- Press Release
- Sep 29, 2022
NASA Hubble Space Telescope Daily Report #4915
HUBBLE SPACE TELESCOPE DAILY REPORT #4915
PERIOD COVERED: 5am August 21 – 5am August 24, 2009 (DOY 233/09:00z-236/09:00z)
UVIS G280 Flux Calibration
Flux calibration, image displacement, and spectral trace of the UVIS G280 grism will be established using observations of the HST flux standard start GD71. Accompanying direct exposures will provide the image displacement measurements and wavelength zeropoints for dispersed exposures. The calibrations will be obtained at the central position of each CCD chip and at the center of the UVIS field. No additional field- dependent variations will be derived.
IR Gain Measurement
The gain of the IR channel of WFC3 will be measured using a series of internal flat fields. Using knowledge gained from ground testing, we propose to collect flat field ramps which will be used to create photon transfer curves and give a measure of the gain. By using two filters centered at similar wavelengths but differing bandwidths, we will be able to search for any flux-dependent changes in the the measure of the gain.
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.
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.
Cycle 17: UVIS Bowtie Monitor
Ground testing revealed an intermittent hysteresis type effect in the UVIS detector (both CCDs) at the level of ~1%, lasting hours to days. Initially found via an unexpected bowtie-shaped feature in flatfield ratios, subsequent lab tests on similar e2v devices have since shown that it is also present as simply an overall offset across the entire CCD, i.e., a QE offset without any discernable pattern. These lab tests have further revealed that overexposing the detector to count levels several times full well fills the traps and effectively neutralizes the bowtie. Each visit in this proposal acquires a set of three 3×3 binned internal flatfields: the first unsaturated image will be used to detect any bowtie, the second, highly-exposed image will neutralize the bowtie if it is present, and the final image will allow for verification that the bowtie is gone.
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).
SBC Dark Current Measurement
This takes a series of SBC dark measurements over a continuous period of about 6 hours (4 orbits). The aim is to collect dark images during an extended SBC on time. Earlier measurements indicate that the dark current increases with SBC on time and may also be increasing with overall SBC use. The 6-hour time matches the longest time used by any observer. As with all SBC observations this needs continuous SAA free time.
Monitoring FGS2R2 Distortion and Alignment After SMOV4
This proposal monitors changes in the FGS2R2 distortion and alignment after SMOV4 by observing selected stars in M35 in Position mode. Data from each epoch are compared to track changes in FGS2R2. When the rate of change becomes sufficiently slow, FGS2R2 will be cleared for a mini-OFAD and FGS-FGS alignment calibration (carried out in another phase 2 proposal).
Long Term Stability of FGS1R in Position Mode
This proposal resumes the Long Term Monitoring of FGS1R in Position Mode using stars in M35 that are a subset of the FGS “OFAD catalog” using both the “fall” and “spring” seasons (the spring orient was not available under two gyro mode). The data acquired by this proposal are used to update the FGS1R “rhoA & kA” parameters that are associated with the OFAD solution that is applicable at the observation’s epoch. These values are critical to support sub-milli arcsecond astrometry with FGS1R.
This particular proposal also include a FGS3 visit to M35 for post SM4 verification of its calibration status.
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.
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.
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.
CCD Dark Monitor Part 1
Monitor the darks for the STIS CCD.
A Calibration Database for Stellar Models of Asymptotic Giant Branch Stars
Studies of galaxy formation and evolution rely increasingly on the interpretation and modeling of near-infrared observations. At these wavelengths, the brightest stars are intermediate mass asymptotic giant branch (AGB) stars. These stars can contribute nearly 50% of the integrated luminosity at near infrared and even optical wavelengths, particularly for the younger stellar populations characteristic of high-redshift galaxies (z>1). AGB stars are also significant sources of dust and heavy elements. Accurate modeling of AGB stars is therefore of the utmost importance.
The primary limitation facing current models is the lack of useful calibration data. Current models are tuned to match the properties of the AGB population in the Magellanic Clouds, and thus have only been calibrated in a very narrow range of sub- solar metallicities. Preliminary observations already suggest that the models are overestimating AGB lifetimes by factors of 2-3 at lower metallicities. At higher (solar) metallicities, there are no appropriate observations for calibrating the models.
