arXiv subjects

Izumi Hachisu

Publications and source records attributed to Izumi Hachisu.

106 records · Page 6Linked to original sources

arXiv2002

Revised analysis of the supersoft X-ray phase, helium enrichment, and turn-off time in the 2000 outburst of recurrent nova CI Aquilae

Recurrent nova CI Aquilae has entered the final decline phase a bit before May of 2001, about 300 days after the optical maximum, showing the slowest evolution among recurrent novae. Based on the optically thick wind mass-loss theory of the thermonuclear runaway model, we have estimated the turn-off time of the CI Aql 2000 outburst. It is in late March of 2001 after a luminous supersoft X-ray source phase lasts 150 days (from November of 2000 until March of 2001). We have also obtained, by fitting our theoretical light curves with the 1917 and 2000 outbursts, the white dwarf (WD) mass to be M_{WD}= 1.2 \pm 0.05 M_\sun, the helium enrichment of the envelope is He/H = 0.5 by number, the mass of the hydrogen-rich envelope on the WD at the optical maximum is ΔM_{max} = 8.0 x 10^{-6} M_\sun, and the average mass accretion rate is \dot M_{acc}= 1.0 x 10^{-7} M_\sun/yr during the quiescent phase between the 1917 and 2000 outbursts. Using these obtained values, we have consistently reproduced the light curve in quiescence as well as of the two outbursts. We have also discussed the possibility whether or not CI Aql will explode as a Type Ia supernova in a future.

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arXiv2001

Evolution of binaries producing Type Ia supernovae, luminous supersoft X-ray sources, and recurrent novae

We have been proposing two evolutionary paths to Type Ia supernovae (SNe Ia), which are called the supersoft X-ray source (SSS) channel and the symbiotic channel, depending on the orbital separation just prior to an SN Ia explosion. The essential difference of our treatment is inclusion of strong, optically thick winds on mass-accreting white dwarfs (WDs) in binary evolutions when the mass accretion rate on to WDs exceeds a critical rate of ~ 1 x 10^{-6} Mo/yr. Once optically thick winds blow from the WD, the binary can avoid forming a common envelope in some cases. So that the WDs are able to grow up to the Chandrasekhar mass and explode as an SN Ia, showing SSS or recurrent nova phenomena in the way to SNe Ia. Thus, the accretion wind process of WDs can open new channels to SNe Ia. We have modeled the LMC supersoft source RX J0513.9-6951 as an example of the systems in the accretion wind phase. Further inclusions of two other elementary processes make the channels much wider; these are the case BB mass transfer in the SSS channel and the strong orbital shrinkage during the superwind phase of the primary star in the symbiotic channel. As a result, the estimated birth rate of SNe Ia via these two channels becomes compatible with the observation in our Galaxy. Interestingly, the U Sco and T CrB subclasses of recurrent novae can be naturally understood as a part of evolutionary stages in these two SSS and symbiotic channels to SNe Ia, respectively. Thus we have a unified picture of binary evolutions to SNe Ia, luminous SSS, and recurrent novae.

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arXiv2001

Revised analysis of the supersoft X-ray phase, helium enrichment, and turn-off time in the 2000 outburst of the recurrent nova CI Aquilae

The recurrent nova CI Aquilae entered the final decline phase a bit before May of 2001, showing the slowest evolution among the recurrent novae. Based on the optically thick wind mass-loss theory of the thermonuclear runaway model, we have estimated the turn-off time of the CI Aql 2000 outburst in March of 2001, after a supersoft X-ray source (SSS) phase lasts 150 days from December of 2000 until May of 2001. Fitting our theoretical light curves with both the 1917 and 2000 outbursts, we also obtained the WD mass to be M_{WD}= 1.2 \pm 0.05 M_\sun, helium enrichment of ejecta, He/H ~ 0.5 by number, the mass of the hydrogen-rich envelope on the WD of ΔM ~ 6 x 10^{-6} M_\sun at the optical maximum, which is indicating an average mass accretion rate of \dot M_{acc} ~ 0.8 x 10^{-7} M_\sun yr^{-1} during the quiescent phase between the 1917 and 2000 outbursts.

