Observations of comets with high-resolution, wide-field. instruments. Jeff Morgenthaler. Who is Jeff Morgenthaler? Evolution of H

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1 Partial list of things to do Discovery of problem with OH photodissociation cross section Evolution of H O in cometary comæ Comet intro Who is Jeff Morgenthaler? Outline Jeff Morgenthaler Observations of comets with high-resolution, wide-field instruments

2 2 Jeff Morgenthaler soft ( kev) X-ray instrumentation MIT senior thesis: X-ray CCD quantum efficiency (Morgenthaler 1990) Wisconsin junior graduate student: X-ray Quantum Calorimeter (XQC) sounding rocket payload development (McCammon et al. 2002) 1995 Present soft X-ray background Ph.D. thesis: Shuttle STS-54 payload Diffuse X-ray Spectrometer (DXS) (Morgenthaler 1998; Sanders et al. 2001) Standard model: X-rays from a million degree plasma in the interstellar medium New twist: X-rays from charge exchange of solar wind ions, a process observed in comets (Lisse et al. 1996; Cravens 1997) Wisconsin Postdoc: Analyze comet Hale-Bopp optical emission line data (Morgenthaler et al. 2001, 2002a,b; Harris et al. 2002; Oliversen et al. 2002) NASA GSFC NRC postdoc: Io plasma torus observations using oxygen emission from Io s atmosphere (Oliversen et al. 2001) 2004? University of Washington postdoc: Get Walt Harris tenure

3 3 Where do comets come from? The primordial solar nebula Nebular collapse, planetary formation Dynamical things happen, planet orbits change, etc. Leftover planetesimals Rocky asteroids (2 3.5 AU) Icy Kuiper belt objects ( AU) Oort cloud objects (500 50,000 AU) dynamically ejected by planets primordial interstellar Dynamical evolution Apparition

4 % 4 What does a comet look like? Based on what we see coming off of comets, they are: Mostly water 5 15% CO % Other molecules, including organics % dust may or may not be similar to interstellar dust (as if interstellar dust has any typical form) More-or-less homogeneous comet fragments look like comets Dirty snowballs

5 Pudding with a skin vs. a ball of rice Deep Impact mission may help decide Need ground-based observations 2005 July 4 Comets evolve over many perihelion passages Comet nucleus often splits Dust is liberated particles follow comet orbit modified by radiation pressure Form coma more-or-less spherical distribution of gas density ranges from near atmospheric to interplanetary like a planetary atmosphere without gravity Ion tail solar radiation and charge exchange with solar wind ions ionizes some coma gas ions accelerated by solar wind acceleration moderated by collisions with neutrals, CO, other volatiles sublime 5 What happens to comets when they get close to the sun?

6 6 Fig. 1. Comet Hale-Bopp image courtesy of H. Mikuz & B. Kambic (

7 Ions interact with the solar wind (ion tail) and drag through neutrals (mass loading) and photodissociation products expand isotropically unless a strong reso- Neutral nance line induces a tailward force (Na and H) Ratio of each reaction rate to total is the branching ratio (BR) Quiet sun, at 1 AU, water lifetime = s (23 hours) Reciprocal of the sum of the reaction rates is the total lifetime Need a good solar spectrum and goes Different parts of solar spectrum do different things to photodissociates and ionizes in sunlight cross section to figure out where everything 7 Understanding evolution of H O in cometary comæ

8 # Morgenthaler et al. (2001); T Tozzi, Feldman, & Festou (1998). The van Dishoeck & Dalgarno OH cross sections have been calculated for a heliocentric velocity of -14 km s, appropriate for Hale-Bopp 1997 early March. H, Huebner et al. (1992); V, van Dishoeck & Dalgarno (1984); M, ".. BR H!! BR H BR H BR H BR H BR V Reaction BR Quiet Sun Active Sun Ref. Table 1. Photodissociation Branching Ratios 8

9 & ) $ $ +, +,- +., & (' * (1) No complex Q( -factor Much less quenching than radio transitions forbidden O( in The to P) transition occurs 1983) via the bright forbidden 6300, 6363 Å doublet s (Froese Fischer & Saha % decays promptly to the metastablë state OH resonant fluorescence is observed in the near UV at 3080 Å interpretation is complicated by a velocity dependent -factor (e.g. Schleicher & A Hearn 1988) OH rotational transitions are observable in the radio at 18 cm these transitions are easily quenched (e.g. Schloerb 1988) Dello Russo et al. 2000) is hard to observe directly hot band fluorescence in IR (Mumma et al. 1996; ) depends only on aperture photometry and branching ratios: 9 Observables

