He II recombination lines as a test of the nature of SN Ia progenitors in elliptical galaxies

To date, the question of which progenitor channel can reproduce the observed rate of Type Ia supernovae (SNe Ia) remains unresolved, with the single and double degenerate scenarios remaining the leading contenders. The former implies a large population of hot accreting white dwarfs with photospheric temperatures of T ~ 10^5-10^6 K during some part of their accretion history. We show that in early-type galaxies, a population of accreting white dwarfs large enough to reproduce the SN Ia rate would contribute significantly to the ionizing UV radiation expected from the stellar population. For mean stellar ages < ~5 Gyr, single degenerate progenitors would dominate the ionizing background produced by stars, increasing the continuum beyond the He II-ionizing limit more than ten-fold. This opens a new avenue for constraining the progenitors of SNe Ia, through consideration of the spatially extended low-ionization emission-line regions now found in many early-type galaxies. Modelling the expected emission, we show that one can constrain the contribution of the single degenerate channel to the SN Ia rate in E/S0 galaxies from upper limits on the luminosity of He II recombination lines in the optical and FUV. We discuss future directions, as well as possible implications for the evolution of SNe Ia in old stellar populations.Comment: 12 pages, 13 figures, MNRA

Cultural trauma: Ron Eyerman and the founding of a new research paradigm

The field of cultural trauma has reached the status of a research paradigm. Ron Eyerman has played a central role in this development. Since he first embarked on research into cultural trauma with several colleagues in 1999, Eyerman has maintained an intensive preoccupation with the topic, resulting in the publication of numerous books and essays. In this article, I review the development of Eyerman’s approach to cultural trauma, with the broader aim of shedding light on this new research paradigm. I focus on several key themes in Eyerman’s work, including the relationship between event and representation; the significance of affect and emotion; the role of collective memory; the adoption of a dramaturgical perspective; and a multidimensional research methodology. To conclude, I discuss potential new directions in the study of cultural trauma

Balmer-Dominated Shocks Exclude Hot Progenitors for Many Type Ia Supernovae

The evolutionary mechanism underlying Type Ia supernova explosions remains unknown. Recent efforts to constrain progenitor models based on the influence that their high energy emission would have on the interstellar medium (ISM) of galaxies have proven successful. For individual remnants, Balmer-dominated shocks reveal the ionization state of hydrogen in the immediately surrounding gas. Here we report deep upper limits on the temperature and luminosity of the progenitors of four Type Ia remnants with associated Balmer filaments: SN 1006, 0509-67.5, 0519-69.0, and DEM L71. For SN 1006, existing observations of helium line emission in the diffuse emission ahead of the shock provide an additional constraint on the helium ionization state in the vicinity of the remnant. Using the photoionization code Cloudy, we show that these constraints exclude any hot, luminous progenitor for SN 1006, including stably hydrogen or helium nuclear-burning white dwarfs, as well as any Chandrasekhar-mass white dwarf accreting matter at $\gtrsim 9.5\times10^{-8}M_{\odot}/$yr via a disk. For 0509-67.5, the Balmer emission alone rules out any such white dwarf accreting $\gtrsim 1.4\times10^{-8}M_{\odot}/$yr. For 0519-69.0 and DEM L71, the inferred ambient ionization state of hydrogen is only weakly in tension with a recently hot, luminous progenitor, and cannot be distinguished from e.g., a relatively higher local Lyman continuum background, without additional line measurements. Future deep spectroscopic observations will resolve this ambiguity, and can either detect the influence of any luminous progenitor or rule out the same for all resolved SN Ia remnants.Comment: 9 pages, 3 figures, 1 table. Accepted for publication in Ap

No hot and luminous progenitor for Tycho's supernova

Type Ia supernovae have proven vital to our understanding of cosmology, both as standard candles and for their role in galactic chemical evolution; however, their origin remains uncertain. The canonical accretion model implies a hot and luminous progenitor which would ionize the surrounding gas out to a radius of $\sim$10--100 parsecs for $\sim$100,000 years after the explosion. Here we report stringent upper limits on the temperature and luminosity of the progenitor of Tycho's supernova (SN 1572), determined using the remnant itself as a probe of its environment. Hot, luminous progenitors that would have produced a greater hydrogen ionization fraction than that measured at the radius of the present remnant ($\sim$3 parsecs) can thus be excluded. This conclusively rules out steadily nuclear-burning white dwarfs (supersoft X-ray sources), as well as disk emission from a Chandrasekhar-mass white dwarf accreting $\gtrsim 10^{-8}M_{\odot}$yr$^{-1}$ (recurrent novae). The lack of a surrounding Str\"omgren sphere is consistent with the merger of a double white dwarf binary, although other more exotic scenarios may be possible.Comment: 17 pages, 2 figures, including supplementary information. Original accepted manuscript (before copyediting/formatting by Nature Astronomy

