40 research outputs found
Constraining the degree of the dominant mode in QQ Vir
We present early results of the application of a method which uses multicolor
photometry and spectroscopy for \ell discrimination. This method has been
successfully applied to the pulsating hot subdwarf Balloon 090100001. Here we
apply the method to QQ Vir (PG1325+101). This star was observed
spectroscopically and photometrically in 2008. Details on spectroscopy can be
found in Telting et al. (2010) while photometry and preliminary results on \ell
discrimination are provided here. The main aim of this work was to compare the
value of the \ell parameter derived for the main mode in QQ Vir to previously
published values derived by using different methods.Comment: Proceedings of The Fourth Meeting on Hot Subdwarf Stars and Related
Objects held in China, 20-24 July 2009. Accepted for publication in
Astrophysics and Space Scienc
Multiwavelength variability of the radio quasar J2042+7508
In this paper, we present our results of study on the long term multiwavelength variability properties of the quasar J2042+7508 (4C +74.26) – a giant radio source located at the redshift of 0.104. This source exhibits interesting emission and structural properties when observed in various wavelengths, including X-ray, optical and radio frequencies. Therefore, exploring these properties through multifrequency variability studies presents a great importance to our understanding of the evolution of quasars and radio-loud unification schemes. We found a trend of anticorrelation with time lag of about three months between optical and radio light curves. A weak correlation with a longer time lag of about 230 days might also exist. Using the structure function method, applied to our six years long, optical data, we arrived at a conclusion that the quasar variability with amplitude of about 0.3 magnitude, is likely caused by an accretion disk instability
Determination of physical parameters of the eclipsing binary V729 Cyg
We report new BVRI photometric observations of an eclipsing, massive binary V729 Cyg taken between 2008 and 2011. We performed light curve modeling of the new data and those available in the literature using the Wilson-Devinney code. The best fit was obtained for a contact configuration, similarly to results derived previously by other investigators. However, a huge temperature difference of about 10 000K - 12 000K was derived, inconsistent with theoretical calculations. Ruling out a possibility of V729 Cyg being a semi-detached system harbouring an accretion disk, we determined physical parameters of components
Optical variability of eight FRII-type quasars with 13-yr photometric light curves
We characterize the optical variability properties of eight lobe-dominated
radio quasars (QSOs): B2 070937, FBQS J095206.3235245, PG 1004130,
[HB89] 1156631, [HB89] 1425267, [HB89] 1503691, [HB89] 1721343, 4C
74.26, systematically monitored for a duration of 13 years since 2009. The
quasars are radio-loud objects with extended radio lobes that indicate their
orientation close to the sky plane. Five of the eight QSOs are classified as
giant radio quasars. All quasars showed variability during our monitoring, with
magnitude variations between 0.3 and 1 mag for the least variable and the most
variable QSO, respectively. We performed both structure function (SF) analysis
and power spectrum density (PSD) analysis for the variability characterization
and search for characteristic timescales and periodicities. As a result of our
analysis, we obtained relatively steep SF slopes ( ranging from 0.49 to
0.75) that are consistent with the derived PSD slopes (2--3). All the
PSDs show a good fit to single power law forms, indicating a red-noise
character of variability between 13 years and weeks timescales. We did
not measure reliable characteristic timescales of variability from the SF
analysis which indicates that the duration of the gathered data is too short to
reveal them. The absence of bends in the PSDs (change of slope from 1 to
0) on longer timescales indicates that optical variations are most likely
caused by thermal instabilities in the accretion disk.Comment: Accepted for publication in ApJS; 17 pages, 5 figures, 5 table
Optical variability of eight FRII-type quasars with 13 yr photometric light curves
