7952( 4) - 03/18/98 11:24 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 7952 Version: 4 Check-in Date: 11-Mar-1998 14:06:08 1.Proposal Title: Are free-floating brown dwarfs single? ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO/DD 7 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: EDUARDO MARTIN UNIVERSITY OF CALIFORNIA AT BERKELEY CoI: Gibor Basri University of California at Berkeley N 7952( 4) - 03/18/98 11:24 - [ 2] ------------------------------------------------------------------------------------ 5. Abstract Very recently the first two free-floating brown dwarfs have been discovered. They have been published in the last few weeks (Delfosse et al. 1997 AA, 327, L25; Ruiz et al. 1997 ApJ, 491, L107). High resolution Keck spectroscopy has confirmed strong lithium lines in both of them (Martin et al. 1997, AA, 327, L29; Basri et al. 1997, in "Cool Stars X"). The temperature and lithium of these brown dwarfs imply that they are less massive than 60 Jupiters and younger than 1 Gyr. If they have companions, those would be still less massive and thus would be low-mass brown dwarfs or giant planets. NICMOS observations can detect companions with masses as low as ~ 5 Jupiters around these brown dwarfs at separations comparable to our solar system's outer planets. This proposal was not submitted to the most recent TAC because the two discovery papers had not yet been accepted for publication. The need for NICMOS implies that the proposed observations cannot wait until the next TAC for evaluation. Brown Dwarfs (BDs) have become astronomical objects only in the last 2 years. In 1995, the first two uncontrovertible BDs were announced, one in the Pleiades cluster (Teide1, Rebolo et al. 1995, Nature, 377, 129) and the other in the vicinity of a nearby star (Gliese 229B, Nakajima et al. 1995, Nature, 378, 463). Both of them have been subsequently confirmed with follow- up spectroscopic observations (Rebolo et al. 1996, ApJ, 469, L53; Matthews et al. 1996, AJ, 112, 1678). More BDs are continuing to be revealed in the Pleiades cluster (Zapatero- Osorio et al. 1997, 491, L81) indicating that they are quite numerous. Wide field deep searches are also starting to provide the first discoveries of nearby free- floating BDs. The first two such objects have just been published. It is fortunate that we are still in time to use HST NICMOS to look for faint companions to them. The presence of lithium in both BDs confirms that they have substellar masses of less than 60 Jupiters because otherwise this fragile element would had been burned and depleted (Magazzu et al. 1993, ApJ, 404, L17). It also implies that they are quite young, because BDs cool to lower temperatures and fade to lower luminosities with time. If these BDs had been older they would not have been detected yet. The present surveys are flux-limited and hence they favour the detection of young BDs which are still up in their cooling tracks. The youth of these BDs implies that it is easier to detect even lower mass companions orbiting them. HST NICMOS is needed because of its combination of high spatial resolution and sensitivity to very cool objects. It has already been shown that HST/NICMOS has much superior expected performance for detecting companions to BDs than HST/WFPC or any ground-based instrument currently available (see HST proposal 7899). The two nearby BDs that we propose to observe have distances of only about 10--15 parsecs. Thus, the likelihood of detecting companions is much increased with respect to the more distant BDs of the Pleiades. Both BDs have high galactic latitude and high proper motions. Thus, we do not expect a high density of background objects, and we will check the proper motion of any faint close companion in a few months. ------------------------------------------------------------------------------------ 7952( 4) - 03/18/98 11:24 - [ 3] Observations Description ------------------------ We have estimated the brightness differences between our targets and companions of masses in the range 10 to 5 Jupiters. We have assumed a plausible range of masses and ages for our targets of 60 to 50 Jupiters and 1 to 0.5 Gigayears, respectively. Using the latest evolutionary calculations (Burrows et al. 1997 in "Brown Dwarfs and Extrasolar Planets" ASP Conf. Series, Vol. 134, in press), we obtain magnitude differences between 4 and 9 mag. in the H-band depending on the possible combinations of masses and ages. The magnitude differences in J and K are always larger than in H. Thus, H-band is the privileged window for this search. We propose to use the NIC2-F165M combination, which gives an excellent compromise of spatial resolution and throughput. The broader F165W filter is not desirable because it includes deep molecular bands in very cool objects and increases the magnitude differences. We estimate that one orbit per target is sufficient for a 5 sigma detection of companions down to 5 Jupiter masses separated from the primary more than about 1.5 AU. If our targets have companions at the same distance than Jupiter from the Sun, it will be relatively easy to resolve them with NICMOS. