Quantitative optical and near-infrared spectroscopy of molecular hydrogen towards HH91A

Integral-field spectroscopy of molecular hydrogen in the optical wavelength region and complementary long-slit near-infrared spectroscopy are presented towards HH91A.The detection of some 200 H_2 lines arising from ro-vibrational levels up to v'=8 ranging between 7700A and 2.3 microns is reported. The emission arises from thermally excited gas where the bulk of the material is at 2750 K and where 1% is at 6000 K. The total column density of shocked gas is N(H_2) = 10^{18} cm^{-2}. Non-thermal excitation scenarios such as UV-fluorescence do not contribute to the excitation of H_2 towards HH91A. The emission is explained in terms of a slow non-dissociative J-shock which propagates into a low-density medium which has been swept-up by previous episodes of outflows which have occurred in the evolved HH90/91 complex.Comment: A&A accepte

Observations of rotationally resolved C3 in translucent sight lines

The rotationally resolved spectrum of the A ^1Pi_u <- X ^1Sigma^+_g 000-000 transition of C3, centered at 4051.6A, has been observed along 10 translucent lines of sight. To interpret these spectra, a new method for the determination of column densities and analysis of excitation profiles involving the simulation and fitting of observed spectra has been developed. The populations of lower rotational levels (J<14) in C3 are best fit by thermal distributions that are consistent with the kinetic temperatures determined from the excitation profile of C2. Just as in the case of C2, higher rotational levels (J>14) of C3 show increased nonthermal population distributions in clouds which have been determined to have total gas densities below ~500 cm-3.Comment: 12 pages, 4 figures, accepted for publication in The Astrophysical Journa

Multimodal self- and other-positioning on Wikipedia user pages

In the analysis of digital communication, there is a growing interest in how people construct their identities through interaction with each other. Multimodal self- and other-positioning can be seen as a key to the analysis of identity in the framework of interaction analysis. But so far, the focus of many linguistic studies has clearly been on the microanalysis of the purely verbal dimension of small episodes of identity construction in digital communication. Consequently, there is little empirical examination of how self- and other-positioning is shaped discursively, mediated institutionally and realized multimodally. Analysing Wikipedia user pages, the paper follows a multimodal approach that advocates at the same time the integration of discourse and interaction analytic aspects of positioning. So far, the user pages as a locus of (self-) positioning in Wikipedia are completely underexamined in the constantly growing field of linguistic and media-scientific analyses of the collaborative online encyclopaedia, although self-representation can be understood as a prerequisite for participation in digital communication. On the wiki-supported user pages, engaged Wikipedia authors permanently elaborate on their online personas. Simultaneously they negotiate roles and positions in interaction on the corresponding user talk pages. The overall goal is to achieve powerful positions to have a high impact on the collaborative content production in the digital discourses of the online encyclopaedia. Three Wikipedia-specific multimodal resources are considered for the outlined analysis: when constructing identities-in-interaction Wikipedia authors make use of the Babel User Templates, they grant digital prizes and distinctions, and they integrate images on their user pages, which they borrow from the huge image repositories of Wikimedia Commons

Off-line processing of ERS-1 synthetic aperture radar data with high precision and high throughput

The first European remote sensing satellite ERS-1 will be launched by the European Space Agency (ESA) in 1989. The expected lifetime is two to three years. The spacecraft sensors will primarily support ocean investigations and to a limited extent also land applications. Prime sensor is the Active Microwave Instrumentation (AMI) operating in C-Band either as Synthetic Aperture Radar (SAR) or as Wave-Scatterometer and simultaneously as Wind-Scatterometer. In Europe there will be two distinct types of processing for ERS-1 SAR data, Fast Delivery Processing and Precision Processing. Fast Delivery Proceessing will be carried out at the ground stations and up to three Fast Delivery products per pass will be delivered to end users via satellite within three hours after data acquisition. Precision Processing will be carried out in delayed time and products will not be generated until several days or weeks after data acquisition. However, a wide range of products will be generated by several Processing and Archiving Facilities (PAF) in a joint effort coordinated by ESA. The German Remote Sensing Data Center (Deutsches Fernerkundungsdatenzentrum DFD) will develop and operate one of these facilities. The related activities include the acquisition, processing and evaluation of such data for scientific, public and commercial users. Based on this experience the German Remote Sensing Data Center is presently performing a Phase-B study regarding the development of a SAR processor for ERS-1. The conceptual design of this processing facility is briefly outlined

HH135/HH136 - a luminous H2_2 outflow towards a high-mass protostar

Near-infrared observations towards the luminous IRAS source IRAS11101-5928 and the associated Herbig-Haro objects HH135/HH136 are presented. The observations reveal the presence of a well-collimated, parsec-sized H$_2$ outflow with a total H$_2$ luminosity of about $2L_\odot$. The bulk of the molecular gas is characterized by a ro-vibrational excitation temperature of $2000\pm200$ K. A small fraction (0.3%) of the molecular gas is very hot, with excitation temperatures around 5500 K. The molecular emission is associated with strong [FeII] emission. The H$_2$ and [FeII] emission characteristics indicate the presence of fast, dissociative J-shocks at speeds of $v_\mathrm{s} \approx$ 100 km s$^{-1}$. Electron densities of $n_\mathrm{e}$ = 3500-4000 cm$^{-3}$ are inferred from the [FeII] line ratios. The large H$_2$ luminosity combined with the very large source luminosity suggests that the high-mass protostar that powers the HH135/HH136 flow forms via accretion, but with a significantly increased accretion rate compared to that of low-mass protostars

