Detection and Characterization of Exo Asteroid Belts

Transcription

1 Detection and Characterization of Exo Asteroid Belts Kate Su Steward Observatory University of Arizona

2 Solar System s Debris Disk Two leftover planetesimal (parent body) belts Asteroid Belt (2 4 AU): km size bodies its structure greatly influenced by Jupiter Kuiper Belt (30 50 AU): large icy bodies the inner edge maintained by Neptune edge on view Sun face on view ice line distance not to scale

3 Methods of Detecting of Exo Asteroid Belts Spatially Resolving Dust Components temperature K 40 50K exo AB exo pc Sun like star: 3 AU 30 AU Early type star: 10 AU 100 AU Nearby stars Fab4 are prime targets, but stellar photospheres are bright

4 Methods of Detecting of Exo Asteroid Belts Spatially Resolving Dust Components exo AB exo pc Sun like star: 3 AU 30 AU Early type star: 10 AU 100 AU Nearby stars Fab4 are prime targets, but stellar photospheres are bright Spectrally Separating Dust Components edge on view of a planetary system distance not to scale??? distance, r dust temperature ~ 1500 K K terrestrial zone 150 K asteroidal zone 50 K Kuiper belt zone 2 m 5 10 m 24 m m peak wavelength of emission, (r) disk halo

5 Massive Asteroid Belt around Lep The first paper pointed out the detection of an exo Asteroid belt by Chen & Jura 2001 (Before Spitzer Era!) scaled excess flux mjy

6 Inner vs. Outer Zones in Debris Disks Illustration Fomalhaut (A3V) MIPS 24 μm MIPS 70 μm SCUBA 850 μm 7.7 pc Eridani (K2V) Stapelfeldt et al pericenter glow Holland et al pc All images are in the same orientation and angular size. clumpy structure Backman et al Greaves et al. 1998

7 Challenges of Identifying of Exo Asteroid Belts Identification with SED only Stars dominate the signal/noise at short wavelengths, making the detection of faint warm excess challenging subject to photospheric extrapolation flux density (mjy) flux contaminated from the cold ring IRS excess after nomial phot. sub IRS excess with +/ 2% phot. unc. One BB of 171 K 10 1 Two BBs of 167 K K uncertainty wavelength (μm)

8 Challenges of Identifying of Exo Asteroid Belts Identification with SED only Stars dominate the signal/noise at short wavelengths, making the detection of faint warm excess challenging subject to photospheric extrapolation SED models are degenerate weak warm excesses can arise from 1 Dragged in grains van Lieshout Cometary delivery Lebreton+13 3 Grain properties like grain size distribution Kennedy & Wyatt 2013 van Lieshout+ 2014

9 Challenges of Identifying of Exo Asteroid Belts Identification with SED only Stars dominate the signal/noise at short wavelengths, making the detection of faint warm excess challenging subject to photospheric extrapolation SED models are degenerate weak warm excesses can arise from 1 Dragged in grains van Lieshout Cometary delivery Lebreton+13 3 Grain properties like grain size distribution Kennedy & Wyatt 2013 Identification with marginally Resolved Images van Lieshout Barely separating the cold and warm components Dragged in grains, under the influence of PR and stellar wind drags, from the cold component can mimic a warm component due to temperature effect Eri, Reidemeister+2011 Unresolved between the star and the warm component Excesses can be star related, e.g., free free emission from stellar wind Fomalhaut, Acke+2012 Stellar Subtractions for nearby stars are challenging subject to saturation

10 Is there a Central Component in the Vega Disk? Herschel PACS 70 m (Fomalhaut s debris twin) photosphere subtracted solid: star+disk dashed: disk only

11 Is there a Central Component in the Vega Disk? Herschel PACS 70 m Spitzer MIPS 24 m photosphere subtracted photosphere subtracted Saturated! solid: star+disk dashed: disk only after phot. sub. Su et al. 2013

