4,721 research outputs found
Newer drugs for focal epilepsy in adults
A 28 year old woman sees her general practitioner after experiencing what sounds like a convulsion without any apparent provoking factor. Over the past month she has also had “blank spells” during which her husband noticed her to be unresponsive. Her general practitioner suspects she may have developed focal epilepsy and refers her to an epilepsy specialist. The specialist elicits from the patient and her husband additional features in the history that are highly compatible with seizures arising from the temporal lobe (lip smacking, ipsilateral motor automatism, and contralateral dystonia) and confirms the diagnosis by finding focal epileptiform discharges on electroencephalography and cortical dysplasia in the left temporal lobe on brain imaging. To prevent further seizures the specialist advises treatment with antiepileptic drugs (AEDs). The patient is reluctant to start treatment because she has read that AEDs have many adverse effects, could interact with her oral contraception, and are harmful for babies. She wonders if there are newer AEDs that for her might be better than the traditional ones
Spectroscopy of a Globular Cluster in the Local Group dIrr NGC 6822
We present low-resolution Keck spectroscopy for the globular cluster H VIII
in the Local Group dIrr galaxy NGC 6822. We find the metallicity of the cluster
to be [Fe/H]= -1.58 +/- 0.28 and the age of the cluster to be 3-4 Gyr, slightly
older than but consistent with previous age estimates. H VIII seems to be more
metal-poor than most intermediate-age globular clusters in the Local Group, and
appears most similar to the anomalous Small Magellanic Cloud clusters Lindsay
113 and NGC 339.Comment: 5 pages, including 3 figures. Accepted by MNRAS, uses mn2e.cl
Hubble Space Telescope Imaging of the Globular Cluster System around NGC 5846
Bimodal globular cluster metallicity distributions have now been seen in a
handful of large ellipticals. Here we report the discovery of a bimodal
distribution in the dominant group elliptical NGC 5846, using the Hubble Space
Telescope's Wide Field and Planetary Camera 2 (WFPC2). The two peaks are
located at V-I = 0.96 and 1.17, which roughly correspond to metallicities of
[Fe/H] = -1.2 and -0.2 respectively. The luminosity functions of the blue and
red subpopulations appear to be the same, indicating that luminosity does not
correlate with metallicity within an individual galaxy's globular cluster
system. Our WFPC2 data cover three pointings allowing us to examine the spatial
distribution of globular clusters out to 30 kpc (or 2.5 galaxy effective
radii). We find a power law surface density with a very flat slope, and a
tendency for globular clusters to align close to the galaxy minor axis. An
extrapolation of the surface density profile, out to 50 kpc, gives a specific
frequency S_N = 4.3 +/- 1.1. Thus NGC 5846 has a much lower specific frequency
than other dominant ellipticals in clusters but is similar to those in groups.
The central galaxy regions reveal some filamentary dust features, presumably
from a past merger or accretion of a gas-rich galaxy. This dust reaches to the
very nucleus and so provides an obvious source of fuel for the radio core. We
have searched for proto-globular clusters that may have resulted from the
merger/accretion and find none. Finally, we briefly discuss the implications of
our results for globular cluster formation mechanisms.Comment: 22 pages, Latex. To be published in the Astronomical Journal. Full
paper available at http://www.ucolick.org/~forbes/home.htm
Extragalactic Globular Clusters in the Near Infrared I: A comparison between M87 and NGC 4478
We compare optical and near infrared colours of globular clusters in M87, the
central giant elliptical in Virgo, and NGC 4478, an intermediate luminosity
galaxy in Virgo, close in projection to M87. Combining V and I photometry
obtained with the WFPC2 on HST and Ks photometry obtained with the NIRC on Keck
1, we find the broad range in colour and previously detected bi-modality in
M87. We confirm that NGC 4478 only hosts a blue sub-population of globular
clusters and now show that these clusters' V-I and V-K colours are very similar
to those of the halo globular clusters in Milky Way and M31. Most likely, a
metal-rich sub-population never formed around this galaxy (rather than having
formed and been destroyed later), probably because its metal-rich gas was
stripped during its passage through the centre of the Virgo cluster.
