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HST/STIS Imaging of the HR 4796A Debris Ring

HST/STIS Imaging of the HR 4796A Debris Ring. Glenn Schneider. Steward Observatory University of Arizona. A.J. Weinberger (UCLA) E.E. Becklin (UCLA) B.A. Smith (U. Hawaii) D.C. Hines (UofA) M.D Silverstone (UofA) E. Malumuth (GSFC) NICMOS IDT & EONS Teams. HR 4796A.

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HST/STIS Imaging of the HR 4796A Debris Ring

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  1. HST/STIS Imaging of the HR 4796A Debris Ring Glenn Schneider Steward Observatory University of Arizona A.J. Weinberger (UCLA) E.E. Becklin (UCLA) B.A. Smith (U. Hawaii) D.C. Hines (UofA) M.D Silverstone (UofA) E. Malumuth (GSFC) NICMOS IDT & EONS Teams

  2. HR 4796A Young (~8±3 Myr; Stauffer 1995) “Vega-like” A0V M.S. star. Koerner et al. (1998) Koerner et al. (1998) and Jayawardhana et al. (1998) independently imaged the disk in the mid-IR. An inner depleted region was evident in 20.8mm image, and reproduced with a model suggesting: Large amount of circumstellar dust inferred from IRAS excess, Ldisk/L* = 5 x 10-3 (Jura 1991), TWICE that of b Pictoris. Tdust = 110K suggested lack of material @ r < 40AU, and grains > 3mm @ 40AU < r < 20 AU to be bound (Jura 1995). Member of TW Hya Association (Webb et al, 1999), at a distance of 67±3pc (Hipparchos). i =72°± ; rin = 55AU; rout = 80AU; PA=28°±6°. 6°9°

  3. The Dusty Disk/Planet Connection? Current theories of disk/planet evolution suggest a presumed epoch of planet-building via the formation and agglomerative growth of embryonic bodies, and the subsequent accretion of gaseous atmospheres onto hot giant planets, is attendant with a significant decline in the gas-to-dust ratios in the remnant protostellar environments. In this critical phase of newly formed (or forming) extra-solar planetary systems, posited from a few megayears to a few tens of megayears, the circumstellar environments become dominated by a second-generation population of dust containing larger grains arising from the collisional erosion of planetesimals.

  4. Observing scattered light from circumstellar debris has been observationally challenging because of the very high Star:Disk contrast ratios in such systems. 1984 - B.A. Smith & R.J. Terrile 6" radius coronagraphic mask, Las Campanas (discovery image) Until very recently the large, and nearly edge-on disk around b Pictoris remained the only such disk imaged. b Pictoris Need space, or ground-based/AO*, coronagraphic systems. * but still very challenging. Resolved imaging spatial distribution of dust/debris. Direct (Scattered Light) Imaging of Dusty Debris Asymmetries (radial & azimuthal): • May implicate low-mass perturbers (planets) from: Rings, Central Holes, Gaps, Clumps, Arcs, Arclets • Help Elucidate the scattering & physical properties of the grains.

  5. HST Provides... Very high stability and repeatability of Point Spread Function. Strehl ratios 95—98% depending upon imaging mode. Near-IR (NICMOS) and Optical (STIS) coronagraphy with rejection factors of a few to ~ 10 within a few arcseconds of an occulted star. Sub-arcsecond spatial resolution (~ 50—160mas at 0.5—1.6mm). (E.g., see poster [77.17] in this special session).

  6. F160W -1.0 -0.5 0.0 N 0.5 E mJy/pixel 1.0 0 20 40 60 80 Arc Seconds (Y) F110W -1.0 FLUX DENSITY 12.8±1.0mJy @ 1.1mm 12.5±2.0mJy @ 1.6mm H(F160W) = 12.35± J(F110W) = 12.92±0.08 -0.5 0.160.19 0.0 N 0.5 E Tdust ~ Ldisk/L* 1.4±0.2x10-3 @ 1.1mm 2.4±0.5x10-3 @ 1.6mm mJy/pixel 1.0 0 20 40 60 80 100  1.5  1.0  0.5 0.0 -0.5 -1.0 -1.5 Arc Seconds (X) NICMOS Observations of the HR 4796A Circumstellar Debris Ring GEOMETRY PA = 26.8°±0.6° i = 73.1°±1.2° a = 1.05”±0.02” MORPHOLOGY r = 70AU width < 14AU “abrupt” truncation “clear” @ r < 50 AU NIR scattered flux in goodagreement with visible absorption & mid-IR re-radiation.

