Aperture Corrections Research Articles

THE HST /ACS COMA CLUSTER SURVEY. II. DATA DESCRIPTION AND SOURCE CATALOGS

The Coma cluster was the target of a HST-ACS Treasury program designed for deep imaging in the F475W and F814W passbands. Although our survey was interrupted by the ACS instrument failure in 2007, the partially completed survey still covers ~50% of the core high-density region in Coma. Observations were performed for 25 fields that extend over a wide range of cluster-centric radii (~1.75 Mpc) with a total coverage area of 274 arcmin^2. The majority of the fields are located near the core region of Coma (19/25 pointings) with six additional fields in the south-west region of the cluster. In this paper we present reprocessed images and SExtractor source catalogs for our survey fields, including a detailed description of the methodology used for object detection and photometry, the subtraction of bright galaxies to measure faint underlying objects, and the use of simulations to assess the photometric accuracy and completeness of our catalogs. We also use simulations to perform aperture corrections for the SExtractor Kron magnitudes based only on the measured source flux and half-light radius. We have performed photometry for ~73,000 unique objects; one-half of our detections are brighter than the 10-sigma point-source detection limit at F814W=25.8 mag (AB). The slight majority of objects (60%) are unresolved or only marginally resolved by ACS. We estimate that Coma members are 5-10% of all source detections, which consist of a large population of unresolved objects (primarily GCs but also UCDs) and a wide variety of extended galaxies from a cD galaxy to dwarf LSB galaxies. The red sequence of Coma member galaxies has a constant slope and dispersion across 9 magnitudes (-21<M_F814W<-13). The initial data release for the HST-ACS Coma Treasury program was made available to the public in 2008 August. The images and catalogs described in this study relate to our second data release.

Fast acquisition aperture correction in prestack depth migration using beamlet decomposition

Wave-equation-based acquisition aperture correction in the local angle domain can improve image amplitude significantly in prestack depth migration. However, its original implementation is inefficient because the wavefield decomposition uses the local slant stack (LSS), which is demanding computationally. We propose a faster method to obtain the image and amplitude correction factor in the local angle domain using beamlet decomposition in the local wavenumber domain. For a given frequency, the image matrix in the local wavenumber domain for all shots can be calculated efficiently. We then transform the shot-summed image matrix from the local wavenumber domain to the local angle domain (LAD). The LAD amplitude correction factor can be obtained with a similar strategy. Having a calculated image and correction factor, one can apply similar acquisition aperture corrections to the original LSS-based method. For the new implementation, we compare the accuracy and efficiency of two beamlet decompositions: Gabor-Daubechies frame (GDF) and local exponential frame (LEF). With both decompositions, our method produces results similar to the original LSS-based method. However, our method can be more than twice as fast as LSS and cost only twice the computation time of traditional one-way wave-equation-based migrations. The results from GDF decomposition are superior to those from LEF decomposition in terms of artifacts, although GDF requires a little more computing time.

THE ACS VIRGO CLUSTER SURVEY XVI. SELECTION PROCEDURE AND CATALOGS OF GLOBULAR CLUSTER CANDIDATES

We present catalogs of globular cluster candidates for the 100 galaxies of the Advanced Camera for Surveys Virgo Cluster Survey, a large program to carry out imaging of early-type members of the Virgo Cluster using the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope. We describe the procedure used to select bona fide globular cluster candidates out of the full list of detections based on model-based clustering methods with the use of expected contamination catalogs constructed using blank field observations and which are customized for each galaxy. We also present the catalogs of expected contaminants for each of our target galaxies. For each detected source we measure its position, magnitudes in the F475W ( Sloan g) and F850LP ( Sloan z) bandpasses, and half-light radii by fitting point-spread function convolved King models to the observed light distribution. These measurements are presented for 20,375 sources, of which 12,763 are likely to be globular clusters. Finally, we detail the calculation of the aperture corrections adopted for the globular cluster photometry.

