0----- Attempting Submission 1 (Mon Jul 21 23:46:01 GMT 2014) -----Measuring the Milky Way Mass with the Proper Motion of Leo TThe Milky Way has long been used to study galaxy evolution and cosmology, but these studies are currently limited by the large uncertainty in its dark matter halo mass. The halo mass is poorly constrained mainly because it is difficult to find appropriate tracers of the potential at large Galacto-centric distances. Satellite galaxies are the best such tracers, and recent cosmological simulations have shown a well-defined relationship between a satellite's orbital energy -- which depends on halo mass -- and its infall time. The recently discovered dwarf galaxy Leo T is an optimal candidate for measuring the halo mass in two respects. It is the most distant of the MW satellites, providing a probe of the mass distribution at large scales. It is also the only MW dwarf spheroidal galaxy with any gas; this makes it very likely that Leo T is currently falling into to MW for the first time. We propose to measure the bulk proper motion of Leo T using ACS/WFC in order to reconstruct its orbit. Using a well developed method of measuring the stellar proper motions with respect to an absolute reference frame composed of distant galaxies, we will be able to achieve a proper motion uncertainty of 0.03 mas/yr with a two year time baseline. Previous similar HST proper motion programs have shown that this precision is well within reach. A proper motion measurement of this precision, combined with the knowledge of Leo T's infall epoch, will allow for a determination of the mass of the MW within 400 kpc from the Galaxy, which is otherwise impossible. This knowledge will significantly reduce one of the largest uncertainties in interpreting the Milky Way in cosmological context.To measure the PMs of our target dwarf galaxies we plan to observe them in two epochs separated by ~2 years. In order to reach our goal of 1 mas astrometric precision for stars at i = 23, we require an integration time of t = 950 s for each image in F606W, slightly less than half of an HST orbit. We require 24 dither positions to sample the pixel phase as well as produce galaxy templates with high signal to noise. In order to aid in selection of dwarf galaxy members, we request short exposures in the F814W filter in the beginning of each orbit to provide colors for the stars. Observations with t = 427 & 565 s will provide the 3-10% photometry necessary to construct useful color magnitude diagrams of these sources. We have split the observations for this cycle into 4 visits of 3 orbits each. These observations should be taken in within 30 days of each other to optimally combine the data.
These observations should be performed at an ORIENT of 278.982 degrees to match the orientation of observations from cycle 20. We request that these observations in cycle 22 be performed at the end of cycle 22 (after Nov. 2015) in order to maximize the time baseline between cycle 20 and cycle 22. This time baseline will significantly increase the precision of the proper motion measurements compared to observations near the beginning of the cycle.RESOLVED STELLAR POPULATIONS12falsefalse0.00.0falsefalsefalseSUPPORTEDGALAXYDWARF SPHEROIDALJ2000J2000ACS/WFCImagingNoNoF606WACS/WFCImagingNoNoF814WWFC3/UVISImagingNoNoF606WWFC3/UVISImagingNoNoF814WACS/WFCImagingNoNoF606WACS/WFCImagingNoNoF814WWFC3/UVISImagingNoNoF606WWFC3/UVISImagingNoNoF814WTiming link suitability includes constraints ([Group (01 02 03 04) Within 30.0 days])Hst Same orient constraint links visits (01 02 03 04)The scheduling data was generated by CASM 22.2.CASM was run in Phase II mode./private/var/folders/7h/n0hv3b9j1219z6g439np8ct40008tj/T/OPVisit133866894824175713.xmlThis is the first visit for imaging the Leo T Dwarf Spheroidal Galaxy. 