arXiv subjects

R. Baptista

Publications and source records attributed to R. Baptista.

At least 19 recordsLinked to original sources

arXiv2026

The eclipsing novalike cataclysmic variable CRTS SSS100505 J093417-174421

Time-resolved optical photometry, complemented by TESS data and long-term survey light curves, reveals that the transient object CRTS SSS100505 J093417-174421 is an eclipsing novalike cataclysmic variable of the VY~Scl subtype, with an orbital period of 0.16329188(8) d. An analysis of the light curves with eclipse mapping techniques and an entropy landscape procedure indicates an orbital inclination of 81.5 degrees and a mass ratio of 0.45. Eclipse maps reveal two diametrically opposed asymmetric arcs of enhanced emission in the intermediate and outer regions of an accretion disk elongated in the direction perpendicular to the line joining both stars, interpreted as tidally-induced spiral shock arms. The accretion disk is 50 per cent larger in the longer wavelength TESS data than in the optical range, in line with the expected radial temperature gradient of an opaque steady-state disk. The combination of a small optical disk radius (of 21 per cent of the orbital separation) and high orbital inclination explains the relatively faint absolute magnitude of $M_g = 7.44$ for a novalike variable.

astro-ph.SR↗

arXiv2025

Nuclear modification factor within a dynamical approach to the complex entropic index

This work introduces a novel approach to the nuclear deformation factor $R_{\text{AA}}$, grounded in the dynamical effects of the Quark-Gluon Plasma on parton momentum. The approach uses the Blast-Wave method combined with Tsallis Statistics, within the Cooper-Frye freeze-out framework and, by profiting from appropriate simplifications, it gives analytical expressions that describe the observed $R_{\text{AA}}$ for two sets of independent measurements at $\sqrt{s}=2.76$ TeV and $\sqrt{s}=5.02$ TeV. A nonlinear dynamical equation describes the dynamics and leads to log-periodic oscillations. With the analytical solutions for that equation, it is possible to link the dynamical approach with the complex-$q$ formalism, which was proposed to describe the log-oscillations observed in experimental data.

hep-ph↗

arXiv2021

Search for magnetic accretion in SW Sextantis systems

SW Sextantis systems are nova-like cataclysmic variables that have unusual spectroscopic properties, which are thought to be caused by an accretion geometry having part of the mass flux trajectory out of the orbital plane. Accretion onto a magnetic white dwarf is one of the proposed scenarios for these systems. To verify this possibility, we analysed photometric and polarimetric time-series data for a sample of six SW Sex stars. We report possible modulated circular polarization in BO Cet, SW Sex, and UU Aqr with periods of 11.1, 41.2 and 25.7 min, respectively, and less significant periodicities for V380 Oph at 22 min and V442 Oph at 19.4 min. We confirm previous results that LS Peg shows variable circular polarization. However, we determine a period of 18.8 min, which is different from the earlier reported value. We interpret these periods as the spin periods of the white dwarfs. Our polarimetric results indicate that 15% of the SW Sex systems have direct evidence of magnetic accretion. We also discuss SW Sex objects within the perspective of being magnetic systems, considering the latest findings about cataclysmic variables demography, formation and evolution.

astro-ph.SR↗

arXiv2013

Two-loop finiteness of self-energies in higher-derivative SQED3

In the superfield formalism, two higher-derivative kinetic operators (Lee-Wick operators) are implemented into the standard three dimensional supersymmetric quantum electrodynamics for improving its ultraviolet behavior. It is shown in particular that the ghosts associated with these Lee-Wick operators allow to remove all ultraviolet divergences in the scalar and gauge self-energies at two-loop level.

