We report far-infrared and submillimeter observations of supernova 1987A, the star whose explosion was observed on 23 February 1987 in the Large Magellanic Cloud, a galaxy located 160,000 light years ...away. The observations reveal the presence of a population of cold dust grains radiating with a temperature of about 17 to 23 kelvin at a rate of about 220 times the luminosity of the Sun. The intensity and spectral energy distribution of the emission suggest a dust mass of about 0.4 to 0.7 times the mass of the Sun. The radiation must originate from the supernova ejecta and requires the efficient precipitation of all refractory material into dust. Our observations imply that supernovae can produce the large dust masses detected in young galaxies at very high redshifts.
The aromatic features in M101 were studied spectroscopically and photometrically using observations from all three instruments on the Spitzer Space Telescope. The global SED of M101 shows strong ...aromatic feature (commonly called PAH feature) emission. The spatially resolved spectral and photometric measurements of the aromatic feature emission show strong variations with significantly weaker emission at larger radii. We compare these variations with changes in the ionization index (as measured by Ne iii/Ne ii and S iv/S iii, which range from 0.03 to 20 and 0.044 to 15, respectively) and metallicity expressed as image, which ranges from 8.1 to 8.8. Over these ranges, the spectroscopic equivalent widths of the aromatic features from seven H ii regions and the nucleus were found to correlate better with ionization index than metallicity. This implies that the weakening of the aromatic emission in massive star-forming regions is due primarily to processing of the dust grains in these environments, not to differences in how they form. The behavior of the aromatic feature versus ionization index correlation can be described as a constant equivalent width until a threshold in ionization index is reached, above which the equivalent widths decrease with a power-law dependence. This behavior is also seen for the starburst galaxy sample presented in the companion study by Engelbracht and coworkers, which expands the range of Ne iii/Ne ii ratios to 0.03-25 and image values to 7.1-8.8. The form of the correlation explains seemingly contradictory results present in the literature. The behavior of the ratios of different aromatic features versus ionization index does not follow the predictions of existing PAH models of the aromatic features, implying a more complex origin of the aromatic emission in massive star-forming regions.
The Debris Disk Around HR 8799 Su, K. Y. L; Rieke, G. H; Stapelfeldt, K. R ...
Astrophysical journal/The Astrophysical journal,
11/2009, Volume:
705, Issue:
1
Journal Article
Peer reviewed
Open access
We have obtained a full suite of Spitzer observations to characterize the debris disk around HR 8799 and to explore how its properties are related to the recently discovered set of three massive ...planets orbiting the star. We distinguish three components to the debris system: (1) warm dust (T ~ 150 K) orbiting within the innermost planet; (2) a broad zone of cold dust (T ~ 45 K) with a sharp inner edge orbiting just outside the outermost planet and presumably sculpted by it; and (3) a dramatic halo of small grains originating in the cold dust component. The high level of dynamical activity implied by this halo may arise due to enhanced gravitational stirring by the massive planets. The relatively young age of HR 8799 places it in an important early stage of development and may provide some help in understanding the interaction of planets and planetary debris, an important process in the evolution of our own solar system.
We present a catalog of 5324 massive stars in the Small Magellanic Cloud (SMC), with accurate spectral types compiled from the literature, and a photometric catalog for a subset of 3654 of these ...stars, with the goal of exploring their infrared properties. The photometric catalog consists of stars with infrared counterparts in the Spitzer SAGE-SMC survey database, for which we present uniform photometry from 0.3to24 Delta *mm in the UBVIJHKs +IRAC+MIPS24 bands. We compare the color-magnitude diagrams and color-color diagrams to those of stars in the Large Magellanic Cloud (LMC), finding that the brightest infrared sources in the SMC are also the red supergiants, supergiant Be (sgBe) stars, luminous blue variables, and Wolf-Rayet stars, with the latter exhibiting less infrared excess, the red supergiants being less dusty and the sgBe stars being on average less luminous. Among the objects detected at 24 Delta *mm in the SMC are a few very luminous hypergiants, four B-type stars with peculiar, flat spectral energy distributions, and all three known luminous blue variables. We detect a distinct Be star sequence, displaced to the red, and suggest a novel method of confirming Be star candidates photometrically. We find a higher fraction of Oe and Be stars among O and early-B stars in our SMC catalog, respectively, when compared to the LMC catalog, and that the SMC Be stars occur at higher luminosities. We estimate mass-loss rates for the red supergiants, confirming the correlation with luminosity even at the metallicity of the SMC. Finally, we confirm the new class of stars displaying composite A & F type spectra, the sgBe nature of 2dFS1804 and find the F0 supergiant 2dFS3528 to be a candidate luminous blue variable with cold dust.
