remove the betweens to see all the scheduling options visit 1 on single star guiding. Phase on exposure 1 of visit 2. ----- Attempting Submission 11 (Thu Sep 06 18:41:41 GMT 2007) ----- ----- Attempting Submission 12 (Fri Sep 07 13:07:19 GMT 2007) ----- ----- Attempting Submission 13 (Mon Sep 10 12:04:56 GMT 2007) ----- none The Great Spiral Galaxy in Triangulum (M33) is potentially a crucial calibrator for the Cosmic Distance Scale, and thus for determining the age and evolution of the Universe. M33 is viewed face-on, has a simple geometry, large and diverse stellar populations, and morphologies similar to our Galaxy and other more distant galaxies used for distance determinations. Yet currently the M33 distance (d ~ 830 +/- 110 kpc) still has measurement dispersions of 10-15%. We have demonstrated, in our work on the LMC and M31 distances, that double-line eclipsing binaries can serve as excellent "standard candles." Distances derived from eclipsing binaries are basically geometric and essentially free from many assumptions and uncertainties that plague other less direct methods, such as metallicity differences and calibration zeropoints. The absolute radii of the component stars of eclipsing binaries can be determined to better than a few percent from the time-tested analyses of their light and radial velocity curves. With accurate determinations of radii, temperatures, and ISM absorption it is possible to determine reliable distances. We are extending our program of using eclipsing binaries as standard candles to determine an accurate distance to M33. As a first step, we are proposing to carry out HST/ACS spectrophotometry of a well suited ~19th mag ~O7 + ~O7 eclipsing binary system in M33 that has been previously observed from the ground. HST/ACS prism/grism low-resolution spectrophotometry (118-850 nm) is the only missing key element of this program and is used to determine more reliable values for T_eff, [Fe/H], and ISM extinction. These quantities, when combined with the results from existing light and radial velocity curves for the target, yield the stellar masses, radii, luminosities and, importantly, the distance. The proposed HST/ACS program can be carried out effectively with only 1 HST orbit. Based on our previous experience, we expect to reduce the uncertainty of the M33 distance to better than 5-7%, thereby leading to a firmer calibration of the Cosmic Distance Scale and the zeropoint of the Hubble Constant (Ho).

In this initial study we are requesting observations of the M33 EB target that has existing light and radial velocity curves. For this program, 2 HST orbits have been assigned. We have used the APT in its Phase II mode to perform detailed simulations of the exposure times and orbit planning to optimize the resulting datasets. According to the HST orbital constraints and the declination of our target, a maximum visibility of 3180 s is available per orbit. The optimum times for observing our target are in the months of July and September. Our simulations indicate that only one HST orbit is sufficient to achieve full spectral coverage (FUV to near-IR) with the necessary S/N to fulfill the program's goals. Time permitting, we will also secure a V-band image of the target and the surrounding stars in the FOV in order to provide an accurate photometric anchor for the ACS spectrophotometry. Also, having this image will be useful for exploring the region close to the target for fainter companions. We will use the ACS/SBC and WFPC2 to obtain complete spectro/photometric coverage, from 118 to 814 nm. Multiple WPFC2 filters and the ACS/SBC PR110L prism will used. As discussed by Fitzpatrick & Massa (1999, ApJ, 525, 1011) this extended wavelength coverage uniquely disentangles the stellar and interstellar parameters, yielding the quantities: Teff, log g, [Fe/H], E(B-V), and AV. For example, the near UV includes the ~220 nm ISM dust absorption feature that will permit a firm determination of the ISM reddening of the target. Presently the determination of the AV for this star is one of the major contributions to the error budget. Finally, given the eccentric orbit of this EB system, additional eclipse timings will provide the apsidal motion of the system and important information on the internal structure of its components. We are familiar with using the ACS prism setup given our two previous proposals, each making use of HST/ACS low resolution spectrophotometry. Our exposure estimates were carried out using the latest version of the ACS/WFPC2 spectroscopic and imaging online exposure time calculators. We assumed the intrinsic energy distribution of an O7 V type star and an extinction corresponding to E(B-V)~0.14 mag, estimated already from existing B and V photometry of the target. We estimate that S/N in excess of ~40:1 is necessary to secure a spectrum with sufficient quality to allow an accurate determination of the stellar and interstellar parameters. The calculations indicate that an S/N of ~40:1 is obtained with an exposure time of 485 s for PR110L. The following photometric estimates were made for the WFPC2: F170W - 760 s, F218W - 1200 s, F255W - 700 s, F300W - 350 s, F336W - 450 s, F439W - 450 s, F555W - 120 s, F675W, 200 s and F814W - 300 s. This will result in data comparable (in terms of S/N and spectral coverage) to those shown in Fig. 2 for the LMC system HV 982. The orbit planning software confirms that such exposure times nicely fit within an HST orbit when all instrumental overheads are taken into account. From ground-based and WFPC2 observations, the coordinates of the proposed target are known to a precision better than 0.2 arcsec and no problems with target acquisition are expected. HOT STARS 12 false 0.0 false false false false false false SUPPORTED EXT-STAR B0-B2 V-IV This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 01 33 46.1700 +30 44 39.90 J2000 ACS/SBC Spectroscopic No No PR110L ACS/HRC Spectroscopic No No PR200L ACS/HRC Spectroscopic No No G800L ACS/HRC Imaging No No F555W (Tic-Visit :proposal-id 10919 :visit-id "01" :proposal-version -1 :trans-version "20070325" :date "13-Apr-2007 09:50:27.0" :trans-errors '(:WARNINGS 1 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "26" :si-bright-earth-limb-angle 20.0 :data-volume 224080 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 10919 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 10919 :visit-id "01" :orbit-number 1 :pcs-time 355 :si-vis-utilization 2760 :al-overhead-at-end 120 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3152 :pcs-gap 0 ) false 1 0 (Tic-Visit :proposal-id 10919 :visit-id "02" :proposal-version -1 :trans-version "20070325" :date "13-Apr-2007 09:48:33.0" :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 111088 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 10919 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Obset :proposal-id 10919 :visit-id "02" :obset-id "A2" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 10919 :visit-id "02" :orbit-number 1 :pcs-time 355 :si-vis-utilization 2790 :al-overhead-at-end 0 :internal-dur-at-end 160 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3152 :pcs-gap 0 ) false 1 0