Abstract
Biraud1 and Bond2 have recently identified the rapid and erratic variable AP Lib with the radio source PKS 1514–24. The identification of AP Lib from the chart given by Bolton et al.3 for PKS 1514–24 is confirmed in brightness and in position given in the General Catalogue of Variable Stars4. Bond has pointed out that Searle and Bolton5 have noted that AP Lib has no emission lines between 6500 and 4300 Å and that Westerlund and Wall6 have classified AP Lib as an N galaxy. This communication attempts to answer the question raised by Biraud concerning the similarity of AP Lib to BL Lac and describes two spectra (0.5 mm wide) of AP Lib obtained on August 16 and 18, 1971, with the 74-inch telescope at Mount Stromlo Observatory. The spectra cover the wavelength range 6800 to 3600 Å with a resolution of 3 Å (dispersion 100 Å mm−1) and with exposure times of 60 and 90 min. During both exposures the image of AP Lib was observed to be stellar when the seeing image was less than 1.5 arc s in diameter, supporting the classification of AP Lib as an N-type galaxy. Both spectra of AP Lib are continuous over the wavelength range covered and show no features in emission or absorption stronger than 200 mÅ equivalent width which cannot be ascribed to night sky emissions7. It is apparent from the energy distribution in the continuous spectrum that AP Lib, at the time observed, possesses a marked ultraviolet excess relative to stars of similar blue-visual gradient. This is in agreement with the Westerlund and Wall6 photometry of PKS 1514–24. The present results therefore indicate a marked spectrophotometric similarity between AP Lib and BL Lac.
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References
Biraud, F., Nature, 231, 178 (1971).
Bond, H. E., Astrophys. J. Lett., 167, L79 (1971).
Bolton, J., Clarke, M. E., and Ekers, R. D., Austral. J. Phys., 18, 627 (1965).
Kukarkin, B. V., Parenago, P. O., Efremov, Y. I., and Kholopov, P. N., General Catalogue of Variable Stars (third ed.) (Moscow, 1970).
Searle, L., and Bolton, J. G., Astrophys. J. Lett., 154, L101 (1968).
Westerlund, B., and Wall, J., Astron. J., 74, 335 (1969).
Broadfoot, A. L., and Kendall, K. R., J. Geophys. Res., 73, 426 (1968).
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RODGERS, A. Spectrum of AP Lib (≡ PKS 1514–24). Nature Physical Science 233, 75 (1971). https://doi.org/10.1038/physci233075a0
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DOI: https://doi.org/10.1038/physci233075a0
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