Upper limits on the luminosity of the progenitor of type Ia supernova SN2014J

We analysed archival data of Chandra pre-explosion observations of the position of SN2014J in M82. No X-ray source at this position was detected in the data, and we calculated upper limits on the luminosities of the progenitor. These upper limits allow us to firmly rule out an unobscured supersoft X-ray source progenitor with a photospheric radius comparable to the radius of white dwarf near the Chandrasekhar mass (~1.38 M_sun) and mass accretion rate in the interval where stable nuclear burning can occur. However, due to a relatively large hydrogen column density implied by optical observations of the supernova, we cannot exclude a supersoft source with lower temperatures, kT < 80 eV. We find that the supernova is located in the centre of a large structure of soft diffuse emission, about 200 pc across. The mass, ~3x10^4 M_sun and short cooling time of the gas, tau_cool ~ 8 Myrs, suggest that it is a supernova-inflated super-bubble, associated with the region of recent star formation. If SN2014J is indeed located inside the bubble, it likely belongs to the prompt population of type Ia supernovae, with a delay time as short as ~ 50 Myrs. Finally, we analysed the one existing post-supernova Chandra observation and placed upper limit of ~ (1-2) 10^37 erg/s on the X-ray luminosity of the supernova itself.Comment: 8 pages, 6 figure

The Formation of Low-Mass Double White Dwarfs through an Initial Phase of Stable Non-Conservative Mass Transfer

Although many double white dwarfs (DWDs) have been observed, the evolutionary channel by which they are formed from low-mass/long-period red-giant-main-sequence (RG-MS) binaries remains uncertain. The canonical explanations involve some variant of double common-envelope (CE) evolution, however it has been found that such a mechanism cannot produce the observed distribution. We present a model for the initial episode of mass transfer (MT) in RG-MS binaries, and demonstrate that their evolution into double white dwarfs need not arise through a double-CE process, as long as the initial primary's core mass (Md,c) does not exceed 0.46M$_{\odot}$. Instead, the first episode of dramatic mass loss may be stable, non-conservative MT. We find a lower bound on the fraction of transferred mass that must be lost from the system in order to provide for MT, and demonstrate the feasibility of this channel in producing observed low-mass (with M$_{d,c}$ < 0.46M$_{\odot}$) DWD systems.Comment: 2 pages, 1 figure, Conference Proceedings for the International Conference on Binaries, Mykonos, Greec

On the Maximum Mass of Accreting Primordial Supermassive Stars

Supermassive primordial stars are suspected to be the progenitors of the most massive quasars at z~6. Previous studies of such stars were either unable to resolve hydrodynamical timescales or considered stars in isolation, not in the extreme accretion flows in which they actually form. Therefore, they could not self-consistently predict their final masses at collapse, or those of the resulting supermassive black hole seeds, but rather invoked comparison to simple polytropic models. Here, we systematically examine the birth, evolution and collapse of accreting non-rotating supermassive stars under accretion rates of 0.01-10 solar masses per year, using the stellar evolution code KEPLER. Our approach includes post-Newtonian corrections to the stellar structure and an adaptive nuclear network, and can transition to following the hydrodynamic evolution of supermassive stars after they encounter the general relativistic instability. We find that this instability triggers the collapse of the star at masses of 150,000-330,000 solar masses for accretion rates of 0.1-10 solar masses per year, and that the final mass of the star scales roughly logarithmically with the rate. The structure of the star, and thus its stability against collapse, is sensitive to the treatment of convection, and the heat content of the outer accreted envelope. Comparison with other codes suggests differences here may lead to small deviations in the evolutionary state of the star as a function of time, that worsen with accretion rate. Since the general relativistic instability leads to the immediate death of these stars, our models place an upper limit on the masses of the first quasars at birth.Comment: 5 pages, 4 figures. Accepted ApJ letter

Population synthesis of accreting white dwarfs: II. X-ray and UV emission

Accreting white dwarfs (WDs) with non-degenerate companions are expected to emit in soft X-rays and the UV, if accreted H-rich material burns stably. They are an important component of the unresolved emission of elliptical galaxies, and their combined ionizing luminosity may significantly influence the optical line emission from warm ISM. In an earlier paper we modeled populations of accreting WDs, first generating WD with main-sequence, Hertzsprung gap and red giant companions with the population synthesis code \textsc{BSE}, and then following their evolution with a grid of evolutionary tracks computed with \textsc{MESA}. Now we use these results to estimate the soft X-ray (0.3-0.7keV), H- and He II-ionizing luminosities of nuclear burning WDs and the number of super-soft X-ray sources for galaxies with different star formation histories. For the starburst case, these quantities peak at $\sim 1$ Gyr and decline by $\sim 1-3$ orders of magnitude by the age of 10 Gyr. For stellar ages of $\sim$~10 Gyr, predictions of our model are consistent with soft X-ray luminosities observed by Chandra in nearby elliptical galaxies and He II 4686$\AA/\rm{H}{\beta}$ line ratio measured in stacked SDSS spectra of retired galaxies, the latter characterising the strength and hardness of the UV radiation field. However, the soft X-ray luminosity and He~II~4686$\AA/\rm{H}{\beta}$ ratio are significantly overpredicted for stellar ages of $\lesssim 4-8$ Gyr. We discuss various possibilities to resolve this discrepancy and tentatively conclude that it may be resolved by a modification of the typically used criteria of dynamically unstable mass loss for giant stars.Comment: 13 pages, 12 figures, MNRAS accepte

Interstellar H^+_3: possible detection of the 1_(10)→1_(11) transition of H_2D^+

An interstellar line has been detected in emission at the expected submillimeter wavelength of the 1_(10)→1_(11) transition of H_(2)D^+, the deuterated version of the primary ion (H^(+)_(3)) in the favored ion-molecule reaction scheme for interstellar gas phase chemistry. The strength of the line is in approximate agreement with the theoretically anticipated H_(2)D^+ abundance