Jose Alberto Lopez

Magnetically Driven Winds from Post-Asymptotic Giant Branch Stars: Solutions for High-Speed Winds and Extreme Collimation

This paper explores the effects of post-asymptotic giant branch (AGB) winds driven solely by magnetic pressure from the stellar surface. It is found that winds can reach high speeds under this assumption and lead to the formation of highly collimated proto-planetary nebulae. Bipolar knotty jets with periodic features and constant velocity are well reproduced by the models. Several wind models with terminal velocities from a few tens of km s-1 up to 103 km s-1 are calculated, yielding outflows with linear momenta in the range 1036-1040 g cm s-1, and kinetic energies in the range 1042-1047 ergs. These results are in accord with recent observations of proto-planetary nebulae that have pointed out serious energy and momentum deficits if radiation pressure is considered as the only driver for these outflows. Our models strengthen the notion that the large mass loss rates of post-AGB stars, together with the short transition times from the late AGB to the planetary nebula stage, could be directly linked with the generation of strong magnetic fields during this transition stage.

Late AGB Magnetic Cycles: Magnetohydrodynamic Solutions for the Hubble Space Telescope Planetary Nebula Rings

The Hubble Space Telescope (HST) has revealed the existence of multiple, regularly spaced, and faint concentric shells around some planetary nebulae. Here we present two- (and a half) dimensional magnetohydrodynamic numerical simulations of the effects of a solar-like magnetic cycle, with periodic polarity inversions, in the slow wind of an asymptotic giant branch (AGB) star. The stellar wind is modeled with a steady mass-loss at constant velocity. This simple version of a solar-like cycle, without mass-loss variations, is able to reproduce many properties of the observed concentric rings. The shells are formed by pressure oscillations, which drive compressions in the magnetized wind. These pressure oscillations are due to periodic variations in the field intensity. The periodicity of the shells, then, is simply a half of the magnetic cycle since each shell is formed when the magnetic pressure goes to zero during the polarity inversion. As a consequence of the steady mass-loss rate, the density of the shells scales as r-2, and their surface brightness has a steeper drop-off, as observed in the shells of NGC 6543, the best documented case of these HST rings. Deviations from sphericity can be generated by changing the strength of the magnetic field. For sufficiently strong fields, a series of symmetric and equidistant blobs are formed at the polar axis, resembling the ones observed in He 2-90. These blobs are originated by magnetic collimation within the expanding AGB wind.

The Acceleration of the Nebular Shells in Planetary Nebulae in the Milky Way Bulge

We present a systematic study of line widths in the [O III] λ5007 and Hα lines for a sample of 86 planetary nebulae in the Milky Way bulge based on spectroscopy obtained at the Observatorio Astronomico Nacional in the Sierra San Pedro Martir (OAN-SPM) using the Manchester Echelle Spectrograph. The planetary nebulae were selected with the intention of simulating samples of bright extragalactic planetary nebulae. We separate the planetary nebulae into two samples containing cooler and hotter central stars, defined by the absence or presence, respectively, of the He II λ6560 line in the Hα spectra. This division separates samples of younger and more evolved planetary nebulae. The sample of planetary nebulae with hotter central stars has systematically larger line widths, larger radii, lower electron densities, and lower Hβ luminosities. The distributions of these parameters in the two samples all differ at significance levels exceeding 99%. These differences are all in agreement with the expectations from hydrodynamical models, but for the first time confirmed for a homogeneous and statistically significant sample of Galactic planetary nebulae. We interpret these differences as evidence for the acceleration of the nebular shells during the early evolution of these intrinsically bright planetary nebulae. As is the case for planetary nebulae in the Magellanic Clouds, the acceleration of the nebular shells appears to be the direct result of the evolution of the central stars.

