Multi-access on the Chilton Atlas

Baldwin, James

doi:10.1093/comjnl/14.2.119

Cited by 4 publications

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“…The date of the increase in the secondary period is of special significance. According to Baldwin (1971Baldwin ( , 1973 a decrease in the primary period of XZ Cyg was noticed shortly after JD2439000. Extrapolation of the increasingly negative O-C : residuals after that date indicate that this change must have commenced near JD2438500, coincidental to the change in the secondary period.…”

Section: Mag Secondarymentioning

confidence: 99%

“…O-C : residuals were calculated using Klepikova's elements for the primary period when observations made between 1905 and 1963 were considered. For the 1965 to 1973 observations, the elements given by Baldwin (1971Baldwin ( , 1973 were used to take into account the changing primary period of XZ Cyg. The dates of magnitude and O-C : secondary maxima are listed in Table I and are probably accurate to a few days time.…”

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The Blazhko effect in observations of XZ Cyg.

Smith¹

1975

PASP

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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...

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Section: Mag Secondarymentioning

confidence: 99%

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confidence: 99%

The Blazhko effect in observations of XZ Cyg.

Smith¹

1975

PASP

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Control of queues in a permissive society

Thomas¹,

Kent²

1972

Softw Pract Exp

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By attaching anXDS Sigma 2 computer to Atlas via a shared disk, a multi-access facility has been developed without causing any interruption in the day to day running of the Atlas batch processing system. Jobs may be initiated on Atlas from a terminal and results from such jobs may be either returned to files or published on any of the normal Atlas peripherals.A statistics collecting package is included, which allows the gathering of information about any part of the system. Also, modifications can easily be made to the system to test the predictions of such a model. The model described here tries to relate response time to various system loads. In order to allow for the overlapping of disk and CPU time, we have queued the two activities in series.One of the useful side effects of constructing such I model is the focussing of attention on areas of the software which really do affect the response time. The paper outlines the development of this model, which is s t i l l in progress, highlighting some of the milestones and pitfalls encountered so far.KEY WORDS Multi-access Modelling Markov * This paper describes the work undertaken on an extension of a model first used by Scherr at MIT.

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