Search

The NOAO Data Lab aims to provide infrastructure to maximize community use of the high-value survey datasets now being collected with NOAO telescopes and instruments. As a science exploration framework, the Data Lab allow users to access and search databases containing large (i.e. terabyte-scale) catalogs, visualize, analyze, and store the results of these searches, combine search results with data from other archives or facilities, and share these results with collaborators using a shared workspace and/or data publication service. In the process of implementing the needed tools and services, specific science cases are used to guide development of the system framework and tools. The result is a Year-1 capability demonstration that (fully or partially) implements each of the major architecture components in the context of a real-world science use-case. In this paper, we discuss how this model of science-driven development helped us to build a fully functional system capable of executing the chosen science case, and how we plan to scale this system to support general use in the next phase of the project.

Collaborative research/computing environments are essential for working with the next generations of large astronomical data sets. A key component of them is a distributed storage system to enable data hosting, sharing, and publication. VOSpace is a lightweight interface providing network access to arbitrary backend storage solutions and endorsed by the International Virtual Observatory Alliance (IVOA). Although similar APIs exist, such as Amazon S3, WebDav, and Dropbox, VOSpace is designed to be protocol agnostic, focusing on data control operations, and supports asynchronous and third-party data transfers, thereby minimizing unnecessary data transfers. It also allows arbitrary computations to be triggered as a result of a transfer operation: for example, a file can be automatically ingested into a database when put into an active directory or a data reduction task, such as Sextractor, can be run on it. In this paper, we shall describe the VOSpace implementations that we have developed for the NOAO Data Lab. These offer both dedicated remote storage, accessible as a local file system via FUSE, and a local VOSpace service to easily enable data synchronization.

We present PhAst, a new IDL astronomical image viewer, based on the existing ATV application, which has been optimized for astrometry of Near Earth Objects (NEOs). After describing the features of PhAst, we describe how PhAst enabled the recovery of the Virtual Impactor (VI) 2011AX22 and the Potentially Hazardous Asteroid (PHA) 2008OX1. The recovery of 2011AX22 led to a large improvement in the time of perihelion passage and in the semimajor axis and eccentricity of its orbit. The distance of closest approach in May 2055 was moved away from Earth to >1 lunar distance. As a result of the orbital improvement made possible by the successful recovery, NEODyS downgraded 2011AX22 from a VI to a PHA, having ruled out the chance of an Earth impact this century. The recovery of 2008OX1 extended its observational arc to 1303 days—more than 2.5 orbital revolutions. It was confirmed to be a PHA and its orbit was improved sufficiently to permit prediction of its sky position to within 1'' over an interval of 10 years into the future. We discuss the astrometric and photometric performance of PhAst and then conclude by briefly describing future enhancements to the application.

We have analyzed archival Hubble Space Telescope (HST) Wide Field Planetary Camera 2 (WFPC2) observations of the central region of the globular cluster M54. The 12 irregularly timed observations (6 F555W, 6 F814W) were reduced using the HSTphot stellar photometry package. Our statistical analysis of the HSTphot photometry yielded 50 variable stars that are likely RR Lyrae candidates. These candidates were missed by previous ground-based searches for RR Lyraes due to the extreme crowding in the core of M54. We performed two checks on our sample of RR Lyrae candidates to determine how different they were from the other variable candidates. The first test was a numerical analysis comparing the ratio of variable candidates to the total number of stars within the blue horizontal branch, the RR Lyrae region, and the red giant branch. We found ratios of 0.61%, 13%, and 1.1% in these regions, respectively. Our next test was a two-sample Kolmogorov-Smirnov (K-S) test, which allowed us to find out how different our 50 RR Lyrae candidates were from the 50 brightest other variable candidates. According to the K-S test, there is only a 0.0004% probability that these two populations are similar, indicating that our RR Lyrae candidates do indeed exhibit some real fluctuation in their brightness. We sampled the light curves of confirmed RR Lyrae light curves to simulate the HST observing conditions and found that a signature of variability in 2911 out of the 4000 (72%) generated stars. We estimate that there maybe as many as 19 more RR Lyrae candidates that were undetected in the WFPC2 field of view. The presence of additional RR Lyraes has implications into the current Oosterhoff classification for the cluster.

