Field Of NGC Research Articles

CCD Stromgren studies in NGC 6397

view Abstract Citations (33) References (56) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS CCD Stromgren Studies in NGC 6397 Anthony-Twarog, Barbara J. ; Twarog, Bruce A. ; Suntzeff, Nicholas B. Abstract Six fields in NGC 6397 are studied with CCD photometry in the Stromgren y, b, and v systems to expand the number of sampled photometric binaries and study their characteristics. The fiducial sequences for the cluster are determined to assess the binary population, and the fiducial CMD is analyzed to constrain the cluster age and distance. The distribution of the m(1) (b - y) diagram yields potential members, and about 7 percent of the main-sequence members are characterized as composites. An apparent distance modulus of (m - M) = 12.1 is derived from the reddening and Fe/H values, and these values lead to an age of more than 18 x 10 exp 9 yr from the luminosity of the turnoff. The standard main-sequence relations developed by McClure et al. (1987) and Sarajedini and King (1987) are compared to the present values. NGC 6397 is concluded to be one of the oldest clusters in a globular sample with an age spread of 5-6 x 10 exp 9 yr and assumed to reside in the old tail of a broad globular cluster-age distribution. Publication: The Astronomical Journal Pub Date: April 1992 DOI: 10.1086/116140 Bibcode: 1992AJ....103.1264A Keywords: Globular Clusters; Main Sequence Stars; Stellar Composition; Stellar Spectrophotometry; Ubv Spectra; Binary Stars; Charge Coupled Devices; Color-Magnitude Diagram; Metallicity; Stellar Luminosity; Stellar Parallax; Astrophysics; GLOBUALR CLUSTERS: INDIVIDUAL: NGC 6397; TECHNIQUES: PHOTOMETRY full text sources ADS | data products SIMBAD (14)

Linear polarization of stars in seven metal-poor globular clusters

Polarization measurements of more than 250 stars, most of them red giants, in the fields of seven metal-poor globular clusters are presented. Strong spatial variations of the polarization are found in the fields of NGC 4372, NGC 4833, M4, and NGC 6266, and it is concluded that differential reddening is important in these clusters. Mild extinction variations are found across ω Cen and M22, while the insterstellar medium toward NGC 6397 appears fairly uniform. After taking the foreground polarization component into account, no evidence are found for significant intrinsic polarization in any of the stars observed

Neutral hydrogen absorption in the radio spectrum of PKS 0241 + 011

The detection (at about the 3 sigma level) of an absorption feature at a heliocentric velocity of 1172 km/s in the spectrum of PKS 0241 + 011 is presented. The line of sight to the quasar (z-PKS = 1.4) lies well within the optical and H I boundaries of the barred spiral galaxy NGC 1073 (z-gal = 0.004). Two other continuum sources in the field of NGC 1073 do not show any absorption features. 17 refs.

The magnetic fields of NGC 6946 and NGC 4945

Abstract Observations of the face-on galaxy NGC 6946 are inconsistent with a simple bisymmetric large-scale field structure confined to the galactic plane; the magnetic field must also possess significant three-dimensionality. The edge-on galaxy NGC 4945 has an active nucleus and a radio halo. Linear polarization maxima on each side of the central galactic plane suggest the presence of a strongly ordered poloidal magnetic field there.

The late-type stellar content of NGC 2403

The late-type stellar content of three disk fields in NGC 2403 was examined using Cousins RI and VI CCD photometry. The AGB luminosity function has been constructed separately for the inner and outer fields. In both cases, relatively fewer bright AGB stars are seen in the NGC 2403 fields than in the LMC. The shape of the AGB luminosity function for the innermost field is quite different from that of the LMC, and there is an indication that recent star formation may have occurred. Several red and blue supergiants and H II regions are also identified in the field to support this. The luminosity function for the outer NGC 2403 fields appears more similar to that of the LMC, and a difference in the star-formation rate in the two regions of NGC 2403 is suggested. A narrowband photometric technique has been used to identify carbon and M stars in the innermost field. Several late M stars are identified, but the carbon star identifications are, at best, tentative. 38 refs.

The magnetic field profiles of NGC 7331, NGC 2841, and NGC 6946 - A theoretical model

This paper deals with the explanation of gaseous ring patterns in spiral galaxies. The magnetohydrodynamic equations are solved in a steady state model for the gas and the magnetic field distributions in NGC 7331 and NGC 2841. The computations were also carried out for NGC 6946, in order to see whether the same mathematical approach is valid for galaxies with no gas ring. The model takes as its input data the gas pressure from the literature and calculates the magnetic field. The computed synchrotron emission produced by this field is in very good agreement with observations. In NGC 7331 and NGC 2841, a decreasing magnetic field for increasing galactocentric radii is obtained, while the field in NGC 6946 remains essentially constant throughout the galaxy. 53 references.

