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Does the A-type Metallic-Line Star IW Persei Have Non-Uniform Chemical Anomaly on the Surface?

Takeda Y.

Acta Astronomica

2023

Vol. 73, No. 1

35--55

IW Per, a single-lined spectroscopic binary with a short period of 0.92 d, is known to be a A-type metallic-line (Am) star showing anomalous line strengths of specific elements. It was previously reported that its equivalent widths of CaII 3934, SrII 4215, and ScII 4320 lines (important key lines characterizing the Am anomaly) show cyclic variations in accordance with the rotation phase, implying that the chemical peculiarities on the surface are not uniform but of rather patchy distribution. However, no attempts of reconfirmation have been done so far. In order to check the validity of this finding, ten high-dispersion spectra of IW Per covering different phases were analyzed for these lines by using the spectrum-fitting technique to determine the abundances of Ca, Sr, and Sc and the corresponding equivalent widths. It turned out, however, that no firm evidence of such phase-dependent line-strength variations could be found, suggesting that significant chemical inhomogeneity on the surface of IW Per is unlikely to exist, at least during the period of our observations (2010 December). Meanwhile, the abundances of O, Si, Ca, Ba, and Fe resulting from the 6130-6180 Å region corroborate that IW Per is a distinct Am star (though the degree of peculiarity differs from element to element) despite that its rotational velocity (≈100 km/s) is near to the limit of Am phenomenon.