Cassiopeia A Supernova Was of Type IIb Krause, Oliver; Birkmann, Stephan M; Usuda, Tomonori ...
Science (American Association for the Advancement of Science),
05/2008, Letnik:
320, Številka:
5880
Journal Article
Recenzirano
Odprti dostop
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
We present 1–5
μ
m spectroscopy of the young planetary mass companion TWA 27B (2M1207B) performed with NIRSpec on board the James Webb Space Telescope. In these data, the fundamental band of ...CH
4
is absent, and the fundamental band of CO is weak. The nondetection of CH
4
reinforces a previously observed trend of weaker CH
4
with younger ages among L dwarfs, which has been attributed to enhanced nonequilibrium chemistry among young objects. The weakness of CO may reflect an additional atmospheric property that varies with age, such as the temperature gradient or cloud thickness. We are able to reproduce the broad shape of the spectrum with an
ATMO
cloudless model that has
T
eff
= 1300 K, nonequilibrium chemistry, and a temperature gradient reduction caused by fingering convection. However, the fundamental bands of CH
4
and CO are somewhat stronger in the model. In addition, the model temperature of 1300 K is higher than expected from evolutionary models given the luminosity and age of TWA 27B (
T
eff
= 1200 K). Previous models of young L-type objects suggest that the inclusion of clouds could potentially resolve these issues; it remains to be seen whether cloudy models can provide a good fit to the 1–5
μ
m data from NIRSpec. TWA 27B exhibits emission in Paschen transitions and the He I triplet at 1.083
μ
m, which are signatures of accretion that provide the first evidence of a circumstellar disk. We have used the NIRSpec data to estimate the bolometric luminosity of TWA 27B (log
L
/
L
⊙
= −4.466 ± 0.014), which implies a mass of 5–6
M
Jup
according to evolutionary models.
Infrared Echoes near the Supernova Remnant Cassiopeia A Krause, Oliver; Rieke, George H; Birkmann, Stephan M ...
Science (American Association for the Advancement of Science),
06/2005, Letnik:
308, Številka:
5728
Journal Article
Recenzirano
Odprti dostop
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.
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.
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.
The James Webb Space Telescope (JWST) will likely revolutionize transiting exoplanet atmospheric science, due to a combination of its capability for continuous, long duration observations and its ...larger collecting area, spectral coverage, and spectral resolution compared to existing space-based facilities. However, it is unclear precisely how well JWST will perform and which of its myriad instruments and observing modes will be best suited for transiting exoplanet studies. In this article, we describe a prefatory JWST Early Release Science (ERS) Cycle 1 program that focuses on testing specific observing modes to quickly give the community the data and experience it needs to plan more efficient and successful transiting exoplanet characterization programs in later cycles. We propose a multi-pronged approach wherein one aspect of the program focuses on observing transits of a single target with all of the recommended observing modes to identify and understand potential systematics, compare transmission spectra at overlapping and neighboring wavelength regions, confirm throughputs, and determine overall performances. In our search for transiting exoplanets that are well suited to achieving these goals, we identify 12 objects (dubbed "community targets") that meet our defined criteria. Currently, the most favorable target is WASP-62b because of its large predicted signal size, relatively bright host star, and location in JWST's continuous viewing zone. Since most of the community targets do not have well-characterized atmospheres, we recommend initiating preparatory observing programs to determine the presence of obscuring clouds/hazes within their atmospheres. Measurable spectroscopic features are needed to establish the optimal resolution and wavelength regions for exoplanet characterization. Other initiatives from our proposed ERS program include testing the instrument brightness limits and performing phase-curve observations. The latter are a unique challenge compared to transit observations because of their significantly longer durations. Using only a single mode, we propose to observe a full-orbit phase curve of one of the previously characterized, short-orbital-period planets to evaluate the facility-level aspects of long, uninterrupted time-series observations.
PDF
