(62.03) Observational Results from the 2007 March 18 Pluto Stellar Occultation

Jay M. Pasachoff, B. A. Babcock, S. P. Souza, A. J. McKay (Williams College), M. J. Person, J. L. Elliot, A. A. S. Gulbis, C. A. Zuluaga (MIT), J. M. Hill (LBTO), E. V. Ryan, W. H. Ryan (MRO)

• Our MIT-Williams consortium observed the 5-minute occultation by Pluto of the star we call P445.3 from sites in the American southwest on 2007 March 17/18 (18 March, UT).

• 2UCAC 25823784, UCAC magnitude 15.3 (McDonald and Elliot, 2000, AJ 120, 1599)

• Shadow velocity = 6.8 km/s.

• The occultation grazed Pluto’s atmosphere.

Telescopes Used

Large Binoc. Tel. Obs. 8.4 m Babcock, Hill

MMT Obs. 6.5 m Kern, Kulesa, McCarthy, Person

Magdalena Ridge Obs. 2.4 m McKay, E. Ryan, W. Ryan, Souza

US Naval Obs. 1.55 m Levine

Fremont Peak Obs. 0.32 m Meyer, Wolf

At the MMT, the US Naval Observatory telescope, and the Magdalena Ridge Observatory, we were able to use our Portable Occultation, Eclipse, and Transit System (POETS) CCD/GPS/computer instruments

(Steven P. Souza, Bryce A. Babcock, Jay M. Pasachoff, Amanda A. S. Gulbis, James L. Elliot, Michael J. Person, and Joseph W. Gangestad, 2006, "POETS: Portable Occultation, Eclipse, and Transit System," Publ. Astron. Soc. Pacific 118, 1550-1557)

(34.08) Electron-Multiplying CCD Imaging: Effectiveness for Stellar

Occultations by Faint Objects

Amanda A. S. Gulbis, J. L. Elliot, M. J. Person, S. P. Souza, B. A. Babcock, J. M. Pasachoff, A. J. McKay, C. A. Zuluaga

• With POETS (Portable Occultation, Eclipse, and Transit System), at the 2.4-m Magdalena Ridge Observatory near Socorro, New Mexico:

we obtained a partial light curve despite variable cloudiness throughout the 80 min observation. This telescope was the farthest into the occultation path, and thus led to the deepest incursion into Pluto's atmosphere of the starlight of the major telescopes we used.

• We generated light curves by frame-by-frame synthetic-aperture photometry.

Magdalena Ridge Observatory

Magdalena Ridge Observatory

We were able to use one of the 8.4-m mirrors of the Large Binocular Telescope Observatory, still in its engineering stage, though only with its facility guide camera and not with our Portable Occultation, Eclipse, and Transit System (POETS).

Because of our accurate GPS timing, we were able to align the light curve obtained, which included only the second half of the occultation, with results from other telescopes, including the visible, beamsplit light curve obtained by our group with the 6.5-m MMT (Person et al., 2007, this meeting).

Large Binocular Telescope Observatory

The large increase in atmospheric pressure we had earlier measured at the 2002 occultation compared with measurements at the first successful Pluto occultation, in 1988, has ceased, as shown by both the 2006 and the current, 2007 measurements.

High Altitude Structure in Pluto's Atmosphere from the 2007 March 18 Stellar Occultation

Michael J. Person, J. L. Elliot, A. A. S. Gulbis, C. A. Zuluaga, B. A. Babcock, J. M. Pasachoff, A. J. McKay, S. P. Souza, W. B. Hubbard, C. A. Kulesa, D. W. McCarthy, S. D. Kern, S. E. Levine, A. S. Bosh, E. V. Ryan, W. H. Ryan, A. Meyer, J. Wolf, J. M. Hill

• Simultaneous model fitting to all our light curve data yielded 1207 ± 4 km as the half-light shadow radius of Pluto’s atmosphere. This radius is consistent with the 1208 ± 9 km result measured in 2006 (Elliot, et al., AJ 134,1)

• We confirm that the large increase in atmospheric pressure measured between the 1988 and 2002 (Elliot, et al., Nature 424,165; Sicardy, et al., Nature 424, 168) occultations has ceased.

• Number density, pressure, and temperature profiles for Pluto’s atmosphere in the radius range of 1340 – 1460 km (assuming the dominant atmospheric component is N2).

• We interpret the light-curve structure as vertically propagating waves in Pluto’s upper atmosphere, and provide a feasible mechanism for the maintenance of this large-scale coherence in terms of Rossby planetary waves.