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Kepler S.O.,Federal University of Rio Grande do Sul | Fraga L.,Laboratorio Nacional Of Astrofisica | Winget D.E.,University of Texas at Austin | Bell K.,University of Texas at Austin | And 2 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014

We report the discovery of pulsations in the spectroscopic PG 1159 type pre-white dwarf SDSS J075415.12 + 085232.18. Analysis of the spectrum by Werner et al. indicated Teff = 120 000 ± 10 000 K, log g = 7.0 ± 0.3, mass M= 0.52 ± 0.02M⊙, C/He = 0.33 by number. We obtained time series images with the SOAR 4.1 m telescope and 2.1 m Otto Struve telescope at McDonald Observatory and show the star is also a variable PG 1159 type star, with dominant period of 525 s. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Bruch A.,Laboratorio Nacional Of Astrofisica
Astronomy and Astrophysics | Year: 2014

Context. The cataclysmic variable V893 Sco is an eclipsing dwarf nova which, apart from outbursts with comparatively low amplitudes, exhibits a particularly strong variability during quiescence on timescales of days to seconds. Aims. The present study aims to update the outdated orbital ephemerides published previously, to investigate deviations from linear ephemerides, and to characterize non-random brightness variations in a range of timescales. Methods. Light curves of V893 Sco were observed on 40 nights, spanning a total time base of about 14 years. They contain 114 eclipses which were used to significantly improve the precision of the orbital period and to study long-term variations of the time of revolution. Oscillations and similar brightness variations were studied with Fourier techniques in the individual light curves. Results. The orbital period exhibits long-term variations with a cycle time of 10.2 years. They can be interpreted as a light travel time effect caused by the presence of a giant planet with approximately 9.5 Jupiter masses in a 4.5 AU orbit around V893 Sco. On some nights transient semi-periodic variations on timescales of several minutes can be seen which may be identified as quasi-periodic oscillations. However, it is difficult to distinguish whether they are caused by real physical mechanisms or if they are the effect of an accidental superposition of unrelated flickering flares. Simulations to investigate this question are presented. © 2014 ESO.

Bruch A.,Laboratorio Nacional Of Astrofisica
Astronomy and Astrophysics | Year: 2015

Context. Flickering is a ubiquitous phenomenon in cataclysmic variables (CVs). Although the underlying light source is one of the main contributors to the optical radiation, the mechanism leading to flickering is not understood as yet. Aims. The present study aims to contribute to the set of boundary conditions, defined by observations, which must be met by physical models that describe the flickering. In particular, time lags in the occurrence of flickering events at different wavelengths over the optical range are examined. Methods. To this end, the cross-correlation functions (CCFs) of numerous light curves of a sample of CVs are analysed that were observed simultaneously or quasi-simultaneously in different bands of various photometric systems. Results. Deviations of the maxima of the CCFs from zero time-shift indicate a dependence of the flickering activity on the wavelength in the sense that flickering flares reach their maxima slightly earlier in the blue range than in the red. While the available observational material does not permit detecting this individually in all observed systems, the ensemble of all data clearly shows this effect. Particularly instructive are the cases of V603 Aql and TT Ari, where time lags of 15s.1 and 4s.3, respectively, are observed between the U and R bands. In principle this can be understood if during the development of a flickering flare the radiation characteristics of the light source responsible for flickering change such that in the early phases of a flare more short-wavelength radiation is emitted, and later on, the peak of the emission shifts to the red. Respective scenarios are discussed and shown to be in qualitative and quantitative agreement with observations. © ESO, 2015.

