Abstract
We present a new analysis of the rapidly oscillating Ap (roAp) star, 2MASS J19400781 − 4420093 (J1940; V = 13.1). The star was discovered using SuperWASP broad-band photometry to have a ...frequency of 176.39 d−1 (2041.55 μHz; P = 8.2 min; Holdsworth et al. 2014a) and is shown here to have a peak-to-peak amplitude of 34 mmag. J1940 has been observed during three seasons at the South African Astronomical Observatory, and has been the target of a Whole Earth Telescope campaign. The observations reveal that J1940 pulsates in a distorted quadrupole mode with unusual pulsational phase variations. A higher signal-to-noise ratio spectrum has been obtained since J1940's first announcement, which allows us to classify the star as A7 Vp Eu(Cr). The observing campaigns presented here reveal no pulsations other than the initially detected frequency. We model the pulsation in J1940 and conclude that the pulsation is distorted by a magnetic field of strength 1.5 kG. A difference in the times of rotational maximum light and pulsation maximum suggests a significant offset between the spots and pulsation axis, as can be seen in roAp stars.
Résumé
Les traitements antiangiogéniques occupent une place croissante en oncologie. La fréquence de leur utilisation induit l’apparition d’effets secondaires jusqu’alors sous-estimés, notamment ...neurologiques. Nous rapportons un cas de névrite optique attribuée au traitement par sunitinib chez une patiente atteinte d’un cancer du rein.
Abstract More than 36 yr have passed since the discovery of the infrared excess from circumstellar dust orbiting the white dwarf G29-38, which at 17.5 pc it is the nearest and brightest of its class. ...The precise morphology of the orbiting dust remains only marginally constrained by existing data, subject to model-dependent inferences, and thus fundamental questions of its dynamical origin and evolution persist. This study presents a means to constrain the geometric distribution of the emitting dust using stellar pulsations measured at optical wavelengths as a variable illumination source of the dust, which reradiates primarily in the infrared. By combining optical photometry from the Whole Earth Telescope with 0.7–2.5 μ m spectroscopy obtained with SpeX at NASA’s Infrared Telescope Facility, we detect luminosity variations at all observed wavelengths, with variations at most wavelengths corresponding to the behavior of the pulsating stellar photosphere, but toward the longest wavelengths the light curves probe the corresponding time variability of the circumstellar dust. In addition to developing methodology, we find the pulsation amplitudes decrease with increasing wavelength for principal pulsation modes, yet increase beyond ≈2 μ m for nonlinear combination frequencies. We interpret these results as combination modes derived from the principal modes of identical ℓ values and discuss the implications for the morphology of the warm dust. We also draw attention to some discrepancies between our findings and theoretical expectations for the results of the nonlinearity imposed by the surface convection zone on mode–mode interactions and on the behavior of the first harmonic of the highest-amplitude pulsation mode.
Catching profound optical flares in blazars Bhatta, Gopal; Zola, Staszek; Drozdz, M ...
Monthly notices of the Royal Astronomical Society,
02/2023, Letnik:
520, Številka:
2
Journal Article
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ABSTRACT
Flaring episodes in blazars represent one of the most violent processes observed in extra-galactic objects. Studies of such events shed light on the energetics of the physical processes ...occurring in the innermost regions of blazars, which cannot otherwise be resolved by any current instruments. In this work, we present some of the largest and most rapid flares captured in the optical band in the blazars 3C 279, OJ 49, S4 0954+658, TXS 1156+295, and PG 1553+113. The source flux was observed to increase by nearly ten times within a time-scale of a few weeks. We applied several methods of time series analysis and symmetry analysis. Moreover, we also performed searches for periodicity in the light curves of 3C 279, OJ 49 and PG 1553+113 using the Lomb–Scargle method and found plausible indications of quasi-periodic oscillations (QPOs). In particular, the 33- and 22-day periods found in 3C 279, i.e. a 3:2 ratio, are intriguing. These violent events might originate from magnetohydrodynamical instabilities near the base of the jets, triggered by processes modulated by the magnetic field of the accretion disc. We present a qualitative treatment as the possible explanation for the observed large amplitude flux changes in both the source-intrinsic and source-extrinsic scenarios.
