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NASA NTRS1995

HST observations of the ring around SN 1987A

Hubble Space Telescope observations of SN 1987A show that the circumstellar material near the supernova forms a clumpy elliptical ring. We analyze six epochs of images made with the Faint Object Camera (FOC) imaging the lines of (O III) and H beta over the interval 1990 August-1993 October, and three epochs of observations with the Planetary Camera in the continuum and (N II) line over the interval 1992 April-1993 May. The elliptical ring in the (O III) images has a semimajor axis of 858 +/- 11 milliarcsec and a semiminor axis of 621 +/- 11 milliarsce (6.4 x 10(exp 17) and 4.6 x 10(exp 17) +/- 8.1 x 10(exp 15) cm, respectively, for a distance of 50 kpc), which implies an inclination angle of 44 +/- 1, if the ring is a circle inclined to our line of sight. The apparent width of the ring in (O III) is 121 +/- 22 milliarcsec (9.0 x 10(exp 16) +/- 1.6 x 10(exp 16) cm) based on our deconvolved image, which represents an upper limit to the width of the of the ring. The position angle of the major axis on the sky is 89 deg +/- 3 deg. One of the 'clumps' on the ring is a superposed star, whose energy distribution is consistent with an A-type dwarf (V = 20.2 mag) in the Large Magellanic Cloud (LMC) The radial profile of the ring is not symmetric, with the inner boundary sharper than the outer. Based on the radial profiles and the flux interior to the ring, we conclude that the ring is indeed a tilted ring, and not a spheroidal shell. While the observed width of the ring is approximately 10(exp 17) cm, we find that the average path length through the emitting gas is approximately 4 x 10(exp 15) cm, so the filling factor is small. The ring has faded by a factor of approximately equals 3.7 in (O III) from 1990 August to 1993 October. The characteristic electron density from the (O III) lambda 5007 emission line averages 1.2 x 10exp 4)/cu cm, based on recombination models of the emission. Because the fading rate is uncorrelated with the surface brightness, the density appears to be independent of the brightness, which implies significant path length differences through the ring. By assuming the current structure observed in optical lines applies to the early structure in ultraviolet lines, we construct light curve models to compare with early IUE observations. The clumpy structure of the ring has relatively little effect on the light curves. The (O III) images show faint arclike nebulosity probably associated with the bipolar nebula around SN 1987A and projected inside the ring, which may have affected previous observations of the ring. Finally, we find that the fading rate provides evidence, though weak, favoring an expanding ring over a contracting one.

Plait, Philip C.↗

NASA NTRS1996

Convection during Thermally Unstable Solidification of Pb-Sn in a Magnetic Field

Convection and macrosegregation in directionally solidified hypoeutectic Pb-38 wt pct Sn and hypereutectic Pb-64.5 wt pct Sn have been examined during upward and downward growth. Temperature fluctuations are observed along the length of the melt column during downward growth. With increasing Rayleigh number, these fluctuations change from none, to cyclic, to time periodic having multiple harmonics, and finally to random. At the higher convective driving force of 350 K temperature inversion, the transverse magnetic field decreased convective levels, strong random temperature fluctuations (flows) becoming smaller and periodic. The maximum field of 0.45 T was unable to completely eliminate convection. For the lower convective driving force of 150 K temperature inversion, the 0.05 T magnetic field decreased flows, and at 0.15 T, the field caused a dramatic decrease in the characteristic frequency of the temperature fluctuations, indicating a change in the nature of the flow, the waveform of the temperature fluctuations changing from sinusoidal to a pulsed wave. Temperature fluctuations and time delays between thermocouples were used to estimate flow velocities. Irrespective of the convection in the bulk melt (ahead of the mushy zone), longitudinal macrosegregation occurs only if the interdendritic melt mixes with the bulk melt.

Song, H.↗

NASA NTRS1995

Hydrogen Molecules in SN 1987A

The observations of CO and SiO in the infrared spectrum of SN 1987A clearly indicate that molecules can form in the debris of a supernova explosion. Since H2 is not easily observable we compute its abundance theoretically. For conditions typical of the inner (v less than 2500 km/s) envelope of SN 1987A, the fraction of H that is in molecular form rises to approx. 1% by t approx. 800 days. For t less than 500 days the formation is dominated by the gas-phase reactions H + H(+) yields H2(+) + hv; H2(+) + H yields H2 + H(+). Thereafter, the formation is dominated by the reactions H + e yields H(-) + hv; H(-) + H yields H2 + e. At early times the H(-) may absorb approx. 10%-30% of visible photons, contributing to the apparent paucity of H alpha emission. For t greater than 1000 days the abundance of H2 'freezes out' due to the slowing of all reactions. The opacity of the supernova envelope in the range 912 less than lambda less than or approx. equal to 1400 A (the upper limit depending on temperature) is dominated by resonance scattering in the Lyman and Werner bands of H2. The resulting fluorescence emission bands of H2 in the range 1150 less than lambda less than 1650 A may be observable in the UV spectra of supernovae at late times.

