More than 100 methane brown dwarfs, or T dwarfs, have now been discovered in the local field with 2MASS, SLOAN and UKIDSS, opening up a new area of physics describing objects at 450-1400 K. However, very few calibrator objects exist with well established ages and metallicities. A very surprising result from the UKIDSS sample (supported by 2MASS and SLOAN) is that the substellar mass function in the local field appears to decline to lower masses, in marked contrast to the rising initial mass function (IMF) observed in young clusters. Given that such a difference between the present day IMF and the Galactic time-averaged IMF is unlikely, it is very possible that the apparently falling IMF is an artifact of serious errors in either T model atmospheres or the evolutionary isochrones. We propose WFC3 spectroscopy of 4 faint T dwarf calibrators with well established ages and metallicities in the Pleiades and Sigma Ori clusters, and 2 faint field T dwarfs from UKIDSS for comparison. These spectra will constitute vital calibration data for T dwarf atmospheres with a wide range of surface gravities, which will be used to test and improve the model atmospheres. They will also aid preparation for future spectroscopy of the much larger numbers of field T dwarfs to soon be found by VISTA and WISE. These new surveys will permit a more precise measurement of the mass function and detection of even cooler objects.

This project takes slitless WFC3 spectroscopy of 6 brown dwarfs with the G141 grism. One brown dwarf is observed in each of the 6 orbits, in a single visit. COOL STARS 12 false 0.0 0.0 false false false false false false SUPPORTED STAR BROWN DWARF This object was generated by the targetselector and retrieved from the SIMBAD database. J = 20.0 H = 20.0 (Vega mag) J2000 03 55 13.0000 +24 36 15.80 J2000 STAR BROWN DWARF This object was generated by the targetselector and retrieved from the SIMBAD database. J = 20.3 Z = 23.6 H~20.3 (Vega mags) J2000 03 47 19.1900 +25 50 53.30 J2000 STAR BROWN DWARF This object was generated by the targetselector and retrieved from the SIMBAD database. J = 20.3 H = 20.4 (Vega mags) J2000 05 38 10.1000 -02 36 26.00 J2000 STAR BROWN DWARF This object was generated by the targetselector and retrieved from the SIMBAD database. J = 20.9 H = 20.8 (Vega mags) J2000 05 38 14.4900 -02 45 11.80 J2000 STAR BROWN DWARF This object was generated by the targetselector and retrieved from the 2MASS database. J = 19.1 H = 19.7 (Vega mags) J2000 01 59 33.7100 -00 22 4.60 J2000 STAR BROWN DWARF J = 19.0 H = 19.5 (Vega mags) J2000 09 03 7.6200 +07 57 10.80 J2000 WFC3/IR Imaging No No F140W WFC3/IR Spectroscopic No No G141 WFC3/IR Imaging No No F140W WFC3/IR Spectroscopic No No G141 WFC3/IR Imaging No No F140W WFC3/IR Spectroscopic No No G141 WFC3/IR Imaging No No F140W WFC3/IR Spectroscopic No No G141 WFC3/IR Imaging No No F140W WFC3/IR Spectroscopic No No G141 WFC3/IR Imaging No No F140W WFC3/IR Spectroscopic No No G141 POS-TARG DITHER 0.384 This is pattern E4 from the Dithering Stategies ISR by Dahlen et al. LINE 5.165 false false 14.087 4 151.798 WFC3-IR-DITHER-BOX-MIN 1 false The scheduling data was generated by CASM 18.3.1. CASM was run in Phase II mode. Observation of Target 2. The ORIENT ranges are carefully selected to prevent overlap of spectra of stars and galaxies in the field. We want the spectrum to be dispersed towards either Position Angle=263.5 to 269.4 on the sky or PA=273.5 to 282.3 degrees. Calculation is ORIENT=PA+225-0.5+360, where 225 is the WFC3 IR +X instrument orientation and the -0.5 degrees allows for the slight tilt of the spectra with respect to the X-axis. The scheduling window is narrow (about 3 days) so if this is too tight I would suggest reducing the exposure time slightly (e.g. to SAMP=12 per sub-exposure) so that the visit is easier to schedule. There is a fairly bright star located 24 arcsec west of the target but we believe that the 1st order WFC3 spectra will only be 21 arcsec long so there should be no overlap. The zero order image of the bright star should also not overlap. (Tic-Visit :proposal-id 12217 :visit-id "01" :proposal-version -1 :trans-version "20100505" :date "09-Jul-2010 17:25:16.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "30" :si-bright-earth-limb-angle 20.0 :data-volume 1253440 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12217 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12217 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2825 :al-overhead-at-end 0 :internal-dur-at-end 293 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3249 :pcs-gap 0 ) true 1 0 The scheduling data was generated by CASM 18.3.1. CASM was run in Phase II mode. Observation of Target 2. The ORIENT ranges are carefully selected to prevent overlap of spectra of stars and galaxies in the field. For this target a galaxy close by significantly restricted the range of possible angles, as noted in the Phase I proposal. We want the spectrum to be dispersed towards either Position Angle=292.7 to 295.5 on the sky or PA=299.0 to 309.2 degrees. Calculation is ORIENT=PA+225-0.5, where 225 is the WFC3 IR +X instrument orientation and the -0.5 degrees allows for the slight tilt of the spectra with respect to the X-axis. (Tic-Visit :proposal-id 12217 :visit-id "02" :proposal-version -1 :trans-version "20100505" :date "09-Jul-2010 14:22:31.