Uniting old stellar systems: from globular clusters to giant ellipticals

Elliptical galaxies and globular clusters (GCs) have traditionally been regarded as physically distinct entities due to their discontinuous distribution in key scaling diagrams involving size, luminosity and velocity dispersion. Recently this distinctness has been challenged by the discovery of stellar systems with mass intermediate between those of GCs and dwarf ellipticals (such as ultracompact dwarfs and dwarf galaxy transition objects). Here we examine the relationship between the virial and stellar mass for a range of old stellar systems, from GCs to giant ellipticals, and including such intermediate-mass objects (IMOs). Improvements on previous work in this area include the use of (i) near-infrared magnitudes from the Two Micron All Sky Survey (2MASS), (ii) aperture corrections to velocity dispersions, (iii) homogeneous half-light radii and (iv) accounting for the effects of non-homology in galaxies. We find a virial-to-stellar mass relation that ranges from ∼10 4 M ⊙ systems (GCs) to ∼10 12 M⊙ systems (elliptical galaxies). The lack of measured velocity dispersions for dwarf ellipticals with - 16 > M K > - 18 (∼ 10 8 M ⊙ ) currently inhibits our ability to determine how, or indeed if, these galaxies connect continuously with GCs in terms of their virial-to-stellar mass ratios. We find elliptical galaxies to have roughly equal fractions of dark and stellar matter within a virial radius; only in the most massive (greater than 10 12 M ⊙ ) ellipticals does dark matter dominate the virial mass. Although the IMOs reveal slightly higher virial-to-stellar mass ratios than lower mass GCs, this may simply reflect our limited understanding of their initial mass function (and hence their stellar mass-to-light ratios) or structural properties. We argue that most of these IMOs have similar properties to massive GCs, i.e. IMOs are essentially massive star clusters. Only the dwarf spheroidal galaxies exhibit behaviour notably distinct from the other stellar systems examined here, i.e. they display a strongly increasing virial-to-stellar mass ratio (equivalent to higher dark matter fractions) with decreasing stellar mass. The data used in this study are available in electronic format.

Absolute Calibration and Characterization of the Multiband Imaging Photometer for Spitzer. IV. The Spectral Energy Distribution Mode

ABSTRACTThe spectral energy distribution (SED) mode of the Multiband Imaging Photometer for Spitzer (MIPS) aboard the Spitzer Space Telescope provides low-spectral resolution (R ≈ 15–25) spectroscopy in the far-infrared using the MIPS 70 μm detector. A reflective grating provides a dispersion of 1.7 μm per pixel, and an effective wavelength coverage of 52.8–98.7 μm over detector rows 1–27. The final 5 detector rows are contaminated by second-order diffracted light and are left uncalibrated. The flux calibration is based on observations of MIPS calibration stars with 70 μm flux densities of 0.5–15 Jy. The point-source flux calibration accuracy is estimated to be 10% or better down to about 0.5 Jy at the blue end of the spectrum and to ∼2 Jy near the red end. With additional uncertainties from the illumination and aperture corrections included, the surface brightness calibration of extended sources is accurate to ∼15%. Repeatability of better than 5% is found for the SED mode through multiple measurements of several calibration stars.