We observed two fields near M32 with the Advanced Camera for Surveys/High Resolution Channel (ACS/HRC) on board the Hubble Space Telescope (HST). The main field, F1, is 1.8 arcmin from the center of M32; the second field, F2, constrains the M31 background, and is 5.4 arcmin distant. Each field was observed for 16-orbits in each of the F435W (narrow B) and F555W (narrow V) filters. The duration of the observations allowed RR Lyrae stars and other short-period variables to be detected. A population of RR Lyrae stars determined to belong to M32 would prove the existence of an ancient population in that galaxy, a subject of some debate. We detected 17 RR Lyrae variables in F1 and 14 in F2. A 1-sigma upper limit of 6 RR Lyrae variables belonging to M32 is inferred from these two fields alone. Use of our two ACS/WFC parallel fields provides better constraints on the M31 background, however, and implies that $7_{-3}^{+4}$ (68 % confidence interval) RR Lyrae variables in F1 belong to M32. We have therefore found evidence for an ancient population in M32. It seems to be nearly indistinguishable from the ancient population of M31. The RR Lyrae stars in the F1 and F2 fields have indistinguishable mean V-band magnitudes, mean periods, distributions in the Bailey diagram and ratios of RRc to RR(tot) types. However, the color distributions in the two fields are different, with a population of red RRab variables in F1 not seen in F2. We suggest that these might be identified with the detected M32 RR Lyrae population, but the small number of stars rules out a definitive claim., 19 pages, 18 figures, accepted ApJ

We have analyzed two epochs of Hubble Space Telescope Wide Field Planetary Camera 2 observations of the Ursa Minor dwarf spheroidal galaxy using the HSTphot photometric reduction package. We report the detection of nine faint (MV 0.0 mag) red giant variable stars that exhibit low-amplitude brightness fluctuations on 10 minute timescales with amplitudes ranging from 36 to 130 mmag. We have found variability in 14% of the red giants we have observed. If low-amplitude variability of red giants on 10 minute timescales can be verified and should their numbers prove to be at the 10% level or greater of all red giants in some ancient Population II stellar systems, then the observed color spread of the red giant branch of such systems would be broadened by flickering red giants in color-magnitude diagrams based on short (snapshot) observations of a single pair of 10 minute timescale observations in two different filters.

The field of direct imaging is experiencing a considerable growth in the number of available CCD mosaic imagers, especially on large telescopes. To fully exploit the astrometric potential of these imaging devices, we develop a technique, utilizing an astrometric standard, for precision transformation of pixel coordinates into a global coordinate system. We have constructed a new astrometric standard set of 1863 stars in the field of NGC 188 to derive the CCD chip constants for the NOAO CCD Mosaic Imager. The multiple-epoch data on the Mosaic's metrics indicate that this CCD mosaic device may have experienced a one-time nonelastic expansion. We also present a new determination of the pixel scale and the optical field angle distortion constants for the KPNO Mayall 4 m telescope prime focus field corrector. To establish a reliable history of the CCD mosaic imager metrics for current and potential future astrometric applications, we recommend obtaining astrometric calibrations for CCD mosaic imagers on a regular basis. Apart from mechanical positioning of the CCD mosaic camera on the telescope, noticeable changes in the thermal environment of CCD mosaic chips should also prompt new astrometric calibrations. It is shown that, following all precautions, the NOAO CCD Mosaic Imager can produce excellent astrometric results on the Mayall 4 m telescope.

The discovery of variable and transient sources is an essential product of synoptic surveys. The alert stream will require filtering for personalized criteria -- a process managed by a functionality commonly described as a Broker. In order to understand quantitatively the magnitude of the alert generation and Broker tasks, we have undertaken an analysis of the most numerous types of variable targets in the sky -- Galactic stars, QSOs, AGNs and asteroids. It is found that LSST will be capable of discovering ~10^5 high latitude |b| > 20 deg) variable stars per night at the beginning of the survey. (The corresponding number for |b| < 20 deg is orders of magnitude larger, but subject to caveats concerning extinction and crowding.) However, the number of new discoveries may well drop below 100/night within 2 years. The same analysis applied to GAIA clarifies the complementarity of the GAIA and LSST surveys. Discovery of variable galactic nuclei (AGNs) and Quasi Stellar Objects (QSOs) are each predicted to begin at ~3000 per night, and decrease by 50X over 4 years. SNe are expected at ~1100/night, and after several survey years will dominate the new variable discovery rate. LSST asteroid discoveries will start at > 10^5 per night, and if orbital determination has a 50% success rate per epoch, will drop below 1000/night within 2 years., Published in ApJ, 22 pages, 26 figures, 3 tables; subsequent correction of an important error in interpretation of the Besancon models reduces stellar variable numbers significantly, as seen in figures 6-13

