Some Research Programmes Into Galactic Structure at the Galactic Caps Under Way at the Royal Greenwich Observatory

Abstract

The R.G.O. has a continuing programme to investigate both the density and motions of the stellar content of the solar neighbourhood. Gaps in current knowledge are wider for the fainter stars which are found in proportionally greater numbers near the galactic poles. Our approach divides naturally into two questions: (i) What are the proportions of red dwarfs to giants at each apparent magnitude? and (ii) What are the corresponding total numbers of red stars?Question (i) was first tackled by a narrow-band photometric search for M dwarfs (Jones 1973). This approach is continuing and a progress report has been delivered (Jones 1976). To push the search deeper 41 stars in the South Galactic Cap (mostly fainter than V = 15) selected by P.S. Thé from a survey with the Lembang Schmidt as being M2 or later were observed with the Robinson-Wampler Scanner on the 150-inch A.A.T. The Na D lines, CaH and the band at λ5500 tentatively identified by Pesch with CaOH have been measured. Column density calculations of CaOH for giants and dwarfs of different temperatures support Pesch’s identification. Nearly all the stars are dwarfs but only seven appear in proper motion catalogues, (Thé and Staller 1974). At the galactic caps most stars brighter than V = 12 are giants and fainter dwarfs. The transition zone is only 10-14.