The great observatories origins deep survey

Aims. We present the final public data release of the VLT/ISAAC near-infrared imaging survey in the GOODS-South field. The survey covers an area of 172.5, 159.6 and 173.1 arcmin in the J, H, and Ks bands, respectively. For point sources total limiting magnitudes of J = 25.0, H = 24.5, and Ks = 24.4 (5σ, AB) are reached within 75% of the survey area. Thus these observations are significantly deeper than the previous EIS Deep Public Survey which covers the same region. The image quality is characterized by a point spread function ranging between 0.34′′ and 0.65′′ FWHM. The images are registered to a common astrometric grid defined by the GSC 2 with an accuracy of ∼0.06′′ RMS over the whole field. The overall photometric accuracy, including all systematic effects, adds up to 0.05 mag. The data are publicly available from the ESO science archive facility. Methods. We describe the data reduction, the calibration, and the quality control process. The final data set is characterized in terms of astrometric and photometric properties, including the PSF and the curve of growth. We establish an empirical model for the sky background noise in order to quantify the variation of limiting depth and statistical photometric errors over the survey area. We define a catalog of Ks-selected sources which contains JHKs photometry for 7079 objects. Differential aperture corrections were applied to the color measurements in order to avoid possible biases as a result of the variation of the PSF. We briefly discuss the resulting color distributions in the context of available redshift data. Furthermore, we estimate the completeness fraction and relative contamination due to spurious detections for source catalogs extracted from the survey data. For this purpose, an empirical study based on a deep Ks image of the Hubble Ultra Deep Field is combined with extensive image simulations. Results. With respect to previous deep near-infrared surveys, the surface density of faint galaxies has been established with unprecedented accuracy by virtue of the unique combination of depth and area of this survey. We derived galaxy number counts over eight magnitudes in flux up to J = 25.25, H = 25.0, Ks = 25.25 (in the AB system). Very similar faint-end logarithmic slopes between 0.24 and 0.27 mag−1 were measured in the three bands. We found no evidence for a significant change in the slope of the logarithmic galaxy number counts at the faint end.

TheSpitzer Space TelescopeExtragalactic First Look Survey: 24 μm Data Reduction, Catalog, and Source Identification

We present the reduction of the 24 μm data obtained during the first cosmological survey performed by the Spitzer Space Telescope. Images of a region of sky at moderately high Galactic latitude (l = 88.3°, b = +34.9°) were obtained on 2003 December 9-11. The survey consists of a shallow observation of 2.5° × 2° centered at 17h18m, +59°30' (main survey) and a deeper observation of 1° × 0.5° centered at 17h17m, +59°45' (verification survey). Issues with the reduction of the 24 μm MIPS data are discussed and solutions to attenuate instrumental effects are proposed and applied to the data. Approximately 17,000 sources are extracted with a signal-to-noise ratio (S/N) greater than 5. The photometry of the point sources is evaluated through point-spread function (PSF) fitting using an empirical PSF derived from the data. Aperture corrections and the absolute calibration have been checked using stars in the field. Astrometric and photometric errors depend on the S/N of the source varying between 0farcs35^-1 and 5%-15%, respectively, for sources detected at 20-5 σ. The fluxes of the 123 extended sources have been estimated through aperture photometry. The extended sources cover less than 0.3% of the total area of the survey. Based on simulations, the main and verification surveys are 50% complete at 0.3 and 0.15 mJy, respectively. Counterparts have been searched for in optical and radio catalogs. More than 80% of the 24 μm sources have a reliable optical counterpart down to R = 25.5; 16% of the sources have a 20 cm counterpart down to 0.1 mJy and ~80% of the radio-IR associations have a reliable optical counterpart. A residual map is obtained by subtracting point sources detected at the 3 σ level and interpolating the regions occupied by extended sources. Several Galactic clouds with low and intermediate velocities are identified by comparison with neutral hydrogen data from this field.

Constraining the Adaptive Optics Point‐Spread Function in Crowded Fields: Measuring Photometric Aperture Corrections

The point-spread function (PSF) of an adaptive optics (AO) system is often poorly known. This ignorance can lead to significant systematic errors in photometry. Since the degree of AO correction is sensitive to the observing conditions: seeing, wind speed, brightness of the wavefront reference, etc., it would be desirable to estimate the PSF from the data themselves. We have developed a method to estimate the PSF delivered by an AO system in the case where the scene consists of a crowded star field. We model the modulation transfer function (MTF) of several key components of the imaging system. The power spectrum of the image, even a dense star field, can then be used to constrain our model, which in turn can be used to reconstruct the PSF. We show that the method yields reasonable fit parameters and a useful approximation to the PSF when applied to data from laser guide star (LGS) AO system at the Keck Observatory. Comparison of Keck LGS/AO and HST/NICMOS data shows that photometric accuracy of a few percent can be achieved for data with Strehl ratios as low as 4%.

