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J. J. Eldridge

Publications and source records attributed to J. J. Eldridge.

104 records · Page 6Linked to original sources
arXiv2008

Massive stars in their death-throes

The study of the stars that explode as supernovae used to be a forensic study, working backwards from the remnants of the star. This changed in 1987 when the first progenitor star was identified in pre-explosion images. Currently there are 8 detected progenitors with another 21 non-detections, for which only a limit on the pre-explosion luminosity can be placed. This new avenue of supernova research has led to many interesting conclusions, most importantly that the progenitors of the most common supernovae, type IIP, are red supergiants as theory has long predicted. However no progenitors have been detected thus far for the hydrogen-free type Ib/c supernovae which, given the expected progenitors, is an unlikely result. Also observations have begun to show evidence that luminous blue variables, which are among the most massive stars, may directly explode as supernovae. These results contradict current stellar evolution theory. This suggests that we may need to update our understanding.

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arXiv2008

Massive stars exploding in a He-rich circumstellar medium. I. Type Ibn (SN 2006jc-like) events

We present new spectroscopic and photometric data of the type Ibn supernovae 2006jc, 2000er and 2002ao. We discuss the general properties of this recently proposed supernova family, which also includes SN 1999cq. The early-time monitoring of SN 2000er traces the evolution of this class of objects during the first few days after the shock breakout. An overall similarity in the photometric and spectroscopic evolution is found among the members of this group, which would be unexpected if the energy in these core-collapse events was dominated by the interaction between supernova ejecta and circumstellar medium. Type Ibn supernovae appear to be rather normal type Ib/c supernova explosions which occur within a He-rich circumstellar environment. SNe Ibn are therefore likely produced by the explosion of Wolf-Rayet progenitors still embedded in the He-rich material lost by the star in recent mass-loss episodes, which resemble known luminous blue variable eruptions. The evolved Wolf-Rayet star could either result from the evolution of a very massive star or be the more evolved member of a massive binary system. We also suggest that there are a number of arguments in favour of a type Ibn classification for the historical SN 1885A (S-Andromedae), previously considered as an anomalous type Ia event with some resemblance to SN 1991bg.

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arXiv2007

M-Dwarfs at Large Heliocentric Distances

We present an analysis of the faint M star population seen as foreground contaminants in deep extragalactic surveys. We use space-based data to separate such stars from high redshift galaxies in a publically-available dataset, and consider the photometric properties of the resulting sample in the optical and infrared. The inferred distances place these stars well beyond the scale height of the thick disk. We find strong similarities between this faint sample (reaching i'_{AB}=25) and the brighter disk M dwarf population studied by other authors. The optical-infrared properties of the bulk of our sources spanning 6000A-4.5microns are consistent with those 5-10 magnitudes brighter. We also present deep spectroscopy of faint M dwarf stars reaching continuum limits of i'_{AB}~26, and measure absorption line strengths in the CaH2 and TiO5 bands. Both photometrically and spectroscopically, our sources are consistent with metallicities as low as a tenth solar: metal-rich compared with halo stars at similar heliocentric distances. We comment on the possible MACHO identification of M stars at faint magnitudes.

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arXiv2007

A deeper search for the progenitor of the Type Ic Supernova 2002ap

(Abridged) We present a search for the progenitor star of the Type Ic Supernova 2002ap in deep, high quality pre-explosion observations taken with the Canada-France-Hawaii Telescope (CFHT). Aligning high-resolution Hubble Space Telescope (HST) observations of the supernova itself with the archival CFHT images allowed us to pinpoint the location of the progenitor site on the ground based observations. We find that a source visible in the B and R band pre-explosion images close to the position of the SN is (1) not coincident with the SN position within the uncertainties of our relative astrometry, and (2) is still visible ~ 4.7 yrs post-explosion in late-time observations taken with the William Herschel Telescope. We therefore conclude that it is not the progenitor of SN 2002ap. Comparing our luminosity limits with stellar models of single stars at appropriate metallicity (Z=0.008) we conclude that any single star progenitor must have experienced at least twice the standard mass loss rates during pre-Wolf-Rayet evolution, been initially > 30-40M(Sun) and exploded as a Wolf-Rayet star of final mass 10-12M(Sun). Alternatively an initially less massive progenitor may have evolved in an interacting binary system. We constrain any possible binary companion to a main sequence star of < 20M(Sun), a neutron star or a black hole. By combining the pre-explosion limits with the ejecta mass estimates and constraints from X-ray and radio observations we conclude that any binary interaction most likely occurred as Case B mass transfer, either with or without a subsequent common envelope evolution phase.

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arXiv2007

A giant outburst two years before the core-collapse of a massive star

The death of massive stars produces a variety of supernovae, which are linked to the structure of the exploding stars. The detection of several precursor stars of Type II supernovae have been reported, however we do not yet have direct information on the progenitors of the hydrogen deficient Type Ib and Ic supernovae. Here we report that the peculiar Type Ib supernova SN2006jc is spatially coincident with a bright optical transient that occurred in 2004. Spectroscopic and photometric monitoring of the supernova leads us to suggest that the progenitor was a carbon-oxygen Wolf-Rayet star embedded within a helium-rich circumstellar medium. There are different possible explanations for this pre-explosion transient. It appears similar to the giant outbursts of Luminous Blue Variables (LBV) of 60-100 solar mass stars, however the progenitor of SN2006jc was helium and hydrogen deficient. An LBV-like outburst of a Wolf-Rayet star could be invoked, but this would be the first observational evidence of such a phenomenon. Alternatively a massive binary system composed of an LBV which erupted in 2004, and a Wolf-Rayet star exploding as SN2006jc, could explain the observations.

