A Spectroscopic Orbit for HD

Transcription

1 J. Astrophys. Astr. (1981) 2, A Spectroscopic Orbit for HD R. F. Griffin The Observatories, Madingley Road, Cambridge, England, CB3 0HA Received 1981 June 9; accepted 1981 July 24 Abstract. Photoelectric radial-velocity measurements show that the eighth-magnitude star HD is a spectroscopic binary with a period of days. The star has a large proper motion, and is unlikely to have the luminosity corresponding to the spectral type of G8 III favoured by Zaitseva. It is most probably a late-g dwarf. Key words: radial velocities spectroscopic binaries stars, individual HD is an eighth-magnitude late-type star in the constellation Canes Venatici, near the North Galactic Pole. Its position was first determined by Lalande (Delalande 1801; Baily 1847), and its large proper motion, amounting to about 0 41 arcsec per annum in position angle 259, became apparent during the nineteenth century (Robinson and Dreyer 1886). This led to the object s inclusion in many catalogues of proper-motion stars as well as in the more general catalogues; in particular, its position was repeatedly measured at Cincinnati. In Table 1 are collected its designations in some of the more important catalogues. The spectral type of HD is given in the Henry Draper Catalogue (Cannon and Pickering 1920) as K0, and Joy (1947) gives it as dg6. Zaitseva (1973), on the basis of objective-prism spectra at a dispersion of 166 Å mm -1 at Hγ, found an MK type (Morgan, Keenan and Kellman 1943) of G8 III. Such a luminosity seems improbable, because at the implied distance modulus of about 7 magnitudes, corresponding to a distance of 250 pc, the transverse velocity required by the proper motion is almost 500 km s 1. The catalogue compiled by Buscombe (1980) of MK classifications includes a type of K0 V and magnitudes of V = 8 00 and (B V) = 0 69 for HD , but unfortunately (Griffin 1981) it does not give any references. The dwarf luminosity classification is almost certainly correct, but the (B V) colour corresponds to a main-sequence type of G5 rather than K0. Evidently the last word has not yet been said on the spectral type of HD ; but for the moment it appears that the type of dg6 suggested by Joy is as likely as any, and is moreover in excellent accord with the parallax of ± arcsec given in the General Catalogue of Stellar Parallaxes (Schlesinger 1935).

2 310 F. Griffin Table 1. Aliases for HD Figure 1. The computed radial-velocity curve (full line) for HD The photoelectric observations are plotted as filled circles, the Mount Wilson photographic ones as open circles.

3 Spectroscopic orbit for HD Table 2. Photoelectric radial-velocity measurements of HD *Observed, in collaboration with Dr J. Ε. Gunn, with the 200-inch telescope (Griffinand Gunn 1974). Α. 7

4 312 R. F. Griffin Joy (1947) obtained three radial-velocity measurements of HD from the same 36 Å mm 1 Mount Wilson spectrograms that he used to classify it, and he showed it to be a spectroscopic binary. The three velocities were subsequently published individually by Abt (1973). In the course of radial-velocity observations in the North Galactic Pole field, the star came under observation with the photoelectric spectrometer at Cambridge (Griffin 1967) several years ago, and its binary nature was confirmed. The 37 photoelectric observations now available are listed in Table 2, and yield the orbit plotted in Fig. 1 and having the following elements: The Mount Wilson velocities were not taken into account in the orbital solution; they are, however, plotted in Fig. 1, where they are seen to be in fully satisfactory agreement with the computed orbit. The secondary star is not apparent in the radial-velocity traces; it is likely to be a main-sequence star much fainter than the primary. References Abt, H. A. 1973, Astrophys. J. Suppl. Ser., 26, 365. Argelander, F. W. A. 1861, Astronomische Beobachtungen, Adolph Marcus, Bonn, 4, 317. Baily, F. 1847, A Catalogue of Those Stars in the Histoire Celeste Francaise..., R. Taylor and J. Ε. Taylor, London, pp. 619, 620. Boss, B. 1937, General Catalogue of Stars for the Epoch 1950, Carnegie Institution of Washington, 4, 64. Boss, B., Roy, A. J., Varnum, W. B. 1931, Albany Catalogue of Stars for the Epoch 1910, Carnegie Institution of Washington, p Buscombe, W. 1980, Fourth General Catalogue of MK Spectral Classifications, Northwestern University, Evanston. Cannon, A. J., Pickering, E. C. 1920, Ann. Harv. Coll. Obs., 95, 126. Delalande, J. 1801, Histoire Celeste Francaise, Imprimerie de la Republique, Paris, pp. 58, 339. Dunér, Ν. C., Engström, F., Psilander, A. A. 1902, Catalog von Sternen, Engelmann, Leipzig, p Dyson, F. 1935, Second Greenwich Catalogue of Stars for , HMSO, London, p Giclas, H. L., Burnham, R., Jr., Thomas, Ν. G. 1971, Lowell Proper Motion Survey, Lowell Observatory, Flagstaff, p. 74. Griffin, R. F. 1967, Astrophys. J., 148, 465. Griffin, R. F. 1981, J. Brit. astr. Assoc., 91, 297. Griffin, R. F., Gunn, J. Ε. 1974, Astrophys. J., 191, 545. Heckmann, Ο., Dieckvoss, W. 1975, AGK3, Hamburger Sternwarte, Hamburg-Bergedorf, 4, 59. Joy, Α. Η. 1947, Astrophys. J., 105, 96. Luyten, W. J. 1961, A Catalogue of 7127 Stars in the Northern Hemisphere with Proper Motions Exceeding 0.2 Annually, Lund Press, Minneapolis. Morgan, W. W., Keenan, P. C., Kellman, E. 1943, An Atlas of Stellar Spectra with an Outline of Spectral Classification, University of Chicago Press. Porter, J. G. 1892, Cincinnati Publ., No. 12, pp. 133, 243. Porter, J. G. 1895, Cincinnati Publ., No. 13, 35.

5 Spectroscopic orbit for HD Porter, J. G., Yowell, Ε. I., Smith, Ε. 1916, Cincinnati Publ, No. 18, Part II, 88. Porter, J. G., Yowell, Ε. I., Smith, E. 1918, Cincinnati Publ, No. 18, Part IV, 33. Porter, J. G., Yowell, Ε. I., Smith, Ε. S. 1930, Cincinnati Publ., No. 20, 18. Robinson, Τ. R., Dreyer, J. L. E. 1886, Second Armagh Catalogue of 3300 Stars for the Epoch 1875, Thom, Dublin, p. 70. Schlesinger, F. 1935, General Catalogue of Stellar Parallaxes, Yale University Observatory, New Haven, p. 74. Schorr, R. 1936, Bergedorfer Eigenbewegungs-Lexicon, 2 ed-n, Hamburger Sternwarte, Bergedorf, 1, 126. Schorr, R., Kohlschütter, A. 1953, Zweiter Katalog der Astronomischen Gesellschaft, Hamburger Sternwarte, Bonn, 7, 181. Smith, E. S., Herget, P. 1946, Cincinnati Publ., No. 22, 25. Smith, E., Porter, J. G. 1922, Cincinnati Publ., No. 19, 57. Smithsonian Astrophysical Observatory Star Catalog, 1966, Smithsonian Institution, Washington, Part 1. Wilson, R. Ε. 1953, General Catalogue of Stellar Radial Velocities, Carnegie Institution of Washington, p Zaitseva, Ε. I. 1973, Abastumani Bull, No. 44, 55.