Be very careful mixing POS TARG and Center_Pattern = Yes
Be very careful mixing POS TARG and Center_Pattern = Yes
Be very careful mixing POS TARG and Center_Pattern = Yes2020-03-11: Initial Phase II submission
Plans for observations to occur:
Visit 1: Now-April 4
Visit 2: May 8 - June 12
Visit 3: July 18 - August 20
Using a line dither pattern with 5 points and POSTARGS.262237792----- Attempting Submission 1 (Wed Mar 11 07:28:48 GMT 2020) -----Our POSTARGS are small, <0.5 arcsec and our line dither step size is 0.03 arcsec, so I think this should be OK to use with center pattern = TrueDetermining the cause of activity of the first active Trojan, 2019 LD2We request three orbits of observing time to study the recently discovered activity of 2019 LD2, the first Jupiter Trojan asteroid observed to have a comet-like, active appearance. Dynamical models predict that most Trojan Asteroids originated in the TransNeptunian belt and should, therefore, contain volatiles that should be active at the present-day heliocentric distances of the Trojans. The main objective of this program is to observe the coma and near-nucleus region of 2019 LD2 to constrain the cause of its activity as to whether caused by the sublimation of volatiles as the origins of Trojans might suggest, or if the activity is caused by impact or rotational disruption. Thus we will be constraining the possible volatile content of Trojan asteroids by studying 2019 LD2 with HST. We will accomplish this goal by using the high-resolution capabilities to observe the dust behavior of 2019 LD2 and its evolution as it approaches perihelion in March and April 2020 where the sublimation of volatiles is expected to increase and when the orbital plane angle is minimized allowing for the measurement of the perpendicular velocity component of the ejected dust. We will also constrain the 2019 LD2's nucleus size using the advanced high-resolution capabilities of HST. The discovery and confirmation of the activity of 2019 LD2 did not occur until after the regular GO proposal deadline and waiting for cycle 28 will mean the dispersal of dust diagnosing the activity by Solar Radiation pressure. The detection of volatile-driven activity on the first known active Trojan will be tremendously exciting and will be useful for leveraging subsequent observations of this novel type of object.We request a total of three visits each consisting of 1 orbit to characterize the coma of 2019 LD2 with WFC3/UVIS at three different epochs around when the Earth crosses its orbital plane during the first week of April 2020, a few weeks after perihelion passage of this comet on 2020 April 4 UTC and a few weeks to a month after the second visit. Our observation dates for the last two observations are flexible, but we require stricter scheduling for the first observation at around the orbital plane crossing during early April for our science goal of measuring the dust ejection velocity. We will acquire images in the F350LP filter for a maximum throughput of a Solar-like source which is expected for 2019 LD2. Each visit will consist of five 380 s exposures using the F350LP filter and the UVIS2 detector set up. This filter gives us the maximum throughput enabled by WFC3/UVIS in the 300 nm - 800 nm wavelength range for a Solar-like source which is expected of Solar System objects while allowing for a 0.04'' pixel scale. We will use the methodology of Jewitt et al. 2020 for color calibrations of the F350LP filter observations. This will give us a total exposure time of 1900 s while also providing image stacks robust to cosmic-rays. We will use line dithering to reduce the noise from flat-field calibration errors, cosmic rays, and residual images.
We also request moving object support due to the nature of the target. 2019 LD2's apparent motion rate is currently ~25''/hr, which is well within the tracking capability of HST. According to the ephemerides provided by the JPL HORIZONS system (on 2019-10-08 UT), the positional uncertainty of 2019 LD2 is less than a few arcseconds in early April 2020, and should not pose any problem to the pointing. We understand that we have no control over the spacecraft roll angle and will plan our observations so that they place the target within the center of the UVIS2 chip so that the entire extent of the target will appear in the chip regardless of roll angle.The team consists of members with extensive HST and comet observing, modeling and data analysis. The entire team will be involved with the HST observations, reducing the data, interpreting the results and rapid turnaround in preparation of scientific publications. The PI Bryce Bolin (Caltech) has extensive experience in observing comets and reducing comet data contributing to a number of comet-related publications. Co-PI Dr. Dennis Bodewits is an expert on comet activity and coma gas physics and brings extensive experience with space-based observing from missions, HST Chandra, XMM-Newton and the Neil Gehrels-Swift Observatory. Drs Casey M. Lisse (APL) and Yan Fernandez (UCF) are expert comet observers with decades of experience observing comets from ground-based and space-based observatories such as Chandra, Spitzer, Hubble Space Telescope and Deep Impact.Solar System AstronomySolar System Astronomy3falsefalsefalsefalsefalsefalsefalseSUPPORTEDSOLAR SYSTEMYESCOMET2019_LD2TYPE=COMET,Q=4.581143657178035,E=0.1462955970904501,I=11.54447123343416
,O=181.0493574718406,W=120.7533777397608,T=27-MAR-2020:01:04:37,TTimeScale=TDB,EQUINOX=J2000,EPOCH=20-NOV-2018:00:00:00,EpochTimeScale=TDBEARTHWFC3/UVISImagingNoNoF350LPCELESTIALOTHER0.03LINEfalsetrue50LINE1falseUsing ephemeris for target 16077-01-2019LD2ephemeris data for target 16077-01-2019LD2 does not cover planning interval. Physical constraints are assumed to be unschedulable outside of the ephemeris data. Planning interval: 19.213 to 21.089. ephemeris interval: 20.060 to 22.060The scheduling data was generated by CASM 28.0.CASM was run in Phase II mode.I have a strong preference for this observations being carried out as soon as possible so that we can observe as close as possible to the orbital plane crossing occuring in the last week of March.1585699055000257.3019867016004(Tic-Visit
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