THE RELATIONSHIP BETWEEN SPECTRUM AND LIGHT VARIATIONS IN THE MAGNETIC Ap STAR HR 1217 (HD 24712)

• Published in: Publications of the Astronomical Society of the Pacific 1979-10, Vol.91 (543), p.648-656
• Main Author: BONSACK, WALTER K.
• Format: Article
• Language: English
• Subjects: Ap stars; Light; Line spectra; Optical filters; Spectrograms; Stellar spectra; Stellar spectral lines; Variable stars; Visible spectrum; Wavelengths
• ISSN: 0004-6280; 1538-3873
• DOI: 10.1086/130557

Measurements of equivalent widths and line-blocking coefficients have been made from 3850 Å to 5650 Å in the spectrum of HR 1217, using photographic data. The variation of the equivalent widths of the Eu H lines suggests a revised period of 12ḍ460 in order to phase the present data with those of Preston (1972). The variation of equivalent widths shows a dependence of amplitude on atomic number which resembles that found by Preston, but there are clear discontinuities in the relationship. The line blocking coefficient was measured in unweighted 50 Â bands throughout the spectral region, except between 4750 Å and 5200 Å, and weighted by the sensitivity functions of the v, b, and y bands of the Strömgren photometric system. The line blocking variation in the filter bands is found to account for approximately one-half of the light variation observed by Wolff and Morrison (1973); the spectroscopy and photometry considered together demonstrate the need for continuous opacity variation in the filter bands to account for the light variation. Redistribution of flux from the ultraviolet appears to have no significant role in the light variation, which is not unexpected in this cool Ap star.