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Register a new userVLT detection of a red supergiant progenitor of the type IIP supernova 2008bk
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We report the identification of a source coincident with the position of the nearby type II-P supernova (SN) 2008bk in high quality optical and near-infrared pre-explosion images from the ESO Very Large Telescope (VLT). The SN position in the optical and near-infrared pre-explosion images is identified to within about +-70 and +-40 mas, respectively, using post-explosion Ks-band images obtained with the NAOS CONICA adaptive optics system on the VLT. The pre-explosion source detected in four different bands is precisely coincident with SN 2008bk and is consistent with being dominated by a single point source. We determine the nature of the point source using the STARS stellar evolutionary models and find that its colours and luminosity are consistent with the source being a red supergiant progenitor of SN 2008bk with an initial mass of 8.5 +- 1.0 Msun.
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The explosion energy and the ejecta mass of a type IIP supernova make up the basis for the theory of explosion mechanism. So far, these parameters have only been determined for seven events. Type IIP supernova 2008in is another well-observed event for which a detailed hydrodynamic modeling can be used to derive the supernova parameters. Hydrodynamic modeling was employed to describe the bolometric light curve and the expansion velocities at the photosphere level. A time-dependent model for hydrogen ionization and excitation was applied to model the Halpha and Hbeta line profiles. We found an ejecta mass of 13.6 Msun, an explosion energy of 5.05x10^50 erg, a presupernova radius of 570 Rsun, and a radioactive Ni-56 mass of 0.015 Msun. The estimated progenitor mass is 15.5 Msun. We uncovered a problem of the Halpha and Hbeta description at the early phase, which cannot be resolved within a spherically symmetric model. The presupernova of SN 2008in was a normal red supergiant with the minimum mass of the progenitor among eight type IIP supernovae explored by means of the hydrodynamic modeling. The problem of the absence of type IIP supernovae with the progenitor masses <15 Msun in this sample remains open.
We present the discovery of a red supergiant star that exploded as supernova 2003gd in the nearby spiral galaxy M74. The Hubble Space Telescope (HST) and the Gemini Telescope imaged this galaxy 6 to 9 months before the supernova explosion and subsequent HST images confirm the positional coincidence of the supernova with a single,resolved star which is an 8 +4/-2 solar mass red supergiant. This confirms both stellar evolution models and supernova theories which predict that type II-Plateau supernovae have cool red supergiants as their immediate progenitor stars.
The progenitor of the Type IIP SN 2008bk was discovered in pre-explosion griIYJHKs images, acquired with European Southern Observatory Very Large Telescope FORS, HAWK-I and ISAAC instruments and the Gemini GMOS-S 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 SN1987A. 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 SN2008bk acquired with identical instrument and filter configurations as the pre-explosion observations, and confirm that the previously identified red supergiant 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 HST WFC3 UVIS/IR observations. In comparison with MARCS synthetic spectra, we find the progenitor was a highly reddened RSG with luminosity log (L/Lsun)=4.84+/-0.11, corresponding to an initial mass of Minit=12.9+/-1.7Msun. The temperature of the progenitor was hotter than previously expected for RSGs (T ~ 4330K), but consistent with new temperatures derived for RSGs using SED fitting techniques. We show that there is evidence for significant extinction of the progenitor, possibly arising in the CSM; but that this dust yields a similar reddening law to dust found in the ISM (E(B-V)=0.77 with Rv=3.1). [Abridged]
We present a monitoring study of SN 2004A and probable discovery of a progenitor star in pre-explosion HST images. The photometric and spectroscopic monitoring of SN 2004A show that it was a normal Type II-P which was discovered in NGC 6207 about two weeks after explosion. We compare SN 2004A to the similar Type II-P SN 1999em and estimate an explosion epoch of 2004 January 6. We also calculate three new distances to NGC 6207 of 21.0 +/-4.3, 21.4 +/-3.5 and 25.1 +/-1.7Mpc. The former was calculated using the Standard Candle Method (SCM) for SNe II-P, and the latter two from the Brightest Supergiants Method (BSM). We combine these three distances with existing kinematic distances, to derive a mean value of 20.3 +/-3.4Mpc. Using this distance we estimate that the ejected nickel mass in the explosion is 0.046(+0.031,-0.017) Msolar. The progenitor of SN 2004A is identified in pre-explosion WFPC2 F814W images with a magnitude of mF814W = 24.3 +/-0.3, but is below the detection limit of the F606W images. We show that this was likely a red supergiant (RSG) with a mass of 9(+3,-2) Msolar. The object is detected at 4.7 sigma above the background noise. Even if this detection is spurious, the 5 sigma upper limit would give a robust upper mass limit of 12 Msolar for a RSG progenitor. These initial masses are very similar to those of two previously identified RSG progenitors of the Type II-P SNe 2004gd 8(+4,-2) Msolar and 2005cs 9(+3,-2) Msolar).
Cassiopeia A (Cas A) is one of the best studied young Galactic supernova remnants. While providing a rare opportunity to study in detail the remnant of a Type IIb supernova, questions remain regarding the nature of its progenitor, its mass-loss history, and its pre-SN evolution. Here we present an optical investigation of the circumstellar environment around Cas A and find clumpy and filamentary Halpha emission nebulosities concentrated 10-15 pc (10-15 arcminutes) to the north and east. First reported by Minkowski as a faint H II region, these nebulosities exhibit distinct morphological and spectroscopic properties relative to the surrounding diffuse emissions. Compared to neighboring H II regions, these nebulae show stronger [N II] 6548, 6583 A and [S II] 6716, 6731 A emissions relative to Halpha. We show that Cas As highest-velocity ejecta knots are interacting with some of the closest projected emission nebulae, thus providing strong evidence that these nebulae lie at the same distance as the remnant. We interpret these surrounding nebulosities to be the remains of the progenitors red supergiant wind which accumulated against the southern edge of a large extended H II region located north of Cas A. Our findings are consistent with the view that Cas As progenitor underwent considerable mass-loss, first from a fast main-sequence wind, then from a slower, clumpy red supergiant wind, and finally from a brief high-velocity wind, like that from a yellow supergiant.
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