Supernova Nucleosynthesis, Chemical Evolution, and Cosmic Supernova Rate

In the chemical evolution of the Galaxy, Type II supernovae (SNe II)have contributed to the early metal enrichment and later Type Iasupernovae (SNe Ia) have contributed to the delayed enrichment of Fe.In principle, hypothetical pre-galactic population III objects couldcause the earliest heavy element enrichment. Here we present our twonew findings. 1) The peculiar abundance pattern among iron peakelements (Cr, Mn, Co, and Fe) in the very metal poor can be reproducedwith SN II nucleosynthesis yields without invoking the contributionfrom Pop III objects. 2) The observed chemical evolution in the solarneighborhood is well reproduced with the metallicity dependentoccurrence of SNe Ia, where SNe Ia do not occur if the iron abundanceof the progenitors is as low as [Fe/H] ≲ -1. We make theprediction that the cosmic SN Ia rate drops at z ∼ 1-2 because ofthe low-iron abundance, which can be observed with the Next GenerationSpace Telescope. This revised version was published online in July 2006 with corrections to the Cover Date.     

GAIA and the Extragalactic Distance Scale

The local expansion field (v ₂₂₀ <1200 km s^-1) and the cosmic expansion field out to 30 000 km s^-1 are characterized by H ₀ = 58 [km s^-1 Mpc^-1]. While the random error of this determination is small (± 2 units), it may still be affected by systematic errors as large as ±10%>. The local expansion is outlined by Cepheids and by Cepheid-calibrated TF distances of a complete sample of field galaxies and by nearby groups and clusters; the cosmic expansion is defined by Cepheid-calibrated SNe Ia. The main source of systematic errors are therefore the shape and the zero point of the P-L relation of Cepheids and its possible dependence on metallicity. GAIA will essentially eliminate these systematic error sources. Another source of systematic error is due to the homogenization of SNe Ia as to decline rate Δm ₁₅ and color (B-V). GAIA will discover most of the 1100 SNe Ia within 10 000 km s^-1, which will occur during its four-year lifetime. If their photometric parameters can be determined from the ground, they will fix the dependence of the SNe Ia luminosity on Δ m ₁₅ and (B-V) with high accuracy. At the same time they will yield exquisite distances to an equal number of field galaxies. – GAIA will also revolutionize the very local distance scale by determining fundamental distances of the companion galaxies of the Milky Way and even of some spirals in- and possibly outside the Local Group from their rotation curves seen in radial velocities and proper motions. Moreover, GAIA will obtain trigonometric parallaxes of RR Lyrae stars, of red giants defining the TRGB, of stars on the ZAMS, of White Dwarf defining their cooling sequence, and of globular clusters, and determine the metallicity dependence of these distance indicators. It will thus establish a self-controlling network of distance indicators within the Local Group and beyond. This revised version was published online in July 2006 with corrections to the Cover Date.     

The influence of host galaxy morphology on the properties of Type Ia supernovae from the JLA compilation

The observational cosmology with distant Type Ia supernovae (SNe) as standard candles claims that the Universe is in accelerated expansion, caused by a large fraction of dark energy. In this paper we investigate the SN Ia environment, studying the impact of the nature of their host galaxies on the Hubble diagram fitting. The supernovae (192 SNe) used in the analysis were extracted from Joint-Light-curves-Analysis (JLA) compilation of high-redshift and nearby supernovae which is the best one to date. The analysis is based on the empirical fact that SN Ia luminosities depend on their light curve shapes and colors. We confirm that the stretch parameter of Type Ia supernovae is correlated with the host galaxy type. The supernovae with lower stretch are hosted mainly in elliptical and lenticular galaxies. No significant correlation between SN Ia colour and host morphology was found. We also examine how the luminosities of SNe Ia change depending on host galaxy morphology after stretch and colour corrections. Our results show that in old stellar populations and low dust environments, the supernovae are slightly fainter. SNe Ia in elliptical and lenticular galaxies have a higher α (slope in luminosity-stretch) and β (slope in luminosity-colour) parameter than in spirals. However, the observed shift is at the 1-σ uncertainty level and, therefore, can not be considered as significant. We confirm that the supernova properties depend on their environment and that the incorporation of a host galaxy term into the Hubble diagram fit is expected to be crucial for future cosmological analyses.     

