316 research outputs found
Extended Stromgren Photoelectric Photometry in NGC 752
Photoelectric photometry on the extended Stromgren system (uvbyCa) is
presented for 7 giants and 21 main sequence stars in the old open cluster, NGC
752. Analysis of the hk data for the turnoff stars yields a new determination
of the cluster mean metallicity. From 10 single-star members, [Fe/H] = -0.06
+/- 0.03, where the error quoted is the standard error of the mean and the
Hyades abundance is set at [Fe/H] = +0.12. This result is unchanged if all 20
stars within the limits of the hk metallicity calibration are included. The
derived [Fe/H] is in excellent agreement with past estimates using
properly-zeroed m1 data, transformed moderate-dispersion spectroscopy, and
recent high dispersion spectroscopy.Comment: 14 tex'd pages including 2 tables; 2 separate files with eps figures
Accepted for PASP March 200
vbyCaHbeta CCD Photometry of Clusters. VI. The Metal-Deficient Open Cluster NGC 2420
CCD photometry on the intermediate-band vbyCaHbeta system is presented for
the metal-deficient open cluster, NGC 2420. Restricting the data to probable
single members of the cluster using the CMD and the photometric indices alone
generates a sample of 106 stars at the cluster turnoff. The average E(b-y) =
0.03 +/- 0.003 (s.e.m.) or E(B-V) = 0.050 +/- 0.004 (s.e.m.), where the errors
refer to internal errors alone. With this reddening, [Fe/H] is derived from
both m1 and hk, using b-y and Hbeta as the temperature index. The agreement
among the four approaches is reasonable, leading to a final weighted average of
[Fe/H] = -0.37 +/- 0.05 (s.e.m.) for the cluster, on a scale where the Hyades
has [Fe/H] = +0.12. When combined with the abundances from DDO photometry and
from recalibrated low-resolution spectroscopy, the mean metallicity becomes
[Fe/H] = -0.32 +/- 0.03. It is also demonstrated that the average cluster
abundances based upon either DDO data or low-resolution spectroscopy are
consistently reliable to 0.05 dex or better, contrary to published attempts to
establish an open cluster metallicity scale using simplistic offset corrections
among different surveys.Comment: scheduled for Jan. 2006 AJ; 33 pages, latex, includes 7 figures and 2
table
uvbyCa H beta CCD Photometry of Clusters. VII. The Intermediate-Age Anticenter Cluster Melotte 71
CCD photometry on the intermediate-band uvbyCa H beta system is presented for
the anticenter, intermediate-age open cluster, Melotte 71. Restricting the data
to probable single members of the cluster using the color-magnitude diagram and
the photometric indices alone generates a sample of 48 F dwarfs on the
unevolved main sequence. The average E(b-y) = 0.148 +/- 0.003 (s.e.m.) or
E(B-V) = 0.202 +/- 0.004 (s.e.m.), where the errors refer to internal errors
alone. With this reddening, [Fe/H] is derived from both m1 and hk, using H beta
and b-y as the temperature index, with excellent agreement among the four
approaches and a final weighted average of [Fe/H] = -0.17 +/- 0.02 (s.e.m.) for
the cluster, on a scale where the Hyades has [Fe/H] = +0.12. When adjusted for
the higher reddening estimate, the previous metallicity estimates from
Washington photometry and from spectroscopy are now in agreement with the
intermediate-band result. From comparisons to isochrones of appropriate
metallicity, the cluster age and distance are determined as 0.9 +/- 0.1 Gyr and
(m-M) = 12.2 +/- 0.1 or (m-M)_0 = 11.6 +/- 0.1. At this distance from the sun,
Mel 71 has a galactocentric distance of 10.0 kpc on a scale where the sun is
8.5 kpc from the galactic center. Based upon its age, distance, and elemental
abundances, Mel 71 appears to be a less populous analog to NGC 3960.Comment: Accepted for Astronomical Journal. 38 page latex file includes 11
figures and short version of data table. Full table will appear in online AJ
or may be requested from author
A Stromgren view of the multiple populations in globular clusters
We discuss a variety of photometric indices assembled from the uvby Stromgren
system. Our aim is to examine the pros and cons of the various indices to find
the most suitable one(s) to study the properties of multiple populations in
globular clusters (GCs) discovered by spectroscopy. We explore in particular
the capabilities of indices like m_1 and c_y at different metallicities. We
define a new index delta_4=(u-v)-(b-y) to separate first and second stellar
generations in GCs of any metal abundance, since it keeps the sensitivity to
multiple stellar populations over all the metallicity range and at the same
time minimizes the sensitivity to photometric errors. We detecte clear
differences in the red giant branches of the GCs examined, like skewness or
bi/multi-modality in color distribution. We connect the photometric information
with the spectroscopic results on O, Na abundances we obtained in our survey of
GCs. Finally, we compute the effects of different chemical composition on the
Stromgren filters and indices using synthetic spectra.Comment: Accepted for publication on Astronomy and Astrophysics. Figures 1,3,5
degraded in resolutio
VLT multi-epoch radial velocity survey toward NGC 6253. Analysis of three transiting planetary candidates
We measured the radial velocity of 139 stars in the region of NGC 6253,
discussing cluster's membership and binarity in this sample, complementing our
analysis with photometric, proper motion, and radial velocity data available
from previous studies of this cluster, and analyzing three planetary transiting
candidates we found in the field of NGC 6253. Spectra were obtained with the
UVES and GIRAFFE spectrographs at the VLT, during three epochs in August 2008.
