36 research outputs found
3-D ionization structure (in stereoscopic view) of Planetary Nebulae: the case of NGC 1501
Long-slit echellograms of the high excitation planetary nebula NGC1501,
reduced according to the methodology developed by Sabbadin et al. (2000a, b),
allowed us to obtain the ``true'' distribution of the ionized gas in the eight
nebular slices covered by the spectroscopic slit. A 3-D rendering procedure is
described and applied, which assembles the tomographic maps and rebuilds the
spatial structure. The images of NGC 1501, as seen in 12 directions separated
by 15 deg, form a series of stereoscopic pairs giving surprising 3-D views in
as many directions. The main nebula consists of an almost oblate ellipsoid of
moderate ellipticity (a=44 arcsec, a/b=1.02, a/c=1.11), brighter in the
equatorial belt, deformed by several bumps, and embedded in a quite
homogeneous, inwards extended cocoon. Some reliability tests are applied to the
rebuilt nebula; the radial matter profile, the small scale density fluctuations
and the 2-D (morphology) - 3-D (structure) correlation are presented and
analysed. The wide applications of the 3-D reconstruction to the morphology,
physical conditions, ionization parameters and evolutionary status of expanding
nebulae in general (planetary nebulae, nova and supernova remnants, shells
around Population I Wolf-Rayet stars, nebulae ejected by symbiotic stars,
bubbles surrounding early spectral type main sequence stars etc.) are
introduced.Comment: 12 pages + 11 (gif) figures. Accepted for publication in A&A. A
postscript file with figs. can be retrieved at
http://panoramix.pd.astro.it/~sabbadi
Towards a Synthesis of Core-Collapse Supernova Theory
New insights into the mechanism and character of core--collapse supernova
explosions are transforming the approach of theorists to their subject. The
universal realization that the direct hydrodynamic mechanism does not work and
that a variety of hydrodynamic instabilities can influence the viability of
theoretical explosions has ushered in a new era in supernova modeling. In this
paper, I discuss the important physical and technical issues that remain. I
review the neutrino--driven mechanism, the possible roles of Rayleigh--Taylor
instabilities, questions in neutrino transport, and the various observational
constraints within which theorists must operate. However, a consensus has yet
to be achieved among active workers concerning many important details and some
essential phenomenology. This synopsis is meant to accomplish two things: 1) to
focus attention on the interesting problems whose resolution will bring needed
progress, and 2) to assess the current status of the theoretical art.Comment: Eighteen Pages, Elsevier Elsart LaTeX format, no figures, to appear
in Nucl. Phys. A, as a contribution to the Festschrift in honor of Gerald E.
Brown's 70'th Birthday. PostScript version available from
[email protected]
Prospects for Studies of Stellar Evolution and Stellar Death in the JWST Era
I review the prospects for studies of the advanced evolutionary stages of
low-, intermediate- and high-mass stars by the JWST and concurrent facilities,
with particular emphasis on how they may help elucidate the dominant
contributors to the interstellar dust component of galaxies. Observations
extending from the mid-infrared to the submillimeter can help quantify the
heavy element and dust species inputs to galaxies from AGB stars. JWST's MIRI
mid-infrared instrument will be so sensitive that observations of the dust
emission from individual intergalactic AGB stars and planetary nebulae in the
Virgo Cluster will be feasible. The Herschel Space Observatory will enable the
last largely unexplored spectral region, the far-IR to the submillimeter, to be
surveyed for new lines and dust features, while SOFIA will cover the wavelength
gap between JWST and Herschel, a spectral region containing important fine
structure lines, together with key water-ice and crystalline silicate bands.
Spitzer has significantly increased the number of Type II supernovae that have
been surveyed for early-epoch dust formation but reliable quantification of the
dust contributions from massive star supernovae of Type II, Type Ib and Type Ic
to low- and high-redshift galaxies should come from JWST MIRI observations,
which will be able to probe a volume over 1000 times larger than Spitzer.Comment: 24 pages, 19 figures. To appear in `Astrophysics in the Next Decade:
JWST and Concurrent Facilities' (JWST Conference Proceedings), edited by H.
A. Thronson, M. Stiavelli and A. G. G. M. Tielens; Springer Series:
Astrophysics and Space Science Proceeding
Newly discovered Wolf-Rayet and weak emission-line central stars of planetary nebulae
The definitive version can be found at : http://onlinelibrary.wiley.com/ Copyright Royal Astronomical SocietyWe present the spectra of 32 previously unpublished confirmed and candidate Wolf-Rayet ([WR]) and weak emission-line (WELS) central stars of planetary nebulae (CSPNe). 18 stars have been discovered in the Macquarie/AAO/Strasbourg Ha (MASH) PN survey sample, and we have also uncovered 14 confirmed and candidate [WR]s and WELS among the CSPNe of previously known PNe. Spectral classifications have been undertaken using both Acker & Neiner and Crowther, De Marco & Barlow schemes. 22 members in this sample are identified as probable [WR] s; the remaining 10 appear to be WELS. Observations undertaken as part of the MASH spectroscopic survey have now increased the number of known [WR] s by similar to 30 per cent. This will permit a better analysis of [WR] subclass distribution, metallicity effects and evolutionary sequences in these uncommon objects.Peer reviewe
Structural organization and chromosomal localization of three human galanin receptor genes
Human galanin receptor subtypes GALR1, GALR2, and GALR3 are encoded by separate genes that are located on human chromosomes 18q23, 17q25.3, and 22q13.1, respectively. The exon:intron organization of the gene encoding GALR2 (GALNR2) and GALR3 (GALNR3) is conserved, with exon 1 encoding the NH-terminus to the end of transmembrane domain 3 and exon 2 encoding the remainder of the receptor, from the second intracellular loop to the COOH-terminus. This conservation of structural organization is indicative of a common evolutionary origin for GALNR2 and GALNR3. The exon:intron organization of the gene encoding GALR1 (GALNR1) is different from that of GALNR2 and GALNR3, with exon 1 encoding the NH-terminus to the end of transmembrane domain 5, exon 2 encoding the third intracellular loop, and exon 3 encoding the remainder of the receptor, from transmembrane domain 6 to the COOH-terminus. The structural organization of GALNR1 suggests convergent evolution for this gene and represents a structural organization that is unique among genes encoding G-protein-coupled receptors