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Register a new userSN 2021csp -- the explosion of a stripped envelope star within a H and He-poor circumstellar medium
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We present observations of SN 2021csp, a unique supernova (SN) which displays evidence for interaction with H- and He- poor circumstellar material (CSM) at early times. Using high-cadence spectroscopy taken over the first week after explosion, we show that the spectra of SN 2021csp are dominated by C III lines with a velocity of 1800 km s$^{-1}$. We associate this emission with CSM lost by the progenitor prior to explosion. Subsequently, the SN displays narrow He lines before metamorphosing into a broad-lined Type Ic SN. We model the bolometric light curve of SN 2021csp, and show that it is consistent with the energetic ($4times10^{51}$ erg) explosion of a stripped star, producing 0.4 M$_odot$ of 56Ni within a $sim$1 M$_odot$ shell of CSM extending out to 400 R$_odot$.
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In this paper, we discuss the outcomes of the follow-up campaign of SN 2018ijp, discovered as part of the Zwicky Transient Facility survey for optical transients. Its first spectrum shows similarities to broad-lined Type Ic supernovae around maximum light, whereas later spectra display strong signatures of interaction between rapidly expanding ejecta and a dense H-rich circumstellar medium, coinciding with a second peak in the photometric evolution of the transient. This evolution, along with the results of modeling of the first light curve peak, suggests a scenario where a stripped star exploded within a dense circumstellar medium. The two main phases in the evolution of the transient could be interpreted as a first phase dominated by radioactive decays, and an later interaction-dominated phase where the ejecta collide with a pre-existing shell. We therefore discuss SN 2018jp within the context of a massive star depleted of its outer layers exploding within a dense H-rich circumstellar medium.
We report optical and near-infrared observations of SN 2012ca with the Public ESO Spectroscopy Survey of Transient Objects (PESSTO), spread over one year since discovery. The supernova (SN) bears many similarities to SN 1997cy and to other events classified as Type IIn but which have been suggested to have a thermonuclear origin with narrow hydrogen lines produced when the ejecta impact a hydrogen-rich circumstellar medium (CSM). Our analysis, especially in the nebular phase, reveals the presence of oxygen, magnesium and carbon features. This suggests a core collapse explanation for SN2012ca, in contrast to the thermonuclear interpretation proposed for some members of this group. We suggest that the data can be explained with a hydrogen and helium deficient SN ejecta (Type I) interacting with a hydrogen-rich CSM, but that the explosion was more likely a Type Ic core-collapse explosion than a Type Ia thermonuclear one. This suggests two channels (both thermonuclear and stripped envelope core-collapse) may be responsible for these SN 1997cy-like events.
The dominant mechanism and time scales over which stripped-envelope supernovae (SNe) progenitor stars shed their hydrogen envelopes are uncertain. Observations of Type Ib and Ic SNe at late phases could reveal the optical signatures of interaction with distant circumstellar material (CSM) providing important clues on the origin of the necessary pre-SN mass loss. We report deep late-time optical spectroscopy of the Type Ib explosion SN 2004dk 4684 days (13 years) after discovery. Prominent intermediate-width H-alpha emission is detected, signaling that the SN blast wave has caught up with the hydrogen-rich CSM lost by the progenitor system. The line luminosity is the highest ever reported for a SN at this late stage. Prominent emission features of He, Fe, and Ca are also detected. The spectral characteristics are consistent with CSM energized by the forward shock, and resemble the late-time spectra of the persistently interacting Type IIn SNe 2005ip and 1988Z. We suggest that the onset of interaction with H-rich CSM was associated with a previously reported radio rebrightening at ~1700 days. The data indicate that the mode of pre-SN mass loss was a relatively slow dense wind that persisted millennia before the SN, followed by a short-lived Wolf-Rayet phase that preceded core-collapse and created a cavity within an extended distribution of CSM. We also present new spectra of SNe 2014C, PTF11iqb, and 2009ip, all of which also exhibit continued interaction with extended CSM distributions.
In this paper we analyse the pre-explosion spectrum of SN2015bh by performing radiative transfer simulations using the CMFGEN code. This object has attracted significant attention due to its remarkable similarity to SN2009ip in both its pre- and post-explosion behaviour. They seem to belong to a class of events for which the fate as a genuine core-collapse supernova or a non-terminal explosion is still under debate. Our CMFGEN models suggest that the progenitor of SN2015bh had an effective temperature between 8700 and 10000 K, luminosity in the range ~ 1.8-4.74e6 Lsun, contained at least 25% H in mass at the surface, and half-solar Fe abundances. The results also show that the progenitor of SN 2015bh generated an extended wind with a mass-loss rate of ~ 6e-4 to 1.5e-3 Msun/yr and a velocity of 1000 km/s. We determined that the wind extended to at least 2.57e14 cm and lasted for at least 30 days prior to the observations, releasing 5e-5 Msun into the circumstellar medium. In analogy to 2009ip, we propose that this is the material that the explosive ejecta could interact at late epochs, perhaps producing observable signatures that can be probed with future observations. We conclude that the progenitor of SN 2015bh was most likely a warm luminous blue variable of at least 35 Msun before the explosion. Considering the high wind velocity, we cannot exclude the possibility that the progenitor was a Wolf-Rayet star that inflated just before the 2013 eruption, similar to HD5980 during its 1994 episode. If the star survived, late-time spectroscopy may reveal either a similar LBV or a Wolf-Rayet star, depending on the mass of the H envelope before the explosion. If the star exploded as a genuine SN, 2015bh would be a remarkable case of a successful explosion after black-hole formation in a star with a possible minimum mass 35 Msun at the pre-SN stage.
We analyse new ALMA observations of the $^{29}$SiO ($ u$=0, $J$=8$-$7) and SO$_2$($ u$=0, $34_{3,31}$$-$$34_{2,32}$) line emissions of the circumstellar envelope (CSE) of the oxygen-rich AGB star R Dor. With a spatial resolution of $sim$2.3 au, they cover distances below $sim$30 au from the star providing a link between earlier observations and clarifying some open issues. The main conclusions are: 1) Rotation is confined below $sim$15 au from the star, with velocity reaching a maximum below 10 au and morphology showing no significant disc-like flattening. 2) In the south-eastern quadrant, a large Doppler velocity gas stream is studied in more detail than previously possible and its possible association with an evaporating planetary companion is questioned. 3) A crude evaluation of the respective contributions of rotation, expansion and turbulence to the morpho-kinematics is presented. Significant line broadening occurs below $sim$12 au from the star and causes the presence of high Doppler velocity components near the line of sight pointing to the centre of the star. 4) Strong absorption of the continuum emission of the stellar disc and its immediate dusty environment is observed to extend beyond the disc in the form of self-absorption. The presence of a cold SiO layer extending up to some 60 au from the star is shown to be the cause. 5) Line emissions from SO, $^{28}$SiO, CO and HCN molecules are used to probe the CSE up to some 100 au from the star and reveal the presence of two broad back-to-back outflows, the morphology of which is studied in finer detail than in earlier work.
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