Polyphenol-enriched Diet Prevents Coronary Endothelial Dysfunction by Activating the Akt/eNOS Pathway

INTRODUCTION AND OBJECTIVES The Mediterranean diet, rich in polyphenols, has shown to be cardioprotective. However the mechanisms involved remain unknown. We investigated whether supplementation with a pomegranate extract rich in polyphenols renders beneficial effects on coronary function in a clinically relevant experimental model and characterized the underlying mechanisms. METHODS Pigs were fed a 10-day normocholesterolemic or hypercholesterolemic diet. Half of the animals were given a supplement of 625 mg/day of a pomegranate extract (Pomanox; 200 mg punicalagins/day). Coronary responses to escalating doses of vasoactive drugs (acetylcholine, calcium ionophore, and sodium nitroprusside) and L-NG-monomethylarginine (endothelial nitric oxide-synthase inhibitor) were measured using flow Doppler. Akt/endothelial nitric oxide-synthase axis activation, monocyte chemoattractant protein-1 expression, oxidative deoxyribonucleic acid damage in the coronary artery, and lipoprotein resistance to oxidation were evaluated. RESULTS In dyslipidemic animals, Pomanox supplementation prevented diet-induced impairment of endothelial relaxation, reaching vasodilatory values comparable to normocholesterolemic animals upon stimulation with acetylcholine and/or calcium ionophore. These beneficial effects were associated with vascular Akt/endothelial nitric oxide-synthase activation and lower monocyte chemoattractant protein-1 expression. Pomanox supplementation reduced systemic oxidative stress (higher high-density lipoprotein-antioxidant capacity and higher low-density lipoprotein resistance to oxidation) and coronary deoxyribonucleic acid damage. Normocholesterolemic animals elicited similar drug-related vasodilation regardless of Pomanox supplementation. All animals displayed a similar vasodilatory response to sodium nitroprusside and L-NG-monomethylarginine blunted all vasorelaxation responses except for sodium nitroprusside. CONCLUSIONS Pomanox supplementation hinders hyperlipemia-induced coronary endothelial dysfunction by activating the Akt/endothelial nitric oxide-synthase pathway and favorably counteracting vascular inflammation and oxidative damage.

Spatio-kinematic modelling of Abell 65, a double-shelled planetary nebula with a binary central star

We present the first detailed spatio-kinematical analysis and modelling of the planetary nebula Abell 65, which is known to host a post-common envelope, binary, central star system. As such, this object is of great interest in studying the link between nebular morphology and central star binarity. [O III]5007 A and Hα+[N II]6584 A longslit spectra and imagery of Abell 65 were obtained with the Manchester Echelle Spectrometer on the 2.1-m telescope at the San Pedro Martir Observatory (MES-SPM). Further [O III]5007 A longslit spectra were obtained with the Ultraviolet and Visual Echelle Spectrograph on the Very Large Telescope (VLT-UVES). These data were used to develop a spatio-kinematical model for the [O III]5007 A emission from Abell 65. A ‘best-fitting’ model was found by comparing synthetic spectra and images rendered from the model to the data. The model comprises an outer shell and an inner shell, with kinematical ages of 15000 ± 5000 yr kpc−1 and 8000 ± 3000 yr kpc−1, respectively. Both shells have peanut-shaped bipolar structures with symmetry axes at inclinations of (55 ± 10)° (to the line of sight) for the outer shell and (68 ± 10)° for the inner shell. The near alignment between the nebular shells and the binary orbital inclination [of (68 ± 2)°] is strongly indicative that the binary is responsible for shaping the nebula. Abell 65 is one of a growing number of planetary nebulae (seven to date, including Abell 65 itself) for which observations and modelling support the shaping influence of a central binary.

THE DECELERATION OF NEBULAR SHELLS IN EVOLVED PLANETARY NEBULAE

We have selected a group of 100 evolved planetary nebulae (PNe) and study their kinematics based upon spatially-resolved, longslit, echelle spectroscopy. The data have been drawn from the San Pedro Martir Kinematic Catalogue of PNe (Lopez et al. 2012) with the aim of characterizing in detail the global kinematics of PNe at advanced stages of evolution with the largest sample of homogenous data used to date for this purpose.

