We study the full evolution of a 1.313 Msun white dwarf star that descended from a 9 Msun main-sequence progenitor with an initial metallicity of Z=0.02. Using MESA r24.08.01, we calculate its entire evolution from pre-ZAMS to the WD cooling curve, including both the evolution through 139 thermal pulses and the post-AGB phase. The resulting remnant is an ultramassive H-deficient WD, for which the composition, in mass fraction, is 47.7% O16, 39.7% Ne20, 4.2% Mg24, 3.3% Na23 and 0.386% C12 -- corresponding to a total mass of 5 x 10^-3 Msun of C --, surrounded by a 1.5 x 10^-5 Msun He layer. We also investigate the effects of fully suppressing the TP-SAGB stage by adopting a high mass-loss rate only after the second dredge-up, and find only minor differences in the final mass and composition. In addition, we calculate models with and without phase separation during the WD stage, estimating a cooling delay of only 16 Myr. This is the first ultramassive white dwarf sequence for which both the TP-SAGB and post-AGB stages are calculated and, to our knowledge, the most massive WD model from complete evolution for which cooling times and detailed abundance profiles are published
With the Keck I Low-Resolution Imaging Spectrometer we have observed nine white dwarf candidates in the very rich open cluster NGC 2099 (M37). The spectroscopy shows seven to be DA white dwarfs, one to be a DB white dwarf, and one to be a DZ white dwarf. Three of these DA white dwarfs are consistent with singly evolved cluster membership: an ultramassive (1.28$^{+0.05}_{-0.08}$ M$_\odot$) and two intermediate-mass (0.70 and 0.75 M$_\odot$) white dwarfs. Analysis of their cooling ages allows us to calculate their progenitor masses and establish new constraints on the initial-final mass relation…
We announce the discovery of the most massive pulsating hydrogen-atmosphere (DA) white dwarf (WD) ever discovered, GD 518. Model atmosphere fits to the optical spectrum of this star show it is a 12,030 +/- 210 K WD with a log(g) = 9.08 +/- 0.06, which corresponds to a mass of 1.20 +/- 0.03 Msun. Stellar evolution models indicate that the progenitor of such a high-mass WD endured a stable carbon-burning phase, producing an oxygen-neon-core WD. The discovery of pulsations in GD 518 thus offers the first opportunity to probe the interior of a WD with a possible oxygen-neon core. Such a massive WD…
Following the discovery of the T8 subdwarf WISEJ200520.38+542433.9 (Wolf 1130C), with common proper motion to a binary (Wolf 1130AB) consisting of an M subdwarf and a white dwarf, we set out to learn more about the old binary in the system. We find that the A and B components of Wolf 1130 are tidally locked, which is revealed by the coherence of more than a year of V band photometry phase folded to the derived orbital period of 0.4967 days. Forty new high-resolution, near-infrared spectra obtained with the Immersion Grating Infrared Spectrometer (IGRINS) provide radial velocities and a project…
We searched through the entire Gaia EDR3 candidate white dwarf catalogue for stars with proper motions and positions that are consistent with the stars having escaped from the Alpha Persei cluster within the past 81~Myr, the age of the cluster. In this search we found five candidate white dwarf escapees from Alpha Persei and obtained spectra for all five. We confirm that three are massive white dwarfs sufficiently young to have originated in the cluster. All three are more massive than any white dwarf previously associated with a cluster using Gaia astrometry, and possess some of the most mass…
We present nebular phase optical and near-infrared spectroscopy of the Type IIP supernova SN 2012aw combined with NLTE radiative transfer calculations applied to ejecta from stellar evolution/explosion models. Our spectral synthesis models generally show good agreement with the ejecta from a MZAMS = 15 Msun progenitor star. The emission lines of oxygen, sodium, and magnesium are all consistent with the nucleosynthesis in a progenitor in the 14 - 18 Msun range. We also demonstrate how the evolution of the oxygen cooling lines of [O I] 5577 A, [O I] 6300 A, and [O I] 6364 A can be used to constr…
Diffusion of atoms can be important during quiescent phases of stellar evolution. Particularly in the very thin inert envelopes of subdwarf B stars, diffusive movements will considerably change the envelope structure and the surface abundances on a short timescale. Also, the subdwarfs will inherit the effects of diffusion in their direct progenitors, namely giants near the tip of the red giant branch. This will influence the global evolution and the pulsational properties of subdwarf B stars. We investigate the impact of gravitational settling, thermal diffusion and concentration diffusion on …
