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Kato, Takuma; Tsuchiya, Shuichi; Yamauchi, Kaku; Ebana, Ryo; Yamada, Tadashi

doi:10.5956/jriet.35.507

Cited by 9 publications

(9 citation statements)

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“…The peak mass loss rateṀ w,0 is achieved at time t = 0 and lasts for a characteristic duration ∼ ∆t w ∼ weeks which is also assumed to be similar to the optical duration of the nova. At late times t ≫ ∆t w ,Ṁ w decays as a power law ∝ t −2 similar to that predicted for the late optically-thick wind phase (Bath & Shaviv 1976;Kato 1983;Kwok 1983;Prialnik 1986;Yaron et al 2005).…”

Section: Fast Nova Outflowsupporting

confidence: 78%

Shocks in nova outflows – I. Thermal emission

Metzger

Hascoët

Vurm

et al. 2014

Monthly Notices of the Royal Astronomical Society

102

178

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Growing evidence for shocks in nova outflows include (1) multiple velocity components in the optical spectra; (2) hard X-ray emission starting weeks to months after the outburst;(3) an early radio flare on timescales of months, in excess of that predicted from the freely expanding photo-ionized gas; and, perhaps most dramatically, (4) ∼ GeV gamma-ray emission. We present a one dimensional model for the shock interaction between the fast nova outflow and a dense external shell (DES) and its associated thermal X-ray, optical, and radio emission. The lower velocity DES could represent an earlier stage of mass loss from the white dwarf or ambient material not directly related to the thermonuclear runaway. The forward shock is radiative initially when the density of shocked gas is highest, at which times radio emission originates from the dense cooling layer immediately downstream of the shock. Our predicted radio light curve is characterized by sharper rises to maximum and later peak times at progressively lower frequencies, with a peak brightness temperature that is approximately independent of frequency. We apply our model to the recent gamma-ray producing classical nova V1324 Sco, obtaining an adequate fit to the early radio maximum for reasonable assumptions about the fast nova outflow and assuming the DES possesses a characteristic velocity ∼ 10 3 km s −1 and mass ∼ few 10 −4 M ⊙ ; the former is consistent with the velocities of narrow line absorption systems observed previously in nova spectra, while the total ejecta mass of the DES and fast outflow is consistent with that inferred independently by modeling the late radio peak as uniformly expanding photo-ionized gas. Rapid evolution of the early radio light curves require the DES to possess a steep outer density profile, which may indicate that the onset of mass loss from the white dwarf was rapid, providing indirect evidence that the DES was expelled as the result of the thermonuclear runaway event. Reprocessed X-rays from the shock absorbed by the DES at early times are found to contribute significantly to the optical/UV emission, which we speculate may be responsible for the previously unexplained 'plateaus' and secondary maxima in nova optical light curves.

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Section: Fast Nova Outflowsupporting

confidence: 78%

Shocks in nova outflows – I. Thermal emission

Metzger

Hascoët

Vurm

et al. 2014

Monthly Notices of the Royal Astronomical Society

102

178

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“…On the right side to point D, optically thick winds occur, and each envelope solution is constructed including wind mass loss (Kato & Hachisu 1994). Hydrogen shell burning is stable on this branch (Kato 1983).…”

Section: Recurrence Periodsmentioning

confidence: 99%

Shortest Recurrence Periods of Novae

Kato

Saio

Hachisu

et al. 2014

ApJ

146

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Stimulated by the recent discovery of the 1 yr recurrence period nova M31N 2008-12a, we examined the shortest recurrence periods of hydrogen shell flashes on mass-accreting white dwarfs (WDs). We discuss the mechanism that yields a finite minimum recurrence period for a given WD mass. Calculating the unstable flashes for various WD masses and mass accretion rates, we identified a shortest recurrence period of about two months for a non-rotating 1.38 M ⊙ WD with a mass accretion rate of 3.6 × 10 −7 M ⊙ yr −1 . A 1 yr recurrence period is realized for very massive ( 1.3 M ⊙ ) WDs with very high accretion rates ( 1.5 × 10 −7 M ⊙ yr −1 ). We revised our stability limit of hydrogen shell burning, which will be useful for binary evolution calculations toward Type Ia supernovae.

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“…The nova outburst ends when the hydrogen shell burning extinguishes. This nova envelope evolution was calculated by Kato & Hachisu (1994) on the basis of the optically-thick nova wind theory (e.g., Kato 1983).…”

Section: Introductionmentioning

confidence: 99%

THEUBVCOLOR EVOLUTION OF CLASSICAL NOVAE. I. NOVA-GIANT SEQUENCE IN THE COLOR-COLOR DIAGRAM

Hachisu

Kato

2014

ApJ

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We identified a general course of classical nova outbursts in the B − V versus U − B color-color diagram. It is reported that novae show spectra similar to those of A-F supergiants near optical light maximum. However, they do not follow the supergiant sequence in the color-color diagram, neither the blackbody nor the mainsequence sequence. Instead, we found that novae evolve along a new sequence in the pre-maximum and nearmaximum phases, which we call "the nova-giant sequence." This sequence is parallel to but ∆(U − B) ≈ −0.2 mag bluer than the supergiant sequence. This is because the mass of a nova envelope is much (∼ 10 −4 times) less than that of a normal supergiant. After optical maximum, its color quickly evolves back blueward along the same nova-giant sequence and reaches the point of free-free emission (B − V = −0.03, U − B = −0.97), which coincides with the intersection of the blackbody sequence and the nova-giant sequence, and remains there for a while. Then the color evolves leftward (blueward in B − V but almost constant in U − B), owing mainly to the development of strong emission lines. This is the general course of nova outbursts in the colorcolor diagram, which was deduced from eight well-observed novae in various speed classes. For a nova with unknown extinction, we can determine a reliable value of the color excess by matching the observed track of the target nova with this general course. This is a new and convenient method for obtaining the color excesses of classical novae. Using this method, we redetermined the color excesses of 20 well-observed novae. The obtained color excesses are in reasonable agreement with the previous results, which in turn support the idea of our general track of nova outbursts. Additionally, we estimated the absolute V magnitudes of about 30 novae using a method for time-stretching nova light curves to analyze the distance-reddening relations of the novae.

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Cited by 9 publications

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Shocks in nova outflows – I. Thermal emission

Shocks in nova outflows – I. Thermal emission

Shortest Recurrence Periods of Novae

THEUBVCOLOR EVOLUTION OF CLASSICAL NOVAE. I. NOVA-GIANT SEQUENCE IN THE COLOR-COLOR DIAGRAM

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