Đường cong tăng trưởng (chết Wachstumskurve) là một đồ thị hiển thị chiều rộng của một đường hấp thụ tương đương, hoặc rạng rỡ của một dòng khí thải, tăng với số lượng của các nguyên tử sản xuất dòng. Trong một khí quang học mỏng, chiều rộng tương đương với một dòng hấp thụ, hoặc rạng rỡ của một dòng khí thải, là tuyến tính tỷ lệ thuận với số nguyên tử ở mức độ ban đầu của dòng. Chúng ta hãy tưởng tượng, ví dụ, rằng chúng ta có một nguồn bức xạ liên tục của, và, ở. | 1 CHAPTER 11 CURVE OF GROWTH Introduction The curve of growth die Wachftumfturve is a graph showing how the equivalent width of an absorption line or the radiance of an emission line increases with the number of atoms producing the line. In an optically thin gas the equivalent width of an absorption line or the radiance of an emission line is linearly proportional to the number of atoms in the initial level of the line. Let us imagine for example that we have a continuous source of radiation and in front of it we have a homogeneous isothermal slab of gas and that there are W1 atoms per unit area in the line of sight in the lower level of some absorption line. We could double W1 either by doubling the thickness of the slab or by doubling the density of the gas within the slab. Either way if doubling the number of atoms per unit area the column density in level 1 results in a doubling of the equivalent width of the line then the gas is said to be optically thin. More precisely the line is optically thin - for there may well be other lines in the spectrum which are not optically thin. I suppose one could say that a gas is optically thin at the wavelength of a particular line if you can see all of the atoms - even those at the back. In Chapter 9 where we were developing formulas for the equivalent width of a line and in Chapter 10 where we were studying line profiles we were limiting our attention to optically thin lines. We shall depart from this assumption in this Chapter although we shall still assume that our slab of gas is homogeneous same temperature and pressure throughout and in thermodynamic equilibrium. We can see by referring to figure XI. 1 why it is that the equivalent width of an absorption line cannot continue to increase indefinitely and linearly as the column density increases. The figure represents the profile of an absorption line. Strictly speaking the ordinate should read radiance per unit wavelength interval rather than intensity . Profile a