Culhane, Michael↗

NASA NTRS2004

Chandra Observations of the X-ray Environs of SN 1998 bw/GRB 980425

We report X-ray studies of the environs of SN 1998bw and GRB 980425 using the Chandra X-Ray Observatory 1281 days after the GRB. Eight X-ray point sources were localized, three and five each in the original error boxes--S1 and S2--assigned for variable X-ray counterparts to the GRB by BeppoSAX. The sum of the discrete X-ray sources plus continuous emission in S2 observed by CXO on day 1281 is within a factor of 1.5 of the maximum and the upper limits seen by BeppoSAX. We conclude that S2 is the sum of several variable sources that have not disappeared, and therefore is not associated with the GRB. Within S1, clear evidence is seen for a decline of approximately a factor of 12 between day 200 and day 1281. One of the sources in S1, S1a, is coincident with the well-determined radio location of SN 1998bw, and is certainly the remnant of that explosion. The nature of the other sources is also discussed. Combining our observation of the supernova with others of the GRB afterglow, a smooth X-ray light curve, spanning (approx) 1300 days, is obtained by assuming the burst and supernova were coincident at 35. 6 Mpc. When this X-ray light curve is compared with those of the X-ray 'afterglows' of ordinary GRBs, X-ray Flashes, and ordinary supernovae, evidence emerges for at least two classes of lightcurves, perhaps bounding a continuum.

X-RAY SOURCES↗

NASA NTRS2008

The Young Massive Stellar Cluster Sandage-96 after the Explosion of SN 2004DJ in NGC 2403

The bright supernova 2004dj occurred within the young massive stellar cluster Sandage-96 in a spiral arm of NGC 2403, close to other star-forming complexes. New multi-wavelength observations obtained with several ground-based- and space telescopes are combined to study the radiation from Sandage-96 after SN 2004dj faded away. The late-time light curves show that Sandage-96 started to dominate the flux in the optical bands after September, 2006 (+800 days after explosion). The optical fluxes are equal to the pre-explosion ones, suggesting that Sandage-96 has survived the explosion without significant changes in its stellar population. An optical Keck-spectrum obtained at +900 days after explosion shows the dominant blue continuum from the cluster stars shortward of 6000 A as well as strong SN nebular emission lines redward. The integrated SED of the cluster has been extended into the UV-region by archival XMM-Newton and new Swift observations, and compared with theoretical models. The outer parts of the cluster have been resolved by HST allowing the construction of a color-magnitude diagram. The fitting of the cluster SED with theoretical isochrones results in two possible solutions with ages being 9+/-1 Myr and 30+/-10 Myr, depending on the assumed metallicity and the theoretical model family. The isochrone fitting of the color-magnitude diagram indicates that the outer part of the cluster consists of stars having an age dispersion of 16 < t < 63 Myr, which is similar to that of nearby field stars. This age discrepancy may be resolved by the hypothesis that the outskirt of Sandage-96 is contaminated by stars captured from the field during cluster formation. The young age of Sandage-96 and the comparison of its pre- and post-explosion SEDs suggest a progenitor mass of 15 < or equal to M(sub prog) < 25 Stellar Mass.

Vinko, J.↗

NASA NTRS2009

The First X-Ray Proper-Motion Measurements of the Forward Shock in the Northeastern Limb of Sn 1006

We report on the first X-ray proper-motion measurements of the nonthermally-dominated forward shock in the northeastern limb of SN 1006, based on two Chandra observations taken in 2000 and 2008. We find that the proper motion of the forward shock is about 0.48"/yr and does not vary around the rim within the approx.10% measurement uncertainties. The proper motion measured is consistent with that determined by the previous radio observations. The mean expansion index of the forward shock is calculated to be approx..0.54 which matches the value expected based on an evolutionary model of a Type Ia supernova with either a power-law or an exponential ejecta density profile. Assuming pressure equilibrium around the periphery from the thermally-dominated northwestern rim to the nonthermally-dominated northeastern rim, we estimate the ambient density to the northeast of SN 1006 to be approx..0.085/cu cm.

