67 research outputs found
Optical polarization and spectral properties of the H-poor superluminous supernovae SN 2021bnw and SN 2021fpl
New optical photometric, spectrocopic and imaging polarimetry data are
combined with publicly available data to study some of the physical properties
of the two H-poor superluminous supernovae (SLSN) SN 2021bnw and SN 2021fpl.
For each SLSN, the best-fit parameters obtained from the magnetar model with
\texttt{MOSFiT} do not depart from the range of parameter obtained on other
SLSNe discussed in the literature. A spectral analysis with \texttt{SYN++}
shows that SN 2021bnw is a W Type, Fast evolver, while SN 2021fpl is a 15bn
Type, Slow evolver. The analysis of the polarimetry data obtained on SN 2021fpl
at four epochs (+1.8, +20.6, +34.1 and +43.0 days, rest-frame) shows polarization detections in the range 0.8--1 . A comparison of the
spectroscopy data suggests that SN 2021fpl underwent a spectral transition a
bit earlier than SN 2015bn, during which, similarly, it could have underwent a
polarization transition. The analysis of the polarimetry data obtained on SN
2021bnw do not show any departure from symmetry of the photosphere at an
empirical diffusion timescale of 2 (+81.1 days rest-frame). This
result is consistent with those on the sample of W Type SLSN observed at
empirical diffusion timescale 1 with that technique, even though it is
not clear the effect of limited spectral windows varying from one object to the
other. Measurements at higher empirical diffusion timescale may be needed to
see any departure from symmetry as it is discussed in the literature for SN
2017egm.Comment: 29 pages, 13 Figures, 15 Tables, submitted to the MNRA
Herschel Observations of a Potential Core Forming Clump: Perseus B1-E
We present continuum observations of the Perseus B1-E region from the
Herschel Gould Belt Survey. These Herschel data reveal a loose grouping of
substructures at 160 - 500 micron not seen in previous submillimetre
observations. We measure temperature and column density from these data and
select the nine densest and coolest substructures for follow-up spectral line
observations with the Green Bank Telescope. We find that the B1-E clump has a
mass of ~ 100 solar masses and appears to be gravitationally bound.
Furthermore, of the nine substructures examined here, one substructure (B1-E2)
appears to be itself bound. The substructures are typically less than a Jeans
length from their nearest neighbour and thus, may interact on a timescale of ~
1 Myr. We propose that B1-E may be forming a first generation of dense cores,
which could provide important constraints on the initial conditions of
prestellar core formation. Our results suggest that B1-E may be influenced by a
strong, localized magnetic field, but further observations are still required.Comment: 14 pages, 8 figures, published in A&A: Minor calibration correctio
The earliest phases of high-mass star formation, as seen in NGC 6334 by Herschel-HOBYS
To constrain models of high-mass star formation, the Herschel/HOBYS KP aims at discovering massive dense cores (MDCs) able to host the high-mass analogs of low-mass prestellar cores, which have been searched for over the past decade. We here focus on NGC 6334, one of the best-studied HOBYS molecular cloud complexes.
We used Herschel PACS and SPIRE 70-500 µm images of the NGC 6334 complex complemented with (sub)millimeter and mid-infrared data. We built a complete procedure to extract ~0.1 pc dense cores with the getsources software, which simultaneously measures their far-infrared to millimeter fluxes. We carefully estimated the temperatures and masses of these dense cores from their spectral energy distributions (SEDs). We also identified the densest pc-scale cloud structures of NGC 6334, one 2 px x 1 pc ridge and two 0.8 pc x 0.8 pc hubs, with volume-averaged densities of ~105 cm-3.
