Hubble Space Telescope Planetary Camera images of R136

The Planetary Camera of the Hubble Space Telescope has been used to obtain broad and narrowband images ofR136, the core of the massive star cluster 30 Doradus in the Large Magellanic Cloud. R136a, the brightest component ofR136, is shown to have at least 12 separate components, including the eight originally identified by speckle interferometry. Three of the 12 components are previously unidentified close companions of the speckle components. The stars within R136a are found to have luminosities and colors of normal evolved (Wolf-Rayet and blue supergiants) and zero-age main-sequence (ZAMS) massive stars. A narrowband He II filter was used to investigate the Wolf-Rayet stellar population. We find that three stars in R136a are of the Wolf-Rayet type; of the two identified from ground-based data, one is now resolved into two components. We present color-magnitude diagrams and a luminosity function of the stars within the larger region (~2 pc) defined as R136. We find that the stars in R136 are similar in color and luminosity to those of cluster members that lie outside that crowded inner region. The lower end of the color-magnitude diagram corresponds to ZAMS spectral type B3. No red supergiants have been detected within R136. The luminosity per unit area in the inner 1" (0.25 pc) of R136 is ≥ 50 times that of the center of Orion for a comparable area and seven times that of the core of NGC 3603. The luminosity per unit area of all of R136 is comparable to that of Orion but is sustained over 130 times the area. An F336W surface brightness profile is constructed for R136 based on the stellar photometry. The distribution is found to be consistent with a pure power law with l(r}ɑ r^y with y=-1.72±0.06 or with a small core with r_c 5 X 10^4 M_☉ pc^(-3). The implied upper limit on the relaxation time for the cluster is much smaller than the age of 3.5 X 10^6 yrs required by the presence of Wolf-Rayet stars. This suggests that relaxation effects have been very important in determining the observed structure of the cluster unless a large population of lower mass stars is also present

Imaging of the gravitational lens system PG 1115+080 with the Hubble Space Telescope

This paper is the first of a series presenting observations of gravitational lenses and lens candidates, taken with the Wide Field/Planetary Camera (WFPC) of the Hubble Space Telescope (HST). We have resolved the gravitational lens system PG 1115 + 080 into four point sources and a red, extended object that is presumably the lens galaxy; we present accurate relative intensities, colors, and positions of the four images, and lower accuracy intensity and position of the lens galaxy, all at the epoch 1991.2. Comparison with earlier data shows no compelling evidence for relative intensity variations between the QSO components having so far been observed. The new data agree with earlier conclusions that the system is rather simple, and can be produced by the single observed galaxy. The absence of asymmetry in the HST images implies that the emitting region of the quasar itself has an angular radius smaller than about 10 milliarcsec (100 pc for H_0=50, q_0=0.5)

Ionization fronts and shocked flows - The structure of the Orion Nebula at 0".1

We present HST Wide-Field Camera images of a field in the Orion Nebula obtained in emission from [S II], Hβ, and [O II]. The morphology of the [S II] emission is markedly different from the other lines. While Hβ and [O II] are distributed fairly smoothly, [S II] is dominated by filamentary features with widths between 0".1 and 1" which sharply highlight ionization fronts moving into dense neutral material. These photoionization fronts act as probes of the structure of the cavity walls of this blister H II region. Their morphology indicates that while the surfaces into which they are moving are textured, subarcsecond clumps with high density contrast are uncommon. An exception is a bow shock-shaped ionization front seen along the face of a solar system-sized (0".6 = 270 AU) clump which is itself seen in extinction. The field contains a number of HH objects and related structures, many of which were previously recognized as such, but whose complex structure is revealed here by the resolution of HST. These include M42 HH 1, which is seen to be an intricate structure of knots and filaments with a head-tail morphology. M42 HH 2 shows structure from both the shocked cavity walls and the shocked atomic outflow. M42 HH 5-7 break into numerous condensations with an appearance reminiscent of HH 7-11. All objects with a bow shockshaped structure (i.e., M42 HH 1, 5, 7, and 10) show enhanced Hβ emission at the apex of the structure where the shock should be strongest. M42 HH 8 and 9 may be HH objects viewed face-on, or alternatively condensations photoionized by a nearby A or B star. Emission from [S II] traces shocks at the walls of an ionized jet apparently emanating from a star in a dark cloud. This cloud seen in extinction is coincident with H_2 Peak 1, which we propose is on the near side of the nebula