hep-th↗

arXiv2013

Accretion and activity on the post-common-envelope binary RR~Cae

Current scenarios for the evolution of interacting close binaries - such as cataclysmic variables (CVs) - rely mainly on our understanding of low-mass star angular momentum loss (AML) mechanisms. The coupling of stellar wind with its magnetic field, i.e., magnetic braking, is the most promising mechanism to drive AML in these stars. There are basically two properties driving magnetic braking: the stellar magnetic field and the stellar wind. Understanding the mechanisms that drive AML therefore requires a comprehensive understanding of these two properties. RRCae is a well-known nearby (d=20pc) eclipsing DA+M binary with an orbital period of P=7.29h. The system harbors a metal-rich cool white dwarf (WD) and a highly active M-dwarf locked in synchronous rotation. The metallicity of the WD suggests that wind accretion is taking place, which provides a good opportunity to obtain the mass-loss rate of the M-dwarf component. We analyzed multi-epoch time-resolved high-resolution spectra of RRCae in search for traces of magnetic activity and accretion. We selected a number of well-known activity indicators and studied their short and long-term behavior. Indirect-imaging tomographic techniques were also applied to provide the surface brightness distribution of the magnetically active M-dwarf, and reveals a polar feature similar to those observed in fast-rotating solar-type stars. The blue part of the spectrum was modeled using a atmosphere model to constrain the WD properties and its metal enrichment. The latter was used to improve the determination of the mass-accretion rate from the M-dwarf wind. The presence of metals in the WD spectrum suggests that this component arises from accretion of the M-dwarf wind. A model fit to the WD gives Teff=(7260+/-250)K and logg=(7.8+/-0.1) dex with a metallicity of =(-2.8+/-0.1)dex, and a mass-accretion rate of dotMacc=(7+/-2)x1e-16Msun/yr.

astro-ph.SR↗

arXiv2011

The stunted outbursts of UU Aquarii are likely mass-transfer events

We report a time-lapse eclipse mapping analysis of B-band time-series of the nova-like variable UU Aqr along a typical stunted outburst in 2002 August. Disc asymmetries rotating in the prograde sense in the eclipse maps are interpreted as a precessing elliptical disc with enhanced emission at periastron. From the disc expansion velocity a disc viscosity alpha_{hot}= 0.2 is inferred. The outburst starts with a 10-fold increase in uneclipsed light, probably arising in an enhanced disc wind; the disc response is delayed by 2 d. The results are inconsistent with the disc instability model and suggest that the stunted outburst of UU Aqr are the response of its viscous accretion disc to enhanced mass-transfer events.

astro-ph.SR↗

arXiv2011

Eclipse mapping the flickering sources in the dwarf nova HT Cassiopeia

We report results of the eclipse mapping analysis of an ensemble of light curves of HT Cas. The fast response of the white dwarf to the increase in mass transfer rate, the expansion rate of the accretion disc at the same time, and the relative amplitude of the high-frequency flickering indicate that the quiescent disc of HT Has has high viscosity, alpha ~ 0.3-0.7. This is in marked disagreement with the disc-instability model and implies that the outbursts of HT Cas are caused by bursts of enhanced mass-transfer rate from its donor star.

astro-ph.SR↗

arXiv2009

Activity on the M star of QS Vir

We report analysis of VRIJH photometry, and phase-resolved optical spectroscopy of the eclipsing DA white dwarf plus dMe dwarf binary QS Vir. Modeling of the photometric data yields an inclination of $i = 74.9\pm0.6$ and a mass ratio of $q = M_2/M_1 = 0.50\pm0.05$. Our Doppler maps indicate the presence of material in the Roche lobe of the white dwarf, at a location near the M star, likely due to accretion from the stellar wind of the M star (as opposed to Roche-lobe overflow accretion). We also constructed images of the brightness distribution of the M star at different epochs which reveal the location of two stable active regions. Doppler tomography shows that the majority of the Hydrogen and Ca II H&K emission originates on the active M dwarf, likely distributed in two preferred activity longitudes, similar to active regions on BY Dra and FK Comae systems.

