2019 SB Gaia Sprint

Wrap-up — KITP — 2019-03-29

Hans-Walter Rix (MPIA, Heidelberg)

Learned many things, among them

  • the small-scale structure of phase-space -- abundance space is strong and detectable -- Kamdar, Coronado
  • the phase-space spiral twists, as it should -- Johnston

  • wide-binary twins are real (& probably very useful) -- El-Badry
  • GDR2 as a time-domain survey can and will be ``calibrated’’ -- Casey
  • Gaia preselection of close, eclipsing binaries works perfectly -- Schwab

Homework: help Anthony Brown find X MEuro to “do the selection function”

Ellianna Schwab Abrahams (UC Berkeley, CTDI)

What Worked (Time Domain Gaia):

What Didn’t Work (yet!):

  • Measurements of flux RMS detect variability! Pulled lightcurves out of TESS for candidate variables confirming close eclipsing binaries, RR Lyrae and CVs. (With Mowlavi, Rix and Brown)
  • Built a DSD neural net to predict RVs. RVs correlate enough with other features to predict within largest uncertainty (With Jamal, Hogg and Casey)
  • Need to add Bayesian
    framework to
    improve network


CV in both TESS + Gaia Alerts

Thanks Rix, Brown, Casey, Hogg, Price-Whelan,
Rimoldini, Brandt,
Gaensicke & Gaia DPAC!

Alice Quillen (Rochester)

I tried using current velocities and backwards orbits of moving groups, listed by Gagne+18 and with ages less than 60 Myr years, to see if the stars in them formed near spiral arms and find out where were the arms?


Young moving groups seem associated with the “Local spur”. This arm may have wound up -- or two different armlets are required.

Now 60 Myr ago


Also Learned:

-Ringing might have also been caused by a dwarf plunging through the center of the Galaxy.

-VVV measuring proper motions in the bar’s X (resonant model for vertical heating?)

Galactocentric angle degrees

Joel C. Zinn

Ohio State University

  • Responded to referee report on comparison of Gaia distances/radii to asteroseismic distances/radii!
  • Learned about many cool things in discussions with people, e.g.:
    • Halo is not relaxed (Quillen)
    • White dwarf merger rates are consistent with Q branch number density… no Kozai?! (Cheng)
    • Halo stars have unexpected abundance patterns (Matsuno)

Semyeong Oh (Cambridge)

Linear velocity field of 40 m/s/pc

may be detectable with

astrometry + DR2 (statistical) noise

+ 30% RV (1 km/s uncertainty)

for the Hyades cluster.


  • important systematic bias for proper motions of bright sources
  • T. Brandt’s Hipparcos-Gaia calibration removes this and reduces the precision by 5-10 for Hipparcos sources.

Christina Eilers

Max Planck Institute for Astronomy

  • blue and red patterns correspond to density fluctuations in the disk — spiral arms?
  • quadrupolar velocity structure is seen in multiple models of the Galactic bar.
  • vertical & radial velocity dispersions increase where we expect the bar to influence the stellar dynamics.

Thanks to Sarah, Hogg, Ortwin, Chervin, Larry & Hans-Walter

Sarah Pearson

(Flatiron Institute, CCA)

Compared the velocity tensor elements of Eilers’ & Hogg’s APOGEE/Gaia data to the velocity tensor elements of simulated bars

I did this

I learned

SGR induced

(C. Laporte)

….what we should expect to see in the various terms of the velocity tensor

We see the bar in APOGEE/Gaia data and it looks similar to simulated bars

[Will insert plots]

Comparison to Eilers’ plots

In situ

(E. D’Onghia)

with Eilers, Hogg, Laporte, D’Onghia, Rix

and advise from Price-Whelan, Gerhard, Widrow

David W Hogg
(NYU) (MPIA) (Flatiron)

The radial-velocity variations we see (with APOGEE & Gaia) in the Milky Way disk are going to provide evidence for density variations.
(Eilers, Pearson, Laporte)

Related to this, I formulated a method to use disk simulations to build an
empirical-theoretical model of disk patches.

If we are seeing the bar at the Galactic Center, it is at the wrong angle!
(Gerhard, Widrow, Pearson, Laporte, Rix)

We need to sharpen up a proposal to build a set of Gaia selection functions.
(Brown, Fouesneau, Rix, Casey, Price-Whelan)

Patrick LaChance

(University of Wisconsin - Madison)

What I did:

Compare the contributions of different sectors of the U-V plot in different volumes to begin to disentangle moving groups from open clusters

What I Learned:

Getting to work on astronomy research all day is even better than I thought

Cosmological galaxies are not

in an inertial frame

Robyn Sanderson


What I learned this week:

Velocity of disk COM relative to halo COM

Acceleration of COM calculated different ways




So….where are we building our models again?

