#1
|
|||
|
|||
Daily 3723
HUBBLE SPACE TELESCOPE - Continuing to collect World Class Science
DAILY REPORT # 3723 PERIOD COVERED: DOY 299 OBSERVATIONS SCHEDULED ACS/HRC 10185 When does Bipolarity Impose itself on the Extreme Mass Outflows from AGB Stars? An ACS SNAPshot Survey Essentially all well-characterized preplanetary nebulae {PPNe} -- objects in transition between the AGB and planetary nebula evolutionary phases - are bipolar, whereas the mass-loss envelopes of AGB stars are strikingly spherical. In order to understand the processes leading to bipolar mass-ejection, we need to know at what stage of stellar evolution does bipolarity in the mass-loss first manifest itself? Our previous SNAPshot surveys of a PPNe sample {with ACS & NICMOS} show that roughly half our targets observed are resolved, with well-defined bipolar or multipolar morphologies. Spectroscopic surveys of our sample confirm that these objects have not yet evolved into planetary nebulae. Thus, the transformation from spherical to aspherical geometries has already fully developed by the time these dying stars have become preplanetary nebulae. From this new and surprising result, we hypothesize that the transformation to bipolarity begins during the very late AGB phase, and happens very quickly, just before, or as the stars are evolving off the AGB. We propose to test this hypothesis quantitatively, through a SNAPshot imaging survey of very evolved AGB stars which we believe are nascent preplanetary nebulae; with our target list being drawn from published lists of AGB stars with detected heavy mass-loss {from millimeter-wave observations}. This survey is crucial for determining how and when the bipolar geometry asserts itself. Supporting kinematic observations using long-slit optical spectroscopy {with the Keck}, millimeter and radio interferometric observations {with OVRO, VLA & VLBA} are being undertaken. The results from this survey {together with our previous work} will allow us to draw general conclusions about the onset of bipolar mass-ejection during late stellar evolution, and will provide crucial input for theories of post-AGB stellar evolution. Our survey will produce an archival legacy of long-standing value for future studies of dying stars. ACS/HRC 10198 Probing the Dynamics of the Galactic Bar through the Kinematics of Microlensed Stars The observed optical depths to microlensing of stars in the Galactic bulge are difficult to reconcile with our present understanding of Galactic dynamics. The main source of uncertainty in those comparisons is now shifting from microlensing measurements to the dynamical models of the Galactic bar. We propose to constrain the Galactic bar models with proper motion observations of Bulge stars that underwent microlensing by determining both the kinematic identity of the microlensed sources and the importance of streaming motions. The lensed stars are typically farther than randomly selected stars. Therefore, our proper motion determinations for 36 targeted MACHO events will provide valuable constraints on the dynamics of bulge stars as a function of distance. The first epoch data for our proposed events is already available in the HST archive so the project can be completed within a single HST cycle. The exceptional spatial resolution of HST is essential for completion of the project. Constraints on the total mass in the bulge will ultimately lead to the determination of the amount of dark matter in inner Galaxy. ACS/HRC 10332 Starburst Galaxies and Their Population of Super Star Clusters Starbursts are ideally suited to study the evolution of high mass stars, the physics of star formation, and the chemical enrichment of the intergalactic medium {IGM}. Starbursts efficiently form Super Star Clusters {SSC} which may be young protoglobular clusters. High resolution imaging will address two important outstanding issues: 1} how long starbursts last and 2} whether SSCs are indeed young globular clusters. The duration of starbursts is important because: {1} it determines how efficiently a starburst can heat and enrich the IGM; {2} the duration combined with estimates of the fraction of galaxies which host starbursts yields the total number of starbursts a galaxy can suffer. Finally, since local starbursts are analogs to high-z galaxies, the results have implications on