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C. V. Rodrigues

Publications and source records attributed to C. V. Rodrigues.

At least 19 recordsLinked to original sources
arXiv2026

A micronova burst in the intermediate polar IGR J17014-4306

We report the detection of a short optical burst in TESS data of IGR J17014-4306, the eclipsing intermediate polar with the longest known orbital period. The burst lasts 1.56 d and shows multiple peaks, reaching $(9.3 \pm 0.2) \times 10^{33}$ erg s$^{-1}$, and releases a total energy of $(3.25 \pm 0.01) \times 10^{38}$ erg. The burst parameters are consistent with those of a micronova eruption, currently understood as a thermonuclear runaway in the magnetically-confined accretion column. From its energy, we infer a burned column mass of $\sim 1.6 \times 10^{-11}$ M$_\odot$, which implies a recurrence time of $\sim 20$ d. Our search for similar events in long-term Gaia, ASAS-SN, and AAVSO light curves reveals 16 possible fast brightenings over $\sim 11$ yr, suggesting that micronova events may be frequent in IGR J17014-4306. Timing analysis of the TESS data shows that the white-dwarf spin period remains stable before and after the burst. During the burst, however, the power spectrum becomes more complex and exhibits multiple peaks. The classification of IGR J17014-4306 as a micronova brings the total number of confirmed systems to eight. Its extreme orbital period and eclipsing nature make it an ideal test-bed for further studies of magnetically confined thermonuclear burning on white dwarfs.

astro-ph.HE↗
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

Interstellar Polarization Survey. V. Galactic magnetic field tomography in the spiral arms using optical and near-infrared starlight polarization

Interstellar linear polarization occurs when starlight passes through elongated dust grains aligned by interstellar magnetic fields. The observed polarization can come from different dust structures along the line of sight (LOS). By combining polarization measurements with stellar distances, we can study the plane-of-sky Galactic magnetic field (GMF) between the observer and the star and separate the contributions of clouds with different GMF properties. We used optical and near-infrared (NIR) polarization data from three regions in the Galactic plane ($|b|<1^{\circ}$ and $19.\!\!^{\circ}8<l<25.\!\!^{\circ}5$) to perform a polarization decomposition across the Galactic arms. A comparison between optical and NIR data showed an optical-to-NIR polarization ratio of 2 to 3 along the LOS and a consistent polarization angle across both wavelengths in all studied regions, within measurement uncertainties. We applied the Bayesian Inference of Starlight Polarization in one dimension and the Gaussian Mixture Model methods to decompose the polarization in the three regions. Optical and NIR observations complemented each other, consistently identifying nearby ($d\lesssim143$ pc), intermediate ($0.47$ kpc $< d < 1.2$ kpc), and distant ($1.5$ kpc $< d < 2.5$ kpc) polarizing clouds, in agreement with previous findings in the Local Bubble wall, the Local arm, and the Sagittarius arm dust structures. The results from both polarization decomposition methods agree and complement each other. Polarization tomography revealed significant LOS variations in the plane-of-sky magnetic field orientation in two of the three regions. The relative alignment between the magnetic fields traced by starlight polarization and Planck's polarized thermal dust emission at 353 GHz reaffirmed these variations.

astro-ph.GA↗
arXiv2025

Detection of the white-dwarf spin of V1082 Sgr

We report on the discovery of circular polarization modulated with a period of 1.943 +- 0.002 h in the cataclysmic variable V1082 Sgr. These findings unambiguously reveal the rotation of a magnetic white dwarf and establish its intermediate polar (IP) nature. Along with its extraordinary long orbital period, Porb, of 20.8 h, the spin period (Pspin) places this system in an extreme position of the Pspin versus Porb distribution. The circular polarization phase diagram has a single peak and an amplitude smaller than 1%. These data were used to model the post-shock region of the accretion flow on the white-dwarf surface using the CYCLOPS code. We obtained a magnetic field in the white-dwarf pole of 11 MG and a magnetospheric radius consistent with the coupling region at around 2 - 3 white-dwarf radii. The Pspin/Porb value and the estimated magnetic field momentum suggest that V1082 Sgr could be out of spin equilibrium, in a spin-up state, possibly in a stream accretion mode.

