The detectability of mm-wave molecular rotational transitions

Elaborating on a formalism that was first expressed some 40 years ago, we consider the brightness of low-lying mm-wave rotational lines of strongly polar molecules at the threshold of detectability. We derive a simple expression relating the brightness to the line of sight integral of the product of the total gas and molecular number densities and a suitably-defined temperature-dependent excitation rate into the upper level of the transition. Detectability of a line is contingent only on the ability of a molecule to channel enough of the ambient thermal energy into the line and the excitation can be computed in bulk by summing over rates without solving the multi-level rate equations or computing optical depths and excitation temperatures. Results for \hcop, HNC and CS are compared with escape-probability solutions of the rate equations using closed-form expressions for the expected range of validity of our {\it ansatz}, with the result that gas number densities as high as 10^4 \pccc or optical depths as high as 100 can be accommodated in some cases. For densities below a well-defined upper bound, the range of validity of the discussion can be cast as an upper bound on the line brightness which is 0.3 K for the J=1-0 lines and 0.8 - 1.7 K for the J=2-1 lines of these species. The discussion casts new light on interpretation of line brightnesses under conditions of weak excitation, simplifies derivation of physical parameters and eliminates the need to construct grids of numerical solutions of the rate equations.Comment: Accepted for Ap

Limits on chemical complexity in diffuse clouds: search for CH3OH and HC5N absorption

Context: An unexpectedly complex polyatomic chemistry exists in diffuse clouds, allowing detection of species such as C2H, C3H2, H2CO and NH3 which have relative abundances that are strikingly similar to those inferred toward the dark cloud TMC-1 Aims: We probe the limits of complexity of diffuse cloud polyatomic chemistry. Methods: We used the IRAM Plateau de Bure Interferometer to search for galactic absorption from low-lying J=2-1 rotational transitions of A- and E-CH3OH near 96.740 GHz and used the VLA to search for the J=8-7 transition of HC5N at 21.3 GHz. Results: Neither CH3OH nor HC5N were detected at column densities well below those of all polyatomics known in diffuse clouds and somewhat below the levels expected from comparison with TMC-1. The HCN/HC5N ratio is at least 3-10 times higher in diffuse gas than toward TMC-1. Conclusions: It is possible to go to the well once (or more) too ofte

HCO, c-C3H and CF+ : three new molecules in diffuse, translucent and "spiral-arm'' clouds

%methods {We used the EMIR receiver and FTS spectrometer at the IRAM 30m to construct absorption spectra toward bright extra-galactic background sources at 195 kHz spectral resolution ($\approx$ 0.6 \kms). We used the IRAM Plateau de Bure interferometer to synthesize absorption spectra of \hthcop\ and HCO toward the galactic HII region W49.} %results {HCO, \cc3h\ and CF\p\ were detected toward the blazars \bll\ and 3C111 having \EBV\ = 0.32 and 1.65 mag. HCO was observed in absorption from ``spiral-arm'' clouds in the galactic plane occulting W49. The complement of detectable molecular species in the 85 - 110 GHz absorption spectrum of diffuse/translucent gas is now fully determined at rms noise level $\delta_\tau \approx 0.002$ at \EBV\ = 0.32 mag (\AV\ = 1 mag) and $\delta_\tau$/\EBV\ $\approx\ 0.003$ mag$^{-1}$ overall.} %conclusions {As with OH, \hcop\ and \cch, the relative abundance of \cc3h\ varies little between diffuse and dense molecular gas, with N(\cc3h)/N({\it o-c}-\c3h2) $\approx$ 0.1. We find N(CF\p)/N(H$^{13}$CO\p) $\approx 5$, N(CF\p)/N(\cch) $\approx$ 0.005-0.01 and because N(CF\p) increases with \EBV\ and with the column densities of other molecules we infer that fluorine remains in the gas phase as HF well beyond \AV\ = 1 mag. We find N(HCO)/N(H$^{13}$CO\p) = 16 toward \bll, 3C111 and the 40 km/s spiral arm cloud toward W49, implying X(HCO) $\approx 10^{-9}$, about 10 times higher than in dark clouds. The behaviour of HCO is consistent with previous suggestions that it forms from C\p\ and \HH, even when \AV\ is well above 1 mag. The survey can be used to place useful upper limits on some species, for instance N(\hhco)/N(\HH CS) $>$ 32 toward 3C111, compared to 7 toward TMC-1, confirming the possibility of a gas phase formation route to \hhco.}Comment: A\%A in pres

The CO-H2 conversion factor of diffuse ISM: Bright 12CO emission also traces diffuse gas

