arXiv subjects

Wagner Schlindwein

Publications and source records attributed to Wagner Schlindwein.

8 recordsLinked to original sources

arXiv2026

Scientific Validation of the SPARC4 Pipeline: Multi-band Imaging, Polarimetry, and Photometric Time Series for Improved Characterization of Transiting Exoplanets

High-cadence multi-band imaging and polarimetry have important scientific applications in astronomy. Observations of transits of exoplanets are a particular application that requires robust data reduction and analysis. We present the SPARC4 Pipeline, a suite of routines developed to process photometric and polarimetric data obtained with the instrument SPARC4 installed on the 1.6 m telescope at Pico dos Dias Observatory, Brazil. The scientific data products, up to the generation of high-cadence time series, are demonstrated using observations of several transiting exoplanetary systems in both photometric and polarimetric modes. These observations are used to produce stacked calibrated images, yielding sub-arcsecond astrometric accuracy even in sparse fields. The time series of these fields enabled a photometric characterization of the instrument. Observations of polarimetric standard stars yield an instrumental polarization below 0.06% and a linear polarization accuracy of 0.2%. Furthermore, transit observations of seven exoplanets with host-star magnitudes in the range 10.2 < V < 13.9 demonstrate that SPARC4 achieves an average photometric precision of 0.02% for a 15-minute cadence and a polarimetric precision of ~0.02% over hours-long time series. Finally, we jointly model the SPARC4 light curves together with TESS data (or K2 data in the case of HATS-9) using a Bayesian MCMC framework to refine constraints on the physical parameters of the exoplanets, enabling a more accurate determination of orbital periods and planetary radii, and providing improved constraints on the orbital and physical parameters of these hot Jupiters.

astro-ph.EP↗

arXiv2026

The dwarf nova EX Draconis: a short review

EX Draconis (EX Dra) is a long period dwarf nova showing ~2 mag outburst which lasts for ~7 d and recur on a timescale of (20-30) d. Its deep eclipses allows one to trace the changes in surface brightness and radius of its accretion disk along the outburst cycle and to perform critical tests of the predictions of the thermal-viscous disk instability (DI) and the mass transfer outburst (MTO) models proposed to explain dwarf nova outbursts. The results of four critical tests are in clear contradiction with DI while in good agreement with MTO expectations. Furthermore, the observed variations in brightness and outer disk radius throughout EX Dra outbursts are well described by the response of a high-viscosity (alpha = 3-4) accretion disk to events in which the mass transfer rate increases by factors of ~30 for ~7 d, in line with MTO expectations. We further argue that the old expectation of accretion disk theory, alpha <= 1, seems unjustified and contradicts the values derived from dwarf nova outburst decline timescales if they are driven by MTO.

astro-ph.SR↗

arXiv2026

The accretion-driven eruption of the recurrent nova T Corona Borealis

T Corona Borealis (T CrB) is a symbiotic recurrent nova with an $\simeq 80$ yr recurrence interval, the eruptions of which occur on top of a $\simeq 15$ yr long high-brightness state. We show that the high-brightness state is best explained as the response of a high-viscosity ($α=3$) accretion disk to a unique event in which the mass transfer rate from the donor star increases by a factor $\simeq 100$, from $\dot{M}\mathrm{(quies)}= 2 \times 10^{-9} M_\odot$ yr$^{-1}$ up to $\dot{M}\mathrm{(out)}= 1.9 \times 10^{-7} M_\odot$ yr$^{-1}$; it can not be a thermal-viscous disk instability outburst neither a steady nuclear burning event. The constraint that the matter accreted onto the white dwarf in between eruptions equals the envelope mass $M_{ig}$ needed to trigger nova eruptions at the observed recurrence interval requires a white dwarf mass of $M_1= 1.29 M_\odot$, a donor star mass of $M_2= 0.7 M_\odot$, and an inclination of $i= 57.3^o$. As the high-brightness state responds for 95% of $M_{ig}$, the nova eruptions of T CrB are induced by accretion events. Without the 15 yr long enhanced mass transfer events, its nova recurrence interval would be significantly longer, $\simeq 5500$ yr. T CrB exhibits a conspicuous decrease in brightness during the 1-2 yr prior to the nova event. We argue that this pre-eruption dip occurs during the convection phase that precedes the nova eruption and is best explained by the slow, accelerated expansion of the accreted envelope (and inner disk radius) at an average velocity of $v_\mathrm{exp}= 0.02$ km s$^{-1}$ over a 2 yr timescale, likely as a consequence of excess heat being increasingly deposited at the accreted layer by thermonuclear reactions before the nova eruption stage.

astro-ph.SR↗

arXiv2025

Modeling the high-brightness state of the recurrent nova T CrB as an enhanced mass-transfer event

T~Coronae Borealis is the nearest symbiotic recurrent nova. Twice in the last two centuries, in 1866 and 1946, the accreted material ignited on the surface of the white dwarf via runaway thermonuclear fusion reactions and produced a nova eruption. Both eruptions occurred approximately midway through a transient state of high luminosity. A possible explanation of such a state is a dwarf-nova-like outburst, which may arise from a transient increase in the mass-transfer rate of the donor star. We simulate the response of an accretion disk to an event of enhanced mass-transfer that is ``interrupted'' by a pre-eruption dip associated to the convective phase leading to the thermonuclear runaway, and model the resulting optical light curve using the parameters of the T~CrB binary. Our model represents the first attempt to reproduce the transient high-accretion state. The observed brightening can be satisfactorily reproduced by models of an accretion disk with a viscosity parameter $α= 3$, an event of enhanced mass-transfer with a duration of $Δt = 15$\,yr, and quiescent and high-state mass-transfer rates of $2.0 \times 10^{-9} \, M_\odot$\,yr$^{-1}$ and $1.9 \times 10^{-7} \, M_\odot$\,yr$^{-1}$, respectively, while the pre-eruption dip can be reproduced by the small, accelerated expansion of the inner disk radius, at an average velocity of 0.02\,km\,s$^{-1}$. Our model is also capable of reproducing the observed changes in color of T~CrB throughout the transient event.

