Cepheid variables in the LMC cluster NGC 1866. I. New BVRI CCD photometry

We report BV(RI)c CCD photometric data for a group of seven Cepheid variables in the young, rich cluster NGC 1866 in the Large Magellanic Cloud. The photometry was obtained as part of a program to determine accurate distances to these Cepheids by means of the infrared surface brightness technique, and to improve the LMC Cepheid database for constructing Cepheid PL and PLC relations. Using the new data together with data from the literature, we have determined improved periods for all variables. For five fundamental mode pulsators, the light curves are now of excellent quality and will lead to accurate distance and radius determinations once complete infrared light curves and radial velocity curves for these variables become available.Comment: To appear in ApJ Supp., AASTeX, 24 pages, 8 tables, 8 figure

The Opacity of Nearby Galaxies from Counts of Background Galaxies: II. Limits of the Synthetic Field Method

Recently, we have developed and calibrated the Synthetic Field Method (SFM) to derive the total extinction through disk galaxies. The method is based on the number counts and colors of distant background field galaxies that can be seen through the foreground object, and has been successfully applied to NGC 4536 and NGC 3664, two late-type galaxies located, respectively, at 16 and 11 Mpc. Here, we study the applicability of the SFM to HST images of galaxies in the Local Group, and show that background galaxies cannot be easily identified through these nearby objects, even with the best resolution available today. In the case of M 31, each pixel in the HST images contains 50 to 100 stars, and the background galaxies cannot be seen because of the intrinsic granularity due to strong surface brightness fluctuations. In the LMC, on the other hand, there is only about one star every six linear pixels, and the lack of detectable background galaxies results from a ``secondary'' granularity, introduced by structure in the wings of the point spread function. The success of the SFM in NGC 4536 and NGC 3664 is a natural consequence of the reduction of the intensity of surface brightness fluctuations with distance. When the dominant confusion factor is structure in the PSF wings, as is the case of HST images of the LMC, and would happen in M 31 images obtained with a 10-m diffraction- limited optical telescope, it becomes in principle possible to improve the detectability of background galaxies by subtracting the stars in the foreground object. However, a much better characterization of optical PSFs than is currently available would be required for an adequate subtraction of the wings. Given the importance of determining the dust content of Local Group galaxies, efforts should be made in that direction.Comment: 45 pages, 10 Postscript figure

The Opacity of Spiral Galaxy Disks VIII: Structure of the Cold ISM

The quantity of dust in a spiral disk can be estimated using the dust's typical emission or the extinction of a known source. In this paper, we compare two techniques, one based on emission and one on absorption, applied on sections of fourteen disk galaxies. The two measurements reflect, respectively the average and apparent optical depth of a disk section. Hence, they depend differently on the average number and optical depth of ISM structures in the disk. The small scale geometry of the cold ISM is critical for accurate models of the overall energy budget of spiral disks. ISM geometry, relative contributions of different stellar populations and dust emissivity are all free parameters in galaxy Spectral Energy Distribution (SED) models; they are also sometimes degenerate, depending on wavelength coverage. Our aim is to constrain typical ISM geometry. The apparent optical depth measurement comes from the number of distant galaxies seen in HST images through the foreground disk. We measure the IR flux in images from the {\it Spitzer} Infrared Nearby Galaxy Survey in the same section of the disk that was covered by HST. A physical model of the dust is fit to the SED to estimate the dust surface density, mean temperature, and brightness in these disk sections. The surface density is subsequently converted into the average optical depth estimate. The two measurements generally agree. The ratios between the measured average and apparent optical depths of the disk sections imply optically thin clouds in these disks. Optically thick disks, are likely to have more than a single cloud along the line-of-sight.Comment: 31 pages, 5 figures, 4 tables, accepted for publication in A

Malleability of the cortical hand map following a finger nerve block

Electrophysiological studies in monkeys show that finger amputation triggers local remapping within the deprived primary somatosensory cortex (S1). Human neuroimaging research, however, shows persistent S1 representation of the missing hand\u27s fingers, even decades after amputation. Here, we explore whether this apparent contradiction stems from underestimating the distributed peripheral and central representation of fingers in the hand map. Using pharmacological single-finger nerve block and 7-tesla neuroimaging, we first replicated previous accounts (electrophysiological and other) of local S1 remapping. Local blocking also triggered activity changes to nonblocked fingers across the entire hand area. Using methods exploiting interfinger representational overlap, however, we also show that the blocked finger representation remained persistent despite input loss. Computational modeling suggests that both local stability and global reorganization are driven by distributed processing underlying the topographic map, combined with homeostatic mechanisms. Our findings reveal complex interfinger representational features that play a key role in brain (re)organization, beyond (re)mapping

