839 research outputs found
The Effect of Corotation on the Radial Gradient of Metallicity of Spiral Galaxies
The corotation radius in a spiral galaxy is the radius where the spiral
pattern speed has the same velocity of the rotation curve. By compiling results
from the literature for 20 spiral galaxies we verified a strong correlation
between the radius of the minima or inflections of the metallicity distribution
and the corotation radius.Comment: 3 pages, 1 figur
CO observations and investigation of triggered star formation towards N10 infrared bubble and surroundings
We studied the environment of the dust bubble N10 in molecular emission.
Infrared bubbles, first detected by the GLIMPSE survey at 8.0 m, are ideal
regions to investigate the effect of the expansion of the HII region on its
surroundings eventual triggered star formation at its borders. In this work, we
present a multi-wavelength study of N10. This bubble is especially interesting
as infrared studies of the young stellar content suggest a scenario of ongoing
star formation, possibly triggered, on the edge of the HII region. We carried
out observations of CO(1-0) and CO(1-0) emission at PMO 13.7-m
towards N10. We also analyzed the IR and sub-mm emission on this region and
compare those different tracers to obtain a detailed view of the interaction
between the expanding HII region and the molecular gas. We also estimated the
parameters of the denser cold dust condensation and of the ionized gas inside
the shell. Bright CO emission was detected and two molecular clumps were
identified, from which we have derived physical parameters. We also estimate
the parameters for the densest cold dust condensation and for the ionized gas
inside the shell. The comparison between the dynamical age of this region and
the fragmentation time scale favors the "Radiation-Driven Implosion" mechanism
of star formation. N10 reveals to be specially interesting case with gas
structures in a narrow frontier between HII region and surrounding molecular
material, and with a range of ages of YSOs situated in region indicating
triggered star formation.Comment: Version 2 - Submmited to ApJ (under review
First optical images of circumstellar dust surrounding the debris disk candidate HD 32297
Near-infrared imaging with the Hubble Space Telescope recently revealed a
circumstellar dust disk around the A star HD 32297. Dust scattered light is
detected as far as 400 AU radius and the linear morphology is consistent with a
disk ~10 degrees away from an edge-on orientation. Here we present the first
optical images that show the dust scattered light morphology from 560 to 1680
AU radius. The position angle of the putative disk midplane diverges by 31
degrees and the color of dust scattering is most likely blue. We associate HD
32297 with a wall of interstellar gas and the enigmatic region south of the
Taurus molecular cloud. We propose that the extreme asymmetries and blue disk
color originate from a collision with a clump of interstellar material as HD
32297 moves southward, and discuss evidence consistent with an age of 30 Myr or
younger.Comment: 5 pages; Accepted for publication in ApJ Letter
Bimodal chemical evolution of the Galactic disk and the Barium abundance of Cepheids
In order to understand the Barium abundance distribution in the Galactic disk
based on Cepheids, one must first be aware of important effects of the
corotation resonance, situated a little beyond the solar orbit. The thin disk
of the Galaxy is divided in two regions that are separated by a barrier
situated at that radius. Since the gas cannot get across that barrier, the
chemical evolution is independent on the two sides of it. The barrier is caused
by the opposite directions of flows of gas, on the two sides, in addition to a
Cassini-like ring void of HI (caused itself by the flows). A step in the
metallicity gradient developed at corotation, due to the difference in the
average star formation rate on the two sides, and to this lack of communication
between them. In connection with this, a proof that the spiral arms of our
Galaxy are long-lived (a few billion years) is the existence of this step. When
one studies the abundance gradients by means of stars which span a range of
ages, like the Cepheids, one has to take into account that stars, contrary to
the gas, have the possibility of crossing the corotation barrier. A few stars
born on the high metallicity side are seen on the low metallicity one, and
vice-versa. In the present work we re-discuss the data on Barium abundance in
Cepheids as a function of Galactic radius, taking into account the scenario
described above. The [Ba/H] ratio, plotted as a function of Galactic radius,
apparently presents a distribution with two branches in the external region
(beyond corotation). One can re-interpret the data and attribute the upper
branch to the stars that were born on the high metallicity side. The lower
branch, analyzed separately, indicates that the stars born beyond corotation
have a rising Barium metallicity as a function of Galactic radius.Comment: 6 pages, 7 figures, Proceedings of IAU Symposium 29
Nitrogen cycling, forest canopy reflectance, and emergent properties of ecosystems
In Ollinger et al. (1), we reported that mass-based concentrations of nitrogen in forest canopies (%N) are positively associated with whole-canopy photosynthetic capacity and canopy shortwave albedo in temperate and boreal forests, the latter result stemming from a positive correlation between %N and canopy near infrared (NIR) reflectance. This finding is intriguing because a functional link between %N and NIR reflectance could indicate an influence of nitrogen cycling on surface energy exchange, and could provide a means for estimating %N using broad-band satellite sensors
[Accepted Manuscript] Women’s Empowerment and Wellbeing: Evidence from Africa
We use household survey data from Senegal to model the effects of empowerment within the home on married women?s wellbeing. The estimated effects of empowerment are at least as large as more conventional development indicators, such as household income. The size of the empowerment effect is robust to alternative estimation techniques, including an Instrumental Variables estimator
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