Accurate photometry of extended spherically symmetric sources

We present a new method to derive reliable photometry of extended spherically symmetric sources from {\it HST} images (WFPC2, ACS/WFC and NICMOS/NIC2 cameras), extending existing studies of point sources and marginally resolved sources. We develop a new approach to accurately determine intrinsic sizes of extended spherically symmetric sources, such as star clusters in galaxies beyond the Local Group (at distances <~ 20 Mpc), and provide a detailed cookbook to perform aperture photometry on such sources, by determining size-dependent aperture corrections (ACs) and taking sky oversubtraction as a function of source size into account. In an extensive Appendix, we provide the parameters of polynomial relations between the FWHM of various input profiles and those obtained by fitting a Gaussian profile (which we have used for reasons of computational robustness, although the exact model profile used is irrelevant), and between the intrinsic and measured FWHM of the cluster and the derived AC. Both relations are given for a number of physically relevant cluster light profiles, intrinsic and observational parameters. AC relations are provided for a wide range of apertures. Depending on the size of the source and the annuli used for the photometry, the absolute magnitude of such extended objects can be underestimated by up to 3 mag, corresponding to an error in mass of a factor of 15. We carefully compare our results to those from the more widely used DeltaMag method, and find an improvement of a factor of 3--40 in both the size determination and the AC.

Early-type galaxy distances from the Fundamental Plane and surface brightness fluctuations

We compare two methods for deriving distances to early-type galaxies: fundamental plane (FP) and surface brightness fluctuations (SBF) distances for 170 galaxies. A third set of distances is provided by predictions derived from the density field of the IRAS redshift survey. Overall there is good agreement. However, several nearby, low-luminosity, mainly S0 galaxies have systematically low FP distances; we conclude that this is at least partly due to recent star formation and consequently low mass-to-light ratios. The tie between the Cepheid-calibrated SBF distances (Mpc) and the far-field calibrated FP distances (km/s) yields a Hubble constant H_0 = 68 +/- 3 km/s/Mpc, while the comparison between SBF and the IRAS-reconstructed distances yields H_0 = 74 +/- 2 (internal errorbars). Possible explanations for the marginal inconsistency include systematic errors in the redshift survey completeness estimates or in the FP aperture corrections, but at this point, the best estimate of H_0 from early-type galaxies may be a simple average of the above two estimates. After revising the SBF distances to be in agreement with the final set of Key Project Cepheid distances, we conclude H_0 = 73 +/- 4 +/- 11, where the second errorbar represents the total systematic uncertainty in the distance zero point. We also discuss the recently introduced fluctuation star count parameter Nbar as a less demanding alternative to (V-I) for calibrating SBF distances. The Nbar-calibrated SBF method is akin to a hybrid SBF-FP distance indicator, and we find that the use of Nbar actually improves the SBF distances. Further study of Nbar would provide useful constraints for elliptical galaxy formation models. (abridged)

Reprogramming of grip aperture in a double-step virtual grasping paradigm.

The present study investigated the control of manual prehension movements in humans. Subjects grasped luminous virtual discs with the thumb and index finger, and we recorded the instantaneous grip aperture, defined as the 3-D distance between the thumb and index finger. Target size could remain constant (single-step trials) or unexpectedly change shortly after target appearance (double-step trials). In single-step responses, grip aperture varied throughout the movement in a consistent fashion. Double-step responses exhibited distinct corrective modifications, which followed the target change with a latency similar to the normal reaction time. This suggests that visual size information has a fast and continuous access to the processes involved in grip formation. The grip-aperture profiles of single-step responses had a different shape when the target called for an increase than when it called for a decrease in the initial finger distance. The same asymmetry was observed for aperture corrections in double-step trials. These findings indicate that increases and decreases of grip aperture are controlled through separate processes, engaged equally by the appearance and by the size change of a target. Corrections of grip aperture in double-step trials had a higher peak velocity and reached their maximum as well as their final value earlier than the aperture profiles of single-step trials. Nevertheless, the total duration of double-step trials was prolonged. These response characteristics did not fit with either of the three corrective strategies previously proposed for double-step pointing movements, which could indicate that grasping and pointing movements are controlled by different mechanisms. However, more data are needed to substantiate this view.

