Unveiling optical signatures of outflows in accreting white dwarfs

Abstract

Accreting white dwarfs are known to show signatures of wind-type outflows in the ultraviolet. At optical wavelengths, however, wind detections have only been reported for a few sources. We present GTC-10.4m optical spectroscopy of four accreting white dwarfs (BZ Cam, V751 Cyg, MV Lyr, and V425 Cas) observed during luminous epochs, when their optical emission is expected to be dominated by the accretion disc. We focused the analysis on four emission lines: H$\alpha$ and He I $\lambda$5876, $\lambda$6678, $\lambda$7065. Line profiles are complex and variable on short (minutes) and long (days to weeks) time scales, with transient absorption and emission components. Among them, we detect strong blue-shifted absorptions at $\gtrsim 1000$ km s${}^{-1}$. These high-velocity components, present only in the blue wing of the emission lines, are observed in all four sources and could be associated with accretion disc winds. For MV Lyr and V425 Cas, these would represent the first detection of optical outflows in these objects, while in the case of BZ Cam and V751 Cyg, the presence of outflows has been previously reported. This study suggests that, in addition to ultraviolet winds, optical outflows might be also common in accreting white dwarfs. We discuss the observational properties of these winds and their possible similarity to those detected in accreting black holes and neutrons stars.

Accepted for publication in A&A

References in corpus (16)

• Array Programming with NumPy
• SW Sextantis stars: the dominant population of CVs with orbital periods between 3-4 hours
• Hard-state accretion disk winds from black holes: the revealing case of MAXI J1820+070
• Spectroscopic search for new SW Sextantis stars in the 3-4 hour orbital period range -- I
• Near-infrared emission lines trace the state-independent accretion disc wind of the black hole transient MAXI J1820+070
• A persistent ultraviolet outflow from an accreting neutron star binary transient
• The Geometry and Ionization Structure of the Wind in the Eclipsing Nova-like Variables RW Tri and UX UMa
• Thermal and radiation driving can produce observable disk winds in hard-state X-ray binaries
• Hard-state optical wind during the discovery outburst of the black-hole X-ray dipper MAXI J1803-298
• Discovery of optical outflows and inflows in the black hole candidate GRS 1716-249
• Discovery of optical and infrared accretion disc wind signatures in the black hole candidate MAXI J1348-630
• The complex evolution of the X-ray binary transient MAXI J1807+132 along the decay of its discovery outburst
• Simultaneous X-ray and optical spectroscopy of V404 Cygni supports the multi-phase nature of X-ray binary accretion disc winds
• Observations of V592 Cas - An Outflow at Optical Wavelengths
• Optical nebular emission following the most luminous outburst of Aquila X-1
• Structure of the accretion flow of IX Velorum as revealed by high-resolution spectroscopy

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• SIROCCO: A Publicly Available Monte Carlo Ionization and Radiative Transfer Code for Astrophysical Outflows
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• A Diagnostic Kit for Optical Emission Lines Shaped by Accretion Disc Winds