9091( 3) - 05/24/01 11:39 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 9091 Version: 3 Check-in Date: 24-May-2001 11:39:09 1.Proposal Title: Evolution of Star Forming Environments in H II Regions ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 10 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Jeff Hester Arizona State University CoI: Dr. Paul Scowen Arizona State University N CoI: Mr. Kevin Healy Arizona State University N ------------------------------------------------------------------------------------ 5. Abstract There are significant difficulties with the current understanding of the YSO disks and evaporative envelopes in the Orion nebula and how these objects fit into the broader picture of star formation. These are generally imagined to be a long-lived population, yet searches have turned up few such objects anywhere but Orion. Further, the observed masses of the disks in Orion combined with their observed evaporative mass loss rates imply ages for the objects of only a few * 10^4 years. Henney and O'Dell (1999) claim that no solution is possible unless submillimeter determinations of disk masses are off by a factor of 30. We suggest instead that these objects are only 10^4 years old, and that we are catching them as they are being uncovered by the advancing ionization front located only about 2 * 10^17 cm behind the Trapezium. When a YSO is uncovered by an advancing ionization front it will pass through two short-lived stages, first as an evaporating gaseous globule (EGG) such as those seen in M 16, then as an evaporating disk such as those seen in Orion. Such objects will live for only a few * 10^4 years, and should be found only in close proximity to molecular cloud walls. We propose to test this idea by looking for EGGs and silhouette disks in two young clusters and along one molecular cloud wall. ------------------------------------------------------------------------------------ 9091( 3) - 05/24/01 11:39 - [ 2] Observations Description ------------------------ We propose to search for YSO's, EGGs, and evaporating and silhouette disks in WFPC2 images of two young clusters sitting in H II regions, and a third region where an advancing ionization front is viewed from edge-on. The distances of the regions are between 1700 and 2000 pc. We have used the WFPC2 images of Orion to simulate the appearance of silhouette disks at these distances and find that most of the Orion objects should be visible, so long as they are seen against a relatively high signal-to-noise background. Both NGC6611 and NGC6357 provide bright enough HAlpha (F656N) backgrounds to readily identify small resolved absorption features in a two-orbit exposure. We note, for example, that a silhouette disk was easily seen and identified in our earlier observations of the elephant trunks in M16. We will observe each region in S II as well. S II provides an excellent tracer of the locations of ionization fronts both within the nebula and at the surface of EGGs and evaporating disks, and so will allow us to carefully search for objects seen in emission. It provides much better contrast between these objects and the nebular background than does HAlpha. To obtain a census of the stellar population of the regions, we will obtain two CR-SPLIT half- orbit exposures in F547M and F814W. These observations will give us V-I colors for the stars in each clusters. (Note that we use F547M, which is a relatively line-free continuum filter, rather than the tradiational F555W.) More importantly, the broad band images will allow us to distinguish between line and continuum features in the line images. This is especially important when examining images obtained with the relatively ``broad'' F673N filter. Finally, we propose to obtain two-orbit O III images of NGC 6357 and NGC 2174. These are relatively high excition H II regions. O III is needed to complete our observational picture of the structure of the ionized gas in the region and provide a physical context for the observations of YSO environments. (Having O III will also allow us to analyze the structure of the photoionized photoevaporative flows, per se.) Our principle concern with identifying and characterizing small objects seen in emission and extinction is avoiding confusion with hot pixels and other defects on the CCDs, and thoroughly cleaning up cosmic rays. To accomplish this, we will take half of the images of an object at one pointing, then repeat that sequence at a position offset from the first by approximately 5 arcseconds. In other words, the sequence of observations for NGC 6611 will consist of a full-orbit CR- SPLIT HAlpha image, a full orbit CR-SPLIT S II image, and half-orbit CR-SPLIT images in F547M and F814W. We will then repeat this sequence of exposures at a pointing offset by 5" from the first. We will then have four images in each filter, with two of those four images at one pointing and two of those four images at the offset second pointing. The total requirement for NGC 6611 will be 6 orbits. Note that all exposure times are based on experience with observations of M 16 and M 20, which are of comparable surface brightness to the regions studied here. The sequence of observations for NGC 6357 and NGC 2174 will be the same, but with O III added to the rotation for a total of 8 orbits per object. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 9091( 3) - 05/24/01 11:39 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC2174-P1 ISM, HII Region RA= 06H 09M 13.08S +/- 0.01S, J2000 V = 16.0+/-3.0 DEC= +20D 27' 50.1" +/- 0.1" Coordinate Source: OTHER_SOURCE 2 NGC2174-P2 ISM, HII Region RA= 06H 09M 13.17S +/- 0.01S, J2000 V = 16.0+/-3.0 DEC= +20D 27' 45.3" +/- 0.1" Coordinate Source: OTHER_SOURCE 3 NGC6357-P1 ISM, HII Region RA=17H 24M 46.38S +/- 0.01S, J2000 V = 16.0+/-3.0 DEC= -34D 10' 32.2" +/- 0.1" Coordinate Source: OTHER_SOURCE 4 NGC6357-P2 ISM, HII Region RA=17H 24M 45.90S +/- 0.01S, J2000 V = 16.0+/-3.0 DEC= -34D 10' 32.2" +/- 0.1" Coordinate Source: OTHER_SOURCE 5 NGC6611-P1 ISM, HII Region RA=18H 18M 40.83S +/- 0.01S, J2000 V = 16.0+/-3.0 DEC= -13D 47' 55.2" +/- 0.1" Coordinate Source: OTHER_SOURCE 6 NGC6611-P2 ISM, HII Region RA=18H 18M 41.16S +/- 0.01S, J2000 V = 16.0+/-3.0 DEC= -13D 47' 56.5" +/- 0.1" Coordinate Source: OTHER_SOURCE 9091( 3) - 05/24/01 11:39 - [ 4] Visit: 11 Visit Priority: Visit Requirements: ORIENT 247.0D TO 253.0D On Hold Comments: Additional Comments: FIRST POINTING ON NGC 2174 Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 101 NGC2174-P1 WFPC2 IMAGE WFALL-F F547M CLOCKS=NO,CR-SPLIT=0.5, 1 1000 S IX ATD-GAIN=15 ------------------------------------------------------------------------------------------------------------------------------------ 102 NGC2174-P1 WFPC2 IMAGE WFALL-F F814W CLOCKS=NO,CR-SPLIT=0.5, 1 1000 S IX ATD-GAIN=15 ------------------------------------------------------------------------------------------------------------------------------------ 103 NGC2174-P1 WFPC2 IMAGE WFALL-F F656N CLOCKS=NO,CR-SPLIT=0.5, 1 2600 S IX ATD-GAIN=15 ------------------------------------------------------------------------------------------------------------------------------------ 104 NGC2174-P1 WFPC2 IMAGE WFALL-F F673N CLOCKS=NO,CR-SPLIT=0.5, 1 2600 S IX ATD-GAIN=15 ------------------------------------------------------------------------------------------------------------------------------------ 105 NGC2174-P1 WFPC2 IMAGE WFALL-F F502N CLOCKS=NO,CR-SPLIT=0.5, 1 2600 S IX ATD-GAIN=15 ------------------------------------------------------------------------------------------------------------------------------------ 9091( 3) - 05/24/01 11:39 - [ 5] Visit: 12 Visit Priority: Visit Requirements: ORIENT 247.0D TO 253.0D SAME ORIENT AS 11 GROUP 11, 12 WITHIN 7D On Hold Comments: Additional Comments: SECOND POINTING ON NGC 2174 Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 106 NGC2174-P2 WFPC2 IMAGE WFALL-F F547M CLOCKS=NO,CR-SPLIT=0.5, 1 1000 S IX ATD-GAIN=15 ------------------------------------------------------------------------------------------------------------------------------------ 107 NGC2174-P2 WFPC2 IMAGE WFALL-F F814W CLOCKS=NO,CR-SPLIT=0.5, 1 1000 S IX ATD-GAIN=15 ------------------------------------------------------------------------------------------------------------------------------------ 108 NGC2174-P2 WFPC2 IMAGE WFALL-F F656N CLOCKS=NO,CR-SPLIT=0.5, 1 2600 S IX ATD-GAIN=15 ------------------------------------------------------------------------------------------------------------------------------------ 109 NGC2174-P2 WFPC2 IMAGE WFALL-F F673N CLOCKS=NO,CR-SPLIT=0.5, 1 2600 S IX ATD-GAIN=15 ------------------------------------------------------------------------------------------------------------------------------------ 110 NGC2174-P2 WFPC2 IMAGE WFALL-F F502N CLOCKS=NO,CR-SPLIT=0.5, 1 2600 S IX ATD-GAIN=15 ------------------------------------------------------------------------------------------------------------------------------------ 9091( 3) - 05/24/01 11:39 - [ 6] Visit: 21 Visit Priority: Visit Requirements: ORIENT 276.0D TO 280.0D On Hold Comments: Additional Comments: FIRST POINTING ON NGC 6357 Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 201 NGC6357-P1 WFPC2 IMAGE WFALL-F F547M CLOCKS=NO,CR-SPLIT=0.5, 1 1000 S IX ATD-GAIN=15 ------------------------------------------------------------------------------------------------------------------------------------ 202 NGC6357-P1 WFPC2 IMAGE WFALL-F F814W CLOCKS=NO,CR-SPLIT=0.5, 1 1000 S IX ATD-GAIN=15 ------------------------------------------------------------------------------------------------------------------------------------ 203 NGC6357-P1 WFPC2 IMAGE WFALL-F F656N CLOCKS=NO,CR-SPLIT=0.5, 1 2600 S IX ATD-GAIN=15 ------------------------------------------------------------------------------------------------------------------------------------ 