X-rays from planetary nebulae: Unveiling wind collisions and binarity

Planetary nebulae (PNe), the ionized, ejected envelopes of low- to intermediate-mass stars, are thought to be shaped by a nascent fast wind from the spent core (a future white dwarf) that collides with and sweeps up previously ejected material (red and asymptotic branch giant winds). This collision can generate an X-ray emitting hot bubble that fills the swept-up cavity. Circumstellar material in a dense torus or disk, likely due to an interacting binary in the PN nucleus, is widely believed to collimate the winds that shape non-spherical PNe. Hence, PNe offer excellent opportunities to study astrophysical shocks and binary interactions. In my thesis, I address these topics via a comprehensive analysis of new and archival (pointed and serendipitous) X-ray observations performed by Chandra and XMM-Newton X-ray satellite observatories. This analysis yields new information on the X-ray characteristics (detections and non-detections) of over 50 PNe (~40% of which were detected). Based on spatial/spectral analysis of a dozen diffuse X-ray emitting PNe, I confirm that hot bubble temperatures are generally much lower than predicted by simple shock models given measured central star fast wind velocities. Comparison of the X-ray emission and central star properties of the sample PNe with the predictions of heat conduction models indicates that some hot bubbles are regulated by heat conduction, while others appear to require alternative temperature-regulating mechanisms. From new detections of point-like hard X-ray emission from the binary star nuclei of LoTr5, DS1, and HFG1, I demonstrate that the X-ray emission most likely arises from rejuvenated coronae around the spun-up companions in these systems. These results place constraints on putative spun-up binary companions within other PNe in which point-like central sources have gone undetected by XMM and/or Chandra. I conclude with suggestions as to the most promising directions for future X-ray observations of PNe

A Catalog of GALEX Ultraviolet Emission from Asymptotic Giant Branch Stars

We have performed a comprehensive study of the UV emission detected from AGB stars by the Galaxy Evolution Explorer (GALEX). Of the 468 AGB stars in our sample, 316 were observed by GALEX. In the NUV bandpass ($\lambda_{\rm eff} \sim 2310$z A), 179 AGB stars were detected and 137 were not detected. Only 38 AGB stars were detected in the FUV bandpass ($\lambda_{\rm eff} \sim1528$ A). We find that NUV emission is correlated with optical to near infrared emission leading to higher detection fractions among the brightest, hence closest, AGB stars. Comparing the AGB time-variable visible phased light curves to corresponding GALEX NUV phased light curves we find evidence that for some AGB stars the NUV emission varies in phase with the visible light curves. We also find evidence that the NUV emission, and possibly, the FUV emission are anti-correlated with the circumstellar envelope density. These results suggest that the origin of the GALEX-detected UV emission is an inherent characteristic of the AGB stars that can most likely be traced to a combination of photospheric and chromospheric emission. In most cases, UV detections of AGB stars are not likely to be indicative of the presence of binary companions.Comment: Accepted by ApJ; go spurs go

Transplante de microbiota fecal

Dissertação para obtenção do grau de Mestre no Instituto Universitário Egas MonizO microbiota intestinal refere-se ao conjunto de bactérias alojadas no trato gastrointestinal que interagem de vários mecanismos complexos. A perturbação deste verdadeiro ecossistema está na base de várias doenças entéricas sendo a infeção por Clostridium difficile a mais estudada. A modulação dos microbiotas intestinais surge assim como arma terapêutica potencial e tem sido objetivo de numerosos estudos nesse sentido. Entre as várias formas de modulação da microbiota intestinal esta transplantação fecal, uma técnica recente que consiste na introdução de material fecal proveniente de um dador saudável no trato gastrointestinal do doente. Este procedimento implica uma escolha criteriosa do dador, colheita e manipulação adequadas de material fecal, preparação do recetor e administração do conteúdo preparado. Esta revisão foca se sobretudo na modulação do microbiota pela transplantação fecal, com especial enfoque na forma como exerce o seu efeito, nos campos de aplicação da técnica e em todo o procedimento que a transplantação implica, sem esquecer os efeitos adversos e riscos que comporta. E também uma perspetiva da evolução futura da transplantação fecal.The intestinal microbiota refers to the bacteria present in the gastrointestinal tract that interact through several complex mechanisms. The disruption of this truly ecosystem is the basis of many enteric diseases of which the infection by Clostridium difficile the most studied. Therefore, the modulation of intestinal microbiota emerges as a potential therapeutic weapon and has been the subject of many studies. Fecal transplantation is one way amongst others to modulate the intestinal microbiota, a recent technique involving the introduction of fecal material from the gastrointestinal tract of a healthy donor to the tract of the patient. This procedure involves a careful selection of the donor, collection and handling of fecal material, preparation of the recipient and administration of the content previously prepared. This review focuses mostly in the modulation of the microbiota by the fecal transplantation with special regardon how exerts its effects, the fields of application of this technique and the whole procedure involved in the transplantation, without forgetting its adverse effects and its risks. The expected evolution of the fecal transplantation is also mentioned