Katsuda, Satoru↗

NASA NTRS2008

Limits on O VI Emission from the Shocked Circumstellar Gas of SN 1987A

The Far Ultraviolet Spectroscopic Explorer (FUSE) was used to search for emission from the shock interaction of the ejecta of SN 1987A with its circumstellar material. FUSE observations of SN 1987A between 2000 and 2007 did not detect broad OVI emission. However, OVI emission was detected in 2000-2001 with a narrow line width (FWHM <35 kms t ) and a heliocentric radial velocity of +280 km/s. This places the emitting gas at rest relative to the supernova and is interpreted as emission from unshocked circumstellar gas. This narrow emission had disappeared in 2007 (and possibly earlier) as a result of the advancing shock overtaking the H II region that was flash ionized by the supernova explosion in 1987.

Sonneborn, George↗

NASA NTRS2011

Dust and Other Recent Discoveries in SN 1987A

Supernova 1987 A in the Large Magellanic Cloud is one of the most intensively studied objects in the universe and a Rosetta Stone for understanding the explosions of massive stars. Now almost 25 years old, SN 1987 A is a very young supernova remnant, a phase previously unobserved in any other supernova. In this talk I will discuss recent observations from the far ultraviolet to the far-infrared with HST, the VLT, and the Herschel Space Observatory. These data reveal new insights into the composition, geometry, and heating of the explosion debris, the shock interaction with circumstellar material, and dust in the SN 1987 A system.

Sonneborn, George↗

NASA NTRS2011

SN 2010ay is a Luminous and Broad-lined Type Ic Supernova within a Low-metallicity Host Galaxy

We report on our serendipitous pre-discovery detection and detailed follow-up of the broad-lined Type Ic supernova SN2010ay at z approx 0.067 imaged by the Pan-STARRS1 3pi survey just approx 4 days after explosion. Combining our photometric observations with those available in the literature, we estimate the explosion date and the peak luminosity of the SN, M(sub R) approximately equals 20.2 mag, significantly brighter than known GRB-SNe and one of the most luminous SNe Ibc ever discovered. We measure the photospheric expansion velocity of the explosion from our spectroscopic follow-up observations, v(sub ph) approximately equals 19.2 X 10 (exp 3) km/s at approx 40 days after explosion. In comparison with other broad-lined SNe, the characteristic velocity of SN2010ay is 2 - 5 X higher and similar to the measurements for GRB-SNe at comparable epochs. Moreover the velocity declines two times slower than other SNe Ic-BL and GRB-SNe. Assuming that the optical emission is powered by radioactive decay, the peak magnitude implies the synthesis of an unusually large mass of Ni-56, M(sub Ni) = 0.9(+0.1/-0.1) solar mass. Our modeling of the light-curve points to a total ejecta mass, M(sub ej) approx 4.7 Solar Mass, and total kinetic energy, E(sub K,51) approximately equals 11. Thus the ratio of M(sub Ni) to M(sub ej) is at least twice as large for SN2010ay than in GRB-SNe and may indicate an additional energy reservoir. We also measure the metallicity (log(O/H) + 12 = 8.19) of the explosion site within the host galaxy using a high S/N optical spectrum. Our abundance measurement places this SN in the low-metallicity regime populated by GRB-SNe, and approx 0.2(0.5) dex lower than that typically measured for the host environments of normal (broad-lined) Ic supernovae. Despite striking similarities to the recent GRB-SN100316D/2010bh, we show that gamma-ray observations rule out an associated GRB with E(sub gamma) approx < 6 X 10(exp 48) erg (25-150 keV). Similarly, our deep radio follow-up observations with the Expanded Very Large Array rule out relativistic ejecta with energy, E approx > 10(exp 48) erg. These observations challenge the importance of progenitor metallicity for the production of a GRB, and suggest that other parameters also play a key role.

Sanders, N. E.↗

NASA NTRS2012

SN 1987A: The Supernova of the Century

Supernova 1987 A in the Large Magellanic Cloud is one of the most intensively studied objects in the universe and a Rosetta Stone for understanding the explosions of massive stars. Approaching its 25th anniversary, SN 1987 A is a very young supernova remnant, a phase previously unobserved in any other supernova. The supernova of the 20th Century is now the supernova remnant of the 21st Century. In this talk I will discuss recent observations from the far-ultraviolet to the far-infrared with HST, the VLT, Spitzer, and the Herschel Space Observatory. These data reveal new insights into the composition, geometry, and heating of the explosion debris, the shock interaction with circumstellar material, and dust in the SN 1987 A system.

