scholarly journals Symbiotic Stars

1984 ◽  
Vol 80 ◽  
pp. 101-125
Author(s):  
David A. Allen
Keyword(s):  
Current Knowledge ◽  
Gas Flows ◽  
Symbiotic Stars ◽  
Single Star ◽  
Star Models ◽  
Activity Cycles ◽  
Optical Wavelengths ◽  
Orbital Periods ◽  
Future Work ◽  
Coherent Picture

AbstractI review our current knowledge of symbiotic stars. A great many papers have graced the literature in the fifty years of their study, and many data are available on the spectral variations at optical wavelengths these stars undergo. I do not give extensive references to those data, for previous reviews have done so quite adequately. Rather, I concentrate on the extensive widening of the wavebands within which symbiotic stars have been studied over the past few years, and attempt to synthesise the data into a coherent picture.Symbiotic stars are most readily explained as interacting binaries, though single star models may still be tenable for some systems. They are made much more complex than most other interacting binaries by the variety of accreting stars, and because gas flows may be highly structured. Moreover, their study is more difficult than that of dwarf novae because the orbital periods are long compared to the activity cycles of the accretion phenomena.Our data base has expanded enormously with our present spectral Catholicism. But there remains much valuable work to be done with even simple equipment on small telescopes. I suggest in a final section areas for future work.

scholarly journals Models for symbiotic stars in the light of the data

1982 ◽  
Vol 70 ◽  
pp. 253-267
Author(s):  
Michael Friedjung
Keyword(s):  
Accretion Disks ◽  
Radial Velocities ◽  
Symbiotic Stars ◽  
Single Star ◽  
Cool Component ◽  
Cool Star ◽  
Star Models ◽  
Excess Heating

AbstractDifferent single and binary models of symbiotic stars are examined. Single star models encounter a number of problems, and binary models are probable. There are however difficulties in the interpretation of radial velocities. Accretion disks play a role in some cases, but winds especially from the cool component must be taken into account in realistic models. There is some evidence of excess heating of the outer layers of the cool component. Outbursts may be related to sudden changes in the characteristics of the cool star wind.

scholarly journals The effects of surface fossil magnetic fields on massive star evolution: III. The case of τ Sco

2021 ◽  
Author(s):  
Z Keszthelyi ◽  
G Meynet ◽  
F Martins ◽  
A de Koter ◽  
A David-Uraz
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Massive Star ◽  
Slow Rotation ◽  
Single Star ◽  
Surface Magnetic Field ◽  
Fundamental Parameters ◽  
Chemical Enrichment ◽  
Star Models ◽  
Nitrogen Excess

Abstract τ Sco, a well-studied magnetic B-type star in the Uτer Sco association, has a number of surprising characteristics. It rotates very slowly and shows nitrogen excess. Its surface magnetic field is much more complex than a purely dipolar configuration which is unusual for a magnetic massive star. We employ the cmfgen radiative transfer code to determine the fundamental parameters and surface CNO and helium abundances. Then, we employ mesa and genec stellar evolution models accounting for the effects of surface magnetic fields. To reconcile τ Sco’s properties with single-star models, an increase is necessary in the efficiency of rotational mixing by a factor of 3 to 10 and in the efficiency of magnetic braking by a factor of 10. The spin down could be explained by assuming a magnetic field decay scenario. However, the simultaneous chemical enrichment challenges the single-star scenario. Previous works indeed suggested a stellar merger origin for τ Sco. However, the merger scenario also faces similar challenges as our magnetic single-star models to explain τ Sco’s simultaneous slow rotation and nitrogen excess. In conclusion, the single-star channel seems less likely and versatile to explain these discrepancies, while the merger scenario and other potential binary-evolution channels still require further assessment as to whether they may self-consistently explain the observables of τ Sco.

Radiation protection perspective to recurrent medical imaging: what is known and what more is needed?

