Type Ib Supernovae are bluer than Type Ic Supernovae

TL;DR

This study analyzes a large sample of Type Ib and Ic supernovae, revealing that SNe Ib are systematically bluer than SNe Ic, likely due to differences in progenitor envelope stripping.

Contribution

It demonstrates that optical colors can serve as a new probe for understanding mass stripping in massive star evolution, based on homogeneous supernova light curve data.

Findings

SNe Ib are statistically bluer than SNe Ic.

Color differences are likely intrinsic, reflecting different progenitor envelope compositions.

Bluer colors in narrow-line SNe suggest circumstellar matter interaction.

Abstract

Type Ib and Ic supernovae (SNe Ib/Ic) are the bright finale of massive stars that have lost their hydrogen envelopes, making them powerful probes of mass stripping in massive star evolution. The advent of modern large photometric and spectroscopic surveys presents the unique opportunity to investigate systematic differences between these two kinds of SNe. In this study, we analyze a large, homogeneous sample of SNe Ib/Ic light curves from the Zwicky Transient Facility. We find a systematic difference in their optical colors: SNe Ib are, on average, bluer than SNe Ic at a statistically significant level. This difference appears intrinsic, likely reflecting progenitors with different degrees of stripping -- helium-rich for SNe Ib and helium-poor for SNe Ic. In addition, we find that SNe Ib/Ic with narrow lines (SNe Ibn/Icn) are bluer than those without, which might originate from circumstellar matter interaction, with potential connection to fast blue optical transients. We demonstrate that SN colors offer a promising probe of mass stripping in massive stars, potentially providing a useful tool for analyzing large photometric data and improving predictions for the final outcomes of stripped massive stars.