17753( 6) - 10-Sep-2025 16:49:55 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 17753 Version: 6 Check-in Time: 10-Sep-2025 16:49:55 STScI Edit Number: 0 Title Binarity and Accretion Processes in AGB Stars: A UV Study of pi1 Gru ------------------------------------------------------------------------------------ Type Cycle GO 32 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Raghvendra Sahai Jet Propulsion Laboratory Y CoI: Leen Decin Institute of Astronomy, KU Leuven N CoI: Dr. Miguel Montarges Observatoire de Paris - Section de Meudon N CoI: Dr. Alex De Koter Universiteit van Amsterdam N ------------------------------------------------------------------------------------ Abstract The dramatic changes in the geometry and dynamics of the mass-ejection during the death throes of most stars that evolve in a Hubble time (i.e., with initial masses ~1-8 Msun), are widely believed to be due to binarity-induced formation of bound disks that power high-speed collimated jets. But observational evidence of this process are lacking. We propose to obtain multi-epoch UV spectra of the nearby (160 pc) late-spectral-type AGB star, pi1 Gru, that belongs to a newly-discovered class of AGB stars showing strong (and often variable) FUV fluxes -- suggestive of variable accretion of matter onto an accretion disk in a binary system. A STIS spectroscopic study of the prototype of this class, Y Gem, showing the presence of flickering and high-velocity infall and outflows, supports this hypothesis. ALMA observations of pi1 Gru reveal strong departures from spherical symmetery in its dusty molecular wind (spiral structure, fast polar bubbles) and the presence of a close companion at ~6 AU, confirmed by optical imaging using SPHERE/ZIMPOL. We will use the UV spectra of pi1 Gru to fit the UV continuum and derive the temperature and size of the accretion hot-spot. Using CLOUDY modelling, we will fit the emission lines to provide constraints on the physical parameters of the accreting flow. The line profiles, if resolved, will reveal the nature of the companion star. Our study will probe the early formation phase of bound disks in binary AGB stars, and provide valuable insights into the binary-induced accretion processes that make such disks, which have long been theorized to drive collimated outflows that produce aspherical morphologies in post-AGB objects. ------------------------------------------------------------------------------------ Observations Description ------------------------ We will obtain multi-epoch UV spectra of pi1 Gru with COS using the G140L (center=1280 A) and G230L (center=2950 & 3360 A) gratings in TIME-TAG mode. The average GALEX FUV (NUV) flux of pi1 Gru is 277(2680) uy. For this source, using COS ETC, we find: FUV: Using the G140L grating, with Cen.Wave. setting lambda=1280 A(B[916-1195], A[1282-2148]) (spectral resolution R ~ 2000 - 5000), we will get a signal-to-noise ratio, S/N, of ~10 for the continuum with an exposure time of 12 min. 17753( 6) - 10-Sep-2025 16:49:55 - [ 2] NUV: Using the G230L grating with two Cen.Wave settings: (i) setting lambda=3360 A (A[2060-2457], B[3162 -3560] and (ii) setting lambda=2950 A (A[1651-2049], A[2751 3150]) (R ~1550 -2900), we get an S/N of ~10 for the continuum with an exposure time of ~1.1 min. As seen from the study of Y Gem (Setal18), the S/N for the lines will be much higher than for the continuum. The above selection of gratings and setting has been made in order to provide nearly fullwavelength coverage at lambda > 916 A in the FUV and NUV (for lambda < 3200 A) bands (since the G230L NUVB spectrum is expected to have negligible second-order contamination shortward of 3200 A.) There will be a ~300 A gap (between 2460 A and 2750 A) in the NUV spectra that we obtain, but it does not impact our ability to reach the science goals of our study. Stripe C of the COS/ MAMA detector may provide potentially useful data over wavelength bands 1900-2100 A for Cen.Wave.=2950 A and 2164 - 2361 A for Cen.Wave.=3360, with about 5% contamination from the first order spectra (ISR COS 2010-01), but these are not critical for our proposed study. ------------------------------------------------------------------------------------ 17753( 6) - 10-Sep-2025 16:49:55 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 PI.01-GRU STAR, ACCRETION DISK, RA=22H22M44.2084S +/- 0.05", J2000 V = 6.55 AGB STAR, CIRCUMSTELLAR DEC=-45D56'52.79" +/- 0.05" MATTER, S STAR Reference Frame: ICRS Extended: NO Comments: This object was generated by the targetselector and retrieved from the SIMBAD database. Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2000 0.002982454497594567 -0.010338 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 17753( 6) - 10-Sep-2025 16:49:55 - [ 4] Visit: 01 Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 PI.01-GRU COS/FUV ACQ/SEA PSA G140L 1105 STEP-SIZE=1.0, SCAN-SIZE=2, 1 80 S (80 RCH CENTER=DEF S) ------------------------------------------------------------------------------------------------------------------------------------ 2 PI.01-GRU COS/FUV ACQ/PEA PSA G140L 1105 1 80 S (80 KXD S) ------------------------------------------------------------------------------------------------------------------------------------ 3 PI.01-GRU COS/FUV ACQ/PEA PSA G140L 1105 NUM-POS=5, STEP-SIZE=0.9, 1 80 S (80 KD CENTER=FLUX-WT-FLR S) ------------------------------------------------------------------------------------------------------------------------------------ 4 PI.01-GRU COS/FUV TIME-TA PSA G140L 1105 BUFFER-TIME=2000, FP-POS=1 1 440 S (440 G S) ------------------------------------------------------------------------------------------------------------------------------------ 5 PI.01-GRU COS/FUV TIME-TA PSA G140L 1105 BUFFER-TIME=2000, FP-POS=2 1 440 S (440 G S) ------------------------------------------------------------------------------------------------------------------------------------ 6 PI.01-GRU COS/FUV TIME-TA PSA G140L 1105 BUFFER-TIME=2000, FP-POS=3 1 710 S (710 G S) ------------------------------------------------------------------------------------------------------------------------------------ 7 PI.01-GRU COS/FUV TIME-TA PSA G140L 1105 BUFFER-TIME=2000, FP-POS=4 1 710 S (710 G S) ------------------------------------------------------------------------------------------------------------------------------------ 8 PI.01-GRU COS/NUV TIME-TA PSA G230L 2635 BUFFER-TIME=2000, FP-POS=1 1 680 S (680 G S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ PI.01-GRU 1 COS/FUV ACQ/SEA PSA G140L 1105 none none none none 1 N/A RCH PI.01-GRU 2 COS/FUV ACQ/PEA PSA G140L 1105 none none none none 1 N/A KXD PI.01-GRU 3 COS/FUV ACQ/PEA PSA G140L 1105 none none none none 1 N/A KD PI.01-GRU 4 COS/FUV TIME-TA PSA G140L 1105 none none none none 1 N/A G PI.01-GRU 5 COS/FUV TIME-TA PSA G140L 1105 none none none none 1 N/A G PI.01-GRU 6 COS/FUV TIME-TA PSA G140L 1105 none none none none 2 N/A G 17753( 6) - 10-Sep-2025 16:49:55 - [ 5] Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ PI.01-GRU 7 COS/FUV TIME-TA PSA G140L 1105 none none none none 2 N/A G PI.01-GRU 8 COS/NUV TIME-TA PSA G230L 2635 none none none none 2 N/A G 17753( 6) - 10-Sep-2025 16:49:55 - [ 6] Visit: 02 Visit Requirements: AFTER 01 BY 300 D TO 370 D On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 PI.01-GRU COS/FUV ACQ/SEA PSA G140L 1105 STEP-SIZE=1.0, SCAN-SIZE=2, 1 80 S (80 RCH CENTER=DEF S) ------------------------------------------------------------------------------------------------------------------------------------ 2 PI.01-GRU COS/FUV ACQ/PEA PSA G140L 1105 1 80 S (80 KXD S) ------------------------------------------------------------------------------------------------------------------------------------ 3 PI.01-GRU COS/FUV ACQ/PEA PSA G140L 1105 NUM-POS=5, STEP-SIZE=0.9, 1 80 S (80 KD CENTER=FLUX-WT-FLR S) ------------------------------------------------------------------------------------------------------------------------------------ 4 PI.01-GRU COS/FUV TIME-TA PSA G140L 1105 BUFFER-TIME=2000, FP-POS=1 1 494 S (494 G S) ------------------------------------------------------------------------------------------------------------------------------------ 5 PI.01-GRU COS/FUV TIME-TA PSA G140L 1105 BUFFER-TIME=2000, FP-POS=2 1 507 S (507 G S) ------------------------------------------------------------------------------------------------------------------------------------ 6 PI.01-GRU COS/FUV TIME-TA PSA G140L 1105 BUFFER-TIME=2000, FP-POS=3 1 750 S (750 G S) ------------------------------------------------------------------------------------------------------------------------------------ 7 PI.01-GRU COS/FUV TIME-TA PSA G140L 1105 BUFFER-TIME=2000, FP-POS=4 1 750 S (750 G S) ------------------------------------------------------------------------------------------------------------------------------------ 8 PI.01-GRU COS/NUV TIME-TA PSA G230L 2635 BUFFER-TIME=2000, FP-POS=1 1 662 S (662 G S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ PI.01-GRU 1 COS/FUV ACQ/SEA PSA G140L 1105 none none none none 1 N/A RCH PI.01-GRU 2 COS/FUV ACQ/PEA PSA G140L 1105 none none none none 1 N/A KXD PI.01-GRU 3 COS/FUV ACQ/PEA PSA G140L 1105 none none none none 1 N/A KD PI.01-GRU 4 COS/FUV TIME-TA PSA G140L 1105 none none none none 1 N/A G PI.01-GRU 5 COS/FUV TIME-TA PSA G140L 1105 none none none none 1 N/A G PI.01-GRU 6 COS/FUV TIME-TA PSA G140L 1105 none none none none 2 N/A G 17753( 6) - 10-Sep-2025 16:49:55 - [ 7] Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ PI.01-GRU 7 COS/FUV TIME-TA PSA G140L 1105 none none none none 2 N/A G PI.01-GRU 8 COS/NUV TIME-TA PSA G230L 2635 none none none none 2 N/A G 17753( 6) - 10-Sep-2025 16:49:55 - [ 8] Summary Form for Proposal 17753 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures PSA ------------------------------------------------------------------------------------------------------------------------------------ Configurations COS/FUV, COS/NUV ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ/PEAKD, ACQ/PEAKXD, ACQ/SEARCH, TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BUFFER-TIME=2000, CENTER=DEF, CENTER=FLUX-WT-FLR, FP-POS=1, FP-POS=2, FP-POS=3, FP-POS=4, NUM-POS=5, SCAN-SIZE=2, STEP-SIZE=0.9, STEP-SIZE=1.0 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements AFTER 01 BY 300 D TO 370 D ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G140L, G230L ------------------------------------------------------------------------------------------------------------------------------------ Target Names PI.01-GRU ------------------------------------------------------------------------------------------------------------------------------------