On the phases of variations of radii of the chromospheres and photospheres of Cepheids / О соотношении фаз изменения радиусов хромосфер и фотосфер цефеид

Melnikov, O.A. and Мельников, О. (1942) On the phases of variations of radii of the chromospheres and photospheres of Cepheids / О соотношении фаз изменения радиусов хромосфер и фотосфер цефеид. აბასთუმნის ასტროფიზიკური ობსერვატორიის ბიულეტენი / Bulletin of the Abastumani Astrophysical Observatory (6). pp. 79-95.

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Abstract

Numerous investigations on the distribution of energy in the spectra of stars of F-G type prove that this distribution approximately corresponds to the black body. From this standpoint the work by A. Cox is very important. The author has 3 pointed out that the distribution of energy in spectra of Ccpheids corresponds to that in normal stars of the same spectral class and therefore, does not differ greatly from the distribution for the black body. The other, very important contribution to the knowledge on Cepheids Is the work by W. Becker and W. Strohmeier. In this work the most accurate curves of brightness for two regions of spectrum are given. W. Becker works are devoted to the theoretical discussion of these data. The author, basing his work upon the principal experimental tact—the correlation of phases between the light curve and the light velocity curve—considers the radii of the photosphere at the minimum and maximum of brightness to be equal and having a mean value. This assumption enabled him to write a formula for the amplitude in stellar magnitudes; The comparison of amplitudes calculated alter the definite color temperatures by means of the formula (1) with the amplitude values observed, showed that the latter were almost twice as little (Table II). According to Becker this fact is indicative of a great deviation of the photospheric radiation of Cepheids from that of the black body. The obtained inverse differences of the temperatures show a non-linear dependence. Having obtained radiation temperatures (which, according to Becker's discussion, coincided with the effective^temperatures* Becker calculated the variation of the radius I of the photosphere for each of the phases by the formula (2). However, the other invenstigators considered tile behaviour of the chromosphere in the variable Held of radiation to be different from the behaviour of deep layers of the atmosphere, which pulsate adiabatically. In connection with the explanation of the apparent difference of phases of variation curves of radii of the photosphere and chromosphere by the fact of the deviation of radiation of Cepheids from the radiation of the black body seems to be of a great interest. A new theoretical problem comes to light at the same time. what is the cause of the light curve being in the phase with the variation of the radium derivative of the photosphere and not in the phase with the variation of the radius itself? On account of that it seemed to as of interest to work at the data by Becker in a different way. The fact is that treating radii at the time of their maximum and minimum brightness as identical, we "displace- the curve of the radius variation of the photosphere up to its coincidence with that for the chromosphere. But the equality of radii at their maximum and minimum is the effect, resulting from the velocity curve observed. If we base upon this fact, no other result than the coincidence of the phases of radii variation of the chromosphere and of the photosphere, can be obtained. Similar conclusions on the deviation of radiation of Cepheids from that for the black body have been drawn by A. N. Cox. However, E. H. Bleksley' has pointed out that, on the contrary, observations made by Cox, on the introduction of a term depending upon the ratio of radii, lead to the conclusion that the radiation of Cepheids does not deviate from that of the black body. The amplitudes of monochromatic brightness curves for two wave-lengths may be recorded as (4). The values (s) are amplitudes caused only by temperature fluctuations. These very amplitudes, and not A1 and A2 observed, must agree with the values calculated by the formula (1). The list of stars, for which the above effect has been investigated, is Riven on the page 87. The differential displacements of individual lines have been also detected by W. S. Adams and R. San ford" and, quite recently on spectrograms with groat dispersion, - by W. S. Adams50. At the present state of the problem, we may consider, that the effect is within the observation errors for spectrographs with moderate dispersion. However, we have also to admit that there exists a certain increase of the pulsation amplitude with the height in the chromosphere of Cepheids. There exists also a retardation of curves, attributed to higher levels in the chromosphere. This problem has been fully discussed by B. V. Kukarkin. The same effect of retardation of curves, attributed to higher levels of the photosphere, has been also detected when investigating light curves (B. V. Kukarkin). This problem, as well as the problem of increasing the pulsation amplitude with the height in the chromosphere is of a considerable importance. In order to explain the difference of phases of variation of the chromospheric and photospheric radii, as passing gradually from the lower to high layers, we should have observed the inverse effect-The velocity curves, attributed to the higher layers in the chromosphere would have exceeded the curves of the lower layers. From the photometrical data we obtain the relative radii for the maximum and minimum. Disregarding the differences of phases, we obtain the maximum and minimum radii of eight Cepheids (the temperatures of which are known with sufficient exactness). Using color temperatures (such a possibility has already been pointed out before), we obtain by formulae (7) mean absolute magnitudes of eight Cepheids. Table III contains these data. From Table III we see that the deviations of absolute magnitudes from the "period-luminosity" curve of Shapley are considerable. The above calculations show that the "pulsation parallaxes" cannot have any reliable or actual importance. In Fig. 4 we show the dependence of the logarithm o! the mean radius of Cepheids upon the logarithm of the period, obtained in the present investigation. However, we consider this «mean radius*, as well as that obtained by Becker as fictitious, due to the unreliable fundamental physical principles. November, 1940.

Item Type: Article
Subjects: Q Science > QB Astronomy
Divisions: Institutes > Evgeny Kharadze Abastumani National Astrophysical Observatory
Depositing User: თამარ ჭაღიაშვილი
Date Deposited: 16 Jul 2018 10:11
Last Modified: 16 Jul 2018 10:11
URI: http://eprints.iliauni.edu.ge/id/eprint/8232

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