arXiv:1305.6997 Spectroscopy of Type Ia Supernovae by the Carnegie Supernova Project (apresentado pelo Ribamar)
Abstract: This is the first release of optical spectroscopic data of low-redshift Type Ia supernovae (SNe Ia) by the Carnegie Supernova Project including 604 previously unpublished spectra of 93 SNe Ia. The observations cover a range of phases from 12 days before to over 150 days after the time of B-band maximum light. With the addition of 228 near-maximum spectra from the literature we study the diversity among SNe Ia in a quantitative manner. For that purpose, spectroscopic parameters are employed such as expansion velocities from spectral line blueshifts, and pseudo-equivalent widths (pW). The values of those parameters at maximum light are obtained for 78 objects, thus providing a characterization of SNe Ia that may help to improve our understanding of the properties of the exploding systems and the thermonuclear flame propagation. Two objects, namely SNe 2005M and 2006is, stand out from the sample by showing peculiar Si II and S II velocities but otherwise standard velocities for the rest of the ions. We further study the correlations between spectroscopic and photometric parameters such as light-curve decline rate and color. In agreement with previous studies, we find that the pW of Si II absorption features are very good indicators of light-curve decline rate. Furthermore, we demonstrate that parameters such as pW2(SiII4130) and pW6(SiII5972) provide precise calibrations of the peak B-band luminosity with dispersions of ~0.15 mag. In the search for a secondary parameter in the calibration of peak luminosity for SNe Ia, we find a ~2--3-sigma correlation between B-band Hubble residuals and the velocity at maximum light of S II and Si II lines.
arXiv:1305.7457 Testing modified gravity with Planck: the case of coupled dark energy (apresentado pelo Tiago)
Abstract: The Planck collaboration has recently published maps of the Cosmic Microwave Background (CMB) radiation, in good agreement with a LCDM model, a fit especially valid for multipoles l > 40. We explore here the possibility that dark energy is dynamical and gravitational attraction between dark matter particles is effectively different from the standard one in General Relativity: this is the case of coupled dark energy models, where dark matter particles feel the presence of a fifth force, larger than gravity by a factor beta^2. We investigate constraints on the strength of the coupling beta in view of Planck data. Interestingly, we show that a non-zero coupling is compatible with data and find a likelihood peak at beta = 0.036 \pm 0.016 (Planck + WP + BAO) (compatible with zero at 2sigma). The significance of the peak increases to beta = 0.066 \pm 0.018 (Planck + WP + HST) (around 3.6sigma) when Planck is combined to Hubble Space Telescope data. This peak comes mostly from the small difference between the Hubble parameter determined with CMB measurements and the one coming from astrophysics measurements. In this sense, future observations and further tests of current observations are needed to determine whether the discrepancy is due to systematics in any of the datasets. Our aim here is not to claim new physics but rather to show how Planck data can be used to provide information on dynamical dark energy and modified gravity, allowing us to test the strength of an effective fifth force between dark matter particles with precision smaller than 2%.
arXiv:1305.7067 One year of monitoring of the Type IIb supernova SN 2011dh (apresentado pela Beatriz)
Abstract: Optical $UBVRI$ photometry and low resolution spectroscopy of the type IIb supernova SN 2011dh in M51 are presented, covering the first year after the explosion. The light curve and spectral evolution are discussed. The early phase light curve evolution of SN 2011dh is very similar to SN 1993J and SN 2008ax. In the late phase, however, SN 2011dh declines faster than SN 1993J. The late phase decline in the $B$-band is steeper than in the $R$ and $I$ bands, indicating the possibility of dust formation. With a peak $V$-band absolute magnitude of $M_V = -17.123\pm0.18$ mag, SN 2011dh is a marginally faint type IIb event. The reddening corrected colour curves of SN 2011dh are found to be redder than other well studied type IIb supernovae. The bolometric light curve indicates $\sim$ 0.09 M$_\odot$ of $^{56}$Ni is synthesized during the explosion. The HeI lines were detected in the spectra during the rise to maximum. The nebular spectra of SN 2011dh show a box shaped emission in the red wing of the [OI] 6300-6363 \AA\ feature, that is attributed to H$\alpha$ emission from a shock excited circumstellar material. The analysis of nebular spectra indicates that $\sim 0.2$ M$_\odot$ of oxygen was ejected during the explosion. Further, the [CaII]/[OI] line ratio in the nebular phase is $\sim$ 0.7, indicating a progenitor with a main sequence mass of 10-15 M$_\odot$.
arXiv:1306.0285 Calibrating the fundamental plane with SDSS DR8 data (apresentado pelo Ribamar)
Abstract: In this paper, we present a calibration of the fundamental plane using SDSS Data Release 8. We analyse about 93000 elliptical galaxies up to z<0.2, the largest sample used for the calibration of the fundamental plane so far. We incorporate up-to-date K-corrections and use GalaxyZoo data for the classification of the galaxies in our sample. We derive independent fundamental plane fits in all five Sloan filters u, g, r, i, z. A direct fit using a volume weighted least squares method is applied to obtain the coefficients of the fundamental plane, which implicitly corrects for the Malmquist bias. We achieve an accuracy of 15% for the fundamental plane as a distance indicator. We provide a detailed discussion on the calibrations and their influence on the resulting fits. These re-calibrated fundamental plane relations form a well-suited anchor for large-scale peculiar velocity studies in the nearby universe. Aside from the fundamental plane, we discuss the redshift distribution of the elliptical galaxies, and their global parameters.