14246( 4) - 11-Nov-2015 20:03:49 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 14246 Version: 4 Check-in Time: 11-Nov-2015 20:03:49 STScI Edit Number: 0 Title The Fastest Rotating Stars ------------------------------------------------------------------------------------ Type Cycle GO 23 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Douglas R. Gies Georgia State University Research Y Foundation CoI: Mr. Zhao Guo Georgia State University Research N Foundation ------------------------------------------------------------------------------------ Abstract The VLT FLAMES Survey of the massive stars in the Tarantula Nebula region of the LMC has led to the discovery of the two fastest rotating stars: VFTS 102 and 285 with V sin i = 610 and 609 km/sec. These two O-dwarfs may be single stars born with extraordinarily high angular momentum or they may have been spun up in a binary system by mass transfer or merger. Extreme rotators like these suffer gravity darkening that makes their equatorial regions cooler than the polar zones, so that the equatorial parts close to the limb contribute less flux and create narrower lines. We show how HST/COS spectroscopy of the far-ultraviolet spectra can be used with the optical rotational line broadening to estimate this gravity darkening effect and to determine the ratios of equatorial to critical rotation velocity for these two stars. This ratio is key to describing the bipolar winds of rapidly rotating stars, and the COS spectra will record the important wind lines in the FUV for comparison with models of asymmetric winds. The COS spectra will yield estimates of the stellar masses, radii, rotation rates, and abundances that will help us assess the origin and destiny of these remarkable stars in particular and massive rotating stars in general. ------------------------------------------------------------------------------------ Observations Description ------------------------ We propose to obtain COS observations of the FUV spectrum of VFTS 102 and 285 using the G130M grating to cover most of the range from 1150 to 1450 with a resolving power of 18, 000 (although we may make a modest reduction in resolving power by spectral smoothing in the data analysis stage to increase the signal-to-noise ratio). Our primary goal is to obtain cross-correlation functions of the FUV photospheric lines with model spectra. Numerical tests with model spectra indicate that we can estimate the FWHM of the cross-correlation function to better than 5% accuracy (comparable to the optical measurements of V sin i; 14246( 4) - 11-Nov-2015 20:03:49 - [ 2] Ramirez-Agudelo et al. 2013) with a signal-to-noise ratio of S/N = 10 per resolution element, so our goal is to obtain a S/N = 10 at 1310 in a single visit to each target. This S/N is also adequate for our investigation of the line morphology of the wind lines of Si III 1206, N V 1240, and Si IV 1400. We used the COS ETC and assumed that the spectral energy distributions are given by reddened versions of Castelli & Kurucz model spectra for the spectral classifications of the two targets. The model spectra were normalized using the UIT B1 magnitudes (effective wavelength = 1521 Angstroms) of the targets from Parker et al. (1998, AJ, 116, 180) and B-V colors from Evans et al. (2011), and the extinctions were estimated using intrinsic colors from Wegner (1994) and a ratio of total-to- selective extinction of R = 3.41 (LMC average). The COS ETC gave exposure times of 4500 and 440 seconds for VFTS 102 and 285, respectively (the latter being hotter and less reddened). Following the example in the Instrument Handbook, we would obtain this result through several exposures at each of four FP-POS spectral offsets and two or three CENWAVE positions in order to fill in the gap in spectral coverage between the two COS detectors. All these exposures would be made in standard TIME-TAG mode. We estimate that there are 54 minutes of visibility per orbit for the declination of both targets (delta = -69 deg). In the first orbit, we require 3 minutes for acquisition, 5 minutes for COS FUV acquisition and search, 2 minutes for PEAKXD cross dispersion peakup, and 5 minutes for PEAKD peakup in the dispersion direction. This leaves 39 minutes for science exposures. In succeeding orbits, we need 4 minutes for re-acquisition, yielding a net of 50 minutes for science exposure. Thus, for the fainter target, VFTS 102, we are requesting three orbits (with 4, 4, and 4 sub-exposures for each of 3 CENWAVE positions; this will require orbits 1, 2, and 3, respectively). We can obtain all the sub-exposures (four in each of 2 CENWAVE positions) in a single orbit for the brighter target, VFTS 285. Dr. Hugues Sana kindly provided F275W AB magnitudes for both stars based upon unpublished HST observations: m(F275W) = 15.044 for VFTS-102 m(F275W) = 14.013 for VFTS-285 The COS ETC calculations