5 research outputs found

    Plateau emission from Orion in the CO J=17−16 Line

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    High-resolution spectra of the J=17−16 CO line (1956 GHz) in the BN-KL region of Orion have been obtained with a heterodyne spectrometer. The profiles show a broad component with 30 km s⁻¹ (FWHM) linewidth and a narrower 8 km s⁻¹ component. The broader plateau emission detected over a range of transitions from J=1–0 to J=17−16 is analyzed under the assumptions of thermal equilibrium and optically thin wings to deduce an excitation temperature of 180 ± 50 K and minimum column density of 1 X 10¹⁸ cm⁻² for CO in this component

    Heterodyne spectroscopy of C II in molecular clouds

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    High-resolution spectra of the 158 μm fine-structure line of ionized carbon have been obtained with a heterodyne spectrometer toward a number of galactic molecular clouds. Strongly reversed C II line profiles are seen in sources noted for similar behavior in low-J ¹²CO. The C⁺ producing the optically thick (τ≥1) absorption component is cool or subthermally excited, with excitation temperatures typically less than 25–50 K. Column densities for the absorption component are ≥10¹⁸ cm⁻², similar to values predicted by UV-photodissociation models for C II emitting gas. Thus the total C⁺ column density in the vicinity of these molecular clouds is significantly greater than previously estimated from integrated intensity measurements

    H2D+ observations give an age of at least one million years for a cloud core forming Sun-like stars

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    The age of dense interstellar cloud cores, where stars and planets form, is a crucial parameter in star formation and difficult to measure. Some models predict rapid collapse(1,2), whereas others predict timescales of more than one million years (ref. 3). One possible approach to determining the age is through chemical changes as cloud contraction occurs, in particular through indirect measurements of the ratio of the two spin isomers (ortho/para) of molecular hydrogen, H-2, which decreases monotonically with age(4-6). This has beendone for the dense cloud core L183, for which the deuterium fractionation of diazenylium(N2H+) was used as a chemical clock to infer(7) that the core has contracted rapidly (on a timescale of less than 700,000 years). Among astronomically observable molecules, the spin isomers of the deuterated trihydrogen cation, ortho-H2D+ and para-H2D+, have the most direct chemical connections to H-2 (refs 8-12) and their abundance ratio provides a chemical clock that is sensitive to greater cloud core ages. So far this ratio has not been determined because para-H2D+ is very difficult to observe. The detection of its rotational ground-state line has only now become possible thanks to accurate measurements of its transition frequency in the laboratory(13), and recent progress in instrumentation technology(14,15). Here we report observations of ortho-and para-H2D+ emission and absorption, respectively, from the dense cloud core hosting IRAS 16293-2422 A/B, a group of nascent solar-type stars (with ages of less than 100,000 years). Using the ortho/para ratio in conjunction with chemical models, we find that the dense core has been chemically processed for at least one million years. The apparent discrepancy with the earlier N2H+ work(7) arises because that chemical clock turns off sooner than the H2D+ clock, but both results imply that star-forming dense cores have ages of about one million years, rather than 100,000 years

    Cool outflows in galaxies and their implications

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