The Role of Speckle Imaging in Exoplanet Characterization

Nic Scott

Lead Research Scientist

BAERI/NASA ARC

nicscott.org

https://www.gemini.edu/node/21236 Credit: Gemini Observatory/NSF/AURA/Artwork by Joy Pollard

Exoplanets can't hide their secrets from innovative new instrument

https://phys.org/news/2019-08-exoplanets-secrets-instrument.html

Exoplanet traced to home star in binary system

https://astronomynow.com/2019/09/05/exoplanet-traced-to-home-star-in-binary-system/

Space science research highlight: High-resolution imaging and exoplanets

https://www.nasa.gov/feature/space-science-research-highlight-high-resolution-imaging-and-exoplanets


Hidden Secrets of Elusive Exoplanet Revealed by Innovative New Instrument

https://scitechdaily.com/hidden-secrets-of-elusive-exoplanet-revealed-by-innovative-new-instrument/

 

1''

speckle

aperture photometry

blue

red

High-resolution Imaging Transit Photometry of Kepler-13AB -Howell et al.  

2019AJ....158..113H

Both speckle analysis and high speed aperture photometry performed with `Alopeke confirmed that the highly irratiated gas giant, Kepler-13b orbits Kepler-13A.

a single star, a circle representing the isoplanatic patch, and the small star shapes are "speckles"

a single star, a circle representing the isoplanatic patch, and the small star shapes are "speckles"

a single star, the smaller circles show worse seeing and smaller isoplanatic patches, each producing "speckles"

a single star, a circle representing the isoplanatic patch, and the small star shapes are "speckles"

a single star, the smaller circles show worse seeing and smaller isoplanatic patches, each producing "speckles"

a binary pair, close enough that they share an isoplanatic patch, producing "speckles" that correspond to their separation & position angle

a single star, a circle representing the isoplanatic patch, and the small star shapes are "speckles"

a single star, the smaller circles show worse seeing and smaller isoplanatic patches, each producing "speckles"

a binary pair, close enough that they share an isoplanatic patch, producing "speckles" that correspond to their separation & position angle

a binary pair, wherein the ratio of their separation to the isoplanatic patch size is such that their "speckles" are not correlated

a single star, a circle representing the isoplanatic patch, and the small star shapes are "speckles"

a single star, the smaller circles show worse seeing and smaller isoplanatic patches, each producing "speckles"

a binary pair, close enough that they share an isoplanatic patch, producing "speckles" that correspond to their separation & position angle

a binary pair, wherein the ratio of their separation to the isoplanatic patch size is such that their "speckles" are not correlated

Kepler-13AB

The Rayleigh criterion and the tyranny of the atmosphere

\Theta = 1.22 \lambda/d
\approx \lambda / r_0

but in atmosphere, turbulent cells limit resolution to 

Fizeau & Michelson

Brown & Twiss

1850s

1890s

1920 - measured Betelgeuse (with Pease)

1956 - HBT effect, correlation b/t coherent photons

detail lost to the atmosphere can be regained through interferometric analysis 

Intensity interferometry

Labeyrie

1970

Text

a method to obtain diffraction-limited resolution across the full aperture of a large telescope

 long exposure

speckles blur

produce Airy pattern

true images are impossible, only centrosymmetric objects can be reconstructed

speckle pattern is the Fourier transform of telescope pupil

autocorrelation of speckles

(in Fourier space)

modulus

(time-averaged intensity)

Knox & Thompson

cross-spectrum, a 2nd order correlation

1974

non-symmetric input

long exposure avg

Labeyrie technique

Knox & Thompson method

mean square of the image transform

modulus of the object transform

autocorrelation of the image transform

phase of the object transform

diffraction-limited image of the object

unambiguous reconstruction of arbitrary shapes but has            ambiguity

+

180\degree

The importance of phase in image reconstruction

Osherovich et al.

In 1980’s bispectral analysis was found to have higher S/N and be less susceptible to systematic error.

