Do Hydrogen-Deficient Carbon Stars Have Winds?

We present high resolution spectra of the five known hydrogen-deficient carbon (HdC) stars in the vicinity of the 10830 angstrom line of neutral helium. In R Coronae Borealis (RCB) stars the He I line is known to be strong and broad, often with a P Cygni profile, and must be formed in the powerful winds of those stars. RCB stars have similar chemical abundances as HdC stars and also share greatly enhanced O-18 abundances with them, indicating a common origin for these two classes of stars, which has been suggested to be white dwarf mergers. A narrow He I absorption line may be present in the hotter HdC stars, but no line is seen in the cooler stars, and no evidence for a wind is found in any of them. The presence of wind lines in the RCB stars is strongly correlated with dust formation episodes so the absence of wind lines in the HdC stars, which do not make dust, is as expected.NSFScience and Technology FacilitiesCouncilthe National Research CouncilCONICYTAustralian Research CouncilMinistﾴerio da Ciﾴencia e TecnologiaSECYTMcDonald Observator

On the binary helium star DY Centauri: Chemical composition and evolutionary state

DY Cen has shown a steady fading of its visual light by about 1 magnitude in the last 40 years suggesting a secular increase in its effective temperature. We have conducted non-LTE and LTE abundance analyses to determine the star's effective temperature, surface gravity, and chemical composition using high-resolution spectra obtained over two decades. The derived stellar parameters for three epochs suggest that DY Cen has evolved at a constant luminosity and has become hotter by about 5000 K in 23 years. We show that the derived abundances remain unchanged for the three epochs. The derived abundances of the key elements, including F and Ne, are as observed for the extreme helium stars resulting from a merger of an He white dwarf with a C-O white dwarf. Thus, DY Cen by chemical composition appears to be also a product of a merger of two white dwarfs. This appearance seems to be at odds with the recent suggestion that DY Cen is a single-lined spectroscopic binary.Comment: Accepted to ApJ with 8 Figures and 5 Table

Buckling of elastic circular plates with an elastically restrained edges against rotation and internal elastic ring support

The buckling of elastic circular plates with an internal elastic ring support and elastically restrained edges against rotation and simply supported is concerned. The classical plate theory is used to derive the governing differential equation. This work presents the existence of buckling mode switching with respect to the radius of internal elastic ring support. The plate may buckle in an axisymmetric mode in general, but when the radius of the ring support becomes small, the plate may buckle in an asymmetric mode. The cross-over ring support radius varies from 0.09891 to 0.1545 times the plate radius, depending on the rotational stiffness of the elastic restraint at the edges and elastic restraint of the ring. The optimum radius of the internal elastic ring support for maximum buckling load is also determined. Extensive data is tabulated so that pertinent conclusions can be arrived at on the influence of rotational restraint, translational restraint of internal elastic ring support, Poisson’s ratio, and other boundary conditions on the buckling of uniform isotropic circular plates. The numerical results obtained are in good agreement with the previously published data.Розглянуто випучування пружної круглої пластинки з внутрішнім кріпленням у вигляді пружного кільця і зовнішньою границею, яка обмежує пружне обертання і є вільно опертою. Виведено диференціальні рівняння, що описують задачу, для чого використано класичну теорію пластинок. Запропоновано доведення існування перемикання на моду випучування в залежності від радіуса внутрішнього кільця. Пластинка може випучуватися, взагалі кажучи, за осесиметричною модою, але для малого радіуса кільця пластинка може випучуватися за неосесиметричною модою. Перехідне значення відношення радіуса кільця до радіуса пластинки змінюється від 0,9891 до 0,1545 в залежності від жорсткості кільця і обмеження на обертання на зовнішній границі пластинки. Також визначено максимальний радіус кільця, пов'язаний з максимальним значенням навантаження. Числові дані згруповані таким чином, що вони дозволяють зробити висновки щодо впливу обмеження на обертання, обмеження на поступальний рух кільця, коефіцієнта Пуассона та інших граничних умов на випучування однорідної круглої пластинки. Отримані числові результати добре узгоджуються з даними, опублікованими раніше

