! $Id: 5466,v 7.1 1995/01/04 14:22:33 pepsa Exp $
coverpage:
title_1: THE INTERACTION BETWEEN IO AND THE PLASMA
title_2: TORUS: DIRECT MEASUREMENT OF THE MASS LOADING RATE CYCLE4MEDIUM
sci_cat: SOLAR SYSTEM
sci_subcat: SATELLITES
proposal_for: GO
pi_fname: IMKE
pi_lname: DE PATER
pi_inst: 1500
pi_country: US
pi_phone: 510-642-1947
hours_pri: 5.05
num_pri: 2
hrs: Y
time_crit: Y
funds_amount: 75000
funds_length: 12
! end of coverpage
abstract:
line_1: We propose to make the first direct measurement of the slow-down of the Io
line_2: plasma torus in the immediate vicinity of Io. The slow-down is a direct
line_3: measure of the rate of ionization of neutral material from Io that will
line_4: provide critical information about the origin and maintenance of the torus,
line_5: about the details of the interaction between the torus and the satellite,
line_6: and about the nature and coverage of the Io atmosphere. Current understanding
line_7: in these areas is extremely tenuous due to the lack of concrete observations.
line_8: We will unambiguously determine the slow-down at Io by measuring the rotation
line_9: velocity of the torus from the Doppler shift of OII 2471 A emission observed
line_10: with Io in the aperture as the torus plane passes through the satellite.
line_11: This method has been used in our intensive ground-based study to measure
line_12: the slow-down, and thus the mass loading rate, at almost all points in the
line_13: torus, however no visible wavelength measurements are possible at the crucial
line_14: point where the torus passes through Io because the satellite is far too
line_15: bright at these wavelengths to allow detection of the ion emissions. By
line_16: contrast, in the UV the Io continuum is negligible compared with the torus
line_17: emissions, and the measurement of the slow-down is comparatively easy. The
line_18: results coming from this observation will have a large and immediate impact
line_19: on our knowledge of the Io atmosphere and of the physical mechanisms involved
line_20: in the torus-Io interaction.
!
! end of abstract
general_form_proposers:
lname: DE PATER
fname: IMKE
inst: 1500
country: USA
!
lname: BROWN
fname: MICHAEL
inst: 1500
country: USA
!
lname: MCGRATH
fname: MELISSA
inst: 3470
country: USA
!
! end of general_form_proposers block
general_form_text:
question: 3
section: 1
line_1: We propose high-resolution observations of OII 2471 A emission in the
line_2: Io plasma torus using the GHRS echelle-B to precisely measure the
line_3: Doppler shift of the emission line, from which the mass loading rate in the
line_4: torus can be inferred. The emission line will be observed with Io
line_5: in the aperture at dusk (western) elongation as the torus plane is
line_6: passing through Io and also in the same spot but with Io far
line_7: from the aperture and the torus in the same geometric configuration.
line_8: A comparison of the velocity shift between these two spectra will yield
line_9: a direct measure of the slow-down caused by mass loading
line_10: in the immediate vicinity of the satellite.
line_12: The OII line was chosen because it will give the most counts of any
line_13: known torus emission line (the SII emission at 1729 A is brighter,
line_14: but echelle-B is approximately twenty times less sensitive at that
line_15: wavelength), and we will observe at western elongation because torus
line_16: emissions are known to be brightest on that side. Ground-based observations
line_17: of [SII] 6731 A emission show typical FWHM linewidths of about 25 km/s,
line_18: so we expect a similar value for the OII emission. Filled-aperture
line_19: resolution at 2471 A is about 0.17 A, or 20 km/s, so we expect this
line_20: emission to be marginally resolved. For significant scientific results,
line_21: we require the ability to distinguish velocity shifts of about 4 km/s,
line_22: which should be achievable with moderate signal to noise at this resolution.
