Astrophysics and Space Science

, Volume 30, Issue 2, pp 481–522 | Cite as

Étude du système AX Mon

  • A. Peton
Article

Résumé

Nous avons divisé cette étude en 4 parties principales.

Nous montrons dans la première partie l'importance du rôle de l'enveloppe sur la composition et les variations spectrales, l'influence, du mouvement orbital sur l'intensité des absorption d'enveloppe et la décroissance constante de l'étendue de l'enveloppe pendant les 11 ans couverts par nos observations.

L'étude dans la seconde partie de la raie Feii λ 4233 permet de dégager l'influence du mouvement orbital et notamment son action sur la fine absorption d'enveloppe, montre la décroissance de l'étendue de l'enveloppe par l'intermédiaire d'un système de courbes isophases, indique que l'émission est maximum au maximum d'extension de l'enveloppe et que la raie d'émission photosphérique est visible sur tous les cycles au voisinage de la phase 0.500 de la période orbitale.

L'examen des vitesses montre qu'il existe une pulsation des zones émissives liée au mouvement orbital. L'accélération des couches internes change de sens en allant de l'apoastre au périastre, tandis que l'accélération des couches extérieures augmente. Ces mouvements provoquent des changements de densité qui peuvent expliquer les variations d'intensité du spectre métallique de l'enveloppe.

Dans la troisième partie nous examinons le comportement des variations photométriques de AX Mon relativement à trois échelles de temps:
  1. (a)

    à très court terme (≤4 hr), les variations peuvent être importantes et atteindre 0.1 mag. Elles semblent caractéristiques d'une éjection de matière, sous forme de jets gazeux très chauds.

     
  2. (b)

    à court terme (>1 jour), les variations peuvent être interprétées comme des variations d'absorption des couches basses de l'enveloppe: elles sont liées à l'intensité des absorptions satellites de la raie Feii λ 4233.

     
  3. (c)

    à moyen terme (≤3 ans), nous observons une diminution sensible de l'amplitude des variations du type b, mais aucun changement de la valeur moyenne autour de laquelle s'effectuent les variations. Cette remarque nous a permis de déterminer les indices de AX Mon (V=6.77;B−V=+0.33;U−B=−0.66). L'amplitude de ces variations semble d'autant plus grande que l'enveloppe est plus étendue.

     

Nous montrons dans la dernière partie que le type spectral de l'étoile chaude du système AX Mon peut être estimé à B0.5 V et celui de l'étoile froide à K2 II.

Le rapport de masse est estimé en choisissant la courbe de vitesse des raies à caractère α Cygni pour représenter l'étoile B. Ce choix conduit à des résultats en très bon accord avec l'observation.

Dans le modèle qui en résulte, la secondaire remplit entièrement son lobe de Roche et permet des échanges de masse de l'étoile K vers l'étoile B. L'anglei élevé (i=79°) permet une observation quasiéquatoriale et explique pourquoi, malgré la faible excentricité, nous pouvons observer des effets de marée et les changements spectraux qui en résultent.

Abstract

We have divided this investigation into four main parts.

In the first part, we study the ways in which the envelope affects the composition and the spectral variations, and the orbital motion acts on the envelope absorption intensities and how the extent of the envelope constantly decreases during the 11 yr of our observations. This phenomenon regarding AX Mon has not been previously reported in the literature. However, it explains the appearance of the α Cygni spectrum which occurs according to an arbitrary integral multiple of the orbital periods.

Two absorbing envelopes seem to exist: an exterior shell of hydrogen and an interior metallic shell, which appears only when the last hydrogen line of the Balmer series of the envelope is H 27.

In the second part, the study of the line Feii λ 4233 shows the influence of the orbital motion on the profile and, in particular, its effect on the absorption in the envelope. The decrease of the extent of the envelope is shown by means of a series of ‘isophase curves’, which indicates that there is maximum emission whenever, there is maximum envelope extension.

