Assigned ID: 991 ----- Attempting Submission 1 (Sat Feb 27 00:52:40 GMT 2010) ----- A new Acquisition has been implemented to avoid Gain Sag in the FUV detectors. ----- Attempting Submission 1 (Thu Jul 08 21:16:48 GMT 2010) ----- ----- Attempting Submission 2 (Mon Nov 15 19:30:19 GMT 2010) ----- ----- Attempting Submission 3 (Thu Dec 16 19:16:11 GMT 2010) ----- We propose to carry out FUV spectrophotometry with COS/HST for an in-depth study of the chromosphere & transition region (TR) of the solar twin 18 Sco. This 5th mag G2 V star is an important star as a nearly perfect match to the Sun and is known as the "Closest-ever Solar Twin" (Porto de Mello & da Silva 1997). 18 Sco has nearly identical physical properties (e.g. SpType, Mass, Teff, L, R, log g, [Fe/H], Ca II HK, Lx, rotation, etc.) to the Sun. Recent studies of Ca II HK emission from Lowell Observatory (J. Hall, priv. comm.) indicate Ca II emissions are close to the Sun's and undergo a solar-like ~7-11 yr magnetic activity cycle. The proposed observations (using two consecutive HST orbits) are a crucial part of our ongoing "Sun in Time" program of solar-type stars across the electromagnetic spectra. We are proposing to utilize the enhanced FUV sensitivity of HST/COS (with the G 130M/G 160M elements) to obtain high S/N medium resolution, FUV (1150-1750Å) spectrophotometry of the only remaining unexplored spectral region of this important star. The FUV region contains many crucial chromospheric and TR emission diagnostics including C III 1175A, Si III 1206A, Ly-a 1215A, N V 1240A, OI 1305A, C II 1335A, Si IV 1400A, C IV 1550A, He II 1640A, C I 1660A as well as many other weaker emissions. These line emissions originate from plasmas from 8,000 K to 300,000 K, and are vital for understanding the star's magnetically heated chromosphere and TR. We plan to analyze this spectrum to determine the physical properties of 18 Sco's corona, TR and chromosphere and, importantly, to compare these line strengths and ratios to the corresponding FUV line emissions of the Sun (e.g. SUSIM, SOLSTICE) at a similar magnetic activity phase. This study provides an important check on the magnetic behavior of our present Sun and solar like stars. For example, is our Sun "normal" for its age and mass? If confirmed as a precise match to our Sun (and the data obtained thus far look like it is), 18 Sco would be important for follow-up studies in asteroseismology, extrasolar planet searches, and could serve as a surrogate for the "Night-Time Sun.” In addition, as noted by Turnbull (2004), 18 Sco is one of the most promising nearby candidates for hosting life based on analysis of the HabCat list of stars. In spite of extensive observations at many other wavelengths, the best yet solar twin - 18 Sco - has not been observed in the FUV region where the most powerful diagnostic emission lines are located. With the planned COS spectroscopy, we will at long last complete the spectral coverage of this important solar twin.

We plan to observe 18 Sco with both the G140L and G130M spectral elements to provide thorough coverage of the FUV region, while at the same time returning good spectral resolution on important emission lines such as Lyman alpha and O I 1310. COOL STARS 12 false 0.0 0.0 false false false false false false SUPPORTED STAR G V-IV General object info retrieve from Simbad. Proper Motions and Parallax obtained from "Hipparcos, the New Reduction" catalog of van Leeuwen, 2007. J2000 16 15 37.2703 -08 22 9.99 J2000 COS/FUV Spectroscopic No No G130M 1291 COS/FUV Spectroscopic No No G160M 1589 1292526891336 C:\Users\Scott\AppData\Local\Temp\OPVisit20603.xml The scheduling data was generated by CASM 18.3.1. CASM was run in Phase II mode. (Tic-Visit :proposal-id 12303 :visit-id "01" :proposal-version -1 :trans-version "20100902" :date "16-Dec-2010 14:14:51.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "31" :si-bright-earth-limb-angle 20.0 :data-volume 582864 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12303 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12303 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2909 :al-overhead-at-end 0 :internal-dur-at-end 397 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3242 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12303 :visit-id "01" :orbit-number 2 :pcs-time 222 :si-vis-utilization 3020 :al-overhead-at-end 0 :internal-dur-at-end 371 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3242 :pcs-gap 0 ) true 2 0