astro-ph.SR↗

arXiv2008

New Complexities in the Low-State line profiles of AM Herculis

When accretion temporarily ceases in the polar AM Her, the emission line profiles are known to develop several distinct components, whose origin remains poorly understood. The new low-state spectra reported here have a more favorable combination of spectral resolution (R~4500), time resolution (~3-min exposures), and S/N than earlier work, revealing additional details of the orbital dependence of the line profiles. The central strong feature of H-alpha is found to be composed of two components of similar strength, one having K~100 km/sec and phased with the motion of the secondary star, the other having little or no detectable radial velocity variations. We attribute the central line component to gas near the coupling region, perhaps with a contribution from irradiation of the secondary star. The two satellite components have RV offsets of ~+/-250 km/sec on either side of the central strong H-alpha peak. These satellites most likely arise in large loops of magnetically confined gas near the secondary star due to magnetic activity on the donor star and/or interactions of the magnetic fields of the two stars. Doppler maps show that these two satellite features have concentrations at velocities that match the velocity locations of L4 and L5 in the system.

astro-ph↗

arXiv2007

Cyclical period changes in HT Cas: a clear difference between systems above and below the period gap

We report the identification of cyclical changes in the orbital period of the eclipsing cataclysmic variable HT Cas. We measured new white dwarf mid-eclipse timings and combined with published measurements to construct an observed-minus-calculated diagram covering 29 years of observations. The data present cyclical variations that can be fitted by a linear plus sinusoidal function with period 36 yr and semi-amplitude ~ 40 s. The statistical significance of this period by an F-test is larger than 99.9 per cent. We combine our results with those in the literature to revisit the issue of cyclical period changes in cataclysmic variables and their interpretation in terms of a solar-type magnetic activity cycle in the secondary star. A diagram of fractional period change (Delta P/P) versus the angular velocity of the active star (Omega) for cataclysmic variables, RS CVn, W UMa and Algols reveal that close binaries with periods above the gap (secondaries with convective envelopes) satisfy a relationship Delta P/P \propto Omega^{-0.7+/-0.1}. Cataclysmic variables below the period gap (with fully convective secondaries) deviate from this relationship by more than 3-sigma, with average fractional period changes ~ 5 times smaller than those of the systems above the gap.

astro-ph↗

arXiv2007

A multicolor near-infrared study of the dwarf nova IP Peg

We report the analysis of $JHK_{s}$ light curves of the eclipsing dwarf nova IP Peg in quiescence. The light curves are dominated by the ellipsoidal variation of the mass-donor star, with additional contributions from the accretion disc and anisotropic emission from the bright spot. A secondary eclipse is visible in the $J$ and $H$ light curves, with 2% and 3% of the flux disappearing at minimum light, respectively. We modeled the observed ellipsoidal variation of the secondary star (including possible illumination effects on its inner face) to find a mass ratio of $q = 0.42$ and an inclination of $i = 84.5^{o} $, consistent in the three bands within the uncertainties. Illumination effects are negligible. The secondary is responsible for 83%, 84% and 88% of the flux in $J$, $H$ and $K_{s}$, respectively. We fitted a black body spectrum to the $JHK_{s}$ fluxes of the secondary star to find a temperature of $T_{bb} = 3100\pm500 K$ and a distance of $d=115\pm30$ pc to the system. We subtracted the contribution of the secondary star and applied 3-D eclipse mapping techniques to the resulting light curves to map the surface brightness of a disc with half-opening angle $α$ and a circular rim at the radius of the bright spot. The eclipse maps show enhanced emission along the stream trajectory ahead of the bright spot position, providing evidence of gas stream overflow. The inferred radial brightness-temperature distribution in the disc is flat for $R < 0.3R_{L1}$ with temperatures $\simeq 3500K$ and colors consistent with those of cool opaque radiators.

astro-ph↗

arXiv2007

A study of the evolution of the accretion disk of V2051 Oph through two outburst cycles

