Browsing by Author "Oliveira, R. Lopes de"
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Item CTCV J2056-3014: An X-Ray-faint Intermediate Polar Harboring an Extremely Fast-spinning White Dwarf(IOP, 2020-07-30) Oliveira, R. Lopes de; Bruch, A.; Rodrigues, C. V.; Oliveira, A. S.; Mukai, K.We report on XMM-Newton X-ray observations that reveal CTCV J2056-3014 to be an unusual accretion-powered, intermediate polar (IP) system. It is a member of the class of X-ray-faint IPs whose space density remains unconstrained but potentially very high, with L x,0.3–12 keV of 1.8 × 10³¹ erg s⁻¹. We discovered a coherent 29.6 s pulsation in X-rays that was also revealed in our reanalysis of published optical data, showing that the system harbors the fastest-spinning, securely known white dwarf (WD) so far. There is no substantial X-ray absorption in the system. Accretion occurs at a modest rate (~6 × 10⁻¹² M ⊙ yr⁻¹) in a tall shock above the WD, while the star seems to be spinning in equilibrium and to have low magnetic fields. Further studies of CTCV J2056-3014 potentially have broad implications on the origin of magnetic fields in WDs, on the population and evolution of magnetic cataclysmic variables, and also on the physics of matter around rapidly rotating magnetic WDs.Item Developing the Physical Understanding of Intermediate Polars: An X-Ray Study of TV Col and V2731 Oph(IOP Publishing, 2019-08-02) Oliveira, R. Lopes de; Mukai, K.The X-rays in intermediate polars (IPs) originate in a compact region near the surface of a magnetic white dwarf (WD) and interact with the complex environment surrounding the emission region. Here we report a case study of two IPs, TV Col and V2731 Oph, with selected archival X-ray observations (NuSTAR, Swift, Suzaku, and XMMNewton). For TV Col, we were successful in simultaneously accounting for the primary X-rays, the secondary X-rays due to Compton scattering and fluorescence, and the effects of local absorbers. In this case, we were able to demonstrate that the shock height is small, based on the high reflection amplitude; hence, the maximum temperature of the post-shock region can be used to derive the WD mass of 0.735 ± 0.015 Me. Despite the high specific accretion rate required to explain the small shock height, we do not detect any spin modulation in our NuSTAR data, consistent with the modest amount of complex absorption seen spectroscopically. We argue that our results are robust because they are based on the joint temporal–spectral analysis of broadband X-ray data. The spectrum of V2731 Oph is more highly absorbed. Through our analysis of the Suzaku data, we present a spectral model with nitrogen overabundance without the previously claimed soft blackbody that should be further explored. We have been unable to constrain the reflection amplitude for V2731 Oph; this and the detection of spin modulation above 10 keV suggest that it may have a tall shock. Hence, we only derive a lower limit to the mass of its WD (>0.9 Me).Item J-PLUS: Two-dimensional analysis of the stellar population in NGC 5473 and NGC 5485(ESO, 2019-01-12) Roman, I. San; Sanchez-Blazquez, P.; Cenarro, A. J.; Diaz-Garcia, L. A.; Lopez-Sanjuan, C.; Varela, J.; Vilella-Rojo, G.; Akras, S.; Bonoli, S.; Chies Santos, A. L.; Coelho, P.; Cortesi, A.; Ederoclite, A.; Jiménez-Teja, Y.; Logroño-García, R.; Oliveira, R. Lopes de; Nogueira-Cavalcante, J. P.; Orsi, A.; Ramió, H. Vázquez; Viironen, K.; Cristóbal-Hornillos, D.; Dupke, R.; Marín-Franch, A.; Oliveira, C. Mendes de; Moles, M.; Sodré, L.Context. The spatial variations of stellar population properties within a galaxy are intimately related to their formation process. Therefore, spatially resolved studies of galaxies are essential to uncover their formation and assembly. Although the arrival of integral field unit (IFU) surveys has brought a significant breakthrough in the field, recent techniques that combine photometric multifilter surveys with spectral fitting diagnostics have opened a new, relatively low-cost way to disentangle the stellar population of spatially resolved galaxies compared to IFU surveys. Aims. The Javalambre Photometric Local Universe Survey (J-PLUS) is a dedicated multifilter designed to observed ~ 8500 deg2 of the northern sky using 12 narrowband, intermediate-band, and broadband filters in the optical range. In this study, we test the potential of the multifilter observation carried out with J-PLUS to investigate the properties of spatially resolved nearby galaxies. Methods. We present detailed 2D maps of stellar population properties, i.e., age, metallicity, extinction, and stellar mass surface density, for two early-type galaxies observed in the J-PLUS and CALIFA surveys. These galaxies are NGC 5473 and NGC 5485. Radial structures are also compared and luminosity- and mass-weighted profiles are derived. We use MUFFIT to process the J-PLUS photometric multifilter observations, and STARLIGHT and STECKMAP to analyze IFU CALIFA data. Results. We demonstrate the scientific potential of J-PLUS/MUFFIT to explore the spatially resolved stellar populations of local galaxies. We find significant discrepancies between the results from the various analysis methods. While radial stellar population gradients obtained with J-PLUS/MUFFIT and the IFU technique CALIFA/STECKMAP are more in agreement, radial stellar population gradients largely differ when CALIFA/STARLIGHT methodology is used. A comparison of the absolute values reveals the existence of intrinsic systematic differences. Age and metallicity radial profiles derived from J-PLUS/MUFFIT are very similar when luminosity- or mass-weighted properties are used, suggesting that the contribution of a younger component is small and the star formation history of these early-type galaxies are well represented by mainly an old single stellar population component. Conclusions. We present the potential of J-PLUS to explore the unresolved stellar populations of spatially extended local galaxies. A comparison between the three methodologies reveals some discrepancies suggesting that the specific characteristics of each method causes important differences. We conclude that the ages, metallicities, and extinction derived for individual galaxies not only depend on the chosen models but also depend on the method used. Future work is required to evaluate in detail the origin of these differences and to quantify the impact that di erent fitting routines have on the derived stellar population properties.Item Soft and hard X-ray dips in the light curves of γ Cassiopeiae(Oxford University Press, 2019-07-26) Smith, M. A.; Oliveira, R. Lopes deThe available six archival XMM–Newton observations of the anomalous X-ray emitter γ Cas (B0.5 IVe) have been surveyed for the presence of soft X-ray ‘dips’ in X-ray light curves. In addition to discovering such events in the soft band (≤2 keV), we show that sometimes they are accompanied by minor, nearly simultaneous dips in the hard X-ray band. Herein, we investigate how these occurrences can be understood in the ‘magnetic star–disc interaction’ hypothesis proposed in the literature to explain the hard, variable X-ray emission of this Be star. In this scenario, the soft X-ray dips are interpreted as transits by comparatively dense, soft X-ray-absorbing blobs that move across the lines of sight to the surface of the Be star. We find that these blobs have similar properties as the ‘cloudlets’ responsible for migrating subfeatures in UV and optical spectral lines and therefore may be part of a common distribution of co-rotating occulters. The frequencies, amplitudes, and longevities of these dips vary widely. Additionally, the most recent spectra from 2014 July suggest that the ‘warm’ (kT ≈ 0.6–4 keV) plasma sources responsible for some of the soft flux are much more widely spread over the Be star’s surface than the hot plasma sites that dominate the flux at all X-ray energies. We finally call attention to a sudden drop in all X-ray energies of the 2014 light curve of γ Cas and a similar sudden drop in a light curve of the ‘analog’ HD 110432. We speculate that these could be related to appearances of particularly strong soft X-ray dips several hours earlier.