2021 ◽  
pp. 20210477
Author(s):  
Jenia Vassileva ◽  
Ola Holmberg
Keyword(s):  
Radiation Protection ◽  
Current Knowledge ◽  
Clinical History ◽  
Patient Specific ◽  
Individual Radiosensitivity ◽  
Dose Saving ◽  
End Stage ◽  
Future Work ◽  
Standardised Patient

This review summarises the current knowledge about recurrent radiological imaging and associated cumulative doses to patients. The recent conservative estimates are for around 0.9 million patients globally who cumulate radiation doses above 100 mSv, where evidence exists for cancer risk elevation. Around one in five is estimated to be under the age of 50. Recurrent imaging is used for managing various health conditions and chronic diseases such as malignancies, trauma, end-stage kidney disease, cardiovascular diseases, Crohn’s disease, urolithiasis, cystic pulmonary disease. More studies are needed from different parts of the world to understand the magnitude and appropriateness. The analysis identified areas of future work to improve radiation protection of individuals who are submitted to frequent imaging. These include access to dose saving imaging technologies; improved imaging strategies and appropriateness process; specific optimisation tailored to the clinical condition and patient habitus; wider utilisation of the automatic exposure monitoring systems with an integrated option for individual exposure tracking in standardised patient-specific risk metrics; improved training and communication. The integration of the clinical and exposure history data will support improved knowledge about radiation risks from low doses and individual radiosensitivity. The radiation protection framework will need to respond to the challenge of recurrent imaging and high individual doses. The radiation protection perspective complements the clinical perspective, and the risk to benefit analysis must account holistically for all incidental and long-term benefits and risks for patients, their clinical history and specific needs. This is a step toward the patient-centric health care.

A Program for an Investigation of the Rudder-Torque Problem

1965 ◽  
Vol 2 (03) ◽  
pp. 282-298
Author(s):  
Karl E. Schoenherr
Keyword(s):  
Research Program ◽  
Current Knowledge ◽  
Lateral Force ◽  
The Status ◽  
The Subject ◽  
Future Work ◽  
Marine Engineers

Panel H-10 (Controllability) of The Society of Naval Architects and Marine Engineers Technical and Research Program was requested to undertake an investigation of existing uncertainties in pre-calculating rudder torque and lateral force. In order to become quickly familiar with the subject and prospects therein, the Panel commissioned the author of this paper to survey the status of current knowledge of the subject and prepare a report of the findings. In particular, this report was to identify the most promising approaches for future work leading to an ultimate solution of the problem and to include technical descriptions of proposed programs for an exhaustive investigation, all of which are discussed in this paper.

Periodic Variability on Time-scales of Decades to Centuries in Magnetic Ap Stars: Challenges and Strategies

2017 ◽  
Vol 14 (S339) ◽  
pp. 106-109
Author(s):  
G. Mathys
Keyword(s):  
Time Scales ◽  
Current Knowledge ◽  
Main Sequence Stars ◽  
Unique Challenge ◽  
Origin And Evolution ◽  
Rotation Periods ◽  
Orbital Periods ◽  
The One ◽  
Ap Stars ◽  
Incomplete Picture

AbstractRecent studies have revealed the existence of a significant population of Ap stars with extremely long rotation periods, and the frequent occurrence of Ap stars in wide binaries. Those results represent new constraints on the understanding of the origin and evolution of Ap stars, and (by extension) of all upper-main-sequence stars. Current knowledge of Ap stars with the longest rotation and orbital periods remains incomplete, on the one hand because in many cases the periods of interest are longer than the time-spans over which relevant observations have been obtained, and on the other hand because some important subsets of Ap stars have been omitted from the studies that have been carried out until now. Additional observations over time-scales of decades to centuries are needed to complement the current incomplete picture. Securing them with the required accuracy and time coverage, and ensuring that their full exploitation will ultimately be possible, represents a unique challenge in time-domain astronomy.

scholarly journals Carbon Depletion in Case B Mass Transfer Algol-Type Binaries

1992 ◽  
Vol 151 ◽  
pp. 355-358
Author(s):  
Tae S. Yoon ◽  
Kent Honeycutt
Keyword(s):  
Mass Transfer ◽  
Mass Loss ◽  
Similar Type ◽  
Single Star ◽  
Star Models ◽  
Promising Tool ◽  
Carbon Abundance ◽  
Processed Material ◽  
C And N ◽  
Larger Sample

The surface carbon abundances of Algol secondaries are known to be low compared to field stars of similar type. The C and N anomalies of these G and K subgiants are undoubtedly due to the exposure of CN cycle processed material as mass transfer removes the outer layers of the star. Therefore the carbon abundance is a promising tool for helping fix the evolutionary state of Algols, particularly the amount of mass which has been lost from the secondary. We report here the carbon abundance of 12 Algol secondaries as deduced from the g-band in spectra obtained during photometric totality. We compare the abundances to those from models of single stars of appropriate age and mass. The values of log ∊(C) for this sample fall 0.25–0.75 dex below field G and K giants, and 1.25–1.75 dex above “stripped” single star models. This larger sample supports the conclusions of Parthasarthy et al. regarding mixing and mass loss, which they deduced from a smaller sample of carbon abundances.

