Polarization in the Lagoon nebula

A V-band polarimetric survey of stars associated with the Lagoon nebula was conducted. The data were combined with existing photometric and spectroscopic observations in order to investigate the alignment of magnetic field lines with identifiable symmetry axes and to evaluate the nature of dust in the immediate vicinity. Although stars are not in general highly polarized, electric vectors align with the minor axis of the Lagoon nebula, perpendicular to the major axis of the spatial distribution of massive stars. The observations indicate that the collapse of the molecular cloud progenitor was inhibited along directions perpendicular to magnetic field lines. Considering the low polarization efficiency and the high ratio of total to selective extinction, smaller grains of intranebular dust appear to have been destroyed

Effect of Several Auxiliary Ligands on the Extraction of Manganese(II) With 4-Benzoyl-3-methyl-1-phenyl-5-pyrazolone

The effect of 2-methyl pyridine N-oxide, 4-methyl pyridine N-oxide, pyridine N-oxide, 8-aminoquinoline, dibenzyl sulfoxide on the extraction of manganese(II) by 4-benzoyl-3-methyl-1-phe-\u27 nyl-5-pyrazolone (BMPP) in benzene from an aqueous buffered solution was studied. Synergistic enhancement was observed in all systems. Equilibrtum extraction constants and adduct formation constants were calculated. The results showed that synergistic extraction is due to the formation of adducts such as Mn(BMPP)2B where B represents the auxiliary ligand

Suppressed star formation in circumnuclear regions in Seyfert galaxies

Feedback from black hole activity is widely believed to play a key role in regulating star formation and black hole growth. A long-standing issue is the relation between the star formation and fueling the supermassive black holes in active galactic nuclei (AGNs). We compile a sample of 57 Seyfert galaxies to tackle this issue. We estimate the surface densities of gas and star formation rates in circumnuclear regions (CNRs). Comparing with the well-known Kennicutt-Schmidt (K-S) law, we find that the star formation rates in CNRs of most Seyfert galaxies are suppressed in this sample. Feedback is suggested to explain the suppressed star formation rates.Comment: 1 color figure and 1 table. ApJ Letters in pres

An Old Cluster in NGC 6822

We present spectroscopy of two clusters in the dwarf irregular galaxy NGC 6822. From these we deduce an age for Cluster VII of 11 Gyr and [Fe/H] = -1.95 +/- 0.15 dex. Cluster VII appears to be an analog of the metal-poor galactic globular clusters. Cluster VI is found to be much younger and more metal rich, with an age of approximately 2 Gyr. Its derived metallicity, [Fe/H], of approximately -1.0 dex is comparable to that of the gas seen today in NGC 6822. The existence of a metal-poor old cluster in NGC 6822 rules out models for the chemical evolution of this galaxy with significant prompt initial enhancement. We find that a star formation rate which is constant with time and is within a factor of two of the present star formation rate can reproduce the two points on the age-metallicity relationship for NGC 6822 over the past 10 Gyr defined by these two clusters.Comment: 8 pages; accepted for publication in A

Observations of NGC 4151 During 1970 in the Optical and Infra-red

Observations of NGC 4151 at seven wavelengths from 0.3 to 3.4 microns made during the 1970 season are presented. Variations are found at all observed wavelengths but the optical and infra-red light curves are different: an optical maximum was reached in April but the galaxy continued brightening at 2.2 μ . until the end of June. The energy distributions of the point source and the background galaxy have been separated and that of the point source Closely resembles that of the quasar 3C273. The general form of the light curves can possibly be attributed to a dust model for the infra-red emission but this would be ruled out if suspected rapid infra-red variations are confirmed

The star formation properties of disk galaxies: Halpha imaging of galaxies in the Coma supercluster

We present integrated H alpha measurements obtained from imaging observations of 98 late-type galaxies, primarily selected in the Coma supercluster. These data, combined with H alpha photometry from the literature, include a magnitude selected sample of spiral (Sa to Irr) galaxies belonging to the "Great Wall" complete up to mp=15.4, thus composed of galaxies brighter than Mp=-18.8 (H0=100 km Mpc^-1 s^-1). The frequency distribution of the H alpha E.W., determined for the first time from an optically complete sample, is approximately gaussian peaking at E.W. ~25 A. We find that, at the present limiting luminosity, the star formation properties of spiral+Irr galaxies members of the Coma and A1367 clusters do not differ significantly from those of the isolated ones belonging to the Great Wall. The present analysis confirms the well known increase of the current massive star formation rate (SFR) with Hubble type. Moreover perhaps a more fundamental anticorrelation exists between the SFR and the mass of disk galaxies: low-mass spirals and dwarf systems have present SFRs ~50 times higher than giant spirals. This result is consistent with the idea that disk galaxies are coeval, evolve as "closed systems" with exponentially declining SFR and that the mass of their progenitor protogalaxies is the principal parameter governing their evolution. Massive systems having high initial efficiency of collapse, or a short collapse time-scale, have retained little gas to feed the present epoch of star formation. These findings support the conclusions of Gavazzi & Scodeggio (1996) who studyed the color-mass relation of a local galaxy sample and agree with the analysis by Cowie et al. (1996) who traced the star formation history of galaxies up to z>1.Comment: 13 pages (LateX) + 24 figures + 4 tables. To appear in Astronomical Journal, April 1998 issu

Observations of NGC 4151 During 1970 in the Optical and Infra-red

Observations of NGC 4151 at seven wavelengths from 0.3 to 3.4 microns made during the 1970 season are presented. Variations are found at all observed wavelengths but the optical and infra-red light curves are different: an optical maximum was reached in April but the galaxy continued brightening at 2.2 μ . until the end of June. The energy distributions of the point source and the background galaxy have been separated and that of the point source Closely resembles that of the quasar 3C273. The general form of the light curves can possibly be attributed to a dust model for the infra-red emission but this would be ruled out if suspected rapid infra-red variations are confirmed

Development of silicon planar P-I-N photodiode

Optical receivers are used to detect optical power and to extract the information that is being transmitted. The incident optical power is detected by a photo detector, usually a PIN or avalanche photodiode (APD). A PIN or APD is an amplitude modulation envelope photo detector, insensitive to phase or small changes in wavelength. It generates an electrical output that reproduces the envelope of the received optical signal (Li, 2000). The most widely deployed photodiode for all lightwave applications is the PIN photodiode where its performance and characteristics are well understood and documented (Campbell, 1995)