Zero-age Main-sequence Mass Research Articles

Very massive stars, pair-instability supernovae and intermediate-mass black holes with the sevn code

Understanding the link between massive ($\gtrsim 30$ M$_{\odot{}}$) stellar black holes (BHs) and their progenitor stars is a crucial step to interpret observations of gravitational-wave events. In this paper, we discuss the final fate of very massive stars (VMSs), with zero-age main sequence (ZAMS) mass $>150$ M$_{\odot}$, accounting for pulsational pair-instability supernovae (PPISNe) and for pair-instability supernovae (PISNe). We describe an updated version of our population synthesis code SEVN, in which we added stellar evolution tracks for VMSs with ZAMS mass up to $350 $M$_{\odot{}}$ and we included analytical prescriptions for PPISNe and PISNe. We use the new version of SEVN to study the BH mass spectrum at different metallicity $Z$, ranging from $Z=2.0\times 10^{-4}$ to $Z=2.0\times 10^{-2}$. The main effect of PPISNe and PISNe is to favour the formation of BHs in the mass range of the first gravitational-wave event (GW150914), while they prevent the formation of remnants with mass 60 - 120 M$_{\odot{}}$. In particular, we find that PPISNe significantly enhance mass loss of metal-poor ($Z\leq 2.0\times 10^{-3}$) stars with ZAMS mass $60\leq $M$_{\mathrm{ZAMS}}/$M$_{\odot{}}\leq 125$. In contrast, PISNe become effective only for moderately metal-poor ($Z<8.0\times 10^{-3}$) VMSs. VMSs with M$_{\rm ZAMS}\gtrsim{}220$ M$_\odot$ and $Z<10^{-3}$ do not undergo PISNe and form intermediate-mass BHs (IMBHs, with mass $\gtrsim 200 $M$_{\odot{}}$) via direct collapse.

Hot gas around SN 1998bw: Inferring the progenitor from its environment

Spatially-resolved spectroscopy of the environments of explosive transients carries detailed information about the physical properties of the stellar population that gave rise to the explosion, and thus the progenitor itself. Here, we present new observations of ESO184-G82, the galaxy hosting the archetype of the $\gamma$-ray burst/supernova connection, GRB 980425/SN 1998bw, obtained with the integral-field spectrograph MUSE mounted at the Very Large Telescope. These observations have yielded detailed maps of emission-line strength for various nebular lines, as well as physical parameters such as dust extinction, stellar age, and oxygen abundance on spatial scales of 160 pc. The immediate environment of GRB 980425 is young (5-8 Myr) and consistent with a mildly-extinguished ($A_V\sim0.1\ \mathrm{mag}$) progenitor of zero-age main-sequence mass between 25 $M_{\odot}$ and 40 $M_{\odot}$ and oxygen abundance 12+log(O/H)~8.2 ($Z\sim0.3\ {Z}_\odot$), which is slightly lower than the one of an integrated measurement of the galaxy (12+log(O/H)~8.3) and a prominent nearby HII region (12+log(O/H)~8.4). This region is significantly younger than the explosion site, and we argue that a scenario in which the GRB progenitor formed in this environment and was subsequently ejected appears very unlikely. We show that empirical strong-line methods based on [OIII] and/or [NII] are inadequate to produce accurate maps of oxygen abundance at the level of detail of our MUSE observation as these methods strongly depend on the ionization state of the gas. The metallicity gradient in ESO184-G82 is -0.06 dex kpc$^{-1}$, indicating that the typical offsets of at most few kpc for cosmological GRBs on average have a small impact on oxygen abundance measurements at higher redshift.

