1,226 research outputs found
Supernovae
The properties of supernovae (SNe) are reviewed. It is shown that the
observed characteristics of the morphological classes of SNe (types Ia, Ib/c,
II) can be explained in terms of two basic explosion mechanisms, i.e. core
collapse of massive stars and thermonuclear explosion of low/moderate mass
stars.
The study of SNe can provide valuable insight in the late phases of the
evolution of their progenitors and, therefore, can constrain the theory of
stellar evolution quite tightly.
Also, bright SNe of type Ia can be used to probe the Universe up to high
redshifts, allowing us to measure cosmological constants and to gain valuable
information on the formation and evolution of galaxies.
The case of SN 1987A is discussed in some detail: it appears that in this
event a number of predictions were astonishingly well verified but still many
aspects were completely at variance with "common wisdom" expectations,
indicating that the SN phenomenon is still not fully understood.Comment: 12 pages, 2 figures - Invited Lecture at the International Summer
School "Experimental Physics of Gravitational Waves", Urbino (Italy), 6-19
September, 1999, eds. G. Calamai, M. Mazzoni, R. Stanga & F. Vetrano,, World
Scientific -- Singapore, in pres
Observations of supernova 1979c in M 100
The IUE observations of supernova 1979c in M 100 are presented and discussed. The main results are: (1) the bulk of the energy is in the form of continuous emission which is radiated by the main SN envelope; (2) the absorption features originate mostly in both the disks and the haloes of our Galaxy and M 100; and (3) the emission lines are produced in a highly ionized shell which has a radius greater than twice the radius of the main envelope and consists of compressed circumstellar material in which the abundance ratio N/C is about 30 times higher than solar
Stellar populations in the Magellanic Clouds: looking through the dust
We present the first results of our study of stellar populations in the Large
and Small Magellanic Clouds based on multi-band WFPC2 observations of "random"
fields taken as part of the "pure parallel" programme carried out with the HST
as a service to the community.Comment: Two pages, one figure, to appear in the proceedings of IAU Symposium
241 "Stellar Populations as Building Blocks of Galaxies", eds. A. Vazdekis
and R. Peletie
Radio and infrared properties of young stars
Observing young stars, or more appropriately, pre-main-sequence (PMS) stars, in the infrared and at radio frequencies has the advantage over optical observation in that the heavy extinction associated with a star forming region is only a minor problem, so that the whole region can be studied thoroughly. Therefore, it means being able to: (1) search for stars and do statistical studies on the rate of star formation; (2) determine their luminosity, hence, to study luminosity functions and initial mass functions down to low masses; and (3) to study their spectra and, thus, to determine the prevailing conditions at and near the surface of a newly born star and its relations with the surrounding environment. The third point is of principal interest. The report limits itself to a consideration of the observations concerning the processes of outflows from, and accretion onto, PMS stars and the theory necessary to interpret them. Section 2 discusses the radiative processes relevant in stellar outflows. The main observational results are presented in Section 3. A discussion of the statistical properties of stellar winds from PMS stars are given in Section 4
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