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Photometric Properties of Peculiar Red Giants

  • Conference paper
Cool Stars with Excesses of Heavy Elements

Part of the book series: Astrophysics and Space Science Library ((ASSL,volume 114))

Abstract

Four quite different kinds of information are commonly obtained through photometric observations: (1) magnitudes and colors on various systems; (2) energy distributions, leading to estimates of effective temperature, tests of model atmospheres, and the detection of companions or circumstellar shells; (3) spectroscopic data from narrow-band photometry of strong spectral features; and (4) light curves of variable stars. The photometric properties of the peculiar red giants — the cool carbon and S-type stars, and the warmer R-type carbon stars, CH stars, barium stars, and related objects — are reviewed with emphasis on what can be learned from each of these kinds of photometric data.

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References

  • Aaronson, M. 1984, in IAU Symp. No. 108, Structure and Evolution of the Magellanic Clouds, ed. S. van den Bergh and K. S. de Boer (Reidel), p. 183.

    Google Scholar 

  • Aaronson, M., Da Costa, G. S., Hartigan, P., Mould, J. R., Norris, J., and Stockman, H. S. 1984, Astrophys. J. (Letters) 277, L9.

    Google Scholar 

  • Alexander, J. B., and Branch, D. 1974, Mon. Not. Roy. Astron. Soc. 167, 539.

    ADS  Google Scholar 

  • Alksne, Z., Alksnis, A., and Dzervitis, U. 1983, Properties of Carbon Stars of the Galaxy ( Riga: Acad. Sci. Latvian S.S.R.).

    Google Scholar 

  • Augason, G. C., Bregman, J. D., Johnson, H. R., and Witteborn, F. C. 1984, preprint.

    Google Scholar 

  • Baird, S. R. 1981, Astrophys. J. 245, 208.

    Article  ADS  Google Scholar 

  • Baird, S. R. 1982, Astrophys. J. 252, 305.

    Article  ADS  Google Scholar 

  • Baumert, J. H. 1971, in Proc. Conf. on Late-Type Stars, ed. G. W. Lock- wood and H. M. Dyck ( Kitt Peak Nat’l Obs. Contrib. No. 554 ), p. 155.

    Google Scholar 

  • Baumert, J. H. 1972, Ph.D. dissertation, Ohio State University.

    Google Scholar 

  • Baumert, J. H. 1974, Astrophys. J. 190, 85.

    Article  ADS  Google Scholar 

  • Bessell, M. S., Wood, P. R., and Lloyd Evans, T. 1983, Mon. Not. Roy. Astron. Soc. 202, 59.

    ADS  Google Scholar 

  • Bidelman, W. P. 1980, Publ. Warner and Swasey Obs. 2, No. 6.

    Google Scholar 

  • Blackwell, D. E., and Shallis, M. J. 1977, Mon. Not. Roy. Astron. Soc. 180, 177.

    ADS  Google Scholar 

  • Blackwell, D. E., Petford, A. D., and Shallis, M. J. 1980, Astron. Astrophys. 82, 249.

    ADS  Google Scholar 

  • Blanco, V. M., McCarthy, M. F., and Blanco, B. M. 1980, Astrophys. J. 242, 938.

    Article  ADS  Google Scholar 

  • Bohm-Vitense, E. 1980, Astrophys. J. (Letters) 239, L79.

    Google Scholar 

  • Bond, H, E. 1984, in Future of Ultraviolet Astronomy Based on Six Years of IUE Research, NASA (in press).

    Google Scholar 

  • Bond, H. E., and Neff, J. S. 1969, Astrophys. J. 158, 1235.

    Article  ADS  Google Scholar 

  • Campbell, L. 1955, Studies of Long Period Variables ( Cambridge: Amer. Assoc. Variable Star Observers).

    Google Scholar 

  • Catchpole, R. M., Robertson, B. S. C., Lloyd Evans, T. H. H., Feast, M. W., Glass, I. S., and Carter, B. S. 1979, S. African Astron. Obs. Circulars 1, 61.