We characterize the optical variability properties of eight lobe-dominated radio quasars (QSOs): B2 0709+37, FBQS J095206.3+235245, PG 1004+130, [HB89] 1156+631, [HB89] 1425+267, [HB89] 1503+691, [HB89] 1721+343, and 4C +74.26, systematically monitored for a duration of 13 yr since 2009. The quasars are radio-loud objects with extended radio lobes that indicate their orientation close to the sky plane. Five of the eight QSOs are classified as giant radio quasars. All quasars showed variability during our monitoring, with magnitude variations between 0.3 and 1 mag for the least variable and the most variable QSOs, respectively. We performed both structure function (SF) analysis and power spectral density (PSD) analysis for the variability characterization and search for characteristic timescales and periodicities. As a result of our analysis, we obtained relatively steep SF slopes (α ranging from 0.49 to 0.75) that are consistent with the derived PSD slopes (∼2–3). All the PSDs show a good fit to single power-law forms, indicating a red-noise character of variability between timescales of ∼13 yr and weeks. We did not measure reliable characteristic timescales of variability from the SF analysis, which indicates that the duration of the gathered data is too short to reveal them. The absence of bends in the PSDs (change of slope from ≥1 to ∼0) on longer timescales indicates that optical variations are most likely caused by thermal instabilities in the accretion disk
Optical monitoring of FRII-type radio quasars
We present preliminary results of optical monitoring of sample of FRII-type radio quasars. The optical observations were made with three telescopes, among them one robotic, spanning a time interval longer than two years. Variability in the range of a fraction of a magnitude was observed for all eight targets. We applied the structure function to analyse the brightness changes. The slope of the structure function is only consistent with the disk instability model for two sources; the other sources show values between of the disk instability and starburst models. Finally we argue that such monitoring would be most suitable as a long-term, complementary program for robotic telescopes
Gaia21bty: An EXor lightcurve exhibiting an FUor spectrum
Gaia21bty, a pre-main sequence star that previously had shown aperiodic dips
in its light curve, underwent a considerable mag
brightening that occurred over a few months between 2020 October - 2021
February. The Gaia lightcurve shows that the star remained near maximum
brightness for about months, and then started slowly fading over the next
2 years, with at least three superimposed 1 mag sudden rebrightening
events. Whereas the amplitude and duration of the maximum is typical for EXors,
optical and near-infrared spectra obtained at the maximum are dominated by
features which are typical for FUors. Modelling of the accretion disc at the
maximum indicates that the disc bolometric luminosity is 43 L and the
mass accretion rate is M yr, which are
typical values for FUors even considering the large uncertainty in the distance
( kpc). Further monitoring is necessary to understand the
cause of the quick brightness decline, the rebrightening, and the other
post-outburst light changes, as our multi-colour photometric data suggest that
they could be caused by a long and discontinuous obscuration event. We
speculate that the outburst might have induced large-scale inhomogeneous dust
condensations in the line of sight leading to such phenomena, whilst the FUor
outburst continues behind the opaque screen.Comment: Accepted to MNRA
Photometric and spectroscopic study of the burst-like brightening of two Gaia-alerted young stellar objects
Young stars show variability on different time-scales from hours to decades,
with a range of amplitudes. We studied two young stars, which triggered the
Gaia Science Alerts system due to brightenings on a time-scale of a year.
Gaia20bwa brightened by about half a magnitude, whereas Gaia20fgx brightened by
about two and half magnitudes. We analyzed the Gaia light curves, additional
photometry, and spectra taken with the Telescopio Nazionale Galileo and the
Gran Telescopio Canarias. Several emission lines were detected toward
Gaia20bwa, including hydrogen lines from H to H, Pa,
Br, and lines of Ca II, O I, and Na I. The H and Br
lines were detected toward Gaia20fgx in emission in its bright state, with
additional CO lines in absorption, and the Pa line with an inverse P
Cygni profile during its fading. Based on the Br lines the accretion
rate was yr for Gaia20bwa and
yr for Gaia20fgx during their bright
state. The accretion rate of Gaia20fgx dropped by almost a factor of 10 on a
time-scale of half a year. The accretion parameters of both stars were found to
be similar to those of classical T Tauri stars, lower than those of young
eruptive stars. However, the amplitude and time-scale of these brightenings
place these stars to a region of the parameter space, which is rarely populated
by young stars. This suggests a new class of young stars, which produce
outbursts on a time-scale similar to young eruptive stars, but with smaller
amplitudes.Comment: Accepted to MNRA