  7. F160W -1.0 -0.5 0.0 N 0.5 E mJy/pixel 1.0 0 20 40 60 80 Arc Seconds (Y) F110W -1.0 -0.5 0.0 N 0.5 E mJy/pixel 1.0 0 20 40 60 80 100  1.5  1.0  0.5 0.0 -0.5 -1.0 -1.5 Arc Seconds (X) NICMOS Observations of the HR 4796A Circumstellar Debris Ring Anisotropies NE ansa ~ 15% brighter than SW ansa. Suggestion of preferential (forward) scattering to SE. Implications Possible dynamical confinement of particles by one or more unseen bodies. Mean particle size > few mm. debris origin, not I.S. dust.

  8. HR 4796A Circumstellar Debris Ring NICMOS Additional processing recovered ring flux closer in and suggested somewhat higher inclination (~76°). “Clumpiness” due to residuals in PSF subtraction, not attributed to structure of ring.

  9. HR 4796A Circumstellar Debris Ring STIS

  10. OBSERVATIONS

  11. STIS Observations of the HR 4796A Circumstellar Debris Ring Orient #1 HR 4796A

  12. STIS Observations of the HR 4796A Circumstellar Debris Ring Orient #1 HR 4796A HR 4748 (PSF)

  13. STIS Observations of the HR 4796A Circumstellar Debris Ring Orient #1 Orient #2 HR 4796A DOrient = 16° HR 4748 (PSF)

  14. STIS Observations of the HR 4796A Circumstellar Debris Ring Orient #1 Orient #2 HR 4796A DOrient = 16° HR 4748 (PSF)

  15. STIS Observations of the HR 4796A Circumstellar Debris Ring Orient #1 Orient #2 + _ HR 4796A HR 4748 (PSF)

  16. Edge Brightening& Tendrils From Decentering Defocus& Zonal Artifacts From “Breathing” STIS Observations of the HR 4796A Circumstellar Debris Ring Orient #1 Orient #2 PSF Subtractions

  17. Better Focus Match Better Position Match Better Focus Match Better Position Match STIS Observations of the HR 4796A Circumstellar Debris Ring PSF Orient #1 PSF Orient #2 PSF Subtractions

  18. STIS Observations of the HR 4796A Circumstellar Debris Ring PSF Orient #1 PSF Orient #2 2-rollssamplesregionsotherwiseobscuredby wedge& spikes N E PSF Subtractions

  19. STIS Wedge and Diffraction Spike Masks Orient #1 Orient #2 N E Individually Unsampled or Corrupted Regions

  20. STIS Observations of the HR 4796A Circumstellar Debris Ring PSF Orient #1 PSF Orient #2 N E Masked PSF Subtractions

  21. COMBINATION&POST-PROCESSING

  22. STIS Observations of the HR 4796A Circumstellar Debris Ring 4 3 N 2 1 E 0 Combined (Weighted) Mask

  23. STIS Observations of the HR 4796A Circumstellar Debris Ring N E But... Combined Image-20% to +100%Stretch

  24. STIS Observations of the HR 4796A Circumstellar Debris Ring Empirically determined background correction... GlobalBackgroundNulling Not PerfectlyAchieved Due To PSF Mis-Matches N E Combined Image-5% to +5%Stretch

  25. STIS Observations of the HR 4796A Circumstellar Debris Ring N E < +2% Peak Flux

  26. STIS Observations of the HR 4796A Circumstellar Debris Ring N E < 2% Flux & No Wedge/Spikes

  27. STIS Observations of the HR 4796A Circumstellar Debris Ring Interpolate across regions of disk flux With variable length/width 2D-Gaussian kernel N E Masked Background-5% to +5%Stretch