Astrometry, on the International Celestial Reference Frame (epoch J2000.0), is presented for the Walker (1994, PASP, 106, 828) stars in the Omega Centauri (= NGC 5139 = C1323-1472) Hubble Space Telescope Wide Field/Planetary Camera (WF/PC) calibration field of Harris et al. (1993, AJ, 105, 1196). Harris et al. stars were first identified on a WFPC2 observation of the omega Cen HST calibration field. Relative astrometry of the Walker stars in this field was then obtained using Walker's CCD positions and astrometry derived using the STSDAS METRIC task on the positions of the Harris et al. stars on the WFPC2 observation. Finally, the relative astrometry, which was based on the HST Guide Star Catalog, is placed on the International Celestial Reference Frame with astrometry from the USNO-A2.0 catalog. An ASCII text version of the astrometric data of the Walker stars in the omega Cen HST calibration field is available electronically in the online version of the article.

Applying the standard weighted mean formula, [ ∑iniσi-2]/[∑ iσi-2], to determine the weighted mean of data, ni, drawn from a Poisson distribution, will, on average, underestimate the true mean by ~1 for all true mean values larger than ~3 when the common assumption is made that the error of the ith observation is σi = max (√ni, 1). This small, but statistically significant offset, explains the long-known observation that chi-square minimization techniques which use the modified Neyman's χ2 statistic, χN2 ≡ ∑i (ni-yi)2/max (ni, 1), to compare Poisson-distributed data with model values, yi, will typically predict a total number of counts that underestimates the true total by about 1 count per bin. Based on my finding that the weighted mean of data drawn from a Poisson distribution can be determined using the formula [ ∑i [ ni + min (ni, 1)](ni + 1)-1]/[ ∑i (ni + 1)-1], I propose that a new χ2 statistic, χ2γ ≡ ∑i [ ni + min (ni, 1) - yi]-2]/[ni + 1], should always be used to analyze Poisson-distributed data in preference to the modified Neyman's χ2 statistic. I demonstrate the power and usefulness of χγ2 minimization by using two statistical fitting techniques and five χ2 statistics to analyze simulated X-ray power-law 15 channel spectra with large and small counts per bin. I show that χγ2 minimization with the Levenberg-Marquardt or Powell's method can produce excellent results (mean slope errors 3%) with spectra having as few as 25 total counts.

We present our analysis of archival Hubble Space Telescope Wide Field Planetary Camera 2 observations in F555W (~V) and F450W (~B) of the intermediate-age populous star cluster NGC 416 in the Small Magellanic Cloud galaxy. We use published photometry of two other SMC populous star clusters, Lindsay 1 and Lindsay 113, to investigate the age sequence of these three star clusters. We estimate that these clusters have age ratios of age_NGC416/age_L1 ~= 0.73 +- 0.05 and age_L113/age_L1 ~= 0.52 +- 0.09, using an extrapolation of the d_(B-V) method (which uses the color difference between the red horizontal branch and the red giant branch as an age indicator) of Sarajedini, Lee, & Lee [ApJ, 450, 712 (1995)]. These age ratios provide absolute age estimates of 6.6 +- 0.5 Gyr and 4.7 +- 0.8 Gyr for NGC 416 and Lindsay 113, respectively, assuming that Lindsay 1 is 9 Gyr old. Metallicities and reddenings for NGC 416, Lindsay 1, and Lindsay 113, respectively, were determined using the simultaneous reddening and metallicity (SRM) method of Sarajedini & Layden [AJ, 113, 264, (1997)]. Accurate (relative) ages for the intermediate-age populous clusters in the Small Magellanic Cloud (e.g. via deep main sequence photometry) would allow the d_(B-V) method to be recalibrated with star clusters that are significantly younger than 7 Gyr. An extended d_(B-V) method could prove to be a very useful age diagnostic for future studies of the intermediate-age metal-poor stellar populations in Local Group galaxies where accurate main-sequence turnoff photometry at M_V ~= +4 mag is currently not practical., 10 pages (LaTeX+aaspp4.sty), 1 table (in LaTeX file) and 2 figures (PostScript format). The PostScript version of the paper, table, and full-resolution figures is available at http://www.noao.edu/noao/staff/mighell/ngc416 To appear in the Astrophysical Journal Letters