astro-ph.SR↗
arXiv2024

Interstellar Polarization Survey. IV. Characterizing the magnetic field strength and turbulent dispersion using optical starlight polarization in the diffuse interstellar medium

Angular dispersion functions are typically used to estimate the fluctuations in polarization angle around the mean magnetic field orientation in dense regions, such as molecular clouds. The technique provides accurate turbulent to regular magnetic field ratios, $\langle B_t^2\rangle^{1/2}/B_{pos}$, which are often underestimated by the classic Davis-Chandrasekhar-Fermi method. We assess the technique's suitability to characterize the turbulent and regular plane-of-sky magnetic field in low-density structures of the nearby interstellar medium (ISM), particularly when the turbulence outer scale, $δ$, is smaller than the smallest scale observed, $\ell_{min}$. We use optical polarization maps of three intermediate-latitude fields ($|b| \gtrsim 7.\!\!^{\circ}5$) with dimensions of $0.\!\!^{\circ}3 \times 0.\!\!^{\circ}3$, sourced from the Interstellar Polarization Survey--General ISM (IPS-GI) catalog. We decomposed the HI emission detected by the Galactic All-Sky Survey (GASS) within our fields to estimate the multiphase ISM properties associated with the structure coupled to the magnetic field. We produced maps of the plane-of-sky magnetic field strength ($B_{pos}$), mass density ($ρ$), and turbulent velocity dispersion ($σ_{v,turb}$). In the regions with well-defined structures at $d<400$ pc, the average $B_{pos}$ ranges from ${\sim}3 μ$G to ${\sim}9 μ$G, depending on the method and physical properties. In the region where structures extend up to $1000$ pc, $B_{pos}$ varies from ${\sim}1 μ$G to ${\sim}3 μ$G. The results agree with previous estimations in the local, diffuse ISM. Finally, optical starlight polarization and thermal dust polarization at 353 GHz consistently reveal a highly regular plane-of-sky magnetic field orientation unfazed by diffuse dust structures observed at $12 μ$m.

astro-ph.GA↗
arXiv2024

Magnetic fields in the Southern Coalsack and beyond

Starlight polarimetry, when combined with accurate distance measurements, allows for exploration of the three-dimensional structure of local magnetic fields in great detail. We present optical polarimetric observations of stars in and close to the Southern Coalsack, taken from the Interstellar Polarization Survey (IPS). Located in five fields of view approximately $0.3^{o}$ by $0.3^{o}$ in size, these data represent the highest density of optical polarimetric observations in the Southern Coalsack to date. Using these data, combined with accurate distances and extinctions based on Gaia data, we are able to characterize the magnetic field of the Coalsack and disentangle contributions to the polarization caused by the Southern Coalsack and a background structure. For the Southern Coalsack, we find an average magnetic field orientation of $θ\sim 75^{o}$ with respect to the Galactic north pole and an average plane-of-sky magnetic field strength of approximately $B_{POS}=10$ $μG$, using the Davis-Chandrasekhar-Fermi (DCF) method. These values are in agreement with some earlier estimates of the Coalsack's magnetic field. In order to study the distant structure, we introduce a simple method to separate and isolate the polarization of distant stars from foreground contribution. For the distant structure, which we estimate to be located at a distance of approximately 1.3-1.5 kpc, we find an average magnetic field orientation of $θ\sim100^{o}$ and we estimate a field strength of $B_{POS}\sim10 \ μG$, although this will remain highly uncertain until the precise nature of the distant structure can be uncovered.

astro-ph.GA↗
arXiv2023

Interstellar Polarization Survey III: Relation Between Optical Polarization and Reddening in the General Interstellar Medium

