6676( 6) - 11/20/96 13:27 - [ 0] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6676 Version: 6 Check-in Date: 20-Nov-1996 13:24:59 1.Proposal Title: Rapid UV Variability: The Contribution of Flare Heating in the Atmospheres of Active, Evolved Stars ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle COOL STARS GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Dr. Steven Saar Smithsonian Astrophysical Observatory CoI: Dr. Jay Bookbinder Smithsonian Astrophysical Observatory N ------------------------------------------------------------------------------------ 6. Abstract The question of the contribution of flares and microflares to the non-radiatively heated outer atmospheres of late-type stars has been studied with very limited success for over a decade using IUE, a variety of X--ray satellites, and ground- based studies. HST presents the best opportunity to place a firm lower limit on the fraction of the transition region flux resulting from short timescale events. Our analysis of HST data on one M dwarf shows that up to 60\% of the transition region flux is directly attributable to stellar flares and microflares. This leaves little room for the traditional ``quiescent" emission. Such a result, if confirmed for other stars, promises to revitalize the study of their outer atmospheres, with the recognition that they are far more dynamic than static. We now propose to observe two active, evolved stars to probe the importance of flare heating in their outer atmospheres: the RS CVn binary II Peg, and FK Comae, a rapidly rotating single giant (possibly the result of a coalesced binary). It is important to make these observations before STIS, since the even moderate flares on these stars could saturate the MAMA detectors in strong lines. ------------------------------------------------------------------------------------ Observations Description ------------------------ The GHRS G140L grating (LSA), centered at 1433 A, will be employed to study a series of both chromospheric lines and transition region lines. This setting will allow us to study variability in : C II (1340 A) and the O I (1305 A) line (if we can work around the geocoronal O I contribution); and the Si IV (1400 A) and C IV (1550 A) lines for the transition region. That C IV and Si IV are formed at very similar temperatures, can be used to help confirm our variability analysis - both lines must register valid events. The G140L grating of the GHRS was selected primarily because of its higher sensitivity and lower scattered light below 1500 A, where most of the lines lie, enabling us to take shorter observations than had we used the FOS. IUE measurement have established flux at earth of f(C IV) = 1.0E-12 ergs/cm**2/s/A for II Peg (Simon \\& Fekel 1987). With an efficiency of 67E+11 counts/s/diode per incident ergs/cm**2/s/A at C IV for the G140L, we should obtain 6.7 counts/s at C IV for II Peg. Since during flares this value can easily increase this by a factor of 10 or more, we should have ample counts to study flares and microflares in these stars. Note that even moderate (7 x) flares require the GHRS, as the STIS MAMA's will saturate above 50 counts/s/pixel (the largest flare in our AD Leo observations, still quite small by dMe standards, showed a 90 times enhancement in C IV; Bookbinder et al. 1992). Our request of 2 orbits will yield approximately 1 hour of on target observations for each star. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- We plan an extensive suite of coordinated observations for our targets. Optical spectra of chromospheric diagnostics as well as photometry are planned. We will attempt doppler imaging and magnetic doppler imaging (e.g., Saar et al. 1992) of II Peg and direct magnetic field measurements with the CSHELL at NASA's IRTF. ------------------------------------------------------------------------------------ Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 6676( 6) - 11/20/96 13:27 - [ 1] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 HD224085 STAR,K V-IV RA=23H 55M 04.05S +/- 0.1S, J2000 V= -18.1 V = 7.4+/-0.2 DEC=28D 38' 01.3" +/- 0.3" B-V = 1.01+/-0.05 F-LINE(1550.0)=1.0+/-0.5e-12 W-LINE(1550.0)=1.0+/-0.2 Comments: HIPPARCOS COORDINATES USED DUE TO STAR BRIGHTNESS Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) J2000 0.044 0.027 0.034 6676( 6) - 11/20/96 13:27 - [ 2] Visit: 01 Visit Requirements: BETWEEN 10-AUG-1996 AND 20-DEC-1996 On Hold Comments: Additional Comments: "BETWEEN" DATES NOT AN ABSOLUTE REQUIREMENT, BUT HIGHLY DESIREABLE FOR COORDINATION WITH GROUND-BASED OBSERVATIONS Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 HD224085 HRS ACQ 2.0 MIRROR-N2 BRIGHT=RETURN 1 1.8 S ONBOARD ACQ FOR 20-30 Comments: PLEASE NOTIFY P.I. WHEN DATES ARE SCHEDULED OR CHANGED (FOR COORDINATED OBSERVATIONS) IN ACQ EXPECT ABOUT 10500 CTS/S, HENCE STEP-TIME 0.2 SEC ------------------------------------------------------------------------------------------------------------------------------------ 20 HD224085 HRS RAPID 2.0 G160M 1550.0 SAMPLE-TIME=10.0 1 1715 S ------------------------------------------------------------------------------------------------------------------------------------ 30 HD224085 HRS RAPID 2.0 G140L 1433.0 SAMPLE-TIME=1.0 1 2638 S ------------------------------------------------------------------------------------------------------------------------------------ 6676( 6) - 11/20/96 13:27 - [ 3] Summary Form for Proposal 6676 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations HRS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ RAPID ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BRIGHT=RETURN SAMPLE-TIME=10.0 SAMPLE-TIME=1.0 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category COOL STARS ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BETWEEN 10-AUG-1996 AND 20-DEC-1996 ONBOARD ACQ FOR 20-30 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR-N2 G160M G140L ------------------------------------------------------------------------------------------------------------------------------------ Target Names HD224085 ------------------------------------------------------------------------------------------------------------------------------------