Modelling the Type Ic SN 2004aw: a moderately energetic explosion of a massive C+O star without a GRB

An analysis of the Type Ic supernova (SN) 2004aw is performed by means of models of the photospheric and nebular spectra and of the bolometric light curve. SN2004aw is shown not to be ``broad-lined'', contrary to previous claims, but rather a ``fast-lined'' SN Ic. The spectral resemblance to the narrow-lined Type Ic SN1994I, combined with the strong nebular [O I] emission and the broad light curve, point to a moderately energetic explosion of a massive C+O star. The ejected 56Ni mass is ~0.2 Msun. The ejecta mass as constrained by the models is ~3-5 Msun, while the kinetic energy is estimated as KE ~3-6 e51 ergs. The ratio KE/Mej, the specific energy which influences the shape of the spectrum, is therefore ~1. The corresponding zero-age main-sequence mass of the progenitor star may have been ~23-28 Msun. Tests show that a flatter outer density structure may have caused a broad-lined spectrum at epochs before those observed without affecting the later epochs when data are available, implying that our estimate of KE is a lower limit. SN2004aw may have been powered by either a collapsar or a magnetar, both of which have been proposed for gamma-ray burst-supernovae. Evidence for this is seen in the innermost layers, which appear to be highly aspherical as suggested by the nebular line profiles. However, any engine was not extremely powerful, as the outer ejecta are more consistent with a spherical explosion and no gamma-ray burst was detected in coincidence with SN2004aw.

The Progenitor-Remnant Connection of Neutrino-Driven Supernovae Across the Stellar Mass Range

AbstractWe perform hydrodynamic supernova (SN) simulations in spherical symmetry for progenitor models with solar metallicity across the stellar mass range from 9.0 to 120 M⊙ to explore the progenitor-explosion and progenitor-remnant connections based on the neutrino-driven mechanism. We use an approximative treatment of neutrino transport and replace the high-density interior of the neutron star (NS) by an inner boundary condition based on an analytic proto-NS core-cooling model, whose free parameters are chosen to reproduce the observables of SN 1987A and the Crab SN for theoretical models of their progenitor stars.Judging the fate of a massive star, either a neutron star (NS) or a black hole (BH), solely by its structure prior to collapse has been ambiguous. Our work and previous attempts find a non-monotonic variation of successful and failed supernovae with zero-age main-sequence mass. We identify two parameters based on the “critical luminosity” concept for neutrino-driven explosions, which in combination allows for a clear separation of exploding and non-exploding cases.Continuing our simulations beyond shock break-out, we are able to determine nucleosynthesis, light curves, explosion energies, and remnant masses. The resulting NS initial mass function has a mean gravitational mass near 1.4 M⊙. The average BH mass is about 9 M⊙ if only the helium core implodes, and 14 M⊙ if the entire pre-SN star collapses. Only ~10% of SNe come from stars over 20 M⊙, and some of these are Type Ib or Ic.

NUMERICAL MODELING OF THE EARLY LIGHT CURVES OF TYPE IIP SUPERNOVAE

ABSTRACT The early rise of Type IIP supernovae (SN IIP) provides important information for constraining the properties of their progenitors. This can, in turn, be compared to pre-explosion imaging constraints and stellar models to develop a more complete picture of how massive stars evolve and end their lives. Using the SuperNova Explosion Code (SNEC), we model the first 40 days of SNe IIP to better understand what constraints can be derived from their early light curves. We use two sets of red supergiant (RSG) progenitor models with zero-age main sequence masses in the range between and . We find that the early properties of the light curve depend most sensitively on the radius of the progenitor, and thus provide a relation between the g-band rise time and the radius at the time of explosion. This relation will be useful for deriving constraints on progenitors from future observations, especially in cases where detailed modeling of the entire rise is not practical. When comparing to observed rise times, the radii we find are a factor of a few larger than previous semi-analytic derivations and are generally in better agreement with what is found with current stellar evolution calculations as well as direct observations of RSGs.

The multifaceted Type II-L supernova 2014G from pre-maximum to nebular phase

We present multi-band ultraviolet, optical, and near-infrared photometry, along with visual-wavelength spectroscopy, of supernova (SN) 2014G in the nearby galaxy NGC 3448 (25 Mpc). The early-phase spectra show strong emission lines of the high ionisation species He II/N IV/C IV during the first 2-3 d after explosion, traces of a metal-rich CSM probably due to pre-explosion mass loss events. These disappear by day 9 and the spectral evolution then continues matching that of normal Type II SNe. The post-maximum light curve declines at a rate typical of Type II-L class. The extensive photometric coverage tracks the drop from the photospheric stage and constrains the radioactive tail, with a steeper decline rate than that expected from the $^{56}$Co decay if $\gamma$-rays are fully trapped by the ejecta. We report the appearance of an unusual feature on the blue-side of H$\alpha$ after 100 d, which evolves to appear as a flat spectral feature linking H$\alpha$ and the O I doublet. This may be due to interaction of the ejecta with a strongly asymmetric, and possibly bipolar CSM. Finally, we report two deep spectra at ~190 and 340 d after explosion, the latter being arguably one of the latest spectra for a Type II-L SN. By modelling the spectral region around the Ca II, we find a supersolar Ni/Fe production. The strength of the O I $\lambda\lambda$6300,6363 doublet, compared with synthetic nebular spectra, suggests a progenitor with a zero-age main-sequence mass between 15 and 19 M$_\odot$.

