380 research outputs found
The Disappearance of the Progenitors of Supernovae 1993J and 2003gd
Using images from the Hubble Space Telescope (HST) and the Gemini Telescope
we confirm the disappearance of the progenitors of two Type II supernovae
(SNe), and evaluate the presence of other stars associated with them. We find
that the progenitor of SN 2003gd, an M-supergiant star, is no longer observed
at the SN location, and determine its intrinsic brightness using image
subtraction techniques. The progenitor of SN 1993J, a K-supergiant star, is
also no longer present, but its B-supergiant binary companion is still
observed. The disappearance of the progenitors confirms that these two SNe were
produced by Red Supergiants.Comment: Science, in press, published online 19/03/09, 28 pages (MS+SOM)
(high-res figures available at
http://www.dark-cosmology.dk/~justyn/research/
The Progenitor of SN 2005cs in the Whirlpool Galaxy
The progenitor of SN 2005cs, in the galaxy M51, is identified in
pre-explosion HST ACS WFC imaging. Differential astrometry, with post-explosion
ACS HRC F555W images, permitted the identification of the progenitor with an
accuracy of 0.006". The progenitor was detected in the F814W pre-explosion
image with I=23.3+/-0.2, but was below the detection thresholds of the F435W
and F555W images, with B<24.8 and V<25 at 5-sigma. Limits were also placed on
the U and R band fluxes of the progenitor from pre-explosion HST WFPC2 F336W
and F675W images. Deep images in the infra-red from NIRI on the Gemini-North
telescope were taken 2 months prior to explosion, but the progenitor is not
clearly detected on these. The upper limits for the JHK magnitudes of the
progenitor were J<21.9,H<21.1 and K<20.7. Despite having a detection in only
one band, a restrictive spectral energy distribution of the progenitor star can
be constructed and a robust case is made that the progenitor was a red
supergiant with spectral type between mid-K to late-M. The spectral energy
distribution allows a region in the theoretical HR diagram to be determined
which must contain the progenitor star. The initial mass of the star is
constrained to be M(ZAMS)=9+3/-2 M_solar, which is very similar to the
identified progenitor of the type II-P SN 2003gd, and also consistent with
upper mass limits placed on five other similar SNe. The upper limit in the deep
K-band image is significant in that it allows us to rule out the possibility
that the progenitor was a significantly higher mass object enshrouded in a dust
cocoon before core-collapse. This is further evidence that the trend for type
II-P SNe to arise in low to moderate mass red supergiants is real.Comment: Accepted (31/08/05) for publication in MNRAS Letter
On the nature of the progenitors of three type II-P supernovae: 2004et, 2006my and 2006ov
The pre-explosion observations of the type II-P supernovae 2006my, 2006ov and
2004et, are re-analysed. In the cases of supernovae 2006my and 2006ov we argue
that the published candidate progenitors are not coincident with their
respective supernova sites in pre-explosion Hubble Space Telescope
observations. We therefore derive upper luminosity and mass limits for the
unseen progenitors of both these supernovae, assuming they are red supergiants:
2006my (log L/Lsun = 4.51; mass < 13Msun) and 2006ov (log L/Lsun = 4.29; mass <
10Msun). In the case of supernova 2004et we show that the yellow-supergiant
progenitor candidate, originally identified in Canada France Hawaii Telescope
images, is still visible ~3 years post-explosion in observations from the
William Herschel Telescope. High-resolution Hubble Space Telescope and Gemini
(North) adaptive optics late-time imagery reveal that this source is not a
single yellow supergiant star, but rather is resolved into at least three
distinct sources. We report the discovery of the unresolved progenitor as an
excess of flux in pre-explosion Isaac Newton Telescope i'-band imaging.
Accounting for the late-time contribution of the supernova using published
optical spectra, we calculate the progenitor photometry as the difference
between the pre- and post-explosion, ground-based observations. We find the
progenitor was most likely a late K to late M-type supergiant of 8 +5/-1 Msun.
