----- Submission 1 (Thu May 12 09:29:34 GMT 2005) ----- There is a warning for the NIC2 exposures: Warning (Orbit Planner) PATTERN POSITION OUTSIDE APERTURE This is due to the use of POS-TARG to construct a continuous mosaic of all 25 NIC2 fields. This has been discussed with Beth Perriello and Al Schultz that said that the warnings were expected and could be safely ignored. The IMF in NGC6611: the environmental influence on the formation of low-mass stars and brown dwarfs We propose to use HST with ACS and NICMOS to survey the central area of the young (2 Myr) cluster NGC6611 in the Eagle Nebula, with the goal of constructing the low-mass and substellar Initial Mass Function (IMF). We plan to obtain deep images in I (F775W) and Z (F850LP) with ACS/WFC, and deep images in J (F110W) and H (F160W) for 25 NICMOS/NIC2 fields within the 202" x 202" ACS/WFC field. Using a proven technique based on the use of IZJH color-magnitude and color-color diagrams to identify and determine the masses of the low-mass pre-main sequence cluster members, we are thus able to construct the IMF down to masses of 0.02-0.03 Msun. With an intense ionizing radiation field but a relatively low density, NGC6611 provides a unique laboratory in which to test the importance of photoevaporation and density on the formation of low-mass stars and brown dwarfs, through comparison with the IMFs determined for the different environments in the Orion Nebular Cluster, Taurus and IC348. This will not only offer substantial new insight into the physics of star formation, but also have important ramifications for estimating the global star formation rates at high redshift, the efficiency of galactic chemical evolution and the contribution of sub-stellar mass objects to the baryonic dark matter content of the Universe.
This program is made of two parts: i) ACS/WFC F775 (I) and F850 (Z) observations of one field; ii) NICMOS/NIC2 F110 (J) and F160 (H) observations of 25 fields within the area imaged with ACS/WFC. A total of 7 orbits were allocated distributed as follows: 2 orbits with ACS/WFC, one for each filter; 5 orbits with NICMOS/NIC2. These orbits are distributed over 2 visits. The targets are fields of stars, not individual objects. The position of the fields was checked on GSC SURVEY PLATE 064B. - We observe a single ACS/WFC field in I and Z. - The total exposure time per filter is 2000s, split into 4 dithered exposures of 500s. - The dithering pattern chosen is DITHER-LINE (4 points, 3.011 arcsec spacing) and the aims of the strategy are: remove blemishes and hot pixels, cosmic ray hit rejection and bridge the 2.5 arcsec interchip gap. As we are performing a dithering pattern, it is not necessary to do a cr_split (cr_split=no). - We choose to operate with gain=2 because it completely samples the full well depth --- with only marginally larger readout noise than gain=1. This is important in our observations, as the field includes targets with a large range of magnitudes. - These observations occupy 2 orbits, one per filter, that are performed on the same visit. This visit has no orient requirements. - These exposures allow us to compute (I-Z) colours with 10 per cent accuracy, at a magnitude limit of I=25 mag. - We observe 25 NIC2 fields in J and H to form a continuous mosaic covering ~2.5 arcmin squared. - The total exposure time per field per filter is 128s, split into 4 dithered exposures (samp-seq=step8, nsamp=9). - The dithering pattern chosen is SPIRAL-DITH (4 points, 1 arcsec spacing) and the aims of the strategy are: remove grot and bad pixels, sensitivity variations and the image of the coronagraphic hole, and create some overlap between the fields in the mosaic. - At each dither position, exposures are taken in both filters, before the telescope moves to the next position, in order to minimize overheads. - The mosaic is constructed by using the POS-TARG feature and Special Target (position) Requirements. This guarantees that the orient will be fixed and the x- and y-axis of the different tiles will align. - In each orbit, 5 fields are observed in both filters; all 5 orbits are grouped in the same visit. GS acquisitions are performed both in the first and fifth orbit. - The orient of this visit is restricted to the interval 260-280, to make sure the mosaic falls on the desired area in the sky. This does not greatly affect the visits's schedulability. - These exposures allow us to compute (J-H) colours with 10 per cent accuracy, at a magnitude limit of J=21.5 mag. Visit 01 has no orient constrains. The orient of Visit 02 is restricted to the interval 260-280, to make sure the mosaic falls on the desired area in the sky. This does not greatly affect the visit's schedulability. 12 false 0.0 false false false false false SUPPORTED STELLAR CLUSTER OB ASSOCIATION STAR FORMING REGION OPEN CLUSTER Desired magnitudes limits: I = 25, Z= 24.5, J= 21.5, H= 20.5 (standard filters) M16 EAGLE-NEBULA J2000 00 00 0.0000 +00 00 0.00 J2000 STELLAR CLUSTER OB ASSOCIATION STAR FORMING REGION Desired magnitudes limits: I = 25, Z= 24.5, J= 21.5, H= 20.5 (standard filters) M16 EAGLE-NEBULA J2000 00 00 0.0000 +00 00 0.00 J2000 POS-TARG DITHER 3.011 LINE false false 4 85.28 ACS-WFC-DITHER-LINE 1 false POS-TARG DITHER DITHER 1.0 NIC-XSTRIP-DITH false false 4 0.0 POS-TARG NIC-SPIRAL-DITH 0.0 2 false (Tic-Visit :proposal-id 10533 :visit-id "01" :proposal-version -1 :trans-version "20050323" :date "10-May-2005 16:41:34.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 2273792 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 10533 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 10533 :visit-id "01" :orbit-number 1 :pcs-time 367 :si-vis-utilization 2728 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3251 :pcs-gap 0 ) (Tic-Orbit :proposal-id 10533 :visit-id "01" :orbit-number 2 :pcs-time 367 :si-vis-utilization 2642 :al-overhead-at-end 0 :internal-dur-at-end 349 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3251 :pcs-gap 0 ) true 2 0 (Tic-Visit :proposal-id 10533 :visit-id "02" :proposal-version -1 :trans-version "20050323" :date "10-May-2005 16:43:11.0" :trans-errors '(:WARNINGS 24 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 5 :saa-model "23" :si-bright-earth-limb-angle 20.0 :data-volume 2208784 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 10533 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Obset :proposal-id 10533 :visit-id "02" :obset-id "A2" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 10533 :visit-id "02" :orbit-number 1 :pcs-time 367 :si-vis-utilization 2689 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3251 :pcs-gap 0 ) (Tic-Orbit :proposal-id 10533 :visit-id "02" :orbit-number 2 :pcs-time 367 :si-vis-utilization 2686 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3251 :pcs-gap 0 ) (Tic-Orbit :proposal-id 10533 :visit-id "02" :orbit-number 3 :pcs-time 367 :si-vis-utilization 2686 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3251 :pcs-gap 0 ) (Tic-Orbit :proposal-id 10533 :visit-id "02" :orbit-number 4 :pcs-time 367 :si-vis-utilization 2643 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3251 :pcs-gap 0 ) (Tic-Orbit :proposal-id 10533 :visit-id "02" :orbit-number 5 :pcs-time 367 :si-vis-utilization 2649 :al-overhead-at-end 0 :internal-dur-at-end 136 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3251 :pcs-gap 0 ) false 5 0