H I observations of the elliptical galaxies NGC 2974 and NGC 5018

Two ellipticals, NGC 2974 and NGC 5018, selected because of their relatively strong infrared fluxes, were detected in H I in VLA 21 cm observations. NGC 2974 has a regular distribution of gas. The H I appears to be in a rotating disk with the rotation axis well aligned with the optical minor axis of the galaxy. In contrast, NGC 5018 contains little hydrogen, which may be flowing into it from the nearby spiral NGC 5022. The H I distribution of NGC 5022 is distorted toward NGC 5018. Three other H I features in the field of NGC 5018/5022 are probably gas-rich dwarfs which may have played some part in the acquisition of gas by the elliptical galaxy. The radio continuum map at 21 cm shows two sources near NGC 5018, one at its center and another about one arcmin away. 41 references.

Kinematical and Spectral Evidences of Complex Structure of NGC 1275 Nucleus

The analysis of the available data about spectral observations of nucleus and gas velocity field in NGC 1275 leads to a conclusion on the presence in the nucleus of several spatially separated variable sources responsible for a complex variable emission in Hβ and [OIII] lines profiles.

Luminous late-type stars in NGC 300

A 15 square arcmin field in NGC 300 was observed through 4 filters with the CTIO 4 m prime focus CCD. Two of the filters were broad-band V and I and the other two isolated TiO (λ7800) and CN (λ8100). With this filter set, it is possible to unambiguously distinguish late-type carbon stars from M stars. Sixteen late-type C stars and 25 cool M stars were discovered in the NGC 300 field. Two of the latter stars may lie in the foreground. The ratio of C to M stars indicates a modestly metal-deficient system ([Fe/H] = -0.5). A new distance modulus to NGC 300 is derived using carbon stars, and the value (m-M)<SUB>0</SUB> = 25.87 is significantly smaller than most in the current literature. The full asymptotic giant branch (AGB) luminosity function of the field observed is obtained and compared with that for the LMC.

Spatiokinematical models of five planetary nebulae

The [O III] and Hα expansion velocity fields in the planetary nebulae NGC 6058 and 6804 and the [O III], Hα and [N II] expansion velocity fields in NGC 6309, 6751 and 6818, were obtained from high dispersion spectra. We have derived spatiokinematical models of the nebulae assuming an expansion velocity of the gas proportional to the distance from the central star and using the expansion velocity–radius correlation given by Sabbadin et al. (1984b). The observational parameters of the nebulae (radius, mass and expansion velocity) and of the exciting stars (temperature, radius and luminosity) closely fit the evolutionary model suggested by Sabbadin et al. for this class of objects. NGC 6818 is an optically thick nebula in a rather early evolutionary phase, NGC 6309, 6751 and 6804 are thick nebulae close to the transition from thick to thin; NGC 6058 is an evolved planetary nebula in the thin phase.

UBVRI photometry in the field of NGC 2264

UBVRI photometry in the field of NGC 2264

Study of the extremely young open cluster NGC 6530

Photoelectric magnitudes and colours in the UBV system have been determined for 101 stars in the field of NGC 6530. The interstellar reddening across the cluster varies from 0.25 to 0.48 mag, with an average value of 0.35 mag. The distance modulus to the cluster is estimated at 11.3 mag and age of 2x10 6 yr is ascribed. The cluster luminosity function is compared with the general luminosity function and the initial luminosity function. Star numbers 304 and 338 are in the early stages of their evolution while star numbers 171, 284 and 338 are probably variables.

Red variable stars in the Magellanic Clouds - II. The field of NGC 371 in the SMC

Red variable stars in the Magellanic Clouds - II. The field of NGC 371 in the SMC

Red variable stars in the Magellanic Clouds - III. Carbon stars in the field of NGC 419 (SMC)

Red variable stars in the Magellanic Clouds - III. Carbon stars in the field of NGC 419 (SMC)

A new mapping of the velocity field of NGC 1275.

A new mapping of the velocity field of NGC 1275.

The velocity field of NGC 4258.

The velocity field of NGC 4258.

Photographic photometry in the field of NGC 2264.

Photographic photometry in the field of NGC 2264.

Observations of Galaxies with Large amounts of Dust. III. Velocity Field in NGC 3077

view Abstract Citations (14) References (5) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Observations of Galaxies with Large amounts of Dust. III. Velocity Field in NGC 3077 Demoulin, Marie-Helene Abstract NGC 3077 is a small Irr-II galaxy. Spectra taken in various directions do not show any velocity dif- ferences larger than the precision of the measurements, except in the direction P.A. = 1500, and the small velocity gradient in this direction cannot be interpreted as rotation Publication: The Astrophysical Journal Pub Date: July 1969 DOI: 10.1086/150052 Bibcode: 1969ApJ...157...81D full text sources ADS | data products SIMBAD (1) NED (1) Related Materials (2) Part 1: 1969ApJ...157...69D Part 2: 1969ApJ...157...75D

Properties of Galaxies: the Neutral Hydrogen Distribution and Radial-Velocity Field of NGC 925.

Properties of Galaxies: the Neutral Hydrogen Distribution and Radial-Velocity Field of NGC 925.

The Velocity Field in NGC 6181.

The Velocity Field in NGC 6181.