364 research outputs found
Discovery of a new group of double-periodic RR Lyrae stars in the OGLE-IV photometry
We report the discovery of a new group of double-periodic RR Lyrae stars from
the analysis of the OGLE-IV Galactic bulge photometry. In 11 stars identified
in the OGLE catalog as first overtone pulsators (RRc stars) we detect
additional longer period variability of low amplitude, in the mmag regime. One
additional star of the same type is identified in a published analysis of the
Kepler space photometry. The period ratio between the shorter first overtone
period and a new, longer period lies in a narrow range around 0.686. Thus, the
additional period is longer than the expected period of the undetected radial
fundamental mode. The obvious conclusion that addition periodicity corresponds
to a gravity or a mixed mode faces difficulties, however.Comment: 5 pages, 4 figures, accepted for publication in MNRAS Letter
Double-mode radial-non-radial RR Lyrae stars. OGLE-IV photometry of two high cadence fields in the Galactic bulge
We analyse the OGLE-IV photometry of the first overtone and double-mode RR
Lyrae stars (RRc/RRd) in the two fields towards the Galactic bulge observed
with high cadence. In 27 per cent of RRc stars we find additional non-radial
mode, with characteristic period ratio, P x /P 1O \in (0.6, 0.64). It strongly
corroborates the conclusion arising from the analysis of space photometry of
RRc stars, that this form of pulsation must be common. In the Petersen diagram
the stars form three sequences. In 20 stars we find two or three close
secondary modes simultaneously. The additional modes are clearly
non-stationary. Their amplitude and/or phase vary in time. As a result, the
patterns observed in the frequency spectra of these stars may be very complex.
In some stars the additional modes split into doublets, triplets or appear as a
more complex bands of increased power. Subharmonics of additional modes are
detected in 20 per cent of stars. They also display a complex structure.
Including our previous study of the OGLE-III Galactic bulge data, we have
discovered 260 RRc and 2 RRd stars with the additional non-radial mode, which
is the largest sample of these stars so far. The additional mode is also
detected in two Blazhko RRc stars, which shows that the modulation and
additional non-radial mode are not exclusive.Comment: 18 pages, 14 figures, accepted for publication in MNRA
Blazhko effect and the Petersen diagram
Pulsations in RR Lyrae stars and classical Cepheids were thought to be
relatively simple since they typically pulsate only in one or two radial modes.
This picture changes at a closer look when modulation or additional
low-amplitude signals are detected. I will review different multi-periodic
groups known among classical pulsators, including stars showing the Blazhko
modulation.Comment: Invited review at 2022 RR Lyrae and Cepheids conference on La Palma,
9 pages, 2 figure
Empirical, Analytical Methods for Surface Settlement Prediction Due to TBM-Tunnelling in Dutch Soft Soil
TBM-tunnelling in soft soil causes a 3D-ground deformation field, developing in longitudinal direction (parallel to the axis of the tunnel) and transverse direction (perpendicular to the axis of the tunnels). Empirical based methods are used for the prediction of the distribution of ground movements in both directions. Consequently the differential settlements are used to predict the damage risks of adjacent buildings due to TBM-tunnelling in the design stage. The Gaussian-curve is commonly applied for the prediction of green field ground movements transverse to the tunnel axis. Different authors derived methods for determining the characteristic inputparameter i, being the point of inflexion for the settlement trough on surface level for tunnelling projects all over the world. The i-value determines the steepness of the trough. This paper presents a comparison between the different approaches derived from data of projects outside the Netherlands and the field data from three recently bored Dutch tunnelling projects (i.e. the Second Heinenoord Tunnel, the Botlek Railway Tunnel and the Sophia Railway Tunnel). Recommendations are suggested for the use of the empirical methods for Dutch soil conditions representing soft soil and high groundwater level
Modeling of multimode radially pulsating High-Amplitude Delta Scuti stars from the OGLE Galactic bulge sample
Thanks to relatively firm mode identification, possible based on period
ratios only, High Amplitude Delta Scuti Stars pulsating in at least three
radial modes are promising targets for asteroseismic inference. In this study
we used the most numerous sample of HADS from the OGLE inner bulge fields that
likely pulsate in either three or four radial modes simultaneously. We have
computed a grid of pulsation models along evolutionary tracks and determined
the physical parameters of stars by matching their pulsation periods and period
ratios. For 176 HADS we determined physical parameters, i.e. masses,
luminosities, effective temperatures, metallicities and ages. We present the
distribution of physical parameters and discuss their properties. We selected
16 candidates for SX Phoenicis stars.Comment: 13 pages, 14 figures, 2 tables, accepted for publication in MNRA
Petersen Diagram Revolution
Over the recent years, the Petersen diagram for classical pulsators, Cepheids
and RR Lyr stars, populated with a few hundreds of new multiperiodic variables.