Stellar photometry with the Hubble Space Telescope Wide-field/Planetary camera - A progress report

We describe the prospects for the use of the Wide-Field/Planetary Camera (WFPC) for stellar photometry. The large halos of the point-spread function (PSF) resulting from spherical aberration and from spatial, temporal, and color variations of the PSF are the main limitations to accurate photometry. Degradations caused by crowding are exacerbated by the halos of the PSF. Here we attempt to quantify these effects and determine the current accuracy of stellar photometry with the WFPC. In realistic cases, the brighter stars in crowded fields have 0.09 mag errors; fainter stars have larger errors depending on the degree of crowding. We find that measuring Cepheids in Virgo Cluster galaxies is not currently possible without inordinate increases in exposure times

Reduction of PG:1115+080 Images

The data are three exposures in PC6 through F785LP obtained on March 3, 1991. The exposure times are 120, 400, and 400 seconds. The data are reduced with the "standard" WFPC reduction scheme: A-to-D correction, DC bias subtraction, AC bias subtraction, dark current subtraction, preflash subtraction, and flat field normalization, using the best available calibration data. The exposures are combined into a weighted average normalized to 400 seconds exposure time, so one DN (data number) is about 17.25 electrons. At this step, cosmic rays are removed by intercomparison of the three images

Esophageal motor abnormalities in scleroderma and related diseases

Esophageal motor activity was measured by intra-esophageal pressure recordings in 53 patients with scleroderma and 29 patients with other collagen diseases. The purpose of the study was to determine the relationship of motor abnormalities to esophageal symptoms, to compare the abnormalities in scleroderma with those in other collagen diseases, and to try to increase understanding of the responsible mechanism. Methacholine was given to 36 of the 53 patients with scleroderma to confirm that the Mecholyl test is negative in scleroderma and to see whether intraluminal pressure changes accompany the resulting improvement in esophageal emptying.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44360/1/10620_2005_Article_BF02233564.pd

Hubble Space Telescope WFPC2 Imaging of M16: Photoevaporation and Emerging Young Stellar Objects

We present Hubble Space Telescope WFPC2 images of elephant trunks in the H II region M16. There are three principle results of this study. First, the morphology and stratified ionization structure of the interface between the dense molecular material and the interior of the H II region is well understood in terms of photoionization of a photoevaporative flow. Photoionization models of an empirical density profile capture the essential features of the observations, including the extremely localized region of [S II] emission at the interface and the observed offset between emission peaks in lower and higher ionization lines. The details of this structure are found to be a sensitive function both of the density profile of the interface and of the shape of the ionizing continuum. Interpretation of the interaction of the photoevaporative flow with gas in the interior of the nebula supports the view that much of the emission from H II regions may arise in such flows. Photoionization of photoevaporative flows may provide a useful paradigm for interpreting a wide range of observations of H II regions. Second, we report the discovery of a population of small cometary globules that are being uncovered as the main bodies of the elephant trunks are dispersed. Several lines of evidence connect these globules to ongoing star formation, including the association of a number of globules with stellar objects seen in IR images of M16 or in the continuum HST images themselves. We refer to these structures as evaporating gaseous globules, or "EGGs." These appear to be the same type of object as the nebular condensations seen previously in M42. The primary difference between the two cases is that in M16 we are seeing the objects from the side, while in M42 the objects are seen more nearly face-on against the backdrop of the ionized face of the molecular cloud. We find that the "evaporating globule" interpretation naturally accounts for the properties of objects in both nebulae, while avoiding serious difficulties with the competing "evaporating disk" model previously applied to the objects in M42. More generally, we find that disk-like structures are relatively rare in either nebula. Third, the data indicate that photoevaporation may have uncovered many EGGs while the stellar objects in them were still accreting mass, thereby freezing the mass distribution of the protostars at an early stage in their evolution. We conclude that the masses of stars in the cluster environment in M16 are generally determined not by the onset of stellar winds, as in more isolated regions of star formation, but rather by disruption of the star forming environment by the nearby O stars