7756( 4) - 01/21/98 11:53 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 7756 Version: 4 Check-in Date: 12-Sep-1997 09:55:34 1.Proposal Title: Density Diagnostics for the Dynamic Atmospheres of LPV Stars ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO/CAR 7 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: DONALD LUTTERMOSER EAST TENNESSEE STATE UNIVERSITY CoI: Dr. George H. Bowen Iowa State University N ------------------------------------------------------------------------------------ 5. Abstract This proposal is a carry over from Cycle 6. Four orbits have been allocated to the PI in Cycle 7 to conclude this program. This proposal has been modified from the Cycle 6 proposal to reflect the change in instruments from GHRS to STIS. We propose to use the STIS onboard HST to probe the temperature-density structure of the shocked atmospheres of long-period variable (LPV, Mira-type) stars. We wish to obtain STIS echelle spectra in order to obtain the C II multiplet near 2325A and the Mg II h & k lines near 2800A for the bright Mira-type star R Leo near maximum UV brightness (optical phase 0.42). The echelle spectrum also will give us access to other important emission features such as Fe I and Fe II. With this spectrum, we will make comparisons (1) with previous GHRS and IUE spectra of the semiregular variable g Her, in order to investigate the differences in the atmospheric structures of these 2 variable types, and (2) to synthetic spectra from representative dynamic models we have generated. These NLTE radiative transfer calculations have shown that the radiation field of the inner shocks dominate the ionization throughout the entire atmosphere. The calculations also have shown the C II intersystem lines are the best diagnostic to supply electron density information of the inner shock region, the first time such a diagnostic has been measured for these stars. These spectrum comparisons are fundamental in the understanding of mass loss in this critical stage of a star's evolution. ------------------------------------------------------------------------------------ 7756( 4) - 01/21/98 11:53 - [ 2] Observations Description ------------------------ We have selected to observe R Leo as our representative Mira star due to the large amount of ground-based and space-based data we already have in our possession and the NLTE synthetic spectra we have already generated for this star. In Cycle 6, we obtained GHRS spectra for R Leo at phase 0.12 and R Hya (a near duplicate of R Leo) at phase 0.26. To get more complete phase coverage, we now will obtain STIS spectra of R Leo near light-curve phase 0.42 (26 Feb 1998, V = 7.6) when the UV emission lines are near their peak brightness. Miras are visually at their brightest near phase 0.0 and at minima near 0.5-0.6. From comparisons to the dynamic models, phase 0.9 corresponds to the emergence of a strong inner shock from the photosphere. Mg II is typically not seen with IUE at this phase. Phase 0.15 corresponds to this shock residing between the photosphere and chromosphere in the models, and Mg II first becoming visible in IUE spectra and we were able to record it at the earliest phase ever with HRS (phase 0.12 in R Leo). Mg II is typically at its brightest at phases 0.3-0.4, when this shock arrives and heats the chromosphere. Finally at phase 0.7, Mg II disappears as this shock continues to travel outward. The observing date mentioned above does not have to be followed exactly, we can still get the same science out of the data with a +/-3 day window from this date. This 7 day window is mainly constrained by scheduling availability when R Leo is near phase 0.4. R Leo is visible from HST for 54 minutes per orbit. Due to greater sensitivity of STIS over GHRS, we will obtain one echelle spectrum for our visit that will obtain both the Mg II and the C II lines instead of two separate spectrograms (as was done with GHRS). This also will enable us to record other emission features of interest such as the Fe II (UV1), (UV62), and (UV63) lines which have been seen with IUE at low dispersion. We will use the E230M grating with the secondary tilt set to a central wavelength of 2561A giving a spectral range of 2157-2965A at a resolution of 30,000. The total exposure time has been determined from the RPS2 software such that we get the maximum exposure time possible for a 4 orbit observation with HST/STIS. Photon count rates and signal-to-noise calculations were determined with the STIS ETC software package as shown in Table 1. In this table, we list (1) the peak flux in a given feature as determined by either IUE and GHRS observations and scaled NLTE synthetic spectra, (2) the counts per second per pixel, based upon these fluxes and the sensitivity function of the wavelength in question, (3) the total counts in the strongest line of the multiplet, and (4) the expected signal-to-noise for this feature. We expect the count rates for our weakest emission features (e.g., C II at 2325A) to be greater than the NUV-MAMA dark counts (1.25E-4 counts/sec/pixel) and the approximate sky background counts (see Table 1). The 9762 second exposure time corresponds to 162.7 minutes which can be achieved in 4 orbits with the standard overheads taken into account. This exposure time should give us a signal-to-noise of 5 for the strongest of the C II lines. The peak local count rate should be 4.9 counts/sec/pixel in the strongest emission line (e.g., Mg II h) and a global count rate of 688 counts/sec (see STIS/ETC ID 25521 and 25540). The number of exposures is 4, one taken each orbit. Standard calibrations will be adequate and we will be using the 0.2x0.2 arcsecond slit for the science data. Since we require to record as many