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A Planet’s Rocky Road to Success: Spitzer Observations of Debris Disks

A Planet’s Rocky Road to Success: Spitzer Observations of Debris Disks G. H. Rieke, for the MIPS team major contributors are Chas Beichman, Geoff Bryden, Nadya Gorlova, Beth Holmes, James Muzerolle, John Stansberry, Karl Stapelfeldt, Kate Su, David Trilling, Erick Young,

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A Planet’s Rocky Road to Success: Spitzer Observations of Debris Disks

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  1. A Planet’s Rocky Road to Success: Spitzer Observations of Debris Disks G. H. Rieke, for the MIPS team major contributors are Chas Beichman, Geoff Bryden, Nadya Gorlova, Beth Holmes, James Muzerolle, John Stansberry, Karl Stapelfeldt, Kate Su, David Trilling, Erick Young, Jane Morrison, Karl Gordon, and Karl Misselt

  2. A Planet’s Rocky Road to Success: Spitzer Observations of Debris Disks G. H. Rieke, for the MIPS team major contributors are Chas Beichman, Geoff Bryden, Nadya Gorlova, Beth Holmes, James Muzerolle, John Stansberry, Karl Stapelfeldt, Kate Su, David Trilling, Erick Young, Jane Morrison, Karl Gordon, and Karl Misselt Summary: Spitzer provides the means to study the first stages of planet formation in some detail, and to connect them with theories for the evolution of the early Solar System.

  3. A Planet’s Rocky Road to Success: Spitzer Observations of Debris Disks G. H. Rieke, for the MIPS team major contributors are Chas Beichman, Geoff Bryden, Nadya Gorlova, Beth Holmes, James Muzerolle, John Stansberry, Karl Stapelfeldt, Kate Su, David Trilling, Erick Young, Jane Morrison, Karl Gordon, and Karl Misselt Summary: Spitzer provides the means to study the first stages of planet formation in some detail, and to connect them with theories for the evolution of the early Solar System. • Can all stars (excepting certain binaries) form terrestrial planets? • How are terrestrial planets built around other stars? • Can we use other systems to test theories for the formation of • the Teerrestrial planets?* * in the solar system

  4. Protoplanetary Disks are the residual interstellar gas and dust left from the formation of a star.

  5. HST has imaged some famous protoplanetary and transitional circumstellar disks. Still, our understanding of them is generally limited to a few examples. HH 30

  6. HST has imaged some famous protoplanetary and transitional circumstellar disks. Still, our understanding of them is generally limited to a few examples. Do all stars form with potentially planet-forming disks? HH 30

  7. Low resolution spectra and even photometry with Spitzer can constrain the structure of protoplanetary disks.

  8. IRS photosphere • Spectral Comparisons • TW Hya has amorphous • silicates and a dust • clearing very close • (roughly < 1 AU) • to the star (note • absence of excess • emission at • 4 - 7mm) • Hen 3-600 has crystalline • silicates, and more • material very close • to the star. silicates large grains From Uchida et al. 2004, ApJS, 154, 439

  9. IRS Disk Clearing in Young Stars: In some cases, spectra demonstrate very thorough clearing at < 1 MYr • Class I T Tau stars (i.e, with large • far infrared excess) show • a large variety of clearing • of the inner disks, including • CoKu Tau 4, thoroughly • cleared to well beyond 1 AU. • These stars are very young, • probably < 1 Myr. From Watson et al. 2004, ApJS, 154, 391

  10. IRS Disk Clearing in Young Stars: In some cases, spectra demonstrate very thorough clearing at < 1 MYr How common is this behavior? • Class I T Tau stars (i.e, with large • far infrared excess) show • a large variety of clearing • of the inner disks, including • CoKu Tau 4, thoroughly • cleared to well beyond 1 AU. • These stars are very young, • probably < 1 Myr. From Watson et al. 2004, ApJS, 154, 391

  11. Spitzer Photometric Probes of Protoplanetary Disks: NGC 7129: Embedded cluster at an age of ~ 1 Myr and distance of ~ 1 kpc. From Muzerolle et al. 2004, ApJS, 154, 379

  12. Spitzer Photometric Probes of Proto- planetary Disks: Combined IRAC/MIPS survey of NGC 7129 shows a number of sources with small excesses out to 8mm, but strong ones at 24mm. It appears that protoplanetary disk clearing has already occurred within an AU of these stars. From Muzerolle et al. 2004, ApJS, 154, 379