    ADS  Google Scholar 

  • Catchpole, R. M., Robertson, B. S. C., and Warren, P. R. 1977, Mon. Not. Roy. Astron. Soc. 181, 391.

    ADS  Google Scholar 

  • Cottrell, P. L. 1979, Mon. Not. Roy. Astron. Soc. 189, 13.

    Google Scholar 

  • Cottrell, P. L., and Lambert, D. L. 1982, Astrophys. J. 261, 595.

    Article  ADS  Google Scholar 

  • Davis, D. N. 1934, Publ. Astron. Soc. Pacific 46, 267.

    Article  ADS  Google Scholar 

  • Dominy, J. F., and Lambert, D. L. 1983, Astrophys. J. 270, 180.

    Article  ADS  Google Scholar 

  • Dzervitis, U. 1981, Investigations of the Sun and Red Stars, No. 13, p. 22.

    Google Scholar 

  • Eaton, J. A., Johnson, H. R., O’Brien, G. T., and Baumert, J. H. 1984, Astrophys. J. (in press).

    Google Scholar 

  • Eggen, O. J. 1972a, Astrophys. J. 174, 45.

    Article  ADS  Google Scholar 

  • Eggen, O. J. 1972b, Astrophys. J. 177, 489.

    Article  ADS  Google Scholar 

  • Eggen, O. J. 1972c, Mon. Not. Roy. Astron. Soc. 159, 403.

    ADS  Google Scholar 

  • Eggen, O. J. 1975, Publ. Astron. Soc. Pacific 87, 111.

    Article  ADS  Google Scholar 

  • Faÿ, T. D. 1974, Astrophys. J. 190, 597.

    Article  ADS  Google Scholar 

  • Faÿ, T., and Honeycutt, R. K. 1972, Astron. J. 77, 29.

    Article  ADS  Google Scholar 

  • Faÿ, T., Honeycutt, R. K., and Warren, W. H., Jr. 1973, in Conference on Red Giant Stars, ed. H. R. Johnson, J. P. Mutschlecner, and B. F. Peery, Jr. ( Bloomington: Indiana Univ. ), p. 130.

    Google Scholar 

  • Faÿ, T. D., and Ridgway, S. T. 1976, Astrophys. J. 203, 600.

    Article  ADS  Google Scholar 

  • Faÿ, T. D., Warren, W. H. Jr., Johnson, H. R., and Honeycutt, R. K. 1974, Astron. J. 79, 634.

    Article  ADS  Google Scholar 

  • Feast, M. W., Catchpole, R. M,, and Glass, I. S. 1976, Mon. Not. Roy. Astron. Soc. 174, 81 P.

    Google Scholar 

  • Feast, M. W., Robertson, B. S. C., Catchpole, R. M., Lloyd Evans, T., Glass, I. S., and Carter, B. S. 1982, Mon. Not. Roy. Astron. Soc. 201, 439.

    ADS  Google Scholar 

  • Fix, J. D. 1976, Astrophys. J. 203, 463.

    Article  ADS  Google Scholar 

  • Fix, J. D., and Neff, J. S. 1975, Mon. Not. Roy. Astron. Soc. 173, 83 P.

    ADS  Google Scholar 

  • Forrest, W. J., Gillett, F. C., and Stein, W. A. 1975, Astrophys. J. 195, 423.

    Article  ADS  Google Scholar 

  • Frogel, J. A., and Blanco, V. M. 1984, in IAU Symp. No. 105, Observational Tests of the Stellar Evolution Theory, ed. A. Maeder and A. Renzini (Reidel), p. 175.

    Google Scholar 

  • Frogel, J. A., Cohen, J. G., Persson, S. E., and Elias, J. H. 1981, in Physical Processes in Red Giants, ed. I. Iben, Jr., and A. Renzini (Reidel), p. 159.

    Google Scholar 

  • Frogel, J. A., Dickinson, D. F., and Hyland, A. R. 1975, Astrophys. J. 201, 392.

    Article  ADS  Google Scholar 

  • Frogel, J. A., and Hyland, A. R. 1972, Mém. Soc. Roy. Sci. Liège, 6th Ser., 3, 111.

