Faint Supernovae Research Articles

Nucleosynthesis in Supernovae

We present the status and open problems of nucleosynthesis in supernova explosions of both types, responsible for the production of the intermediate mass, Fe-group and heavier elements (with the exception of the main s-process). Constraints from observations can be provided through individual supernovae (SNe) or their remnants (e.g. via spectra and gamma-rays of decaying unstable isotopes) and through surface abundances of stars which witness the composition of the interstellar gas at their formation. With a changing fraction of elements heavier than He in these stars (known as metallicity) the evolution of the nucleosynthesis in galaxies over time can be determined. A complementary way, related to gamma-rays from radioactive decays, is the observation of positrons released in $\beta^{+}$ -decays, as e.g. from $^{26}\mbox{Al}$ , $^{44}\mbox{Ti}$ , $^{56,57}\mbox{Ni}$ and possibly further isotopes of their decay chains (in competition with the production of $e^{+}e^{-}$ pairs in acceleration shocks from SN remnants, pulsars, magnetars or even of particle physics origin). We discuss (a) the role of the core-collapse supernova explosion mechanism for the composition of intermediate mass, Fe-group (and heavier?) ejecta, (b) the transition from neutron stars to black holes as the final result of the collapse of massive stars, and the relation of the latter to supernovae, faint supernovae, and gamma-ray bursts/hypernovae, (c) Type Ia supernovae and their nucleosynthesis (e.g. addressing the $^{55}\mbox{Mn}$ puzzle), plus (d) further constraints from galactic evolution, $\gamma$ -ray and positron observations. This is complemented by the role of rare magneto-rotational supernovae (related to magnetars) in comparison with the nucleosynthesis of compact binary mergers, especially with respect to forming the heaviest r-process elements in galactic evolution.

OGLE-2014-SN-073 as a fallback accretion powered supernova

Abstract We investigate the possibility that the energetic Type II supernova OGLE-2014-SN-073 is powered by a fallback accretion following the failed explosion of a massive star. Taking massive hydrogen-rich supernova progenitor models, we estimate the fallback accretion rate and calculate the light-curve evolution of supernovae powered by the fallback accretion. We find that such fallback accretion powered models can reproduce the overall observational properties of OGLE-2014-SN-073. It may imply that some failed explosions could be observed as energetic supernovae like OGLE-2014-SN-073 instead of faint supernovae as previously proposed.

Abundance analysis of a CEMP-no star in the Carina dwarf spheroidal galaxy

Carbon-enhanced metal-poor (CEMP) stars bear important imprints of the early chemical enrichment of any stellar system. While these stars are known to exist in copious amounts in the Milky Way halo, detailed chemical abundance data from the faint dwarf spheroidal (dSph) satellites are still sparse, although the relative fraction of these stars increases with decreasing metallicity. Here, we report the abundance analysis of a metal-poor ([Fe/H]=$-2.5$ dex), carbon-rich ([C/Fe]=1.4 dex) star, ALW-8, in the Carina dSph using high-resolution spectroscopy obtained with the ESO/UVES instrument. Its spectrum does not indicate any over-enhancements of neutron capture elements. Thus classified as a CEMP-no star, this is the first detection of this kind of star in Carina. Another of our sample stars, ALW-1, is shown to be a CEMP-$s$ star, but its immediate binarity prompted us to discard it from a detailed analysis. The majority of the 18 chemical elements we measured are typical of Carina's field star population and also agree with CEMP stars in other dSph galaxies. Similar to the only known CEMP-no star in the Sculptor dSph and the weak-$r$-process star HD 122563, the lack of any strong barium-enhancement is accompanied by a moderate overabundance in yttrium, indicating a weak $r$-process activity. The overall abundance pattern confirms that, also in Carina, the formation site for CEMP-no stars has been affected by both faint supernovae and by standard core collapse supernovae. Whichever process was responsible for the heavy element production in ALW-8 must be a ubiquitous source to pollute the CEMP-no stars, acting independently of the environment such as in the Galactic halo or in dSphs.

