2002/08/09 by Brian E. Wood, Margarita Karovska, John C. Raymond · 2 citations
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysics and Star Formation Studies #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/341478
published as Astrophys.J. 575 (2002) 1057-1077 · 49 pages, 16 figures; AASTEX v5.0 plus EPSF extensions in mkfig.sty; accepted by ApJ
arxiv created 2002/08/09 · openalex publication_date 2002/08/20 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/31
We analyze Lyα fluoresced H 2 lines observed in the UV spectrum of Mira B. We identify 13 different sequences fluoresced by 13 different H 2 transitions within the Lyα line. The observed H 2 line ratios within these sequences imply significant line opacity, so we use a Monte Carlo radiative transfer code to model the line ratios, correcting for opacity effects. We find that the observed line ratios can best be reproduced by assuming that the H 2 is fluoresced in a layer between the observer and Mira B with a temperature and column density of T = 3600 K and log N (H 2 ) = 17.3, respectively. The strengths of H 2 absorption features within the Lyα line are roughly consistent with this temperature and column. We use the total flux fluoresced within the 13 sequences to infer the Lyα profile seen by the H 2 . In order to explain differences between the shape of this and the observed profile, we have to assume that the observed profile suffers additional interstellar (or circumstellar) H I Lyα absorption with a column density of about log N (H ) = 20.35. We also have to assume that the observed profile is about a factor of 2.5 lower in flux than the profile seen by the H 2 , and a couple of possible explanations for this behavior are presented. Several lines of evidence lead us to tentatively attribute the fluoresced emission to H 2 that is heated in a photodissociation front within Mira A's wind a few AU from Mira B, although it is possible that interaction between the winds of Mira A and B may also play a role in heating the H 2 . We estimate a Mira B mass-loss rate of = 5 × 10 -13 M ☉ yr -1 and a terminal velocity of V ∞ = 250 km s -1 , based on wind absorption features in the Mg II h and k lines. We note, however, that the wind is variable and IUE Mg II spectra suggest significantly higher mass-loss rates during the IUE era.