photons as possible to detect the C II lines, we will forgo any ACQ/PEAK observations and rely on the initial ACQ exposure to center the star. We plan to use the CCD for target acquisition. R Leo will be at approximately V = 7.6 at phase 0.42 (26 Feb 1998), which for an exposure time of 0.5 second through the F28X50OIII filter gives 1400 ADU for the brightest pixel in the stellar image and the total number of electrons for the stellar image should be around 7600. These values were ascertained by running the STIS ETC software with a Kurucz spectrum for a M2 I star at V=7.6 (see STIS/ETC ID 25516). However, R Leo is an M8 III star which means its flux will be weaker at 5000A than an M2 I star. As such, the numbers reported above for our 0.5 second exposure were obtained by running the M2 I spectrum at 0.1 seconds (see STIS/ETC ID 25511). Finally, we sent a FITS file containing the star field with R Leo near the center and ran it through the STIS Target Acquisition Simulator. The simulator accurately found the position of the star. ------------------------------------ --------------------------- Table 1: Estimated UV Emission Line Fluxes for an Exposure Time of 9800 Seconds with the E230M Grating =============================================================== Star: R Leo Phase: 0.42 or 0.40 Date: 26 Feb 1998 or 30 Dec 1998 Visit: 1 Number of Orbits: 4 --------------------------------------------------------------- Line: C II] 2328A Mg II 2802A ------------------------------------------------------------- -- Peak Flux (erg/s/cm^2/A): 2.0E-14 2.0E-11 Source Counts/pixel: 150. 210,000. Background Counts/pixel: 29.4 29.4 Signal-to-Noise: 5.1 7100. ----------------- ---------------------------------------------- Real Time Justification ----------------------- The observation must be made within 3 days of the date suggested in the Description of Observations section. This star is a Mira-type variable. The brightness and line flux strengths change over a cycle period, which last on the order of a year for these stars. The estimated flux and exposure time was deduced for a specific phase (namely, near maximum UV brightness). This along with the severe scheduling constraint for observations of R Leo near phase 0.4 require the visit to be obtained within 3 days the date requested. Calibration Justification ------------------------- None. Standard wavecals will be sufficient for these observations. Additional Comments ------------------- None. ------------------------------------------------------------------------------------ 7756( 4) - 01/21/98 11:53 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: ------------------------------------------------------------------------------------ 7756( 4) - 01/21/98 11:53 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 HD84748 STAR,LONG PERIOD RA=9H 47M 33.44S +/- J2000 V = 12. V = 7.6+/-0.5 VARIABLE,AGB STAR,M III 0.10S,DEC=11D 25' 43.6" +/- 1.0" B-V = +1.68+/-0.20 -I E(B-V) = 0.0 TYPE=M8III F(2800)=2+/-1e-11 F(2325)=2+/-1e-14 F-CONT(2800)=2+/-1e-14 F-CONT(2325)=2+/-1e-16 Comments: The fluxes correspond to phase 0.42 (312 day period) on 26-FEB-1998. They also correspond to a backup secondary date of 30-DEC-1998 (phase 0.40). The UV line flux strengths can vary from one cycle to the next at a given phase. The above flux numbers are averaged values based upon past IUE observations and NLTE synthetic spectra. Coords are from Hipparcos INCA. Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 1985.05 -0.0004 -0.0440 0.020 7756( 4) - 01/21/98 11:53 - [ 5] Visit: 01 Visit Priority: Visit Requirements: BETWEEN 24-Feb-1998 AND 01-Mar-1998 BETWEEN 27-Dec-1998 AND 02-Jan-1999 On Hold Comments: Additional Comments: R Leo is near visual light variability phase 0.40. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 HD84748 STIS/C ACQ F28X50O MIRROR 1 0.5 S ONBOARD ACQ FOR 2-5 CD III Comments: Brightest pixel in stellar image approximately 11,000 electrons, total electrons in image approximately 60,000, and S/N = 240 for stellar image (STIS/ETC ID 24543). ------------------------------------------------------------------------------------------------------------------------------------ 2 HD84748 STIS/N ACCUM 0.2X0.2 E230M 2561 1 2303 S UV-MAM A Comments: Orbit #1 exposure. ------------------------------------------------------------------------------------------------------------------------------------ 3 HD84748 STIS/N ACCUM 0.2X0.2 E230M 2561 1 2678 S UV-MAM A Comments: Orbit #2 exposure. ------------------------------------------------------------------------------------------------------------------------------------ 4 HD84748 STIS/N ACCUM 0.2X0.2 E230M 2561 1 2678 S UV-MAM A Comments: Orbit #3 exposure. ------------------------------------------------------------------------------------------------------------------------------------ 5 HD84748 STIS/N ACCUM 0.2X0.2 E230M 2561 1 2678 S UV-MAM A Comments: Orbit #4 exposure. ------------------------------------------------------------------------------------------------------------------------------------ 7756( 4) - 01/21/98 11:53 - [ 6] Summary Form for Proposal 7756 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD STIS/NUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO/CAR ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BETWEEN 24-Feb-1998 AND 01-Mar-1998 BETWEEN 27-Dec-1998 AND 02-Jan-1999 ONBOARD ACQ FOR 2-5 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR E230M ------------------------------------------------------------------------------------------------------------------------------------ Target Names HD84748 ------------------------------------------------------------------------------------------------------------------------------------