COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 3099 Konkoly Observatory Budapest 15 October 1987 HU ISSN 0374-0676 H-ALPHA VARIABLES IN THE FIELD OF NGC7000, IC5068 AND IC5070 In the course of a program to detect H-alpha emission stars in different Milky Way fields a 36 sq. deg. field was observed in Cygnus containing the NGC7000, IC5068 and IC5070 HII regions. The observations were carried out on several nights in 1979 with the 40" Schmidt telescope of the Byurakan Astrophysical Observatory. ( For more details of these observations see Melikyan et al. 1987). It was known that in this region there were about 300 H-alpha emission stars found by Merrill and Burwell (1949, 1950), Herbig (1958), Welin (1973), Tsvetkov (1975), Tsvetkov and Tsvetkova (1978). Melikyan et al. have found 33 new H-alpha emission objects in their survey and 7 of them appeared to show variations in the H-alpha intensity. They have identified altogether 42 H-alpha variables in this region. They classified the intensity of the emission in five categories: 0=no emission, 1= weak, 2= medium, 3= strong and 4= very strong. These results are summarized in Table 1. where the 1st column gives the name of the objects (LkHalpha, BHalpha, UHalpha mean objects found in the Lick survey, in Byurakan and by Welin, respectively; asterisks designate stars discovered by Melikyan et al.). Columns 2-5 (designated with H1 to H4) give the classified intensities published in the cited literature, observed by Melikyan et al. on the nights of 25.07.79, 26.07.79 and 11.09.79, respectively. Table 1. Name H1 H2 H3 H4 Remarks Name H1 H2 H3 H4 Remarks LkHalpha 145 2 4 3 1 IR BHalpha 16 3 2 1 1 IR LkHalpha 146 2 0 0 2 3* 0 0 1 3 LkHalpha 147 2 3 2 1 8* 0 3 9 1 LkHalpha 150 1 0 2 1 11* 0 1 1 3 IR LkHalpha 151 2 0 1 1 15* 0 0 3 2 LkHalpha 154 2 3 1 3 16* 0 1 1 3 LkHalpha 155 3 2 2 2 IR 19* 0 2 2 3 LkHalpha 150 2 0 0 2 20* 0 1 0 3 LkHalpha 159 2 0 0 2 UHalpha 9 2 2 2 3 LkHalpha 160 2 0 2 2 UHalpha 14 2 0 0 3 IR LkHalpha 161 2 0 1 2 UHalpha 17 1 3 3 3 LkHalpha 164 2 1 1 1 UHalpha 26 3 0 2 3 LkHalpha 166 1 2 2 1 UHalpha 29 1 2 3 3 LkHalpha 171 3 0 2 3 UHalpha 39 1 2 3 3 LkHalpha 174 2 2 0 0 UHalpha 44 2 4 4 4 LkHalpha 176 3 1 1 2 UHalpha 62 2 0 0 3 LkHalpha 177 2 0 1 3 UHalpha 79 1 0 0 2 LkHalpha 178 1 2 2 2 UHalpha 101 1 0 0 3 LkHalpha 179 1 2 2 1 UHalpha 104 2 0 0 3 LkHalpha 188 2 2 3 1 LkHalpha 182 2 9 2 3 LkHalpha 187 1 0 0 1 LkHalpha 192 2 0 0 3 ( IR designate objects identified with IRAS point sources ) Table 2. Correlations: H1 H2 H3 H4 H1 1.0000 -.0289 -.0999 -.0954 H2 -.0289 1.0000 .6462** -.0919 H3 -.0999 .6462** 1.0000 .0171 H4 -.0954 -.0919 .0171 1.0000 N of cases: 42 1-tailed Signif: ** - .001 Table 3.a-c Crosstabulation: H1 By H2 H2-> Count Row 0 1 2 3 4 Total H1 0 2 3 1 1 7 1 4 5 1 10 2 11 1 3 3 2 20 3 2 1 2 5 Column 19 5 11 5 2 42 Total 45.2 11.9 26.2 11.9 4.8 100.0 Crosstabulation: H2 By H3 H3-> Count Row 0 1 2 3 4 Total H2 0 10 4 4 1 19 1 1 4 5 2 1 1 6 3 11 3 1 2 2 5 4 1 1 2 Column 12 10 12 7 1 42 Total 28.6 23.8 28.6 16.7 2.4 100.0 Crosstabulation: H3 By H4 H4-> Count Row 0 1 2 3 4 Total H3 0 1 1 4 6 12 1 3 2 5 10 2 4 3 5 12 3 3 1 3 7 4 1 1 Column 1 11 10 19 1 42 Total 2.4 26.2 23.8 45.2 2.4 100.0 In order to study the stochastic behaviour of the H-alpha variability we compared columns 2-5 pairwise by computing the linear correlations between them. These correlations are summarized in Table 2. As one can infer from this table, columns H2 and H3 show a correlation at a high level of significance. To present the dependence between the different columns in more detail we present cross-tabulations of H1 to H2 in Tables 3a-c. Again, one can see that H2 and H3 reveal very strong tie but no dependence can be found between the other columns. We can explain this fact on the following way: H2 and H3 designate data on consecutive nights whereas the time differences between observations corresponding to the other columns are much greater. Therefore, it is natural to suppose that there is an average covariance length of a few days in the stochastic process representing the H-alpha variability of the sources. To set up this hypothesis on a more sound basis we need further observations, possibly on consecutive nights. As a byproduct of this work we might even get the functional form of the dependence of covariances on the time difference between the observations. L.G. BALAZS N.D. MELIKYAN Konkoly Observatory, Byurakan Astrophysical Observatory, Hungary USSR S.Yu. MELNIKOV and V.S SHEVCHENKO Tashkent Astronomical Institute, USSR References: Herbig, G.H.: 1958, Astrophys. J., 128, 259 [BIBCODE 1958ApJ...128..259H ] Melikyan, N.D., Shevchenko. V.S., Melnikov, S.Yu.: 1987, IBVS No. 3073 Merrill, P.W. and Burwell. C.G.: 1949, Astrophys. J., 110, 387 [BIBCODE 1949ApJ...110..387M ] Merrill, P.W. and Burwell. C.G.: 1950, Astrophys. J., 112, 72 [BIBCODE 1950ApJ...112...72M ] Tsvetkov, M.K.: 1975, Astrofizika, 11, 579 [BIBCODE 1975Afz....11..579T ] Tsvetkov, M.K., Tsvetkova, K.P.: 1978, IBVS No. 1447 Welin, G.: 1973, Astron. and Astrophys., Suppl. Ser., 9, 183 [BIBCODE 1973A&AS....9..183W ]