1,224 research outputs found
No Increase of the Red-Giant-Branch Tip Luminosity Toward the Center of M31
We present observations with the Hubble Space Telescope Wide Field Planetary
Camera 2 of three fields centered on super-metal-rich globular clusters in the
bulge of M31. Our (I,V-I) color-magnitude diagrams reach as faint as I ~ 26.5
mag and clearly reveal the magnitude of the first ascent red giant branch (RGB)
tip. We find that the apparent I magnitude of the RGB tip does not become
brighter near the center of M31 as concluded by previous investigators. Our
observations and artificial star experiments presented in this study strongly
support the idea that previous very bright stars were likely the result of
spurious detections of blended stars due to crowding in lower resolution
images. On the contrary, our observations indicate that, at a mean projected
galactocentric distance of 1.1 kpc, the RGB tip is some 1.3 magnitudes fainter
than it is at 7 kpc. An analysis of this difference in RGB tip magnitude
suggests that the M31 bulge stellar population has a mean metallicity close to
that of the Sun.Comment: Accepted for publication in ApJ, June 20, 1999 issu
Direct detection of galaxy stellar halos : NGC 3957 as a test case
We present a direct detection of the stellar halo of the edge-on S0 galaxy
NGC 3957, using ultra-deep VLT/VIMOS V and R images. This is achieved with a
sky subtraction strategy based on infrared techniques. These observations allow
us to reach unprecedented high signal-to-noise ratios up to 15 kpc away from
the galaxy center, rendering photon-noise negligible. The 1 sigma detection
limits are R = 30.6 mag/arcsec^2 and V = 31.4 mag/arcsec^2. We conduct a
thorough analysis of the possible sources of systematic errors that could
affect the data: flat-fielding, differences in CCD responses, scaling of the
sky background, the extended halo itself, and PSF wings. We conclude that the
V-R colour of the NGC 3957 halo, calculated between 5 and 8 kpc above the disc
plane where the systematic errors are modest, is consistent with an old and
preferentially metal-poor normal stellar population, like that revealed in
nearby galaxy halos from studies of their resolved stellar content. We do not
find support for the extremely red colours found in earlier studies of diffuse
halo emission, which we suggest might have been due to residual systematic
errors.Comment: Accepted for publication in A&A - "language edited
Resolved Stellar Populations of Super-Metal-Rich Star Clusters in the Bulge of M31
We have applied the MCS image deconvolution algorithm (Magain, Courbin & Sohy
1998) to HST/WFPC2 V, I data of three M31 bulge globular clusters (G170, G177,
and G198) and control fields near each cluster. All three clusters are clearly
detected, with an increase in stellar density with decreasing radius from the
cluster centers; this is the first time that stars have been resolved in bulge
clusters in the inner regions of another galaxy. From the RGB slopes of the
clusters and the difference in I magnitude between the HB and the top of the
RGB, we conclude that these three clusters all have roughly solar metallicity,
in agreement with earlier integrated-light spectroscopic measurements. Our data
support a picture whereby the M31 bulge clusters and field stars were born from
the same metal-rich gas, early in the galaxy formation.Comment: 7 pages, 4 Postscript figures, accepted for publication in A&
The Metallicity Distribution Function of Field Stars in M31's Bulge
We have used Hubble Space Telescope Wide Field Planetary Camera 2
observations to construct a color-magnitude diagram (CMD) for the bulge of M31
at a location ~1.6 kpc from the galaxy's center. Using scaled-solar abundance
theoretical red giant branches with a range of metallicities, we have
translated the observed colors of the stars in the CMD to abundances and
constructed a metallicity distribution function (MDF) for this region. The MDF
shows a peak at [M/H]~0 with a steep decline at higher metallicities and a more
gradual tail to lower metallicities. This is similar in shape to the MDF of the
Milky Way bulge but shifted to higher metallicities by ~0.1 dex. As is the case
with the Milky Way bulge MDF, a pure closed box model of chemical evolution,
even with significant pre-enrichment, appears to be inconsistent with the M31
bulge MDF. However, a scenario in which an initial infall of gas enriched the
bulge to an abundance of [M/H] ~ -1.6 with subsequent evolution proceeding as a
closed box provides a better fit to the observed MDF. The similarity between
the MDF of the M31 bulge and that of the Milky Way stands in stark contrast to
the significant differences in the MDFs of their halo populations. This
suggests that the bulk of the stars in the bulges of both galaxies were in
place before the accretion events that occurred in the halos could influence
them.Comment: 12 pages, 9 figures, accepted for publication in The Astronomical
Journal, October 200
HST-NICMOS Observations of M31's Metal Rich Globular Clusters and Their Surrounding Fields: I. Techniques
We have obtained HST-NICMOS observations of five of M31's most metal rich
globular clusters. These data allow photometry of individual stars in the
clusters and their surrounding fields. However, to achieve our goals -- obtain
accurate luminosity functions to compare with their Galactic counterparts,
determine metallicities from the slope of the giant branch, identify long
period variables, and estimate ages from the AGB tip luminosity, we must be
able to disentangle the true properties of the population from the
observational effects associated with measurements made in very crowded fields.
