arXiv subjects

P. Rodríguez-Gil

Publications and source records attributed to P. Rodríguez-Gil.

At least 19 recordsLinked to original sources

arXiv2025

The evolutionary history of ultra-compact accreting binaries. I. Chemical abundances and formation channel of the eclipsing AM CVn system ZTF J225237.05-051917.4 from HST spectroscopy

AM Canum Venaticorum (AM CVn) stars are ultra-compact binary systems composed of a white dwarf (WD) primary accreting from a H-deficient donor. They are important as potential progenitors of Type Ia supernovae and laboratories for gravitational-wave studies, yet their evolutionary history remains unsolved. Three formation channels have been proposed: the WD channel, the He-star channel, and the cataclysmic variable (CV) channel. We aim to provide the first accurate measurements of the fundamental parameters of the accretor in ZTFJ225237.05-051917.4, including the abundances of key elements such as C, N, and Si, by analysing UV spectra obtained with the Hubble Space Telescope. These measurements provide new insight into the system's evolutionary history and establish it as a benchmark to develop our pipeline for application to a larger sample of AM CVns. We determine the binary parameters from photometric modelling and constrain the atmospheric parameters of the WD accretor, including Teff, logg, and chemical abundances, by fitting the UV spectrum with synthetic spectral models. We then infer the system's formation channel by comparing our results with theoretical evolutionary models. We measure a Teff=23300$\pm$600K and a surface gravity of logg=8.4$\pm$0.3, which implies an accretor mass of 0.86$\pm$0.16 solar masses. We find a high N/C abundance ratio by mass of >153. The accretor is significantly hotter than previous estimates based on simplified blackbody fits to the spectral energy distribution, underscoring the importance of detailed spectral modelling for determining accurate system parameters. Our results show that UV spectroscopy is well-suited to constraining the formation channels of AM CVn systems. We conclude that the He-star channel can be excluded based on the high N/C ratio, while the WD and CV channels remain consistent with the observations.

astro-ph.SR↗

arXiv2023

Dynamical mass of the white dwarf in XY Ari: a test for intermediate polar X-ray spectral models

We present a dynamical study of the eclipsing intermediate polar XY Ari based on time-resolved near-infrared spectroscopy obtained with the EMIR spectrograph on the 10.4-m Gran Telescopio Canarias. Using main sequence template spectra taken with the same instrument setup as the target spectra, we measure a radial velocity amplitude of the late K-type donor star $K_2=256 \pm 2$ km s$^{-1}$. We also obtain the rotational broadening of its photospheric lines $v_\mathrm{rot} \sin i = 141 \pm 3$ km s$^{-1}$. From these and the eclipse geometry, we derive a donor-to-white-dwarf mass ratio $q = M_2/M_1 = 0.62 \pm 0.02$, an orbital inclination $i = 80.8^{\circ} \pm 0.5^{\circ}$ and dynamical masses $M_{1} = 1.21 \pm 0.04 \, \mathrm{M}_{\odot}$ and $M_2 = 0.75 \pm 0.04 \, \mathrm{M}_{\odot}$ ($1 σ$). This result places the white dwarf in XY Ari as one of the three most massive known in a cataclysmic variable. Comparison with white dwarf mass estimates from X-ray spectral studies could indicate the necessity of an improvement of the X-ray models and/or analysis techniques, as a number of X-ray white dwarf masses are in disagreement with the dynamical mass value.

