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3. Results

3.1. Absolute elements

As already discussed in Sect. 2, the amplitude tex2html_wrap_inline1153 of the radial velocity curve of the primary component has two probable values (Popper 1989) and hence is uncertain. Taking tex2html_wrap_inline1349, one gets, from the presently derived photometric mass ratio tex2html_wrap_inline1399 of 0.1985, a value of tex2html_wrap_inline1401 for tex2html_wrap_inline1153. This value of tex2html_wrap_inline1153 is almost the same(within errors) as that of tex2html_wrap_inline1407 tex2html_wrap_inline1409 derived by Popper (1989) from H lines for which the systemic velocity, V0, is the same as that for the cooler component. Hence, we conclude that, within observational errors, the derived photometric mass ratio is equal to that of the spectroscopic mass ratio obtained by Popper (1989) from the H lines and hence would yield reliable absolute elements. Combining the values of tex2html_wrap_inline1413 and tex2html_wrap_inline1349 with the other required parameters from Table 2 (click here) and using the relevant equations, we derived the absolute elements of AU Mon with their errors, as given in Table 3 (click here).

Bolometric corrections (B.C) of tex2html_wrap_inline1417 for the primary and tex2html_wrap_inline1419 for the secondary are used (Popper 1980). In deriving tex2html_wrap_inline1421, we used tex2html_wrap_inline1423 and tex2html_wrap_inline1425.

3.2. Spectral types of the components

As the light curve of only one pass band is available for analysis, it is not possible to derive the colours of the individual components and find their spectral types. However, the derived temperature of 6000 K and bigger size tex2html_wrap_inline1431 of the secondary component with a log g value of 2.5 suggest it to be of spectral type F9-G0III-II (Allen 1976; Popper 1980; Schmidt-Kaler 1982). According to Dr. Morgan (in Sahade & Cesco 1945) the secondary component is a star of near F0 spectral type. As already stated in Sects. 1 and 2, the observed spectral type of the primary component is B5. According to Dr. Morgan (in Sahade & Cesco 1945) the intensity of H lines in this component was of the same order as in a B5IV star. When compared to a main sequence B5 star, the derived radius of the primary component is larger by about 35%, its log g value (3.76) lies in between the log g values for a B5V (4.04) and B5III (3.49) stars (Schmidt-Kaler 1982) and it has already filled about 25% of its Roche lobe (tex2html_wrap_inline1439=0.534; Plavec & Kratochvil 1964). All these properties indicate a slight evolution of the primary component and confirm its classification to be B5IV. Hence AU Mon consists of B5IV plus F9-G0III-II stars as its components.

3.3. Distance modulus

As the difference in the absolute visual magnitudes tex2html_wrap_inline1441 of the secondary and primary components is 1.38 (Table 3 (click here)), the ratio of their luminosities tex2html_wrap_inline1443 is equal to 0.28. From this ratio, one can calculate the combined visual absolute magnitude tex2html_wrap_inline1441 of AU Mon to be -2.04. The apparent visual magnitude tex2html_wrap_inline1449 at maximum of AU Mon was recorded as 8.5 (Batten 1967) and 8.3 (Wood et al. 1980). Taking an average of these values, along with the combined tex2html_wrap_inline1381 and assuming no space reddening the distance modulus (m-M) of AU Mon is derived as 10.44, from which a distance of tex2html_wrap_inline1455 pc is obtained. However, Peters (1994) suggested a reddening of tex2html_wrap_inline1457 for this system. If this were the case, space absorption tex2html_wrap_inline1459 equals tex2html_wrap_inline1461 (Allen 1976), from which a distance of tex2html_wrap_inline1463 pc is obtained for AU Mon. For a comparison, the system parameters, as reported by Lorenzi (1982) and Giuricin et al. (1982) along with those obtained from the present analysis are given in Table 4 (click here).


Parameter Lorenzi Giuricin Present
(1982)et al. (1982)studies
Method 1 2 3
tex2html_wrap_inline1165K 15500* 15000* 15500*
tex2html_wrap_inline1235K 5300 6600 6000
q - 0.2* 0.1985
tex2html_wrap_inline1477 82.0 78.4 78.74
tex2html_wrap_inline1233 0.93 0.645 0.659
tex2html_wrap_inline1481 0.07 0.355 0.341
l3 - - 0.0
tex2html_wrap_inline1287 0.18 0.115 0.131+
tex2html_wrap_inline1297 0.18 0.242 0.249+
tex2html_wrap_inline1493 - 2.98 3.16
tex2html_wrap_inline1495 - 2.20 2.07
tex2html_wrap_inline1497 6.5* 6.0* 5.93
tex2html_wrap_inline1503 1.4 1.2 1.18
tex2html_wrap_inline1505 7.5 4.6 5.28
tex2html_wrap_inline1507 7.5 9.7 10.04
Sp.typ (Pri) B5V B5V B5IV
Sp.typ (Sec)-early F F9-G0III-II
Table 4: AU Mon: Comparison of system parameters obtained from different studies

  *Assumed values



Russell-Merrill Wood's WINK Wilson-Devinney.

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