Optical starlight can be partially polarized while propagating through the dusty, magnetized interstellar medium. The polarization efficiency describes the polarization intensity fraction per reddening unit, P$_V$/E($B-V$), related to the interstellar dust grains and magnetic field properties. The maximum value observed, [P$_V$/E$(B-V)]_{max}$, is thus achieved under optimal polarizing conditions of the interstellar medium. Therefore, the analysis of polarization efficiency observations across the Galaxy contributes to the study of magnetic field topology, small-scale magnetic fluctuations, grain-alignment efficiency, and composition. Infrared observations from $Planck$ satellite have set [P$_V$/E$(B-V)]_{max}$ to 13$\%$ mag$^{-1}$. However, recent optical polarization observations in $Planck$'s highly polarized regions showed polarization efficiency values between 13.6$\%$ mag$^{-1}$ and 18.2$\%$ mag$^{-1}$ (depending on the extinction map used), indicating that [P$_V$/E$(B-V)]_{max}$ is not well constrained yet. We used $V$-band polarimetry of the Interstellar Polarization Survey (consisting of $\sim$10500 high-quality observations distributed in 34 fields of $0.3^{\circ}\times0.3^{\circ}$) to accurately estimate the polarization efficiency in the interstellar medium. We estimated the upper limit of P$_V$/E($B-V$) with the weighted $99th$ percentile of the field. In five regions, the polarization efficiency upper limit is above 13$\%$ mag$^{-1}$. Furthermore, we found [P$_V$/E$(B-V)]_{max} = 15.8^{+1.3}_{-0.9}\%$ mag$^{-1}$ using diffuse intermediate latitude ($|b|>7.5^{\circ}$) regions with apparently strong regular Galactic magnetic field in the plane-of-sky. We studied the variations of P$_V$/E($B-V$) across the sky and tested toy models of polarization efficiency with Galactic longitude that showed some correspondence with a uniform spiral magnetic field.

astro-ph.GA↗
arXiv2022

Interstellar Polarization Survey II: General Interstellar Medium

Magnetic fields permeate the entire Galaxy and are essential to, for example, the regulation of several stages of the star formation process and cosmic ray transportation. Unraveling its properties, such as intensity and topology, is an observational challenge that requires combining different and complementary techniques. The polarization of starlight due to the absorption by field-aligned non-spherical dust grains provides a unique source of information about the interstellar magnetic field in the optical band. This work introduces a first analysis of a new catalog of optical observations of linearly polarized starlight in the diffuse interstellar medium (ISM), the Interstellar Polarization Survey, General ISM (IPS-GI). We used data from the IPS-GI, focusing on 38 fields sampling lines of sight in the diffuse medium. The fields are about 0.3$^{\circ}$ by 0.3$^{\circ}$ in size and each of them contains $\sim1000$ stars on average. The IPS-GI catalog has polarimetric measurements of over 40000 stars, over 18000 of which have ${P}/σ_{P} > 5$. We added distances and other parameters from auxiliary catalogs to over 36000 of these stars. We analyzed parameter distributions and correlations between parameters of a high-quality subsample of 10516 stars (i.e. $\sim275$ stars per field). As expected, the degree of polarization tends to increase with the extinction, producing higher values of polarization at greater distances or at lower absolute Galactic latitudes. Furthermore, we find evidence for a large-scale ordered Galactic magnetic field.

astro-ph.GA↗
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↗
arXiv2020

Recovering variable stars in large surveys: EA$_{\rm up}$ Algol-type class in the Catalina Survey

The discovery and characterization of Algol eclipsing binaries (EAs) provide an opportunity to contribute for a better picture of the structure and evolution of low-mass stars. However, the cadence of most current photometric surveys hinders the detection of EAs since the separation between observations is usually larger than the eclipse(s) duration and hence few measurements are found at the eclipses. Even when those objects are detected as variable, their periods can be missed if an appropriate oversampling factor is not used in the search tools. In this paper, we apply this approach to find the periods of stars cataloged in the Catalina Real-Time Transient Survey (CRTS) as EAs having unknown period (EA$_{\rm up}$). As a result, the periods of $\sim 56\%$ of them were determined. Eight objects were identified as low-mass binary systems and modeled with the Wilson \& Devinney synthesis code combined with a Monte-Carlo Markov Chain optimization procedure. The computed masses and radii are in agreement with theoretical models and show no evidence of inflated radii. This paper is the first of a series aiming to identify suspected binary systems in large surveys.

