11304( 2) - 06/14/07 14:09 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 11304 Version: 2 Check-in Time: 14-Jun-2007 18:09:02 STScI Edit Number: 0 Title The L/T Transition in the Photospheres of Young Sub-Stellar Companions ------------------------------------------------------------------------------------ Type Cycle Parallel Pointing Tolerance GO 16 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Stanimir A. Metchev University of California - Los Angeles CoI: Dr. Kevin Luhman The Pennsylvania State University N CoI: Dr. Massimo Marengo Smithsonian Institution Astrophysical Y Observatory ------------------------------------------------------------------------------------ Abstract We propose 3.6-8.0 micron IRAC photometry and 5.5?22 micron low-resolution IRS spectroscopy and imaging of the sub-stellar companions to the ~0.3 Gyr old stars HN Peg and HD 203030. The spectral types of the two secondaries span the critical transition between L and T dwarfs, which is characterized by a rapid sedimentation of dust and appearance of methane in sub-stellar photospheres. HN Peg B (T2.5) and HD 203030 B (L7.5) are the youngest known brown dwarfs at this transition, and present a unique opportunity to examine the role of surface gravity in the process. Both objects stand out from 1-10 Gyr L/T transition dwarfs in the field because they are underluminous in the near-IR compared to the expected luminosities for their ages. Probable reasons include: (1) a decrease in the effective temperature at the onset of methane formation at lower surface gravities in sub-stellar photospheres, or (2) a shift in the emitted flux from the near-IR to the mid-IR region of the SED of young brown dwarfs. The mid-IR is key for distinguishing between these two hypotheses because it contains several fundamental molecular transitions that create deep absorption bands in the SEDs of L and T dwarfs, and that are inaccessible for study from the ground. Our existing IRAC photometry of HN Peg B does reveal a 0.3- 0.5 mag excess in its 3.6-8.0 micron SED. However, this excess is insufficient to account for the lower luminosity of HN Peg B, and indicates that both of the above hypotheses may hold true to certain degrees. With the present proposal we aim to independently confirm the gravity-dependent behavior of L/T transition photospheres in the mid-IR through IRAC photometry of HD 203030 B. We will also seek the culprit for the mid-IR excess of HN Peg B through low resolution spectroscopy and peak-up imaging with IRS. To check for possible duplicity of HN Peg B as the reason for its excess, we request high angular resolution imaging with HST to complement our lower resolution Spitzer imaging. ------------------------------------------------------------------------------------ 11304( 2) - 06/14/07 14:09 - [ 2] Observations Description ------------------------ NIC 1 images of target HN Peg B in F090M, F110W and F170 filters. The target is dithered between 5 positions within the NIC1 field of view. At each dither position we obtain 1 MULTIACCUM image in each of the three filters. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- We have adopted the observing strategy of HST Program 10247. ------------------------------------------------------------------------------------ 11304( 2) - 06/14/07 14:09 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 HNPEGB STAR, BROWN DWARF RA=21H44M28.4450S +/- 0.1", J2000 V = 20.0+/-4.0 DEC=+14D46'7.43" +/- 0.1" J = 15.8; H = 15.4; K = 15.1 Reference Frame: ICRS Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 1998.8 0.015405 -0.11345 0.0 11304( 2) - 06/14/07 14:09 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type NIC-SPIRAL-DITH Pattern_Purpose DITHER Number_Of_Points 5 Point_Spacing 1.3 Line_Spacing Coordinate_Frame POS-TARG Pattern_Orient 0.0 Angle_Between_Sides Center_Pattern YES ------------------------------------------------------------------------------------------------------------------------------------ 11304( 2) - 06/14/07 14:09 - [ 5] Visit: 01 Visit Priority: Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 HNPEGB NIC1 MULTIAC NIC1 F090M CAMERA-FOCUS=DEF, 1 DEF SEQ 1-3 NON-INT; PATTERN CUM SAMP-SEQ=SPARS4,NSAMP=7 1 1-3 ------------------------------------------------------------------------------------------------------------------------------------ 2 HNPEGB NIC1 MULTIAC NIC1 F110W CAMERA-FOCUS=DEF, 1 DEF CUM SAMP-SEQ=SPARS32,NSAMP=7 ------------------------------------------------------------------------------------------------------------------------------------ 3 HNPEGB NIC1 MULTIAC NIC1 F170M CAMERA-FOCUS=DEF, 1 DEF CUM SAMP-SEQ=SPARS32,NSAMP=11 ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ HNPEGB 1 NIC1 MULTIAC NIC1 F090M 1 none none none 1 N/A CUM HNPEGB 1 NIC1 MULTIAC NIC1 F090M 2 none none none 1 N/A CUM HNPEGB 1 NIC1 MULTIAC NIC1 F090M 3 none none none 1 N/A CUM HNPEGB 1 NIC1 MULTIAC NIC1 F090M 4 none none none 1 N/A CUM HNPEGB 1 NIC1 MULTIAC NIC1 F090M 5 none none none 1 N/A CUM HNPEGB 2 NIC1 MULTIAC NIC1 F110W 1 none none none 1 N/A CUM HNPEGB 2 NIC1 MULTIAC NIC1 F110W 2 none none none 1 N/A CUM HNPEGB 2 NIC1 MULTIAC NIC1 F110W 3 none none none 1 N/A CUM HNPEGB 2 NIC1 MULTIAC NIC1 F110W 4 none none none 1 N/A CUM HNPEGB 2 NIC1 MULTIAC NIC1 F110W 5 none none none 1 N/A CUM HNPEGB 3 NIC1 MULTIAC NIC1 F170M 1 none none none 1 N/A CUM HNPEGB 3 NIC1 MULTIAC NIC1 F170M 2 none none none 1 N/A CUM HNPEGB 3 NIC1 MULTIAC NIC1 F170M 3 none none none 1 N/A CUM 11304( 2) - 06/14/07 14:09 - [ 6] Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ HNPEGB 3 NIC1 MULTIAC NIC1 F170M 4 none none none 1 N/A CUM HNPEGB 3 NIC1 MULTIAC NIC1 F170M 5 none none none 1 N/A CUM 11304( 2) - 06/14/07 14:09 - [ 7] Summary Form for Proposal 11304 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures NIC1 ------------------------------------------------------------------------------------------------------------------------------------ Configurations NIC1 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes MULTIACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CAMERA-FOCUS=DEF SAMP-SEQ=SPARS4 NSAMP=7 SAMP-SEQ=SPARS32 NSAMP=11 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements SEQ 1-3 NON-INT; PATTERN 1 1-3; ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F090M F110W F170M ------------------------------------------------------------------------------------------------------------------------------------ Target Names HNPEGB ------------------------------------------------------------------------------------------------------------------------------------