5,839 research outputs found
Optical Spectroscopy of Type Ia Supernovae
We present 432 low-dispersion optical spectra of 32 Type Ia supernovae (SNe
Ia) that also have well-calibrated light curves. The coverage ranges from 6
epochs to 36 epochs of spectroscopy. Most of the data were obtained with the
1.5m Tillinghast telescope at the F. L. Whipple Observatory with typical
wavelength coverage of 3700-7400A and a resolution of ~7A. The earliest spectra
are thirteen days before B-band maximum; two-thirds of the SNe were observed
before maximum brightness. Coverage for some SNe continues almost to the
nebular phase. The consistency of the method of observation and the technique
of reduction makes this an ideal data set for studying the spectroscopic
diversity of SNe Ia.Comment: Accepted for publication in the Astronomical Journal, 109 pages
(including data table), 44 figures, full resolution figures at
http://www.noao.edu/noao/staff/matheson/Iaspec.ps.g
Diabetes-social and economic perspectives in the new Millenium
Prevalence of diabetes is increasing in pandemic proportions, particularly in developing countries like India. The recent reports from the World Health Organization rates India as the country with the largest number of diabetic subjects in the world. The Chennai Urban Population Study (CUPS), The Chennai Urban Rural Epidemiology Study (CURES) and the National Urban Diabetes Survey (NUDS) revealed rising prevalence of diabetes in India. Some of the significant risk factors associated with diabetes are similar worldwide, but their intensities vary between races, regions and countries. The reason for escalation of diabetes prevalence in India could be attributed to a combination of genetic factors and environmental factors due to urbanization and industrialization, which has led to sedentary lifestyle, physical inactivity, stress and obesity arising from energy and fat rich diets. The long-term complications of diabetes occurring during the most productive years of their lives create a devastating burden of morbidity and mortality, which poses an economic and social burden both at the individual and at the national level. Compared to non-diabetic individuals, diabetic individuals are more than twice as costly to treat, mainly due to the high costs related with management of associated complications. Prevention seems to be the need of the hour to tackle this epidemic. This article highlights the social and economic implications of diabetes in India and emphasis the measures required to prevent diabetes
The Optical Afterglow of GRB 011211
We present early-time optical photometry and spectroscopy of the optical
afterglow of the gamma-ray burst GRB 011211. The spectrum of the optical
afterglow contains several narrow metal lines which are consistent with the
burst occurring at a redshift of 2.140 +/- 0.001. The optical afterglow decays
as a power law with a slope of alpha = 0.83 +/- 0.04 for the first
approximately two days after the burst at which time there is evidence for a
break. The slope after the break is at least 1.4. There is evidence for rapid
variations in the R-band light approximately 0.5 days after the burst. These
variations suggest that there are density fluctuations near the gamma-ray burst
on spatial scales of approximately 40--125 AU. The magnitude of the break in
the light curve, the spectral slope, and the rate of decay in the optical,
suggest that the burst expanded into an ambient medium that is homogeneous on
large scales. We estimate that the local particle density is between
approximately 0.1 and 10 cm^{-3} and that the total gamma-ray energy in the
burst was 1.2--1.9 x 10^{50} erg. This energy is smaller than, but consistent
with, the ``standard'' value of (5 +/- 2) x 10^{50} erg. Comparing the observed
color of the optical afterglow with predictions of the standard beaming model
suggests that the rest-frame V-band extinction in the host galaxy is less than
approximately 0.03 mag.Comment: 17 pages, 4 figures, AASTeX 5.02, to appear in AJ Referee's report
incorporated, minor changes in the tex
RJK Observations of the Optical Afterglow of GRB 991216
We present near-infrared and optical observations of the afterglow to the
Gamma-Ray Burst (GRB) 991216 obtained with the F. L. Whipple Observatory 1.2-m
telescope and the University of Hawaii 2.2-m telescope. The observations range
from 15 hours to 3.8 days after the burst. The temporal behavior of the data is
well described by a single power-law decay with index -1.36 +/-0.04,
independent of wavelength. The optical spectral energy distribution, corrected
for significant Galactic reddening of E(B-V)=0.626, is well fitted by a single
power-law with index -0.58 +/- 0.08. Combining the IR/optical observations with
a Chandra X-ray measurement gives a spectral index of -0.8 +/- 0.1 in the
synchrotron cooling regime. A comparison between the spectral and temporal
power-law indices suggest that a jet is a better match to the observations than
a simple spherical shock.Comment: Accepted to the Astrophysical Journal, 12 pages, 4 postscript figure
The Luminosity of SN 1999by in NGC 2841 and the Nature of `Peculiar' Type Ia Supernovae
We present UBVRIJHK photometry and optical spectroscopy of the so-called
'peculiar' Type Ia supernova 1999by in NGC 2841. The observations began one
week before visual maximum light which is well-defined by daily observations.
The light curves and spectra are similar to those of the prototypical
subluminous event SN 1991bg. We find that maximum light in B occurred on 1999
May 10.3 UT (JD 2,451,308.8 +/- 0.3) with B=13.66 +/- 0.02 mag and a color of
B_max-V_max=0.51 +/- 0.03 mag. The late-time color implies minimal dust
extinction from the host galaxy. Our photometry, when combined with the recent
Cepheid distance to NGC 2841 (Macri et al. 2001), gives a peak absolute
magnitude of M_B=-17.15 +/- 0.23 mag, making SN 1999by one of the least
luminous Type Ia events ever observed. We estimate a decline rate parameter of
dm15(B)=1.90 mag, versus 1.93 for SN 1991bg, where 1.10 is typical for
so-called 'normal' events. We compare SN 1999by with other subluminous events
and find that the B_max-V_max color correlates strongly with the decline rate
and may be a more sensitive indicator of luminosity than the fading rate for
these objects. We find a good correlation between luminosity and the depth of
the spectral feature at 580 nm, which had been attributed solely to Si II. We
show that in cooler photospheres the 580 nm feature is dominated by Ti II,
which provides a simple physical explanation for the correlation. Using only
subluminous Type Ia supernovae we derive a Hubble parameter of H_0=75 +12 -11
km/s Mpc, consistent with values found from brighter events.Comment: 36 preprint pages including 18 figures. Near-IR photometry of the SN
has been added to the paper. Scheduled to appear in ApJ vol. 613 (September
2004). High-resolution version available from
http://www.nd.edu/~pgarnavi/sn99by/sn99by.p
The Strongly Polarized Afterglow of GRB 020405
We report polarization measurements and photometry for the optical afterglow
of the gamma-ray burst GRB 020405. We measured a highly significant 9.9%
polarization (in V band) 1.3 days after the burst and argue that it is
intrinsic to the GRB. The light curve decay is well fitted by a
power-law; we do not see any evidence for a break between 1.24 and 4.3 days
after the burst. We discuss these measurements in the light of several models
of GRB afterglows.Comment: submitted to ApJ
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