The V-I, V-K colours are close to the predicted colours from SSP models for
old populations. However, M87 hosts a few red clusters that are best explained
by intermediate ages (a few Gyr). Generally, there is evidence that the red,
metal-rich sub-population has a complex colour structure and is itself composed
of clusters spanning a large metallicity and, potentially, age range. This
contrasts with the blue, metal-poor population which appears very homogeneous
in all galaxies observed so far.Comment: accepted in A&A, 13 pages using the A&A macr
Globular Clusters in NGC 4365: New K-band Imaging and a Reassessment of the Case for Intermediate-age Clusters
We study the globular cluster (GC) system of the Virgo giant elliptical
galaxy NGC 4365, using new wide-field VIK imaging. The GC colour distribution
has (at least) two peaks, but the colours of the red GCs appear more strongly
weighted towards intermediate colours compared to most other large ellipticals
and the integrated galaxy light. The intermediate-color/red peak may itself be
composed of two sub-populations, with clusters of intermediate colours more
concentrated towards the centre of the galaxy than both the blue and red GCs.
Nearly all intermediate-colour and red GCs in our sample show an offset towards
red V-K and/or blue V-I colours compared to SSP models for old ages in a
(V-K,V-I) diagram. This has in the past been interpreted as evidence for
intermediate ages. We also combine our VIK data with previously published
spectroscopy. The differences between observed and model colour-metallicity
relations are consistent with the offsets observed in the two-colour diagram,
with the metal-rich GCs being too red (by about 0.2 mag) in V-K and too blue
(by about 0.05 mag) in V-I compared to the models at a given metallicity. These
offsets cannot easily be explained as an effect of younger ages. We conclude
that, while intermediate GC ages cannot be definitively ruled out, an
alternative scenario is more likely whereby all the GCs are old but the
relative number of intermediate-metallicity GCs is greater than typical for
giant ellipticals. The main obstacle to reaching a definitive conclusion is the
lack of robust calibrations of integrated spectral and photometric properties
for stellar populations with near-solar metallicity. In any case, it is
puzzling that the intermediate-colour GCs in NGC 4365 are not accompanied by a
corresponding shift of the integrated galaxy light towards bluer colours.Comment: 23 pages, including 20 figures and 5 tables. Accepted for publication
in A&
Detailed abundances from integrated-light spectroscopy: Milky Way globular clusters
We test the performance of our analysis technique for integrated-light
spectra by applying it to seven well-studied Galactic GCs that span a wide
range of metallicities. Integrated-light spectra were obtained by scanning the
slit of the UVES spectrograph on the ESO Very Large Telescope across the
half-light diameters of the clusters. We modelled the spectra using resolved
HST colour-magnitude diagrams (CMDs), as well as theoretical isochrones, in
combination with standard stellar atmosphere and spectral synthesis codes. The
abundances of Fe, Na, Mg, Ca, Ti, Cr, and Ba were compared with literature data
for individual stars in the clusters. The typical differences between iron
abundances derived from our integrated-light spectra and those compiled from
the literature are less than 0.1 dex. A larger difference is found for one
cluster (NGC 6752), and is most likely caused primarily by stochastic
fluctuations in the numbers of bright red giants within the scanned area. As
expected, the alpha-elements (Ca, Ti) are enhanced by about 0.3 dex compared to
the Solar-scaled composition, while the [Cr/Fe] ratios are close to Solar. When
using up-to-date line lists, our [Mg/Fe] ratios also agree well with literature
data. Our [Na/Fe] ratios are, on average, 0.08-0.14 dex lower than average
values quoted in the literature, and our [Ba/Fe] ratios may be overestimated by
0.20-0.35 dex at the lowest metallicities. We find that analyses based on
theoretical isochrones give very similar results to those based on resolved
CMDs. Overall, the agreement between our integrated-light abundance
measurements and the literature data is satisfactory. Refinements of the
modelling procedure, such as corrections for stellar evolutionary and non-LTE
effects, might further reduce some of the remaining offsets.Comment: 35 pages, 16 figures, accepted for A&
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