Previous studies of type IIP supernovae have inferred that progenitor masses recovered from hydrodynamic models are higher than 15 Msun. To verify the progenitor mass of this supernova category, we attempt a parameter determination of the well-observed luminous type IIP supernova 2004et. We model the bolometric light curve and the photospheric velocities of SN 2004et by means of hydrodynamic simulations in an extended parameter space. From hydrodynamic simulations and observational data, we infer a presupernova radius of 1500 Rsun, an ejecta mass of 24.5 Msun, an explosion energy of 2.3x10^{51…
The recent detection in archival HST images of an object at the the location of supernova (SN) iPTF13bvn may represent the first direct evidence of the progenitor of a Type Ib SN. The object's photometry was found to be compatible with a Wolf-Rayet pre-SN star mass of ~11 Msun. However, based on hydrodynamical models we show that the progenitor had a pre-SN mass of ~3.5 Msun and that it could not be larger than ~8 Msun. We propose an interacting binary system as the SN progenitor and perform evolutionary calculations that are able to self-consistently explain the light-curve shape, the absence…
A set of hydrodynamical models based on stellar evolutionary progenitors is used to study the nature of SN 2011dh. Our modeling suggests that a large progenitor star ---with R ~200 Rsun---, is needed to reproduce the early light curve of SN 2011dh. This is consistent with the suggestion that the yellow super-giant star detected at the location of the SN in deep pre-explosion images is the progenitor star. From the main peak of the bolometric light curve and expansion velocities we constrain the mass of the ejecta to be ~2 Msun, the explosion energy to be E= 6-10 x 10^50 erg, and the 56Ni mass …
We investigate the fundamental properties of core-collapse Supernova (SN) progenitors from single stars at solar metallicity. We combine Geneva stellar evolutionary models with initial masses of Mini=20-120 Msun with atmospheric/wind models using CMFGEN. We provide synthetic photometry and high-resolution spectra of hot stars at the pre-SN stage. For Mini=9-20 Msun, we supplement our analysis using publicly available MARCS model atmospheres of RSGs. We employ observational criteria of spectroscopic classification and find that massive stars, depending on Mini and rotation, end their lives as r…
HD188112 is an extremely low mass white dwarf in a close binary system. According to a previous study, the mass of HD188112 is $\sim$0.24 Msun and a lower limit of 0.73 Msun could be put for the mass of its unseen companion, a compact degenarate object. We used HST STIS spectra to measure the rotational broadening of UV metallic lines in HD188112, in order to put tighter constraints on the mass of its companion. By assuming that the system in is synchronous rotation, we derive a companion mass between 1.05 and 1.25 Msun. We also measure abundances for magnesium, silicon, and iron, respectively…
Evolution of a supernova type Ia progenitor requires formation of a CO white dwarf, which implies a dependence on the C burning rate (CBR). It can also be affected by the recently identified possibility of C flame quenching by convective boundary mixing. We present first results of our study of the combined effect of these two potential sources of uncertainty on the SN Ia progenitor evolution. We consider the possibility that the CBR is higher than its currently recommended value by as much as a factor of 1000 if unidentified resonances are important, or that it is significantly lower because …
The groundbreaking detection of gravitational waves produced by the inspiralling and coalescence of the black hole (BH) binary GW150914 confirms the existence of "heavy" stellar-mass BHs with masses >25 Msun. Initial modelling of the system by Abbott et al. (2016a) supposes that the formation of black holes with such large masses from the evolution of single massive stars is only feasible if the wind mass-loss rates of the progenitors were greatly reduced relative to the mass-loss rates of massive stars in the Galaxy, concluding that heavy BHs must form in low-metallicity (Z < 0.25-0.5 Zsun) e…
Core-collapse supernova (SN) explosions mark the end of the tumultuous life of massive stars. Determining the nature of their progenitors is a crucial step towards understanding the properties of SNe. Until recently, no progenitor has been directly detected for SN of type Ibc, which are believed to come from massive stars that lose their hydrogen envelope through stellar winds and from binary systems where the companion has stripped the H envelope from the primary. Here we analyze recently reported observations of iPTF13bvn, which could possibly be the first detection of a SN Ib progenitor bas…
