Презентация на тему «Design Considerations for Directly Imaging Earth-like Exoplanets»

Design Considerations for Directly Imaging Earth-like Exoplanets

Garreth Ruane gjr8334@rit.edu Chester F. Carlson Center for Imaging Science Rochester Institute of Technology

Question: What telescope specifications are necessary to directly

image and characterize planets in the “habitable zone” of nearby stars?

Outline

Introduction Exoplanetary Science Short history of direct imaging High-contrast imaging technology Candidate stars Hipparcos Design specification Conclusions

Exoplanetary Science

Detections

Methods

770 confirmed More than 2300 candidates

Radial velocities Planetary transits Transit timing variation Gravitational microlensing Astrometry Pulsar timing Features in circumstellar disks Direct imaging

Missions

Current MOST (Canada) COROT (France) Kepler (NASA) Under Development Gaia (ESA) JWST (NASA)

History of Direct imaging

History of Direct Imaging

2004: First direct image, 2M1207b 27 planetary systems have been imaged since 2004.

VLT NACO (8 m) J-band image of 2M1207 [Mohanty et. al. 2006]

VLT NACO (8 m) NIR image of 2M1207 [ESO]

Beta Pictoris b (2008)

[ESO/A.-M. Lagrange et al. 2009]

HR 8799 (2008/2010)

Keck L’-band image of HR 8799 [Marois et. al. 2010]

LkCa 15 b (2011)

[Kraus and Ireland 2011]

What do these systems have in common

Large planets Large separation Low contrast Hot Jupiters/Young? Emit in infrared High contrast astronomical imaging seeks to resolve cool planets very close to bright stars.

High contrast imaging

High-contrast imaging terminology

Contrast Inner working angle Outer working angle Discovery space

Contrast

[Lyon and Clampin 2012]

Inner Working Angle

[Lyon and Clampin 2012]

Outer Working Angle

Limited by the field of view of the optics Can be limited by actuators

Discovery Space

Field of view

IWA

Sky Angle

OWA

High-contrast imaging technology

Lyot coronagraph

[Sivaramakrishnan et al. 2001]

High-contrast imaging technology

Apodizing phase plate coronagraph

[Kenworthy et al. 2010]

Instruments in use

VLT NACO/APP coronagraph Keck NIRC-2 Gemini NICI/Lyot coronagraph HST NICMOS STIS ACS/HCR JWST NIRCam

Image credit: ESO

Next generation technology

NASA’s New Worlds Observer

4-m telescope plus starshade has star:planet limiting contrast of 10-11 at IWA = 50 mas

[http://newworlds.colorado.edu]

Next generation technology

Optical vortex coronagraph

z

Mask

PP1

Lyot Stop

Detector

L3

L1

L2

?’, ?’

r, ?

?, ?

O1

Next generation technology

Optical vortex coronagraph

z

Mask

PP1

Lyot Stop

Detector

L3

L1

L2

?’, ?’

r, ?

?, ?

O1

Next generation technology

Vortex coronagraph

[Serabyn et al. 2010]

Candidate stars

“Habitable” Zone

Image credit: NASA/Ames/JPL-Caltech

HabCat: A catalog of nearby “habitable” systems

Originally targets selected for SETI Derived from the Hipparcos catalog 17,129 stars out of about 118,218 Criteria for HabCat Candidates Stars must be at least 3 Gyr old. Stars must be non-variable. Stars must be capable of harboring terrestrial planets (measured by [Fe/H]). Stars must support a dynamically stable habitable zone.

[Turnbull et al. 2003]

The HabCat catalog

Size of habitable zone

[Turnbull et al. 2004]

Habitable Zone

[Image Credit: ESO]

Can we resolve planets in the HZ

Diameter [m]

IWA [mas]

# of HabCat Stars

1

226.9

1

2

113.4

9

4

56.7

86

8

28.4

1167

16

14.2

9092

Planet-Star Contrast

[Lyon and Clampin 2012]

Luminosity Ratio of Earth-like planet

Plot of luminosity ratio of a terrestrial planet in the HZ of HabCat stars.

Aperture Flux

[Lyon and Clampin 2012]

Aperture Flux of an Earth-like planet

Plot of aperture flux for a 6.5 m (JWST) aperture in the J-band due to a terrestrial planet in the HZ of HabCat stars.