astro-ph.SR↗

arXiv2024

SPARC4 control system

SPARC4 is a new astronomical instrument developed entirely by Brazilian institutions, currently installed on the 1.6-m Perkin-Elmer telescope of the Pico dos Dias Observatory. It allows the user to perform photometric or polarimetric observations simultaneously in the four SDSS bands (g, r, i, and z). In this paper, we describe the control system developed for SPARC4. This system is composed of S4ACS, S4ICS, and S4GUI softwares and associated hardware. S4ACS is responsible for controlling the four EMCCD scientific cameras (one for each instrument band). S4ICS controls the sensors and motors responsible for the moving parts of SPARC4. Finally, S4GUI is the interface used to perform observations, which includes the choice of instrument configuration and image acquisition parameters. S4GUI communicates with the instrument subsystems and with some observatory facilities, needed during the observations. Bench tests were performed for the determination of the overheads added by SPARC4 control system in the acquisition of photometric and polarimetric series of images. In the photometric mode, SPARC4 allows the acquisition of a series of 1400 full-frame images, with a deadtime of 4.5 ms between images. Besides, several image series can be concatenated with a deadtime of 450 ms plus the readout time of the last image. For the polarimetric mode, measurements can be obtained with a deadtime of 1.41 s plus the image readout time between subsequent waveplate positions. For both photometric and polarimetric modes, the user can choose among operating modes with image readout times between 5.9 ms and 1.24 s, which ultimately defines the instrument temporal performance.

astro-ph.IM↗

arXiv2024

Mass-transfer Outburts reborn: Modeling the light curve of the dwarf nova EX Draconis

EX Draconis is an eclipsing dwarf nova that shows outbursts with moderate amplitude ($\simeq 2$ mag) and a recurrence timescale of $\simeq 20$-30 d. Dwarf novae outbursts are explained in terms of either a thermal-viscous instability in the disc or an instability in the mass transfer rate of the donor star (MTIM). We developed simulations of the response of accretion discs to events of enhanced mass transfer, in the context of the MTIM, and applied them to model the light curve and variations in the radius of the EX Dra disc throughout the outburst. We obtain the first modeling of a dwarf nova outburst by using $χ^2$ to select, from a grid of simulations, the best-fit parameters to the observed EX Dra outbursts. The observed time evolution of the system brightness and the changes in the radius of the outer disc along the outburst cycle are satisfactorily reproduced by a model of the response of an accretion disc with a viscosity parameter $α= 4.0$ and a quiescent mass transfer rate $\dot{M}_2 (\textrm{quiescence}) = 4.0 \times 10^{16}$ g/s to an event of width $Δt = 6.0 \times 10^5$ s ($\sim 7$ d) where the mass-transfer rate increases to $\dot{M}_2 (\textrm{outburst}) = 1.5 \times 10^{18}$ g/s.

astro-ph.SR↗

arXiv2021

Challenging the disk instability model: I -- The case of YZ LMi

Observations of YZ LMi show enhanced emission along the stream trajectory beyond impact at disk rim during outbursts as well as when the quiescent disk is large. We investigated whether these features can be explained in terms of either gas stream overflow or penetration within the frameworks of the disk-instability (DIM) and the mass-transfer instability (MTIM) models of outbursting disks. Gas stream overflow is not possible because the vertical scaleheight of the stream is significantly lower than that of the outer disk and because there is no combination of parameters which enables stream overflow on a larger disk while preventing it on a smaller disk. Stream penetration requires the gas stream to be denser than the outer disk regions. This requirement cannot be met by a low-viscosity DIM disk because its density is significantly larger than that of the gas stream over the whole range of mass transfer rates where the thermal-viscous instability occurs. On the other hand, the high-viscosity MTIM disk has much lower densities which decrease with increasing radius, easily allowing for gas stream penetration during outbursts (when mass transfer rate and stream density increase) as well as in large quiescent disks. The observed features are not consistent with DIM, but can be plausibly explained by MTIM. These results suggest that the outbursts of YZ LMi are the response of a high-viscosity disk to bursts of enhanced mass transfer rate. In this case, the outburst decline timescale of (2-3) d implies a viscosity parameter in the range alpha=3-4.

astro-ph.SR↗

arXiv2018

Mapping the accretion disc of the short period eclipsing binary SDSS J0926+3624

We report the analysis of time-series of optical photometry of SDSS J0926+3624 collected with the Liverpool Robotic Telescope between 2012 February and March while the object was in quiescence. We combined our median eclipse timing with those in the literature to revise the ephemeris and confirm that the binary period is increasing at a rate $\dot{P}=(3.2 \pm 0.4)\times 10^{-13} \, s/s$. The light curves show no evidence of either the orbital hump produced by a bright spot at disc rim or of superhumps; the average out-of-eclipse brightness level is consistently lower than previously reported. The eclipse map from the average light curve shows a hot white dwarf surrounded by a faint, cool accretion disc plus enhanced emission along the gas stream trajectory beyond the impact point at the outer disc rim, suggesting the occurrence of gas stream overflow/penetration at that epoch. We estimate a disc mass input rate of $\dot{M}=(9 \pm 1)\times 10^{-12}\,M_\odot \,yr^{-1}$, more than an order of magnitude lower than that expected from binary evolution with conservative mass transfer.

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