6010( 14) - 07/23/96 15:19 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6010 Version: 14 Check-in Date: 23-Jul-1996 15:13:51 1.Proposal Title: Lyman Alpha Observations of High Radial Velocity Stars ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle Cool Stars GO 5 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: JAY BOOKBINDER CFA CoI: Dr. Ken Gayley Bartol Reseach Institute N CoI: Dr. Wayne Landsman N CoI: Dr. James E. Neff Pennsylvania State University N CoI: Dr. David Soderblom STScI N ------------------------------------------------------------------------------------ 6. Abstract The H I Lyman-Alpha line is probably the most important cooling channel for transition regions in late-type stars, and it directly or indirectly influences the formation of numerous other UV lines, yet it is the least studied line in the far UV. Accurate intrinsic stellar line profiles would be of immense use both as a diagnostic of stellar transition regions and for studies of the local interstellar medium (LISM), including determining the D/H ratio. An additional use is to determine the intrinsic stellar Ly-Alpha flux from low-dispersion observations. However, the absorption of most of the stellar flux by interstellar material and the high geocoronal background in IUE has seriously complicated the analysis of this line. It is possible to circumvent, to a large extent, the influence of the LISM on the intrinsic stellar profile by observing stars with radial velocities high enough to Doppler shift a significant fraction of the emission line out of the LISM absorption core. Motivated by the success of our previous IUE and HST programs that focussed on giant stars, we have selected 7 dwarf stars covering a range of spectral types, with radial velocities from 150 to over 300 km/sec for detailed studies of their Ly-Alpha profiles. ------------------------------------------------------------------------------------ 6010( 14) - 07/23/96 15:19 - [ 2] Observations Description ------------------------ Target Selection ---------------- We propose to obtain medium dispersion Ly- Alpha line profiles from dwarf stars covering a wide range of spectral types (from late-F to early-M are included) -- see Table I. Individual target selection for this program is based primarily on the radial velocity of the star, since it is the ISM absorption due to hydrogen that is the primary uncertainty and limitation in obtaining accurate intrinsic stellar Ly-Alpha fluxes and line profiles. The stellar radial velocities listed in Table I are relative to the predicted ISM flow velocity (Crutcher 1982). A radial velocity of 150 km/sec corresponds (at Ly-Alpha) to 0.6 Angstrom. Since the stellar line width for typical dwarf stars is on the order of 1 Angstrom (see Figure 1; Landsman and Simon (1993), it is clear that for the selected targets the ISM absorption is effectively removed from at least one side of the line core. The increased flux made available by avoiding the ISM absorption aids in making these moderate dispersion observations feasible. Our previous IUE programs (CSJJB and LGKJB) on giant stars ( e.g., Delta Lep) showed that acceptable results can be obtained even when the radial velocity is as low as 99 km/sec (see Figure 2) the star, since the total ISM absorption depends upon the column density towards the target, though for some of targets, ( e.g., HD 14439) the stellar radial velocity sufficiently high to shift the entire Ly-Alpha profile off of the ISM absorption. Tertiary selection criteria were for stars that do not lie near the ecliptic, and stars that lie in directions known to have a low column density of intervening hydrogen (e.g., the IIIrd galactic quadrant). The brightest stars meeting these criteria were selected. Instrument Configuration ------------------------ We will employ the G160M grating and the Small Science Aperture of the GHRS for the Ly-Alpha observations. This configuration ensures that the geocoronal emission will only affect about 1 Angstrom of the spectrum, and that the Ly-Alpha features of our target stars will be well in the wings of the geocoronal feature. In addition to the Lyman-Alpha observation, we will obtain a short observation of the Mg II lines using the G270M grating (centered at 2800 Angstrom) and the LSA. The Mg II profiles will permit us to measure independently the characteristics of the LISM in each line of sight, as well as aid in modeling the atmospheres. Exposure Time Estimates ---------------------- - The exposure times for moderate resolution (R = 12,500 at Ly-Alpha) GHRS spectra have estimated on the basis of low-S/N, low- and high-dispersion IUE spectrum of the Ly-Alpha line for a variety of dwarf stars of similar spectral types (Landsman and Simon 1993). The time estimates assumed the use of the small science aperture, and the sensitivities quoted (GHRS Handbook V. 5.0, May 1994) for the G160M grating (neither scattered light nor dark counts are important in this experiment). These observations will be of sufficient duration to produce a spectrum with a S/N > 15 at the half-power point, which is adequate for modeling. The typical exposure time is about 100 minutes. The Mg II lines (at R=20,000) can be obtained 15 minute exposures (S/N ~ 15 near the half-power point), based on IUE spectra and the GHRS handbook sensitivities (5.0, May 1994) of the G270M grating using the large science aperture. Other Considerations -------------------- We are necessarily requesting that all of the stars in the target list be observed in the current cycle, given the large number of orbits requested. This list represents a complete sample of the high velocity dwarf