Assigned ID: 254 ----- Attempting Submission 1 (Fri Feb 26 03:45:02 GMT 2010) ----- ----- Attempting Submission 1 (Thu Jul 08 01:37:10 GMT 2010) ----- The Stellar Winds of Evolved, Braked O-Type Magnetic Oblique Rotators Magnetic fields have recently been discovered on several massive stars, but their origin and influence on the evolution of these stars are poorly understood. Two of these objects, HD 191612 and HD 108, are of particular interest. Very recent spectropolarimetric observations have shown that they are most likely magnetic oblique rotators, like the young O star Theta1 Ori C, whose 15d periodically variable field was found somewhat earlier. However, the two new objects are much slower rotators, unusually so for O stars, with periods of 538d and 50-60yrs, respectively, and there are other indications that they are older. They provide an opportunity to study the efficiency of wind braking of magnetic O stars through angular momentum loss. We shall perform STIS high-resolution UV spectroscopy of HD 191612 and HD 108 (phase resolved for the former) to derive more complete estimates of fundamental quantities than available from optical data alone. We shall measure the mass-loss rates from the UV wind profiles, which will constrain the extreme wind confinement of these stars and establish whether the large H-alpha emission variations are wind-related or geometrical. We shall also derive more accurate ages and stellar surface properties. In turn, these results will support a more definitive discussion of the angular momentum evolution versus the ages of HD 191612 and HD 108, and of the comparison with the younger and faster Theta1 Ori C.
These are straightforward spectroscopic observations, for which the STIS E140M and E230M echelles are the configurations of choice, providing complete FUV and NUV spectral coverage at high resolution and S/N within a single orbit. The FUV contains the high-priority stellar-wind resonance lines of N~V, Si~IV, and C~IV, as well as weaker subordinate, metastable wind lines of He~II and N~IV. The NUV adds several He absorption lines that are useful photospheric diagnostics, to compare with those in the optical. At the declination of HD~191612, the visibility period is 55~min. Guide-star and target acquisitions consume 6~min each; no ACQ-PEAK is required with the 0.2~arcsec square aperture that we shall use. The instrument overheads are 16~min. Thus, 27~min are available for spectroscopic exposures, which is more than ample for our target and configurations. For an O8 spectral type and S/N of 40, the STIS ETC gives exposure times of 600 and 100~sec for E140M and E230M, respectively. Depending on the Phase~II overheads, we may do two exposures in each configuration to increase the data quality. Our target is safe for observation in the above configurations per the ETC. For HD~108 the visibility period is 59~min. Acquisitions and instrument overheads are as above, except that this star is too bright for E230M with the 0.2X0.2 aperture, so we shall have to use the 0.1X0.03 that requires a two-stage peakup, adding 12~min to the overheads. Still, 19~min are left for scientific exposures, which are just 300~sec in the FUV and 100~sec in the NUV. Again, the exposure times may be increased, or two exposures obtained in each region. Both stars are isolated from any other bright stars, so there will be no field safety concerns. HOT STARS 12 false 0.0 0.0 false false false false false false SUPPORTED STAR CIRCUMSTELLAR MATTER DISK EMISSION LINE STAR OF WIND This object was generated by the targetselector and retrieved from the SIMBAD database. E(B-V)=0.58, SpT=O6f?p-O8fp J2000 20 09 28.6102 +35 44 1.29 J2000 STAR CIRCUMSTELLAR MATTER DISK EMISSION LINE STAR OF WIND This object was generated by the targetselector and retrieved from the SIMBAD database. E(B-V)=0.49, SpT=O6f?p-O8fp J2000 00 06 3.3861 +63 40 46.76 J2000 STIS/FUV-MAMA Spectroscopic No No E140M 1425 STIS/NUV-MAMA Spectroscopic No No E230M 2707 STIS/FUV-MAMA Spectroscopic No No E140M 1425 STIS/NUV-MAMA Spectroscopic No No E230M 2707 STIS/FUV-MAMA Spectroscopic No No E140M 1425 STIS/NUV-MAMA Spectroscopic No No E230M 2707 STIS/FUV-MAMA Spectroscopic No No E140M 1425 STIS/NUV-MAMA Spectroscopic No No E230M 2707 STIS/FUV-MAMA Spectroscopic No No E140M 1425 STIS/NUV-MAMA Spectroscopic No No E230M 2707 /user/walborn/cycle18/191612/OP-cache/12179-v01.xml The scheduling data was generated by CASM 18.3.1. CASM was run in Phase II mode. (Tic-Visit :proposal-id 12179 :visit-id "01" :proposal-version -1 :trans-version "20100505" :date "07-Jul-2010 19:30:39.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 313600 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12179 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12179 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2899 :al-overhead-at-end 0 :internal-dur-at-end 377 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3301 :pcs-gap 0 ) true 1 0 /user/walborn/cycle18/191612/OP-cache/12179-v02.xml The scheduling data was generated by CASM 18.3.1. CASM was run in Phase II mode. (Tic-Visit :proposal-id 12179 :visit-id "02" :proposal-version -1 :trans-version "20100505" :date "07-Jul-2010 19:41:04.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 313568 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12179 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12179 :visit-id "02" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2803 :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 3301 :pcs-gap 0 ) true 1 0 /user/walborn/cycle18/191612/OP-cache/12179-v03.xml The scheduling data was generated by CASM 18.3.1. CASM was run in Phase II mode. (Tic-Visit :proposal-id 12179 :visit-id "03" :proposal-version -1 :trans-version "20100505" :date "07-Jul-2010 19:41:33.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 313568 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12179 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12179 :visit-id "03" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2803 :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 3301 :pcs-gap 0 ) true 1 0 /user/walborn/cycle18/191612/OP-cache/12179-v04.xml The scheduling data was generated by CASM 18.3.1. CASM was run in Phase II mode. (Tic-Visit :proposal-id 12179 :visit-id "04" :proposal-version -1 :trans-version "20100505" :date "07-Jul-2010 19:40:29.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 313568 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12179 :visit-id "04" :obset-id "04" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12179 :visit-id "04" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2803 :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 3301 :pcs-gap 0 ) true 1 0 /var/tmp/OPVisit34434.xml The scheduling data was generated by CASM 18.3.1. CASM was run in Phase II mode. (Tic-Visit :proposal-id 12179 :visit-id "05" :proposal-version -1 :trans-version "20100505" :date "07-Jul-2010 21:14:34.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 315280 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12179 :visit-id "05" :obset-id "05" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12179 :visit-id "05" :orbit-number 1 :pcs-time 333 :si-vis-utilization 3088 :al-overhead-at-end 0 :internal-dur-at-end 377 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3516 :pcs-gap 0 ) true 1 0