2,084 research outputs found
Extragalactic Planetary Nebulae: tracers of the chemical evolution of nearby galaxies
The study of the chemical composition of Planetary Nebulae in external
galaxies is of paramount importance in the fields of stellar evolution and of
the chemical enrichment history of galaxies. In the last years a number of
spectroscopic studies with 6-8m-class telescopes have been devoted to this
subject improving our knowledge of, among other, the time-evolution of the
radial metallicity gradient in disk galaxies, the chemical evolution of dwarf
galaxies, and the stellar evolution at low metallicity.Comment: 8 pages, 4 figures, Invited Review to IAU Symposium 283, "Planetary
Nebulae: an Eye to the Future", Tenerife, 25-29 July 201
Open clusters towards the Galactic center: chemistry and dynamics. A VLT spectroscopic study of NGC6192, NGC6404, NGC6583
In the framework of the study of the Galactic metallicity gradient and its
time evolution, we present new high-resolution spectroscopic observations
obtained with FLAMES and the fiber link to UVES at VLT of three open clusters
(OCs) located within 7~kpc from the Galactic Center (GC): NGC~6192,
NGC~6404, NGC~6583. We also present new orbit determination for all OCs with
Galactocentric distances (R8~kpc and metallicity from
high-resolution spectroscopy. We aim to investigate the slope of the inner disk
metallicity gradient as traced by OCs and at discussing its implication on the
chemical evolution of our Galaxy. We have derived memberships of a group of
evolved stars for each clusters, obtaining a sample of 4, 4, and 2 member stars
in NGC~6192, NGC~6404, and NGC~6583, respectively. Using standard LTE analysis
we derived stellar parameters and abundance ratios for the iron-peak elements
Fe, Ni, Cr, and for the -elements Al, Mg, Si, Ti, Ca. We calculated the
orbits of the OCs currently located within 8~kpc from the GC, and discuss their
implication on the present-time radial location. {The average metallicities of
the three clusters are all oversolar: [Fe/H]= (NGC~6192),
(NGC 6404), (NGC 6583). They are in qualitative
agreement with their Galactocentric distances, being all internal OCs, and thus
expected to be metal richer than the solar neighborhood. The abundance ratios
of the other elements over iron [X/Fe] are consistent with solar values. The
clusters we have analysed, together with other OC and Cepheid data, confirm a
steep gradient in the inner disk, a signature of an evolutionary rate different
than in the outer disk.Comment: 17 pages, 13 figures, A&A accepted for publicatio
Metal production in M33: space and time variations
Nearby galaxies are ideal places to study in detail metallicity gradients and
their time evolution. We consider chemical abundances of a new sample of \hii\
regions complemented with previous literature data-sets. We compare \hii\
region and PN abundances obtained with a common set of observations taken at
MMT. With an updated theoretical model, we follow the time evolution of the
baryonic components and chemical abundances in the disk of M33, assuming that
the galaxy is accreting gas from an external reservoir. Supported by a uniform
sample of nebular spectroscopic observations, we conclude that: {\em i}) the
metallicity distribution in M33 is very complex, showing a central depression
in metallicity probably due to observational bias; {\em ii}) the metallicity
gradient in the disk of M33 has a slope of -0.037 0.009 dex kpc in
the whole radial range up to 8 kpc, and -0.044 0.009 dex kpc
excluding the central kpc; {\em iii}) there is a small evolution of the slope
with time from the epoch of PN progenitor formation to the present-time.}Comment: A&A accepted, 15 Pags, 13 Figs, language correctio
FAMA: An automatic code for stellar parameter and abundance determination
The large amount of spectra obtained during the epoch of extensive
spectroscopic surveys of Galactic stars needs the development of automatic
procedures to derive their atmospheric parameters and individual element
abundances. Starting from the widely-used code MOOG by C. Sneden, we have
developed a new procedure to determine atmospheric parameters and abundances in
a fully automatic way. The code FAMA (Fast Automatic MOOG Analysis) is
presented describing its approach to derive atmospheric stellar parameters and
element abundances. The code, freely distributed, is written in Perl and can be
used on different platforms. The aim of FAMA is to render the computation of
the atmospheric parameters and abundances of a large number of stars using
measurements of equivalent widths as automatic and as independent of any
subjective approach as possible. It is based on the simultaneous search for
three equilibria: excitation equilibrium, ionization balance, and the
relationship between \fei\ and the reduced equivalent widths. FAMA also
evaluates the statistical errors on individual element abundances and errors
due to the uncertainties in the stellar parameters. The convergence criteria
