160 research outputs found
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
UVSat: a concept of an ultraviolet/optical photometric satellite
Time-series photometry from space in the ultraviolet can be presently done
with only a few platforms, none of which is able to provide wide-field
long-term high-cadence photometry. We present a concept of UVSat, a twin space
telescope which will be capable to perform this kind of photometry, filling an
observational niche. The satellite will host two telescopes, one for
observations in the ultraviolet, the other for observations in the optical
band. We also briefly show what science can be done with UVSat.Comment: 6 pages, 2 figures, accepted for publication in the Proceedings of
the PAS (Proc. of the 2nd BRITE Science conference, Innsbruck
Radio and optical intra-day variability observations of five blazars
We carried out a pilot campaign of radio and optical band intra-day
variability (IDV) observations of five blazars (3C66A, S5 0716+714, OJ287,
B0925+504, and BL Lacertae) on December 18--21, 2015 by using the radio
telescope in Effelsberg (Germany) and several optical telescopes in Asia,
Europe, and America. After calibration, the light curves from both 5 GHz radio
band and the optical R band were obtained, although the data were not smoothly
sampled over the sampling period of about four days. We tentatively analyse the
amplitudes and time scales of the variabilities, and any possible periodicity.
The blazars vary significantly in the radio (except 3C66A and BL Lacertae with
only marginal variations) and optical bands on intra- and inter-day time
scales, and the source B0925+504 exhibits a strong quasi-periodic radio
variability. No significant correlation between the radio- and optical-band
variability appears in the five sources, which we attribute to the radio IDV
being dominated by interstellar scintillation whereas the optical variability
comes from the source itself. However, the radio- and optical-band variations
appear to be weakly correlated in some sources and should be investigated based
on well-sampled data from future observations.Comment: 6 pages, 6 figures, accepted by MNRA
Radial Velocity Studies of Close Binary Stars. XI
Radial-velocity measurements and sine-curve fits to the orbital radial
velocity variations are presented for ten close binary systems: DU Boo, ET Boo,
TX Cnc, V1073 Cyg, HL Dra, AK Her, VW LMi, V566 Oph, TV UMi and AG Vir. By this
contribution, the DDO program has reached the point of 100 published radial
velocity orbits. The radial velocities have been determined using an improved
fitting technique which uses rotational profiles to approximate individual
peaks in broadening functions.
Three systems, ET Boo, VW LMi and TV UMi, were found to be quadruple while AG
Vir appears to be a spectroscopic triple. ET Boo, a member of a close visual
binary with years, was previously known to be a multiple
system, but we show that the second component is actually a close,
non-eclipsing binary. The new observations enabled us to determine the
spectroscopic orbits of the companion, non-eclipsing pairs in ET Boo and VW
LMi. The particularly interesting case is VW LMi, where the period of the
mutual revolution of the two spectroscopic binaries is only 355 days.
While most of the studied eclipsing pairs are contact binaries, ET Boo is
composed of two double-lined detached binaries and HL Dra is single-lined
detached or semi-detached system. Five systems of this group were observed
spectroscopically before: TX Cnc, V1073 Cyg, AK Her (as a single-lined binary),
V566 Oph, AG Vir, but our new data are of much higher quality than the previous
studies.Comment: Accepted by AJ, August 2006, 10 figures, 3 table
PENELLOPE IV. A comparison between optical forbidden lines and UV lines in the Orion OB1b and -Ori associations
Observing the spatial distribution and excitation processes of atomic and
molecular gas in the inner regions (< 20 au) of young (< 10 Myr) protoplanetary
disks helps us to understand the conditions for the formation and evolution of
planetary systems. In the framework of the PENELLOPE and ULLYSES projects, we
aim to characterize the atomic and molecular component of protoplanetary disks
in a sample of 11 Classical T Tauri Stars (CTTs) of the Orion OB1 and
-Orionis associations. We analyzed the flux-calibrated
optical-forbidden lines and the fluorescent ultraviolet progressions
using spectra acquired with ESPRESSO at VLT, UVES at VLT and HST-COS. Line
morphologies were characterized through Gaussian decomposition. We then focused
on the properties of the narrow low-velocity (FWHM < 40 and
|| < 30 ) component (NLVC) of the [OI] 630 nm line, compared
with the properties of the UV- lines. We found that the [OI]630 NLVC