Sonneborne, George↗

NASA NTRS2012

Early Radio and X-Ray Observations of the Youngest Nearby Type Ia Supernova PTF 11kly (SN 2011fe)

On August 24 (UT) the Palomar Transient Factory (PTF) discovered PTF11kly (SN 2011fe), the youngest and most nearby type Ia supernova (SN Ia) in decades. We followed this event up in the radio (centimeter and millimeter bands) and X-ray bands, starting about a day after the estimated explosion time. We present our analysis of the radio and X-ray observations, yielding the tightest constraints yet placed on the pre-explosion mass-loss rate from the progenitor system of this supernova. We find a robust limit of M(raised dot) less than or equal to 10(exp -8) (w /100 kilometers per second ) solar mass yr(exp -1) from sensitive X-ray non-detections, as well as a similar limit from radio data, which depends, however, on assumptions about microphysical parameters. We discuss our results in the context of single-degenerate models for SNe Ia and find that our observations modestly disfavor symbiotic progenitor models involving a red giant donor, but cannot constrain systems accreting from main sequence or sub-giant stars, including the popular supersoft channel. In view of the proximity of PTF11kly and the sensitivity of our prompt observations we would have to wait for a long time (decade or longer) in order to more meaningfully probe the circumstellar matter of Ia supernovae.

Horesh, Assaf↗

NASA NTRS2013

Chandra Observations of SN 1987A: The Soft X-Ray Light Curve Revisited

We report on the present stage of SN 1987A as observed by the Chandra X-Ray Observatory. We reanalyze published Chandra observations and add three more epochs of Chandra data to get a consistent picture of the evolution of the X-ray fluxes in several energy bands. We discuss the implications of several calibration issues for Chandra data. Using the most recent Chandra calibration files, we find that the 0.5-2.0 keV band fluxes of SN 1987A have increased by approximately 6 x 10(exp-13) erg s(exp-1)cm(exp-2) per year since 2009. This is in contrast with our previous result that the 0.5-2.0 keV light curve showed a sudden flattening in 2009. Based on our new analysis, we conclude that the forward shock is still in full interaction with the equatorial ring.

Helder, E. A.↗

NASA NTRS2014

Co(x)Ni(4-x)Sb(12-y)Sn(y) Ternary Skutterudites: Processing and Thermoelectric Properties

Skutterudites have proven to be a useful thermoelectric system as a result of their high figure of merit, favorable mechanical properties, and good thermal stability. Binary skutterudites have received the majority of interest in recent years, as a result of successful double and triple filling schemes. Ternary skutterudites, such as Ni4Sb7Sn5, also demonstrate good thermoelectric performance, with high power factor and low thermal conductivity. Ternary skutterudites, as contrasted to binary systems, provide more possibility for tuning electronic structure as substitutions can be studied on three elements. The Co(x)Ni(4-x)Sb(12-y)Sn(y) system has been investigated as both a p- and n-type thermoelectric material, stable up to 200 C. The system is processed through a combination of solidification, mechanical alloying, and hot pressing steps. Rietveld structure refinement has revealed an interesting occupancy of Sn on both the 24g Wyckoff position with Sb as well as the 2a position as a rattler. In addition to thermoelectric properties, detailed processing routes have been investigated on the system.

Seebeck effect↗

NASA NTRS2016

NASA Near Earth Network (NEN) and Space Network (SN) CubeSat Communications

There has been a recent trend to increase capability and drive down the Size, Weight and Power (SWAP) of satellites. NASA scientists and engineers across many of NASA's Mission Directorates and Centers are developing exciting CubeSat concepts and welcome potential partnerships for CubeSat endeavors. From a "Telemetry, Tracking and Command (TT&C) Systems and Flight Operations for Small Satellites" point of view, small satellites including CubeSats are a challenge to coordinate because of existing small spacecraft constraints, such as limited SWAP and attitude control, and the potential for high numbers of operational spacecraft. The NASA Space Communications and Navigation (SCaN) Program's Near Earth Network (NEN) and Space Network (SN) are customer driven organizations that provide comprehensive communications services for space assets including data transport between a mission's orbiting satellite and its Mission Operations Center (MOC). This paper presents how well the SCaN networks, SN and NEN, are currently positioned to support the emerging small small satellite and CubeSat market as well as planned enhancements for future support.

