12259( 2) - 01-Jul-2010 12:33:53 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 12259 Version: 2 Check-in Time: 01-Jul-2010 12:33:53 STScI Edit Number: 0 Title A Mysterious Unseen Companion Lurking at 30 Parsecs ------------------------------------------------------------------------------------ Type Cycle GO 18 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Wei-Chun Jao Georgia State University Research Foundation CoI: Dr. Todd J. Henry Georgia State University Research N Foundation ------------------------------------------------------------------------------------ Abstract Astrometric perturbations are the result of unseen, sometimes mysterious, companions. When resolved, the systems provide crucial mass measurements for the components. Here we propose to use HST/STIS to image an unseen companion that causes the largest astrometric perturbation among 500 nearby stars observed using the CTIO 0.9m telescope since 1999. The primary is a red dwarf at 30 pc with V=16.86 and spectral type M5.0V, while the system has been detected by GALEX in the near-UV. From the astrometry and photometry, we can rule out that the companion is red dwarf, a brown dwarf, or a normal white dwarf. All three of the remaining possibilities are extraordinary --- a very cool white dwarf, a neutron star, or a black hole --- making the companion one of the most unusual objects in the solar neighborhood. We propose to use HST/STIS imaging at NUV and FUV wavelengths to resolve this intriguing system to confirm its nature and constrain its mass. ------------------------------------------------------------------------------------ Observations Description ------------------------ Our primary goal is to use HST/STIS+MAMA to resolve this unseen companion. This binary system, with a M5.0V primary, shows the largest astrometric perturbation (~200 mas) detected in the CTIOPI (Cerro Tololo Inter-american Observatory Parallax Investigation) program in the past 5 years. It also shows abnormally larger near-UV flux than usual M5.0V dwarfs. This unseen companion could be a cool white dwarf, a neutron star or a black hole, from initial analysis of ground-based photometry and astrometry data. We propose to utilize STIS/NUV+MAMA imaging mode with a resolution of 0.0243"/pixel to resolve this binary system. We plan to use two filters, F25CN270 and F25CN182 at NUV. For each filter, we plan to observe a two-pointing line dithering pattern in the X-axis with an offset about 10 pixels. Because we would like to have enough signals on both components, we request the longest exposure it can has in one orbit. Furthermore, a well-exposed image allows us to centroid on both components to get accurate separation and position angle. For example, according to the ETC for STIS imaging mode, a single 3000-sec exposure 12259( 2) - 01-Jul-2010 12:33:53 - [ 2] at F25CN270 for a M5.0V and a 4500K white dwarf at 30 pc yield S/N of about 4 and 30, respectively. At the short wavelength region with F25CN182 filter, we expect only this white dwarf secondary could show up, and it could have a S/N about 8 with a single 3000 sec exposure. The color of this unseen companions allow us to compare with white dwarf models or black body to constrain the spectral type or flavor of it. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 12259( 2) - 01-Jul-2010 12:33:53 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 2MA18XX-68XX STAR, DA, M V-IV, RA=18H48M21.0100S +/- 0.1", J2000 V = 16.86 NEUTRON STAR DEC=-68D55'34.10" +/- 0.1" Reference Frame: ICRS Comments: Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2000.0 -0.0593484769403671 -1.2466 0.03392 ------------------------------------------------------------------------------------------------------------------------------------ 12259( 2) - 01-Jul-2010 12:33:53 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type LINE Pattern_Purpose DITHER Number_Of_Points 2 Point_Spacing 0.2433 Line_Spacing Coordinate_Frame POS-TARG Pattern_Orient 0 Angle_Between_Sides Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 12259( 2) - 01-Jul-2010 12:33:53 - [ 5] 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| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 2MA18XX-68X STIS/NUV ACCUM F25CN270 MIRROR 1 3086 S PATTERN 1 1 X -MAMA ------------------------------------------------------------------------------------------------------------------------------------ 2 2MA18XX-68X STIS/NUV ACCUM F25CN182 MIRROR 1 3330 S PATTERN 1 2 X -MAMA ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ 2MA18XX-68XX 1 STIS/NUV ACCUM F25CN270 MIRROR 1 none none none 1 N/A -MAMA 2MA18XX-68XX 1 STIS/NUV ACCUM F25CN270 MIRROR 2 none none none 2 3349.0 S -MAMA 2MA18XX-68XX 2 STIS/NUV ACCUM F25CN182 MIRROR 1 none none none 3 N/A -MAMA 2MA18XX-68XX 2 STIS/NUV ACCUM F25CN182 MIRROR 2 none none none 4 3349.0 S -MAMA 12259( 2) - 01-Jul-2010 12:33:53 - [ 6] Summary Form for Proposal 12259 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures F25CN182, F25CN270 ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/NUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PATTERN 1 1, PATTERN 1 2 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR ------------------------------------------------------------------------------------------------------------------------------------ Target Names 2MA18XX-68XX ------------------------------------------------------------------------------------------------------------------------------------