A TWO-PARAMETER CRITERION FOR CLASSIFYING THE EXPLODABILITY OF MASSIVE STARS BY THE NEUTRINO-DRIVEN MECHANISM

ABSTRACT Thus far, judging the fate of a massive star (either a neutron star [NS] or a black hole) solely by its structure prior to core collapse has been ambiguous. Our work and previous attempts find a nonmonotonic variation of successful and failed supernovae with zero-age main-sequence mass, for which no single structural parameter can serve as a good predictive measure. However, we identify two parameters computed from the pre-collapse structure of the progenitor, which in combination allow for a clear separation of exploding and nonexploding cases with only a few exceptions (∼1%–2.5%) in our set of 621 investigated stellar models. One parameter is M 4, defining the normalized enclosed mass for a dimensionless entropy per nucleon of s = 4, and the other is &mgr; 4 &Congruent; ( dm / M &CircleDot; ) / ( dr / 1000 km ) &mid; s = 4 ?> , being the normalized mass derivative at this location. The two parameters μ 4 and M 4 μ 4 can be directly linked to the mass-infall rate, M &DiacriticalDot; ?> , of the collapsing star and the electron-type neutrino luminosity of the accreting proto-NS, L &ngr; e &prop; M ns M &DiacriticalDot; ?> , which play a crucial role in the “critical luminosity” concept for the theoretical description of neutrino-driven explosions as runaway phenomena of the stalled accretion shock. All models were evolved employing the approach of Ugliano et al. for simulating neutrino-driven explosions in spherical symmetry. The neutrino emission of the accretion layer is approximated by a gray transport solver, while the uncertain neutrino emission of the 1.1 M ⊙ proto-NS core is parameterized by an analytic model. The free parameters connected to the core-boundary prescription are calibrated to reproduce the observables of SN 1987A for five different progenitor models.

Hydrodynamic simulations of the interaction between giant stars and planets

We present the results of hydrodynamic simulations of the interaction between a 10 Jupiter mass planet and a red or asymptotic giant branch stars, both with a zero-age main sequence mass of 3.5 $M_\odot$. Dynamic in-spiral timescales are of the order of few years and a few decades for the red and asymptotic giant branch stars, respectively. The planets will eventually be destroyed at a separation from the core of the giants smaller than the resolution of our simulations, either through evaporation or tidal disruption. As the planets in-spiral, the giant stars' envelopes are somewhat puffed up. Based on relatively long timescales and even considering the fact that further in-spiral should take place before the planets are destroyed, we predict that the merger would be difficult to observe, with only a relatively small, slow brightening. Very little mass is unbound in the process. These conclusions may change if the planet's orbit enhances the star's main pulsation modes. Based on the angular momentum transfer, we also suspect that this star-planet interaction may be unable to lead to large scale outflows via the rotation-mediated dynamo effect of Nordhaus and Blackman. Detectable pollution from the destroyed planets would only result for the lightest, lowest metallicity stars. We furthermore find that in both simulations the planets move through the outer stellar envelopes at Mach-3 to Mach-5, reaching Mach-1 towards the end of the simulations. The gravitational drag force decreases and the in-spiral slows down at the sonic transition, as predicted analytically.

