Theory of Stellar Oscillations

In recent years, astronomers have witnessed major progresses in the field of stellar physics. This was made possible thanks to the combination of a solid theoretical understanding of the phenomena of stellar pulsations and the availability of a tremendous amount of exquisite space-based asteroseismic data. In this context, this chapter reviews the basic theory of stellar pulsations, considering small, adiabatic perturbations to a static, spherically symmetric equilibrium. It starts with a brief discussion of the solar oscillation spectrum, followed by the setting of the theoretical problem, including the presentation of the equations of hydrodynamics, their perturbation, and a discussion of the functional form of the solutions. Emphasis is put on the physical properties of the different types of modes, in particular acoustic (p-) and gravity (g-) modes and their propagation cavities. The surface (f-) mode solutions are also discussed. While not attempting to be comprehensive, it is hoped that the summary presented in this chapter addresses the most important theoretical aspects that are required for a solid start in stellar pulsations research.Comment: Lecture presented at the IVth Azores International Advanced School in Space Sciences on "Asteroseismology and Exoplanets: Listening to the Stars and Searching for New Worlds" (arXiv:1709.00645), which took place in Horta, Azores Islands, Portugal in July 201

An Introduction to Data Analysis in Asteroseismology

A practical guide is presented to some of the main data analysis concepts and techniques employed contemporarily in the asteroseismic study of stars exhibiting solar-like oscillations. The subjects of digital signal processing and spectral analysis are introduced first. These concern the acquisition of continuous physical signals to be subsequently digitally analyzed. A number of specific concepts and techniques relevant to asteroseismology are then presented as we follow the typical workflow of the data analysis process, namely, the extraction of global asteroseismic parameters and individual mode parameters (also known as peak-bagging) from the oscillation spectrum.Comment: Lecture presented at the IVth Azores International Advanced School in Space Sciences on "Asteroseismology and Exoplanets: Listening to the Stars and Searching for New Worlds" (arXiv:1709.00645), which took place in Horta, Azores Islands, Portugal in July 201

Kepler-22b: A 2.4 Earth-radius Planet in the Habitable Zone of a Sun-like Star

A search of the time-series photometry from NASA's Kepler spacecraft reveals a transiting planet candidate orbiting the 11th magnitude G5 dwarf KIC 10593626 with a period of 290 days. The characteristics of the host star are well constrained by high-resolution spectroscopy combined with an asteroseismic analysis of the Kepler photometry, leading to an estimated mass and radius of 0.970 +/- 0.060 MSun and 0.979 +/- 0.020 RSun. The depth of 492 +/- 10ppm for the three observed transits yields a radius of 2.38 +/- 0.13 REarth for the planet. The system passes a battery of tests for false positives, including reconnaissance spectroscopy, high-resolution imaging, and centroid motion. A full BLENDER analysis provides further validation of the planet interpretation by showing that contamination of the target by an eclipsing system would rarely mimic the observed shape of the transits. The final validation of the planet is provided by 16 radial velocities obtained with HIRES on Keck 1 over a one year span. Although the velocities do not lead to a reliable orbit and mass determination, they are able to constrain the mass to a 3{\sigma} upper limit of 124 MEarth, safely in the regime of planetary masses, thus earning the designation Kepler-22b. The radiative equilibrium temperature is 262K for a planet in Kepler-22b's orbit. Although there is no evidence that Kepler-22b is a rocky planet, it is the first confirmed planet with a measured radius to orbit in the Habitable Zone of any star other than the Sun.Comment: Accepted to Ap

Accurate fundamental parameters and detailed abundance patterns from spectroscopy of 93 solar-type Kepler targets