and the UV- lines are strongly correlated in terms of peak velocities,
full width at half maximum, and luminosity. The luminosities of the [OI]630
NLVC and UV- correlate with the accretion luminosity with a similar
slope, as well as with the luminosity of the CIV 154.8, 155 nm doublet. We
discuss such correlations in the framework of the currently suggested
excitation processes for the [OI]630 NLVC. Our results can be interpreted in a
scenario in which the [OI]630 NLVC and UV- have a common disk origin
with a partially overlapped radial extension. We also suggest that the
excitation of the [OI] NLVC is mainly induced by stellar FUV continuum photons
more than being of thermal origin. This study demonstrates the potential of
contemporaneous wide-band high-resolution spectroscopy in linking different
tracers of protoplanetary disks.Comment: 24 pages, 15 figures, 6 tables. Accepted for publication in Astronomy
& Astrophysic
Whole Earth Telescope observations of the pulsating subdwarf B star PG 0014+067
PG 0014+067 is one of the most promising pulsating subdwarf B stars for
seismic analysis, as it has a rich pulsation spectrum. The richness of its
pulsations, however, poses a fundamental challenge to understanding the
pulsations of these stars, as the mode density is too complex to be explained
only with radial and nonradial low degree (l < 3) p-modes without rotational
splittings. One proposed solution, for the case of PG 0014+067 in particular,
assigns some modes with high degree (l=3). On the other hand, theoretical
models of sdB stars suggest that they may retain rapidly rotating cores, and so
the high mode density may result from the presence of a few rotationally-split
triplet (l=1), quintuplet (l=2) modes, along with radial (l=0) p-modes. To
examine alternative theoretical models for these stars, we need better
frequency resolution and denser longitude coverage. Therefore, we observed this
star with the Whole Earth Telescope for two weeks in October 2004. In this
paper we report the results of Whole Earth Telescope observations of the
pulsating subdwarf B star PG 0014+067. We find that the frequencies seen in PG
0014+067 do not appear to fit any theoretical model currently available;
however, we find a simple empirical relation that is able to match all of the
well-determined frequencies in this star.Comment: 19 pages, preprint of paper accepted for publication in The
Astrophysical Journa
Dietary and Behavioral Interventions Protect against Age Related Activation of Caspase Cascades in the Canine Brain
Lifestyle interventions such as diet, exercise, and cognitive training represent a quietly emerging revolution in the modern approach to counteracting age-related declines in brain health. Previous studies in our laboratory have shown that long-term dietary supplementation with antioxidants and mitochondrial cofactors (AOX) or behavioral enrichment with social, cognitive, and exercise components (ENR), can effectively improve cognitive performance and reduce brain pathology of aged canines, including oxidative damage and Aβ accumulation. In this study, we build on and extend our previous findings by investigating if the interventions reduce caspase activation and ceramide accumulation in the aged frontal cortex, since caspase activation and ceramide accumulation are common convergence points for oxidative damage and Aβ, among other factors associated with the aged and AD brain. Aged beagles were placed into one of four treatment groups: CON – control environment/control diet, AOX– control environment/antioxidant diet, ENR – enriched environment/control diet, AOX/ENR– enriched environment/antioxidant diet for 2.8 years. Following behavioral testing, brains were removed and frontal cortices were analyzed to monitor levels of active caspase 3, active caspase 9 and their respective cleavage products such as tau and semaphorin7a, and ceramides. Our results show that levels of activated caspase-3 were reduced by ENR and AOX interventions with the largest reduction occurring with combined AOX/ENR group. Further, reductions in caspase-3 correlated with reduced errors in a reversal learning task, which depends on frontal cortex function. In addition, animals treated with an AOX arm showed reduced numbers of cells expressing active caspase 9 or its cleavage product semaphorin 7A, while ENR (but not AOX) reduced ceramide levels. Overall, these data demonstrate that lifestyle interventions curtail activation of pro-degenerative pathways to improve cellular health and are the first to show that lifestyle interventions can regulate caspase pathways in a higher animal model of aging
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