Browsing by Author "Mennickent, RE"

Now showing 1 - 6 of 6
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    A direct distance to the Large Magellanic Cloud Cepheid HV 12198 from the infrared surface brightness technique
    (2000) Gieren, WP; Storm, J; Fouqué, P; Mennickent, RE; Gómez, M
    We report on the first application of the infrared surface brightness technique on a Cepheid in the Large Magellanic Cloud, the variable HV 12198 in the young globular cluster NGC 1866. From this one star, we determine a distance modulus of 18.42 +/- 0.10 (random and systematic uncertainty) to the cluster. When the results on further member Cepheids in NGC 1866 become available, we expect to derive the distance to the LMC with a +/-3%-4% accuracy, including systematic errors, from this technique.
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    Coupled long-term photometric and V/R variations in Be stars: evidence for prograde global one-armed disk oscillations
    (1997) Mennickent, RE; Sterken, C; Vogt, N
    We review theoretical work on global oscillations of Be star disks and summarize possible observational tests. In addition, we analyze existing records on photometric data and V/R ratio for a sample of 6 V/R variable Be stars. Five stars showed coupled long-term photometric-V/R variations. In all cases the photometric extrema coincided with times of V = R transits, the fainter state being followed by a V < R phase. V 1294 Aql, 48 Lib and MXPup showed anticorrelated c(1) and b - y colors during light cycles, the stars being redder in b - y when brightest. 48 Lib shows a complex color behaviour, exhibiting two minima during a V/R cycle and a pronounced b - y drop just at maximum light. In addition, this star shows enigmatic, non-periodic, eclipse-like features in its light curve. In general, the V/R-photometric observations can bi grouped in three main groups, depending on the degree of correlation exhibited by the V/R ratio and the photometric fluxes and the rate of change of the u flux. These groups are compatible with prograde global disk oscillations observed under different system inclinations.
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    Doppler tomography of the dwarf novae VY Aquari and WX Ceti
    (2006) Mennickent, RE; Unda-Sanzana, E; Tappert, C
    Aims. We present the optical spectroscopy of the dwarf novae VY Aqr and WX Cet in quiescence.
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    Long-term photometry of Be stars -: III.: Evidence for periodic outbursts of λ Eri and photometric activity in HR 2142
    (1998) Mennickent, RE; Sterken, C; Vogt, N
    Stromgren differential uvby photometry of lambda Eri and HR 2142 is analyzed. The data were taken during the time interval 1983-1994 in the framework of the Long-Term Photometry of Variables project at La Silla. lambda Eri exhibited four photometric events (probably associated with line emission episodes) that last several months and which were characterized by a common pattern of change in all passbands (similar to +/-10(-3) mag/day) along with an apparent decrease of the amplitude of the short-term variability and an increase of the stellar temperature. A. search for periodicities reveals that these events fit a 486 d recurrence time. On the other hand, HR 2142 showed a relatively "quiet" long-term photometric behaviour, the orbital period being detected only marginally in the photometric data set. In contrast, a 344 d period optimally fits the data. We discuss the possibility of an internal "clock" regulating the outburst activity of lambda Eri and show that the photometric variability of HR 2142 can hardly be explained by its interacting binary nature. We also discuss an empirical relationship found between partial derivative c(1)/partial derivative u and v sini in a sample of 11 Be stars.
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    Long-term photometry of be stars .2. Periodic variations on time scales of days to months
    (1996) Sterken, C; Vogt, N; Mennickent, RE
    Stromgren differential uvby photometry of 4 Be stars is analysed. The data were taken during the time interval 1983-1994 in the framework of the Long-Term Photometry of Variables project at La Silla. We detected in these four stars periodic photometric variations with periods between 4 and 93 days. The two cases with the longest periods (FT CMa with P = 87.(d)9 and FY CMa with P = 92.(d)7) did not have any previously known periodic variability. In three of the four cases the periodic oscillation was coherent and always present during the 10 years of monitoring.
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    Spectroscopic analysis of tremendous-outburst-nova candidates
    (2005) Schmidtobreick, L; Tappert, C; Bianchini, A; Mennickent, RE
    In the course of a long-term project investigating classical novae with large outburst amplitudes, we have performed optical spectroscopy of several old-nova candidates. We here present the spectra of the candidates V630 Sgr, XXTau, CQVel, V842 Cen, and V529 Ori, that hitherto lacked such classification. While the first four show spectra typical of cataclysmic variables and can thus be identified as such, V529 Ori is probably misclassified. Of special interest are the two systems XXTau and V842 Cen, which show signs of being low mass transfer systems. As such they can be used to judge the evolution scenarios for novae. In particular, given the rather young age of their outbursts, it appears more likely that these systems are not on their way into hibernation (i.e., cutting off mass transfer for a longer period of time), but are simply settling down towards their original configuration of comparatively low, but steady, mass transfer, such as for dwarf novae.