Mid-IR and Far-IR Spectroscopic Measurements & Variability. Kate Su (University of Arizona)

Transcription

1 Mid-IR and Far-IR Spectroscopic Measurements & Variability Kate Su (University of Arizona)

2 Five Zones of Debris Dust edge-on view of the Fomalhaut planetary system distance, r 1500 K very hot dust 500 K hot dust??? discovered by HST T d ~ 1 r disk halo b exo-zodi probed by NIR interferometry exo-zodi probed by MIR interferometry 150 K warm dust probed by Spitzer & Hersche, ALMA (?) 50 K cold dust probed by Spitzer, Herschel, HST, and partially by ALMA tailored for the Fomalhaut Planetary System

3 Far-Infrared Spectroscopy Trace Material in the cold Zone ISO Long Wavelength Spectrometer (LWS) Herbig Ae/Be Stars: crystalline silicates, crystalline water ice, phyllosilicates No debris disks ( 2 orders of mag. fainter) HD HD Malfait et al. 1998, 1999

4 Far-Infrared Spectroscopy Trace Material in the cold Zone Spitzer MIPS/MIPS-SED mode (R 20 in the range of mm) crystalline water ice feature in HD amorphous olivine crystalline water ice Chen et al. 2008

5 Far-Infrared Spectroscopy Trace Material in the cold Zone Spitzer MIPS/MIPS-SED mode Su et al Block bottom

6 Far-Infrared Spectroscopy Trace Material in the cold Zone Spitzer MIPS/MIPS-SED mode Su et al Herschel/PACS Block bottom 69 mm Mg-rich, Fe-poor (1%) crystalline olivine feature 1% * of total dust mass de Vries+ 2012

7 Far-Infrared Spectroscopy Trace Material in the cold Zone Spitzer MIPS/MIPS-SED mode Su et al mm Mg-rich, Fe-poor crystalline olivine feature (Forsterite, Mg 2 SiO 4 ) 5% of total dust mass (Su et al. 2015)

8 Far-Infrared Spectroscopy Trace Material in the cold Zone? Spitzer MIPS/MIPS-SED mode Su et al. 2015

9 Far-Infrared Spectroscopy Trace Material in the cold Zone? Spitzer MIPS/MIPS-SED mode Su et al. 2015

10 Mid-Infrared Spectroscopy Trace Material in the Inner Zone? Can Excess Emission Trace Dust Location? Blue diamonds: MIPS 24 and 70 mm phot. Green lines: IRS spectra Purple lines: MIPS-SED spectra Many papers on mid-ir spectroscopy of a sample of debris disks: Chen+ 2006; Beichman+ 2006; Carpenter+2009; Molales+2009; Chen+2009; Lawler+2009; Dodson- Robinson+2011; Morales+2011; Moor+2011, Olofsson+2012; Ballering+ 2013; Chen+2014; Kennedy+ 2014; Ballering+ 2014; Mittal many others on specific objects

11 Similar Dust Temperature Distribution Stars selected based on 24 mm excesses with ages <1 Gyr : 19 solar-like and 50 early-type stars (Morales et al. 2011) Similar T d distributions between solar-like and early-type stars!

12 Dust Temperature Distribution Based on 300 debris disks observed with Spitzer IRS (10-35 mm spectra), Spitzer MIPS and Herschel PACS photometry data KBO-like Asteroid-like Terrestrial Based on results published before 2014

13 How Many Two-Temperature Disks? KBO-like Asteroid-like Terrestrial 20% 30% by simple counting Based on results published before 2014

14 How Many Two-Temperature Disks? KBO-like Asteroid-like Terrestrial Based on results published before % 30% by simple counting Many biases in the sample Kennedy+2014 toward brighter disks large errors (dominated by stellar photospheres) for faint warm components warm components can be due to solid-state features MIR excesses decay much faster than FIR excesses (age factor)

15 How Many Two-Temperature Disks? KBO-like Asteroid-like Terrestrial Based on results published before % 30% by simple counting Many biases in the sample Kennedy+2014 toward brighter disks large errors (dominated by stellar photospheres) for faint warm components warm components can be due to solid-state features MIR excesses decay much faster than FIR excesses (age factor) Two ratio plot (R f vs. R T ) R T = T w T c R f = f w f c

16 How Many Two-Temperature Disks? Use R f vs. R T plot to identify interesting objects Crv

17 How Many Two-Temperature Disks? Use R f vs. R T plot to identify interesting objects Crv Crv

18 How Many Two-Temperature Disks? Use R f vs. R T plot to identify interesting objects Crv Crv Many high R f & R T (bright and hot disks) objects from Chen+2014.

19 How Many Two-Temperature Disks? Use R f vs. R T plot to identify interesting objects Crv Crv Many high R f & R T (bright and hot disks) objects from Chen Chen+ 2014

20 How Many Two-Temperature Disks? Use R f vs. R T plot to identify interesting objects Crv Crv Many high R f & R T (bright and hot disks) objects from Chen Chen Using only IRS + MIPS 70 mm point, there should be a cutoff of R T ( 7) where the data cannot provide accurate dust temperature estimates. The presence of a hot belt in these systems requires further confirmation.