We present the first secondary eclipse and phase curve observations for the highly eccentric hot Jupiter HAT-P-2b in the 3.6, 4.5, 5.8, and 8.0 \mu m bands of the Spitzer Space Telescope. The 3.6 and 4.5 \mu m data sets span an entire orbital period of HAT-P-2b, making them the longest continuous phase curve observations obtained to date and the first full-orbit observations of a planet with an eccentricity exceeding 0.2. We present an improved non-parametric method for removing the intrapixel sensitivity variations in Spitzer data at 3.6 and 4.5 \mu m that robustly maps position-dependent flux variations. We find that the peak in planetary flux occurs at 4.39+/-0.28, 5.84+/-0.39, and 4.68+/-0.37 hours after periapse passage with corresponding maxima in the planet/star flux ratio of 0.1138%+/-0.0089%, 0.1162%+/-0.0080%, and 0.1888%+/-0.0072% in the 3.6, 4.5, and 8.0 \mu m bands respectively. We compare our measured secondary eclipse depths to the predictions from a one-dimensional radiative transfer model, which suggests the possible presence of a transient day side inversion in HAT-P-2b's atmosphere near periapse. We also derive improved estimates for the system parameters, including its mass, radius, and orbital ephemeris. Our simultaneous fit to the transit, secondary eclipse, and radial velocity data allows us to determine the eccentricity and argument of periapse of HAT-P-2b's orbit with a greater precision than has been achieved for any other eccentric extrasolar planet. We also find evidence for a long-term linear trend in the radial velocity data. This trend suggests the presence of another substellar companion in the HAT-P-2 system, which could have caused HAT-P-2b to migrate inward to its present-day orbit via the Kozai mechanism., Comment: 25 pages, 18 figures, Accepted to ApJ

Currently, most microprocessors use multiple cores to increase performance while limiting power usage. Some processors use not just a few cores, but tens of cores or even 100 cores. One such many-core microprocessor is the Maestro processor, which is based on Tilera's TILE64 processor. The Maestro chip is a 49-core, general-purpose, radiation-hardened processor designed for space applications. The Maestro processor, unlike the TILE64, has a floating-point coprocessor in each core for improved floating point performance. The Maestro processor runs at up to 350 MHz clock frequency. On the Maestro processor, we implemented an FFT and an image processing application called CRBLASTER and evaluated the performance. The FFT is a well-known and commonly used signal processing kernel. CRBLASTER is a parallel-processing image-analysis application that does cosmic-ray rejection on CCD (charge-coupled device) images using the embarrassingly-parallel L. A. COSMIC algorithm. Both applications were written in C. CRBLASTER uses the high-performance computing industry standard Message Passing Interface (MPI) library. The achieved performance of the FFT was up to 3,813 MFLOPS, and the speedup compared to single tile was 46.4 using 49 tiles. The speedup for CRBLASTER, which was memory-bound, was up to 12.5 using 36 tiles.

We use deep HST ACS/HRC observations of a field within M32 (F1) and an M31 background field (F2) to determine the star formation history (SFH) of M32 from its resolved stellar population. We find that 2-5Gyr old stars contribute \som40%+/- 17% of M32's mass, while 55%+/-21% of M32's mass comes from stars older than 5 Gyr. The mass-weighted mean age and metallicity of M32 at F1 are =6.8+/-1.5 Gyr and =-0.01+/-0.08 dex. The SFH additionally indicates the presence of young (=9.2+/-1.2 Gyr and =-0.10+/-0.10 dex, respectively. Our results suggest that the inner disk and spheroid populations of M31 are indistinguishable from those of the outer disk and spheroid. Assuming the mean age of M31's disk at F2 (\sim1 disk scale length) to be 5-9 Gyr, our results agree with an inside-out disk formation scenario for M31's disk., Comment: Accepted to ApJ. 24 pages, 18 figures. A high-resolution version can be downloaded from http://www.astro.rug.nl/~monachesi/monachesi-sfh.pdf