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arXiv2001

V2487 Ophiuchi: A strong candidate for a recurrent nova and a progenitor of Type Ia supernova

The light curve of the 1998 outburst of V2487 Ophiuchi (Nova Oph 1998) shows a very rapid decline (t_3 ~ 9 day) and a mid-plateau phase from 10 to 30 days after the optical maximum, which are characteristics common to the U Sco subclass of the recurrent novae. We have numerically reproduced light curves of the 1998 outburst based on a thermonuclear runaway model with optically thick winds. The results show that the mass of the white dwarf (WD) is as massive as 1.35 \pm 0.01 M_\sun; the envelope mass of the WD at the optical maximum is ~ 6 x 10^{-6} M_\sun; the hydrogen content of the WD envelope is as low as X ~ 0.1 by mass weight. The mass transfer rate in quiescence is roughly estimated to be \~ 1.5 x 10^{-7} M_\sun yr^{-1} and, therefore, that the recurrence period of nova outbursts is about 40 yr. Since the WD mass may be now growing at a rate of ~ 2 x 10^{-8} M_\sun yr^{-1}, V2487 Oph is a strong candidate for a progenitor of a Type Ia supernova.

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arXiv2001

Prediction of supersoft X-ray phase, helium enrichment, and turn-off time in recurrent nova CI Aquilae 2000 outburst

Recurrent nova CI Aquilae is still bright 300 days after the optical maximum, showing the slowest evolution among recurrent novae. We predict the turn-off time of CI Aql 2000 outburst coming in August 2001 after a supersoft X-ray source (SSS) phase lasts 250 days. We also predict helium enrichment of ejecta, He/H = 0.25 by number. Observational confirmations are urgently required. Based on the optically thick wind mass-loss theory of the thermonuclear runaway model, we have also estimated the WD mass to be 1.2 +- 0.05 Msun by fitting our theoretical light curves with the 1917 and 2000 outbursts. The mass of the hydrogen-rich envelope on the WD is also estimated to be 6 x 10^{-6} Msun at the optical maximum, indicating an average mass accretion rate of 0.7 x 10^{-7} Msun/yr during the quiescent phase between the 1917 and 2000 outbursts. Using these obtained values, we have consistently reproduced the light curve in quiescence as well as the two outburst phases. Thus, we predict the turn-off time to be in August 2001 for the 2000 outburst. We strongly recommend soft X-ray observations to detect SSS until August 2001 because the massive wind phase have already ended in December 2000 followed by an SSS phase that very likely lasts until August 2001.

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arXiv2001

Recurrent novae as a progenitor system of Type Ia supernovae. I. RS Ophiuchi subclass --- Systems with a red giant companion

Theoretical light curves of four recurrent novae in outburst are modeled to obtain various physical parameters. They are those with a red giant companion, T CrB, RS Oph, V745 Sco, and V3890 Sgr. Our model includes irradiations of the companion star and the accretion disk together with a shadowing effect on the companion by the accretion disk. The early visual light curves are well reproduced with a thermonuclear runaway model on a very massive white dwarf of 1.37 Mo for T CrB, 1.37 Mo for RS Oph with low metallicity (Z=0.004), 1.35 Mo for V745 Sco, and 1.35 Mo for V3890 Sgr. Each envelope mass at the optical maximum is also estimated to be 3 x 10^{-6}, 2 x 10^{-6}, 5 x 10^{-6}, and 3 x 10^{-6} Mo, indicating an average mass accretion rate of 0.4 x 10^{-7}, 1.2 x 10^{-7}, 0.9 x 10^{-7}, and 1.1 x 10^{-7} Mo/yr during the quiescent phase. Although a large part of the envelope mass is blown in the wind, each WD can retain a substantial part of the envelope mass after hydrogen burning ends. Thus, we have obtained net mass-increasing rates of the WDs as 0.1 x 10^{-7}, 0.12 x 10^{-7}, 0.05 x 10^{-7}, and 0.11 x 10^{-7} Mo/yr. These results strongly indicate that the WDs in the recurrent novae have now grown up to near the Chandrasekhar mass limit and will soon explode as a Type Ia supernova if the WDs consist of carbon and oxygen. We also include a radiation-induced warping instability of the accretion disk to reproduce the second peak of T CrB outbursts. Thus, we have clarified the reason why only T CrB shows a secondary maximum but the other three systems do not.

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arXiv2000

A theoretical light-curve model for the 1985 outburst of RS Ophiuchi

A theoretical light-curve model of the 1985 outburst of RS Ophiuchi is presented based on a thermonuclear runaway (TNR) model. The system consists of a very massive white dwarf (WD) with an accretion disk (ACDK) and a red giant (RG). The early phase of the V light curve is well reproduced only by the bloated WD photosphere of the TNR model on a 1.35 +/- 0.01 M_sun WD while the later phase is dominated both by the irradiated ACDK and by the irradiated RG underfilling the inner critical Roche lobe. The UV light curve is also well reproduced by the same model with the distance of 0.6 kpc to RS Oph. The envelope mass at the optical peak is estimated to be 2 x 10^{-6} M_sun, indicating a rather high mass accretion rate of 1.2 x 10^{-7} M_sun yr^{-1} between the 1967 and the 1985 outbursts. About 90% of the envelope mass is blown off in the outburst wind while the residual 10% (2 x 10^{-7} M_sun) has been left and added to the helium layer of the WD. The net increasing rate of the WD mass is 1.2 x 10^{-8} M_sun yr^{-1}. Thus, RS Oph is certainly a strong candidate for a Type Ia supernova progenitor.

