English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

We investigate the origin of the H$\alpha$-like structure seen in late-phasenebular spectra of type IIb supernovae (SNe IIb) at $\sim 200$ days after theexplosion. We compare the luminosities of emission lines in the nebular spectrawith the light curve peak magnitudes to reveal their power sources. In thiswork, we analyze 7 SNe IIb, as well as 2 SNe Ib (SN 2007Y and iPTF 13bvn) thatshow the H$\alpha$-like emission in their nebular spectra. The luminosity ofthe H$\alpha$-like emission shows a tight correlation with the light curve peakmagnitude, sharing the same behavior with other nebular lines. This resultindicates that the H$\alpha$-like emission is powered by the radiative decay of$^{56}$Co. The line flux is then expected to roughly follow the mass of theemitting layer. The variation expected from the diversity of the H-richenvelope mass among SNe IIb (reaching nearly to an order of magnitude) ishowever not seen, suggesting that it is most likely contributed predominantlyby [N II], not by H$\alpha$. While further analysis is limited by the availablesample size, we find a hint that SNe IIb with a double-peak light curve, whichis interpreted as an outcome of the more extended and massive hydrogenenvelope, tend to show excess in the luminosity of the H$\alpha$-like featurethan those with a single-peak light curve. This behavior indicates possibleadditional contribution from H$\alpha$. Additionally, we also find acorrelation between the [Ca II]/[O I] ratio and the post-maximum decline rate,indicating that the [Ca II]/[O I] can be used as a diagnostics for theprogenitor mass.

The origin of the H$\alpha$-like structure in nebular spectra of type IIb supernovae