….even when there’s no LMC...

Position of disk COM relative to halo COM

theme of the week: diffuse disequilibrium

(in science and life)

  • Reconstruct gravitational potentials of MW-like galaxies/halos using Latte simulations (Sanderson, Vasiliev)
    • Initial analysis (see right) is a best case scenario: no M31, no LMC
    • Milky Way is not an inertial frame
  • Use simulations to test effects of LMC on stellar halo (Cunningham, Sanderson)
  • Use simulations + synthetic Gaia surveys to reconstruct 3-D dust distribution (Anderson)
  • Public service notice: use cosmological Gaia mocks!

Andrew Wetzel (UC Davis)

(stolen from Sanderson)

Siddharth Mishra-Sharma (NYU)


  • How to perform Gaussian process regression on a sphere (with lots of help and code from Tim Brandt and Hamish Silverwood).


  • Constructed model of the Gaia DR2 quasar proper motion field with GP regression.
    • Can use to characterize measurement systematics?
    • But not yet to look for substructure!
  • Used this method to construct un(??)biased power spectrum estimator.

Alexandra Borukhovetskaya(University of Wisconsin - Madison)

undergraduate student working with Elena D’Onghia

What I came to do:

Learn Arcturus ages, metallicities, and clustering techniques.

What I did:

  • Found ages and metallicities for known members of Arcturus.
  • Ran algorithm (SNN) with adjusted parameters to find several new candidate members.
  • Compared ages and metallicities of candidate members to those of known members

What I plan to do in the future:

Continue modifying and improving the algorithm to find new members and gain insight into the origin of Arcturus.

Harshil Kamdar (Harvard)

What I Did: finished writing up a paper on v wide (>10 pc) co-moving pairs due to disrupting star clusters in the disk, worked w/ Coronado & Rix on interpreting small-scale structure in combined chemodynamical space (Gaia+LAMOST).

What I Learned: sampling points to follow a correlation function is hard

Hamish Silverwood

ICC University of Barcelona


-Red Clump & Giants RVS samples corrected using cross match to 2MASS - thwarted at the last minute by a string encoding problem in Pandas.


-GPflow & GPyTorch running in 2D with heteroskedastic noise (i.e. uncertainties - surprisingly non-trivial).

-GPR on e.g. vRvR data (left) - needs work.

-Derivatives of latent function f(x) with GPflow machinery (1D example above) - still quite rough, red line should match green line.

Anthony Brown (Leiden Observatory)

What I did

  • Struck gold!
  • Put my RUWE code on github
  • Answered tons of questions on Gaia DR2

select source_id, ra, ra_error, dec, dec_error, parallax, parallax_error, parallax_over_error, pmra,pmra_error, pmdec, pmdec_error, ra_dec_corr, ra_parallax_corr, ra_pmra_corr, ra_pmdec_corr, dec_parallax_corr, dec_pmra_corr, dec_pmdec_corr, parallax_pmra_corr, parallax_pmdec_corr,

pmra_pmdec_corr, radial_velocity, radial_velocity_error,phot_g_mean_mag, phot_bp_mean_mag, phot_rp_mean_mag, bp_rp, g_rp, bp_g,

2.5/log(10)*phot_g_mean_flux_over_error as phot_g_mean_mag_error,

2.5/log(10)*phot_bp_mean_flux_over_error as phot_bp_mean_mag_error,

2.5/log(10)*phot_rp_mean_flux_over_error as phot_rp_mean_mag_error,

sqrt(astrometric_chi2_al/(astrometric_n_good_obs_al-5)) as uwe

from gaiadr2.gaia_source

where parallax_over_error>5

and radial_velocity is not null

and astrometric_params_solved=31

and rv_nb_transits > 3

Do some radial velocity cleaning...

What I learned

  • Phase spiral is not ‘just moving groups’
  • Some of use do want to work on the selection function
    • Look for funding
  • So many creative ways to use the Gaia data!

Cecilia Mateu (UdelaR)

What I Did+Learned:

  • Provided astropy reference frames for streams in galstreams library (+Adrian Price-Whelan)
  • Made galstreams Python 3 compliant
  • Many RR Lyrae in Pal5's tails
  • Many streams are (very) difficult to confirm, but many (some?) do show up in PS1 photometry (w. Nora Shipp, A. P-W, Sarah Pearson, Giuliano Iorio)
  • Learned many cool astropy tools


  • Gaia RR Lyrae Gold!

