arXiv subjects

W. E. Kerzendorf

Publications and source records attributed to W. E. Kerzendorf.

22 records · Page 2Linked to original sources

arXiv2016

No evidence for younger stellar generations within the intermediate age massive clusters NGC 1783, NGC 1696 and NGC 411

Recently, Li et al. (2016) claimed to have found evidence for multiple generations of stars in the intermediate age clusters NGC 1783, NGC 1696 and NGC 411 in the Large and Small Magellanic Clouds (LMC/SMC). Here we show that these young stellar populations are present in the field regions around these clusters and are not likely associated with the clusters themselves. Using the same datasets, we find that the background subtraction method adopted by the authors does not adequately remove contaminating stars in the small number Poisson limit. Hence, we conclude that their results do not provide evidence of young generations of stars within these clusters.

astro-ph.GA↗

arXiv2014

Spectroscopy of the Type Ia supernova 2011fe past 1000 days

In this letter we present an optical spectrum of SN 2011fe taken 1034 d after the explosion, several hundred days later than any other spectrum of a Type Ia supernova (disregarding light-echo spectra and local-group remnants). The spectrum is still dominated by broad emission features, with no trace of a light echo or interaction of the supernova ejecta with surrounding interstellar material. Comparing this extremely late spectrum to an earlier one taken 331 d after the explosion, we find that the most prominent feature at 331 d - [Fe III] emission around 4700 A - has entirely faded away, suggesting a significant change in the ionisation state. Instead, [Fe II] lines are probably responsible for most of the emission at 1034 d. An emission feature at 6300-6400 A has newly developed at 1034 d, which we tentatively identify with Fe I λ6359, [Fe I] λλ6231, 6394 or [O I] λλ6300, 6364. Interestingly, the features in the 1034-d spectrum seem to be collectively redshifted, a phenomenon that we currently have no convincing explanation for. We discuss the implications of our findings for explosion models, but conclude that sophisticated spectral modelling is required for any firm statement.

astro-ph.SR↗

arXiv2014

Very late photometry of SN 2011fe

The Type Ia supernova SN 2011fe is one of the closest supernovae of the past decades. Due to its proximity and low dust extinction, this object provides a very rare opportunity to study the extremely late time evolution ($>900$ days) of thermonuclear supernovae. In this Letter, we present our photometric data of SN 2011fe taken at an unprecedented late epoch of $\approx 930$ days with GMOS-N mounted on the Gemini North telescope ($g=23.43 \pm 0.28$, $r=24.14 \pm 0.14$, $i=23.91 \pm 0.18$, and $z=23.90 \pm 0.17$) to study the energy production and retention in the ejecta of SN 2011fe. Together with previous measurements by other groups, our result suggests that the optical supernova light curve can still be explained by the full thermalization of the decay positrons of Co56. This is in spite of theoretical predicted effects (e.g. infrared catastrophe, positron escape, and dust) that advocate a substantial energy redistribution and/or loss via various processes that result in a more rapid dimming at these very late epochs.

astro-ph.SR↗

arXiv2009

Subaru high-resolution spectroscopy of Star G in the Tycho supernova remnant

It is widely believed that Type Ia supernovae (SN Ia) originate in binary systems where a white dwarf accretes material from a companion star until its mass approaches the Chandrasekhar mass and carbon is ignited in the white dwarf's core. This scenario predicts that the donor star should survive the supernova explosion, providing an opportunity to understand the progenitors of Type Ia supernovae.In this paper we argue that rotation is a generic signature expected of most non-giant donor stars that is easily measurable. \citep{2004Natur.431.1069R} examined stars in the center of the remnant of SN 1572 (Tycho's SN) and showed evidence that a subgiant star (Star G by their naming convention) near the remnant's centre was the system's donor star. We present high-resolution (R \simeq 40000) spectra taken with the High Dispersion Spectrograph on Subaru of this candidate donor star and measure the star's radial velocity as $79\pm 2$ \kms with respect to the LSR and put an upper limit on the star's rotation of 7.5 \kms. In addition, by comparing images that were taken in 1970 and 2004, we measure the proper motion of Star G to be $μ_l = -1.6 \pm 2.1$ \masyr and $μ_b = -2.7 \pm 1.6$ \masyr. We demonstrate that all of the measured properties of Star G presented in this paper are consistent with those of a star in the direction of Tycho's SN that is not associated with the supernova event. However, we discuss an unlikely, but still viable scenario for Star G to be the donor star, and suggest further observations that might be able to confirm or refute it.

astro-ph.SR↗