12 research outputs found
HST-NICMOS Observations of Terzan 5: Stellar Content and Structure of the Core
We report results from HST-NICMOS imaging of the extremely dense core of the
globular cluster Terzan 5. This highly obscured bulge cluster has been
estimated to have one of the highest collision rates of any galactic globular
cluster, making its core a particularly conducive environment for the
production of interacting binary systems. We have reconstructed high-resolution
images of the central 19"x19" region of Terzan 5 by application of the drizzle
algorithm to dithered NIC2 images in the F110W, F187W, and F187N near-infrared
filters. We have used a DAOPHOT/ALLSTAR analysis of these images to produce the
deepest color-magnitude diagram (CMD) yet obtained for the core of Terzan 5. We
have also analyzed the parallel 11"X11" NIC1 field, centered 30" from the
cluster center and imaged in F110W and F160W, and an additional NIC2 field that
is immediately adjacent to the central field. This imaging results in a clean
detection of the red-giant branch and horizontal branch in the central NIC2
field, and the detection of these plus the main-sequence turnoff and the upper
main sequence in the NIC1 field. We have constructed an H versus J-H CMD for
the NIC1 field. We obtain a new distance estimate of 8.7 kpc, which places
Terzan 5 within less than 1 kpc of the galactic center. We have also determined
a central surface-density profile which results in a maximum likelihood
estimate of 7.9" +/- 0.6" for the cluster core radius. We discuss the
implications of these results for the dynamical state of Terzan 5.Comment: 17 pages, 9 figures, accepted for publication in ApJ, for May 20,
200
VLT-FLAMES Analysis of 8 giants in the Bulge Metal-poor Globular Cluster NGC 6522: Oldest Cluster in the Galaxy?
NGC 6522 has been the first metal-poor globular cluster identified in the
bulge by W. Baade. Despite its importance, very few high resolution abundance
analyses of stars in this cluster are available in the literature. The bulge
metal-poor clusters may be important tracers of the early chemical enrichment
of the Galaxy. The main purpose of this study is the determination of
metallicity and elemental ratios in individual stars of NGC 6522. High
resolution spectra of 8 giants of the bulge globular cluster NGC 6522 were
obtained at the 8m VLT UT2-Kueyen telescope with the FLAMES+GIRAFFE
spectrograph. Multiband V,I,J,Ks} photometry was used to derive effective
temperatures as reference values. Spectroscopic parameters are derived from FeI
and FeII lines, and adopted for the derivation of abundance ratios. The present
analysis provides a metallicity [Fe/H] = -1.0+-0.2. The alpha-elements Oxygen,
Magnesium and Silicon show [O/Fe]=+0.4, [Mg/Fe]=[Si/Fe]= +0.25, whereas Calcium
and Titanium show shallower ratios of [Ca/Fe]=[Ti/Fe]=+0.15. The
neutron-capture r-process element Europium appears to be overabundant by
[Eu/Fe]=+0.4. The neutron-capture s-elements La and Ba are enhanced by
[La/Fe]=+0.35 and [Ba/Fe]=+0.5. The large internal errors, indicating the large
star-to-star variationin the Ba and Eu abundances, are also discussed. The
moderate metallicity combined to a blue Horizontal Branch (BHB), are
characteristics similar to those of HP~1 and NGC 6558, pointing to a population
of very old globular clusters in the Galactic bulge. Also, the abundance ratios
in NGC 6522 resemble those in HP 1 and NGC 6558. The ultimate conclusion is
that the bulge is old, and went through an early prompt chemical enrichment.Comment: 18 pages, 16 figures. Astronomy & Astrophysics, accepte
R Coronae Borealis stars in the Galactic Bulge discovered by EROS-2
Rare types of variable star may give unique insight into short-lived stages
of stellar evolution. The systematic monitoring of millions of stars and
advanced light curve analysis techniques of microlensing surveys make them
ideal for discovering also such rare variable stars. One example is the R
Coronae Borealis (RCB) stars, a rare type of evolved carbon-rich supergiant. We
have conducted a systematic search of the EROS-2 database for the Galactic
catalogue Bulge and spiral arms to find Galactic RCB stars. The light curves of
100 million stars, monitored for 6.7 years (from July 1996 to February
2003), have been analysed to search for the main signature of RCB stars, large
and rapid drops in luminosity. Follow-up spectroscopy has been used to confirm
the photometric candidates. We have discovered 14 new RCB stars, all in the
direction of the Galactic Bulge, bringing the total number of confirmed
Galactic RCB stars to about 51. After reddening correction, the colours and
absolute magnitudes of at least 9 of the stars are similar to those of
Magellanic RCB stars. This suggests that these stars are in fact located in the
Galactic Bulge, making them the first RCB stars discovered in the Bulge. The
localisation of the 5 remaining RCBs is more uncertain: 4 are either located
behind the Bulge at an estimated maximum distance of 14 kpc or have an unusual
thick circumstellar shell; the other is a DY Per RCB which may be located in
the Bulge, even if it is fainter than the known Magellanic DY Per. From the
small scale height found using the 9 new Bulge RCBs,
pc (95% C.L.), we conclude that the RCB stars follow a disk-like distribution
inside the Bulge.Comment: 20 pages, 26 figures, Accepted in A&
Bursts, eclipses, dips and a refined position for the luminous low-mass X-ray binary in the globular cluster Terzan 6
GRS 1747-312 is a bright transient X-ray source in the globular cluster
Terzan 6 with quasi-periodic outbursts approximately every 4.5 months. We
carried out 2-60 keV target-of-opportunity observations during eight outbursts
with the Proportional Counter Array on the RXTE satellite, for a total exposure
time of 301 ks, and detect the first unambiguous thermonuclear X-ray bursts
from this source. This identifies the compact accretor in this binary as a
neutron star. The neutron star identification implies that twelve out of
thirteen luminous (above 10^36 erg/s X-ray sources in Galactic globular
clusters harbor neutron stars, with AC211's nature (in M15) remaining elusive.