Malleability of the cortical hand map following a finger nerve block

Electrophysiological studies in monkeys show that finger amputation triggers local remapping within the deprived primary somatosensory cortex (S1). Human neuroimaging research, however, shows persistent S1 representation of the missing hand's fingers, even decades after amputation. Here, we explore whether this apparent contradiction stems from underestimating the distributed peripheral and central representation of fingers in the hand map. Using pharmacological single-finger nerve block and 7-tesla neuroimaging, we first replicated previous accounts (electrophysiological and other) of local S1 remapping. Local blocking also triggered activity changes to nonblocked fingers across the entire hand area. Using methods exploiting interfinger representational overlap, however, we also show that the blocked finger representation remained persistent despite input loss. Computational modeling suggests that both local stability and global reorganization are driven by distributed processing underlying the topographic map, combined with homeostatic mechanisms. Our findings reveal complex interfinger representational features that play a key role in brain (re)organization, beyond (re)mapping

Reaction rate of NaOCl in contact with bovine dentine: effect of activation, exposure time, concentration and pH

Abstract Macedo RG, Wesselink PR, Zaccheo F, Fanali D, van der Sluis LWM. Reaction rate of NaOCl in contact with bovine dentine: effect of activation, exposure time, concentration and pH. International Endodontic Journal. Aim To determine the influence of activation method (ultrasound or laser), concentration, pH and exposure time on the reaction rate (RR) of NaOCl when in contact with dentinal walls. Methodology The walls from standardized root canals in bovine incisors were exposed to a standardized volume of sodium hypochlorite (NaOCl) with different concentrations (2% and 10%), pH (5 and 12) and exposure times (1 and 4 min). Two irrigation protocols were tested: passive ultrasonic irrigation or laser activated irrigation with no activation as the control. The activation interval lasted 1 min followed by a rest interval of 3 min with no activation. The RR was determined by measuring the iodine concentration using an iodine/thiosulfate titration method. Results Exposure time, concentration and activation method influenced the reaction rate of NaOCl whereas pH did not. Conclusions Activation is a strong modulator of the reaction rate of NaOCl. During the rest interval of 3 min, the consumption of available chlorine increased significantly. This effect seems to be more pronounced after irrigant activation by laser. pH did not affect the reaction rate of 2% NaOCl

Passive ultrasonic irrigation of the root canal: a review of the literature.

Abstract van der Sluis LWM, Versluis M, Wu MK, Wesselink PR. Passive ultrasonic irrigation of the root canal: a review of the literature. International Endodontic Journal, 40, 415-426, 2007. Ultrasonic irrigation of the root canal can be performed with or without simultaneous ultrasonic instrumentation. When canal shaping is not undertaken the term passive ultrasonic irrigation (PUI) can be used to describe the technique. In this paper the relevant literature on PUI is reviewed from a MEDLINE database search.Passive ultrasonic irrigation can be performed with a small file or smooth wire (size 10-20) oscillating freely in the root canal to induce powerful acoustic microstreaming. PUI can be an important supplement for cleaning the root canal system and, compared with traditional syringe irrigation, it removes more organic tissue, planktonic bacteria and dentine debris from the root canal. PUI is more efficient in cleaning canals than ultrasonic irrigation with simultaneous ultrasonic instrumentation. PUI can be effective in curved canals and a smooth wire can be as effective as a cutting K-file. The taper and the diameter of the root canal were found to be important parameters in determining the efficacies of dentine debris removal. Irrigation with sodium hypochlorite is more effective than with water and ultrasonic irrigation is more effective than sonic irrigation in the removal of dentine debris from the root canal. The role of cavitation during PUI remains inconclusive. No detailed information is available on the influence of the irrigation time, the volume of the irrigant, the penetration depth of the instrument and the shape and material properties of the instrument. The influence of irrigation frequency and intensity on the streaming pattern as well as the complicated interaction of acoustic streaming with the adherent biofilm needs to be clarified to reveal the underlying physical mechanisms of PUI

The Pulsation of Chi Cygni Imaged by Optical Interferometry; a Novel Technique to Derive Distance and Mass of Mira Stars