CHEMICAL DIVERSITY IN THE ULTRA-FAINT DWARF GALAXY TUCANA II*

ABSTRACT We present the first detailed chemical abundance study of the ultra-faint dwarf galaxy Tucana II, based on high-resolution Magellan/MIKE spectra of four red giant stars. The metallicities of these stars range from [Fe/H] = −3.2 to −2.6, and all stars are low in neutron-capture abundances ([Sr/Fe] and [Ba/Fe] < −1). However, a number of anomalous chemical signatures are present. One star is relatively metal-rich ([Fe/H] = −2.6) and shows [Na, α, Sc/Fe] < 0, suggesting an extended star formation history with contributions from AGB stars and SNe Ia. Two stars with [Fe/H] < −3 are mildly carbon-enhanced ([C/Fe] ∼ 0.7) and may be consistent with enrichment by faint supernovae, if such supernovae can produce neutron-capture elements. A fourth star with [Fe/H] = −3 is carbon-normal, and exhibits distinct light element abundance ratios from the carbon-enhanced stars. This carbon-normal star implies that at least two distinct nucleosynthesis sources, both possibly associated with Population III stars, contributed to the early chemical enrichment of this galaxy. Despite its very low luminosity, Tucana II shows a diversity of chemical signatures that preclude it from being a simple “one-shot” first galaxy yet still provide a window into star and galaxy formation in the early universe.

Does the chemical signature of TYC 8442–1036–1 originate from a rotating massive star that died in a faint explosion?

Context. We have recently investigated the origin of chemical signatures observed in Galactic halo stars by means of a stochastic chemical evolution model. We have found that rotating massive stars are a promising way to explain several signatures observed in these fossil stars. Aims. In the present paper we discuss how the extremely metal-poor halo star TYC 8442-1036-1, for which we have now obtained detailed abundances from VLT-UVES spectra, fits into the framework of our previous work. Methods. We apply a standard 1D LTE analysis to the spectrum of this star. We measure the abundances of 14 chemical elements; for Na, Mg, Ca, Sc, Ti, V, Cr, Mn, Fe, Ni and Zn we compute the abundances using equivalent widths; for C, Sr and Ba we obtain the abundances by means of synthetic spectra generated by MOOG. Results. We find an abundance of [Fe/H]= $-$3.5 $\pm$0.13 dex based on our high resolution spectrum; this points to an iron content lower by a factor of three (0.5 dex) compared to the one obtained by a low resolution spectrum. The star has a [C/Fe] = 0.4 dex, and it is not carbon enhanced like most of the stars at this metallicity. Moreover, this star lies in the plane [Ba/Fe] vs. [Fe/H] in a relatively unusual position, shared by a few others galactic halo stars that is only marginally explained by our past results. Conclusions. The comparison of the model results with the chemical abundance characteristics of this group of stars can be improved if we consider in our model the presence of faint supernovae coupled with rotating massive stars. These results seem to imply that rotating massive stars and faint supernovae scenarios are complementary to each other, and are both required in order to match the observed chemistry of the earliest phases of the chemical enrichment of the Universe.

Limits on Population III star formation with the most iron-poor stars

We study the impact of star-forming minihaloes, and the initial mass function (IMF) of Population III (Pop III) stars, on the Galactic halo metallicity distribution function (MDF) and on the properties of C-enhanced and C-normal stars at [Fe/H] < −3. For our investigation we use a data-constrained merger tree model for the Milky Way formation, which has been improved to self-consistently describe the physical processes regulating star formation in minihaloes, including the poor sampling of the Pop III IMF. We find that only when star-forming minihaloes are included the low-Fe tail of the MDF is correctly reproduced, showing a plateau that is built up by C-enhanced metal-poor stars imprinted by primordial faint supernovae. The incomplete sampling of the Pop III IMF in inefficiently star-forming minihaloes (<10−3 M⊙ yr−1) strongly limits the formation of pair-instability supernovae (PISNe), with progenitor masses mPopIII = [140–260] M⊙, even when a flat Pop III IMF is assumed. Second-generation stars formed in environments polluted at >50 per cent level by PISNe are thus extremely rare, corresponding to ≈0.25 per cent of the total stellar population at [Fe/H] < −2, which is consistent with recent observations. The low-Fe tail of the MDF strongly depends on the Pop III IMF shape and mass range. Given the current statistics, we find that a flat Pop III IMF model with mPopIII = [10–300] M⊙ is disfavoured by observations. We present testable predictions for Pop III stars extending down to lower masses, with mPopIII = [0.1–300] M⊙.

