0Assigned ID: 5753
----- Attempting Submission 1 (Tue Mar 26 22:34:22 GMT 2024) -----
HST Phase I Proposal 5753 successfully submitted.
Receipt: # 5753-1
----- Attempting Submission 2 (Tue Mar 26 22:57:45 GMT 2024) -----
HST Phase I Proposal 5753 successfully submitted.
Receipt: # 5753-2
----- Attempting Submission 3 (Tue Mar 26 23:23:23 GMT 2024) -----
HST Phase I Proposal 5753 successfully submitted.
Receipt: # 5753-3
----- Attempting Submission 4 (Tue Mar 26 23:57:43 GMT 2024) -----0----- Attempting Submission 1 (Wed Aug 07 23:31:20 GMT 2024) -----An HST probe of JWST white dwarf debris disk mineralogies: energetic impacts or extrasolar crusts?Recent JWST MIRI spectroscopic observations covering 5-12 microns unveil a dramatic excess of dusty debris over the well-characterized photosphere of three polluted white dwarf stars. The JWST spectra reveal solid-state emission features that require glassy silica (SiO2) species associated with energetic impacts or differentiation processes that produced Earth-like crustal material. Ultraviolet spectroscopic observations will provide measurements and constraints on the elemental constituents of the debris, including those that dominate terrestrial rocks (Si, Mg, Fe), as well as other important tracers of planetary assembly and structure. The proposed experiment will distinguish between Fe-poor material in a planetary crust, where the high silica content has resulted from (past) differentiation, and silica resulting from highly energetic impacts between primitive material that may have occurred during the post-main sequence phase.Our primary goal is to detect Fe, Mg, and Si in two white dwarf stars, GaiaJ0547-4847 and WDJ0802+5631. This goal will require ultraviolet spectroscopy of each white dwarf using their own specific instrumental setup.
GaiaJ0547-4847 will be observed with STIS/G230L as low resolution coverage over the 1800-3000 Ang range is sufficient to probe all desired elements (and will additionally yield detection of or a stringent limit on C). We use the GALEX-measured NUV magnitude of 17.08 to estimate how much time on source is necessary to obtain our desired signal-to-noise assuming a small amount of interstellar reddening (consistent with the location of the star in the Galaxy). Focusing on the spectral region around C, we find that with 4,700 seconds of integration time we can obtain signal-to-noise ~35 per resolution element near 1960 Ang which should lead to signal-to-noise per resolution element of ~60 for spectral regions around Mg, Fe, and Si. The requested signal-to-noise values will allow us to robustly distinguish between a giant impact between primitive rocky bodies and a planetary crust interpretation for the material orbiting and polluting GaiaJ0547-4847.
WDJ0802+5631 will be observed with STIS/E230M to assess narrow absorption lines of Fe, Mg, and Si in the atmosphere of this DA white dwarf. There is no UV flux measurement available for WDJ0802+5631 so we estimate its expected flux level based off of spectral energy distribution fitting to optical and infrared data combined with an accurate atmospheric model that fits them. To distinguish between the two competing models (crustal material or a giant impact) we need to obtain signal-to-noise >~5 per resolution element in the 2500-2800 Ang region. With 25,000 seconds on source we find that we can obtain signal-to-noise between 6-10 in the desired region and thus will be able to achieve our science goals.
All exposure time estimates are made using the STIS ETC assuming standard background parameters and with a white dwarf spectral energy distribution matched to the parameters and flux level of our targets. Our requested time estimates for STIS are increased assuming 21 minutes of overhead (including all spacecraft, acquisition, and exposure overheads as suggested in the STIS manual) per visit and 6.5 minutes of observatory overhead per additional orbit (spacecraft acquisition). We split visits for WDJ0802+5631 into groups of 3 or 4 orbits to aid in scheduling and maintain the health of the MAMA detector. In sum, we request 2 orbits total for STIS observations of GaiaJ0547-4847 and 10 orbits total for WDJ0802+5631.
Observations will be done in the TIME-TAG mode and use the STIS CCD for acquisition. We opt for the 50CCD acquisition filter for our generally bluer target stars.
The target white dwarf stars are ICRS objects (Gaia DR3 position with less than 0.1" positional uncertainty), are the brightest sources within a 7" radius (and thus should dominate the 5"x5" acqusition field-of-view regardless of where they land in it), have an estmated or measured UV flux, and are safe for STIS detectors in our desired setups.PI Melis is an expert in circumstellar disks -- epecially mid-infrared observations and modeling -- and in white dwarf planetary systems. He has extensive experience working with HST ultraviolet data.
Dr. Farihi is a leader in the observations of circumstellar debris disks and white dwarf pollution, and has discovered the majority of disks at white dwarfs observed with Spitzer. He has led several key studies on how the accretion takes place, and published over a dozen papers based on Hubble results, including detailed abundance studies confirming Earth-like debris at numerous polluted white dwarfs. He is PI of the first JWST survey of white dwarf debris disks.
Dr. Kate Su is a senior scientist at the Space Science Institute. She is an experienced user of Spitzer, Herschel, ALMA and SOFIA in studying debris disks to better understand the formation and evolution of planetary systems and provide insights into the underlying planetary architectures. She is a member of JWST MIRI GTO team and leads an on-going JWST GO2 program to observe young rocky planet forming (i.e., giant-impact) disks with MIRI/MRS to search for the presence of silica dust and use their different polymorphs to study the impact conditions.
Dr. Redfield is a leading expert in the observation of circumstellar, interstellar, and planetary atmosphere absorption. He has extensive experience with the spectrographs on HST, notably producing a model of the physical and morphological structure of the gas and dust in the immediate vicinity of the Sun and the nearest stars. He was the first to detect atmospheric absorption in an exoplanet atmosphere from the ground, as well as the first to demonstrate the circumstellar gas transiting WD1145+017 has an eccentric orbit.
Prof. Dufour will lead the modeling effort to obtain atmospheric abundances for each target. He is a world expert in the physical characterization of white dwarf stars.Exoplanets and Exoplanet FormationStellar Physics and Stellar Types6falsefalsetruefalsefalsefalsefalsefalseSUPPORTEDSTARDZNOGAIAJ0547-4847J2000J2000mNUV=17.08STARDANOJ2000J2000The scheduling data was generated by CASM 32.0.CASM was run in Phase I mode.STIS/NUV-MAMASpectroscopicNoNoG230L2376The scheduling data was generated by CASM 32.0.CASM was run in Phase I mode.STIS/NUV-MAMASpectroscopicNoNoE230M2561/Users/cmelis/observing/hst/cycle32/phaseii/OP-cache/jwstwds_cycle32_phaseii-v01.xmlThe scheduling data was generated by CASM 32.1.1.CASM was run in Phase II mode.(Tic-Visit
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