!
question: 4
section: 1
line_1: The goal of this program is to observe the velocity of the Io plasma torus
line_2: as it passes through Io. Because Io will be within the aperture of the HRS
line_3: during the exposures, this observation can only be done in the UV. At visible
line_4: wavelengths, continuum emission from Io swamps the relatively weak torus
line_5: emission. This fact has been confirmed by our extensive ground based
line_6: observations of the rotation velocity of the torus (Brown 1992); we have
line_7: shown that even with long and repeated exposures and careful continuum
line_8: subtraction it is impossible to obtain a usable visible wavelength spectrum
line_9: as the torus plane passes through Io. In contrast, in the UV continuum
line_10: emission from Io is negligible, so obtaining a good spectrum of the torus
line_11: passing through Io is comparatively easy. The only other observatory with UV
line_12: capability is the IUE, but it has neither the required sensitivity (no torus
line_13: emissions are detectable at high resolution) nor the required spectral
line_14: resolution to measure a small deviation from corotation velocity (on the
line_15: order of 4 km/s) in the immediate vicinity of Io. The comparison spectrum,
line_16: taken without Io in the aperture, could, in principle, be observed
line_17: elsewhere, but we feel very strongly that because we require the ability
line_18: to measure a velocity shift as small as 1/5 of a resolution element
line_19: (filled-aperture resolution at 2471 A is about 20 km/s) precise and
line_20: reliable scientific results can only be obtained by a
line_21: direct comparison between two spectra of the same emission line taken with
line_22: the same instrument under the same observing conditions.
!
question: 4
section: 2
line_1: The brightness of the OII 2471 A emission has been measured by the
line_2: GHRS at lower resolution to be about 50 R (McGrath et al. 1993). Using
line_3: the most recent Echelle-B sensitivity and ripple correction we calculate
line_4: a count rate of 1.0 X 10^-2 counts/diode-sec. For the S/N calculation
line_5: we included an average dark count rate of 1.2 X 10^-2 counts/diode-sec,
line_6: a value of 0.03 for the inter-order background grating scattered light,
line_7: and 0.11 for the fraction of time spent measuring the inter-order
line_8: background during the observation. Because these extended emissions
line_9: will be oversampled by the large aperture, we will bin the data by a
line_10: factor of two to increase S/N at no expense of resolution. We then find
line_11: that an exposure time of 160 min is required to maintain a S/N of 6.
line_12: It is crucial that these observations are made as Io is inside the
line_13: central part of the torus. Io never stays within this region for more
line_14: than 120 minutes, so an observation can never be made over more than
line_15: two orbits. Including time for on-board acquisition during the first
line_16: orbit, we assume that we will obtain about 40 minutes of on-target
line_17: exposure during two orbits. Thus the observation with Io in the
line_18: aperture will require four separate visits to complete a 160 minute
line_19: exposure. Appropriate torus-Io geometric configurations occur
line_20: approximately 10 times every 35 days.
line_21: The exposures without Io in the aperture need to reproduce as closely
line_22: as possible the torus configuration of the preceding observations,
line_23: thus we also estimate four separate visits to complete the 160 minute exposure.
!
question: 5
section: 1
line_1: This program is highly time-critical. The goal is to observe the Io
line_2: plasma torus as the torus plane passes through Io at western elongation,
line_3: so the observations must be scheduled carefully. (Correct torus-Io geometric
line_4: configurations occur about once every 3.5 days.) Because Io only stays within
line_5: the central part of the torus for about 120 minutes, each observation can
line_6: last no more than two orbits. We will therefore require four separate
line_7: visits, each at the appropriate torus-Io geometry, to complete the
line_8: observation. The spectra will be compared with similar spectra taken
line_9: with the torus in the same geometric configuration but with Io far from
line_10: the field of view. These observations will need to be scheduled to
line_11: reproduce as closely as possible torus configuration of the first
line_12: observations in order to make a meaningful comparison between the two
line_13: spectra. (Correct torus geometric configurations with Io far from the
line_14: aperture occur about once every twenty hours).
line_16: In addition, all observations should take place when the other
line_17: Galilean satellites are far removed to avoid contaminating light.