A New Radio Molecular Line Survey of Planetary Nebulae: HNC/HCN as a Diagnostic of Ultraviolet Irradiation

Certain planetary nebulae contain shells, filaments, or globules of cold gas and dust whose heating and chemistry are likely driven by UV and X-ray emission from their central stars and from wind-collision-generated shocks. We present the results of a survey of molecular line emission in the 88-236 GHz range from nine nearby (<1.5 kpc) planetary nebulae spanning a range of UV and X-ray luminosities, using the 30 m telescope of the Institut de Radioastronomie Millimetrique. Rotational transitions of thirteen molecules, including CO isotopologues and chemically important trace species, were observed and the results compared with and augmented by previous studies of molecular gas in PNe. Lines of the molecules HCO+, HNC, HCN, and CN, which were detected in most objects, represent new detections for five planetary nebulae in our study. Specifically, we present the first detections of 13CO (1-0, 2-1), HCO+, CN, HCN, and HNC in NGC 6445; HCO+ in BD+303639; 13CO (2-1), CN, HCN, and HNC in NGC 6853; and 13CO (2-1) and CN in NGC 6772. Flux ratios were analyzed to identify correlations between the central star and/or nebular UV and X-ray luminosities and the molecular chemistries of the nebulae. This analysis reveals a surprisingly robust dependence of the HNC/HCN line ratio on PN central star UV luminosity. There exists no such clear correlation between PN X-rays and various diagnostics of PN molecular chemistry. The correlation between HNC/HCN ratio and central star UV luminosity demonstrates the potential of molecular emission line studies of PNe for improving our understanding of the role that high-energy radiation plays in the heating and chemistry of photodissociation regions.Comment: 17 pages, 17 figures, 6 tables, accepted for publication in Astronomy & Astrophysic

Serendipitous Chandra X-ray Detection of a Hot Bubble within the Planetary Nebula NGC 5315

We report the serendipitous detection of the planetary nebula NGC 5315 by the Chandra X-ray Observatory. The Chandra imaging spectroscopy results indicate that the X-rays from this PN, which harbors a Wolf-Rayet (WR) central star, emanate from a TX 2.5 × 106 K plasma generated via the same wind collisions that have cleared a compact ( 8000 AU radius) central cavity within the nebula. The inferred X-ray luminosity of NGC 5315 is 2.5 × 1032 erg s−1 (0.3-2.0 keV), placing this object among the most luminous such “hot bubble” X-ray sources yet detected within PNe. With the X-ray detection of NGC 5315, objects with WR-type central stars now constitute a clear majority – 2 – of known examples of diffuse X-ray sources among PNe; all such “hot bubble” PN X-ray sources display well-defined, quasi-continuous optical rims. We therefore assert that X-ray-luminous hot bubbles are characteristic of young PNe with large central star wind kinetic energies and closed bubble morphologies. However, the evidence at hand also suggests that processes such as wind and bubble temporal evolution, as well as heat conduction and/or mixing of hot bubble and nebular gas, ultimately govern the luminosity and temperature of superheated plasma within PNe

Limits on the HI content of the dwarf galaxy Hydra II

Sensitive 21cm HI observations have been made with the Green Bank Telescope toward the newly-discovered Local Group dwarf galaxy Hydra II, which may lie within the leading arm of the Magellanic Stream. No neutral hydrogen was detected. Our 5-sigma limit of MHI < 210 solar masses for a 15 km/s linewidth gives a gas-to-luminosity ratio MHI/L_V < 2.6 x 10^{-2} Mo / Lo. The limits on HI mass and MHI/L_V are typical of dwarf galaxies found within a few hundred kpc of the Milky Way. Whatever the origin of Hydra II, its neutral gas properties are not unusual.Comment: Accepted for publication in Astronomy & Astrophysic