Very slow classical Cepheids - Theoretical models with periods longer than 50 days

1984 ◽  
Vol 281 ◽  
pp. 811 ◽  
Author(s):  
T. R. Carson ◽  
R. B. Stothers
Keyword(s):  
Theoretical Models ◽  
Classical Cepheids

scholarly journals Theoretical Models of W Virginis Variables

1985 ◽  
Vol 82 ◽  
pp. 246-249
Author(s):  
Alan Bridger
Keyword(s):  
Theoretical Models ◽  
Stellar Mass ◽  
Theoretical Studies ◽  
Classical Cepheids

W Virginis variables are the population II counterparts of the classical cepheids, although they do not show quite the same trends as are seen in the latter. Theoretical studies of the population II cepheids have not been very extensive until recent studies of the shorter period variables (BL Herculis variables, with periods between 1 and 10 days). The variables with periods above 10 days (up to about 50 days) have only been studied by a few authors, modelling the prototype star (W Vir) (.g. Christy 1966; Davis 1974). Although these models qualitatively reproduced the observations they were not very successful, and were based on a stellar mass (0.88 Mʘ) that now seems likely to be too high.

scholarly journals Theoretical Models for Classical Cepheids. II. Period‐Luminosity, Period‐Color, and Period‐Luminosity‐Color Relations

1999 ◽  
Vol 512 (2) ◽  
pp. 711-723 ◽  
Author(s):  
Giuseppe Bono ◽  
Filippina Caputo ◽  
Vittorio Castellani ◽  
Marcella Marconi
Keyword(s):  
Theoretical Models ◽  
Classical Cepheids

scholarly journals Theoretical Models for Classical Cepheids: Mean Magnitudes and Colors and the Evaluation of Distance, Reddening and Metallicity

2000 ◽  
Vol 176 ◽  
pp. 338-342 ◽  
Author(s):  
Marcella Marconi ◽  
Filippina Caputo ◽  
Vincenzo Ripepi
Keyword(s):  
Theoretical Models ◽  
Host Galaxy ◽  
Filter Method ◽  
Chemical Compositions ◽  
Distance Modulus ◽  
Light Cycle ◽  
Classical Cepheids ◽  
A Minor ◽  
Minor Extent

AbstractWe present a detailed analysis of theoretical period–luminosity (PL) and period–luminosity–color (PLC) relations of classical Cepheids, as derived from nonlinear, nonlocal, time-dependent convective pulsating models with different masses and chemical compositions. The predicted PL and PLC relations turn out to depend on the pulsator metallicity and, to a minor extent, on the adopted averages (magnitude-weighted or intensity-weighted) over the light cycle in different bands. We show that the determination of the reddening and true distance modulus of a galaxy from the observed PL and PLC relations is constrained by the metallicity sensitivity of these relations. Moreover, the metallicity sensitivity itself provides us with a powerful tool for deriving self-consistent evaluations of distance, reddening and metallicity of the host galaxy, once Cepheid measurements in at least three photometric bands are available. To illustrate this point, we apply our relations to the BVK data for Cepheids in the Magellanic Clouds, assuming to be unaware of their metallicities. The three filter method is finally adopted to evaluate the metallicity of galactic Cepheids (BVI data) as a function of their position.

scholarly journals Surface Brightness Radii and Distances of Cepheids and the Period-Radius Relationship

1985 ◽  
Vol 82 ◽  
pp. 38-42
Author(s):  
W. P. Gieren
Keyword(s):  
Surface Brightness ◽  
Theoretical Models ◽  
Long Period ◽  
Classical Cepheids ◽  
Short Period ◽  
Absolute Magnitudes ◽  
Considerable Support

Recently Gieren (1984) has derived accurate radii and distances of a sample of short-period classical Cepheids using the surface brightness (SB) method introduced by Barnes & Evans (1976). The results indicated that the period-radius (P-R) relationship obtained from SB radii might possess a slope close to the value of 0.82 defined by the Cepheids in clusters and associations (Fernie, 1983) and in conflict with the values obtained from Baade-Wesselink radii and from theoretical models (see Fernie, 1983). Since this finding would lend considerable support to the presently accepted absolute magnitudes of the cluster Cepheids, it was decided to obtain SB radii and distances of well-observed long-period Cepheids in order to strengthen the P-R relationship obtained from the SB technique.

scholarly journals Detailed chemical composition of classical Cepheids in the LMC cluster NGC 1866 and in the field of the SMC

2017 ◽  
Vol 608 ◽  
pp. A85 ◽  
Author(s):  
B. Lemasle ◽  
M. A. T. Groenewegen ◽  
E. K. Grebel ◽  
G. Bono ◽  
G. Fiorentino ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Theoretical Models ◽  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
Main Body ◽  
Depth Direction ◽  
Classical Cepheids ◽  
Age Relations ◽  
First Time ◽  
Detailed Chemical