!
!
question: 9
section: 1
line_1: 1. GO 2627 - Io's Atmosphere and its Interaction with the Plasma Torus
line_2: M. McGrath, co-I.
line_4: 2. GO 2625 - Excitation Processes for the Outer Planet UV Emissions, M.
line_5: McGrath co-I.
line_7: 3. GO 3616 - The Upper Atmospheres of Uranus and Neptune,
line_8: M. McGrath, PI.
line_10: 4. GO 3617 - The Ultraviolet Emissions of Titan, M. McGrath, PI.
line_12: 5. GO 3618 - Excitation Processes for the Outer Planet UV Emissions--
line_13: Cycle 2 Continuation, M. McGrath, PI.
line_15: 6. GO 4353 - Hubble Space Telescope Imaging of Io, M. McGrath, PI.
line_17: 7. GO 4600 - FUV Spectrscopy of Io's SO2 Atmosphere and Surface,
line_18: M. McGrath, co-I.
!
question: 9
section: 2
line_1: 1. GO 2627 - cycle 1 program, observations completed successfully in
line_2: March and May 1992. Observations have resulted in the first detection of
line_3: [OII]2471 emission from the Io plasma torus; the first UV detection of the
line_4: Io SO2 atmospheric absorption bands (only the third time the SO2 atmosphere
line_5: of Io has been detected directly) yielding a measurement of the atmospheric
line_6: density, pressure, and coverage; and spatial scans of Io neutral S and O
line_7: atmospheric emissions, resulting in a factor of 3 improvement in the spatial
line_8: resolution of these constituents compared with previous IUE measurements.
line_10: 2. GO 4353 - cycle 3 program, not yet completed. Some data obtained on
line_11: May 10, 1993; remaining observations scheduled for week of May 24, 1993.
line_12: No results to date.
line_14: 3. GO 4600 - no data obtained to date.
!
question: 10
section: 1
line_1:
line_2: These observation fit into our ongoing ground-based (at Berkeley) and
line_3: space-based (at STScI) programs to determine the interaction between
line_4: Io and the plasma torus and the Jovian magnetosphere. The data will be
line_5: analyzed using the same facilities and techniques that are being used
line_6: in our current study of torus rotation velocities. We will provide
line_7: extensive ground-based support from Lick Observatory during the periods
line_8: of the observations to characterize the state of the torus and the
line_9: neutral clouds, and we also hope to obtain observations of the Io-torus
line_10: system from the Keck telescope during these times.
!
!end of general form text
general_form_address:
lname: de Pater
fname: Imke
category: PI
inst: 1500
addr_1: Department of Astronomy
addr_2: University of California
city: Berkeley
state: CA
zip: 94720
country: USA
phone: 510-642-1947
telex: imke@bkyast.berkeley.edu
!
! end of general_form_address records
! No fixed target records found
solar_system_targets:
targnum: 1
name_1: TORUS-WITH-IO
descr_1: TORUS JUPITER
lev1_1: STD=JUPITER
lev2_1: STD=IO
wind_1: WND1=25-FEB-94 TO 22-JUN-94,
wind_2: WND2=1-DEC-94 TO 1-JAN-99,
wind_3: OLG OF IO BETWEEN 246 280, CML OF
wind_4: JUPITER FROM EARTH BETWEEN 109 235
wind_5: SEP OF GANYMEDE IO FROM EARTH GT 5",
wind_6: SEP OF EUROPA IO FROM EARTH GT 5",
wind_7: SEP OF CALLISTO IO FROM EARTH GT 5"
comment_1: EXPOSURE OF THE IO PLASMA TORUS AT
comment_2: THE POSITION OF IO WITH IO AT
comment_3: ELONGATION, AND THE TORUS AT A CML
comment_4: OF NEAR 200 IN ORDER FOR IO TO BE
comment_5: IN THE DENSEST REGION OF TORUS.