Distributions of supernovae of different types along the radius and in <Emphasis Type="Italic">z</Emphasis> coordinate of galaxies

The distributions of supernovae of different types and subtypes along the radius and in z coordinate of galaxies have been studied. We show that among the type Ia supernovae (SNe Ia) in spiral galaxies, SNe Iax and Ia-norm have, respectively, the largest and smallest concentration to the center; the distributions of SNe Ia-91bg and Ia-91T are similar. A strong concentration of SNe Ib/c to the central regions has been confirmed. In spiral galaxies, the supernovae of all types strongly concentrate to the galactic plane; the slight differences in scale height correlate with the extent to which the classes of supernovae are associated with star formation.     

How old are SN Ia progenitor systems? New observational constraints on the distribution of time delays from GALEX

The time delay between the formation of the progenitor systems of Type Ia supernovae (SNe Ia) and their detonation is a vital discriminant between the various progenitor scenarios that have been proposed for them. We use Sloan Digital Sky Survey optical and Galaxy Evolution Explorer ( GALEX ) ultraviolet observations of the early-type host galaxies of 21 nearby SNe Ia and quantify the presence or absence of any young stellar population to constrain the minimum time delay for each supernova. We find that early-type host galaxies lack 'prompt' SNe Ia with time delays of ≲100 Myr and that ∼70 per cent SNe Ia have minimum time delays of 275 Myr–1.25 Gyr, with a median of 650 Myr, while at least 20 per cent SNe Ia have minimum time delays of at least 1 Gyr at 95 per cent confidence and two of these four SNe Ia are likely older than 2 Gyr. The distribution of minimum time delays observed matches most closely the expectation for the single-degenerate channel with a main sequence donor. Furthermore, we do not find any evidence that subluminous SNe Ia are associated with long time delays.     

Supernovae with ''super-Hipparcos''

GAIA is the 'super- Hipparcos ' satellite scheduled for launch in 2010 by the European Space Agency. It is a scanning satellite that carries out multi-colour, multi-epoch photometry on all objects brighter than 20th mag. We conduct detailed simulations of supernovae (SNe) detection by GAIA . Supernovae of each type are chosen according to the observed distributions of absolute magnitudes, and located in nearby galaxies according to the local large-scale structure. Using an extinction model of the Galaxy and the scanning law of the GAIA satellite, we calculate how many SNe are detectable as a function of the phase of the light curve. Our study shows that GAIA will report data on ∼21 400 SNe during the five-year mission lifetime, of which ∼14 300 are SNe Ia, ∼1400 are SNe Ib/c and ∼5700 are SNe II. Using the simulations, we estimate that the numbers caught before maximum are ∼6300 SNe Ia, ∼500 SNe Ib/c and ∼1700 SNe II. During the mission lifetime, GAIA will issue about 5 SNe alerts a day.
The most distant SNe accessible to GAIA are at a redshift   z ∼ 0.14  and so GAIA will provide a huge sample of local SNe. There will be many examples of the rarer subluminous events, over-luminous events, SNe Ib/c and SNe II-L. SNe rates will be found as a function of galaxy type, as well as extinction and position in the host galaxy. Amongst other applications, there may be about 26 SNe each year for which detection of gravitational waves is possible and about 180 SNe each year for which detection of gamma-rays is possible. GAIA 's astrometry will provide the SN position to better than milliarcseconds, offering opportunities for the identification of progenitors in nearby galaxies and for studying the spatial distribution of SNe of different types in galaxies.     

WD + He star systems as the progenitors of Type Ia supernovae and their surviving companion stars

Employing Eggleton’s stellar evolution code with the optically thick wind assumption, we have systematically studied the WD + He star channel of Type Ia supernovae (SNe Ia), in which a carbon–oxygen WD accretes material from a He main-sequence star or a He subgiant to increase its mass to the Chandrasekhar mass. We mapped out the parameter spaces for producing SNe Ia. According to a detailed binary population synthesis approach, we find that the Galactic SN Ia birthrate from this channel is ～0.3×10^?3 yr^?1, and that this channel can produce SNe Ia with short delay times (～45–140 Myr). We also find that the surviving companion stars in this channel have a high spatial velocity (>400 km/s) after the SN explosion, which could be an alternative origin for hypervelocity stars (HVSs), especially for HVSs such as US 708.     

