518 research outputs found
Characterization of single-crystal synthetic diamond for multi-watt continuous-wave Raman lasers
A continuous-wave diamond Raman laser is demonstrated with an output power of 5.1 W at 1217 nm. This Raman laser is intracavity pumped by a side-pumped Nd:YLF rod laser: a 43-fold brightness enhancement between the Nd:YLF and diamond Raman lasers is observed, with the M2 beam propagation factor of the diamond Raman laser measured to be <; 1.2. Although higher output powers are demonstrated in a similar configuration using KGd(WO4)2 (KGW) as the Raman laser material (6.1 W), the brightness enhancement is much lower (2.5 fold) due to the poorer beam quality of the KGW Raman laser (M2 <; 6). The Raman gain coefficient of single-crystal synthetic diamond at a pump wavelength of 1064-nm is also measured: a maximum value of 21±2 cm/GW is returned compared to 5.7±0.5 cm/GW for KGW at the same wavelength
NGC 7789: An Open Cluster Case Study
We have obtained high-resolution spectra of 32 giants in the open cluster NGC
7789 using the Wisconsin-Indiana-Yale-NOAO Hydra spectrograph. We explore
differences in atmospheric parameters and elemental abundances caused by the
use of the linelist developed for the Gaia-ESO Survey (GES) compared to one
based on Arcturus used in our previous work. [Fe/H] values decrease when using
the GES linelist instead of the Arcturus-based linelist; these differences are
probably driven by systematically lower (~ -0.1 dex) GES surface gravities.
Using the GES linelist we determine abundances for 10 elements - Fe, Mg, Si,
Ca, Ti, Na, Ni, Zr, Ba, and La. We find the cluster's average metallicity
[Fe/H] = 0.03 +/- 0.07 dex, in good agreement with literature values, and a
lower [Mg/Fe] abundance than has been reported before for this cluster (0.11
+/- 0.05 dex). We also find the neutron-capture element barium to be highly
enhanced - [Ba/Fe] = +0.48 +/- 0.08 - and disparate from cluster measurements
of neutron-capture elements La and Zr (-0.08 +/- 0.05 and 0.08 +/- 0.08,
respectively). This is in accordance with recent discoveries of supersolar Ba
enhancement in young clusters along with more modest enhancement of other
neutron-capture elements formed in similar environments.Comment: 15 pages, 9 figures, Table 1 typo fixe
Classification using distance nearest neighbours
This paper proposes a new probabilistic classification algorithm using a
Markov random field approach. The joint distribution of class labels is
explicitly modelled using the distances between feature vectors. Intuitively, a
class label should depend more on class labels which are closer in the feature
space, than those which are further away. Our approach builds on previous work
by Holmes and Adams (2002, 2003) and Cucala et al. (2008). Our work shares many
of the advantages of these approaches in providing a probabilistic basis for
the statistical inference. In comparison to previous work, we present a more
efficient computational algorithm to overcome the intractability of the Markov
random field model. The results of our algorithm are encouraging in comparison
to the k-nearest neighbour algorithm.Comment: 12 pages, 2 figures. To appear in Statistics and Computin
Trumpler 20 - an old and rich open cluster
We show that the open cluster Trumpler 20, contrary to the earlier findings,
is actually an old Galactic open cluster. New CCD photometry and
high-resolution spectroscopy are used to derive the main parameters of this
cluster. At [Fe/H]=-0.11 for a single red giant star, the metallicity is
slightly subsolar. The best fit to the color-magnitude diagrams is achieved
using a 1.3 Gyr isochrone with convective overshoot. The cluster appears to
have a significant reddening at E(B-V)=0.46 (for B0 spectral type), although
for red giants this high reddening yields the color temperature exceeding the
spectroscopic T_eff by about 200 K. Trumpler 20 is a very rich open cluster,
containing at least 700 members brighter than M_V=+4. It may extend over the
field-of-view available in our study at 20'x20'.Comment: 7 pages, 5 figures; accepted for publication in MNRA
Variable stars in the field of the old open cluster Melotte 66
We report the results of photometric monitoring of the Melotte 66 field in
BVI filters. Ten variables were identified with nine being new discoveries. The
sample includes eight eclipsing binaries of which four are W UMa type stars,
one star is a candidate blue straggler. All four contact binaries are likely
members of the cluster based on their estimated distances. Ten blue stars with
U-B<-0.3 were detected inside a 14.8 x 22.8 arcmin^2 field centred on the
cluster. Time series photometry for 7 of them showed no evidence for any
variability. The brightest object in the sample of blue stars is a promising
candidate for a hot subdwarf belonging to the cluster. We show that the
anomalously wide main sequence of the cluster, reported in some earlier
studies, results from a combination of two effects: variable reddening occuring
across the cluster field and the presence of a rich population of binary stars
in the cluster itself. The density profile of the cluster field is derived and
the total number of member stars with 16<V<21 or 2.8<M_{V}<7.8 is estimated
conservatively at about 1100.Comment: 8 pages, 12 figures, accepted to MNRAS - 29 June 200
A kinematic study of Open Clusters: implications for their origin
The Galactic population of open clusters provides an insight into star
formation in the Galaxy. The open cluster catalogue by Dias et al.(2002b) is a
rich source of data, including kinematic information. This large sample made it
possible to carry out a systematic analysis of 481 open cluster orbits, using
parameters based on orbit eccentricity and separation from the Galactic plane.
