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RR lyrae variable pulsations and the Oosterhoff groups

Description: It is concluded that Oosterhoff group I clusters have 0.55 M/sub sun/ stars and group II clusters have 0.65 M/sub sun/ stars. The Y value is always about 0.29. Mean log L/L/sub sun/ values are 1.66 and 1.78 giving M/sub bol/ = 0.60 and 0.30 for the RR Lyrae variables in these two groups of clusters. For field RR Lyrae variables at M = approx. 0.5 M/sub sun/ or less, perhaps M/sub bol/ = 0.90 or even larger as Clube and Jones propose. Apparently all evolution is blueward for RR Lyrae variables, and the color overlap of F and 1H pulsators is not real. (GHT)
Date: January 1, 1981
Creator: Cox, A.N.
Partner: UNT Libraries Government Documents Department

Stellar-opacity calculations. I. Lecture 2

Description: In this study of stellar structure, evolution, stability, and pulsation or explosion, there are three very vital pieces of physical information needed. We assume the composition is known from observations of assumption. To construct a model of a star we then need to know the nuclear generation rates which give the luminosity the star emits, the pressure and energy equation of state which determines the flow of radiation through the star. It is the equation of state and opacity that we will be discussing in the next two lectures.
Date: March 14, 1983
Creator: Cox, A.N.
Partner: UNT Libraries Government Documents Department

Constraints on stellar evolution from pulsations

Description: Consideration of the many types of intrinsic variable stars, that is, those that pulsate, reveals that perhaps a dozen classes can indicate some constraints that affect the results of stellar evolution calculations, or some interpretations of observations. Many of these constraints are not very strong or may not even be well defined yet. In this review we discuss only the case for six classes: classical Cepheids with their measured Wesselink radii, the observed surface effective temperatures of the known eleven double-mode Cepheids, the pulsation periods and measured surface effective temperatures of three R CrB variables, the delta Scuti variable VZ Cnc with a very large ratio of its two observed periods, the nonradial oscillations of our sun, and the period ratios of the newly discovered double-mode RR Lyrae variables. Unfortunately, the present state of knowledge about the exact compositions; mass loss and its dependence on the mass, radius, luminosity, and composition; ;and internal mixing processes, as well as sometimes the more basic parameters such as luminosities and surface effective temperatures prevent us from applying strong constraints for every case where currently the possibility exists.
Date: January 1, 1983
Creator: Cox, A.N.
Partner: UNT Libraries Government Documents Department

Solar opacities constrained by solar neutrinos and solar oscillations

Description: This review discusses the current situation for opacities at the solar center, the solar surface, and for the few million kelvin temperatures that occur below the convection zone. The solar center conditions are important because they are crucial for the neutrino production, which continues to be predicted about 4 times that observed. The main extinction effects there are free-free photon absorption in the electric fields of the hydrogen, helium and the CNO atoms, free electron scattering of photons, and the bound-free and bound-bound absorption of photons by iron atoms with two electrons in the 1s bound level. An assumption that the iron is condensed-out below the convection zone, and the opacity in the central regions is thereby reduced, results in about a 25 percent reduction in the central opacity but only a 5 percent reduction at the base of the convection zone. Furthermore, the p-mode solar oscillations are changed with this assumption, and do not fit the observed ones as well as for standard models. A discussion of the large effective opacity reduction by weakly interacting massive particles also results in poor agreement with observed p-mode oscillation frequencies. The much larger opacities for the solar surface layers from the Los Alamos Astrophysical Opacity Library instead of the widely used Cox and Tabor values show small improvements in oscillation frequency predictions, but the largest effect is in the discussion of p-mode stability. Solar oscillation frequencies can serve as an opacity experiment for the temperatures and densities, respectively, of a few million kelvin and between 0.1 and 10 g/cm/sup 3/. Current oscillation frequency calculations indicate that possibly the Opacity Library values need an increase of typically 15 percent just at the bottom of the convection zone at 3 /times/ 10/sup 6/K. 41 refs., 15 figs., 1 tab.
Date: August 15, 1989
Creator: Cox, A.N.
Partner: UNT Libraries Government Documents Department