Weigelt & Lohmann

1977-1983

double star simulation

bispectrum modulus

triple correlation

record PSF of object

produce synthetic reference star by shifting the speckle pattern

phase is preserved

Speckle masking/triple correlation theory/bispectral analysis, a 3rd order correlation

deconvolve

  true images

Fringe spacing

Fringe orientation

Fringe Depth

Binary separation

Binary position angle

Binary magnitude difference

1s

40s

20min

An aside on Lucky Imaging

  • reaches higher resolution than typical seeing
  • does not utilize Fourier analysis
  • not capable of reaching the diffraction limit
  • requires a very large number of  images

http://inspirehep.net/record/823349/plots

Fried

1978

record a large series of images

discard instances of poor resolution

combine the remainder through shift-and-add techniques

Can reach high angular resolution and is often confused with speckle imaging.

Changes in technology

ICCDs

EMCCDs

  • CCD + image intensifier tube
  • amplify signal prior to ADC
  • tube gating and amplification
  • up to 500kHz
  • lower resolution and low QE
  • interline detector      50% QE
  • CCD + series of HV gain registers
  • + photoelectric events w/ each register
  • greatly amplified signal w/ single readout of the array
  • 2008: Tokovinin published the first speckle imaging results
  • frame transfer, QE > 90%, low readout noise
  • higher S/N than ICCDs
  • 10-100 times faster than a CCD
  • active pixel sensor: amplification and  conversion happens directly on each pixel
  • cheap, less power and lower gain needed
  • higher S/N, 
  • fast readout
  • no clocking the charge across the array
  • further on-chip processing can be added

CMOS (complementary metal–oxide–semiconductor)

EMCMOS

  • each pixel has a series of HV registers
  • + photoelectric events w/ each register

2015: first EMCMOS results reported by Brugière

Publications

SAO/NASA ADS “Bumblebee” search: ‘‘speckle’’ - ‘‘speckle noise’’

  • limited to astronomy and refereed
  • removed AO speckle noise references
  • excluded AO and spectroscopic techniques
  • constrained to 1970+ sorted by citation count

This search returned 1,139 papers with 26,624 total citations

release of EMCCDs

& start of large speckle survey programs.

Instrument Programs -

  • often non-hierarchical or bottom-up
  • if successful, use may spread to the broader community
  • many for a specific use and have a finite lifespan
  • limitations of the technology or availability of people
  • many have quiescent phases
  • information is limited to what is publicly available (update your websites)

The following table lists current or recently active major optical speckle imaging programs along with a few IR speckle and lucky imaging instruments and selected other high-resolution programs.

Disclaimer

Title Text

Title Text

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Source: Wikimedia​

Author:

Cmglee

 

DSSI/NESSI/`Alopeke/Zorro

Speckle

  • 10mas/pxl
  • mag limit ~17
  • contrast limit ~8

Wide Field

  • 73mas/pxl

Speckle

  • 18mas/pxl
  • mag limit ~14
  • contrast limit ~6

Wide Field

  • 81mas/pxl

0.011'' @u

0.026'' @832nm

0.025'' @u

0.060'' @832nm

6.7''

60''

19''

56''

Science Programs

58 total proposals

138.3 total nights

(NOAO 2016A to 2019B)

  • Constrain NEA diameters. Image SS objects
  • Determine multiplicity of nearby K and M-dwarfs, does it vary across spectral type?
  • Imaging of brown dwarfs and distant large planets, particularly around M dwarfs
  • Investigate differences in planetary system architectures between multiple vs not (known) multiple host stars
  • Examine long-term RV trends/determine binarity of RV planet hosts.  
  • K2, TESS follow-up
  • Provide an unbiased sample for TESS, so statistical determinations of planet occurrence rates can be made
  • Occultations, transit photometry, pulsar time scales, observe pulsating WDs at high cadence
  • Interacting binary systems, jets, CVs, R Aquarii
  • WR stars - jets, outflows

Some proposals:

HST R Aquarii

Science Results Highlights

  • optical, NIR imaging of host stars of KOIs
  • ~ 90% of the confirmed & candidate exoplanet hosts
  • separations, PA, and dm for all detected, bound and LoS companion stars.
  • 2297 companions around 1903 primary stars
    • ~ 10% obs stars 1+ companions w/i 1”
    • ~ 30% w/i 4”
  • correction factors for exoplanet radii caused by the dilution of the transit depth
    • decreases the number of KOI planets with radii smaller than 2 Earth radii by 2% - 23%

 2017AJ....153...71F

Furlan's previous results applied to planets w/ known masses & radii, analyze the effects of a close stellar companion on planetary density.