We perform stellar evolution simulation of first stars and calculate stellar yields from the first supernovae. The initial masses are taken from 12 to 140 Msun to cover the whole range of core-collapse supernova progenitors, and stellar rotation is included, which results in efficient internal mixing. A weak explosion is assumed in supernova yield calculations, thus only outer distributed matter, which is not affected by the explosive nucleosynthesis, is ejected in the models. We show that the initial mass and the rotation affect the explosion yield. All the weak explosion models have abundanc…
Type IIb supernovae (SNe) present a unique opportunity for understanding the progenitors of stripped-envelope (SE) SNe as the stellar progenitor of several Type IIb SNe have been identified in pre-explosion images. In this paper, we use Bayesian inference and a large grid of non-rotating solar-metallicity single and binary stellar models to derive the associated probability distributions of single and binary progenitors of the Type IIb SN 2016gkg using existing observational constraints. We find that potential binary star progenitors have smaller pre-SN hydrogen-envelope and helium-core masses…
Using the intrinsic PSR J1903+0327 parameters evaluated from radio observations (mass, rotation period and dipole magnetic field deduced from the timing properties) we calculate the mass of its neutron star progenitor, M_i, at the onset of accretion. Simultaneously, we derive constraints on average accretion rate Mdot and the pre-accretion magnetic field B_i. Spin-up is modelled by accretion from a thin disk, using the magnetic-torque disk-pulsar coupling model proposed by Kluzniak and Rappaport (2007), improved for the existence of relativistic marginally-stable circular orbit. Orbital parame…
SN 2004et is one of the nearest and best-observed Type IIP supernovae, with a progenitor detection as well as good photometric and spectroscopic observational coverage well into the nebular phase. Based on nucleosynthesis from stellar evolution/explosion models we apply spectral modeling to analyze its 140-700 day evolution from ultraviolet to mid-infrared. We find a M_ZAMS= 15 Msun progenitor star (with an oxygen mass of 0.8 Msun) to satisfactorily reproduce [O I] 6300, 6364 Å and other emission lines of carbon, sodium, magnesium, and silicon, while 12 Msun and 19 Msun models under- and overp…
We investigate the evolution of Type Ib/c supernova (SN Ib/c) progenitors in close binary systems, using new evolutionary models that include the effects of rotation, with initial masses of 12 - 25 Msun for the primary components, and of single helium stars with initial masses of 2.8 - 20 Msun. We find that, despite the impact of tidal interaction on the rotation of primary stars, the amount of angular momentum retained in the core at the presupernova stage in different binary model sequences converge to a value similar to those found in previous single star models. This amount is large enough…
The explosion energy and the ejecta mass of a type IIP supernova make up the basis for the theory of explosion mechanism. So far, these parameters have only been determined for seven events. Type IIP supernova 2008in is another well-observed event for which a detailed hydrodynamic modeling can be used to derive the supernova parameters. Hydrodynamic modeling was employed to describe the bolometric light curve and the expansion velocities at the photosphere level. A time-dependent model for hydrogen ionization and excitation was applied to model the Halpha and Hbeta line profiles. We found an e…
We study the formation and destruction of molecules in the ejecta of Population III supernovae (SNe) using a chemical kinetic approach to follow the evolution of molecular abundances from day 100 to day 1000 after explosion. The chemical species included range from simple di-atomic molecules to more complex dust precursor species. All relevant chemical processes that are unique to the SN environment are considered. Our work focuses on zero-metallicity progenitors with masses of 20, 170, and 270 Msun, and we study the effect of different levels of heavy element mixing and the inward diffusion o…
Evolution and final fate of solar metallicity stars in the mass range 7-15 Msun. I. The transition from AGB to SAGB stars, Electron Capture and Core Collapse Supernovae progenitors
