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    <h2 class="entry-title">
      <a href="https://keflavich.github.io/blog/tuesday-afternoon-talks.html" rel="bookmark"
         title="Permalink to Tuesday Afternoon Talks">Tuesday Afternoon Talks</a></h2>
 
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  <footer class="post-info">
    <abbr class="published" title="2013-10-01T16:15:00-06:00">
      2013/10/01
    </abbr>
    <address class="vcard author">
      By <a class="url fn" href="https://keflavich.github.io/blog/author/adam-ginsburg.html">Adam Ginsburg</a>
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  <div class="entry-content">
    <div class="section" id="pm-tobias-fritz-germany-nuclear-cluster-of-the-milky-way-15-5-minutes">
<h2>4:15-4:35 pm Tobias Fritz (Germany): Nuclear Cluster of the Milky Way (15 + 5 minutes)</h2>
<img alt="" src="https://keflavich.github.io/blog/iau303/images/fritz.jpg" style="width: 800px;" />
<dl class="docutils">
<dt>Model fitting of nuclear cluster: Sersic, etc.</dt>
<dd><ul class="first last simple">
<li>unusually bright nuclear cluster for its size</li>
</ul>
</dd>
</dl>
<p>Globular cluster origin of nuclear cluster</p>
<div class="section" id="questions">
<h3>Questions:</h3>
<blockquote>
<ul class="simple">
<li>Q: Round component consistent with inspiraling globular cluster.  What about
spectral properties?</li>
<li>A: No.  Metallicity difficult.</li>
</ul>
</blockquote>
</div>
</div>
<div class="section" id="pm-tuan-do-canada-measuring-the-physical-properties-of-the-milky-way-nuclear-star-cluster-with-3d-stellar-kinematics-15-5-minutes">
<h2>4:35-4:55 pm Tuan Do (Canada): Measuring the physical properties of the Milky Way Nuclear Star Cluster with 3D stellar kinematics (15 + 5 minutes)</h2>
<img alt="" src="https://keflavich.github.io/blog/iau303/images/do.jpg" style="width: 800px;" />
<dl class="docutils">
<dt>Dynamics of CMZ stars</dt>
<dd><ul class="first last simple">
<li>Massive black hole affects dynamics of a cluster</li>
<li>testing presence of cusps
+ old stars have no cusp
+ young stars have a cusp, but not dynamically relaxed</li>
<li>what is the true stellar density profile?
+ can't determine by counting
+ kinematics can help
+ old stars randomly distributed
+ young stars concentrated</li>
<li>did the stats right
+ no binning
+ individual likelihoods
+ unfortunately, this is new</li>
<li>flat slope, no anisotropy</li>
<li>correlation between parameters, particularly the slope and BH mass</li>
<li>edge of core poorly constrained</li>
<li>infalling IMBH or SMBH destroys stellar cusp
+ observational constraints on IMBHs poor</li>
<li>QUESTION: Do the fits improve at all if you impose a GC distance?
+ Answered: Can merge with PDF from stellar orbits</li>
</ul>
</dd>
</dl>
<div class="section" id="question">
<h3>Question</h3>
<blockquote>
<ul class="simple">
<li>Q: Inconsistent with 7.7 kpc distance to CMZ?</li>
<li>A: no, consistent within 1-sigma</li>
<li>Q: How do you contrain R_0 with this approach?</li>
<li>A: radial velocities give absolute scale.  Proper motions must also have
some scale.  Match the scales to get R_0</li>
<li>Q: Don't use any information outside 0.5 parsecs.  Shouldn't you include it?
