INVERTED POPULATION OF HYDROGEN ATOMS IN A TURBULENT COSMIC PLASMA

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Submitted on 1 Jan 1979

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INVERTED POPULATION OF HYDROGEN ATOMS IN A TURBULENT COSMIC PLASMA

I. Ojringel

To cite this version:

I. Ojringel. INVERTED POPULATION OF HYDROGEN ATOMS IN A TURBULENT COSMIC PLASMA. Journal de Physique Colloques, 1979, 40 (C7), pp.C7-719-C7-720.

�10.1051/jphyscol:19797348�. �jpa-00219342�

JOURNAL DE PHYSIQUE CoZZoque C7, suppZ6ment au n07, Tome 40, JuiZZet, 2979, page C7- 714

INVERTED POPULATION OF HYDROGEN ATOMS IN A TURBULENT COSMIC PLASMA

I.M. Ojringel.

Sibizmir, Siberian Branch, U.S. S. R. Academy of Sciences, Irkutsk.

The role of plasma effects in the ernis- could be signifiantly improved if the hy- sion of atomic systems was dealt with in drogen a,tom8 are assumed to be in a plas- a number of papers /I

-

^6/. Part of this ma with the mrofrequency type of wave work was devoted to the investigation of turbulence (whistlers). As a rule, the spectral line broadening during collisions whistler turbulence is anisotropic

-

^let

of an atom with charged particles /I

-

^2/,

a

be the solid angle in which the whis- other authors considered the effect of tler wave vectors are involved. The level plasma turbulence on the processes of emi- of whistler turbulence can be determined ssion (absorption) of quanta. by atoms. using the effective temperature Teff which And both the effects of spectral line bro- can exceed by orders of magnitude the ki- adening by plasma turbulence /3

-

^{4/ and}

the induced processes of emission of plas- mons by atoms were studied /5

-

^{6 / .}

As is well known /7/, such a sta.te is possible in the interstellar medium when the hydrogen atoms are almost not ionized, and the electron density is enough to give an intense plasma, turbulence.

In /8/, it waa shown that Sf the hydro- gen atoms are in a field of intense ultra- violet emission

3 4

216 f 912 0 A then inter- action of their spins with light quanta can produce in such a, medium an inverted population with respect to the A =21 cm li- ne emission.

Unfortunately, the criteria. for the ap- pearance of the inverted population turned out to be very strict to apply to real con- ditions of the interstellar medium.

In this paper it is shown that the pos- sibility of producing inverted population

netic temperature of gas or the electron temperature.

The interaction of spins of atoms, Ly- man quanta and whistlers a.lso leads up to inverted population. The consideration of this problem was performed by the same me- thod as in /8/, but terms describing the interaction of atoms with plasma wavea we- re a.dded into the equa.tions of balance.

In /9/, it was shown that transitions in atoms with participation of electromagne- tic waves with 3 =21 cm prove to be less effective than transitions with whistlers if the condition:

T . ~ . / ^T~ >> 4 5 9 ~ % ~ / 3 R g 9;

⁽¹

is valid, where T is the radiant tempera- ture in the Ax21 cm line,gp = c d 4 is Langmuir frequency, and

3,

^=I 420.4 MHz is the frequency of the dm21 crn line.

Plasma. transitions here interconnect Zee- man sublevels of the upper level of super- thin structure of the main atom's state HI.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19797348

When hydrogen al~ms are excited by iso- ma1 (not inverted) population has encoun- tropic nonpolarized Lyman emission, from

analysis of the equations of balance we have the following relation for spin tern- peratures T,, of a.11 sublevels

is the phase emission density of Lyman quanta, The denotations 34,

, -

Y 4 and ?z are taken from / 8 / ; in the denominatoer of

( a ) ,

smell positive terms xa(+)/gg were omit-

a 6 + P

ted, where

Qes42n8 (x ¹

^{(here n, ia the}

whistler phase density).

From (2) it followc~e that with declining

dn

(9)

<

^{0 1,} the spin temperatu- epectrum (-

res are positive, but already at any slow-

d n ( ~ ,

^/%( 9 ) ly increming spectry (-

d9

+x-

¹

the spin tempera.tures become negative:

Thus, excitation of circularly and line- arly polarized radio emission at 3. =21 cm occurs in this case. In calculations we disregarded collisional transitions sinee In turbulent plasma., transitions with par- ticipation of whistlers are more effective.

Obviously, for a detailed analysis of obser- va.tional data, a more complete calculation is needed with account of all possible tramsitions in equations of balance. In this paper, such a probLem was not posed.

We wished to indicate a. principal possibi- lity of producing inverted population in the A=21 cm line under real space condi- tions.

The interpretation of the available ob-

tered no special difficulties so far, and this allows the question to be posed of the reality of the existence of maser en- hancement in the d =21 cm line. In this connection, we would like to make another remark.

The determination of magnetic fields in dense clouds of interstellar gas using the observed circular polarization in the wings of the jL =21 cm absorption line gave values of magnetic field strengths one or even two orders larger than the values of field strengths determined by other methods for average conditions in interstellar space. A conventional expli- cation is that in dense clouds, gas com- pression is followed by a respective inc- rease in magnetic field. However, it is not excluded tha,t maser enhancement of e- mission due to whistler turbulence is here the case, then the magnetic field strengths thus found are overestimated.

R E F E R E N C E S

1. I.I.Sobelman, Introduction to a.tomic spectra theory, Pizmatgiz, 1963.

2 , H.R,Griem, Spectra.1 line broadening by

plasmas, Acad. Press, 1974.

3.

G,V.Sholin, Dm SSSR, 195, 589, 1970,

4.

D.G.Yakovlev, ZhTP, 42, 1550, 1972.

5- 1-I-Sobelman, E.L.Feinberg, JEFF, 34, 494, 1958.

6. S.A.Ka.plan, E,B.Kleiman, I.U,Ojringel, Astron. Zh., 49, 294, 1972,

7.

S.A.Kaplan, V.IT.Tsytbvich, Plaama As- trophysics, I.,Nauka, 1972.

8. D.A.Varhsalovich, JETF, 52, 242, 1967.

9. S.A.Kaplan, E.B.Kleiman, I.M.Ojringe1, Aetron. Zh., 54, 1305, 1978.

servations of 21 cm line in intersetellar apace in terms of our understanding of nor-