using these estimates led to exposure times that are a 14246( 4) - 11-Nov-2015 20:03:49 - [ 3] factor of 3.1 and 3.9 times lower for VFTS-102 and VFTS-285, repectively, than given above. Given this uncertainty, the BUFFER-TIME estimates were lowered by these factors (and the recommended 2/3) from the ETC calculations in order to be sure the buffers do not reach full capicity. ------------------------------------------------------------------------------------ 14246( 4) - 11-Nov-2015 20:03:49 - [ 4] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 VFTS-102 EXT-STAR, MAIN SEQUENCE RA=05H37M39.2400S +/- 0.01S, J2000 V = 15.70 +/- 0.10 E(B-V)=0.63+/-0.10 O DEC=-69D09'51.12" +/- 0.1" Reference Frame: ICRS Extended: NO Comments: This object was generated by the targetselector and retrieved from the SIMBAD database. UIT m(B1)=14.55 F(1521)=5.5E-15 erg/s/cm^2/Angstrom Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2000.0 -1.8742860237103174E-5 -0.0013 0. ------------------------------------------------------------------------------------------------------------------------------------ 2 VFTS-285 EXT-STAR, MAIN SEQUENCE RA=05H38M17.3400S +/- 0.02S, J2000 V = 15.63 +/- 0.10 E(B-V)=0.23+/-0.10 O DEC=-69D05'42.14" +/- 0.3" Reference Frame: ICRS Extended: NO Comments: This object was generated by the targetselector and retrieved from the SIMBAD database. UIT m(B1)=12.66 F(1521)=3.1E-14 erg/s/cm^2/Angstrom Note that target VFTS-285 has a close companion VFTS-290 that is similar in brightness at a separation of 4 arcsec. Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2000.0 -7.473445918105549E-5 -2.3E-4 0 ------------------------------------------------------------------------------------------------------------------------------------ 14246( 4) - 11-Nov-2015 20:03:49 - [ 5] Visit: 01 Visit Requirements: On Hold Comments: Additional Comments: 3 orbit visit 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 VFTS-102 COS/NUV ACQ/IMA PSA MIRRORB 1 51.0 S (51 GE S) Comments: COS NUV image acquisition sequence. ------------------------------------------------------------------------------------------------------------------------------------ 2 VFTS-102 COS/FUV TIME-TA PSA G130M 1309 FP-POS=1, BUFFER-TIME=565 1 565 S (565 G S) ------------------------------------------------------------------------------------------------------------------------------------ 3 VFTS-102 COS/FUV TIME-TA PSA G130M 1309 FP-POS=2, BUFFER-TIME=565 1 565 S (565 G S) ------------------------------------------------------------------------------------------------------------------------------------ 4 VFTS-102 COS/FUV TIME-TA PSA G130M 1309 FP-POS=3, BUFFER-TIME=565 1 565 S (565 G S) ------------------------------------------------------------------------------------------------------------------------------------ 5 VFTS-102 COS/FUV TIME-TA PSA G130M 1309 FP-POS=4, BUFFER-TIME=565 1 565 S (565 G S) ------------------------------------------------------------------------------------------------------------------------------------ 6 VFTS-102 COS/FUV TIME-TA PSA G130M 1300 FP-POS=1, BUFFER-TIME=681 1 681 S (681 G S) ------------------------------------------------------------------------------------------------------------------------------------ 7 VFTS-102 COS/FUV TIME-TA PSA G130M 1300 FP-POS=2, BUFFER-TIME=681 1 681 S (681 G S) ------------------------------------------------------------------------------------------------------------------------------------ 8 VFTS-102 COS/FUV TIME-TA PSA G130M 1300 FP-POS=3, BUFFER-TIME=681 1 681 S (681 G S) ------------------------------------------------------------------------------------------------------------------------------------ 9 VFTS-102 COS/FUV TIME-TA PSA G130M 1300 FP-POS=4, BUFFER-TIME=681 1 681 S (681 G S) ------------------------------------------------------------------------------------------------------------------------------------ 10 VFTS-102 COS/FUV TIME-TA PSA G130M 1318 FP-POS=1, BUFFER-TIME=681 1 681 S (681 G S) ------------------------------------------------------------------------------------------------------------------------------------ 11 VFTS-102 COS/FUV TIME-TA PSA G130M 1318 FP-POS=2, BUFFER-TIME=681 1 681 S (681 G S) ------------------------------------------------------------------------------------------------------------------------------------ 12 VFTS-102 COS/FUV TIME-TA PSA G130M 1318 FP-POS=3, BUFFER-TIME=681 1 681 S (681 G S) ------------------------------------------------------------------------------------------------------------------------------------ 13 VFTS-102 COS/FUV TIME-TA PSA G130M 1318 FP-POS=4, BUFFER-TIME=681 1 681 S (681 G S) ------------------------------------------------------------------------------------------------------------------------------------ 14246( 4) - 11-Nov-2015 20:03:49 - [ 6] 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 | ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ VFTS-102 1 COS/NUV ACQ/IMA PSA MIRRORB none none none none 1 N/A GE VFTS-102 2 COS/FUV TIME-TA PSA G130M 1309 none none none none 1 N/A G VFTS-102 3 COS/FUV TIME-TA PSA G130M 1309 none none none none 1 N/A G VFTS-102 4 COS/FUV TIME-TA PSA G130M 1309 none none none none 1 N/A G VFTS-102 5 COS/FUV TIME-TA PSA G130M 1309 none none none none 1 N/A G VFTS-102 6 COS/FUV TIME-TA PSA G130M 1300 none none none none 2 N/A G VFTS-102 7 COS/FUV TIME-TA PSA G130M 1300 none none none none 2 N/A G VFTS-102 8 COS/FUV TIME-TA PSA G130M 1300 none none none none 2 N/A G VFTS-102 9 COS/FUV TIME-TA PSA G130M 1300 none none none none 2 N/A G VFTS-102 10 COS/FUV TIME-TA PSA G130M 1318 none none none none 3 N/A G VFTS-102 11 COS/FUV TIME-TA PSA G130M 1318 none none none none 3 N/A G VFTS-102 12 COS/FUV TIME-TA PSA G130M 1318 none none none none 3 N/A G VFTS-102 13 COS/FUV TIME-TA PSA G130M 1318 none none none none 3 N/A G 14246( 4) - 11-Nov-2015 20:03:49 - [ 7] Visit: 02 Visit Requirements: On Hold Comments: Additional Comments: 1 orbit visit 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 VFTS-285 COS/NUV ACQ/IMA PSA MIRRORB 1 11.0 S (11 GE S) Comments: COS NUV image acquisition sequence. ------------------------------------------------------------------------------------------------------------------------------------ 2 VFTS-285 COS/FUV TIME-TA PSA G130M 1300 FP-POS=1, BUFFER-TIME=195 1 195 S (195 G S) ------------------------------------------------------------------------------------------------------------------------------------ 3 VFTS-285 COS/FUV TIME-TA PSA G130M 1300 FP-POS=2, BUFFER-TIME=195 1 195 S (195 G S) ------------------------------------------------------------------------------------------------------------------------------------ 4 VFTS-285 COS/FUV TIME-TA PSA G130M 1300 FP-POS=3, BUFFER-TIME=195 1 195 S (195 G S) ------------------------------------------------------------------------------------------------------------------------------------ 5 VFTS-285 COS/FUV TIME-TA PSA G130M 1300 FP-POS=4, BUFFER-TIME=195 1 195 S (195 G S) ------------------------------------------------------------------------------------------------------------------------------------ 6 VFTS-285 COS/FUV TIME-TA PSA G130M 1318 FP-POS=1, BUFFER-TIME=191 1 191 S (191 G S) ------------------------------------------------------------------------------------------------------------------------------------ 7 VFTS-285 COS/FUV TIME-TA PSA G130M 1318 FP-POS=2, BUFFER-TIME=191 1 191 S (191 G S) ------------------------------------------------------------------------------------------------------------------------------------ 8 VFTS-285 COS/FUV TIME-TA PSA G130M 1318 FP-POS=3, BUFFER-TIME=191 1 191 S (191 G S) ------------------------------------------------------------------------------------------------------------------------------------ 9 VFTS-285 COS/FUV TIME-TA PSA G130M 1318 FP-POS=4, BUFFER-TIME=191 1 191 S (191 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 | ------------------------------------------------------------------------------------------------------------------------------------ VFTS-285 1 COS/NUV ACQ/IMA PSA MIRRORB none none none none 1 N/A GE VFTS-285 2 COS/FUV TIME-TA PSA G130M 1300 none none none none 1 N/A G VFTS-285 3 COS/FUV TIME-TA PSA G130M 1300 none none none none 1 N/A G VFTS-285 4 COS/FUV TIME-TA PSA G130M 1300 none none none none 1 N/A G 14246( 4) - 11-Nov-2015 20:03:49 - [ 8] 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 | ------------------------------------------------------------------------------------------------------------------------------------ VFTS-285 5 COS/FUV TIME-TA PSA G130M 1300 none none none none 1 N/A G VFTS-285 6 COS/FUV TIME-TA PSA G130M 1318 none none none none 1 N/A G VFTS-285 7 COS/FUV TIME-TA PSA G130M 1318 none none none none 1 N/A G VFTS-285 8 COS/FUV TIME-TA PSA G130M 1318 none none none none 1 N/A G VFTS-285 9 COS/FUV TIME-TA PSA G130M 1318 none none none none 1 N/A G 14246( 4) - 11-Nov-2015 20:03:49 - [ 9] Summary Form for Proposal 14246 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures PSA ------------------------------------------------------------------------------------------------------------------------------------ Configurations COS/FUV, COS/NUV ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ/IMAGE, TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BUFFER-TIME=191, BUFFER-TIME=195, BUFFER-TIME=565, BUFFER-TIME=681, FP-POS=1, FP-POS=2, FP-POS=3, FP-POS=4 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G130M, MIRRORB ------------------------------------------------------------------------------------------------------------------------------------ Target Names VFTS-102, VFTS-285 ------------------------------------------------------------------------------------------------------------------------------------