- Press Release
- Oct 7, 2022
NASA Hubble Space Telescope Daily Report #4914
HUBBLE SPACE TELESCOPE DAILY REPORT #4914
PERIOD COVERED: 5am August 20 – 5am August 21, 2009 (DOY 232/09:00z-233/09:00z)
ACS CCD Monitoring and Calibration for WFC3
This program is a smaller version of our routine CCD monitoring program, designed to run throughout SMOV, after which our regular Cycle 17 CAL proposal will begin. This program obtains the bias and dark frames needed to generate reference files for calibrating science data, and allows us to monitor detector noise and the growth of hot pixels.
Searching for the Bottom of the Initial Mass Function
The measurement of the minimum mass of the IMF would provide a fundamental test of theories of star and planet formation. In a Cycle 13 program, we used ACS and ground- based near-IR imaging and spectroscopy to measure the IMF down to a completeness limit of 10 M_Jup (i~24) in a 800″x1000″ area in the southern subcluster of the Chamaeleon I star-forming region (2 Myr, 160 pc). There is no sign of a low-mass cutoff in this IMF measurement. To provide a better constraint on the minimum mass of the IMF, we propose to obtain ACS images of this field again and use the two ACS epochs to identify substellar cluster members down to the detection limit of the data (i~27) via their proper motions. In this way, we will improve the completeness limit of our IMF measurement to 3 M_Jup. In addition, to improve the number statistics of our measurement of the substellar IMF in Chamaeleon I, we propose to double the number of objects in the IMF sample by performing ACS imaging of a second field toward the northern subcluster.
CCD Stability Monitor
This program will verify that the low frequency flat fielding, the photometry, and the geometric distortion are stable in time and across the field of view of the CCD arrays. A moderately crowded stellar field in the cluster 47 Tuc is observed with the ACS (at the cluster core) and WFC3 (6 arcmin West of the cluster core) using the full suite of broad and narrow band imaging filters. The positions and magnitudes of objects will be used to monitor local and large scale variations in the plate scale and the sensitivity of the detectors and to derive an independent measure of the detector CTE. The UV sensitivity for the SBC and ACS will be addressed in the UV contamination monitor program (11886, PI=Smith).
One additional orbit will be obtained at the beginning of the cycle will allow a verification of the CCD gain ratios for WFC3 using gain 2.0, 1.4, 1.0, 0.5 and for ACS using gain 4.0 and 2.0. In addition, one subarray exposure with the WFC3 will allow a verification that photometry obtained in full-frame and in sub-array modes are repeatable to better than 1%. This test is important for the ACS Photometric Cross- Calibration program (11889, PI=Bohlin) which uses sub-array exposures.
The Ages of Globular Clusters and the Population II Distance Scale
Globular clusters are the oldest objects in the universe whose age can be accurately determined. The dominant error in globular cluster age determinations is the uncertain Population II distance scale. We propose to use FGS 1R to obtain parallaxes with an accuracy of 0.2 milliarcsecond for 9 main sequence stars with [Fe/H] < -1.5. This will determine the absolute magnitude of these stars with accuracies of 0.04 to 0.06mag. This data will be used to determine the distance to 24 metal-poor globular clusters using main sequence fitting. These distances (with errors of 0.05 mag) will be used to determine the ages of globular clusters using the luminosity of the subgiant branch as an age indicator. This will yield absolute ages with an accuracy 5%, about a factor of two improvement over current estimates. Coupled with existing parallaxes for more metal-rich stars, we will be able to accurately determine the age for globular clusters over a wide range of metallicities in order to study the early formation history of the Milky Way and provide an independent estimate of the age of the universe.
The Hipparcos database contains only 1 star with [Fe/H] < -1.4 and an absolute magnitude error less than 0.18 mag which is suitable for use in main sequence fitting. Previous attempts at main sequence fitting to metal-poor globular clusters have had to rely on theoretical calibrations of the color of the main sequence. Our HST parallax program will remove this source of possible systematic error and yield distances to metal- poor globular clusters which are significantly more accurate than possible with the current parallax data. The HST parallax data will have errors which are 10 times smaller than the current parallax data. Using the HST parallaxes, we will obtain main sequence fitting distances to 11 globular clusters which contain over 500 RR Lyrae stars. This will allow us to calibrate the absolute magnitude of RR Lyrae stars, a commonly used Population II distance indicator.
Revealing the Physical Nature of Infrared Luminous Galaxies at 0.3
Boron Abundances in Rapidly Rotating Early-B Stars
Models of rotation in early-B stars predict that rotationally driven mixing should deplete surface boron abundances during the main-sequence lifetime of many stars. However, recent work has shown that many boron depleted stars are intrinsically slow rotators for which models predict no depletion should have occurred, while observations of nitrogen in some more rapidly rotating stars show less mixing than the models predict. Boron can provide unique information on the earliest stages of mixing in B stars, but previous surveys have been biased towards narrow-lined stars because of the difficulty in measuring boron abundances in rapidly rotating stars.The two targets observed as part of our Cycle 13 SNAP program 10175, just before STIS failed, demonstrate that it is possible to make useful boron abundance measurements for early-B stars with Vsin(i) above 100 km/s. We propose to extend that survey to a large enough sample of stars to allow statistically significant tests of models of rotational mixing in early-B stars.
