247 research outputs found
Unresolved versus resolved: testing the validity of young simple stellar population models with VLT/MUSE observations of NGC 3603
CONTEXT. Stellar populations are the building blocks of galaxies including
the Milky Way. The majority, if not all extragalactic studies are entangled
with the use of stellar population models given the unresolved nature of their
observation. Extragalactic systems contain multiple stellar populations with
complex star formation histories. However, their study is mainly based upon the
principles of simple stellar populations (SSP). Hence, it is critical to
examine the validity of SSP models. AIMS. This work aims to empirically test
the validity of SSP models. This is done by comparing SSP models against
observations of spatially resolved young stellar population in the
determination of its physical properties, i.e. age and metallicity. METHODS.
Integral field spectroscopy of a young stellar cluster in the Milky Way, NGC
3603, is used to study the properties of the cluster both as a resolved and
unresolved stellar population. The unresolved stellar population is analysed
using the H equivalent width as an age indicator, and the ratio of
strong emission lines to infer metallicity. In addition, spectral energy
distribution (SED) fitting using STARLIGHT, is used to infer these properties
from the integrated spectrum. Independently, the resolved stellar population is
analysed using the color-magnitude diagram (CMD) for age and metallicity
determination. As the SSP model represents the unresolved stellar population,
the derived age and metallicity are put to test whether they agree with those
derived from resolved stars. RESULTS. The age and metallicity estimate of NGC
3603 derived from integrated spectroscopy are confirmed to be within the range
of those derived from the CMD of the resolved stellar population, including
other estimates found in the literature. The result from this pilot study
supports the reliability of SSP models for studying unresolved young stellar
populations.Comment: 9 pages, 5 figures, accepted to A&
Spectropolarimetry of Type II supernovae (I) Sample, observational data and interstellar polarization
We investigate polarization spectra of hydrogen-rich core-collapse supernovae
(Type~II SNe). The polarization signal from SNe contains two independent
components: intrinsic SN polarization and interstellar polarization (ISP). From
these components, we can study the SN explosion geometry and the dust
properties in their host galaxies or in the Milky Way. In this first paper,
using a new improved method, we investigate the properties of the ISP
components of 11 well-observed Type~II SNe. As a result of our analysis, we
find that 10 out of these 11 SNe showed a steady ISP component with a
polarization degree \%, while one SN was consistent with zero
ISP. As for the wavelength dependence, SN~2001dh (and possibly SN~2012aw)
showed a non-Milky-Way-like ISP likely originating from the interstellar dust
in their respective host galaxies: their polarization maxima were located at
short wavelengths (~\AA). Similar results have been obtained
previously for highly reddened SNe. The majority of the SNe in our sample had
too large uncertainties in the wavelength dependence of their ISP components to
consider them further. Our work demonstrates that, by applying this method to a
larger SN sample, further investigation of the ISP component of the SN
polarization can provide new opportunities to study interstellar dust
properties in external galaxies.Comment: 35 pages, 36 figures, accepted for publication in A&
Unraveling the Infrared Transient VVV-WIT-06: The Case for the Origin as a Classical Nova
Indexación: Scopus.E.Y.H. acknowledges the support provided by the National Science Foundation under Grant No. AST-1613472 and by the Florida Space Grant Consortium. L.G. acknowledges support from the FINCA visitor programme. The research work at the Physical Research Laboratory is funded by the Department of Space, Government of India. Facility: Magellan: Baade(FIRE).The enigmatic near-infrared transient VVV-WIT-06 underwent a large-amplitude eruption of unclear origin in 2013 July. Based on its light curve properties and late-time post-outburst spectra, various possibilities have been proposed in the literature for the origin of the object, namely a Type I supernova, a classical nova (CN), or a violent stellar merger event. We show that, of these possibilities, an origin in a CN outburst convincingly explains the observed properties of VVV-WIT-06. We estimate that the absolute K-band magnitude of the nova at maximum was M k = -8.2 ±0.5, its distance d = 13.35 ±2.18 kpc, and the extinction A v = 15.0 ±0.55 mag. © 2018. The American Astronomical Society. All rights reserved.https://iopscience.iop.org/article/10.3847/1538-4357/aae5d
Constraints on core-collapse supernova progenitors from explosion site integral field spectroscopy
Observationally, supernovae (SNe) are divided into subclasses pertaining to
their distinct characteristics. This diversity reflects the diversity in the
progenitor stars. It is not entirely clear how different evolutionary paths
leading massive stars to become a SN are governed by fundamental parameters
such as progenitor initial mass and metallicity. This paper places constraints
on progenitor initial mass and metallicity in distinct core-collapse SN
subclasses, through a study of the parent stellar populations at the explosion
sites. Integral field spectroscopy (IFS) of 83 nearby SN explosion sites with a
median distance of 18 Mpc has been collected and analysed, enabling detection
and spectral extraction of the parent stellar population of SN progenitors.
