Observing Planetary and Pre-Planetary Nebulae with the James Webb Space Telescope

Round 1

Reviewer 1 Report

This work was presented in a meeting whose main aim was to discuss the prospects for research in the field of planetary nebulae in the coming years, and foster international collaborations to pursue it. The article fulfils this goal, presenting a detailed review of the main research lines in the field that  take advantage of the launch of the JWST, with quantitative information that will serve as a guidance for future proposals for the  telescope. I am happy to recommend it for publication as it is, with only a couple of minor suggestions:

1) as the article is focussed on binarity, a reference of the recent book by H.M.J Boffin and D. Jones "The importance of binaries in the formation and evolution of planetary nebulae" Springer Briefs in Astronomy, 2019, should not be missing".

2) A clearer description of parameters of  stars in Table 1 would improve its readability. Now these are somewhat hidden in the text, and some symbols are not clear (e.g. Mi, perhaps putting the post-AGB mass would be more appropriate).

Author Response

1) reference added

2) stellar parameters have been made clear, initial mass of Wd replaced by post-AGB mass

Reviewer 2 Report

The comments are in the attached file.

Comments for author File: Comments.pdf

Author Response

I have made changes as suggested. My responses below follow each point from the referee and are preceded by my initials RS

1) In the introductory section, (a) provide at least a little discussion of
alternatives to the binary hypothesis, (b) provide more clarity about what
sort of binary interactions may be needed for shaping PNe, and (c) do not
indicate that nearly all PNe have significant observed departures from
spherical symmetry. In addition, it may be useful to change the text
to acknowledge that the AGB shells are not all simply spherical as
the text strongly implies currently.

RS: modified appropriately; references were provided for details of the
several binary mechanisms mentioned (more details will take more page
space and appear unnecessary given that this is paper is a review of
what JWST can do).

(2) Either Table 1 should have a more representative PNe central star
temperature included or the text should be revised to indicate that
the contrast between the PNe central star and any low mass main sequence
companion is likely to be somewhat smaller than the Table indicates in
the general case. One may be able to select only hot central stars for
such an observation, but it seems more likely that stars would be
selected for observation by, say, K-band or WISE W2 brightness rather
than by the temperature. Some of the objects with very high estimated
stellar temperatures such as NGC 6302 have the star obscured or
have a very bright nebular background, and would not be suitable
candidates for such an observation.

RS: table and text modified appropriately to include a (more
representative) lower Teff CSPN.

(3) Figure 3 and the associated discussion in the text do not convince
me that the type of modelling described in the review is going to give
us significant information about the dust types and properties in these
objects. I am of the option that the author needs to describe things
better to make the point, and not to seemly gloss over some of the
difficulties and limitations involved. I am not saying that the author
is trying to mislead, but just that the tone here seems more optimistic
than I think is warranted.

RS: text modified to elaborate on how SED modeling of JWST spectra and
photometry can help constrain specific properties of the circumstellar
region.

(4) The summary paragraph seems weak to me, and I recommend that it be
improved.

RS: text improved.
--------------------------------------------------
Detailed comments:
page 1, line 4
There is still considerable debate in the literature about whether the
AGB stars are the main source of dust in the ISM; massive stars and
supernovae may contribute the larger share of the material. In any case
it is clear that the ISM dust is heavily processed. I suggest removing
the work "dominantly" here.

RS: done

line 7
"round" should in my view be changed to "spherical" Recent indications
suggest that AGB envelopes are not as spherical as had been assumed in
the past. See for example Randall et al. (2020), A&A, 636, A123. It is
at best somewhat imprecise to present a simple picture that AGB dust
shells are spherical and then suddenly in the post-AGB phase it changes,
as is implied here. The above paper is just one of a number of results
in the last decade or so that indicate that the AGB dust shells are not
always close to spherical.

RS: we have kept the word "round" as it is less precise than spherical,
so encompasses AGB envelopes with some minor departures from sphericity.
We have added a fotnote to Section 1 that mentions that there are well
known objects whose CSEs are not round.

line 23/24 ".. a vast fraction of stars...affected by strong binary
interactions"
I object to this statement. Yes a large fraction of stars, say 60% to 80%,
are in binary systems or more complex stellar systems, but there are plenty
of isolated stars or stars with only very wide companions. There is clearly
a difference between a majority and "a vast fraction". Further, it is not
clear that wider binaries will produce the strong interactions that are stated
to be important here. Yes of course one can point to many instances where
strong binary interactions appear to be shaping PNe and PPNe but one can
also assemble a list of a fair number of these objects that appear to have
more circular morphology as we see them. It is not clear to me that one
can make this type of sweeping statement in the face of images of the sub-set
of PNe that have what appear to be close to spherical morphology. Objects
such as Abell 8 and Abell 39 are good examples of what I am refering to.
Such objects are a minority, but not so rare as to need a lot of work to
find.

