Type Ib Events Research Articles

How much hydrogen is in Type Ib and IIb supernova progenitors?

ABSTRACT Core-collapse supernovae showing little or no hydrogen (denoted by Type IIb and Ib, respectively) are the explosions of massive stars that have lost some or most of their outer envelopes. How they lose their mass is unclear, but it likely involves binary interaction. So far, seven progenitors of such supernovae have been identified in pre-explosion imaging (five for Type IIb events and two for Type Ib events). Here, we evolve detailed binary stellar evolution models in order to better understand the nature of these progenitors. We find that the amount of hydrogen left in the envelope at the time of explosion greatly depends on the post-interaction mass-loss rate. The leftover hydrogen, in turn, strongly affects progenitor properties, such as temperature and photospheric radius, in non-trivial ways. Together with extinction and distance uncertainties in progenitor data, it is difficult to deduce an accurate progenitor hydrogen mass from pre-explosion imaging. We quantify this uncertainty and find that available data are consistent with a proposed Type Ib–IIb hydrogen mass threshold of ${\approx}0.033\, \mathrm{M}_\odot$, implying that even Type Ib progenitors are not pure helium stars. These results alleviate the proposed tension between the Type Ib classification of SN 2019yvr and its candidate progenitor properties. We also estimate the brightness of a surviving 2019yvr progenitor companion, which might be detected in future observations.

MULTI-WAVELENGTH OBSERVATIONS OF SUPERNOVA 2011ei: TIME-DEPENDENT CLASSIFICATION OF TYPE IIb AND Ib SUPERNOVAE AND IMPLICATIONS FOR THEIR PROGENITORS

We present X-ray, UV/optical, and radio observations of the stripped-envelope, core-collapse supernova (SN) 2011ei, one of the least luminous SNe IIb or Ib observed to date. Our observations begin with a discovery within 1 day of explosion and span several months afterward. Early optical spectra exhibit broad, Type II-like hydrogen Balmer profiles that subside rapidly and are replaced by Type Ib-like He-rich features on the timescale of one week. High-cadence monitoring of this transition suggests that absorption attributable to a high velocity (> 12,000 km/s) H-rich shell is not rare in Type Ib events. Radio observations imply a shock velocity of v = 0.13c and a progenitor star mass-loss rate of 1.4 x 10^{-5} Msun yr^{-1} (assuming wind velocity v_w=10^3 km/s). This is consistent with independent constraints from deep X-ray observations with Swift-XRT and Chandra. Overall, the multi-wavelength properties of SN 2011ei are consistent with the explosion of a lower-mass (3-4 Msun), compact (R* <= 1x10^{11} cm), He core star. The star retained a thin hydrogen envelope at the time of explosion, and was embedded in an inhomogeneous circumstellar wind suggestive of modest episodic mass-loss. We conclude that SN 2011ei's rapid spectral metamorphosis is indicative of time-dependent classifications that bias estimates of explosion rates for Type IIb and Ib objects, and that important information about a progenitor star's evolutionary state and mass-loss immediately prior to SN explosion can be inferred from timely multi-wavelength observations.

Hydrogen and helium traces in type Ib-c supernovae

The spectroscopic properties of a selected optical photospheric spectra of core collapse supernovae (CCSNe) are investigated.Special attention is devoted to traces of hydrogen at early phases. The generated spectra are found to match the observed ones reasonably well, including a list of only 23 candidate ions. Guided by SN Ib 1990I, the observed trough near 6300\AA is attributed to H$\alpha$ in almost all Type Ib events, although in some objects it becomes too weak to be discernible, especially at later phases. Alternative line identifications are discussed. Differences in the way hydrogen manifests its presence within CCSNe are highlighted. In Type Ib SNe, the H$\alpha$ contrast velocity (i.e. line velocity minus the photospheric velocity) seems to increase with time at early epochs, reaching values as high as 8000 km s$^{-1}$ around 15-20 days after maximum and then remains almost constant. The derived photospheric velocities, indicate a lower velocity for Type II SNe 1987A and 1999em as compared to SN Ic 1994I and SN IIb 1993J, while Type Ib events display a somewhat larger variation. The scatter, around day 20, is measured to be $\sim$5000 km s$^{-1}$. Following two simple approaches, rough estimates of ejecta and hydrogen masses are given. A mass of hydrogen of approximately 0.02 $M_\odot$ is obtained for SN 1990I, while SNe 1983N and 2000H ejected $\sim$0.008 $M_\odot$ and $\sim$0.08 $M_\odot$ of hydrogen, respectively. SN 1993J has a higher hydrogen mass, $\sim 0.7$ $M_\odot$ with a large uncertainty. A low mass and thin hydrogen layer with very high ejection velocities above the helium shell, is thus the most likely scenario for Type Ib SNe. Some interesting and curious issues relating to oxygen lines suggest future investigations.

