Showing papers by "Duilia F. de Mello published in 1998"
TL;DR: In this paper, the authors modeled the light curve and spectra of the explosion of a 26 M☉ star in NGC 1536 with a solar abundance and low Teff.
Abstract: SN 1997D in NGC 1536 is possibly the least luminous and energetic Type II supernova discovered to date. The entire light curve is subluminous, never reaching MV=-14.65. The radioactive tail follows the 56Co decay slope. In the case of a nearly complete trapping of the γ-rays, the 56Ni mass derived from the tail brightness is extremely small, ~0.002 M☉. At discovery, the spectra showed a red continuum and line velocities on the order of 1000 km s−1. The luminosity and the photospheric expansion velocity suggest that the explosion occurred about 50 days before discovery and that a plateau probably followed. Model light curves and spectra of the explosion of a 26 M☉ star successfully fitted the observations. Low-mass models are inconsistent with the observations. The radius of the progenitor, constrained by the prediscovery upper limits, is R0 300 R☉. A low explosion energy of ~4 × 1050 ergs is then required in the modeling. The strong Ba II lines in the photospheric spectra are reproduced with a solar abundance and low Teff. A scenario in which the low 56Ni mass observed in SN 1997D is due to fallback of material onto the collapsed remnant of the explosion of a 25-40 M☉ star appears to be favored over the case of the explosion of an 8-10 M☉ star with low 56Ni production.
174 citations
TL;DR: In this paper, the authors modeled the light curves and spectra of the explosion of a 26 \M\ star successfully fit the observations and showed that the explosion occurred about 50 days before discovery, and that a plateau probably followed.
Abstract: SN 1997D in NGC 1536 is possibly the least luminous and energetic Type II supernova discovered to date. The entire light curve is subluminous, never reaching $M_V = -14.65$. The radioactive tail follows the 56Co decay slope. In the case of nearly complete trapping of the $\gamma$-rays, the 56Ni mass derived from the tail brightness is extremely small, $\sim 0.002$ \M. At discovery the spectra showed a red continuum and line velocities of the order of 1000 \kms. The luminosity and the photospheric expansion velocity suggest that the explosion occurred about 50 days before discovery, and that a plateau probably followed. Model light curves and spectra of the explosion of a 26 \M\ star successfully fit the observations. Low mass models are inconsistent with the observations. The radius of the progenitor, constrained by the prediscovery upper limits, is \r0 \ltsim 300 \R. A low explosion energy of $\sim 4 \times 10^{50}$ ergs is then required in the modeling. The strong \ion{Ba}{2} lines in the photospheric spectra are reproduced with a solar abundance and low $T_{eff}$. A scenario in which the low 56Ni mass observed in SN 1997D is due to fall--back of material onto the collapsed remnant of the explosion of a 25--40 \M star appears to be favored over the case of the explosion of an 8--10 \M\ star with low 56Ni production.
172 citations
TL;DR: In this article, the authors constructed a continuum free HeII map, which was used to identify Wolf-Rayet (WR) stars recently found by ground-based spectroscopy and to locate diffuse nebular emission.
Abstract: I Zw 18 is the most metal poor star-forming galaxy known and is an ideal laboratory to probe stellar evolution theory at low metallicities. Using archival HST WFPC2 imaging and FOS spectroscopy we were able to improve previous studies. We constructed a continuum free HeII map, which was used to identify Wolf-Rayet (WR) stars recently found by ground-based spectroscopy and to locate diffuse nebular emission. Most of the HeII emission is associated with the NW stellar cluster, clearly displaced from the surrounding shell-like [OIII] and Halpha emission. We found evidence for HeII sources, compatible with 5--9 WNL stars and/or compact nebular HeII emission, as well as residual diffuse emission. Only one of them is outside the NW cluster. We have calculated evolutionary tracks for massive stars and synthesis models at the appropriate metallicity (Z ~ 0.02 Zsun). These single star models predict a mass limit M_WR ~ 90 Msun for WR stars to become WN and WC/WO. For an instantaneous burst model with a Salpeter IMF extending up to M_up ~ 120-150 Msun our model predictions are in reasonable agreement with the observed equivalent widths. Our model is also able to fully reproduce the observed equivalent widths of nebular HeII emission due to the presence of WC/WO stars. This quantitative agreement and the spatial correlation of nebular HeII with the stellar cluster and the position of WR stars shown from the ground-based spectra further supports the hypothesis that WR stars are responsible for nebular HeII emission in extra-galactic HII regions. (Abridged abstract)
52 citations
TL;DR: In this article, the authors constructed a continuum-free He II λ4686 map, which was used to identify Wolf-Rayet (W-R) stars recently found by ground-based spectroscopy and locate diffuse nebular emission.
