A Cometary Bow Shock and Mid-Infrared Emission Variations Revealed in Spitzer Observations of HD 34078 and IC 405
We present new infrared observations of the emission/reflection nebulaIC 405 obtained with the Spitzer Space Telescope. Infrared images in thefour IRAC bands (3.6, 4.5, 5.8, and 8.0 μm) and two MIPS bands (24and 70 μm) are complemented by IRS spectroscopy (5-30 μm) of twonebular filaments. The IRAC (8.0 μm) and MIPS imaging shows evidenceof a bow shock associated with the runaway O9.5 V star, HD 34078,created by the interaction between the star and nebular material. Theratio of emission at 24 to 70 μm is higher in the immediate vicinityof HD 34078 than in the outer filaments, providing evidence for elevateddust temperatures (Td>~90 K) in the shock region. Thenebular imaging reveals that the morphology is band dependent, withvarying contributions from aromatic emission features, H2,and dust emission. Nebular spectroscopy is used to quantify thesecontributions, showing several aromatic emission bands between 6-14μm, the S(5), S(3), S(2), and S(1) pure rotational emission lines ofH2, and atomic fine-structure lines of Ne, S, and Ar. Thelow-dispersion spectra provide constraints on the ionization state ofthe large molecules responsible for the aromatic infrared features.H2 rotational temperatures of the two bright nebularfilaments are determined from the observed line strengths. An averageT(H2)~400 K is inferred, with evidence for additionalnonuniform excitation by UV photons in the intense radiation field of HD34078. The photoexcitation hypothesis is supported by direct measurementof the far-UV H2 fluorescence spectrum, obtained with FUSE.Based in part on observations made with the Spitzer Space Telescope,which is operated by the Jet Propulsion Laboratory, California Instituteof Technology, under a contract with NASA.
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Image-Processing Techniques for the Creation of Presentation-Quality Astronomical Images
The quality of modern astronomical data and the agility of currentimage-processing software enable the visualization of data in a way thatexceeds the traditional definition of an astronomical image. Twodevelopments in particular have led to a fundamental change in howastronomical images can be assembled. First, the availability ofhigh-quality multiwavelength and narrowband data allow for images thatdo not correspond to the wavelength sensitivity of the human eye,thereby introducing ambiguity in the usage and interpretation of color.Second, many image-processing software packages now use a layeringmetaphor that allows for any number of astronomical data sets to becombined into a color image. With this technique, images with as many aseight data sets have been produced. Each data set is intensity-scaledand colorized independently, creating an immense parameter space thatcan be used to assemble the image. Since such images are intended fordata visualization, scaling and color schemes must be chosen that bestillustrate the science. A practical guide is presented on how to use thelayering metaphor to generate publication-ready astronomical images fromas many data sets as desired. A methodology is also given on how to useintensity scaling, color, and composition to create contrasts in animage that highlight the scientific detail. Examples of image creationare discussed.
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Polarization Observations of the Anomalous Microwave Emission in the Perseus Molecular Complex with the COSMOSOMAS Experiment
The anomalous microwave emission detected in the Perseus molecularcomplex by Watson et al. has been observed at 11 GHz through dualorthogonal polarizations with the COSMOSOMAS experiment. Stokes U and Qmaps were obtained at a resolution of ~0.9d for a 30°×30°region including the Perseus molecular complex. Faint polarized emissionhas been measured; we find Q=-0.2%+/-1.0% andU=-3.4+1.8-1.4%, both at the 95% confidence level,with a systematic uncertainty estimated to be lower than 1% determinedfrom tests of the instrumental performance using unpolarized sources inour map as null hypothesis. The resulting total polarization level isΠ=3.4+1.5-1.9%. These are the first constraintson the polarization properties of an anomalous microwave emissionsource. The low level of polarization seems to indicate that theparticles responsible for this emission in the Perseus molecular complexare not significantly aligned in a common direction over the wholeregion, as a consequence of either a high structural symmetry in theemitting particle or a low-intensity magnetic field. Our weak detectionis fully consistent with predictions from electric dipole emission andresonance relaxation at this frequency.