RS: We have qualified the fraction likely affected by binary
interactions by adding the percentages given by the referee.

A secondary concern here is what is the author thinking of in terms of binary
interactions? I am thinking in terms of stellar binaries. Of course one can
make the case for interactions with planets as well, whether hot Jupiters or
other such things as we commonly see in exoplanet surveys. If one extends
the case to any companion one then has the difficult question of hot big a
planet may need to be to produce a significant morphological influence on
the host star in the AGB or post-AGB phase. I am rather doubtful that an
earth-like planet could influence PPNe or PNe morphology, for example. It
appears that the author is only thinking of stellar companions, but it would
be good to clarify this one way or another.

RS: We have added a footnote about this.

Also, a general comment: whilst binarity is typically thought to be the
most likely cause of the aspherical structures there are suggestions that
other processes may also be a cause (e.g. magnetic fields) and in a review
it would be better to at least mention these alternatives rather than
describing only the binarity hypothesis.

RS: We have added mention of alternative hypotheses.

Page 2, line 37
line 51
typographical error "include)the"
"6.5-meter diameter"Since the JWST mirror is segmented it does not,
strictly speaking, have a diameter. It may be better to quote the light
gathering area of the segmented mirror which is estimated to be 25.306
square meters, or say "6.5 meter wide" instead. Since the clear aperture
is quoted as 25 square meters on line 54 I suggest the latter change.
Yes I know that a number of the JWST pages refer to the mirror as being
6.5 meters in diameter. Hence the author is free to ignore this detail.

RS: fixed as suggested.

line 57
"...at 1.5x10^6 km..."
This is the (approximate) distance from the Earth and should be stated
as such. The telescope is not going to be in orbit around the Earth, but
around the Sun. Saying "..at 1.5x10^6 km from the Earth..." would be
preferable.

RS: fixed as suggested.

line 78
"...4QPM (4-quadrant phase mask)..."
It would be better to reverse this to "...4-quadrant phase mask
(4QPM)...".

RS: fixed as suggested.

line 82
"...the sky saturates the detection in a >0.18'' exposure."
This does not make sense to me. I am guessing that it saturates in a > 0.18
second exposure. Why it is called arc-seconds not seconds is unclear.

RS: fixed (was a typo).

Page 3, line 89
The slew time is quoted as 30 min here. This is the time used in the
Astronomers Proposal Tool as a generic mean slew time. It is the
estimated slew time for a 53 degree slew on-sky, and should be noted as
such. Slews may be in general be shorter than this because the
scheduling will attempt to minimize slews.

RS: fixed as suggested.

Page 4, Table 1
While we know that PNe can have stellar temperatures as high as 100000 K
to 160000 K, the values given in this Table, such hot PNe central stars
are not the majority. If one looks at Villaver, Stanghellini, and Shaw
(2007), ApJ, 656, 831 for example of the 30 PNe central stars in the LMC
that have temperature determinations in their Table 4 there are 6 or 7
objects with temperatures above 100000 K depending on whether one takes
the He or H Zanstra temperature. The average temperature of the stars
below 100000 K is 64000 K or so, if one believes the HeII Zanstra
temperature, and is lower than this if one uses the H Zanstra
temperature. It would be more representative to do the calculations in
Table 1 for say 65000 K and 100000 K rather than 100000 K and 160000 K.
Or one might add a lower temperature to the Table. The main point is,
40% excesses as in Table 1 for the higher temperature at 5.6 to 10
microns will be unusual not the norm, and something more like 5% to 10%
excesses will be far more common in the type of example that is being
presented here unless one selects only the hottest stars. Asmany of the
interesting and well-studied PNe have stars that are cooler than 100000
K they would likely be targets for such an observation.

RS: fixed as suggested.

Page 5, line 142
"([47](Setal17)" needs a closing bracket. I also think one should find a
better abbreviation for the paper rather than just using the first letter of
the first author's name. However that is a matter of taste, and I see that
the author has done this in previous papers.

RS: we have kept Setal17 as it has been used in orebious papers.

line 151 "magellanic" should be "Magellanic".

RS: fixed as suggested.

line 155 grazing envelope ejection was abbreviated as GEE on line 40 so it
should not be repeated here.

RS: fixed as suggested.

line 173 "few" should not be in italics here "(~ few x 10^3 years)".