Variable equation of state for Bianchi type-VI<Subscript>0</Subscript> dark energy models

We present dark energy models in an anisotropic Bianchi type-VI₀ (B-VI₀) space-time with a variable equation of state (EoS). The EoS for dark energy ω is found to be time dependent and its existing range for derived models is in good agreement with the recent observations of SNe Ia data (Knop et al. in Astrophys. J. 598:102 2003), SNe Ia data with CMBR anisotropy and galaxy clustering statistics (Tegmark et al. in Astrophys. J. 606:702, 2004b) and latest a combination of cosmological datasets coming from CMB anisotropies, luminosity distances of high redshift type Ia supernovae and galaxy clustering (Hinshaw et al. in Astrophys. J. Suppl. 180:225, 2009; Komatsu et al. in Astrophys. J. Suppl. 180:330, 2009). The cosmological constant Λ is found to be a positive decreasing function of time and it approaches a small positive value at late time (i.e. the present epoch) which is corroborated by results from recent supernovae Ia observations. The physical and geometric aspects of the models are also discussed in detail.     

Intensive supernovae searches

In the coming years, a number of projects will start intensive supernovæsearches resulting in an increase of the current statistics by a factor of 10. At low redshift, the Nearby Supernova Factory will detect and follow spectrophotometricly ～ 400 of SNe Ia with a redshift at z ～ 0.05, and improve our understanding of the intrinsic properties of SNe Ia. At high redshift, the large imager Megacam at the Canada-France-Hawaii Telescope running in a survey mode, will make it possible to detect and follow a large amount of high redshift supernovae. Using Megacam during 5 years ～ 1000 Type Ia SNe will be detected, at z ranging from 0.3 to 1.2, and ～ 700 will be used for measuring the cosmological parameters via the Hubble diagram. They will provide a measurement of the cosmic equation of state parameter w. A first test run search was done last spring at the CFHT, using the current imager: the `CFH 12k'. Detection procedure and preliminary results are presented in this article.     

Evolution of the number of accreting white dwarfs with shell nuclear burning and the SNe Ia rate

We analyze the time evolution of the number of accreting white dwarfs with surface shell hydrogen burning in semidetached and detached binaries. We consider the case where continuous star formation with a constant rate takes place in a stellar system over 10¹⁰ Gyr and the case of a starburst in which the same mass of stars is formed over 10⁹ Gyr. The evolution of the number of white dwarfs is compared with the evolution of the rate of events that are usually considered as SNe Ia and/or accretion-induced collapses, i.e., the accumulation of a Chandrasekhar mass by white dwarfs or the merger of white dwarf pairs with a total mass greater than or equal to the Chandrasekhar one. In stellar systems with a starburst, the supersoft X-ray sources observed at t = 10¹⁰ yr are most likely not the progenitors of SNe Ia. The same is true for a significant fraction of the sources in systems with a constant star formation rate. In both cases, the merger of white dwarfs is the dominant mechanism of SNe Ia. In symbiotic binaries, accreting CO dwarfs do not accumulate enough mass for an SNe Ia explosion, while ONeMg dwarfs finish their evolution by an accretion-induce collapse with the formation of a neutron star.     

Gravitational lensing of type Ia supernovae by galaxy clusters

We propose a method to remove the mass-sheet degeneracy that arises when the mass of galaxy clusters is inferred from gravitational shear. The method utilizes high-redshift standard candles that undergo weak lensing. Natural candidates for such standard candles are type Ia supernovae (SNe Ia).
When corrected with the light-curve shape (LCS), the peak magnitude of SNe Ia provides a standard candle with an uncertainty in apparent magnitude of Δ m ≃0.1–0.2. Gravitational magnification of a background SN Ia by an intervening cluster would cause a mismatch between the observed SN Ia peak magnitude compared with that expected from its LCS and redshift. The average detection rate for SNe Ia with a significant mismatch of ≥2Δ m behind a cluster at z ≃0.05–0.15 is about 1–2 supernovae per cluster per year at J , I , R ≲25–26.
Since SNe are point-like sources for a limited period, they can experience significant microlensing by massive compact halo objects (MACHOs) in the intracluster medium. Microlensing events caused by MACHOs of ∼10⁻⁴ M⊙ are expected to have time-scales similar to that of the SN light curve. Both the magnification curve by a MACHO and the light curve of a SN Ia have characteristic shapes that allow us to separate them. Microlensing events caused by MACHOs of smaller mass can unambiguously be identified in the SN light curve if the latter is continuously monitored. The average number of identifiable microlensing events per nearby cluster ( z ≲0.05) per year is ∼0.02 ( f /0.01), where f is the fraction of the cluster mass in MACHOs of masses 10⁻⁷< M _macho/M⊙<10⁻⁴.     