The existence of satellite components to the red or violet gives evidence for the existence of heterogeneous velocity layers, contracting more rapidly than the bulk of the envelope during the cycle 100 and expanding more rapidly during cycle 116. The study of theV/R ratio shows that this ratio is independent of the orbital motion and always remains bigger than one. Some layers fall down to the photosphere as the envelope decreases (cycle 100 to 108). These layers participate in the general motion of the envelope (cycles 109 to 112) and then are strongly accelerated towards the border when the general contraction in the envelope increases again (cycles 112 to 116).

The nature of the radial velocities indicates a pulsation of the emission layers which is connected with the orbital motion. The direction of the acceleration in the internal layers is reversed from apastron to periastron, while at the same time the acceleration of the internal layers increases. These motions cause changes in the density which could explain the variations of intensity in the spectrum of the envelope.

In the third part, we study the photometric variations referring to three time-scales:
  1. (a)

    very short time-scale variations (≤4 hr). These variations can be important, reaching 0.1 mag, and can be described by a model matter ejection in very hot gaseous streams.

     
  2. (b)

    short time-scale variations (>1 day). These variations are connected with the intensity of the satellite absorptions of the line Feii λ 4233 and could be interpreted as absorption variations in the low layers of the envelope.

     
  3. (c)

    long time-scale variations (≤3 yr). We observe a perceptible decrease of the amplitude of (b) type variations, but no change in their mean value. We can then determine the AX Mon indices (V=6.77;B−V=+0.33;U−B=−0.66). The amplitude of the variations seems to increase as the envelope increases.

     

In the fourth part, we show that the spectral type of the hotter star can be estimated to be B0.5 V and for the cold star to be K2 II. The mass-ratio is estimated by choosing the velocity curve of the α Cygni spectrum to represent the B star, this choice leading to results which agree very well with the observations. In the resulting model, the secondary star fills the Roche's lobe and mass exchange can occur between the K star and the B star. The large value of the inclination (i=79°) leads to a quasiequatorial observation and explains why, in spite of the small eccentricity, we can observe tidal effects and the resulting spectral changes.

The study of the evolution of the system by means of the theories by Crawford and Plavec shows that the mass exchange began with the commencement of nuclear reactions at the border of the B star. During this evolution, the role of the two components has changed, the original primary becoming the secondary. In this assumption, the present system has exchanged about half of the permitted mass.

The emissive zone radius is estimated to be 70R by means of Sobolev's theory. This zone is entirely contained within the Roche's lobe of the star and is very sensitive to the gravitational action of the K star.

