solar masses. Hydrostatic carbon burning is followed by explosive neon burning at temperatures of around 2.5 x 109K. Under these conditions, phosphorus (31P) can be formed, although complex side reactions also occur. In comparison with the formation of... 

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