Short communication
J Phys Astr, Volume: 7( 2)

Microturbulent Velocity in the Atmospheres of G Spectral Classes Star

*Correspondence:
MA Jafarov, Department of Astrophysics, Baku State University, Z Khalilov Str. 23, AZ 1148, Baku, Azerbaijan, E-Mail: [email protected]

Received: March 22, 2019; Accepted: April 03, 2019; Published: April 10, 2019

Citation: Samedov ZA, Jafarov MA. Microturbulent Velocity in the Atmospheres of G Spectral Classes Star. J Phys Astron. 2019;7(2):179.

Abstract

The microturbulence is investigated in the atmospheres of some G spectral classes stars by the atmosphere model. The microturbulent velocities are determined on the basis of comparison of the values measured from observation and theoretically calculated equivalent widths of lines FeII. It has been found that the microturbulent velocity (𝜉𝑡 ) depends on the surface gravity (g) in the atmospheres of the star: 𝜉𝑡 decreases with increasing g. The microturbulent velocity is less in the stars with intense atmosphere.

Keywords

Stars; Microturbulence; Fundamental parameters; Chemical composition

Introduction

As is known that even though all expansion mechanisms are taken into account, it is not possible to explain the observed profiles of spectral lines in the spectrum of the star. Thus, it is assumed that in addition to the thermal (heat) movements of the atoms there are also non-thermal (non-heat) movements in the star atmospheres, which are called turbulent movements. Turbulence is assumed as one of the mechanisms that extend the spectral line in astrophysics.

It was empirically found that the observed Doppler width of the spectral lines cannot be explained by the thermal (heat) movement of atoms.

Through the expression

equation

it needs to introduce the parameters equation The paremeter equation is expressed as the microturbulence parameter

Let’s note that there is no generalized physical theory of the microturbulence. The investigation of the microturbulence in the atmospheres of the star is important for two reasons: First, to determine the chemical composition, and second, to understand the nature of this event.

Determination of Microturbulent Velocity

The microturbulent velocity is determined in the atmospheres of the stars using the atmosphere model for the G-spectral classes HR8304 (G8II), HR8179 (G5II), HR8778 (G8IV) stars.

The observations materials of the stars were obtained on a 2-meter telescope of Shamakhi Astrophysical Observatory of ANAS.

The determination of the microturbulent velocity using the model method is based on the study of the equivalent widths in a wide range of neutral atoms or ions spectral lines of any element. The equivalent widths equation of the spectral lines of the considered element is calculated by giving different values to the microturbulent velocity and and it is compared with the equivalent widths measured from observation. The abundance of elementequation is calculated for the different values of the mikroturbulent velocity equation in each spectral line, The abundance of element lgε does not depend on the equivalent widths equation of its spectral lines. equation is determine the atmosphere of the investigated star which corresponds to the graph.

The most lines in the studied spectrum of the stars are the equation and thenequation lines. However, the effect of the LTT extremes to the neutral iron lines is significant. If the calculations are carried out in LTT, the abundance determined on the equation lines is less than the abundance when refused from LTT [1]. Unlike equation lines there is no effect of the LTT extremes to the equation lines. Therefore, in the atmosphere of the star, the microturbulent velocity equation and the iron abundance are determined on equation lines. Only the weak lines are used when determining the microturbulent velocity equation. These lines are formed in deep layers of the atmosphere, these layers are parallel and in LTT form.

The fundamental parameters of the stars-effective temperature equation and surface gravityequation are determined on the basis of comparison of observed and theoretical values of some spectral and photometric quantities [2,3]. The obtained values are shown in TABLE 1.

HR Sp equation equation equation km/s equation
HR8304 G8II 5010 2.1 3.2 7.56
HR8179 G5III 5200 2.7 2.0 7.32
HR8778 G8IV 5300 3.2 1.8 7.51

TABLE 1. equation parameters of the stars.

Knowing the effective temperature and surface gravity of the stars are calculated their models.

The iron abundance equation is calculated by giving different values to the microturbulent velocity in the atmosphere of each star on these models. The iron abundance is determined on the basis of comparison of the values measured from observation and theoretically calculated equivalent width of the lines equation . Theoretically equivalent width of spectral lines is calculated by DASA programs. The atomic data of the spectral lines are taken from the database VALD 2 [4]

The determined abundance equation on the different equivalent widths of equation the dependence graphs from equation are shown in FIG. 1 in the studied atmospheres of the stars.

physics-astronomy-microturbulent-velocity

FIG. 1. Determination of the microturbulent velocity in the atmosphere of stars.

As seen from FIG. 1 there is no correlation between equation and equation when

equation

The value of the microturbulent equation = 1.1 km/s in the solar atmosphere is determined in [5].

TABLE 1 shows the investigated parameters equation for the studied stars.

The dependence graphic of the microturbulent velocity equation from surface gravityequation on the star surface (FIG. 2) is plotted.

physics-astronomy-microturbulent-velocity

FIG. 2. The dependence of the microturbulent velocity on the surface gravity in the atmospheres of the stars. As is shown in the figure the equation depends onequation decreases whenequation increases. The microturbulent velocity is less in the stars with an intense atmosphere.

Main results

1. The microturbulence velocities are determined using the atmosphere model method:

For the HR8304 (G8II) star, equation= 3.2 km/s

For the HR8179 (G5III) star, equation= 2.0 km/s

For the HR8778 (G8IV) star, equation= 108km/s

2. It has been found that the microturbulent velocity (equation) depends on the surface gravity (g) in the atmospheres of the star: equation decreases with increasing “g”. The microturbulent velocity is less in the stars with an intense atmosphere

References

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