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "30" :si-bright-earth-limb-angle 20.0 :data-volume 1148976 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12217 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12217 :visit-id "02" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2605 :al-overhead-at-end 0 :internal-dur-at-end 521 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3257 :pcs-gap 0 ) true 1 0 The time on source had to be reduced for this target from the usual 4x603 sec (NSAMP=13) to 4x553 sec (NSAMP=12) in order to allow the visit to be scheduled, owing to the restrictions on the ORIENT angle. The scheduling data was generated by CASM 18.3.1. CASM was run in Phase II mode. Observation of Target 3. The ORIENT ranges are carefully selected to prevent overlap of spectra of stars and galaxies in the field. 1283720948000 262.780999290465 (Tic-Visit :proposal-id 12217 :visit-id "03" :proposal-version -1 :trans-version "20100505" :date "09-Jul-2010 18:59:04.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "30" :si-bright-earth-limb-angle 20.0 :data-volume 1253440 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12217 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12217 :visit-id "03" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2825 :al-overhead-at-end 0 :internal-dur-at-end 293 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3234 :pcs-gap 0 ) true 1 0 The scheduling data was generated by CASM 18.3.1. CASM was run in Phase II mode. Observation of Target 4. The ORIENT ranges are carefully selected to prevent overlap of spectra of stars and galaxies in the field. 1286338231000 276.0611833557539 (Tic-Visit :proposal-id 12217 :visit-id "04" :proposal-version -1 :trans-version "20100505" :date "09-Jul-2010 19:25:33.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "30" :si-bright-earth-limb-angle 20.0 :data-volume 1253440 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12217 :visit-id "04" :obset-id "04" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12217 :visit-id "04" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2825 :al-overhead-at-end 0 :internal-dur-at-end 293 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3234 :pcs-gap 0 ) true 1 0 The scheduling data was generated by CASM 18.3.1. CASM was run in Phase II mode. Observation of Target 5. The ORIENT ranges are carefully selected to prevent overlap of spectra of 2 stars in the field. 1285347780000 248.4414683542591 (Tic-Visit :proposal-id 12217 :visit-id "05" :proposal-version -1 :trans-version "20100505" :date "09-Jul-2010 19:41:53.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "30" :si-bright-earth-limb-angle 20.0 :data-volume 1253440 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12217 :visit-id "05" :obset-id "05" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12217 :visit-id "05" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2825 :al-overhead-at-end 0 :internal-dur-at-end 293 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3234 :pcs-gap 0 ) true 1 0 The scheduling data was generated by CASM 18.3.1. CASM was run in Phase II mode. Observation of Target 6. The ORIENT ranges are carefully selected to prevent overlap of spectra of several stars in the field. 1286252416000 280.0 (Tic-Visit :proposal-id 12217 :visit-id "06" :proposal-version -1 :trans-version "20100505" :date "09-Jul-2010 20:09:19.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "30" :si-bright-earth-limb-angle 20.0 :data-volume 1253440 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12217 :visit-id "06" :obset-id "06" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12217 :visit-id "06" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2825 :al-overhead-at-end 0 :internal-dur-at-end 293 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3242 :pcs-gap 0 ) true 1 0 Observation of Target 6. The ORIENT ranges are carefully selected to prevent overlap of spectra of several stars in the field. This is a repeat of visit 6 which failed due to a spacecraft problem. (Tic-Visit :proposal-id 12217 :visit-id "06" :proposal-version -1 :trans-version "20100505" :date "09-Jul-2010 20:09:19.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "30" :si-bright-earth-limb-angle 20.0 :data-volume 1253440 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12217 :visit-id "06" :obset-id "06" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12217 :visit-id "06" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2825 :al-overhead-at-end 0 :internal-dur-at-end 293 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3242 :pcs-gap 0 ) false 1 0