A cross-correlation with high-mass star formation signposts suggests a mass threshold of 75 Mʘ for MDCs in NGC 6334. MDCs have temperatures of 9.5-40K, masses of 75-1000 Mʘ, and densities of 1 x 105- 7 x 107 cm-3. Their mid-infrared emission is used to separate 6 IR-bright and 10 IR-quiet protostellar MDCs while their 70 µm emission strength, with respect to fitted SEDs, helps identify 16 starless MDC candidates. The ability of the latter to host high-mass prestellar cores is investigated here and remains questionable. An increase in mass and density from the starless to the IR-quiet and IR-bright phases suggests that the protostars and MDCs simultaneously grow in mass. The statistical lifetimes of the high-mass prestellar and protostellar core phases, estimated to be 1-7 x 104 yr and at most 3 x 105 yr respectively, suggest a dynamical scenario of high-mass star formation.
The present study provides good mass estimates for a statistically significant sample, covering the earliest phases of high-mass star formation. High-mass prestellar cores may not exist in NGC 6334, favoring a scenario presented here, which simultaneously forms clouds and high-mass protostars
SN 2021gno: a Calcium-rich transient with double-peaked light curves
We present extensive ultraviolet (UV) and optical photometric and optical
spectroscopic follow-up of supernova (SN)~2021gno by the "Precision
Observations of Infant Supernova Explosions" (POISE) project, starting less
than two days after the explosion. Given its intermediate luminosity, fast
photometric evolution, and quick transition to the nebular phase with spectra
dominated by [Ca~II] lines, SN~2021gno belongs to the small family of
Calcium-rich transients. Moreover, it shows double-peaked light curves, a
phenomenon shared with only four other Calcium-rich events. The projected
distance from the center of the host galaxy is not as large as other objects in
this family. The initial optical light-curve peaks coincide with a very quick
decline of the UV flux, indicating a fast initial cooling phase. Through
hydrodynamical modelling of the bolometric light curve and line velocity
evolution, we found that the observations are compatible with the explosion of
a highly-stripped massive star with an ejecta mass of and a
Ni mass of . The initial cooling phase (first light
curve peak) is explained by the presence of an extended circumstellar material
comprising with an extension of .
We discuss if hydrogen features are present in both maximum-light and nebular
spectra, and its implications in terms of the proposed progenitor scenarios for
Calcium-rich transients.Comment: 21 pages, 13 figures, accepted for publication in MNRA
A census of dense cores in the Aquila cloud complex: SPIRE/PACS observations from the <i>Herschel</i> Gould Belt survey
We present and discuss the results of the Gould Belt survey (HGBS) observations in an ~11 area of the Aquila molecular cloud complex at ~ 260 pc, imaged with the SPIRE and PACS photometric cameras in parallel mode from to . Using the multi-scale, multi-wavelength source extraction algorithm , we identify a complete sample of starless dense cores and embedded (Class 0-I) protostars in this region, and analyze their global properties and spatial distributions. We find a total of 651 starless cores, ~60% ± 10% of which are gravitationally bound prestellar cores, and they will likely form stars in the future. We also detect 58 protostellar cores. The core mass function (CMF) derived for the large population of prestellar cores is very similar in shape to the stellar initial mass function (IMF), confirming earlier findings on a much stronger statistical basis and supporting the view that there is a close physical link between the stellar IMF and the prestellar CMF. The global shift in mass scale observed between the CMF and the IMF is consistent with a typical star formation efficiency of ~40% at the level of an individual core. By comparing the numbers of starless cores in various density bins to the number of young stellar objects (YSOs), we estimate that the lifetime of prestellar cores is ~1 Myr, which is typically ~4 times longer than the core free-fall time, and that it decreases with average core density. We find a strong correlation between the spatial distribution of prestellar cores and the densest filaments observed in the Aquila complex. About 90% of the -identified prestellar cores are located above a background column density corresponding to ~ 7, and ~75% of them lie within filamentary structures with supercritical masses per unit length ≳16 . These findings support a picture wherein the cores making up the peak of the CMF (and probably responsible for the base of the IMF) result primarily from the gravitational fragmentation of marginally supercritical filaments. Given that filaments appear to dominate the mass budget of dense gas at , our findings also suggest that the physics of prestellar core formation within filaments is responsible for a characteristic “efficiency” ~ for the star formation process in dense gas