SN Ib 1990I: Clumping and dust in the ejecta?

Photometry and spectra of the type Ib SN 19901 are presented and analysed, covering about 400 days of evolution. The good quality of the data allow one to set reliably the supernova age (i.e. both date of maximum and explosion time estimates are given). The presence of optical helium lines is shown. SN 19901 seems to show high velocities compared to a sample of type Ib events. The nebular emission lines display a high degree of asymmetry and the presence of fine structures, suggestive of non-spherical clumping in the ejecta of SN 19901. Using the [O I] 6300,64 A flux, we estimate a lower limit on the oxygen mass to fall in the range (0.7-1.35) M ○. . The oxygen mass requires a filling factor as small as ∼10 -2 on day 254, indicating a highly clumpy distribution of the oxygen material. The amplitude and evolution of the [Ca II]/[O I] flux ratio is similar to that observed in a sample of SNe Ib/c events and thus suggests similar progenitor masses. A blueshift of order 600 km s -1 is reported in the [O I] 6300,64 A after day 254. The [Ca II] 7307.5 A emission profile appears blueshifted as well at late epochs. We recover the quasi-bolometric BVRI light curve of SN 19901. The constructed bolometric light curve shows a change of slope at late phases, with an e-folding time of 60 ± 2 d in the [50:200] d time interval, considerably faster than the one of 56 Co decay (i.e. 111.3 d), suggesting that the γ-rays escape with lower deposition, owing to the low mass nature of the ejecta. After day 200, an e-folding time ≃47 ± 2.8 d is measured. While the light curves of SNe 19901 and 1993J are similar in the [30:100] d time range, they tend to behave differently after day 200. A simplified γ-ray deposition model is applied after adding a contribution of about 35% to the computed pseudo-bolometric light curves to account for near-IR luminosities to estimate the ejecta and 56 Ni masses (M( 56 Ni) = 0.11 M ○. and M ej = 3.7 M ○. ). The deficit in luminosity is estimated to be about 50% around day 308. The observed spectral blueshift combined with the dramatic and sudden drop in the pseudo-bolometric light curve and (B - V) colour is interpreted to be a consequence of dust condensation in the ejecta of SN 19901 around day 250.

Charge transfer in helium-rich supernova plasma

Charge transfer rate coefficients are estimated using Landau-Zener and modified Demkov approximations. The coefficients, augmented by those available from the literature, are used in statistical equilibrium equations describing the state of helium-rich supernova plasma. Such a plasma may describe both Type Ib and Type Ic supernova ejecta. The hypothesis that extensive mixing of metals with helium in Type Ic supernovae may provide a catalyst for rapid charge transfer that weakens the helium line emission by altering the excitation balance is tested. It is shown that charge transfer as a mechanism for suppressing helium line emission is ineffective unless the metal abundance is comparable to or larger than the helium abundance. This result supports an earlier conclusion that Type Ic supernovae must be helium poor relative to Type Ib events.

Late-time optical spectra of SN1987A

Optical study of late-time nebular emission provided the first direct evidence for the presence of radioactive 56Co in the ejecta of Type Ia supernovae1 and yielded conclusive evidence that Type Ib events constitute a physically distinct class of supernovae2. Hydrogen-rich Type II supernovae have not been studied in detail in the nebular phase, but SN1987A provides an unprecedented opportunity to probe the structure and composition of the ejecta by modelling the nebular spectrum. Here we investigate the late-time nebular spectra of SN1987A by computing the emergent spectra from model atmospheres. The new features of this calculation are the inclusion of a complex model hydrogen atom and the self-consistent treatment of an opaque lower boundary which approximates the observed continuum. We adopt hydrodynamic models reported in the literature, which are known to reproduce the observed light curve and γ-ray and X-ray spectra, and we obtain qualitative agreement with observed optical spectra. By examining the effect of mixing core material into the envelope, we conclude that the metals in the hydrogen-rich envelope make a substantial contribution to the optical nebular lines even for models with no outward mixing of the core material; however, a significant fraction of the energy emitted in 56Co decay must be deposited in the envelope to produce the observed linewidths and hydrogen line strengths.