    Google Scholar 

  • Fujita, Y. 1970, Interpretation of Spectra and Atmospheric Structure in Cool Stars ( Tokyo: Univ. of Tokyo Press).

    Google Scholar 

  • Gauzit, M. J. 1959, Ann. d’Astrophys. 22, 781.

    ADS  Google Scholar 

  • Gehrz, R. D., and Woolf, N. J. 1971, Astrophys. J. 165, 285.

    Article  ADS  Google Scholar 

  • Gillett, F. C., Merrill, K. M., and Stein, W. A. 1971, Astrophys. J. 164, 83.

    Article  ADS  Google Scholar 

  • Goebel, J. H., Bregman, J, D., Cooper, D. M., Goorvitch, D., Langhoff, S. R., and Witteborn, F. C. 1983, Astrophys. J. 270, 190.

    Google Scholar 

  • Goebel, J. H., Bregman, J. D., Goorvitch, D., Strecker, D. W., Puetter, R. C., Russell, R. W., Soifer, B. T., Willner, S. P., Forrest, W. J., Houck, J. R., and McCarthy, J. F. 1980, Astrophys. J. 235, 104.

    Article  ADS  Google Scholar 

  • Goebel, J. H., Bregman, J. D., Strecker, D. W., Witteborn, F. C., and Erickson, E. F. 1978, Astrophys. J. (Letters) 222, L129.

    Article  ADS  Google Scholar 

  • Goebel, J, H., Bregman, J. D., Witteborn, F. C., Taylor, B. J., and Willner, S. P. 1981, Astrophys. J. 246, 455.

    Google Scholar 

  • Golay, M. 1974, Introduction to Astronomical Photometry (Reidel).

    Google Scholar 

  • Gow, C. E. 1976, Astron. J. 81, 993.

    Article  ADS  Google Scholar 

  • Gow, C. E. 1977, Publ. Astron. Soc. Pacific 89, 510.

    Article  ADS  Google Scholar 

  • Greene, A. E., and Wing, R. F. 1975, Astrophys. J. 200, 688.

    Article  ADS  Google Scholar 

  • Griffin, R. F., and Redman, R. O. 1960, Mon. Not. Roy. Astron. Soc. 120, 287.

    ADS  Google Scholar 

  • Hackwell, J. A. 1972, Astron. Astrophys. 21, 239.

    ADS  Google Scholar 

  • Hackwell, J. A. 1972, Astron. Astrophys. 21, 239.

    ADS  Google Scholar 

  • Hayes, D. S., Joyce, R. R., Ridgway, S. T., Rinsland, C. P., and Wing, R. F. 1980, Bull. Amer. Astron. Soc. 12, 837.

    ADS  Google Scholar 

  • Johnson, H. L. 1966, Ann. Rev. Astron. Astrophys. 4, 193.

    Article  ADS  Google Scholar 

  • Johnson, H. R., and Ake, T. B. 1984, in Cool Stars, Stellar Systems, and the Sun, ed. S. L. Baliunas and L. Hartmam(Springer-Verlag), p. 362.

    Google Scholar 

  • Johnson, H. R., and Ake, T. B. 1984, in Cool Stars, Stellar Systems, and the Sun, ed. S. L. Baliunas and L. Hartmam(Springer-Verlag), p. 362.

    Google Scholar 

  • Johnson, H. R., and O’Brien, G. T. 1983, Astrophys. J. 265, 952.

    Article  ADS  Google Scholar 

  • Keenan, P. C. 1954, Astrophys. J. 120, 484.

    Article  ADS  Google Scholar 

  • Keenan, P. C., and Morgan, W. W. 1941, Astrophys. J. 94, 501.

    Article  ADS  Google Scholar 

  • Little, S. J., Little-Marenin, I. R., and Wing, R. F. 1980, Bull. Amer. Astron. Soc. 12, 828.

    ADS  Google Scholar 

  • Little-Marenin, I. R., Little, S. J., and Wing, R. F. 1979, Bull. Amer. Astron. Soc. 11, 646.

