Molecular Hydrogen Disks Around T Tauri Stars
We propose to measure the properties of planetary system-sized disks around Sun-like, pre-main sequence stars by imaging the inner parts of these disks for the first time in gaseous emission from their most dominant constituent, molecular hydrogen gas. Specifically, we will use the F212N filter and NICMOS to determine the spatial distribution of ro-vibrational H2 emission from protoplanetary disks around selected classical and weak-lined T Tauri stars. The target stars are among those detected by members of this team through high resolution, ground-based infrared spectroscopy. The spectra reveal H2 emission at the rest velocities of the stars and at positions spatially coincident with the stars at the spatial resolution of the spectroscopic data. This imaging experiment, which is impossible to do using ground-based facilities, is possible using the NICMOS camera aboard the HST because the point spread function of this system is extremely stable and can be measured to a very high accuracy. This experiment is an important test of the interpretation that the 2.122 micron H2 line emission seen toward T Tauri stars is produced at distances of 10 to 30 AU from the stars, the region in which giant planets are expected to form around these stars. These observations will contribute toward developing a better understanding of the process, likelihood, and timescale for the formation of planets around Sun-like stars.
Each of 5 target stars has a near-identical point-source calibrator (same K magnitude and near-IR colors). The goal is to get high SNR measurements of the PSF for the calibrator and identical measurements of the target stars without reaching the non-linear regime for the detectors. Our 'signal' is the difference between these pairs of images.
The observations are straightforward. Ten orbits, one star per orbit. One camera/fitler (NIC2, F212N) combination for the entire 10 orbits. The same NIC-SPIRAL-DITH-CHOP pattern for all ten orbits with the same CHOP (4.826" = 63.5 px) and the same DITH (1.543" = 20.3 px) for all ten orbits. The pattern, the chop length, and the dither size are all selected to obtain a well sampled PSF and to keep the star on the NIC2 array in both CHOP positions.
The only difference between the orbits is the selected pre-defined MULTIACCUM sample sequence for each orbit and the number of steps in the SPIRAL pattern. This sequence is identical for each star in a given target/calibrator pair. For each pair, the K magnitude determines the sample sequence, with a goal of obtaining a maximum flux level of approximately 80% of 'saturation' (as estimated using the NICMOS Exposure Time Calculator; once this sample sequence is determined, the number of steps in the SPIRAL pattern is selected to maximize use of the available visibility time during each orbit.
The five calibrator stars were not identified in the original proposal; however, time was allocated (one orbit per calibrator; five total calibrators) for these observations.
The calibrator stars in the proposal are selected on the basis of having K magnitudes as nearly identical to the targets as possible and having J-H, H-K, and J-K colors as nearly identical to the targets unreddenned colors as possible (selected from the 2MASS database) and then further identified (Hipparcos/Tycho database) as being non-variable, single stars. Otherwise, the calibrators are almost or entirely never-studied objects.
ISM AND CIRCUMSTELLAR MATTER
12
false
0.0
0.0
false
false
false
false
false
SUPPORTED
STAR
T TAURI STAR
K=6.227
DOAR21
J2000
16 26 3.0300
-24 23 36.40
J2000
STAR
T TAURI STAR
K=8.163
J2000
04 39 17.7800
+22 21 3.50
J2000
STAR
T TAURI STAR
K=7.239
J2000
04 51 47.3700
+30 47 13.90
J2000
STAR
T TAURI STAR
K=7.999
J2000
11 12 24.4900
-76 37 5.88
J2000
STAR
T TAURI STAR
K=8.199
J2000
11 02 25.1200
-77 33 35.95
J2000
CALIBRATION
POINT SPREAD FUNCTION
K=6.229
HD7199
HIP5529
J2000
00 00 0.0000
+00 00 0.00
J2000
CALIBRATION
POINT SPREAD FUNCTION
K=8.163
GSC08973-0837
TYC8973-837-1
J2000
00 00 0.0000
+00 00 0.00
J2000
CALIBRATION
POINT SPREAD FUNCTION
K=7.238
BD+29-3192
TYC2104-1043-1
J2000
00 00 0.0000
+00 00 0.00
J2000
CALIBRATION
POINT SPREAD FUNCTION
K=7.999
NLTT22052
GSC01959-00442
J2000
00 00 0.0000
+00 00 0.00
J2000
CALIBRATION
POINT SPREAD FUNCTION
K=8.168
LTT3222
J2000
00 00 0.0000
+00 00 0.00
J2000
NIC2
Imaging
No
No
F212N
NIC2
Imaging
No
No
F212N
NIC2
Imaging
No
No
F212N
NIC2
Imaging
No
No
F212N
NIC2
Imaging
No
No
F212N
POS-TARG
DITHER
BACKGROUND
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1.543
NIC-SPIRAL-DITH-CHOP
false
false
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0.0
POS-TARG
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DITHER
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POS-TARG
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