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arXiv2000

A Theoretical Light-Curve Model for the Recurrent Nova V394 Coronae Austrinae

A theoretical light curve for the 1987 outburst of V394 Coronae Austrinae (V394 CrA) is modeled to obtain various physical parameters of this recurrent nova. We then apply the same set of parametersto a quiescent phase and confirm that these parameters give a unified picture of the binary. The early visual light curve (1-10 days after the optical maximum) is well reproduced by a thermonuclear runaway model on a very massive WD close to the Chandrasekhar limit (1.37 +- 0.01 M_sun). The ensuing plateau phase (10-30 days) is also reproduced by the combination of a slightly irradiated MS and a fully irradiated flaring-up disk with a radius ~1.4 times the Roche lobe size. The best fit parameters are the WD mass 1.37 M_sun, the companion mass 1.5 M_sun (0.8-2.0 M_sun is acceptable), the inclination angle of the orbit i~65-68 degree, and the flaring-up rim ~0.30 times the disk radius. The envelope mass at the optical peak is estimated to be ~6 x 10^{-6} M_sun, which indicates an average mass accretion rate of 1.5 x 10^{-7} M_sun yr^{-1} during the quiescent phase between the 1949 and 1987 outbursts. In the quiescent phase, the observed light curve can be reproduced with a disk size of 0.7 times the Roche lobe size and a rather slim thickness of 0.05 times the accretion disk size at the rim. About 0.5 mag sinusoidal variation of the light curve requires the mass accretion rate higher than ~1.0 x 10^{-7} M_sun yr^{-1}, which is consistent with the above estimation from the 1987 outburst. These newly obtained quantities are exactly the same as those predicted in a new progenitor model of Type Ia supernovae.

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arXiv2000

A Model for the Quiescent Phase of the Recurrent Nova U Scorpii

A theoretical light curve is constructed for the quiescent phase of the recurrent nova U Scorpii in order to resolve the existing distance discrepancy between the outbursts (6 kpc) and the quiescences (14 kpc). Our U Sco model consists of a very massive white dwarf (WD), an accretion disk (ACDK) with a flaring-up rim, and a lobe-filling, slightly evolved, main-sequence star (MS). The model properly includes an accretion luminosity of the WD, a viscous luminosity of the ACDK, a reflection effect of the MS and the ACDK irradiated by the WD photosphere. The B light curve is well reproduced by a model of 1.37 M_sun WD + 1.5 M_sun MS (0.8---2.0 M_sun MS is acceptable) with an ACDK having a flaring-up rim, and the inclination angle i~80 degree. The calculated color is rather blue (B-V~0.0) for a suggested mass accretion rate of 2.5 x 10^{-7} M_sun yr^{-1}, thus indicating a large color excess of E(B-V)~0.56 with the observational color of B-V=0.56 in quiescence. Such a large color excess corresponds to an absorption of A_V~1.8 and A_B~2.3, which reduces the distance to 6-8 kpc. This is in good agreement with the distance estimation of 4-6 kpc for the latest outburst. Such a large intrinsic absorption is very consistent with the recently detected period change of U Sco, which is indicating a mass outflow of ~3 x 10^{-7} M_sun yr^{-1} through the outer Lagrangian points in quiescence.

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arXiv2000

Type Ia Supernovae: Progenitors and Evolution with Redshift

Relatively uniform light curves and spectral evolution of Type Ia supernovae (SNe Ia) have led to the use of SNe Ia as a ``standard candle'' to determine cosmological parameters. Whether a statistically significant value of the cosmological constant can be obtained depends on whether the peak luminosities of SNe Ia are sufficiently free from the effects of cosmic and galactic evolutions. Here we first review the single degenerate scenario for the Chandrasekhar mass white dwarf (WD) models of SNe Ia. We identify the progenitor's evolution and population with two channels: (1) the WD+RG (red-giant) and (2) the WD+MS (near main-sequence He-rich star) channels. In these channels, the strong wind from accreting WDs plays a key role, which yields important age and metallicity effects on the evolution. We then address the questions whether the nature of SNe Ia depends systematically on environmental properties such as metallicity and age of the progenitor system and whether significant evolutionary effects exist. We suggest that the variation of the carbon mass fraction $X$(C) in the C+O WD (or the variation of the initial WD mass) causes the diversity of the brightness of SNe Ia. This model can explain the observed dependences of SNe Ia brightness on the galaxy types and the distance from the galactic center. Finally, applying the metallicity effect on the evolution of SN Ia progenitors, we make a prediction of the cosmic supernova rate history as a composite of the supernova rates in different types of galaxies.

