Assigned ID: 946 ----- Attempting Submission 1 (Sat Feb 27 00:44:53 GMT 2010) ----- ----- Attempting Submission 1 (Wed Jun 30 21:13:42 GMT 2010) ----- A Mysterious Unseen Companion Lurking at 30 Parsecs 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.
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 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. HOT STARS 12 false 0.0 0.0 false false false false false false SUPPORTED STAR DA M V-IV NEUTRON STAR J2000 18 48 21.0100 -68 55 34.10 J2000 STIS/NUV-MAMA Imaging No No F25CN270 STIS/NUV-MAMA Imaging No No F25CN182 STIS/FUV-MAMA Imaging No No F25QTZ STIS/FUV-MAMA Imaging No No F25SRF2 POS-TARG DITHER 0.2433 LINE false false 2 0 LINE 1 false /nfs/whiting2/jao2/jao/recons/proposal/HST.propos/cycle18/OP-cache/12259-v01.xml The scheduling data was generated by CASM 18.3.1. CASM was run in Phase II mode. (Tic-Visit :proposal-id 12259 :visit-id "01" :proposal-version -1 :trans-version "20100505" :date "30-Jun-2010 12:04:27.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 4 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 278320 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12259 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12259 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 3266 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3599 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12259 :visit-id "01" :orbit-number 2 :pcs-time 222 :si-vis-utilization 3377 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3599 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12259 :visit-id "01" :orbit-number 3 :pcs-time 222 :si-vis-utilization 3377 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3599 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12259 :visit-id "01" :orbit-number 4 :pcs-time 222 :si-vis-utilization 3377 :al-overhead-at-end 0 :internal-dur-at-end 452 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3599 :pcs-gap 0 ) true 4 0