To:  Dr. Judith Pipher
     Editor, AJ

Subject:  AJ manuscript AAS06497
          "Kinematics of the Horsehead Nebula & IC~434 Ionization Front in CO and C+"

Dear Judy 

I am re-submitting the above mentioned manuscript. We thank the referee for his comments and corrections.   Below,  I describe the changes made to the paper.  The changes (except typos) are highlighted in the text using bold font, {\bf }

- The \software command has been implemented as required. 

Short reply to referee - 
GENERAL COMMENTS & ABSTRACT:

- The paper presenting analysis of the same data set (Pabst et al. 2017) is now cited in the abstract and text.  At the end of our manuscript, we have inserted a brief comparisons between Pabst et al. and our study. 

- The emission line is now referred to as [CII] and the species as CII. 

1. INTRODUCTION: 

- I have inserted references in the introductory paragraph as suggested by the referee. 

- Added discussion of the FUV luminosity of sigma-Orion and the FUV flux incident on the Horsehead in Habing-field units.

- Transition labels have been added to the CO and C(18)O observations discussed in the Introduction.

- The earlier work by Zhou et al. (1993) is now briefly described.

2. OBSERVATIONS


- A new paragraph describing the software tools used has been added.

3. OBSERVATIONS (RESULTS):

- Regarding the suggestion that we should show some spectra, we would like not to do this for several reasons:  a) We already have an abundance of figures, and b) Figures 5 and 5 show the spectra in the form of spatial-velocity diagrams which clearly illustrate the cloud kinematics and intensity structure over representative strips.  These presentations convey more information than plots of individual spectra.  c) We will make the data cubes available so interested readers can plot their own. d) Pabst et al 2017 present a few spectra from the same data.

However, to address this need to show the kinematic differenced between C+ and CO, we added 8 R.A-velocity cuts comparing C+ in green with  CO 3-2 in red (Figures 12 & 13).  These Figures illustrate the complex kinematics, in CO and C+. 

- We refrain from a detailed discussion of the CO 3-2/2-1 since the  data were obtained with different telescopes and the relative calibration of intensities is highly uncertain.   
In the Horsehead, I(CO 3-2) ~ 6 K; I(12CO 2-1) ~ 15 K while I(13CO 2-1) ~ 7 K.  A brief comment mentioning this has been added to the text.       

- There is weak [C+] emission from the HII region;  this is discussed in the text in bullet 6) in Section 3. RESULTS.  This section has been expanded to discuss the differences in line properties. 

- A comment about Figure tables.  Unfortunately, our software generates (m/s) units on the spatial velocity diagrams.  It is difficult to convert the spatial velocity axes into the more convenient km/s units;  thus, we would like to keep the current labels.

- We added a new Figure showing the locations of the areas tabulated in Table 1. 

- Table 1 had been re-done and re-formated to show the coordinates  of the regions, the region radii, and the the line parameters.   Since we do NOT have a direct measure of the temperature in the PDR, we elected to estimate column densities using a wide range of temperatures and densities which bracket the likely values.
  


Thank you.  Best,

John Bally