21 research outputs found
Exploring the pulsational properties of two ZZ Ceti stars
Context. We continued our ground-based observing project with the season-long
observations of ZZ Ceti stars at Konkoly Observatory. Our present targets are
the newly discovered PM J22299+3024, and the already known LP 119-10 variables.
LP 119-10 was also observed by the TESS (Transiting Exoplanet Survey Satellite)
space telescope in 120-second cadence mode.
Methods. We performed standard Fourier analysis of the daily, weekly, and the
whole data sets, together with test data of different combinations of weekly
observations. We then performed asteroseismic fits utilising the observed and
the calculated pulsation periods. For the calculations of model grids necessary
for the fits, we applied the 2018 version of the White Dwarf Evolution Code.
Results. We derived six possible pulsation modes for PM J22299+3024, and five
plus two TESS pulsation frequencies for LP 119-10. Note that further pulsation
frequencies may be present in the data sets, but we found their detection
ambiguous, so we omitted them from the final frequency list. Our asteroseismic
fits of PM J22299+3024 give 11 400 K and 0.46 Msun for the effective
temperature and the stellar mass. The temperature is ~800 K higher, while the
mass of the model star is exactly the same as it was earlier derived by
spectroscopy. Our model fits of LP~119-10 put the effective temperature in the
range of 11 800 - 11 900 K, which is again higher than the spectroscopic 11 290
K value, while our best model solutions give M* = 0.70 Msun mass for this
target, near to the spectroscopic value of 0.65 Msun, likewise in the case of
PM J22299+3024. The seismic distances of our best-fitting model stars agree
with the Gaia astrometric distances of PM J22299+3024 and LP 119-10 within the
errors, validating our model results.Comment: 12 pages, 15 figures, accepted for publication in Astronomy &
Astrophysic
Ground-Based Observations of the ZZ Ceti Star HS 1625+1231
We present the results of our detailed light curve analysis of the ZZ Ceti star HS 1625+1231. We collected photometric time series data at Konkoly Observatory on 14 nights, and performed Fourier analysis of these data sets. We detected 11 significant frequencies, where six of them are found to be independent pulsation modes in the 514-881 s period range. By utilizing these frequencies, we performed preliminary asteroseismic investigations to give constraints on the main physical parameters, and to derive seismic distances for the star. Finally, we compared the astrometric distance provided by the Gaia EDR3 data with those seismic distances. Our selected model, considering both the spectroscopic measurements and the distance value provided by Gaia, has Teff=11 000 K and M*=0.60 M⊙
Asteroseismology of the heartbeat star KIC 5006817
This paper summarizes the project work on asteroseismology at the ERASMUS+
GATE 2020 Summer school on space satellite data. The aim was to do a global
asteroseismic analysis of KIC 5006817 and quantify its stellar properties using
the high-quality, state of the art space missions data. We employed the
aperture photometry to analyze the data from the Kepler space telescope and the
Transiting Exoplanet Survey Satellite (TESS). Using the lightkurve Python
package, we have derived the asteroseismic parameters and calculated the
stellar parameters using the scaling relations. Our analysis of KIC 5006817
confirmed its classification as a heartbeat binary. The rich oscillation
spectrum facilitate estimating power excess () at
145.500.50 Hz and large frequency separation () to be
11.630.10 Hz. Our results showed that the primary component is a
low-luminosity, red-giant branch star with a mass, radius, surface gravity, and
luminosity of 1.530.07 M, 5.910.12 R, 3.080.01
dex, and 19.660.73 L, respectively. The orbital period of the
system is 94.830.05 d.Comment: 13 pages, 4 figures, 2 tables; Based on the project work at ERASMUS+
GATE 2020 Summer school; To be published in Contrib. Astron. Obs. Skalnat\'e
Ples
Study of changes in the pulsation period of 148 Galactic Cepheid variables
