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.
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.
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 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.
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 OJ 287 is a quasi-periodic quasar with roughly 12 year optical cycles. It displays prominent outbursts that are predictable in a binary black hole model. The model predicted a major optical ...outburst in 2015 December. We found that the outburst did occur within the expected time range, peaking on 2015 December 5 at magnitude 12.9 in the optical R-band. Based on Swift/XRT satellite measurements and optical polarization data, we find that it included a major thermal component. Its timing provides an accurate estimate for the spin of the primary black hole, . The present outburst also confirms the established general relativistic properties of the system such as the loss of orbital energy to gravitational radiation at the 2% accuracy level, and it opens up the possibility of testing the black hole no-hair theorem with 10% accuracy during the present decade.
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.
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.
Aims.
We aim to investigate variations in the arrival time of coherent stellar pulsations due to the light-travel time effect to test for the presence of sub-stellar companions. Those companions are ...the key to one possible formation scenario of apparently single sub-dwarf B stars.
Methods.
We made use of an extensive set of ground-based observations of the four large amplitude
p
-mode pulsators DW Lyn, V1636 Ori, QQ Vir, and V541 Hya. Observations of the TESS space telescope are available on two of the targets. The timing method compares the phase of sinusoidal fits to the full multi-epoch light curves with phases from the fit of a number of subsets of the original time series.
Results.
Observations of the TESS mission do not sample the pulsations well enough to be useful due to the (currently) fixed two-minute cadence. From the ground-based observations, we infer evolutionary parameters from the arrival times. The residual signals show many statistically significant periodic signals, but no clear evidence for changes in arrival time induced by sub-stellar companions. The signals can be explained partly by mode beating effects. We derive upper limits on companion masses set by the observational campaign.
Metastatic colorectal cancer (mCRC) frequently occurs in elderly patients. However, data from a geriatric tailored randomized trial about tolerance to and the efficacy of doublet chemotherapy (CT) ...with irinotecan in the elderly are lacking. The benefit of first-line CT intensification remains an issue in elderly patients.
Elderly patients (75+) with previously untreated mCRC were randomly assigned in a 2 × 2 factorial design (four arms) to receive 5-FU (5-fluorouracil)-based CT, either alone (FU: LV5FU2 or simplified LV5FU2) or in combination with irinotecan IRI: LV5FU2–irinotecan or simplified LV5FU2–irinotecan (FOLFIRI). The CLASSIC arm was defined as LV5FU2 or LV5FU2–irinotecan and the SIMPLIFIED arm as simplified LV5FU2 or FOLFIRI. The primary end point was progression-free survival (PFS). Secondary end points were overall survival (OS), safety and objective response rate (ORR).
From June 2003 to May 2010, 71 patients were randomly assigned to LV5FU2, 71 to simplified LV5FU2, 70 to LV5FU2–irinotecan and 70 to FOLFIRI. The median age was 80 years (range 75–92 years). No significant difference was observed for the median PFS: FU 5.2 months versus IRI 7.3 months, hazard ratio (HR) = 0.84 (0.66–1.07), P = 0.15 and CLASSIC 6.5 months versus SIMPLIFIED 6.0 months, HR = 0.85 (0.67–1.09), P = 0.19. The ORR was superior in IRI (P = 0.0003): FU 21.1% versus IRI 41.7% and in CLASSIC (P = 0.04): CLASSIC 37.1% versus SIMPLIFIED 25.6%. Median OS was 14.2 months in FU versus 13.3 months in IRI, HR = 0.96 (0.75–1.24) and 15.2 months in CLASSIC versus 11.4 months in SIMPLIFIED, HR = 0.71 (0.55–0.92). More patients presented grade 3–4 toxicities in IRI (52.2% versus 76.3%).
In this elderly population, adding irinotecan to an infusional 5-FU-based CT did not significantly increase either PFS or OS. Classic LV5FU2 was associated with an improved OS compared with simplified LV5FU2.
NCT00303771.
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