RS: fixed as suggested.

line 174 It is my experience that trying to fit a 2-dimensional or
3-dimensional dust shell model to either photometry or spectroscopy
without any constraints from imaging will not produce a unique result.
The parameter space is large and one does not get a good "mapping" from
the spectral characteristics alone to the parameters. line 177 In
various cases where PPNe are known to have circumstellar disks, such as
in the Red Rectangle, the dust grains therein appear to be large
(because the absorption is relatively independent of wavelength). The
same thing is concluded for the Boomerang Nebula in the Sahai,
Vlemmings, and Nyman (2017) paper, although that is said to be post-RGB
not post-AGB, so I am not entirely convinced by a model for a disk that
uses very small grains as in model 2 in Figure 3 and in the discussion
here. In any case the large discrepancies of both models in Figure 3
with the 8 micron point undermine any claim that these models produce a
good fit. One might argue that the 8 micron measurement and the 12
micron upper limit (presumably Spitzer IRAC and WISE respectively)
suggest a strong, discrete feature at around 8 microns, but if the
spectrum is dominated by strong PAH emission and this is due to the
7.7/8.6 micron features then both models using silicates are not
suitable. In general Figure 3 does not seem to me to provide a strong
support to the argument that we can derive physical properties by
fitting photometry as is stated on line 174. Things will be improved if
one has spectroscopy rather than photometry over the wavelengths say 8
to 20 microns as MIRI can provide, but this is not really made clear in
the text. With a spectrum over the area where features are predicted the
constraints will be much better than from photometry alone. I suggest
that the author think about revising the text to make this clearer. In
those cases where the spectrum has no diagnostic features of the main
dust component, as in cases where amorphous carbon is thought to be the
main dusttype, even with spectroscopy the fitting is likely to run into
uniqueness issues where a number of different models fit the data
equally well depending on what sizes or cross-sections are assumed for
the dust grain. One aspect of this lack of uniqueness is that often the
same object is fit by different groups and the parameters that result
are wildly different from one group to another in papers in the
literature. Hence it is difficult to determine what the properties of
the objects actually are.

RS: We had already mentioned in detail the advantage of using JWST
spectroscopic observations. Text has been improved to make this clearer.
The figure/model is simply representative of what can be done at present
with photometry alone (but is based on an extensive modeling effort
which part of a paer under preparation), and how spectroscopic
observations would improve the constraints from models.

Note that while "PAH" is used here this not described in the text
until page 8.

RS: fixed as suggested.

Page 6, Figure 3
Why does the y axis label spell out Watt but abbreviate meter in m^2?
Also it would be better to have larger axis labels, tick labels, and
text within the plot so people can read it without magnification. In the
caption "in prep." might has well be put as "in preparation", and in I
am of the opinion that should be in normal text rather than in italics.

RS: fixed.

The acronym NRM in the Figure caption is not defined as far as I can see.
While usage of this abbreviation for Mathis, Rumpl, and Nordsieck (1977) is
common in the literature it still needs to be defined.

RS: fixed as suggested.

Figure 4
In the caption the abbreviation AMI is used for Aperture Masking
Interferometry, but where the term is introduced on line 183 the
abbreviation is not given. Also, it is better to say "three months"
rather than "1/4 of the Webb orbital period".

RS: fixed as suggested.

Page 7
line 214
Where "IRAS 16432-3814" is mentioned, make sure to use a minus sign not
a single dash. Both instances on the page seem to have a dash, which is
normally due to using 16432-3814 rather than 16432$-$3814 in LaTeX. The
start of the sentence "Unless this object is unique," is not needed. One
can just say "Such rings or other extended cool, dusty, structures
probably exist around other PNe."

RS: fixed as suggested.

Page 8, lines 216 to 220
The difficultly with making dust radiative transfer models of PPNe and
PNe for predicting MIRI observations is that we do not know if the
structure thatwill be seen is on the same angular scales as, say,
existing HST images of such objects. In general one finds that with
better angular resolution the nebular structures appear fractal and the
structure that is seen remains at the limit of the image resolution. One
would not have predicted the fine structure seen in the PN IC 418 from
the optical and infrared images that we had from the ground, and it is
not certain that the HST images actually fully resolve the structure. In
any case I am not aware of any instances where dust shell models are
made with structure on this angular scale. But the saturation, if is
occurs, will happen where these small scale structures are seen. I do
not have specific recommendations about how such considerations may
affect the text here, but the author may wish to be a bit more cautious
about such statements.

RS: fixed as suggested.