We present a detailed spectroscopic study of 93 solar-type stars that are targets of the NASA/Kepler mission and provide detailed chemical composition of each target. We find that the overall metallicity is well-represented by Fe lines. Relative abundances of light elements (CNO) and alpha-elements are generally higher for low-metallicity stars. Our spectroscopic analysis benefits from the accurately measured surface gravity from the asteroseismic analysis of the Kepler light curves. The log g parameter is known to better than 0.03 dex and is held fixed in the analysis. We compare our Teff determination with a recent colour calibration of V-K (TYCHO V magnitude minus 2MASS Ks magnitude) and find very good agreement and a scatter of only 80 K, showing that for other nearby Kepler targets this index can be used. The asteroseismic log g values agree very well with the classical determination using Fe1-Fe2 balance, although we find a small systematic offset of 0.08 dex (asteroseismic log g values are lower). The abundance patterns of metals, alpha elements, and the light elements (CNO) show that a simple scaling by [Fe/H] is adequate to represent the metallicity of the stars, except for the stars with metallicity below -0.3, where alpha-enhancement becomes important. However, this is only important for a very small fraction of the Kepler sample. We therefore recommend that a simple scaling with [Fe/H] be employed in the asteroseismic analyses of large ensembles of solar-type stars.Comment: MNRAS, in press, 12 page