LIGHT CURVES OF CORE-COLLAPSE SUPERNOVAE WITH SUBSTANTIAL MASS LOSS USING THE NEW OPEN-SOURCE SUPERNOVA EXPLOSION CODE (SNEC)

We present the SuperNova Explosion Code (SNEC), an open-source Lagrangian code for the hydrodynamics and equilibrium-diffusion radiation transport in the expanding envelopes of supernovae. Given a model of a progenitor star, an explosion energy, and an amount and distribution of radioactive nickel, SNEC generates the bolometric light curve, as well as the light curves in different wavelength bands assuming black body emission. As a first application of SNEC, we consider the explosions of a grid of 15 M_⊙ (at zero-age main sequence) stars whose hydrogen envelopes are stripped to different extents and at different points in their evolution. The resulting light curves exhibit plateaus with durations of ∼20 − 100 days if & 1.5 − 2 M_⊙ of hydrogen-rich material is left and no plateau if less hydrogen-rich material is left. The shorter plateau lengths are unlike the Type IIP supernova light curves typically observed in nature. This suggests that, at least for zero-age main sequence masses . 20 M_⊙, hydrogen mass loss occurs as an all or nothing process, perhaps pointing to the important role binary interactions play in observed mass-stripped supernovae (i.e., Type Ib/c events). These light curves are also unlike what is typically seen for Type IIL supernovae, arguing that simply varying the amount of mass loss cannot explain these events. The most stripped models begin to show double-peaked light curves similar to what is often seen for Type IIb supernovae, confirming previous work that these supernovae can come from progenitors that have a small amount of hydrogen and a radius of ∼ 500 R_⊙.

Systematic features of axisymmetric neutrino-driven core-collapse supernova models in multiple progenitors

Abstract We present an overview of two-dimensional (2D) core-collapse supernova simulations employing a neutrino transport scheme by the isotropic diffusion source approximation. We study 101 solar-metallicity, 247 ultra metal-poor, and 30 zero-metal progenitors covering zero-age main sequence mass from 10.8 M⊙ to 75.0 M⊙. Using the 378 progenitors in total, we systematically investigate how the differences in the structures of these multiple progenitors impact the hydrodynamics evolution. By following a long-term evolution over 1.0 s after bounce, most of the computed models exhibit neutrino-driven revival of the stalled bounce shock at ∼200–800 ms postbounce, leading to the possibility of explosion. Pushing the boundaries of expectations in previous one-dimensional studies, our results confirm that the compactness parameter ξ that characterizes the structure of the progenitors is also a key in 2D to diagnosing the properties of neutrino-driven explosions. Models with high ξ undergo high ram pressure from the accreting matter onto the stalled shock, which affects the subsequent evolution of the shock expansion and the mass of the protoneutron star under the influence of neutrino-driven convection and the standing accretion-shock instability. We show that the accretion luminosity becomes higher for models with high ξ, which makes the growth rate of the diagnostic explosion energy higher and the synthesized nickel mass bigger. We find that these explosion characteristics tend to show a monotonic increase as a function of the compactness parameter ξ.

Massive stars on the verge of exploding: the properties of oxygen sequence Wolf-Rayet stars

Context. Oxygen sequence Wolf-Rayet (WO) stars represent a very rare stage in the evolution of massive stars. Their spectra show strong emission lines of helium-burning products, in particular highly ionized carbon and oxygen. The properties of WO stars can be used to provide unique constraints on the (post-)helium burning evolution of massive stars, as well as their remaining lifetime and the expected properties of their supernovae. Aims. We aim to homogeneously analyse the currently known presumed-single WO stars to obtain the key stellar and outflow properties and to constrain their evolutionary state. Methods. We use the line-blanketed non-local thermal equilibrium atmosphere code cmfgen to model the X-Shooter spectra of the WO stars and deduce the atmospheric parameters. We calculate dedicated evolutionary models to determine the evolutionary state of the stars. Results. The WO stars have extremely high temperatures that range from 150 kK to 210 kK, and very low surface helium mass fractions that range from 44% down to 14%. Their properties can be reproduced by evolutionary models with helium zero-age main sequence masses of $M_{\mathrm{He, ini}} = 15-25 M_{\odot}$ that exhibit a fairly strong (on the order of a few times $10^{-5} M_{\odot} \mathrm{yr}^{-1}$), homogeneous ($f_\mathrm{c} > 0.3$) stellar wind. Conclusions. WO stars represent the final evolutionary stage of stars with estimated initial masses of $M_{\mathrm{ini}} = 40-60 M_{\odot}$. They are post core-helium burning and predicted to explode as type Ic supernovae within a few thousand years.