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Fluorescent Molecular Hydrogen Emission in IC 63: FUSE, Hopkins Ultraviolet Telescope, and Rocket Observations
We present far-ultraviolet observations of IC 63, an emission/reflectionnebula illuminated by the B0.5 IV star γ Cas, located 1.3 pc fromthe nebula. Molecular hydrogen fluorescence was detected first in IC 63by IUE and later at shorter wavelengths by ORFEUS. Here we present FarUltraviolet Spectroscopic Explorer (FUSE) observations toward threelocations in the nebula, complemented by Hopkins Ultraviolet Telescope(HUT) data on the central nebular position. In addition, we present asounding rocket calibration of a FUSE spectrum of γ Cas. Molecularhydrogen fluorescence is detected in all three FUSE pointings. Theintensity of this emission, as well as the contributions from otherspecies, are seen to vary with position. The absolute flux calibrationof the sounding rocket data allows us to reliably predict the radiationfield incident on IC 63. We use these data to test models of thefluorescent process. Our modeling resolves the perceived discrepancybetween the existing ultraviolet observations and achieves asatisfactory agreement with the H2 rotational structureobserved with FUSE.
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Rocket and Far Ultraviolet Spectroscopic Explorer Observations of IC 405: Differential Extinction and Fluorescent Molecular Hydrogen
We present far-ultraviolet spectroscopy of the emission/reflectionnebula IC 405 obtained by a rocket-borne long-slit spectrograph and theFar Ultraviolet Spectroscopic Explorer (FUSE). Both data sets show arise in the ratio of the nebular surface brightness to stellar flux(S/F*) of approximately 2 orders of magnitude toward the blueend of the far-UV bandpass. Scattering models using simple dustgeometries fail to reproduce the observed S/F* for realisticgrain properties. The high spectral resolution of the FUSE data revealsa rich fluorescent molecular hydrogen spectrum ~1000" north of the starthat is clearly distinguished from the steady blue continuum. TheS/F* remains roughly constant at all nebular pointings,showing that fluorescent molecular hydrogen is not the dominant cause ofthe blue rise. We discuss three possible mechanisms for the ``bluedust'': differential extinction of the dominant star (HD 34078), unusualdust-grain properties, and emission from nebular dust. We conclude thatuncertainties in the nebular geometry and the degree of dust clumpingare most likely responsible for the blue rise. As an interestingconsequence of this result, we consider how IC 405 would appear in aspatially unresolved observation. If IC 405 were observed with a spatialresolution of less than 0.4 pc, for example, an observer would infer afar-UV flux that was 2.5 times the true value, giving the appearance ofa stellar continuum that was less extinguished than radiation from thesurrounding nebula, an effect that is reminiscent of the observedultraviolet properties of starburst galaxies.
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Merged catalogue of reflection nebulae
Several catalogues of reflection nebulae are merged to create a uniformcatalogue of 913 objects. It contains revised coordinates,cross-identifications of nebulae and stars, as well as identificationswith IRAS point sources.The catalogue is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/399/141
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Examination of the Interstellar Spectrum of AE AUR for Long-Term Changes
The runaway O9.5 V star AE Aur is moving across the line of sight behindthe curtain provided by the emission/reflection nebula IC 405. Theinterstellar line spectrum of AE Aur was examined on a HIRES spectrogramobtained in 1998 to determine if there had been any change since theoriginal high-resolution observations by Adams in the 1940s. Noequivalent widths were published by Adams, so only a comparison ofradial velocities was possible. No significant changes over theintervening half-century were detected; during that time the crossmotion of AE Aur in the plane of the sky amounted to about 1450 AU.Similarly, no convincing changes were found in the interstellar Ca IIlines of the runaway O star mu Col.
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Briefly noted: Irish astronomy (poem)
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Socket stars: UBVRJIK radial profiles
Visual inspectin of stars embedded in H II nebulae has shown asignificant fraction to be surrounded by nearly symmetric extendedregions within which the nebular brightness is apparently significantlyfainter than is typical for the surrounding area. These 'socket stars'might be caused by a bubble in the nebula blown out by a stellar wind orthey might be caused by a circumstellar envelope of dust hiding theemission behind the star. As such, the sockets could be the firstmanifestation of a previously unknown component of pre-main-sequencestars. Unfortunately, no quantitative proof of the existence of socketshas been presented. To fill this need, I have imaged 10 socket stars andsix background stars with CCD cameras and infrared array cameras. Fromthese images, I have constructed radial plots which should reveal dipsin brightness immediately outside the seeing disk. The radial plots donot show any evidence for the existence of sockets. A detailedexamination of the photographs orginally used to identify the socketsshow that the causes of these reports are (1) artifacts resulting fromthe photographic process of dodging and (2) random coincidence of starswith local minima in nebular brightness. Thus, I conclude that 'socketstars' do not exist.
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WO ist der Himmel AM buntesten ?