astro-ph.SR↗

arXiv2023

The planetary nebula NGC 6153 through the eyes of MUSE

In this contribution, we present the results of a study on the high abundance discrepancy factor (ADF $\sim$ 10) planetary nebula (PN) NGC 6153 with MUSE. We have constructed flux maps for dozens of emission lines, that allowed us to build spatially resolved maps of extinction, electron temperature ($T_{\rm e}$), electron density ($n_{\rm e}$), and ionic abundances. We have simultaneously constructed ADF maps for O$^+$ and O$^{2+}$ and found that they centrally peak in this PN, with a remarkable spatial coincidence with the low $T_{\rm e}$ found from recombination line diagnostics. This finding strongly supports the hypothesis that two distinct gas phases co-exist: one cold and metal-rich, and a second warm and with ``normal'' metal content. We show that to build $T_{\rm e}$([N II]) and ionic abundance maps of low-ionization species for these objects, recombination contribution to the auroral [N II] and [O II] lines must be properly evaluated and corrected.

astro-ph.GA↗

arXiv2022

A refined dynamical mass for the black hole in the X-ray transient XTE J1859+226

We present two contiguous nights of simultaneous time-resolved GTC spectroscopy and WHT photometry of the black hole X-ray transient XTE J1859+226, obtained in 2017 July during quiescence. Cross-correlation of the individual spectra against a late K-type spectral template enabled us to constrain the orbital period to $0.276 \pm 0.003$ d and the radial velocity semi-amplitude of the donor star to $K_2 = 550 \pm 59$ km s$^{-1}$. An ellipsoidal modulation is detected in the photometric $r$- and $i$-band light curves, although it is strongly contaminated by flickering activity. By exploiting correlations between the properties of the double-peaked H$α$ emission-line profile and the binary parameters, we derived an orbital inclination of $66.6 \pm 4.3$ deg, a refined $K_2 = 562 \pm 40$ km s$^{-1}$ and mass ratio $q = M_2/M_1 = 0.07 \pm 0.01$. From these values we obtained an updated black hole mass of $M_1 = 7.8 \pm 1.9$ M$_\odot$. An independent mass estimate based on X-ray timing agrees well with our value, which gives further support for the outburst QPO triplet being explained by the relativistic precession model. We also obtained a companion star mass $M_2 = 0.55 \pm 0.16$ M$_\odot$, which is consistent with its K5-K7 V spectral type.

astro-ph.HE↗

arXiv2022

A tentative 114-minute orbital period challenges the ultra-compact nature of the X-ray binary 4U 1812-12

We present a detailed time-resolved photometric study of the ultra-compact X-ray binary candidate 4U 1812-12. The multicolor light curves obtained with HiPERCAM on the 10.4-m Gran Telescopio Canarias show an aprox 114 min modulation similar to a superhump. Under this interpretation, this period should lie very close to the orbital period of the system. Contrary to what its other observational properties suggest (namely, persistent dim luminosity, low optical-to-X-ray flux ratio and lack of hydrogen features in the optical spectrum), this implies that 4U1812-12 is most likely not an ultra-compact X-ray binary, which are usually defined as systems with orbital periods lower than 80 min. We discuss the nature of the system, showing that a scenario in which 4U 1812-12 is the progenitor of an ultra-compact X-ray binary may reconcile all the observables.

astro-ph.HE↗

arXiv2021

The intermediate polar cataclysmic variable GK Persei 120 years after the nova explosion: a first dynamical mass study

We present a complete dynamical study of the intermediate polar and dwarf nova cataclysmic variable GK Per (Nova Persei 1901) based on a multi-site optical spectroscopy and $R$-band photometry campaign. The radial velocity curve of the evolved donor star has a semi-amplitude $K_2=126.4 \pm 0.9 \, \mathrm{km}\,\mathrm{s}^{-1}$ and an orbital period $P=1.996872 \pm 0.000009 \, \mathrm{d}$. We refine the projected rotational velocity of the donor star to $v_\mathrm{rot} \sin i = 52 \pm 2 \, \mathrm{km}\,\mathrm{s}^{-1}$ which, together with $K_2$, provides a donor star to white dwarf mass ratio $q=M_2/M_1=0.38 \pm 0.03$. We also determine the orbital inclination of the system by modelling the phase-folded ellipsoidal light curve and obtain $i=67^{\circ} \pm 5^{\circ}$. The resulting dynamical masses are $M_{1}=1.03^{+0.16}_{-0.11} \, \mathrm{M}_{\odot}$ and $M_2 = 0.39^{+0.07}_{-0.06} \, \mathrm{M}_{\odot}$ at $68$ per cent confidence level. The white dwarf dynamical mass is compared with estimates obtained by modelling the decline light curve of the $1901$ nova event and X-ray spectroscopy. The best matching mass estimates come from the nova light curve models and an X-ray data analysis that uses the ratio between the Alfvén radius in quiescence and during dwarf nova outburst.