    ADS  Google Scholar 

  • Lloyd Evans, T. 1983a, Mon. Not. Roy. Astron. Soc. 204, 975.

    ADS  Google Scholar 

  • Lloyd Evans, T. 1983b, Mon. Not. Roy. Astron. Soc. 204, 985.

    ADS  Google Scholar 

  • Lloyd Evans, T. 1984, Mon. Not. Roy. Astron. Soc. 209, 825.

    ADS  Google Scholar 

  • Lockwood, G. W., and Wing, R. F. 1971, Astrophys. J. 169, 63.

    Article  ADS  Google Scholar 

  • Lockwood, G. W., and Wing, R. F. 1982, Mon. Not. Roy. Astron. Soc, 198, 385.

    ADS  Google Scholar 

  • Lü, P. K., Dawson, D. W., Upgren, A. R., and Weis, E. W. 1983, Astrophys. J. Suppl. 52, 169.

    Article  ADS  Google Scholar 

  • Lü, P. K., and Sawyer, D. 1979, Astrophys. J. 231, 144.

    Article  ADS  Google Scholar 

  • Lü, P. K., and Upgren, A. R. 1979, Astron. J. 84, 101.

    Article  ADS  Google Scholar 

  • Luck, R. E., and Lambert, D. L. 1981, Astrophys. J. 245, 1018.

    Article  ADS  Google Scholar 

  • MacConnell, D. J., Frye, R. L., and Upgren, A. R. 1972, Astron. J. 77, 384.

    Article  ADS  Google Scholar 

  • Mannery, E. J., and Wallerstein, G. 1970, Astron. J. 75, 169.

    Article  ADS  Google Scholar 

  • McClure, R. D. 1979, in Problems of Calibration of Multicolor Photometric Systems, ed. A. G. D. Philip, Dudley Obs. Report No. 14, p. 83.

    Google Scholar 

  • McClure, R. D. 1983, Astrophys. J. 268, 264.

    Article  ADS  Google Scholar 

  • McClure, R. D. 1984a, Publ. Astron. Soc. Pacific 96, 117.

    Article  ADS  Google Scholar 

  • McClure, R. D. 1984b, Astrophys. J. (Letters) 280, L31

    Google Scholar 

  • McClure, R. D. 1984c, in IAU Symp. No. 105, Observational Tests of the Stellar Evolution Theory, ed. A. Maeder and A. Renzini (Reidel), p. 187.

    Google Scholar 

  • McClure, R. D., Fletcher, J. M., and Nemec, J. M. 1980, Astrophys. J. (Letters) 238, L35.

    Google Scholar 

  • McClure, R. D., and Forrester, W. T. 1981, Publ. Dominion Astrophys. Obs. 15, No. 14.

    Google Scholar 

  • McClure, R. D., Forrester, W. T., and Gibson, J. 1974, Astrophys. J. 189, 409.

    Article  ADS  Google Scholar 

  • Mendoza V., E. E. 1967, Bol. Tonantzintla y Tacubaya 4, 114.

    Google Scholar 

  • Mendoza V., E. E., and Johnson, H. L. 1965, Astrophys. J. 141, 161.

    Google Scholar 

  • Merrill, K. M., and Ridgway, S. T. 1979, Ann. Rev. Astron. Astrophys. 17, 9.

    Article  ADS  Google Scholar 

  • Merrill, K. M., and Stein, W. A. 1976a, Publ. Astron. Soc. Pacific 88, 285.

    Article  ADS  Google Scholar 

  • Merrill, K. M., and Stein, W. A. 1976b, Publ. Astron. Soc. Pacific 88, 294.

    Article  ADS  Google Scholar 

  • Merrill, K. M., and Stein, W. A. 1976c, Publ. Astron. Soc. Pacific 88, 874.

    Article  ADS  Google Scholar 

  • Neugebauer, G., and Leighton, R. B. 1969, Two-Micron Sky Survey–A Preliminary Catalog (NASA SP-3047).

    Google Scholar 

  • Palmer, L. G. 1980, Ph.D. dissertation, Ohio State University.