From the parent stellar population spectrum, the initial mass and metallicity
of the coeval progenitor are derived by means of comparison to simple stellar
population models and strong-line methods. Additionally, near-infrared IFS was
employed to characterise the star formation history at the explosion sites. No
significant metallicity differences are observed among distinct SN types. The
typical progenitor mass is found to be highest for SN Ic, followed by type Ib,
then types IIb and II. SN IIn is the least associated with young stellar
populations and thus massive progenitors. However, statistically significant
differences in progenitor initial mass are observed only when comparing SNe IIn
with other subclasses. Stripped-envelope SN progenitors with initial mass
estimate lower than 25~ are found; these are thought to be the result
of binary progenitors. Confirming previous studies, these results support the
notion that core-collapse SN progenitors cannot arise from single-star channel
only, and both single and binary channels are at play in the production of
core-collapse SNe. [ABRIDGED]Comment: 18 pages, 10 figures, accepted to A&
Statistical studies of supernova environments
Investigations of the environments of SNe allow statistical constraints to be made on progenitor properties. We review progress that has been made in this field. Pixel statistics using tracers of e.g. star formation within galaxies show differences in the explosion sites of, in particular SNe types II and Ibc (SNe II and SNe Ibc), suggesting differences in population ages. Of particular interest is that SNe Ic are significantly more associated with H-alpha emission than SNe Ib, implying shorter lifetimes for the former. In addition, such studies have shown that the interacting SNe IIn do not explode in regions containing the most massive stars, which suggests that at least a significant fraction of their progenitors arise from the lower end of the core-collapse SN mass range. Host HII region spectroscopy has been obtained for a significant number of core-collapse events, however definitive conclusions have to-date been elusive. Single stellar evolution models predict that the fraction of SNe Ibc to SNe II should increase with increasing metallicity, due to the dependence of mass-loss rates on progenitor metallicity. We present a meta-analysis of host HII region oxygen abundances for CC SNe. It is concluded that the SN II to SN Ibc ratio shows little variation with oxygen abundance, with only a suggestion that the ratio increases in the lowest bin. Radial distributions of different SNe are discussed, where a central excess of SNe Ibc has been observed within disturbed galaxy systems, which is difficult to ascribe to metallicity or selection effects. Environment studies are evolving to enable studies at higher spatial resolutions than previously possible, while in addition the advent of wide-field integral field unit instruments allows galaxy-wide spectral analyses which will provide fruitful results to this field. Some example contemporary results are shown in that direction
Studying the environment of AT2018cow with MUSE
AT2018cow was the nearest and best studied example of a new breed of extra-galactic, luminous and rapidly-evolving transient. Both the progenitor systems and explosion mechanisms of these rapid transients remain a mystery { the energetics, spectral signa- tures, and timescales make them challenging to interpret in established classes of super- novae and tidal disruption events. The rich, multi-wavelength data-set of AT2018cow has still left several interpretations viable to explain the nature of this event. In this paper we analyse integral- eld spectroscopic data of the host galaxy, CGCG137-068, to compare environmental constraints with leading progenitor models. We nd the explosion site of AT2018cow to be very typical of core-collapse supernovae (known to form from stars with MZAMS 8-25 M ), and infer a young stellar population age at the explosion site of few 10Myr, at slightly sub-solar metallicity. When comparing to expectations for exotic intermediate-mass black hole (IMBH) tidal disruption events, we nd no evidence for a potential host system of the IMBH. In particular, there are no abrupt changes in metallicity or kinematics in the vicinity of the explosion site, ar- guing against the presence of a distinct host system. The proximity of AT2018cow to strong star-formation in the host galaxy makes us favour a massive stellar progenitor for this event.Science & Technology Facilities Council (STFC)