Abstract: I Zw 18 is the most metal-poor star-forming galaxy known and is an ideal laboratory to probe stellar evolution theory at low metallicities. Using archival Hubble Space Telescope WFPC2 imaging and Faint Object Spectrograph spectroscopy, we were able to improve previous studies. We constructed a continuum-free He II λ4686 map, which was used to identify Wolf-Rayet (W-R) stars recently found by ground-based spectroscopy and to locate diffuse nebular emission. Most of the He II λ4686 emission is associated with the northwest stellar cluster clearly displaced from the surrounding shell-like [O III] and Hα emission. We found evidence for He II sources, compatible with five to nine WNL stars and/or compact nebular He II λ4686 emission, as well as residual diffuse emission. Only one of them is outside the northwest cluster. We have done an extensive comparison between our results and the recent ground-based data used by Izotov et al. and Legrand et al. to identify WN and WC stars in I Zw 18. The differences between the various data may be understood in terms of varying slit locations, continuum fits, and contamination by nebular lines. We have calculated evolutionary tracks for massive stars and synthesis models at the appropriate metallicity (Z ≈ 0.02 Z☉). These single-star models predict a mass limit MWR ≈ 90 M☉ for W-R stars to become WN and WC/WO. For an instantaneous burst model with a Salpeter initial mass function extending up to Mup ≈ 120-150 M☉, our model predictions are in reasonable agreement with the observed equivalent widths. Our model is also able to fully reproduce the observed equivalent widths of nebular He II λ4686 emission due to the presence of WC/WO stars. This quantitative agreement and the spatial correlation of nebular He II λ4686 with the stellar cluster and the position of W-R stars shown from the ground-based spectra further supports the hypothesis that W-R stars are responsible for nebular He II emission in extragalactic H II regions.
47 citations
TL;DR: In this paper, a local sample of 14 isolated pairs of galaxies was used to study the properties of the local pairs, including color, morphology, morphological properties, and activity.
Abstract: We present photometric analysis of a local sample of 14 isolated pairs of galaxies. The photometric properties analyzed in the local pairs are: colors, morphol- ogy, tidal eects and activity. We verify that close pairs have an excess of early{type galaxies and many ellipti- cal galaxies in this pairs are, in fact, lenticular galaxies. Many late{pairs in our sample show strong tidal damage and blue star formation regions. We conclude that pairs of dierent morphologies may have passed through dier- ent evolution processes which violently transformed their morphology. Pairs with at least one early{type compo- nent may be descendents of groups of galaxies. However, late{type pairs are probably long{lived showing clearly signs of interaction. Some of them could be seen as an early stage of mergers. These photometric databases will be used for future comparison with more distant pairs in order to study galaxy evolution.
6 citations
Posted Content•
TL;DR: In this article, a study of the gaseous and stellar emission in I Zw18, the most metal-poor star-forming galaxy known, is presented, where the authors find evidence for HeII sources compatible with 5-9 Wolf-Rayet stars and/or compact nebular HeII emission.
Abstract: We present a study of the gaseous and stellar emission in I Zw18, the most metal-poor star-forming galaxy known. Archival HST WFPC2 and FOS data have been used to analyze the spatial distribution of [OIII], Halpha, and HeII 4686. The latter is used to identify Wolf-Rayet stars found by ground-based spectroscopy and to locate nebular HeII emission. Most of the HeII emission is associated with the NW stellar cluster, displaced from the surrounding shell-like [OIII] and Halpha emission. We found evidence for HeII sources compatible with 5-9 WNL stars and/or compact nebular HeII emission as well as residual diffuse emission. New evolutionary tracks and synthesis models at the appropriate metallicity predict a mass limit M_WR ~90 Msun for WR stars to become WN and WC/WO. The observed equivalent widths of the WR lines are in good agreement with an instantaneous burst model with a Salpeter IMF extending up to M_up ~ 120-150 Msun. Our model is also able to fully reproduce the observed equivalent widths of nebular HeII emission due to the presence of WC/WO stars. This finding together with the spatial distribution of nebular HeII further supports the hypothesis that WR stars are responsible for nebular HeII emission in extra-galactic HII regions. Finally we discuss the implications on stellar mass loss, chemical yields, final stellar masses, and the ionizing flux of starburst galaxies at very low metallicities.