33 research outputs found
Family & Kin Relationships: All or Multiple
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Voluntary Associations: All or Multiple
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The 3-D shaping of NGC 6741: a massive, fast-evolving Planetary Nebula at the recombination--reionization edge
We infer the gas kinematics, diagnostics and ionic radial profiles, distance
and central star parameters, nebular photo- ionization model, spatial structure
and evolutionary phase of the PN NGC 6741 by means of long-slit high-resolution
spectra at nine position angles. NGC 6741 (distance ~2.0 kpc, age ~1400 yr,
ionized mass Mion ~0.06 Mo) is a dense (electron density up to 12,000 cm^(-3)),
high-excitation, almost- prolate ellipsoid, surrounded by a sharp
low-excitation skin (the ionization front), and embedded into a spherical
(radius ~ 0.080 pc), almost-neutral, high-density (n(HI) ~7 x 10^3 atoms
cm^(-3)) halo containing a large fraction of the nebular mass (Mhalo>0.20 Mo).
The kinematics, physical conditions and ionic structure indicate that NGC 6741
is in a deep recombination phase, started about 200 years ago, and caused by
the quick luminosity drop of the massive (M*=0.66-0.68 Mo), hot (logT* ~ 5.23)
and faint (log L*/Lo ~ 2.75) post--AGB star, which has exhausted the
hydrogen-shell nuclear burning and is moving along the white dwarf cooling
sequence. The general expansion law of the ionized gas in NGC 6741, Vexp (km
s^(-1)=13 x R", fails in the innermost, highest-excitation layers, which move
slower than expected. The observed deceleration is ascribable to the luminosity
drop of the central star, and appears in striking contrast to recent reports
inferring that acceleration is a common property of the Planetary Nebulae
innermost layers. Some general implications on the shaping mechanisms of
Planetary Nebulae are discussed.Comment: 27 pages, 18 figures, accepted for publication in A&A, movies of the
reconstructed nebula are available at http://web.pd.astro.it/sabbadin
The 3--D ionization structure of NGC 6818: a Planetary Nebula threatened by recombination
Long-slit NTT+EMMI echellograms of NGC 6818 (the Little Gem) at nine equally
spaced position angles, reduced according to the 3-D methodology introduced by
Sabbadin et al. (2000a,b), allowed us to derive: the expansion law, the
diagnostics and ionic radial profiles, the distance and the central star
parameters, the nebular photo-ionization model, the 3-D reconstruction in He
II, [O III] and [N II], the multicolor projection and a series of movies. The
Little Gem results to be a young (3500 years), optically thin (quasi-thin in
some directions) double shell (Mion~0.13 Msun) at a distance of 1.7 kpc, seen
almost equatorial on: a tenuous and patchy spherical envelope (r~0.090 pc)
encircles a dense and inhomogeneous tri-axial ellipsoid (a/2~0.077 pc,
a/b~1.25, b/c~1.15) characterized by a hole along the major axis and a pair of
equatorial, thick moustaches. NGC 6818 is at the start of the recombination
phase following the luminosity decline of the 0.625 Msun central star, which
has recently exhausted the hydrogen shell nuclear burning and is rapidly moving
toward the white dwarf domain (log T*~5.22 K; log(L*/Lsun)~3.1). The nebula is
destined to become thicker and thicker, with an increasing fraction of neutral,
dusty gas in the outermost layers. Only over some hundreds of years the plasma
rarefaction due to the expansion will prevail against the slower and slower
stellar decline, leading to a gradual re-growing of the ionization front. The
exciting star of NGC 6818 (mV~17.06) is a visual binary: a faint, red companion
(mV~17.73) appears at 0.09 arcsec in PA=190deg, corresponding to a separation
>=150 AU and to an orbital period >=1500 yearsComment: 23 pages, 18 figures, A&A accepted. 12 movies of NGC 6818 are
available at http://web.pd.astro.it/sabbadin The paper may also be retrivied
at http://web.pd.astro.it/supern/preprints.htm
Common Genetic Variants Contribute to Risk of Transposition of the Great Arteries.
RATIONALE: Dextro-transposition of the great arteries (D-TGA) is a severe congenital heart defect which affects approximately 1 in 4,000 live births. While there are several reports of D-TGA patients with rare variants in individual genes, the majority of D-TGA cases remain genetically elusive. Familial recurrence patterns and the observation that most cases with D-TGA are sporadic suggest a polygenic inheritance for the disorder, yet this remains unexplored.
OBJECTIVE: We sought to study the role of common single nucleotide polymorphisms (SNPs) in risk for D-TGA.
METHODS AND RESULTS: We conducted a genome-wide association study in an international set of 1,237 patients with D-TGA and identified a genome-wide significant susceptibility locus on chromosome 3p14.3, which was subsequently replicated in an independent case-control set (rs56219800, meta-analysis P=8.6x10
CONCLUSIONS: This work provides support for a polygenic architecture in D-TGA and identifies a susceptibility locus on chromosome 3p14.3 nea
Recreational Associations: All or Multiple
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Professional Sports All or Multiple
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