  13. Disk clearing in NGC 2068/2071: ~ 0.5 MYr dashed line - average T Tau dotted line - photosphere dot-dash line - TW Hya Muzerolle, private communication

  14. Other approaches also indicate that some protoplanetary disks clear very quickly. • 16 + 8% of 0.5 Myr-old stars have no 3.6mm excess (Haisch et al. (2001)) • In r Oph, we have selected 17 stars (from Bontemps et al. 2001) with • luminosity > 1 Lsun and of class II or III. Six have negligible • excesses between 2 and 14mm. These objects are probably • ~ 0.5 MYr old. • A CO (J = 2-1) survey of 12 weak-lined T Tau stars yielded, for 11 of them, • upper limits of 6 X 10-7 Msunfor the mass of gas in their circumstellar • disks. A 1.3mm continuum survey set upper limits of 2 X 10-4 Msun to the • dust mass in the disks (Duvert et al 2000) • It is estimated that the solar system required a disk mass of about • 0.01 Msun(Carpenter 2002) We are discovering that many of these systems clear quickly close-in to the star

  15. Other approaches also indicate that some protoplanetary disks clear very quickly. • 16 + 8% of 0.5 Myr-old stars have no 3.6mm excess (Haisch et al. (2001)) • In r Oph, we have selected 17 stars (from Bontemps et al. 2001) with • luminosity > 1 Lsun and of class II or III. Six have negligible • excesses between 2 and 14mm. These objects are probably • ~ 0.5 MYr old. • A CO (J = 2-1) survey of 12 weak-lined T Tau stars yielded, for 11 of them, • upper limits of 6 X 10-7 Msunfor the mass of gas in their circumstellar • disks. A 1.3mm continuum survey set upper limits of 2 X 10-4 Msun to the • dust mass in the disks (Duvert et al 2000) • It is estimated that the solar system required a disk mass of about • 0.01 Msun(Carpenter 2002) We are discovering that many of these systems clear quickly close-in to the star What happens in the ones that retain disks? How do they form planets?

  16. After the gas has cleared from the protoplanetary disk, terrestrial planet building continues through collisions of the planet embryos. Artist’s concept by Chris Butler

  17. This stage may have eventually led to colossal collisions between large bodies, such as the one responsible for the formation of the moon. ….. four hours later From Bill Hartmann, 1 hour after the collision

  18. This accretion end game has only been accessible in computer • simulations* - the traces are obviously largely erased in the solar • system and out of reach around other stars. • Chambers, 2001, Icarus, 152, 205 • Kenyon & Bromley 2004, ApJL, 602, L133 * and space art

  19. 6 7 8 6 7 8 Log time(yr) Log time(yr) Detailed numerical simulations suggest that the 20mm flux from a system in the accretion end game will show spikes as a result of major collisions that throw debris into circumstellar space. Q - Q0 is the excess 20mm emission above the stellar photosphere, Q0. Kenyon & Bromley 2004

  20. 6 7 8 6 7 8 Log time(yr) Log time(yr) Detailed numerical simulations suggest that the 20mm flux from a system in the accretion end game will show spikes as a result of major collisions that throw debris into circumstellar space. Q - Q0 is the excess 20mm emission above the stellar photosphere, Q0. But is this picture correct? If so, how long does it last and what is the detailed behavior?

  21. 6 7 8 6 7 8 Log time(yr) Log time(yr) Detailed numerical simulations suggest that the 20mm flux from a system in the accretion end game will show spikes as a result of major collisions that throw debris into circumstellar space. Q - Q0 is the excess 20mm emission above the stellar photosphere, Q0. But is this picture correct? If so, how long does it last and what is the detailed behavior? One test is to image nearby systems and look for evidence of large collisions.

  22. Spitzer images of the nearest systems often show a familiar structure. e Eri 850mm to the left (Greaves et al. 1998); 70mm to the right (MIPS)

  23. The pattern is similar, but much elevated in brightness, to that in the solar system. Zodiacal cloud

  24. Disk becomes more asymmetric from submm to infrared, then fills in at 24mm. The asymmetry might be a resonance maintained by a massive planet. The filling-in is due to PR drag or to other processes that create particles < 100 AU from the star - comets, asteroid collisions Stapelfeldt et al. (2004, ApJS, 154, 458) Fomalhaut

  25. high resolution smoothed, star removed smoothed star Vega 1.3-mm data indicate similar structure to Fomalhaut. (Wilner et al. 2002, ApJL, 569, L115) model comparison with observation

  26. Spitzer images of Vega should be nearly identical to Fomalhaut, but face-on. Predicted Spitzer view of Vega system at 24mm (model from submm data of Wilner et al. 2002)

  27. Actual Spitzer Image at 70mm (Su et al., in prep.) (upper left shows model image to same scale)

  28. Although Vega and Fomalhaut are “twin” stars*, their debris systems look completely different! * They have similar masses, ages, distances, and spectral energy distributions.

