Toward a unified light-curve model for multiwavelength observations of V1974 Cygni (Nova Cygni 1992)

Izumi Hachisu, Mariko Kato

Research output: Contribution to journalArticle

22 Citations (Scopus)

Abstract

We present a unified model for optical, ultraviolet (UV), and X-ray light curves of V1974 Cygni (Nova Cygni 1992). Based on an optically thick wind model of nova outbursts, we have calculated light curves and searched for the best-fit model that is consistent with optical, UV, and X-ray observations. Our best-fit model is a white dwarf (WD) of mass 1.05 M⊙ with a chemical composition of X = 0.46, C + N + O = 0.15, and Ne = 0.05 by mass weight. Both supersoft X-ray and continuum UV 1455 Å light curves are well reproduced. Supersoft X-rays emerged on day ∼250 after the outburst, which is naturally explained by our model: our optically thick winds cease on day 245, and supersoft X-rays emerge from self-absorption by the winds. The X-ray flux keeps a constant peak value for ∼3OO days followed by a quick decay on day ∼600. The duration of the X-ray flat peak is well reproduced by steady hydrogen shell burning on the WD. The optical light curve is also explained by the same model if we introduce free-free emission from optically thin ejecta. A t-1.5 slope of the observed optical and infrared fluxes is very close to the slope of our modeled free-free light curve during the optically thick wind phase. Once the wind stops, optical and infrared fluxes should follow a t-3 slope, derived from a constant mass of expanding ejecta. An abrupt transition from a t -1.5 slope to a t-3 slope at day ∼200 is naturally explained by the change from the wind phase to the postwind phase on day ∼200. The development of hard X-ray flux is also reasonably understood as originating in the shock between the wind and the companion star. The distance to V1974 Cyg is estimated to be ∼1.7 kpc with E(B-V)-0.32 from the light-curve fitting for the continuum UV 1455 Å.

Original languageEnglish
Pages (from-to)1094-1099
Number of pages6
JournalAstrophysical Journal
Volume631
Issue number2 I
DOIs
Publication statusPublished - 2005 Oct 1

Fingerprint

light curve
slopes
x rays
ejecta
outburst
weight (mass)
continuums
companion stars
self absorption
curve fitting
ultraviolet radiation
chemical composition
shock
hydrogen
shell
decay

ASJC Scopus subject areas

  • Space and Planetary Science

Cite this

Toward a unified light-curve model for multiwavelength observations of V1974 Cygni (Nova Cygni 1992). / Hachisu, Izumi; Kato, Mariko.

In: Astrophysical Journal, Vol. 631, No. 2 I, 01.10.2005, p. 1094-1099.

Research output: Contribution to journalArticle

Hachisu, Izumi ; Kato, Mariko. / Toward a unified light-curve model for multiwavelength observations of V1974 Cygni (Nova Cygni 1992). In: Astrophysical Journal. 2005 ; Vol. 631, No. 2 I. pp. 1094-1099.
@article{febadae55c6a4b968eca7cab933e56b6,
title = "Toward a unified light-curve model for multiwavelength observations of V1974 Cygni (Nova Cygni 1992)",
abstract = "We present a unified model for optical, ultraviolet (UV), and X-ray light curves of V1974 Cygni (Nova Cygni 1992). Based on an optically thick wind model of nova outbursts, we have calculated light curves and searched for the best-fit model that is consistent with optical, UV, and X-ray observations. Our best-fit model is a white dwarf (WD) of mass 1.05 M⊙ with a chemical composition of X = 0.46, C + N + O = 0.15, and Ne = 0.05 by mass weight. Both supersoft X-ray and continuum UV 1455 {\AA} light curves are well reproduced. Supersoft X-rays emerged on day ∼250 after the outburst, which is naturally explained by our model: our optically thick winds cease on day 245, and supersoft X-rays emerge from self-absorption by the winds. The X-ray flux keeps a constant peak value for ∼3OO days followed by a quick decay on day ∼600. The duration of the X-ray flat peak is well reproduced by steady hydrogen shell burning on the WD. The optical light curve is also explained by the same model if we introduce free-free emission from optically thin ejecta. A t-1.5 slope of the observed optical and infrared fluxes is very close to the slope of our modeled free-free light curve during the optically thick wind phase. Once the wind stops, optical and infrared fluxes should follow a t-3 slope, derived from a constant mass of expanding ejecta. An abrupt transition from a t -1.5 slope to a t-3 slope at day ∼200 is naturally explained by the change from the wind phase to the postwind phase on day ∼200. The development of hard X-ray flux is also reasonably understood as originating in the shock between the wind and the companion star. The distance to V1974 Cyg is estimated to be ∼1.7 kpc with E(B-V)-0.32 from the light-curve fitting for the continuum UV 1455 {\AA}.",
author = "Izumi Hachisu and Mariko Kato",
year = "2005",
month = "10",
day = "1",
doi = "10.1086/432656",
language = "English",
volume = "631",
pages = "1094--1099",
journal = "Astrophysical Journal",
issn = "0004-637X",
publisher = "IOP Publishing Ltd.",
number = "2 I",

