7417( 11) - 10/13/97 10:32 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 7417 Version: 11 Check-in Date: 13-Oct-1997 10:30:30 1.Proposal Title: Probing the Very Low Mass IMF: Brown Dwarf Stars in Star--Forming Regions ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 7 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: MICHAEL R. MEYER STEWARD OBSERVATORY CoI: John Carpenter Institute for Astronomy-Hawaii N CoI: Hua Chen Steward Observatory N CoI: Catherine Dougados Observatoire de Grenoble N CoI: Lynne Hillenbrand University of California-Berkeley N CoI: Steve Strom University of Massachusetts N CoI: France Allard Witchita State University N ------------------------------------------------------------------------------------ 5. Abstract We propose to characterize the shape of the IMF near the sub-- stellar limit from HST observations of the rich embedded cluster associated with the Mon R2 nebula. This newly--formed cluster (age < 1 Myr) contains more than 100 stars whose luminosities suggest masses ranging from 0.03-0.4 M_\odot. Our study will be performed in two steps; first constructing an observed H--R diagram for a flux-- limited sample of stars within cluster; and then estimating the stellar mass for each star with the aid of PMS evolutionary tracks. Recent observations and model calculations suggest that low resolution (R ~ 200) J-- and H--band spectra obtained with NICMOS will permit classification of a large number of stars with the accuracy needed to place the stars on the H--R diagram. Due the difficulties experienced by the NIC3 camera, we have chosen to alter our program to take advantage of the unique capabilities still afforded by NICMOS with NIC2. Our overall goal -- characterizing the shape of the initial mass function of the Mon R2 cluster -- remains the same. However we now combine a deep infrared imaging survey of the cluster with narrow-- band filter photometry aimed at deriving both the extinction and effective temperature of a sample complete down to 0.05 Msun. While we cannot derive the detailed shape of the IMF in the sub--stellar regime from this reconstituted program, we will still be able to discern whether or not the initial mass function of the Mon R2 cluster turns over near the hydrogen burning limit, or continues to rise well into the brown dwarf regime. ------------------------------------------------------------------------------------ 7417( 11) - 10/13/97 10:32 - [ 2] Observations Description ------------------------ We have outlined a program of deep near--IR imaging in order to characterize the stellar population of Mon R2 down into the brown dwarf regime. The J- H- and K- band survey should be sensitive to stars down the the hydrogen burning limit at an age of up to 3 x10^6 yrs see through Av < 29.0m (J-band); Av < 33.0m (H-band) and Av < 47.0m (K-band). These limits correspond to 10sigma detection limits of J < 24.0m; H < 21.0m; and K < 20.0m. This will be the deepest highest resolution survey of an embedded cluster to date. We will perform spiral-dither maps resulting in 4 x 4 mosaics of the Mon R2 cluster covering 65" x 65". Each mosaic position will be offset by 15.45" leaving 20 % overlap of 50 pixels (3.75") with the previous position. This will allow us to construct a perfectly registered mosaic from the data itself, even with small telescope pointing errors. Then the target will be repositioned (+3.45", +3.45") and the spiral dither pattern repeated in order to remove bad pixels, correct for cosmic rays, and the coronographic hole in the NIC2 images. We have chosen filters F110W for the J-band, F160W for the H-band, and F207M for the K- band. The reason for choosing F207M was two-fold; i) we should have to obtain separate background measurements for this filter as the observations will still be read-noise limited; and ii) F207M does not overlap