9 research outputs found
Young massive star clusters as probes for stellar evolution, cluster dynamics and long term survival
In dieser Arbeit präsentiere ich eine astrometrische und photometrische Studie von drei jungen und massereichen Sternhaufen in der Milchstrasse um ihre Struktur, Dynamik und Kinematik beschreiben. Ich führe die erste astrometrische Studie eines Galaktischen Starbursthaufens mit Hilfe von HST-WFPC2 durch. Ich leite ein Alter von 1Myr für NGC3603YoungCluster und eine Entfernung von 6.75kpc ab. Die Geschwindigkeitsdispersion liegt bei 4.75±0.8km/s und vergleichbare Geschwindigkeiten bei unterschiedlichen Massen weisen auf einen nicht virialisierten Sternhaufen hin. Der Vergleich von dynamischer und photometrischer Masse deutet auf eine hohe Sternentstehungseffizienz hin und auf dynamische Zeitskalen zeigen, daß sich der Sternhaufen nach wenigen Gyr in das Galaktische Feld auflöst. VLT-MAD Beobachtungen von Trumpler14 zeigen eine homogene AO korrigierte PSF über das 2' Gesichtsfeld. Die photometrische Analyse von Trumpler14 belegt, dass das grösste Sternentstehungereignis des Sternhaufens vor 1Myr stattfand. Die Massenfunktion fällt bei ~0.5Msun ab, konsistent mit der Kroupa-IMF und zeigt einen nicht massensegregierten Sternhaufen bei Sternen von bis zu 3M sun. Nahinfrarotbeobachtungen von RSGC1 zeigen einen elongierten Sternhaufen mit einem Alter von 10±1Myr der an der Spitze des Galaktischen Balken bei einer Distanz von 6kpc liegt. Ich messe einen Kernradius von 1.3±0.4pc und ein Verhältnis von blauen zu roten Überriesen von 2.6±0.4, welches Schlüsselinformationen für die Nach-Hauptreihenentwicklung von massereichen Sternen bietet. In jedem der drei Sternhaufen wurde eine flache Massenfunktion abgeleitet die eine erhöhte Anzahle von massereicheren Sternen in den Kerngebieten der Sternhaufen darstellt
A Giant Planet Around a Metal-poor Star of Extragalactic Origin
Stars in their late stage of evolution, such as Horizontal Branch stars, are
still largely unexplored for planets. We report the detection of a planetary
companion around HIP 13044, a very metal-poor star on the red Horizontal
Branch, based on radial velocity observations with a high-resolution
spectrograph at the 2.2-m MPG/ESO telescope. The star's periodic radial
velocity variation of P=16.2 days caused by the planet can be distinguished
from the periods of the stellar activity indicators. The minimum mass of the
planet is 1.25 Jupiter masses and its orbital semi-major axis 0.116 AU. Because
HIP 13044 belongs to a group of stars that have been accreted from a disrupted
satellite galaxy of the Milky Way, the planet most likely has an extragalactic
origin.Comment: 32 pages, 9 Figure
The visitor from an ancient galaxy: A planetary companion around an old, metal-poor red horizontal branch star
We report the detection of a planetary companion around HIP 13044, a
metal-poor red horizontal branch star belonging to a stellar halo stream that
results from the disruption of an ancient Milky Way satellite galaxy. The
detection is based on radial velocity observations with FEROS at the 2.2-m
MPG/ESO telescope. The periodic radial velocity variation of P=16.2 days can be
distinguished from the periods of the stellar activity indicators. We computed
a minimum planetary mass of 1.25 Jupiter masses and an orbital semimajor axis
of 0.116 AU for the planet. This discovery is unique in three aspects: First,
it is the first planet detection around a star with a metallicity much lower
than few percent of the solar value; second, the planet host star resides in a
stellar evolutionary stage that is still unexplored in the exoplanet surveys;
third, the planetary system HIP 13044 most likely has an extragalactic origin
in a disrupted former satellite of the Milky Way.Comment: 5 pages, 2 figures, 2 tables, submitted to the Proceedings of the
276th IAU Symposium "The Astrophysics of Planetary Systems
Assessment of Stellar Stratification in Three Young Star Clusters in the Large Magellanic Cloud
(abridged) We present a comprehensive study of stellar stratification in
young star clusters in the Large Magellanic Cloud (LMC). We apply our recently
developed effective radius method for the assessment of stellar stratification
on imaging data obtained with the Advanced Camera for Surveys of three young
LMC clusters to characterize the phenomenon and develop a comparative scheme
for its assessment in such clusters. The clusters of our sample, NGC 1983, NGC
2002 and NGC 2010, are selected on the basis of their youthfulness, and their
variety in appearance, structure, stellar content, and surrounding stellar
ambient. Our photometry is complete for magnitudes down to m_814 ~ 23 mag,
allowing the calculation of the structural parameters of the clusters, the
estimation of their ages and the determination of their stellar content. Our
study shows that each cluster in our sample demonstrates stellar stratification
in a quite different manner and at different degree from the others.