We present the one-year long observing campaign of SN 2012A which exploded in the nearby (9.8 Mpc) irregular galaxy NGC 3239. The photometric evolution is that of a normal type IIP supernova. The absolute maximum magnitude, with MB = -16.23 +- 0.16 mag. SN2012A reached a peak luminosity of about 2X10**42 erg/s, which is brighter than those of other SNe with a similar 56Ni mass. The latter was estimated from the luminosity in the exponential tail of the light curve and found to be M(56Ni) = 0.011 +-0.004 Msun. The spectral evolution of SN 2012A is also typical of SN IIP, from the early spectra …
Close double degenerate binaries are one of the favoured progenitor channels for type Ia supernovae, but it is unclear how many suitable systems there are in the Galaxy. We report results of a large radial velocity survey for double degenerate (DD) binaries using the UVES spectrograph at the ESO VLT (ESO SN Ia Progenitor surveY - SPY). Exposures taken at different epochs are checked for radial velocity shifts indicating close binary systems. We observed 689 targets classified as DA (displaying hydrogen-rich atmospheres), of which 46 turned out to possess a cool companion. We measured radial ve…
We identify SDSS J130033.48+590407.0 as a common proper motion companion to the well-studied DA white dwarf PG 1258+593 (GD322). The system lies at a distance of 68 +/- 3 pc, where the angular separation of 16.1 +/- 0.1 arcsec corresponds to a minimum binary separation of 1091 +/- 7 AU. SDSS J1300+5904 is a cool (Teff = 6300 +/- 300K) magnetic white dwarf (B ~ 6 MG). PG 1258+593 is a hydrogen-rich (DA) white dwarf with Teff=14790 +/- 77 K and log(g) = 7.87 +/- 0.02. Using the white dwarf mass-radius relation implies the masses of SDSS J1300+5904 and PG 1258+593 are 0.54 +/- 0.06 Msun and 0.54 …
We present an alternative technique for measuring the precursor masses of transient events in stars undergoing late stage stellar evolution. We use the well-established techniques of stellar population modeling to age-date the stars surrounding the site of the recent transient event in NGC 300 (NGC 300 OT2008-1). The surrounding stars must share a common turnoff mass with the transient, since almost all stars form in stellar clusters that remain physically associated for periods longer than the lifetime of the most massive stars. We find that the precursor of NGC 300 OT2008-1 is surrounded by …
The explosion of ultra-stripped stars in close binaries may explain new discoveries of weak and fast optical transients. We have demonstrated that helium star companions to neutron stars (NSs) may evolve into naked metal cores as low as ~1.5 Msun, barely above the Chandrasekhar mass limit, by the time they explode. Here we present a new systematic investigation of the progenitor evolution leading to such ultra-stripped supernovae (SNe), in some cases yielding pre-SN envelopes of less than 0.01 Msun. We discuss the nature of these SNe (electron-capture vs iron core-collapse) and their observati…
Through comparison of pre- and post-explosion images obtained with the Wide Field and Planetary Camera 2 onboard the Hubble Space Telescope, we have isolated a supergiant star prior to explosion at nearly the same position as the high-luminosity SN II-P 2008cn. We provide evidence that this supergiant may well be the progenitor of the SN, although this identification is not entirely unambiguous due mainly to the distance to the host galaxy (NGC 4603), 33.3 Mpc. The progenitor candidate has a more yellow color than generally would be expected and, if a single star, would require that it explode…
We perform binary stellar evolutionary calculations following the simultaneous evolution of both stars in the system to study a potential progenitor system for the Type IIb supernova 2011dh. Pre-explosion photometry as well as light-curve modeling have provided constraints on the physical properties of the progenitor system. Here we present a close binary system that is compatible with such constraints. The system is formed by stars of solar composition with 16 Msun + 10 Msun on a circular orbit with an initial period of 125 days. The primary star ends its evolution as a yellow supergiant with…
A precise knowledge of the masses of supernova progenitors is essential to answer various questions of modern astrophysics, such as those related to the dynamical and chemical evolution of Galaxies. In this paper we revise the upper bound for the mass of the progenitors of CO white dwarfs (\mup) and the lower bound for the mass of the progenitors of normal type II supernovae (\mups). In particular, we present new stellar models with mass between 7 and 10 \msun, discussing their final destiny and the impact of recent improvements in our understanding of the low energy rate of the \c12c12 reacti…
