The Blazhko effect in observations of XZ Cyg.

Abstract

An analysis was made of the Blazhko effect in the RR Lyrae star XZ Cyg using 410 times and brightnesses of primary maxima obtained between 1905 and 1973. A secondary periodicity was found to exist for XZ Cyg, the period of this variation being about 57438 until JD2438500 (1964) and thereafter about 58^7. Mean curves are derived for the 57438 and 58^7 variations. It is shown that the increase in the secondary period can be explained under the assumption that the secondary period is a beat period involving interference between the primary periodicity and another periodicity. Key words: Blazhko effect -period change -RR Lyrae stars This paper discusses the Blazhko effect in observations of the RR Lyrae variable star XZ Cygni (HD ext 239124 = BD +56° 2257). The Blazhko effect is a regular variation in the shape of the light curve of an RR Lyrae star which can be attributed to the presence of multiple periodicities. As of 1970, secondary periods had been found for 24 RR Lyrae "ab" stars and 3 RR Lyrae "c" stars (Detre 1970). It has been suggested that a substantial fraction of RR Lyrae stars would show a Blazhko effect if sufficiently numerous and accurate observations were available.XZ Cyg was recognized to be variable by L. Ceraski in 1905. It was found to be an RR Lyrae "ab" variable with period (P 0 ) about 04467 and visual amplitude around 1™4. S. N. Blazhko (1922) discovered that the light curve of XZ Cyg did not precisely repeat from cycle to cycle. Instead, the magnitude attained at maximum varied by 0^3 to 0^4 for different cycles. In similar fashion, the observed epochs of maximum light did not fall precisely at the times predicted from the mean period. Rather, the residuals for the epochs of maximum light (O-C : residuals) were as great as ±04)2. Blazhko explained these fluctuations in terms of a secondary periodicity (Pi) of length 5744 (123P 0 ) and a tertiary periodicity of lesser amplitude and length %P lt Subsequently, studies of the Blazhko effect in XZ Cyg were made by Rybka (1933) Klepikova (1958), and Baldwin (1973). These studies confirmed the existence of Blazhko's secondary periodicity, while yielding seemingly contradictory results as regards additional periodicities. Muller, using photoelectric observations for 1948-52, explained the observed O-C : residuals and maximum magnitude fluctuations through a secondary period of 57424 and a tertiary period of either 414)8 (89.34 P 0 ) or 43 d 91 (94.12 P 0 ). Klepikova, from observations spanning the years 1905 to 1954, found that a secondary period of 574410 (123.040 P 0 ) could approximately explain the observed fluctuations, but that a better fit could be made if variations of period 414)2 (89.23 P 0 ) and 3461 d (7418 P 0 ) were posited also. Balazs, however, found a tertiary period of 1534} (329.6 P 0 ), and recently Baldwin, from observations made between 1965 and 1972, found the rather larger value of 584316 for the length of the secondary period.In light of the discordant results given above, it was decided to analyze the Blazhko effect in...

Blazhko stars: Always distorted?

“…Although this relation may differ from star to star, we transformed the PS67 radial velocities of RV UMa accordingly, to estimate its metallic line radial velocity amplitudes in different Blazhko phases. 34565;38665;41544;42622;43401;44147 40.80 RV UMa 36733.7;37815.4 90.785 Ephemeris of XZ Cyg is taken from Smith (1975). Blazhko periods and maximum epochs for the other stars are determined from the collections of photometric data by Szeidl et al (1997), Szeidl et al (2001), Nagy (1998), andKovács (1995) for RR Lyr, XZ Dra, RS Boo, and RV UMa, respectively.…”

The Changing Blazhko Effect of XZ Cygni

“…These indicated that, at about the time that the primary period of XZ Cyg fell to its minimum, the Blazhko period of XZ Cyg increased to about 58.4 d, or perhaps slightly more. An O-C diagram illustrating this change in the Blazhko period is included in Smith (1975). As a check and an extension of these earlier results, we have analyzed observations of XZ Cyg reported since 1965 to the RR Lyrae Committee of the American Association of Variable Star Observers (AAVSO).…”

“…Shortly after the decline in the primary period of XZ Cyg, observers began to report a coincident increase in its 57.4 d Blazhko period Kunchev 1975;Smith 1975). These indicated that, at about the time that the primary period of XZ Cyg fell to its minimum, the Blazhko period of XZ Cyg increased to about 58.4 d, or perhaps slightly more.…”

“…In the 1960s, however, XZ Cyg underwent striking changes. , Smith (1975), , and reported that the Blazhko period of XZ Cyg abruptly lengthened to about 58.4 d in the mid 1960s. This change in the Blazhko period was coincident with a sharp decrease in the primary pulsation period, which took place in several steps (Bezdenezhny 1988;Baldwin & Samolyk 2003).…”