are not fixed 'a priori' but are based on the quality of the spectra. In this
paper we present tests performed on the Solar spectrum EWs which tests the
dependency on the initial parameters, and the analysis of a sample of stars
observed in Galactic open and globular clusters.Comment: A&A accepted, 12 pages, 6 figures, 3 table
The Herschel Virgo Cluster Survey. IX. Dust-to-gas mass ratio and metallicity gradients in four Virgo spiral galaxies
Using Herschel data from the Open Time Key Project the Herschel Virgo Cluster
Survey (HeViCS), we investigated the relationship between the metallicity
gradients expressed by metal abundances in the gas phase as traced by the
chemical composition of HII regions, and in the solid phase, as traced by the
dust-to-gas mass ratio. We derived the radial gradient of the dust-to-gas mass
ratio for all galaxies observed by HeViCS whose metallicity gradients are
available in the literature. They are all late type Sbc galaxies, namely
NGC4254, NGC4303, NGC4321, and NGC4501. We examined different dependencies on
metallicity of the CO-to-H conversion factor (\xco), used to transform the
CO observations into the amount of molecular hydrogen. We found that in
these galaxies the dust-to-gas mass ratio radial profile is extremely sensitive
to choice of the \xco\ value, since the molecular gas is the dominant component
in the inner parts. We found that for three galaxies of our sample, namely
NGC4254, NGC4321, and NGC4501, the slopes of the oxygen and of the dust-to-gas
radial gradients agree up to 0.6-0.7R using \xco\ values in the
range 1/3-1/2 Galactic \xco. For NGC4303 a lower value of \xco
10 is necessary. We suggest that such low \xco\ values might be due to a
metallicity dependence of \xco (from close to linear for NGC4254, NGC4321, and
NGC4501 to superlinear for NGC4303), especially in the radial regions
R0.6-0.7R where the molecular gas dominates. On the other hand, the
outer regions, where the atomic gas component is dominant, are less affected by
the choice of \xco, and thus we cannot put constraints on its value.Comment: 13 pages, 8 figures, A&A accepte
A kinematic study of planetary nebulae in the dwarf irregular galaxy IC10
We present positions, kinematics, and the planetary nebula luminosity
function (PNLF) for 35 planetary nebulae (PNe) in the nearest starburst galaxy
IC10 extending out to 3kpc from the galaxy's centre. We take advantage of the
deep imaging and spectroscopic capabilities provided by the spectrograph FOCAS
on the 8.2m Subaru telescope. The PN velocities were measured through the
slitless-spectroscopy technique, which allows us to explore the kinematics of
IC10 with high precision. Using these velocities, we conclude that there is a
kinematic connection between the HI envelope located around IC10 and the
galaxy's PN population. By assuming that the PNe in the central regions and in
the outskirts have similar ages, our results put strong observational
constraints on the past tidal interactions in the Local Group. This is so
because by dating the PN central stars, we, therefore, infer the epoch of a
major episode of star formation likely linked to the first encounter of the HI
extended envelope with the galaxy. Our deep [OIII] images also allow us to use
the PNLF to estimate a distance modulus of 24.1+/-0.25, which is in agreement
with recent results in the literature based on other techniques.Comment: 10 pages, 9 figures, 2 tables. Accepted for publication in MNRA
A deep narrowband survey for planetary nebulae at the outskirts of M33
Context: Planetary nebulae (PNe) are excellent tracers of stellar populations
with low surface brightness, and therefore provide a powerful method to detect
and explore the rich system of substructures discovered around the main spiral
galaxies of the Local Group. Aims: We searched the outskirts of the Local Group
spiral galaxy M33 (the Triangulum) for PNe to gain new insights into the
extended stellar substructure on the northern side of the disc and to study the
existence of a faint classical halo. Methods: The search is based on wide field
imaging covering a 4.5 square degree area out to a maximum projected distance
of about 40 kpc from the centre of the galaxy. The PN candidates are detected
by the combination of images obtained in narrowband filters selecting the
[OIII] and H + [NII] nebular lines and in the continuum
g' and r' broadband filters. Results:Inside the bright optical disc of M33,
eight new PN candidates were identified, three of which were spectroscopically
confirmed. No PN candidates were found outside the limits of the disc. Fourteen
additional sources showing [OIII] excess were also discovered. Conclusions:The
absence of bright PN candidates in the area outside the galaxy disc covered by
this survey sets an upper limit to the luminosity of the underlying population
of , suggesting the lack of a massive
classical halo, which is in agreement with the results obtained using the RGB
population.Comment: 13 pages, 18 figure
- …