627 research outputs found
Characterization of open cluster remnants
Despite progress in the theoretical knowledge of open cluster remnants and
the growing search for observational identifications in recent years, open
questions still remain. The methods used to analyze open cluster remnants and
criteria to define them as physical systems are not homogeneous. In this work
we present a systematic method for studying these objects that provides a view
of their properties and allows their characterization. Eighteen remnant
candidates are analyzed by means of photometric and proper motion data. These
data provide information on objects and their fields. We establish criteria for
characterizing open cluster remnants, taking observational uncertainties into
account. 2MASS J and H photometry is employed (i) to study structural
properties of the objects by means of radial stellar density profiles, (ii) to
test for any similarity between objects and fields with a statistical
comparison method applied to the distributions of stars in the CMDs, and (iii)
to obtain ages, reddening values, and distances from the CMD, taking an index
of isochrone fit into account. The UCAC2 proper motions allowed an objective
comparison between objects and large solid angle offset fields. The objective
analysis based on the present methods indicates 13 open-cluster remnants in the
sample. Evidence of the presence of binary stars is found, as expected for
dynamically evolved systems. Finally, we infer possible evolutionary stages
among remnants from the structure, proper motion, and CMD distributions. The
low stellar statistics for individual objects is overcome by means of the
construction of composite proper motion and CMD diagrams. The distributions of
remnants in the composite diagrams resemble the single-star and unresolved
binary star distributions of open clusters.Comment: 16 pages, 15 figures, A&A accepte
A possible sequential star formation in the giant molecular cloud G174+2.5
We investigate the nature of 14 embedded clusters (ECs) related to a group of
four H II regions Sh2-235, Sh2-233, Sh2-232, and Sh2-231 in the giant molecular
cloud G174 + 2.5. Projected towards the Galactic anticentre, these objects are
a possible example of the collect and collapse scenario. We derive
astrophysical parameters (age, reddening, distance, core and cluster radii) for
the ECs and investigate the relationship among their parameters. Parameters are
derived with field decontaminated 2MASS colour-magnitude diagrams (CMDs) and
stellar radial density profiles (RDPs). The CMDs of these young clusters are
characterised by a poorly-populated main sequence and a significant number of
pre-main sequence stars, affected by differential reddening. The ECs are KKC
11, FSR 784, Sh2-235 E2, Sh2-235 Cluster, Sh2-233SE Cluster, BDSB 73, Sh2-235B
Cluster, BDSB 72, BDSB 71, Sh2-232 IR, PCS 2, and the newly found clusters CBB
1 and CBB 2. We were able to derive fundamental parameters for all ECs in the
sample. Structural parameters are derived for FSR 784, Sh2-235 Cluster and
Sh2-235E2.Comment: 14 pages and 15 figures; MNRAS 201
Astrophysical parameters of 14 open clusters projected close to the Galactic plane
Astrophysical parameters (\textit{age, reddening, distance, core and cluster
radii}) of 14 open clusters (OCs) projected close to the Galactic plane are
derived with 2MASS photometry. The OCs are Be 63, Be 84, Cz 6, Cz 7, Cz 12, Ru
141, Ru 144, Ru 172, FSR 101, FSR 1430, FSR 1471, FSR 162, FSR 178 and FSR 198.
The OCs Be 63, Be 84, Ru 141, Ru 144, and Ru 172 are studied in more detail
than in previous works, while the others have astrophysical parameters derived
for the first time. The open clusters of the sample are located at
kpc from the Sun and at Galactocentric distances
kpc, with age in the range 10 Myr to 1.5 Gyr and reddening in the
range mag. The core and cluster radii are in the range
pc and pc, respectively. Cz 6 and FSR 198 are the youngest OCs of
this sample, with a population of pre-main sequence (PMS) stars, while FSR 178
is the oldest cluster.Comment: 11 pages, 14 figures - accepted by A&
Population synthesis of HII galaxies
We study the stellar population of galaxies with active star formation,
determining ages of the stellar components by means of spectral population
synthesis of their absorption spectra. The data consist of optical spectra of
185 nearby () emission line galaxies. They are mostly HII
galaxies, but we also include some Starbursts and Seyfert 2s, for comparison
purposes. They were grouped into 19 high signal-to-noise ratio template
spectra, according to their continuum distribution, absorption and emission
line characteristics. The templates were then synthesized with a star cluster
spectral base. The synthesis results indicate that HII galaxies are typically
age-composite stellar systems, presenting important contribution from
generations up to as old as 500 Myr. We detect a significant contribution of
populations with ages older than 1 Gyr in two groups of HII galaxies. The age
distributions of stellar populations among Starbursts can vary considerably
despite similarities in the emission line spectra. In the case of Seyfert 2
groups we obtain important contributions of old population, consistent with a
bulge. From the diversity of star formation histories, we conclude that typical
HII galaxies in the local universe are not systems presently forming their
first stellar generation.Comment: 12 pages, 4 figures, MNRAS in pres
Photosynthetic activity in grafted and ownrooted Erbaluce grapevines trained to four trellis systems
Photosynthetic activity of grafted (Kober 5BB) and ownrooted grapevines (cv. Erbaluce) trained to four trellis systems (alternate curtain, central curtain with one or two canes and pergola) was assessed for three years. The overall photosynthetic response to training, the seasonal and diurnal photosynthetic trends and the response of the training systems to different photosynthetic photon flux densities were evaluated. The training systems had a significant influence on the rate of photosynthetic assimilation: the two central curtains generally had higher rates of CO2 uptake compared to the vines which were trained to pergola and to alternate curtain. With one exception Kober 5BB improved net assimilation rates