Stars more massive than about 8 Msun end their lives as a Supernova (SN), an event of fundamental importance Universe-wide. Theoretically, these stars have been expected to be either at the red supergiant, blue supergiant, or Wolf-Rayet stage before the explosion. We performed coupled stellar evolution and atmospheric modeling of stars with initial masses between 20 Msun and 120 Msun. We found that the 20 Msun and 25 Msun rotating models, before exploding as SN, have spectra that do not resemble any of the aforementioned classes of massive stars. Rather, they have remarkable similarities with …
Type IIP supernova progenitors are often surrounded by dense circumstellar media that may result from mass-loss enhancement of the progenitors shortly before their explosions. Previous light-curve studies suggest that the mass-loss rates are enhanced up to ~ 0.1 Msun/yr, assuming a constant wind velocity. However, density of circumstellar media at the immediate stellar vicinity can be much higher than previously inferred for a given mass-loss rate if wind acceleration is taken into account. We show that the wind acceleration has a huge impact when we estimate mass-loss rates from early light c…
We investigate the possibility of a super-luminous Type Ic core-collapse supernovae producing a large amount of 56Ni. Very massive stars with a main-sequence mass larger than 100 Msun and a metallicity 0.001 < Z < 0.004 are expected to explode as super-luminous Type Ic supernovae. Stars with ~ 110 - 150 Msun and Z < 0.001 would explode as Type Ic pulsational pair-instability supernovae if the whole H and He layers has been lost by the mass loss during pulsational pair-instability. We evaluate the total ejecta mass and the yields of 56Ni, O, and Si in core-collapse supernovae evolved from very …
We present the results of a photometric and spectroscopic monitoring campaign of SN 2012ec, which exploded in the spiral galaxy NGC 1084, during the photospheric phase. The photometric light curve exhibits a plateau with luminosity L= 0.9 x 10^{42} erg/s and duration ~90 days, which is somewhat shorter than standard Type II-P supernovae. We estimate the nickel mass as 0.040 +/- 0.015 Msun from the luminosity at the beginning of the radioactive tail of the light curve. The explosion parameters of SN 2012ec were estimated from the comparison of the bolometric light curve and the observed tempera…
We examine the possibility that very massive stars greatly exceeding the commonly adopted stellar mass limit of 150 Msun may be present in young star clusters in the local universe. We identify ten candidate clusters, some of which may host stars with masses up to 600 Msun formed via runaway collisions. We estimate the probabilities of these very massive stars being in eclipsing binaries to be >30%. Although most of these systems cannot be resolved at present, their transits can be detected at distances of 3 Mpc even under the contamination of the background cluster light, due to the large ass…
Taking into account the rotation of mass-accreting white dwarfs (WDs) whose masses exceed the Chandrasekhar mass, we extend our new single degenerate model for the progenitors of Type Ia supernovae (SNe Ia), accounting for two types of binary systems, those with a main sequence companion and those with a red-giant (RG) companion. We present a mass distribution of WDs exploding as SNe Ia, where the WD mass ranges from 1.38 to 2.3 Msun. These progenitor models are assigned to various types of SNe Ia. A lower mass range of WDs (1.38 Msun < M_WD <~ 1.5 Msun), which are supported by rigid rotation,…
SN 2011ja was a bright (I = -18.3) Type II supernova occurring in the nearby edge on spiral galaxy NGC 4945. Flat-topped and multi-peaked H-alpha and H-beta spectral emission lines appear between 64 - 84 days post-explosion, indicating interaction with a disc-like circumstellar medium inclined 30-45 degrees from edge-on. After day 84 an increase in the H- and K-band flux along with heavy attenuation of the red wing of the emission lines are strong indications of early dust formation, likely located in the cool dense shell created between the forward shock of the SN ejecta and the reverse shock…