Dead or Alive? Long-term evolution of SN 2015bh (SNhunt275)

Supernova (SN) 2015bh (or SNhunt275) was discovered in NGC 2770 on 2015 February with an absolute magnitude of Mr ~ -13.4 mag, and was initially classified as a SN impostor. Here we present the photometric and spectroscopic evolution of SN 2015bh from discovery to late phases (~ 1 yr after). In addition, we inspect archival images of the host galaxy up to ~ 21 yr before discovery, finding a burst ~ 1 yr before discovery, and further signatures of stellar instability until late 2014. Later on, the luminosity of the transient slowly increases, and a broad light curve peak is reached after about three months. We propose that the transient discovered in early 2015 could be a core-collapse SN explosion. The pre-SN luminosity variability history, the long-lasting rise and faintness first light curve peak suggests that the progenitor was a very massive, unstable and blue star, which exploded as a faint SN because of severe fallback of material. Later on, the object experiences a sudden brightening of 3 mag, which results from the interaction of the SN ejecta with circumstellar material formed through repeated past mass-loss events. Spectroscopic signatures of interaction are however visible at all epochs. A similar chain of events was previously proposed for the similar interacting SN 2009ip.

DETECTION OF PHOSPHORUS, SULPHUR, AND ZINC IN THE CARBON-ENHANCED METAL-POOR STAR BD+44 493*

ABSTRACT The carbon-enhanced metal-poor star BD+44°493 ([Fe/H] = −3.9) has been proposed as a candidate second-generation star enriched by metals from a single Pop III star. We report the first detections of P and S and the second detection of Zn in any extremely metal-poor carbon-enhanced star, using new spectra of BD+44°493 collected by the Cosmic Origins Spectrograph on the Hubble Space Telescope. We derive [P/Fe] = −0.34 ± 0.21, [S/Fe] = +0.07 ± 0.41, and [Zn/Fe] = −0.10 ± 0.24. We increase by 10-fold the number of Si i lines detected in BD+44°493, yielding [Si/Fe] = +0.15 ± 0.22. The [S/Fe] and [Zn/Fe] ratios exclude the hypothesis that the abundance pattern in BD+44°493 results from depletion of refractory elements onto dust grains. Comparison with zero-metallicity supernova (SN) models suggests that the stellar progenitor that enriched BD+44°493 was massive and ejected much less than 0.07 M ⊙ of 56Ni, characteristic of a faint SN.

Abundances of carbon-enhanced metal-poor stars as constraints on their formation

An increasing fraction of carbon-enhanced metal-poor (CEMP) stars is found as their iron abundance, [Fe/H], decreases below [Fe/H] = -2.0. The CEMP-s stars have the highest absolute carbon abundances, [C/H], and are thought to owe their enrichment in carbon and the slow neutron-capture (s-process) elements to mass transfer from a former asymptotic giant-branch (AGB) binary companion. The most Fe-poor CEMP stars are normally single, exhibit somewhat lower [C/H] than CEMP-s stars, but show no s-process element enhancement (CEMP-no stars). CNO abundance determinations offer clues to their formation sites. C, N, Sr, and Ba abundances (or limits) and 12C/13C ratios where possible are derived for a sample of 27 faint metal-poor stars for which the X-shooter spectra have sufficient S/N ratios. These moderate resolution, low S/N (~10-40) spectra prove sufficient to perform limited chemical tagging and enable assignment of these stars into the CEMP sub-classes (CEMP-s and CEMP-no). According to the derived abundances, 17 of our sample stars are CEMP-s and three are CEMP-no, while the remaining seven are carbon-normal. For four CEMP stars, the sub-classification remains uncertain, and two of them may be pulsating AGB stars. The derived stellar abundances trace the formation processes and sites of our sample stars. The [C/N] abundance ratio is useful to identify stars with chemical compositions unaffected by internal mixing, and the [Sr/Ba] abundance ratio allows us to distinguish between CEMP-s stars with AGB progenitors and the CEMP-no stars. Suggested formation sites for the latter include faint supernovae with mixing and fallback and/or primordial, rapidly-rotating, massive stars (spinstars). X-shooter spectra have thus proved to be valuable tools in the continued search for their origin. Abridged.