Investigating period changes of classical Cepheids through the framework of O - C diagrams provides a unique insight to the evolution and nature of these variable stars. In this work, the new or extended O - C diagrams for 148 Galactic classical Cepheids are presented. By correlating the calculated period change rates with the Gaia EDR3 colours, we obtain observational indications for the non-negligible dependence of the period change rate on the horizontal position within the instability strip. We find period fluctuations in 59 Cepheids with a confidence level of 99 per cent, which are distributed uniformly over the inspected period range. Correlating the fluctuation amplitude with the pulsation period yields a clear dependence, similar to the one valid for longer period pulsating variable stars. The non-negligible amount of Cepheids showing changes in their O - C diagrams that are not or not only of evolutionary origin points towards the need for further studies for the complete understanding of these effects. One such peculiar behaviour is the large amplitude period fluctuation in short period Cepheids, which occurs in a significant fraction of the investigated stars. The period dependence of the fluctuation strength and its minimum at the bump Cepheid region suggests a stability enhancing mechanism for this period range, which agrees with current pulsation models
The Weakening Outburst of the Young Eruptive Star V582 Aur
V582 Aur is a pre-main sequence FU Orionis type eruptive star, which entered
a brightness minimum in 2016 March due to changes in the line-of-sight
extinction. Here, we present and analyze new optical , , and
band multiepoch observations and new near-infrared , and band
photometric measurements from 2018 January2019 February, as well as publicly
available mid-infrared WISE data. We found that the source shows a significant
opticalnear-infrared variability, and the current brightness minimum has not
completely finished yet. If the present dimming originates from the same
orbiting dust clump that caused a similar brightness variation in 2012, than
our results suggest a viscous spreading of the dust particles along the orbit.
Another scenario is that the current minimum is caused by a dust structure,
that is entering and leaving the inner part of the system. The WISE
measurements could be consistent with this scenario. Our long-term data, as
well as an accretion disk modeling hint at a general fading of V582 Aur,
suggesting that the source will reach the quiescent level in 80 years.Comment: 8 pages, 4 figures, accepted for publication in Ap
Wandering near the red edge: photometric observations of three cool ZZ Ceti stars
We summarize our findings on three cool ZZ Ceti type pulsating white dwarfs.
We determined eight independent modes in HS 0733+4119, of which seven are new
findings. For GD 154, we detected two new eigenmodes, and the recurrence of the
pulsational behaviour first observed in 1977. We discuss that GD 154 does not
only vary its pulsations between a multiperiodic and a quasi-monoperiodic
phase, but there are also differences between the relative amplitudes of the
near-subharmonics observed in the latter phase. In the complex pulsator, Ross
808, we compared the pre- and post Whole Earth Telescope campaign measurements,
and determined two new frequencies besides the ones observed during the
campaign. Studying these stars can contribute to better understanding of
pulsations close to the empirical ZZ Ceti red edge. All three targets are in
that regime of the ZZ Ceti instability strip where short-term amplitude
variations or even outbursts are likely to occur, which are not well-understood
theoretically.Comment: 15 pages, 13 figures, accepted for publication in Monthly Notices of
the Royal Astronomical Societ
A Multi-Epoch, Multiwavelength Study of the Classical FUor V1515 Cyg Approaching Quiescence
Historically, FU Orionis-type stars are low-mass, pre-main-sequence stars. The members of this class experience powerful accretion outbursts and remain in an enhanced accretion state for decades or centuries. V1515 Cyg, a classical FUor, started brightening in the 1940s and reached its peak brightness in the late 1970s. Following a sudden decrease in brightness, it stayed in a minimum state for a few months, then started brightening for several years. We present the results of our ground-based photometric monitoring complemented with optical/near-infrared spectroscopic monitoring. Our light curves show a long-term fading with strong variability on weekly and monthly timescales. The optical spectra show P Cygni profiles and broad blueshifted absorption lines, common properties of FUors. However, V1515 Cyg lacks the P Cygni profile in the Ca II 8498 Å line, a part of the Ca infrared triplet, formed by an outflowing wind, suggesting that the absorbing gas in the wind is optically thin. The newly obtained near-infrared spectrum shows the strengthening of the CO bandhead and the FeH molecular band, indicating that the disk has become cooler since the last spectroscopic observation in 2015. The current luminosity of the accretion disk dropped from the peak value of 138 L ⊙ to about 45 L ⊙, suggesting that the long-term fading is also partly caused by the dropping of the accretion rate