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

A new precise mass for the progenitor of the Type IIP SN 2008bk

The progenitor of the Type IIP supernova (SN) 2008bk was discovered in pre-explosion g&#39;r&#39;i&#39;IYJHK(s) images, acquired with European Southern Observatory Very Large Telescope FOcal Reducer and low dispersion Spectrograph, High Acuity Wide field K-band Imager and Infrared Spectrometer and Array Camera instruments and the Gemini Multi-Object Spectrograph-South instrument. The wealth of pre-explosion observations makes the progenitor of this SN one of the best studied, since the detection of the progenitor of SN 1987A. Previous analyses of the properties of the progenitor were hampered by the limited quality of the photometric calibration of the pre-explosion images and the crowded nature of the field containing the SN. We present new late-time observations of the site of SN 2008bk acquired with identical instrument and filter configurations as the pre-explosion observations, and confirm that the previously identified red supergiant (RSG) star was the progenitor of this SN and has now disappeared. Image subtraction techniques were used to conduct precise photometry of the now missing progenitor, independently of blending from any nearby stars. The nature of the surrounding stellar population and their contribution to the flux attributed to the progenitor in the pre-explosion images are probed using Hubble Space Telescope Wide Field Camera 3 Ultraviolet-Visible/Infrared observations. In comparison with MARCS synthetic spectra, we find the progenitor was a highly reddened RSG with luminosity log(L/L-circle dot) = 4.84(-0.12)(+0.10), corresponding to an initial mass of M-init = 12.9(-1.8)(+1.6)M(circle dot). The temperature of the progenitor was hotter than previously expected for RSGs (T similar to 4330 K), but consistent with new temperatures derived for RSGs using spectral energy distribution fitting techniques. We show that there is evidence for significant extinction of the progenitor, possibly arising in the circumstellar medium, but that this dust yields a similar reddening law to dust found in the interstellar medium (E(B - V) = 0.77 with R-V = 3.1). Our improved analysis, which carefully accounts for the systematics, results in a more precise and robust mass estimate, making the progenitor of SN 2008bk the most well understood progenitor of a Type IIP SN from pre-explosion observations.</p

Whatever happened to the progenitors of supernovae 2008cn, 2009kr and 2009md?

We present new late-time, high-resolution observations of the sites of supernovae (SNe) 2008cn, 2009kr and 2009md, acquired with the Hubble Space Telescope. In all instances, significant flux from the SNe is still recovered at late times. We show that the previous identification of the progenitor of SN 2008cn was actually a blend of two sources, whose locations are resolved in these new observations. We suggest that the progenitor of SN 2008cn was actually a red supergiant with Minit < 16 M⊙. In the late-time observations of SN 2009kr, we find that the pre-explosion source (previously thought to be a yellow supergiant) is most probably a small compact cluster with mass ∼6000 M⊙. In late-time F814W observations of the site of SN 2009md, we find a single point source with identical brightness to the pre-explosion source, suggesting some caution in assuming that the pre-explosion source was the progenitor

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

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