We present the detection of non-radial oscillations in a hot, helium-atmosphere white dwarf using 78.7 days of nearly uninterrupted photometry from the Kepler space telescope. With an effective ...temperature >30,000 K, PG 0112+104 becomes the hottest helium-atmosphere white dwarf known to pulsate. The rich oscillation spectrum of low-order g-modes includes clear patterns of rotational splittings from consecutive sequences of dipole and quadrupole modes, which can be used to probe the rotation rate with depth in this highly evolved stellar remnant. We also measure a surface rotation rate of 10.17404 hr from an apparent spot modulation in the K2 data. With two independent measures of rotation, PG 0112+104 provides a remarkable test of asteroseismic inference.
Kepler and TESS Observations of PG 1159-035 Oliveira da Rosa, Gabriela; Kepler, S. O.; Córsico, Alejandro H. ...
The Astrophysical journal,
09/2022, Letnik:
936, Številka:
2
Journal Article
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Abstract
PG 1159-035 is the prototype of the PG 1159 hot (pre-)white dwarf pulsators. This important object was observed during the Kepler satellite K2 mission for 69 days in 59 s cadence mode and by ...the TESS satellite for 25 days in 20 s cadence mode. We present a detailed asteroseismic analysis of those data. We identify a total of 107 frequencies representing 32
ℓ
= 1 modes, 27 frequencies representing 12
ℓ
= 2 modes, and eight combination frequencies. The combination frequencies and the modes with very high
k
values represent new detections. The multiplet structure reveals an average splitting of 4.0 ± 0.4
μ
Hz for
ℓ
= 1 and 6.8 ± 0.2
μ
Hz for
ℓ
= 2, indicating a rotation period of 1.4 ± 0.1 days in the region of period formation. In the Fourier transform of the light curve, we find a significant peak at 8.904 ± 0.003
μ
Hz suggesting a surface rotation period of 1.299 ± 0.002 days. We also present evidence that the observed periods change on timescales shorter than those predicted by current evolutionary models. Our asteroseismic analysis finds an average period spacing for
ℓ
= 1 of 21.28 ± 0.02 s. The
ℓ
= 2 modes have a mean spacing of 12.97 ± 0.4 s. We performed a detailed asteroseismic fit by comparing the observed periods with those of evolutionary models. The best-fit model has
T
eff
= 129, 600 ± 11 100 K,
M
*
= 0.565 ± 0.024
M
⊙
, and
log
g
=
7.41
−
0.54
+
0.38
, within the uncertainties of the spectroscopic determinations. We argue for future improvements in the current models, e.g., on the overshooting in the He-burning stage, as the best-fit model does not predict excitation for all of the pulsations detected in PG 1159-035.
We investigate the possibility of nearly equally spaced periods in 13 hot subdwarf B (sdB) stars observed with the Kepler spacecraft and one observed with CoRoT. Asymptotic limits for gravity ...(g-)mode pulsations provide relationships between equal-period spacings of modes with differing degrees ℓ and relationships between periods of the same radial order n but differing degrees ℓ. Period transforms, Kolmogorov-Smirnov tests and linear least-squares fits have been used to detect and determine the significance of equal-period spacings. We have also used Monte Carlo simulations to estimate the likelihood that the detected spacings could be produced randomly.
Period transforms for nine of the Kepler stars indicate ℓ= 1 period spacings, with five also showing peaks for ℓ= 2 modes. 12 stars indicate ℓ= 1 modes using the Kolmogorov-Smirnov test while another shows solely ℓ= 2 modes. Monte Carlo results indicate that equal-period spacings are significant in 10 stars above 99 per cent confidence, and 13 of the 14 are above 94 per cent confidence. For 12 stars, the various methods find consistent period spacings to within the errors, two others show some inconsistencies, likely caused by binarity, and the last has significant detections but the mode assignment disagrees between the methods.
We use asymptotic period spacing relationships to associate observed periods of variability with pulsation modes for ℓ= 1 and 2. From the Kepler first-year survey sample of 13 multiperiodic g-mode pulsators, five stars have several consecutive overtones making period spacings easy to detect, six others have fewer consecutive overtones but period spacings are readily detected, and two stars show marginal indications of equal-period spacings. We also examine a g-mode sdB pulsator observed by CoRoT with a rich pulsation spectrum, and our tests detect regular period spacings.
