Cassiopeia A Supernova Was of Type IIb Krause, Oliver; Birkmann, Stephan M; Usuda, Tomonori ...
Science,
05/2008, Letnik:
320, Številka:
5880
Journal Article
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Cassiopeia A is the youngest supernova remnant known in the Milky Way and a unique laboratory for supernova physics. We present an optical spectrum of the Cassiopeia A supernova near maximum ...brightness, obtained from observations of a scattered light echo more than three centuries after the direct light of the explosion swept past Earth. The spectrum shows that Cassiopeia A was a type IIb supernova and originated from the collapse of the helium core of a red supergiant that had lost most of its hydrogen envelope before exploding. Our finding concludes a long-standing debate on the Cassiopeia A progenitor and provides new insight into supernova physics by linking the properties of the explosion to the wealth of knowledge about its remnant.
Abstract We present two-dimensional near-infrared temperature maps of the canonical hot Jupiter WASP-43b using a phase-curve observation with JWST NIRSpec/G395H. From the white-light planetary ...transit, we improve constraints on the planet’s orbital parameters and measure a planet-to-star radius ratio of 0.15883 − 0.00053 + 0.00056 . Using the white-light phase curve, we measure a longitude of maximum brightness of 6.9 − 0 .° 5 + 0 .° 5 east of the substellar point and a phase-curve offset of 10.0 − 0 .° 8 + 0 .° 8 . We also find a ≈4 σ detection of a latitudinal hotspot offset of − 13.4 − 1 .° 7 + 3 .° 2 , the first significant detection of a nonequatorial hotspot in an exoplanet atmosphere. We show that this detection is robust to variations within planetary parameter uncertainties, but only if the transit is used to improve constraints, showing the importance of transit observations to eclipse mapping. Maps retrieved from the NRS1 and NRS2 detectors are similar, with hotspot locations consistent between the two detectors at the 1 σ level. Our JWST data show brighter (hotter) nightsides and a dimmer (colder) dayside at the shorter wavelengths relative to fits to Spitzer 3.6 and 4.5 μ m phase curves. Through comparison between our phase curves and a set of general circulation models, we find evidence for clouds on the nightside and atmospheric drag or high metallicity reducing the eastward hotspot offset.
Abstract Spectra of young benchmark brown dwarfs with well-known ages are vital to characterize other brown dwarfs, for which ages are in general not known. These spectra are also crucial to test ...atmospheric models, which have the potential to provide detailed information about the atmospheres of these objects. However, to test atmospheric models optimally, medium-resolution, long-wavelength-coverage spectra with well-understood uncertainties are ideal, such as the spectra provided by the NIRSpec instrument on board the James Webb Space Telescope. In this paper, we present medium-resolution JWST/NIRSpec spectra of two young brown dwarfs, TWA 28 (M9.0) and TWA 27A (M9.0), and one planetary-mass object, TWA 27B (L6.0), members of the TW Hydrae Association (age ∼ 10 Myr). We show the richness of the atomic lines and molecular bands present in the spectra. All objects show signs of a circumstellar disk, via a near-infrared excess and/or via emission lines. We matched a set of cloudless atmospheric spectra ( ATMO ), and cloudy atmospheric spectra ( BT-Settl ) to our NIRSpec spectra, and analyzed which wavelength ranges and spectral features both models reproduce best. Both models derive consistent parameters for the three sources, and predict the existence of CH 4 at 3.35 μ m in TWA 27B. Nonetheless, in contrast to other slightly older objects with similar spectral type, like PSO 318.5–22 and VHS 1256b, this feature is not present in the spectrum of TWA 27B. The lack of the CH 4 feature might suggest that the L–T transition of very young dwarfs starts at later spectral types than for older brown dwarfs.
Two images of Cassiopeia A obtained at 24 micrometers with the Spitzer Space Telescope over a 1-year time interval show moving structures outside the shell of the supernova remnant to a distance of ...more than 20 arc minutes. Individual features exhibit apparent motions of 10 to 20 arc seconds per year, independently confirmed by near-infrared observations. The observed tangential velocities are at roughly the speed of light. It is likely that the moving structures are infrared echoes, in which interstellar dust is heated by the explosion and by flares from the compact object near the center of the remnant.
The fate of massive cold clumps, their internal structure, and collapse need to be characterized to understand the initial conditions for the formation of high-mass stars, stellar systems, and the ...origin of associations and clusters. We explore the onset of star formation in the 75 M SMM1 clump in the region ISOSS J18364-0221 using infrared and (sub-)millimeter observations including interferometry. This contracting clump has fragmented into two compact cores SMM1 North and South of 0.05 pc radius, having masses of 15 and 10 M , and luminosities of 20 L and 180 L . SMM1 South harbors a source traced at 24 and 70 mm, drives an energetic molecular outflow, and appears supersonically turbulent at the core center. SMM1 North has no infrared counterparts and shows lower levels of turbulence, but also drives an outflow. Both outflows appear collimated, and parsec-scale near-infrared features probably trace the outflow-powering jets. We derived mass outflow rates of at least 4 X 10-5 M yr-1 and outflow timescales of less than 104 yr. Our HCN(1-0) modeling for SMM1 South yielded an infall velocity of 0.14 km s-1 and an estimated mass infall rate of 3 X 10-5 M yr-1. Both cores may harbor seeds of intermediate- or high-mass stars. We compare the derived core properties with recent simulations of massive core collapse. They are consistent with the very early stages dominated by accretion luminosity.
A large amount (about three solar masses) of cold (18 K) dust in the prototypical type II supernova remnant Cassiopeia A was recently reported. It was concluded that dust production in type II ...supernovae can explain how the large quantities (∼ 108 solar masses) of dust observed in the most distant quasars could have been produced within only 700 million years after the Big Bang. Foreground clouds of interstellar material, however, complicate the interpretation of the earlier submillimetre observations of Cas A. Here we report far-infrared and molecular line observations that demonstrate that most of the detected submillimetre emission originates from interstellar dust in a molecular cloud complex located in the line of sight between the Earth and Cas A, and is therefore not associated with the remnant. The argument that type II supernovae produce copious amounts of dust is not supported by the case of Cas A, which previously appeared to provide the best evidence for this possibility.
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