thesis plan

Constraints on Extrasolar Planet Populations from VLT NACO/SDI and

MMT SDI Direct Imaging Surveys: Giant Planets are Rare at Large

Separations(2008 ApJ in press)

Eric L. Nielsen, Steward Observatory

Laird M. Close, Beth A. Biller (Steward), Elena Masaciadri (INAF-Osservatori Astrofisico di

Arcetri), and Rainer Lenzen (Max-Planck-Institut fur Astronomie)

Thesis Committee Meeting, December 6, 2007

Thesis Plan● Chapter 1: Examining the Validity of Models for Young, Low-Mass

Objects. Completed – Close et al. 2005 Nature 433, 286, Nielsen et al. 2005 AN 326, 1033, Thatte et al. 2007 MNRAS 378, 1229, Close et al. 2007 ApJ 665, 736.

● Chapter 2: Target Selection and Survey Design for Direct Imaging Surveys for Extrasolar Planets

– Part I: MMT/VLT SDI survey. Completed – Nielsen et al. 2006, Biller et al. 2007 ApJS, 173, 143.

– Part II: NICI survey. In progress, expected completion Fall 2008.● Chapter 3: Constraints on Extrasolar Planet Populations from VLT

NACO/SDI and MMT SDI Direct Imaging Surveys: Giant Planets are Rare at Large Separations. Completed – Nielsen et al. 2008 ApJ in press.

● Chapter 4:Constraining Extrasolar Planet Populations Using Null Results from Multiple Direct Imaging Surveys. In progress, expected completion Spring 2008.

● Chapter 5: The Smallest Trans-Neptunian Objects: Measuring the Faint-End Slope of the KBO Luminosity Function with the LBT. In progress, expected completion (assuming successful acquisition of data) Fall 2008.

Chapter 1: Examining the Validity of Models for Young, Low-Mass Objects: AB Dor C

Nielsen et al. 2006

● AB Dor C (~M5.5) indirectly detected from VLBI observations of radio-bright AB Dor A (K1V)

● Detected with VLT Simultaneous Differential Imaging (SDI) in 2004

● Combination of reflex motion and C position allowed very accurate mass measurement (0.090 +/- 0.005 M_sun) of AB Dor C

● Initial age determination, spectra, and NIR fluxes suggested DUSTY models were underpredicting mass by a factor of 2.Close et al. 2005


Close et al. 2007

● Age for the AB Dor Moving Group was pushed up from 50 to 70 Myr

● VLT Integral Field Spectroscopy provided a better measure of the spectrum, at a more favorable observing epoch (0.22” separation between A and C, instead of 0.155”), with twice the exposure time. New reduction preserves the spectral slope.

● New spectral type is 2.5 subclasses earlier (from M8 to M5.5), agreeing with models.


Close et al. 2007

● AB Dor C is now in good agreement with DUSTY models

● High precision orbital solution (~5% error on mass) for AB Dor C, and its membership in a moving group, makes it a good constraint on tracks for young, low-mass objects

● Simultaneous Differential Imaging (SDI) Technique for imaging close companions at very high contrasts.

● Wollaston beam splitters produce four identical beams, passed through a quad-filter, with narrow band passes at 1.575, 1.600, and 1.625 microns.

Model planet spectrum from D. Sudarsky (private communication), eps Eri spectrum from Meyer et al. 1998. Titan image from L. Close and M. Hartung.

Chapter 2: Target Selection and Survey Design for Direct Imaging Surveys for Extrasolar Planets. Part I:

SDI

● A good direct imaging target is young, nearby, and has a late spectral type, but what's the best combination of these three properties?

● In general, surveys should be optimized to maximize the number of expected planet detections—a null result when 5 planets were expected is much more meaningful than one where you expect to detect 0.5 planets. Plus, of course, you're more likely to find a planet in the first case!


SDI

Nielsen et al. 2008

● For each target star, we have a contrast plot: how faint a companion we can detect as a function of radius

● Run Monte Carlo simulations of a large number of planets with full orbital parameters, use models of planet luminosities (Burrows et al. 2003, and Baraffe et al. 2003) to compare contrast curve to simulated planets

● For this target star, and with particular distributions of mass and semi-major axis, determine what fraction of simulated planets could be detected.

● Compare target stars based on detection probability.


SDI

Nielsen et al. 2008

● 50 night survey for extrasolar planets, slated to begin in early 2008.

● Will use Monte Carlo simulations for target selection, folding in knowledge from SDI survey

● Work with Mike Liu and Beth Biller (IfA) to determine from NICI commissioning data the optimal observing strategy (large number of stars with shallow observations, or smaller, more targeted sample with deep observations?)

