Low Effective Temperature Research Articles

Electron-phonon scattering rates in antimony: radio-frequency size effect

Temperature-dependent radio-frequency size effect data have been obtained for many orbits on the Fermi surface of antimony. These data are analysed according to a model in which the electron-phonon scattering frequencies are proportional to T3, but because of a low effective Debye temperature for the small pieces of Fermi surface, the logarithm of the amplitudes of the data is proportional to T2. The electron-phonon scattering frequencies are determined for both holes and electrons and are found to be highly anisotropic in each case.

Macroscopic quantum electrodynamic effects in a superconducting ring containing a Josephson weak link

The problem of coherent flux tunnelling across a Josephson weak link enclosed by a thick superconducting (‘SQUID‘) ring in terms of quantum electrodynamics is considered. We show that for a low effective noise temperature (≃few K) in the SQUID ring and with the weak link capacitance ≲3 × 10−15, such a process should be observable. Experimental evidence is given to justify this claim.

Mass loss from metal-poor stars

1. IntroductionIt is essential to consider the effect of mass loss to understand the distribution of supergiant stars in the HR diagram. This research concerns the evolution of massive stars with X=0.700 and Z=0.001 during the phases up to central Heexhaustion with the inclusion of mass loss. Such low value of Z has been chosen in order to allow a comparison with the supergiant stars of SMC. The rate of mass loss is formulated as in Chiosi, Nasi and Sreenivasan (1978). More specifically, in the range of high effective temperatures, we adopt the mass-loss rate relationship for radiation pressure driven wind of Castor, Abbott and Klein (1975), whereas in the range of low effective temperatures we assume the mass loss rate to be driven by the acoustic flux mechanism of Fusi Pecci and Renzini (1975).

Massive Stars: Evolution with Mass Loss. III. Low Metal Stars, and WR's in SMC

In this paper we investigate the effect of mass loss by stellar wind on the evolution from the main sequence to the He exhaustion stage of stars in the range of mass 20 to 100 M⊙ with low metal abundance. To this purpose we compute the set of evolutionary sequences with initial mass 20, 30, 40, 60, 80, and 100 M⊙ and chemical composition parameters X=0.700, Z=0.001. The models are first computed at constant mass to provide the fundamental network to which we compare the mass losing models. This choice of the initial chemical composition is aimed to represent the case of luminous supergiants in the Small Magellanic Cloud. The rate of mass loss follows the formulation of Castor, Abbot and Klein (1975), but it incorporates the effect of different metal content in the regions of high effective temperatures in the HR diagram. The rate of mass loss for models at low effective temperature is given by the acoustic flux mechanism according to the formulation of Chiosi, Nasi and Sreenivasan (1978). The results are compared with those of Chiosi, Nasi and Sreenivasan (1978), and those of Chiosi, Nasi and Bertelli (1979) for normal metal abundance supergiant stars of the Galaxy. On the basis of the present results we suggest an interpretative scenario for the existence of single WR stars in galaxies of different chemical composition. These results allow us to interpret also the different percentages of WR's among subclasses that are observed in the Galaxy, LMC, and SMC (Conti and Vanbeveren, 1979).

Temperatures and radii of O stars

Angular diameters have been estimated for 18 O and 142 B stars using absolute intermediate-band photometry in the near infrared and they have been combined with integrated fluxes to yield effective temperatures. The effective temperatures of the O stars lie in the range 30000 K to about 47000 K. For a given subtype, the luminosity class I stars have lower effective temperatures than the main-sequence stars by about 1000 K. The absorption-line spectral types of the supergiants of types O and B reflect electron temperatures which are higher than can be maintained by the integrated flux which flows through the stellar atmosphere. Distances have been estimated for all the stars and linear diameters found. The average radius for an 08 to 09.5 supergiant is about 23.3 R⊙; the radii for luminosity class III and Class V O stars lie in the range 6.8 to 10.7⊙ R.

On the possibility of electron-hole liquid formation in GaAs

At low effective carrier temperatures electron-hole liquid formation would be expected in GaAs due to the experimental value of the electron-hole plasma binding energy (Φ exp = 4.8 meV) which lies approximately 3 meV lower than theoretically expected. However, experimentally no evidence for the formation of a liquid is found: The carrier density is proportional to the temperature down to 7 K.

Collision studies with a single molecular beam

Collision rates of some excited-state processes can be studied at low effective temperatures with a single atomic or molecular beam. Effects dependent on the orientation of the collision axis can also be observed in resonant collisions. Useful relative-velocity distributions are given.

