Browsing by Subject "circumstellar"

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Analytical Light Curve Models Of Superluminous Supernovae: Chi(2)-Minimization Of Parameter Fits
(2013-08) Chatzopoulos, Emmanouil; Wheeler, J. Craig; Vinko, Jozsef; Horvath, Z. L.; Nagy, A.; Chatzopoulos, Emmanouil; Wheeler, J. Craig; Vinko, Jozsef
We present fits of generalized semi-analytic supernova (SN) light curve (LC) models for a variety of power inputs including Ni-56 and Co-56 radioactive decay, magnetar spin-down, and forward and reverse shock heating due to supernova ejecta-circumstellar matter (CSM) interaction. We apply our models to the observed LCs of the H-rich superluminous supernovae (SLSN-II) SN 2006gy, SN 2006tf, SN 2008am, SN 2008es, CSS100217, the H-poor SLSN-I SN 2005ap, SCP06F6, SN 2007bi, SN 2010gx, and SN 2010kd, as well as to the interacting SN 2008iy and PTF 09uj. Our goal is to determine the dominant mechanism that powers the LCs of these extraordinary events and the physical conditions involved in each case. We also present a comparison of our semi-analytical results with recent results from numerical radiation hydrodynamics calculations in the particular case of SN 2006gy in order to explore the strengths and weaknesses of our models. We find that CS shock heating produced by ejecta-CSM interaction provides a better fit to the LCs of most of the events we examine. We discuss the possibility that collision of supernova ejecta with hydrogen-deficient CSM accounts for some of the hydrogen-deficient SLSNe (SLSN-I) and may be a plausible explanation for the explosion mechanism of SN 2007bi, the pair-instability supernova candidate. We characterize and discuss issues of parameter degeneracy.
Dust And The Type II-Plateau Supernova 2004dj
(2011-05) Meikle, W. P. S.; Kotak, R.; Farrah, D.; Mattila, S.; Van Dyk, S. D.; Andersen, A. C.; Fesen, R.; Filippenko, Alexei V.; Foley, Ryan J.; Fransson, C.; Gerardy, C. L.; Hoflich, Peter A.; Lundqvist, P.; Pozzo, M.; Sollerman, Jesper; Wheeler, J. Craig; heeler, J. Craig
We present mid-infrared (MIR) spectroscopy of a Type II-plateau supernova, SN 2004dj, obtained with the Spitzer Space Telescope, spanning 106-1393 days after explosion. MIR photometry plus optical/near-IR observations are also reported. An early-time MIR excess is attributed to emission from non-silicate dust formed within a cool dense shell (CDS). Most of the CDS dust condensed between 50 days and 165 days, reaching a mass of 0.3 x 10(-5) M-circle dot. Throughout the observations, much of the longer wavelength (> 10 mu m) part of the continuum is explained as an IR echo from interstellar dust. The MIR excess strengthened at later times. We show that this was due to thermal emission from warm, non-silicate dust formed in the ejecta. Using optical/near-IR line profiles and the MIR continua, we show that the dust was distributed as a disk whose radius appeared to be shrinking slowly. The disk radius may correspond to a grain destruction zone caused by a reverse shock which also heated the dust. The dust-disk lay nearly face-on, had high opacities in the optical/near-IR regions, but remained optically thin in the MIR over much of the period studied. Assuming a uniform dust density, the ejecta dust mass by 996 days was (0.5 +/- 0.1) x 10(-4) M-circle dot and exceeded 10(-4) M-circle dot by 1393 days. For a dust density rising toward the center the limit is higher. Nevertheless, this study suggests that the amount of freshly synthesized dust in the SN 2004dj ejecta is consistent with that found from previous studies and adds further weight to the claim that such events could not have been major contributors to the cosmic dust budget.
Late-Time Spectral Observations Of The Strongly Interacting Type Ia Supernova PTF11Kx
(2013-08) Silverman, Jeffrey M.; Nugent, Peter E.; Gal-Yam, Avishay; Sullivan, Mark; Howell, D. Andrew; Filippenko, Alexei V.; Pan, Yen-Chen; Cenko, S. Bradley; Hook, Isobel M.; Silverman, Jeffrey M.