1.25-mm observations of a complete sample of IRAS galaxies -- II. Dust properties

We present 1.25 mm continuum data for a southern galaxy sample selected from the IRAS PSC and complete to S_60=2 Jy. Two thirds of the galaxies have been detected and significant limits on the remaining objects have been set. We find, on a statistical basis, indications that the dust emission in these galaxies is somewhat more centrally concentrated than that of the optical light, possibly tracing a higher metal content in the inner galactic regions. This result also allows to estimate the aperture corrections to the millimetric data. The latter, together with IRAS photometric data, have been used to compare the broad-band FIR/mm spectra with a simple dust model. According to their far-IR/mm spectrum, the sample galaxies show a dichothomy: almost half of the objects, those displaying bright 25-60um fluxes ascribed to warm dust residing in 'starburst' regions, are characterized by higher values of the bolometric (optical + FIR) luminosity, of the dust-to-gas mass ratio, of the dust optical depths and of the overall extinction. A complementary class of objects dominated by cold dust ('cirrus') shows opposite trends. Because of the favourable observational setup, selection wavelength and completeness, we believe these data provide an exhaustive and unbiased view of dust properties in spiral galaxies.

Deep galaxy counts in the K band with the Kech telescope

We present deep galaxy counts in the K (⋋ 2.2 micrometer) band, obtained at the W. M. Keck 10 m telescope. The data reach limiting magnitudes K approximately 24 mag, about 5 times deeper than the deepest published K-band images to date. The counts are performed in three small (approximately 1 min), widely separated high-latitude fields. Extensive Monte Carlo tests were used to derive the completeness corrections and minimize photometric biases. The counts continue to rise, with no sign of a turnover, down to the limits of our data, with the logarithmic slope of d log N/dm = 0.315 +/- 0.02 between K = 20 and 24 mag. This implies a cumulative surface density of approximately 5 x 10^5 galaxies/sq deg, or approximately 2 x 10^10 over the entire sky, down to K = 24 mag. Our counts are in good agreement with, although slightly lower than, those from the Hawaii Deep Survey by Cowie and collaborators; the discrepancies may be due to the small differences in the aperture corrections. We compare our counts with some of the available theoretical predictions. The data do not require models with a high value of Omega_0, but can be well fitted by models with no (or little) evolution, and cosmologies with a low value of Omega_0. Given the uncertainties in the models, it may be premature to put useful constrains on the value of Omega_0 from the counts alone. Optical-to-IR colors are computed, using CCD data obtaind previously at Palomar. We find a few red galaxies with (r-K) approximately greater than 5 mag, or (i-K) approximately greater than 5 mag; these may be ellipticals at z approximately 1. While the redshift distribution of galaxies in our counts is still unknown, the flux limits reached would allow us to detect unobscured L_* galaxies out to substantial redshifts (z greater than 3?)

HST IMAGING OF THE LARGE MAGELLANIC CLOUD: THE FIELD STAR POPULATION NEAR 30 DORADUS

ABSTRACT We present deep color-magnitude diagrams for two fields in the Large Magellanic Cloud, located about 6 arcminutes from 30 Doradus. The data are from images taken with the Hubble Space Telescope's Wide Field Camera, as part of the Medium Deep Survey Key Project. We describe a procedure for measuring stellar magnitudes in relatively crowded HST images based on aperture corrections. This procedure is used to obtain color-magnitude diagrams containing a total of ~7200 stars with 18 < V < 24. The color-magnitude diagrams shows a well populated main-sequence, and a pronounced giant branch concentrated at V ~ 20. There is tentative evidence for a population of low metallicity main-sequence stars, which may confirm the suggestion that the LMC has, like spiral galaxies, a metal-poor, spheroidal component.