SN 2009ib: a Type II-P supernova with an unusually long plateau

We present optical and near-infrared photometry and spectroscopy of SN 2009ib, a Type II-P supernova in NGC 1559. This object has moderate brightness, similar to those of the intermediate-luminosity SNe 2008in and 2009N. Its plateau phase is unusually long, lasting for about 130 d after explosion. The spectra are similar to those of the subluminous SN 2002gd, with moderate expansion velocities. We estimate the 56Ni mass produced as 0.046 ± 0.015 M⊙. We determine the distance to SN 2009ib using both the expanding photosphere method (EPM) and the standard candle method. We also apply EPM to SN 1986L, a Type II-P SN that exploded in the same galaxy. Combining the results of different methods, we conclude the distance to NGC 1559 as D = 19.8 ± 3.0 Mpc. We examine archival, pre-explosion images of the field taken with the Hubble Space Telescope, and find a faint source at the position of the SN, which has a yellow colour [(V − I)0 = 0.85 mag]. Assuming it is a single star, we estimate its initial mass as MZAMS = 20 M⊙. We also examine the possibility, that instead of the yellow source the progenitor of SN 2009ib is a red supergiant star too faint to be detected. In this case, we estimate the upper limit for the initial zero-age main sequence (ZAMS) mass of the progenitor to be ∼14–17 M⊙. In addition, we infer the physical properties of the progenitor at the explosion via hydrodynamical modelling of the observables, and estimate the total energy as ∼0.55 × 1051 erg, the pre-explosion radius as ∼400 R⊙, and the ejected envelope mass as ∼15 M⊙, which implies that the mass of the progenitor before explosion was ∼16.5–17 M⊙.

THE BLACK HOLE FORMATION PROBABILITY

A longstanding question in stellar evolution is which massive stars produce black holes (BHs) rather than neutron stars (NSs) upon death. It has been common practice to assume that a given zero-age main sequence (ZAMS) mass star (and perhaps a given metallicity) simply produces either an NS or a BH, but this fails to account for a myriad of other variables that may effect this outcome, such as spin, binarity, or even stochastic differences in the stellar structure near core collapse. We argue that instead a probabilistic description of NS versus BH formation may be better suited to account for the current uncertainties in understanding how massive stars die. We present an initial exploration of the probability that a star will make a BH as a function of its ZAMS mass, $P_{\rm BH}(M_{\rm ZAMS})$. Although we find that it is difficult to derive a unique $P_{\rm BH}(M_{\rm ZAMS})$ using current measurements of both the BH mass distribution and the degree of chemical enrichment by massive stars, we demonstrate how $P_{\rm BH}(M_{\rm ZAMS})$ changes with these various observational and theoretical uncertainties. We anticipate that future studies of Galactic BHs and theoretical studies of core collapse will refine $P_{\rm BH}(M_{\rm ZAMS})$ and argue that this framework is an important new step toward better understanding BH formation. A probabilistic description of BH formation will be useful as input for future population synthesis studies that are interested in the formation of X-ray binaries, the nature and event rate of gravitational wave sources, and answering questions about chemical enrichment.

STOCHASTIC MICROHERTZ GRAVITATIONAL RADIATION FROM STELLAR CONVECTION

High-Reynolds-number turbulence driven by stellar convection in main-sequence stars generates stochastic gravitational radiation. We calculate the wave-strain power spectral density as a function of the zero-age main-sequence mass for an individual star and for an isotropic, universal stellar population described by the Salpeter initial mass function and redshift-dependent Hopkins-Beacom star formation rate. The spectrum is a broken power law, which peaks near the turnover frequency of the largest turbulent eddies. The signal from the Sun dominates the universal background. For the Sun, the far-zone power spectral density peaks at $S(f_\mathrm{peak}) = 5.2 \times 10^{-52}$ Hz$^{-1}$ at frequency $f_\mathrm{peak} = 2.3 \times 10^{-7}$ Hz. However, at low observing frequencies $f < 3 \times 10^{-4}$ Hz, the Earth lies inside the Sun's near zone and the signal is amplified to $S_\mathrm{near}(f_\mathrm{peak}) = 4.1 \times 10^{-27}$ Hz$^{-1}$ because the wave strain scales more steeply with distance ($\propto d^{-5}$) in the near zone than in the far zone ($\propto d^{-1}$). Hence the Solar signal may prove relevant for pulsar timing arrays. Other individual sources and the universal background fall well below the projected sensitivities of the Laser Interferometer Space Antenna and next-generation pulsar timing arrays. Stellar convection sets a fundamental noise floor for more sensitive stochastic gravitational-wave experiments in the more distant future.