Sukanya Chakrabarti (RIT)

Worked on : what caused the disturbances in the outer HI disk of the Milky Way ?

Sampling Gaia PMs

Zhen Yuan

(Shanghai Astronomical Observatory)



  • Got Member Probability of each star around

Pal 5 from Photometry

Sprint & Eugene Vasiliev (IoA, Cambridge)

Thx for the advice from Nora, Adrian, David, and Giuliano !

Motivation and Future Plans:

  • Get tail members with 6D → Disruption Process
  • Hunting for UFD

You will see magic happens after combining probabilities from photometry & astrometry in Eugene’s slide!


  • How to execute a project efficiently
  • I need another PhD in Astronomy

  • Happened to find Phase-Space Slices of Gaia Sausage using StarGO https://github.com/salamander14/StarGO

Sprint & Tadafumi Matsuno (PhD student, NAOJ) and Kohei Hattori (U of Michigan)

You will see what we can infer from the slices in Kohei’s slide!

Eugene Vasiliev (Institute of Astronomy, Cambridge)

Search for tidal tails around globular clusters with Gaia astrometry and DECam photometry

With Zhen Yuan and valuable advice from Adrian, Ana, Sarah P., Jason H., Nora, Giuliano

Pal 5

NGC 288

Learned Gaussian ProcessesⓇ, Matched FilteringTM.

Developed the membership selection pipeline combining Gaussian Mixture for parallax+PM and Matched Filtering for CMD

Re-discovered tails around Pal 5, NGC 288.

Not found anything around NGC 5897, NGC 7089, …

Plan to continue the search for other cluster tails...

Kohei Hattori (U of Michigan)

phase-space slice of the Gaia Sausage

With Tadafumi Matsuno (PhD student, NAOJ) and Zhen Yuan (SHAO).

StarGO package (by Zhen Yuan) is powerful in finding substructure.

Red: Solar neighbor / Black: total sample

Elena D’Onghia (work with Boquan Chen)

We use SNN algorithm (Chen et al. 2018) to cluster in 5 dimension to

rebuild Orion. Two clumps are newly discovered.

This approach opens us the possibility to study how star formation occurs in Orion.

This is an example of the superiority of SNN on DBSCAN.

  • Two clusters one dense one less dense

(2)-(3) DBSCAN recoves one group

(4) SNN recovers both groups

Lorenzo Rimoldini (University of Geneva, CH)

Classification of variable objects in all Gaia DR2 (without time series):

> better than you might expect

>> it can be useful before DR3 (SDSS-V, TESS, ...)

>>> help in gathering rare variable classes

>>>> millions of new variable candidates soon!

Learned about streams, complementary data sets, interesting color-color plots combining optical, IR and radio, features of AGBs in the radio band, some details about Gaia as well :)

Please email me by the end of April if you want to make sure your class of interest is included!

Giuliano Iorio (Institute of Astronomy, Cambridge)

  • Pal 5: 2 RRab, 4 RRc
  • Stream: 16 RRab, 6 RRc

Membership likelihood for RRLs in Pal 5 stream

Thanks to Cecilia, Adrian, Nora, Eugene, Elianna for advice and useful discussions

What I did:

Learned: Galstreams, what is a GP, a lot of interesting way to use Gaia Data.

What I found:

A lof of RRLs!!

To do: Improve background model, analyse other streams, Pal5 stream model.

No other variables

Larry Widrow

Queen’s University

Productive discussions on phase space spirals with Kathryn, Chervin … radially plunging satellites with Heidi, and GP blah blah blah with Lauren and Hamish, to be continued in Gaia “brisk walk” during and after the conference

Gauthier, Dubinski, LMW 2006

LMW, Chequers et al 2014

Spekkens & Sellwood 2007

With Hogg:

Infer surface density from moments of the velocity field --- here, a linear model on pixels of simulation.

Probably makes more sense to go after the FR , Fphi...learn rather than assume the Jeans/CBE (cf. Alice and Hamish)

<Vz> <Vphi> <zVz>

<Vz^2> Var(Vphi) <VRVphi>

Density model residual

Josh Simon

Carnegie Observatories

Thanks to:

Lauren Anderson

Anthony Brown

Andy Casey

Kohei Hattori

Tadafumi Matsuno

Zhen Yuan

for helpful advice and questions

Sample of 11475 metal-poor MSTO candidates; ~50% complete and ~89% pure

RGB selection is still in progress, but will have lower completeness (~25%) and purity (~67%)

I learned: (1) It works!

(2) How to cross-match on the Gaia Archive

(3) The memory limit of my laptop

I did:

Color code: amplitude of local corrections with respect to DR2.

