111 research outputs found
An extensive photometric study of the Blazhko RR Lyrae star MW Lyr: II. Changes in the physical parameters
The analysis of the multicolour photometric observations of MW Lyr, a large
modulation amplitude Blazhko variable, shows for the first time how the mean
global physical parameters vary during the Blazhko cycle. About 1-2 percent
changes in the mean radius, luminosity and surface effective temperature are
detected. The mean radius and temperature changes are in good accordance with
pulsation model results, which show that these parameters do indeed vary within
this order of magnitude if the amplitude of the pulsation changes
significantly. We interpret the phase modulation of the pulsation to be a
consequence of period changes. Its magnitude corresponds exactly what one
expects from the detected changes of the mean radius assuming that the
pulsation constant remains the same during the modulation. Our results indicate
that during the modulation the pulsation remains purely radial, and the
underlying mechanism is most probably a periodic perturbation of the stellar
luminosity with the modulation period.Comment: 10 figures, 2 tables. Accepted for publication in MNRA
MOST light-curve analysis of the gamma Dor pulsator HR 8799, showing resonances and amplitude variations
Context The central star of the HR 8799 system is a gamma Doradus-type pulsator. The system harbours four planetary-mass companions detected by direct imaging, and is a good solar system analogue. The masses of the companions are not known accurately, because the estimation depends strongly on the age of the system, which is also not known with sufficient accuracy. Asteroseismic studies of the star might help to better constrain the age of HR\,8799. We organized an extensive photometric and multi-site spectroscopic observing campaign for studying the pulsations of the central star.
Aims The aim of the present study is to investigate the pulsation properties of HR 8799 in detail via the ultra-precise 47-d-long nearly continuous photometry obtained with the MOST space telescope, and to find as many independent pulsation modes as possible, which is the prerequisite of an asteroseismic age determination.
Methods We carried out Fourier analysis of the wide-band photometric time series.
Results e find that resonance and sudden amplitude changes characterize the pulsation of HR 8799. The dominant frequency is always at f_1 = 1.978 d^-1. Many multiples of one ninth of the dominant frequency appear in the Fourier spectrum of the MOST data: n/9 f_1, where n = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 13, 14, 17, 18\}. Our analysis also reveals that many of these peaks show strong amplitude decrease and phase variations even on the 47-d time-scale. The dependencies between the pulsation frequencies of HR 8799 make the planned subsequent asteroseismic analysis rather difficult. We point out some resemblance between the light curve of HR 8799 and the modulated pulsation light curves of Blazhko RR Lyrae stars
The triple-mode pulsating variable V823 Cas
Based on extended multicolour CCD photometry of the triple-mode radial
pulsator V823 Cas we studied the properties of the coupling frequencies invoked
by nonlinear processes. Our results support that a resonance connection as
suggested by Antonello & Aikawa (1998) affects the mode coupling behaviour. The
P1/P0 period ratio of V823 Cas has an "out of range" value if compared with the
period ratios of the known double mode pulsators, while the P2/P1 period ratio
is normal. The periods and period ratios cannot be consistently interpret
without conflict with pulsation and/or evolution models. We attempt to
interpret this failure by the suggestion that at present, the periods of V823
Cas are in a transient, resonance affected state, thus do not reflect the true
parameters of the object. The anomalous period change behaviour of the
fundamental and second overtone modes supports this idea. We have also raised
the possibility that a f0 + f2 = 2f1 resonance may act in triple mode
pulsators.Comment: 10 pages, 7 figures, 5 tables. Accepted for publication in Astronomy
and Astrophysic
An extensive photometric study of the Blazhko RR Lyrae star MW Lyr: I. Light curve solution
We have obtained the most extensive and most accurate photometric data of a
Blazhko variable MW Lyr during the 2006-2007 observing seasons. The data within
each 0.05 phase bin of the modulation period (P_m=1/f_m) cover the entire light
cycle of the primary pulsation period (P_0=1/f_0), making possible a very
rigorous and complete analysis. The modulation period is found to be 16.5462 d,
which is about half of that was reported earlier from visual observations.
Previously unknown features of the modulation have been detected. Besides the
main modulation frequency f_m, sidelobe modulation frequencies around the
pulsation frequency and its harmonics appear at +/- 2 f_m, +/- 4 f_m, and +/-
12.5 f_m separations as well. Residual signals in the prewhitened light curve
larger than the observational noise appear at the minimum-rising branch-maximum
phase of the pulsation, which most probably arise from some stochastic/chaotic
behaviour of the pulsation/modulation. The Fourier parameters of the mean light
curve differ significantly from the averages of the Fourier parameters of the
observed light curves in the different phases of the Blazhko cycle.
Consequently, the mean light curve of MW Lyrae never matches its actual light
variation. The Phi_21, Phi_31 phase differences in different phases of the
modulation show unexpected stability during the Blazhko cycle. A new
phenomenological description of the light curve variation is defined that
separates the amplitude and phase (period) modulations utilising the phase
coherency of the lower order Fourier phases.Comment: Accepted for publication in MNRAS. 15 pages, 14 figures, and 7
printed tables (2 of them available in electronic form
Long-term photometric monitoring of RR Lyr stars in M3
The period-change behaviour of 134 RR Lyrae stars in the globular cluster
Messier 3 (M3) is investigated on the ~120-year time base of the photometric
observations. The mean period-change rates (\beta \approx 0.01 d Myr^-1) of the
subsamples of variables exhibiting the most regular behaviour are in good
agreement with theoretical expectations based on Horizontal-Branch stellar
evolution models. However, a large fraction of variables show period changes
that contradict the evolutionary expectations. Among the 134 stars studied, the
period-change behaviour of only 54 variables is regular (constant or linearly
changing), slight irregularities are superimposed on the regular variations in
23 cases and the remaining 57 stars display irregular period variations. The
light curve of ~50 per cent of the RRab stars is not stable, i.e., these
variables exhibit Blazhko modulation. The large fraction of variables with
peculiar behaviour (showing light-curve modulation and/or irregular O-C
variation) indicate that, probably, variables with regular period changes
incompatible with their evolutionary stages also could display some kind of
instability of the pulsation light curve and/or period, but the available
observations have not disclosed it yet. The temporal appearence of the Blazhko
effect in some stars, and the 70-90 years long regular changes preceded or
followed by irregular, rapid changes of the pulsation period in some cases
support this hypothesis.
[...] Abstract truncated due to the limitations of astroph. See full abstract
in the paper.Comment: 22 pages, 14 figures, accepted for publication in MNRA
Affordable spectroscopy for 1m-class telescopes: recent developments and applications
Doppler observations of exoplanet systems have been a very expensive technique, mainly due to the high costs of high-resolution stable spectrographs. Recent advances in instrumentation enable affordable Doppler planet detections with surprisingly small optical telescopes. We investigate the possibility of measuring Doppler reflex motion of planet hosting stars with small-aperture telescopes that have traditionally been neglected for this kind of studies. After thoroughly testing the recently developed and commercially available Shelyak eShel echelle spectrograph, we demonstrated that it is routinely possible to achieve velocity precision at the 100 m s(-1) level, reaching down to +/- 50 m s(-1) for the best cases. We describe our off-the-shelf instrumentation, including a new 0.5m RC telescope at the Gothard Astrophysical Observatory of Lorand Eotvos University equipped with an intermediate resolution fiber-fed echelle spectrograph. We present some follow-up radial velocity measurements of planet hosting stars and point out that updating the orbital solution of Doppler-planets is a very important task that can be fulfilled with sub-meter sized optical telescopes without requesting very expensive telescope times on 2-4 m (or larger) class telescopes
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