Double-mode pulsation

Description: Double mode pulsation is a very pervasive phenomenon in stars all over the Hertzsprung-Russell diagram. In order of increasing radius, examples are: ZZ Ceti stars, the sun, the delta Scuti stars, RR Lyrae variables, the ..beta.. Cephei variables and those related to them, Cepheids, and maybe even the Mira stars. These many modes have been interpreted as both radial and nonradial modes, but in many cases the actual mode has not been clearly identified. Yellow giants seem to be the most simple pulsators with a large majority of the RR Lyrae variables and Cepheids showing only one pulsation period. We limit this review to those very few cases for classical Cepheids and RR Lyrae variables which display two modes. For these we know many facts about these stars, but the actual cause of the pulsation in two modes simultaneously remains unknown.
Date: July 30, 1982
Creator: Cox, A.N.
Partner: UNT Libraries Government Documents Department

Supergiant radial and nonradial pulsations. Lecture 10

Description: The stars that we consider here have luminosities above 10,000 solar luminosities and masses above 15 solar masses. We contact the 53 Per stars such as ..nu.. Ori, 10 Lac, and iota CMa at our lower luminosity limit, and at the most luminous limit, we have the famous stars eta Car, Cyg OB12, and P Cyg. Evolution tracks including a reasonable mass loss rate are given for 15, 30, 60, and 120 solar masses. It appears that our pulsators have masses less than 60 solar masses, but how do the most luminous stars observed survive mass loss. Do they have masses above 100 solar masses as indicated, or are these stars somehow superluminous due to their erratic mass loss behavior. Popper (1980) studying the masses in binary systems has never found one with a value greater than 27 solar masses.
Date: March 14, 1983
Creator: Cox, A.N.
Partner: UNT Libraries Government Documents Department

PG1159 variables

Description: A 0.6 solar mass model is discussed that has a temperature ranging from 100,000 K for its surface effective temperature to a maximum of almost 200 million K, and then a decrease to about 85 million K at the center. This temperature inversion is caused by strong neutrino losses at the high central densities. These internal densities range from 10/sup -6/ to 10/sup +6/ g/cm/sup 3/ from the surface to the center. For luminosities considerably lower than the 1.075 x 10/sup 35/ erg/sec for this model, the central temperature inversion disappears and the central density grows larger. For the PG1159 class of stars however, there is always this inversion.
Date: January 1, 1985
Creator: Cox, A.N.
Partner: UNT Libraries Government Documents Department

Linear nonradial pulsation theory. Lecture 7

Description: Many of the upper main-sequence stars pulsate in spheroidal nonradial modes. We know this to be true in numerous cases, as we have tabulated for the ..beta.. Cephei and delta Scuti variables in previous lectures. However, we cannot identify the actual mode for any star except for the low-order pressure p and f modes of our sun. It remains a great challenge to clearly state what really is occurring, in the process we learn more about how stars evolve and pulsate.
Date: March 14, 1983
Creator: Cox, A.N.
Partner: UNT Libraries Government Documents Department

Modes, masses, metallicities, and magnitudes of RR Lyrae variables

Description: The author reviews past and recent developments in the study of RR Lyrae variables. He provides supporting evidence for a large helium content but remains uncertain as to their masses and luminosities. Time dependent convection is offered as a probable explanation for the double mode pulsations of these stars. 25 refs., 8 figs., 3 tabs.
Date: July 1, 1987
Creator: Cox, A.N.
Partner: UNT Libraries Government Documents Department

Pulsations of delta Scuti stars

Description: A general review of the pulsating {delta} Scuti variables is given including the observed light curves and positions of the stars in the Hertzsprung-Russell diagram. Theoretical interpretations from evolution and pulsation calculations give their masses, radii, luminosities, and even their approximate internal compositions. Three models of these stars are discussed and used to study the nonlinear hydrodynamic behavior of these stars. The hydrodynamic equations and the Stellingwerf method for obtaining strictly periodic solutions are outlined. Problems of allowing for time-dependent convection and its great sensitivity to temperature and density are presented. Tentative results to date do not show any tendency for amplitudes to grow to large unobserved amplitudes, in disagreement with an earlier suggestion by Stellingwerf. It is found that the very small growth rates of the pulsations may even be too small to be useful in seeking a periodic solution. 15 refs., 8 figs., 3 tabs.
Date: January 1, 1989
Creator: Cox, A.N.
Partner: UNT Libraries Government Documents Department