Carbon-enhanced metal-poor stars in dwarf galaxies

We investigate the frequency and origin of carbon-enhanced metal-poor (CEMP) stars in Local Group dwarf galaxies by means of a statistical, data-calibrated cosmological model for the hierarchical build-up of the Milky Way and its dwarf satellites. The model self-consistently explains the variation with dwarf galaxy luminosity of the observed: i) frequency and [Fe/H] range of CEMP stars; ii) metallicity distribution functions; iii) star formation histories. We show that if primordial faint supernovae dominated the early metal enrichment, then CEMP-no stars enriched by the first stellar generations should be present in all dwarf galaxies, with similar number of stars and CEMP fractions at [Fe/H]$< -4$. We demonstrate that the probability to observe a star that is carbon-enhanced within a given [Fe/H] range strongly depends on the luminosity of the dwarf galaxy and, on average, it is an order of magnitude lower in "classical" Sculptor-like dSph galaxies ($P\leq 0.02$) than in the least luminous ultra-faint dwarfs ($P \approx 0.1$). In addition, we explain why it may be easier to find CEMP-no stars at [Fe/H]$\approx -2$ in classical dSph galaxies than in ultra-faint dwarfs. These are consequences of the dramatic variation in the fraction of stars at [Fe/H]$<-3$ with galaxy luminosity: $\geq 40\%$ for galaxies with $L<10^5L_{\odot}$, and $\leq 0.2\%$ for $L>10^{7}L_{\odot}$. We present model predictions for the low Fe-tail and CEMP fraction of stars in dwarf galaxies, with particular emphasis on the Sculptor dSph, that can be used to shed light on the properties of the first stars.

Inhomogeneous chemical enrichment in the Galactic Halo

AbstractIn a galaxy, chemical enrichment takes place in an inhomogeneous fashion, and the Galactic Halo is one of the places where the inhomogeneous effects are imprinted and can be constrained from observations. I show this using my chemodynamical simulations of Milky Way type galaxies. The scatter in the elemental abundances originate from radial migration, merging/accretion of satellite galaxies, local variation of star formation and chemical enrichment, and intrinsic variation of nucleosynthesis yields. In the simulated galaxies, there is no strong age-metallicity relation. This means that the most metal-poor stars are not always the oldest stars, and can be formed in chemically unevolved clouds at later times. The long-lifetime sources of chemical enrichment such as asymptotic giant branch stars or neutron star mergers can contribute at low metallicities. The intrinsic variation of yields are important in the early Universe or metal-poor systems such as in the Galactic halo. The carbon enhancement of extremely metal-poor (EMP) stars can be best explained by faint supernovae, the low [α/Fe] ratios in some EMP stars naturally arise from low-mass (~ 13 - 15M⊙) supernovae, and finally, the [α/Fe] knee in dwarf spheroidal galaxies can be produced by subclasses of Type Ia supernovae such as SN 2002cx-like objects and sub-Chandrasekhar mass explosions.