3 orbits are required to complete this visit. For each visit we will do a set of 6-point dithering. The ORIENT should be as close to 278.982 as possible in order to match the first epoch of observation to limit systematic uncertainties in the proper motion measurements. We request that these visits should be completed within 30 days of each other to ensure that there is no significant proper motion between the visits in order to optimally combine the data for this epoch. We request that the visits be made in late 2015 in order to obtain the longest time baseline for the proper motion measurement -- this will enable a significantly better proper motion measurement compared to observing in the beginning of Cycle 22.(Tic-Visit
:proposal-id 13770
:visit-id "01"
:proposal-version -1
:trans-version "20140605"
:date "17-Jul-2014 15:15:29.0"
:trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0
:FATAL-ERRORS 0 :CONTINUABLE-FATALS 0)
:number-of-orbits 3
:saa-model "29"
:si-bright-earth-limb-angle 20.0
:data-volume 5156768
:tdrss-contact-duration 0
:coron NIL
)
(Tic-Obset
:proposal-id 13770
:visit-id "01"
:obset-id "01"
:pcs-mode "FGS"
)
(Tic-Orbit
:proposal-id 13770
:visit-id "01"
:orbit-number 1
:pcs-time 333
:si-vis-utilization 2898
:al-overhead-at-end 0
:internal-dur-at-end 352
:dark-offset NIL
:dark-utilization 0
:max-dark-utilization 1920
:low-sky "N"
:pcs-visibility 3231
:pcs-gap 0
)
(Tic-Orbit
:proposal-id 13770
:visit-id "01"
:orbit-number 2
:pcs-time 222
:si-vis-utilization 3009
:al-overhead-at-end 0
:internal-dur-at-end 352
:dark-offset NIL
:dark-utilization 0
:max-dark-utilization 1920
:low-sky "N"
:pcs-visibility 3231
:pcs-gap 0
)
(Tic-Orbit
:proposal-id 13770
:visit-id "01"
:orbit-number 3
:pcs-time 222
:si-vis-utilization 3009
:al-overhead-at-end 0
:internal-dur-at-end 1015
:dark-offset NIL
:dark-utilization 0
:max-dark-utilization 1920
:low-sky "N"
:pcs-visibility 3231
:pcs-gap 0
)true30Timing link suitability includes constraints ([Group (01 02 03 04) Within 30.0 days])Hst Same orient constraint links visits (01 02 03 04)The scheduling data was generated by CASM 22.2.CASM was run in Phase II mode./Users/tdo/Documents/proposals/hst_cycle_22_leoT/phase2/OP-cache/cycle22_leoT_phase2-v02.xmlThis is the second visit for imaging the Leo T Dwarf Spheroidal Galaxy. 3 orbits are required to complete this visit. For each visit we will do a set of 6-point dithering.(Tic-Visit
:proposal-id 13770
:visit-id "02"
:proposal-version -1
:trans-version "20140605"
:date "15-Jul-2014 14:21:23.0"
:trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0
:FATAL-ERRORS 0 :CONTINUABLE-FATALS 0)
:number-of-orbits 3
:saa-model "29"
:si-bright-earth-limb-angle 20.0
:data-volume 5156768
:tdrss-contact-duration 0
:coron NIL
)
(Tic-Obset
:proposal-id 13770
:visit-id "02"
:obset-id "02"
:pcs-mode "FGS"
)
(Tic-Orbit
:proposal-id 13770
:visit-id "02"
:orbit-number 1
:pcs-time 333
:si-vis-utilization 2898
:al-overhead-at-end 0
:internal-dur-at-end 352
:dark-offset NIL
:dark-utilization 0
:max-dark-utilization 1920
:low-sky "N"
:pcs-visibility 3231
:pcs-gap 0
)
(Tic-Orbit
:proposal-id 13770
:visit-id "02"
:orbit-number 2
:pcs-time 222
:si-vis-utilization 3009
:al-overhead-at-end 0
:internal-dur-at-end 352
:dark-offset NIL
:dark-utilization 0
:max-dark-utilization 1920
:low-sky "N"
:pcs-visibility 3231
:pcs-gap 0
)
(Tic-Orbit
:proposal-id 13770
:visit-id "02"
:orbit-number 3
:pcs-time 222
:si-vis-utilization 3009
:al-overhead-at-end 0
:internal-dur-at-end 1015
:dark-offset NIL
:dark-utilization 0
:max-dark-utilization 1920
:low-sky "N"
:pcs-visibility 3231
:pcs-gap 0
