6071( 3) - 12/15/95 15:26 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6071 Version: 3 Check-in Date: ********** 1.Proposal Title: The temperature structure in the wind of the pre-main sequence Herbig Ae star AB Aurigae ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle Hot Stars GO 5 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Claude Catala Observatoire de Paris, Section de Meudon CoI: Theodore Simon University of Hawaii Y CoI: Torsten Boehm Landessternwarte Heidelberg N ------------------------------------------------------------------------------------ 6. Abstract The Herbig Ae/Be stars are pre-main sequence objects of intermediate mass, and, according to standard stellar evolution theory, they are not supposed to possess outer convection zones. Despite this absence of convection, they show evidence for intense activity, which may be magnetic in origin. The model proposed so far to explain the various line profiles observed in these stars includes an extended chromosphere with temperatures of the order of 15,000--20,000 K. A few Herbig Ae/Be stars were recently detected as X-ray sources by ROSAT, but no evidence for temperatures typical of solar-type transition regions has ever been found in these stars. This lack of evidence may be the result of the low sensitivity of the instruments used so far. Using the GHRS, we propose to make a deep search for N V resonance lines near 1240 Angstrom in the spectrum of AB Aur, the star which is the prototype of this class. A non-detection would confirm the moderate temperature chromosphere model, while a positive detection would indicate the presence of temperatures above 100,000 K and would thus impose strong constraints on the mechanisms of nonradiative energy deposition in the atmospheres of these stars. ------------------------------------------------------------------------------------ 6071( 3) - 12/15/95 15:26 - [ 2] Observations Description ------------------------ We propose to use the GHRS to obtain a spectrum of AB Aur in the region of the N V resonance lines (1238.8, 1242.8) having a S/N in the range of 20--50. We also propose to record a spectrum with comparable S/N ratio in the region of the C IV resonance lines (1548.2, 1550.8), so that we can compare and model the profiles of the two sets of lines. The two spectra must be obtained within a few hours of each other, because we know that the line spectrum of AB Aur varies on a time scale of about one day due to streams in the wind. A spectral resolution of the order of 10--20,000 will be sufficient for our purpose, because the wide C IV lines of AB Aur typically extend to velocities of 300 kms^-1, and because we expect the same type of line width for the N V lines. Such a resolution can be obtained with the G140M grating and the 2 arcsec aperture (LSA), after a 2-pixel sliding mean of the spectra. The G140M grating + D1 detector combination is preferable to the G160M + D2 combination because the G140M grating has 30% higher resolving power than the G160M grating at these short wavelengths, the D1 detector is solar-blind, and its background count rate is lower by 25%. The G160M + D2 combination has the higher sensitivity at 1550 Angstrom, but the resolution and solar-blind response advantages of the G140M + D1 configuration outweigh the savings in exposure time at C IV (which amount to a few minutes at best for the short C IV exposure according to our estimated observing timeline). The observations will be made using the standard observing modes to reduce fixed pattern noise, detector granularity, geomagnetically-induced image motion, and undersampling. From the flux of about 2 * 10^-13 erg cm^-2 s^-1 ang^-1, measured in low (~ 8 Angstrom) dispersion by IUE at 1240 Angstrom for AB Aur, we infer a count rate through the large aperture of about 0.088 count s^-1 diode^-1 with the G140M grating and D1 detector. A two-pixel averaged S/N ratio of 30:1 can be obtained in 98 minutes of integration (which will extend over 3 orbits of the spacecraft). The flux at 1550 Angstrom\ is of the order of 4 * 10^-12 erg cm^-2 s^-1 ang^-1, yielding an expected count rate of 0.94 counts s^-1 diode^-1. A 15 min exposure will result in a S/N ratio = 40:1 for 2 pixel averaging. The 2- pixel sliding mean can be applied to the data without significant loss of resolution for our purposes. Real Time Justification ----------------------- None. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 6071( 3) - 12/15/95 15:26 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 6071( 3) - 12/15/95 15:26 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 HD31293 STAR, AE, A0-A3 V-IV RA = 04H 55M 45.9S +/- 1", 2000 V = 18.0 V = 7.05 +/- 0.4 DEC=+30D 33' 03.9" +/- 1" B-V = 0.13 +/- 0.2 E(B-V) = 0.2 +/- 0.1 F-CONT(1550) = 3 +/- 1 E-12 F-CONT(1240) = 2 +/- 0.5 E-13 6071( 3) - 12/15/95 15:26 - [ 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 HD31293 HRS ACQ 2.0 MIRROR-N1 SEARCH-SIZE = 1 9S ONBOARD ACQuisition FOR 20-30 3, BRIGHT = RETURN ------------------------------------------------------------------------------------------------------------------------------------ 20 HD31293 HRS ACCUM 2.0 G140M 1549 FP-SPLIT = STD, 1 979.2S DOPPLER = ON, STEP-PATT = 5 ------------------------------------------------------------------------------------------------------------------------------------ 30 HD31293 HRS ACCUM 2.0 G140M 1240 FP-SPLIT = STD, 4 1523.2S DOPPLER = ON, STEP-PATT = 5 ------------------------------------------------------------------------------------------------------------------------------------ 6071( 3) - 12/15/95 15:26 - [ 6] Summary Form for Proposal 6071 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations HRS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters SEARCH-SIZE = 3 BRIGHT = RETURN STEP-PATT = 5 DOPPLER = ON ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category Hot Stars ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ONBOARD ACQuisition FOR 20-30 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR-N1 G140M ------------------------------------------------------------------------------------------------------------------------------------ Target Names HD31293 ------------------------------------------------------------------------------------------------------------------------------------