ABSTRACT
In this study, we revisit public data on the supersoft X-ray source CAL 83 in the Large Magellanic Cloud. A significant part of our analysis is focused on XMM–Newton X-ray observations, in ...which updated data reduction procedures and quality assessment were applied. We report on the capability of publicly available hot atmosphere models in describing the source’s soft X-ray spectrum. By gathering historical flux measurements in multiple wavelengths and comparing them with the fluxes derived from the X-ray analysis, we find that an ∼360 kK phenomenological blackbody model describes the spectral energy distribution of CAL 83 fairly well. We also retrieve data from the XMM–Newton ultraviolet (UV)/optical camera, which is co-aligned with the X-ray instruments and provides strictly simultaneous measurements. These observations demonstrate that the X-ray emission is definitely anti-correlated with emission at longer wavelengths on a time-scale of days to weeks. A closer look at simultaneous X-ray and UV count rates in single light curves reveals that the anti-correlated behaviour is actually present on time-scales as short as minutes, suggesting that the origin of variable emission in the system is not unique.
ABSTRACT
In this study, we present an analysis of over 34 yr of observational data from CAL 87, an eclipsing supersoft X-ray source. The primary aim of our study, which combines previously analysed ...measurements as well as unexplored publicly available data sets, is to examine the orbital period evolution of CAL 87. After meticulously and consistently determining the eclipse timings, we constructed an O − C (observed minus calculated) diagram using a total of 38 data points. Our results provide confirmation of a positive derivative in the system’s orbital period, with a determined value of $\dot{P}=+\, 8.18\pm 1.46\times 10^{-11}$ s s−1. We observe a noticeable jitter in the eclipse timings and additionally identify a systematic delay in the X-ray eclipses compared to those observed in longer wavelengths. We discuss the interplay of the pertinent factors that could contribute to a positive period derivative and the inherent variability in the eclipses.
ABSTRACT
1E 1740.7−2942 is one of the strongest hard X-ray emitters in the Galactic Centre region, believed to be a black hole in a high-mass X-ray binary system. Although extensively studied in ...X-rays, many aspects about the underlying nature of the system are still unknown. For example, X-ray data analyses of 1E 1740.7−2942 to date have not yet unveiled the signature of a reflection component, whose modelling could be used to estimate parameters such as the spin of the black hole and inclination of the disc. We report here on the determination of these parameters from the analysis of the reflection component present in a public NuSTAR observation which has not been subject to any previous study. We include XMM–Newton and INTEGRAL data to build a combined spectrum, enabling a joint analysis of both the disc and comptonization components. Results point to a relatively high inclination disc ≳ 50° (3 σ) and a near-maximum speed rotating black hole. The former is in agreement with a previous radio study and the latter is reported here for the first time. Lastly, we follow the methodology of recent efforts to weigh black holes with only X-ray spectra and find results that suggest a black hole mass of about 5 M⊙ for 1E 1740.7−2942.
We present an analysis of eclipse timings of the post-common envelope binary NSVS 14256825, which is composed of an sdOB star and a dM star in a close orbit (P sub(orb) = 0.110374 days). High-speed ...photometry of this system was performed between 2010 July and 2012 August. Ten new mid-eclipse times were analyzed together with all available eclipse times in the literature. We revisited the (O - C) diagram using a linear ephemeris and verified a clear orbital period variation. On the assumption that these orbital period variations are caused by light travel time effects, the (O - C) diagram can be explained by the presence of two circumbinary bodies, even though this explanation requires a longer baseline of observations to be fully tested. The orbital periods of the best solution would be Pc ~ 3.5 years and Pd ~ 6.9 years. The corresponding projected semi-major axes would be ac sin ic ~ 1.9 AU and ad sin id ~ 2.9 AU. The masses of the external bodies would be Mc ~ 2.9 M sub(Jupiter) and Md ~ 8.1 M sub(Jupiter), if we assume their orbits are coplanar with the close binary. Therefore NSVS 14256825 might be composed of a close binary with two circumbinary planets, though the orbital period variations is still open to other interpretations.
