1. Using K2 To Find Free-floating Planets
Now with more microlensing!
Credit: NASA
Hello everyone, thank you…
My name is Calen…
Specifically, how can and will we use K2 to find FFP candidates, and how do we ultimately vet and confirm them?
Calen B. Henderson (JPL NPP Fellow)
K2C9 Microlensing Science Team Member
K2 Science Conference
Tu, 3/Nov/2015

2. Exoplanet Demographics
Kepler: close-in planets, over a thousand detections, thousands more candidates
In ~10 years WFIRST will continue the census begun by Kepler for planets near and beyond the snow line.
It will also be sensitive to FFPs, which are detectable only through microlensing, but is at least a decade away.
K2C9 provides opportunity to probe this reservoir of planets next year!!
Important for resolving tension between theory and observations and also as pathfinding for WFIRST (360, 60x3, 5 years, 60x3)
Adapted from:
Spergel+ (2015) arXiv:

3. Single Object Lensing Light Curve
[Free-floating Planet (FFP) Candidate]
Before jumping into the drama…
Light curve of a microlensing event due to a single lensing mass
Symmetric in time
Sumi+ (2011) Nature, 473, 349

4. Single Object Lensing Light Curve
[Free-floating Planet (FFP) Candidate] tE
The most salient feature of any light curve of a lensing event due to a single lensing mass is the timescale, which is characteristically short, on the order of days or even hours, for a low-mass lens such as a FFP.
Sumi+ (2011) Nature, 473, 349

5. Putative FFP Population
In 2011, the MOA collaboration announced the discovery of an excess of short-timescale events.
As shown here, the timescale distribution is well-fit by either a broken power-law or a log-normal function for events longer than two days.
Below that threshold, however, the models they use significantly underpredict the number of expected events.
Sumi+ (2011) Nature, 473, 349

6. Putative FFP Population
~700 MEarth
per star!!
Timescale scales as the square root of the mass of the lensing object, so they ascribe this excess to a reservoir of Jupiter-mass objects and find that there are approximately 700 Earth masses of these FFPCs per star in the galaxy.
How does this compare to observations of bound exoplanets and theoretical simulations?
Sumi+ (2011) Nature, 473, 349

7. First look in the outer reaches of planetary architecture
Bowler et al. conducted a survey of 122 young, nearby M-dwarfs
No planets  upper limit that ~10% of single M-dwarfs harbor 1—13M_J planet between 10 and 100AU
1: Bowler+ (2015) ApJS, 216, 7

8. Including statistical frequency of planets combining RV and microlensing detections as well as low-mass close-in planets only accessible to transit
approximately doubles this total
2: Clanton & Gaudi (2014) ApJ, 791, 91 // 3: Fressin+ (2013) ApJ, 766, 81

9. By comparison, as I mentioned previously, the short-timescale events from MOA imply ~700 Earth masses of FFP candidates per star
Thus, if all of these are indeed FFPs, these objects necessarily dominate the mass budget of planet formation
4: Sumi+ (2011) Nature, 473, 349

10. Furthermore, simulations of dynamical interactions during planet formation and evolution only eject roughly 5% of this, or 40 Earth masses of planet per star, nowhere near the MOA limit.
There are thus clear issues in attempting to resolve this microlensing-detected population with observations of bound planets as well as theoretical predictions.
5: Pfyffer+ (2015) ApJ, 579, 37

11. Not so Fast: From Short tE to FFP
tE = f(Dl,Ml,vrel)
The timescale of a microlensing event is a function of several physical properties, including the mass of the lens, the distance to the lens, and the relative transverse velocity of the lens and source.
It is crucial, then, to definitively determine that the cause of the short timescale for these events is indeed a low-mass object.
Sumi+ (2011) Nature, 473, 349