We show that the XCO factor, which converts the CO luminosity into the column density of molecular hydrogen has similar values for dense, fully molecular gas and for diffuse, partially molecular gas. We discuss the reasons of this coincidence and the consequences for the understanding of the interstellar medium.Comment: 5 pages, 1 PostScript figure. To be published in the proceedings of the Zermatt 2010 conference: "Conditions and impact of star formation: New results with Herschel and beyond". Uses EAS LaTeX macro

A Search for Consistent Jet and Disk Rotation Signatures in RY Tau

We present a radial velocity study of the RY Tau jet-disk system, designed to determine whether a transfer of angular momentum from disk to jet can be observed. Many recent studies report on the rotation of T Tauri disks, and on what may be a signature of T Tauri jet rotation. However, due to observational difficulties, few studies report on both disk and jet within the same system to establish if the senses of rotation match and hence can be interpreted as a transfer of angular momentum. We report a clear signature of Keplerian rotation in the RY Tau disk, based on Plateau de Bure observations. We also report on the transverse radial velocity profile of the RY Tau jet close to the star. We identify two distinct profile shapes: a v-shape which appears near jet shock positions, and a flat profile which appears between shocks. We do not detect a rotation signature above 3 sigma uncertainty in any of our transverse cuts of the jet. Nevertheless, if the jet is currently in steady-state, the errors themselves provide a valuable upper limit on the jet toroidal velocity of 10 km/s, implying a launch radius of < 0.45 AU. However, possible contamination of jet kinematics, via shocks or precession, prevents any firm constraint on the jet launch point, since most of its angular momentum could be stored in magnetic form rather than in rotation of matter.Comment: 10 pages, 7 figures, accepted by The Astrophysical Journa

Revisiting the theory of interferometric wide-field synthesis

After several generations of interferometers in radioastronomy, wide-field imaging at high angular resolution is today a major goal for trying to match optical wide-field performances. All the radio-interferometric, wide-field imaging methods currently belong to the mosaicking family. Based on a 30 years old, original idea from Ekers & Rots, we aim at proposing an alternate formalism. Starting from their ideal case, we successively evaluate the impact of the standard ingredients of interferometric imaging. A comparison with standard nonlinear mosaicking shows that both processing schemes are not mathematically equivalent, though they both recover the sky brightness. In particular, the weighting scheme is very different in both methods. Moreover, the proposed scheme naturally processes the short spacings from both single-dish antennas and heterogeneous arrays. Finally, the sky gridding of the measured visibilities, required by the proposed scheme, may potentially save large amounts of hard-disk space and cpu processing power over mosaicking when handling data sets acquired with the on-the-fly observing mode. We propose to call this promising family of imaging methods wide-field synthesis because it explicitly synthesizes visibilities at a much finer spatial frequency resolution than the one set by the diameter of the interferometer antennas.Comment: 22 pages, 6 PostScript figures. Accepted for publication in Astronomy & Astrophysics. Uses aa LaTeX macros

Imaging diffuse clouds: Bright and dark gas mapped in CO

We wish to relate the degree scale structure of galactic diffuse clouds to sub-arcsecond atomic and molecular absorption spectra obtained against extragalactic continuum background sources. To do this, we used the ARO 12m telescope to map J=1-0 CO emission at 1' resolution over 30' fields around the positions of 11 background sources occulted by 20 molecular absorption line components, of which 11 had CO emission counterparts. We compare maps of CO emission to sub-arcsec atomic and molecular absorption spectra and to the large-scale distribution of interstellar reddening. The main results are: 1) Typical covering factors of individual features at the 1 K.km/s level were 20%. 2) CO-H2 conversion factors as much as 4-5 times below the mean value N(H2)/Wco = 2e20 H2 cm^-2 /(K.km/s) are required to explain the luminosity of CO emission at/above the level of 1 K.km/s. Small conversion factors and sharp variability of the conversion factor on arcminute scales are due primarily to CO chemistry and need not represent unresolved variations in reddening or total column density. Hence, like FERMI and PLANCK we see some gas that is dark in CO and other gas in which CO is overluminous per H2. A standard CO-H2 conversion factor applies overall owing to balance between the luminosities per H2 and surface covering factors of bright and dark CO., but with wide variations.Comment: 23 pages, 22 PostScript figures. Accepted for publication in Astronomy \& Astrophysics. Uses aa LaTeX macro

PEMBELAJARAN MEMPRODUKSI TEKS PROSEDUR KOMPLEKS BERDASARKAN KAIDAH KEBAHASAAN DENGAN MENGGUNAKAN METODE PICTURE AND PICTURE PADA SISWA KELAS X SMK PASUNDAN 3 BANDUNG TAHUN PELAJARAN 2015/201