  28. STIS Observations of the HR 4796A Circumstellar Debris Ring N E Re-Masked Interpolated Background-5% to +5%Stretch

  29. STIS Observations of the HR 4796A Circumstellar Debris Ring N E Interpolated Background Subtracted-5% to +5%Stretch

  30. STIS Observations of the HR 4796A Circumstellar Debris Ring Combined Image - Resampled

  31. RESULTS (thus far)from this image

  32. HR 4796A RING GEOMETRY (Least-Squares Isophotal Ellipse Fit) Ansal Separation (Peaks) = 2.107” ± 0.0045” Major Axis of BFE = 2.114” ± 0.0055" P.A. of Major Axis (E of N) = 27.06° ± 0.18° Major:Minor Axial Length = (3.9658 ± 0.034): 1 Inclination of Pole to LOS = 75.73° ± 0.12° Photocentric Offset from BFE(Y) = -0.0159" ± 0.0048" Photocentric Offset from BFE(X) = +0.0031" ± 0.0028"

  33. HR 4796A Circumstellar Debris Ring - WIDTH * * Slightly asymmetric WIDTH AT NE ANSA FWHM: 12.9±0.7AU 9.6% Dring 1-e-1: 7.5±0.4AU 11.9% Rring Brightness (Normalized to NE Ansa) Measured = 0.197” PSFpoint source= 0.043” FWHM ring= 0.192” 1-e-1 = 0.126”

  34. RING GEOMETRY - Least-Squares Isophotal Ellipse Fit Ansal Separation (Peaks) = 2.107” ± 0.0045” Major Axis of BFE = 2.114” ± 0.0055" P.A. of Major Axis (E of N) = 27.06° ± 0.18° Major:Minor Axial Length = (3.9658 ± 0.034): 1 Inclination of Pole to LOS = 75.73° ± 0.12° Photocentric Offset from BFE(Y) = -0.0159" ± 0.0048" Photocentric Offset from BFE(X) = +0.0031" ± 0.0028"

  35. “FACE-ON” PROJECTION - With Flux Conservation

  36. Spatially Resolved Relative PHOTOMETRY of the Ring

  37. N-Sigma Brightness Ratio (Percent)

  38. PHOTOMETRIC ERROR ESTIMATION

  39. N-Sigma Brightness Ratio (Percent)

  40. Aperture Photometry STIS(leff 0.58 mm): F(ring[unobscured])/F(star) = 0.00049 ± 0.000036 (7.3%) NICMOS (leff 1.10 mm): F(ring[unobscured])/F(star) = 0.00083 ± 0.00012 (14.3%) NICMOS (leff 1.60 mm): F(ring[unobscured])/F(star) = 0.00140 ± 0.00029 (20.8%)

  41. Wavelength Dependent Scattering Efficiency (Color)

  42. Ring geometry/astrometry defined by NICMOS improved by higher resolution STIS observations. Notably, i 2.6° larger than original (published) NICMOS solution. “Left/Right” brightness anisotropy or ~20% along at least 50° wide diametrically opposed arcs centered on ansae. “Front/Back” brightness anisotropy, roughly symmetric in both L/R “hemispheres”, increasing with longitudinal distance from ansae to 35% difference at 30° from ansae. Characteristic width ~ 10% of 70AU radius ring. Spatially resolved photometry of ring with ±2% uncertainty at ansae (1”), and ±6—8% uncertainty at 0.6—0.5”. Ring is uniformly RED from “V” to H with 1:1.7:2.9 spectral reflectance in CCD50(“V”):F110W(1.1mm):F160W(H). SUMMARY

  43. SUMMARY We eagerly await the opportunity to continue exploiting these capabilities when both are re-awakened and fully restored to service. A unique venue for sub-arcsecond high contrast imaging in the near-IR and optical is afforded by HST/NICMOS & STIS.

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