Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.stsci.edu/jwst/doc-archive/presentations/DavidLafreniere.pdf Дата изменения: Unknown Дата индексирования: Tue Feb 5 11:53:23 2013 Кодировка: Поисковые слова: http www.astronomy.ru forum index.php topic 4644.0.html

The science potential of JWST for exoplanet studies
David LafreniХre UniversitИ de MontrИal & NIRISS Science Team


JWST main exoplanet themes discussed here
! Transit spectroscopy ! Study composition, chemistr y, and physical conditions in atmosphere of the planet ! Giant planet imaging
! Search for new planets,

study planet formation ! Characterize known planets, luminosity, Teff, logg, etc.


Transit spectroscopy, current capabilities
E.g. GJ 1214b A super-Earth around an M dwarf
HST/WFC3 In 10 hr, =2x10-4 at R=50

Berta et al. 2012

Current precision limited to a few 10-4 in photometr y or low resolution spectroscopy, due to aperture, platform stability, detector and instrument systematics, and atmosphere. From space, with a large aperture, a wide spectral coverage, and carefully designed instruments, JWST will revolutionize this science!


The same obser vations with JWST/NIRISS
0.988 0.987 0.986 0.985 0.984

H/He rich atmosphere ("mini-Neptune")

GJ 1214b H/He rich atmosphere
2000 ppm

Flux in-transit relative to out-of-transit

0.983 0.8 0.988 0.987 0.986 0.985 0.984 0.983 1.4 0.988 0.987 0.986 0.985 0.984 0.983

0.9

1.0

1.1

1.2

1.3

1.36 hr total (1 transit)
=2.1e-4 at R=660

1.5

1.6

1.7

1.8

1.9

JWST/NIRISS
2.0

GJ1214b (M4.5V) J=9.8 =1.36 h (1 visit) R=660 at 1.25 µm
2.1 2.2 Wavelength (µm) 2.3 2.4 2.5

Red cur ve is input model, black cur ve is simulated obser vation (with error envelope)

Model from Miller-Ricci et al. 2010


The same obser vations with JWST/NIRISS
Water rich atmosphere ("Water world")

0.9868

6.8 hr total = 70 ppm GJ 1214b H2O rich atmosphere at R = 165

Flux(in)/Flux(out)

0.9866 0.9864 0.9862
JWST/NIRISS

170 ppm
GJ1214b (M4.5V) J=9.8 =6.8 h (5 visits) R=165 at 1.25 µm

1.0

Model from Miller-Ricci et al. 2010

1.5 Wavelength (µm)

2.0

2.5

Same model


Transit spectroscopy possibilities
Around a G dwarf Transit depth Jupiter/Neptune Super Earth Earth 10 10
-2 -4

Transit Spectroscopy few 10
-4 -4 -5

D o a b le ? Yes, in detail Yes, at low res Maybe, at low res D o a b le ? Yes, in detail Yes, in detail Yes, at low res

7x10
-4

10-5 to 3x10 10-6 to 5x10

Around an M dwarf Transit depth Jupiter/Neptune Super Earth Earth 10 10
-1 -3

Transit Spectroscopy 10
-3 -3

7x10
-3

10-4 to 3x10 10-5 to 10
-4

For reference, with NIRISS, for J=8 star in 10 hr at R=700, we reach 3 of 2x10-4


JWST for transit/eclipse spectroscopy
Instrument NIRISS NIRSpec Mode Grism, crossdispersed, slit-less Grating, wide slit (1.6") NIRCam MIRI Grism, slit-less Resolving power 700 Wavelength range (µm) 0.6 - 2.5 1.0 - 5.0 1.0 - 1.8 1.7 - 3.0 2.9 - 5.0 2.4 - 5.0 5.0 - 11.0 5.0 7.7 11.918.3 7.7 11.9 18.3 - 28.3

Prism, wide slit (1.6") 100 1000 or 2700

2000

Prism, 0.6" slit or slit- 100 less IFU (0.2" - 0.27"/pixel) 2400 - 3600

Many possibilities, complementar y in their resolution and wavelength coverage.


JWST for exoplanet imaging
JWST is not geared for as high a contrast as ground-based xAO planet finders (GPI, Sphere, HiCIAO, P1640), and has lower angular resolution. BUT
! Access to wavelengths unavailable with ground-based xAO ! Diffraction limit achieved without need for bright WFS star ! Much reduced sky background in the near- and mid-infrared ! Larger aperture than previous space telescopes ! Instruments have coronagraphic or interferometric capabilities

JWST is highly complementar y to ground-based xAO instruments


JWST direct exoplanet imaging
Instrument Mode NIRCam MIRI Lyot coronagraph Four-quadrant phase mask coronagraph Contrast 10-5 at 1" to <10 beyond 2" 10-4 at 1" to <10 beyond 2"
-6

Comments

Detectability

IWA=0.4"-0.8" Jupiters > 50 AU =2.1-4.6 µm Saturn mass > 100 AU IWA=0.4" =11 µm Jupiters > 50 AU

-5

NIRISS

Aperture masking 10-4 at 0.07"-0.4" =3.8 - 4.8 µm Few Jupiters at 5-50 AU interferometr y (AMI) Inside IWA of coronagraphs NIRISS AMI Pupil mask with 7 sub-apertures Non-redundant baselines Use of interferometric techniques provide a resolution of 0.5/D=0.07"


Characterization of known planets: e.g. GPI planets at 4.5 µm
Expected GPI planet properties Ground-based L' & M' limits

NIRISS AMI limit


Giant planets around low-mass stars
! How massive? Where? How often? ! cf more massive stars? ! Low-mass stars are fainter ! Many can't be obser ved by xAO systems ! Contrast less important, depth more important ! So JWST ideal! ! NIRISS AMI: M=8 for a 50 Myr 0.2 M¤ star reaches

1-3 Mjup, at 3-20 AU for 50 pc

!

NIRCam/MIRI: <<1 MJup at >50 AU (Unique to JWST)


Search for giant planets in SFRs
! Are giant planets formed by 1 Myr? 5 Myr? ! Nearest (150 pc) star forming regions are

Are they more numerous, on unstable orbits? often enshrouded in gas and dust
! Not amenable to xAO ! So need JWST!

! Most stars are faint in optical (I>8)

! NIRISS AMI: 1-2 MJup at 10-60 AU !

NIRCam: 0.1 MJup at >120 AU


Summar y
! For transit spectroscopy, JWST will be superior to ground-

based facilities and previous space telescopes, it will revolutionize the field and it will

! Easily constrain the atmosphere composition, chemistr y and

physical properties for Jupiters and Neptunes, and for a few super-Earths. ! Possibly detect some atmospheric spectral features for a few earth-sized planets.
! For giant planet imaging, JWST will be mainly

complementar y to ground-based facilities and will
! Characterize known planets at longer wavelengths. ! Find new planets in regimes or around targets that are not

accessible from the ground.


END