【摘要】 许多观测表明,与Mira变星成协的SiO脉泽源具有与OH脉泽源不同的频谱特征,后者大多有明显的窄的双峰,用辐射压驱动的膨胀壳层模型可以解释它们,但SiO脉泽频谱却表现为较大的径向速度弥散,以及变化多样的频谱形态.本文根据扰动在可压缩流体中传播的原理,提出了恒星脉动对恒星大气速度结构影响的一种模型.计算表明,这一分析模型能较满意地解释与典型Mira变星成协的SiO脉泽频谱的平均速度范围,对SiO脉泽速度宽度与恒星光学位相的关系,本文也进行了分析,与观测现象基本符合.更多还原

【Abstract】 Many observations show that the spectra of sio maser sources associated with Mira Variables have larger spread of radial velocity and various spectral patterns. According to the theory of disturbance propagation in compressible fluid, we propose that the stellar pulsation should exert art influence on the structure of velocity 6f the gas. This model is able to satisfactorily interpret the average velocity extent of SiO maser spectra. The relationship between the Velocity width of SiO maser emission and stellar optical phase has been analysed, the result is in agreement with observations on the whole.I. Theoretical ModelThis paper suppose that owing to the stellar pulsation, the velocity, pressure, density and the radiation pressure in the stellar envelope undergo a disturbance. On the assumption of spherical Symmetry, the above quantities can be, written as:where V0, p0, p0, FRO represent the mean velocity, pressure, density and the radiation pressure without pulsation, respectively, and they are all constants; υ’(r.t), p’(r-t), p’(r.t) and F’R (r.t) are the disturbance quantities. It can be proved that p’ << p0,p<<C p0, F’R << FRO, but υ’ may be no less than υ0[5]. The radiation pressuretake Kv(r) =1[6], thenwhere we consider F’R(r.t) to be independent of r. Substitute(1) into the continuity equation and Euler’s equation of hydrodynamics. Neglecting the second-order terms of disturbance quantities and cbnsidering that υ0, ρ0, p0 and FRO satisfy the hydrodynamic equations of steady state, thus the equations become the following forms in spherical coordinates:Considering that:(1) The velocity is non-curl, so that we can introduce a velocity potential φ(r.t) and(2) The process is adiabatic, then p = α2ρ, where a represents the sound speed and it is a constant.And assuming that the stellar pulsation is harmonic, we can takewhere α is the angular frequency of stellar pulsation. Finally, an equation about φ(r) is givenThe, solution of equation (7) isThus,From (9) we can see that the principal terms of υ’(r.t) are in the form of spherical ware. The first term of the right expresses a wave propagating out from the center of envelope at the velocity α + υ0. And the second term is a ware converging from infinity at the velocity α-υ0. However, the latter may be insignificant for the boundless space. The third term indicates the influence of’ radiation pressure variation on the disturbance velocity. The real part of (9) is the useful solution of our problem: where the integrate constant C1 is determined by the periodical boundary condition. Ⅱ. The results of the modelAccording to the statistical data of typical Mira parameters and the periodical boundarycondition at the initial, υ’(R,0) = 6km/s[4], we choose the values of ω, R, Teff, Teff,max, υo as well as α, and then determine the integrate constant C1. Thus, the final expression of the disturbance velocity isBecause it is generally acknowledged that the envelope of SiO meser is situated at r> 1.8.R, the starting situation of sio maser is therefore chosen as 2R. The results calculated-by us are listed in Table 2. from the results some conclusions may be achieved:(1) The disturbance velocity decreases vibratorily with increasing r. The amplitude of υ’ tends to zero about 20R. In the light of the difference between situations of SiO and OH, we can see that the SiO maser is greatly affected by the stellar pulsation, but almost none of OH maser are affected by it. Therefore, SiO spectra line is wider than each of OH double peaks.(2) The largest width of SiO spectra is determined by the absolute amplitude of the maximum υ’ near 2R. Because the SiO maser sources are distributed over the whole depth of the envelope, the spectral, pattern obserred is a synthetical effect of SiO emissions from different situations along the sight line. Consequently, when υ’ at 2R is zero, another maximum of υ’ would occur at some place near 2R, so that a wider spectra can still be kept. The variation of the largest width with stellar optical phase is not sensitive. This result is c更多还原