DUST PRODUCTION FACTORIES IN THE EARLY UNIVERSE: FORMATION OF CARBON GRAINS IN RED-SUPERGIANT WINDS OF VERY MASSIVE POPULATION III STARS

We investigate the formation of dust in a stellar wind during the red-supergiant (RSG) phase of a very massive Population III star with the zero-age main sequence mass of 500 M_sun. We show that, in a carbon-rich wind with a constant velocity, carbon grains can form with a lognormal-like size distribution, and that all of the carbon available for dust formation finally condense into dust for wide ranges of the mass-loss rate ((0.1-3)x10^{-3} M_sun yr^{-1}) and wind velocity (1-100 km s^{-1}). We also find that the acceleration of the wind driven by newly formed dust suppresses the grain growth but still allows more than half of gas-phase carbon to be finally locked up in dust grains. These results indicate that at most 1.7 M_sun of carbon grains can form in total during the RSG phase of 500 M_sun Population III stars. Such a high dust yield could place very massive primordial stars as important sources of dust at the very early epoch of the universe if the initial mass function of Population III stars was top-heavy. We also briefly discuss a new formation scenario of carbon-rich ultra-metal-poor stars considering the feedback from very massive Population III stars.

Comprehensive photometric study of the eclipsing binary AW UMa

Due to its extreme mass ratio, the system AW UMa is considered as one of the most interesting contact binaries. In the present paper, a total of 1289 observations in VRI band were carried out from on 2006 March 7, 8, and 9 at Piszkesteto, Mountain Station of the Konkoly observatory (Hungary). VRI light curves were constructed and a photometric solution of these light curves was obtained by means of Willson-Devinney code. The results show that the primary component is more massive and hotter than the primary component by ∼140 K. A secular period decrease with a rate dP/dE=2.436×10−10 day/cycle was detected. Based on the physical parameters of the system, we investigate the evolutionary state of the components. The primary component is above the zero age main sequence (ZAMS) track, while the secondary component has a larger radius and luminosity than expected from its ZAMS mass.

ON THE ORIGIN OF THE B-STARS IN THE GALACTIC CENTER

We present a new directly-observable statistic which uses sky position and proper motion of stars near the Galactic center massive black hole to identify populations with high orbital eccentricities. It is most useful for stars with large orbital periods for which dynamical accelerations are difficult to determine. We apply this statistic to a data set of B-stars with projected radii 0."1 < p < 25" (~0.004 - 1 pc) from the massive black hole in the Galactic center. We compare the results with those from N-body simulations to distinguish between scenarios for their formation. We find that the scenarios favored by the data correlate strongly with particular K-magnitude intervals, corresponding to different zero-age main-sequence (MS) masses and lifetimes. Stars with 14 < mK < 15 (15 - 20 solar masses, t_{MS} = 8-13 Myr) match well to a disk formation origin, while those with mK > 15 (<15 solar masses, t_{MS} >13 Myr), if isotropically distributed, form a population that is more eccentric than thermal, which suggests a Hills binary-disruption origin.