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Bibliographie

  1. Allen, C. W.: 1963,Astrophysical Quantities, Univ. London, The Athlone Press.Google Scholar
  2. Beals, C. S.: 1951,Publ. Dominion Astrophys. Obs. Victoria 9, 1.Google Scholar
  3. Blaauw, A.: 1963, in A. Strand (ed.),Basic Astronomical Data, p. 383.Google Scholar
  4. Boulon, J.: 1963,J. Obs. 46, 187.Google Scholar
  5. Briot, D.: 1971,Astron. Astrophys. 11, 57.Google Scholar
  6. Bunker, A. F.: 1941Publ. Dominion Astrophys. Obs. Victoria 53, 334.Google Scholar
  7. Burbidge, E. M. and Burbidge, G. R.: 1954,Astrophys. J. 119, 501.Google Scholar
  8. Chalonge, D. and Divan, L.: 1952,Ann. Astrophys. 15, 201.Google Scholar
  9. Cowley, A. P.: 1964,Astrophys. J. 139, 817.Google Scholar
  10. Crawford, J. A.: 1955,Astrophys. J.,121, 71.Google Scholar
  11. Delplace, A. M.: 1970,Astron. Astrophys. 7, 459.Google Scholar
  12. Delplace, A. M.: 1971,Astron. Astrophys. 10, 246.Google Scholar
  13. Delplace, A. M., Herman, R., and Peton, A.: 1968, ‘Non-Periodic Phenomena in Variable Stars’,IAU Colloq., Budapest, p. 223.Google Scholar
  14. Doazan, V.: 1962,Compt. Rend. Acad. Sci. Paris,5, 56.Google Scholar
  15. Doazan, V.: 1965,Ann. Astrophys. 28, 1.Google Scholar
  16. Gaposchkin, S.: 1942,Harvard Bull. 916, 3.Google Scholar
  17. Gaposchkin, C. P.: 1952,Harv. Ann. 118, 3.Google Scholar
  18. Groeneveld, I.: 1944,Veröffentl. Astron. Rechen-Inst. Heidelberg 14, 43.Google Scholar
  19. Guthnick, P. and Prager, R.: 1930,Astron. Nachr. 239, 13.Google Scholar
  20. Hardrop, J. and Strittmatter, P. A.: 1968,Astrophys. J. 153, 465.Google Scholar
  21. Harris, III, D. L.: 1963,Stars and Stellar Systems 3, 263.Google Scholar
  22. Harris, III, D. L., Strand, A. A., and Worley, C. E.: 1963,Stars and Stellar Systems 3, 273.Google Scholar
  23. Hiltner, W. A.: 1956,Astrophys. J., Suppl,II, 389.Google Scholar
  24. Hiltner, W. A. and Johnson, H. L.: 1956,Astrophys. J. 124, 367.Google Scholar
  25. Hyland, A. R.: 1969, in O. W. Gingerich (ed.),Theory and Observation of Normal Stellar Atmosphere, MIT Press, Cambridge, Mass.Google Scholar
  26. Iben, I.: 1967,Astrophys. J. 147, 624.Google Scholar
  27. Johnson, H. L.: 1958,Lowell Observatory Bull. No.90, p. 37.Google Scholar
  28. Johnson, H. L. and Morgan, W. W.: 1953,Astrophys. J. 117, 313.Google Scholar
  29. Kippenhahn, R. and Weigert, A.: 1967,Z. Astrophys. 65, 251.Google Scholar
  30. Kuiper, G. P. and Johnson, J. R.: 1956,Astrophys. J. 123, 90.Google Scholar
  31. Limber, N.: 1969,Stellar Rotation, p. 274.Google Scholar
  32. Limber, N. and Marlborough, J. M.: 1968,Astrophys. J. 152, 811.Google Scholar
  33. Lynds, C. S.: 1959,Astrophys. J. 130, 577.Google Scholar
  34. Martel, M. T.: 1972, private communication.Google Scholar
  35. Mendoza, E. E.: 1958,Astrophys. J. 128, 207.Google Scholar
  36. Merrill, P. W.: 1923,Publ. Astron. Soc. Pacific 35, 303.Google Scholar
  37. Merrill, P. W.: 1948,Astrophys. J. 108, 481.Google Scholar
  38. Merrill, P. W.: 1952,Astrophys. J. 116, 498.Google Scholar
  39. Morgan, W. W., Code, A. D., and Whitford, A. E.: 1955,Astrophys. J., Suppl. II, 41.Google Scholar
  40. Morton, D. C. and Adams, T. F.: 1968,Astrophys. J. 151, 611.Google Scholar
  41. Ozemre, K.: 1967,Ann. Astrophys. 30, 495.Google Scholar
  42. Peton, A.: 1971,Compt. Rend. Acad. Sci. Paris 273, 1062.Google Scholar
  43. Plaskett, J. S.: 1923,Publ. Astron. Soc. Pacific 35, 145.Google Scholar
  44. Plaskett, J. S.: 1927,Publ. Dominion Astrophys. Obs. Victoria 4, 1.Google Scholar
  45. Plavec, M.: 1968,Adv. Astron. Astrophys. 6, 201.Google Scholar
  46. Schmidt-Kaler, Th.: 1965, in Voigt (ed.),Astron. Astrophys. Google Scholar
  47. Sobolev, V. V.: 1960,Moving Envelopes of Stars, Harvard Union Press, Mass.Google Scholar
  48. Stebbins, J., Huffer, C. M., and Whitford, A. E.: 1939,Astrophys. J. 91, 20.Google Scholar
  49. Struve, O.: 1943,Astrophys. J. 98, 212.Google Scholar
  50. Walborn, N.: 1972,Astron. J. 77, 312.Google Scholar

Copyright information

© D. Reidel Publishing Company 1974

Authors and Affiliations

  • A. Peton
    • 1
  1. 1.Observatoire de Marseille et Observatoire de Haute ProvenceFrance

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