13 research outputs found
The Blazhko behaviour of RR Geminorum II -- long-term photometric results
Context. RR Gem is one of the few Blazhko RR Lyrae that has photometric
observations available extended enough to study the long-term courses of its
pulsation and modulation properties in detail.
Aims. We investigate the pulsation and modulation properties and the
relations between them in RR Gem using photometric observations from the past
70 years in order to gain further insight into the nature of the Blazhko
modulation.
Methods. We studied the photographic, photoelectric, and CCD light curves
obtained at the Konkoly Observatory and other authors' published maxima
observations. Detailed analysis of the light curves, maximum brightness, and
O-C data are carried out.
Results. RR Gem showed modulation most of the time it was observed. The
modulation amplitude showed strong variations from the undetectable level (less
than 0.04 mag in maximum brightness) to about 0.20 mag. The amplitudes of the
amplitude and phase modulations showed parallel changes, thus the total 'power'
of the modulation have changed during the past 70 years. Parallel changes in
the pulsation and modulation periods occur with a d P_mod / d P_puls = 1.6 +/-
0.8 * 10^3 ratio. We also detected 0.05-0.1 mag changes in the mean maximum
brightness and mean pulsation amplitude.Comment: Accepted for publication in Astronomy and Astrophysics. About 12
pages, 9 figures, 15 tables (3 of them appear in the paper, the others are
only available electronically at the CDS
Studying Blazhko RR Lyrae stars with the 24-inch telescope of the Konkoly Observatory
About a dozen field RR Lyrae stars have been observed with the 24-inch
Heyde-Zeiss telescope of the Konkoly Observatory at Sv\'abhegy, Budapest, since
its refurbishment in 2003. Most of the observing time is allocated for the
investigation of the Blazhko modulation, a phenomenon that still does not have
a satisfactory explanation. The obtained multicolour CCD observations are
unique in extent. The accuracy of the measurements makes it possible to detect
low amplitude modulation of the light curve as well. The discovery of Blazhko
stars with low modulation amplitudes warns that the incidence rate of the
Blazhko modulation is, in fact, much larger than it was previously expected.
This makes the efforts exploring the cause of the modulation even more
important. A summary of our measurements and results achieved during the last 3
years is presented.Comment: Accepted for publication in Astronomische Nachrichten (Astronomical
Notes). 4 pages, 3 fig
Long-term photometric behaviour of XZ Dra Binarity or magnetic cycle of a Blazhko type RRab star
The extended photometry available for XZ Dra, a Blazhko type RR Lyrae star,
makes it possible to study its long-term behavior. It is shown that its
pulsation period exhibit cyclic, but not strictly regular variations with
approx. 7200 d period. The Blazhko period (approx. 76 d) seems to follow the
observed period changes of the fundamental mode pulsation with dP_B/dP_0=7.7 x
10^4 gradient. Binary model cannot explain this order of period change of the
Blazhko modulation, nevertheless it can be brought into agreement with the O-C
data of the pulsation. The possibility of occurrence of magnetic cycle is
raised.Comment: 13 pages, 11 figures (submitted to A&A
The Blazhko behavior of RV UMa
RV UMa is one of the most extensively studied RR Lyrae stars showing Blazhko
modulation. Its photometric observations cover more than 90 years. The
published photoelectric observations of RV UMa obtained at the Konkoly
Observatory (Kanyo, 1976) were re-considered and completed with previously
unpublished data. During the time interval of the observations the periods of
both the pulsation and the modulation varied within the ranges of 0.000007 and
0.9 days, respectively. We have found a definite but not strict inverse
relation between the pulsation and modulation periods of RV UMa.Comment: 4 pages, 5 figures, accepted for publication in A
Period Changes of Variables and Evolutionary Paths in the Hertzsprung-Russell Diagram
The theory of Random walkhas been applied to the O-C diagrams of variable stars, and a method has been outlined for the determination of the standard deviation, sigma, of random period-fluctuations, which is free from uncertainties in the expectation value of the period. It is shown, that sigma is an important parameter of variable stars. It seems to be correlated with the rapidity of evolution: the period of a repidly evolving star becomes strongly fluctuating