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arXiv1999

A Theoretical Light-Curve Model for the 1999 Outburst of U Scorpii

A theoretical light curve for the 1999 outburst of U Scorpii is presented in order to obtain various physical parameters of the recurrent nova. Our U Sco model consists of a very massive white dwarf (WD) with an accretion disk and a lobe-filling, slightly evolved, main-sequence star (MS). The model includes a reflection effect by the companion and the accretion disk together with a shadowing effect on the companion by the accretion disk. The early visual light curve (t ~ 1-15 days after maximum) is well reproduced by a thermonuclear runaway model on a very massive WD close to the Chandrasekhar limit (M_{WD}= 1.37 \pm 0.01 M_\odot), in which optically thick winds blowing from the WD play a key role in determining the nova duration. The duration of the strong wind phase (t~0-17 days) is very consistent with the BeppoSAX supersoft X-ray detection at t~19-20 days because supersoft X-rays are self-absorbed by the massive wind. The envelope mass at the peak is estimated to be ~3x10^{-6} M_\odot, which is indicating an average mass accretion rate ~2.5x10^{-7} M_\odot yr^{-1} during the quiescent phase between 1987 and 1999. These quantities are exactly the same as those predicted in a new progenitor model of Type Ia supernovae.

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arXiv1999

Type Ia Supernova Progenitors, Environmental Effects, and Cosmic Supernova Rates

Relatively uniform light curves and spectral evolution of Type Ia supernovae (SNe Ia) have led to the use of SNe Ia as a ``standard candle'' to determine cosmological parameters, such as the Hubble constant, the density parameter, and the cosmological constant. Whether a statistically significant value of the cosmological constant can be obtained depends on whether the peak luminosities of SNe Ia are sufficiently free from the effects of cosmic and galactic evolutions. Here we first review the single degenerate scenario for the Chandrasekhar mass white dwarf (WD) models of SNe Ia. We identify the progenitor's evolution and population with two channels: (1) the WD+RG (red-giant) and (2) the WD+MS (near main-sequence He-rich star) channels. In these channels, the strong wind from accreting white dwarfs plays a key role, which yields important age and metallicity effects on the evolution. We then address the questions whether the nature of SNe Ia depends systematically on environmental properties such as metallicity and age of the progenitor system and whether significant evolutionary effects exist. We suggest that the variation of the carbon mass fraction $X$(C) in the C+O WD (or the variation of the initial WD mass) causes the diversity of the brightness of SNe Ia. This model can explain the observed dependence of SNe Ia brighness on the galaxy types. Finally, applying the metallicity effect on the evolution of SN Ia progenitors, we make a prediction of the cosmic supernova rate history as a composite of the supernova rates in different types of galaxies.

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arXiv1999

A Wide Symbiotic Channel to Type Ia Supernovae

As a promising channel to Type Ia supernovae (SNe Ia), we have proposed a symbiotic binary system consisting of a white dwarf (WD) and a low mass red-giant (RG), where strong winds from the accreting WD play a key role to increase the WD mass to the Chandrasekhar mass limit. Here we propose two new evolutionary processes which make the symbiotic channel to SNe Ia much wider. (1) We first show that the WD + RG close binary can form from a wide binary even with such a large initial separation as $a_i \lesssim 40000 R_\odot$. Such a binary consists of an AGB star and a low mass main-sequence (MS) star, where the AGB star is undergoing superwind before becoming a WD. If the superwind at the end of AGB evolution is as fast as or slower than the orbital velocity, the wind outflowing from the system takes away the orbital angular momentum effectively. As a result the wide binary shrinks greatly to become a close binary. Therefore, the WD + RG binary can form from much wider binaries than our earlier estimate. (2) When the RG fills its inner critical Roche lobe, the WD undergoes rapid mass accretion and blows a strong optically thick wind. Our earlier analysis has shown that the mass transfer is stabilized by this wind only when the mass ratio of RG/WD is smaller than 1.15. Our new finding is that the WD wind can strip mass from the RG envelope, which could be efficient enough to stabilize the mass transfer even if the RG/WD mass ratio exceeds 1.15. With the above two new effects (1) and (2), the symbiotic channel can account for the inferred rate of SNe Ia in our Galaxy.

