83 research outputs found
The HII Region KR 140: Spontaneous Formation of a High Mass Star
We have used a multiwavelength data set from the Canadian Galactic Plane
Survey (CGPS) to study the Galactic HII region KR 140, both on the scale of the
nebula itself and in the context of the star forming activity in the nearby
W3/W4/W5 complex of molecular clouds and HII regions. From both radio and
infrared data we have found a covering factor of about 0.5 for KR 140 and we
interpret the nebula as a bowl-shaped region viewed close to face on.
Extinction measurements place the region on the near side of its parent
molecular cloud. The nebula is kept ionized by one O8.5 V(e) star, VES 735,
which is less than a few million years old. CO data show that VES 735 has
disrupted much of the original molecular cloud for which the estimated mass and
density are about 5000 and 100 cm, respectively. KR 140 is
isolated from the nearest star forming activity, in W3. Our data suggest that
KR 140 is an example of spontaneous (i.e., non-triggered) formation of,
unusually, a high mass star.Comment: 46 pages; includes 15 figures; accepted by the Ap
Group analysis of structure equations for stars in radiative and convective equilibrium
It is proposed to use the Lie group theory of symmetries of differential
equations to investigate the system of equations describing a static star in a
radiative and convective equilibrium. It is shown that the action of an
admissible group induces a certain algebraic structure in the set of all
solutions, which can be used to find a family of new solutions. We have
demonstrated that, in the most general case, the equations admit an infinite
parameter group of quasi-homologous transformations. We have found invariants
of the symmetries group which correspond to the fundamental relations
describing a physical characteristic of the stars such as the
Hertzsprung-Russell diagram or the mass-luminosity relation. In this way we can
suggest that group invariants have not only purely mathematical sense, but
their forms are closely associated with the basic empirical relations.Comment: LaTeX2e, 13page
Empirically Constrained Color-Temperature Relations. II. uvby
(Abriged) A new grid of theoretical color indices for the Stromgren uvby
photometric system has been derived from MARCS model atmospheres and SSG
synthetic spectra for cool dwarf and giant stars. At warmer temperatures this
grid has been supplemented with the synthetic uvby colors from recent Kurucz
atmospheric models without overshooting. Our transformations appear to
reproduce the observed colors of extremely metal-poor turnoff and giant stars
(i.e., [Fe/H]<-2). Due to a number of assumptions made in the synthetic color
calculations, however, our color-temperature relations for cool stars fail to
provide a suitable match to the uvby photometry of both cluster and field stars
having [Fe/H]>-2. To overcome this problem, the theoretical indices at
intermediate and high metallicities have been corrected using a set of color
calibrations based on field stars having accurate IRFM temperature estimates
and spectroscopic [Fe/H] values. Encouragingly, isochrones that employ the
transformations derived in this study are able to reproduce the observed CMDs
(involving u-v, v-b, and b-y colors) for a number of open and globular clusters
(including M92, M67, the Hyades, and 47Tuc) rather well. Moreover, our
interpretations of such data are very similar, if not identical, with those
given by VandenBerg & Clem (2003, AJ, 126, 778) from a consideration of BV(RI)c
observations for the same clusters. In the present investigation, we have also
analyzed the observed Stromgren photometry for the classic Population II
subdwarfs, compared our "final" (b-y)-Teff relationship with those derived
empirically in a number of recent studies, and examined in some detail the
dependence of the m1 index on [Fe/H].Comment: 70 pages, 26 figures. Accepted for publication in AJ (Feb 2004).
Postscript version with high resolution figures and complete Table 3
available at http://astrowww.phys.uvic.ca/~jclem/uvb
The Age-Metallicity Relation in the Thin Disk of the Galaxy
HST trigonometric distances, photometric metallicities, isochronic ages from
the second revised version of the Geneva--Copenhagen survey, and uniform
spectroscopic Fe and Mg abundances from our master catalog are used to
construct and analyze the age--metallicity and age-relative Mg abundance
relations for stars of the thin disk. The influences of selection effects are
discussed in detail. It is demonstrated that the radial migration of stars does
not lead to appreciable distortions in the age dependence of the metallicity.
During the first several billion years of the formation of the thin disk, the
interstellar material in this disk was, on average, fairly rich in heavy
elements ( ~-0.2) and poorly mixed. However, the metallicity dispersion
continuously decreased with age, from \sigma_{[Fe/H]}~0.22 to ~0.13. All this
time, the mean relative abundance of Mg was somewhat higher than the solar
value (~0.1). Roughly four to five billion years ago, the mean
metallicity began to systematically increase, while retaining the same
dispersion; the mean relative Mg abundance began to decrease immediately
following this. The number of stars in this subsystem increased sharply at the
same time. These properties suggest that the star-formation rate was low in the
initial stage of formation of the thin disk, but abruptly increased about four
to five billion years ago.Comment: 16 page, 7 figures, accepted 2011, Astron. Rep., v.55, No.8,
p.667-68
Plant-soil interactions and acclimation to temperature of microbial-mediated soil respiration may affect predictions of soil CO2 efflux
Predictors of emergency room visits or acute hospital admissions prior to death among hospice palliative care clients in Ontario: a retrospective cohort study
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