TOPoS

In the course of the TOPoS (Turn Off Primordial Stars) survey, aimed at discovering the lowest metallicity stars, we have found several carbon-enhanced metal-poor (CEMP) stars. We here present our analysis of six CEMP stars. Calcium and carbon are the only elements that can be measured in all six stars. The range is -5.0<=[Ca/H]< -2.1 and 7.12<=A(C)<=8.65. For star SDSS J1742+2531 we were able to detect three FeI lines from which we deduced [Fe/H]=-4.80, from four CaII lines we derived [Ca/H]=-4.56, and from synthesis of the G-band we derived A(C)=7.26. For SDSS J1035+0641 we were not able to detect any iron lines, yet we could place a robust (3sigma) upper limit of [Fe/H]< -5.0 and measure the Ca abundance, with [Ca/H]=-5.0, and carbon, A(C)=6.90. No lithium is detected in the spectrum of SDSS J1742+2531 or SDSS J1035+0641, which implies a robust upper limit of A(Li)<1.8 for both stars. Our measured carbon abundances confirm the bimodal distribution of carbon in CEMP stars, identifying a high-carbon band and a low-carbon band. We propose an interpretation of this bimodality according to which the stars on the high-carbon band are the result of mass transfer from an AGB companion, while the stars on the low-carbon band are genuine fossil records of a gas cloud that has also been enriched by a faint supernova (SN) providing carbon and the lighter elements. (Abridged)

Decoding the stellar fossils of the dusty Milky Way progenitors

We investigate the metallicity distribution function (MDF) in the Galactic halo and the relative fraction of carbon-normal and carbon-rich stars. To this aim, we use an improved version of the semi-analytical code GAlaxy MErger Tree and Evolution (gamete), that reconstructs the hierarchical merger tree of the Milky Way (MW), following the star formation history and the metal and dust evolution in individual progenitors. The predicted scaling relations between the dust, metal and gas masses for MW progenitors show a good agreement with observational data of local galaxies and of gamma-ray burst (GRB) host galaxies at 0.1 < z < 6.3. Comparing the simulated and the observed MDF, we find that in order to predict the formation of hyper-iron-poor stars at [Fe/H] < −4, faint supernova (SN) explosions have to dominate the metal yields produced by Population III (Pop III) stars, disfavouring a Pop III initial mass function that extends to stellar masses >140 M⊙, into the Pair-Instability SN progenitor mass range. The relative contribution of C-normal and C-enhanced stars to the MDF and its dependence on [Fe/H] points to a scenario where the Pop III/II transition is driven by dust cooling, and the first low-mass stars form when the dust-to-gas ratio in their parent clouds exceeds a critical value of |${\cal D}_{\rm crit} = 4.4 \times 10^{-9}$|⁠. Other transition criteria do not predict any C-normal stars below [Fe/H] < −4, at odds with observations.

THE ORIGIN OF THE MOST IRON-POOR STAR

We investigate the origin of carbon-enhanced metal-poor (CEMP) stars starting from the recently discovered $\rm [Fe/H]<-7.1$ star SMSS J031300 (Keller et al. 2014). We show that the elemental abundances observed on the surface of SMSS J031300 can be well fit by the yields of faint, metal free, supernovae. Using properly calibrated faint supernova explosion models, we study, for the first time, the formation of dust grains in such carbon-rich, iron-poor supernova ejecta. Calculations are performed assuming both unmixed and uniformly mixed ejecta and taking into account the partial destruction by the supernova reverse shock. We find that, due to the paucity of refractory elements beside carbon, amorphous carbon is the only grain species to form, with carbon condensation efficiencies that range between (0.15-0.84), resulting in dust yields in the range (0.025-2.25)M$_{\odot}$. We follow the collapse and fragmentation of a star forming cloud enriched by the products of these faint supernova explosions and we explore the role played by fine structure line cooling and dust cooling. We show that even if grain growth during the collapse has a minor effect of the dust-to-gas ratio, due to C depletion into CO molecules at an early stage of the collapse, the formation of CEMP low-mass stars, such as SMSS J031300, could be triggered by dust cooling and fragmentation. A comparison between model predictions and observations of a sample of C-normal and C-rich metal-poor stars supports the idea that a single common pathway may be responsible for the formation of the first low-mass stars.

