1,118 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
Characterization of separability and entanglement in - and -dimensional systems by single-qubit and single-qutrit unitary transformations
We investigate the geometric characterization of pure state bipartite
entanglement of - and -dimensional composite
quantum systems. To this aim, we analyze the relationship between states and
their images under the action of particular classes of local unitary
operations. We find that invariance of states under the action of single-qubit
and single-qutrit transformations is a necessary and sufficient condition for
separability. We demonstrate that in the -dimensional case the
von Neumann entropy of entanglement is a monotonic function of the minimum
squared Euclidean distance between states and their images over the set of
single qubit unitary transformations. Moreover, both in the - and
in the -dimensional cases the minimum squared Euclidean distance
exactly coincides with the linear entropy (and thus as well with the tangle
measure of entanglement in the -dimensional case). These results
provide a geometric characterization of entanglement measures originally
established in informational frameworks. Consequences and applications of the
formalism to quantum critical phenomena in spin systems are discussed.Comment: 8 pages, 1 figur
Carbon and nitrogen abundances of individual stars in the Sculptor dwarf spheroidal galaxy
We present [C/Fe] and [N/Fe] abundance ratios and CH({\lambda}4300) and
S({\lambda}3883) index measurements for 94 red giant branch (RGB) stars in the
Sculptor dwarf spheroidal galaxy from VLT/VIMOS MOS observations at a resolving
power R= 1150 at 4020 {\AA}. This is the first time that [N/Fe] abundances are
derived for a large number of stars in a dwarf spheroidal. We found a trend for
the [C/Fe] abundance to decrease with increasing luminosity on the RGB across
the whole metallicity range, a phenomenon observed in both field and globular
cluster giants, which can be interpreted in the framework of evolutionary
mixing of partially processed CNO material. Both our measurements of [C/Fe] and
[N/Fe] are in good agreement with the theoretical predictions for stars at
similar luminosity and metallicity. We detected a dispersion in the carbon
abundance at a given [Fe/H], which cannot be ascribed to measurement
uncertainties alone. We interpret this observational evidence as the result of
the contribution of different nucleosynthesis sources over time to a not
well-mixed interstellar medium. We report the discovery of two new
carbon-enhanced, metal-poor stars. These are likely the result of pollution
from material enriched by asymptotic giant branch stars, as indicated by our
estimates of [Ba/Fe]> +1. We also attempted a search for dissolved globular
clusters in the field of the galaxy by looking for the distinctive C-N pattern
of second population globular clusters stars in a previously detected, very
metal-poor, chemodynamical substructure. We do not detect chemical anomalies
among this group of stars. However, small number statistics and limited spatial
coverage do not allow us to exclude the hypotheses that this substructure forms
part of a tidally shredded globular cluster.Comment: 18 pages, 14 figures, 3 tables. Accepted to A&
Photometry and the Metallicity Distribution of the Outer Halo of M31
We have conducted a wide-field CCD-mosaic study of the resolved red-giant
branch (RGB) stars of M31, in a field located 20 kpc from the nucleus along the
SE minor axis. In our (I, V-I) color-magnitude diagram, RGB stars in the top
three magnitudes of the M31 halo are strongly present. Photometry of a more
distant control field to subtract field contamination is used to derive the
`cleaned' luminosity function and metallicity distribution function (MDF) of
the M31 halo field. From the color distribution of the foreground Milky Way
halo stars, we find a reddening E(V-I)= 0.10 +/- 0.02 for this field, and from
the luminosity of the RGB tip, we determine a distance modulus (m-M)_o = 24.47
+/- 0.12 (= 783 +/- 43 kpc). The MDF is derived from interpolation within an
extensive new grid of RGB models (Vandenberg et al. 2000). The MDF is dominated
by a moderately high-metallicity population ([m/H]~ -0.5) found previously in
more interior M31 halo/bulge fields, and is much more metal-rich than the
[m/H]~ -1.5 level in the Milky Way halo. A significant (~30% - 40%, depending
on AGB star contribution) metal-poor population is also present. To first
order, the shape of the MDF resembles that predicted by a simple,
single-component model of chemical evolution starting from primordial gas with
an effective yield y=0.0055. It strongly resembles the MDF recently found for
the outer halo of the giant elliptical NGC 5128 (Harris et al. 2000), though
NGC 5128 has an even lower fraction of low-metallicity stars. Intriguingly, in
both NGC 5128 and M31, the metallicity distribution of the globular clusters in
M31 does not match the halo stars; the clusters are far more heavily weighted
to metal-poor objects. We suggest similarities in the formation and early
evolution of massive, spheroidal stellar systems.Comment: to appear in the Astronomical Journal; 43 pages, including 15 figure
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
The Pristine survey II: a sample of bright stars observed with FEROS
Extremely metal-poor (EMP) stars are old objects formed in the first Gyr of
the Universe. They are rare and, to select them, the most successful strategy
has been to build on large and low-resolution spectroscopic surveys. The
combination of narrow- and broad band photometry provides a powerful and
cheaper alternative to select metal-poor stars. The on-going Pristine Survey is
adopting this strategy, conducting photometry with the CFHT MegaCam wide field
imager and a narrow-band filter centred at 395.2 nm on the CaII-H and -K lines.
