Photometry of cepheid variables
Qualitative photometric analysis system for metal-rich and metal-poor cepheid variable stars
Kelsall, T. N.↗
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A general survey of classical cepheid variable stars
Classical Cepheid variables and their spectra, infrared astronomy, and interstellar matter
Wilson, R. M.↗
Multicolor photometry of supergiants and Cepheids
Color indices for stellar spectrophotometry of Cepheid variable and supergiant stars
Kelsall, T.↗
Methods used to determine the intrinsic colors of supergiants and cepheids
Reddening effects in determining intrinsic color of supergiant and cepheid variable stars
Kelsall, T.↗
Velocity gradients and microturbulence in Cepheids
Variations of the microturbulent velocity with phase and height in the atmosphere were reported in classical Cepheids. It is shown that these effects can be understood in terms of variations of the velocity gradient in the atmospheres of these stars.
Karp, A. H.↗
Velocity gradients and microturbulence in Cepheids.
Variations of the microturbulent velocity with phase and height in the atmosphere have been reported in classical Cepheids. It is shown that these effects can be understood in terms of variations of the velocity gradient in the atmospheres of these stars.
Karp, A. H.↗
Cepheid Modeling
Mathematical techniques are used to model the instability behavior of Cepheid variables.
Fischel, D.↗
Ultraviolet observations of classical Cepheids by OAO-2
OAO-2 observations of eight bright classical Cepheids in the wavelength region 1910 A to 4250 A are presented. The data for RT Aurigae, alpha Ursa Minoris, delta Cephei, and gamma Ophiuchi show excellent agreement with ground based photometry in the wavelength region of overlap and are consistent with a simple extrapolation of light curve properties from the visible region. However, in the ultraviolet, the light curve of beta Doradus shows two small flux bumps, at phases of 0.75 and 0.85, in addition to the well known bump at phase 0.0. All three bumps should probably be associated with the arrival of shocks at the stellar surface.
Hutchinson, J. L.↗
Observations of long-period Cepheids between l = 294 and 331 deg
Photoelectric and spectroscopic observations of long-period Cepheids, as well as 21-cm profiles in the directions of these young stars, are presented for the Crux-Centaurus-Circinus-Norma section of the Milky Way. The UBV data have been used to revise periods and light-curve parameters and ultimately to calculate the distances of these stars. From the spectroscopic information velocity estimates have been made. Finally, the stellar velocities have been compared with H I gas motions detected along the same line of sight. These results are briefly discussed with a view to understanding the spiral structure of the region.
Grayzeck, E. J.↗
Observations of classical cepheids
The observations of classical Cepheids are reviewed. The main progress that has been made is summarized and some of the problems yet to be solved are discussed. The problems include color excesses, calibration of color, duplicity, ultraviolet colors, temperature-color relations, mass discrepancies, and radius determination.
Pel, J. W.↗
Ultraviolet spectroscopy of F and G supergiants with IUE. I - First results of Cepheid variables
The analysis deals with the bright Cepheids observed from the IUE satellite, over several days, at a speed and spectral resolution suitable to study both the cores of Mg II at 2796 and 2803 A and the presence and strength of the more prominent emission lines in the far ultraviolet. The observations are discussed in some detail. Some qualitative results are examined.
Parsons, S. B.↗
Chromospheres of classical Cepheids
The International Ultraviolet Explorer spectra of five classical Cepheids were obtained in the short and the long wavelength regions at low dispersion, curves and emission line strengths were obtained from the low resolution spectra. The amplitudes of the light curves increase with decreasing wavelength except around 1550 A where the amplitude is surprisingly small. The emission line fluxes behave differently in the various stars and it appears that bumps in the ultraviolet light curves are related to the behavior of the chromospheres. However, the strengths of the emission lines are roughly comparable to nonvariable stars of similar temperature and luminosity. The high resolution spectra were used to study the fluxes of the emission from the Mg II h and k lines. It is found that the emission components come and go during the cycles and the behavior differs from one star to another, with generally stronger and more persistent emission at longer periods. This is compared with the times of appearance of the Ca II H and K emission features and provides insight into the way in which the chromosphere reacts to shock waves generated by the pulsation of the star.