In all cases we conclude that future, high-resolution observations of the
supernova sites will be required to confirm these results.Comment: 43 pages (pre-print format), 12 figures, 10 tables. Significant
revision following referee's comments. Accepted for publication in MNRA
VLT Spectropolarimetry of the optical transient in NGC300. Evidence for asymmetry in the circumstellar dust
AIMS: The main goal of this work is to study possible signs of asymmetry in
the bright optical transient in NGC300, with the aim of getting independent
information on the explosion mechanism, the progenitor star and its
circumstellar environment.
METHODS: Using VLT-FORS1 we have obtained low-resolution optical linear
spectropolarimetry of NGC300 OT2008-1 on two epochs, 48 and 55 days after the
discovery, covering the spectral range 3600--9330A.
RESULTS: The data show a continuum polarization at a very significant level.
At least two separate components are identified. The first is characterized by
a strong wavelength dependency and a constant position angle (68.6+/-0.3
degrees), which is parallel to the local spiral arm of the host galaxy. The
second shows a completely different position angle (151.3+/-0.4) and displays a
mild but statistically significant evolution between the two epochs. While the
former is identified as arising in the interstellar dust associated with
NGC300, the latter is most likely due to continuum polarization by dust
scattering in the circumstellar environment. No line depolarization is detected
in correspondence of the most intense emission lines, disfavoring electron
scattering as the source of intrinsic polarization. This implies a very small
deviation from symmetry in the continuum-forming region. Given the observed
level of intrinsic polarization, the transient must be surrounded by a
significant amount of dust (>4x10^-5 Msun), asymmetrically distributed within a
few thousand AU. This most likely implies that one or more asymmetric outflow
episodes took place during the past history of the progenitor.Comment: Accepted for publication in Astronomy and Astrophysics. 16 pages, 16
figure
The type IIb SN 2008ax: the nature of the progenitor
A source coincident with the position of the type IIb supernova (SN) 2008ax
is identified in pre-explosion Hubble Space Telescope (HST) Wide Field
Planetary Camera 2 observations in three optical filters. We identify and
constrain two possible progenitor systems: (i) a single massive star that lost
most of its hydrogen envelope through radiatively driven mass loss processes,
prior to exploding as a helium-rich Wolf-Rayet star with a residual hydrogen
envelope, and (ii) an interacting binary in a low mass cluster producing a
stripped progenitor. Late time, high resolution observations along with
detailed modelling of the SN will be required to reveal the true nature of this
progenitor star.Comment: 5 pages, 2 figures, resolution of figure 1 reduced, figure 2 revised,
some revision following referee's comments, accepted for publication in MNRAS
letter
Towards a farmer-feasible soil health assessment that is globally applicable
Acknowledgements This work was supported by a NERC (Natural Environment Research Council) Doctoral Training Partnership grant (NE/S007407/1), Syngenta Crop Protection AG and the ClieNFarms project which received funding from the European Union’s Horizon 2020 Societal Challenges Program under the grant agreement No 101036822. For the purpose of open access, the authors have applied a Creative Commons Attribution (CC BY) licence to any Author Accepted Manuscript version arising from this submission.Peer reviewedPostprin
Properties of extragalactic dust inferred from linear polarimetry of Type Ia Supernovae
Aims: The aim of this paper is twofold: 1) to investigate the properties of
extragalactic dust and compare them to what is seen in the Galaxy; 2) to
address in an independent way the problem of the anomalous extinction curves
reported for reddened Type Ia Supernovae (SN) in connection to the environments
in which they explode. Methods: The properties of the dust are derived from the
wavelength dependence of the continuum polarization observed in four reddened
Type Ia SN: 1986G, 2006X, 2008fp, and 2014J. [...] Results: All four objects
are characterized by exceptionally low total-to-selective absorption ratios
(R_V) and display an anomalous interstellar polarization law, characterized by
very blue polarization peaks. In all cases the polarization position angle is
well aligned with the local spiral structure. While SN~1986G is compatible with
the most extreme cases of interstellar polarization known in the Galaxy,
SN2006X, 2008fp, and 2014J show unprecedented behaviours. The observed
deviations do not appear to be connected to selection effects related to the
relatively large amounts of reddening characterizing the objects in the sample.
