1,810 research outputs found
The 3-D ionization structure and evolution of NGC 7009 (Saturn Nebula)
Tomographic and 3-D analyses for extended, emission-line objects are applied
to long-slit ESO NTT + EMMI high-resolution spectra of the intriguing planetary
nebula NGC 7009, covered at twelve position angles. We derive the gas expansion
law, the diagnostics and ionic radial profiles, the distance and the central
star parameters, the nebular photo-ionization model and the spatial recovery of
the plasma structure and evolution. The Saturn Nebula (distance~1.4 kpc,
age~6000 yr, ionized mass~0.18 Mo) consists of several interconnected
components, characterized by different morphology, physical conditions,
excitation and kinematics. The internal shell, the main shell, the streams and
the ansae expand at V(exp)~4.0xR" km/s, the outer shell, the caps and the
equatorial pseudo-ring at V(exp)~3.15xR" km/s, and the halo at V(exp)~10 km/s.
We compare the radial distribution of the physical conditions and the line
fluxes observed in the eight sub-systems with the theoretical profiles coming
from the photo-ionization code CLOUDY, inferring that all the spectral
characteristics of NGC 7009 are explainable in terms of photo-ionization by the
central star, a hot (logT*~4.95) and luminous (log L*/Lo~3.70) 0.60--0.61 Mo
post--AGB star in the hydrogen-shell nuclear burning phase. The 3--D shaping of
the Saturn Nebula is discussed within an evolutionary scenario dominated by
photo-ionization and supported by the fast stellar wind: it begins with the
superwind ejection, passes through the neutral, transition phase (lasting ~
3000 yr), the ionization start (occurred ~2000 yr ago), and the full ionization
of the main shell (~1000 yr ago), at last reaching the present days: the whole
nebula is optically thin to the UV stellar flux, except the caps and the ansae.Comment: accepted for pub. in A&A, 28 pages, 14 figures, full text with
figures available at http://web.pd.astro.it/supern/ps/h4665.ps, movies on the
3D structure available at http://web.pd.astro.it/sabbadin
Type II Supernovae as Standardized Candles
We present evidence for a correlation between expansion velocities of the
ejecta of Type II plateau supernovae and their bolometric luminosities during
the plateau phase. This correlation permits one to standardize the candles and
decrease the scatter in the Hubble diagram from ~1 mag to a level of 0.4 and
0.3 mag in the V and I bands, respectively. When we restrict the sample to the
eight objects which are well in the Hubble flow (cz > 3,000 km/s) the scatter
drops even further to only 0.2 mag (or 9% in distance), which is comparable to
the precision yielded by Type Ia supernovae and far better than the ``expanding
photosphere method'' applied to Type II supernovae. Using SN 1987A to calibrate
the Hubble diagrams we get Ho=55+/-12.Comment: 9 pages, 3 figures, 1 table, accepted by ApJ
VLT Spectropolarimetry of the optical transient in NGC300. Evidence for asymmetry in the circumstellar dust
AIMS: The main goal of this work is to study possible signs of asymmetry in
the bright optical transient in NGC300, with the aim of getting independent
information on the explosion mechanism, the progenitor star and its
circumstellar environment.
METHODS: Using VLT-FORS1 we have obtained low-resolution optical linear
spectropolarimetry of NGC300 OT2008-1 on two epochs, 48 and 55 days after the
discovery, covering the spectral range 3600--9330A.
RESULTS: The data show a continuum polarization at a very significant level.
At least two separate components are identified. The first is characterized by
a strong wavelength dependency and a constant position angle (68.6+/-0.3
degrees), which is parallel to the local spiral arm of the host galaxy. The
second shows a completely different position angle (151.3+/-0.4) and displays a
mild but statistically significant evolution between the two epochs. While the
former is identified as arising in the interstellar dust associated with
NGC300, the latter is most likely due to continuum polarization by dust
scattering in the circumstellar environment. No line depolarization is detected
in correspondence of the most intense emission lines, disfavoring electron
scattering as the source of intrinsic polarization. This implies a very small
deviation from symmetry in the continuum-forming region. Given the observed
level of intrinsic polarization, the transient must be surrounded by a
significant amount of dust (>4x10^-5 Msun), asymmetrically distributed within a
few thousand AU. This most likely implies that one or more asymmetric outflow
episodes took place during the past history of the progenitor.Comment: Accepted for publication in Astronomy and Astrophysics. 16 pages, 16
figure
Observed and Physical Properties of Core-Collapse Supernovae
I use photometry and spectroscopy data for 24 Type II plateau supernovae to
examine their observed and physical properties. This dataset shows that these
objects encompass a wide range of ~5 mag in their plateau luminosities, their
expansion velocities vary by x5, and the nickel masses produced in these
explosions go from 0.0016 to 0.26 Mo. From a subset of 16 objects I find that
the explosion energies vary between 0.6x and 5.5x10^51 ergs, the ejected masses
encompass the range 14-56 Mo, and the progenitors' radii go from 80 to 600 Ro.
