An analysis of W Virginis.

Abstract

view Abstract Citations (5) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS An analysis of W Virginis. Abt, Arthur Abstract W Virgin is is believed to be a typical population II Cepheid. A study of this star was therefore made to provide a comparison with the classical Cepheids. The data consist of a photoelectric light curve by Kron and Gordon, a photoelectric color curve by Whitford and Code, and spectra of dispersion 10 Amm by Sanford and Abt. The radial velocity curve, derived by R. F. Sanford, is discontinuous. Just before maximicrons light a set of weak absorption lines appears at -95 kmsec. These lines quickly strengthen with time and move longward. Then they fade and disappear with a velocity of -40 km$sec just after the next light maximum. So for several days around maximum light two sets of weak absorption lines are present. The radial velocity curve was integrated over time to obtain displacements. These show a symmetrical expansion and contraction with a total displacement of 36 million kilometers, or 50 solar radii. The displacement curve, however, shows an overlap of cycles such that when the upper part of the atmosphere is contracting, the lower part is expanding. The curve suggests that the period of pulsation is twice the period of light variation and the time between pulses is just one-half the duration of one pulse. The colors were used to derive effective temperatures and bolometric corrections to the light curve. From these we obtained relative radii, which show a radius change by a factor of at least three. However, when the relative radii curve was fitted to the displacement curve to get the scale of the changes, a maximum radius less than the total displacement was derived. The method fails probably because the continuous and line spectra are formed predominantly in parts of an extended atmosphere that have different motions. Curves of growth indicate that during phases of double lines the excitation temperatures for the shortward components, which are formed lower in the atmosphere, are 8000 to 10000 hotter than those for the longward components. The electron pressure reaches a minimum at maxi- *Of papers presented at the Joint Meeting of the Americaii Astronomical Society and the Astronomical Society of the Pacific, Victoria, B. C., June 25-28, 1952. t Submitted as partial fulfillment of the requirements for Ph.D. at the California Institute of Technology. μm expansion. ionization temperatures were calculated. The various determinations of the temperature at any one phase indicate too large a range for a normal stellar atmosphere; in an extended atmosphere the temperature gradient could be large enough to give the observed temperature range'. The star shows a large spectrum-color difference. The ionization temperatures indicate a range in spectral types from Fo to F8, while the colors correspond to F4 to K2. The largest difference occurs at maximum expansion. The classical Cepheids show no such differences; an unreddened one of the same period would have a spectral type range of F7 to G9. The spectrumcolor difference for W Virginis may be due to an extended atmosphere or to the impossibility of using the color-effective temperature relation of population I stars for population II giants. Moitnt W?lson and Palomar Observatories, Carnegie Institution of Washington, and Calsfornia Institute of Technology. Publication: The Astronomical Journal Pub Date: October 1952 DOI: 10.1086/106732 Bibcode: 1952AJ.....57..158A full text sources ADS | data products SIMBAD (1)