In recent years, several close post-common-envelope eclipsing binaries have been found to show cyclic eclipse timing variations (ETVs). This effect is usually interpreted either as the gravitational ...interaction among circumbinary bodies and the host binary-known as the light travel time (LTT) effect-or as the quadrupole moment variations in one magnetic active component-known as the Applegate mechanism. In this study, we present an analysis of the ETV and the magnetic cycle of the close binary KIC 10544976. This system is composed of a white dwarf and a red dwarf in a short orbital period (0.35 days) and was monitored by ground-based telescopes between 2005 and 2017 and by the Kepler satellite between 2009 and 2013. Using the Kepler data, we derived the magnetic cycle of the red dwarf by two ways: the rate and energy of flares and the variability due to spots. Both methods resulted in a cycle of ∼600 days, which is in agreement with magnetic cycles measured for single low-mass stars. The orbital period of KIC 10544976 shows only one long-term variation which can be fitted by an LTT effect with period of ∼16.8 yr. Hence, one possible explanation for the ETVs is the presence of a circumbinary body with a minimal mass of ∼13.4 MJup. In the particular scenario of coplanarity between the external body and the inner binary, the third body mass is also ∼13.4 MJup. In this case, the circumbinary planet must either have survived the evolution of the host binary or have been formed as a consequence of its evolution.
ABSTRACT
New time-series analysis tools are needed in disciplines as diverse as astronomy, economics, and meteorology. In particular, the increasing rate of data collection at multiple wavelengths ...requires new approaches able to handle these data. The panchromatic correlated indices $K^{(s)}_{(fi)}$ and $L^{(s)}_{(pfc)}$ are adapted to quantify the smoothness of a phased light-curve resulting in new period-finding methods applicable to single- and multiband data. Simulations and observational data are used to test our approach. The results were used to establish an analytical equation for the amplitude of the noise in the periodogram for different false alarm probability values, to determine the dependency on the signal-to-noise ratio, and to calculate the yield rate for the different methods. The proposed method has similar efficiency to that found for the string length period method. The effectiveness of the panchromatic and flux-independent period finding methods in single as well as multiple wavebands that share a fundamental frequency is also demonstrated in real and simulated data.
We use the star count model of Ortiz & Lepine to perform an unprecedented exploration of the most important Galactic parameters comparing the predicted counts with the Two Micron All Sky Survey ...observed star counts in the J, H, and K sub(s) bands for a grid of positions covering the whole sky. The comparison is made using a grid of lines of sight given by the HEALPix pixelization scheme. The resulting best-fit values for the parameters are; 2120 + or - 200 pc for the radial scale length and 205 + or - 40 pc for the scale height of the thin disk, with a cental hole of 2070 super(+2000) sub(-800) pc for the same disk, 3050 + or - 500 pc for the radial scale length and 640 + or - 70 pc for the scale height of the thick disk, 400 + or - 100 pc for the cental dimension of the spheroid, 0.0082 + or - 0.0030 for the spheroid to disk density ratio, and 0.57 + or - 0.05 for the oblate spheroid parameter.
Abstract
We have carried out a campaign to characterize the hot Jupiters WASP-5b, WASP-44b and WASP-46b using multiband photometry collected at the Observatório do Pico Dos Dias in Brazil. We have ...determined the planetary physical properties and new transit ephemerides for these systems. The new orbital parameters and physical properties of WASP-5b and WASP-44b are consistent with previous estimates. In the case of WASP-46b, there is some quota of disagreement between previous results. We provide a new determination of the radius of this planet and help clarify the previous differences. We also studied the transit time variations including our new measurements. No clear variation from a linear trend was found for the systems WASP-5b and WASP-44b. In the case of WASP-46b, we found evidence of deviations indicating the presence of a companion but statistical analysis of the existing times points to a signal due to the sampling rather than a new planet. Finally, we studied the fractional radius variation as a function of wavelength for these systems. The broad-band spectrums of WASP-5b and WASP-44b are mostly flat. In the case of WASP-46b we found a trend, but further measurements are necessary to confirm this finding.
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