Conclusions: The dust responsible for the polarization of these four SN is most
likely of interstellar nature. The polarization properties can be interpreted
in terms of a significantly enhanced abundance of small grains. The anomalous
behaviour is apparently associated with the properties of the galactic
environment in which the SN explode, rather than with the progenitor system
from which they originate. For the extreme case of SN2014J, we cannot exclude
the contribution of light scattered by local material; however, the observed
polarization properties require an ad hoc geometrical dust distribution.Comment: 10 pages, 6 figures, accepted for publication in Astronomy and
Astrophysic
A deeper search for the progenitor of the Type Ic Supernova 2002ap
(Abridged) We present a search for the progenitor star of the Type Ic
Supernova 2002ap in deep, high quality pre-explosion observations taken with
the Canada-France-Hawaii Telescope (CFHT). Aligning high-resolution Hubble
Space Telescope (HST) observations of the supernova itself with the archival
CFHT images allowed us to pinpoint the location of the progenitor site on the
ground based observations. We find that a source visible in the B and R band
pre-explosion images close to the position of the SN is (1) not coincident with
the SN position within the uncertainties of our relative astrometry, and (2) is
still visible ~ 4.7 yrs post-explosion in late-time observations taken with the
William Herschel Telescope. We therefore conclude that it is not the progenitor
of SN 2002ap. Comparing our luminosity limits with stellar models of single
stars at appropriate metallicity (Z=0.008) we conclude that any single star
progenitor must have experienced at least twice the standard mass loss rates
during pre-Wolf-Rayet evolution, been initially > 30-40M(Sun) and exploded as a
Wolf-Rayet star of final mass 10-12M(Sun). Alternatively an initially less
massive progenitor may have evolved in an interacting binary system. We
constrain any possible binary companion to a main sequence star of < 20M(Sun),
a neutron star or a black hole. By combining the pre-explosion limits with the
ejecta mass estimates and constraints from X-ray and radio observations we
conclude that any binary interaction most likely occurred as Case B mass
transfer, either with or without a subsequent common envelope evolution phase.Comment: 20 pages, 11 figures (resolution of images reduced), 6 tables.
Accepted for publication in MNRAS 2007 July 27 (received 2007 July 23; in
original form 2007 June 04
Mass limits for the progenitor star of supernova 2001du and other type II-P supernovae
The supernova SN2001du in the galaxy NGC1365 (19+/-2Mpc), is a core-collapse
event of type II-P. Images of this galaxy, have been taken with HST
approximately 6.6 years before discovery and include the supernova position on
the WFPC2 field of view. We have observed the supernova with the WFPC2 to allow
accurate differential astrometry of SN2001du on the pre-explosion frames. There
is a marginal detection (3-sigma) of a source close to the supernova position
on the prediscovery V-band frame, however it is not precisely coincident and we
do not believe it to be a robust detection of a point source. We conclude that
there is no stellar progenitor at the supernova position and derive sensitivity
limits of the prediscovery images which provide an upper mass limit for the
progenitor star. We estimate that the progenitor had a mass of less than
15M_sol. We revisit two other nearby SNe II-P which have high quality
pre-explosion images, and refine the upper mass limits for the progenitor
stars. Finally we compile all the direct information available for the
progenitors of eight nearby core-collapse supernovae and compare their mass
estimates. These are compared with the latest stellar evolutionary models of
pre-supernova evolution which have attempted to relate metallicity and mass to
the supernovae type. Reasonable agreement is found for the lower mass events
(generally the II-P), but some discrepancies appear at higher masses.
(abridged).Comment: Minor changes, accepted for publication in MNRAS, full resolution
version on http://www.ast.cam.ac.uk/~sjs/papers/sn2001du_smartt.p
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