Study of Cepheid Variables as a Joint Spectroscopy Project

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In the late 1940's, P.C. Keenan and J.A. Hynek conducted exploration of the near-IR with the then available 1-N photographic plates. They noted (1950) that an O I triplet feature at 777.2 to 777.5 nm., arising from a metastable state in the oxygen atom, was particularly strong in absorption in highly luminous stars, ranging from types B8III/B8Ia through G2Ib/Ia, with equivalent widths of 0.6 to 2.3 Angstroms. It was pointed out by Keenan (as part of a detector dissertation project in 1962, on a 1.75-m telescope) that Cepheid variables live within this region of the HR diagram, and several Cepheid variable stars were selected as target stars along with several dozen stable stars in the luminosity classes III through Ia, and spectral types from late-B through early-M. The predicted variation in the triplet was observed, but not then studied in detail. The case will be made that exploitation of small amateur telescopes (perhaps as a joint campaign), equipped with the currently available spectrographs/CCD cameras, can outperform the earlier telescopes of the 2-meter class, and allow investigation of this type of spectral feature. The increase of quantum efficiency from about 2-4% to 60-80% allows a 14-20 inch system, devoting 100% to the task at hand, to tackle the targets requiring more than 2.2 meters in the days when telescope time for only a few nights per year was available. In the present instance, we would like to investigate whether the spectral feature reaches its peak absorption in phase with the maximum light output from the pulsing star, or does it lag or lead it. With the same instrument, or with a co-mounted companion, we can monitor the U, B, V, or R stellar output while collecting the spectra. Other small-telescope spectroscopy projects might be found from reviews of the literature from the mid-1900s.

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