astro-ph.SR↗
arXiv2019

Characterization of the SPARC4 CCDs

We present the photometric characterization of the four iXon Ultra 888 CCD cameras of the SPARC4 instrument, which will be installed on the 1.6 m telescope of the Pico dos Dias Observatory in Brazil. We applied experimental methodologies for a systematic characterization of the read noise, electronic gain, dark current, and quantum efficiency of the CCDs. We have analyzed the statistical distribution of the read noise, and also its spatial gradient and temporal variability, where we obtained an average value of the read noise of 6.33 electrons. We applied the Janesick method to determine the electronic gain, where we obtained an average value of 3.35 e-/ADU. We have also obtained an average dark current of 0.00014 e-/pix/s for CCD internal temperature of -70 oC. We have inspected the dependency of the dark current with temperature and the spatial distribution of the dark current, where we found a variable profile in the CCD 9917. We developed an experiment using a bench mounted monochromator to obtain the spectral dependency of the quantum efficiency in the spectral range between 350 nm and 1100 nm, where we measured the quantum efficiency for each camera. The camera 9915 presents the highest quantum efficiency of 95.8 %. Our results are compared with those from the manufacturer. These experiments allow us to diagnose the performance of these CCD cameras, an important sub-system of the SPARC4 instrument. It also provides a systematic way for monitoring the aging of the CCDs.

astro-ph.IM↗
arXiv2017

Exploratory Spectroscopy of Magnetic Cataclysmic Variables Candidates and Other Variable Objects

The increasing number of synoptic surveys made by small robotic telescopes, such as the photometric Catalina Real-Time Transient Survey (CRTS), represents a unique opportunity for the discovery of variable sources and improves the statistical samples of such classes of objects. Our goal is the discovery of magnetic Cataclysmic Variables (mCVs). These are rare objects, which probe interesting accretion scenarios controlled by the white dwarf magnetic field. In particular, improved statistics of mCVs would help to address open questions on their formation and evolution. We performed an optical spectroscopy survey to search for signatures of magnetic accretion in 45 variable objects selected mostly from the CRTS. In this sample we found 32 CVs, 22 being mCV candidates from which 13 are previously unreported as such. If the proposed classifications are confirmed, it would represent an increase of 4% in the number of known polars and 12% in the number of known IPs. A fraction of our initial sample was classified as extragalactic sources or other types of variable stars by the inspection of the identification spectra. Despite the inherent complexity in identifying a source as a mCV, variability-based selection followed by spectroscopic snapshot observations has proved to be an efficient strategy for their discoveries, being a relatively inexpensive approach in terms of telescope time.

astro-ph.SR↗
arXiv2015

A New Optical Polarization Catalog for the Small Magellanic Cloud: The Magnetic Field Structure

We present a new optical polarimetric catalog for the Small Magellanic Cloud (SMC). It contains a total of 7207 stars, located in the Northeast (NE) and Wing sections of the SMC and part of the Magellanic Bridge. This new catalog is a significant improvement compared to previous polarimetric catalogs for the SMC. We used it to study the sky-projected interstellar magnetic field structure of the SMC. Three trends were observed for the ordered magnetic field direction at position angles of $(65 \pm 10)$ deg, $(115 \pm 10)$ deg, and $(150 \pm 10)$ deg. Our results suggest the existence of an ordered magnetic field aligned with the Magellanic Bridge direction and SMC's Bar in the NE region, which have position angles roughly at $115.4$ deg and $45$ deg, respectively. However, the overall magnetic field structure is fairly complex. The trends at $115$ deg and $150$ deg may be correlated with the SMC's bimodal structure, observed in Cepheids' distances and HI velocities. We derived a value of $B_{sky} = (0.947 \pm 0.079)~μG$ for the ordered sky-projected magnetic field, and $δB = (1.465 \pm 0.069)~μG$ for the turbulent magnetic field. This estimate of $B_{sky}$ is significantly larger (by a factor of $\sim10$) than the line-of-sight field derived from Faraday rotation observations, suggesting that most of the ordered field component is on the plane of the sky. A turbulent magnetic field stronger than the ordered field agrees with observed estimates for other irregular and spiral galaxies. For the SMC the $B_{sky}/δB$ ratio is closer to what is observed for our Galaxy than other irregular dwarf galaxies.