  29. The Vega system is huge! ~ 600 AU

  30. For Vega, a constant color temperature with radius from 24 to 70mm indicates we are seeing small grains heated stochastically and being driven out of the system by photon pressure. Photon pressure is dominant for grains < 10mm in size grains in thermal equilibrium run of color temp with radius

  31. 24mm Fits to the radial profile at the three MIPS bands are consistent with a radiation- pressure- driven wind, with a central hole similar in size to the hole in the ring seen in the mm-wave.

  32. 70mm Fits to the radial profile at the three MIPS bands are consistent with a radiation- pressure- driven wind, with a central hole similar in size to the hole in the ring seen in the mm-wave.

  33. 160mm Fits to the radial profile at the three MIPS bands are consistent with a radiation- pressure- driven wind, with a central hole similar in size to the hole in the ring seen in the mm-wave.

  34. The infrared radiometric properties of the Vega system are dominated by small grains (< 10mm) that have a short lifetime within the system (~ 300 yr) and may originate in the ring of larger grains seen in the mm-wave.

  35. Another eccentric debris system: HD 69830 is a ~ 3 Gyr old K0V star. Its debris system excess is strong at 24mm (unusual for a star of this age) and non-existent at 70mm (even more unusual)

  36. Subtracting the photosphere, it is apparent that the excess is purely crystalline silicate grains of size 1mm or less (Beichman et al.)

  37. This star poses a similar problem to Vega: such small grains have a short lifetime around the star. • Assume that the small grains are maintained by a standard collisional • cascade. Then the grain size distribution is given by • n(a) da = C a-3.5 da (Dohnanyi 1968) • Integrating up to 100km parent bodies, the required mass is ~ 104 • times the mass actually seen in the radiating grains • The Poynting-Robertson loss time for this system and grain size is • ~ 105 years • To maintain the system in its current configuration for 3GYr would • require ~ 10Mearth or more (if we assume the activity has tended • to decay over this time) • For Vega, the problem is similar to an order of magnitude worse • because of the ~ 300 yr grain lifetime against photon pressure

  38. The most likely explanation for both stars is that the debris systems have been greatly augmented by some recent, major event.

  39. The most likely explanation for both stars is that the debris systems have been greatly augmented by some recent, major event. Do we see anything similar in other stars?

  40. The SEDs of debris systems show a huge variety, consistent with many of them being dominated by a single, recent event. youngest intermediate oldest from Rieke et al. 2005

  41. Enough anecdotal examples! What is the overall pattern?

  42. Enough anecdotal examples! What is the overall pattern? We now look at debris disk behavior on a statistical basis • Use sample of 266 stars within a factor of 1.5 of 2.5 Msun • Take ages from cluster, moving group membership • Supplement with ages from HR diagram • Concentrate on 24mm excesses, since can detect photospheres • at high SNR at this wavelength, so debris disk sample is complete. • Probes debris systems from ~ 5 to ~ 50 AU.

  43. NGC 2547 is a cluster of age ~ 25Myr and at a distance of ~ 450pc. (Young et al. 2004, ApJS, 154, 428)

  44. one relatively low mass cluster member has a very large 24mm excess. Main sequence Decreasing mass NGC 2547: 25 Myr old cluster and many other ~A stars have modest excess

  45. M47 is a ~ 100 Myr old cluster

  46. P1121has a K - [24] excess of ~ 3.7 magnitudes! It is a late F star. (Gorlova et al. 2004, ApJS, 154, 448) Many ~A stars have modest excesses.

  47. age from HRD 4 Msun 200 MYr 400 MYr age from cluster, moving groups 800 MYr 1.5 Msun Determining overall behavior requires a larger sample at 24mm: Sample of 266 stars on the HR Diagram (from Rieke et al., ApJ in press).

  48. Ages have large uncertainties, but are adequate to examine debris system behavior.

  49. 24mm excesses decay over ~ 200 Myr - in fact, many stars of all ages have no, or very little excess.

  50. Upper envelope of the excesses goes as 1/t.

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