I get the right mass if I do</li>
<li>A: Will help, but velocity dispersion dominated by nearest stars</li>
<li>Q: Anisotropy in cluster.  Get rid of red supergiants somehow?  Tangential
or radial?</li>
<li>A: Hard to know.  Very little anisotropy.</li>
</ul>
</blockquote>
</div>
</div>
<div class="section" id="pm-mark-wardle-australia-star-formation-within-0-5-pc-of-sgra-15-5-minutes">
<h2>4:55-5:15 pm Mark Wardle (Australia): Star Formation within 0.5 pc of SgrA* (15 + 5 minutes)</h2>
<img alt="" src="https://keflavich.github.io/blog/iau303/images/wardle.jpg" style="width: 800px;" />
<p>&quot;Highest I've ever been for a talk&quot;</p>
<dl class="docutils">
<dt>High densities needed to overcome tidal shear</dt>
<dd><ul class="first last simple">
<li>big cloud -&gt; Hoyle-Littleton accretion
+ self-intersecting orbit on the backside of the cloud</li>
<li>central hole because accreted?</li>
<li>high magnetic pressure in disk: 10x greater than gas</li>
<li>B-fields suppress fragmentation</li>
<li>Black hole takes bite out of cloud</li>
<li>optically thick disk: sigma T_eff^4 cooling
+ heating due to starlight, accretion</li>
<li>twisting knobs to figure out where accretion disk turns into fragmenting disk
+ inside, magnetically active / supported
+ outside (0.04 pc) fragmenting
+ further out: grav stable</li>
<li>maybe high accretion rate drove fermi bubble</li>
<li>accretion rate consistent with 10^6 Msun/Gyr -&gt; build Sgr A*</li>
</ul>
</dd>
</dl>
<div class="section" id="questions-1">
<h3>Questions</h3>
<blockquote>
<ul class="simple">
<li>Q Mitch: Grav unstable region globally unstable?</li>
<li>A: Has to do with the disk height.  h/r very small, not an issue</li>
<li>Q Fred Lo: We don't see any of this observationally.  All history?</li>
<li>A: Yes, this all happened a few Myr ago.</li>
<li>Q: Eddington accretion: what happens to rest of star formation and the disk?</li>
<li>A: I think it's OK - star formation 10^4-10^5 years, but dump time 10^5-10^6 yrs</li>
<li>Q: Bonnel &amp; Rice did simulations.  Why need more?</li>
<li>A: B-fields?  Eqn of state?  Radiative cooling?  Crazy enough initial conditions?</li>
<li>A Farhad: didn't include radial distribution of stars</li>
<li>Q: How do you start with 0-angular-momentum cloud?</li>
<li>A: Lots of junk around, maybe collisions do it.  I don't have a good answer.
Depends on how big a fluffy cloud you use.</li>
<li>Q Fred Lo: What observational signature remains?</li>
<li>A: Maybe kinematics</li>
</ul>
</blockquote>
</div>
</div>
<div class="section" id="pm-andrea-ghez-usa-probing-general-relativity-with-short-period-stars-at-the-galactic-center-15-5-minutes">
<h2>5:15-5:35 pm Andrea Ghez (USA): Probing General Relativity with Short Period Stars at the Galactic Center (15 + 5 minutes)</h2>
<!-- .. image:: |static|/iau303/images/ghez.jpg -->
<!-- :width: 800px -->
<dl class="docutils">
<dt>Why continue studies of GC stars?</dt>
<dd><ul class="first last">
<li><p class="first">Test GR</p>
</li>
<li><p class="first">Role of BH in galaxies</p>
</li>
<li><p class="first">Depth of potential 100x greater, on mass scale 10^6 larger than other tests</p>
</li>
<li><p class="first">simplest tests
+ Relativistic redshift (easy)
+ Precession of periapse</p>
</li>
<li><p class="first">SO-2 &quot;star of the show&quot;
+ next close approach in 2018.5
+ relativistic signal ~200 km/s
+ need very accurate keplerian orbit first
+ radial velocity from BrG</p>
</li>
<li><p class="first">absolute reference frame is tough
+ masers give the reference frame, but require larger field</p>
</li>
<li><p class="first">full orbital coverage with astrometry
+ 13-parameter model</p>
</li>
<li><p class="first">Systematic drift in reference frame
+ There is a major source of systematic error
+ Spatial variation in PSF (AO issue) is the worst systematic
+ drift term prevents bias
+ 5 km/s uncertainty projected by 2018</p>
<blockquote>
<ul class="simple">
<li>5-sigma GR detection</li>
</ul>
</blockquote>
</li>
<li><p class="first">GEMS to make reference frame</p>
</li>
<li><p class="first">TMT could do 2-yr orbits</p>
</li>
</ul>
</dd>
</dl>
<div class="section" id="questions-2">
<h3>Questions</h3>
<blockquote>
<ul class="simple">
<li>Q Ostriker: Could the SMBH be sloshing?  Can you allow for that?  What about acceleration?</li>
<li>A: Mark Reid did calculation.  Limit ~3 km/s for present BH velocity.