Epi-illumination optical design for fluorescence polarization measurements in flow systems

An epi-illumination design for fluorescence polarization measurements is introduced in flow cytometry with the optical axis orthogonally aligned to the cell stream. Various optical components and designs are discussed with respect to their influence on polarization measurements. Using the epi-configuration, paired measurements with the direction of polarization of the exciting light changed orthogonally are proposed for the compensation of system anisotropies and electronic mismatch. Large aperture corrections are employed for the excitation as well as for the emission pathway. Additional parameters such as fluorescence at 90 degrees, multiangle light scattering, and high precision cell-sizing by internally calibrated time of the flight measurements, as described previously, remain available with the design proposed here. Fluorescent latex microspheres, stained intracellular DNA, and algae have been used to test performance.

ON APERTURE CORRECTIONS FOR COMET MAGNITUDE ESTIMATES

ABSTRACT The results of a study into the effects of aperture on the observed brightness of comets are presented. Observations of 22 comets were used to determine the average aperture corrections for refractors and reflectors. The resulting aperture correction for refractors was only slightly less than that found by Bobrovnikoff. However, the aperture correction for reflectors was found to be less than one-third the value found by Bobrovnikoff for refractors. Key words: comets - magnitude estimate

Aperture corrections for sound-absorption measurement with light scattering: Danielmeyer, H.G. Journal of the Acoustical Society of America Vol 47, No 1 (part 2) (January 1970) pp 151–154 (2357)

CREB-binding protein (CBP) and p300 are transcriptional coactivators involved in numerous biological processes that affect cell growth, transformation, differentiation, and development. In this study, we provide evidence of the involvement of homeodomain-interacting protein kinase 2 (HIPK2) in the regulation of CBP activity. We show that HIPK2 interacts with and phosphorylates several regions of CBP. We demonstrate that serines 2361, 2363, 2371, 2376, and 2381 are responsible for the HIPK2-induced mobility shift of CBP C-terminal activation domain. Moreover, we show that HIPK2 strongly potentiates the transcriptional activity of CBP. However, our data suggest that HIPK2 activates CBP mainly by counteracting the repressive action of cell cycle regulatory domain 1 (CRD1), located between amino acids 977 and 1076, independently of CBP phosphorylation. Our findings thus highlight a complex regulation of CBP activity by HIPK2, which might be relevant for the control of specific sets of target genes involved in cellular proliferation, differentiation and apoptosis.

Aperture Corrections for Sound-Absorption Measurements with Light Scattering

Even small collection angles in the receiving optics can appreciably broaden, distort, and shift Brillouin lines observed in a light-scattering experiment, thereby causing errors in both sound absorption and sound velocity. A general expression for the observed lineshape is derived for a Lorentzian scattering line in terms of the distribution of thermal phonons and the shape of the collection aperture. Relaxational effects are also considered. For a square aperture, a closed-form solution is obtained and discussed. Applicable correction formulas for the true linewidth and lineshift are derived. To first approximation, Brillouin line is the sum of two arctan functions.

Some Remarks on the Question of Aperture Corrections in Interferometric Length Measurements

Some Remarks on the Question of Aperture Corrections in Interferometric Length Measurements

PHOTOGRAPHIC TIME AND APERTURE CORRECTIONS AT FINITE WORKING DISTANCES

School Science and MathematicsVolume 55, Issue 1 p. 56-65 PHOTOGRAPHIC TIME AND APERTURE CORRECTIONS AT FINITE WORKING DISTANCES Ronald L. Ives, Ronald L. Ives Cornell Aeronautical Laboratory, Inc.Search for more papers by this author Ronald L. Ives, Ronald L. Ives Cornell Aeronautical Laboratory, Inc.Search for more papers by this author First published: January 1955 https://doi.org/10.1111/j.1949-8594.1955.tb16841.xAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Volume55, Issue1January 1955Pages 56-65 RelatedInformation