In this paper we present the results of the spectroscopic follow-up conducted
on a sample of 26 stars at the bright end of the magnitude range of the Survey
(g<=15), using FEROS at the MPG/ESO 2.2 m telescope. From our chemical
investigation on the sample, we conclude that this magnitude range is too
bright to use the SDSS gri bands, which are typically saturated. Instead the
Pristine photometry can be usefully combined with the APASS gri photometry to
provide reliable metallicity estimates.Comment: AN accepte
The early days of the Sculptor dwarf spheroidal galaxy
We present the high resolution spectroscopic study of five -3.9<=[Fe/H]<=-2.5
stars in the Local Group dwarf spheroidal, Sculptor, thereby doubling the
number of stars with comparable observations in this metallicity range. We
carry out a detailed analysis of the chemical abundances of alpha, iron peak,
light and heavy elements, and draw comparisons with the Milky Way halo and the
ultra faint dwarf stellar populations. We show that the bulk of the Sculptor
metal-poor stars follows the same trends in abundance ratios versus metallicity
as the Milky Way stars. This suggests similar early conditions of star
formation and a high degree of homogeneity of the interstellar medium. We find
an outlier to this main regime, which seems to miss the products of the most
massive of the TypeII supernovae. In addition to its value to help refining
galaxy formation models, this star provides clues to the production of cobalt
and zinc. Two of our sample stars have low odd-to-even barium isotope abundance
ratios, suggestive of a fair proportion of s-process; we discuss the
implication for the nucleosynthetic origin of the neutron capture elements.Comment: Replacement after language editio
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
Spectral Energy Distributions and Age Estimates of 172 Globular Clusters in M31
In this paper we present CCD multicolor photometry for 172 globular clusters
(GCs), taken from the Bologna catalog (Battistini et al. 1987), in the nearby
spiral galaxy M31. The observations were carried out by using the National
Astronomical Observatories 60/90 cm Schmidt Telescope in 13 intermediate-band
filters, which covered a range of wavelength from 3800 to 10000A. This provides
a multicolor map of M31 in pixels of 1.7"*1.7". By aperture photometry, we
obtain the spectral energy distributions (SEDs) for these GCs. Using the
relationship between the BATC intermediate-band system used for the
observations and the UBVRI broad-band system, the magnitudes in the B and V
bands are derived. The computed V and B-V are in agreement with the values
given by Battistini et al. (1987) and Barmby et al. (2000). Finally, by
comparing the photometry of each GC with theoretical stellar population
synthesis models, we estimate ages of the sample GCs for different
metallicities. The results show that nearly all our sample GCs have ages more
than 10^{9} years, and most of them are around 10^{10} years old. Also, we find
that GCs fitted by the metal-poor model are generally older than ones fitted by
the metal-rich model.Comment: 38 pages, 7 figures will appear in the February 2003 issue of A
VLT/FLAMES spectroscopy of red giant branch stars in the Fornax dwarf spheroidal galaxy
Fornax is one of the most massive dwarf spheroidal galaxies in the Local
Group. The Fornax field star population is dominated by intermediate age stars
but star formation was going on over almost its entire history. It has been
proposed that Fornax experienced a minor merger event. Despite recent progress,
only the high metallicity end of Fornax field stars ([Fe/H]>-1.2 dex) has been
sampled in larger number via high resolution spectroscopy. We want to better
understand the full chemical evolution of this galaxy by better sampling the
whole metallicity range, including more metal poor stars. We use the VLT-FLAMES
multi-fibre spectrograph in high-resolution mode to determine the abundances of
several alpha, iron-peak and neutron-capture elements in a sample of 47
individual Red Giant Branch stars in the Fornax dwarf spheroidal galaxy. We
combine these abundances with accurate age estimates derived from the age
probability distribution from the colour-magnitude diagram of Fornax. Similar
to other dwarf spheroidal galaxies, the old, metal-poor stars of Fornax are
typically alpha-rich while the young metal-rich stars are alpha-poor. In the
classical scenario of the time delay between SNe II and SNe Ia, we confirm that
SNe Ia started to contribute to the chemical enrichment at [Fe/H] between -2.0
and -1.8 dex. We find that the onset of SNe Ia took place between 12-10 Gyrs
ago. The high values of [Ba/Fe], [La/Fe] reflect the influence of SNe Ia and
AGB stars in the abundance pattern of the younger stellar population of Fornax.
Our findings of low [alpha/Fe] and enhanced [Eu/Mg] are compatible with an
initial mass function that lacks the most massive stars and with star formation
that kept going on throughout the whole history of Fornax. We find that massive
stars kept enriching the interstellar medium in alpha-elements, although they
were not the main contributor to the iron enrichment.Comment: Resubmitted to A&A (18/09/2014) after Referee's comment
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