82 research outputs found
Stellar Populations and the Local Group Membership of the Dwarf Galaxy DDO 210
We present deep BVI CCD photometry of the stars in the dwarf galaxy DDO 210.
The color-magnitude diagrams of DDO 210 show a well-defined red giant branch
(RGB) and a blue plume. The tip of the RGB is found to be at I_TRGB = 20.95 +/-
0.10 mag. From this the distance to DDO 210 is estimated to be d = 950 +/- 50
kpc. The corresponding distance of DDO 210 to the center of the Local Group is
870 kpc, showing that it is a member of the Local Group. The mean metallicity
of the red giant branch stars is estimated to be [Fe/H] = -1.9 +/- 0.1 dex.
Integrated magnitudes of DDO 210 within the Holmberg radius (r_H=110 arcsec =
505 pc) are derived to be M_B=-10.6 +/- 0.1 mag and M_V=-10.9 +/- 0.1 mag. B
and V surface brightness profiles of DDO 210 are approximately consistent with
an exponential law with scale lengths r_s(B) = 161 pc and r_s(V) = 175 pc. The
brightest blue and red stars in DDO 210 (BSG and RSG) are found to be among the
faintest in the nearby galaxies with young stellar populations: _{BSG}
= -3.41 +/- 0.11 mag and _{RSG} = -4.69 +/- 0.13 mag. An enhancement of
the star formation rate in the recent past (several hundred Myrs) is observed
in the central region of DDO 210. The opposite trend is observed in the outer
region of the galaxy, suggesting a possible two-component structure of the kind
disk/halo found in spiral galaxies. The real nature of this two-component
structure must, however, be confirmed with more detailed observations.Comment: Latex file, 17 pages with 9 figures, uses emulateapj.sty To appear in
the AJ (in August 1999
The short-duration GRB 050724 host galaxy in the context of the long-duration GRB hosts
We report optical and near-infrared broad band observations of the
short-duration GRB 050724 host galaxy, used to construct its spectral energy
distribution (SED). Unlike the hosts of long-duration gamma-ray bursts (GRBs),
which show younger stellar populations, the SED of the GRB 050724 host galaxy
is optimally fitted with a synthetic elliptical galaxy template based on an
evolved stellar population (age ~2.6 Gyr). The SED of the host is difficult to
reproduce with non-evolving metallicity templates. In contrast, if the short
GRB host galaxy metallicity enrichment is considered, the synthetic templates
fit the observed SED satisfactorily. The internal host extinction is low (A_v
\~< 0.4 mag) so it cannot explain the faintness of the afterglow. This short
GRB host galaxy is more massive (~5x10^10 Mo) and luminous (~1.1 L*) than most
of the long-duration GRB hosts. A statistical comparison based on the ages of
short- and long-duration GRB host galaxies strongly suggests that
short-duration GRB hosts contain, on average, older progenitors. These findings
support a different origin for short- and long-duration GRBs.Comment: A&A in pres
The non-thermal superbubble in IC 10 : the generation of cosmic ray electrons caught in the act
Superbubbles are crucial for stellar feedback, with supposedly high (of the order of 10 per cent) thermalization rates. We combined multiband radio continuum observations from the Very Large Array (VLA) with Effelsberg data to study the non-thermal superbubble (NSB) in IC 10, a starburst dwarf irregular galaxy in the Local Group. Thermal emission was subtracted using a combination of Balmer Hα and VLA 32 GHz continuum maps. The bubble’s nonthermal spectrum between 1.5 and 8.8 GHz displays curvature and can be well fitted with a standard model of an ageing cosmic ray electron population. With a derived equipartition magnetic field strength of 44 ±8 μG, and measuring the radiation energy density from Spitzer MIPS maps as 5±1×10−11 erg cm−3, we determine, based on the spectral curvature, a spectral age of the bubble of 1.0 ± 0.3 Myr. Analysis of the LITTLE THINGS HI data cube shows an expanding HI hole with 100 pc diameter and a dynamical age of 3.8 ± 0.3 Myr, centred to within 16 pc on IC 10 X-1, a massive stellar mass black hole (M > 23 M⊙). The results are consistent with the expected evolution for a superbubble with a few massive stars, where a very energetic event like a Type Ic supernova/hypernova has taken place about 1 Myr ago. We discuss alternatives to this interpretationPeer reviewe
The early spectral evolution of SN 2004dt
Aims. We study the optical spectroscopic properties of Type Ia Supernova (SN
Ia) 2004dt, focusing our attention on the early epochs.
Methods. Observation triggered soon after the SN 2004dt discovery allowed us
to obtain a spectrophotometric coverage from day -10 to almost one year (~353
days) after the B band maximum. Observations carried out on an almost daily
basis allowed us a good sampling of the fast spectroscopic evolution of SN
2004dt in the early stages. To obtain this result, low-resolution, long-slit
spectroscopy was obtained using a number of facilities.
