J/A+A/***/*** CO line profile parameters R_1/2 and alpha as a function of input parameters ================================================================================ The photodissociation of CO in circumstellar envelopes Groenewegen M.A.T =2017A&A...**..**G ================================================================================ ADC_Keywords: Radio lines ; Stars, late-type ; Mass loss Keywords: Astrochemistry - Stars: AGB and post-AGB - Stars: winds, outflows - Radio lines: stars Abstract: Carbon monoxide is the most abundant molecule after H_2 and is important for chemistry in circumstellar envelopes around late-type stars. The size of the envelope is important when modelling low-J transition lines and deriving mass-loss rates from such lines. Now that ALMA is coming to full power the extent of the CO emitting region can be measured directly for nearby asymptotic giant branch (AGB) stars. In parallel, it has become obvious in the past few years that the strength of the interstellar radiation field (ISRF) can have a significant impact on the interpretation of the emission lines. In this paper an update and extension of the classical Mamon et al. (1988; ApJ 328, 797) paper is presented; these authors provided the CO abundance profile, described by two parameters, as a function of mass-loss rate and expansion velocity. Following recent work an improved numerical method and updated H_2 and CO shielding functions are used and a larger grid is calculated that covers more parameter space, including the strength of the ISRF. The effect of changing the photodissociation radius on the low-J CO line intensities is illustrated in two cass Description: The results of extensive CO photodissociation calculations are presented. The CO profile is described by the radius at which the abundance has dropped to half its initial value (R_1/2) and a shape parameter (alpha). File Summary: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- ReadMe 80 . This file Tab1.dat 49 20262 CO photodissociation parameters -------------------------------------------------------------------------------- Byte-by-byte Description of file: Tab1.dat ----------------------------------------------------------------------------- Bytes Format Units Label Explanations ----------------------------------------------------------------------------- 1- 8 E8.2 Msol/yr Mdot Mass-loss rate 10- 13 F4.1 km/s V Gas expansion velocity 15- 22 E8.2 - f_CO CO abundance relative to H_2 24- 29 F6.2 - chi Strength of the radiation field 31- 35 F5.1 K T_ex Excitation temperature 36- 44 F8.2 1.E15 cm R_1/2 Half radius 46- 50 F5.2 - alpha Shape parameter of the CO profile -------------------------------------------------------------------------------- ================================================================================ (End) Martin Groenewegen 17-Aug-2017