Analysis of Vibration Natural Frequencies of Rotationally Restrained and Simply Supported Circular Plate with Weakened Interior Circle Due to an Angular Crack

Получено точное решение для описания колебаний шарнирно закрепленной по внешнему краю круговой пластины с ограничением по вращению, которая ослаблена круговой трещиной. Рассчитаны частоты шести первых мод колебаний пластины для различных значений упругих характеристик шарнирного защемления, радиуса круговой трещины и степени ослабления пластины трещиной. Наличие трещины моделируется в виде фиктивного упругого закрепления пластины по линии трещины. Показано, что ослабление пластины трещиной приводит к снижению собственной частоты колебаний на 30%. Предполагается, что использование результатов точного решения является перспективным при оценке влияния трещины на колебания круговой пластины с внешним шарнирным закреплением и ограничением по вращению и верификации данных, полученных приближенными численными методами, включая метод конечных элементов.Отримано точний розв’язок для опису коливань шарнірно закріпленої по зовнішньому краю кругової пластини з обмеженням по обертанню, яка послаблена круговою тріщиною. Розраховано частоти шести перших мод коливань пластини для різних значень пружних характеристик шарнірного затиснення, радіуса кругової тріщини та міри послаблення пластини тріщиною. Наявність тріщини моделюється у вигляді фіктивного пружного закріплення пластини по лінії тріщини. Показано, що послаблення пластини тріщиною призводить до зниження власної частоти коливань на 30%. Припускається, що використання результатів точного розв’язку є перспективним при оцінці впливу тріщини на коливання кругової пластини із зовнішнім шарнірним закріпленням і обмеженням по обертанню та верифікації даних, що отримані наближеними числовими методами, включаючи з метод скінченних елементів

Studies on lead-zinc mineralization in Karempudi area, Guntur District, Andhra Pradesh

The geological formations near Karempudi area in Guntur District of Andhra Pradesh (Lat. 16°20' and 16°26'; Long. 79° 38'40" and 79°45') consist of slaty shales of Cumbum, Irlakonda quartzites, Kolumnala slates and shales with intercalations of siliceous dolomitic limestones and Sreesailam quartzites of Krishna Series, forming a perfect conformable sequence, all the formations striking N.E.-S.W. and dipping on average 25°S.E. The Srisailam quartzites are overlaid unconformably by Palnad limestones (Narjis) of Jammalamadugu stage of Kurnool Series with a constant dip of 8-12° in the same direction. The Krishna Series were subjected to local but intense structural disturbances resulting in an overfold. Subsequent to the overfolding, lead mineralization has taken place in dolomitic limestones. The lead-zinc minerals of Karempudi consist of Galena, Sphalerite, Jamesonite, Tetrahedrite as primary minerals, and Anglesite as secondary mineral; there is association of chalcopyrite with Sphalerite. The textures are due to replacement and unmixing. The paragenetic sequence of the minerals is established to be sphalerite, chalcopyrite, galena, jamesonite, tetrahedrite and anglesite. Correlation of field to laboratory studies revealed that the minerals are of hydrothermal (hypogene) origin. The structural and lithological favourability and controlling of the mineralisation are also explained. Anglesite owes its origin to the oxidation of galena due to air-water processes. The mineralization is surmised to have taken place in Pre-Palnads and Post-Krishna times

The Hot R Coronae Borealis Star DY Centauri is a Binary

The remarkable hot R Coronae Borealis (RCB) star DY Cen is revealed to be the first and only binary system to be found among the RCB stars and their likely relatives, including the extreme helium stars and the hydrogen-deficient carbon stars. Radial velocity determinations from 1982 to 2010 have shown that DY Cen is a single-lined spectroscopic binary in an eccentric orbit with a period of 39.67 days. It is also one of the hottest and most H-rich member of the class of RCB stars. The system may have evolved from a common envelope to its current form.Spanish Ministry of Economy and Competitiveness AYA-2011-27754McDonald Observator