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arXiv2007

Asymmetric Wolf-Rayet winds: implications for GRB afterglows

Recent observations of Wolf-Rayet (WR) binaries WR151 and WR155 infer that their stellar winds are asymmetric. We show that such asymmetries can alter the stellar-wind bubble structure, bringing the wind-termination shock closer to the WR star. If the wind asymmetry is caused by rotation, the wind density and distance to the wind-termination shock are both decreased along the rotation axis by a factor of a few for the observed equator-to-pole wind density ratio of WR151. If this asymmetry lasts until core-collapse the time taken to reach the wind-termination shock by supernova ejecta or a gamma-ray burst jet is reduced. This leads to a distorted structure of the supernova ejecta and makes it more likely a constant density environment is inferred from gamma-ray burst afterglow observations.

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arXiv2007

Ruling out a massive-assymptoic giant-branch star as the progenitor of supernova 2005cs

We calculate the predicted UBVRIJHK absolute magnitudes for models of supernova progenitors and apply the result to the case of supernova 2005cs. We agree with previous results that the initial mass of the star was of low, around 6 to 8 M(sun). However such stars are thought to go through second dredge-up to become AGB stars. We show that had this occurred to the progenitor of 2005cs it would have been observed in JHK pre-explosion images. The progenitor was not detected in these bands and therefore we conclude that it was not an AGB star. Furthermore if some AGB stars do produce supernovae they will have a clear signature in pre-explosion near-infrared images. Electron-capture supernovae are thought to occur in AGB stars, hence the implication is that 2005cs was not an electron-capture supernova but was the collapse of an iron core.

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arXiv2006

Massive binaries, Wolf-Rayet stars and supernova progenitors

Binary stars are important for a full understanding of stellar evolution. We present a summary of how predictions of the relative supernova rates varies between single and binary stars. We also show how the parameter space of different supernova types differs between single and binary stars. We then consider an important question of how to infer a supernova progenitor's properties from pre-explosion imaging and present rescent work of producing synthe tic colours for our stellar models to make a direct comparison with any detections or limits obtained on supernova progentiors from pre-explosion images.

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arXiv2005

The circumstellar environment of Wolf-Rayet stars & Gamma-ray burst afterglows

We study the evolution of the circumstellar medium of massive stars. We pay particular attention to Wolf-Rayet stars that are thought to be the progenitors of some long Gamma-Ray Bursts. We detail the mass-loss rates we use in our stellar evolution models and how we estimate the stellar wind speeds during different phases. With these details we simulate the interactions between the wind and the interstellar medium to predict the circumstellar environment around the stars at the time of core-collapse. We then investigate how the structure of the environment might affect the GRB afterglow. We find that when the afterglow jet encounters the free-wind to stalled-wind interface that rebrightening occurs and a bump is seen in the afterglow light curve. However our predicted positions of this interface are too distant from the site of the GRB to reach while the afterglow remains observable. The values of the final-wind density, A_{*}, from our stellar models are similar to the values inferred from observed afterglow lightcurves and those from observed Wolf-Rayet stars. However we do not reproduce the lowest observed A_{*} values below 0.3. For these cases we suggest that the progenitors could have been a WO type Wolf-Rayet star, be in a close binary or very low metallicity star. Finally we turn our attention to the matter of stellar wind material producing absorption lines in the afterglow spectra. We discuss the observational signatures of two Wolf-Rayet stellar types, WC and WO, in the afterglow lightcurve and spectra. We also indicate how it may be possible to constrain the initial mass and metallicity of a GRB progenitor by using the inferred wind density and wind velocity.

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arXiv2004

The Progenitors of Core-Collapse Supernovae

We present maps of the nature of single star progenitors of supernovae and their remnants in mass and metallicity space. We find our results are similar to others but we have gone further in varying the amount of mixing and using various mass-loss schemes to see how the maps change. We find that extra-mixing, in the form of convective overshooting, moves boundaries such as the minimum mass for a supernova or WR star to lower masses. We also find that the pre-WR mass-loss determines the shape of our maps. We find that different mass-loss rates lead to quite different results. We find that the rise in luminosity at 2nd dredge-up places quite tight constraints on the masses of some progenitors and in particular the progenitor of supernova 2003gd.

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arXiv2003

A more detailed look at the Opacities for Enriched Carbon and Oxygen Mixtures

We have included opacity tables in our stellar evolution code that enable us to accurately model the structure of stars composed of mixtures with carbon and oxygen independently enhanced relative to solar. We present tests to demonstrate the effects of the new tables. Two of these are practical examples, the effect on the evolution of a thermally pulsing asymptotic giant branch star and a Wolf-Rayet Star. The changes are small but perceptible.

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