12 research outputs found
A Jupiter-mass planet around the K0 giant HD 208897
For over 10 years, we have carried out a precise radial velocity (RV) survey
to find substellar companions around evolved G,K-type stars to extend our
knowledge of planet formation and evolution. We performed high precision RV
measurements for the giant star HD 208897 using an iodine (I2) absorption cell.
The measurements were made at T\"UB\.ITAK National Observatory (TUG, RTT150)
and Okayama Astrophysical Observatory (OAO). For the origin of the periodic
variation seen in the RV data of the star, we adopted a Keplerian motion caused
by an unseen companion. We found that the star hosts a planet with a minimum
mass of m2sini=1.40MJ, which is relatively low compared to those of known
planets orbiting evolved intermediate-mass stars. The planet is in a nearly
circular orbit with a period of P=353 days at about 1 AU distance from the host
star. The star is metal rich and located at the early phase of ascent along the
red giant branch. The photometric observations of the star at Ankara University
Kreiken Observatory (AUKR) and the HIPPARCOS photometry show no sign of
variation with periods associated with the RV variation. Neither bisector
velocity analysis nor analysis of the Ca II and Halpha lines shows any
correlation with the RV measurements
Recurrent star-spot activity and differential rotation in KIC 11560447
We present a detailed analysis of surface inhomogeneities on the K1-type subgiant component of the rapidly rotating eclipsing binary KIC 11560447, using high-precision Kepler light curves spanning nearly 4 yr, which corresponds to about 2800 orbital revolutions. We determine the system parameters precisely, using high-resolution spectra from the 2.1-m Otto Struve Telescope at the McDonald Observatory. We apply the maximum entropy method to reconstruct the relative longitudinal spot occupancy. Our numerical tests show that the procedure can recover large-scale random distributions of individually unresolved spots, and it can track the phase migration of up to three major spot clusters. By determining the drift rates of various spotted regions in orbital longitude, we suggest a way to constrain surface differential rotation and we show that the results are consistent with periodograms. The K1IV star exhibits two mildly preferred longitudes of emergence, indications of solar-like differential rotation, and a 0.5–1.3-yr recurrence period in star-spot emergence, accompanied by a secular increase in the axisymmetric component of spot occupancy
Monitoring spots via the TESS data strengthened by the ETV behaviour : an investigation on the contact binary PP Lac
The Blazhko effect of RR Lyrae in 2003-2004
Aims.Extensive photometry of RR Lyr was obtained over a
421-day interval in 2003–2004, covering more than 10 Blazhko cycles
in a multisite campaign. The length and density of this data set allow for
a detailed analysis.
Methods.We used Fourier techniques to study RR Lyr's behavior over the pulsation
and the Blazhko cycle. We propose a two-frequency model for decomposing the
frequency spectrum.
Results.The light variations were fitted with the main radial frequency, its harmonics up
to 11th order, and the detected
triplet frequencies. No significant quintuplet components were found in the
frequency spectrum. Given the total time span of the measurements, we can now unambiguously
conclude that the Blazhko period has become notably shorter than the previously known value of 40.8 days, whereas
the main pulsation period remained
roughly the same. Changes in the modulation period have been reported for
other well-studied Blazhko variables.
They challenge the explanations for the
Blazhko effect which
link the modulation period directly to the rotation period.
The new photometry reveals an interval in the pulsation cycle of RR Lyr during
which the star's intensity barely changes over the Blazhko cycle.
This interval occurs during the infalling motion and
between the supposed phases of the early and the main shock. The data also
permit a more detailed study of the light curve shape at different phases in the
Blazhko period through Fourier parameters