We observed 24 transitions of eclipses of the X-ray emitting region by the
companion star and are able to improve the accuracy of the orbital period by a
factor of 10^4. The period is P=0.514980303(7) d. We do not detect a period
derivative with an upper limit of |\dot{P}/P|=3X10^-8 yr^{-1}. Archival Chandra
data were analyzed to further refine the X-ray position, and the cluster's
center of gravity was re-determined from optical data resulting in a correction
amounting to 2 core radii. We find that GRS 1747-312 is 0.2+/-0.2 core radii
from the cluster center.Comment: Accepted by A&
Variable Stars in Galactic Globular Clusters
Based on a search of the literature up to May 2001, the number of known
variable stars in Galactic globular clusters is approximately 3000. Of these,
more than 2200 have known periods and the majority (approximately 1800) are of
the RR Lyrae type. In addition to the RR Lyrae population, there are
approximately 100 eclipsing binaries, 120 SX Phe variables, 60 Cepheids
(including population II Cepheids, anomalous Cepheids and RV Tauri) and 120
SR/red variables. The mean period of the fundamental mode RR Lyrae variables is
0.585, for the overtone variables it is 0.342 (0.349 for the first-overtone
pulsators and 0.296 for the second-overtone pulsators) and approximately 30%
are overtone pulsators. These numbers indicate that about 65% of RR Lyrae
variables in Galactic globular clusters belong to Oosterhoff type I systems.
The mean period of the RR Lyrae variables in the Oosterhoff type I clusters
seems to be correlated with metal abundance in the sense that the periods are
longer in the more metal poor clusters. Such a correlation does not exist for
the Oosterhoff type II clusters. Most of the Cepheids are in clusters with blue
horizontal branches.Comment: 45 pages, 10 figures, to be published in AJ November 200
Depo iz Musje jame pri Skocjanu na Krasu. Depojske najbde bronaste in zelezne dobe na Slovenskem II / Il ripostiglio della Grotta delle Mosche presso San Canziano del Carso. Ripostigli dell'et\ue0 del bronzo e del ferro in Slovenia II
Fatal outbreak of human toxoplasmosis along the Maroni River: epidemiological, clinical, and parasitological aspects.
International audienceBACKGROUND: Well-documented outbreaks of human toxoplasmosis infection are infrequently reported. Here, we describe a community outbreak of multivisceral toxoplasmosis that occurred in Patam, a Surinamese village near the French Guianan border. METHODS: From the end of December 2003 through the middle of January 2004, 5 adult patients in Patam, including 2 pregnant women, were initially hospitalized for multivisceral toxoplasmosis. A French-Surinamese epidemiological investigation was conducted in the village; inquiries and clinical examinations were performed, and blood and environmental samples were obtained. For all serologically confirmed cases of toxoplasmosis, molecular analysis and mouse inoculations were performed for diagnosis and genetic characterization of Toxoplasma gondii. RESULTS: The hospitalized patients, who did not have any immunodeficiencies, presented with an infectious disease with multivisceral involvement. Serological examination confirmed acute toxoplasmosis. One adult died, and a neonate and a fetus with congenital toxoplasmosis also died. During the investigation, 4 additional acute cases of toxoplasmosis were diagnosed among the 33 villagers. Only 3 inhabitants had serological evidence of previous T. gondii infection. In total, we reported 11 cases of toxoplasmosis: 8 multivisceral cases in immunocompetent adults, resulting in 1 death; 2 cases of lethal congenital toxoplasmosis in a neonate and a fetus; and 1 symptomatic case in a child. Molecular analysis demonstrated that identical isolates of only 1 atypical strain were responsible for at least 5 of the 11 cases of toxoplasmosis in the outbreak. No epidemiological sources could be linked to this severe community-wide outbreak of toxoplasmosis. CONCLUSION: This report is in agreement with the particular features of toxoplasmosis involving atypical strains that were recently described in French Guiana