Malignant islet-cell tumors of the pancreas

Although malignant islet-cell tumors are uncommon, they are an important group of pancreatic neoplasms because appropriate treatment can often result in effective palliation even though cure is infrequent. In general, these tumors are relatively slow growing so that a combination of surgical and chemotherapeutic measures may prove very beneficial. In some patients with tumors hypersecreting insulin, gastrin, glucagon, or vasoactive intestinal polypeptide (VIP), the hormonal effects of the neoplasm can be life-threatening. Surgical treatment must, therefore, consider both the functional and malignant characteristics of the individual tumor. In many patients with functional tumors, surgical debulking of the primary tumor may be indicated even when a curative resection cannot be accomplished. Some malignancies may be cured by an appropriate pancreatic resection even when peripancreatic lymph nodes are already involved. Although a Whipple procedure is not indicated when hepatic metastases are present, this procedure may cure tumors localized to the pancreatic head and/or peripancreatic lymph nodes. Because hepatic metastases are usually multiple and involve both lobes, liver resections, other than wedge excisions of peripherally located functional metastases, are not indicated. Malignant nonfunctioning islet-cell tumors are probably best treated with systemic or regional chemotherapy when metastatic. Surgical resections or bypass procedures may be infrequently useful in those cases in which the primary tumor causes either duodenal or bile duct obstruction. The most effective methods used to control hepatic metastases are systemic and hepatic arterial chemotherapy. An alternative is selective hepatic artery embolization. Recently, an implantable hepatic arterial infusion pump has been used with encouraging results in this group of patients. The chemotherapeutic agents that have been most effective in the treatment of hepatic metastases include streptozotocin, DTIC, and fluorouracil . Les tumeurs insulaires malignes sont rares mais elles présentent un grand intérêt car si le traitement entraîne exceptionnellement leur guérison il assure une survie des malades qui en sont porteurs. Ce sont en effet des tumeurs malignes à développement lent, sensibles à l'action de l'association de la chimiothérapie et de la chirurgie. Chez certains sujets les tumeurs secrétant de l'insuline, de la gastrine, du glucagon, du V.I.P. peuvent mettre en jeu la vie du malade sous l'effet de l'hypersecrétion hormonale. Le traitement chirurgical dépend de ce fait, des caractères fonctionnels et du degré de malignité de chaque type de tumeur. En présence de lésions hypersecrétantes l'exérèse de la tumeur primitive doit être envisagée alors même que la possibilité d'obtenir une guérison définitive ne peut être escomptée. Il est aussi à noter que certaines lésions malignes ont été traitées avec succès alors que les ganglions lymphatiques correspondants étaient déjà envahis. Si l'opération est contre-indiquée en présence de métastases hépatiques la duodénopancréatectomie céphalique s'applique aux tumeurs insulaires céphaliques qu'elles s'accompagnent ou non d'un envahissement des ganglions juxta-pancréatiques. Du fait que les métastases hépatiques sont souvent multiples et qu'elles intéressent les deux lobes l'action sur le foie se limite à l'éxérèse des métastases accessibles à la résection hépatique segmentaire. Les tumeurs insulaires malignes qui ne sont pas hypersecrétantes relèvent de la chimiothérapie par voie générale ou de la chimiothérapie régionale dès lors qu'elles s'accompagnent de métastases. C'est seulement lorsque ces lésions entraînent une obstruction de la voie biliaire principale ou du duodénum que la résection ou les anastomoses de dérivation sont indiquées. La chimiothérapie par voie générale ou par la voie de l'artère hépatique ou encore l'embolisation de cette dernière représentent les meilleures méthodes de traitement des métastases hépatiques. L'emploi récent de pompes à infusion de l'artère hépatique a donné des résultats intéressants chez ces malades. Les agents chimiques les plus efficaces sont la streptozotocine, le DTIC et le Fluorouracil. Aunque los tumores malignos de células insulares del páncreas son raros, éstos constituyen un grupo importante entre las neoplasias pancreáticas por cuanto el tratamiento apropiado con frecuencia resulta en una paliación efectiva a pesar de que la curación sea poco frecuente. En general estos tumores son de crecimiento lento y la combinación de la cirugía con quimioterapia puede llegar a ser beneficiosa. En algunos pacientes con tumores que hipersecretan insulina, gastrina, glucagón o VIP (polipéptido vasoactivo intestinal), los efectos hormonales del neoplasma pueden poner en peligro la vida. Por ello el tratamiento quirúrgico debe considerar tanto las caracteristicas funcionales como las de malignidad de cada tumor en particular. En muchos pacientes con neoplasmas funcionantes, el debultamiento quirúrgico del tumor primario puede estar indicado cuando la resección curativa no es realizable. Algunas neoplasias malignas pueden ser curadas mediante una resección pancreática adecuada a pesar de que los ganglios linfáticos peripancreáticos ya se hallen afectados. Aún cuando el procedimiento de Whipple no esta indicado en presencia de metástasis hepáticas, esta operación puede curar tumores localizados en la cabeza del páncreas y/o en los ganglios linfáticos peripancreáticos. Debido a que las metástasis hepáticas generalmente son múlitples y afectan a ambos lóbulos, las resecciones hepáticas, diferentes de las resecciones en cuña para lesiones funcionantes localizadas en la periferie del higado no están indicadas. Los tumores malignos no funcionantes de células insulares probablemente deben ser tratadas con quimioterapia sistémica o regional cuando se encuentren en fase metastásica. Las resecciones quirúrgicas o los procedimientos derivativos infrecuentemente son de utilidad en aquellos casos en los cuales el tumor primario causa obstrucción duodenal o del conducto biliar. Los métodos de mayor efectividad en el control de las metéstasis hepáticas son los de quimioterapia sistémica y arterial hepática. Una alternativa es la embolización selectiva de la arteria hepática. Recientemente ha venido a ser utilizada una bomba implantable de infusión arterial heptica con resultados halagadores en este grupo de pacientes. Los agentes quimioterapéuticos que han probado ser de mayor efectividad en el tratamiento de las metástasis hepáticas incluyen la estreptozotocina, la dimetiltrizenoimidazol carboxamida (DTIC) y el Fluorouracilo.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/41316/1/268_2005_Article_BF01656036.pd

Perspectives in Global Helioseismology, and the Road Ahead

We review the impact of global helioseismology on key questions concerning the internal structure and dynamics of the Sun, and consider the exciting challenges the field faces as it enters a fourth decade of science exploitation. We do so with an eye on the past, looking at the perspectives global helioseismology offered in its earlier phases, in particular the mid-to-late 1970s and the 1980s. We look at how modern, higher-quality, longer datasets coupled with new developments in analysis, have altered, refined, and changed some of those perspectives, and opened others that were not previously available for study. We finish by discussing outstanding challenges and questions for the field.Comment: Invited review; to appear in Solar Physics (24 pages, 6 figures

Oscillation mode linewidths of main-sequence and subgiant stars observed by Kepler

International audienc