arXiv subjects

A. Álvarez-Hernández

Publications and source records attributed to A. Álvarez-Hernández.

5 recordsLinked to original sources

arXiv2025

The orbital period and inclination of the neutron star X-ray transient MAXI J1807+132

The neutron star X-ray transient MAXI J1807+132 has undergone outbursts in 2017, 2019, and 2023. We conducted an $R$-band time series photometry campaign using the Isaac Newton Telescope during the 2022 quiescent state. We detected a periodic variation in the light curve, consistent with ellipsoidal modulation, which allowed us to determine an orbital period of $P_{\rm orb} = 4.258 \pm 0.008$ hr. By modelling the light curve, we obtained a binary inclination of $ i = 72\pm5 \, °$ and a mass ratio $q = 0.24^{+0.19}_{-0.14}$ ($68$ per cent confidence level). Furthermore, our analysis supports an early M-dwarf companion that contributes between 30 and 50 per cent to the total flux in the $R$-band. We extend the previously established absolute magnitude versus orbital period correlation for black hole X-ray transients to neutron star systems. We applied the correlation to MAXI J1807+132, estimating its distance as $6.3 \pm 0.7$ kpc and its height above the Galactic plane to be $1.6 \pm 0.2$ kpc.

astro-ph.HE↗

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↗

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↗

arXiv2020

The binary mass ratio in the black hole transient MAXI J1820+070

We present intermediate resolution spectroscopy of the optical counterpart to the black hole X-ray transient MAXI J1820+070 (=ASASSN-18ey) obtained with the OSIRIS spectrograph on the 10.4-m Gran Telescopio Canarias. The observations were performed with the source close to the quiescent state and before the onset of renewed activity in August 2019. We make use of these data and K-type dwarf templates taken with the same instrumental configuration to measure the projected rotational velocity of the donor star. We find $v_{rot} \sin i = 84 \pm 5$ km s$^{-1}$ ($1\!-\!σ$), which implies a donor to black-hole mass ratio $q = {M_2}/{M_1} = 0.072 \pm 0.012$ for the case of a tidally locked and Roche-lobe filling donor star. The derived dynamical masses for the stellar components are $M_1 = (5.95 \pm 0.22)\sin ^{-3}i$ $M_\odot$ and $M_2 = (0.43 \pm 0.08) \sin^{-3}i$ $M_\odot$. The use of $q$, combined with estimates of the accretion disk size at the time of the optical spectroscopy, allows us to revise our previous orbital inclination constraints to $66^{\circ} < i < 81^{\circ}$. These values lead to 95% confidence level limits on the masses of $5.73 <M_1(M_\odot) < 8.34$ and $0.28 < M_2(M_\odot) < 0.77$. Adopting instead the $63 \pm 3^{\circ}$ orientation angle of the radio jet as the binary inclination leads to $M_1 = 8.48^{+0.79}_{-0.72} M_\odot$ and $M_2 = 0.61^{+0.13}_{-0.12} M_\odot$ ($1\!-\!σ$).

astro-ph.HE↗

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↗