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arXiv1999

A New Interpretation for the Second Peak of T Coronae Borealis Outbursts: A Tilting Disk around a Very Massive White Dwarf

A new interpretation for the second peak of T Coronae Borealis (T CrB) outbursts is proposed based on a thermonuclear runaway (TNR) model. The system consists of a very massive white dwarf (WD) with a tilting accretion disk and a lobe-filling red-giant. The first peak of the visual light curve of T CrB outbursts is well reproduced by the TNR model on a WD close to the Chandrasekhar mass ($M_{\rm WD} \gtrsim 1.35 ~M_\odot$), while the second peak is reproduced by the combination of the irradiated M-giant and the irradiated tilting disk. The derived fitting parameters are the WD mass $M_{\rm WD} \sim 1.35 ~M_\odot$, the M-giant companion mass $M_{\rm RG} \sim 0.7 M_\odot$ ($0.6-1.0 M_\odot$ is acceptable), the inclination angle of the orbit $i \sim 70 \arcdeg$, and the tilting angle of the disk $i_{\rm prec} \sim 35 \arcdeg$. These parameters are consistent with the recently derived binary parameters of T CrB.

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arXiv1999

A New Evolutionary Path to Type Ia Supernovae: Helium-Rich Super-Soft X-Ray Source Channel

We have found a new evolutionary path to Type Ia supernovae (SNe Ia) which has been overlooked in previous work. In this scenario, a carbon-oxygen white dwarf (C+O WD) is originated, not from an asymptotic giant branch star with a C+O core, but from a red-giant star with a helium core of $\sim 0.8-2.0 M_\odot$. The helium star, which is formed after the first common envelope evolution, evolves to form a C+O WD of $\sim 0.8-1.1 M_\odot$ with transferring a part of the helium envelope onto the secondary main-sequence star. This new evolutionary path, together with the optically thick wind from mass-accreting white dwarf, provides a much wider channel to SNe Ia than previous scenarios. A part of the progenitor systems are identified as the luminous supersoft X-ray sources or the recurrent novae like U Sco, which are characterized by the accretion of helium-rich matter. The white dwarf accretes hydrogen-rich, helium-enhanced matter from a lobe-filling, slightly evolved companion at a critical rate and blows excess matter in the wind. The white dwarf grows in mass to the Chandrasekhar mass limit and explodes as an SN Ia. A theoretical estimate indicates that this channel contributes a considerable part of the inferred rate of SNe Ia in our Galaxy, i.e., the rate is about ten times larger than the previous theoretical estimates for white dwarfs with slightly evolved companions.

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arXiv1998

Low-Metallicity Inhibition of Type Ia Supernovae and Galactic and Cosmic Chemical Evolution

We introduce a metallicity dependence of Type Ia supernova (SN Ia) rate into the Galactic and cosmic chemical evolution models. In our SN Ia progenitor scenario, the accreting white dwarf (WD) blows a strong wind to reach the Chandrasekhar mass limit. If the iron abundance of the progenitors is as low as [Fe/H] < -1, then the wind is too weak for SNe Ia to occur. Our model successfully reproduces the observed chemical evolution in the solar neighborhood. We make the following predictions which can test this metallicity effect: 1) SNe Ia are not found in the low-iron abundance environments such as dwarf galaxies and the outskirts of spirals. 2) The cosmic SN Ia rate drops at z \sim 1-2 due to the low-iron abundance, which can be observed with the Next Generation Space Telescope. At z > 1-2, SNe Ia can be found only in the environments where the timescale of metal enrichment is sufficiently short as in starburst galaxies and ellipticals. The low-metallicity inhibition of SNe Ia can shed new light on the following issues: 1) The limited metallicity range of the SN Ia progenitors would imply that ``evolution effects'' are relatively small for the use of high redshift SNe Ia to determine the cosmological parameters. 2) WDs of halo populations are poor producers of SNe Ia, so that the WD contribution to the halo mass is not constrained from the iron abundance in the halo. 3) The abundance patterns of globular clusters and field stars in the Galactic halo lack of SN Ia signatures in spite of their age difference of several Gyrs, which can be explained by the low-metallicity inhibition of SNe Ia. 4) It could also explain why the SN Ia contamination is not seen in the damped Lyαsystems for over a wide range of redshift.

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