UKIRT follow-up observations of the old open cluster FSR0358 (Kirkpatrick1)
We aim to characterise the properties of the stellar clusters in the Milky
Way. Utilising an expectation-maximisation method we determined that the
cluster FSR0358, originally discovered by J.D.Kirkpatrick, is the most likely
real cluster amongst the cluster candidates from Froebrich et al.. Here we
present new deep high resolution near infrared imaging of this object obtained
with UKIRT. The analysis of the data reveals that FSR0358 (Kirkpatrick1) is a
5+-2Gyr old open cluster in the outer Milky Way. Its age, metallicity of
Z=0.008 and distance from the Galactic Centre of 11.2kpc are typical for the
known old open galactic clusters. So far six of the FSR cluster candidates have
been identified as having an age above 5Gyr. This shows the significance of
this catalogue in enhancing our knowledge of the oldest open clusters in the
Galaxy.Comment: 8 pages, 1 table, 5 figures, accepted for publication by MNRAS, a
version with higher resolution figures can be found at
http://astro.kent.ac.uk/~df
AL 3 (BH 261): a new globular cluster in the Galaxy
AL~3 (BH 261), previously classified as a faint open cluster candidate, is
shown to be a new globular cluster in the Milky Way, by means of B, V and I
Color-Magnitude Diagrams. The main feature of AL~3 is a prominent blue extended
Horizontal Branch. Its Color-Magnitude Diagrams match those of the intermediate
metallicity cluster M~5. The cluster is projected in a rich bulge field, also
contaminated by the disk main sequence. The globular cluster is located in the
Galactic bulge at a distance from the Sun d = 6.00.5 kpc. The
reddening is E(B-V)=0.360.03 and the metallicity is estimated to be [Fe/H]
-1.30.25. AL~3 is probably one of the least massive globular
clusters of the Galaxy.Comment: 6 figures. Astrophysical Journal Letters, in pres
Synthetic spectra of H Balmer and HeI absorption lines. II: Evolutionary synthesis models for starburst and post-starburst galaxies
We present evolutionary stellar population synthesis models to predict the
spectrum of a single-metallicity stellar population, with a spectral sampling
of 0.3 A in five spectral regions between 3700 and 5000 A. The models, which
are optimized for galaxies with active star formation, synthesize the profiles
of the hydrogen Balmer series (Hb, Hg, Hd, H8, H9, H10, H11, H12 and H13) and
the neutral helium absorption lines (HeI 4922, HeI 4471, HeI 4388, HeI 4144,
HeI 4121, HeI 4026, HeI 4009 and HeI 3819) for a burst with an age ranging from
1 to 1000 Myr, and different assumptions about the stellar initial mass
function. Continuous star formation models lasting for 1 Gyr are also
presented. The input stellar library includes NLTE absorption profiles for
stars hotter than 25000 K and LTE profiles for lower temperatures. The
temperature and gravity coverage is 4000 K <Teff< 50000 K and 0.0< log g$< 5.0,
respectively.
The models can be used to date starburst and post-starburst galaxies until 1
Gyr. They have been tested on data for clusters in the LMC, the super-star
cluster B in the starburst galaxy NGC 1569, the nucleus of the dwarf elliptical
NGC 205 and a luminous "E+A" galaxy. The full data set is available for
retrieval at http://www.iaa.es/ae/e2.html and at
http://www.stsci.edu/science/starburst/, or on request from the authors at
[email protected]: To be published in ApJS. 48 pages and 20 figure
The Dusty Starburst Nucleus of M33
We have thoroughly characterized the ultraviolet to near-infrared (0.15 - 2.2
micron) spectral energy distribution (SED) of the central parsec of the M33
nucleus through new infrared photometry and optical/near-infrared spectroscopy,
combined with ultraviolet/optical observations from the literature and the HST
archive. The SED shows evidence for a significant level of attenuation, which
we model through a Monte Carlo radiative transfer code as a shell of clumpy
Milky Way-type dust (tau_V ~ 2 +/- 1). The discovery of Milky Way-type dust
(with a strong 2175 A bump) internal to the M33 nucleus is different from
previous work which has found SMC-like dust (no bump) near starburst regions.
The amount by which dust can be processed may be related to the mass and age of
the starburst as well as the extent to which the dust can shield itself. Our
starburst models include the effects of this dust and can fit the SED if the
nucleus was the site of a moderate (~10^8 L_sun at 10 Myrs) episode of coeval
star formation about 70 Myrs ago. This result is quite different from previous
studies which resorted to multiple stellar populations (between 2 and 7)
attenuated by either no or very little internal dust. The M33 nuclear starburst
is remarkably similar to an older version (70 Myr versus 10 Myr) of the
ultra-compact starburst in the center of the Milky Way.Comment: 29 pages, 9 embedded figures, ApJ, in pres
Discovery of new Milky Way star cluster candidates in the 2MASS point source catalog III. Follow-up observations of cluster candidates in the Galactic Center region
This paper is part of a project to search the inner Milky Way for hidden
massive clusters and to address the question of whether our Galaxy still forms
clusters similar to the progenitors of the present-day globular clusters.
We report high angular resolution deep near-infrared imaging of 21 cluster
candidates selected from the catalogues of Bica et al. (2003) and Dutra et
al.(2003) in a region around the Galactic Center. These catalogues were created
from visual inspection of the 2MASS images. Seven objects appear to be genuine
clusters, and for these objects we present estimates of extinction, distance
and in some cases age and mass.
Our estimated masses range from 1200 to 5500 solar masses. These clusters are
thus significantly smaller than any Galactic globular cluster, and indicate
that the formation of massive young clusters such as Arches and Quintuplet is
not common in the present-day Milky Way.
The remaining 14 objects are either not clusters or cannot be classified
based on our data.Comment: 8 pages, 19 figures, accepted for publication in A&
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