Browsing by Author "Mehner, A."

Now showing 1 - 6 of 6
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    450 d of Type II SN 2013ej in optical and near-infrared
    (OXFORD UNIV PRESS, 2016) Yuan, Fang; Jerkstrand, A.; Valenti, S.; Sollerman, J.; Seitenzahl, I. R.; Pastorello, A.; Schulze, S.; Chen, T. W.; Childress, M. J.; Fraser, M.; Fremling, C.; Kotak, R.; Ruiter, A. J.; Schmidt, B. P.; Smartt, S. J.; Taddia, F.; Terreran, G.; Tucker, B. E.; Barbarino, C.; Benetti, S.; Elias Rosa, N.; Gal Yam, A.; Howell, D. A.; Inserra, C.; Kankare, E.; Lee, M. Y.; Li, K. L.; Maguire, K.; Margheim, S.; Mehner, A.; Ochner, P.; Sullivan, M.; Tomasella, L.; Young, D. R.
    We present optical and near-infrared photometric and spectroscopic observations of SN 2013ej, in galaxy M74, from 1 to 450 d after the explosion. SN 2013ej is a hydrogen-rich supernova, classified as a Type IIL due to its relatively fast decline following the initial peak. It has a relatively high peak luminosity (absolute magnitude M-V =-17.6) but a small 56Ni production of similar to 0.023 M-circle dot. Its photospheric evolution is similar to other Type II SNe, with shallow absorption in the H a profile typical for a Type IIL. During transition to the radioactive decay tail at similar to 100 d, we find the SN to grow bluer in B - V colour, in contrast to some other Type II supernovae. At late times, the bolometric light curve declined faster than expected from Co-56 decay and we observed unusually broad and asymmetric nebular emission lines. Based on comparison of nebular emission lines most sensitive to the progenitor core mass, we find our observations are best matched to synthesized spectral models with a M-ZAMS = 12-15 M-circle dot progenitor. The derived mass range is similar to but not higher than the mass estimated for Type IIP progenitors. This is against the idea that Type IIL are from more massive stars. Observations are consistent with the SN having a progenitor with a relatively low-mass envelope.
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    Cosmic evolution and metal aversion in superluminous supernova host galaxies
    (2018) Schulze, Steve; Krühler, T.; Leloudas, G.; Gorosabel, J.; Mehner, A.; Buchner, J.; Kim, Sam; Ibar, Edo; Amorín, Ricardo; Herrero Illana, Rubén; Anderson, Joseph; Bauer, Franz Erik
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    Interacting supernovae and supernova impostors. LSQ13zm : an outburst heralds the death of a massive star
    (2016) Tartaglia, L.; Pastorello, A.; Sullivan, M.; Baltay, C.; Rabinowitz, D.; Nugent, P.; Drake, A. J.; Djorgovski, S. G.; Gal-Yam, A.; Bauer, Franz Erik; Barsukova, E. A.; Goranskij, V. P.; Valeev, A. F.; Fatkhullin, T.; Schulze, S.; Mehner, A.; Fabrika, S.; Taubenberger, S.; Nordin, J.; Valenti, S.
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    Spectroscopy of superluminous supernova host galaxies : A preference of hydrogen-poor events for extreme emission line galaxies
    (2015) Leloudas, G.; Schulze, S.; Kruhler, T.; Gorosabel, J.; Christensen, L.; Mehner, A.; De Ugarte Postigo, A.; Amorin, R.; Thone, C.; Bauer, Franz Erik
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    The MUSE view of the host galaxy of GRB 100316D
    (2017) Izzo, L.; Thöne, C. C.; Schulze, S.; Mehner, A.; Flores, H.; Cano, Z.; De Ugarte Postigo, A.; Kann, D. A.; Amorín, R.; Bauer, Franz Erik
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    X-Shooting ULLYSES: Massive stars at low metallicity IV. Spectral analysis methods and exemplary results for O stars
    (2024) Sander, A. A. C.; Bouret, J. -C.; Bernini-Peron, M.; Puls, J.; Backs, F.; Berlanas, S. R.; Bestenlehner, J. M.; Brands, S. A.; Herrero, A.; Martins, F.; Maryeva, O.; Pauli, D.; Ramachandran, V.; Crowther, P. A.; Gomez-Gonzalez, V. M. A.; Gormaz-Matamala, A. C.; Hamann, W. -R.; Hillier, D. J.; Kuiper, R.; Larkin, C. J. K.; Lefever, R. R.; Mehner, A.; Najarro, F.; Oskinova, L. M.; Schoesser, E. C.; Shenar, T.; Todt, H.; ud-Doula, A.; Vink, J. S.
    Context. The spectral analysis of hot, massive stars is a fundamental astrophysical method of determining their intrinsic properties and feedback. With their inherent, radiation-driven winds, the quantitative spectroscopy for hot, massive stars requires detailed numerical modeling of the atmosphere and an iterative treatment in order to obtain the best solution within a given framework. Aims. We present an overview of different techniques for the quantitative spectroscopy of hot stars employed within the X-Shooting ULLYSES collaboration, ranging from grid-based approaches to tailored spectral fits. By performing a blind test for selected targets, we gain an overview of the similarities and differences between the resulting stellar and wind parameters. Our study is not a systematic benchmark between different codes or methods; our aim is to provide an overview of the parameter spread caused by different approaches. Methods. For three different stars from the XShooting ULLYSES sample (SMC O5 star AzV 377, LMC O7 star Sk -69 degrees 50, and LMC O9 star Sk-66 degrees 171), we employ different stellar atmosphere codes (CMFGEN, Fastwind, PoWR) and different strategies to determine their best-fitting model solutions. For our analyses, UV and optical spectroscopy are used to derive the stellar and wind properties with some methods relying purely on optical data for comparison. To determine the overall spectral energy distribution, we further employ additional photometry from the literature. Results. The effective temperatures found for each of the three different sample stars agree within 3 kK, while the differences in log g can be up to 0.2 dex. Luminosity differences of up to 0.1 dex result from different reddening assumptions, which seem to be systematically larger for the methods employing a genetic algorithm. All sample stars are found to be enriched in nitrogen. The terminal wind velocities are surprisingly similar and do not strictly follow the u infinity-Teff relation. Conclusions. We find reasonable agreement in terms of the derived stellar and wind parameters between the different methods. Tailored fitting methods tend to be able to minimize or avoid discrepancies obtained with coarser or increasingly automatized treatments. The inclusion of UV spectral data is essential for the determination of realistic wind parameters. For one target (Sk -69 degrees 50), we find clear indications of an evolved status.