Some catalogs: no patterns

Others: stripes along RA or Dec + large scale patterns.

Banding due to old ground-based positions used to build proper motions. Larger scale patterns: reference system differences, or rotation.

Adventures in de-biasing old asteroid astrometry.

TODO: apply to DR2 pm correction for rotation (Lindegren’s doc); check current results vs. astropy method for position propagation.

Discovered this week: interesting intersections between dynamics in the Galaxy and the Solar System…. Ideas for an article! ….Sprinting ! It works!

Juna Kollmeier (@ Doc right now unfortunately)

GG Catalog Progress

GG Brown Dwarfs: Faherty (Done)

GG White Dwarfs: Gaensicke (Done)

GG: CMD: Brown (Done)

GG: 6D Phase Space: Brown (Done)

Owners Needed:

GG Globulars

GG Spiral (Is there a spiral?)

GG Local

GG Red Clump (Hawkins?)


GG Low Z (Simon?)


Where to host these?

I’m Andy Casey (Monash) and this week I self-calibrated and simulated the astrometric and radial motion jitter for single stars (w/ Rix and Price-Whelan)

the “binary fraction”

simulated AEN

  • p.d.f. Of a source being a single star given astrometric/radial jitter (and colours/.mags)

  • radial velocity semi-amplitude for binary systems

Jason Sanders (IoA, Cambridge)

Aim: 3d bulge kinematics from RVS

Bulge-like kinematics!

Distances from isochrones → in front of bulge?

But net rotation about ~ 8kpc → distances OK

[Fe/H] & Teff from random forest on WISE & 2MASS

Vertical met grad.

Newberg et al. (2007)

Nora Shipp

Re-discovering & confirming stellar streams

m-M = 14 - 18.5

[Fe/H] = -2

Age = 12 Gyr

Alexa Villaume (University of California Santa Cruz)

Observed color - Synthetic color

Asked a lot of questions about sources of uncertainties and quality flags in DR2 (thank you Anthony and Morgan!)


Quality flags

are not

always informative

Learned: Apples-to-apples comparisons between synthetic and observed photometry is complicated and many corrections are needed

Timothy Brandt, UCSB

Kareem’s wide binaries can calibrate parallax uncertainties. Formal uncertainties are 20-30% underestimates? Only addresses spatially uncorrelated errors...

Hints of magnitude-dependent zero-point offset (couple μas/mag)?

Emily Cunningham (UCSC)

  • I worked with Sanderson and Wetzel on how we can quantify and measure the impact of an LMC-like interaction on the velocity field of a mostly accreted stellar halo.
  • I estimated the parameters of the velocity ellipsoid over different octants in the sky using RR Lyrae! In the Milky Way (Pan-STARRS) and the Ananke mocks for the Latte simulations.

Milky Way

m12m: Latte/Ananke

Adrian Price-Whelan (Princeton)

w/ Cecilia Mateu: coordinate frames for stellar streams in galstreams

→ Next: we will clean up the library and provide other metadata for streams

w/ Nora Shipp: what “known” streams in the north can be confirmed?

→ Next: compute significance for candidate rediscoveries, repeat with DECaLS?

w/ Cecilia+Giuliano Iorio: RR Lyrae in the Pal 5 stream, >15 candidates

→ Next: fit stream models to new distance information, improve MSTO filter

w/ Ana Bonaca: Improving models of the GD-1 stream

  • How to use new RV measurements to improve fit of “spur”
  • Better global models of the stream (Fail!)

→ Next: Figure out what is going on with the stream track?!

2D density model

P5. Astro Viz work! Thanks to Nora for data on Streams! Movies forthcoming

Luis Quiroga-Nuñez
(Leiden Observatory/JIVE)


SiO maser emission

No Coincidences in Gaia

Coincidences in Gaia+2MASS (~400, %100 MIRA!)

David Mykytyn, New York University

  • Managed to learn a decent kernel density for the main sequence stars
  • Very close (alas not close enough yet) to be able to generate the “binary sequence”
  • Hopefully this will happen very soon?
  • Learnt KDE in PCA space, and transformed it backwards into the real CM space

Morgan Fouesneau (MPIA, Heidelberg)

What I learned this week among other things

  • Estimating Gaia’s small field of view correlations
  • Wide-binary identical twins are real - good for parallax validation
  • Effort to have Gaia selection function(s) [but will be painful to build]

What I did this week

  • Dynamics of M31 HII regions using biased Gaia astrometry

  • (incomplete) Empirical star cluster model

Actually stars!

Not looking at stars - epic fail!

