No description available.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1970. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Pulsation constants and period ratios are given for the first six radial pulsation modes of a set of seven polytropes with indices ranging from n = 2.25 to n = 4.00. The polytrope results are combined with published theoretical data from stellar model pulsation calculations and observational data on thirteen double mode variables in the Cepheid instability strip to obtain four interpolation formulae relating fundamental periods Po, pulsation constants Qo, and period ratios P1 /P0 and P2 /P1. The derived relations are used to obtain accurate densities for the thirteen observed variables, which include six dwarf Cepheids or AI Vel stars, one S Sct star, one RR Lyr star, and five Cepheids. Approximate masses and luminosities are obtained for some of these stars. The probable connection between mass- luminosity ratios and the existence of double mode variables is discussed.

No description available.

No description available.

A theoretical study of population II variables with periods in the range 10 - 20 days (W Virginis variables) is presented. A modified hydrodynamic Christy code is used in conjunction with the Carson opacities, in preference to the Los Alamos tables, following the work of Carson, Stothers and Vemury on the shorter period BL Herculis variables. Twenty-five survey models are presented, along with nine other comparison models of varying masses and opacities. A study of the observations shows that the division of these variables into two types by observers might be explained by a slightly different mass for each type, thus making the division dependent on the star's previous evolution. The non-linear results obtained by this study show that a mass of 0.6 M☉ is a good one to use, and that M = 0.5 M☉ makes little difference (although M = 0.8 M☉ seems to be too high). The results in general compare well with the observations, as both also show the split into two types of light curve. Three good models of individual stars are presented, on a par with the models of BL Herculis published by Carson, Stothers and Vemury. The bumps in the light and velocity curves of many of the models seem to be real, caused by the Christy "echo". A few of the models show some RV Tauri behaviour. One in particular shows very strange behaviour, involving a violent 81ternation of light curve shapes. Models constructed using the Los Alamos opacities do not produce results as consistent with observations as those of the main survey. The study shows that these stars can be represented by hydrodynamic models of mass 0.6 M☉ using the Carson opacities, but also that convection may be important in the cooler stars in order to model them accurately. This indicates the direction in which further theoretical work may lie.

Thesis--University of Florida. / Description based on print version record. Typescript. Vita. Includes bibliographical references (leaves 180-181).