the initial formation timescale of galaxies. Starburst duration will be determined from HRC imaging of two face-on starburst galaxies rich in SSCs. The UV to optical colors of the SSCs, which represent single burst chronometers, will yield their reddening and ages. The range of ages gives the starburst duration. The nature of SSCs will be investigated by imaging four of the nearest starbursts in three bands. By comparing the sizes of their SSCs at different wavelengths we will address the issue of whether SSCs suffer from early mass segregation. Without some mass segregation the velocity dispersions of SSCs suggest that they are deficient in low mass stars, and hence may not represent true proto-globular clusters. ACS/HRC 10390 Serendipitous detection of a debris disk near the Sun We report the unexpected detection of the Fomalhaut debris disk in scattered light during one orbit of observation for our Cycle 12 program GO9862. This is a major discovery because Fomalhaut is now the closest {7.7 pc} and oldest {~200 Myr} debris disk detected in reflected light. We would like to request Director's Discretionary Time to further study the Fomalhaut disk. The goals are to image the disk around its entire perimeter, increase the signal-to-noise of the detection, and to obtain data at a second wavelength. We will perform a high-resolution study of radial and azimuthal disk asymmetries that are thought to arise from perturbations by planet-mass companions, and we will constrain the physical properties of grain material by obtaining the color of the disk. Because our original Cycle 12 program was designed to study point sources in the field, and the ACS/HRC coronagraph is a limited lifetime resource, it is necessary to acquire these additional data via Director's Discretionary Time during Cycle 13. The observational challenge of high contrast cannot be met by other observatories, and these data will complement new Spitzer results on the Fomalhaut disk at mid and far-infrared wavelengths. ACS/HRC/WFC 10367 ACS CCDs daily monitor- cycle 13 - part 1 This program consists of a set of basic tests to monitor, the read noise, the development of hot pixels and test for any source of noise in ACS CCD detectors. The files, biases and dark will be used to create reference files for science calibration. This programme will be for the entire lifetime of ACS. ACS/WFC/NIC/NIC3/WFPC2 10246 The HST survey of the Orion Nebula Cluster We propose a Treasury Program of 104 HST orbits to perform the definitive study of the Orion Nebula Cluster, the Rosetta stone of star formation. We will cover with unprecedented sensitivity {23-25 mag}, dynamic range {~12 mag}, spatial resolution {50mas}, and simultaneous spectral coverage {5 bands} a ~450 square arcmin field centered on the Trapezium stars. This represents a tremendous gain over the shallow WFC1 study made in 1991 with the aberrated HST on an area ~15 times smaller. We maximize the HST observing efficiency using ACS/WFC and WFPC2 in parallel with two opposite roll angles, to cover the same total field. We will assemble the richest, most accurate and unbiased HR diagram for pre-main-sequence objects ever made. Combined with the optical spectroscopy already available for ~1000 sources and new deep near-IR imaging and spectroscopy {that we propose as Joint HST-NOAO observations}, we will be able to attack and possibly solve the most compelling questions on stellar evolution: the calibration of pre-main-sequence evolutionary tracks, mass segration and the variation of the initial mass function in different environments, the evolution of mass accretion rates vs. age and environment, disk dissipation in environments dominated by hard vs. soft-UV radiation, stellar multiplicity vs. disk fraction. In addition, we expect to discover and classify an unknown, but substantial, population of pre-Main Sequence binaries, low mass stars and brown dwarfs down to ~10 MJup. This is also the best possible way to discover dark silhouette disks in the outskirts of the Orion Nebula and study their evolutionary status through multicolor imaging. This program is timely and extremely well leveraged to other programs targeting Orion: the ACS H-alpha survey of the Orion Nebula, the recently completed 850ks ultradeep Chandra survey, the large GTO programs to be performed with SIRTF, plus