FAINT POPULATION III SUPERNOVAE AS THE ORIGIN OF THE MOST IRON-POOR STARS

The most iron-deficient stars in the Milky Way provide important observational constraints on the nature of astrophysical objects that have enriched the primordial gas with heavy elements from which these stars were formed. Among them, the recently discovered iron-deficient star SMSS J031300.36-670839.3 shows a remarkable chemical composition with non-detection of iron ([Fe/H]$<-7.1$) and large enhancement of carbon and magnesium relative to calcium. We investigate the supernova yields of metal-free (Population III) stars to interpret the observed abundance pattern for this star. We report that the high [C/Ca] and [C/Mg] ratios and upper limits determined for other elemental abundances are well reproduced with the yields of core-collapse supernovae (that have normal kinetic energies of explosion $E$ of $E_{51}=E/10^{51}$erg$=1$) or hypernovae ($E_{51}\geq 10$) of the Population III 25$M_{\odot}$ or 40$M_{\odot}$ stars. The best-fit model assumes that the explosion of the Population III progenitor undergoes extensive matter mixing and fallback, leaving behind a black hole remnant. In these models, Ca is produced by static/explosive O burning and incomplete Si burning in the Population III supernova/hypernova, in contrast to the suggestion that Ca is originated from the hot CNO cycle during the presupernova evolution. Among the five most iron-poor stars with [Fe/H]$<-4.5$, four carbon-enhanced stars are consistent with the faint supernova models with the ejected mass of $^{56}$Ni less than 10$^{-3}M_{\odot}$.

THE ORIGIN OF LOW [α/Fe] RATIOS IN EXTREMELY METAL-POOR STARS

We show that the low ratios of $\alpha$ elements (Mg, Si, and Ca) to Fe recently found for a small fraction of extremely metal-poor stars can be naturally explained with the nucleosynthesis yields of core-collapse supernovae, i.e., $13-25M_\odot$ supernovae, or hypernovae. For the case without carbon enhancement, the ejected iron mass is normal, consistent with observed light curves and spectra of nearby supernovae. On the other hand, the carbon enhancement requires much smaller iron production, and the low [$\alpha$/Fe] of carbon enhanced metal-poor stars can also be reproduced with $13-25M_\odot$ faint supernovae or faint hypernovae. Iron-peak element abundances, in particular Zn abundances, are important to put further constraints on the enrichment sources from galactic archaeology surveys.

A hadronic scenario for HESS J1818–154

Aims: G15.4+0.1 is a faint supernova remnant (SNR) that has recently been associated with the gamma-ray source HESS J1818-154. We investigate a hadronic scenario for the production of the gamma-ray emission. Methods: Molecular 13CO (J=1-0) taken from the Galactic Ring Survey (GRS) and neutral hydrogen (HI) data from the Southern Galactic Plane Survey (SGPS) have been used in combination with new 1420 MHz radio continuum observations carried out with the Giant Metrewave Radio Telescope (GMRT). Results: From the new observations and analysis of archival data we provided for the first time a reliable estimate for the distance to the SNR G15.4+0.1 and discovered molecular clouds located at the same distance. On the basis of HI absorption features, we estimate the distance to G15.4+0.1 in 4.8+/-1.0 kpc. The 13CO observations clearly show a molecular cloud about 5 arcmin in size with two bright clumps, labeled A and B, clump A positionally associated with the location of HESS J1818-154 and clump B in coincidence with the brightest northern border of the radio SNR shell. The HI absorption and the 13CO emission study indicates a possible interaction between the molecular material and the remnant. We estimate the masses and densities of the molecular gas as (1.2+/-0.5)X10^3 M_sun and (1.5+/-0.4)X10^3 cm^-3 for clump A and (3.0+/-0.7)X10^3 M_sun and (1.1+/-0.3)X10^3 cm^-3 for clump B. Calculations show that the average density of the molecular clump A is sufficient to produce the detected gamma-ray flux, thus favoring a hadronic origin for the high-energy emission.