    Google Scholar 

  • Palmer, L. G., and Wing, R. F. 1982, Astron. J. 87, 1739.

    Article  ADS  Google Scholar 

  • Piccirillo, J. 1976, Publ. Astron. Soc. Pacific 88, 680.

    Article  ADS  Google Scholar 

  • Piccirillo, J. 1977, Ph.D. dissertation, Indiana University.

    Google Scholar 

  • Piccirillo, J. 1980, Mon. Not. Roy. Astron. Soc. 190, 441.

    ADS  Google Scholar 

  • Preston, G. W., Krzeminski, W., Smak, J., and Williams, J. A. 1963, Astrophys. J. 137, 401.

    Article  ADS  Google Scholar 

  • Price, S. D., and Walker, R. G. 1976, The AFGL Four Color Infrared Sky Survey: Catalog of Observations at 4.2, 11.0, 19.8, and 27.4 μm, AFGL-TR-76-0208.

    Google Scholar 

  • Querci, F., Querci, M., Wing, R. F., Cassatella, A., and Heck, A. 1982, Astron. Astrophys. 111, 120.

    ADS  Google Scholar 

  • Richer, H. B. 1981, in Physical Processes in Red Giants, ed. I. Iben, Jr., and A. Renzini (Reidel), p. 153.

    Google Scholar 

  • Richer, H. B. 1981, in Physical Processes in Red Giants, ed. I. Iben, Jr., and A. Renzini (Reidel), p. 153.

    Google Scholar 

  • Ridgway, S. T., Jacoby, G. H., Joyce, R. R., and Wells, D. C. 1980, Astron. J. 85, 1496.

    Article  ADS  Google Scholar 

  • Rinsland, C. P., and Wing, R. F., 1982, Astrophys. J. 262, 201.

    Article  ADS  Google Scholar 

  • Rosino, L. 1951, Astrophys. J. 113, 60.

    Article  ADS  Google Scholar 

  • Sanford, R. F. 1928, Astrophys. J. 68, 408.

    Article  ADS  Google Scholar 

  • Scargle, J. D., and Strecker, D. W. 1979, Astrophys. J. 228, 838.

    Article  ADS  Google Scholar 

  • Smak, J. 1968, Acta Astron. 18, 317.

    ADS  Google Scholar 

  • Smak, J., and Wing, R. F. 1979, Acta Astron. 29, 187.

    ADS  Google Scholar 

  • Spinrad, H., and Newburn, R. L., Jr. 1965, Astrophys. J. 141, 965.

    Article  ADS  Google Scholar 

  • Spinrad, H., Pyper, D. M., Newburn, R. L. Jr., and Younkin, R. L. 1966, Astrophys. J. 143, 291.

    Article  ADS  Google Scholar 

  • Straizys, V. 1978, Bull. Vilnius Astron. Obs., No. 47, p. 7.

    ADS  Google Scholar 

  • Straizys, V. 1983, Metal-Deficient Stars ( Vilnius: Institute of Physics of the Lithuanian S.S.R.).

    Google Scholar 

  • Tsuji, T. 1981, J. Astrophys. Astron. 2, 95.

    Article  ADS  Google Scholar 

  • Upgren, A. R., Lü, P. K., and MacConnell, D. J. 1977, Publ. Astron. Soc. Pacific 89, 552.

    Article  ADS  Google Scholar 

  • Vardya, M. S. 1966, Observatory 86, 162.

    ADS  Google Scholar 

  • Veteŝnik, M. 1984a, Bull. Astron. Inst. Czech. 35, 65.

    ADS  Google Scholar 

  • Veteŝnik, M. 1984b, Bull. Astron. Inst. Czech. 35, 74.

    ADS  Google Scholar 

  • Walker, A. R. 1976, Mon. Not. Roy. Astron. Soc. 174, 609.

    ADS  Google Scholar 

  • Wallerstein, G. 1968, Astrophys. J. 151, 1011.

    Article  ADS  Google Scholar 

  • Wallerstein, G. 1973, Ann. Rev. Astron. Astrophys. 11, 115.