We present infrared interferometric imaging of the S-type Mira star Chi Cygni. The object was observed at four different epochs in 2005-2006 with the IOTA optical interferometer (H band). Images show up to 40% variation in the stellar diameter, as well as significant changes in the limb darkening and stellar inhomogeneities. Model fitting gave precise time-dependent values of the stellar diameter, and reveals presence and displacement of a warm molecular layer. The star radius, corrected for limb darkening, has a mean value of 12.1 mas and shows a 5.1mas amplitude pulsation. Minimum diameter was observed at phase 0.94+/-0.01. Maximum temperature was observed several days later at phase 1.02+/-0.02. We also show that combining the angular acceleration of the molecular layer with CO (Delta v = 3) radial velocity measurements yields a 5.9+/-1.5 mas parallax. The constant acceleration of the CO molecules -- during 80% of the pulsation cycle -- lead us to argument for a free-falling layer. The acceleration is compatible with a gravitational field produced by a 2.1(+1.5/-0.7) solar mass star. This last value is in agreement with fundamental mode pulsator models. We foresee increased development of techniques consisting in combining radial velocity with interferometric angular measurements, ultimately allowing total mapping of the speed, density, and position of the diverse species in pulsation driven atmospheres.Comment: 36 pages, accepted in Ap

Distances, ages, and epoch of formation of globular clusters

We review the results on distances and absolute ages of galactic globular clusters (GCs) obtained after the release of the Hipparcos catalogue. Several methods for the Population II local distance scale are discussed, exploiting NEW RESULTS for RR Lyraes in the Large Magellanic Cloud (LMC). We find that the so-called Short and Long Distance Scales may be reconciled whether a consistent reddening scale is adopted for Cepheids and RR Lyrae variables in the LMC. Distances and ages for the 9 clusters discussed in Paper I are re-derived using an enlarged sample of local subdwarfs, which includes about 90% of the metal-poor dwarfs with accurate parallaxes (Delta p/p < 0.12) in the whole Hipparcos catalogue. On average, our revised distance moduli are decreased by 0.04 mag with respect to Paper I. The corresponding age of the GCs is t=11.5+-2.6 Gyr (95% confidence range). The relation between Mv(ZAHB) and metallicity for the nine programme clusters turns out to be Mv(ZAHB)=(0.18+-0.09)([Fe/H]+1.5)+(0.53+-0.12).Thanks to Hipparcos the major contribution to the total error budget associated with the subdwarf fitting technique has been moved from parallaxes to photometric calibrations, reddening and metallicity scale. This total uncertainty still amounts to about +-0.12 mag. Comparing the corresponding (true) LMC distance modulus 18.64+-0.12 mag with other existing determinations, we conclude that at present the best estimate for the distance of the LMC is: 18.54+-0.03+-0.06, suggesting that distances from the subdwarf fitting method are 1 sigma too long. Consequently, our best estimate for the age of the GCs is revised to: Age = 12.9+-2.9 Gyr (95% confidence range). The best relation between Mv(ZAHB) and [Fe/H] is: Mv(ZAHB) =(0.18+-0.09)([Fe/H]+1.5)+(0.63+-0.07).Comment: 76 pages, 6 encapsulated figures and 6 tables. Latex, uses aasms4.sty. Revised and improved version, with new data on field RR Lyraes in LMC. Accepted in the Astrophysical Journa

Subaru and Swift observations of V652 Herculis: resolving the photospheric pulsation

High-resolution spectroscopy with the Subaru High Dispersion Spectrograph, and Swift ultraviolet photometry are presented for the pulsating extreme helium star V652 Her. Swift provides the best relative ultraviolet photometry obtained to date, but shows no direct evidence for a shock at ultraviolet or X-ray wavelengths. Subaru has provided high spectral and high temporal resolution spectroscopy over six pulsation cycles (and eight radius minima). These data have enabled a line-by-line analysis of the entire pulsation cycle and provided a description of the pulsating photosphere as a function of optical depth. They show that the photosphere is compressed radially by a factor of at least 2 at minimum radius, that the phase of radius minimum is a function of optical depth and the pulse speed through the photosphere is between 141 and 239 km s−1 (depending how measured) and at least 10 times the local sound speed. The strong acceleration at minimum radius is demonstrated in individual line profiles; those formed deepest in the photosphere show a jump discontinuity of over 70 kms−1 on a time-scale of 150 s. The pulse speed and line profile jumps imply a shock is present at minimum radius. These empirical results provide input for hydrodynamical modelling of the pulsation and hydrodynamical plus radiative transfer modelling of the dynamical spectra