7380( 9) - 04/15/99 17:41 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 7380 Version: 9 Check-in Date: 15-Apr-1999 17:40:47 1.Proposal Title: Imagery of IC 349 ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 7 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: George Herbig Institute for Astronomy CoI: Theodore Simon Institute for Astronomy Y ------------------------------------------------------------------------------------ 5. Abstract IC 349 is the brightest area in the Pleiades reflection nebulosity, by a factor of about 15. Discovered visually by Barnard in 1890, it is a difficult object because it is only about 30"\ from 23 Tau, of V=4.2. It is fan-shaped with the axis pointing ve ry nearly toward 23 Tau. Its blue color and the fact that its spectrum appears identical to that of the star shows that it also is a reflection nebula. The general Pleiades nebulosity is the result of a chance encounter between the cluster and a molecul ar cloud which may be a fragment of the Tau-Aur MC complex. It is proposed that the semi-stellar object at the head of IC 349 is part of that cloud and is being dissipated in the radiation field of 23 Tau as it approaches that star. The shape of the fan of IC 349 is compatible with a model in which small dust particles ejected from the nucleus are being swept away by radiation pressure from 23 Tau. It is unknown whether the nucleus is a dust- enshrouded pre-main-sequence star or a dense condensation of gas and dust several hundred A.U. in diameter. Multicolor imaging with the Planetary Camera is proposed here which may reveal whether such a protostar lies inside the nucleus, and will also display the morphology of the entire IC 349 nebula in much more exquisite detail than can be achieved from the ground. ------------------------------------------------------------------------------------ 7380( 9) - 04/15/99 17:41 - [ 2] Observations Description ------------------------ The nucleus of IC 349 is located 25"\ in p.a. 164^degrees from the bright star 23 Tauri, which provides its illumination. It is proposed to center the field (Planetary Camera with 0arcs046 pixels) near the nucleus (at the apex of the fan-shaped nebular I C 349), but with a slight offset (~7") so as to ensure that 23 Tau is safely outside the field of the PC while both the nucleus and nebula are within the field. We will also want to prevent having 23 Tau fall within the Bright Object Avoidance Regions alo ng the +U3 axis (as discussed in the WFPC Handbook). Both objectives can be met with the proper choice of HST roll angle. The nucleus appears non-stellar in ground-based photos; its V and \bv\ as measured through apertures of three sizes are: begincente r begintabularcccc Aper.Diam. & V & \bv & Mean V Sfc Brightness, (arcsec) & & & (mag per arcsec^2) , 2.1 & 16.14 & -0.16 & 17.49 , 3.8 & 15.36 & -0.20 & 17.99 , 5.0 & 15.02 & -0.21 & 18.27 , endtabular endcenter From thes e, we can estimate the following exposure times and signal-to-noise ratios (using the WWW WFPC Exposure Time Calculator) with the Planetary Camera, binned 1 * 1 pixel: begincenter begintabularlcc Filter & Exposure (sec) & Estimated S/N , F439W (B ) & 600 & 10--14 , F555W (V) & 300 & 14--21 , F814W (I) & 200 & 10-- 14 , F1042M (IR) & 600 & 1--20 , endtabular endcenter The range in S/N makes allowance for slight variation in surface brightness and color in the environs of the nucleus. These estimates depend upon how one treats the magnitudes of a non-stellar source. The reason for requesting the IR exposure is to see if a central point source appears at that wavelength if not at B, V, or I. If a late -type K or M star is emb edded within the nucleus, then we should be able to achieve a S/N of 20 or more in the 600 second F1042M exposure, down to V=20. The corresponding limit at I (for S/N = 20) is V = 23. It is estimated that these 4 exposures plus overhead (3 minutes per fi lter) will consume 40 minutes. Guide star acquisition (which will be used to ensure more accurate co- registration of the separate frames), and any small angle maneuver of HST (to adjust the position the nucleus) will take another 10 minutes. The visibili ty of the target at this declination is 53 minutes, so the whole series of images can be acquired in a single orbit. Real Time Justification ----------------------- ORIENT option to select roll angle of observation in order to place bright star outside the PC field of view and outside the WFPC Bright Star Avoidance Area JHK photometry and high-angular resolution CO spectroscopy from Mauna Kea. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 7380( 9) - 04/15/99 17:41 - [ 3] Data Distribution Paper Products: Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: ------------------------------------------------------------------------------------ 7380( 9) - 04/15/99 17:41 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 IC349-APEX ISM, Reflection Nebula RA=03H 46M 20.00S +/- 1", 2000 SURF(V) = 17.5+/-0.5 DEC=23D 56' 28.0" +/- 1" SURF(B) = 17.3+/-0.5 7380( 9) - 04/15/99 17:41 - [ 5] Visit: 01 Visit Priority: Visit Requirements: ORIENT 90D TO 150D ORIENT 180D TO 240D On Hold Comments: Additional Comments: 23 Tau lies 25" N and 7" W. Falls on WFC. Therefore, avoid orientation of 165D, which puts 23 Tau very close to (0, 0) corner of PC. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 IC349-APEX WFPC2 IMAGE PC1-FIX F439W 4300 CR-SPLIT=DEF 1 600 S ------------------------------------------------------------------------------------------------------------------------------------ 11 IC349-APEX WFPC2 IMAGE PC1-FIX F555W 5398 CR-SPLIT=DEF 1 300 S ------------------------------------------------------------------------------------------------------------------------------------ 12 IC349-APEX WFPC2 IMAGE PC1-FIX F814W 7921 CR-SPLIT=DEF 1 200 S ------------------------------------------------------------------------------------------------------------------------------------ 13 IC349-APEX WFPC2 IMAGE PC1-FIX F1042M 10184 CR-SPLIT=0.5 1 600 S ------------------------------------------------------------------------------------------------------------------------------------ 7380( 9) - 04/15/99 17:41 - [ 6] Summary Form for Proposal 7380 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures PC1-FIX ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=DEF CR-SPLIT=0.5 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 90D TO 150D ORIENT 180D TO 240D ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F439W F555W F814W F1042M ------------------------------------------------------------------------------------------------------------------------------------ Target Names IC349-APEX ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 4300 5398 7921 10184 ------------------------------------------------------------------------------------------------------------------------------------