scholarly journals The GALAH survey: unresolved triple Sun-like stars discovered by the Gaia mission

2019 ◽  
Vol 487 (2) ◽  
pp. 2474-2490 ◽  
Author(s):  
Klemen Čotar ◽  
Tomaž Zwitter ◽  
Gregor Traven ◽  
Janez Kos ◽  
Martin Asplund ◽  
...  
Keyword(s):  
Correction Factor ◽  
Spectral Type ◽  
Triple System ◽  
Stellar System ◽  
Solar Spectrum ◽  
Data Driven ◽  
Single Star ◽  
Photometric And Spectroscopic Observations ◽  
Data Release ◽  
Orbital Periods

Abstract The latest Gaia data release enables us to accurately identify stars that are more luminous than would be expected on the basis of their spectral type and distance. During an investigation of the 329 best solar twin candidates uncovered among the spectra acquired by the GALAH survey, we identified 64 such overluminous stars. In order to investigate their exact composition, we developed a data-driven methodology that can generate a synthetic photometric signature and spectrum of a single star. By combining multiple such synthetic stars into an unresolved binary or triple system and comparing the results to the actual photometric and spectroscopic observations, we uncovered 6 definitive triple stellar system candidates and an additional 14 potential candidates whose combined spectrum mimics the solar spectrum. Considering the volume correction factor for a magnitude-limited survey, the fraction of probable unresolved triple stars with long orbital periods is ∼2 per cent. Possible orbital configurations of the candidates were investigated using the selection and observational limits. To validate the discovered multiplicity fraction, the same procedure was used to evaluate the multiplicity fraction of other stellar types.

scholarly journals Symbiotic Stars in the Magellanic Clouds

2004 ◽  
Vol 194 ◽  
pp. 33-34
Author(s):  
Joanna Mikołajewska
Keyword(s):  
Binary Systems ◽  
Milky Way ◽  
Magellanic Clouds ◽  
Symbiotic Stars ◽  
Orbital Periods

AbstractOrbital periods and other parameters of symbiotic binary systems in the LMC and SMC are presented and discussed. In particular, the symbiotic stars in the MCs are compared with those in the Milky Way.

“Undisturbed” Evolution in Binaries

1989 ◽  
Vol 8 ◽  
pp. 145-148
Author(s):  
J. Andersen
Keyword(s):  
Binary Systems ◽  
Single Star ◽  
Future Work

AbstractThe use of binary systems as tools for testing models for single-star (“undisturbed”) evolution is briefly reviewed. Recent successes and directions for future work are discussed.

Thèmes d'inquiétudes et tendance à s'inquiéter chez les aînés

1998 ◽  
Vol 17 (4) ◽  
pp. 361-371 ◽  
Author(s):  
Céline Doucet ◽  
Robert Ladouceur ◽  
Mark H. Freeston ◽  
Michel J. Dugas
Keyword(s):  
Older Adults ◽  
Current Knowledge ◽  
The Elderly ◽  
The Third ◽  
Penn State Worry Questionnaire ◽  
Penn State ◽  
State Worry ◽  
Future Work ◽  
Anxiety Questionnaire ◽  
Group 1

ABSTRACTThe present study examines worry themes and the tendency to worry in older adults. The sample, which is made up of 162 participants, is divided into three groups. The first group includes 47 participants aged from 55 to 64 years old (the youngest subjects). The second group consists of 56 participants aged from 65 to 74 years old. Finally, the third group includes 59 participants who are 75 years old or older (the oldest subjects). Participants completed the Worry and Anxiety Questionnaire, the Worry Domains Questionnaire for Older Adults and the Penn State Worry Questionnaire. For all subjects combined, the most frequently reported worry theme was health, followed by relationships with family and friends. The results show that participants in group 1 (the youngest subjects) worry more about their future, work and finances than those in the other two groups. The results also show that participants in the first two groups have a greater tendency to worry and report a greater number of worries than those in the third group (the oldest subjects). The study's findings are discussed in light of current knowledge of worry among the elderly.

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