Resubmit to correct typos. ----- Submission 3 (Fri Jun 24 16:36:58 GMT 2005) ----- This SNAP program offers an inexpensive, simple program to search for low-mass companions of field OB stars. Do field OB stars exist in true isolation, as suggested by a recent Galactic study, or are they the tip of the iceberg on a small cluster of low-mass stars as predicted by the cluster mass function and stellar IMF? Short ACS/WFC V and I observations proposed here may easily resolve this issue for field OB stars in the Small Magellanic Cloud. Truly isolated OB stars represent a theoretical challenge and variation from clusters, in mode of star formation, and have important consequences for our understanding of the field stellar population in galaxies. Small clusters around the field OB stars, on the other hand, may confirm the universality of the stellar clustering law and IMF.

ACS/WFC exposure times of 9 sec in V and 18 sec in I allow a S/N ~ 10 for an F0 V star (by ACS/WFC ETC), and S/N ~ 3 for a G2V star in I, assuming a DM = 19.0, thereby probing masses as low as ~ 1.1 M_sun. (Phase I originally proposed for longer observations, probing to 0.1 M_sun. This turns out not to be possible within the same SNAP timeframe because of saturation of the primary OB star, but our new depth of 1.1 M_sun does not significantly alter the science goals.) The simplicity of these short observations offers an ideal program for SNAP observing. Since the de Wit et al. (2004) study showed only 12% of their O stars to have clustered companions, most of our SMC sample should also be expected to be loner stars. In the event that companions are found, the V-I color-magnitude diagram will strongly constrain their spectral types and masses. We use the 2K subarray on WFC1 to reduce readout time, while maintaining large area coverage. Short exposures of 3 sec in V and 9 sec in I are necessary to avoid saturation of the dominant OB star. A second, deeper 6-sec exposure in will saturate the central star, but will probe the fainter population. 12 false 0.0 false false false false false SUPPORTED STAR GIANT O SUPERGIANT O This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 00 00 0.0000 +00 00 0.00 J2000 STAR B0-B2 III-I This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 00 00 0.0000 +00 00 0.00 J2000 STAR B0-B2 III-I Coordinates and stellar parameters from Massey et al. 1995, ApJ 438, 188 J2000 00 00 0.0000 +00 00 0.00 J2000 STAR B0-B2 III-I This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 00 00 0.0000 +00 00 0.00 J2000 STAR B0-B2 III-I This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 00 00 0.0000 +00 00 0.00 J2000 STAR B0-B2 III-I This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 00 00 0.0000 +00 00 0.00 J2000 STAR MAIN SEQUENCE O This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 00 00 0.0000 +00 00 0.00 J2000 STAR GIANT O This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 00 00 0.0000 +00 00 0.00 J2000 STAR WOLF RAYET - WN SUPERGIANT O MAIN SEQUENCE O GIANT O COMPOSITE SPECTRAL TYPE J2000 00 00 0.0000 +00 00 0.00 J2000 STAR MAIN SEQUENCE O This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 00 00 0.0000 +00 00 0.00 J2000 STAR GIANT O This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 00 00 0.0000 +00 00 0.00 J2000 STAR GIANT O This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 00 00 0.0000 +00 00 0.00 J2000 STAR MAIN SEQUENCE O This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 00 00 0.0000 +00 00 0.00 J2000 STAR B0-B2 III-I This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 00 00 0.0000 +00 00 0.00 J2000 STAR MAIN SEQUENCE O This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 00 00 0.0000 +00 00 0.00 J2000 STAR MAIN SEQUENCE O This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 00 00 0.0000 +00 00 0.00 J2000 STAR B0-B2 III-I This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 00 00 0.0000 +00 00 0.00 J2000 POS-TARG DITHER 0.146 LINE false false 2 47.17 ACS-WFC-DITHER-LINE 1 false /usr/Erie1/msoey/scitex/props/hst05/OP-cache/Oey_phase2_rev3-v01.xml 1119629815352 (Tic-Visit :proposal-id 10629 :visit-id "01" :proposal-version -1 :trans-version "20050323" :date "24-Jun-2005 12:16:53.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 351232 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 10629 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 10629 :visit-id "01" :orbit-number 1 :pcs-time 367 :si-vis-utilization 1484 :al-overhead-at-end 0 :internal-dur-at-end 115 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3658 :pcs-gap 0 ) true 1 0 /usr/Erie1/msoey/scitex/props/hst05/OP-cache/Oey_phase2_rev3-v02.xml 1119630146146 (Tic-Visit :proposal-id 10629 :visit-id "02" :proposal-version -1 :trans-version "20050323" :date "24-Jun-2005 12:22:25.