1,110 research outputs found
Observable Signatures of Planet Accretion in Red Giant Stars I: Rapid Rotation and Light Element Replenishment
The orbital angular momentum of a close-orbiting giant planet can be
sufficiently large that, if transferred to the envelope of the host star during
the red giant branch (RGB) evolution, it can spin-up the star's rotation to
unusually large speeds. This spin-up mechanism is one possible explanation for
the rapid rotators detected among the population of generally slow-rotating red
giant stars. These rapid rotators thus comprise a unique stellar sample
suitable for searching for signatures of planet accretion in the form of
unusual stellar abundances due to the dissemination of the accreted planet in
the stellar envelope. In this study, we look for signatures of replenishment in
the Li abundances and (to a lesser extent) 12C/13C, which are both normally
lowered during RGB evolution. Accurate abundances were measured from high
signal-to-noise echelle spectra for samples of both slow and rapid rotator red
giant stars. We find that the rapid rotators are on average enriched in lithium
compared to the slow rotators, but both groups of stars have identical
distributions of 12C/13C within our measurement precision. Both of these
abundance results are consistent with the accretion of planets of only a few
Jupiter masses. We also explore alternative scenarios for understanding the
most Li-rich stars in our sample---particularly Li regeneration during various
stages of stellar evolution. Finally, we find that our stellar samples show
non-standard abundances even at early RGB stages, suggesting that initial
protostellar Li abundances and 12C/13C may be more variable than originally
thought.Comment: Accepted for publication in the Astrophysical Journal. 29 pages in
emulateapj format, including 16 figures and 12 tables. Tables 4 and 8 are
provided in their entirety as plain text ancillary files (and will also be
available in the electronic edition of ApJ
Chemical Abundances Of Three Metal-Poor Globular Clusters (NGC 6287, NGC 6293, And NGC 6541) In The Inner Halo
We present a chemical abundance study of three inner old halo clusters NGC
6287, NGC 6293, and NGC 6541, finding [Fe/H] = -2.01 +/- 0.05, -1.99 +/- 0.02,
and -1.76 +/- 0.02, respectively, and our metallicity measurements are in good
agreement with previous estimates. The mean alpha-element abundances of our
program clusters are in good agreement with other globular clusters, confirming
previous results. However, the individual alpha-elements appear to follow
different trends. The silicon abundances of the inner halo clusters appear to
be enhanced and the titanium abundances appear to be depleted compared to the
intermediate halo clusters. Our results also appear to oppose to those of
metal-rich bulge giants studied by McWilliam and Rich, who found that bulge
giants are titanium enhanced and silicon deficient. In particular, [Si/Ti]
ratios appear to be related to Galactocentric distances,in the sense that
[Si/Ti] ratios decrease with Galactocentric distance. We propose that
contributions from different masses of the SNe II progenitors that enriched
proto-globular cluster clouds' elemental abundances and the different initial
physical environments surrounding the proto-globular clusters clouds are
responsible for this gradient in [Si/Ti] ratios versus Galactocentric distances
of the "old halo" globular clusters. On the other hand, our program clusters'
enhanced s-process elemental abundances suggest that the formation timescale of
our program clusters might be as short as a few times 10^8 yr after the star
formation is initiated in the Galaxy's central regions, if the s-process site
is intermediate mass AGB stars.Comment: Accepted for publication in AJ (Sept. 2002
Stellar abundances and ages for metal-rich Milky Way globular clusters - Stellar parameters and elemental abundances for 9 HB stars in NGC6352
[ABRIDGED] Metal-rich globular clusters provide important tracers of the
formation of our Galaxy. Moreover, and not less important, they are very
important calibrators for the derivation of properties of extra-galactic
metal-rich stellar populations. Nonetheless, only a few of the metal-rich
globular clusters in the Milky Way have been studied using high-resolution
stellar spectra to derive elemental abundances. In this paper we present
elemental abundances for nine HB stars in the metal-rich globular cluster
NGC6352. The elemental abundances are based on high-resolution, high
signal-to-noise spectra obtained with VLT/UVES. The elemental abundances have
been derived using standard LTE calculations. We find that NGC6352 has [Fe/H]=
-0.55, is enhanced in the alpha-elements to about +0.2 dex for Ca, Si, and Ti
relative to Fe. For the iron-peak elements we find solar values. Based on the
spectroscopically derived stellar parameters we find that an E(B-V)=0.24 and
(m-M) roughly equal to 14.05 better fits the data than the nominal values. An
investigation of log(gf)-values for suitable FeI lines lead us to the
conclusion that the commonly used correction to the May et al.(1974) data