● Ensure that even with a null result, NICI data can provide results of scientific interest

Chapter 2: Target Selection and Survey Design for Direct Imaging Surveys for Extrasolar Planets. Part II:

NICI

● It's easier to find massive (about the mass of Jupiter and above) and close in (orbits a few years or less) planets

● About 1 in 8 planet hosts has more than one detected planet

● Most of the long-period planets (a~4-6 AU) are in systems that already have a detected inner planet

Image from exoplanets.org

Chapter 3: Constraints on Extrasolar Planet Populations from VLT NACO/SDI and MMT SDI Direct

Imaging Surveys

● Considering target stars with and without detected planets shows that the more metals a star has, the more likely it is to host a planet (within 4 years, 2.5 AU, and above 1.6 Jupiter masses)

● Overall, about 5% of all stars have such a planetFischer and Valenti 2005


Imaging Surveys

● Run Monte Carlo simulations for multiple mass/semi-major axis grid points, combine results.

● Within inner contour, if GJ 182 had a planet of mass ~7 MJup, and a~20 AU, we'd have had an 80% chance of detecting it.

● Nominal SDI field of view is ~60 AU, but it's possible to see longer period planets for fortuitous combinations of orbital parameters(Thanks to Remi Soummer for the idea

of making completeness plots like this)


Imaging Surveys

Nielsen et al. 2008

● Planet fraction (fp): fraction of stars with a planet of a given mass and semi-major axis

● Contours show upper limits on planet fraction as a function of planet mass and semi-major axis, at 68% (red) and 95% (blue) confidence levels

● Black dots are known radial velocity planets, for comparison

● Less than 20% of stars can have planets more massive than 3 MJup between 20 and 100 AU, at 95% confidence.


Imaging Surveys

Nielsen et al. 2008

● 200 planets give us pretty good statistics, so we can fit simple functions to the behavior of mass, semi-major axis, and eccentricity of giant planets

● All that's left to figure out is what planets do beyond a few AU, where radial velocity can't find them so easily

Planet distributions from exoplanets.orgMass fit from Butler et al. 2006, semi-major axis power law from Cumming et al. 2008 (in prep). Figures from Nielsen et al. 2008.


Imaging Surveys

● If we assume power law distributions for mass and semi-major axis, we can find the fraction of planets we could detect for any target star (if the star has one planet, this is the chance of detecting that planet)

● For this star, with this semi-major axis distribution (power law index -0.61, upper cut-off 70 AU), we can detect 10% of the simulated planets (the blue points)


Imaging Surveys

Nielsen et al. 2008

● Green lines are power laws of different indices, red lines are the upper cut-offs.

● At each intersection is the confidence to which we can (or can't) exclude that model

● We can't constrain the most pessimistic model (a-1), but we can rule out the model suggested by Cumming et al. 2008 (a-0.61) with an upper cut-off of 75 AU, at 95% confidence.


Imaging Surveys

Nielsen et al. 2008

● Use radial velocity results (Fischer & Valenti 2005) to normalize the distributions, given how many planets are within 2.5 AU (although we include M stars, and they didn't)

● A distribution with a positive power-law index is pretty much ruled out, with some constraints on an index of -0.61

Thanks to Daniel Apai for the idea for plotting the results this way. Nielsen et al. 2008.


Imaging Surveys

● Monte Carlo Simulations assign each planet full orbital parameters, so if a target star is observed at multiple epochs (even with different telescopes and observing techniques), the same planets can be advanced in their orbits to later observational epochs, and compared to new contrast curve.

● A simulated planet is considered detected if it lies above any contrast curve for that target star

● (In most cases the orbital motion is a minor effect, especially when talking about observations over two years for a simulated planet at 30 AU, but it is calculated for completeness)

● Technique already used for Nielsen et al. 2008.

Chapter 4: Constraints on Extrasolar Planet Populations Using Null Results from Multiple Direct

Imaging Surveys

● VLT NACO H/Ks band survey: 22 stars (Masciadri et al. 2005)

– Status: Finished, ready to add to other results (Nielsen et al. 2008)

● MMT/VLT SDI survey: 48 stars (Biller et al. 2007)

– Status: Finished, ready to add to other results (Nielsen et al. 2008)

● Gemini GDPS survey: 85 stars (Lafreniere et al. 2007)

– Status: Computing Results Now● ~120 unique stars. ● Other published surveys? VLT L-band (Kasper et al.

2007)?


Imaging Surveys

● Marley et al. 2007 have published models of planetary luminosity that begin with core accretion models, rather than assuming arbitrarily hot initial conditions. Once spectra become available, these should be included in the calculation alongside Burrows et al. 2003 and Baraffe et al. 2003 models.

● Johnson et al. 2008 have compared planet fractions among M-stars, FGK stars, and subgiants (were A stars during their main sequence lives). They found a correlation between stellar mass and planet fraction (higher mass stars are more likely to host giant planets). This, too, can be incorporated into our results.