Nucleosynthesis in Stars and the Chemical Enrichment of Galaxies

After the Big Bang, production of heavy elements in the early Universe takes place starting from the formation of the first stars, their evolution, and explosion. The first supernova explosions have strong dynamical, thermal, and chemical feedback on the formation of subsequent stars and evolution of galaxies. However, the nature of the Universe's first stars and supernova explosions has not been well clarified. The signature of the nucleosynthesis yields of the first stars can be seen in the elemental abundance patterns observed in extremely metal-poor stars. Interestingly, those patterns show some peculiarities relative to the solar abundance pattern, which should provide important clues to understanding the nature of early generations of stars. We thus review the recent results of the nucleosynthesis yields of mainly massive stars for a wide range of stellar masses, metallicities, and explosion energies. We also provide yields tables and examine how those yields are affected by some hydrodynamical effects during supernova explosions, namely, explosion energies from those of hypernovae to faint supernovae, mixing and fallback of processed materials, asphericity, etc. Those parameters in the supernova nucleosynthesis models are constrained from observational data of supernovae and metal-poor stars. Nucleosynthesis yields are then applied to the chemical evolution model of our Galaxy and other types of galaxies to discuss how the chemical enrichment process occurred during evolution.

Supernova Discoveries 2010–2011: Statistics and Trends

ABSTRACTWe have inspected all supernova discoveries reported during 2010 and 2011, a total of 538 events during 2010 and 926 events during 2011. This number includes a small number of supernova impostors (bright extragalactic eruptions) but not novae or events that turned out to be Galactic stars. We examine the statistics of all discovered objects, as well as those of the subset of spectroscopically-confirmed events. In these 2 years we see the rise of wide-field non-targeted supernova surveys to prominence, with the largest numbers of events reported by the CRTS and PTF surveys (572 and 393 events in total respectively, contributing together 74% of all reported discoveries in 2011), followed by the integrated contribution of numerous amateurs (184 events). Among spectroscopically-confirmed events the PTF (393 events) leads, followed by CRTS (170 events), and amateur discoveries (144 events). Traditional galaxy-targeted surveys, such as LOSS and CHASE, maintain a strong contribution (86 and 61 events, respectively) with high spectroscopic completeness (∼90%). It is interesting to note that the community managed to provide substantial spectroscopic follow-up for relatively brighter amateur discoveries (〈m〉 = 16.5 mag), but significant less help for fainter (and much more numerous) events promptly released by the CRTS (〈m〉 = 18.6 mag). Inspecting discovery magnitude and redshift distributions we find that PS1 discoveries have similar properties (〈m〉 = 21.6 mag, 〈z〉 = 0.23) to events found in previous seasons by cosmology-oriented projects (e.g., SDSS-II), while PTF (〈m〉 = 19.2 mag, 〈z〉 = 0.095) and CRTS (〈m〉 = 18.6 mag, 〈z〉 = 0.049) populate the relatively unexplored phase space of faint supernovae (SNe) (>19 mag) in nearby galaxies (mainly PTF), and events at 0.05 < z < 0.2 (CRTS and PTF). Examining the specific question of reporting channels over the previous dozen years, we find that traditional reports via CBET telegrams now account only for a minority of SN discoveries.

Supernova Yields for Chemical Evolution Modeling

AbstractWe review the recent results of the nucleosynthesis yields of massive stars. We examine how those yields are affected by some hydrodynamical effects during the supernova explosions, namely, explosion energies from those of hypernovae to faint supernovae, mixing and fallback of processed materials, asphericity, etc. Those parameters in the supernova nucleosynthesis models are constrained from observational data of supernovae and metal-poor stars. The elemental abundance patterns observed in extremely metal-poor stars show some peculiarities relative to the solar abundance pattern, which suggests the important contributions of hypernovae and faint supernovae in the early chemical enrichment of galaxies. These constraints on supernova nucleosynthesis are taken into account in the latest yield table for chemical evolution modeling.