with F160W perhaps providing additional spectroscopic information on the spectral energy distribution of the source. The loss in sensitivity due to our choice of the F207M filter is compensated by the fact that we would incurr large additional overheads in ``chopping'' to remove the thermal background from the F205W filter. We have chosen the narrow-band filter F165M in order to form the temperature sensitive F160W/F165M filter. The wings of the F160W filter are dominated by broad H2O absorption bands which when ratioed with the F165M narrow-band filter form a spectral-type indicator. We estimate that with filter -photometric measurements good to +- 1.4 % (1 % per filter) we can estimate effective temperatures to within +- 100 K at temperatures < 3000 K. While this filter-index remains to be calibrated (primarily through our previous ground- based spectroscopic samples of late-type stars within our target fields), we feel confident that we will be able to at least distinguish those stars with Teff < 3000 and those Teff > 3000. This temperature corresponds to that expected for a brown dwarf at the age of the Mon R2 cluster. Thus the ratio of stars cooler than and hotter than 3000 K will provide an estimate of the ratio of brown dwarfs to stellar mass obejcts in Mon R2. This is a compromise program from our original goal of constructing the frequency distribution of spectral types for stars in the cluster, but will still allow us to assess whether or not the mass function turns over near the hydrogen burning limit in Mon R2. This filter-photometric index is (weakly) dependent on extinction. However the "J-H" vs. F160W/F165M color-color diagram will allow us to estimate both Teff and Av. The J-H measurements are essential for estimating the magnitude of the extinction and its effect on our estimate of effective temperature. We have assumed that infrared excess emission can safely be ignored at wavelengths < 2.0 microns. While there is some evidence supporting this in the literature, we feel it is crucial to estimate the magnitude of possible infrared excess by obtaining K-band measurements as well. For stars with very large H-K excess, we will have to consider the possible effects this can have on both our extinction estimates as well as determination of effective temperature. We note that the imaging survey will be at much higher spatial resolution than our originally proposed observations. We hope to make use of this fact to assess the effects of newly resolved binaries on the shape of the IMF. Real Time Justification ----------------------- We have utilized our full 14 orbits as efficiently as possible. We require the integration times given in order to achieve 1 % photometry in the H-band filter index for stars 10^6 yrs old (the estimated age of the cluster) down to 0.05 Msun viewed through Av < 15.0m of extinction. This will allow us to estimate temperatures +- 100 K for Teff < 3000 K. The J- and K-band limits were chosen to complete sample this population as well as go deep enough to fully assess the cluster population more than halfway thorugh the dense molecular cloud core. This will tell us whether or not we are fully sampling the stellar population of the cluster with our "spectroscopic" survey or merely scratching the surface of a more deeply embedded heretofore unknown population. This will be the deepest high resolution survey of an embedded cluster of which we are aware. Calibration Justification ------------------------- None requested. Additional Comments ------------------- ------------------------------------------------------------------------------------ 7417( 11) - 10/13/97 10:32 - [ 3] Data Distribution Media: ELECTRONIC Blocking Factor: 10 Ship To: Steward Observatory, University of Arizona, Tucson, AZ 85721-0065 Ship Via: Email: mmeyer@as.arizona.edu ------------------------------------------------------------------------------------ 7417( 11) - 10/13/97 10:32 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 MON-R2-POS1 STELLAR CLUSTER,STAR RA=6H 5M 18.98S +/- 0.0S,DEC=-6D B1950 H = 10+/-0.3 FORMING REGION 22' 32.82" +/- 0.0" 2 MON-R2-POS2 STELLAR CLUSTER,STAR RA=6H 5M 19.08S +/- 0.0S,DEC=-6D B1950 H = 10+/-0.3 FORMING REGION 22' 31.34" +/- 0.0" 7417( 11) - 10/13/97 10:32 - [ 5] Visit: 01 Visit Priority: Visit Requirements: ORIENT 300D TO 330D SCHED 100% On Hold Comments: Additional Comments: 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 MON-R2-POS1 NIC2 MULTIAC NIC2-FI F110W 1.10 SAMP-SEQ=STEP32,NSAMP=15, 1 DEF PAR 11-12 WITH 10 CUM X PATTERN=SPIRAL-DITH,NUM-POS=16, DITH-SIZE=15.45, PATTERN-ORIENT=DETECTOR ------------------------------------------------------------------------------------------------------------------------------------ 11 MON-R2-POS1 NIC1 MULTIAC NIC1-FI F110M 1.10 SAMP-SEQ=STEP32,NSAMP=15 1 DEF CUM X ------------------------------------------------------------------------------------------------------------------------------------ 12 MON-R2-POS1 NIC3 MULTIAC NIC3-FI F110W 1.10 SAMP-SEQ=STEP32,NSAMP=15 1 DEF CUM X ------------------------------------------------------------------------------------------------------------------------------------ 20 MON-R2-POS2 NIC2 MULTIAC NIC2-FI F110W 1.10 SAMP-SEQ=STEP32,NSAMP=15, 1 DEF PAR 21-22 WITH 20 CUM X PATTERN=SPIRAL-DITH,NUM-POS=16, DITH-SIZE=15.45, PATTERN-ORIENT=DETECTOR ------------------------------------------------------------------------------------------------------------------------------------ 21 MON-R2-POS2 NIC1 MULTIAC NIC1-FI F110M 1.10 SAMP-SEQ=STEP32,NSAMP=15 1 DEF CUM X ------------------------------------------------------------------------------------------------------------------------------------ 22 MON-R2-POS2 NIC3 MULTIAC NIC3-FI F110W 1.10 SAMP-SEQ=STEP32,NSAMP=15 1 DEF CUM X ------------------------------------------------------------------------------------------------------------------------------------ 30 MON-R2-POS1 NIC2 MULTIAC NIC2-FI F160W 1.60 SAMP-SEQ=STEP16,NSAMP=17, 1 DEF PAR 31-32 WITH 30 CUM X PATTERN=SPIRAL-DITH,NUM-POS=16, DITH-SIZE=15.45, PATTERN-ORIENT=DETECTOR ------------------------------------------------------------------------------------------------------------------------------------ 31 MON-R2-POS1 NIC1 MULTIAC NIC1-FI F145M 1.45 SAMP-SEQ=STEP16,NSAMP=17 1 DEF CUM X ------------------------------------------------------------------------------------------------------------------------------------ 32 MON-R2-POS1 NIC3 MULTIAC NIC3-FI F110W 1.10 SAMP-SEQ=STEP16,NSAMP=17 1 DEF CUM X ------------------------------------------------------------------------------------------------------------------------------------ 40 MON-R2-POS2 NIC2 MULTIAC NIC2-FI F160W 1.60 SAMP-SEQ=STEP16,NSAMP=17, 1 DEF PAR 41-42 WITH 40 CUM X PATTERN=SPIRAL-DITH,NUM-POS=16, DITH-SIZE=15.45, PATTERN-ORIENT=DETECTOR ------------------------------------------------------------------------------------------------------------------------------------ 41 MON-R2-POS2 NIC1 MULTIAC NIC1-FI F145M 1.45 SAMP-SEQ=STEP16,NSAMP=17 1 DEF CUM X ------------------------------------------------------------------------------------------------------------------------------------ 42 MON-R2-POS2 NIC3 MULTIAC NIC3-FI F110W 1.10 SAMP-SEQ=STEP16,NSAMP=17 1 DEF CUM X ------------------------------------------------------------------------------------------------------------------------------------ 7417( 11) - 10/13/97 10:32 - [ 6] Visit: 02 Visit Priority: Visit Requirements: SAME ORIENT AS 1 SCHED 100% On Hold Comments: Additional Comments: Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 50 MON-R2-POS1 NIC2 MULTIAC NIC2-FI F165M 1.65 SAMP-SEQ=STEP32,NSAMP=16, 1 DEF PAR 51-52 WITH 50 CUM X