3,876 research outputs found
A comparative study on the reliability of open cluster parameters
Context. Open clusters are known as excellent tracers of the structure and chemical evolution of the Galactic disk, however, the accuracy and reliability of open cluster parameters is poorly known.
Aims: In recent years, several studies aimed to present homogeneous open cluster parameter compilations, which are based on some different approaches and photometric data. These catalogues are excellent sources to facilitate testing of the actual accuracy of open cluster parameters.
Methods: We compare seven cluster parameter compilations statistically and with an external sample, which comprises the mean results of individual studies. Furthermore, we selected the objects IC 4651, NGC 2158, NGC 2383, NGC 2489, NGC 2627, NGC 6603, and Trumpler 14, with the main aim to highlight differences in the fitting solutions.
Results: We derived correction terms for each cluster parameter, using the external calibration sample. Most results by the compilations are reasonable scaled, but there are trends or constant offsets of different degree. We also identified one data set, which appears too erroneous to allow adjustments. After the correction, the mean intrinsic errors amount to about 0.2 dex for the age, 0.08 mag for the reddening, and 0.35 mag for the distance modulus. However, there is no study that characterises the cluster morphologies of all test cases in a correct and consistent manner. Furthermore, we found that the largest compilations probably include at least 20 percent of problematic objects, for which the parameters differ significantly. These could be among others doubtful or unlikely open clusters that do not facilitate an unambiguous fitting solution
Behavioral and Distributional Effects of Environmental Policy Introduction
This paper summarizes research presented at the FEEM-NBER Conference on the Behavioral and Distributional Effects of Environmental Policy, held in Milan Italy in June 1999.
A photometric study of the young open cluster NGC 1220
We present UBV CCD observations obtained in the field of the northern open
cluster NGC 1220, for which little information is available. We provide also BV
CCD photometry of a field 5 northward of NGC 1220 to take into
account field star contamination. We argue that NGC 1220 is a young compact
open cluster, for which we estimate a core radius in the range
arcmin. We identify 26 likely candidate members with spectral type earlier than
, down to =15.00 mag on the basis of the position in the two-colour
Diagram and in the Colour Magnitude Diagrams (CMDs). By analyzing the
distribution of these stars in the colour-colour and CMDs, we find that NGC
1220 has a reddening E mag, is placed pc
distant from the Sun, and has an age of about 60 Myrs. The cluster turns out to
be located about 120 pc above the Galactic plane, relatively high with respect
to its age.Comment: 7 pages, 8 eps figures, accepted for publication in A&
Exact response of the non-relativistic harmonic oscillator
Using Greens function and operator techniques we give a closed expression
for the response of a non-relativistic system interacting through confining,
harmonic forces. The expression for the incoherent part permits rapid
evaluation of coefficients in a 1/q expansion. A comparison is made with
standard approximation methods.Comment: 9p.; INFN-ISS 93/2; WIS-93/50/Jun-P
On the existence of young embedded clusters at high Galactic latitude
Careful analyses of photometric and star count data available for the nine
putative young clusters identified by Camargo et al. (2015, 2016) at high
Galactic latitudes reveal that none of the groups contain early-type stars, and
most are not significant density enhancements above field level. 2MASS colours
for stars in the groups match those of unreddened late-type dwarfs and giants,
as expected for contamination by (mostly) thin disk objects. A simulation of
one such field using only typical high latitude foreground stars yields a
colour-magnitude diagram that is very similar to those constructed by Camargo
et al. (2015, 2016) as evidence for their young groups as well as the means of
deriving their reddenings and distances. Although some of the fields are
coincident with clusters of galaxies, one must conclude that there is no
evidence that the putative clusters are extremely young stellar groups.Comment: Accepted for publication (MNRAS
UB CCD photometry of the old, metal rich, open clusters NGC 6791, NGC 6819 and NGC 7142
We report on a UV-oriented imaging survey in the fields of the old,
metal-rich open clusters, NGC 6791, NGC 6819 and NGC 7142. These three clusters
represent both very near and ideal stellar aggregates to match the distinctive
properties of the evolved stellar populations, as in elliptical galaxies and
bulges of spirals. The CMD of the three clusters is analyzed in detail, with
special emphasis to the hot stellar component. We report, in this regard, one
new extreme horizontal-branch star candidate in NGC 6791. For NGC 6819 and
7142, the stellar luminosity function points to a looser radial distribution of
faint lower Main Sequence stars, either as a consequence of cluster dynamical
interaction with the Galaxy or as an effect of an increasing fraction of binary
stars toward the cluster core, as actually observed in NGC 6791 too.Comment: 12 pages with 15 Figures & 5 Tables. To appear in the Astronomical
Journa
On the assessment of the nature of open star clusters and the determination of their basic parameters with limited data
Our knowledge of stellar evolution and of the structure and chemical
evolution of the Galactic disk largely builds on the study of open star
clusters. Because of their crucial role in these relevant topics, large
homogeneous catalogues of open cluster parameters are highly desirable.
Although efforts have been made to develop automatic tools to analyse large
numbers of clusters, the results obtained so far vary from study to study, and
sometimes are very contradictory when compared to dedicated studies of
individual clusters. In this work we highlight the common causes of these
discrepancies for some open clusters, and show that at present dedicated
studies yield a much better assessment of the nature of star clusters, even in
the absence of ideal data-sets. We make use of deep, wide-field, multi-colour
photometry to discuss the nature of six strategically selected open star
clusters: Trumpler~22, Lynga~6, Hogg~19, Hogg~21, Pismis~10 and Pismis~14. We
have precisely derived their basic parameters by means of a combination of star
counts and photometric diagrams. Trumpler~22 and Lynga~6 are included in our
study because they are widely known, and thus provided a check of our data and
methodology. The remaining four clusters are very poorly known, and their
available parameters have been obtained using automatic tools only. Our results
are in some cases in severe disagreement with those from automatic surveys.Comment: 22 pages, 16 figures, in pres
A new look at Sco OB1 association with Gaia DR2
We present and discuss photometric optical data in the area of the OB
association Sco OB1 covering about 1 squared degree. UBVI photometry is
employed in tandem with Gaia DR2 data to investigate the 3 dimensional
structure and the star formation history of the region. By combining parallaxes
and proper motions we identify 7 physical groups located between the young open
cluster NGC 6231 and the bright nebula IC4628. The most prominent group
coincides with the sparse open cluster Trumpler 24. We confirm the presence of
the intermediate age star cluster VdB-Hagen 202, which is unexpected in this
environment, and provide for the first time estimates of its fundamental
parameters. After assessing individual groups membership, we derive mean proper
motion components, distances, and ages. The seven groups belong to two
different families. To the younger family (family I) belong several pre-Main
Sequence stars as well. These are evenly spread across the field, and also in
front of VdB-Hagen 202. VdB-Hagen 202 and two smaller, slightly detached,
groups of similar properties form family II, which do not belong to the
association, but are caught in the act of passing through it. As for the
younger population, this forms an arc-like structure from the bright nebula IC
4628 down to NGC 6231, as previously found. Moreover, the pre-Main Sequence
stars density seems to increase from NGC 6231 northward to Trumpler 24
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