Submission 2 2020-03-06 23:06PM 1357696477 Assigned ID: 761 ----- Attempting Submission 1 (Fri Mar 06 20:50:35 GMT 2020) ----- HST Phase I Proposal 761 successfully submitted. Receipt: # 761-1 ----- Attempting Submission 2 (Fri Mar 06 23:06:50 GMT 2020) ----- HST Phase I Proposal 761 successfully submitted. Receipt: # 761-2 Epoch of target chosen using the Gaia DR2 2015.5 epoch, rather than the J2000 epoch to reduce error in position. -1716191272 ----- Attempting Submission 1 (Tue Jun 23 12:23:42 GMT 2020) ----- There is vast evidence establishing the survival of exoplanets through the evolution of their host stars into white dwarfs (WDs). A key signature that betrays the presence of planetary systems around WDs is a compact (~ 1 Solar radius) debris disc, formed from the tidal disruption of planetesimals and detectable as an infrared flux excess. These discs accrete onto the WDs polluting their otherwise pristine H or He atmospheres, and the analysis of adequate optical and UV spectroscopy of these systems allows reconstruction of bulk composition of the disrupted planetesimals. A rare subset of debris discs host gas that can be observed through double-peaked emission profiles, tracers of "fresh" disruption events which provide dynamical and geometric information on the disc. In a search for debris disc hosts we have identified the gaseous debris disc host, WD J2100+2122. The WD has an effective temperature of 26760 K, making it by far the hottest gaseous debris disc host known to date and challenges the standard model of debris discs. The emission profiles from the disc are unusual; where all known gaseous debris discs are dominated by the 860nm Ca triplet emission, the spectrum of WD J2100+2122 exhibits an array of Fe emission features. The peculiar emission features can either be explained by (i) the high temperature of the WD heating the disc and thereby changing the line strengths, or (ii) the composition of the accreted body being Fe-enhanced/Ca-depleted. To determine the correct scenario, we require a single orbit of COS spectroscopy to fully characterise the elemental abundance of the accreted planetesimal using the plethora of absorption lines available in the FUV. We wish to observe the target WD2100+2122 for a single orbit, as this is a bright, hot DA white dwarf which has signs of strong metal pollution. We will observe the target in two FUV settings, with central wavelengths 1291 and 1222. We will expose in the 1222 cen wave setting for longer to account for the sensitivity drop off to shorter wavelengths. Copied below is the techincal description from the submitted proposal. The main scientific goal of this proposal is to measure the photospheric abundances of the WDJ2100+2122 - polluted by the accretion of a planetary body. This study requires sufficiently high spectral resolution to avoid blending of the individual elements (Figure 3), which would hinder accurate individual abundance determinations. A resolution of ~20000 as offered by the COS 130M grating is ideal for the task, and the instrument provides sufficient sensitivity to carry out the observations with a modest investment of HST time. We will cover the far-ultraviolet (FUV) part of the spectrum with one orbit of COS G130M observations, with two central wavelength settings of 1222A and 1291A with an effective wavelength coverage 1080-1430A. These central wavelengths were chosen to cover a large range of potential photopsheric lines that can be used to determine the composition of the debris disc. As our aim is to determine the photopsheric abundance of the white dwarf, we require a S/N >= 30, which has been used successfully in previous polluted white dwarf studies. Using our model spectrum as input for the Exposure Time Calculator, we find that we reach this S/N in ~750s on-target exposure time for the 1291A central wavelength setting. We will obtain an exposure of the same length using the 1222A central wavelength setting, with a combined time of 30 mins which is well within the estimated visibility of the target of ~ 53mins even including overheads for guide star acquisition, target acquisition, and detector readout. Any excess time will be used to obtain an additional exposure in the 1222A central wavelength setting to increase the S/N in the wavelength range 1080-1120 A. Manser is an expert on gaseous debris discs around white dwarfs and has pioneered the analysis of these dynamic systems. He generated the first image of a gaseous debris disc, as well discovering a planetesimal orbiting within a gaseous debris disc using subtle variations in the radial velocity profiles of the gaseous emission. He will lead the overall analysis between the composition of the planetary material in the white dwarf atmosphere and the multiple emission profiles from the gaseous debris disc. Gentile Fusillo has been using large astronomical surveys to (a) identify white dwarfs, most recently producing the first all-sky catalogue of white dwarfs using Gaia DR2, and (b) to then search for white dwarfs with signature of evolved planetary systems. Dennihy has also been using large astronomical surveys to identify planetary systems around white dwarfs. He identified WDJ2100+2122 and obtained follow-up spectroscopy of the system which revealed emission features from a gaseous debris disc. Gaensicke has been PI of 20 HST programs, carrying out far-ultraviolet spectroscopy of white dwarfs, including large, medium, small GO programs and several snapshot programs. He has in-depth experience in the analysis and interpretation of the observations of accreting white dwarfs, both in binary systems, and evolved planetary systems. He will assist with the implementation of observations and the analysis. Toloza is an expert in modelling white dwarf atmospheres using the code of Detlev Koester (2010, MmSAI, 81, 921), and has determined composition models for many HST/COS polluted white dwarf spectra. She will lead the compositional analysis of the spectra we propse to obtain here. Exoplanets and Exoplanet Formation 6 false false true false false false false SUPPORTED STAR ACCRETION DISK DA EXTRA-SOLAR PLANETARY SYSTEM NO J2000 J2000 GALEX FUV = 13.80 COS/FUV Spectroscopic No No G130M 1291 COS/FUV Spectroscopic No No G130M 1222 1592911930521 The scheduling data was generated by CASM 28.2. CASM was run in Phase II mode. /Volumes/Storage/PhD_files/proposals/HST_2020/WDJ2100/OP-cache/WDJ2100+2122_BTG-v01.xml (Tic-Visit :proposal-id 16314 :visit-id "01" :proposal-version -1 :trans-version "20200518" :date "23-Jun-2020 12:32:10.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "31" :si-bright-earth-limb-angle 20.0 :data-volume 661120 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 16314 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 16314 :visit-id "01" :orbit-number 1 :pcs-time 393 :si-vis-utilization 2764 :al-overhead-at-end 0 :internal-dur-at-end 369 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3157 :pcs-gap 0 ) true 1 0