We present high spatial resolution mid- and far-infrared images of the Vega debris disk obtained with the Multiband Imaging Photometer for Spitzer (MIPS). The disk is well resolved, and its angular ...size is much larger than found previously. The radius of the disk is at least 43" (330 AU), 70" (543 AU), and 105" (815 AU) in extent at 24, 70, and 160 km, respectively. The disk images are circular, smooth, and without clumpiness at all three wavelengths. The radial surface brightness profiles follow radial power laws of r super(-3) or r super(-4) and imply an inner boundary at a radius of 11" c 2" (86 AU). Assuming an amalgam of amorphous silicate and carbonaceous grains, the disk can be modeled as an axially symmetric and geometrically thin disk, viewed face-on, with the surface particle number density following an inverse radial power law. The disk radiometric properties are consistent with a range of models using grains of sizes 61 to 650 km. The exact minimum and maximum grain size limits depend on the adopted grain composition. However, all of these models require an r super(-1) surface number density profile and a total mass of (3 c 1.5) x 10 super(-3) M sub( )in grains. We find that a ring, containing grains larger than 180 km and at radii of 86-200 AU from the star, can reproduce the observed 850 km flux, while its emission does not violate the observed MIPS profiles. This ring could be associated with a population of larger asteroidal bodies analogous to our own Kuiper Belt. Cascades of collisions starting with encounters among these large bodies in the ring produce the small debris that is blown outward by radiation pressure to much larger distances, where we detect its thermal emission. The relatively short lifetime (<1000 yr) of these small grains and the observed total mass, 63 x 10 super(-3) M sub( ), set a lower limit on the dust production rate, 610 super(15) g s super(-1). This rate would require a very massive asteroidal reservoir for the dust to be produced in a steady state throughout Vega's life. Instead, we suggest that the disk we imaged is ephemeral and that we are witnessing the aftermath of a large and relatively recent collisional event, and a subsequent collisional cascade.
New images of M31 at 24, 70, and 160 km taken with the Multiband Imaging Photometer for Spitzer (MIPS) reveal the morphology of the dust in this galaxy. This morphology is well represented by a ...composite of two logarithmic spiral arms and a circular ring (radius 610 kpc) of star formation offset from the nucleus. The two spiral arms appear to start at the ends of a bar in the nuclear region and extend beyond the star-forming ring. As has been found in previous work, the spiral arms are not continuous, but composed of spiral segments. The star-forming ring is very circular except for a region near M32 where it splits. The lack of well-defined spiral arms and the prominence of the nearly circular ring suggest that M31 has been distorted by interactions with its satellite galaxies. Using new dynamical simulations of M31 interacting with M32 and NGC 205, we find that, qualitatively, such interactions can produce an offset, split ring like that seen in the MIPS images.
The recent star formation (SF) in the early-type spiral galaxy M81 is characterized using imaging observations from the far-ultraviolet to the far-infrared. We compare these data with models of the ...stellar, gas, and dust emission for subgalactic regions. Our results suggest the existence of a diffuse dust emission not directly linked to the recent star formation. We find a radial decrease of the dust temperature and dust mass density, and in the attenuation of the stellar light. The IR emission in M81 can be modeled with three components: (1) cold dust with a temperature < super(T c) > = 18 c 2 K, concentrated near the H II regions but also presenting a diffuse distribution; (2) warm dust with < super(T w) > = 53 c 7K, directly linked with the H II regions; and (3) aromatic molecules, with diffuse morphology peaking around the H II regions. We derive several relationships to obtain total IR luminosities from IR monochromatic fluxes, and we compare five different star formation rate (SFR) estimators for H II regions in M81 and M51: the UV, Ha, and three estimators based on Spitzer data. We find that the Ha luminosity absorbed by dust correlates tightly with the 24 km emission. The correlation with the total IR luminosity is not as good. Important variations from galaxy to galaxy are found when estimating the total SFR with the 24 km or the total IR emission alone. The most reliable estimations of the total SFRs are obtained by combining the Ha emission (or the UV) and an IR luminosity (especially the 24 km emission), which probe the unobscured and obscured SF, respectively. For the entire M81 galaxy, about 50% of the total SF is obscured by dust. The percentage of obscured SF ranges from 60% in the inner regions of the galaxy to 30% in the outer zones.
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