PATTERN=SPIRAL-DITH,NUM-POS=16, DITH-SIZE=15.45, PATTERN-ORIENT=DETECTOR ------------------------------------------------------------------------------------------------------------------------------------ 51 MON-R2-POS1 NIC1 MULTIAC NIC1-FI F145M 1.45 SAMP-SEQ=STEP32,NSAMP=16 1 DEF CUM X ------------------------------------------------------------------------------------------------------------------------------------ 52 MON-R2-POS1 NIC3 MULTIAC NIC3-FI F160W 1.60 SAMP-SEQ=STEP32,NSAMP=16 1 DEF CUM X ------------------------------------------------------------------------------------------------------------------------------------ 60 MON-R2-POS2 NIC2 MULTIAC NIC2-FI F165M 1.65 SAMP-SEQ=STEP32,NSAMP=16, 1 DEF PAR 61-62 WITH 60 CUM X PATTERN=SPIRAL-DITH,NUM-POS=16, DITH-SIZE=15.45, PATTERN-ORIENT=DETECTOR ------------------------------------------------------------------------------------------------------------------------------------ 61 MON-R2-POS2 NIC1 MULTIAC NIC1-FI F145M 1.45 SAMP-SEQ=STEP32,NSAMP=16 1 DEF CUM X ------------------------------------------------------------------------------------------------------------------------------------ 62 MON-R2-POS2 NIC3 MULTIAC NIC3-FI F160W 1.60 SAMP-SEQ=STEP32,NSAMP=16 1 DEF CUM X ------------------------------------------------------------------------------------------------------------------------------------ 70 MON-R2-POS1 NIC2 MULTIAC NIC2-FI F207M 2.07 SAMP-SEQ=STEP16,NSAMP=15, 1 DEF PAR 71-72 WITH 70 CUM X PATTERN=SPIRAL-DITH,NUM-POS=16, DITH-SIZE=15.45, PATTERN-ORIENT=DETECTOR ------------------------------------------------------------------------------------------------------------------------------------ 71 MON-R2-POS1 NIC1 MULTIAC NIC1-FI F165M 1.65 SAMP-SEQ=STEP16,NSAMP=15 1 DEF CUM X ------------------------------------------------------------------------------------------------------------------------------------ 72 MON-R2-POS1 NIC3 MULTIAC NIC3-FI F175W 1.75 SAMP-SEQ=STEP16,NSAMP=15 1 DEF CUM X ------------------------------------------------------------------------------------------------------------------------------------ 80 MON-R2-POS2 NIC2 MULTIAC NIC2-FI F207M 2.07 SAMP-SEQ=STEP16,NSAMP=15, 1 DEF PAR 81-82 WITH 80 CUM X PATTERN=SPIRAL-DITH,NUM-POS=16, DITH-SIZE=15.45, PATTERN-ORIENT=DETECTOR ------------------------------------------------------------------------------------------------------------------------------------ 81 MON-R2-POS2 NIC1 MULTIAC NIC1-FI F165M 1.65 SAMP-SEQ=STEP16,NSAMP=15 1 DEF CUM X ------------------------------------------------------------------------------------------------------------------------------------ 82 MON-R2-POS2 NIC3 MULTIAC NIC3-FI F175W 1.75 SAMP-SEQ=STEP16,NSAMP=15 1 DEF CUM X ------------------------------------------------------------------------------------------------------------------------------------ 7417( 11) - 10/13/97 10:32 - [ 7] Summary Form for Proposal 7417 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations NIC2 NIC1 NIC3 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes MULTIACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters SAMP-SEQ=STEP32 NSAMP=15 PATTERN=SPIRAL-DITH NUM-POS=16 DITH-SIZE=15.45 PATTERN-ORIENT=DETECTOR NSAMP=17 SAMP-SEQ=STEP16 NSAMP=16 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 300D TO 330D SCHED 100% PAR 11-12 WITH 10 PAR 21-22 WITH 20 PAR 31-32 WITH 30 PAR 41-42 WITH 40 SAME ORIENT AS 1 SCHED 100% PAR 51-52 WITH 50 PAR 61-62 WITH 60 PAR 71-72 WITH 70 PAR 81-82 WITH 80 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F110W F110M F160W F145M F165M F207M F175W ------------------------------------------------------------------------------------------------------------------------------------ Target Names MON-R2-POS1 MON-R2-POS2 ------------------------------------------------------------------------------------------------------------------------------------