Dark energy model in anisotropic Bianchi type-III space-time with variable EoS parameter

A new dark energy model in anisotropic Bianchi type-III space-time with variable equation of state (EoS) parameter has been investigated in the present paper. To get the deterministic model, we consider that the expansion θ in the model is proportional to the eigen value s² ₂\sigma^{2}_{~2} of the shear tensor s^j _i\sigma^{j}_{~i}. The EoS parameter ω is found to be time dependent and its existing range for this model is in good agreement with the recent observations of SNe Ia data (Knop et al. in Astrophys. J. 598:102, 2003) and SNe Ia data with CMBR anisotropy and galaxy clustering statistics (Tegmark et al. in Astrophys. J. 606:702, 2004). It has been suggested that the dark energy that explains the observed accelerating expansion of the universe may arise due to the contribution to the vacuum energy of the EoS in a time dependent background. Some physical aspects of dark energy model are also discussed.     

Ia超新星的几个问题

首先利用Ａｓｉａｇｏ 超新星星表对Ｉａ 超新星作了统计分析。其次用具有精确测光的Ｉａ 超新星对其均匀性及多样性进行了研究。旋涡星系中Ｉａ 超新星的产生率比椭圆星系的要高。最亮的Ｉａ 超新星只出现于晚型旋涡星系中;而旋涡星系及早型的椭圆星系都是暗Ｉａ 超新星的寄主星系。离星系中心越近Ｉａ 超新星的光度弥散有增加的趋势,但这一趋势对蓝Ｉａ 超新星不明显。利用色指数可将Ｉａ 超新星划分为蓝超新星及红超新星。蓝Ｉａ 超新星构成了相对均匀的Ｉａ 超新星样本,是较好的距离指示器;而红Ｉａ 超新星的存在则表明了Ｉａ 超新星整体多样性的特点。最后,我们还探讨了Ｉａ 超新星中碳点火的非线性问题。     

Studying the diverse nature of faint galaxies in nearby clusters of the WINGS sample

We present the first results of our X‐shooter observations for a sample of dwarf (–17 < M_B < –15) galaxies in nearby (0.04 < z < 0.07) galaxy clusters. This luminosity range is fundamental to trace the evolution of higher‐z star‐forming cluster galaxies down to the present day, and to explore the galaxy scaling relations of early‐type galaxies over a broad mass range. Thanks to high resolution and availability of several lines we can derive the velocity dispersion of the galaxies in this range of luminosities and we begin the construction of the fundamental plane of faint early‐type galaxies (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

WD+MS systems as the progenitor of SNe Ia

The single-degenerate (SD) channel for the progenitors of type Ia supernovae (SNe Ia) is one of the most popular channels, in which a carbon–oxygen white dwarf (CO WD) accretes hydrogen-rich material from its companion, increases its mass to the Chandrasekhar mass limit, and then explodes as a SN Ia. We show the initial and final parameter space for SNe Ia in a ( $\log P^{\mathrm{i}},M_{2}^{\mathrm{i}}$ ) plane and find that the positions of some famous recurrent novae, as well as a supersoft X-ray source (SSS), RX J0513.9-6951, are well explained by our model. The model can also explain the space velocity and mass of Tycho G, which is now suggested to be the companion star of Tycho’s supernova. Our study indicates that the SSS, V Sge, might be the potential progenitor of supernovae like SN 2002ic if the delayed dynamical-instability model due to Han and Podsiadlowski (Mon. Not. R. Astron. Soc. 368:1095, 2006) is appropriate. Following the work of Meng et al. (Mon. Not. R. Astron. Soc. 395:2103, 2009a), we found that the SD model (WD+MS) with an optically thick wind can explain the birth rate of supernovae like SN 2006X and reproduce the distribution of the color excess of SNe Ia. The model also predicts that at least 75% of all SNe Ia may show a polarization signal in their spectra.     

