MASTER OT J030227.28+191754.5: A Dwarf Nova at a Massive Oxygen–Neon White Dwarf System?

Kimura, M.; Kashiyama, Kazumi; Shigeyama, Toshikazu; Tampo, Yusuke; Yamada, S.; Enoto, T.

doi:10.3847/1538-4357/acd933

ApJ

2023

DOI: 10.3847/1538-4357/acd933

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MASTER OT J030227.28+191754.5: A Dwarf Nova at a Massive Oxygen–Neon White Dwarf System?

M. Kimura

Kazumi Kashiyama

Toshikazu Shigeyama

et al.

Abstract: We present timing and spectral analysis results of the NICER and NuSTAR observations of the dwarf nova MASTER OT J030227.28+191754.5 during the 2021–2022 outburst. The soft X-ray component was found to be dominated by blackbody radiation with a temperature of ∼30 eV and also showed prominent oxygen and neon emission lines. The blackbody luminosity exceeded 1034 erg s−1, which is consistent with theoretical predictions, and then decreased more than an order of magnitude in 3.5 days. The inferred abundances of o… Show more

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2024

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Cited by 3 publications

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A disc wind origin for the optical spectra of dwarf novae in outburst

Tampo,

Knigge,

Long

et al. 2024

Monthly Notices of the Royal Astronomical Society

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Many high-state cataclysmic variables (CVs) exhibit blue-shifted absorption features in their ultraviolet (UV) spectra – a smoking-gun signature of outflows. However, the impact of these outflows on optical spectra remains much more uncertain. During its recent outburst, the eclipsing dwarf nova V455 And displayed strong optical emission lines whose cores were narrower than expected from a Keplerian disc. Here, we explore whether disc + wind models developed for matching UV observations of CVs can also account for these optical spectra. Importantly, V455 And was extremely bright at outburst maximum: the accretion rate implied by fitting the optical continuum with a standard disc model is $\dot{M}_{\rm acc} \simeq 10^{-7}~{\rm M}_\odot ~{\rm yr^{-1}}$. Allowing for continuum reprocessing in the outflow helps to relax this constraint. A disc wind can also broadly reproduce the optical emission lines, but only if the wind is (i) highly mass-loaded, with a mass-loss rate reaching $\dot{M}_{\rm wind} \simeq 0.4 \dot{M}_{\rm acc}$, and/or (ii) clumpy, with a volume filling factor $f_V \simeq 0.1$. The same models can describe the spectral evolution across the outburst, simply by lowering $\dot{M}_{\rm acc}$ and $\dot{M}_{\rm wind}$. Extending these models to lower inclinations and into the UV produces spectra consistent with those observed in face-on high-state CVs. We also find, for the first time in simulations of this type, P-Cygni-like absorption features in the Balmer series, as have been observed in both CVs and X-ray binaries. Overall, dense disc winds provide a promising framework for explaining multiple observational signatures seen in high-state CVs, but theoretical challenges persist.

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A disc wind origin for the optical spectra of dwarf novae in outburst

Tampo,

Knigge,

Long

et al. 2024

Monthly Notices of the Royal Astronomical Society

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MASTER OT J030227.28+191754.5: An unprecedentedly energetic dwarf nova outburst

Tampo,

Kato,

Isogai

et al. 2024

Publications of the Astronomical Society of Japan

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We present a detailed study of the MASTER OT J030227.28$+$191754.5 outburst in 2021–2022, which reached an amplitude of $10.2\:$mag and a duration of $60\:$d. The detections of (1) the double-peaked optical emission lines, and (2) the early and ordinary superhumps, established that MASTER OT J030227.28$+$191754.5 is an extremely energetic WZ Sge-type dwarf nova (DN). Based on the superhump observations, we obtained its orbital period and mass ratio as $0.05986(1)\:$d and 0.063(1), respectively. These values are within a typical range for low-mass-ratio DNe. According to the binary parameters derived based on the thermal–tidal instability model, our analyses showed that (1) the standard disk model requires an accretion rate $\simeq\!\! 10^{20}\:$g$\:$s$^{-1}$ to explain its peak optical luminosity, and (2) large mass was stored in the disk at the outburst onset. These factors cannot be explained solely by the impact of its massive ($\gtrsim\!\! 1.15\, M_{\odot }$) primary white dwarf implied by Kimura et al. (2023, ApJ, 951, 124). Instead, we propose that the probable origin of this enormously energetic DN outburst is the even lower quiescence viscosity than other WZ Sge-type DNe. This discussion is qualitatively valid for most possible binary parameter spaces unless the inclination is low enough ($\lesssim\!\! 40^\circ$) for the disk to be bright, explaining the outburst amplitude. Such low inclinations, however, would not allow detectable amplitude of early superhumps in the current thermal–tidal instability model. The optical spectra at outburst maximum showed strong emission lines of the Balmer, He i, and He ii series, the core of which is narrower than $\sim \! 800\:$km$\:$s$^{-1}$. Considering its binary parameters, a Keplerian disk cannot explain this narrow component, but the presumable origin is disk winds.

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X-Ray Spectroscopy of the Dwarf Nova Z Chamaeleontis in Quiescence and Outburst Using the XMM-Newton Observatory

Balman,

Schlegel,

Godon

et al. 2024

ApJ

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We present X-ray spectroscopy of the SU UMa–type dwarf nova Z Chamaeleontis using the European Photon Imaging Camera and reflection grating spectrometer (RGS) instruments on board the XMM-Newton observatory. The quiescent system can be modeled by collisional equilibrium (CIE) or nonequilibrium plasma models, yielding a kT of 8.2–13.0 keV at a luminosity of (5.0–6.0) × 1030 erg s−1. The spectra yield better χ ν 2 using partially covering absorbers of cold and/or photoionized nature. The ionized absorber has an equivalent N H = (3.4–5.9) × 1022 cm−2 and a log(ξ) = 3.5–3.7 with a (50–60)% covering fraction when the VNEI model (XSPEC) is used. The line diagnosis in quiescence shows no resonance lines, with only the forbidden lines of Ne, Mg, and Si detected. The H-like C, O, Ne, and Mg are detected. The strongest line is O viii, with (2.7–4.6) × 10−14 erg s−1 cm−2. The quiescent X-ray-emitting plasma is not collisional and not in ionization equilibrium, which is consistent with hot ADAF-like accretion flows. The line diagnosis in the outburst shows He-like O and Ne, with intercombination lines being the strongest, along with weaker resonance lines. This indicates the plasma is more collisional and denser, but not yet in CIE, revealing ionization timescales of (0.97–1.4) × 1011 s cm−3. The R ratios in the outburst yield electron densities of (7–90) × 1011 cm−3 and the G ratios yield electron temperatures of (2–3) × 106 K. The outburst luminosity is (1.4–2.5) × 1030 erg s−1. The flow is inhomogeneous in density. All detected lines are narrow, with widths limited by the resolution of RGS, yielding Keplerian rotational velocities <1000 km s−1. This is too low for boundary layers, consistent with the nature of ADAF-like hot flows.

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MASTER OT J030227.28+191754.5: A Dwarf Nova at a Massive Oxygen–Neon White Dwarf System?

Cited by 3 publications

References 55 publications

A disc wind origin for the optical spectra of dwarf novae in outburst

A disc wind origin for the optical spectra of dwarf novae in outburst

MASTER OT J030227.28+191754.5: An unprecedentedly energetic dwarf nova outburst

X-Ray Spectroscopy of the Dwarf Nova Z Chamaeleontis in Quiescence and Outburst Using the XMM-Newton Observatory

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