  • 50 planets orbiting 26 stars in the Kepler field
  • transit dillution         planet radii      , planet density 
  • with faint companion star, density may decrease by ~ 3x

2017AJ....154...66F

close ~ 0.5” companions of Kepler and K2 planet candidate hosts and the inferred exoplanet radius distribution.

  • Fulton gap is robust regarding undetected stellar companions
  • gap became broader & shallower when accounting for possible undetected stellar companions
  • core composition of super-Earth and sub-Neptune exoplanets may not have so strong a divide as is suggested initially
  • w/o high-resolution imaging of Kepler and TESS host stars, the exoplanet radius distribution will be incorrectly inferred.

 

2018AJ....156..292T

Fulton

mini-neptunes

super-Earths

  • Large radius errors originally hid distribution features
  • Fulton gap revealed after CKS (10% stellar radius errors)
  • Accounting for binarity shifts gap in the distribution

brightest companion 1''

brightest companion 2''

Shift from 1.8 to 2.2 

  • increased water/ice vs pure Si rock
R_E
  • 170 KOI companions < 2”
    • AO, speckle, lucky, or HST
  • constrained stellar properties
  • assessed the probability that the companions are physically bound
  • 60 - 80% of companions < 1”  
  • > 90% of companions < 0.5” were found to be bound
  • assuming the planet is equally likely to be orbiting the primary or secondary, unless they are vetted, nearly half of all Kepler planets may have radii underestimated by an average of 65%.

 2017AJ....153..117H

  • DSSI @ G-S
  • highest-resolution images to date
  • 27 mas
  • imaging from 0.32 to 14.5 au
  • excludes all possible stellar and brown dwarf companions

 2016ApJ...829L...2H

  • Detection % vs. projected angular separation for TRAPPIST-1.
  • 5σ detection limit convolved with the detection likelihood.
  • eliminates all companions in the blue region
    • separations of 0.32–17 au
  • Numbers are the dmag & spectral type limits at the corresponding points.
    • ex. all companions earlier than T7 are eliminated < ∼8 au.

observed

bound (simulated)

line-of-sight (simulated)

K2 binaries detectable with DSSI-

2018AJ....156...31M

2019AJ....157..211M

  • Speckle imaging can detect potential companions to the left of the dashed lines
    • eliminating companions that may cause false positives or dilute transits.
  • Solid gray lines show the contrast ratios at which planet radii will have 1% and 0.1% correction factors due to the presence of a stellar companion.

Future

  • Quad-channel
  • Wave-front sensing
  • Possible near-IR channel?
  • DSSI heritage at the DCT+NPOI
  • novel construction

QWSSI

PI: van Belle

NEAs

  • sizes
    • radar typically quotes 40% uncertainties
    • albedo/radar size mismatch
  • shapes
    • adapt stellar surface modeling tools
    • light curve inversion/illumination model 

a~2.8AU

d~270km x 80km

(neck~50-65km)

model: Franck Marchis

Phaethon

Dec 2017 ~ 0.07AU

d~6km

Point source PS

Phaethon power spectrum (resolved)

Seeing-limited

Reconstructed

42''

Two-color wide-field speckle reconstruction

from NESSI

  • 0.25'' resolution from 500 frames (20s)
  • compromise b/t angres and contrast
  • Seeing ~ 0.85''

3-4x improvement over native seeing

Reconstruction

coming

Text

Text

M13

  • astrometry of clusters
  • very early results and little calibration or modelling over the FoV

Reconstructed

Seeing-limited

Abs astrometry residuals

~6-7 mas

4.2 mas

Further improvement possible to obtain ~0.02 pix (~0.4mas)

  • optics, dither, deeper obs

0.05 mag accuracy on aperture photometry

FWHM ~7pix (0.57'')

FWHM ~4pix (0.3'')

Pluto opposition

SOFIA occultation target duplicity

WF and speckle optics

Conv and EMCCD imaging

466/832 and g/i filters

TNO Varda ⌀~700km, d~50au

multiplicity is the single largest source of error to occultation path prediction

next steps: grisms & h-alpha filters

  • observe jets of Wolf-Rayet stars in h-alpha compared to "continuum" SDSS

HST WR 124

  • leverage the 0.01"/pixel plate scale of the instruments
  • extremely sensitive EMCCD, large aperture (Gemini), low-dispersion grism 
  • sci case1: high-z transients, GRBs 
  • sci case2: exoplanet host flares

https://www.frontiersin.org/articles/10.3389/fspas.2018.00025/full

Conclusions

  • a brief history and introduction has attempted to set the stage for the current research
  • highlighting the relevance of high angular resolution imaging to exoplanet and stellar research
  • high demand for speckle imaging observing
  • development of future community instruments
  • small space telescopes, optimized for large surveys of the sky, like TESS and GAIA, perform relatively poorly at high-contrast, sub-arcsecond resolution where speckle imaging excels
  • a cost-effective, efficient means to reach the diffraction limit with single aperture telescopes