stars brighter than m_v=10 meeting our selection criteria. The outlook of this program is long-term, and stars not observed in this round will be requested in future cycles. Our list, from highest to lowest, is: HD6755, HD6833, GL630.1, HD191408, HD14439, and HD167740. For studies of the LISM, GL278C and GL630.1 are most important, as they accurately reflect the Pop I stars of the solar neighborhood. Unfortunately, they also require the longest observations. Real Time Justification ----------------------- Two of the targets (Gl278C, Gl630.1) in our program are binary systems with a very high radial velocity swing that is used to remove the Ly-Alpha emission from the ISM absorption. For these two systems, we will require time observations to ensure that the observations are made at orbital quadratures. Calibration Justification ------------------------- None. Additional Comments ------------------- ------------------------------------------------------------------------------------ 6010( 14) - 07/23/96 15:19 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 6010( 14) - 07/23/96 15:19 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 HD6755 STAR,F3-F9, RA=01H 9M 43.068S +/- J2000 V = -320 V = 7.73+/-0.5 0.1S,DEC=61D 32' 50.2" +/- 1.0" B-V = 0.72 Comments: Coordinates from Hipparchos catalog Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) J2000 0.0889 0.07 0.0 2 HD6833 STAR,K III-I, RA=01H 9M 52.261S +/- J2000 V = -245 V = 7.1+/-0.5 0.1S,DEC=54D 44' 20" +/- 1" B-V = 1.17 Comments: Coordinates from Hipparchos catalog Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) J2000 0.002 0.03 0.0 6010( 14) - 07/23/96 15:19 - [ 5] Visit: 01 Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 HD6833 HRS ACQ 2.0 MIRROR-N2 BRIGHT=RETURN,SEARCH-SIZE=5 1 5 S ONBOARD ACQ FOR 15-30 Comments: STEP-TIME = 0.2s ------------------------------------------------------------------------------------------------------------------------------------ 15 WAVE HRS ACCUM SC2 G160M 1205-12 1 DEF 43 ------------------------------------------------------------------------------------------------------------------------------------ 20 HD6833 HRS ACCUM 2.0 G270M 2780-28 STEP-PATT=5 3 244.8 S 20 Comments: Check on S/N for use of FP-SPLIT ------------------------------------------------------------------------------------------------------------------------------------ 30 HD6833 HRS ACQ/PEA 0.25 MIRROR-N2 SEARCH-SIZE=5 1 7.5 S ONBOARD ACQ FOR 40-50 KUP Comments: STEP-TIME = 0.3s ------------------------------------------------------------------------------------------------------------------------------------ 40 HD6833 HRS ACCUM 0.25 G160M 1205-12 STEP-PATT=5 11 299.2 S SHADOW 43 ------------------------------------------------------------------------------------------------------------------------------------ 45 WAVE HRS ACCUM SC2 G160M 1205-12 1 DEF 43 ------------------------------------------------------------------------------------------------------------------------------------ 50 HD6833 HRS ACCUM 0.25 G160M 1205-12 STEP-PATT=5 10 299.2 S SHADOW 43 ------------------------------------------------------------------------------------------------------------------------------------ 6010( 14) - 07/23/96 15:19 - [ 6] Visit: 02 Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 HD6755 HRS ACQ 2.0 MIRROR-N2 BRIGHT=RETURN,SEARCH-SIZE=5 1 10 S ONBOARD ACQ FOR 15-30 Comments: STEP-TIME = 0.4s ------------------------------------------------------------------------------------------------------------------------------------ 15 WAVE HRS ACCUM SC2 G160M 1205-12 STEP-PATT=4 1 DEF 43 ------------------------------------------------------------------------------------------------------------------------------------ 20 HD6755 HRS ACCUM 2.0 G270M 2780-28 STEP-PATT=5 3 244.8 S 20 Comments: Check on S/N for use of FP-SPLIT ------------------------------------------------------------------------------------------------------------------------------------ 30 HD6755 HRS ACQ/PEA 0.25 MIRROR-N2 SEARCH-SIZE=5 1 12.5 S ONBOARD ACQ FOR 40-50 KUP Comments: STEP-TIME = 0.5s ------------------------------------------------------------------------------------------------------------------------------------ 40 HD6755 HRS ACCUM 0.25 G160M 1205-12 STEP-PATT=5 11 299.2 S SHADOW 43 ------------------------------------------------------------------------------------------------------------------------------------ 45 WAVE HRS ACCUM SC2 G160M 1205-12 STEP-PATT=4 1 DEF 43 ------------------------------------------------------------------------------------------------------------------------------------ 50 HD6755 HRS ACCUM 0.25 G160M 1205-12 STEP-PATT=5 10 299.2 S SHADOW 43 ------------------------------------------------------------------------------------------------------------------------------------ 6010( 14) - 07/23/96 15:19 - [ 7] Summary Form for Proposal 6010 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations HRS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACCUM ACQ/PEAKUP ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BRIGHT=RETURN SEARCH-SIZE=5 STEP-PATT=5 STEP-PATT=4 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category Cool Stars ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ONBOARD ACQ FOR 15-30 ONBOARD ACQ FOR 40-50 SHADOW ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR-N2 G160M G270M ------------------------------------------------------------------------------------------------------------------------------------ Target Names HD6833 WAVE HD6755 ------------------------------------------------------------------------------------------------------------------------------------