We follow the changes in the structure of the accretion disk of the dwarf nova V2051 Oph along two separate outbursts in order to investigate the causes of its recurrent outbursts. We apply eclipse mapping techniques to a set of light curves covering a normal (July 2000) and a low-amplitude (August 2002) outburst to derive maps of the disk surface brightness distribution at different phases along the outburst cycles. The sequence of eclipse maps of the 2000 July outburst reveal that the disk shrinks at outburst onset while an uneclipsed component of 13 per cent of the total light develops. The derived radial intensity distributions suggest the presence of an outward-moving heating wave during rise and of an inward-moving cooling wave during decline. The inferred speed of the outward-moving heating wave is ~ 1.6 km/s, while the speed of the cooling wave is a fraction of that. A comparison of the measured cooling wave velocity on consecutive nights indicates that the cooling wave accelerates as it travels towards disk center, in contradiction with the prediction of the disk instability model. From the inferred speed of the heating wave we derive a viscosity parameter alpha_{hot} ~ 0.13, comparable to the measured viscosity parameter in quiescence. The 2002 August outburst had lower amplitude (ΔB ~ 0.8 mag) and the disk at outburst maximum was smaller than on 2000 July. For an assumed distance of 92 pc, we find that along both outbursts the disk brightness temperatures remain below the minimum expected according to the disk instability model. The results suggest that the outbursts of V2051 Oph are caused by bursts of increased mass transfer from the mass-donor star.

astro-ph↗

arXiv2006

HST/FOS Spectral Mapping of V2051 Ophiuchi in a Low State

We report a study of the spectra and structure of the accretion disk of the dwarf nova V2051 Ophiuchi while the star was in an unusual faint brightness state during 1996. The differences between the UV resonant lines and continuum disk surface brightness distributions indicate a vertically extended disk with the emission from these lines arising from the upper atmospheric layers. Distinct emission along the stream trajectory suggests the occurrence of gas stream overflow. Spatially resolved spectra show that the lines are in emission at all disk radii. The Balmer decrement becomes shallower with increasing radius. The FWHMs of the emission lines show differences with respect to that expected for a gas in Keplerian rotation and the line intensities drop with a radial dependency of $I\propto R^{-1.78}$. The uneclipsed light contributes about 5 - 10 per cent of the total flux, and its spectrum is dominated by a Balmer jump and strong lines in emission. Broad absorption bands, possibly due to Fe II, are present in the spectra of the disk side farther away from the secondary star, suggesting it arises from absorption by a extended gas region above the disk; the differences between the spectra of the hemisphere farther from and nearer to the secondary star are interpreted in terms of chromospheric emission from a disc with a non-negligible opening angle (limb brightening effect). Stellar atmosphere model fits to the extracted white dwarf spectrum lead to a temperature $T_{WD}= 9500 ^{+2900}_{-1900} K$ and a distance of $d = 67 ^{+22}_{-25} pc$ if the inner disk is opaque, or $d = 92 ^{+30}_{-35} pc$ if the inner disk is optically thin.

astro-ph↗

arXiv2005

Tracing the spiral arms in IP Pegasi

We report the analysis of time-resolved spectroscopy of IP Pegasi in outburst with eclipse mapping techniques to investigate the location and geometry of the observed spiral structures. We were able to obtain an improved view of the spiral structures with the aid of light curves extracted in velocity bins matching the observed range of velocities of the spiral arms combined with a double default map tailored for reconstruction of asymmetric structures. Two-armed spiral structures are clearly seen in all eclipse maps. The arms are located at different distances from the disc centre. The ``blue'' arm is farther out in the disc (R= 0.55 +/- 0.05 R_{L1}) than the ``red'' arm (R= 0.30 +/- 0.05 R_{L1}). There are evidences that the velocity of the emitting gas along the spiral pattern is lower than the Keplerian velocity for the same disc radius. The discrepancy is smaller in the outer arm (measured velocities 10-15 per cent lower than Keplerian) and is more significant in the inner arm (observed velocities up to 40 per cent lower than Keplerian). We measured the opening angle of the spirals from the azimuthal intensity distribution of the eclipse maps to be ϕ= 25 +/- 3 degrees. A comparison with similar measurements on data at different outburst stages reveals that the opening angle of the spiral arms in IP Peg decreases while the outbursting accretion disc cools and shrinks, in agreement with the expected evolution of a tidally driven spiral wave. The sub-Keplerian velocities along the spiral pattern and the clear correlation between the opening angle of the spirals and the outburst stage favors the interpretation of these asymmetric structures as tidally-induced spiral shocks.