Context. Cepheids are excellent tracers of young stellar populations. They play a crucial role in astrophysics as standard candles. The chemistry of classical Cepheids in the Milky Way is now quite well-known, however despite a much larger sample, the chemical composition of Magellanic Cepheids has been only scarcely investigated. Aims. For the first time, we study the chemical composition of several Cepheids located in the same populous cluster: NGC 1866, in the Large Magellanic Cloud (LMC). To also investigate the chemical composition of Cepheids at lower metallicity, we look at four targets located in the Small Magellanic Cloud (SMC). Our sample allows us to increase the number of Cepheids with known metallicities in the LMC/SMC by 20%/25% and the number of Cepheids with detailed chemical composition in the LMC/SMC by 46%/50%. Methods. We use canonical spectroscopic analysis to determine the chemical composition of Cepheids and provide abundances for a good number of α, iron-peak, and neutron-capture elements. Results. We find that six Cepheids in the LMC cluster NGC 1866 have a very homogeneous chemical composition, also consistent with red giant branch (RGB) stars in the cluster. Period–age relations that include no or average rotation indicate that all the Cepheids in NGC 1866 have a similar age and therefore belong to the same stellar population. Our results are in good agreement with theoretical models accounting for luminosity and radial velocity variations. Using distances based on period-luminosity relations in the near- or mid-infrared, we investigate for the first time the metallicity distribution of the young population in the SMC in the depth direction. Preliminary results show no metallicity gradient along the SMC main body, but our sample is small and does not contain Cepheids in the inner few degrees of the SMC.

Analytical Electron Microscopy of Surface-Modified Ceramics

1985 ◽  
Vol 43 ◽  
pp. 276-279
Author(s):  
P. S. Sklad
Keyword(s):  
Electron Microscopy ◽  
Analytical Electron Microscopy ◽  
Theoretical Models ◽  
Ceramic Materials ◽  
Solute Concentration ◽  
Second Phase ◽  
Analytical Electron ◽  
Implantation Techniques ◽  
Lattice Damage ◽  
Surface Modified

Over the past several years, it has become increasingly evident that materials for proposed advanced energy systems will be required to operate at high temperatures and in aggressive environments. These constraints make structural ceramics attractive materials for these systems. However it is well known that the condition of the specimen surface of ceramic materials is often critical in controlling properties such as fracture toughness, oxidation resistance, and wear resistance. Ion implantation techniques offer the potential of overcoming some of the surface related limitations.While the effects of implantation on surface sensitive properties may be measured indpendently, it is important to understand the microstructural evolution leading to these changes. Analytical electron microscopy provides a useful tool for characterizing the microstructures produced in terms of solute concentration profiles, second phase formation, lattice damage, crystallinity of the implanted layer, and annealing behavior. Such analyses allow correlations to be made with theoretical models, property measurements, and results of complimentary techniques.

On the Relationship Between General Auditory Sensitivity and Speech Perception: An Examination of Pitch and Lexical Tone Perception in 4- to 6-Year-Old Children

2020 ◽  
Vol 63 (2) ◽  
pp. 487-498
Author(s):  
Puisan Wong ◽  
Man Wai Cheng
Keyword(s):  
Speech Perception ◽  
Theoretical Models ◽  
Developmental Trajectory ◽  
Auditory Sensitivity ◽  
Pitch Discrimination ◽  
Lexical Tone ◽  
Perceptual Training ◽  
Lexical Tones ◽  
Tone Perception ◽  
Tone Discrimination

Purpose Theoretical models and substantial research have proposed that general auditory sensitivity is a developmental foundation for speech perception and language acquisition. Nonetheless, controversies exist about the effectiveness of general auditory training in improving speech and language skills. This research investigated the relationships among general auditory sensitivity, phonemic speech perception, and word-level speech perception via the examination of pitch and lexical tone perception in children. Method Forty-eight typically developing 4- to 6-year-old Cantonese-speaking children were tested on the discrimination of the pitch patterns of lexical tones in synthetic stimuli, discrimination of naturally produced lexical tones, and identification of lexical tone in familiar words. Results The findings revealed that accurate lexical tone discrimination and identification did not necessarily entail the accurate discrimination of nonlinguistic stimuli that followed the pitch levels and pitch shapes of lexical tones. Although pitch discrimination and tone discrimination abilities were strongly correlated, accuracy in pitch discrimination was lower than that in tone discrimination, and nonspeech pitch discrimination ability did not precede linguistic tone discrimination in the developmental trajectory. Conclusions Contradicting the theoretical models, the findings of this study suggest that general auditory sensitivity and speech perception may not be causally or hierarchically related. The finding that accuracy in pitch discrimination is lower than that in tone discrimination suggests that comparable nonlinguistic auditory perceptual ability may not be necessary for accurate speech perception and language learning. The results cast doubt on the use of nonlinguistic auditory perceptual training to improve children's speech, language, and literacy abilities.

Positive Arousal Enhances the Consolidation of Item Memory

2015 ◽  
Vol 74 (2) ◽  
pp. 91-104 ◽  
Author(s):  
Bo Wang
Keyword(s):  
Episodic Memory ◽  
Memory Consolidation ◽  
Source Memory ◽  
Emotional Arousal ◽  
Theoretical Models ◽  
Memory Test ◽  
Learning Phase ◽  
Item Memory ◽  
Memory Tests ◽  
Immediate Memory

Emotional arousal induced after learning has been shown to modulate memory consolidation. However, it is unclear whether the effect of postlearning arousal can extend to different aspects of memory. This study examined the effect of postlearning positive arousal on both item memory and source memory. Participants learned a list of neutral words and took an immediate memory test. Then they watched a positive or a neutral videoclip and took delayed memory tests after either 25 minutes or 1 week had elapsed after the learning phase. In both delay conditions, positive arousal enhanced consolidation of item memory as measured by overall recognition. Furthermore, positive arousal enhanced consolidation of familiarity but not recollection. However, positive arousal appeared to have no effect on consolidation of source memory. These findings have implications for building theoretical models of the effect of emotional arousal on consolidation of episodic memory and for applying postlearning emotional arousal as a technique of memory intervention.

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