Problem: assume linear velocities, but that is not always a safe assumption.
If BH accelerating, would create &quot;nonphysical&quot; accelerations.</li>
<li>Q: Many things spiral into center, will lead to oscillations in BH motion</li>
<li>Q Stocke: How big an effect is blending with unseen stars?</li>
<li>A: We simulate it. But, trying to simulate something we don't understand.  &lt;0.1 mas</li>
<li>Q: Contributions from resonant relaxation, encounters with other stars.</li>
<li>A: Skipped the slide that shows this.  For GR, insignificant, but for
precession of periapse, have to worry.</li>
<li>Q: What about the velocity component?</li>
<li>A: small effect on velocity.</li>
</ul>
</blockquote>
</div>
</div>
<div class="section" id="discussion-section">
<h2>Discussion Section</h2>
<blockquote>
<ul class="simple">
<li>Q: IMFs shallower than salpeter.</li>
<li>A Lu: Hard to decouple from dynamical history.  push on spectroscopy to
lower masses.  Decouple young and old populations</li>
<li>A Fritz: instrument sensitivity limit... VLT can detect CO bandheads...?</li>
<li>How well do we know it's 2 populations, or maybe it's just 1 population?
Assumptions disagree, not measurements</li>
<li>Stocke: Background is changing in center.  Can you use fluctuation analysis
to determine brightness of lower mass stars?</li>
<li>Lu: Very challenging for young stars because they're a small fraction of the
total luminosity.   Foal(?) et al did good work on older star populations</li>
<li>Arches cluster: Hui Dong found 4 runaways of same mass as the 12 stars in
the Arches cluster.  Maybe as many runaways as cluster stars?  Half of
cluster stars kicked out.  Do dynamical models predict this?</li>
<li>[silence]</li>
<li>Find massive stars in &quot;other 3/4&quot; (I'm lost...). Need spectroscopy</li>
<li>Ghez: Role of binary stars in ejections.</li>
<li>Missing half of cluster mass?</li>
<li>Ghez: Role of interaction with black hole?  Clusters not evolving in isolation</li>
<li>Arches 2.5 Myr old.  Largest stars could just start... evolving?</li>
<li>Most difficult objects to explain are LBVs.  LBVs outside of cores of
clusters.  How do you get very massive binaries out of cores?
All LBVs found are outside cores.</li>
<li>Role of binaries.  New evolutionary models.  LBVs that must be &lt;2 Myr, WCs
must be &gt;4 Myr.  Contradiction?</li>
<li>New evolutionary models say many stars come from rejuvenation.  Massive blue
stragglers.</li>
<li>In situ formation?  What fraction should be expected to be formed in situ?</li>
<li>How confident are we about mass-luminosity relation for stars?</li>
<li>Lu: On main sequence, confident, but post-main-sequence is uncertain.  We
drop them in our analysis.  Pre-main sequence is a problem in Arches.
Arches fitted with only main-sequence stars</li>
<li>very difficult with rotation included</li>
<li>Distance to the Galactic center &quot;decreasing at an alarming rate&quot;.  Does determination
conflict with any other indicators?  What does that mean?</li>
<li>Ghez: Mark Reid likes lower R_0.  All consistent within uncertainties</li>
<li>Do simulations for S stars include interactions between stars?</li>
<li>Ghez: Not in most recent version, but in an earlier version</li>
<li>How does this test of GR compare with other tests of GR around Sgr A*?</li>
<li>Ghez: Event Horizon Telescope, GRAVITY.</li>
<li>Different systematics.</li>
<li>Are HST data consistent with BH at center?</li>
<li>Tuan Do: Same reference frame.  BH defined to be at center.  Velocity can
drift, but not position</li>
</ul>
</blockquote>
</div>

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