Initial Mass Function Of Stars Research Articles

On star formation in cooling flows of clusters of galaxies

A correlation between the masses of cooling flows in clusters of galaxies and the absolute magnitudes of the central parts of the brightest galaxies of the clusters is detected. This correlation is consistent with star formation in the cooling flows according to an initial mass function of stars truncated at stellar masses corresponding to absolute magnitudes in the most probable cases between +7 and +2.

A theory of sequential fragmentation and its astronomical applications

A theory of sequential fragmentation is presented that describes a cascade of fragmentation and refragmentation,i.e., continued comminution. It is shown that the theory reproduces one of the two major empirical descriptors that have traditionally been used to describe the mass distributions from fragmentation experiments. Additional experimental evidence is presented to further validate the theory, and includes explosive aerosolization, grinding in a ball mill, and simulated volcanic action. Also presented are some astronomical applications of the theory including infalling extraterrestrial material, siderophile concentrations in black magnetic spherules of possible meteoritic origin, the asteroids, the distribution of galactic masses, and the initial mass function of stars

Determining mass-to-light ratios in elliptical galaxies

If the endstate of cooling hot gas in elliptical galaxies is a population of optically dark, low-mass stars near the galactic cores, the mass-to-light ratio could be expected to vary significantly with projected radius. No strong variation in M/L is observed. To investigate the sensitivity and reliability of observational mass-to-light determinations for a variety of galactic parameters, model galaxies having de Vaucouleurs profiles (but with central cores and outer cutoffs), variable velocity ellipsoid structure, and extended dark halos are constructed. Spurious radial variations in M/L can occur when none are present if the properties of the galactic models are processed similar to observational data. Conversely, when a population of diffuse dark stellar matter is added near the galactic cores, large gradients in M/L can escape detection. However, the magnitude of the central velocity dispersion and its variation with projected radius within the effective radius both suggest that a component of dark stars is unlikely to be more massive than about 30 times the core mass of luminous stars. This restriction is important in establishing the initial mass function of stars in elliptical galaxies and the history of winds and cooling inflows in the interstellar medium. 35 references.

A photometric survey of the rich OB association NGC 206 in M31

A detailed UBV photometric survey of the stellar content of the rich OB association NGC 206 has been carried out with two high-quantum-efficiency area detectors. Weighted mean B band magnitudes are derived and used to construct a differential luminosity function, which is in turn transformed to an absolute scale using the estimated total absorption value of 1.15 + or - 0.13 and the geometric distance modulus of 24.07. The B band luminosity function for NGC 206 is transformed to a present day mass function. An initial mass function (IMF) is derived whose power law fit gives a mass-function index value of -2.0 + or - 0.3. This value is consistent with several independent determinations of the slope of the IMF for massive stars. The brightness of the most massive stars in NGC 206 is found to correlate most strongly with the integrated magnitude of the spiral arms and somewhat less with the integrated old-disk luminosity. This indicates that bulge luminosities should be considered in refining the use of the brightest blue stars as extragalactic distance indicators.

Comparison of a theory of sequential fragmentation with the initial mass function of stars

A one-parameter theory of sequential fragmentation is formulated, validated, and compared with the Initial Mass Function of stars. The agreement is excellent.

The age spread and initial mass function of NGC 3293 - Implications for the formation of clusters

UBV photographic photometry to Vapprox.16.5 (M/sub v/ = +3.5) has been obtained for over 350 stars in the field of the young cluster NGC 3293. The main sequence of the cluster is populated with stars at least as faint as M/sub v/ = 2.8 +- 0.2, implying a contraction age (tau/sub c/) of at least 25 +- 10 million years. This is significantly greater than its nuclear age (tau/sub N/) of 6 +- 2 million years, implying that (if tau/sub c/ and tau/sub N/ are correctly given by the stellar models): (1) there is an age spread of at least 20 +- 10 million years, and (2) the lower-mass stars formed first. The luminosity function has been derived in an approximate manner to M/sub v/ = +5; since the cluster is too young to have lost a significant number of stars by evaporation, these data may be used to derive an initial mass function (IMF). This shows that the cluster has an excess of high-mass stars by comparison with the IMF of field stars. The age spread, color-magnitude diagram, and IMF of NGC 3293 are probably typical of galactic clusters, suggesting that: (1) clusters with O-star members are already moremore » than 10 or 20 million years old, (2) star formation in clusters is a gradual process which is probably driven by the gravitational collapse of a clumpy, turbulent molecular cloud, and terminated by the formation of massive stars, and (3) the initial mass function varies with time during the cluster formation period.« less

Mass spectra of young stars

In an effort to understand the factors that determine the initial mass function of stars, the available data on the mass spectra of young stars in different regions have been studied for possible correlations with the properties of the associated molecular clouds and the spatial distributions of the stars. There appear to be differences in the stellar mass spectra in different regions: for example in Taurus, where the molecular gas is relatively dispersed and the stars are in scattered small groups, the stars are predominantly of low mass, whereas in Orion, where the gas is in massive condensed clouds and the stars are mostly in a single large cluster, the mass spectrum is relatively depleted in low-mass stars. The most massive stars appear to form in the dense cores of forming clusters or associations, and the mass of the most massive young star increases systematically with the mass of the associated molecular cloud. The data are consistent with a picture in which molecular cloud cores grow by accretion and become progressively more massive and condensed, while forming stars in larger and more condensed clusters and with a mass spectrum that increasingly favours massive stars. In this picture the more massive stars form by accumulation processes, rather than by fragmentation, in the dense core regions of protoclusters. Stellar winds may play an important role in limiting the masses that forming stars can attain; if so, the maximum stellar mass should increase with the density of the ambient gas and with the amount of turbulence present, a prediction that is in agreement with observations.

Wolf-Rayet Stars Featured in Emission-Line Galaxies

Emission-line galaxies contain a large number of hot stars responsible for the emissive gas. They offer the opportunity of investigating the initial mass function of stars in regions of active star formation. So far, only integral properties of the ionizing complexes in giant H II regions or emission-line galaxies have been used (Lequeux et al., 1981) but no direct emission-line stellar feature has been thoroughly analyzed.

Interpretation of Isotopic Abundances in Interstellar Clouds

The abundances of elements in the interstellar medium (ISM) result from a complex sequence of nucleosynthetic processes which started some ten billion years ago in the Big Bang and are still going on. Their study and in particular their comparison with the stellar and the solar system abundances may give clues to: i) the properties of the early Universe, ii) the evolution of galaxies (rate of star formation, Initial Mass Function of stars, stellar nucleosynthesis and rate of ejection of matter by stars), and iii) the flux of low-energy cosmic rays. (See e.g. Reeves 1974, Audouze and Tinsley 1976).