should not be employed. Note: only the postscript reproduces the finding chart
correctly.Comment: 24 pages (including on-line only table with all equivalent width
measurements), 12 figures, Accepted for publication in A&A. Note: only the
postscript reproduces the finding chart correctl
New Measurements of Doubly Ionized Iron Group Spectra by High Resolution Fourier Transform and Grating Spectroscopy
We report new measurements of doubly ionized iron group element spectra, important in the analysis of B-type (hot) stars whose spectra they dominate. These measurements include Co III and Cr III taken with the Imperial College VUV Fourier transform (FT) spectrometer and measurements of Co III taken with the normal incidence vacuum spectrograph at NIST, below 135 nm. We report new Fe III grating spectra measurements to complement our FT spectra. Work towards transition wavelengths, energy levels and branching ratios (which, combined with lifetimes, produce oscillator strengths) for these ions is underway
Intra- and interspecific polymorphisms ofLeishmania donovani andL. tropica minicircle DNA
A pair of degenerate polymerase chain reaction (PCR) primers (LEI-1, TCG GAT CC[C,T] [G,C]TG GGT AGG GGC GT; LEI-2, ACG GAT CC[G,C] [G,C][A,C]C TAT [A,T]TT ACA CC) defining a 0.15-kb segment ofLeishmania minicircle DNA was constructed. These primers amplified not only inter- but also intraspecifically polymorphic sequences. Individual sequences revealed a higher intraspecific than interspecific divergence. It is concluded that individual sequences are of limited relevance for species determination. In contrast, when a data base of 19 different sequences was analyzed in a dendrographic plot, an accurate species differentiation was feasible
Abundances in Stars from the Red Giant Branch Tip to Near the Main Sequence Turn Off in M5
We present the iron abundance and abundance ratios for 18 elements with
respect to Fe in a sample of stars with a wide range in luminosity from
luminous giants to stars near the turnoff in the globular cluster M5. The
analyzed spectra, obtained with HIRES at the Keck Observatory, are of high
dispersion (R=35,000). We find that the neutron capture, the iron peak and the
alpha-element abundance ratios show no trend with Teff, and low scatter around
the mean between the top of the RGB and near the main sequence turnoff To
within the precision of the measurements (~0.1 dex), gravitationally induced
heavy element diffusion does not appear to be present among the stars near the
main sequence turnoff studied here. Our work and other recent studies suggest
that heavy element diffusion is inhibited in the surface layers of metal poor
stars. Differences in the Na abundance from star to star which extend to the
main sequence turnoff are detected in our sample in M5. The anti-correlation
between O and Na abundances, observed in other metal poor globular clusters, is
not detected in our sample, but it may be hidden among stars with only upper
limits for their O abundances. Overall the abundance ratios of M5 appear very
similar to those of M71, with the possible exception of the neutron capture
element Ba, where we argue that the apparent difference may be due to
difficulties in the analysis. As in M71, the alpha-elements Mg, Ca, Si and Ti
are overabundant relative to Fe. The results of our abundance analysis of 25
stars in M5 provide further evidence of abundance variations among specific
light elements at unexpectedly low luminosities, which cannot be explained by
our current understanding of stellar evolution.Comment: 56 pages, 14 figures, AJ in press (Jan 2003
New Analyses of Star-to-Star Abundance Variations Among Bright Giants in the Mildly Metal-Poor Globular Cluster M5
We present a chemical composition analysis of 36 giant stars in the mildly
metal-poor globular cluster M5 (NGC 5904). The analysis makes use of high
resolution data acquired at the Keck I telescope as well as a re-analysis of
high resolution spectra acquired for an earlier study at Lick Observatory. We
employed two analysis techniques: one, adopting standard spectroscopic
constraints, and two, adopting an analysis consistent with the non-LTE precepts
as recently described by Thevenin & Idiart. The abundance ratios we derive for
magnesium, silicon, calcium, scandium, titanium, vanadium, nickel, barium and
europium in M5 show no significant abundance variations and the ratios are
comparable to those of halo field stars. However, large variations are seen in
the abundances of oxygen, sodium and aluminum, the elements that are sensitive
to proton-capture nucleosynthesis. In comparing the abundances of M5 and M4
(NGC 6121), another mildly metal-poor globular cluster, we find that silicon,
aluminum, barium and lanthanum are overabundant in M4 with respect to what is
seen in M5, confirming and expanding the results of previous studies. In
comparing the abundances between these two clusters and others having
comparable metallicities, we find that the anti-correlations observed in M5 are
similar to those found in more metal-poor clusters, M3, M10 and M13, whereas
