D. Cohen
19-28 Nov 2011

*This document contains some suggested edits and new text for Emma's paper on Chandra x-ray line profiles

I've left some citations only loosely described; let me know if you need help tracking the details down.  (Note that you can get ADS to return bibtex formatted citation information.)  

I've annotated the manuscript (see scanned pngs of the first five pages), but I'm not familiar enough with them to use the official copyediting symbols (e.g. for capitalization or removing text); please let me know if you see margin notes or edits that you're having trouble interpreting. 

Finally, some places where my edits are ambiguous or incomplete (e.g. Vink citation in abstract) involve items where I've asked our other coauthors to answer or contribute something.  So, details are pending their replies. 


Title: Measuring mass-loss rates and constraining shock physics using X-ray line profiles of O stars from the Chandra archive

Author list: 

Emma E. Wollman (Caltech)
David H. Cohen (Swarthmore)
Maurice A. Leutenegger (Goddard & UMBC)
Jon O. Sundqvist (U. Delaware)
Alex W. Fullerton (STScI)
Janos Zsargo (Instituto PolitŽcnico Nacional, Escuela Superior de F’sica y Matem‡ticas, C.P. 07738, Mexico, D.F., Mexico)
Stanley P. Owocki (U. Delaware)

(Note that I've published papers with all of these authors in the last two years, so their detailed affiliations can be found in those papers - http://astro.swarthmore.edu/~cohen/papers.html)


Abstract: We quantitatively investigate the extent of wind absorption signatures in the X-ray grating spectra of all non-magnetic, effectively single O stars in the Chandra archive via line-profile fitting. Under the usual assumption of a spherically symmetric wind with embedded shocks, we confirm previous claims that some objects show little or no wind absorption. However, other objects do show asymmetric and blue shifted line profiles, indicative of wind absorption. For these stars, we are able to derive wind mass-loss rates from the ensemble of line profiles, and find values modestly lower than those predicted by Vink, and consistent with H-alpha if clumping factors of $f_{rm cl} \approx 20$ are assumed. The same profile fitting indicates an onset radius of X-rays typically at $r \approx 1.5$ \Rstar, and terminal velocities for the X-ray emitting wind component that are consistent with that of the bulk wind. Both of these results are in agreement with the predictions of numerical simulations of embedded wind shocks due to the line-driving instability. We explore the likelihood that the stars in the sample that do not show significant wind absorption signatures in their line profiles have at least some X-ray emission that arises from colliding wind shocks with a close binary companion.   


Intro: 

*Emma, it's well-written, but I think there are a few things we should add, and some minor restructuring that would be advisable.  I'm going to give you detailed edits on the marked-up manuscript and some suggested text, here.  I'm certainly open to further editing and rearranging by you, but let's use this as a starting point.  Let me know if you've got any questions about the thinking behind these suggestions. 

After Emma's 1st P, append: 

In recent years there has been increased awareness of large systematic uncertainties in many mass-loss rate diagnostics, primarily due to wind clumping, rendering the actual mass-loss rates of O stars somewhat controversial (e.g. Hamann et al. 2008). X-rays provide a good clumping-insensitive mass-loss rate diagnostic via the effect of wind attenuation on the X-ray emission line profile shapes. The asymmetry and blue shift due to wind attenuation was observed in the first Chandra and XMM grating observations to be less than expected (Kahn et al. 2001; Cassinelli et al. 2001), indicating lower mass-loss rates than those derived from Halpha estimates that ignore clumping.  Initial, quantitative X-ray line profile mass-loss rate determinations in zeta Pup show a mass-loss rate reduction of a factor of three (Cohen et al. 2010). A similar value is found for the very early O supergiant, HD 93129A, where the X-ray mass-loss rate is consistent with Halpha if clumping is accounted for (Cohen et al. 2011). 

Somewhere (ideal if it could fit into the first two paragraphs, maybe above, before "InitialâÉ", but I'm not sure): 

However some O stars showed X-ray emission lines that appear to not have any signatures of wind attenuation in their line profiles, which are generally symmetric and unshifted, and sometimes relatively narrow (Miller et al. 2002). 

Then when we talk about what we're going to do in this paper, we could note that only by fitting profile models can we quantify the extent to which the oddball stars really are incompatible with wind absorption, and by extension, with the standard EWS scenario. Something like: 

It is useful to subject even those stars where CWS X-rays are likely to be present to the same EWS-oriented line-profile analysis in order to quantify the line shape properties and specifically the degree of broadening and wind absorption in such systems.

Somewhere also (and maybe related to what's immediately above -- the O stars that don't show wind signatures) we should note that we exclude from our study known CWS binary X-ray sources (e.g. gamma2 Vel).  And we can perhaps suggest that some of the stars that show no wind absorption signatures in their profiles could also be affected by CWS X-ray emission but at a milder level (perhaps noting also Marc's recent paper showing that some close systems have soft emission and lower Lxs). 
**OK, this obviously should go in sec. 2.2; and most of it is already there, basically.  

**The big-picture question I still haven't answered in my own mind is how we should frame the analysis of the objects that really don't show much in the way of wind absorption signatures.  Should we take a "naive" view and apply the OC01 profile model to them and then derive Mdot from the taustar values and only then say, "oh, gee, look at this mysterious result"?  The other extreme would be to just say, early on in the paper, that ~half the stars in the sample don't show wind absorption signatures and then in Fig. 3, for example, we'd just show the results for the four stars -- eps Ori, zeta Ori, xi Per, 9 Sgr -- that are well behaved.