PTF11kx was a Type Ia supernova (SN Ia) that showed time-variable absorption features, including saturated Ca II H and K lines that weakened and eventually went into emission. The strength of the emission component of H alpha gradually increased, implying that the SN was undergoing significant interaction with its circumstellar medium (CSM). These features, and many others, were blueshifted slightly and showed a P-Cygni profile, likely indicating that the CSM was directly related to, and probably previously ejected by, the progenitor system itself. These and other observations led Dilday et al. to conclude that PTF11kx came from a symbiotic nova progenitor like RS Oph. In this work we extend the spectral coverage of PTF11kx to 124-680 rest-frame days past maximum brightness. The late-time spectra of PTF11kx are dominated by Ha emission (with widths of full width at half-maximum intensity approximate to 2000 km s(-1)), strong Ca II emission features (similar to 10,000 km s(-1) wide), and a blue "quasi-continuum" due to many overlapping narrow lines of Fe II. Emission from oxygen, He I, and Balmer lines higher than Ha is weak or completely absent at all epochs, leading to large observed H alpha/H beta intensity ratios. The H alpha emission appears to increase in strength with time for similar to 1 yr, but it subsequently decreases significantly along with the Ca II emission. Our latest spectrum also indicates the possibility of newly formed dust in the system as evidenced by a slight decrease in the red wing of H alpha. During the same epochs, multiple narrow emission features from the CSM temporally vary in strength. The weakening of the H alpha and Ca II emission at late times is possible evidence that the SN ejecta have overtaken the majority of the CSM and agrees with models of other strongly interacting SNe Ia. The varying narrow emission features, on the other hand, may indicate that the CSM is clumpy or consists of multiple thin shells.
Planet Formation in Circumbinary Configurations: Turbulence Inhibits Planetesimal Accretion
(2012-12) Meschiari, Stefano; Meschiari, Stefano
The existence of planets born in environments highly perturbed by a stellar companion represents a major challenge to the paradigm of planet Formation. In numerical simulations, the presence of a close binary companion stirs up the relative velocity between planetesimals, which is fundamental in determining the balance between accretion and erosion. However, the recent discovery of circumbinary planets by Kepler establishes that planet Formation in binary systems is clearly viable. We perform N-body simulations of planetesimals embedded in a protoplanetary disk, where planetesimal phasing is frustrated by the presence of stochastic torques, modeling the expected perturbations of turbulence driven by the magnetorotational instability. We examine perturbation amplitudes relevant to dead zones in the midplane (conducive to planet Formation in single stars), and find that planetesimal accretion can be inhibited even in the outer disk (4-10 AU) far from the central binary, a location previously thought to be a plausible starting point for the Formation of circumbinary planets.
Transitional Disks As Signposts Of Young, Multiplanet Systems
(2011-09) Dodson-Robinson, Sarah E.; Salyk, Colette; Dodson-Robinson, Sarah E.; Salyk, Colette
Although there has yet been no undisputed discovery of a still-forming planet embedded in a gaseous protoplanetary disk, the cleared inner holes of transitional disks may be signposts of young planets. Here, we show that the subset of accreting transitional disks with wide, optically thin inner holes of 15 AU or more can only be sculpted by multiple planets orbiting inside each hole. Multiplanet systems provide two key ingredients for explaining the origins of transitional disks. First, multiple planets can clear wide inner holes where single planets open only narrow gaps. Second, the confined, non-axisymmetric accretion flows produced by multiple planets provide a way for an arbitrary amount of mass transfer to occur through an apparently optically thin hole without overproducing infrared excess flux. Rather than assuming that the gas and dust in the hole are evenly and axisymmetrically distributed, one can construct an inner hole with apparently optically thin infrared fluxes by covering a macroscopic fraction of the hole's surface area with locally optically thick tidal tails. We also establish that other clearing mechanisms, such as photoevaporation, cannot explain our subset of accreting transitional disks with wide holes. Transitional disks are therefore high-value targets for observational searches for young planetary systems.