10 3 0 # 1 Conventional narrow-band filters don t work if narrow enough, lose too much to cometary redshift variation Spectral separation from airglow requires # resolution Background subtraction works if airglow stable Minimum spectral resolving power is / 0 4 or 80 km s Must separate cometary [O I] from cometary NH (geocentric velocity dependent) (/ 0 ' 2Å) and airglow [O I] Observational difficulties: If [O I] 6300 Å observations are so easy, why do we get it wrong? (1998) found: Results derived from observations of the forbidden oxygen lines are particularly discrepant, nearly always yielding water production rates larger than those derived from other datasets. Using radio, optical, and UV derived Q( ) values from comet Halley, Schleicher et al. 10 Problem

11 Observational difficulties have been solved Medium- to high-resolution long-slit or multi-object spectroscopy (e.g., Fink & Hicks 1996; Combi et al. 1999, fig. 3) Fabry-Pérot imaging and spectroscopy figs. 2 3 Fourier transform spectroscopy (e.g. Michelson or Spatial Heterodyne Spectroscopy) Bonus: high sensitivity due to large FOV and ability to match FOV to coma size, even at high resolving power

12 Voigt fit to bi.txt; chi^2 = 328 fit data resid (Plot generated Tue Jul 25 09:30:50 CDT 2000) Fig. 2. Wisconsin H-alpha Mapper (WHAM) spectrum (left) and image (right) of comet Hyakutake on 1996 March 23. Analysis conducted by high school interns Michelle Krok and Kyle Ripp.

13 9 # 13 Fig. 3. WHAM spectrum (left) and image (right) of Comet Hale-Bopp, from 1997 March 5 showing relative ease of [O I] 6300 Å detection even over an airglow-dominated 1 FOV. Resolving power of the WHAM Fabry-Pérot is 30,000, or 10 km s, (Tufte 1997; Morgenthaler et al. 2001; Haffner et al. 2003). Note unexplained tailward extension in the [O I] distribution.

14 OH radio or optical data needed to constrain OH lifetime Velocity resolved observations needed to constrain energetics BR4 Observations already exist for all of these This work shows BR3 needs to change Need to publish a paper on this Wide-field [O I] 6300 Å observations of Comets Hyakutake and Halley show a similar effect No model dependent aperture correction needed Only error could be in the branching ratios (Equation 1) WHAM observations corroborated by [O I] observations of three other instruments (Morgenthaler et al. 2001) WHAM spectroscopic observations were sensitive enough (0.1 R sensitivity limit in 30 s exposures) to detect all the [O I] emission coming from Hale-Bopp Wide-field [O I] 6300 Å observations of Hale-Bopp yielded Q( 3 4 times higher than other techniques ) values a factor of 14 Problem intensifies and suggests a solution

15 & Fig. 4. Hale-Bopp ( ) values from various works (Morgenthaler et al. 2001). 15

16 = : :.. 1 ' ; <= Fig. 5. Comet Hale-Bopp, 1 >5 6 7 #, ; ' # 16, Q( ) =

17 We need millions more graduate students We need to get efficient with those we have Computers (which are a waste of time!) are probably the answer Use of CCD cameras has increased complexity of data reduction and analysis by more than one million-fold Hyakutake dust images Hyakutake HCN That is just water! Tailward asymetry in [O I] 6300 Å emission Observations of Several effects seen in the Hale-Bopp data have not even been touched Only some of these data have been properly reduced Large amounts of data exist to constrain the photochemical models Wide-field obsevations of comets motivate modification of OH photochemistry 17 Summary

18 Haffner, L. M., Reynolds, R. J., Tufte, S. L., Madsen, G. J., Jaehnig, K. P., & Percival, J. W., The Wisconsin HDMapper Northern Sky Survey, ApJS, Vol. 149, p , Froese Fischer, C., & Saha, H. P., Multiconfiguration Hartree-Fock results with Breit-Pauli corrections for forbidden transitions in the configuration, Phys. Rev. A, Vol. 28, p , ACB Fink, U., & Hicks, M. D., A survey of 39 comets using CCD spectroscopy, ApJ, Vol. 459, p , Dello Russo, N., Di Santi, M. J., Magee-Sauer, K., Novak, R., & Rettig, T. W., Water Production and Release in Comet C/1995 O1 Hale-Bopp, Icarus, Vol. 143, p , Cravens, T. E., Comet Hyakutake x-ray source: Charge transfer of solar wind heavy ions, Geophys. Res. Lett., Vol. 24, p , Combi, M. R., Cochran, A. L., Cochran, W. D., Lambert, D. L., & Johns-Krull, C. M., Observation and Analysis of High-Resolution Optical Line Profiles in Comet Hyakutake (C/1996 B2), ApJ, Vol. 512, p , REFERENCES

