7851( 3) - 02/03/98 21:07 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 7851 Version: 3 Check-in Date: 03-Feb-1998 21:06:17 1.Proposal Title: A Deep Infrared Census of the W3-IRS 5 Star Cluster ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 7 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Theodore Simon University of Hawaii CoI: John Rayner University of Hawaii N CoI: S. T. Megeath MIT Haystack Observatory N ------------------------------------------------------------------------------------ 5. Abstract Near--infrared surveys of giant molecular clouds have shown that many, if not most, stars of all masses form in dense clusters. Consequently, understanding how such clusters form is one of the premier problems in star formation. We propose a survey of the W3--Main region, focussing on a site of compact and ultracompact H II regions in the vicinity of the IRS 5 infrared source. This complex of sources is an excellent example of OB star/cluster formation prior to the disruption of the parental molecular cloud; NICMOS observations of this region should provide insight into the initial properties of embedded clusters before the onset of the rapid dynamical evolution which occurs once the natal gas is evaporated. Previous ground- based observations of this region identify a population of low mass stars (presumably PMS T Tauri stars) associated with IRS 5, but are plagued by confusion with nebulosity and stars. High resolution NICMOS observations will substantially reduce this confusion and provide a higher detection rate in important wavelength bands at Lambda < 2micron. From these data we can make great progress in understanding the initial configurations of young clusters and in determining whether OB stars can form in relative isolation (indicating that cluster formation is not an essential trait of high mass star formation). We can also constrain the initial mass function in a very young and dense region of star formation, which we have not been able to do from the ground. ------------------------------------------------------------------------------------ 7851( 3) - 02/03/98 21:07 - [ 2] Observations Description ------------------------ The observations will cover two fields associated with W3-- Main: one centered on the embedded cluster associated with IRS 5, the other centered on a nearby reference field <2' away, which will be used to measure the PSF as well as the thermal background of HST (for Lambda > 2micron). The program will start with high resolution images of IRS 5 in Camera 1, through the F110W filter and then the F160W filter. The exposure times, 2.1 ks in F110W and 3.0 ks in F160W, are chosen to achieve signal-to-noise ratios (SNR) of >~10 for reddened cool star flux levels corresponding to m_J = 23 and m_H = 22, respectively (3 magnitudes fainter than the brightness limits in Megeath et al. 1996). The exposure times have been derived using the NICMOS point source Exposure Time Calculator (ETC). In either band, the exposure can be divided in half and offset slightly on the sky between halves to facilitate the removal of bad pixels from the final image. Including approximately 5 minutes for slewing to a nearby bright star for a short PSF exposure, and slewing back to IRS 5, we find that one orbit is needed in each filter (i.e., a total of 2). Following a switch to Camera 2, the entire area shown in outline within the box in Fig. 2 will be imaged in three filters: F110W, F160W, and F222M. In the F110W and F160W filters, each 50" x 50" field will be covered by a 9 step spiral dith, starting from IRS 5 and offsetting by 17"\\ to the next position. We adopt exposure times of 221 seconds for both F110W and F160W; according to the ETC, these times should ensure SNR of ~10 for m_J = 22 and m_H = 21. Using ~5 minutes for a snapshot of the nearby reference field, we estimate the mosaic will take one orbit per band in each of F110W and F160W. A further two orbits will be needed to map the same area in the F222M filter, a higher cost being imposed by the need to measure the thermal background of HST. At each location, we will stop to integrate for 152 seconds, ensuring a SNR of 10 for m_K = 18 per the ETC. For this observation, we propose to use a 3-by-3 spiral-dith-chop pattern. A chopping position and/or distance will be selected in Phase II from our large scale ground-based maps of W3. Based on the 56 minute per orbit visibility of W3 (see, however, below), and using the latest telescope and camera overheads listed in the update to the Cycle 7 Call for Proposals (for guide star acquisition, NICMOS setup, multiaccum readout, filter and camera switch, and slew offsets), we have devised an observing timeline for the program just described, which meets the time constraints for each of the 6 orbits that we are requesting here. Assuming that Camera 1 will be operated in parallel with Camera 2, we note in passing that a portion of the boxed region shown in Fig. 2 will also be mapped at high resolution in F110W and F160W, extending the area of the cluster that will be covered at high resolution (but at a much higher flux detection limit than we expect to achieve in our initial deep integrations on IRS 5). In turn, parallel observations during the Camera 1 observations centered on IRS 5 will image an adjacent region of W3 with Camera 2, but the location of this field will not be known until the observations are scheduled. Real Time Justification ----------------------- W3 lies in the CVZ of HST. In accordance with instructions given in the NICMOS Call for Proposals, we do not take this into account in estimating the number of spacecraft orbits required to carry out our NICMOS observing program. Our time request is predicated on a visibility period of 56 minutes per orbit. However, assuming the full 96 minute visibility that becomes possible within the CVZ, we very roughly estimate that our entire GO program can be executed in slightly more than 3 orbits. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 7851( 3) - 02/03/98 21:07 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: ------------------------------------------------------------------------------------ 7851( 3) - 02/03/98 21:07 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 W3-IRS5 STELLAR CLUSTER, OB RA=02H 25M 40.0S +/- 0.5", 2000 K = 12.0+/-0.5 ASSOCIATION DEC=+62D 05' 52.0" +/- 0.5" 2 W3-IRS5- STELLAR CLUSTER, OB RA=02H 25M 50.0S +/- 0.5", 2000 K = 12.0+/-0.5 BAKGRD ASSOCIATION DEC=+62D 04' 10.0" +/- 0.5" Comments: Fake flux for sky backgrd region 7851( 3) - 02/03/98 21:07 - [ 5] Visit: 01 Visit Priority: 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 ------------------------------------------------------------------------------------------------------------------------------------ 11 W3-IRS5 NIC1 MULTIAC NIC1 F110W PATTERN=SPIRAL-DITH,NUM-POS=4, 1 DEF PARallel 12 WITH 11 CUM DITH-SIZE=0.76,SAMP-SEQ=STEP128, NSAMP=13 Comments: Assumes return to origin at W3-IRS 5 ------------------------------------------------------------------------------------------------------------------------------------ 12 ANY NIC2 MULTIAC NIC2 F110W SAMP-SEQ=STEP128,NSAMP=13 1 DEF CUM Comments: Assumes return to origin at W3-IRS 5 ------------------------------------------------------------------------------------------------------------------------------------ 21 W3-IRS5 NIC1 MULTIAC NIC1 F160W PATTERN=SPIRAL-DITH,NUM-POS=4, 1 DEF PARallel 22 WITH 21 CUM DITH-SIZE=0.76,SAMP-SEQ=STEP128, NSAMP=15 Comments: Assumes return to origin at W3-IRS 5 ------------------------------------------------------------------------------------------------------------------------------------ 22 ANY NIC2 MULTIAC NIC2 F160W SAMP-SEQ=STEP128,NSAMP=15 1 DEF CUM Comments: Assumes return to origin at W3-IRS 5 ------------------------------------------------------------------------------------------------------------------------------------ 31 W3-IRS5 NIC2 MULTIAC NIC2 F110W PATTERN=SPIRAL-DITH-CHOP, 1 DEF PARallel 32 WITH 31 CUM NUM-POS=18,DITH-SIZE=17.0, CHOP-SIZE=1.0,SAMP-SEQ=STEP32, NSAMP=11 Comments: Assumes return to origin at W3-IRS 5 ------------------------------------------------------------------------------------------------------------------------------------ 32 ANY NIC1 MULTIAC NIC1 F110W SAMP-SEQ=STEP32,NSAMP=11 1 DEF CUM Comments: Assumes return to origin at W3-IRS 5 ------------------------------------------------------------------------------------------------------------------------------------ 41 W3-IRS5 NIC2 MULTIAC NIC2 F160W PATTERN=SPIRAL-DITH-CHOP, 1 DEF PARallel 42 WITH 41 CUM NUM-POS=18,DITH-SIZE=17.0, CHOP-SIZE=1.0,SAMP-SEQ=STEP32, NSAMP=11 Comments: Assumes return to origin at W3-IRS 5 ------------------------------------------------------------------------------------------------------------------------------------ 42 ANY NIC1 MULTIAC NIC1 F110W SAMP-SEQ=STEP32,NSAMP=11 1 DEF CUM Comments: Assumes return to origin at W3-IRS 5 ------------------------------------------------------------------------------------------------------------------------------------ 51 W3-IRS5 NIC2 MULTIAC NIC2 F222M PATTERN=SPIRAL-DITH-CHOP, 1 DEF PARallel 52 WITH 51 CUM NUM-POS=18,DITH-SIZE=17.0, CHOP-SIZE=1.0,SAMP-SEQ=STEP32, NSAMP=11 Comments: Assumes return to origin at W3-IRS 5 ------------------------------------------------------------------------------------------------------------------------------------ 7851( 3) - 02/03/98 21:07 - [ 6] Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 52 ANY NIC1 MULTIAC NIC1 F160W SAMP-SEQ=STEP32,NSAMP=11 1 DEF CUM Comments: Assumes return to origin at W3-IRS 5 ------------------------------------------------------------------------------------------------------------------------------------ 61 W3-IRS5-BAK NIC2 MULTIAC NIC2 F222M PATTERN=SPIRAL-DITH,NUM-POS=9, 1 DEF PARallel 62 WITH 61 GRD CUM DITH-SIZE=6.4,SAMP-SEQ=STEP128, NSAMP=10 Comments: Assumes return to origin ------------------------------------------------------------------------------------------------------------------------------------ 62 ANY NIC1 MULTIAC NIC1 F110W SAMP-SEQ=STEP128,NSAMP=10 1 DEF CUM Comments: Assumes return to origin ------------------------------------------------------------------------------------------------------------------------------------ 63 W3-IRS5-BAK NIC2 MULTIAC NIC2 F222M PATTERN=SPIRAL-DITH,NUM-POS=9, 1 DEF PARallel 64 WITH 63 GRD CUM DITH-SIZE=6.4,SAMP-SEQ=STEP128, NSAMP=9 Comments: Assumes return to origin ------------------------------------------------------------------------------------------------------------------------------------ 64 ANY NIC1 MULTIAC NIC1 F160W SAMP-SEQ=STEP128,NSAMP=9 1 DEF CUM Comments: Assumes return to origin ------------------------------------------------------------------------------------------------------------------------------------ 7851( 3) - 02/03/98 21:07 - [ 7] Summary Form for Proposal 7851 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations NIC1 NIC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes MULTIACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters PATTERN=SPIRAL-DITH NUM-POS=4 DITH-SIZE=0.76 SAMP-SEQ=STEP128 NSAMP=13 NSAMP=15 NSAMP=11 SAMP-SEQ=STEP32 CHOP-SIZE=1.0 DITH-SIZE=17.0 NSAMP=10 NSAMP=9 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PARallel 12 WITH 11 PARallel 22 WITH 21 PARallel 32 WITH 31 PARallel 42 WITH 41 PARallel 52 WITH 51 PARallel 62 WITH 61 PARallel 64 WITH 63 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F110W F160W F222M ------------------------------------------------------------------------------------------------------------------------------------ Target Names W3-IRS5 ANY W3-IRS5-BAKGRD ------------------------------------------------------------------------------------------------------------------------------------