We use Monte Carlo simulations to estimate the significance of the detections in individual stars. From the simulations, it is determined that regular period spacings in 10 of the 14 stars are very unlikely to be random, another two are moderately unlikely to be random and two are mostly unconstrained.
We find a common ℓ= 1 period spacing spanning a range from 231 to 272 s allowing us to correlate pulsation modes with 222 periodicities and that the ℓ= 2 period spacings are related to the ℓ= 1 spacings by the asymptotic relationship
. We briefly discuss the impact of equal-period spacings which indicate low-degree modes with a lack of significant mode trappings.
Abstract
White dwarf WD 1145+017 is orbited by several clouds of dust, possibly emanating from actively disintegrating bodies. These dust clouds reveal themselves through deep, broad, and evolving ...transits in the star's light curve. Here, we report two epochs of multiwavelength photometric observations of WD 1145+017, including several filters in the optical, Ks and 4.5 μm bands in 2016 and 2017. The observed transit depths are different at these wavelengths. However, after correcting for excess dust emission at Ks and 4.5 μm, we find the transit depths for the white dwarf itself are the same at all wavelengths, at least to within the observational uncertainties of ∼5–10 per cent. From this surprising result, and under the assumption of low optical depth dust clouds, we conclude that there is a deficit of small particles (with radii s ≲ 1.5 μm) in the transiting material. We propose a model wherein only large particles can survive the high equilibrium temperature environment corresponding to 4.5 h orbital periods around WD 1145+017, while small particles sublimate rapidly. In addition, we evaluate dust models that are permitted by our measurements of infrared emission.
Background: Data from prospective clinical trials are needed to better define standards of care in elderly patients with advanced ovarian carcinoma and to demonstrate the interest of Comprehensive ...Geriatric Assessment (CGA) in this fragile and heterogeneous population. Patients and methods: From July 1998 to October 2000, 83 advanced ovarian carcinoma patients >70 years old received carboplatin AUC 5 and cyclophosphamide 600 mg/m2, on day 1 of six 28-day cycles. The clinical and biological geriatric covariates prospectively studied were: comorbidities, comedications, cognitive functions (Mini-Mental test), nutritional status and autonomy. Results: Patient characteristics were: median age 76 years, serous histology (73%), FIGO stage III (75%), optimal initial surgery (21%) and performance status (PS) ≥2 (44%). Sixty patients (72%) received six chemotherapy cycles without severe toxicity (STox) or tumor progression. Multivariate analysis retained three factors as independent predictors of STox: symptoms of depression at baseline (P = 0.006), dependence (P = 0.048) and PS ≥2 (P = 0.026). Independent prognostic factors identified for overall survival (Cox model) were depression (P = 0.003), FIGO stage IV (P = 0.007) and more than six different comedications per day (P = 0.043). Conclusion: CGA could predict STox and overall survival of elderly advanced ovarian carcinoma patients.
We report on the analysis of 34 years of photometric observations of the pulsating helium atmosphere white dwarf GD358. The complete data set includes archival data from 1982 to 2006, and 1195.2 hr ...of new observations from 2007 to 2016. From this data set, we extract 15 frequencies representing g-mode pulsation modes, adding 4 modes to the 11 modes known previously. We present evidence that these 15 modes are = 1 modes, 13 of which belong to a consecutive sequence in radial overtone k. We perform a detailed asteroseismic analysis using models that include parameterized, complex, carbon and oxygen core composition profiles to fit the periods. Recent spectroscopic analyses place GD358 near the red edge of the DBV instability strip, at 24,000 500 K and a of 7.8 0.08 dex. The surface gravity translates to a mass range of 0.455-0.540 . Our best-fit model has a temperature of 23,650 K and a mass of 0.5706 . That is slightly more massive than what is suggested by the most recent spectroscopy. We find a pure helium layer mass of 10−5.50, consistent with the result of previous studies and the outward diffusion of helium over time.
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