astro-ph.SR↗

arXiv2021

HiPERCAM: a quintuple-beam, high-speed optical imager on the 10.4-m Gran Telescopio Canarias

HiPERCAM is a portable, quintuple-beam optical imager that saw first light on the 10.4-m Gran Telescopio Canarias (GTC) in 2018. The instrument uses re-imaging optics and 4 dichroic beamsplitters to record $u_s g_s r_s i_s z_s$ ($320-1060$ nm) images simultaneously on its five CCD cameras, each of 3.1 arcmin (diagonal) field of view. The detectors in HiPERCAM are frame-transfer devices cooled thermo-electrically to 183 K, thereby allowing both long-exposure, deep imaging of faint targets, as well as high-speed (over 1000 windowed frames per second) imaging of rapidly varying targets. A comparison-star pick-off system in the telescope focal plane increases the effective field of view to 6.7 arcmin for differential photometry. Combining HiPERCAM with the world's largest optical telescope enables the detection of astronomical sources to $g_s \sim 23$ in 1 s and $g_s \sim 28$ in 1 h. In this paper we describe the scientific motivation behind HiPERCAM, present its design, report on its measured performance, and outline some planned enhancements.

astro-ph.IM↗

arXiv2021

A transmission spectrum of the planet candidate WD 1856+534 b and a lower limit to its mass

The cool white dwarf WD 1856+534 was found to be transited by a Jupiter-sized object with a mass at or below 14 M$_{\rm{Jup}}$. We used the GTC telescope to obtain and analyse photometry and low resolution spectroscopy of six transits of WD 1856+534 b, with the intention to derive the slope of the transmission spectrum, towards an eventual detection of Rayleigh scattering of the particles in its atmosphere. Such a slope, assuming a cloud-free atmosphere dominated by Rayleigh scattering, could be translated into an estimation of the mass of WD 1856+534 b. However, the resultant transmission spectrum is essentially flat, and therefore permits only the determination of lower mass limits of 2.4 M$_{\rm{Jup}}$ at the 2-$σ$ level, or 1.6 M$_{\rm{Jup}}$ at 3-$σ$. These limits have implications for some of the proposed formation scenarios for the object. We elaborate on the potential effects of clouds and hazes in our estimations, based on previous studies of Jupiter and Titan. In addition, we detected an H$α$ absorption feature in the combined spectrum of the host white dwarf, that leads to the assignation of a DA classification and allows derivation of an independent set of atmospheric parameters. Furthermore, the epochs of five transits were measured with sub-second precision, which demonstrates that additional objects more massive than $\approx$5 M$_{\rm{Jup}}$ and with periods longer than $O(100)$ days could be detected through the light travel time effect

astro-ph.EP↗

arXiv2020

When the disc's away, the stars will play: dynamical masses in the nova-like variable KR Aur with a pinch of accretion