Despite this great diversity several regularities emerge, which reveal that
there is a continuum in the properties of these objects from the faint,
low-energy, nickel-poor SNe 1997D and 1999br, to the bright, high-energy,
nickel-rich SN 1992am. This study provides evidence that more massive
progenitors produce more energetic explosions, thus suggesting that the outcome
of the core collapse is somewhat determined by the envelope mass. I find also
that supernovae with greater energies produce more nickel. Similar
relationships appear to hold for Type Ib/c supernovae, which suggests that both
Type II and Type Ib/c supernovae share the same core physics. When the whole
sample of core collapse objects is considered, there is a continous
distribution of energies below 8x10^51 ergs. Far above in energy scale and
nickel production lies the extreme hypernova 1998bw, the only supernova firmly
associated to a GRB.Comment: 25 pages, 7 figures, accepted for Part 1 of Astrophysical Journa
O Papel Da Laparoscopia DiagnĂłstica Em Ginecologia
Laparoscopy is a diagnostic method that is currently becoming consolidated for therapeutic use. It consists of endoscopically viewing the abdominal cavity. The aim here was to evaluate the indications for diagnostic videolaparoscopy and the intraoperative findings in an endoscopic gynecology clinic at a tertiary-level hospital over the last five years. DESIGN AND SETTING: Retrospective descriptive study on all diagnostic videolaparoscopy procedures of the last five years carried out in the endoscopic gynecology clinic of a tertiary-level hospital. METHODS: The medical records of 618 women who underwent diagnostic laparoscopy between 2008 and 2012 were analyzed. The clinical characteristics of these women, the indications for videolaparoscopy and the intraoperative findings were evaluated. RESULTS: The womenâs mean age was 32 ± 6.4 years. Most of the women had already undergone at least one previous operation (60%), which was most frequently a cesarean. The indications for performing videolaparoscopy were infertility in 57%, chronic pelvic pain in 27% and others (intrauterine device, adnexal tumor, ectopic pregnancy or pelvic inflammatory disease) in 16%. The main laparoscopic findings were tubal alterations in the group with infertility (59.78%) and peritoneal alterations in the group with chronic pelvic pain (43.54%). CONCLUSION: The main indications for videolaparoscopy in gynecology were infertility and chronic pelvic pain. However, in most procedures, no abnormalities justifying these complaints were found. © 2016, Associacao Paulista de Medicina. All rights reserved.1341707
Detection of Noble Gas Scintillation Light with Large Area Avalanche Photodiodes (LAAPDs)
Large Area Avalanche Photodiodes (LAAPDs) were used for a series of
systematic measurements of the scintillation light in Ar, Kr, and Xe gas.
Absolute quantum efficiencies are derived. Values for Xe and Kr are consistent
with those given by the manufacturer. For the first time we show that argon
scintillation (128 nm) can be detected at a quantum efficiency above 40%.
Low-pressure argon gas is shown to emit significant amounts of non-UV
radiation. The average energy expenditure for the creation of non-UV photons in
argon gas at this pressure is measured to be below 378 eV.Comment: 16 pages, 7 figure
The diversity of Type Ia Supernovae: evidence for systematics?
The photometric and spectroscopic properties of 26 well observed Type Ia
Supernovae (SNeIa) were analyzed with the aim to explore SNIa diversity. The
sample includes (Branch-)normal SNe as well as extreme events like SNe 1991T
and 1991bg, while the truly peculiar SNIa, SN2000cx and SN2002cx are not
included in our sample . A statistical treatment reveals the existence of three
different groups. The first group (FAINT) consists of faint SNeIa similar to
SN1991bg, with low expansion velocities and rapid evolution of SiII velocity. A
second group consists of ``normal'' SNeIa, also with high temporal velocity
gradient (HVG), but with brighter mean absolute magnitude =-19.3 and
higher expansion velocities than the FAINT SNe. The third group includes both
``normal'' and SN1991T-like SNeIa: these SNe populate a narrow strip in the
SiII velocity evolution plot, with a small velocity gradient (SVG), but have
absolute magnitudes similar to HVGs. While the FAINT and HVG SNeIa together
seem to define a relation between RSi(II) and Dm15(B), the SVG ones either do
not conform with that relation or define a new, looser one. The RSi(II)
pre-maximum evolution of HVGs is strikingly different from that of SVGs. The
impact of this evidence on the understanding of SNIa diversity, in terms of
explosion mechanisms, degree of ejecta mixing, and ejecta-CSM interaction, is
discussed.Comment: 9 pages, 3 figures, accepted for publication to ApJ; few referee's
comments adde
Supernova search at intermediate z. I. Spectroscopic analysis
We study 8 supernovae discovered as part of the International Time Programme
(ITP) project ``Omega and Lambda from Supernovae and the Physics of Supernova
Explosions'' at the European Northern Observatory (ENO). The goal of the
project is to increase the sample of intermediate redshift (0.1<z<0.4) SNe Ia
for testing properties of SNe Ia along z and for enlarging the sample in the
Hubble diagram up to large z.Comment: 2 pages, 2 figures, 1 table, to appear in ``1604-2004: Supernovae as
Cosmological Lighthouses'', (extended text upon request
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