Complex dynamics in a simple model of pulsations for Super-Asymptotic Giant Branch Stars

When intermediate mass stars reach their last stages of evolution they show pronounced oscillations. This phenomenon happens when these stars reach the so-called Asymptotic Giant Branch (AGB), which is a region of the Hertzsprung-Russell diagram located at about the same region of effective temperatures but at larger luminosities than those of regular giant stars. The period of these oscillations depends on the mass of the star. There is growing evidence that these oscillations are highly correlated with mass loss and that, as the mass loss increases, the pulsations become more chaotic. In this paper we study a simple oscillator which accounts for the observed properties of this kind of stars. This oscillator was first proposed and studied by Icke et al. [Astron.Astrophys. 258, 341 (1992)] and we extend their study to the region of more massive and luminous stars - the region of Super-AGB stars. The oscillator consists of a periodic nonlinear perturbation of a linear Hamiltonian system. The formalism of dynamical systems theory has been used to explore the associated Poincare map for the range of parameters typical of those stars. We have studied and characterized the dynamical behaviour of the oscillator as the parameters of the model are varied, leading us to explore a sequence of local and global bifurcations. Among these, a tripling bifurcation is remarkable, which allows us to show that the Poincare map is a nontwist area preserving map. Meandering curves, hierarchical-islands traps and sticky orbits also show up. We discuss the implications of the stickiness phenomenon in the evolution and stability of the Super-AGB stars.Comment: 13 pages, 9 figure

First comparison of retroperitoneal versus transperitoneal robot-assisted nephroureterectomy with bladder cuff : a single center study

Introduction. After recent presentation of the first complete robot-assisted retroperitoneal nephroureterectomy with bladder cuff (RRNU) for patients with upper tract urothelial cancer (UTUC), we aimed to compare this new surgical technique with robot-assisted transperitoneal nephroureter ectomy (TRNU) representing the current standard of care. Methods. Robot-assisted nephroureterectomies (NUs) were retrospectively analyzed and compared based on two groups: transperitoneal versus retroperitoneal approach. Baseline data were collected for patient demographics, tumor characteristics, intra- (EAUiaiC) and postoperative (Clavien-Dindo) complications, and perioperative variables. Tumor characteristics included grade of malignancy, clinical stage, and surgical margin status. Short-term follow-up data including 30-day readmission rates were collected. Statistical analyses were performed assuming a significant p-value of < 0.05. Results. The analysis includes perioperative patient data after proven UTUC of 24 TRNU versus 12 RRNU (mean age: 70 versus 71 years; BMI: 25.9 versus 26.1 kg/m 2 ; CCI score ≥ 4: 83% versus 75%; ASA score ≥ 3: 37% vs 33%). Intraoperative (16.4% vs 0%, p = 0.35) and postoperative (25% vs 12.5%, p = 0.64) complications demonstrated no significant discrepancy. Notably, RRNU demonstrated significantly shorter surgery time (p < 0.05) and length of stay (p < 0.05). There was no significant difference in histopathological tumor characteristics, whereas significantly more lymph nodes were removed through RRNU (11.0±3.3 vs. 6.4±5.1, p < 0.05). Finally, no statistical difference was shown in short-term follow-up. Conclusion. We report the first head-to-head comparison between RRNU and TRNU. RRNU proves to be a safe and feasible approach which appears to be non-inferior to TRNU. RRNU expands the spectrum of minimally invasive treatment options, particularly for patients with major previous abdominal surgery

Planets and Axisymmetric Mass Loss

Bipolar planetary nebulae (PNe), as well as extreme elliptical PNe are formed through the influence of a stellar companion. But half of all PN progenitors are not influenced by any stellar companion, and, as I show here, are expected to rotate very slowly on reaching the upper asymptotic giant branch; hence they expect to form spherical PNe, unless they are spun-up. But since most PNe are not spherical, I argue that about 50 percents of AGB stars are spun-up by planets, even planets having a mass as low as 0.01 times the mass of Jupiter, so they form elliptical PNe. The rotation by itself will not deform the AGB wind, but may trigger another process that will lead to axisymmetric mass loss, e.g., weak magnetic activity, as in the cool magnetic spots model. This model also explains the transition from spherical to axisymmetric mass loss on the upper AGB. For such low mass planets to substantially spin-up the stellar envelope, they should enter the envelope when the star reaches the upper AGB. This "fine-tuning" can be avoided if there are several planets on average around each star, as is the case in the solar system, so that one of them is engulfed when the star reaches the upper AGB.Comment: 8 pages, 1 figure. To appear in the proceedings of the conference, "Post-AGB Objects (proto-planetary nebulae) as a Phase of Stellar Evolution", Torun, Poland, July 5-7, 2000, eds. R. Szczerba, R. Tylenda, and S.K. Gorn

The Spitzer Spectroscopic Survey of S-type Stars

S-type AGB stars are thought to be in the transitional phase between M-type and C-type AGB stars. Because of their peculiar chemical composition, one may expect a strong influence of the stellar C/O ratio on the molecular chemistry and the mineralogy of the circumstellar dust. In this paper, we present a large sample of 87 intrinsic galactic S-type AGB stars, observed at infrared wavelengths with the Spitzer Space Telescope, and supplemented with ground-based optical data. On the one hand, we derive the stellar parameters from the optical spectroscopy and photometry, using a grid of model atmospheres. On the other, we decompose the infrared spectra to quantify the flux-contributions from the different dust species. Finally, we compare the independently determined stellar parameters and dust properties. For the stars without significant dust emission, we detect a strict relation between the presence of SiS absorption in the Spitzer spectra and the C/O ratio of the stellar atmosphere. These absorption bands can thus be used as an additional diagnostic for the C/O ratio. For stars with significant dust emission, we define three groups, based on the relative contribution of certain dust species to the infrared flux. We find a strong link between group-membership and C/O ratio. We show that these groups can be explained by assuming that the dust-condensation can be cut short before silicates are produced, while the remaining free atoms and molecules can then form the observed magnesium sulfides or the carriers of the unidentified 13 and 20 micron features. Finally, we present the detection of emission features attributed to molecules and dust characteristic to C-type stars, such as molecular SiS, hydrocarbons and magnesium sulfide grains. We show that we often detect magnesium sulfides together with molecular SiS and we propose that it is formed by a reaction of SiS molecules with Mg.Comment: Accepted for publication in A&