High resolution observations have been made of a number of southern Cepheids to make an observational and theoretical study of Cepheid variables using radial velocities. The stars studied were part of a long term programme to observe southern variable stars, from which a valuable database of radial velocities gathered over a long period were available. Sixteen échelle spectrograph orders in the wavelength region 5400 - 8600Å were used, which included a number of absorption lines covering a range of species and excitation potentials. The line bisector technique was used to measure stellar and telluric lines and to obtain radial velocities. To improve the precision of the radial velocities we used telluric lines to calibrate the observations to a common reference frame. The radial velocities have a precision of ~300ms⁻¹ allowing the detection of velocity differences of ~1 kms⁻¹ with confidence. The radial velocity data obtained at Mount John University Observatory (MJUO) was combined with data from various sources to determine the orbits of any Cepheids exhibiting orbital motion. The various orbital parameters were determined for a number of systems and where radial velocities for the companions exist, some estimate of the mass was made. The precision of the radial velocities obtained from MJUO also allowed us to search for line level effects for a number of species among the Cepheid spectra. A number of IAU standard stars were observed to calibrate the radial velocities obtained at MJUO to the IAU standard scale. The radial velocities from MJUO were found not to differ significantly from the IAU values. Binary Cepheids are particularly useful in the determination of Cepheid masses, which are still an active topic for astronomical research. The value of the MJUO data was that it provided a consistent set of data against which other sources of data could be compared. For 8 of the Cepheids new or improved orbital solutions were found. They are Y Car, YZ Car, AX Cir, BP Cir, S Mus, V636 Sco, V350 Sgr, W Sgr and T Mon. Of these 8 systems, 3 had radial velocities for their respective companions which allowed the determination of the mass of the Cepheids. Masses were determined for the 9 day Cepheid S Mus (6.0±0.4M⊙), the double mode Cepheid Y Car (4.5±1.8 M⊙) and the 5 day Cepheid V350 Sgr (6.0±0.9 M⊙). New results presented here include the first orbital solution for the binary Cepheid AX Cir, a completely revised orbital solution for the binary Cepheid YZ Car which established its eccentricity, and orbital motion. The binary Cepheid BP Cir however was found to require a new pulsation period of 2.39819d to fit the observed pulsational velocities. Observations of the suspected binary Y Oph show it to be an unusual Cepheid with no evidence of binarity (~0.5 kms⁻¹) in our data. Finally, the 5 day Cepheid W Sgr was observed to have the lowest orbital amplitude measured. We discussed the line level effects found in our observations, where a number of spectral lines were observed to show departures from the Fei velocity curve. Line level effects were observed in H⍺, CaⅡ, BaⅡ, FeⅡ, SiⅠ and SiⅡ. Most of the Cepheids were observed to show the same progression of line level effects, with the best example being the bright Cepheid β Dor. The SiⅡ velocities indicate that these lines have the lowest velocity amplitude and form deeper in the atmosphere than the FeⅠ, where as the CaⅡ and H⍺ lines were all observed to have much greater velocity amplitudes with the peak of these velocity curves occurring later, in pulsational phase. These observations are consistent with the lines forming at different depths as a density wave propagates through the atmosphere. X Sgr is peculiar due to its interesting spectra which at certain phases show line doubling and at most other phases the lines were asymmetric. These observations are interpreted to support the idea that X Sgr has strong shock waves present and that X Sgr has greater atmospheric transparency in the spectral region near 6000Å. We also present the results of dynamical modelling of a pulsating Cepheid. Using a non-linear radiative hydrodynamic code developed by A. Fokin, we have modelled two Cepheids, AX Cir and YZ Car. These models have then been compared with the observations obtained here. After extensive modelling using the latest OP opacities, it has been determined that the Cepheid AX Cir can be modelled using parameters L = 2050 L⊙, M = 4.8 M⊙ and Teff = 5900K. The model reproduced the observed stellar characteristics, such as the photometric amplitude and pulsational period. Comparison between the observations and the model for the selected spectral lines, FeⅠ 5576Å, SiⅡ 6347Å, BaⅡ 5853Å and CaⅡ 8542Å show good agreement with similar amplitudes and velocity curves. With no strong shock waves being produced by the model, the observed line level effects can be explained by a density wave. The 18 day Cepheid YZ Car was chosen to explore the capabilities of the radiative hydrodynamic code for a long period Cepheid. The best model developed that reproduced the observed stellar characteristics had parameters L = 9350 L⊙, M = 7.7 M⊙ and Teff = 5590K. The period was 18.314 days and the bolometric light curve agreed well with the observed visual light curve. Comparison of the theoretical and observed radial velocities showed good agreement.