}

TY - JOUR

T1 - Toward a unified light-curve model for multiwavelength observations of V1974 Cygni (Nova Cygni 1992)

AU - Hachisu, Izumi

AU - Kato, Mariko

PY - 2005/10/1

Y1 - 2005/10/1

N2 - We present a unified model for optical, ultraviolet (UV), and X-ray light curves of V1974 Cygni (Nova Cygni 1992). Based on an optically thick wind model of nova outbursts, we have calculated light curves and searched for the best-fit model that is consistent with optical, UV, and X-ray observations. Our best-fit model is a white dwarf (WD) of mass 1.05 M⊙ with a chemical composition of X = 0.46, C + N + O = 0.15, and Ne = 0.05 by mass weight. Both supersoft X-ray and continuum UV 1455 Å light curves are well reproduced. Supersoft X-rays emerged on day ∼250 after the outburst, which is naturally explained by our model: our optically thick winds cease on day 245, and supersoft X-rays emerge from self-absorption by the winds. The X-ray flux keeps a constant peak value for ∼3OO days followed by a quick decay on day ∼600. The duration of the X-ray flat peak is well reproduced by steady hydrogen shell burning on the WD. The optical light curve is also explained by the same model if we introduce free-free emission from optically thin ejecta. A t-1.5 slope of the observed optical and infrared fluxes is very close to the slope of our modeled free-free light curve during the optically thick wind phase. Once the wind stops, optical and infrared fluxes should follow a t-3 slope, derived from a constant mass of expanding ejecta. An abrupt transition from a t -1.5 slope to a t-3 slope at day ∼200 is naturally explained by the change from the wind phase to the postwind phase on day ∼200. The development of hard X-ray flux is also reasonably understood as originating in the shock between the wind and the companion star. The distance to V1974 Cyg is estimated to be ∼1.7 kpc with E(B-V)-0.32 from the light-curve fitting for the continuum UV 1455 Å.

AB - We present a unified model for optical, ultraviolet (UV), and X-ray light curves of V1974 Cygni (Nova Cygni 1992). Based on an optically thick wind model of nova outbursts, we have calculated light curves and searched for the best-fit model that is consistent with optical, UV, and X-ray observations. Our best-fit model is a white dwarf (WD) of mass 1.05 M⊙ with a chemical composition of X = 0.46, C + N + O = 0.15, and Ne = 0.05 by mass weight. Both supersoft X-ray and continuum UV 1455 Å light curves are well reproduced. Supersoft X-rays emerged on day ∼250 after the outburst, which is naturally explained by our model: our optically thick winds cease on day 245, and supersoft X-rays emerge from self-absorption by the winds. The X-ray flux keeps a constant peak value for ∼3OO days followed by a quick decay on day ∼600. The duration of the X-ray flat peak is well reproduced by steady hydrogen shell burning on the WD. The optical light curve is also explained by the same model if we introduce free-free emission from optically thin ejecta. A t-1.5 slope of the observed optical and infrared fluxes is very close to the slope of our modeled free-free light curve during the optically thick wind phase. Once the wind stops, optical and infrared fluxes should follow a t-3 slope, derived from a constant mass of expanding ejecta. An abrupt transition from a t -1.5 slope to a t-3 slope at day ∼200 is naturally explained by the change from the wind phase to the postwind phase on day ∼200. The development of hard X-ray flux is also reasonably understood as originating in the shock between the wind and the companion star. The distance to V1974 Cyg is estimated to be ∼1.7 kpc with E(B-V)-0.32 from the light-curve fitting for the continuum UV 1455 Å.

UR - http://www.scopus.com/inward/record.url?scp=27744445390&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=27744445390&partnerID=8YFLogxK

U2 - 10.1086/432656

DO - 10.1086/432656

M3 - Article

VL - 631

SP - 1094

EP - 1099

JO - Astrophysical Journal

JF - Astrophysical Journal

SN - 0004-637X

IS - 2 I

ER -