59 research outputs found
High Resolution mid-Infrared Imaging of SN 1987A
Using the Thermal-Region Camera and Spectrograph (T-ReCS) attached to the
Gemini South 8m telescope, we have detected and resolved 10 micron emission at
the position of the inner equatorial ring (ER) of supernova SN 1987A at day
6067. ``Hot spots'' similar to those found in the optical and near-IR are
clearly present. The morphology of the 10 micron emission is globally similar
to the morphology at other wavelengths from X-rays to radio. The observed
mid-IR flux in the region of SN1987A is probably dominated by emission from
dust in the ER. We have also detected the ER at 20 micron at a 4 sigma level.
Assuming that thermal dust radiation is the origin of the mid-IR emission, we
derive a dust temperature of 180^{+20}_{-10} K, and a dust mass of 1.- 8.
10^{-5} Mo for the ER. Our observations also show a weak detection of the
central ejecta at 10 micron. We show that previous bolometric flux estimates
(through day 2100) were not significantly contaminated by this newly discovered
emission from the ER. If we assume that the energy input comes from radioactive
decays only, our measurements together with the current theoretical models set
a temperature of 90 leq T leq 100 K and a mass range of 10^{-4} - 2. 10^{-3} Mo
for the dust in the ejecta. With such dust temperatures the estimated thermal
emission is 9(+/-3) 10^{35} erg s^{-1} from the inner ring, and 1.5 (+/-0.5)
10^{36} erg s^{-1} from the ejecta. Finally, using SN 1987A as a template, we
discuss the possible role of supernovae as major sources of dust in the
Universe.Comment: aastex502, 14 pages, 4 figures; Accepted for publication in ApJ
Content changed: new observations, Referee's comments and suggestion
The birth place of the type Ic Supernova 2007gr
We report our attempts to locate the progenitor of the peculiar type Ic SN
2007gr in HST pre-explosion images of the host galaxy, NGC 1058. Aligning
adaptive optics Altair/NIRI imaging of SN 2007gr from the Gemini (North)
Telescope with the pre-explosion HST WFPC2 images, we identify the SN position
on the HST frames with an accuracy of 20 mas. Although nothing is detected at
the SN position we show that it lies on the edge of a bright source, 134+/-23
mas (6.9 pc) from its nominal centre. Based on its luminosity we suggest that
this object is possibly an unresolved, compact and coeval cluster and that the
SN progenitor was a cluster member, although we note that model profile fitting
favours a single bright star. We find two solutions for the age of this assumed
cluster; 7-/+0.5 Myrs and 20-30 Myrs, with turn-off masses of 28+/-4 Msun and
12-9 Msun respectively. Pre-explosion ground-based K-band images marginally
favour the younger cluster age/higher turn-off mass. Assuming the SN progenitor
was a cluster member, the turn-off mass provides the best estimate for its
initial mass. More detailed observations, after the SN has faded, should
determine if the progenitor was indeed part of a cluster, and if so allow an
age estimate to within ~2 Myrs thereby favouring either a high mass single star
or lower mass interacting binary progenitor.Comment: 12 pages, 3 figures, resolution of fig 1. has been reduced, some
revision based on referee's comments, Accepted ApJL 27 Nov 200
Five Years of Mid-Infrared Evolution of the Remnant of SN 1987A: The Encounter Between the Blast Wave and the Dusty Equatorial Ring
We have used the Spitzer satellite to monitor the mid-IR evolution of SN
1987A over a 5 year period spanning the epochs between days 6000 and 8000 since
the explosion. The supernova (SN) has evolved into a supernova remnant (SNR)
and its radiative output is dominated by the interaction of the SN blast wave
with the pre-existing equatorial ring (ER). The mid-IR spectrum is dominated by
emission from ~180 K silicate dust, collisionally-heated by the hot X-ray
emitting gas with a temperature and density of ~5x10^6 K and 3x10^4 cm-3,
respectively. The mass of the radiating dust is ~1.2x10^(-6) Msun on day 7554,
and scales linearly with IR flux. The infrared to soft-X-ray flux ratio is
roughly constant with a value of 2.5. Gas-grain collisions therefore dominate
the cooling of the shocked gas. The constancy of of this ratio suggests that
very little grain processing or gas cooling have occurred throughout this
epoch. The shape of the dust spectrum remained unchanged during the
observations while the total flux increased with a time dependence of t^(0.87),
t being the time since the first encounter between the blast wave and the ER.