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 351232 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 10629 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 10629 :visit-id "02" :orbit-number 1 :pcs-time 367 :si-vis-utilization 1484 :al-overhead-at-end 0 :internal-dur-at-end 115 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3658 :pcs-gap 0 ) true 1 0 /usr/Erie1/msoey/scitex/props/hst05/OP-cache/Oey_phase2_rev3-v03.xml 1119630149628 (Tic-Visit :proposal-id 10629 :visit-id "03" :proposal-version -1 :trans-version "20050323" :date "24-Jun-2005 12:22:28.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 351232 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 10629 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 10629 :visit-id "03" :orbit-number 1 :pcs-time 367 :si-vis-utilization 1484 :al-overhead-at-end 0 :internal-dur-at-end 115 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3658 :pcs-gap 0 ) true 1 0 /usr/Erie1/msoey/scitex/props/hst05/OP-cache/Oey_phase2_rev3-v04.xml 1119630152828 (Tic-Visit :proposal-id 10629 :visit-id "04" :proposal-version -1 :trans-version "20050323" :date "24-Jun-2005 12:22:32.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 351232 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 10629 :visit-id "04" :obset-id "04" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 10629 :visit-id "04" :orbit-number 1 :pcs-time 367 :si-vis-utilization 1484 :al-overhead-at-end 0 :internal-dur-at-end 115 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3658 :pcs-gap 0 ) true 1 0 /usr/Erie1/msoey/scitex/props/hst05/OP-cache/Oey_phase2_rev3-v05.xml 1119630155770 (Tic-Visit :proposal-id 10629 :visit-id "05" :proposal-version -1 :trans-version "20050323" :date "24-Jun-2005 12:22:34.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 351232 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 10629 :visit-id "05" :obset-id "05" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 10629 :visit-id "05" :orbit-number 1 :pcs-time 367 :si-vis-utilization 1484 :al-overhead-at-end 0 :internal-dur-at-end 115 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3658 :pcs-gap 0 ) true 1 0 /usr/Erie1/msoey/scitex/props/hst05/OP-cache/Oey_phase2_rev3-v06.xml 1119630158580 (Tic-Visit :proposal-id 10629 :visit-id "06" :proposal-version -1 :trans-version "20050323" :date "24-Jun-2005 12:22:37.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 351232 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 10629 :visit-id "06" :obset-id "06" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 10629 :visit-id "06" :orbit-number 1 :pcs-time 367 :si-vis-utilization 1484 :al-overhead-at-end 0 :internal-dur-at-end 115 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3658 :pcs-gap 0 ) true 1 0 /usr/Erie1/msoey/scitex/props/hst05/OP-cache/Oey_phase2_rev3-v07.xml 1119630161317 (Tic-Visit :proposal-id 10629 :visit-id "07" :proposal-version -1 :trans-version "20050323" :date "24-Jun-2005 12:22:40.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 351232 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 10629 :visit-id "07" :obset-id "07" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 10629 :visit-id "07" :orbit-number 1 :pcs-time 367 :si-vis-utilization 1484 :al-overhead-at-end 0 :internal-dur-at-end 115 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3658 :pcs-gap 0 ) true 1 0 /usr/Erie1/msoey/scitex/props/hst05/OP-cache/Oey_phase2_rev3-v08.xml 1119630164070 (Tic-Visit :proposal-id 10629 :visit-id "08" :proposal-version -1 :trans-version "20050323" :date "24-Jun-2005 12:22:43.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 351232 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 10629 :visit-id "08" :obset-id "08" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 10629 :visit-id "08" :orbit-number 1 :pcs-time 367 :si-vis-utilization 1484 :al-overhead-at-end 0 :internal-dur-at-end 115 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3658 :pcs-gap 0 ) true 1 0 /usr/Erie1/msoey/scitex/props/hst05/OP-cache/Oey_phase2_rev3-v09.xml 1119630166805 (Tic-Visit :proposal-id 10629 :visit-id "09" :proposal-version -1 :trans-version "20050323" :date "24-Jun-2005 12:22:46.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 351232 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 10629 :visit-id "09" :obset-id "09" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 10629 :visit-id "09" :orbit-number 1 :pcs-time 367 :si-vis-utilization 1484 :al-overhead-at-end 0 :internal-dur-at-end 115 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3658 :pcs-gap 0 ) true 1 0 /usr/Erie1/msoey/scitex/props/hst05/OP-cache/Oey_phase2_rev3-v10.xml 1119630169596 (Tic-Visit :proposal-id 10629 :visit-id "10" :proposal-version -1 :trans-version "20050323" :date "24-Jun-2005 12:22:48.