Neb Duric

Two views of the Andromeda Galaxy H-alpha and far infrared

A complete H-alpha image of the Andromeda Galaxy (M31) is presented allowing the first direct measurement of the total H-alpha luminosity which is (7.3 +/- 2.4) x 10(exp 6) solar luminosity. The H-alpha emission is associated with three morphologically distinct components; a large scale star-forming ring, approximately 1.65 deg in diameter, contributing 66% of the total H-alpha emission, a bright nucleus contributing 6% of the total H-alpha emission with the remaining 28% contributed by a previously unidentified component of extended and filamentary H-alpha emission interior to the star forming ring. The correspondence between the H-alpha image and the Infrared Astronomy Satellite (IRAS) far-infrared high resolution image is striking when both are convolved to a common resolution of 105 arcsec. The close correspondence between the far-infrared and H-alpha images suggests a common origin for the two emissions. The star-forming ring contributes 70% of the far-infrared luminosity of M31. Evidence that the ring emission is energized by high mass stars includes the fact that peaks in the far-infrared emission coincide identically with H II regions in the H-alpha image. In addition, the far-infrared to H-alpha luminosity ratio within the star-forming ring is similar to what one would expect for H II regions powered by stars of spectral types ranging between O9 and B0. The origin of the filamentary H-alpha and far-infrared luminosity interior to the star-forming ring is less clear, but it is almost certainly not produced by high mass stars.

New 325 MHz observations of H II galaxies - The mechanisms that shape the unusual radio spectra

Original article can be found at: http://adsabs.harvard.edu/abs/ Copyright American Astronomical Society. DOI: 10.1086/172780 [Full text of this article is not available in the UHRA]

X-RAY EMISSION FROM AN EXPANDING SUPERGIANT SHELL IN IC 2574

We present a multiwavelength study of a supergiant shell within the violent interstellar medium of the nearby dwarf galaxy IC 2574, which is a member of the M81 group of galaxies. Neutral hydrogen (H i) observations obtained with the Very Large Array (VLA) reveal a prominent expanding supergiant H i shell in the northeast quadrant of IC 2574 which is thought to be produced by the combined effects of stellar winds and supernova explosions. It measures roughly pc in size and is expanding at »25 km s 21 . The H i data suggest 1000 # 500 an age of » yr; the energy input must have been of order ergs. Massive star-forming 6 53 1.4 # 10 (2.6 5 1) # 10 regions, as traced by Ha emission, are situated predominantly on the rim of this H i shell. This supports the view that the accumulated H i on the rim has reached densities that are high enough for secondary star formation to commence. VLA radio continuum observations at cm show that these star-forming regions are the main l 5 6 sources of radio continuum emission in this galaxy. This emission is mainly thermal in origin. Soft X-ray emission from within the H i hole is detected by a pointed ROSAT PSPC observation. The emission is resolved, coinciding in size and orientation with the H i shell. These spatial properties suggest that the emission is generated by an X-ray‐emitting plasma located within the H i shell, although a contribution from X-ray binaries cannot be completely ruled out. The X-ray luminosity within the 0.11‐2.4 keV energy range is 38

Reconstruction and visualization of planetary nebulae

From our terrestrially confined viewpoint, the actual three-dimensional shape of distant astronomical objects is, in general, very challenging to determine. For one class of astronomical objects, however, spatial structure can be recovered from conventional 2D images alone. So-called planetary nebulae (PNe) exhibit pronounced symmetry characteristics that come about due to fundamental physical processes. Making use of this symmetry constraint, we present a technique to automatically recover the axisymmetric structure of many planetary nebulae from photographs. With GPU-based volume rendering driving a nonlinear optimization, we estimate the nebulas local emission density as a function of its radial and axial coordinates and we recover the orientation of the nebula relative to Earth. The optimization refines the nebula model and its orientation by minimizing the differences between the rendered image and the original astronomical image. The resulting model allows creating realistic 3D visualizations of these nebulae, for example, for planetarium shows and other educational purposes. In addition, the recovered spatial distribution of the emissive gas can help astrophysicists gain deeper insight into the formation processes of planetary nebulae.

Hα, far infrared & thermal radio continuum emission within the late-type spiral galaxy M33

New Hα imaging observations have revealed the morphology of the emission line gas and permitted the first measurement of the total Hα luminosity for the late-type spiral galaxy M33. The total Hα luminosity of M33 is (7.06±1.40)×106 L⊙ and is dominated by emission from HII regions. The Hα image is compared with 6 and 20 cm thermal radio continuum images in order to quantify the extinction to HII regions in M33. The extinction is found to be high locally, but low globally. The extinction to the high surface brightness cores of HII regions corresponds to Av∼1 magnitude on average with no systematic dependence on radius. However, the extinction correction to the global Hα flux is much lower with Av∼0.00 to 0.4 magnitudes. The difference suggests that the extinction is virtually negligible to the low surface brightness Hα emission outside the high surface brightness cores of HII regions. The Hα image is compared with a high resolution far infrared image, obtained with the Infrared Astronomical Satellite (IRAS)...