We propose a WFC3/IR SNAP survey of nearby galaxies to create a large database of AGB populations spanning the full range of metallicities and star formation histories. Because of their intrinsically red colors and dusty circumstellar envelopes, tracking the numbers and bolometric fluxes of AGB stars requires the NIR observations we propose here. The resulting observations of nearby galaxies with deep ACS imaging offer the opportunity to obtain large (100-1000’s) complete samples of AGB stars at a single distance, in systems with well-constrained star formation histories and metallicities.
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.
A Deep Exploration of Classes of Long Period Variable Stars in M31
We propose a thrifty but information-packed investigation with WFC3/IR F160W and F110W providing crucial information about Long Period Variables in M31, at a level of detail that has recently allowed the discovery of new variable star classes in the Magellanic Clouds, a very different stellar population. These observations are buttressed by an extensive map of the same fields with ACS and WFC3 exposures in F555W and F814W, and a massive ground-based imaging patrol producing well-sampled light curves for more than 400,000 variable stars. Our primary goal is to collect sufficient NIR data in order to analyze and classify the huge number of long-period variables in our catalog (see below) through Period Luminosity (P/L) diagrams. We will produce accurate P/L diagrams for both the bulge and a progression of locations throughout the disk of M31. These diagrams will be similar in quality to those currently in the Magellanic Clouds, with their lower metallicity, radically different star formation history, and larger spread in distance to the variables. M31 offers an excellent chance to study more typical disk populations, in a manner which might be extended to more distant galaxies where such variables are still visible, probing a much more evenly spread progenitor age distribution than cepheids (and perhaps useful as a distance scale alternative or cross- check). Our data will also provide a massive and unique color-magnitude dataset; we expect that this study will produce several important results, among them a better understanding of P/L and P/L-color relations for pulsating variables which are essential to the extragalactic distance ladder. We will view these variables at a common distance over a range of metallicities (eliminating the distance-error vs. metallicity ambiguity between the LMC and SMC), allow further insight into possible faint-variable mass-loss for higher metallicities, and in general produce a sample more typical of giant disk galaxies predominant in many studies.
A Search for Astrometric Companions to Very Low-Mass, Population II Stars
We propose to carry out a SNAPshot search for astrometric companions in a subsample of very low-mass, halo subdwarfs identified within 120 parsecs of the Sun. These ultra- cool M subdwarfs are local representatives of the lowest-mass H burning objects from the Galactic Population II. The expected 3-4 astrometric doubles that will be discovered will be invaluable in that they will be the first systems from which gravitational masses of metal-poor stars at the bottom of the main sequence can be directly measured.
UVIS and IR Pointing Stability
This calibration proposal measures the pointing stability of the WFC3 UVIS and IR channels.
Three conditions will be tested: 1) 2-orbit stability after sitting at a constant thermal attitude for 10 orbits 2) 2-orbit stability after sitting at a hot thermal attitude for 10 orbits and then slewing to a cold attitude 3) 2-orbit stability after sitting at a cold thermal attitude for 10 orbits and then slewing to a hot attitude
Stability measurements will be made by a series of short observations of a globular cluster.
This activity confirms COS sensitivity versus wavelength over the entire observable spectrum for all FUV gratings and central wavelength settings. Obtain quick look sensitivity visit early in SMOV. Later, after wavelength calibration is verified, perform a precise-centering acquisition and observe an appropriate HST flux standard star (chosen from the HST prime standard and FASTEX lists) with the PSA. (A limited BOA characterization is obtained in Visit 13 using primary standard GD153.) No off aperture- center observations are performed in this activity (see COS32, program 11490, for off- center characterizations). Spectra will be obtained to meet a Poisson S/N criterion of ~30 per sensitivity extraction bin or higher; substantially higher S/N characterization will be utilized in routine Cycle 17 calibration.
COS FUV Target Acquisition Algorithm Verification
Verify the ability of the COS FSW to place an isolated point source at the center of the aperture, both for the BOA and PSA, using dispersed light from the object using the FUV gratings. The various options for target centering should be exercised and shown to work properly. This test is for acquisitions in dispersed-light mode only. This program is modeled from SMOV activity summary COS28.
This program should be executed two or more weeks after visit 12 of 11469, and after the SIAF update, so that we have confirmed that NUV imaging acquisitions work properly with the BOA.