Herschelobservations of the W3 GMC (II): clues to the formation of clusters of high-mass stars
The W3 giant molecular cloud is a prime target for investigating the formation of high-mass stars and clusters. This second study of W3 within the HOBYS Key Program provides a comparative analysis of subfields within W3 to further constrain the processes leading to the observed structures and stellar population. Probability density
functions (PDFs) and cumulative mass distributions (CMDs) were created from dust column density maps, quantified as extinction AV. The shape of the PDF, typically represented with a lognormal function at low Av “breaking” to a power-law tail at high Av, is influenced by various processes including turbulence and selfgravity. The breaks can also be identified, often more readily, in the CMDs. The PDF break from lognormal (Av(SF)» 6–10 mag) appears to shift to higher Av by stellar feedback, so that high-mass star-forming regions tend to have higher PDF breaks. A second break at Av> 50 mag traces structures formed or influenced by a dynamic process. Because such a process has been suggested to drive high-mass star formation in W3, this second
break might then identify regions with potential for hosting high-mass stars/clusters. Stellar feedback appears to be a major mechanism driving the local evolution and state of regions within W3. A high initial star formation efficiency in a dense medium could result in a self-enhancing process, leading to more compression and favorable
star formation conditions (e.g., colliding flows), a richer stellar content, and massive stars. This scenario would be compatible with the “convergent constructive feedback” model introduced in our previous Herschel study
First results from the <i>Herschel</i> Gould Belt Survey in Taurus
The whole of the Taurus region (a total area of 52 deg2) has been observed by the Herschel Spectral and Photometric Imaging Receiver (SPIRE) and Photodetector Array Camera and Spectrometer (PACS) instruments at wavelengths of 70, 160, 250, 350 and 500 μm as part of the Herschel Gould Belt Survey. In this paper we present the first results from the part of the Taurus region that includes the Barnard 18 and L1536 clouds. A new source-finding routine, the Cardiff Source-finding AlgoRithm (CSAR), is introduced, which is loosely based on CLUMPFIND, but that also generates a structure tree, or dendrogram, which can be used to interpret hierarchical clump structure in a complex region. Sources were extracted from the data using the hierarchical version of CSAR and plotted on a mass-size diagram. We found a hierarchy of objects with sizes in the range 0.024-2.7 pc. Previous studies showed that gravitationally bound prestellar cores and unbound starless clumps appeared in different places on the mass-size diagram. However, it was unclear whether this was due to a lack of instrumental dynamic range or whether they were actually two distinct populations. The excellent sensitivity of Herschel shows that our sources fill the gap in the mass-size plane between starless and pre-stellar cores, and gives the first clear supporting observational evidence for the theory that unbound clumps and (gravitationally bound) prestellar cores are all part of the same population, and hence presumably part of the same evolutionary sequence
First BISTRO Observations of the Dark Cloud Taurus L1495A-B10: The Role of the Magnetic Field in the Earliest Stages of Low-mass Star Formation
We present BISTRO Survey 850 μm dust emission polarization observations of the L1495A-B10 region of the Taurus molecular cloud, taken at the James Clerk Maxwell Telescope (JCMT). We observe a roughly triangular network of dense filaments. We detect nine of the dense starless cores embedded within these filaments in polarization, finding that the plane-of-sky orientation of the core-scale magnetic field lies roughly perpendicular to the filaments in almost all cases. We also find that the large-scale magnetic field orientation measured by Planck is not correlated with any of the core or filament structures, except in the case of the lowest-density core. We propose a scenario for early prestellar evolution that is both an extension to, and consistent with, previous models, introducing an additional evolutionary transitional stage between field-dominated and matter-dominated evolution, observed here for the first time. In this scenario, the cloud collapses first to a sheet-like structure. Uniquely, we appear to be seeing this sheet almost face on. The sheet fragments into filaments, which in turn form cores. However, the material must reach a certain critical density before the evolution changes from being field dominated to being matter dominated. We measure the sheet surface density and the magnetic field strength at that transition for the first time and show consistency with an analytical prediction that had previously gone untested for over 50 yr
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