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 351232 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 10629 :visit-id "10" :obset-id "10" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 10629 :visit-id "10" :orbit-number 1 :pcs-time 367 :si-vis-utilization 1484 :al-overhead-at-end 0 :internal-dur-at-end 115 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3658 :pcs-gap 0 ) true 1 0 /usr/Erie1/msoey/scitex/props/hst05/OP-cache/Oey_phase2_rev3-v11.xml 1119630172408 (Tic-Visit :proposal-id 10629 :visit-id "11" :proposal-version -1 :trans-version "20050323" :date "24-Jun-2005 12:22:51.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 351232 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 10629 :visit-id "11" :obset-id "11" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 10629 :visit-id "11" :orbit-number 1 :pcs-time 367 :si-vis-utilization 1484 :al-overhead-at-end 0 :internal-dur-at-end 115 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3658 :pcs-gap 0 ) true 1 0 /usr/Erie1/msoey/scitex/props/hst05/OP-cache/Oey_phase2_rev3-v12.xml 1119630175163 (Tic-Visit :proposal-id 10629 :visit-id "12" :proposal-version -1 :trans-version "20050323" :date "24-Jun-2005 12:22:54.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 351232 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 10629 :visit-id "12" :obset-id "12" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 10629 :visit-id "12" :orbit-number 1 :pcs-time 367 :si-vis-utilization 1484 :al-overhead-at-end 0 :internal-dur-at-end 115 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3658 :pcs-gap 0 ) true 1 0 /usr/Erie1/msoey/scitex/props/hst05/OP-cache/Oey_phase2_rev3-v13.xml 1119630177985 (Tic-Visit :proposal-id 10629 :visit-id "13" :proposal-version -1 :trans-version "20050323" :date "24-Jun-2005 12:22:57.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 351232 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 10629 :visit-id "13" :obset-id "13" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 10629 :visit-id "13" :orbit-number 1 :pcs-time 367 :si-vis-utilization 1484 :al-overhead-at-end 0 :internal-dur-at-end 115 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3658 :pcs-gap 0 ) true 1 0 /usr/Erie1/msoey/scitex/props/hst05/OP-cache/Oey_phase2_rev3-v14.xml 1119630180799 (Tic-Visit :proposal-id 10629 :visit-id "14" :proposal-version -1 :trans-version "20050323" :date "24-Jun-2005 12:23:00.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 351232 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 10629 :visit-id "14" :obset-id "14" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 10629 :visit-id "14" :orbit-number 1 :pcs-time 367 :si-vis-utilization 1484 :al-overhead-at-end 0 :internal-dur-at-end 115 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3658 :pcs-gap 0 ) true 1 0 /usr/Erie1/msoey/scitex/props/hst05/OP-cache/Oey_phase2_rev3-v15.xml 1119630183545 (Tic-Visit :proposal-id 10629 :visit-id "15" :proposal-version -1 :trans-version "20050323" :date "24-Jun-2005 12:23:02.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 351232 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 10629 :visit-id "15" :obset-id "15" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 10629 :visit-id "15" :orbit-number 1 :pcs-time 367 :si-vis-utilization 1484 :al-overhead-at-end 0 :internal-dur-at-end 115 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3658 :pcs-gap 0 ) true 1 0 /usr/Erie1/msoey/scitex/props/hst05/OP-cache/Oey_phase2_rev3-v16.xml 1119630186340 (Tic-Visit :proposal-id 10629 :visit-id "16" :proposal-version -1 :trans-version "20050323" :date "24-Jun-2005 12:23:05.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 351232 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 10629 :visit-id "16" :obset-id "16" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 10629 :visit-id "16" :orbit-number 1 :pcs-time 367 :si-vis-utilization 1484 :al-overhead-at-end 0 :internal-dur-at-end 115 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3658 :pcs-gap 0 ) true 1 0 /usr/Erie1/msoey/scitex/props/hst05/OP-cache/Oey_phase2_rev3-v17.xml 1119630189137 (Tic-Visit :proposal-id 10629 :visit-id "17" :proposal-version -1 :trans-version "20050323" :date "24-Jun-2005 12:23:08.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 351232 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 10629 :visit-id "17" :obset-id "17" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 10629 :visit-id "17" :orbit-number 1 :pcs-time 367 :si-vis-utilization 1484 :al-overhead-at-end 0 :internal-dur-at-end 115 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3658 :pcs-gap 0 ) true 1 0