21 Debris Disk Variability HD a highly stirred system Beichman <3.3% change over 4 years

22 Debris Disk Variability HD a highly stirred system Beichman variable nonvariable <3.3% change over 4 years

23 A Different Class of Debris Disks The discovery of debris disk variability (Meng et al. 2012; Melis et al. 2012) suggests a new class of debris disks: Traditional Extreme Disk emission shows no change on yearly timescale (no change in HD 69830) Disk variability on monthly to yearly timescale (ID8 and others, Meng et al. 2015) f d 10-4, dominated by cold ( 80 K) disk (like the HIP105338) and only <1% with hot component within 1 AU like HD Found around all stages of stellar evolution, from 10 Myr to 10 Gyr. Dust is sustained by collisional cascade of km size bodies down to blowout size ( mm); time scale for disk variability is on the order of 10 3 to 10 6 years. Implication Bright and hot excesses usually starting at 3-5 mm with f d 10-2 and T d 400 K. All around stars from 10 Myr to 200 Myr (era of terrestrial planet formation) with one exception BD The presence of large amounts of small grains are related to stochastic, large impacts among big asteroids ( 500 km); the short timescale disk variability is consistent with the aftermath of such large impacts (ID8).

24 flatten excess (mjy) excess flux density (mjy) Spitzer 3.6 and 4.5 mm Monitoring for ID8 Relatively flat in 2012 Brightening event during the visibility gap Exponential flux decay: t days ( 1 yr) Quasi-periodic rising and falling behavior with 26 days and 33 days between peaks. After subtracting off the assumed base lines (dash lines in the upper panel).

25 flatten excess (mjy) excess flux density (mjy) Spitzer 3.6 and 4.5 mm Monitoring for ID8 Relatively flat in 2012 Brightening event during the visibility gap Exponential flux decay: t days ( 1 yr) Quasi-periodic rising and falling behavior with 26 days and 33 days between peaks. Detailed SED modeling suggests the dust in ID8 locates at AU (Olofsson+ 2012). After subtracting off the assumed base lines (dash lines in the upper panel).

26 flatten excess (mjy) excess flux density (mjy) Spitzer 3.6 and 4.5 mm Monitoring for ID8 Relatively flat in 2012 Brightening event during the visibility gap Exponential flux decay: t days ( 1 yr) Quasi-periodic rising and falling behavior with 26 days and 33 days between peaks. Detailed SED modeling suggests the dust in ID8 locates at AU (Olofsson+ 2012). After subtracting off the assumed base lines (dash lines in the upper panel). Two Major Challenges: (1) 1 yr time scale is too slow to be due to radiation blowout (2) 33 day period corresponds to 0.2 AU, which is twice closer than the dust location inferred from SED modeling.

27 Our Best Scenario Impact between two large (at least Vesta-size) asteroids Brightening: new dust produced by fragments and vapor condensates Decline: collisional destruction of vapor-produced condensates/droplets Gaspar s model suggests droplet size of 1 mm has a decay time scale of 1 yr.

28 Our Best Scenario Impact between two large (at least Vesta-size) asteroids Brightening: new dust produced by fragments and vapor condensates Decline: collisional destruction of vapor-produced condensates/droplets Gaspar s model suggests droplet size of 1 mm has a decay time scale of 1 yr. Quasi-Periodicity: orbital evolution of an impact produced cloud (A) an optically thick Keplerian-shearing cloud on a highly inclined, eccentric orbit (Meng et al. 2014). Two observed periods are first and second overtones of a genuine period of 75 days (0.35 AU) Jackson et al. in prep.

29 Our Best Scenario Impact between two large (at least Vesta-size) asteroids Brightening: new dust produced by fragments and vapor condensates Decline: collisional destruction of vapor-produced condensates/droplets Gaspar s model suggests droplet size of 1 mm has a decay time scale of 1 yr. Quasi-Periodicity: orbital evolution of an impact produced cloud (A) an optically thick Keplerian-shearing cloud on a highly inclined, eccentric orbit (Meng et al. 2014). Two observed periods are first and second overtones of a genuine period of 75 days (0.35 AU) (B) an optical thickness effect of on a highly inclined, circular orbit (Jackson et al. in prep) between the collision point/anti-collision line and inclination, P orb = 2P 1 + 2P days (0.46 AU) Jackson et al. in prep.

30 Future Direction JWST Era Mineralogical Monitoring with the James Webb Space Telescope (JWST) Spitzer IRS spectra Existing Spitzer mid-ir spectra show a rich variety of solid-state features. (dark gray dashed lines mark features from silica, and light gray ones for forsterite).

31 Future Direction JWST Era Mineralogical Monitoring with the James Webb Space Telescope (JWST) Spitzer IRS spectra Existing Spitzer mid-ir spectra show a rich variety of solid-state features. (dark gray dashed lines mark features from silica, and light gray ones for forsterite). High S/N and spectral resolution spectra with JWST can probe the detailed physical process of impacts through freshly generated dust. Time evolution of solid-state features: forsterite-rich to silica-rich then to forsterite-rich? ( /2009)