Context
We present the optical studies (ugriz, BVRI) of a type IIb supernova SN2015as. Super-
novae(SNe) IIb show a variety both in light curve and spectral features. An analysis of this
has been done. Data has been taken from 104-cm Sampurnanand Telescope, 130-cm Dev-
asthal Fast Optical Telescope (DFOT), 200-cm Himalayan Chandra Telescope and 182-cm
Asiago Ekar Telescope. Four epochs of UV data has also been taken with Swift UVOT.
Aim
We study the optical light curve evolution of a Type IIb supernova (SN) 2015as starting from
1 to 150 day after discovery and the spectral evolution of this SN at two epochs. We also
present the apparent, absolute magnitude light curve and colour curve of SN2015as.
Method
Raw data(Optical) taken from different telescopes was first preprocessed using IRAF soft-
ware. Basic photometric reductions has been done using the DAOPHOT package.
Results and Discussion
Although the peak of the BVRI lightcurve could not be covered since the first observation
was taken after 17days from discovery, but the ugriz evolution was studied from 2 days after
discovery. We fit a spline function to r and i bands to estimate peak magnitude and time.
The r and i band light curves peaked around 22 and 27 days respectively after explosion with
a peak magnitude of 14.26 and 14.96 respectively. The extinction corrected (V-I) and (R-I)
light curves show that the SN 2015as is much bluer than other SN of this group. Also, the
absolute magnitude curve for the V band shows that the absolute magnitude is much less
as compared to other members of this group and peaks around -17 mag. From the spectral
evolution, we see that the +19 day spectrum of SN2015as showed broad P-cygni absorption
of Hα (λ6563Å) and absorption due to Hβ, Hγ
and Ca II H and K. The spectra around 19
days also shows He features at λ5876Å. This marks the property of type IIb SN that shows
transition from initial H to He features. Also, in late time spectra red region shows OI and
Mg II lines.