0Assigned ID: 5376
----- Attempting Submission 1 (Tue Mar 26 09:53:50 GMT 2024) -----
HST Phase I Proposal 5376 successfully submitted.
Receipt: # 5376-1
----- Attempting Submission 2 (Tue Mar 26 18:09:19 GMT 2024) -----
HST Phase I Proposal 5376 successfully submitted.
Receipt: # 5376-2According to the last email from STScI (2024-01-17), we added a second ACQ/PEAK at the beginning of each STIS visit, using 0.2x0.09 aperture.
We also changed the aperture used for wavelength calibration of exp 6 to 0.2x0.09.-898124577----- Attempting Submission 1 (Fri Aug 16 12:17:12 GMT 2024) -----
----- Attempting Submission 2 (Mon Aug 26 08:32:33 GMT 2024) -----
----- Attempting Submission 3 (Fri Sep 27 08:49:38 GMT 2024) -----
----- Attempting Submission 4 (Tue Oct 08 08:27:04 GMT 2024) -----
HST Phase II Proposal 17790 successfully submitted.
Receipt: # 17790-4
----- Attempting Submission 5 (Tue Oct 08 08:28:07 GMT 2024) -----
----- Attempting Submission 6 (Sat Jan 18 13:21:17 GMT 2025) -----The C/Fe and dust-to-ice ratios in Beta Pictoris exocometsExocomets are small icy bodies analogues to comets in our solar system, placed on eccentric orbits and producing extended tails of dust and gas near their periastra. When transiting in front of their host star, the exocometary tails can be detected using photometry and absorption spectroscopy, as already done in several systems. The most iconic case is undoubtedly Beta Pic, which continuously displays variable absorption in many spectral lines (e.g. Fe, Ca, C, O) due to the high rate of exocometary transits in this system.
Despite decades of observations, we still have very few information on the composition of these objects, depriving us of valuable knowledge for understanding their formation processes and history. However, significant progress was recently made with the development of the "exocomet curve of growth" technique, which allows realiable measurements of exocometary column densities using absorption spectroscopy.
Here we propose to take advantage of this new tool to estimate, for the first time, 1) the ionisation state in several Beta Pic comets and 2) their C/Fe ratios, by targeting very specific UV lines with STIS and COS. The ionisation state will be characterized by measuring the column densities of many refractory species (Fe, Ni, Mn...) with different ionisation energies. The C/Fe ratio will be measured through the study of the C I and Fe II lines accessible with STIS. This ratio will directly lead to the estimate of the dust-to-ice ratio in several Beta Pic comets, yielding valuable insight on the role played by exocomets in the evolution of planetary system and allowing for comparison between solar and extrasolar comets.The goal of HST program 17790 is to determine the ionisation state and C/Fe ratio of Beta Pic exocomets, by studying their absorption signatures in various UV lines of their host star spectrum.
Our program will be divided into four visits, each visit targetting the same spectral range (1150 - 2900 A). To ensure that a fresh set of exocomets is detected at each visit, we request that two consecutive visits be separated by at least 5 days.
Each visit will consist of four consecutive orbits (3 with STIS, 1 with COS), with the following settings:
- 1 STIS orbit in the NUV/MAMA / E230H configuration, splitted into two exposures:
- 1 exposure targetting the 2013 A cenwave (1874 - 2151 A, including Zn II and Cr II lines), with the 0.1x0.03 aperture;
- 1 exposure targetting the 2762 A cenwave (2623 - 2900 A, including Fe II, Cr II and Mg II II lines), with the 31x0.05NDA aperture;
- 1 STIS orbit in the FUV/MAMA / E140H configuration, with the following exposure:
- 1 exposure targetting the 1598 A cenwave (1497 - 1699 A, including C I, Fe II lines from ), with the 0.2x0.2 aperture;
- 1 STIS orbit in the NUV/MAMA / E230H configuration, splitted into three exposures:
- 1 exposure targetting the 1763 A cenwave (1624 - 1901 A, including lines from S I, Fe II, Ni II, Si II, Al III), with the 0.2x0.2 aperture;
- 1 exposure targetting the 2263 A cenwave (2124 - 2401 A, including Fe II, Ni and Co II lines), with the 0.1x0.03 aperture;
- 1 exposure targetting the 2513 A cenwave (2374 - 2651 A, including Fe II and Mn II lines), with the 0.1x0.03 aperture;
- 1 COS orbit in the FUV / G130 M configuration, targetting the 1291 A cenwave. Both segments will be used (B[1137-1274], A[1292-1432]), allowing the observation of S II, C I, C II, O I and N I lines. In order to use both FP-POS=3 and FP-POS=4, we split this orbit into two separate exposures targetting the same wavelength range.
To avoid blending between separate cometary features, we always use the gratting with the highest spectral resolution (E230H, 140H, G130M). The apertures have been chosen so that the brightness limit of 200,000 count/s is respected for all A5V stellar models provided by the ETC and all wavelength settings. We organised the different STIS exposures so as to observe all Cr II lines during orbit #1, and all Ni II lines during orbit #3. To compensate for the low flux of Beta Pic in the far-UV, we dedicate a full orbit (#2) to the observation of the C I bands at 1560 and 1660 A.
For each visit, we expect to detect between 1 and 3 individual exocomets. The ionisation state in each of these object will be recovered through the comparison between the observed composition in refractory ions (S I, Fe II, Ni II, Mn II, Al III...) and photospheric abundances. Then, the C/Fe ratio of each exocomet will then be estimated through the analysis of C I and Fe II lines. Over the four visits, we expect to be able to measure this ratio in 8 +- 3 exocomets, opening the way for comparison between Beta Pic exocomet families.All team members have long term expertise in both HST data analysis (STIS, ACS, COS) and modeling of
exocomets transits. They are co-authors of more than one hundred papers on exoplanets atmospheres and
observation of exocomets (including 6 papers in Nature publications, with a recent paper in Nature Scientific
Reports on exocomets in Beta Pic : Lecavelier et al. 2022). They are first authors of a dozen of papers directly
related to HST observations covering both theoretical and observational aspects of exoplanetary science. They
have been PIs of a total of 9 HST programs on exoplanets transit, circumstellar disks and exocomets
observations, including one on-going program in Cycle 31.Exoplanets and Exoplanet Formation6falsefalsefalsefalsefalsefalseSUPPORTEDSTARA4-A9 V-IVNOThis object was generated by the targetselector and retrieved from the SIMBAD database.
SIMBAD listed proper motion for this target. When retrieving targets with PM from SIMBAD, APT requests the coordinates be calculated with an epoch of the year 2000. Do not modify this epoch. Always review coordinates using the Target Confirmation tool, which graphically displays the PM.J2000COS/FUVSpectroscopicNoNoG130M1291STIS/FUV-MAMASpectroscopicNoNoE140H1598STIS/NUV-MAMASpectroscopicNoNoE230H1763STIS/NUV-MAMASpectroscopicNoNoE230H2263STIS/NUV-MAMASpectroscopicNoNoE230H2563STIS/NUV-MAMASpectroscopicNoNoE230H2812Timing link suitability includes constraints ([Sequence (01 02) within 0.2 days])The scheduling data was generated by CASM 33.0.CASM was run in Phase II mode.C:\Users\admin\Desktop\OP-cache\17790_phase_2-v01.xml(Tic-Visit
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