I describe the performance of CRBLASTER, a parallel-processing cosmic-ray application, on the new 49-core MAESTRO processor which is based on the Tilera Corporation 64core TILE64 processor. CRBLASTER was initially ported to the TILE64 processor using hardware and software provided by the OPERA project which developed the MAESTRO processor for the United States Government. Writing parallel-processing applications is very similar for the TILE64 and the MAESTRO processors. The port of CRBLASTER from the TILE64 processor to the MAESTRO simulator took only 6 hours in October 2009. CRBLASTER is a scientific application which spends most of its time doing doubleprecision floating point computations. The TILE64 processor has no floating point hardware assist – all floating point computations on the TILE64 processor must be emulated in software. Each MAESTRO core (tile) has an integrated IEEE 754 compliant floating point unit (FPU). In theory, scientific applications that do a lot of floating point computations should perform significantly faster on the MAESTRO processor than on the TILE64 processor when the clock rates are normalized. The actual performance of CRBLASTER running on 1 to 45 cores on an early MAESTRO developement board (MDB) is described in detail. One major result is that CRBLASTER running on 30 or more cores typically achieves speedup factors of 20 or more. The 100 MHz MDB running CRBLASTER on the standard 750×750 pixel input test image takes 32.82 s (wall time). CRBLASTER running on one core of an Apple Mac Pro with dual 2.8 GHz Quad-Core Intel Xeons takes 5.29 s (wall time) with the same input image. The 100 MHz MDB — with floating point operations emulated in software — has the measured equivalent computational power of a 450 MHz CPU with a FPU. If the speed of the MDB can be increased to 260 MHz, the computational power of the MDB should then be equivalent to a 1.17 GHz CPU with a FPU. The MAESTRO processor definitely has the potential to be an enabling technology for the next generation of NASA astrophysical missions.

We present the deepest optical color-magnitude diagram (CMD) to date of the local elliptical galaxy M32. We have obtained F435W and F555W photometries based on Hubble Space Telescope (HST) Advanced Camera for Surveys/High-Resolution Channel images for a region 110 '' from the center of M32 (F1) and a background field (F2) about 320 '' away from M32 center. Due to the high resolution of our Nyquist-sampled images, the small photometric errors, and the depth of our data (the CMD of M32 goes as deep as F435W similar to 28.5 at 50% completeness level), we obtain the most detailed resolved photometric study of M32 yet. Deconvolution of HST images proves to be superior than other standard methods to derive stellar photometry on extremely crowded HST images, as its photometric errors are similar to 2x smaller than other methods tried. The location of the strong red clump in the CMD suggests a mean age between 8 and 10 Gyr for [Fe/H] = -0.2 dex in M32. We detect for the first time a red giant branch bump and an asymptotic giant branch (AGB) bump in M32 which, together with the red clump, allow us to constrain the age and metallicity of the dominant population in this region of M32. These features indicate that the mean age of M32's population at similar to 2' from its center is between 5 and 10 Gyr. We see evidence of an intermediate-age population in M32 mainly due to the presence of AGB stars rising to M-F555W similar to -2.0. Our detection of a blue component of stars (blue plume) may indicate for the first time the presence of a young stellar population, with ages of the order of 0.5 Gyr, in our M32 field. However, it is likely that the brighter stars of this blue plume belong to the disk of M31 rather than to M32. The fainter stars populating the blue plume indicate the presence of stars not younger than 1 Gyr and/or BSSs in M32. The CMD of M32 displays a wide color distribution of red giant branch stars indicating an intrinsic spread in metallicity with a peak at [Fe/H] similar to -0.2. There is not a noticeable presence of blue horizontal branch stars, suggesting that an ancient population with [Fe/H]

Many astronomical image-analysis programs are based on algorithms that can be described as being embarrassingly parallel, where the analysis of one subimage generally does not affect the analysis of another subimage. Yet few parallel-processing astrophysical image-analysis programs exist that can easily take full advantage of todays fast multi-core servers costing a few thousands of dollars. A major reason for the shortage of state-of-the-art parallel-processing astrophysical image-analysis codes is that the writing of parallel codes has been perceived to be difficult. I describe a new fast parallel-processing image-analysis program called crblaster which does cosmic ray rejection using van Dokkum's L.A.Cosmic algorithm. crblaster is written in C using the industry standard Message Passing Interface (MPI) library. Processing a single 800×800 HST WFPC2 image takes 1.87 seconds using 4 processes on an Apple Xserve with two dual-core 3.0-GHz Intel Xeons; the efficiency of the program running with the 4 processors is 82%. The code can be used as a software framework for easy development of parallel-processing image-anlaysis programs using embarrassing parallel algorithms; the biggest required modification is the replacement of the core image processing function with an alternative image-analysis function based on a single-processor algorithm. I describe the design, implementation and performance of the program.