These two parameters may be indicative of origin, and we find them to be
correlated. We also find them to be correlated with metallicity, another
parameter suggested elsewhere to be a marker for origin in that high values of
any of these two parameters generally indicates a low metallicity ([Fe/H]
Solar0.2 dex). The resulting analysis points to four open clusters in the
catalogue being of extra-Galactic origin by impact of high velocity cloud on
the disk: Berkeley21, 32, 99, and Melotte66, with a possible further four due
to this origin (NGC2158, 2420, 7789, IC1311). A further three may be due to
Galactic globular cluster impact on the disk i.e of internal Galactic origin
(NGC6791, 1817, and 7044).Comment: 14 pages, 816 figures, accepted for publication in MNRAS 14-May-201
Elemental abundance differences in the 16 Cygni binary system: a signature of gas giant planet formation?
The atmospheric parameters of the components of the 16Cygni binary system, in
which the secondary has a gas giant planet detected, are measured accurately
using high quality observational data. Abundances relative to solar are
obtained for 25 elements with a mean error of 0.023 dex. The fact that 16CygA
has about four times more lithium than 16CygB is normal considering the
slightly different masses of the stars. The abundance patterns of 16CygA and B,
relative to iron, are typical of that observed in most of the so-called solar
twin stars, with the exception of the heavy elements (Z>30), which can,
however, be explained by Galactic chemical evolution. Differential (A-B)
abundances are measured with even higher precision (0.018 dex, on average). We
find that 16CygA is more metal-rich than 16CygB by 0.041+/-0.007 dex. On an
element-to-element basis, no correlation between the A-B abundance differences
and dust condensation temperature (Tc) is detected. Based on these results, we
conclude that if the process of planet formation around 16CygB is responsible
for the observed abundance pattern, the formation of gas giants produces a
constant downwards shift in the photospheric abundance of metals, without a Tc
correlation. The latter would be produced by the formation of terrestrial
planets instead, as suggested by other recent works on precise elemental
abundances. Nevertheless, a scenario consistent with these observations
requires the convective envelopes of 1 Msun stars to reach their present-day
sizes about three times quicker than predicted by standard stellar evolution
models.Comment: ApJ, in pres
Survey for Transiting Extrasolar Planets in Stellar Systems. II. Spectrophotometry and Metallicities of Open Clusters
We present metallicity estimates for seven open clusters based on
spectrophotometric indices from moderate-resolution spectroscopy. Observations
of field giants of known metallicity provide a correlation between the
spectroscopic indices and the metallicity of open cluster giants. We use \chi^2
analysis to fit the relation of spectrophotometric indices to metallicity in
field giants. The resulting function allows an estimate of the target-cluster
giants' metallicities with an error in the method of \pm0.08 dex. We derive the
following metallicities for the seven open clusters: NGC 1245,
[m/H]=-0.14\pm0.04; NGC 2099, [m/H]=+0.05\pm0.05; NGC 2324, [m/H]=-0.06\pm0.04;
NGC 2539, [m/H]=-0.04\pm0.03; NGC 2682 (M67), [m/H]=-0.05\pm0.02; NGC 6705,
[m/H]=+0.14\pm0.08; NGC 6819, [m/H]=-0.07\pm0.12. These metallicity estimates
will be useful in planning future extra-solar planet transit searches since
planets may form more readily in metal-rich environments.Comment: 38 pages, including 12 figures. Accepted for publication in A
The Infrared Ca II triplet as metallicity indicator
From observations of almost 500 RGB stars in 29 Galactic open and globular
clusters, we have investigated the behaviour of the infrared Ca II triplet
(8498, 8542 and 8662 \AA) in the age range 13Age/Gyr0.25 and the
metallicity range [Fe/H] +0.47. These are the widest ranges of
ages and metallicities in which the behaviour of the Ca II triplet lines has
been investigated in a homogeneous way. We report the first empirical study of
the variation of the CaII triplet lines strength, for given metallicities, with
respect to luminosity. We find that the sequence defined by each cluster in the
Luminosity-Ca plane is not exactly linear. However, when only stars in
a small magnitude interval are observed, the sequences can be considered as
linear. We have studied the the Ca II triplet lines on three metallicities
scales. While a linear correlation between the reduced equivalent width (
or ) versus metallicity is found in the \citet{cg97} and \citet{ki03}
scales, a second order term needs to be added when the \citet{zw84} scale is
adopted. We investigate the role of age from the wide range of ages covered by
our sample. We find that age has a weak influence on the final relationship.
Finally, the relationship derived here is used to estimate the metallicities of
three poorly studied open clusters: Berkeley 39, Trumpler 5 and Collinder 110.
For the latter, the metallicity derived here is the first spectroscopic
estimate available.Comment: 52 pages, 16 figures, accepted for publication in Astronomical
Journa
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