12. Satellite Parallax I: Spitzer
Credit: NASA/JPL-Caltech
Credit: Krzysztof Ulaczyk
By taking data simultaneously from the ground and from space, it is possible to measure a quantity known as the satellite parallax.
This effect qualitatively refers to the shift in the time and magnitude of the source magnification due to the large spatial baseline between Earth and a satellite.
Here is a light curve due to a single lensing mass from a recent Spitzer campaign spanning 2014 and 2015 that has measured this satellite parallax for nearly 200 objects, including several planets and binary stars.
Yee+ (2015) ApJ, 802, 76

13. Satellite Parallax I: Spitzer
Credit: NASA/JPL-Caltech
Credit: Krzysztof Ulaczyk
A secure satellite parallax measurement provides the mass to and distance of the lens system.
In the case of a short-timescale event, this confirms that it is in fact due to a low-mass object.
However, these objects are inaccessible to Spitzer due to the time lag between the selection of targets and their actual observation
πE helps determine (Ml, Dl)
Yee+ (2015) ApJ, 802, 76

14. Satellite Parallax II: K2 Campaign 9
7/April  1/July, 2016
~4 square-degrees
πE for ~few hundred events
Campaign Details
Enter K2.
Its campaign 9 will conduct a several square degree microlensing survey toward the Galactic bulge.
By working in concert with OGLE, it will measure the satellite parallax for an estimated several hundred events

15. Satellite Parallax II: K2 Campaign 9
Spatial distribution of microlensing events from 2015 during the same time window as K2’s C9
Courtesy of Matthew Penny

16. Vetting FFP Candidates in the NIR
After measuring the masses for several short-timescale events, the next step is to distinguish between a planet that is bound to but widely separated from its host star and one that is truly free-floating.
This requires taking NIR high-resolution photometry at two different epochs
The image on the left shows ground-based data for a microlensing event.
The column on the right shows how the overwhelming majority of stars not dynamically associated with the event will be resolved out in the high-resolution image.
Batista+ (2014) ApJ, 780, 54

17. Vetting FFP Candidates in the NIR
Procedure
Hs from ground-based light curve data
Hl+s from AO follow-up
Arithmetic!
Search for excess flux
The procedure, then, is as follows:
The H-band flux of the source can be determined from ground-based light curve data.
The H-band flux of the microlensing target, the lens plus the source, can be measured from the follow-up AO data.
By the power of math, these can be subtracted and any excess flux gives evidence for a lens host star.
A lack of additional light indicates that the planet may be gravitationally unbound.
Batista+ (2014) ApJ, 780, 54

18. CTIO 1.3m: ANDICAM Credit: CBH
The must urgent task, then, is to martial ground-based NIR resources capable of measuring the NIR source flux during the event.
One avenue is targeted follow-up:
Dual-channel optical+NIR photometer
Targeted follow-up simultaneously in I and H-band
However, tough due to timescale

19. CTIO 1.3m: ANDICAM Keck: NIRC2 Credit: CBH
Credit: Ethan Tweedle Photography
A second idea that is a bit crazier is to use AO ToO triggers
NIRC2 AO on Keck
 Trigger ToO observations for FFPCs

20. Courtesy of Matthew Penny
CTIO 1.3m: ANDICAM
Credit: CBH
Courtesy of Matthew Penny
Keck: NIRC2
Credit: Ethan Tweedle Photography
Particularly

21. Summary MOA survey discovery of excess of short-timescale
microlensing events
FFP candidates!!
Tension between observation and theory
Dominate mass budget of planet formation
Not accounted for by dynamical ejection
K2C9 can measure masses and distances to FFP candidates!
NIR observations necessary:
During event to get NIR source flux
High-resolution follow-up, to search for possible host star

22. Bonus Features

23. Johnson+ (2010) PASP, 122, 905

24. Clanton & Gaudi (2014) ApJ, 791, 91

25. Bowler+ (2015) ApJS, 216, 7 Keck+Subaru <40pc, <300Myr
122 targets (44 are close visual binaries)
78 single M-dwarfs
No planets
Bowler+ (2015) ApJS, 216, 7

26. Credit: NASA/JPL-Caltech