Planning is underway for a possible post-cryogenic mission with the Spitzer Space Telescope. Only Channels 1 and 2 (3.6 and 4.5 µm) of the Infrared Array Camera (IRAC) will be operational; they will have unmatched sensitivity from 3 to 5 microns until the James Webb Space Telescope is launched. At SPIE Orlando, Mighell described his NASA-funded MATPHOT algorithm for precision stellar photometry and astrometry and presented MATPHOT-based simulations that suggested Channel 1 stellar photometry may be significantly improved by modeling the nonuniform RQE within each pixel, which, when not taken into account in aperture photometry, causes the derived flux to vary according to where the centroid falls within a single pixel (the pixel-phase effect). We analyze archival observations of calibration stars and compare the precision of stellar aperture photometry, with the recommended 1-dimensional and a new 2-dimensional pixel-phase aperture-flux correction, and MATPHOT-based PSF-fitting photometry which accounts for the observed loss of stellar flux due to the nonuniform intrapixel quantum efficiency. We show how the precision of aperture photometry of bright isolated stars corrected with the new 2-dimensional aperture-flux correction function can yield photometry that is almost as precise as that produced by PSF-fitting procedures. This timely research effort is intended to enhance the science return not only of observations already in Spitzer data archive but also those that would be made during the Spitzer Warm Mission.

We present astronomical results from K-band adaptive optics (AO) observations of the wide binary system σ Corona Borealis with the Lick Observatory natural guide star adaptive optics system on 2004 August 27-29. Seeing conditions were excellent and the AO compensation was very good, with Strehl ratios reaching 50% at times. The stellar images were reduced using three different analysis techniques: (1) Parametric Blind Deconvolution, (2) Multi-Frame Blind Deconvolution, and (3) the MATPHOT stellar photometry code. The relative photometric and astrometric precision achievable with these three analysis methods are compared. Future directions that this research can go towards achieving the goal of routinely obtaining precise and accurate photometry and astrometry based on near-infrared AO observations are described.

The performance of an adaptive optics system is typically given in terms of the Strehl ratio of a point spread function (PSF) measured in the focal plane of the system. The Strehl ratio measures the normalized peak intensity of the PSF compared to that of an ideal PSF, i.e. aberration-free, through the system. One advantage of this metric is that it has been shown to be proportional to the rms wavefront error via the Marechel approximation. Thus, Strehl ratio measurements are used to determine the performance of the system. Measurement of the Strehl ratio is frequently problematic in the presence of noise as can be the peak determination for critically sampled data. We have looked at alternative metrics, in particular the S1 sharpness metric. This metric measures the compactness of the PSF by the normalized sum of the squared image intensity and therefore relates to the intensity variance of the image. Using simulated AO PSFs, we show that there is a unique relationship between S1 and the Strehl ratio and we can therefore relate it back to the rms wavefront error.

Innovative image analysis software has the potential to act as a technology driver for advancing the state-of-the- art in the design of space telescopes and space-based instrumentation. Total mission costs can sometimes be significantly reduced by using innovative compact optical designs that create ugly Point Spread Functions. Most traditional astronomical image analysis techniques, like precision stellar photometry and astrometry, were developed for the analysis of ground-based image data and many photometric reduction codes cleverly take full advantage of the blurring caused by the Earth's atmosphere. Image data from space-based cameras, however, is typically characterized by having significant amounts of power at high spatial frequencies. Mission designers have a penchant to approve of optical designs that are undersampled. Although excellent justifications can often be made for using complex optical designs that have ugly Point Spread Functions (e.g., reduced total mission cost) or for using detectors that are too big at a given wavelength (e.g., giving a wider field-of-view), the analysis of resultant image data from these designs is frequently problematical. Reliance upon traditional ground-based image analysis codes may preclude the use of innovative space-based optical designs if such designs are rejected during the design review process for the very practical reason that there is no proven way to accurately analyze the resultant image data. I discuss ongoing research efforts to develop new image analysis algorithms specifically for space-based cameras that may help NASA and ESA to enhance the scientific returns from future astrophysical missions while possibly lowering total mission costs.

The key features of the MATPHOT algorithm for precise and accurate stellar photometry and astrometry using discrete Point Spread Functions are described. A discrete Point Spread Function (PSF) is a sampled version of a continuous PSF which describes the two-dimensional probability distribution of photons from a point source (star) just above the detector. The shape information about the photon scattering pattern of a discrete PSF is typically encoded using a numerical table (matrix) or a FITS image file. Discrete PSFs are shifted within an observational model using a 21-pixel-wide damped sinc function and position partial derivatives are computed using a five-point numerical differentiation formula. Precise and accurate stellar photometry and astrometry is achieved with undersampled CCD observations by using supersampled discrete PSFs that are sampled 2, 3, or more times more finely than the observational data. The precision and accuracy of the MATPHOT algorithm is demonstrated by using the C-language MPD code to analyze simulated CCD stellar observations; measured performance is compared with a theoretical performance model. Detailed analysis of simulated Next Generation Space Telescope observations demonstrate that millipixel relative astrometry and millimag photometric precision is achievable with complicated space-based discrete PSFs. For further information about MATPHOT and MPD, including source code and documentation, see http://www.noao.edu/staff/mighell/matphot, 19 pages, 22 figures, accepted for publication in MNRAS