Growth depression and food requirements of fattening pigs at low environmental temperatures when housed either on concrete slats or straw

SUMMARY1. Four experiments, each with two groups of eight pigs, were performed in a controlled environment room equipped with two pens. One pen had straw as bedding and the other had slats. The animals were exposed to temperatures of about 17°C at the initial weight (20 to 25 kg). The temperature was lowered by about 1°C per 10 kg body-weight increase, to 8 to 12°C at the end of the fattening period (80 to 100 kg).Animals on slats were kept 4·7 to 5·3°C below the calculated zone of thermoneutrality and the animals on straw 2·0 to 2·6°C above the lower limit of thermoneutrality. In Experiments 1 and 2 the animals in both pens received the same amount of food per day and in Experiments 3 and 4 animals on slats received more food to give the same body·weight gain as on straw. Feeding level on straw was about 93 g/kg0·75 per day.2. In Experiments 1 and 2, body-weight gain on slats was reduced due to the lower effective temperature. After adjusting for feeding level, the reduction in daily gain was calculated as 18·5 and 11·8 g per °C below thermoneutrality. In Experiments 3 and 4 the extra food needed to maintain the same rate of gain on slats as on straw was respectively 18·1 and 45·5 g per °C below thermoneutrality.3. Carcass length of animals on slats was less than on straw.

The pulsation periods of stars with convection zones.

view Abstract Citations (19) References (18) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The pulsation periods of stars with convection zones. Cogan, B. C. Abstract Pulsation periods of model envelopes with different mixing lengths have been computed. Varying the mixing length has little effect upon the periods of typical Cepheids. Models representing the double-mode Cepheid U TrA show that this star may have a normal mass ( 4 M0) if it has a low effective temperature and if a large mixing length is appropriate. It is argued that both these conditions are possible and may be true for double-mode Cepheids generally. Subject headings: stars: Cepheids - stars: interiors - stars: pulsation Publication: The Astrophysical Journal Pub Date: February 1977 DOI: 10.1086/154999 Bibcode: 1977ApJ...211..890C full text sources ADS | data products SIMBAD (1)

Synthesis of Classification Dispersion Spectra from Stellar Atmospheres Theory and from High Dispersion Spectra

The ATLAS programme has been corrected and modified for use at low effective temperatures. A grid of unblanketed model atmospheres has been generated for the region G5-K5, V-II. A spectrum synthesis programme has been written for the calculation of flux vs wavelength for selected regions of the spectrum. Temperature distributions from the grid of continuum models and from published blanketed models will be used along with published oscillator strengths as input data for the spectral synthesis programme.Spectrograms of MK standards have been taken at 12 Å mm−1 and 120 Å mm−1. The University of Toronto PDS microdensitometer system has been programmed to allow comparison between the synthesized spectra and the observed spectra to determine the effects of effective temperature, surface gravity, microturbulence, and abundance on classification criteria.

Ultraviolet energy distributions of luminous early-type stars from TD1 satellite observations

view Abstract Citations (28) References (14) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Ultraviolet energy distributions of luminous early-type stars from TD1 satellite observations. Humphries, C. M. ; Nandy, K. ; Kontizas, E. Abstract Ultraviolet spectra are presented for supergiants, giants, and main-sequence stars in the spectral type range from B0 to A2. The observations were obtained in the spectral range A with the S2/68 Ultraviolet Sky Survey Telescope in the TD1 satellite. The effect of luminosity has been studied by comparing the ultraviolet energy distributions of luminous and main-sequence stars of the same spectral type. The flux deficiencies which are observed in the energy distributions of luminous stars are interpreted as the result of lower effective temperatures for luminous stars than for corresponding main-sequence stars, and an estimate is given of the effective temperature scale for B-type supergiants. Subject headings: early-type stars - spectra, ultraviolet - spectrophotometry Publication: The Astrophysical Journal Pub Date: January 1975 DOI: 10.1086/153310 Bibcode: 1975ApJ...195..111H Keywords: Early Stars; Energy Spectra; Spaceborne Astronomy; Stellar Spectrophotometry; Ultraviolet Spectra; Satellite Observation; Stellar Luminosity; Ubv Spectra; Ultraviolet Radiation; Space Radiation full text sources ADS | data products SIMBAD (22)

Luminosities and temperatures of M dwarf stars from infrared photometry

Bolometric magnitudes for a large number of M type dwarf stars, obtained by broadband infrared photometry at 1.65, 2.2, and 3.5 microns, are reviewed. The data obtained indicate that one parameter is sufficient to describe the blanketing in all of the UBVRI bands for all types of M dwarfs. In general, late M dwarfs seem to have lower effective temperatures than are predicted by theoretical models.