We obtained time-resolved optical photometry and spectroscopy of the nova-like variable KR Aurigae in the low state. The spectrum reveals a DAB white dwarf and a mid-M dwarf companion. Using the companion star's $i$-band ellipsoidal modulation we refine the binary orbital period to be $P = 3.906519 \pm 0.000001$ h. The light curve and the spectra show flaring activity due to episodic accretion. One of these events produced brightness oscillations at a period of 27.4 min, that we suggest to be related with the rotation period of a possibly magnetic white dwarf at either 27.4 or 54.8 min. Spectral modelling provided a spectral type of M4-5 for the companion star and $T_{1}=27148 \pm 496$ K, $\log g=8.90 \pm 0.07$, and $\log (\mathrm{He/H})= -0.79^{+0.07}_{-0.08}~~$ for the white dwarf. By simultaneously fitting absorption- and emission-line radial velocity curves and the ellipsoidal light curve, we determined the stellar masses to be $M_1 = 0.94^{+0.15}_{-0.11}~$ $M_\odot$ and $M_2 = 0.37^{+0.07}_{-0.07}~$ $M_\odot$ for the white dwarf and the M-dwarf, respectively, and an orbital inclination of $47^{+1^{\rm o}}_{-2^{\rm o}}$. Finally, we analyse time-resolved spectroscopy acquired when the system was at an $i$-band magnitude of 17.1, about 1.3 mag brighter than it was in the low state. In this intermediate state the line profiles contain an emission S-wave delayed by $\simeq 0.2$ orbital cycle relative to the motion of the white dwarf, similar to what is observed in SW Sextantis stars in the high state.

astro-ph.SR↗

arXiv2020

IGAPS: the merged IPHAS and UVEX optical surveys of theNorthern Galactic Plane

The INT Galactic Plane Survey (IGAPS) is the merger of the optical photometric surveys, IPHAS and UVEX, based on data from the Isaac Newton Telescope (INT) obtained between 2003 and 2018. Here, we present the IGAPS point source catalogue. It contains 295.4 million rows providing photometry in the filters, i, r, narrow-band Halpha, g and U_RGO. The IGAPS footprint fills the Galactic coordinate range, |b| < 5deg and 30deg < l < 215deg. A uniform calibration, referred to the Pan-STARRS system, is applied to g, r and i, while the Halpha calibration is linked to r and then is reconciled via field overlaps. The astrometry in all 5 bands has been recalculated on the Gaia DR2 frame. Down to i ~ 20 mag (Vega system), most stars are also detected in g, r and Halpha. As exposures in the r band were obtained within the IPHAS and UVEX surveys a few years apart, typically, the catalogue includes two distinct r measures, r_I and r_U. The r 10sigma limiting magnitude is ~21, with median seeing 1.1 arcsec. Between ~13th and ~19th magnitudes in all bands, the photometry is internally reproducible to within 0.02 magnitudes. Stars brighter than r=19.5 have been tested for narrow-band Halpha excess signalling line emission, and for variation exceeding |r_I-r_U| = 0.2 mag. We find and flag 8292 candidate emission line stars and over 53000 variables (both at >5sigma confidence). The 174-column catalogue will be available via CDS Strasbourg.

astro-ph.IM↗

arXiv2019

Latest advances in the abundance discrepancy problem in photoionized nebulae

In this paper, we will focus on the advances made in the last few years regarding the abundance discrepancy problem in ionized nebulae. We will show the importance of collecting deep, high-quality data of H II regions and planetary nebulae taken with the most advanced instruments attached to the largest ground-based telescopes. We will also present a sketch of some new scenarios proposed to explain the abundance discrepancy.

astro-ph.SR↗

arXiv2018

The 1989 and 2015 outbursts of V404 Cygni: a global study of wind-related optical features