19 Morgenthaler, J. P., Ph.D. thesis, The Study of the Diffuse X-ray Background between Morgenthaler, J. P., Bachelor s thesis, The Study of X-ray CCD Soft X-ray Quantum Efficiency, Massachusetts Institute of Technology, McCammon, D., Almy, R., Apodaca, E., Bergmann Tiest, W., Cui, W., Deiker, S., Galeazzi, M., Juda, M., Lesser, A., Mihara, T., Morgenthaler, J. P., Sanders, W. T., Zhang, J., Figueroa-Feliciano, E., Kelley, R. L., Moseley, S. H., Mushotzky, R. F., Porter, F. S., Stahle, C. K., & Szymkowiak, A. E., A High Spectral Resolution Observation of the Soft X-Ray Diffuse Background with Thermal Detectors, ApJ, Vol. 576, p , Lisse, C. M., Dennerl, K., Englhauser, J., Harden, M., Marshall, F. E., Mumma, M. J., Petre, R., Pye, J. P., Ricketts, M. J., Schmitt, J., Trumper, J., & West, R. G., Discovery of X-ray and Extreme Ultraviolet Emission from Comet C/Hyakutake 1996 B2, Sci, Vol. 274, p , Huebner, W. F., Keady, J. J., & Lyon, S. P., Solar photo rates for planetary atmospheres and atmospheric pollutants, Astrophys. Space Sci., Vol. 195, p , Comet C/1995 O1 (Hale-Bopp), ApJ, Vol. 578, p , Harris, W. M., Scherb, F., Mierkiewicz, E. J., Oliversen, R. J., & Morgenthaler, J. P., Production, Outflow Velocity, and Radial Distribution of and OH in the Coma of

20 HGFE Oliversen, R. J., Doane, N. E., Scherb, F., Harris, W. M., & Morgenthaler, J. P., Measure- for Interstellar Origin, Sci, Vol. 272, p , Mumma, M. J., Di Santi, M. A., Dello Russo, N., Fomenkova, M., Magee-Sauer, K., Kaminski, C. D., & Xie, D. X., Detection of Abundant Ethane and Methane, along with Carbon Monoxide and Water, in Comet C I 1996 B2 Hyakutake: Evidence Morgenthaler, J. P., Harris, W. M., Scherb, F., Roelser, F. L., Anderson, C. M., Doane, N. E., & Oliversen, R. J., The Gas Production Rate and Coma Structure of Comet C/1995 O1 (Hale-Bopp), Earth, Moon, Planets, Vol. 90, p , 2002b. Morgenthaler, J. P., Harris, W. M., Scherb, F., Doane, N. E., & Oliversen, R. J., Velocity- Resolved Observations of HDEmission from Comet C/1995 O1 (Hale-Bopp), Earth, Moon, Planets, Vol. 90, p , 2002a. Morgenthaler, J. P., Harris, W. M., Scherb, F., Anderson, C. M., Oliversen, R. J., Doane, N. E., Combi, M. R., Marconi, M. L., & Smyth, W. H., Large Aperture [O I] 6300 Å Photometry of Comet Hale-Bopp: Implications for the Photochemistry of OH, ApJ, Vol. 563, p , ev and 280 ev with the Diffuse X-ray Spectrometer (DXS), University of Wisconsin Madison, 1998.

21 21 ments of [C I] 9850 Å Emission from Comet Hale-Bopp, ApJ, Vol. 581, No. 1, p , Oliversen, R. J., Scherb, F., Smyth, W. H., Freed, M. E., Woodward, R. C., Marconi, M. L., Retherford, K. D., Lupie, O. L., & Morgenthaler, J. P., Sunlit Io Atmospheric [O I] 6300 Å Emission and the Plasma Torus, J. Geophys. Res., Vol. 106, No. A11, p , Sanders, W. T., Edgar, R. J., Kraushaar, W. L., McCammon, D., & Morgenthaler, J. P., Spectra of the 1/4 kev X-ray Diffuse Background from the Diffuse X-Ray Spectrometer Experiment, ApJ, Vol. 554, p , Schleicher, D. G., & A Hearn, M. F., The Fluorescence of Cometary OH, ApJ, Vol. 331, p , Schleicher, D. G., Millis, R. L., & Birch, P. V., Narrowband photometry of comet P/Halley: Variation with heliocentric distance, season, and solar phase angle, Icarus, Vol. 132, p , Schloerb, F. P., Collisional Quenching of Cometary Emissions in the 18 cm OH Transitions, Astrophysics, Vol. 332, p , 1988.

22 This preprint was prepared with the AAS LJTEX macros v5.0. van Dishoeck, E. F., & Dalgarno, A., The Dissociation of OH and OD in Comets by Solar Radiation, Icarus, Vol. 59, p , Tufte, S. L., Ph.D. thesis, The WHAM spectrometer, design, performance characteristics and first results, University of Wisconsin Madison, Cometary Comae, A&A, Vol. 330, p , Tozzi, G. P., Feldman, P. D., & Festou, M. C., Origin and Production of Atoms in