astro-ph↗

arXiv2005

V4140 Sgr: a short period dwarf nova with a peculiar behavior

We report on time series of CCD photometry of V4140 Sgr between 1991 and 2001. The analysis reveals that the object was in the decline from an outburst in 1992 and again in outburst in 2001. The historical light curve collected by amateur astronomers shows low amplitude (1-2 mag) outbursts 5-10 days long, recurrent every 80-90 days, confirming its dwarf nova nature. We derive an outburst decline time scale of 1.2 days mag$^{-1}$. Eclipse mapping techniques were applied to data both in quiescence and in outburst to derive accretion disc surface brightness maps. A distance of $d = 170 \pm 30$ pc is obtained from a method similar to that used to constrain the distance to open clusters. From this distance, disc radial brightness temperature distributions are determined. The temperatures in the quiescent disc vary from $6 000$ K in the inner regions to $3 000$ K near the outer disc and are flatter than the $T \propto r^{-{3/4}}$ law for optically thick steady-state disc. The outburst occurs mainly with a significant increase in brightness of the intermediate and outer disc regions. The disc temperatures remain below the critical effective temperature $T_{\rm crit}$ at all disc radii during outburst. The radial temperature distributions in quiescence and in outburst are significantly different from those of other dwarf novae of similar orbital period. These results cannot be explained within the framework of the disc instability model. We suggest that the small amplitude outbursts of V4140 Sgr are caused by bursts of enhanced mass transfer rate from the secondary star.

astro-ph↗

arXiv2005

HST/FOS Time-resolved spectral mapping of IP Pegasi at the end of an outburst

We report an eclipse mapping analysis of time-resolved ultraviolet spectroscopy covering three eclipses of the dwarf nova IP Pegasi on the late decline of the 1993 May outburst. The eclipse maps of the first run show evidence of one spiral arm, suggesting that spiral structures may still be present in the accretion disc 9 days after the onset of the outburst. In the spatially resolved spectra the most prominent lines appear in emission at any radius, being stronger in the inner disc regions. The spectrum of the gas stream is clearly distinct from the disc spectrum in the intermediate and outer disc regions, suggesting the occurrence of gas stream overflow. The full width half maximum of C IV is approximately constant with radius, in contrast to the expected $v\propto{R^{-1/2}}$ law for a gas in Keplerian orbits. This line probably originates in a vertically extended region (chromosphere + disc wind). The uneclipsed component contributes $\sim{4}$ % of the flux in C IV in the first run, and becomes negligible in the remaining runs. We fit stellar atmosphere models to the spatially resolved spectra. The radial run of the disc color temperature for the three runs is flatter than the expected $T\propto{R^{-3/4}}$ law for steady-state optically thick discs models, with $T\simeq{20000}$ K in the inner regions and $T\simeq{9000}$ K in the outer disc regions. The solid angles that result from the fits are smaller than expected from the parameters of the system. The radial run of the solid angle suggests that the disc is flared in outburst, and decreases in thickness toward the end of the outburst.

astro-ph↗

arXiv2004

Eclipse mapping of the stream and disk flickering components in V2051 Oph

We report on the investigation of the spatial distribution of the flickering sources in the dwarf nova V2051 Oph with eclipse mapping techniques. Low-frequency flickering originates in the gas stream and is related to the mass transfer process, whereas high-frequency flickering arises in the accretion disk and is probably connected to magneto-hydrodynamic turbulence.

astro-ph↗

arXiv2004

HST spectral mapping of V2051 Ophiuchi in a low state

V2051 Oph is an eclipsing dwarf novae with an orbital period of 90 min. This system belongs to a small group of ultrashort period eclipsing dwarf nova together with Z Cha, OY Car and HT Cas. We report a study of the spectra and structure of the accretion disc of the V2051 Oph while the star was in an unusual, faint brightness state during 1996. The analysis is based on high-speed ultraviolet and optical spectroscopy secured with the Hubble Space Telescope.

astro-ph↗