These observations are consistent with the transitioning of the blast wave from
free expansion to a Sedov phase as it propagates into the main body of the ER.Comment: Accepted for publication in the ApJ, 11 pages, 11 figure
Photometric Evolution of SNe Ib/c 2004ao, 2004gk and 2006gi
Photometric observations of three core collapse supernovae (SNe 2004ao,
2004gk and 2006gi), covering about 200 days of evolution are presented and
analyzed. The photometric behaviour of the three objects is consistent with
their membership of the envelope-stripped type Ib/c class. Pseudo-bolometric
light curves are constructed. The corresponding measured -folding times are
found to be faster compared to the Co decay (i.e. 111.3 d), suggesting
that a proportion of -rays increasing with time have escaped without
thermalization, owing to the low mass nature of the ejecta. SN 2006gi has
almost identical post maximum decline phase luminosities as SN 1999ex, and
found to be similar to both SNe 1999dn and 1999ex in terms of the
quasi-bolometric shape, placing it among the fast decliner Ib objects. SN
2004ao appears to fit within the slow decliner Ib SNe. SNe 2004ao and 2004gk
display almost identical luminosities in the [50-100] days time interval,
similar to SN 1993J. A preliminary simplified ray deposition model is
described and applied to the computed pseudo-bolometric light curves, allowing
one to find a range in the ejecta and Ni masses. The optical and
quasi-bolometric light curves, and the colour evolution of SN 2004gk are
found to show a sudden drop after day 150. Correlating this fact to dust
formation is premature and requires further observational evidence.Comment: Accepted for publication in The Astrophysical Journal; (11
two-columns Pages, 11 figures, 6 Tables; Scheduled for publication in April
2011
X-Ray Emission from Multi-Phase Shock in the Large Magellanic Cloud Supernova Remnant N49
The supernova remnant (SNR) N49 in the Large Magellanic Cloud has been
observed with the Advanced CCD Imaging Spectrometer (ACIS) on board the {\it
Chandra X-Ray Observatory}. The superb angular resolution of the {\it
Chandra}/ACIS images resolves a point source, the likely X-ray counterpart of
soft gamma-ray repeater SGR 052666, and the diffuse filaments and knots
across the SNR. These filamentary features represent the blast wave sweeping
through the ambient interstellar medium and nearby dense molecular clouds. We
detect metal-rich ejecta beyond the main blast wave shock boundary in the
southwest of the SNR, which appear to be explosion fragments or ``bullets''
ejected from the progenitor star. The detection of strong H-like Si line
emission in the eastern side of the SNR requires multi-phase shocks in order to
describe the observed X-ray spectrum, whereas such a multi-phase plasma is not
evident in the western side. This complex spectral structure of N49 suggests
that the postshock regions toward the east of the SNR might have been reheated
by the reverse shock off the dense molecular clouds while the blast wave shock
front has decelerated as it propagates into the dense clouds. The X-ray
spectrum of the detected point-like source is continuum dominated and can be
described with a power law of 3. This provides a confirmation
that this point-like X-ray source is the counterpart of SGR 052666 in the
quiescent state.Comment: Total 22 pages (in ApJ emulater style), including 8 figures (2 color
figs). Accepted by ApJ For high quality images, contact with
[email protected]
Understanding How Inequality in the Distribution of Income Affects Health
Research on the determinants of health has almost exclusively focused on the individual but it seems clear we cannot understand or improve patterns of population health without engaging structural determinants at the societal level. This article traces the development of research on income distribution and health to the most recent epidemiologic studies from the USA that show how income inequality is related to age-adjusted mortality within the 50 States. (r 520.62, p 5 0.0001) even after accounting for absolute levels of income. We discuss potential material, psychological, social and behavioral pathways through which income distribution might be linked to health status. Distributional aspects of the economy are important determinants of health and may well provide one of the most pertinent indicators of overall social well-being.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66686/2/10.1177_135910539700200303.pd