Imaging Surveys

● LBT time available this spring with the red and blue prime focus cameras for a limited number of projects.

● Working with David Trilling and collaborators on a proposal to use the LBT to detect Kuiper Belt Objects

● Emphasis is on faintest detectable objects: the behavior of the break in the power law slope is set by currently unknown material properties of KBOs

● With two independent 8m telescopes surveying the same field, can probe to very faint magnitudes

Figure from Bernstein et al. 2004

Chapter 5: The Smallest Trans-Neptunian Objects: Measuring the Faint-End Slope of the KBO Luminosity

Function

● Apply Monte Carlo modeling of orbits to KBOs

● Create a synthetic population of KBOs based on known objects in order to optimize survey design

● Simulations will inform both data taking (telescope must track to follow KBO motion due to parallax and orbits) and data reduction (frames must be shifted numerous times, in many directions, to coadd correctly to allow detection of faintest KBOs.


Function

● Timing of this project is uncertain: this chapter will be dropped from the thesis plan if proposal is rejected, or if data cannot be taken, or if data are taken but are of too low quality, etc.

● Project PI is David Trilling, with collaborators including Laird Close, Renu Malhotra and others. This project is still in initial stages, so final data product and division of labor is currently unclear


Function

Thesis Plan● Chapter 1: Examining the Validity of Models for Young, Low-Mass

Objects. Completed – Close et al. 2005 Nature 433, 286, Nielsen et al. 2005 AN 326, 1033, Thatte et al. 2007 MNRAS 378, 1229, Close et al. 2007 ApJ 665, 736.

● Chapter 2: Target Selection and Survey Design for Direct Imaging Surveys for Extrasolar Planets

– Part I: MMT/VLT SDI survey. Completed – Nielsen et al. 2006, Biller et al. 2007 ApJS, 173, 143.

– Part II: NICI survey. In progress, expected completion Fall 2008.● Chapter 3: Constraints on Extrasolar Planet Populations from VLT

NACO/SDI and MMT SDI Direct Imaging Surveys: Giant Planets are Rare at Large Separations. Completed – Nielsen et al. 2008 ApJ in press.

● Chapter 4:Constraining Extrasolar Planet Populations Using Null Results from Multiple Direct Imaging Surveys. In progress, expected completion Spring 2008.

● Chapter 5: The Smallest Trans-Neptunian Objects: Measuring the Faint-End Slope of the KBO Luminosity Function with the LBT. In progress, expected completion (assuming successful acquisition of data) Fall 2008.

Extra material

Speckles with SDI

Image from Laird Close and Beth Biller

SDI: Suppressing Speckle Noise

Image from Laird Close and Beth Biller

Assumed Extrasolar Planet Distributions

Radial velocity distributions from exoplanets.org

Simulation ResultsVLT NACO SDI, 40 minutes of data, 6% of planets detected

GMT ExAOC, 2.8 hours of data, 35% of planets detected

Trends with Age and Distance

Target List and Properties of

Detected Planets

For each target star, simulate 100,000 planets, compute fraction above sensitivity curve (y-value of each point), and median value of separation between star and planet for detected planets (x-value)

Survey Design

● For each instrument, choose the best 30, 40, 50, and 60 stars based on percentage of planets that are detectable

● Best stars are observed early on in a survey, with a slower gain in planets detected as less optimal stars are observed.

Papers● SDI

– Biller, B. A., Close, L. M., Lenzen, R., Brandner, W., McCarthy, D. W., Nielsen, E. L., and Hartung, M. SPIE 5490, 389 2004.

● AB Dor C– Close, L. M., Lenzen, R., Guirado, J. C., Nielsen, E. L.,

Mamajek, E. E., Brandner, W., Hartung, M., Lidman, C., and Biller, B.A., Nature 433 286 2005

– Nielsen, E. L., Close, L. M., Guirado, J. C., Biller, B. A., Lenzen, R., Brandner, W., Hartung, M., and Lidman, C. Astron. Nachr. submitted 2005, astro-ph/0509400

● Planet Simulations– Nielsen, E. L., Close, L. M., and Biller, B. A., proceedings

to IAUC 200, in prep 2005.

Conclusions● The SDI technique is able to move beneath the

speckle noise floor to the photon noise limit, as shown by the AB Dor C detection, making it a very powerful search method

● A survey for self-luminous, giant extrasolar planets is being conducted for young, nearby stars, using SDI cameras at the 8.2m VLT and 6.5m MMT

● Basic simulations of planet populations, extrapolating from what we already know about exoplanets, can inform survey target selection (as we're doing for the current VLT/MMT SDI survey) and design of future planet-search instruments (ability to detect planets is set largely by the inner working radius)

thesis plan

Documents

ab dor cab dor c

bright ab dor

ab dor cage

imaging close companions

mmt sdi direct imaging

validity of models

lowmass objectsclose

underpredicting mass