The MATPHOT algorithm for digital Point Spread Function (PSF) CCD stellar photometry is described. A theoretical photometric and astrometric performance model is presented for PSF-fitting stellar photometry. MATPHOT uses a digital representation of the sampled PSF consisting of a numerical table (e.g., a matrix or a FITS image) instead of an analytical function. MATPHOT achieves accurate stellar photometry with under-sampled CCD observations with super-sampled PSFs. MATPHOT currently locates a PSF within the observational model using a 21-pixel-wide damped sinc interpolation function. Position partial derivatives of the observational model are determined using numerical differentiation techniques. Results of MATPHOT-based design studies of the optical performance of the Next Generation Space Telescope are presented; observations of bright stars analyzed with the MATPHOT algorithm can yield millimag photometric errors with millipixel relative astrometric errors -- or better -- if observed with a perfect detector. Plans for the future development of a parallel-processing version of the MATPHOT algorithm using Beowulf clusters are described. All of the C source code and documentation for MATPHOT is freely available as part of the MXTOOLS package for IRAF (http://www.noao.edu/staff/mighell/mxtools). This work is supported by a grant from NASA's Office of Space Science.

We present our analysis of archival Hubble Space Telescope Wide Field Planetary Camera 2 (WFPC2) observations in F450W (~B) and F555W (~V) of the intermediate- age populous star clusters NGC 121, NGC 339, NGC 361, NGC 416, and Kron 3 in the Small Magellanic Cloud. We use published photometry of two other SMC populous star clusters, Lindsay 1 and Lindsay 113, to investigate the age sequence of these seven populous star clusters in order to improve our understanding of the formation chronology of the SMC. We analyzed the V vs (B-V) and M_V vs (B-V)_0 color-magnitude diagrams of these populous Small Magellanic Cloud star clusters using a variety of techniques and determined their ages, metallicities, and reddenings. These new data enable us to improve the age-metallicity relation of star clusters in the Small Magellanic Cloud. In particular, we find that a closed-box continuous star-formation model does not reproduce the age-metallicity relation adequately. However, a theoretical model punctuated by bursts of star formation is in better agreement with the observational data presented herein., 20 pages (LaTeX+aaspp4.sty), 10 tables (PostScript format) and 14 figures (PostScript format). The PostScript version of the paper, tables, and full-resolution figures is available at http://www.noao.edu/noao/staff/mighell/oldsmc/ To appear in the Astronomical Journal (accepted 1998 August 10)

We present our analysis of Hubble Space Telescope Wide Field Planetary Camera 2 observations in F555W (~V) and F814W (~I) of the Carina dwarf spheroidal galaxy. The resulting V vs (V-I) color-magnitude diagrams reach V ~ 27.1 mag. The reddening of Carina is estimated to be E(V-I) = 0.08 +- 0.02 mag. A new estimate of the distance modulus of Carina, (m-M)_0 = 19.87 +- 0.11 mag, has been derived primarily from existing photometry in the literature. The apparent distance moduli in V and I were determined to be (m-M)_V = 20.05 +- 0.11 mag and (m-M)_I = 19.98 +- 0.12 mag, respectively. These determinations assumed that Carina has a metallicity of [Fe/H] = -1.9 +- 0.2 dex. This space-based observation, when combined with previous ground-based observations, is consistent with (but does not necessarily prove) the following star formation scenario. The Carina dwarf spheroidal galaxy formed its old stellar population in a short burst (=< 3 Gyr) at about the same time the Milky Way formed its globular clusters. The dominant burst of intermediate-age star formation then began in the central region of the galaxy where stars formed for several billion years before the process of star formation became efficient enough in the outer regions of the galaxy to allow for the formation of large numbers of stars. There has been negligible star formation during the last few billion years. This observation provides evidence that at least some dwarf galaxies can have complex global star formation histories with local variations of the rate of star formation as a function of time and position within the galaxy., 23 pages (LaTeX+aaspp4.sty), 4 tables and 9 figures (Postscript, gzipped tar file). Postscript version of paper, tables, and full-resolution figures available at http://www.noao.edu/noao/staff/mighell/carina.html To appear in the Astronomical Journal

The nearest massive members of the Local Group- M31, M32, and M33- give us a window on the stellar populations and dust in the central 100 pc of galaxies. We report new imaging of the stellar populations and dust in the central 100 pc of these galaxies using HST and WFPC2.