The mean radial velocity of the cluster is -29.11+/-0.85 km/s. Using both
radial velocities and proper motions we found 35 cluster's members, among which
12 are likely cluster's close binary systems. One star may have a sub-stellar
companion, requiring a more intensive follow-up. Our results are in good
agreement with past radial velocity and photometric measurements. Furthermore,
using our photometry, astrometry and spectroscopy we identified a new sub-giant
branch eclipsing binary system, member of the cluster. The cluster's close
binary frequency at 29% +/- 9% (34% +/-10% once including long period
binaries), appears higher than the field binary frequency equal to (22% +/- 5%,
though these estimates are still consistent within the uncertainties. Among the
three transiting planetary candidates the brightest one (V=15.26) is worth to
be more intensively investigated with higher percision spectroscopy. We
discussed the possibility to detect sub-stellar companions (brown dwarfs and
planets) with the radial velocity technique (both with UVES/GIRAFFE and HARPS)
around turn-off stars of old open clusters [abridged].Comment: 25 pages, 18 figures, 8 tables. Accepted for publication in A&
Theoretical stellar models for old galactic clusters
We present new evolutionary stellar models suitable for old Population I
clusters, discussing both the consequences of the most recent improvements in
the input physics and the effect of element diffusion within the stellar
structures. Theoretical cluster isochrones are presented, covering the range of
ages from 1 to 9 Gyr for the four selected choices on the metallicity Z= 0.007,
0.010, 0.015 and 0.020. Theoretical uncertainties on the efficiency of
superadiabatic convection are discussed in some details. Isochrone fitting to
the CM diagrams of the two well observed galactic clusters NGC2420 and M67
indicates that a mixing length parameter alpha = 1.9 appears adequate for
reproducing the observed color of cool giant stars. The problems in matching
theoretical preditions to the observed slope of MS stars are discussed.Comment: 7 pages, 14 postscript figures, accepted for publication on MNRA
The ability of intermediate-band Stromgren photometry to correctly identify dwarf, subgiant, and giant stars and provide stellar metallicities and surface gravities
[Abridged] Several large scale photometric and spectroscopic surveys are
being undertaken to provide a more detailed picture of the Milky Way. Given the
necessity of generalisation in the determination of, e.g., stellar parameters
when tens and hundred of thousands of stars are considered it remains important
to provide independent, detailed studies to verify the methods used in the
surveys. We evaluate available calibrations for deriving [M/H] from Stromgren
photometry and develop the standard sequences for dwarf stars to reflect their
metallicity dependence and test how well metallicities derived from ugriz
photometry reproduce metallicities derived from the well-tested system of
Stromgren photometry. We use a catalogue of dwarf stars with both Stromgren
uvby photometry and spectroscopically determined iron abundances (in total 451
dwarf stars with 0.3<(b-y)_0<1.0). We also evaluate available calibrations that
determine log g. A larger catalogue, in which metallicity is determined
directly from uvby photometry, is used to trace metallicity-dependent standard
sequences for dwarf stars. We derive new standard sequences in the c_1,0 versus
(b-y)_0 plane and in the c_1,0 versus (v-y)_0 plane for dwarf stars with 0.40 <
(b-y)_0 < 0.95 and 1.10 < (v-y)_0 < 2.38. We recommend the calibrations by
Ramirez & Me'endez (2005) for deriving metallicities from Stromgren photometry
and find that intermediate band photometry, such as Stromgren photometry, more
accurately than broad band photometry reproduces spectroscopically determined
[Fe/H]. Stromgren photometry is also better at differentiating between dwarf
and giant stars. We conclude that additional investigations of the differences
between metallicities derived from ugriz photometry and intermediate-band
photometry, such as Stromgren photometry, are required.Comment: Accepted for publication in A&A, 34 pages, including on-line materia
Stroemgren photometry of the Bulge: the Baade's Window and the globular cluster NGC 6522
We present Ca-uvby Stroemgren photometry of the Baade's Window, including the
Galactic globular cluster NGC 6522. We separate field and cluster stars by
adopting color-color planes and proper motions. We then estimate the global
metallicity of red-giants (RGs) in NGC 6522 by using a new theoretical
metallicity calibration of the Stroemgren index hk presented in Calamida et al.