comment_6: CML OF JUPITER BETWEEN 289 55
comment_7: IS ACCEPTABLE, AS LONG AS ALL
comment_8: OBS ARE MADE IN THIS RANGE.
fluxnum_1: 1
fluxval_1: V=5.02
fluxnum_2: 2
fluxval_2: W-LINE(2471)=0.21 +/- 0.05
fluxnum_3: 2
fluxval_3: SURF-LINE(2471)=13 +/- 4 E-15
fluxnum_4: 2
fluxval_4: SIZE=20 +/- 5
!
targnum: 2
name_1: TORUS-WITHOUT-IO
descr_1: TORUS JUPITER
lev1_1: STD=JUPITER
lev2_1: TYPE=TORUS,
lev2_2: LONG=90,
lev2_3: LAT=0,
lev2_4: RAD=4.22E05,
lev2_5: POLE_LAT=+90
wind_1: WND1=25-FEB-94 TO 22-JUN-94,
wind_2: WND2=1-DEC-94 TO 1-JAN-99,
wind_3: OLG OF IO BETWEEN 0 180,
wind_4: CML OF JUPITER FROM EARTH
wind_5: BETWEEN 109 235
comment_1: EXPOSURE OF THE IO PLASMA TORUS WELL
comment_2: AWAY FROM IO, BUT WITH THE SAME CML
comment_3: OF TARGET 1. THE EXPOSURE SHOULD BE
comment_4: IN THE ORBITAL PLANE OF IO, AND NOT
comment_5: IN THE CENTRIFUGAL PLANE OF THE TORUS
comment_6: (HENCE POLE_LATE= +90).
comment_7: CML OF JUPITER BETWEEN 289 55
comment_8: IS ACCEPTABLE, AS LONG AS ALL
comment_9: OBS ARE MADE IN THIS RANGE.
fluxnum_1: 1
fluxval_1: W-LINE(2471)=0.21 +/- 0.05
fluxnum_2: 1
fluxval_2: SURF-LINE(2471)=13 +/- 4 E-15
fluxnum_3: 1
fluxval_3: SIZE=20 +/- 5
!
!
! end of solar system targets
! No generic target records found
exposure_logsheet:
linenum: 1.000
targname: TORUS-WITH-IO
config: HRS
opmode: ACQ
aperture: 2.0
sp_element: MIRROR-N2
num_exp: 1
time_per_exp: 10S
fluxnum_1: 1
priority: 1
param_1: SEARCH-SIZE=5
param_2: BRIGHT=RETURN
req_1: CYCLE 4;
req_2: ONBOARD ACQ FOR 2;
req_3: GROUP 1-11 WITHIN 120D;
req_4: group 1-3 within 1 d;
comment_1: FROM PREVIOUS IO ACQUISITIONS, WE
comment_2: ESTIMATE A STEP TIME OF 0.4 SEC.
comment_3: BECAUSE OF TEMPORAL CHANGES OBSERVED
comment_4: WITHIN THE TORUS, ALL EXPOSURES
comment_5: SHOULD BE WITHIN ONE JOVIAN
comment_6: APPARITION.
!
linenum: 2.000
targname: TORUS-WITH-IO
config: HRS
opmode: ACCUM
aperture: 2.0
sp_element: ECH-B
wavelength: 2471
num_exp: 8
time_per_exp: 5M
s_to_n: 6
s_to_n_time: 160M
fluxnum_1: 2
priority: 1
param_1: STEP-PATT=DEF
param_2: FP-SPLIT=STD
param_3: CENSOR=YES
req_1: CYCLE 4
comment_1: GO IMMEDIATELY TO ACCUM MODE.
comment_2: NO PEAKUP IS PERFORMED, BECAUSE
comment_3: TARGET IS TORUS SURROUNDING IO,
comment_4: SO CENTERING OF IO W/O APERTURE
comment_5: IS UNIMPORTANT.