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: ------------------------------------------------------------------------------------ 7952( 4) - 03/18/98 11:24 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 KELU1 STAR, Brown Dwarf RA=13H 05M 40.2S +/- 0.1S,DEC=- J2000 V = 22.1 25D 41' 06.0" +/- 1.0" I = 16.8 J = 13.2 2 DENISJ1228- STAR, Brown Dwarf RA=12H 28M 15.29S +/- 0.1S,DEC=- J2000 V = 23 1547 15D 47' 34.5" +/- 1.0" I = 18.2 J = 14.4 7952( 4) - 03/18/98 11:24 - [ 5] Visit: 01 Visit Priority: Visit Requirements: SCHED 90% 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 ------------------------------------------------------------------------------------------------------------------------------------ 1 KELU1 NIC1 MULTIAC NIC1-FI F110M PATTERN=XSTRIP-DITH,NUM-POS=2, 1 DEF PAR 2-3 WITH 1 POS TARG CUM X DITH-SIZE=1.105,SAMP-SEQ=STEP64, 0.552,0 NSAMP=15 ------------------------------------------------------------------------------------------------------------------------------------ 2 ANY NIC2 MULTIAC NIC2 F110W SAMP-SEQ=SPARS64,NSAMP=9 1 DEF CUM ------------------------------------------------------------------------------------------------------------------------------------ 3 ANY NIC3 MULTIAC NIC3 F110W SAMP-SEQ=SPARS64,NSAMP=9 1 DEF CUM ------------------------------------------------------------------------------------------------------------------------------------ 4 KELU1 NIC1 MULTIAC NIC1-FI F145M PATTERN=XSTRIP-DITH,NUM-POS=2, 1 DEF PAR 5-6 WITH 4 POS TARG CUM X DITH-SIZE=1.105,SAMP-SEQ=STEP64, 0.552,0 NSAMP=14 ------------------------------------------------------------------------------------------------------------------------------------ 5 ANY NIC2 MULTIAC NIC2 F165M SAMP-SEQ=SPARS64,NSAMP=8 1 DEF CUM ------------------------------------------------------------------------------------------------------------------------------------ 6 ANY NIC3 MULTIAC NIC3 G096 SAMP-SEQ=SPARS64,NSAMP=8 1 DEF CUM ------------------------------------------------------------------------------------------------------------------------------------ 7 KELU1 NIC1 MULTIAC NIC1-FI F165M PATTERN=XSTRIP-DITH,NUM-POS=2, 1 DEF PAR 8-9 WITH 7 POS TARG CUM X DITH-SIZE=1.105,SAMP-SEQ=STEP64, 0.552,0 NSAMP=14 ------------------------------------------------------------------------------------------------------------------------------------ 8 ANY NIC2 MULTIAC NIC2 F180M SAMP-SEQ=SPARS64,NSAMP=8 1 DEF CUM ------------------------------------------------------------------------------------------------------------------------------------ 9 ANY NIC3 MULTIAC NIC3 G096 SAMP-SEQ=SPARS64,NSAMP=8 1 DEF CUM ------------------------------------------------------------------------------------------------------------------------------------ 7952( 4) - 03/18/98 11:24 - [ 6] Visit: 02 Visit Priority: Visit Requirements: SCHED 90% 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 ------------------------------------------------------------------------------------------------------------------------------------ 1 DENISJ1228- NIC1 MULTIAC NIC1-FI F110M PATTERN=XSTRIP-DITH,NUM-POS=2, 1 DEF PAR 2-3 WITH 1 POS TARG 1547 CUM X DITH-SIZE=1.105,SAMP-SEQ=STEP64, 0.552,0 NSAMP=15 ------------------------------------------------------------------------------------------------------------------------------------ 2 ANY NIC2 MULTIAC NIC2 F110W SAMP-SEQ=SPARS64,NSAMP=9 1 DEF CUM ------------------------------------------------------------------------------------------------------------------------------------ 3 ANY NIC3 MULTIAC NIC3 F110W SAMP-SEQ=SPARS64,NSAMP=9 1 DEF CUM ------------------------------------------------------------------------------------------------------------------------------------ 4 DENISJ1228- NIC1 MULTIAC NIC1-FI F145M PATTERN=XSTRIP-DITH,NUM-POS=2, 1 DEF PAR 5-6 WITH 4 POS TARG 1547 CUM X DITH-SIZE=1.105,SAMP-SEQ=STEP64, 0.552,0 NSAMP=14 ------------------------------------------------------------------------------------------------------------------------------------ 5 ANY NIC2 MULTIAC NIC2 F165M SAMP-SEQ=SPARS64,NSAMP=8 1 DEF CUM ------------------------------------------------------------------------------------------------------------------------------------ 6 ANY NIC3 MULTIAC NIC3 G096 SAMP-SEQ=SPARS64,NSAMP=8 1 DEF CUM ------------------------------------------------------------------------------------------------------------------------------------ 7 DENISJ1228- NIC1 MULTIAC NIC1-FI F165M PATTERN=XSTRIP-DITH,NUM-POS=2, 1 DEF PAR 8-9 WITH 7 POS TARG 1547 CUM X DITH-SIZE=1.105,SAMP-SEQ=STEP64, 0.552,0 NSAMP=14 ------------------------------------------------------------------------------------------------------------------------------------ 8 ANY NIC2 MULTIAC NIC2 F180M SAMP-SEQ=SPARS64,NSAMP=8 1 DEF CUM ------------------------------------------------------------------------------------------------------------------------------------ 9 ANY NIC3 MULTIAC NIC3 G096 SAMP-SEQ=SPARS64,NSAMP=8 1 DEF CUM ------------------------------------------------------------------------------------------------------------------------------------ 7952( 4) - 03/18/98 11:24 - [ 7] Summary Form for Proposal 7952 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations NIC1 NIC2 NIC3 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes MULTIACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters PATTERN=XSTRIP-DITH NUM-POS=2 DITH-SIZE=1.105 SAMP-SEQ=STEP64 NSAMP=15 NSAMP=9 SAMP-SEQ=SPARS64 NSAMP=14 NSAMP=8 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO/DD ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements SCHED 90% PAR 2-3 WITH 1 POS TARG 0.552,0 PAR 5-6 WITH 4 POS TARG 0.552,0 PAR 8-9 WITH 7 POS TARG 0.552,0 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F110M F110W F145M F165M G096 F180M ------------------------------------------------------------------------------------------------------------------------------------ Target Names KELU1 ANY DENISJ1228-1547 ------------------------------------------------------------------------------------------------------------------------------------