Penelitian ini bertujuan untuk memberikan gambaran mengenai kemampuan penulis melaksanakan pembelajaran memproduksi teks Prosedur kompleks dan untuk mengetahui kemampuan siswa kelas X SMK Pasundan 3 Bandung dalam memproduksi teks prosedur kompleks berdasarkan kaidah kebahasaan dengan menggunakan metode picture and picture . Perumusan masalah yang penulis ajukan adalah: 1) Apakah penulis mampu melaksanakan pembelajaran memproduksi teks prosedur kompleks berdasarkan kaidah kebahasaan dengan me nggunakan metode picture and picture pada siswa kelas X ? 2) Apakah siswa kelas X mampu memproduksi teks prosedur kompleks berdasarkan kaidah kebahasaan dengan menggunakan metode picture and picture ? 3) Efektifkah metode picture and picture di terapkan dalam pembelajaran mem produksi teks prosedur kompleks berdasarkan kaidah kebahasaan pada siswa kelas X ? Hipotesis yang penulis rumuskan yai tu: 1) Penulis mampu melaksanakan pembelajara n memproduksi teks prosedur kompleks berdasarkan kaidah kebahasaan dengan menggunakan metode picture and picture pada siswa kelas X tahun pelajaran 2015/2016. 2) Siswa kelas X mampu memproduksi teks prosedur ko mpleks berdasarkan kaidah kebahasaan dengan menggunakan metode picture and picture . 3) Metode picture and picture efektif digunakan dalam pembelajaran memproduksi teks prosedur kompleks berdasarkan kaidah kebahasaan pada siswa kelas X . Adapun hasil penelitiannya sebagai berikut. 1. Penulis mampu merencanakan dan melaksanakan pembelajaran memproduksi teks prosedur kompleks kelas X . H al ini terbukti dari hasil nilai perencanaan dan pelaksanaan pembelajaran sebesar 3, 7 dengan kategori baik sekali (A). 2. Siswa kelas X mampu memproduksi teks prosedur kompleks berdasarkan kaidah kebahasaan. Hal ini terbukti dari nilai rata - rata pretest sebesar 45 dan nilai rata - rata postest sebesar 76. Jadi, adanya peningkatan 31 atau 13,4%. 3. Metode picture and picture efektif digunakan dalam pembelajaran memproduksi teks prosedur kompleks, H al ini terbukti dari hasil perhitungan statistik dengan hasil t hitung > t tabel yaitu yaitu 4,7 > 2,14 pada tingkat kepercayaan 9 5%, dan derajat kebebasan sebesar 22. Berdasarkan fakta tersebut, penulis menyimpulkan bahwa penulis berhasil melakukan pembelajaran memproduksi teks prosedur kompleks berdasarkan kaidah kebahasaan dengan menggunakan metode picture and picture . Kata kunci : Memproduksi, Teks Prosedur Kompleks, Kaidah Kebahasaan, Metode Picture and Pictur

Intermittency of interstellar turbulence: extreme velocity-shears and CO emission on milliparsec scale

The condensation of diffuse gas into molecular clouds occurs at a rate driven largely by turbulent dissipation. This process still has to be caught in action and characterized. A mosaic of 13 fields was observed in the CO(1-0) line with the IRAM-PdB interferometer in the translucent environment of two low-mass dense cores. The large size of the mosaic compared to the resolution (4 arcsec) is unprecedented in the study of the small-scale structure of diffuse molecular gas. Eight weak and elongated structures of thicknesses as small as 3 mpc (600 AU) and lengths up to 70mpc are found. These are not filaments because once merged with short-spacing data, they appear as the sharp edges of larger-scale structures. Six out of eight form quasi-parallel pairs at different velocities and different position angles. This cannot be the result of chance alignment. The velocity-shears estimated for the three pairs include the highest ever measured far from star forming regions (780 km/s/pc). Because the large scale structures have sharp edges, with little or no overlap, they have to be thin CO-layers. Their edges mark a sharp transition between a CO-rich component and a gas undetected in the CO line because of its low CO abundance, presumably the cold neutral medium. We propose that these sharp edges are the first directly-detected manifestations of the intermittency of interstellar turbulence. The large velocity-shears reveal an intense straining field, responsible for a local dissipation rate several orders of magnitude above average, possibly at the origin of the thin CO-layers.Comment: 16 pages, 11 figures, Accepted for publication in Astronomy and Astrophysic