Ricardo Demarco
Pontificia Universidad Católica de Chile, Santiago
The study of the absolute luminosities of 29 supernovae (SNe) type Ia in the Calan/Tololo survey confirms a relation between the peak luminosity of the SNe and the decline rate as measured by the light curve. Moreover, there is a relation between the luminosities of the SNe and their environment: late-type galaxies contain the brightest SNe and their light curves show a slow-decline rate, whereas elliptical galaxies have not produced slow-decline SNe. Our project has as a goal to verify the relation between the peak of the light curve and the morphological type of the host galaxy by updating the morphological type of the host galaxy for 4 SNe of the Calan/Tololo survey and considering as well 8 high-z SNe. However, the focus of the project was not the SNe themselves, but rather their host galaxies. The data set consisted of 12 SNe type Ia (SN1992ae, SN1992au, SN1992bi, SN1992bp, SN1992br, SN1995K, SN1995ao, SN1995ap, SN1996F SN1996G, SN1996H, SN1996U), four of which (SN1992ae, SN1992au, SN1992bp, SN1992br) were from the Calan/Tololo survey and the rest from the high-z search. All the images used for this project were taken with the WFPC2 of the HST with the filters F450W (for Calan/Tololo) and F702W (for high-z). The redshift ranges from 0.01 < z < 0.62 within the sample.
First of all, the calibration files for each image were updated. Then, the position of the host galaxy in the HST image was found for each SNe. Because of the resolution of the HST images, it was possible to update the morphological type of the host galaxy for the 4 SNe in the Calan/Tololo survey. Moreover, it was possible to determine roughly the morphological type of the host galaxy for the high-z SNe. In some cases, however, this work was quite difficult, and in others impossible, because of the low surface brightness of the galaxies. Finally, the galaxy types and the delta-mag(15) vs. galaxy type plot were updated. The results obtained from these updated galaxy types are in agreement with the relation between the peak luminosity of SNe Ia and the host galaxy type. We also obtained the position of the SN with respect to the center of its host galaxy and a reference star. Finally, we performed aperture photometry on each galaxy, to determine the instrumental magnitudes. Because of the low surface brightness of some of the galaxies, picking the correct aperture was difficult. Furthermore, in some cases the photometry was complicated by the presence of a bright nearby object, such as a star or galaxy. In the future we plan to determine the physical distance to each galaxy, assuming a universe with a positive cosmological constant. In addition, we will make a better estimate of the errors in the distance measurements and determine the standard magnitudes for the host galaxies.