Modeling repulsive gravity with creation

There is a growing interest among cosmologists for theories with negative energy scalar fields and creation, in order to model a repulsive gravity. The classical steady state cosmology proposed by Bondi, Gold & Hoyle in 1948, was the first such theory which used a negative kinetic energy creation field to invoke creation of matter. We emphasize that creation plays a very crucial role in cosmology and provides a natural explanation to the various explosive phenomena occurring in local (z < 0.1) and extra galactic universe. We exemplify this point of view by considering the resurrected version of this theory — the quasi-steady state theory, which tries to relate creation events directly to the large scale dynamics of the universe and supplies more natural explanations of the observed phenomena. Although the theory predicts a decelerating universe at the present era, it explains successfully the recent SNe Ia observations (which require an accelerating universe in the standard cosmology), as we show in this paper by performing a Bayesian analysis of the data.     

Improving the calibration of Type Ia supernovae using late-time light curves

The use of Type Ia supernovae (SNe Ia) as cosmological standard candles is a key to solving the mystery of dark energy. Improving the calibration of SNe Ia increases their power as cosmological standard candles. We find tentative evidence for a correlation between the late-time light-curve slope and the peak luminosity of SNe Ia in the B band; brighter SNe Ia seem to have shallower light-curve slopes between 100 and 150 d from maximum light. Using a Markov Chain Monte Carlo (MCMC) analysis in calibrating SNe Ia, we are able to simultaneously take into consideration the effect of dust extinction, the luminosity and light-curve width correlation (parametrized by  Δ m ₁₅  ), and the luminosity and late-time light-curve slope correlation. For the available sample of 11 SNe Ia with well-measured late-time light curves, we find that correcting for the correlation between luminosity and late-time light-curve slope of the SNe Ia leads to an intrinsic dispersion of 0.12 mag in the Hubble diagram. Our results have significant implications for future supernova surveys aimed to illuminate the nature of dark energy.     

Are Type Ia Supernovae Reliable Distance Indicators？

Recent applications of type Ia supernovae(SNe Ia)in cosmology have successfully revealed the accelerating expansion of the universe.However,as distance indicators used in measuring the expansion history of the universe and probing the nature of dark energy,these objects must pass more strict tests.We propose a K-S test to investigate if there exists any systematic bias when deriving the luminosity distances under the standard candle assumption. Two samples,one comprising 71 high-redshift SNe Ia and the other,44 nearby ones,are used in our investigation.We find that it is likely there exists a bias in the adopted samples,which is probably caused by a systematic error,e.g.in the color parameter used in the luminosity calibration and a bias may be caused by the SN evolution or by varying properties of the dust surrounding the SNe Ia.     

Spectral and photometric monitoring of distant core-collapse supernovae in the SAO RAS

This paper describes the aims, objectives and first results of the observational program for the study of distant core-collapse supernovae (SNe) with redshifts z ≲ 0.3. This work is done within the framework of an international cooperation program on the SNe monitoring at the 6-m BTA telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences, and other telescopes. We study both the early phases of events (SN type determination, redshift estimation, and a search for manifestations of a wind envelope), and the nebular phase (the effects of explosion asymmetry). The SNe, associated with cosmic gamma-ray bursts are of particular interest. An interpretation of our observational data along with the data obtained on other telescopes is used to test the existing theoretical models of both the SN explosion, and the surrounding circumstellar medium. In 2009 we observed 30 objects; the spectra were obtained for 12 of them. We determined the types, phases after maximum, and redshifts for five SNe (SN 2009db, SN 2009dy, SN 2009dw, SN 2009ew, SN 2009ji). Based on the obtained photometric data a discovery of two more SNe was confirmed (SN 2009bx and SN 2009cb). A study of two type II supernovae in the nebular phase (SN 2008gz and SN 2008in) is finalized, four more objects (SN 2008iy, SN 2009ay, SN 2009bw, SN 2009de) are currently monitored.