8713( 2) - 03/03/00 09:31 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 8713 Version: 2 Check-in Date: 03-Mar-2000 09:29:36 1.Proposal Title: The Photoevaporation of Protostellar Envelopes in the NGC 281 Young Stellar Cluster ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 9 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: S. Megeath Harvard-Smithsonian Center for Astrophysics CoI: Dr. Tom Wilson Steward Observatory N ------------------------------------------------------------------------------------ 5. Abstract We propose HAlpha, SII, SIII and R--band WFPC2 imaging of the NGC 281 nebula. This region, which we have studied intensively at near--infrared and radio wavelengths, contains a rich cluster of young, low--mass stars emerging from an edge--on molecular gas/H, ii region interface. With the WFPC2 images, we plan to search for <= 2000 AU sized evaporating globules, or EGGs, similar to those detected in M16 by Hester et al. (1996). These globules are thought to be accreting envelopes surrounding young protostars. By comparing the proposed WFPC2 imaging with our existing near-- infrared (NIR) data, we can estimate the fraction of stars which emerge from the molecular cloud enshrouded in EGGs. The goal is to determine whether most stars in the NGC 281 cluster emerge from the clouds still cloaked in their protostellar envelopes, or whether they disrupt their envelopes prior to emergence. From this analysis, we will ascertain whether photoevaporation by external OB stars plays a significant role in terminating protostellar accretion in young clusters. ------------------------------------------------------------------------------------ 8713( 2) - 03/03/00 09:31 - [ 2] Observations Description ------------------------ We plan to observe one position in three narrow band filters, F656N (HAlpha), F673N (SII), and F953N (SIII), and one broad band filter, F675W (R). The ground based HAlpha images in Fig. 1 shows the molecular cloud/H, ii interface. The observed emission is variable; however, HAlpha emission is detected throughout the region planned for WFPC2 observations. The weakest detected signal is 1.5* 10^-15 erg cm^-2 s^-1 arcsec^-2; a 5 Sigma detection would require 1800 seconds of exposure time. We will use an equivalent time for the SII and SIII filter. Integrations with the F675W filter will be used to assess the continuum emission in the narrow band filters. In addition, we plan to perform R--band photometry on the cluster stars. A 1200s integration in the F675W filters will give > 5Sigma detections of the 40 members in our NIR sample with A_V < 7. Dithering and exposure splitting will be used to minimize the effect of bad pixels and cosmic rays. We estimate we need three orbits. During each orbit, we will observe in one narrow band filters for 1800 sec and the F675W filter for 400 sec (total F675W integration time after three orbits will be 1200 s). Real Time Justification ----------------------- We have already obtained and reduced supporting near--IR, ISOCAM, millimeter, and VLA centimeter data (see Megeath & Wilson 1997, AJ 114, 106). Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 8713( 2) - 03/03/00 09:31 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC281-WEST ISM, IONIZATION FRONT, RA=00H 52M 27.29S +/- 1", J2000 SURF-LINE(656)=1.5e-15 STAR FORMING REGION, DEC=56D 34' 4.8" +/- 1" HII REGION, MOLECULAR CLOUD, STELLAR CLUSTER, 8713( 2) - 03/03/00 09:31 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type LINE Pattern_Purpose DITHER Number_Of_Points 2 Point_Spacing 0.3535 Coordinate_Frame POS-TARG Pattern_Orient 45.0 Center_Pattern YES ------------------------------------------------------------------------------------------------------------------------------------ 8713( 2) - 03/03/00 09:31 - [ 5] Visit: 01 Visit Priority: Visit Requirements: ORIENT 150D TO 245D 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 NGC281-WEST WFPC2 IMAGE WFALL-F F656N 1 2700 S IX ------------------------------------------------------------------------------------------------------------------------------------ 20 NGC281-WEST WFPC2 IMAGE WFALL-F F673N 1 2700 S IX ------------------------------------------------------------------------------------------------------------------------------------ 30 NGC281-WEST WFPC2 IMAGE WFALL-F F675W ATD-GAIN=15,CR-SPLIT=0.5 2 240 S PATTERN 1 30-40 IX ------------------------------------------------------------------------------------------------------------------------------------ 40 NGC281-WEST WFPC2 IMAGE WFALL-F F814W ATD-GAIN=15,CR-SPLIT=0.5 1 200 S IX ------------------------------------------------------------------------------------------------------------------------------------ 8713( 2) - 03/03/00 09:31 - [ 6] Summary Form for Proposal 8713 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures WFALL-FIX ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ATD-GAIN=15 CR-SPLIT=0.5 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 150D TO 245D PATTERN 1 30-40 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F656N F673N F675W F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC281-WEST ------------------------------------------------------------------------------------------------------------------------------------