Time filter

Source Type

Bruch A.,Laboratorio Nacional Of Astrofisica | Monard B.,Bronberg and Kleinkaroo Observatories
New Astronomy | Year: 2017

Although comparatively bright, the cataclysmic variable GY Hya has not attracted much attention in the past. As part of a project to better characterize such systems photometrically, we observed light curves in white light, each spanning several hours, at Bronberg Observatory, South Africa, in 2004 and 2005, and at the Observatório do Pico dos Dias, Brazil, in 2014 and 2016. These data permit to study orbital modulations and their variations from season to season. The orbital period, already known from spectroscopic observations of Peters and Thorstensen (2005), is confirmed through strong ellipsoidal variations of the mass donor star in the system and the presence of eclipses of both components. A refined period of 0.34723972 (6) days and revised ephemeries are derived. Seasonal changes in the average orbital light curve can qualitatively be explained by variations of the contribution of a hot spot to the system light together with changes of the disk radius. The amplitude of the ellipsoidal variations and the eclipse contact phases permit to put some constraints on the mass ratio, orbital inclination and the relative brightness of the primary and secondary components. There are some indications that the disk radius during quiescence, expressed in units of the component separation, is smaller than in other dwarf novae. © 2017 Elsevier B.V.


Bruch A.,Laboratorio Nacional Of Astrofisica | Diaz M.P.,University of Sao Paulo
New Astronomy | Year: 2017

As part of a project to better characterize comparatively bright but so far little studied cataclysmic variables in the southern hemisphere, we have obtained spectroscopic and photometric data of the nova-like variables LS IV −08° 3 and HQ Mon, and of the Z Cam type dwarf nova ST Cha. The spectra of all systems are as expected for their respective types. We derive improved orbital ephemeris of LS IV −08° 3 and map its accretion disk in the light of the Hα emission using Doppler tomography. We find that the emission has a two component origin, arising in the outer parts of the accretion disk and possibly on the illuminated face of the secondary star. The light curve of LS IV −08° 3 exhibits a low level of flickering and indications for a modulation on the orbital period. Spectroscopy of HQ Mon suggests an orbital period of ≈ 5h.15 which is incompatible with previous (uncertain) estimates. The light curves show the typical low scale flickering of UX UMa type nova-like systems, superposed upon variations on longer time scales. During one night a modulation with a period of ≈ 41m is observed, visible for at least 4 hours. However, it does not repeat itself in other nights. A spectroscopic orbital period of ≈ 5h.5 is derived for ST Cha. A previously suspected period of 6h.8 (or alternatively 9h.6), based on historical photographic photometry is incompatible with the spectroscopic period. Moreover, we show that our new as well as previous photometry does not contain evidence for the quoted photometric period. © 2016


Repetto P.,Laboratorio Nacional Of Astrofisica | Martinez-Garcia E.E.,National Institute of Astrophysics, Optics and Electronics | Rosado M.,National Autonomous University of Mexico | Gabbasov R.,Institute Ciencias Basicas e Ingenierias
Monthly Notices of the Royal Astronomical Society | Year: 2015

In this paper, we investigate the outer and inner mass distributions of the irregular galaxies UGC4284 and UGC11861, taking advantage of published HI and Hα high-resolution rotation curves and constraining the stellar disc of both galaxies throughout stellar population synthesis studies. In addition, we take into account the gas content of both galaxies deriving the HI+He rotation curve. The deduced baryonic rotation curves (star+gas) are inadequate to account for the total mass of UGC 4284 and UGC 11861, for that reason we examine the possibility of dark matter (DM) to explain the incongruity between the observed HI and Hα rotation curves of UGC 4284 and UGC 11861 and the derived baryonic rotation curves. We consider NFW, Burkert, DiCintio, Einasto, and the Stadel DM haloes, to analyse the DM content of UGC 4284 and UGC 11861. The principal results of this work are that cored DM models better reproduce the DM Hα and HI rotation curves of UGC 11861 and the DM HI rotation curve of UGC 4284, while the Hα rotation curve of UGC 4284 is better reproduced by a cuspy DiCintio DM model. In general, cored exponential two-parameter models Einasto and Stadel give better fits than Burkert. This trend, as well as to confirm past results, presents for the first time a comparison between two different exponential DM models, Einasto and Stadel, in an attempt to better constrain the range of possible exponential DM models applied to real galaxies. © 2015 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Garcia-Rissmann A.,Laboratorio Nacional Of Astrofisica | Rodriguez-Ardila A.,Laboratorio Nacional Of Astrofisica | Rodriguez-Ardila A.,University of Hawaii at Manoa | Sigut T.A.A.,University of Western Ontario | And 2 more authors.
Astrophysical Journal | Year: 2012

