The recent discovery that the Neptune-like exoplanet GJ 436 b transits its host star has presented us the first chance to observationally study ice giant formation beyond our solar system (Gillon et al. 2007). Using Directors Discretionary time, we propose to obtain a high-precision light curve of the GJ 436 b transit with the FGS in order to improve the current radius determination for this planet. Measuring a precise radius for GJ 436 b will allow us to ascertain whether the planet has a pure water vapor or H/He envelope like Uranus and Neptune. Knowing this will constrain its formation and evolution and help place our own solar system ice giants in a broader context. Additionally, a precise radius for GJ 436 b will be a necessity for interpreting the certain follow-up observations of this unique system.

enter description here COOL STARS 0 false 0.0 false false false false false false SUPPORTED STAR M V-IV LOW MASS COMPANION EXTRA-SOLAR PLANET J2000 11 42 11.0941 +26 42 23.65 J2000 STAR G V-IV J2000 11 42 12.1056 +26 46 7.86 J2000 STAR G V-IV J2000 11 42 20.2896 +26 45 37.30 J2000 STAR G V-IV J2000 00 00 0.0000 +00 00 0.00 J2000 FGS POS No F583W The phase requirement is attached to the first photometric reference star, not the transit target, GJ436. Given that the observation of GJ436-REF-1 begins at the indicated phase, and that the observations of GJ436-REF-1 and GJ436-REF-2 with overheads take a total of 281 seconds, our phases have been adjusted by -281 seconds (= -0.0012 in phase) so that the GJ 436 exposure starts at the required phase of the transit. Phase = 0 is assumed to be the midpoint of the transit. This particular visit should capture a little after transit mid-point through egress. (Tic-Visit :proposal-id 11309 :visit-id "01" :proposal-version -1 :trans-version "20070325" :date "02-Jul-2007 10:43:50.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "05" :si-bright-earth-limb-angle 15.5 :data-volume 0 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11309 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11309 :visit-id "01" :orbit-number 1 :pcs-time 355 :si-vis-utilization 2791 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3149 :pcs-gap 0 ) false 1 0 The phase requirement is attached to the first photometric reference star, not the transit target, GJ436. Given that the observation of GJ436-REF-1 begins at the indicated phase, and that the observations of GJ436-REF-1 and GJ436-REF-2 with overheads take a total of 281 seconds, our phases have been adjusted by -281 seconds (= -0.0012 in phase) so that the GJ 436 exposure starts at the required phase of the transit. Phase = 0 is assumed to be the midpoint of the transit. This particular visit should capture a little before ingress to just before transit mid-point. (Tic-Visit :proposal-id 11309 :visit-id "02" :proposal-version -1 :trans-version "20070325" :date "02-Jul-2007 10:43:55.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "05" :si-bright-earth-limb-angle 15.5 :data-volume 0 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11309 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11309 :visit-id "02" :orbit-number 1 :pcs-time 269 :si-vis-utilization 2791 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3149 :pcs-gap 0 ) false 1 0 The phase requirement is attached to the first photometric reference star, not the transit target, GJ436. Given that the observation of GJ436-REF-1 begins at the indicated phase, and that the observations of GJ436-REF-1 and GJ436-REF-2 with overheads take a total of 281 seconds, our phases have been adjusted by -281 seconds (= -0.0012 in phase) so that the GJ 436 exposure starts at the required phase of the transit. Phase = 0 is assumed to be the midpoint of the transit. This particular visit should be centered on the transit mid-point. (Tic-Visit :proposal-id 11309 :visit-id "03" :proposal-version -1 :trans-version "20070325" :date "02-Jul-2007 10:43:59.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "05" :si-bright-earth-limb-angle 15.5 :data-volume 0 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11309 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11309 :visit-id "03" :orbit-number 1 :pcs-time 355 :si-vis-utilization 2791 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3149 :pcs-gap 0 ) false 1 0 The phase requirement is attached to the first photometric reference star, not the transit target, GJ436. Given that the observation of GJ436-REF-1 begins at the indicated phase, and that the observations of GJ436-REF-1 and GJ436-REF-2 with overheads take a total of 281 seconds, our phases have been adjusted by -281 seconds (= -0.0012 in phase) so that the GJ 436 exposure starts at the required phase of the transit. Phase = 0 is assumed to be the midpoint of the transit. This particular visit should capture a little after transit mid-point through egress. (Tic-Visit :proposal-id 535 :visit-id "04" :proposal-version -1 :trans-version "20070325" :date "09-Jul-2007 09:33:31.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "05" :si-bright-earth-limb-angle 15.5 :data-volume 0 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 535 :visit-id "04" :obset-id "04" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 535 :visit-id "04" :orbit-number 1 :pcs-time 269 :si-vis-utilization 2745 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3149 :pcs-gap 0 ) false 1 0 The phase requirement is attached to the first photometric reference star, not the transit target, GJ436. Given that the observation of GJ436-REF-1 begins at the indicated phase, and that the observations of GJ436-REF-1 and GJ436-REF-2 with overheads take a total of 281 seconds, our phases have been adjusted by -281 seconds (= -0.0012 in phase) so that the GJ 436 exposure starts at the required phase of the transit. Phase = 0 is assumed to be the midpoint of the transit. This particular visit should capture a little before ingress to just before transit mid-point. (Tic-Visit :proposal-id 535 :visit-id "05" :proposal-version -1 :trans-version "20070325" :date "09-Jul-2007 09:40:01.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "05" :si-bright-earth-limb-angle 15.5 :data-volume 0 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 535 :visit-id "05" :obset-id "05" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 535 :visit-id "05" :orbit-number 1 :pcs-time 269 :si-vis-utilization 2805 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3149 :pcs-gap 0 ) false 1 0 The phase requirement is attached to the first photometric reference star, not the transit target, GJ436. Given that the observation of GJ436-REF-1 begins at the indicated phase, and that the observations of GJ436-REF-1 and GJ436-REF-2 with overheads take a total of 281 seconds, our phases have been adjusted by -281 seconds (= -0.0012 in phase) so that the GJ 436 exposure starts at the required phase of the transit. Phase = 0 is assumed to be the midpoint of the transit. This particular visit should be centered on the transit mid-point. (Tic-Visit :proposal-id 535 :visit-id "06" :proposal-version -1 :trans-version "20070325" :date "09-Jul-2007 09:34:14.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "05" :si-bright-earth-limb-angle 15.5 :data-volume 0 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 535 :visit-id "06" :obset-id "06" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 535 :visit-id "06" :orbit-number 1 :pcs-time 269 :si-vis-utilization 2805 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3149 :pcs-gap 0 ) false 1 0