VLT Spectropolarimetry Of The Fast Expanding Type Ia SN 2006X
(2009-12) Patat, F.; Baade, D.; Hoflich, P.; Maund, J. R.; Wang, L.; Wheeler, J. C.; Maund, J. R.; Wheeler, J. C.
Aims. The main goal of this study is to probe the ejecta geometry and to get otherwise unobtainable information about the explosion mechanism of type Ia Supernovae (SNe). Methods. Using VLT-FORS1 we performed optical spectropolarimetric observations of the type Ia SN 2006X on 7 pre-maximum epochs (day -10 to day -1) and one post-maximum epoch (+39 days). Results. The SN shows strong continuum interstellar polarization reaching about 8% at 4000 angstrom, characterized by a wavelength dependency that is substantially different from that of the Milky-Way dust mixture. Several SN features, like Si II 6355 angstrom and the Ca II IR triplet, present a marked evolution. The Ca II near-IR triplet shows a pronounced polarization (similar to 1.4%) already on day -10 in correspondence with a strong high-velocity feature (HVF). The Si II polarization peaks on day -6 at about 1.1% and decreases to 0.8% on day -1. By day +39 no polarization signal is detected for the Si II line, while the Ca II IR triplet shows a marked re-polarization at the level of 1.2%. As in the case of another strongly polarized SN (2004dt), no polarization was detected across the O I 7774 angstrom absorption. Conclusions. The fast-expanding SN 2006X lies on the upper edge of the relation between peak polarization and decline rate, and it confirms previous speculations about a correlation between degree of polarization, expansion velocity, and HVF strength. The polarization of Ca II detected in our last epoch, the most advanced ever obtained for a type Ia SN, coincides in velocity with the outer boundary of the Ca synthesized during the explosion (15 000-17 000 km s(-1)) in delayed-detonation models. This suggests a large scale chemical inhomogeneity as produced by off-center detonations, a rather small amount of mixing, or a combination of both effects. In contrast, the absence of polarization at the inner edge of the Ca-rich layer (8000-10 000 km s(-1)) implies a substantial amount of mixing in these deeper regions.
VLT Spectropolarimetry Of The Type Ia SN 2005ke A Step Towards Understanding Subluminous Events
(2012-09) Patat, F.; Hoflich, P.; Baade, D.; Maund, J. R.; Wang, L.; Wheeler, J. C.; Wheeler, J. C.
Aims. In this study we try to answer the question whether or not subluminous Type Ia supernovae have additional distinctive properties when examined from the point of view of the explosion geometry. Methods. We have performed optical spectropolarimetric observations of the Type Ia SN 2005ke at 3 epochs (days -8, -7, and +76). The explosion properties are derived by comparing the data to explosion and radiation transfer models. Results. The supernova shows polarimetric properties that are very similar to the only other subluminous event for which spectropolarimetry is available, i.e. SN 1999by. The data present a very marked dominant axis, which is shared by both the continuum and lines such as Si II lambda 6355, suggesting that the relatively large, global asymmetry is common to the photosphere and the line-forming region. The maximum polarization degree observed in the Si II lambda 6355 absorption reaches 0.39 +/- 0.08%. At variance with what is seen in core-normal Type Ia, SN 2005ke displays significant continuum polarization, which grows from the blue to the red and peaks at about 7000 angstrom, reaching similar to 0.7%. The properties of the polarization and flux spectra can be understood within the framework of a subluminous delayed-detonation (DD), or pulsating DD scenario, or white dwarf (WD) mergers. The difference in appearance with respect to core-normal SNe Ia is caused by low photospheric temperatures in combination with layers of unburned C, and more massive layers of the products of explosive C and O burning. The comparatively high level of continuum polarization is explained in terms of a significant global asymmetry (similar to 15%), which is well reproduced by an oblate ellipsoidal geometry within the general context of a DD explosion. Conclusions. Our results suggest that SN 2005ke arose either from a single-degenerate system in which the WD is especially rapidly rotating, close to the break-up velocity, or from a double-degenerate merger. Based on the current polarization data, we cannot distinguish between these two possibilities. Possible tests are discussed.