The black hole transient V404 Cygni exhibited a bright outburst in June 2015 that was intensively followed over a wide range of wavelengths. Our team obtained high time resolution optical spectroscopy (~90 s), which included a detailed coverage of the most active phase of the event. We present a database consisting of 651 optical spectra obtained during this event, that we combine with 58 spectra gathered during the fainter December 2015 sequel outburst, as well as with 57 spectra from the 1989 event. We previously reported the discovery of wind-related features (P-Cygni and broad-wing line profiles) during both 2015 outbursts. Here, we build diagnostic diagrams that enable us to study the evolution of typical emission line parameters, such as line fluxes and equivalent widths, and develop a technique to systematically detect outflow signatures. We find that these are present throughout the outburst, even at very low optical fluxes, and that both types of outflow features are observed simultaneously in some spectra, confirming the idea of a common origin. We also show that the nebular phases depict loop patterns in many diagnostic diagrams, while P-Cygni profiles are highly variable on time-scales of minutes. The comparison between the three outbursts reveals that the spectra obtained during June and December 2015 share many similarities, while those from 1989 exhibit narrower emission lines and lower wind terminal velocities. The diagnostic diagrams presented in this work have been produced using standard measurement techniques and thus may be applied to other active low-mass X-ray binaries.

astro-ph.HE↗

arXiv2018

Fast spectrophotometry of WD 1145+017

WD 1145+017 is currently the only white dwarf known to exhibit periodic transits of planetary debris as well as absorption lines from circumstellar gas. We present the first simultaneous fast optical spectrophotometry and broad-band photometry of the system, obtained with the Gran Telescopio Canarias (GTC) and the Liverpool Telescope (LT), respectively. The observations spanned $5.5$ h, somewhat longer than the $4.5$-h orbital period of the debris. Dividing the GTC spectrophotometry into five wavelength bands reveals no significant colour differences, confirming grey transits in the optical. We argue that absorption by an optically thick structure is a plausible alternative explanation for the achromatic nature of the transits that can allow the presence of small-sized ($\simμ$m) particles. The longest ($87$ min) and deepest ($50$ per cent attenuation) transit recorded in our data exhibits a complex structure around minimum light that can be well modelled by multiple overlapping dust clouds. The strongest circumstellar absorption line, Fe II $λ$5169, significantly weakens during this transit, with its equivalent width reducing from a mean out-of-transit value of $2$ Å to $1$ Å in-transit, supporting spatial correlation between the circumstellar gas and dust. Finally, we made use of the Gaia Data Release 2 and archival photometry to determine the white dwarf parameters. Adopting a helium-dominated atmosphere containing traces of hydrogen and metals, and a reddening $E(B-V)=0.01$ we find $T_\mathrm{eff}=15\,020 \pm 520$ K, $\log g=8.07\pm0.07$, corresponding to $M_\mathrm{WD}=0.63\pm0.05\ \mbox{$\mathrm{M}_{\odot}$}$ and a cooling age of $224\pm30$ Myr.

astro-ph.SR↗

arXiv2017

A Recurrent Nova Super-Remnant in the Andromeda Galaxy

Here we report that the most rapidly recurring nova, M31N 2008-12a, which erupts annually, is surrounded by a "nova super-remnant" which demonstrates that M31N 2008-12a has erupted with high frequency for millions of years.

astro-ph.SR↗

arXiv2017

Two white dwarfs in ultrashort binaries with detached, eclipsing, likely substellar companions detected by K2

Using data from the extended Kepler mission in K2 Campaign 10 we identify two eclipsing binaries containing white dwarfs with cool companions that have extremely short orbital periods of only 71.2 min (SDSS J1205-0242, a.k.a. EPIC 201283111) and 72.5 min (SDSS J1231+0041, a.k.a. EPIC 248368963). Despite their short periods, both systems are detached with small, low-mass companions, in one case a brown dwarf, and the other case either a brown dwarf or a low-mass star. We present follow-up photometry and spectroscopy of both binaries, as well as phase-resolved spectroscopy of the brighter system, and use these data to place preliminary estimates on the physical and binary parameters. SDSS J1205-0242 is composed of a $0.39\pm0.02$M$_\odot$ helium-core white dwarf which is totally eclipsed by a $0.049\pm0.006$M$_\odot$ ($51\pm6$M$_J$) brown dwarf companion, while SDSS J1231+0041 is composed of a $0.56\pm0.07$M$_\odot$ white dwarf which is partially eclipsed by a companion of mass $\lesssim 0.095$M$_\odot$. In the case of SDSS J1205-0242 we look at the combined constraints from common-envelope evolution and brown dwarf models; the system is compatible with similar constraints from other post common-envelope binaries given the current parameter uncertainties, but has potential for future refinement.

