1,774 research outputs found
Optical and X-ray Variability in The Least Luminous AGN, NGC4395
We report the detection of optical and X-ray variability in the least
luminous known Seyfert galaxy, NGC4395. The featureless continuum changed by a
factor of 2 in 6 months, which is typical of more luminous AGN. The largest
variation was seen at shorter wavelengths, so that the spectrum becomes
`harder' during higher activity states. In a one week optical broad band
monitoring program, a 20% change was seen between successive nights. In a 1
month period the spectral shape changed from a power law with spectral index
alpha ~0 (characteristic of quasars) to a spectral index alpha ~2 (as observed
in other dwarf AGN). ROSAT HRI and PSPC archive data show a variable X-ray
source coincident with the galactic nucleus. A change in X-ray flux by a factor
\~2 in 15 days has been observed. When compared with more luminous AGN, NGC4395
appears to be very X-ray quiet. The hardness ratio obtained from the PSPC data
suggests that the spectrum could be absorbed. We also report the discovery of
weak CaIIK absorption, suggesting the presence of a young stellar cluster
providing of the order of 10% of the blue light. Using HST UV archive data,
together with the optical and X-ray observations, we examine the spectral
energy distribution for NGC4395 and discuss the physical conditions implied by
the nuclear activity under the standard AGN model. The observations can be
explained by either an accreting massive black hole emitting at about 10^(-3)
L_(Edd) or by a single old compact SNR with an age of 50 to 500 yr generated by
a small nuclear starburst.Comment: 19 pages, 9 figures, to appear in MNRA
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
Análise do custo de produção e da comercialização do melão orgânico produzido na região do Submédio São Francisco.
A região do Submédio São Francisco, que é o terceiro maior pólo de produção de melão do país, vem registrando nas duas últimas décadas uma drástica redução nas áreas de cultivos dessa fruta devido a baixa lucratividade da atividade quando comparada ao desempenho econômico de outros produtos hortifrutícolas explorados na zona. Entretanto, motivados pelo crescimento significativo do mercado de produtos orgânico, os produtores de melão da região estão aderindo a esse processo de cultivo como alternativa para tornar a exploração mais rentável. Considerando que a produção de melão orgânico ainda está em processo de formação na região em análise, torna-se necessário a realização de estudos que revelem o comportamento de seus custos e a rentabilidade da sua exploração. Este trabalho teve como objetivo analisar os custos de produção e de comercialização e a rentabilidade do melão orgânico produzido na região do Submédio São Francisco e comercializado no mercado de São Paulo. O estudo revela que a exploração do melão orgânico na região do Submédio São Francisco é uma atividade rentável, visto que, nos diversos parâmetros de desempenho econômico analisados, os resultados foram bastante expressivos
The Reddening-Free Decline Rate Versus Luminosity Relationship for Type Ia Supernovae
We develop a method for estimating the host galaxy dust extinction for type
Ia supernovae based on an observational coincidence first noted by Lira (1995),
who found that the B-V evolution during the period from 30-90 days after V
maximum is remarkably similar for all events, regardless of light curve shape.
This fact is used to calibrate the dependence of the B(max)-V(max) and
V(max)-I(max) colors on the light curve decline rate parameter delta-m15, which
can, in turn, be used to separately estimate the host galaxy extinction. Using
these methods to eliminate the effects of reddening, we reexamine the
functional form of the decline rate versus luminosity relationship and provide
an updated estimate of the Hubble constant of Ho = 63.3 +- 2.2(internal) +-
3.5(external) km/s/Mpc.Comment: 32 pages, 10 figures, AJ 1999 in pres
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