In this paper we present a careful analysis of photometry in crowded regions,
and show how image blending affects the results and interpretation of such
data. Although this analysis is specifically for our NICMOS observations in
M31, the techniques we develop can be applied to any imaging data taken in
crowded fields; we show how the effects of image blending will even limit NGST.
We use three different techniques to analyze the effects of crowding on our
data, including the insertion of artificial stars (traditional completeness
tests) and the creation of completely artificial clusters. They are used to
derive threshold- and critical-blending radii for each cluster, which determine
how close to the cluster center reliable photometry can be achieved. The
simulations also allow us to quantify and correct for the effects of blending
on the slope and width of the RGB at different surface brightness levels.Comment: AAS LaTeX v5.0, 18 pages. Submitted to the A
Avaliação de óleos comestíveis comercializados no Rio de Janeiro.
Procedeu-se a um levantamento das condições dos óleos vegetais comestíveis comercializados no Rio de Janeiro, aliando-se determinações tradicionais à cromatografia de gás. Utilizaram-se óleos de soja, milho, caroço de algodão, oliva, arroz e mistos. Observaram-se discrepâncias na composição em ácidos graxos principalmente nos óleos de oliva, resultantes provavelmente de misturas com óleo de coco ou babaçu e com soja.bitstream/item/65434/1/CTAA-DOCUMENTOS-13-AVALIACAO-DE-OLEO-COMESTIVEIS-COMERCIALIZADOS-NO-RIO-DE-JANEIRO-FL-02165.pd
WFPC2 Observations of Massive and Compact Young Star Clusters in M31
We present color magnitude diagrams of four blue massive and compact star
clusters in M31: G38, G44, G94, and G293. The diagrams of the four clusters
reveal a well-populated upper main sequence and various numbers of supergiants.
The U-B and B-V colors of the upper main sequence stars are used to determine
reddening estimates of the different lines of sight in the M31 disk. Reddening
values range from E(B-V) = 0.20 +/- 0.10 to 0.31 +/- 0.11. We statistically
remove field stars on the basis of completeness, magnitude and color. Isochrone
fits to the field-subtracted, reddening-corrected diagrams yield age estimates
ranging from 63 +/- 15 Myr to 160 +/- 60 Myr. Implications for the recent
evolution of the disk near NGC 206 are discussed.Comment: 17 pages, Latex, ApJ, in Pres
Evaluating the Potential of Using 5-Azacytidine as an Epimutagen
A number of early flowering lines were induced when 5-azacytidine was applied to germinating flax (Linum usitatissimum L.) seed. The genetics of these lines indicate that the induced changes are epigenetic and probably result from demethylation of the genomic DNA at loci that affect flowering age. Although the growth and development of three stable early flowering lines are altered and the percentage of filled seed was reduced in all three lines compared with controls, measures of seed productivity demonstrated that harvest index was unaffected in two of the lines. In the third, harvest index was lower than normal and both seed set per capsule and seed mass per 100 seed were reduced. Furthermore, six generations after induction this line began to display relatively high levels of polyembryony. The late appearance of this twinning and other aspects related to working with lines induced by 5-azacytidine and using 5-azacytidine as an epimutagen are discussed
The Globular Cluster System of NGC 5128 II. Ages, Metallicities, Kinematics, and Formation
We present a study of the nearby post-merger giant elliptical galaxy, NGC
5128 (Centaurus A), in which we use the properties of its globular cluster (GC)
and planetary nebula (PN) systems to constrain its evolution. Using photometric
and spectroscopic data for 215 GCs presented in Paper I, we study trends in
age, metallicity, and kinematics for the GC system. We confirm that the GC
metallicity distribution is bimodal, and show that these two sub-populations
have different properties. Using spectral line index measurements of the
brightest clusters, the metal-poor GCs have old ages like the Milky Way
globular clusters, while the metal-rich GCs have H-beta line-strengths that
could be interpreted as a mean age of ~5 (+3/-2) Gyr. Both populations appear
to have [Mg/Fe] ratios consistent with that of the Galactic GC system, although
this quantity is not very well-constrained. The kinematics of the metal-rich
GCs are similar to those of the planetary nebulae, exhibiting significant
rotation about a misaligned axis, while the metal-poor GCs have a higher
velocity dispersion and show a weaker kinematic correlation with the field
stars. The total gravitating mass of NGC 5128 derived from the GCs is in
excellent agreement with the value derived from stellar (PN) kinematics. We
suggest that these and other data support a picture in which the main body of
NGC 5128 was formed 3-8 Gyr ago by the dissipational merger of two unequal-mass
disk galaxies supplemented by the continual accretion of both gas-rich and
gas-poor satellites.Comment: 15 pages, 21 figures (figures 14-20 best viewed in color), accepted
for publication in the Astrophysical Journa
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