Science and Technology Development Fund (STDF)
ST/P000495/1European Union (EU)
839090European Union (EU) PGC2018-095317-B-C21Consejo Nacional de Ciencia y Tecnologia (CONACyT) CB-285080 FC-2016-01-1916(UNAM) project
PAPIIT-DGAPA-IN100519European Organisation for Astronomical Research in the Southern Hemisphere under ESO programme
0103.D-0440(A
Helium stars exploding in circumstellar material and the origin of Type Ibn supernovae
Type Ibn supernovae (SNe) are a mysterious class of transients whose spectra exhibit persistently narrow He I lines, and whose bolometric light curves are typically fast evolving and overluminous at peak relative to standard Type Ibc SNe. We explore the interaction scenario of such Type Ibn SNe by performing radiation-hydrodynamics and radiative-transfer calculations. We find that standard-energy helium-star explosions within dense wind-like circumstellar material (CSM) can reach a peak luminosity of a few 10(44) erg s(-1) on day timescales, which is reminiscent of exceptional events such as AT 2018cow. Similar interactions but with weaker winds can lead to Type Ibc SNe with double-peak light curves and peak luminosities in the range similar to 10(42.2) to similar to 10(43) erg s(-1). In contrast, the narrow spectral lines and modest peak luminosities of most Type Ibn SNe are suggestive of a low-energy explosion in an initially less than or similar to 5 M-circle dot helium star, most likely arising from interacting binaries and colliding with a massive helium-rich, probably ejecta-like, CSM at similar to 10(15) cm. Nonlocal thermodynamic equilibrium radiative-transfer simulations of a slow-moving dense shell born out and powered by the interaction compare favorably to Type Ibn SNe such as 2006jc, 2011hw, or 2018bcc at late times and suggest a composition made of about 50% helium, a solar metallicity, and a total ejecta and CSM mass of 1-2 M-circle dot. A lower fractional helium abundance leads to weak or absent He I lines and thus excludes more massive configurations for observed Type Ibn SNe. Further, the dominance of Fe II emission below 5500 angstrom seen in Type Ibn SNe at late times is not predicted at low metallicity. Hence, despite their promising properties, Type Ibn SNe from a pulsational-pair instability in very massive stars, requiring low metallicity, probably have not been observed yet
Type II supernovae as probes of environment metallicity: observations of host HII regions
Spectral modelling of SNII atmospheres indicates a clear dependence of metal
line strengths on progenitor metallicity. This motivates further work to
evaluate the accuracy with which these SNe can be used as metallicity
indicators. To assess this accuracy we present a sample of SNII HII-region
spectroscopy, from which environment abundances are derived. These environment
abundances are compared to the observed strength of metal lines in SN spectra.
Combining our sample with measurements from the literature, we present oxygen
abundances of 119 host HII regions, by extracting emission line fluxes and
using abundance diagnostics. Then, following Dessart et al., these abundances
are compared to equivalent widths of Fe 5018 A at various time and colour
epochs. Our distribution of inferred SNII host HII-region abundances has a
range of ~0.6 dex. We confirm the dearth of SNeII exploding at metallicities
lower than those found (on average) in the Large Magellanic Cloud. The
equivalent width of Fe 5018 A at 50 days post explosion shows a statistically
significant correlation with host HII-region oxygen abundance. The strength of
this correlation increases if one excludes abundance measurements derived far
from SN explosion sites. The correlation significance also increases if we only
analyse a 'gold' IIP sample, and if a colour epoch is used in place of time. In
addition, no evidence is found of correlation between progenitor metallicity
and SN light-curve or spectral properties - except for that stated above with
respect to Fe 5018 A equivalent width - suggesting progenitor metallicity is
not a driving factor in producing the diversity observed in our sample. This
study provides observational evidence of the usefulness of SNII as metallicity
indicators. We finish with a discussion of the methodology needed to use SN
spectra as independent metallicity diagnostics throughout the Universe.Comment: Accepted for publication in Astronomy and Astrophyci
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