High resolution observations have been made of a number of southern Cepheids to make an observational and theoretical study of Cepheid variables using radial velocities. The stars studied were part of a long term programme to observe southern variable stars, from which a valuable database of radial velocities gathered over a long period were available. Sixteen échelle spectrograph orders in the wavelength region 5400 - 8600Å were used, which included a number of absorption lines covering a range of species and excitation potentials. The line bisector technique was used to measure stellar and telluric lines and to obtain radial velocities. To improve the precision of the radial velocities we used telluric lines to calibrate the observations to a common reference frame. The radial velocities have a precision of ~300ms⁻¹ allowing the detection of velocity differences of ~1 kms⁻¹ with confidence. The radial velocity data obtained at Mount John University Observatory (MJUO) was combined with data from various sources to determine the orbits of any Cepheids exhibiting orbital motion. The various orbital parameters were determined for a number of systems and where radial velocities for the companions exist, some estimate of the mass was made. The precision of the radial velocities obtained from MJUO also allowed us to search for line level effects for a number of species among the Cepheid spectra. A number of IAU standard stars were observed to calibrate the radial velocities obtained at MJUO to the IAU standard scale. The radial velocities from MJUO were found not to differ significantly from the IAU values. Binary Cepheids are particularly useful in the determination of Cepheid masses, which are still an active topic for astronomical research. The value of the MJUO data was that it provided a consistent set of data against which other sources of data could be compared. For 8 of the Cepheids new or improved orbital solutions were found. They are Y Car, YZ Car, AX Cir, BP Cir, S Mus, V636 Sco, V350 Sgr, W Sgr and T Mon. Of these 8 systems, 3 had radial velocities for their respective companions which allowed the determination of the mass of the Cepheids. Masses were determined for the 9 day Cepheid S Mus (6.0±0.4M⊙), the double mode Cepheid Y Car (4.5±1.8 M⊙) and the 5 day Cepheid V350 Sgr (6.0±0.9 M⊙). New results presented here include the first orbital solution for the binary Cepheid AX Cir, a completely revised orbital solution for the binary Cepheid YZ Car which established its eccentricity, and orbital motion. The binary Cepheid BP Cir however was found to require a new pulsation period of 2.39819d to fit the observed pulsational velocities. Observations of the suspected binary Y Oph show it to be an unusual Cepheid with no evidence of binarity (~0.5 kms⁻¹) in our data. Finally, the 5 day Cepheid W Sgr was observed to have the lowest orbital amplitude measured. We discussed the line level effects found in our observations, where a number of spectral lines were observed to show departures from the Fei velocity curve. Line level effects were observed in H⍺, CaⅡ, BaⅡ, FeⅡ, SiⅠ and SiⅡ. Most of the Cepheids were observed to show the same progression of line level effects, with the best example being the bright Cepheid β Dor. The SiⅡ velocities indicate that these lines have the lowest velocity amplitude and form deeper in the atmosphere than the FeⅠ, where as the CaⅡ and H⍺ lines were all observed to have much greater velocity amplitudes with the peak of these velocity curves occurring later, in pulsational phase. These observations are consistent with the lines forming at different depths as a density wave propagates through the atmosphere. X Sgr is peculiar due to its interesting spectra which at certain phases show line doubling and at most other phases the lines were asymmetric. These observations are interpreted to support the idea that X Sgr has strong shock waves present and that X Sgr has greater atmospheric transparency in the spectral region near 6000Å. We also present the results of dynamical modelling of a pulsating Cepheid. Using a non-linear radiative hydrodynamic code developed by A. Fokin, we have modelled two Cepheids, AX Cir and YZ Car. These models have then been compared with the observations obtained here. After extensive modelling using the latest OP opacities, it has been determined that the Cepheid AX Cir can be modelled using parameters L = 2050 L⊙, M = 4.8 M⊙ and Teff = 5900K. The model reproduced the observed stellar characteristics, such as the photometric amplitude and pulsational period. Comparison between the observations and the model for the selected spectral lines, FeⅠ 5576Å, SiⅡ 6347Å, BaⅡ 5853Å and CaⅡ 8542Å show good agreement with similar amplitudes and velocity curves. With no strong shock waves being produced by the model, the observed line level effects can be explained by a density wave. The 18 day Cepheid YZ Car was chosen to explore the capabilities of the radiative hydrodynamic code for a long period Cepheid. The best model developed that reproduced the observed stellar characteristics had parameters L = 9350 L⊙, M = 7.7 M⊙ and Teff = 5590K. The period was 18.314 days and the bolometric light curve agreed well with the observed visual light curve. Comparison of the theoretical and observed radial velocities showed good agreement.

We quantify the structure and scale of the Universe using redshift surveys of galaxies and QSOs and observations of Galactic open star clusters. We obtain the galaxy power spectrum from the Durham/UKST Galaxy Redshift Survey. By comparing the shape of the observed power spectrum to the APM real space power spectrum, we quantify the size of the redshift space distortions and find β = Ω(^0.6)/b=0.60±0.35. We also apply counts-in-cells analysis to the Durham/UKST and Stromlo-APM Surveys and measure the skewness directly out to 20h(^-1)Mpc. We find that the skewness measured from CDM models can only be reconciled with that of galaxies if bias is non-linear. We make predictions for the clustering in the 2dF QSO Survey by constructing mock catalogues from the Hubble Volume N-body simulation, with geometry, selection function and clustering matching those expected in the completed Survey. We predict that the correlation function will be reliably measured out to ~ 1, 000h(^-1)Mpc and the power spectrum out to 500h(^-1)Mpc. We measure the power spectrum from the 2dF QSOs observed by January 2000 and find it has a shape of F ~ 0.1. We also find little evolution in the clustering amplitude as a function of redshift. We obtain constraints on the cosmo- logical parameters Ωn and β by combining results from modeling geometric distortions introduced into the clustering pattern due to inconsistent cosmological assumptions and results from the QSO-mass bias. Finally, we consider the scale of the Universe. We check the calibration of the Cepheid Period-Luminosity relation using U,B,V and K'band imaging of Galactic Open Clusters containing Cepheids and measure the distance modulus to the LMC to be 18.51 ±0.10. However, we find anomalous colour-colour diagrams for two clusters and suggest that the effects of metallicity may be greater than previously considered.