Open to the community

  • NOAO proposal process
  • NESSI - WIYN@KPNO
  • `Alopeke - Gemini-N
  • Zorro - Gemini-S
  • Transitioning from block queue operation to Facility Instrument status

Additional References 

Brown, R. H. and Twiss, R. Q., Nature 177, 27{29 (Jan. 1956).
Hanbury Brown, R., Davis, J., and Allen, L. R., MNRAS 137, 375 (1967).
Labeyrie, A., A&A 6, 85 (May 1970).
Knox, K. T. and Thompson, B. J., ApJ 193, L45{L48 (Oct. 1974).
Weigelt, G., Scientifc Importance of High Angular Resolution at Infrared and Optical Wavelengths, Ulrich, M. H. and Kjaer, K., eds., 95{114 (1981).
Weigelt, G., Lowell Observatory Bulletin 9, 144{152 (1983).
Weigelt, G. P., Optics Communications 21, 55{59 (Apr. 1977).
Lohmann, A. W., Weigelt, G., and Wirnitzer, B., Appl. Opt. 22, 4028{4037 (Dec. 1983).

Fried, D. L., Journal of the Optical Society of America (1917-1983) 68, 1651–1658 (Dec. 1978).
Horch, E. P., Veillette, D. R., Baena Galle, R., Shah, S. C.,O'Rielly, G. V., and van Altena, W. F., AJ 137, 5057{5067 (June 2009).

Brugière, T., Mayer, F., Fereyre, P., Gu´erin, C., Dominjon, A., and Barbier, R.,  Nuclear Instruments and Methods in Physics Research A 787, 336–339 (July 2015).
Scott, N. J., Howell, S. B., Horch, E. P., and Everett, M. E., PASP 130, 054502 (May 2018).
Hofmann, K.-H. and Weigelt, G., A&A 278, 328-339 (Oct. 1993).
Law, N. M., Mackay, C. D., and Baldwin, J. E.,  A&A 446, 739{745 (Feb. 2006).
Tokovinin, A. and Cantarutti, R., PASP 120, 170 (Feb. 2008).
Andor, CCD, EMCCD and ICCDComparions & Minimizing Clock Induced Charge.
Howell, S. B., Everett, M. E., Sherry, W., Horch, E., and Ciardi, D. R., AJ 142, 19 (July 2011).

Furlan, E., Ciardi, D. R., Everett, M. E., Saylors, M., Teske, J. K., Horch, E. P., Howell, S. B., van Belle, G. T., Hirsch, L. A., Gautier, III, T. N., Adams, E. R., Barrado, D., Cartier, K. M. S., Dressing C. D., Dupree, A. K., Gilliland, R. L., Lillo-Box, J., Lucas, P. W., and Wang, J.,  AJ 153, 71 (Feb. 2017).
Furlan, E. and Howell, S. B., AJ 154, 66 (Aug. 2017).
Teske, J. K., Ciardi, D. R., Howell, S. B., Hirsch, L. A., and Johnson, R. A.,  ArXiv e-prints (Apr. 2018).
Fulton, B. J., Petigura, E. A., Howard, A. W., Isaacson, H., Marcy, G. W., Cargile, P. A., Hebb, L., Weiss, L. M., Johnson, J. A., Morton, T. D.,Sinuko , E., Cross eld, I. J. M., and Hirsch, L. A., AJ 154, 109 (Sept. 2017).
Hirsch, L. A., Ciardi, D. R., Howard, A. W., Everett, M. E., Furlan, E., Saylors, M., Horch, E. P., Howell, S. B., Teske, J., and Marcy, G. W., AJ 153, 117 (Mar. 2017).

Matson, R. A., Howell, S. B., Horch, E. P., Everett, M. E., ArXiv e-prints (May. 2018)