the behavior in M4 is more like that of the more metal-rich globular cluster
M71. We conclude that among stars in Galactic globular clusters, there is no
definitive ``single'' value of [el/Fe] at a given [Fe/H] for at least some
alpha-capture, odd-Z and slow neutron-capture process elements, in this case,
silicon, aluminum, barium and lanthanum.Comment: 31 pages + 16 figures + 11 tables; accepted for publication in
Sept.2001 Astronomical Journa
The Chemical Composition of Carbon-Rich, Very Metal-Poor Stars: A New Class of Mildly Carbon-Rich Objects Without Excess of Neutron-Capture Elements
We report on an analysis of the chemical composition of five carbon-rich,
very metal-poor stars based on high-resolution spectra. One star, CS22948-027,
exhibits very large overabundances of carbon, nitrogen, and the neutron-capture
elements, as found in the previous study of Hill et al.. This result may be
interpreted as a consequence of mass transfer from a binary companion that
previously evolved through the asymptotic giant branch stage. By way of
contrast, the other four stars we investigate exhibit no overabundances of
barium ([Ba/Fe]<0), while three of them have mildly enhanced carbon and/or
nitrogen ([C+N]+1). We have been unable to determine accurate carbon and
nitrogen abundances for the remaining star (CS30312-100). These stars are
rather similar to the carbon-rich, neutron-capture-element-poor star
CS22957-027 discussed previously by Norris et al., though the carbon
overabundance in this object is significantly larger ([C/Fe]=+2.2). Our results
imply that these carbon-rich objects with ``normal'' neutron-capture element
abundances are not rare among very metal-deficient stars. One possible process
to explain this phenomenon is as a result of helium shell flashes near the base
of the AGB in very low-metallicity, low-mass (M~< 1M_sun) stars, as recently
proposed by Fujimoto et al..
The moderate carbon enhancements reported herein ([C/Fe]+1) are similar to
those reported in the famous r-process-enhanced star CS22892-052. We discuss
the possibility that the same process might be responsible for this similarity,
as well as the implication that a completely independent phenomenon was
responsible for the large r-process enhancement in CS22892-052.Comment: 53 pages, 8 figures, to appear in Ap
Evidence of negative affective state in Cavalier King Charles Spaniels with syringomyelia
Syringomyelia is a common and chronic neurological disorder affecting Cavalier King Charles Spaniels. The condition is putatively painful, but evaluating the affective component of chronic pain in non-human animals is challenging. Here we employed two methods designed to assess animal affect – the judgement bias and reward loss sensitivity tests – to investigate whether Cavalier King Charles Spaniels with syringomyelia (exhibiting a fluid filled cavity (syrinx) in the spinal cord of ≥2mm diameter) were in a more negative affective state than those without the condition. Dogs with syringomyelia did not differ in age from those without the condition, but owners reported that they scratched more (P<0.05), in line with previous findings. They also showed a more negative judgement of ambiguous locations in the judgement bias task (P<0.05), indicating a more negative affective state, but did not show a greater sensitivity to loss of food rewards. These measures were unaffected by whether the dog was or was not receiving pain-relieving medication. Across all subjects, dogs whose owners reported high levels of scratching showed a positive judgement bias (P<0.05), indicating that scratching was not directly associated with a negative affective state. Tests of spontaneous behaviour (latency to jump up to or down from a 30cm high platform) and physiology (thermography of the eye) did not detect any differences. These results provide initial evidence from the judgement bias task that syringomyelia may be associated with negative affect in dogs, and open the way for further and larger studies to confirm findings and investigate the effects of medication in more detail
Accurate VUV Laboratory Measurements of Fe III Transitions for Astrophysical Applications
We report preliminary measurements of Fe III spectra in the 1150 to 2500 A wavelength interval. Spectra have been recorded with an iron-neon Penning discharge lamp (PDL) between 1600 and 2500 A at Imperial College (IC) using high resolution Fourier (FT) transform spectroscopy. These FT spectrometer measurements were extended beyond 1600 A to 1150 A using high-resolution grating spectroscopy at the National Institute of Standards and Technology (NIST). These recorded spectra represent the first radiometrically calibrated measurements of a doubly-ionized iron-group element spectrum combining the techniques of vacuum ultraviolet FT and grating spectroscopy. The spectral range of the new laboratory measurements corresponds to recent HST/STIS observations of sharp-lined B stars and of Eta Carinae. The new improved atomic data can be applied to abundance studies and diagnostics of astrophysical plasmas
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