Specifically, NGC 1983 shows to be partially segregated only for the faintest
stars of the cluster, NGC 2002 shows evidence of strong stellar stratification
for both bright and faint stars, and NGC 2010 is found not to be segregated.
For the parametrization of the phenomenon of stellar stratification and its
quantitative comparison among these clusters, we propose the slope derived from
the change in the effective radius over the corresponding magnitude range as
indicative parameter of the degree of stratification in the clusters. A
positive value of this slope indicates mass segregation in the cluster, while a
negative or zero value signifies the lack of the phenomenon.Comment: To appear in the Astrophysical Journal Vol. 709 (2010), pp. 263-277
Version with low-Resolution gray-scaled figures. Version with full resolution
color figures available from
http://rapidshare.com/files/328406139/Gouliermis_2010.ApJ.709.pd
Dissecting high-mass star-forming regions; tracing back their complex formation history
We present near-infrared JHKs imaging as well as K-band multi-object
spectroscopy of the massive stellar content of W3 Main using LUCI at the LBT.
We confirm 13 OB stars by their absorption line spectra in W3 Main and spectral
types between O5V and B4V have been found. Three massive Young Stellar Objects
are identified by their emission line spectra and near-infrared excess. From
our spectrophotometric analysis of the massive stars and the nature of their
surrounding HII regions we derive the evolutionary sequence of W3 Main and we
find evidence of an age spread of at least 2-3 Myr. While the most massive star
(IRS2) is already evolved, indications for high-mass pre--main-sequence
evolution is found for another star (IRS N1), deeply embedded in an ultra
compact HII region, in line with the different evolutionary phases observed in
the corresponding HII regions. We have detected the photospheres of OB stars
from the more evolved diffuse HII region to the much younger UCHII regions,
suggesting that the OB stars have finished their formation and cleared away
their possible circumstellar disks very fast. Only in the hyper-compact HII
region (IRS5), the early type stars are still surrounded by circumstellar
material.Comment: 6 pages, 4 figures, proceedings of "Stellar Clusters and Associations
- A RIA workshop on GAIA", 23-27 May 2011, Granada, Spai
The Star-forming Region NGC 346 in the Small Magellanic Cloud with Hubble Space Telescope ACS Observations. II. Photometric Study of the Intermediate-Age Star Cluster BS 90
We present the results of our investigation of the intermediate-age star
cluster BS 90, located in the vicinity of the HII region N 66 in the SMC,
observed with HST/ACS. The high-resolution data provide a unique opportunity
for a very detailed photometric study performed on one of the rare
intermediate-age rich SMC clusters. The complete set of observations is
centered on the association NGC 346 and contains almost 100,000 stars down to V
~28 mag. In this study we focus on the northern part of the region, which
covers almost the whole stellar content of BS 90. We construct its stellar
surface density profile and derive structural parameters. Isochrone fits on the
CMD of the cluster results in an age of about 4.5 Gyr. The luminosity function
is constructed and the present-day mass function of BS 90 has been obtained
using the mass-luminosity relation, derived from the isochrone models. We found
a slope between -1.30 and -0.95, comparable or somewhat shallower than a
typical Salpeter IMF. Examination of the radial dependence of the mass function
shows a steeper slope at larger radial distances, indicating mass segregation
in the cluster. The derived half-mass relaxation time of 0.95 Gyr suggests that
the cluster is mass segregated due to its dynamical evolution. From the
isochrone model fits we derive a metallicity for BS 90 of [Fe/H]=-0.72, which
adds an important point to the age-metallicity relation of the SMC. We discuss
our findings on this relation in comparison to other SMC clusters.Comment: Accepted for Publication in ApJ, 12 pages emulateapj TeX style, 10
figure
A Planetary Companion around a Metal-Poor Star with Extragalactic Origin
We report the detection of a planetary companion around HIP 13044, a
metal-poor star on the red Horizontal Branch. The detection is based on radial
velocity observations with FEROS, a high-resolution spectrograph at the 2.2-m
MPG/ESO telescope, located at ESO La Silla observatory in Chile. The periodic
radial velocity variation of P = 16.2 days can be distinguished from the
periods of the stellar activity indicators. We computed a minimum planetary
mass of 1.25 MJup and an orbital semi-major axis of 0.116 AU for the planet.
This discovery is unique in three aspects: First, it is the first planet
detection around a star with a metallicity much lower than few percent of the
solar value; second, the planet host star resides in a stellar evolutionary
stage that is still unexplored in the exoplanet surveys; third, the star HIP
13044 belongs to one of the most significant stellar halo streams in the solar
neighborhood, implying an extragalactic origin of the planetary system HIP
13044 in a disrupted former satellite of the Milky Way.Comment: Part of PlanetsbeyondMS/2010 proceedings
http://arxiv.org/html/1011.660