Long-term evolution in ionization of ejecta illuminated by Eta Carinae

Changes in the flux and spectrum of Eta Carinae (η Car) since 1900 have been attributed to the evolution of the central binary by some. Others suggest evolution in the occulting ejecta. The brightness jump in the 1940s, which coincided with the appearance of narrow forbidden emission lines, may have been caused by the clearing and ionization of intervening circumstellar ejecta. The brightening changed at a slower pace up through 40 yr later. Here we continue earlier studies focused on the long-term, showing that the forbidden line emission increased in the early 1990s with no noticeable increase in the brightness of the Homunculus. We interpret that the increase in narrow-line emission is due to decreased extinction in the line of sight (LOS) from the central binary to the Weigelt clumps. In 2000, the central stellar core increased in brightness at a faster rate without associated changes in the Homunculus. By 2018, hundreds of narrow-line absorptions from singly ionized metals in our LOS from (η Car) disappeared, thought to be caused by increased ionization of metals. These three events (1990, 2000, and 2018) are explained by the dissipation of circumstellar material within the Homunculus close to the binary. Combining these changes with the steadiness of the Homunculus and the primary winds over the past four decades indicates that circumstellar ejecta in our direction have been cleared.Instituto de Astrofísica de La Plat

Ultraviolet Spectropolarimetry with Polstar: Massive Star Binary Colliding Winds

As sources of chemical enrichment, ionizing radiation and energetic feedback, massive stars drive the ecology of their host galaxies despite their relative rarity, additionally to yielding compact remnants, which can generate gravitational waves. The evolution of massive stars is crucially informed by their detailed mass-loss history; however, wind structures on a variety of scales cause important uncertainties on their mass-loss rates. Binary systems can place further constraints on the mass-loss properties of massive stars, especially colliding-wind binaries. In this paper, we review how the proposed MIDEX-scale mission Polstar can critically constrain the physics of colliding winds (and hence radiatively-driven winds in general) with ultraviolet spectropolarimetric observations, providing an unprecedented improvement on the accuracy of the determination of both mass-loss rates and the velocity structure of the winds of massive stars. We propose a sample of 17 targets that will allow us to study a variety of wind-colliding systems spanning a large parameter space using the spatial information yielded by both spectroscopic and polarimetric data obtained with Polstar

The Long-term Spectral Changes of Eta Carinae: Are they Caused by a Dissipating Occulter as Indicated by cmfgen Models?

Eta Carinae ( η Car) exhibits a unique set of P Cygni profiles with both broad and narrow components. Over many decades, the spectrum has changed—there has been an increase in observed continuum fluxes and a decrease in Fe ii and H i emission-line equivalent widths. The spectrum is evolving toward that of a P Cygni star such as P Cygni itself and HDE 316285. The spectral evolution has been attributed to intrinsic variations such as a decrease in the mass-loss rate of the primary star or differential evolution in a latitudinal-dependent stellar wind. However, intrinsic wind changes conflict with three observational results: the steady long-term bolometric luminosity; the repeating X-ray light curve over the binary period; and the constancy of the dust-scattered spectrum from the Homunculus. We extend previous work that showed a secular strengthening of P Cygni absorptions by adding more orbital cycles to overcome temporary instabilities and by examining more atomic transitions. cmfgen modeling of the primary wind shows that a time-decreasing mass-loss rate is not the best explanation for the observations. However, models with a small dissipating absorber in our line of sight can explain both the increase in brightness and changes in the emission and P Cygni absorption profiles. If the spectral evolution is caused by the dissipating circumstellar medium, and not by intrinsic changes in the binary, the dynamical timescale to recover from the Great Eruption is much less than a century, different from previous suggestions

Varieties of habitus and the embodiment of ballet

10.1177/1468794106068023Qualitative Research64535-55

Clinical practice guideline on diagnosis and treatment of hyponatraemia

Hyponatraemia, defined as a serum sodium concentration <135 mmol/l, is the most common disorder of body fluid and electrolyte balance encountered in clinical practice. It can lead to a wide spectrum of clinical symptoms, from subtle to severe or even life threatening, and is associated with increased mortality, morbidity and length of hospital stay in patients presenting with a range of conditions. Despite this, the management of patients remains problematic. The prevalence of hyponatraemia in widely different conditions and the fact that hyponatraemia is managed by clinicians with a broad variety of backgrounds have fostered diverse institution-and speciality-based approaches to diagnosis and treatment. To obtain a common and holistic view, the European Society of Intensive Care Medicine (ESICM), the European Society of Endocrinology (ESE) and the European Renal Association - European Dialysis and Transplant Association (ERA-EDTA), represented by European Renal Best Practice (ERBP), have developed the Clinical Practice Guideline on the diagnostic approach and treatment of hyponatraemia as a joint venture of three societies representing specialists with a natural interest in hyponatraemia. In addition to a rigorous approach to methodology and evaluation, we were keen to ensure that the document focused on patient-important outcomes and included utility for clinicians involved in everyday practice