Detector Signal

[Lyon and Clampin 2012]

Noise Sources

Noise sources: Shot noise of planet and star Zodiacal light Exozodiacal light Background Dark current Read noise

Noise Sources

[Lyon and Clampin 2012]

Noise Sources

Exozodiacal Light Subtraction will be necessary. Preliminary studies will allow better subtraction. Subtraction may cause significant noise. May be important for orbital determination.

[Lyon and Clampin 2012]

Background Sources

Photometric measurements rule out background sources

Signal-to-Noise Ratio

[Lyon and Clampin 2012]

Integration Time

Many HZ planets could be imaged at SNR = 5 under ideal conditions and minimal noise.

Other performance considerations

Aperture obstructions Optical surface quality Polychromatic effects Pointing Postprocessing

Mission specifications

Mission design

Future missions

Photometric measurements Broadband (Spitzer: HD 189733b) Spectroscopy Atmosphere, biomarkers Polarimetry Oceans?

Image credit: (left)Turnbull et. al. 2006 (right) ESO

Conclusions

It is possible to design a mission with current technology that is likely to directly image at least one earth-like planet. With state-of-the-art starlight suppression JWST would have over 200 viable HZ targets. Such a mission would be capable of imaging most planets outside of the HZ. Later spectral types are favored for contrast. These types have very small HZs. Direct imaging opens doors to photometric, spectroscopic, polarimetric studies of exoplanets.

References

Kenworthy, M.A., Quanz, S.P., Meyer, M.R., Kasper, M.E., Lenzen, R., Codona, J.L., Girard, J.H.V., Hinz, P.M., 2010. An apodizing phase plate coronagraph for VLT/NACO. arXiv:1007.3448. Kraus, A.L., Ireland, M.J., 2011. LkCa 15: A Young Exoplanet Caught at Formation? arXiv:1110.3808. Lafreni?re, D., Jayawardhana, R., van Kerkwijk, M.H., 2008. Direct Imaging and Spectroscopy of a Planetary-Mass Candidate Companion to a Young Solar Analog. The Astrophysical Journal 689, L153–L156. Lagrange, A.-M., Gratadour, D., Chauvin, G., Fusco, T., Ehrenreich, D., Mouillet, D., Rousset, G., Rouan, D., Allard, F., Gendron, ?., Charton, J., Mugnier, L., Rabou, P., Montri, J., Lacombe, F., 2009. A probable giant planet imaged in the ? Pictoris disk. Astronomy and Astrophysics 493, L21–L25. Lyon, R.G., Clampin, M., 2012. Space telescope sensitivity and controls for exoplanet imaging. Optical Engineering 51, 011002– 011002–15. Marois, C., Macintosh, B., Barman, T., Zuckerman, B., Song, I.S., Patience, J., Lafreniere, D., Doyon, R., 2008. Direct Imaging of Multiple Planets Orbiting the Star HR 8799. Science 322, 1348–1352. Marois, C., Zuckerman, B., Konopacky, Q.M., Macintosh, B., Barman, T., 2010. Images of a fourth planet orbiting HR 8799. Nature 468, 1080–1083. Mohanty, S., Jayawardhana, R., Hu?lamo, N., Mamajek, E., 2007. The Planetary Mass Companion 2MASS 1207-3932B: Temperature, Mass, and Evidence for an Edge-on Disk. The Astrophysical Journal 657, 1064–1091. Serabyn, E., Mawet, D., Burruss, R., 2010. An image of an exoplanet separated by two diffraction beamwidths from a star. Nature 464, 1018–1020. Sivaramakrishnan, A., Koresko, C.D., Makidon, R.B., Berkefeld, T., Kuchner, M.J., 2001. Ground?based Coronagraphy with High?Order Adaptive Optics. The Astrophysical Journal 552, 397–408. Swartzlander, G.A., 2009. The optical vortex coronagraph. Journal of Optics a-Pure and Applied Optics 11. Turnbull, M., Glassman, T., Roberge, A., Lo, A., Cash, W., 2009. Looking for New Earth in the Coming Decade with Direct Imaging, in: Astro2010: The Astronomy and Astrophysics Decadal Survey. Presented at the astro2010: The Astronomy and Astrophysics Decadal Survey, p. 299. Turnbull, M.C., Tarter, J.C., 2003a. Target Selection for SETI. I. A Catalog of Nearby Habitable Stellar Systems. The Astrophysical Journal Supplement Series 145, 181–198. Turnbull, M.C., Tarter, J.C., 2003b. Target Selection for SETI. II. Tycho?2 Dwarfs, Old Open Clusters, and the Nearest 100 Stars. The Astrophysical Journal Supplement Series 149, 423–436.