COS NUV Spectroscopic Sensitivity
This activity confirms COS sensitivity versus wavelength over the entire observable spectrum for all NUV gratings and central wavelength settings. Perform a precise- centering acquisition and observe an appropriate HST flux standard star (chosen from the HST prime standard and FASTEX lists) with the PSA. A limited BOA characterization is also obtained (see also program 11476, activity COS16). A quick spot check of the sensitivities with the PSA is also executed immediately after the NUV alignment (but at least 7 days after that). No off aperture-center observations are performed in this activity (see program 11477, activity COS17, for off-center characterizations). Spectra will be obtained to meet a Poisson S/N criterion of 20 per resolution element in the central wavelength of the setting; higher S/N characterization will be utilized in routine Cycle 17 calibration.
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.
WFC3 IR Dark Current, Readnoise, and Background
This proposal obtains full-frame, four-amp readout images. Un-illuminated internals are taken at regularly spaced intervals throughout SMOV in order to assess and monitor readnoise and dark current (of both light-sensitive pixels and reference pixels), and bad (warm, hot, dead, variable) pixels. In addition, externals aimed at fields with sparse stellar density are taken to measure diffuse background light.
This program corresponds to WFC3-34.
WFC3 UVIS Dark Current, Readnoise, and CTE
This proposal obtains full-frame, four-amp readout bias and dark frames at regularly- spaced intervals throughout SMOV in order to assess and monitor dark current, bad (warm, hot, dead) pixels, and readnoise. In addition, a set of internals using the WFC3 calsystem are taken to provide a baseline CTE measurement. WFC3-33
UVIS Internal Flats
This proposal will be used to assess the stability of the flat field structure for the UVIS detector. Flat fields will be obtained for all filters using the internal D2 and Tungsten lamps.
This proposal corresponds to Activity Description ID WF19. It should execute only after the following proposals have executed: WF08 – 11421 WF09 – 11422 WF11 – 11424 WF15 – 11428
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.
STIS-26 MAMA Image Stability
The maximum thermal motion of the MAMA detectors occurs in the first portion of the orbit immediately following a large angle maneuver leading to maximum external changes on the portion of axial bay closest to the STIS instrument. By the second orbit on the same target, the thermal motions settle down to a significant displacement right after target rise, a possible change later in the orbit due to sun/bright earth/dark earth/ deep space. We will follow these changes for two orbits with each MAMA with internal lamp and the medium dispersion echelle formats in order to obtain a two-dimension series of reference points on the 2-dimensional detector format. Exposures will be done using the 0.1X0.03 aperture and medium resolution echelle gratings, and will have exposure times of 120 seconds for deep, sharp spectral line images.
For each orbit, six spectral line images will follow each other, then dark frames are interposed with exposure times extending from 300 seconds to 600 seconds. This provides frequent sampling in the portion of the orbit where thermal flexure is largest, while avoiding excessive lamp use when shifts are expected to be slower. The dark frames will also provide a useful addition to the calibration of the MAMA detector dark current.
Note that E140M test is from hot to cold and the E230M test is from cold to hot. If noticeable changes are measured, the complimentary test pair should be considered at a later date.
Identifying the Host Galaxies for Optically Dark Gamma-Ray Bursts
We propose to use the high spatial resolution capabilities of Chandra to obtain precise positions for a sample of Gamma-ray bursts (GRBs) with no optical afterglows, where the optical light is suppressed relative to the X-ray flux. These bursts are likely to be highly obscured and may have different environments from the optically bright GRBs. Our Chandra observations will (unlike Swift-XRT positions) allow for the unique identification of a host galaxy. To locate these host galaxies we will follow up our Chandra positions with deep optical and IR observations with HST. The ultimate aim is to understand any differences between the host galaxies of optically dark and bright GRBs, and how these affect the use of GRBs as tracers of star formation and galaxy evolution at high redshift.
FLIGHT OPERATIONS SUMMARY:
Significant Spacecraft Anomalies: (The following are preliminary reports of potential non-nominal performance that will be investigated.)
COMPLETED OPS REQUEST: (None)
COMPLETED OPS NOTES: (None)
FGS GSAcq 20 20
FGS REAcq 39 39
OBAD with Maneuver 12 12
SIGNIFICANT EVENTS: (None)