12 Debris Disk Twins: Vega and Fomalhaut Vega face on PACS 70 m A0V star, 7.6 pc ~500 Myr far IR excess from particles in an enhanced KB face on asteroid belt with T d ~170 K and f d ~7x10 6 Fomalhaut A4V star, 7.7 pc ~400 Myr far IR excess from particles in an enhanced KB inclined by 67 o asteroid belt with T d ~170 K and f d ~2x10 5 inclined PACS 70 m Su et al. 2013

13 ALMA Cycle 1 Observation of the Fomalhaut Disk Fomalhaut Fomalhaut One point source at the star position with a total flux of 1.9 mjy, consistent with being the stellar photosphere. Rule out any free free emission scenario proposed by Acke+12 (as previous submm/mm observations). Su et al. 2016

14 ALMA Cycle 1 Observation of the Fomalhaut Disk star subtracted Fomalhaut Fomalhaut One point source at the star position with a total flux of 1.9 mjy, consistent with being the stellar photosphere. Rule out any free free emission scenario proposed by Acke+12 (as previous submm/mm observations). Su et al No bright (>3 ) structure near the star within 15 AU radius. A few 1 2 blobs are along the disk circumference dash ellipse of a 13 AU belt assuming the same inclination and position angles as the outer belt, and no offset.

15 Fomalhaut s Inner Debris Structures Our asteroid belt Analog Fixed parameters:. ~2.5 5 μ, ~1 Silicate grains A narrow ring with a width of 2 AU The narrow belt can be at 8 15 AU, with F 870 m <1.3 mjy (3 ) noiseless ALMA simulation w/ star contours of 20, 36 Jy/beam flux density (mjy) Lebreton model 9 AU NR model 13 AU NR model flux contaminated from the cold ring noisy ALMA simulation w/ star subtraction wavelength (μm)

16 The Fomalhaut Debris Disks Spitzer 24 m Stapelfeldt+ 2004; Su Herschel 70 m Acke+2012; Su ALMA 870 m Boley HST 0.6 m Kalas peri center glow arcsec arcsec 1500 K very hot dust 0.1 AU grains under B trapping? 500 K hot dust a few AU grains under P R drag.?? 170 K warm dust 8 15 AU in situ P. B. Su et al. 2016??? b 110 AU Kalas+2008, 2013 not the shepherding planet 50 K cold dust AU in situ P. B. disk halo more than 250 AU grains under radiation pressure.

17 Dusty Disks in Hot White Dwarfs An unexpected discovery of warm dust around hot white dwarfs Su et al. 2007; Chu, Su, Bilikova et al. 2011; Bilikova et al An unresolved infrared excess around the central star a very hot, young white dwarf 110,000 K) in the Helix Nebula (at 219 pc). IRAC (blue and green) + MIPS 24 m (red)

18 Dusty Disk in the Helix Nebula The excess in Helix is consistent with a debris dust at AU a possible rejuvenated exo KBO belt? (Su et al. 2007) 10 2 flux density (mjy) BB of 100 K DDM w/ Silicates IRAC (blue and green) + MIPS 24 m (red) wavelength (μm)

19 Dusty Disk in the Helix Nebula The excess in Helix is consistent with a debris dust at AU a possible rejuvenated exo KBO belt? (Su et al. 2007) flux density (mjy) the Helix BB of 100 K at AU 3 upper limits at submm/mm wavelength (μm)

20 Dusty Disk in the Helix Nebula The excess in Helix is consistent with a debris dust at AU a possible rejuvenated exo KBO belt? (Su et al. 2007) 10 2 flux density (mjy) 10 2 MIPS photometry IRAS color cor. Lep IRS spectrum BB of 190 K at 2 20 AU MIPS SED spectrum flux density (mjy) the Helix BB of 100 K at AU 3 upper limits at submm/mm PACS photometry wavelength (μm) wavelength (μm) a possible rejuvenated exo Asteroid belt? (the massive Lep exo Asteroid belt the Helix A polluted WD?)

21 Thank you, Mike, for being an extraordinary inspiration and role model! You will be deeply missed.