Evidence for Type Ia Supernova Diversity from Ultraviolet Observations with the Hubble Space Telescope
We present ultraviolet (UV) spectroscopy and photometry of four Type Ia supernovae (SNe 2004dt, 2004ef, 2005M, and 2005cf) obtained with the UV prism of the Advanced Camera for Surveys on the Hubble Space Telescope, This dataset provides unique spectral time series down to 2000 A. Significant diversity is seen in the near-maximum-light spectra (approx.2000-3500 A) for this small sample. The corresponding photometric data, together with archival data from Swift Ultraviolet/Optical Telescope observations, provide further evidence of increased dispersion in the UV emission with respect to the optical. The peak luminosities measured in the uvw lIF250W filter are found to correlate with the B-band light-curve shape parameter .(Delta)m15(B), but with much larger scatter relative to the correlation in the broad-band B band (e.g., approx. 0.4 mag versus approx. 0.2 mag for those with 0.8 3(sigma), being brighter than normal SNe Ia such as SN 2005cf by approx. 0,9 mag and approx. 2.0 mag in the uvwl1F250W and uvm2/F220W filters, respectively. We show that different progenitor metallicity or line-expansion velocities alone cannot explain such a large discrepancy. Viewing-angle effects, such as due to an asymmetric explosion, may have a significant influence on the flux emitted in the UV region. Detailed modeling is needed to disentangle and quantify the above effect
Evidence for Type Ia Supernova Diversity from Ultraviolet Observations with the Hubble Space Telescope
We present ultraviolet (UV) spectroscopy and photometry of four Type Ia
supernovae (SNe 2004dt, 2004ef, 2005M, and 2005cf) obtained with the UV prism
of the Advanced Camera for Surveys on the Hubble Space Telescope. This dataset
provides unique spectral time series down to 2000 Angstrom. Significant
diversity is seen in the near maximum-light spectra (~ 2000--3500 Angstrom) for
this small sample. The corresponding photometric data, together with archival
data from Swift Ultraviolet/Optical Telescope observations, provide further
evidence of increased dispersion in the UV emission with respect to the
optical. The peak luminosities measured in uvw1/F250W are found to correlate
with the B-band light-curve shape parameter dm15(B), but with much larger
scatter relative to the correlation in the broad-band B band (e.g., ~0.4 mag
versus ~0.2 mag for those with 0.8 < dm15 < 1.7 mag). SN 2004dt is found as an
outlier of this correlation (at > 3 sigma), being brighter than normal SNe Ia
such as SN 2005cf by ~0.9 mag and ~2.0 mag in the uvw1/F250W and uvm2/F220W
filters, respectively. We show that different progenitor metallicity or
line-expansion velocities alone cannot explain such a large discrepancy.
Viewing-angle effects, such as due to an asymmetric explosion, may have a
significant influence on the flux emitted in the UV region. Detailed modeling
is needed to disentangle and quantify the above effects.Comment: 17 pages, 13 figures, accepted by Ap
The dimensions of prosociality: a cross-cultural lexical analysis
The West is usually portrayed as relatively individualistic. It is further argued that this tendency has influenced academia, leading to an underappreciation of the importance of prosociality. In the interest of exploring this topic, an enquiry was conducted into conceptualisations of prosociality across the world’s cultures. This enquiry focused on so-called untranslatable words, i.e., which lack an exact translation into another language (in this case, English). Through a quasi-systematic search of academic and grey literature, together with additional data collection, over 200 relevant terms were located. An adapted form of grounded theory identified five dimensions: socialising/congregating; morals/ethics; compassion/kindness; interaction/communication; and communality. The analysis sheds light on the dynamics of prosociality, as understood by cultures across the globe. Moreover, the roster of terms featured have the potential to enrich the nomological network in psychology, allowing for a richer conceptualisation of the social dimensions of human functioning
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