HD 188112 is a bright (V = 10.2 mag) hot subdwarf B (sdB) star with a mass too low to ignite core helium burning and is therefore considered as a pre-extremely low mass (ELM) white dwarf (WD). ELM WDs (M $\le$ 0.3 Msun) are He-core objects produced by the evolution of compact binary systems. We present in this paper a detailed abundance analysis of HD 188112 based on high-resolution Hubble Space Telescope (HST) near and far-ultraviolet spectroscopy. We also constrain the mass of the star's companion. We use hybrid non-LTE model atmospheres to fit the observed spectral lines and derive the abun…
We examine the problem of estimating the mass range corresponding to the observed red supergiant (RSG) progenitors of Type IIP supernovae. Using Monte Carlo simulations designed to reproduce the properties of the observations, we find that the approach of Davies & Beasor (2018) significantly overestimates the maximum mass, yielding an upper limit of Mh/Msun=20.5+/-2.6 for an input population with Mh/Msun=18. Our preferred Bayesian approach does better, with Mh/Msun=18.6+/-2.1 for the same input populations, but also tends to overestimate Mh. For the actual progenitor sample and a Salpeter init…
We discuss the properties of the progenitors of core collapse SNe, as they can be deduced from rotating stellar models of single stars. The type of the SN progenitor was determined from the surface abundances at the pre-SN stage. The type of the SN event was obtained from the masses of hydrogen and helium ejected at the time of the core-collapse SN event. We find that the minimum amount of helium ejected by a core-collapse SN (of whatever type) is around 0.3 MSun. There is no difference between the WC and WO stars in the ejected masses of helium, CNO elements, and heavy elements. Also no diffe…
The recent mass measurements of two binary millisecond pulsars, PSR J1614-2230 and PSR J0751+1807 with a mass M=1.97+/-0.04 Msun and M= 1.26 +/- 0.14 Msun, respectively, indicate a wide range of masses for such objects and possibly also a broad spectrum of masses of neutron stars born in core-collapse supernovae. Starting from the zero-age main sequence binary stage, we aim at inferring the birth masses of PSR J1614-2230 and PSR J0751+1807 by taking the differences in the evolutionary stages preceding their formation into account. Using simulations for the evolution of binary stars, we reconst…
We study the evolution of the collapsing core of a 15 Msun blue supergiant supernova progenitor from the core bounce until 1.5 seconds later. We present a sample of hydrodynamic models parameterized to match the explosion energetics of SN 1987A. We find the spatial model dimensionality to be an important contributing factor in the explosion process. Compared to two-dimensional simulations, our three-dimensional models require lower neutrino luminosities to produce equally energetic explosions. We estimate that the convective engine in our models is 4% more efficient in three dimensions than in…
The first four gravitational wave events detected by LIGO were all interpreted as merging black hole binaries (BHBs), opening a new perspective on the study of such systems. Here we use our new population-synthesis code MOBSE, an upgraded version of BSE (Hurley et al. 2002), to investigate the demography of merging BHBs. MOBSE includes metallicity-dependent prescriptions for mass loss of massive hot stars. It also accounts for the impact of the electron-scattering Eddington factor on mass loss. We perform >10^8 simulations of isolated massive binaries, with 12 different metallicities, to study…
In this paper we analyse the pre-explosion spectrum of SN2015bh by performing radiative transfer simulations using the CMFGEN code. This object has attracted significant attention due to its remarkable similarity to SN2009ip in both its pre- and post-explosion behaviour. They seem to belong to a class of events for which the fate as a genuine core-collapse supernova or a non-terminal explosion is still under debate. Our CMFGEN models suggest that the progenitor of SN2015bh had an effective temperature between 8700 and 10000 K, luminosity in the range ~ 1.8-4.74e6 Lsun, contained at least 25% H…
Magnetars are regarded as the most magnetized neutron stars in the Universe. Aiming to unveil what kinds of stars and supernovae can create magnetars, we have performed a state-of-the-art spatially resolved spectroscopic X-ray study of the supernova remnants (SNRs) Kes 73, RCW 103, and N49, which host magnetars 1E 1841-045, 1E 161348-5055, and SGR 0526-66, respectively. The three SNRs are O- and Ne-enhanced and are evolving in the interstellar medium with densities of >1--2 cm$^{-3}$. The metal composition and dense environment indicate that the progenitor stars are not very massive. The proge…