)true30Timing link suitability includes constraints ([Group (01 02 03 04) Within 30.0 days])Hst Same orient constraint links visits (01 02 03 04)The scheduling data was generated by CASM 22.2.CASM was run in Phase II mode./Users/tdo/Documents/proposals/hst_cycle_22_leoT/phase2/OP-cache/cycle22_leoT_phase2-v03.xmlThis is the third visit for imaging the Leo T Dwarf Spheroidal Galaxy. Visit 3 and 4 repeats together repeats the 12 point dither pattern from visit 1 and 2, but offset to cover the chip gap in ACS. 3 orbits are required to complete this visit. For each visit we will do a set of 6-point dithering. We request that these visits should be completed within 30 days of each other to ensure that there is no significant proper motion between the visits in order to optimally combine the data for this epoch.(Tic-Visit
:proposal-id 13770
:visit-id "03"
:proposal-version -1
:trans-version "20140605"
:date "15-Jul-2014 14:22:06.0"
:trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0
:FATAL-ERRORS 0 :CONTINUABLE-FATALS 0)
:number-of-orbits 3
:saa-model "29"
:si-bright-earth-limb-angle 20.0
:data-volume 5156768
:tdrss-contact-duration 0
:coron NIL
)
(Tic-Obset
:proposal-id 13770
:visit-id "03"
:obset-id "03"
:pcs-mode "FGS"
)
(Tic-Orbit
:proposal-id 13770
:visit-id "03"
:orbit-number 1
:pcs-time 333
:si-vis-utilization 2898
:al-overhead-at-end 0
:internal-dur-at-end 352
:dark-offset NIL
:dark-utilization 0
:max-dark-utilization 1920
:low-sky "N"
:pcs-visibility 3231
:pcs-gap 0
)
(Tic-Orbit
:proposal-id 13770
:visit-id "03"
:orbit-number 2
:pcs-time 222
:si-vis-utilization 3009
:al-overhead-at-end 0
:internal-dur-at-end 352
:dark-offset NIL
:dark-utilization 0
:max-dark-utilization 1920
:low-sky "N"
:pcs-visibility 3231
:pcs-gap 0
)
(Tic-Orbit
:proposal-id 13770
:visit-id "03"
:orbit-number 3
:pcs-time 222
:si-vis-utilization 3009
:al-overhead-at-end 0
:internal-dur-at-end 1015
:dark-offset NIL
:dark-utilization 0
:max-dark-utilization 1920
:low-sky "N"
:pcs-visibility 3231
:pcs-gap 0
)true30Timing link suitability includes constraints ([Group (01 02 03 04) Within 30.0 days])Hst Same orient constraint links visits (01 02 03 04)The scheduling data was generated by CASM 22.2.CASM was run in Phase II mode./Users/tdo/Documents/proposals/hst_cycle_22_leoT/phase2/OP-cache/cycle22_leoT_phase2-v04.xmlThis is the fourth visit for imaging the Leo T Dwarf Spheroidal Galaxy. 3 orbits are required to complete this visit. For each visit we will do a set of 6-point dithering. The limits to the ORIENT of 278.982 is chosen to minimize the number of bright sources in the field, as well as to fully image the from the center of the galaxy to the half-light radius at about 1'. We request that these visits should be completed within 30 days of each other to ensure that there is no significant proper motion between the visits in order to optimally combine the data for this epoch.(Tic-Visit
:proposal-id 13770
:visit-id "04"
:proposal-version -1
:trans-version "20140605"
:date "15-Jul-2014 14:22:33.0"
:trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0
:FATAL-ERRORS 0 :CONTINUABLE-FATALS 0)
:number-of-orbits 3
:saa-model "29"
:si-bright-earth-limb-angle 20.0
:data-volume 5156768
:tdrss-contact-duration 0
:coron NIL
)
(Tic-Obset
:proposal-id 13770
:visit-id "04"
:obset-id "04"
:pcs-mode "FGS"
)
(Tic-Orbit
:proposal-id 13770
:visit-id "04"
:orbit-number 1
:pcs-time 333
:si-vis-utilization 2898
:al-overhead-at-end 0
:internal-dur-at-end 352
:dark-offset NIL
:dark-utilization 0
:max-dark-utilization 1920
:low-sky "N"
:pcs-visibility 3231
:pcs-gap 0
)
(Tic-Orbit
:proposal-id 13770
:visit-id "04"
:orbit-number 2
:pcs-time 222
:si-vis-utilization 3009
:al-overhead-at-end 0
:internal-dur-at-end 352
:dark-offset NIL
:dark-utilization 0
:max-dark-utilization 1920
:low-sky "N"
:pcs-visibility 3231
:pcs-gap 0
)
(Tic-Orbit
:proposal-id 13770
:visit-id "04"
:orbit-number 3
:pcs-time 222
:si-vis-utilization 3009
:al-overhead-at-end 0
:internal-dur-at-end 1015
:dark-offset NIL
:dark-utilization 0
:max-dark-utilization 1920
:low-sky "N"
:pcs-visibility 3231
:pcs-gap 0
)true30