    Article  ADS  Google Scholar 

  • Wallerstein, G., Brown, J. A., and Bates, B. A. 1979, Publ. Astron. Soc. Pacific 91, 47.

    Article  ADS  Google Scholar 

  • Westerlund, B. E. 1964, in IAU Symp. No. 20, The Galaxy and the Magellanic Clouds, ed. F. J. Kerr and A. W. Rodgers ( Canberra: Australian Academy of Sciences ), p. 239.

    Google Scholar 

  • Westerlund, B. E., Olander, N., Richer, H. B., and Crabtree, D. R. 1978, Astron. Astrophys. Suppl. 31, 61.

    ADS  Google Scholar 

  • Wildey, R. L., Burbidge, E. M., Sandage, A. R., and Burbidge, G. R. 1962, Astrophys. J. 135, 94.

    Article  ADS  Google Scholar 

  • Williams, P. M. 1975, Mon. Not. Roy. Astron. Soc. 170, 343.

    ADS  Google Scholar 

  • Wing, R. F. 1967, Ph.D. dissertation, Univ. of California, Berkeley.

    Google Scholar 

  • Wing, R. F. 1971, in Proc. Conf. on Late-Type Stars, ed. G. W. Lockwood and H. M. Dyck ( Kitt Peak Natfl Obs. Contrib. No. 554 ), p. 145.

    Google Scholar 

  • Wing, R. F. 1972, Mem. Soc. Roy. Sci. Liege, 6th Ser., 3, 123.

    Google Scholar 

  • Wing, R. F. 1974, Highlights of Astronomy 3, 285.

    ADS  Google Scholar 

  • Wing, R. F. 1979, in IAU Colloq. No. 47, Spectral Classification of the Future, ed. M. F. McCarthy, A. G. D. Philip, and G. V. Coyne (Vatican Obs.), p. 347.

    Google Scholar 

  • Wing, R. F. 1980, in Current Problems in Stellar Pulsation Instabilities, ed. D. Fischel, J. Rountree Lesh, and W. M. Sparks (NASA: TM-80625), p. 533.

    Google Scholar 

  • Wing, R. F. 1982, Trans. I.A.U. 18A, 275.

    Google Scholar 

  • Wing, R. F., Carpenter, K. G., and Wahlgren, G. M. 1983, Atlas of High Resolution IUE Spectra of Late-Type Stars, 2500–3230 K, Perkins Obs. Special Publ. No. 1.

    Google Scholar 

  • Wing, R. F., Gustafsson, B., and Eriksson, K. 1984, in IAU Symp. No. 111, Calibration of Fundamental Stellar Quantities (Reidel), in press.

    Google Scholar 

  • Wing, R. F., and Lange, G. L. 1981, Bull. Amer. Astron. Soc. 13, 546.

    ADS  Google Scholar 

  • Wing, R. F., and Rinsland, C. P. 1981a, Bull. Amer. Astron. Soc. 13, 840.

    ADS  Google Scholar 

  • Wing, R. F., and Rinsland, C. P. 1981b, Revista Mexicana Astron. Astrof. 6, 145.

    ADS  Google Scholar 

  • Wing, R. F., and Stock, J. 1973, Astrophys. J. 186, 979.

    Article  ADS  Google Scholar 

  • Wing, R. F., and Yorka, S. B. 1977, Mon. Not. Roy. Astron. Soc. 178, 383.

    ADS  Google Scholar 

  • Wood, P. R., Bessell, M. S., and Fox, M. W. 1983, Astrophys. J. 272, 99.

    Article  ADS  Google Scholar 

  • Yorka, S. B. 1983, Astron. J. 88, 1816.

    Article  ADS  Google Scholar 

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Wing, R.F. (1985). Photometric Properties of Peculiar Red Giants. In: Jaschek, M., Keenan, P.C. (eds) Cool Stars with Excesses of Heavy Elements. Astrophysics and Space Science Library, vol 114. Springer, Dordrecht. https://doi.org/10.1007/978-94-009-5325-3_10

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