Searcharxiv⌕ Search
Home/Archive/arXiv

arXiv · astro-ph/0403471

The HCO+ emission excess in bipolar outflows

J. M. C Rawlings·M. P. Redman·E. Keto·D. A. Williams
View original source ↗Read source document ↗Export metadata ↓

Abstract

A plausible model is proposed for the enhancement of the abundance of molecular species in bipolar outflow sources. In this model, levels of HCO+ enhancement are considered based on previous chemical calculations, that are assumed to result from shock-induced desorption and photoprocessing of dust grain ice mantles in the boundary layer between the outflow jet and the surrounding envelope. A radiative transfer simulation that incorporates chemical variations within the flow shows that the proposed abundance enhancements in the boundary layer are capable of reproducing the observed characteristics of the outflow seen in HCO+ emission in the star forming core L1527. The radiative transfer simulation also shows that the emission lines from the enhanced molecular species that trace the boundary layer of the outflow exhibit complex line profiles indicating that detailed spatial maps of the line profiles are essential in any attempt to identify the kinematics of potential infall/outflow sources. This study is one of the first applications of a full three dimensional radiative transfer code which incorporates chemical variations within the source.

Explore related subjects

astro-ph

Keep this discovery

BibTeXRIS

J. M. C Rawlings, M. P. Redman, E. Keto, D. A. Williams. 2004-03-19. The HCO+ emission excess in bipolar outflows. https://doi.org/10.1111/j.1365-2966.2004.07855.x

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2017

Pulsar Magnetic Field Oscillation Model and Verification Methods

We constructed the magnetic field oscillation model (hereafter the MO model) by analogizing the periodically reversing phenomenon of the solar magnetic field to pulsars. Almost all kinds of pulsar radiation phenomena are best explained using the MO model, especially polarization characteristics, glitch, generation rate, the geodetic precession of pulsars and the configuration of pulsar-wind nebula of the Crab. The MO model also provides satisfactory explanation for other characteristics of pulsars, e.g., interpulse, spin-down, pulse nulling, beat and pulse drift, the loss rate of the rotating energy, and the accuracy of frequency. We present eight verification methods for the MO model. In addition to pulsars, our MO model can also be used to explain the pulse emission from non-compact stars such as the ultracool dwarf TVLM 513-46546 and the magnetic chemically peculiar star CU Virginis.

astro-ph↗
arXiv2017

Cosmological parameters from WMAP 5-year temperature maps

I calculate a hybrid cross-power spectrum estimator from the WMAP 5-year CMB temperature maps, discuss the goodness of fit, and then constrain cosmological parameters. The spectrum and results are generally consistent with previous results, though the power spectrum error bars are slightly smaller and there are small shifts at high ell. The small improvement in error bars is obtained at very low numerical cost but does not significantly improve parameter constraints. I discuss the accuracy of the likelihood model and how constraints on the optical depth translate into constraints on the reionization history allowing for helium reionization. In the appendices I propose a simple reionization parameterization that determines the history in terms of a mid-point reionization redshift, and suggest a new likelihood approximation for chi-squared-like distributions with varying skewness.

astro-ph↗
arXiv2017

The Statistics of Radio Astronomical Polarimetry: Bright Sources and High Time Resolution

A four-dimensional statistical description of electromagnetic radiation is developed and applied to the analysis of radio pulsar polarization. The new formalism provides an elementary statistical explanation of the modal broadening phenomenon in single pulse observations. It is also used to argue that the degree of polarization of giant pulses has been poorly defined in past studies. Single and giant pulse polarimetry typically involves sources with large flux densities and observations with high time resolution, factors that necessitate consideration of source-intrinsic noise and small-number statistics. Self noise is shown to fully explain the excess polarization dispersion previously noted in single pulse observations of bright pulsars, obviating the need for additional randomly polarized radiation. Rather, these observations are more simply interpreted as an incoherent sum of covariant, orthogonal, partially polarized modes. Based on this premise, the four-dimensional covariance matrix of the Stokes parameters may be used to derive mode-separated pulse profiles without any assumptions about the intrinsic degrees of mode polarization. Finally, utilizing the small-number statistics of the Stokes parameters, it is established that the degree of polarization of an unresolved pulse is fundamentally undefined; therefore, previous claims of highly polarized giant pulses are unsubstantiated. Unpublished supplementary material is appended after the bibliography.

astro-ph↗