Page 8,
line 228
It is often assumed that amorphous carbon is the dominant type of dust
around carbon stars, but we do not really have proof of this. We know
that many of the stars have SiC grains because of the 11.3 micron
feature, but the relation between SiC and the hypothetical amorphous
carbon is quite unclear because amorphous carbon has no spectral
features we can use as diagnostics. It may be better to qualify this to
say that "amorphous carbon is thought to be the major constituent of
circumstellar dust in carbon-rich stars on the AGB". The extra grain
might be graphitic grains or hydrogenated amorphous carbon or something
more soot-like or even coal-like. All of these have been proposed in the
literature.

RS: fixed as suggested.

line 243
Given that there are thousands of DIBs and only 2 of them are associated
with C60+ I would say that this is overstated. There have been a number
of papers relating one or two of the DIBs with various molecules that
are just as convincing as this identification, but it begs the question
of what is producing all the other DIBs. This has always been the issue
with the many proposed DIB carriers; they never can explain why one or a
handful of DIBs match and 1000 others do not. As a general comment here,
I am of the opinion that the MIRI/NIRSpec IFUs may be much more
important in the study of the dust in these objects than is indicated on
lines 252/253. As well as having the prospect of resolving small
structures like a disk that may not be seen from the ground, there is
the question of small structures and variations in dust properties in
the dust shell generally. There have been many attempts to spacially
separate different dust components in PPNe for example, but ground-based
attempts to do this have generally been unsuccessful. The results in
Figure 8 are very nice, but they are unusual in showing any separation
of different components. There is more discussion along this vein in
section 3.4, but that seems to be concentrating on nebular diagnostics
not the PAH features themselves or other dust-related features. If we
are able to spacially resolve differentdust or PAH/C60 components in PNe
or PPNe this will provide important constraints on the formation and
evolution of carriers of these different spectral components.

RS: fixed as suggested.

Page 10, line 268
"NIRCAM" -> "NIRCam"
Figure 9 caption: Needs a closing bracket. As usual I think that various
terms in italics should be in normal case here..."left", "right", "priv.
comm.". Also, the caption should note that the various JWST instrument
mode fields of view are superimposed on the HST image. The NIRSpec boxes
in the Figure should be noted as for the IFUs not long-slit or
micro-shutter array spectroscopy. One could argue that using the NIRSpec
MSA to probe many globules would be an alternative way to assemble
detailed information about the photoionization regions, but this is not
indicated in the text.

RS: fixed as suggested.

lines 280 to 285 The summary paragraph seems to me to be rather weak.
One might indicate in a general sense some of the highlights from the
previous sections here, if briefly. The highlights might be searching
for binary companions, high angular resolution studies of the dust
shells and especially disks, and mapping nebular line diagnostics in the
near-infrared to name three. This need not be very long, but just give a
flavour of the high points of the previous discussion.

RS: fixed as suggested.

line 413
In the copyright notice, "authors" should be "author".

RS: fixed as suggested.

Reviewer 3 Report

The paper is nicely written and structured and comprehensively provides all the required information and aspects of the reviewed topic. I strongly recommend it for publication after implementing the following minor comments in the manuscript:

Line 37: the bracket is placed in the wrong line. It should be places at the  line 36

Line 39: dpAGB, missing the explanation of the abbreviation: “disk-prominent AGB”

Line 61: explain the acronym “PSF”

Line 66: 2.0.1 - - > 2.1

Line 79: precision -- > precise

Line 88:expensive a due to -- > expensive due to

Line 89: post-RGB, provide the explanation of the abbreviation

Line 97: Objects -- > objects

Line 98: Galaxies -- > galaxies

Line 105: delete the double reference “[8]”

Line 107: missing bracket

Table1: Provide some information about the MS star properties i.e. its initial mass

Line116: The bracket should be closed

Line 122: place the bracket before the full stop

Line 129: resulting -->  result

Line 129: explain the abbreviation KBOs (Kuiper Belt Objects)

Line 141: Red Giant Branch (or RGB) -- > RGB (the abbreviation is provided in line 89)

Figure 2: Explain in the caption for what stands the solid blackbody line.

Line 145: the phrase “but the Boomerang’s luminosity…” is rather misleading. I think the author wants to say ““but the Boomerang’s central star luminosity…”

Line 155: delete the double comma the end of the line

Figure 3, caption: delete the double “and” at the 1rst line

Figure 3, caption: Ossenkopf (1992) should be cited properly

Line 258: photodissoication - - > photodissociation

Figures 6,7,8 and 9: a reference about them in the manuscript would help the reader to follow the author's line of argumentation.

Author Response

Changes have been to address as necessary to address all of the points made by the referee, and correct the errors. Please note, in regard to this comment:

"Table1: Provide some information about the MS star properties i.e. its initial mass

RS: initial mass (its a low-mass star on the main-sequence so its mass had not changed), Teff, L were all provided in text, but maybe not clear