In active galactic nucleus spectra, a series of Fe II multiplets form a pseudo-continuum that extends from the ultraviolet to the near-infrared (NIR). This emission is believed to originate in the broad-line region, and it has been known for a long time that pure photoionization fails to reproduce it in the most extreme cases, as does the collisional excitation alone. The most recent models by Sigut & Pradhan include details of the Fe II ion microphysics and cover a wide range in the ionization parameter log U ion = (- 3.0 → -1.3) and density log n H = (9.6 → 12.6). With the aid of such models and a spectral synthesis approach, we studied for the first time in detail the NIR emission of IZw1. The main goals were to confirm the role played by Lyα fluorescence mechanisms in the production of the Fe II spectrum and to construct the first semi-empirical NIR Fe II template that best represents this emission, consequently allowing its clean subtraction in other sources. A good overall match between the observed Fe II+Mg II features with those predicted by the best-fitted model was obtained, corroborating the Lyα fluorescence as a key process to understand the Fe II spectrum. The best model was fine-tuned by applying a deconvolution method to the observed Fe II+Mg II spectrum. This derived semi-empirical template was then fitted to the spectrum of Ark564, showing that it nicely reproduced its observed Fe II+Mg II emission. Our work extends the current set of available Fe II templates into the NIR region. © 2012. The American Astronomical Society. All rights reserved..


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.


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.


Mazzalay X.,Max Planck Institute for Extraterrestrial Physics | Rodriguez-Ardila A.,Laboratorio Nacional Of Astrofisica | Komossa S.,Max Planck Institute for Radio Astronomy | McGregor P.J.,Australian National University
Monthly Notices of the Royal Astronomical Society | Year: 2013

We present adaptive optics-assisted J- and K-band integral field spectroscopy of the inner 300 × 300 pc of the Seyfert 2 galaxy NGC 1068. The data were obtained with the Gemini Near-infrared Integral-Field Spectrograph integral field unit spectrometer, which provided us with high-spatial and high-spectral resolution sampling. The wavelength range covered by the observations allowed us to study the [Ca VIII], [Si VI], [Si VII], [Al IX] and [S IX] coronal line (CL) emission, covering ionization potentials up to 328 eV. The observations reveal very rich and complex structures, both in terms of velocity fields and emission-line ratios. The CL emission is elongated along the NE-SW direction, with the stronger emission preferentially localized to the NE of the nucleus. CLs are emitted by gas covering a wide range of velocities, with maximum blueshifts/redshifts of ~ -1600/1000 km s-1. There is a trend for the gas located on the NE side of the nucleus to be blueshifted while the gas located towards the SW is redshifted. The morphology and the kinematics of the near-infrared CLs are in very good agreement with the ones displayed by low-ionization lines and optical CLs, suggesting a common origin. The line flux distributions, velocity maps, ionization structure (traced by the [Si VII]/[Si VI] emission-line ratio) and low-ionization emission-line ratios (i.e. [Fe II]/Paβ and [Fe II]/[P II]) suggest that the radio jet plays an important role in the structure of the CL region of this object, and possibly in its kinematics. © 2013 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
New Astronomy | Year: 2016

Even among the brighter cataclysmic variables an appreciable number of objects exist about which not much is known. One of them, MU Cen, was observed as part of a small project to better characterize these neglected systems. The temporal variations of the brightness of MU Cen during quiescence were studied in order to find clues to the structure of the system and its behavior on time scales of hours and shorter. Light curves observed in white light at a time resolution of a few seconds and with a duration of several hours, obtained in six nights and spanning a total time base of five months, were investigated using different time series analysis tools, as well as model fits. The light curve of MU Cen is dominated by ellipsoidal variations of the secondary star. The refined orbital period is Porb=0.341883 days. Model fits permit to constrain the temperature of the secondary star to ∼5000 K and the orbital inclination to 50° ≤ i ≤ 65°. The latter result permits estimates of the component masses which are probably somewhat smaller that derived in previous publications. A second persistent period of P2=0.178692 days was also identified. Its origin remains unclear. As all cataclysmic variables, MU Cen exhibits flickering, however, on a rather low level. Its frequency behavior is normal for quiescent dwarf novae. There are indications that the individual flickering events are not always independent but can lead to effects reminiscent of quasi-periodic oscillations. © 2015 Elsevier B.V. All rights reserved.


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.

Loading Laboratorio Nacional Of Astrofisica collaborators
Loading Laboratorio Nacional Of Astrofisica collaborators