On the Calculation of Linear, Nonadiabatic Pulsations of Stellar Models

view Abstract Citations (173) References (16) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS On the Calculation of Linear, Nonadiabatic Pulsations of Stellar Models Castor, John I. Abstract - computational method for treating linear, nonadiabatic radial pulsations of stellar models is presented. The details of the numerical procedure are given. This procedure also fits easily into the frame- work of the Henyey method for the calculation of stellar evolution. It has been found to be very efficient; in general, less time is required for the stability analysis of a given model than for the construction of the model itself. The method is applied to models of RR Lyrae stars previously treated by Christy, who used the nonlinear method. The agreement is good overall; the growth rates obtained are usually within 50 percent of Christy's .The differences are that the periods obtained in the present calculations are 2-3 percent longer than Christy's, and instability is found to extend 400 K higher in effective temperature. The first difference can be attributed to Christy's omission of radiation pressure, while the second is possibly due to nonlinearity at Christy's initiation amplitude. A second set of models analyzed was similar to models treated previously by Baker and Kippenhahn. In the present case, however, the models were constructed without convection. Notable differences were found between the present results and those of Baker and Kippenhahn. These were of the luminosity phase lag, the relative contributions of the H and He ii ionization zones to the growth rate, and the growth rate at low effective temperature. These differences may all be attributed to the effect of convection. For the phase lag, omission of convection produces better agreement with observations. It is shown that the linear approximation is applicable to much larger amplitudes than was previously thought. This is because the structure within the zone of hydrogen ionization is found to have no effect on the pulsation as a whole, provided the zone of hydrogen ionization is geometrically sufficiently thin. Nonlinear effects then become important only when the relative pressure amplitude approaches unity. This conclusion is valid only if convection is negligible in the models. Publication: The Astrophysical Journal Pub Date: May 1971 DOI: 10.1086/150945 Bibcode: 1971ApJ...166..109C full text sources ADS |

THE AGES OF THE HYADES, PRAESEPE, AND COMA STAR CLUSTERS

From a comparison of color magnitude diagrams with evolutionary tracks computed by Auman (1965) and Iben (1965a,fo), the Hyades and Praesepe clusters were thought to have an age of between 4 X 108 years and 5 X 108 years (Barbaro, Dellaporta, and Nobili 1966; Kraft 1967) while the Coma cluster was expected to be somewhat younger since it contains slightly bluer stars. The revised relations between effective temperature (TV), bolometric correction (BC), and color indices of main-sequence stars as derived from interferometric measurements of stellar diameters together with accurate model atmospheres (Morton and Adams 1968), indicate much lower effective temperatures than previously estimated for spectral types between B8 and A5 (cf., Harris 1963); for instance for (B-V) = 0^00, Te has been revised from 10,700° K to 9600° K. This implies considerably larger ages for star clusters in which the turn-off is in this spectral range, since the turn-off is moved farther down the main sequence in the Mv , log Te diagram and hence the stars at the turn-off must be less massive than previously estimated. In order to evaluate the magnitude of this effect, timelines were computed for an artificial star cluster that consists of 45 stars with masses between 1.5 3PI© and 2.25 3K©. The 45 mass values were chosen at random from a collection of 180 values that

On the evolution of the Horizontal Branch stars of metal-poor Globular Clusters

The actual knowledge on Horizontal Branch stars of the metal-poor Globular Clusters of our Galaxy suggests that these stars evolve along the Horizontal Branch from the very blue stars towards lower effective temperature.

Graphite Particle Model for NML Cygnus

THE strong infrared source NML Cygnus1 is typical of a wide class of infrared stars which have been identified with M-type giants or supergiants, or with Mira variables2. The relatively low effective temperatures associated with such stars make them very likely candidates for the production of solid particles. It has recently been shown by one of us3 that graphite particles tend to form in the atmospheres of Mira variables which have only a very small excess of O over C (ref. 4). There is some evidence5 to suggest that an O/C ratio near unity may be appropriate to NML Cygnus as well; the formation of graphite particles in the stellar atmosphere would thus seem entirely plausible. In this communication we discuss the possibility that the infrared radiation from NML Cygnus comes from a circumstellar shell of graphite particles.