204 NGC6357-P1 WFPC2 IMAGE WFALL-F F673N CLOCKS=NO,CR-SPLIT=0.5, 1 2600 S IX ATD-GAIN=15 ------------------------------------------------------------------------------------------------------------------------------------ 205 NGC6357-P1 WFPC2 IMAGE WFALL-F F502N CLOCKS=NO,CR-SPLIT=0.5, 1 2600 S IX ATD-GAIN=15 ------------------------------------------------------------------------------------------------------------------------------------ 9091( 3) - 05/24/01 11:39 - [ 7] Visit: 22 Visit Priority: Visit Requirements: ORIENT 276.0D TO 280.0D SAME ORIENT AS 21 GROUP 21, 22 WITHIN 7D On Hold Comments: Additional Comments: SECOND POINTING ON NGC 6357 Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 206 NGC6357-P2 WFPC2 IMAGE WFALL-F F547M CLOCKS=NO,CR-SPLIT=0.5, 1 1000 S IX ATD-GAIN=15 ------------------------------------------------------------------------------------------------------------------------------------ 207 NGC6357-P2 WFPC2 IMAGE WFALL-F F814W CLOCKS=NO,CR-SPLIT=0.5, 1 1000 S IX ATD-GAIN=15 ------------------------------------------------------------------------------------------------------------------------------------ 208 NGC6357-P2 WFPC2 IMAGE WFALL-F F656N CLOCKS=NO,CR-SPLIT=0.5, 1 2600 S IX ATD-GAIN=15 ------------------------------------------------------------------------------------------------------------------------------------ 209 NGC6357-P2 WFPC2 IMAGE WFALL-F F673N CLOCKS=NO,CR-SPLIT=0.5, 1 2600 S IX ATD-GAIN=15 ------------------------------------------------------------------------------------------------------------------------------------ 210 NGC6357-P2 WFPC2 IMAGE WFALL-F F502N CLOCKS=NO,CR-SPLIT=0.5, 1 2600 S IX ATD-GAIN=15 ------------------------------------------------------------------------------------------------------------------------------------ 9091( 3) - 05/24/01 11:39 - [ 8] Visit: 31 Visit Priority: Visit Requirements: ORIENT 99.0D TO 103.0D On Hold Comments: Additional Comments: FIRST POINTING ON NGC 6611 Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 301 NGC6611-P1 WFPC2 IMAGE WFALL-F F547M CLOCKS=NO,CR-SPLIT=0.5, 1 1000 S IX ATD-GAIN=15 ------------------------------------------------------------------------------------------------------------------------------------ 302 NGC6611-P1 WFPC2 IMAGE WFALL-F F814W CLOCKS=NO,CR-SPLIT=0.5, 1 1000 S IX ATD-GAIN=15 ------------------------------------------------------------------------------------------------------------------------------------ 303 NGC6611-P1 WFPC2 IMAGE WFALL-F F656N CLOCKS=NO,CR-SPLIT=0.5, 1 2600 S IX ATD-GAIN=15 ------------------------------------------------------------------------------------------------------------------------------------ 304 NGC6611-P1 WFPC2 IMAGE WFALL-F F673N CLOCKS=NO,CR-SPLIT=0.5, 1 2600 S IX ATD-GAIN=15 ------------------------------------------------------------------------------------------------------------------------------------ 9091( 3) - 05/24/01 11:39 - [ 9] Visit: 32 Visit Priority: Visit Requirements: ORIENT 99.0D TO 103.0D SAME ORIENT AS 31 GROUP 31, 32 WITHIN 7D On Hold Comments: Additional Comments: SECOND POINTING ON NGC 6611 Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 306 NGC6611-P2 WFPC2 IMAGE WFALL-F F547M CLOCKS=NO,CR-SPLIT=0.5, 1 1000 S IX ATD-GAIN=15 ------------------------------------------------------------------------------------------------------------------------------------ 307 NGC6611-P2 WFPC2 IMAGE WFALL-F F814W CLOCKS=NO,CR-SPLIT=0.5, 1 1000 S IX ATD-GAIN=15 ------------------------------------------------------------------------------------------------------------------------------------ 308 NGC6611-P2 WFPC2 IMAGE WFALL-F F656N CLOCKS=NO,CR-SPLIT=0.5, 1 2600 S IX ATD-GAIN=15 ------------------------------------------------------------------------------------------------------------------------------------ 309 NGC6611-P2 WFPC2 IMAGE WFALL-F F673N CLOCKS=NO,CR-SPLIT=0.5, 1 2600 S IX ATD-GAIN=15 ------------------------------------------------------------------------------------------------------------------------------------ 9091( 3) - 05/24/01 11:39 - [ 10] Summary Form for Proposal 9091 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures WFALL-FIX ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CLOCKS=NO CR-SPLIT=0.5 ATD-GAIN=15 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 247.0D TO 253.0D ORIENT 247.0D TO 253.0D SAME ORIENT AS 11 GROUP 11, 12 WITHIN 7D ORIENT 276.0D TO 280.0D ORIENT 276.0D TO 280.0D SAME ORIENT AS 21 GROUP 21, 22 WITHIN 7D ORIENT 99.0D TO 103.0D ORIENT 99.0D TO 103.0D SAME ORIENT AS 31 GROUP 31, 32 WITHIN 7D ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F547M F814W F656N F673N F502N ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC2174-P1 NGC2174-P2 NGC6357-P1 NGC6357-P2 NGC6611-P1 NGC6611-P2 ------------------------------------------------------------------------------------------------------------------------------------