the availability of 2MASS and various deep JHK surveys of the core recently done with 8m class telescopes. FGS 10387 Monitoring FGS1r's Interferometric Response as a Function of Spectral Color This proposal obtains reference point source Transfer Functions {S-Curves} for FGS1r through the F583W filter and the F5ND attenuator at the center position of the FGS1r FOV for a variety of stars of different spectral types. These Transfer Functions are needed to support the analysis of GO science data for the study of close and wide binary star systems and for determining the angular size and shape of extended sources. This proposal observes stars that have been observed in previous cycles to monitor the long term evolution of the FGS1r S-curves. This proposal also {1} monitors the FGS1r Lateral Color response {using stars Latcol-A and Latcol-B}, {2} calibrates the "Pos/Trans" bias of a star's position as determined from Transfer mode and Position mode observations, and {3} calibrates the shift of a star's centroid when observed with F5ND relative to that when observed with F583W. FGS 9972 Calibrating the Mass-Luminosity Relation at the End of the Main Sequence We propose to use HST-FGS1R to calibrate the mass-luminosity relation {MLR} for stars less massive than 0.2 Msun, with special emphasis on objects near the stellar/brown dwarf border. Our goals are to determine M_V values to 0.05 magnitude, masses to 5 than double the number of objects with masses determined to be less than 0.20 Msun. This program uses the combination of HST-FGS3/FGS1R at optical wavelengths and ground-based infrared interferometry to examine nearby, subarcsecond binary systems. The high precision measurements with HST-FGS3/FGS1R {to 1 mas in the separations} for these faint targets {V = 10--15} simply cannot be equaled by any ground based technique. As a result of these measurements, we are deriving high quality luminosities and masses for the components in the observed systems, and characterizing their spectral energy distributions from 0.5 to 2.2 Mum. Several of the objects included have M 0.1 Msun, placing them at the very end of the stellar main sequence. Three of the targets are brown dwarf candidates, including the current low mass record holder, GJ 1245C, with a mass of 0.062 +/- 0.004 Msun. The payoff of this proposal is high because all 10 of the systems selected have already been resolved with HST- FGS3/FGS1R during Cycles 5--10 and contain most of the reddest objects for which masses can be determined. NIC1/NIC2/NIC3 8793 NICMOS Post-SAA calibration - CR Persistence Part 4 A new procedure proposed to alleviate the CR-persistence problem of NICMOS. Dark frames will be obtained immediately upon exiting the SAA contour 23, and every time a NICMOS exposure is scheduled within 50 minutes of coming out of the SAA. The darks will be obtained in parallel in all three NICMOS Cameras. The POST-SAA darks will be non-standard reference files available to users with a USEAFTER date/time mark. The keyword 'USEAFTER=date/time' will also be added to the header of each POST-SAA DARK frame. The keyword must be populated with the time, in addition to the date, because HST crosses the SAA ~8 times per day so each POST-SAA DARK will need to have the appropriate time specified, for users to identify the ones they need. Both the raw and processed images will be archived as POST-SAA DARKSs. Generally we expect that all NICMOS science/calibration observations started within 50 minutes of leaving an SAA will need such maps to remove the CR persistence from the science images. Each observation will need its own CRMAP, as different SAA passages leave different imprints on the NICMOS detectors. FLIGHT OPERATIONS SUMMARY: Significant Spacecraft Anomalies: (The following are preliminary reports of potential non-nominal performance that will be investigated.) HSTAR 9570: FHST 3 Map failed to lock onto any stars @ 298/08:54Z. COMPLETED OPS REQs: None OPS NOTES EXECUTED: None SCHEDULED SUCCESSFUL FAILURE TIMES FGS Gsacq 13 13 FGS Reacq 02 02 FHST Update 19 19 LOSS of LOCK SIGNIFICANT EVENTS: None |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
EVOLUTION DEAD AT AGE 126 -- R.I.P. | Ed Conrad | Astronomy Misc | 4 | August 21st 04 12:01 AM |
Monitoring NASA Daily ISS Report | JimO | Space Station | 2 | June 1st 04 10:33 PM |