572 research outputs found
Stellar Populations and the White Dwarf Mass Function: Connections To Supernova Ia Luminosities
We discuss the luminosity function of SNe Ia under the assumption that recent
evidence for dispersion in this standard candle is related to variations in the
white dwarf mass function (WDMF) in the host galaxies. We develop a simple
parameterization of the WDMF as a function of age of a stellar population and
apply this to galaxies of different morphological types. We show that this
simplified model is consistent with the observed WDMF of Bergeron et al. (1992)
for the solar neighborhood. Our simple models predict that WDMF variations can
produce a range of more than 1.8 mag in M(SN Ia), which is comparable to
the observed value using the data of Phillips (1993) and van den Bergh (1996).
We also predict a galaxy type dependence of M(SN Ia) under standard
assumptions of the star formation history in these galaxies and show that
M(SN Ia) can evolve with redshift. In principle both evolutionary and
galaxy type corrections should be applied to recover the intrinsic range of
M(SN Ia) from the observed values. Our current inadequate knowledge of the
star formation history of galaxies coupled with poor physical understanding of
the SN Ia mechanism makes the reliable estimation of these corrections both
difficult and controversial. The predictions of our models combined with the
observed galaxy and redshift correlations may have the power to discriminate
between the Chandrasekhar and the sub-Chandrasekhar progenitor scenarios for
SNe Ia.Comment: 20 pages, latex + 7 postscript figures, to be published in AJ,
September 199
Quinze anos de investimento social privado no Brasil: conceito e práticas em construção
Investimento social privado (ISP) é um conceito criado nos anos 1990 por um grupo de executivos e líderes de empresas, fundações e institutos para designar uma forma de atuação social do setor privado, sobretudo empresarial, que buscava se diferenciar de formas mais tradicionais de filantropia. Após 15 anos de existência, o conceito já apresenta alguma repercussão e consistência, tendo sido tema de eventos, estudos, pesquisas e reportagens, porém ainda é pouco explorado no âmbito da pesquisa acadêmica, na qual são mais freqüentes temas correlatos, como responsabilidade social empresarial e as relações entre empresas, governo e sociedade civil. No campo das práticas de ISP, houve avanços em aspectos de ordem político-institucional e estratégico-gerencial, porém ainda há desafios relativos à legitimidade e efetividade das práticas, algo bastante debatido no campo do ISP no Brasil, no qual também se vislumbram diferentes tendências, para os próximos anos. Nessecontexto, os objetivos deste artigo são: a) descrever o histórico de surgimento e construção do conceito de investimento social privado no Brasil; b) apresentar os diferentes tipos de ISP (corporativo, familiar, comunitário, venture philanthropy e diáspora philanthropy, entre outros); c) colocar em discussão desafios e tendências na construção do conceito e nas práticas de investimento social privado. A construção do trabalho está baseada em pesquisa bibliográfica e documental, participação em eventos nacionais e internacionais e engajamento dos autores no contexto de discussão e prática do ISP no Brasil, entre os anos de 1999 e 2008. Entre as conclusões, destaca-se a tendência de diversificação de modelos de investimentosocial e a articulação de redes de aprendizagem sobre o tema, envolvendo diferentes setores
The Hubble Diagram of the Calan/Tololo Type Ia Supernovae and the value of Ho
The Calan/Tololo supernova survey has discovered ~30 Type Ia supernovae out
to z~0.1. Using BVI data for these objects and nearby SNe Ia, we have shown
that there exists a significant dispersion in the intrinsic luminosities of
these objects. We have devised a robust chisquare minimization technique
simultaneously fitting the BVI light curves to parametrize the SN event as a
function of (tb,m, m15(B)) where tb is the time of B maximum, m is the peak BVI
magnitude corrected for luminosity variations, and m15(B) is a single parameter
describing the whole light curve morphology. When properly corrected for
m15(B), SNe Ia prove to be high precision distance indicators,yielding relative
distances with errors 7-10%. The corrected peak magnitudes are used to
construct BVI Hubble diagrams (HD), and with Cepheid distances recently
measured with the HST to four nearby SNe Ia (37C, 72E, 81B, 90N) we derive a
value of the Hubble constant of 63.1+/-3.4 (internal) km/s/Mpc. This value is
~10-15% larger than the value obtained by assuming that SNe Ia are perfect
standard candles. As we have shown in Paper V, there is now strong evidence
that galaxies with younger stellar population appear to host the
slowest-declining, and therefore most luminous SNe Ia. Hence, the use of Pop I
objects such as Cepheids to calibrate the zero point of the SNe Ia HD can
easily bias the results toward luminous SNe Ia, unless the absolute
magnitude-decline relation is taken into account.Comment: 32 pages, figures attached, all tables available, to appear in the
Astronomical Journa
The Absolute Luminosities of the Calan/Tololo Type Ia Supernovae
We examine the absolute luminosities of 29 SNe Ia in the Calan/Tololo survey.
We confirm a relation between the peak luminosity of the SNe and the decline
rate as measured by the light curve, as suggested by Phillips (1993). We derive
linear slopes to this magnitude-decline rate relation in BV(I)kc colors, using
a sample with Bmax-Vmax < 0.2 mag. The scatter around this linear relation (and
thus the ability to measure SNe Ia distances) ranges from 0.13 mag (in the I
band) to 0.17 mag (in the B band). We also find evidence for significant
correlations between the absolute magnitudes or the decline rate of the light
curve, and the morphological type of the host galaxy.Comment: 21 pages, 4 figures, to appear in the Astronomical Journa
The Morphology of Type Ia Supernovae Light Curves
We present a family of six BVI template light curves for SNe Ia for days -5
and +80, based on high-quality data gathered at CTIO. These templates display a
wide range of light curve morphologies, with initial decline rates of their B
light curves between m15(B)=0.87 mag and 1.93 mag. We use these templates to
study the general morphology of SNe Ia light curves. We find that several of
the main features of the BVI templates correlate tightly with m15(B). In
particular, the V light curves, which are probably a reasonably good
approximation of the bolometric light curves, display an orderly progression in
shapes between the most-luminous, slowest-declining events and the
least-luminous, fastest-declining SNe. This supports the idea that the observed
spectroscopic and photometric sequences of SNe Ia are due primarily to one
parameter. Nevertheless, SNe with very similar initial decline rates do show
significant differences in their light curve properties when examined in
detail, suggesting the influence of one or more secondary parameters.Comment: 32 pages, 15 figures, to appear in the Astronomical Journa
A Search for Environmental Effects on Type Ia Supernovae
We use integrated colors and B and V absolute magnitudes of Type Ia supernova
(SN) host galaxies in order to search for environmental effects on the SN
optical properties. With the new sample of 44 SNe we confirm the conclusion by
Hamuy et al. (1996a) that bright events occur preferentially in young stellar
environments. We find also that the brightest SNe occur in the least luminous
galaxies, a possible indication that metal-poorer neighbourhoods produce the
more luminous events. The interpretation of these results is made difficult,
however, due to the fact that galaxies with younger stellar populations are
also lower in luminosity. In an attempt to remove this ambiguity we use models
for the line strengths in the absorption spectrum of five early-type galaxies,
in order to estimate metallicities and ages of the SN host galaxies. With the
addition of abundance estimates from nebular analysis of the emission spectra
of three spiral galaxies, we find possible further evidence that luminous SNe
are produced in metal-poor neighborhoods. Further spectroscopic observations of
the SN host galaxies will be necessary to test these results and assist in
disentangling the age/metallicity effects on Type Ia SNe.Comment: 14 pages, 5 figures, to appear in the September 2000 issue of The
Astronomical Journa
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