The explosion energy and the ejecta mass of a type IIP supernova (SN IIP) derived from hydrodynamic simulations are principal parameters of the explosion theory. However, the number of SNe IIP studied by hydrodynamic modeling is small. Moreover, some doubts exist in regard to the reliability of derived SN IIP parameters. The well-observed type IIP SN 2012A will be studied via hydrodynamic modeling. Their early spectra will be checked for a presence of the ejecta clumpiness. Other observational effects of clumpiness will be explored. Supernova parameters are determined by means of the standard …
Observations spanning a large wavelength range, from X-ray to radio, of the Type IIb supernova 2011hs are presented, covering its evolution during the first year after explosion. The optical light curve presents a narrower shape and a fainter luminosity at peak than previously observed for Type IIb SNe. High expansion velocities are measured from the broad absorption H I and He I lines. From the comparison of the bolometric light curve and the time evolution of the photospheric velocities with hydrodynamical models, we found that SN 2011hs is consistent with the explosion of a 3-4 Msun He-core…
HD49798/RXJ0648.0-4418 is the only known X-ray binary composed of a hot subdwarf and a massive white dwarf (M=1.28+/-0.05 Msun). This system, with an orbital period of 1.55 days, is the outcome of a common envelope evolution, most likely of a pair of stars with initial masses of about 8-10 Msun. When the hot subdwarf, currently in a He-burning phase, will expand again and fill its Roche-lobe, the enhanced mass transfer can rapidly bring the already massive white dwarf above the Chandrasekhar limit. The possible final fate, either a Type Ia supernova explosion or an accretion induced collapse, …
We used a recent grid of stellar models computed with and without rotation to make predictions concerning the WR populations and the frequency of different types of core-collapse SNe. Current rotating models were checked to provide good fits to the following features: solar luminosity and radius at the solar age, main-sequence width, red-giant and red-supergiant (RSG) positions in the HRD, surface abundances, and rotational velocities. Rotating stellar models predict that about half of the observed WR stars and at least half of the type Ibc SNe may be produced through the single-star evolution…
HD 179821 is classified as G5 Ia star. From the IRAS colors and spectral energy distributions it was classified as a post-AGB star. But some studies classify it as a massive (30 to 19 Msun ) post-red supergiant evolving to become a Type II supernova. Its mass and evolutionary status remained a hotly debated question even after several detailed spectroscopic studies as the distance was not known. We use the parallax of HD 179821 from the second Gaia data release, and deduce its distance 2959 +/- 409 pc and its absolute magnitude MV = -5.7 +/- 0.3. Using the absolute magnitude determined in this…
We present the results of optical, near-infrared, and mid-infrared observations of M101 OT2015-1 (PSN J14021678+5426205), a luminous red transient in the Pinwheel galaxy (M101), spanning a total of 16 years. The lightcurve showed two distinct peaks with absolute magnitudes $M_r\leq-12.4$ and $M_r \simeq-12$, on 2014 November 11 and 2015 February 17, respectively. The spectral energy distributions during the second maximum show a cool outburst temperature of $\approx$3700 K and low expansion velocities ($\approx-$300 \kms) for the H I, Ca II, Ba II and K I lines. From archival data spanning 15 …
We investigate the low-luminosity supernova SN 2016bkv and its peculiar early-time interaction. For that, we compute radiative transfer models using the CMFGEN code. Because SN 2016bkv shows signs of interaction with material expelled by its progenitor, it offers a great opportunity to constrain the uncertain evolutionary channels leading to low-luminosity supernovae. Our models indicate that the progenitor had a mass-loss rate of (6.0 +- 2.0) x 1e-4 Msun/yr (assuming a velocity of 150 km/s). The surface abundances of the progenitor are consistent with solar contents of He and CNO. If SN 2016b…
We use the progenitor of SN2012aw to illustrate the consequences of modeling circumstellar dust using Galactic (interstellar) extinction laws that (1) ignore dust emission in the near-IR and beyond; (2) average over dust compositions, and (3) mis-characterize the optical/UV absorption by assuming that scattered photons are lost to the observer. The primary consequences for the progenitor of SN2012aw are that both the luminosity and the absorption are significantly over-estimated. In particular, the stellar luminosity is most likely in the range 10^4.8 < L/Lsun < 10^5.0 and the star was not ext…