CCD Dark Monitor Part 1
Monitor the darks for the STIS CCD.
CCD Bias Monitor-Part 1
Monitor the bias in the 1×1, 1×2, 2×1, and 2×2 bin settings at gain=1, and 1×1 at gain = 4, to build up high-S/N superbiases and track the evolution of hot columns.
STIS CCD Spectroscopic Flats C17
Obtain pixel-to-pixel lamp flat fields for the STIS CCD in spectroscopic mode.
CCD Spectroscopic Dispersion Solution
Constrain wavelength and spatial distortion maps using internal wavecals obtained with all 6 gratings (G230LB, G230MB, G430L, G430M, G750L, G750M) supported for use with the CCD. Data will be obtained for the nearly identical set of 38 central wavelengths used in the 9617 and 10025 programs.
MAMA Dispersion Solutions
Wavelength dispersion solutions will be determined on a yearly basis as part of a long- term monitoring program. Deep engineering wavecals for each MAMA grating will be obtained at common cenwaves. Intermediate settings will also be taken to check the reliability of derived dispersion solutions. Final selection was determined on basis of past monitoring and C17 requirements. The internal wavelength calibrations will be taken using the LINE line lamp. Extra-deep wavecals are included for some echelle modes and first order modes to ensure detection of weak lines.
STIS-20 NUV MAMA Dark Monitor
The STIS NUV-MAMA dark current is dominated by a phosphorescent glow from the detector window. Meta-stable states in this window are populated by cosmic ray impacts, which, days later, can be thermally excited to an unstable state from which they decay, emitting a UV photon. The equilibrium population of these meta-stable states is larger at lower temperatures; so warming up the detector from its cold safing will lead to a large, but temporary, increase in the dark current.
To monitor the decay of this glow, and to determine the equilibrium dark current for Cycle 17, four 1380s NUV-MAMA ACCUM mode darks should be taken each week during the SMOV period. Once the observed dark current has reached an approximate equilibrium with the mean detector temperature, the frequency of this monitor can be reduced to one pair of darks per week.
IR Internal Flat Fields
This program is the same as 11433 (SMOV) and depends on the completion of the IR initial alignment (program 11425). This version contains three instances of 37 internal orbits; to be scheduled early, middle, and near the end of Cycle 17, in order to use the entire 110-orbit allocation.
In this test, we will study the stability and structure of the IR channel flat field images through all filter elements in the WFC3-IR channel. Flats will be monitored, i.e. to capture any temporal trends in the flat fields, and delta flats produced. High signal observations will provide a map of the pixel-to-pixel flat field structure, as well as identify the positions of any dust particles.
WFC3 UVIS CCD Daily Monitor
The behavior of the WFC3 UVIS CCD will be monitored daily with a set of full-frame, four-amp bias and dark frames. A smaller set of 2Kx4K subarray biases are acquired at less frequent intervals throughout the cycle to support subarray science observations. The internals from this proposal, along with those from the anneal procedure (11909), will be used to generate the necessary superbias and superdark reference files for the calibration pipeline (CDBS).
UVIS Hot Pixel Anneal
The on-orbit radiation environment of WFC3 will continually generate new hot pixels. This proposal performs the procedure required for repairing those hot pixels in the UVIS CCDs. During an anneal, the two-stage thermo-electric cooler (TEC) is turned off and the four-stage TEC is used as a heater to bring the UVIS CCDs up to ~20 deg. C. As a result of the CCD warmup, a majority of the hot pixels will be fixed; previous instruments such as WFPC2 and ACS have seen repair rates of about 80%. Internal UVIS exposures are taken before and after each anneal, to allow an assessment of the procedure’s effectiveness in WFC3, provide a check of bias, global dark current, and hot pixel levels, as well as support hysteresis (bowtie) monitoring and CDBS reference file generation. One IR dark is taken after each anneal, to provide a check of the IR detector.
FLIGHT OPERATIONS SUMMARY:
Significant Spacecraft Anomalies: (The following are preliminary reports of potential non-nominal performance that will be investigated.)
COMPLETED OPS REQUEST:
18683-5 – Install WFC3 CS FSW 4.00 and NSSC-I BQ 9.0.6 @ 232/1830z
COMPLETED OPS NOTES: (None)
FGS GSAcq 12 12
FGS REAcq 03 03
OBAD with Maneuver 06 06
Wide Field Camera 3 CS Flight Software version 4.00 and NSSC-I Flight Software version BQ 9.0.6 have been successfully loaded via Ops Request 18683-5