We review our analyses of the OGLE data, which resulted in the significant
extension of the known, and in the discovery of a few new and distinct forms of
multiperiodic pulsation. The showcase includes not only radial mode pulsators,
but also radial-non-radial pulsators and stars with significant modulation
observed on top of the beat pulsation. First theoretical models explaining the
new forms of stellar variability are briefly discussed.Comment: 5 pages; to be published in the proceedings of the 22nd Los Alamos
Stellar Pulsation Conference "Wide-field variability surveys: a 21st-century
perspective", San Pedro de Atacama, Chile, Nov. 28 - Dec. 2, 201
Frequency analysis of OGLE-IV photometry for classical Cepheids in Galactic fields: non-radial modes and modulations
We analyse photometry of 2000 Galactic Cepheids available in the OGLE
Collection of Variable Stars. We analyse both Galactic disk and Galactic bulge
fields; stars classified both as single- and multi-periodic. Our goal was to
search for additional low-amplitude variability.
We extend the sample of multi-mode radial pulsators by identifying ten new
candidates for double-mode and six new candidates for triple-mode pulsation. In
the first overtone OGLE sample, we found twelve Cepheids with additional
periodicity having period ratio . These
periodicities do not correspond to any other radial mode. While such variables
are abundant in the Magellanic Clouds, only one Cepheid of this class was known
in the Galaxy before our analysis. Comparing our sample with the Magellanic
Cloud Cepheids we note a systematic shift towards longer pulsation periods for
more metal rich Galactic stars. Moreover in eleven stars we find one more type
of additional variability, with characteristic frequencies close to half of
that reported in the group with (0.60,\, 0.65) period ratios. Two out of the
above inventory show simultaneous presence of both signals. Most likely, origin
of these signals is connected to excitation of non-radial pulsation modes.
We report three Cepheids with low-amplitude periodic modulation of pulsation:
two stars are single-mode fundamental and first overtone Cepheids and one is a
double-mode Cepheid pulsating simultaneously in fundamental and in first
overtone modes. Only the former mode is modulated. It is a first detection of
periodic modulation of pulsation in this type of double-mode Cepheids.Comment: 16 pages, 14 figures, Accepted in MNRA
Frequency analysis of the first-overtone RR Lyrae stars based on the Extended Aperture Photometry from the K2 data
Additional low-amplitude signals are observed in many RR Lyrae stars, beside
the pulsations in radial modes. The most common ones are short-period signals
forming a period ratio of around 0.60--0.65 with the first overtone, or
long-period signals forming a period ratio of around 0.68. The RR Lyrae stars
may also exhibit quasi-periodic modulation of the light curves, known as the
Blazhko effect. We used the extensive sample of the first-overtone RR Lyrae
stars observed by the Kepler telescope during the K2 mission to search for and
characterize these low-amplitude additional signals. K2 data provides
space-based photometry for a statistically significant sample. Hence this data
is excellent to study in detail pulsation properties of RR Lyrae stars. We used
K2 space-based photometry for RR Lyrae candidates from Campaigns 0-19. We
selected RR Lyrae stars pulsating in the first overtone and performed a
frequency analysis for each star to characterize their frequency contents. We
classified 452 stars as first-overtone RR Lyrae. From that sample, we selected
281 RR stars, 67 RR stars, and 68 Blazhko stars. We found
particularly interesting stars which show all of the above phenomena
simultaneously. We detected signals in RR stars that form period
ratios lower than observed for the majority of stars. These signals likely form
a new sequence in the Petersen diagram, around a period ratio of 0.60. In 32
stars we detected additional signals that form a period ratio close to that
expected in RRd stars, but the classification of these stars as RRd is
uncertain. We also report a discovery of additional signals in eight stars that
form a new group in the Petersen diagram around the period ratio of
0.465-0.490. The nature of this periodicity remains unknown.Comment: 29 pages, 29 figures, 4 tables, accepted for publication in A&A, full
tables are available upon request before publicatio
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