Results. This supernova, which in some absorption lines of its early spectra
showed the highest degree of polarization ever measured in any SN Ia, has a
complex velocity structure in the outer layers of its ejecta. Unburnt oxygen is
present, moving at velocities as high as ~16,700 km/s, with some
intermediate-mass elements (Mg, Si, Ca) moving equally fast. Modeling of the
spectra based on standard density profiles of the ejecta fails to reproduce the
observed features, whereas enhancing the density of outer layers significantly
improves the fit. Our analysis indicates the presence of clumps of
high-velocity, intermediate-mass elements in the outermost layers, which is
also suggested by the spectropolarimetric data.Comment: 13 pages, 15 figures, accepted for pubblication in Astronomy and
Astrophysic
A Spatially Resolved Radio Spectral Index Study of the Dwarf Irregular Galaxy NGC\,1569
© The Author(s) 2018. Published by Oxford University Press on behalf of The Royal Astronomical Society. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.We study the resolved radio continuum spectral energy distribution of the dwarf irregular galaxy, NGC 1569, on a beam-by-beam basis to isolate and study its spatially resolved radio emission characteristics. Utilizing high-quality NRAO Karl G. Jansky Very Large Array observations that densely sample the 1-34 GHz frequency range, we adopt a Bayesian fitting procedure, where we use Hα emission that has not been corrected for extinction as a prior, to produce maps of how the separated thermal emission, non-thermal emission, and non-thermal spectral index vary across NGC1569's main disc. We find a higher thermal fraction at 1 GHz than is found in spiral galaxies (26 -3 +2 per cent) and find an average non-thermal spectral index α =-0.53 ± 0.02, suggesting that a young population of cosmic ray electrons is responsible for the observed non-thermal emission. By comparing our recovered map of the thermal radio emission with literature Hα maps, we estimate the total reddening along the line of sight to NGC1569 to be E(B - V) = 0.49 ± 0.05, which is in good agreement with other literature measurements. Spatial variations in the reddening indicate that a significant portion of the total reddening is due to internal extinction within NGC1569.Peer reviewedFinal Published versio
Exploring the pastiche hegemony of men
In this article I explore the continued hegemony of certain men. I use interview extracts to help think through the notion of pastiche hegemony as a means of understanding how men, and narratives about them, have changed, but unequal power relations persist. In particular, I explore this process within men’s understandings of how they were able to gain and maintain influence and power at work. Through their reflexive reading of the changing shape of late modern Western society, these men believed they were able to craft selves and employ social scripts to produce social influence and power in situational and contingent forms. I argue that it is within this interactional process that the increasingly undermined ideological and material legacy of patriarchy might still be reified. As such, while there is clear evidence highlighting the undermining of men’s ability to assume power, within this article I theoretically unpack how certain men might be able to produce a localized, pastiche hegemony. This article is published as part of a thematic collection on gender studies
Extensive optical and near-infrared observations of the nearby, narrow-lined type Ic SN 2007gr: days 5 to 415
We present photometric and spectroscopic observations at optical and
near-infrared wavelengths of the nearby type Ic SN 2007gr. These represent the
most extensive data-set to date of any supernova of this sub-type, with
frequent coverage from shortly after discovery to more than one year
post-explosion. We deduce a rise time to B-band maximum of 11.5 \pm 2.7 days.
We find a peak B-band magnitude of M_B=-16.8, and light curves which are
remarkably similar to the so-called 'hypernova' SN 2002ap. In contrast, the
spectra of SNe 2007gr and 2002ap show marked differences, not least in their
respective expansion velocities. We attribute these differences primarily to
the density profiles of their progenitor stars at the time of explosion i.e. a
more compact star for SN 2007gr compared to SN 2002ap. From the
quasi-bolometric light curve of SN 2007gr, we estimate that 0.076 0.010
Msun of 56Ni was produced in the explosion. Our near-infrared (IR) spectra
clearly show the onset and disappearance of the first overtone of carbon
monoxide (CO) between ~70 to 175 days relative to B-band maximum. The detection
of the CO molecule implies that ionised He was not microscopically mixed within
the carbon/oxygen layers. From the optical spectra, near-IR light curves, and
colour evolution, we find no evidence for dust condensation in the ejecta out
to about 400 days. Given the combination of unprecedented temporal coverage,
and high signal-to-noise data, we suggest that SN 2007gr could be used as a
template object for supernovae of this sub-class.Comment: A&A accepted; 26 pages & 16 figure
Mapping 123 million neonatal, infant and child deaths between 2000 and 2017
Since 2000, many countries have achieved considerable success in improving child survival, but localized progress remains unclear. To inform efforts towards United Nations Sustainable Development Goal 3.2—to end preventable child deaths by 2030—we need consistently estimated data at the subnational level regarding child mortality rates and trends. Here we quantified, for the period 2000–2017, the subnational variation in mortality rates and number of deaths of neonates, infants and children under 5 years of age within 99 low- and middle-income countries using a geostatistical survival model. We estimated that 32% of children under 5 in these countries lived in districts that had attained rates of 25 or fewer child deaths per 1,000 live births by 2017, and that 58% of child deaths between 2000 and 2017 in these countries could have been averted in the absence of geographical inequality. This study enables the identification of high-mortality clusters, patterns of progress and geographical inequalities to inform appropriate investments and implementations that will help to improve the health of all populations
OPTICAL INVESTIGATIONS OF ENERGY LEVELS IN SOLIDS
Author Institution: Naval Research Laborator
NATO Advanced Study Institute on Confined Electrons and Photons : New Physics and Applications
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