The Radial Velocity Variations in Iota Herculis

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Session 22 -- Stellar Spectroscopy, Atmospheres, Models, Intrinsic Variables, Theory, Part II
Display presentation, Tuesday, June 13, 1995, 9:20am - 6:30pm

[22.12] The Radial Velocity Variations in Iota Herculis

C.L.Mulliss and N.D.Morrison (Ritter Obs., U. of Toledo)

$\iota$ Herculis is a well-studied B3 IV star that exhibits a wide variety of periodic behaviors on many time scales. It has been reported to be a single-lined spectroscopic binary with a period of about 114 days. It has also been observed to display periodic changes in line profiles, wavelengths, and (possibly) equivalent widths due to the effects of pulsation. On the HR diagram, $\iota$ Her is situated between 2 different classes of pulsating variable stars: the 53 Persei class of slowly pulsating stars and the $\beta$ Cephei class of rapidly pulsating stars. For this reason, it has recently been suggested that $\iota$ Her may exhibit the pulsational characteristics of both classes of stars (Mathias, P. and Waelkens, C. 1995, A\&A, submitted).

We have obtained 61 high-resolution CCD/\'echelle spectra of $\iota$ Her with the 1-m telescope of Ritter Observatory. These observations were obtained from February 2, 1994 through March 11, 1995 with a resolution of $R \simeq 25,000$. The exposure times ranged from 300 to 2400 seconds yielding a typical SNR of 100 - 150. The data consist of single observations (1 spectrum per night) as well as many time series of spectra (each with up to 7 spectra taken consecutively over several hours).

We have measured the radial velocity of a strong S II (multiplet 6) absorption line (5453.810\AA) in our spectra. Beginning with a set of approximate orbital elements we applied an iterative process to determine the orbit. We subtracted an orbit from the velocity data, fitted periodic functions to the residuals, subtracted that fit from the data, and repeated the process. Thus, we have obtained separate least-squares solutions for the orbital elements and the short-period pulsational velocity variations. This task was made difficult by the fact that the velocity variations due to pulsations have an amplitude comparable to that of the orbit. Our analysis has yielded a new estimate of the orbital elements and a new description of the short-period residual velocity variations.

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