New Insights on Interstellar Gas-Phase Iron

In this paper, we report on the gas-phase abundance of singly-ionized iron (Fe II) for 51 lines of sight, using data from the Far Ultraviolet Spectroscopic Explorer (FUSE). Fe II column densities are derived by measuring the equivalent widths of several ultraviolet absorption lines and subsequently fitting those to a curve of growth. Our derivation of Fe II column densities and abundances creates the largest sample of iron abundances in moderately- to highly-reddened lines of sight explored with FUSE, lines of sight that are on average more reddened than lines of sight in previous Copernicus studies. We present three major results. First, we observe the well-established correlation between iron depletion and and also find trends between iron depletion and other line of sight parameters (e.g. f(H_2), E_(B-V), and A_V), and examine the significance of these trends. Of note, a few of our lines of sight probe larger densities than previously explored and we do not see significantly enhanced depletion effects. Second, we present two detections of an extremely weak Fe II line at 1901.773 A in the archival STIS spectra of two lines of sight (HD 24534 and HD 93222). We compare these detections to the column densities derived through FUSE spectra and comment on the line's f-value and utility for future studies of Fe II. Lastly, we present strong anecdotal evidence that the Fe II f-values derived empirically through FUSE data are more accurate than previous values that have been theoretically calculated, with the probable exception of f_1112.Comment: Accepted for publication in ApJ, 669, 378; see ApJ version for small updates. 53 total pages (preprint format), 7 tables, 11 figure

Abundances and rotational temperatures of the C2 interstellar molecule towards six reddened early-type stars

Using high-resolution (~85000) and high signal-to-noise ratio (~200) optical spectra acquired with the European Southern Observatory Ultraviolet and Visual Echelle Spectrograph, we have determined the interstellar column densities of C2 for six Galactic lines of sight with E(B- V) ranging from 0.33 to 1.03. For our purposes, we identified and measured absorption lines belonging to the (1, 0), (2, 0) and (3, 0) Phillips bands A1{\Pi}u-X1{\Sigma}+g. We report on the identification of a few lines of the C2 (4, 0) Phillips system towards HD 147889. The curve-of-growth method is applied to the equivalent widths to determine the column densities of the individual rotational levels of C2. The excitation temperature is extracted from the rotational diagrams. The physical parameters of the intervening molecular clouds (e.g. gas kinetic temperatures and densities of collision partners) were estimated by comparison with the theoretical model of excitation of C2.Comment: 11 pages, 3 figures, MNRAS 201

CO and C_2 Absorption Toward W40 IRS 1a

The H II region W40 harbors a small group of young, hot stars behind roughly 9 magnitudes of visual extinction. We have detected gaseous carbon monoxide (CO) and diatomic carbon (C_2) in absorption toward the star W40 IRS 1a. The 2-0 R0, R1, and R2 lines of 12CO at 2.3 micron were measured using the CSHELL on the NASA IR Telescope Facility (with upper limits placed on R3, R4, and R5) yielding an N_CO of (1.1 +/- 0.2) x 10^18 cm^-2. Excitation analysis indicates T_kin > 7 K. The Phillips system of C_2 transitions near 8775 Ang. was measured using the Kitt Peak 4-m telescope and echelle spectrometer. Radiative pumping models indicate a total C_2 column density of (7.0 +/- 0.4) x 10^14 cm^-2, two excitation temperatures (39 and 126 K), and a total gas density of n ~ 250 cm^-3. The CO ice band at 4.7 micron was not detected, placing an upper limit on the CO depletion of delta < 1 %. We postulate that the sightline has multiple translucent components and is associated with the W40 molecular cloud. Our data for W40 IRS 1a, coupled with other sightlines, shows that the ratio of CO/C_2 increases from diffuse through translucent environs. Finally, we show that the hydrogen to dust ratio seems to remain constant from diffuse to dense environments, while the CO to dust ratio apparently does not.Comment: To appear in The Astrophysical Journal 17 pages total, 5 figures Also available at http://casa.colorado.edu/~shuping/research/w40/w40.htm

Digitale Methoden und Werkzeuge für Diskursanalysen am Beispiel Wikipedia

As a relatively new discipline in linguistics, discourse linguistics, in the tradition of Foucault, explores how social realities are constructed in transtextual units. Until now, texts from digital media sources have been barely acknowledged. The goal of this paper is to expand the inventory of methods for discourse analysis in two directions using the example of Wikipedia. First, specific categories for the analysis of discourse in digital media will be described systematically. Second, existing approaches in the field of corpus linguistics and digital methods will be described, keeping in mind the requirements of digital discourse analysis, in order to include them in a methodology for digital discourse analysis

Unusually Weak Diffuse Interstellar Bands toward HD 62542

As part of an extensive survey of diffuse interstellar bands (DIBs), we have obtained optical spectra of the moderately reddened B5V star HD 62542, which is known to have an unusual UV extinction curve of the type usually identified with dark clouds. The typically strongest of the commonly catalogued DIBs covered by the spectra -- those at 5780, 5797, 6270, 6284, and 6614 A -- are essentially absent in this line of sight, in marked contrast with other lines of sight of similar reddening. We compare the HD 62542 line of sight with others exhibiting a range of extinction properties and molecular abundances and interpret the weakness of the DIBs as an extreme case of deficient DIB formation in a dense cloud whose more diffuse outer layers have been stripped away. We comment on the challenges these observations pose for identifying the carriers of the diffuse bands.Comment: 20 pages, 4 figures; aastex; accepted by Ap