@article{BersierFruchterStrolgeretal.2006, author = {Bersier, David and Fruchter, Andrew S. and Strolger, Louis-Gregory and Gorosabel, Javier and Levan, Andrew and Burud, Ingunn and Rhoads, James E. and Becker, Andrew C. and Cassan, Andrew C. and Chornock, Ryan and Covino, Stefano and De Jong, Roelof S. and Dominis, Dijana and Filippenko, Alexei V. and Hjorth, Jens and Holmberg, Johan and Malesani, Daniele and Mobasher, Bahram and Olsen, Kurt A. G. and Stefanon, Mauro and Castro Cer{\´o}n, Jos{\´e} Mar{\´i}a C. and Fynbo, Johan P. U. and Holland, Stephen T. and Kouveliotou, Chryssa and Pedersen, Hans-Georg and Tanvir, Nieal R. and Woosley, S. E.}, title = {Evidence for a supernova associated with the X-ray flash 020903}, issn = {0004-637X}, doi = {10.1086/502640}, year = {2006}, abstract = {We present ground-based and Hubble Space Telescope optical observations of the X-ray flash ( XRF) 020903, covering 300 days. The afterglow showed a very rapid rise in the first day, followed by a relatively slow decay in the next few days. There was a clear bump in the light curve after similar to 25 days, accompanied by a drastic change in the spectral energy distribution. The light curve and the spectral energy distribution are naturally interpreted as describing the emergence and subsequent decay of a supernova ( SN), similar to SN 1998bw. At peak luminosity, the SN is estimated to be 0.8 +/- 0.1 mag fainter than SN 1998bw. This argues in favor of the existence of a SN associated with this XRF. A spectrum obtained 35 days after the burst shows emission lines from the host galaxy. We use this spectrum to put an upper limit on the oxygen abundance of the host at [O/H] <= 0.6 dex. We also discuss a possible trend between the softness of several bursts and the early behavior of the optical afterglow, in the sense that XRFs and X-ray-rich gamma- ray bursts ( GRBs) seem to have a plateau phase or even a rising light curve. This can be naturally explained in models in which XRFs are similar to GRBs but are seen off the jet axis.}, language = {en} } @article{BomansBeckerKleemannetal.2015, author = {Bomans, Dominik J. and Becker, Andrew C. and Kleemann, B. and Weis, K. and Pasquali, A.}, title = {Luminous Wolf-Rayet stars at low metallicity}, series = {Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.-5. June 2015}, journal = {Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.-5. June 2015}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-87635}, pages = {51 -- 54}, year = {2015}, abstract = {The evolution of massive stars in very low metallicity galaxies is less well observationally constrained than in environments more similar to the Milky Way, M33, or the LMC. We discuss in this contribution the current state of our program to search for and characterize Wolf-Rayet stars (and other massive emission line stars) in low metallicity galaxies in the Local Volume.}, language = {en} } @article{BeckerBomansWeis2015, author = {Becker, Andrew C. and Bomans, Dominik J. and Weis, K.}, title = {Finding new Wolf-Rayet stars in the Magellanic Clouds}, series = {Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.-5. June 2015}, journal = {Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.-5. June 2015}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-87618}, pages = {47 -- 50}, year = {2015}, abstract = {Obtaining a complete census of massive, evolved stars in a galaxy would be a key ingredient for testing stellar evolution models. However, as the evolution of stars is also strongly dependent on their metallicity, it is inevitable to have this kind of data for a variety of galaxies with different metallicities. Between 2009 and 2011, we conducted the Magellanic Clouds Massive Stars and Feedback Survey (MSCF); a spatially complete, multi-epoch, broad- and narrow-band optical imaging survey of the Large and Small Magellanic Clouds. With the inclusion of shallow images, we are able to give a complete photometric catalog of stars between B ≈ 18 and B ≈ 19 mag. These observations were augmented with additional photometric data of similar spatial res- olution from UV to IR (e.g. from GALEX, 2MASS and Spitzer) in order to sample a large portion of the spectral energy distribution of the brightest stars (B < 16 mag) in the Magel- lanic Clouds. Using these data, were are able to train a machine learning algorithm that gives us a good estimate of the spectral type of tens of thousands of stars. This method can be applied to the search for Wolf-Rayet-Stars to obtain a sample of candi- dates for follow-up observations. As this approach can, in principle, be adopted for any resolved galaxy as long as sufficient photometric data is available, it can form an effective alternative method to the classical strategies (e.g. He II filter imaging).}, language = {en} }