13447( 11) - 08-Sep-2014 14:49:44 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 13447 Version: 11 Check-in Time: 08-Sep-2014 14:49:44 STScI Edit Number: 8 Title The massive monsters living deep in the Tarantula nebula: How massive are they really? ------------------------------------------------------------------------------------ Type Cycle GO 21 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Selma E. de Mink Carnegie Institution of Washington Y CoI: Dr. Saida Caballero Nieves University of Sheffield Y CoI: Ms. Azalee K. Bostroem Space Telescope Science Institute N CoI: Prof. Paul A. Crowther University of Sheffield N CoI: Dr. Douglas R. Gies Georgia State University Research N Foundation CoI: Dr. Daniel J. Lennon ESA-European Space Astronomy Centre N CoI: Dr. Edmund Nelan Space Telescope Science Institute Y CoI: Dr. Mubdi Rahman The Johns Hopkins University N CoI: Dr. Elena Sabbi Space Telescope Science Institute N CoI: Dr. Hugues Sana Space Telescope Science Institute - ESA N ------------------------------------------------------------------------------------ Abstract The recent suggestion that stars with masses in excess of about 300 solar masses exist in the dense star cluster R136 at heart of the Tarantula Nebula received wide interest. It reopened the debate about the upper stellar-mass limit of the initial mass function (IMF) and it raised the question whether pair-instability supernovae -- originally thought exclusively originate from first generation of pop III stars -- can occur in the vicinity of Milky Way. A major challenge hampering mass estimates of the most massive stars is crowding and unresolved companions. High-resolution imaging from the ground and with HST reaching resolutions of about 0.1 arcsec resolved the brightest source in R136 into three separate components. Unfortunately, the extreme crowding and faintness of the targets prohibits ground-based facilities to reach further towards mili-arcsecond resolution. We propose to exploit the new full two-dimensional calibration program of Fine Guidance Sensor (Nelan, Prop ID 13175) to probe the most luminous stars in R136 for previously unseen companions down to a resolution of 12 mili-arsecond, exploring the separation of about 500-5000 AU. Furthermore, we will characterize the claimed source R136-a1B and if needed revise downward the mass estimates of the most massive stars known date. ------------------------------------------------------------------------------------ Observations Description ------------------------ This is a single CVZ orbit observation to probe the most luminous stars of the central region of R136 using the FGS1r in its high angular resolution TRANSfer mode. The photocenter of this very crowded region will be placed at the POS_TARG(x, y)=(0, 0) location at the center of the FGS1r FOV, near R136-A1. Observations will be made with the F583W filter using one of the possible scan 13447( 11) - 08-Sep-2014 14:49:44 - [ 2] ORIENTations of 18, 108, 198, or 288 degrees over an 9 arcsec by 9 arcsec scan path in order to optimize the projected separation of objects A1, A2, A3, B, and C from field stars. The long scan will require a Continuous Viewing Zone (CVZ) orbit to maximize the SNR and to include the four major science targets in this region. The individual scans will be de-jittered, cross-correlated, coadded, and smoothed to produce high SNR interference fringes in two orthogonal directions. We propose to exploit the new full two-dimensional calibration program of Fine Guidance Sensor (Nelan, ID 13175) to model (and thus remove) the effect of the numerous field stars present in the beam to enable detection of any previously unseen companions in the A, B, C stars down to a resolution of ~15 mili-arsecond. R136 is host to the most massive stars observed to date (Crowther et al. 2010, MNRAS, 408, 731). R136 has previously been observed with FGS, however the specified orientation is needed to characterize the claimed source R136-A1b and the wider FOV will include the most massive stars observed to date: R136-A1, R136-A2, R136-B and R136-C. ------------------------------------------------------------------------------------ 13447( 11) - 08-Sep-2014 14:49:44 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 R136 STELLAR CLUSTER, STAR RA=05H38M42.3840S, J2000 V = 9.5 FORMING REGION DEC=-69D06'3.12" Reference Frame: ICRS ------------------------------------------------------------------------------------------------------------------------------------ 13447( 11) - 08-Sep-2014 14:49:44 - [ 4] Visit: 01 Visit Requirements: CVZ; ORIENT 108D TO 108 D; ORIENT 18D TO 18 D; ORIENT 198D TO 198 D; ORIENT 288D TO 288 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 R136 FGS TRANS 1 F583W SCANS=20, STEP-SIZE=1.0 1 4700 S GS ACQ SCENARIO ONEB1B3 (4700 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 | ------------------------------------------------------------------------------------------------------------------------------------ R136 1 FGS TRANS 1 F583W none none none none 1 N/A 13447( 11) - 08-Sep-2014 14:49:44 - [ 5] Summary Form for Proposal 13447 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 1 ------------------------------------------------------------------------------------------------------------------------------------ Configurations FGS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes TRANS ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters SCANS=20, STEP-SIZE=1.0 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements CVZ, GS ACQ SCENARIO ONEB1B3, ORIENT 108D TO 108 D, ORIENT 18D TO 18 D, ORIENT 198D TO 198 D, ORIENT 288D TO 288 D ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F583W ------------------------------------------------------------------------------------------------------------------------------------ Target Names R136 ------------------------------------------------------------------------------------------------------------------------------------