Schmidt, E. G.↗
Einstein observations of three classical Cepheids
We have looked for X-ray emission from the classical Cepheids delta Cep, beta Dor, and zeta Gem during phases when the latter two stars show emission in low excitation chromospheric lines. No X-ray flux was detected except possibly from zeta Gem at phase 0.26. Derived upper limits are in line with emission flux or upper limits obtained for other F and G supergiants.
Bohm-Vitense, E.↗
The chromospheres of classical Cepheids. II - High-resolution profiles of the Mg II h and k lines. III - A search for transition region emission lines
The profiles of the Mg II h and k lines near 2900 A are studied on the basis of IUE long wavelength camera high resolution spectra for a number of phases of each of five Cepheids. An emission feature often appears at the centers of the two lines, and there are central absorption features as well, due to interstellar or circumstellar gas, which are often multiple and may or may not originate in a region which is at least several tenths of a stellar radius in extent. While the mean flux of the emission is lower than for nonvariable stars of similar temperature and luminosity, the maximum strength of the emission is in keeping with the instantaneous temperature. In the second part of this paper, it is noted that little significant chromospheric emission could be found in the short wavelength region for the shortest period star in the sample, Delta Cep. In order to detect the emissions or place lower limits on the fluxes, longer exposures have been obtained at several critical phases for three of the five stars. While the strength, when detected, is similar to that of nonvariables, the upper limits at other places indicate smaller fluxes than those observed in nonvariable stars.
Schmidt, E. G.↗
The binary companion of the classical Cepheid AW Per
An analysis of IUE spectra of the companion of AW Per shows it to be an extreme BpSi/HeW star with a spectral type of B7 V to B8 V. The flux of the composite spectrum from 1200 A through V is found to be well matched by F7 Ib and B8 V standard stars with Delta M(V) = 3.1 mag. The results suggest that the mass of the Cepheid must be greater than 4.7 solar masses. The flux distribution of the star and the mass limits from the orbit are consistent with a companion that is itself a binary.
Evans, Nancy Remage↗
Emission lines in the long period Cepheid l Carinae
For the Cepheid (l) Carinae with a pulsation period of 35.5 days we have studied the emission line fluxes as a function of pulsational phase in order to find out whether we see chromosphere and transition layer emission or whether we see emission due to an outward moving shock. All emission lines show a steep increase in flux shortly before maximum light suggestive of a shock moving through the surface layers. The large ratio of the C IV to C II line fluxes shows that these are not transition layer lines. During maximum light the large ratio of the C IV to C II line fluxes also suggests that we see emission from a shock with velocities greater than 100 km/sec such that C IV emission can be excited. With such velocities mass outflow appears possible. The variations seen in the Mg II line profiles show that there is an internal absorption over a broad velocity band independent of the pulsational phase. We attribute this absorption to a circumstellar 'shell'. This 'shell' appears to be seen also as spatially extended emission in the O I line at 1300 angstrom, which is probably excited by resonance with Ly beta.
Boehm-Vitense, Erika↗
Multifrequency comparison of Cepheids and nonvariable supergiants
New IUE data and infrared J, H, K, L, and M observations have been obtained for nonvariable yellow supergiants and the prototype classical Cepheid Delta Cephei. These data have been combined with data in the literature to make a comparison between nonvariable yellow supergiants and Delta Cephei from the UV through the near-IR. The supergiant sequence shows a smooth progression of energy distributions with spectral type over this extended wavelength range. The Delta Cephei energy distributions on the descending branch of the light curve (free-fall portion of the pulsation curve) are well matched by supergiant energy distributions with the same (B-V)(0) for most phases. At the hottest phases, however, there is some extra flux at 3000 A as compared with the nonvariables. The Delta Cephei observation on the ascending branch of the light curve ('piston' phase of the pulsation cycle) has slightly more UV light than would be predicted from either the supergiant observations or the free-fall Delta Cephei phases.
Evans, Nancy R.↗