astro-ph.GA↗
arXiv2015

MLS110213:022733+130617: A new eclipsing polar above the period gap

This study confirms MLS110213:022733+130617 as a new eclipsing polar. We performed optical spectroscopic, polarimetric and photometric follow-up of this variable source identified by the Catalina Real Time Transient Survey. Using the mid-eclipse times, we estimated an orbital period of 3.787 h, which is above the orbital period gap of the cataclysmic variables. There are nine other known polars with longer orbital periods, and only four of them are eclipsing. We identified high and low-brightness states and high polarization modulated with the orbital period. The spectra are typical of polars, with strong high ionization emission lines and inverted Balmer decrement. The HeII4686 A line is as strong as Hbeta. We modelled the photometric and polarimetric bright-state light curves using the CYCLOPS code. Our modelling suggests an extended emitting region on the WD surface, with a mean temperature of 9 keV and B in the range 18 -- 33 MG, although the possibility that it could be a two-pole accretor cannot yet be ruled out. The WD mass estimated from the shock temperature is 0.67 Msol. The derived parameters are consistent with the eclipse profile. The distance was estimated as 406+- 54 pc using the Period-Luminosity-Colours method. MLS110213 populates a rare sub-group of polars, near the upper limit of the period distribution, important to understand the evolution of mCVs.

astro-ph.SR↗
arXiv2014

Measuring the continuum polarization with ESPaDOnS

Our goal is to test the feasibility to obtain accurate measurements of the continuum polarization from high-resolution spectra using the spectropolarimetric mode of ESPaDOnS. We used the new pipeline OPERA to reduce recent and archived ESPaDOnS data. A couple of standard polarization stars and several science objects were tested for the linear mode. In addition, the circular mode was tested using several objects from the archive with expected null polarization. Synthetic broad-band polarization was computed from the ESPaDOnS continuum polarization spectra and compared with published values (when available) to quantify the accuracy of the instrument. The continuum linear polarization measured by ESPaDOnS is consistent with broad-band polarimetry measurements available in the literature. The accuracy in the degree of linear polarization is around 0.2-0.3% considering the full sample. The accuracy in polarization position angle using the most polarized objects is better than 5deg. Consistent with this, the instrumental polarization computed for the circular continuum polarization is also between 0.2-0.3%. Our results suggest that measurements of the continuum polarization using ESPaDOnS are viable and can be used to study many astrophysical objects.

astro-ph.IM↗
arXiv2013

Magnetic field dispersion in the neighbourhood of Bok Globules

We performed an observational study of the relation between the interstellar magnetic field alignment and star formation in twenty (20) sky regions containing Bok Globules. The presence of young stellar objects in the globules is verified by a search of infrared sources with spectral energy distribution compatible with a pre main-sequence star. The interstellar magnetic field direction is mapped using optical polarimetry. These maps are used to estimate the dispersion of the interstellar magnetic field direction in each region from a Gaussian fit, sigma_B. In addition to the Gaussian dispersion, we propose a new parameter, eta, to measure the magnetic field alignment that does not rely on any function fitting. Statistical tests show that the dispersion of the magnetic field direction is different in star forming globules relative to quiescent globules. Specifically, the less organised magnetic fields occur in regions having young stellar objects.

astro-ph.SR↗