Abundance analyses of cool extreme helium stars

Extreme helium stars (EHe) with effective temperatures from 8000K to 13000K are among the coolest EHe stars and overlap the hotter R CrB stars in effective temperature. The cool EHes may represent an evolutionary link between the hot EHes and the R CrBs. Abundance analyses of four cool EHes are presented. To test for an evolutionary connection, the chemical compositions of cool EHes are compared with those of hot EHes and R CrBs. Relative to Fe, the N abundance of these stars is intermediate between those of hot EHes and R CrBs. For the R CrBs, the metallicity M derived from the mean of Si and S appears to be more consistent with the kinematics than that derived from Fe. When metallicity M derived from Si and S replaces Fe, the observed N abundances of EHes and R CrBs fall at or below the upper limit corresponding to thorough conversion of initial C and O to N. There is an apparent difference between the composition of R CrBs and EHes; the former having systematically higher [N/M] ratios. The material present in the atmospheres of many R CrBs is heavily CN- and ON-cycled. Most of the EHes have only CN-cycled material in their atmospheres. There is an indication that the CN- and ON-cycled N in EHes was partially converted to Ne by $\alpha$-captures. If EHes are to evolve to R CrBs, fresh C in EHes has to be converted to N. If Ne is found to be normal in R CrBs, the proposal that EHes evolve to R CrBs fails. The idea that R CrBs evolve to EHes is ruled out; the N abundance in R CrBs has to be reduced to the level of EHes, as the C/He which is observed to be uniform across EHes, has to be maintained. Hence, the inferred [N/M], C/He, [Ne/M], and the H-abundances of these two groups indicate that the EHes and the R CrBs may not be on the same evolutionary path.Comment: 24 pages (MNRAS Journal style), 7 tables, 19 figures, Accepted for publication in MNRA

The 1995-1996 Decline of R Coronae Borealis - High Resolution Optical Spectroscopy

A set of high-resolution optical spectra of RCrB acquired before, during, and after its 1995-1996 decline is discussed. All of the components reported from earlier declines are seen. This novel dataset provides new information on these components including several aspects not previously seen in declines of RCrB and other RCBs. In the latter category is the discovery that the decline's onset is marked by distortions of absorption lines of high-excitation lines, and quickly followed by emission in these and in low excitation lines. This 'photospheric trigger' implies that dust causing the decline is formed close to the star. These emission lines fade quickly. After 1995 November 2, low excitation narrow (FWHM ~12 km s-1) emission lines remain. These appear to be a permanent feature, slightly blue-shifted from the systemic velocity, and unaffected by the decline except for a late and slight decrease of flux at minimum light. The location of the warm, dense gas providing these lines is uncertain. Absorption lines unaffected by overlying sharp emission are greatly broadened, weakened, and red-shifted at the faintest magnitudes when scattered light from the star is a greater contributor than direct light transmitted through the fresh soot cloud. A few broad lines are seen at and near minimum light with approxiamately constant flux: prominent among these are the He I triplet series, Na I D, and [N II] lines. These lines are blue-shifted by about 30 km s(-1) relative to the systemic velocity with no change in velocity over the several months for whicht he lines were seen. It is suggested that these lines, especially the He I lines, arise from an accretion disk around an unseen compact companion, which may be a low-mass white dwarf. If so, R CrB is similar to the unusual post-AGB star 89 Her.Comment: 31 pages, 26 figure

Evolution of the optical spectrum of SN 1987a in the large magellanic cloud

The evolution of the spectrum of SN1987a is traced from 1987 February 26 to March 31. Based on the low-resolution spectroscopic data we identify the lines of H, He I, Na I, Fe II, Sc II, Ca II which are known to be present in Type II Supernovae, and also present evidence for the existence of lines of Mg I, CaI, O I, and N I. We discuss the evolution of the Hα profile, and draw attention to its complex structure around March 30. Close to the rest wavelength of Ha a double-peaked structure appeared in the profile with a peak-to-peak separation of ~ 1400 km s−1, suggestive of an expanding shell or disc of gas. Using the available broadband photometric information, we also trace the evolution of the photosphere of SN1987a assuming that it radiates like a supergiant