No coherent rotation

Consistent with random

Strongly doubting

Van der Marel et al. 2019

Something wrong

with photometry


> Discussed:
- Analytic modeling of disequilibria using the continuity equation with Larry and Hamish: can’t resolve all degeneracies, yet.

- Accelerations for Hipparcos-DR2 x-matched stars (courtesy T. Brandt), definitely worth exploring!

- Great breakout on simulations and mock catalogs. Got a flavor of the diversity of philosophies and techniques, going into the available codes, and, most importantly, their scope depending on the scientific problem at hand.

(Brown U.)

> Worked on:

- Responded to referee report for a paper on estimating the local DM content in the solar neighborhood; mild evidence of ‘excess’ matter density (also verified by A. Widmark using an independent technique).

- Will better disequilibria modeling only improve precision and rule out the excess? Can only answer on a case-by-case basis.

- Baby step: started simulating effect of DM halo (final goal: NFW population) + test particle disk on a stellar distribution using galpy potentials (thank you J. Hunt). [Bummed couldn’t make at least 1 pretty plot! :(]

- Implemented A. Brown’s RUWE cut and found no significant change in derived results!

May Gade Pedersen

(KU Leuven, Belgium)


Recreated from Bastian+2018


Isochrone Cloud

What I did:

Constructed Gaia CMD of cluster with known eMSTO. Converted isochrone clouds to Gaia colours and ‘fit’ to observations.

I learned

Principles behind cluster membership
verification. Use appropriate Gaia
passbands for bolometric



Kareem El-Badry (UC Berkeley)

Twinning: excess of equal-mass wide binaries is real!

Made a catalog of 3000 hierarchical triples with RV-variable components

Lots of other ideas:

  • Companions to massive white dwarfs with Sihao Cheng
  • Parallax error calibration with Timothy Brandt
  • Calibrating gyrochronology with Jackie Faherty
  • Kozai mechanism in triples with Juna Kollmeier

Thanks for great discussions with Rix, Casey, Gaensicke, Oh, Hogg, Fouesneau, Brown, Kamdar ++

Still working on the math ¯\_(ツ)_/¯

Jason Hunt (Dunlap/Toronto)

Talked about: Non-axisymmetric structure, actions, galpy, phase space spirals, actual spirals, bars

Worked on: Lots of little things, including paper draft from last sprint, and looked at models of different spiral structure

Simulations from Alex Pettitt

Ana Bonaca (Harvard)

Found GD-1 models with relative radial velocity offsets between the stream and the spur comparable to the observed offset

Lauren Anderson (Flatiron Institute):

Worked on building a 3D dust map of the Milky Way

Simulation: (Almost) reconstructed the “true” dust density in the Latte simulation, the foundation for Ananke. We have the right amplitudes and scales !!

Data: Applied to 105 dust estimates from Gaia with good parallax estimates

Hyper parameters: ℓ ~ 60 pc and σ ~ 80 M/pc3 (optimized from a more local sample)

Sihao Cheng Johns Hopkins University

  • relation between the white dwarf Q branch and wide binary fraction with Kareem El-badry, supporting the idea of Q-branch WDs being WD-WD merger
  • extinction within 250 pc is still uncertain
  • tried to analyse proper motions of Sagittarius Stream bifurcation
  • learned a lot. Some new ideas for my next possible project. Thanks for discussions with Newberg, El-badry, Anderson, Casey, Gänsicke, Zinn, Hunt, etc.

Borja Anguiano (University of Virginia)

Kathryn V Johnston (Columbia)

?? PS-Spirals - where? when? what??
with Chervin Laporte and Larry Widrow

Did: orbits in axisymmetric MW potential
Jphi (=Lz!) => groups with shared history
dvz & dvR “hit” => z-vz
spirals & R-vr sloshing

???? Towards the ORIGIN ????:
“Rewind” spiral in Jphi bins

test approach with N-body sims

limitations: impulsive assumption; local view; moving groups

red: rguide =9 kpc white: rguide =7kpc

Chervin F. P. Laporte (UVic)

PS-spirals (Larry, Kathryn, Anthony locally & Martin Cool Smith+Jason H+Jason S), finding the OLR with DR2 (Jason H), GP blablablah (Larry+Hamish), velocity field of MW (Eilers+Pearson+Hogg), Moving groups Arcturus (Elena D’Onghia)

Did: checked some quick dirty solutions to my problems, didn’t work… but looking forward to next 3 weeks :). Made this movie of the PS-spiral in overdensity to help you hypnotise your guests back home.

Learned: I might have to GP blablablah my way out of this with RC to do what I initially intended to do.

2019 SB Gaia Sprint wrap-up - Google Slides