Convection in Pulsating Stars: Quasi-Adiabatic Cepheid Models.

view Abstract Citations (8) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Convection in Pulsating Stars: Quasi-Adiabatic Cepheid Models. Baker, N. H. ; Gough, D. O. Abstract The time-dependent mixing-length theory described in the previous abstract has been applied, in the quasi-adiabatic approximation, to a series of models of ~ Cephei stars of 7Mo previously studied by Baker and Kippenhahn (Astrophys. J. 142, 868,1965). The hottest models of this series have negligible surface convection zones, but the coolest models have deep convection zones that include the low-lying hydrogen and helium ionization regions. On the basis of the quasi-adiabatic approximation, which is not valid near the surface of our stellar envelopes, we tentatively conclude that the increasing importance of convection in stars of lower effective temperature is responsible for the return to stability at the cool edge of the Cepheid strip. This work has been supported by the National Science Foundation under Grant GP-5568 (N.H.B) and Grant GP-4859 (D.O.G.). Publication: The Astronomical Journal Pub Date: 1967 DOI: 10.1086/110423 Bibcode: 1967AJ.....72Q.784B full text sources ADS | data products SIMBAD (1)

Evolution of Stars of Small Masses in the Pre-Main-Sequence Stages

The structure of the outer envelope with an H-ionization zone and an H2-dissociation zone is investigated for Population I stars of small masses (2M⊙ ≥M ≥0.05M⊙), which have low luminosities (L⊙ ≥L ≥10-3L⊙) and low effective temperatures (6000 °K ≥Te ≥2500 °K), in order to find the surface conduction for the internal structure of these stars. The effective temperature of a star which is wholly convective and which has an H2-dissociation zone is found to be nearly constant in the wide range of its luminosity. Using stellar models composed of a radiative core and a convective envelope together with the above surface condition, the evolution of contracting stars is calculated up to the onset of hydrogen burning and the results are compared with the observed red dwarf stars. It is found that the stars on the zero-age main-sequence have radiative cores for M > 0.26M⊙ but they are wholly convective for 0.26M⊙ ≥M ≥0.08M⊙. The stars less massive than 0.08M⊙ are found to contract toward the configurations of high electron-degeneracy without hydrogen burning.

陸奥灣産ホタテガイの産卵の變動<sup>1)</sup>

Number of swimming larvae and attached spats which are collected by nets and collectors respectively fluctuate with year (Fig. 1). It is conceivable that the changs in appearance of the larvae and spats run parallel with the fluctuation of spawning of the shell. The scallop is induced to spawn by rising in temperature in the laboratory and the low effective temperature of the spawing is 8.0-8.5°C. and the shell is stimulated by only sudden rising above the effective temperature even by 0.5°C. The stimulation for induction of spawning is more effctive in high breeding season, viz. April, and ovarial eggs degenerate with the beginning of May. Basing upon above facts and curves of coast temperature (Fig. 2), the spawning of the scallop in Mutsu Bay is perhaps induced by the sudden rising of water temperature affected by the violent warm current flowed into the bay during the breeding season.

Nuclear Reactions in Stellar Evolution*

(3). Apart from the stars of the main sequence, there is known a large class of stars having very high luminosities but possessing much lower effective temperatures (that is, much greater radii) than the stars of the main sequence of the same luminosities. In the Hertzsprung-Russell diagram these so-called red giants form a rather irregularly distributed group on the upper right side of the main sequence. Because of anomalously large radii these red giants possess very low densities, and the estimated central temperatures are considerably lower than those for the stars of the main sequence (for typical red giants the central densities can be as low as 5 × 10-7 gm./cm.3, and central temperatures less than 1 × 104°C.). Thus it is clear at once that the energy production in these stars cannot be due to the same nuclear reaction as in the stars of the main sequence, and we have to look for reactions taking place at an appreciable rate at much lower temperatures than the carbon-nitrogen cycle. From Table I [p. 575] we see that the nuclei which can be responsible for the energy production at lower temperatures are the isotopes of heavy hydrogen, lithium, beryllium and boron, and, using the data of this table together with formula (1), it is easy to estimate at which temperatures these different processes will be of importance. Then, using the homology transformations, we can calculate the location of stars with different energy-producing reactions in the Hertzsprung–Russell diagram8.