!
linenum: 3.000
targname: TORUS-WITHOUT-IO
config: HRS
opmode: ACCUM
aperture: 2.0
sp_element: ECH-B
wavelength: 2471
num_exp: 11
time_per_exp: 4.4M
s_to_n: 6
s_to_n_time: 160M
fluxnum_1: 1
priority: 2
param_1: STEP-PATT=DEF
param_2: FP-SPLIT=STD
param_3: CENSOR=YES
req_1: CYCLE 4
comment_1: TARGET IS IO PLASMA TORUS. BLIND
comment_2: POINTING TO WITHIN A FEW ARC-SECS
comment_3: SHOULD BE SUFFICIENT,
comment_4: SO NO ACQUISITION IS PERFORMED.
!
linenum: 4.000
targname: TORUS-WITH-IO
config: HRS
opmode: ACQ
aperture: 2.0
sp_element: MIRROR-N2
num_exp: 1
time_per_exp: 10S
fluxnum_1: 1
priority: 1
param_1: SEARCH-SIZE=5
param_2: BRIGHT=RETURN
req_1: CYCLE 4;
req_2: ONBOARD ACQ FOR 5;
req_4: group 4-6 within 1 d;
comment_1: FROM PREVIOUS IO ACQUISITIONS, WE
comment_2: ESTIMATE A STEP TIME OF 0.4 SEC.
comment_3: BECAUSE OF TEMPORAL CHANGES OBSERVED
comment_4: WITHIN THE TORUS, ALL EXPOSURES
comment_5: SHOULD BE WITHIN ONE JOVIAN
comment_6: APPARITION.
!
linenum: 5.000
targname: TORUS-WITH-IO
config: HRS
opmode: ACCUM
aperture: 2.0
sp_element: ECH-B
wavelength: 2471
num_exp: 8
time_per_exp: 5M
s_to_n: 6
s_to_n_time: 160M
fluxnum_1: 2
priority: 1
param_1: STEP-PATT=DEF
param_2: FP-SPLIT=STD
param_3: CENSOR=YES
req_1: CYCLE 4
comment_1: GO IMMEDIATELY TO ACCUM MODE.
comment_2: NO PEAKUP IS PERFORMED, BECAUSE
comment_3: TARGET IS TORUS SURROUNDING IO,
comment_4: SO CENTERING OF IO W/O APERTURE
comment_5: IS UNIMPORTANT.
!
linenum: 6.000
targname: TORUS-WITHOUT-IO
config: HRS
opmode: ACCUM
aperture: 2.0
sp_element: ECH-B
wavelength: 2471
num_exp: 11
time_per_exp: 4.4M
s_to_n: 6
s_to_n_time: 160M
fluxnum_1: 1
priority: 2
param_1: STEP-PATT=DEF
param_2: FP-SPLIT=STD
param_3: CENSOR=YES
req_1: CYCLE 4
comment_1: TARGET IS IO PLASMA TORUS. BLIND
comment_2: POINTING TO WITHIN A FEW ARC-SECS
comment_3: SHOULD BE SUFFICIENT,
comment_4: SO NO ACQUISITION IS PERFORMED.
!
linenum: 7.000
targname: TORUS-WITH-IO
config: HRS
opmode: ACQ
aperture: 2.0
sp_element: MIRROR-N2
num_exp: 1
time_per_exp: 10S
fluxnum_1: 1
priority: 1
param_1: SEARCH-SIZE=5
param_2: BRIGHT=RETURN
req_1: CYCLE 4;
req_2: ONBOARD ACQ FOR 8;
req_4: group 7-9 within 1 d;
comment_1: FROM PREVIOUS IO ACQUISITIONS, WE
comment_2: ESTIMATE A STEP TIME OF 0.4 SEC.
comment_3: BECAUSE OF TEMPORAL CHANGES OBSERVED
comment_4: WITHIN THE TORUS, ALL EXPOSURES
comment_5: SHOULD BE WITHIN ONE JOVIAN
comment_6: APPARITION.
