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- Csengeri, T., et al.
(author)
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Search for high-mass protostars with ALMA revealed up to kilo-parsec scales (SPARKS): I. Indication for a centrifugal barrier in the environment of a single high-mass envelope
- 2018
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 617
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Journal article (peer-reviewed)abstract
- The conditions leading to the formation of the most massive O-type stars are still an enigma in modern astrophysics. To assess the physical conditions of high-mass protostars in their main accretion phase, here we present a case study of a young massive clump selected from the ATLASGAL survey, G328.2551-0.5321. The source exhibits a bolometric luminosity of 1.3 × 104L·, which allows us to estimate that its current protostellar mass lies between ∼11 and 16 M·. We show high angular resolution observations with ALMA that reach a physical scale of ∼400 au. To reveal the structure of this high-mass protostellar envelope in detail at a ∼0.17′′ resolution, we used the thermal dust continuum emission and spectroscopic information, amongst others from the CO (J = 3-2) line, which is sensitive to the high-velocity molecular outflow of the source. We also used the SiO (J = 8-7) and SO2(J = 82,6-71,7) lines, which trace shocks along the outflow, as well as several CH3OH and HC3N lines that probe the gas of the inner envelope in the closest vicinity of the protostar. Our observations of the dust continuum emission reveal a single high-mass protostellar envelope, down to our resolution limit. We find evidence for a compact, marginally resolved continuum source that is surrounded by azimuthal elongations that could be consistent with a spiral pattern. We also report on the detection of a rotational line of CH3OH within its vt= 1 torsionally excited state. This shows two bright emission peaks that are spatially offset from the dust continuum peak and exhibit a distinct velocity component ±4.5 km s-1offset from the systemic velocity of the source. Rotational diagram analysis and models based on local thermodynamic equilibrium assumption require high CH3OH column densities that reach N(CH3OH) = 1.2-2 × 1019cm-2, and kinetic temperatures of the order of 160-200 K at the position of these peaks. A comparison of their morphology and kinematics with those of the outflow component of the CO line and the SO2line suggests that the high-excitation CH3OH spots are associated with the innermost regions of the envelope. While the HC3N v7= 0 (J = 37-36) line is also detected in the outflow, the HC3N v7= 1e (J = 38-37) rotational transition within the first vibrationally excited state of the molecule shows a compact morphology. We find that the velocity shifts at the position of the observed high-excitation CH3OH spots correspond well to the expected Keplerian velocity around a central object with 15 M·consistent with the mass estimate based on the bolometric luminosity of the source. We propose a picture where the CH3OH emission peaks trace the accretion shocks around the centrifugal barrier, pinpointing the interaction region between the collapsing envelope and an accretion disc. The physical properties of the accretion disc inferred from these observations suggest a specific angular momentum several times higher than typically observed towards low-mass protostars. This is consistent with a scenario of global collapse setting on at larger scales that could carry a more significant amount of kinetic energy compared to the core-collapse models of low-mass star formation. Furthermore, our results suggest that vibrationally excited HC3N emission could be a new tracer for compact accretion discs around high-mass protostars.
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- Pessi, T., et al.
(author)
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A characterization of ASAS-SN core-collapse supernova environments with VLT+MUSE I. Sample selection, analysis of local environments, and correlations with light curve properties
- 2023
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In: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 677
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Journal article (peer-reviewed)abstract
- Context. The analysis of core-collapse supernova (CCSN) environments can provide important information on the life cycle of massive stars and constrain the progenitor properties of these powerful explosions. The MUSE instrument at the Very Large Telescope (VLT) enables detailed local environment constraints of the progenitors of large samples of CCSNe. Using a homogeneous SN sample from the All-Sky Automated Survey for Supernovae (ASAS-SN) survey, an untargeted and spectroscopically complete transient survey, has enabled us to perform a minimally biased statistical analysis of CCSN environments.Aims. We analyze 111 galaxies observed by MUSE that hosted 112 CCSNe – 78 II, nine IIn, seven IIb, four Ic, seven Ib, three Ibn, two Ic-BL, one ambiguous Ibc, and one superluminous SN – detected or discovered by the ASAS-SN survey between 2014 and 2018. The majority of the galaxies were observed by the All-weather MUse Supernova Integral field Nearby Galaxies (AMUSING) survey. Here we analyze the immediate environment around the SN locations and compare the properties between the different CCSN types and their light curves.Methods. We used stellar population synthesis and spectral fitting techniques to derive physical parameters for all H II regions detected within each galaxy, including the star formation rate (SFR), Hα equivalent width (EW), oxygen abundance, and extinction.Results. We found that stripped-envelope supernovae (SESNe) occur in environments with a higher median SFR, Hα EW, and oxygen abundances than SNe II and SNe IIn/Ibn. Most of the distributions have no statistically significant differences, except between oxygen abundance distributions of SESNe and SNe II, and between Hα EW distributions of SESNe and SNe II. The distributions of SNe II and IIn are very similar, indicating that these events explode in similar environments. For the SESNe, SNe Ic have higher median SFRs, Hα EWs, and oxygen abundances than SNe Ib. SNe IIb have environments with similar SFRs and Hα EWs to SNe Ib, and similar oxygen abundances to SNe Ic. We also show that the postmaximum decline rate, s, of SNe II correlates with the Hα EW, and that the luminosity and the Δm15 parameter of SESNe correlate with the oxygen abundance, Hα EW, and SFR at their environments. This suggests a connection between the explosion mechanisms of these events to their environment properties.
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