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         title="Permalink to FeO Nondetection in Orion">FeO Nondetection in Orion</a></h2>
 
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    <abbr class="published" title="2018-10-14T15:09:00-06:00">
      2018/10/14
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    <address class="vcard author">
      By <a class="url fn" href="https://keflavich.github.io/blog/author/adam-ginsburg-adamgginsburggmailcom.html">Adam Ginsburg (Adam.G.Ginsburg@gmail.com)</a>
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    <p>I had a Cycle 3 ALMA program <a class="reference external" href="https://almascience.nrao.edu/observing/highest-priority-projects">2015.1.00262.S:
Digging for rusty bullets at an explosion site</a>
that aimed to detect <a class="reference external" href="https://en.wikipedia.org/wiki/Iron(II)_oxide">ferrous oxide, FeO</a>
in the shocked outflows of the Orion nebula.</p>
<p>I haven't published anything on this data set because it resulted in a fairly
boring non-detection.  You can find the source code to retrieve and process
the data from <a class="reference external" href="https://github.com/keflavich/FeO_2015.1.00262.S">here</a>.
The nondetection is several orders of magnitude deeper than previous
ones, but to demonstrate this definitively, we need to do some more modeling
work, which my co-I's and I have decided isn't worth the time, since we're
all flooded with very exciting new ALMA data that has interesting detections
in it (see salts soon).</p>
<p>In brief, we were looking at a location where we know molecules (H2, molecular
hydrogen) and gas-phase iron (Fe II, as seen in in the [Fe II] 1.64 micron lines)
are approximately coincident.  The most likely (and broadly accepted)
explanation is that dust particles are being destroyed (sputtered) in the
high-velocity ($&gt;30$ km/s, up to about $100-200$ km/s) shocks produced in an
outflow.  Since iron in the interstellar medium mostly lives in the cores of
dust grains, we thought it might be released in a molecular form detectable by
ALMA before being split into an atomic, ionized form.</p>
<p>Despite having a good location and a sensitive observation, we didn't detect
any.  It might mean that iron is mostly in a different molecular form, or it
might mean that when iron gets sputtered out of grains, it never goes into
a molecular form at all, instead dissociating straight into atomic form.</p>
<p>There are a few things that, with infinite time, I would do with this data set:</p>
<ol class="arabic simple">
<li>Come up with a formal upper limit on the FeO abundance.</li>
<li>Compare the lines we did detect to the outflows and see if we can better
constrain their physical conditions</li>
<li>Catalog the stars and publish the catalog for comparison to other data sets.
(actually, this is done: <a class="reference external" href="https://github.com/keflavich/FeO_2015.1.00262.S/blob/master/tables/gaussian_fit_table.ipac">this table</a>
contains Gaussian fits to each of the stars in the continuum image (<a class="reference external" href="https://github.com/keflavich/FeO_2015.1.00262.S/blob/master/analysis/contsource_centroids.py">source</a>).)</li>
</ol>
<p>These figure show the apertures we used to extract spectra and search for the
lines, then the spectra of different species for one of the apertures.  The
background image is the H2 (orange) + FeII (cyan) + K-band (mostly white) I
made for my <a class="reference external" href="http://adsabs.harvard.edu/abs/2015A%26A...579A.130B">2015 paper with John Bally</a>.</p>
<img alt="" src="https://keflavich.github.io/blog/images/feo/aperture_overlays.png" style="width: 600px;" />
<img alt="" src="https://keflavich.github.io/blog/images/feo/BulletHeads4_alllines.png" style="width: 600px;" />

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