Homochiral growth through enantiomeric cross-inhibition

The stability and conservation properties of a recently proposed polymerization model are studied. The achiral (racemic) solution is linearly unstable once the relevant control parameter (here the fidelity of the catalyst) exceeds a critical value. The growth rate is calculated for different fidelity parameters and cross-inhibition rates. A chirality parameter is defined and shown to be conserved by the nonlinear terms of the model. Finally, a truncated version of the model is used to derive a set of two ordinary differential equations and it is argued that these equations are more realistic than those used in earlier models of that form.Comment: 20 pages, 6 figures, Orig. Life Evol. Biosph. (accepted

Monoprophylaxis With Cephalosporins for Transrectal Prostate Biopsy After the Fluoroquinolone-Era: A Multi-Institutional Comparison of Severe Infectious Complications

BackgroundTo compare severe infectious complication rates after transrectal prostate biopsies between cephalosporins and fluoroquinolones for antibiotic monoprophylaxis.Material and MethodsIn the multi-institutional cohort, between November 2014 and July 2020 patients received either cefotaxime (single dose intravenously), cefpodoxime (multiple doses orally) or fluoroquinolones (multiple-doses orally or single dose intravenously) for transrectal prostate biopsy prophylaxis. Data were prospectively acquired and retrospectively analyzed. Severe infectious complications were evaluated within 30 days after biopsy. Logistic regression models predicted biopsy-related infectious complications according to antibiotic prophylaxis, application type and patient- and procedure-related risk factors.ResultsOf 793 patients, 132 (16.6%) received a single dose of intravenous cefotaxime and were compared to 119 (15%) who received multiple doses of oral cefpodoxime and 542 (68.3%) who received fluoroquinolones as monoprophylaxis. The overall incidence of severe infectious complications was 1.0% (n=8). No significant differences were observed between the three compared groups (0.8% vs. 0.8% vs. 1.1%, p=0.9). The overall rate of urosepsis was 0.3% and did not significantly differ between the three compared groups as well.ConclusionMonoprophylaxis with third generation cephalosporins was efficient in preventing severe infectious complications after prostate biopsy. Single intravenous dose of cefotaxime and multiday regimen of oral cefpodoxime showed a low incidence of infectious complications &lt;1%. No differences were observed in comparison to fluoroquinolones

The 3 micron spectrum of R Doradus observed with the ISO-SWS

We have modeled the 2.6 - 3.7 um spectrum of the red semiregular variable R Doradus observed with the Short-Wavelength Spectrometer on board the Infrared Space Observatory. The wavelength resolution of the observations varies between R = 2000 - 2500. We have calculated a synthetic spectrum using a hydrostatic model photosphere in spherical geometry. The agreement between the synthetic spectrum and the ISO observations is encouraging, especially in the wavelength region of 2.8 - 3.7 um, suggesting that a hydrostatic model photosphere is adequate for the calculation of synthetic spectra in the near infrared for this moderately varying red giant star. However, an additional absorption component is needed at 2.6- 2.8 um and this discrepancy is discussed. The spectral signatures are dominated by water vapour in the stellar photosphere, but several photospheric OH, CO, and SiO features are also present. The effective temperature and surface gravity derived for R Dor, based on the 2.6 - 3.7 um ISO spectrum and the modeling of it with a hydrostatic model photosphere, are 3000 +- 100 K and log g = 0 +- 1 (cgs), respectively. The spectral region observed is found to be temperature sensitive. The effective temperature given here is slightly higher than those reported in the literature. We also discuss possible reasons for this.Comment: Accepted by A&A, 10 page

The dust condensation sequence in red super-giant stars

Context: Red super-giant (RSG) stars exhibit significant mass loss through a slow and dense wind. They are often considered to be the more massive counter parts of Asymptotic Giant Branch (AGB) stars. While the AGB mass loss is linked to their strong pulsations, the RSG are often only weakly variable. Aim: To study the conditions at the base of the wind, by determining the dust composition in a sample of RSG. The dust composition is thought to be sensitive to the density, temperature and acceleration at the base of the wind. Method: We compile a sample of 27 RSG infrared spectra (ISO-SWS) and supplement these with photometric measurements to obtain the full spectral energy distribution (SED). These data are modelled using a dust radiative transfer code. The results are scrutinised for correlations. Results: We find (1) strong correlations between dust composition, mass-loss rate and stellar luminosity, roughly in agreement with the theoretical dust condensation sequence, (2) the need for a continuous (near-)IR dust opacity and tentatively propose amorphous carbon, and (3) significant differences with AGB star winds: presence of PAHs, absence of 'the' 13 micron band, and a lack of strong water bands. Conclusions: Dust condensation in RSG is found to experience a similar freeze-out process as in AGB stars. Together with the positive effect of the stellar luminosity on the mass-loss rate, this suggests that radiation pressure on dust grains is an important ingredient in the driving mechanism. Still, differences with AGB stars are manifold and thus the winds of RSG deserve separate studies.Comment: 12 pages, 9 figures, accepted for publication in A&