Mazzalay X.,CONICET | Mazzalay X.,Max Planck Institute for Extraterrestrial Physics | Rodriguez-Ardila A.,Laboratorio Nacional Of Astrofisica | Komossa S.,Max Planck Institute for Extraterrestrial Physics
Monthly Notices of the Royal Astronomical Society | Year: 2010

We present an analysis of Space Telescope Imaging Spectrograph (STIS)/Hubble Space Telescope optical spectra of a sample of 10 Seyfert galaxies aimed at studying the structure and physical properties of the coronal-line region (CLR). The high spatial resolution provided by STIS allowed us to resolve the CLR and obtain key information about the kinematics of the CL gas, measure directly its spatial scale, and study the mechanisms that drive the high-ionization lines. We find CLRs extending from just a few parsecs (~10 pc) up to 230 pc in radius, consistent with the bulk of the coronal lines (CLs) originating between the broad-line region and narrow-line region (NLR), and extending into the NLR in the case of [Fe VII] and [Ne V] lines. The CL profiles strongly vary with the distance to the nucleus. We observed line splitting in the core of some of the galaxies. Line peak shifts, both redshift and blueshift, typically reached 500 km s-1, and even higher velocities (1000 km s-1) in some of the galaxies. In general, CLs follow the same pattern of rotation curves as low-ionization lines like [OIII]. From a direct comparison between the radio and the CL emission we find that neither the strength nor the kinematics of the CLs scales in any obvious and strong way with the radio jets. Moreover, the similarity of the flux distributions and kinematics of the CLs and low-ionization lines, the low temperatures derived for the gas, and the success of photoionization models to reproduce, within a factor of a few, the observed line ratios, point towards photoionization as the main driving mechanism of CLs. © 2010 The Authors. Journal compilation © 2010 RAS.

Riffel R.,Federal University of Rio Grande do Sul | Ruschel-Dutra D.,Federal University of Rio Grande do Sul | Pastoriza M.G.,Federal University of Rio Grande do Sul | Rodriguez-Ardila A.,Laboratorio Nacional Of Astrofisica | And 3 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2011

We present SOAR/OSIRIS cross-dispersed near-infrared (NIR) integrated spectra of 12 Galactic globular clusters that are employed to test Maraston NIR evolutionary population synthesis models, and to provide spectral observational constraints to calibrate future models. We measured equivalent widths (Wλ) of the most prominent NIR absorption features: λ 1.49 μm, Mg iλ 1.58 μm, Fe i/Mg i, λ 1.59 μm, Si i, λ 1.71 μm, Mg i, λ 2.21 μm, Na i and λ 2.26 μm, Ca i as well as the λ 1.62 μm, λ 2.29 μm, CO and λ 2.05 μm, CN molecular bands. Optical Wλ of G band (4300 Å), Hβ, Mg2, Fe i (4531, 527 and 5335 Å) and Na i (5897 Å) were also measured. The globular clusters Wλ were compared with model predictions with ages within 4-15 Gyr, and metallicities between 0.005 and 2 Z⊙. Observed integrated colours (B-V, V-I and V-Ks) were also compared with models. The NIR integrated spectra among our sample appear qualitatively similar in most of the absorption features. The Maraston models can properly predict the optical Wλ observed in globular clusters. Regarding the NIR, they do underestimate the strength of Mg i 1.49 μm, but they can reproduce the observed Wλ of Fe i 1.58 μm, Si i 1.59 μm and CO 2.29 μm, in about half of our sample. The remaining objects require the inclusion of intermediate-age populations. Thus, we suggest that the presence of C- and O-rich stars in models is important to reproduce the observed strengths of metallic lines. Another possibility is the lack of α-enhancement in the models. In the case of the optical and NIR Fe i lines, standard models and those that include blue horizontal branch stars produce similar results. A similar trend is observed for Na i 5895 Å, while in the case of the G band, the models with blue horizontal branch do describe better the observations. For most of the sample, the optical to NIR colours are well described by the Maraston models. In general, Maraston models can provide reliable information on the NIR stellar population of galaxies, but only when Wλ and colours are taken together; in other words, Wλ and continuum fluxes should be simultaneously fitted. However, the results should be taken with caution, since the models tend to predict results biased towards young ages. © 2010 The Authors. Journal compilation © 2010 RAS.

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