Schaire, Scott H.↗

NASA NTRS2016

NASA Near Earth Network (NEN) and Space Network (SN) Support of CubeSat Communications

There has been a historical trend to increase capability and drive down the Size, Weight and Power (SWAP) of satellites and that trend continues today. NASA scientists and engineers across many of NASAs Mission Directorates and Centers are developing exciting CubeSat concepts and welcome potential partnerships for CubeSat endeavors. From a Telemetry, Tracking and Command (TTC) Systems and Flight Operations for Small Satellites point of view, small satellites including CubeSats are a challenge to coordinate because of existing small spacecraft constraints, such as limited SWAP and attitude control, and the potential for high numbers of operational spacecraft. The NASA Space Communications and Navigation (SCaN) Programs Near Earth Network (NEN) and Space Network (SN) are customer driven organizations that provide comprehensive communications services for space assets including data transport between a missions orbiting satellite and its Mission Operations Center (MOC). This paper presents how well the SCaN networks, SN and NEN, are currently positioned to support the emerging small small satellite and CubeSat market as well as planned enhancements for future support.

Satellite↗

NASA NTRS2017

Effect of Silicon on Activity Coefficients of P, Bl, CD, SN, and AG in Liquid Fe-Si, and Implications for Differentiation and Core Formation

Cores of differentiated bodies (Earth, Mars, Mercury, Moon, Vesta) contain light elements such as S, C, Si, and O. We have previously measured small effects of Si on metal-silicate partitioning of Ni and Co [1,2], and larger effects for Mo, Ge, Sb, As [2]. The effect of Si on many siderophile elements could be an important, and as yet unquantified, influence on the core-mantle partitioning of SE. Here we report new experiments designed to quantify the effect of Si on the partitioning of Bi, Cd, Sn, Ag, and P between metal and silicate melt. The results will be applied to Earth, Mars, Mercury, Moon, and Vesta, for which we have excellent constraints on the mantle Bi, Cd, Sn, Ag, and P concentrations from mantle and/or basalt samples.

Righter, K.↗

NASA NTRS2017

Constraints on the Progenitor of SN 2010jl and Pre-existing Hot Dust in its Surrounding Medium

A search for the progenitor of SN 2010jl, an unusually luminous core-collapse supernova of Type IIn, using pre-explosion Hubble/WFPC2 and Spitzer/IRAC images of the region, yielded upper limits on the UV and near infrared (IR) fluxes from any candidate star. These upper limits constrain the luminosity and effective temperature of the progenitor, the mass of any pre-existing dust in its surrounding circumstellar medium (CSM), and dust proximity to the star. A lower limit on the CSM dust mass is required to hide a luminous progenitor from detection by Hubble. Upper limits on the CSM dust mass and constraints on its proximity to the star are set by requiring that the absorbed and reradiated IR emission not exceed the IRAC upper limits. Using the combined extinction-IR emission constraints, we present viable M(sub d)-R(sub 1) combinations, where M(sub d) and R(sub 1) are the CSM dust mass and its inner radius. These depend on the CSM outer radius, dust composition and grain size, and the properties of the progenitor. The results constrain the pre-supernova evolution of the progenitor, and the nature and origin of the observed post-explosion IR emission from SN 2010jl. In particular, an eta Car-type progenitor will require at least 4 mag of visual extinction to avoid detection by Hubble. This can be achieved with dust masses greater than approximately equal to 10(exp -3) solar mass (less than the estimated 0.2-0.5 solar mass around eta Car), which must be located at distances of greater than approximately equal to 10(exp 16) cm from the star to avoid detection by Spitzer.

Dwek, Eli↗

NASA NTRS2018

Effect of Silicon on Activity Coefficients of P, Bi, Cd, Sn, and Ag in Liquid Fe-Si, and Implications for Core Formation

Cores of differentiated bodies (Earth, Mars, Mercury, Moon, Vesta) contain light elements such as S, C, Si, and O. We have previously measured small effects of Si on Ni and Co, and larger effects on Mo, Ge, Sb, As metal/silicate partitioning. The effect of Si on metal-silicate partitioning has been quantified for many siderophile elements, but there are a few key elements for which the effects are not yet quantified. Here we report new experiments designed to quantify the effect of Si on the partitioning of Bi, Cd, Sn, Ag, and P between metal and silicate melt. The results will be applied to Earth, Mars, Moon, and Vesta, for which we have good constraints on the mantle Bi, Cd, Sn, Ag, and P concentrations from mantle and/or basalt samples.

Righter, K.↗