A680 Final: SNIa Light Curves

Alex Dvornikov

Type Ia supernovae are often used as cosmic rulers because of their characteristic dimming. To learn about them and about aperture photometry, we found the light curves of PSNJ2131+43 and iPTF15dgq. We observed these two supernovae in the B,V, and R filters for a month (November 11, 2015 to December 13, 2015) using the 40” telescope at Maunt Laguna Observatory. To reduce the images we subtracted the overscan and the master bias, and divided by the master flat.

Besides the novae, we selected 10 reference stars of known magnitude in each field of view. We used the USNOB catalog for the B and R band and the NOMAD catalog for the V band.

PSNJ2131+43 circled in magenta. The 10 reference stars are boxed in green. Stars in relative isolation were preferred.

iPTF15dgq circled in magenta. The 10 reference stars boxed in green.

To register only the stellar flux we subtracted the level of the neighboring sky. To do so, we drew an annulus (2 to 6 FHWM in radius) around each star and, via iterative sigma clipping, rejected the pixels belonging to star light. On a side note, we found the FHWM’s using SExtractor. Then, we simply added the counts within a circular aperture (radius = FHWM) sans the background sky. From error propagation, the flux error is \(\sigma_F = \sqrt{ A \sigma^2 + \frac{F}{G}}\). \(A\) is the aperture area, \(\sigma\) is the deviation of the background sky, \(F\) is the flux, and \(G\) is the gain. Equiped with the fluxes (for both the novae and the reference stars) we set the zero-point and determined the novae magnitudes and errors in magnitudes for each night. \[zps = m_0 + 2.5 \log_{10}(F_0)\] \[zp = median(zps)\] \[m = z