(2011). We find that metallicities estimated by adopting the hk index and the
(Ca-y) color are systematically more metal-rich than metallicities estimated
with hk and the (u-y), (v-y) and (b-y) colors. Current evidence indicate that
the hk metallicity index is affected not only by the Calcium abundance, but
also by another source of opacity.Comment: Proceeding of the RIA Workshop on Gaia "Stellar Clusters &
Associations", Granada, May 23-27, 201
BVRIJHK photometry and proper motion analysis of NGC 6253 and the surrounding field
Context. We present a photometric and astrometric catalog of 187963 stars
located in the field around the old super-metal-rich Galactic open cluster NGC
6253. The total field-of-view covered by the catalog is 34' x 33'. In this
field, we provide CCD BVRI photometry. For a smaller region close to the
cluster's center, we also provide near-infrared JHK photometry. Aims. We
analyze the properties of NGC 6253 by using our new photometric data and
astrometric membership. Methods. In June 2004, we targeted the cluster during a
10 day multi-site campaign, which involved the MPG/ESO 2.2m telescope with its
wide-field imager and the Anglo-Australian 3.9m telescope, equipped with the
IRIS2 near-infrared imager. Archival CCD images of NGC 6253 were used to derive
relative proper motions and to calculate the cluster membership probabilities.
Results. We have refined the cluster's fundamental parameters, deriving
(V_0-M_v)=11.15, E(B - V)=0.15, E(V - I)=0.25, E(V - J)=0.50, and E(V -
H)=0.55. The color excess ratios obtained using both the optical and near
infrared colors indicate a normal reddening law in the direction of NGC 6253.
The age of NGC 6253 at 3.5 Gyr, determined from our best-fitting isochrone
appears to be slightly older than the previous estimates. Finally, we estimated
the binary fraction among the cluster members to be \sim20%-30% and identified
11 blue straggler candidates.Comment: 16 pages, 13 figures, 11 tables. Accepted for publication in A&A.
Catalog avaiable via CD
Kinematics, ages and metallicities for F and G type stars in the solar neighbourhood
A new metallicity distribution and an age-metallicity relation are presented
for 437 nearby F and G turn-off and sub-giant stars selected from radial
velocity data of Nidever et al. Photometric metallicities are derived from
uvby-H\beta photometry, and the stellar ages from the isochrones of Bergbusch &
VandenBerg as transformed to photometry using the methods of Clem et al.
The X (stellar-population) criterion of Schuster et al., which combines both
kinematic and metallicity information, provides 22 thick-disk stars.
\sigma_{\rm W} = 32 \pm 5 km s^{-1}, = 154 \pm 6 km s^{-1} and
= -0.55 \pm 0.03 dex for these thick-disk stars, which is in agreement
with values from previous studies of the thick disk. \alpha -element abundances
which are available for some of these thick-disk stars show the typical
alpha-element signatures of the thick disk, supporting the classification
procedure based on the criteria. Both the scatter in metallicity at a given
age and the presence of old, metal-rich stars in the age-metallicity relation
make it difficult to decide whether or not an age-metallicity relation exists
for the older thin-disk stars. For ages greater than 3 Gyr, our results agree
with the other recent studies that there is almost no correlation between age
and metallicity, \Delta ([M/Fe])/\Delta(age) = -0.01 \pm 0.005 dex Gyr^{-1}.
For the 22 thick-disk stars there is a range in ages of 7-8 Gyr, but again
almost no correlation between age and metallicity.Comment: 11 pages, including 10 figures and 3 tables, accepted for publication
in MNRA
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