64 research outputs found
Star clusterings in the Carina complex: UBVRI photometry of Bochum 9, 10 and 11
We report on the first UBVRI CCD photometry of three poorly known star
clusterings in the region of Eta Carinae: Bochum9, Bochum10 and Bochum11. We
found that they are young, rather poor and loose open clusters. We argue that
Bochum9 is probably a small and loose cluster with about 30 probable members
having E(B-V)=0.63, located 4.6 kpc far from the Sun, beyond the Carina spiral
arm. Similarly, Bochum10 is a sparse aggregate with 14 probable members having
E(B-V)=0.47 and at a distance of 2.7 kpc from the Sun. Finally, Bochum11 is a
less than 4x10^6 yrs old cluster for which we identify 24 members. It has a
reddening E(B-V)=0.58, and lies between Bochum10 and 9, at 3.5 kpc from the
Sun. We propose that in the field of the cluster some stars might be pre Main
Sequence (MS) candidates.Comment: 12 pages, 16 figures. Accepted for publication in MNRA
Spectropolarimetric diagnostics of thermonuclear supernova explosions
Even at extragalactic distances, the shape of supernova ejecta can be
effectively diagnosed by spectropolarimetry. We present here results for 17
Type Ia supernovae that allow a statistical study of the correlation among the
geometric structures and other observable parameters of Type Ia supernovae.
These observations suggest that their ejecta typically consist of a smooth,
central iron rich core and an outer layer with chemical asymmetries. The degree
of this peripheral asphericity is correlated with the light-curve decline rate
of Type Ia supernovae. These observations lend strong support to
delayed-detonation models of Type Ia supernovae.Comment: To Appear in Scienc
Metal abundances in extremely distant Galactic old open clusters. II. Berkeley 22 and Berkeley 66
We report on high resolution spectroscopy of four giant stars in the Galactic
old open clusters Berkeley~22 and Berkeley~66 obtained with HIRES at the Keck
telescope. We find that and for
Berkeley~22 and Berkeley~66, respectively. Based on these data, we first revise
the fundamental parameters of the clusters, and then discuss them in the
context of the Galactic disk radial abundance gradient. We found that both
clusters nicely obey the most updated estimate of the slope of the gradient
from \citet{fri02} and are genuine Galactic disk objects.Comment: 20 pages, 6 eps figures, accepted for publication in the Astronomical
Journa
Pre-Maximum Spectropolarimetry of the Type Ia SN 2004dt
We report observations of SN 2004dt obtained with the Very Large Telescope of
the European Southern Observatory on August 13.30, 2004 when the supernova was
more than a week before optical maximum. SN 2004dt showed strong lines of
\ion{O}{1}, \ion{Mg}{2}, \ion{Si}{2}, and \ion{Ca}{2} with typical velocities
of absorption minimum around 17,000 \kms. The line profiles show material
moving at velocities as high as 25,000 \kms in these lines. The observations
also reveal absorption lines from \ion{S}{2} and \ion{Si}{3} with a velocity of
only 11,000 \kms. The highest velocity in the \ion{S}{2} features can be traced
no higher than 15,000 \kms, much lower than those of O, Mg, Si, and Ca. SN
2004dt has a polarization spectrum unlike any previously observed. The
variation of the polarization across some \ion{Si}{2} lines approaches 2%,
making SN 2004dt the most highly polarized SN Ia ever observed. In contrast,
the strong line of O I at 777.4 nm shows little or no polarization signature.
The degree of polarization points to a richly-structured partially burned
silicon layer with substantial departure from spherical symmetry. A geometry
that would account for the observations is one in which the distribution of
oxygen is essentially spherically symmetric, but with bubbles of
intermediate-mass elements with significant opacity within the oxygen
substrate.Comment: Submitted to Ap
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