We present a new computational approach to the inversion of solar photospheric Stokes polarization profiles, under the Milne-Eddington model, for vector magnetography. Our code, named GENESIS (GENEtic Stokes Inversion Strategy), employs multi-threaded parallel-processing techniques to harness the computing power of graphics processing units GPUs, along with algorithms designed to exploit the inherent parallelism of the Stokes inversion problem. Using a genetic algorithm (GA) engineered specifically for use with a GPU, we produce full-disc maps of the photospheric vector magnetic field from polarized spectral line observations recorded by the Synoptic Optical Long-term Investigations of the Sun (SOLIS) Vector Spectromagnetograph (VSM) instrument. We show the advantages of pairing a population-parallel genetic algorithm with data-parallel GPU-computing techniques, and present an overview of the Stokes inversion problem, including a description of our adaptation to the GPU-computing paradigm. Full-disc vector magnetograms derived by this method are shown, using SOLIS/VSM data observed on 2008 March 28 at 15:45 UT.

We present our analysis of archival Hubble Space Telescope Wide Field Planetary Camera 2 (WFPC2) observations in F450W (~B) and F555W (~V) of the intermediate-age populous star clusters NGC 121, NGC 339, NGC 361, NGC 416, and Kron 3 in the Small Magellanic Cloud. We use published photometry of two other SMC populous star clusters, Lindsay 1 and Lindsay 113, to investigate the age sequence of these seven star clusters in order to improve our understanding of the formation chronology of the SMC. We analyzed the V vs B–V and MV vs (B–V)o color-magnitude diagrams of these populous Small Magellanic Cloud star clusters using a variety of techniques and determined their ages, metallicities, and reddenings. These new data enable us to improve the age-metallicity relation of star clusters in the Small Magellanic Cloud. In particular, we find that a closed-box continuous star-formation model does not reproduce the age-metallicity relation adequately. However, a theoretical model punctuated by bursts of star formation is in better agreement with the observational data. The full details of this analysis are reported in Mighell, Sarajedini, & French (1998, AJ, 116, 2395).

Observations of the recently discovered dwarf galaxy in Tucana, which is a likely member of the Local Group, are presented. The system is highly flattened and classified as dE5. An upper limit on the distance modulus of 24.75 is determined from a V, V-I color-magnitude diagram. This galaxy has a B-R color of 1.1, and with the upper limit to the distance modulus, an absolute R magnitude of −10. This apparently isolated dwarf system, being on the opposite side of the Milky Way from most of the Local Group, may provide important constraints on Local Group dynamics

Discussion d'un algorithme d'ajustement aux moindres carres, non lineaire, base sur la methode de Marquardt et capable de produire une photometrie stellaire precise des observations CCD de champs stellaires charges. la performance de cet algorithme est mesuree en utilisant des observations CCD reelles et simulees, et comparee avec les erreurs photometriques estimees par l'algorithme et la theorie

We assume that the density of sites of technical civilizations emitting suitable signals whether purposeful or unintentional is proportional to the stellar density at any location in our Galaxy, as modelled by Bahcall and Soneira 1980. A wide variety of possible radio luminosity functions O(L) for these civilizations is then assumed and for each the number of detectable signals per square degree over the sky is calculated. We find that most detectable signals occur at galactic latitudes of 10° or less and longitudes within 90° of the galactic center, a region which covers only 9 per cent of the entire sky. This result holds for a wide range of O(L) types, including Gaussian distributions and power law functions with slopes less than 2.5, or any combination of these. The Milky Way is much less preferred, but still advantageous, for cases of steep power law functions (slopes greater than 2.5) or Gaussian functions with mean luminosities so low that any existing civilizations can only be detected at distances less than 0.5 kpc. The only cases where low galactic latitudes are not advantageous are (1) for frequencies of operation less than 600 MHz where the deleterious effects on signal-to-noise ratios of the natural galactic background emission become dominant, and (2) in searches for narrowband (≤ 1 Hz) signals at frequencies less than 2 GHz where significant interstellar broadening of signals occurs over distances of ≳10 kpc. Furthermore, all of the above results have broader applicability: they are equally valid for searches for any type of natural radio phenomenon if its probability of occurrence is proportional to stellar density.