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The Program to Link the HIPPARCOS Reference Frame to an Extragalactic Reference System Using the Fine Guidance Sensors of the Hubble Space Telescope
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....114.2796H&db_key=AST
| Periodic and aperiodic variations in TT Arietis. Results from an international campaign.
Results based on the 30 best nightly runs are reported. The moments of33 brightness maxima and 35 minima show large scatter of phases within0.6^p^-interval. The value of the primary photometric period ofP=0.132953+/-13x10^-6^d differs from the previously published ones.Periodograms for detrended nightly runs show significant peaks atdifferent frequencies from 28 to 103c/d. The most prominent peakscorrespond to periods of 23.7, 15.2, 27.5 and 51.6min. This argues fortransient quasi-periodic oscillations (QPO) occurring at few preferredtime scales rather than for a QPO with a time scale decreasing from27min in 1962 to 17min in 1985 (Semeniuk et al. 1987). Such behaviourmay be explained by the "beat-frequency model" (Hollander & vanParadijs 1992). It seems that in TT Ari we observe contributions ofseveral instability mechanisms with similar time scales. At higherfrequencies 90-900 c/d the periodogram for all observations obeys apower law with an index γ=1.600+/-0.008. This value coincideswithin error estimates with that of γ=1.51+/-0.04 obtained for amean periodogram. Such apparent red noise may be owed to the QPOs. Thevariations in UBVRI are highly correlated. A method for determination ofrelative colours of "slow", "fast correlated" variations and an"uncorrelated noise" is proposed. Corresponding parameters aredetermined. Values U-B=-1.04mag, -1.24mag, -1.35mag and B-V=0.19mag,0.05mag, 0.12mag for "mean brightness", "fast" and "slow" variations,respectively.
| Cataclysmic Variable TT Arietis Observed at Bucharest Observatory During 1994
New photoelectric observations of the cataclysmic variable TT Arietisobtained in 1994's observational season are presented. The observationswere performed in Filter B only, using a 50 cm Cassegrain telescope ofthe Bucharest Observatory.
| Four Periods of Tt-Arietis
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| Photometric Observations of TT Ari
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