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Infrared Emission from "Socket" Stars in HII Regions
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On structural patterns in H II regions
High-resolution photographs of H II regions show that a large number ofstars embedded in the nebulosities appear to be surrounded by 'emply'spaces. This phenomenon seems to be quite common but has escapedattention up to now. The effect is not a photographic one, nor does itarise in the half-tone reproduction processes employed in publications,but no satisfactory explanation is apparent.
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Neutral hydrogen in isolated galaxies. IV - Results for the Arecibo sample
A standard sample for the comparison of the H I content of galaxies invarious intergalactic environments is presently defined by means ofobservations of 324 isolated galaxies lying in the declination rangeaccessible to the Arecibo 305-m telescope. Both mapping and single pointspectra are used to compute the integral properties of these galaxies.Neutral hydrogen was detected in 288 of the 324 galaxies surveyed, andit is noted that the optical diameter of a spiral disk is bettercorrelated with the hydrogen mass than the morphological type. When usedto define a measure of H I content, the isolated galaxy sample canpredict 'normalcy' with an accuracy that carries a standard error ofabout 0.20 in the log of the H I mass, if a dependence on disk size, aswell as type, is taken into account.
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Decameter observations of the nebulae IC 405 and IC 410
Results are presented of absorption measurements of the H II regions IC405 and IC 410 obtained at five freequencies between 12.6 and 25 MHzwith 0.5-1.0 deg resolution using the UTR-2 radio telescope. The averagenonthermal radiation density of the interstellar medium at 12.6 MHztoward IC 405 is determined to be 135 K/pc, whereas it is found to be 37K/pc toward IC 410. It is found that the kinetic temperature of IC 410is 11,000 K and that the electron density is approximately 12/cu cm.Calculations are presented for several other physical parameters towardthe center of IC 410: optical depth at 25 MHz = 8, emission measure =8,000 pc/cm exp 6, and mass = 3400 solar masses.
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Catalog of CO radial velocities toward galactic H II regions
This is a catalog of 242 molecular cloud complexes which are associatedwith optical H II regions. CO observations were made toward all but fiveof the H II regions in the Sharpless catalog and toward 62 additionalsuspected H II regions, 33 of which are previously uncataloged. Radialvelocities are tabulated for each molecular cloud complex found to beassociated with an H II region. The CO antenna temperature and linewidth are given for the most intense CO line seen toward each source.The catalog also summarizes previous CO observations as well as theoptical distances to the stars exciting the H II regions. Radio-quiet HII regions (those with 1.4 GHz flux densities less than 100 mJy) arefound to be well correlated with objects having no associated CO. A listof kinematically distinct complexes is tabulated to facilitateinvestigations of the motions of the complexes.
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CO observations of galactic reflection nebulae
Carbon monoxide emission has been observed toward about 35 galacticreflection nebulae. The peaking of CO temperatures near the hotter starsindicates substantial local heating of the gas and dust by the embeddedstars. Wide low-level emission wings are seen on several of the (C-12)Oline profiles; these are most plausibly interpreted as due to cloudmaterial accelerated by such processes as radiation pressure from thenewborn stars.
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H II regions of the northern Milky Way: medium-large-field photographic atlas and catalogue.
Abstract image available at:http://adsabs.harvard.edu/abs/1976A&AS...25...25D
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Observational Evidence of Collisional Excitation in Two Diffuse Nebulae
Abstract image available at:http://adsabs.harvard.edu/abs/1972ApJ...171..279C
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Abundances of the Elements in Caseous Nebulae
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A Comparison between Radio and Optical Radial Velocities of H N Regions
Abstract image available at:http://adsabs.harvard.edu/abs/1970A&A.....7..322G
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The Effective Temperatures of the O Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1969ApJ...158..629M&db_key=AST
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Survey of radio sources observed in the continuum near 1420 MHz, declinations -5 to +70.
Abstract image available at:http://adsabs.harvard.edu/abs/1968AJ.....73..135G
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Radial Velocities and Kinematics of Galactic H II Regions
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1968ApJ...151..473M&db_key=AST
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OH Absorption in the Galaxy
Abstract image available at:http://adsabs.harvard.edu/abs/1968ApJS...15..131G
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Observations of the Hydrogen Recombination Line 158α in Galactic H II Regions
Abstract image available at:http://adsabs.harvard.edu/abs/1967ApJ...150..435D
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Ricerche sulle associazioni T - Nota I: Variabili nuove nella zona di NGC 1579 ed IC 405
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Determination of electron temperature in diffuse nebulae.
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A catalogue of discrete sources observed at 400 Mc/s
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Catalogue of radio sources in the galactic plane
Abstract image available at:http://adsabs.harvard.edu/abs/1963AJ.....68..181W
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A Survey of Galactic Radiation at 960 Mc/s
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