Theoretical interpretations of anomalous Cepheid pulsations

Description: Anomalous Cepheids are variable stars found in metal poor systems, with a low mass main sequence turnoff, that are significantly brighter (0.4 to 1.0 magnitude) than the RR Lyrae variables in the same system. They do have similar periods and effective temperatures. In dwarf spheroidal systems such as Draco, Leo II, Sculptor and Ursae Major, they are quite common, but they are rare in globular clusters. Only one is well known in the globular cluster NGC 5466 (Zinn and Dahn, 1976), but there are other possible candidates in M15 and omega Cen. Similar objects are found in the SMC, but none are seen in the LMC.
Date: January 1, 1985
Creator: Cox, A.N. & Proffett, C.R.
Partner: UNT Libraries Government Documents Department

Nonlinear study of AI Velorum

Description: Using results from earlier studies of double-mode dwarf Cepheids by Cox, King, and Hodson, hydrodynamic calculations were undertaken for AI Vel. The earlier derived evolution theory mass of 1.8 M sub solar, a luminosity of of 23 L sub solar and a T/sub e/ of 7500/sup 0/K give the observed period of 0.11 day and the observed period ratio PI/sub 1//PI/sub 0/ = 0.773. A cooler T/sub e/ than the observed one (7620/sup 0/K) was used because 7620/sup 0/K is beyond the fundamental pulsation mode blue edge. The composition used is X = 0.70 Z = 0.01. This lower than normal Z is necessary to make the period ratio as large as observed. The goal is to see if double-mode behavior, due to either mode switching or a permanent state, can be predicted for the model. Progress in converging the model to a periodic pulsation solution by the von Sengbusch--Stellingwerf relaxation method will be reported. 17 references.
Date: January 1, 1979
Creator: Cox, A.N. & Hodson, S.W.
Partner: UNT Libraries Government Documents Department

Some investigations about the Carson opacities

Description: Accurate opacities for stellar composition mixtures are needed for all studies of stellar structure, evolution, stability, and pulsation. Three problem areas where increased opacities would be welcome are: the observed broadening of the upper main sequence that can be produced with larger opacities that tend to expand the stars; the existence of the double-mode Cepheids and their anomalously low period ratios which can be predicted to be lower, as observed, if opacities are larger; and the small sensitivity of the low mass population II horizontal branch luminosity to the metal content of their compositions that would be more effective if their opacity were increased. Several other problems that could be solved by larger opacities have been widely discussed, but we feel that they are not justifiably an opacity problem. The conclusion of our considerations are that the Thomas-Fermi method for getting opacities used by Carson and his collaborators does not produce values appreciably different from those obtained without this method at Los Alamos, and that these persistent astrophysical problems must be solved in other ways. We here propose a possible error in the Carson opacities, and, further, we mention another that seems to be the correct reconciliation between these two opacity sets.
Date: January 1, 1983
Creator: Cox, A.N. & Kidman, R.B.
Partner: UNT Libraries Government Documents Department

Stability of the low degree five minute solar oscillations

Description: In this paper we discuss the decay rate for many of the low degree p modes observed as 5 minute oscillations of the sun. This report is an expanded version of the presentation at Snowmass. These theoretical results use the completely nonadiabatic linear theory of Saio and Cox (1980). Our solar model is based on the evolution results of Christensen-Dalsbgaard (1982). Equation of state and opacity data come from the Los Alamos Opacity Library of Huebner, Merts, Magee, and Argo (1977). We compute rates for modes ranging from radial (l = 0) to the nonradial ones with l = 5 for overtones 10 through 28.
Date: January 1, 1983
Creator: Kidman, R.B. & Cox, A.N.
Partner: UNT Libraries Government Documents Department

Light and velocity curves of bump Cepheids

Description: We present light and velocity curves for eight hydrodynamic bump Cepheid models. All of the models were converged to the fundamental mode solution using a relaxation technique developed by Stellingwerf (1974). Our use of this method assures that the time behavior repeats each period to better than one part in a thousand. The motivation for this work was to help Buchler, at the University of Florida, to develop his theory of modal interactions in pulsating stars. 4 refs., 8 figs.
Date: January 1, 1985
Creator: Cox, A.N. & Proffett, C.R.
Partner: UNT Libraries Government Documents Department