!
linenum: 8.000
targname: TORUS-WITH-IO
config: HRS
opmode: ACCUM
aperture: 2.0
sp_element: ECH-B
wavelength: 2471
num_exp: 8
time_per_exp: 5M
s_to_n: 6
s_to_n_time: 160M
fluxnum_1: 2
priority: 1
param_1: STEP-PATT=DEF
param_2: FP-SPLIT=STD
param_3: CENSOR=YES
req_1: CYCLE 4
comment_1: GO IMMEDIATELY TO ACCUM MODE.
comment_2: NO PEAKUP IS PERFORMED, BECAUSE
comment_3: TARGET IS TORUS SURROUNDING IO,
comment_4: SO CENTERING OF IO W/O APERTURE
comment_5: IS UNIMPORTANT.
!
linenum: 9.000
targname: TORUS-WITHOUT-IO
config: HRS
opmode: ACCUM
aperture: 2.0
sp_element: ECH-B
wavelength: 2471
num_exp: 11
time_per_exp: 4.4M
s_to_n: 6
s_to_n_time: 160M
fluxnum_1: 1
priority: 2
param_1: STEP-PATT=DEF
param_2: FP-SPLIT=STD
param_3: CENSOR=YES
req_1: CYCLE 4
comment_1: TARGET IS IO PLASMA TORUS. BLIND
comment_2: POINTING TO WITHIN A FEW ARC-SECS
comment_3: SHOULD BE SUFFICIENT,
comment_4: SO NO ACQUISITION IS PERFORMED.
!
linenum: 10.000
targname: TORUS-WITH-IO
config: HRS
opmode: ACQ
aperture: 2.0
sp_element: MIRROR-N2
num_exp: 1
time_per_exp: 10S
fluxnum_1: 1
priority: 1
param_1: SEARCH-SIZE=5
param_2: BRIGHT=RETURN
req_1: CYCLE 4;
req_2: ONBOARD ACQ FOR 11;
req_4: group 10-11 within 1 d;
comment_1: FROM PREVIOUS IO ACQUISITIONS, WE
comment_2: ESTIMATE A STEP TIME OF 0.4 SEC.
comment_3: BECAUSE OF TEMPORAL CHANGES OBSERVED
comment_4: WITHIN THE TORUS, ALL EXPOSURES
comment_5: SHOULD BE WITHIN ONE JOVIAN
comment_6: APPARITION.
!
linenum: 11.000
targname: TORUS-WITH-IO
config: HRS
opmode: ACCUM
aperture: 2.0
sp_element: ECH-B
wavelength: 2471
num_exp: 8
time_per_exp: 5M
s_to_n: 6
s_to_n_time: 160M
fluxnum_1: 2
priority: 1
param_1: STEP-PATT=DEF
param_2: FP-SPLIT=STD
param_3: CENSOR=YES
req_1: CYCLE 4
comment_1: GO IMMEDIATELY TO ACCUM MODE.
comment_2: NO PEAKUP IS PERFORMED, BECAUSE
comment_3: TARGET IS TORUS SURROUNDING IO,
comment_4: SO CENTERING OF IO W/O APERTURE
comment_5: IS UNIMPORTANT.
!
!
! linenum: 12.000
! targname: TORUS-WITHOUT-IO
! config: HRS
! opmode: ACCUM
! aperture: 2.0
! sp_element: ECH-B
! wavelength: 2471
! num_exp: 8
! time_per_exp: 4.4M
! s_to_n: 6
! s_to_n_time: 160M
! fluxnum_1: 1
! priority: 2
! param_1: STEP-PATT=DEF
! param_2: FP-SPLIT=STD
! param_3: CENSOR=YES
! req_4: CYCLE 4
! comment_1: TARGET IS IO PLASMA TORUS. BLIND
! comment_2: POINTING TO WITHIN A FEW ARC-SECS
! comment_3: SHOULD BE SUFFICIENT,
! comment_4: SO NO ACQUISITION IS PERFORMED.
!
! end of exposure logsheet
! No scan data records found