Storm characterization and coastal hazards in the Yucatan Peninsula

ABSTRACT Mendoza, E.T., Trejo-Rangel., M. A., Salles, P., Appendini, C.M., Lopez-Gonzalez, J. and Torres-Freyermuth, A., 2013. Storm characterization and coastal vulnerability in the Yucatan Peninsula A preliminary coastal hazard potential assessment due to storm impacts in terms of erosion and flooding for the Yucatan coast is presented. Firstly, a 30-year wave hindcast is employed in order to characterize the coastal storms by creating a 5-class storm scale in terms of wave information. Subsequently, the storm classification is converted to one based on the consequences over 26 beach profile sections located along the Yucatan coast. The storm consequences were classified according to their flood and erosion potential by means of parametric and numerical model results which are correlated with key beach characteristics such as beach width and maximum beach height. According to the obtained results, the storms were characterized in five different categories and it was found that the Yucatan coast presents higher threat to flood than to erosion during the impact of storms.

Photoionized gaseous nebulae and magnetized stellar winds: The evolution and shaping of H II regions and planetary nebulae

The early evolution of hydrogen+ (H II) regions is controlled by the properties of the star-forming cloud cores. The observed density distributions in some young H II regions indicate that the power-law stratifications can be steeper than r−2. Ionization fronts can overrun these gradients and the ionized outflows are strongly accelerated along these steep density distributions. Thus, photoionized regions can either reach pressure equilibrium inside the inner parts of the high-pressure cores [with sizes and densities similar to those observed in ultra compact (UC) H II regions], or create bright H II regions with extended emission. The density inhomogeneities engulfed within the ionization fronts create corrugations in the front, which in turn drive instabilities in the ionization-shock (I-S) front. These instabilities grow on short time scales and lead to the fragmentation of the dense shells generated by the shock fronts. Thus, new clumps are continuously created from the fragmented shell, and the result...

The multi-polar planetary nebula NGC 5189

NGC 5189 is a particularly interesting planetary nebula (PN) displaying multiple bipolar structures. This type of morphology is generally attributed to multiple mass loss events believed to originate from a precessing central source. In order to better understand this, once dubbed chaotic PN, we have investigated optical imaging combined with low- and high- resolution spectroscopic data to dissect its components. The imaging reveals three and possibly four well defined bipolar lobes showing a misalignment with respect to the central torus, although sharing the same geometric center. The high nitrogen levels detected in the elongated filaments/condensations surrounding the nebula and at the torus location highlight the presence of low ionization structures as well as the possible occurrence of shocks in the areas perturbed by large dynamical motions. Finally the kinematical study indicates moderate expansion velocities (35 km.s−1 in the western lobe, 33 km.s−1 in the central region and 44 km.s−1 in the eastern lobe). We also notice the asymmetry of the [NII] distribution and the velocities inside NGC 5189 between its North-West and South-East components.

The Value of an Intervention for Improving Secondary Prevention in Patients Undergoing Cardiac Surgery

Given that treatment for secondary prevention in patients undergoing cardiac surgery is underused, we devised a hospital intervention to increase its implementation. The intervention involved all physicians in the department of cardiac surgery agreeing to complete a report on each patient before hospital discharge. The document recorded the indications for the recommended treatments, and prompted for details of the drugs prescribed, the doses used, the reasons for not prescribing the recommended drugs, if that was the case, and the use of alternative medicines. The efficacy of the intervention was evaluated by comparing the rate of drug use in the year in which it was introduced (2003, n=341) with retrospective data on the rate in the previous year (n=369). The rates of use of aspirin, statins, angiotensin-converting enzyme inhibitors, and beta-blockers by patients who required them all showed an absolute increase, of 13.4%, 38.3%, 21.8%, and 21.5%, respectively. In conclusion, the introduction of a simple and inexpensive intervention was able to significantly increase the use of drugs for secondary prevention in patients undergoing cardiac surgery.