Variable star research at Los Alamos

Description: Three major areas of variable star research at Los Alamos are carried out: (1) a study using improved Cepheid light curves in order to define more precisely the Hertzsprung sequence, in collaboration with John Castor and John Cox; (2) the suggestion by A. Cox that helium enrichment occurs in the stellar envelope, by a stellar wind, which may explain many of the mass anomalies, this work being with G. Michaud, D. King, R. Deupree, and S. Hodson; and (3) the study of Cepheid and RR Lyrae colors to compare directly to the observations. A brief discussion of the present status of each of these research programs will be given. 25 references.
Date: January 1, 1978
Creator: Davis, C.G.; Cox, A.N. & Adams, T.F.
Partner: UNT Libraries Government Documents Department

Constraints of observations of solar oscillations on solar models with mixing by turbulent diffusion

Description: The pulsational behavior of solar models with mixing produced by turbulent diffusion has been investigated, for both p (pressure) modes and g (gravity) modes. It is found that while a small amount of mixing may be allowed by the observed data on solar oscillations, values of the pseudo-Reynolds number large enough to reduce the predicted neutrino counting rate to the level seen by the /sup 37/Cl experiment are in conflict with published solar oscillation data. 8 references, 8 figures, 2 tables.
Date: January 1, 1984
Creator: Cox, A.N.; Kidman, R.B. & Newman, M.J.
Partner: UNT Libraries Government Documents Department

Radial pulsation analyses of DA dwarfs

Description: A careful study is made of realistic white dwarf envelopes with new opacities in order to identify any destabilizing mechanisms present in the models with a future application to a nonradial study. The initial results showed that the high order radial overtones were unstable. An extension is now made to various chemical compositions and slightly more realistic radii. This always shows that there is an instability strip lying at a certain temperature range depending upon the composition. The radial eigenfunctions are shown and the growth rates discussed. Also the work function integral is given. The possible mechanism and observational problems for these unstable modes are considered. 17 references. (JFP)
Date: January 1, 1979
Creator: Starrfield, S.; Cox, A.N. & Hodson, S.W.
Partner: UNT Libraries Government Documents Department

Masses and pulsations of BL Herculis variables

Description: From linear results, the masses of BL Her variables must be nearer to 0.55 M /sub sun/ than 0.75 M /sub sun/ if the bump phase transition (resonance) is to be located anywhere near the observed period range of 1./sup d/5 to 1./sup d/7. The nonlinear results are consistent with the Simon resonance concept, but demonstrate that light and velocity curve shapes are a nonlinear phenomenon that require nonlinear period ratios to display the resonances only in the narrow, observed range of 1./sup d/5 to 1./sup d/7. The mass near 0.55 M /sub sun/ is in good agreement with evolution calculations (Sweigart and Gross, 1976) and nonlinear pulsation studies of Carson, Stothers, and Vemury (1981) and Stothers (1981).
Date: January 1, 1981
Creator: Hodson, S.W.; Cox, A.N. & King, D.S.
Partner: UNT Libraries Government Documents Department

Oscillations of solar models with internal element diffusion

Description: Two precision solar models have been constructed with the Iben evolution program, one with no diffusion of the internal atomic nuclei, and another that includes the effects of gravitational settling, thermal diffusion, and concentration gradient diffusion on the element abundances. This paper reports the results of these models. 8 figs., 3 tabs.
Date: January 1, 1987
Creator: Cox, A.N.; Guzik, J.A. & Kidman, R.B.
Partner: UNT Libraries Government Documents Department

Nonlinear RR Lyrae models with new Livermore opacities

Description: A.N. Cox recently showed that a 20% opacity decrease in the 20,000--30,000 K region as indicated by the new Livermore OPAL opacities reconciles the discrepancy between pulsation and evolution masses of double-mode RR Lyrae variables. Nonlinear hydrodynamic calculations were performed for RR Lyrae models of mass 0l75 M{circle dot}, 51 L{circle dot}, and Z=0.0001 including this opacity decrease. The Stellingwerf periodic relaxation method was used to converge the models to a limit cycle, and the Floquet matrix eigenvalues calculated to search for a tendency of the fundamental mode to grow from the full-amplitude overtone solution, and the overtone mode to grow from the full-amplitude fundamental solution, thereby predicting double-mode behavior. Models of T{sup eff} < 7000 K with the opacity decrease have positive fundamental-mode growth rates in the overtone solution, in contrast to earlier results by Hodson and Cox, and models with T{sub eff} < 7000 have positive 1st overtone growth rates in the fundamental-mode behavior was not found.
Date: January 1, 1992
Creator: Guzik, J.A. & Cox, A.N.
Partner: UNT Libraries Government Documents Department