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arXiv2016

Imaging the elusive H-poor gas in planetary nebulae with large abundance discrepancy factors

The discrepancy between abundances computed using optical recombination lines (ORLs) and collisionally excited lines (CELs) is a major, unresolved problem with significant implications for the determination of chemical abundances throughout the Universe. In planetary nebulae (PNe), the most common explanation for the discrepancy is that two different gas phases coexist: a hot component with standard metallicity, and a much colder plasma enhanced in heavy elements. This dual nature is not predicted by mass loss theories, and direct observational support for it is still weak. In this work, we present our recent findings that demonstrate that the largest abundance discrepancies are associated with close binary central stars. OSIRIS-GTC tunable filter imaging of the faint O II ORLs and MUSE-VLT deep 2D spectrophotometry confirm that O II ORL emission is more centrally concentrated than that of [O III] CELs and, therefore, that the abundance discrepancy may be closely linked to binary evolution.

astro-ph.SR↗

arXiv2016

The double-degenerate, super-Chandrasekhar nucleus of the planetary nebula Henize 2-428

The planetary nebula (PN) stage is the ultimate fate of stars with mass 1 to 8 solar masses (M$_\odot$). The origin of their complex morphologies is poorly understood, although several mechanisms involving binary interaction have been proposed. In close binary systems, the orbital separation is short enough for the primary star to overfill its Roche lobe as it expands during the Asymptotic Giant Branch (AGB) phase. The excess material ends up forming a common-envelope (CE) surrounding both stars. Drag forces would then result in the envelope being ejected into a bipolar PN whose equator is coincident with the orbital plane of the system. Systems in which both stars have ejected their envelopes and evolve towards the white dwarf (WD) stage are called double-degenerates. Here we report that Henize 2-428 has a double-degenerate core with a combined mass unambiguously above the Chandrasekhar limit of 1.4 M$_\odot$. According to its short orbital period (4.2 hours) and total mass (1.76 M$_\odot$), the system should merge in 700 million years, triggering a Type Ia supernova (SN Ia) event. This finding supports the double-degenerate, super-Chandrasekhar evolutionary channel for the formation of SNe Ia.

astro-ph.SR↗

arXiv2015

The binary millisecond pulsar PSR J1023+0038 during its accretion state - I. Optical variability

We present time-resolved optical photometry of the binary millisecond `redback' pulsar PSR J1023+0038 (=AY Sex) during its low-mass X-ray binary phase. The light curves taken between 2014 January and April show an underlying sinusoidal modulation due to the irradiated secondary star and accretion disc. We also observe superimposed rapid flaring on time-scales as short as ~20 s with amplitudes of ~0.1-0.5 mag and additional large flare events on time-scales of ~5-60 min with amplitudes ~0.5-1.0 mag. The power density spectrum of the optical flare light curves is dominated by a red-noise component, typical of aperiodic activity in X-ray binaries. Simultaneous X-ray and UV observations by the Swift satellite reveal strong correlations that are consistent with X-ray reprocessing of the UV light, most likely in the outer regions of the accretion disc. On some nights we also observe sharp-edged, rectangular, flat-bottomed dips randomly distributed in orbital phase, with a median duration of ~250 s and a median ingress/egress time of ~20 s. These rectangular dips are similar to the mode-switching behaviour between disc `active' and `passive' luminosity states, observed in the X-ray light curves of other redback millisecond pulsars. This is the first time that the optical analogue of the X-ray mode-switching has been observed. The properties of the passive and active state light curves can be explained in terms of clumpy accretion from a trapped inner accretion disc near the corotation radius, resulting in rectangular, flat-bottomed optical and X-ray light curves.

astro-ph.HE↗