SUPERNOVA REMNANT PROGENITOR MASSES IN M31

Using HST photometry, we age-date 59 supernova remnants (SNRs) in the spiral galaxy M31 and use these ages to estimate zero-age main sequence masses (MZAMS) for their progenitors. To accomplish this, we create color-magnitude diagrams (CMDs) and use CMD fitting to measure the recent star formation history (SFH) of the regions surrounding cataloged SNR sites. We identify any young coeval population that likely produced the progenitor star and assign an age and uncertainty to that population. Application of stellar evolution models allows us to infer the MZAMS from this age. Because our technique is not contingent on precise location of the progenitor star, it can be applied to the location of any known SNR. We identify significant young SF around 53 of the 59 SNRs and assign progenitor masses to these, representing a factor of 2 increase over currently measured progenitor masses. We consider the remaining 6 SNRs as either probable Type Ia candidates or the result of core-collapse progenitors that have escaped their birth sites. The distribution of recovered progenitor masses is bottom heavy, showing a paucity of the most massive stars. If we assume a single power law distribution, dN/dM proportional to M^alpha, we find a distribution that is steeper than a Salpeter IMF (alpha=-2.35). In particular, we find values of alpha outside the range -2.7 to -4.4 inconsistent with our measured distribution at 95% confidence. If instead we assume a distribution that follows a Salpeter IMF up to some maximum mass, we find that values of M_max greater than 26 Msun are inconsistent with the measured distribution at 95% confidence. In either scenario, the data suggest that some fraction of massive stars may not explode. The result is preliminary and requires more SNRs and further analysis. In addition, we use our distribution to estimate a minimum mass for core collapse between 7.0 and 7.8 Msun.

THE PROGENITOR MASS OF SN 2011dh FROM STELLAR POPULATION ANALYSIS

Using Hubble Space Telescope (HST) photometry, we characterize the age of the stellar association in the vicinity of supernova (SN) 2011dh and use it to infer the zero-age main sequence mass (M_{ZAMS}) of the progenitor star. We find two distinct and significant star formation events with ages of <6 and 17^{+3}_{-4} Myrs, and the corresponding M_{ZAMS} are >29 and 13^{+2}_{-1} M_{Sun}, respectively. These two bursts represent 18^{+4}_{-9}% (young) and 64^{+10}_{-14}% (old) of the total star formation in the last 50 Myrs. Adopting these fractions as probabilities suggests that the most probable M_{ZAMS} is 13^{+2}_{-1} M_{Sun}. These results are most sensitive to the luminosity function along the well-understood main sequence and are less sensitive to uncertain late-stage stellar evolution. Therefore, they stand even if the progenitor suffered disruptive post-main-sequence evolution (e.g. eruptive mass loss or binary Roche-lobe overflow). Progenitor identification will help to further constrain the appropriate population. Even though pre-explosion images show a yellow supergiant (YSG) at the site of the SN, panchromatic SN light curves suggest a more compact star as the progenitor. In spite of this, our results suggest an association between the YSG and the SN. Not only was the star located at the SN site, but reinforcing an association, the star's bolometric luminosity is consistent with the final evolutionary stage of the 17 Myr old star burst. If the YSG disappears, then M_{ZAMS}=13^{+2}_{-1} M_{Sun}, but if it persists, then our results allow the possibility that the progenitor was an unseen star of >29 M_{Sun}.

Habitability of super-Earth planets around main-sequence stars including red giant branch evolution: models based on the integrated system approach

AbstractIn a previous study published in Astrobiology, we focused on the evolution of habitability of a 10 M⊕ super-Earth planet orbiting a star akin to the Sun. This study was based on a concept of planetary habitability in accordance with the integrated system approach that describes the photosynthetic biomass production taking into account a variety of climatological, biogeochemical and geodynamical processes. In the present study, we pursue a significant augmentation of our previous work by considering stars with zero-age main-sequence masses between 0.5 and 2.0 M⊙ with special emphasis on models of 0.8, 0.9, 1.2 and 1.5 M⊙. Our models of habitability consider geodynamical processes during the main-sequence stage of these stars as well as during their red giant branch evolution. Pertaining to the different types of stars, we identify the so-called photosynthesis-sustaining habitable zone (pHZ) determined by the limits of biological productivity on the planetary surface. We obtain various sets of solutions consistent with the principal possibility of life. Considering that stars of relatively high masses depart from the main-sequence much earlier than low-mass stars, it is found that the biospheric lifespan of super-Earth planets of stars with masses above approximately 1.5 M⊙ is always limited by the increase in stellar luminosity. However, for stars with masses below 0.9 M⊙, the lifespan of super-Earths is solely determined by the geodynamic timescale. For central star masses between 0.9 and 1.5 M⊙, the possibility of life in the framework of our models depends on the relative continental area of the super-Earth planet.