113 research outputs found
Multiple episodes of star formation in the CN15/16/17 molecular complex
We have started a campaign to identify massive star clusters inside bright
molecular bubbles towards the Galactic Center. The CN15/16/17 molecular complex
is the first example of our study. The region is characterized by the presence
of two young clusters, DB10 and DB11, visible in the NIR, an ultra-compact HII
region identified in the radio, several young stellar objects visible in the
MIR, a bright diffuse nebulosity at 8\mu m coming from PAHs and sub-mm
continuum emission revealing the presence of cold dust. Given its position on
the sky (l=0.58, b=-0.85) and its kinematic distance of ~7.5 kpc, the region
was thought to be a very massive site of star formation in proximity of the
CMZ. The cluster DB11 was estimated to be as massive as 10^4 M_sun. However the
region's properties were known only through photometry and its kinematic
distance was very uncertain given its location at the tangential point. We
aimed at better characterizing the region and assess whether it could be a site
of massive star formation located close to the Galactic Center. We have
obtained NTT/SofI JHKs photometry and long slit K band spectroscopy of the
brightest members. We have additionally collected data in the radio, sub-mm and
mid infrared, resulting in a quite different picture of the region. We have
confirmed the presence of massive early B type stars and have derived a
spectro-photometric distance of ~1.2 kpc, much smaller than the kinematic
distance. Adopting this distance we obtain clusters masses of M(DB10) ~ 170
M_sun and M(DB11) ~ 275 M_sun. This is consistent with the absence of any O
star, confirmed by the excitation/ionization status of the nebula. No HeI
diffuse emission is detected in our spectroscopic observations at 2.113\mu m,
which would be expected if the region was hosting more massive stars. Radio
continuum measurements are also consistent with the region hosting at most
early B stars.Comment: Accepted for publication in Astronomy and Astrophysics. Fig. 1 and 3
presented in reduced resolutio
Deep near-infrared imaging of W3 Main: constraints on stellar cluster formation
Embedded clusters like W3 Main are complex and dynamically evolving systems
that represent an important phase of the star formation process. We aim at the
characterization of the entire stellar content of W3 Main in a statistical
sense to identify possible differences in evolutionary phase of the stellar
populations and find clues about the formation mechanism of this massive
embedded cluster. Methods. Deep JHKs imaging is used to derive the disk
fraction, Ks-band luminosity functions and mass functions for several
subregions in W3 Main. A two dimensional completeness analysis using artificial
star experiments is applied as a crucial ingredient to assess realistic
completeness limits for our photometry. We find an overall disk fraction of 7.7
2.3%, radially varying from 9.4 3.0 % in the central 1 pc to 5.6
2.2 % in the outer parts of W3 Main. The mass functions derived for three
subregions are consistent with a Kroupa and Chabrier mass function. The mass
function of IRSN3 is complete down to 0.14 Msun and shows a break at M
0.5 Msun. We interpret the higher disk fraction in the center as evidence for a
younger age of the cluster center. We find that the evolutionary sequence
observed in the low-mass stellar population is consistent with the observed age
spread among the massive stars. An analysis of the mass function variations
does not show evidence for mass segregation. W3 Main is currently still
actively forming stars, showing that the ionizing feedback of OB stars is
confined to small areas ( 0.5 pc). The FUV feedback might be influencing
large regions of the cluster as suggested by the low overall disk fraction.Comment: 15 pages, 13 figures, accepted by A&
Age spread in Galactic star forming region W3 Main
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 an age spread of 2-3 Myr.Comment: 4 pages, 2 figures, To appear in conference proceedings of "370 years
of Astronomy in Utrecht
Cost effectiveness of personalized treatment in women with early breast cancer: the application of OncotypeDX and Adjuvant! Online to guide adjuvant chemotherapy in Austria
PCN106 Overview on Cost-Effectiveness Results of Decision-Analytic Studies for the Treatment of Multiple Myeloma
PRM109 Visualizing Methods For Discrete-Event-Simulations Using The Example Of A Breast Cancer Decision-Analytic Model
Age spread in W3 Main: LBT/LUCI near-infrared spectroscopy of the massive stellar content
We present near-infrared multi-object spectroscopy and JHKs imaging of the
massive stellar content of the Galactic star-forming region W3 Main, obtained
with LUCI at the Large Binocular Telescope. We confirm 15 OB stars in W3 Main
and derive spectral types between O5V and B4V from their absorption line
spectra. Three massive Young Stellar Objects are identified by their emission
line spectra and near-infrared excess. The color-color diagram of the detected
sources allows a detailed investigation of the slope of the near-infrared
extinction law towards W3 Main. Analysis of the Hertzsprung Russell diagram
suggests that the Nishiyama extinction law fits the stellar population of W3
Main best (E(J-H)/E(H-Ks) = 1.76 and R_(Ks) = 1.44). 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 derive a stellar mass of W3 Main of (4 +- 1)
10^3 Msun, by extrapolating from the number of OB stars using a Kroupa IMF and
correcting for our spectroscopic incompleteness. We have detected the
photospheres of OB stars from the more evolved diffuse HII region to the much
younger UCHII regions, suggesting that these stars have finished their
formation and cleared away their circumstellar disks very fast. Only in the
hyper-compact HII region (IRS5), the early type stars seem to be still
surrounded by circumstellar material.Comment: Accepted by ApJ, 14 pages, 4 figure
The Massive Stellar Population in the Young Association LH 95 in the LMC
We present a spectroscopic study of the most massive stars in the young (4
Myr old) stellar cluster LH 95 in the Large Magellanic Cloud. This analysis
allows us to complete the census of the stellar population of the system,
previously investigated by us down to 0.4 solar masses with deep HST Advanced
Camera for Surveys photometry. We perform spectral classification of the five
stars in our sample, based on high resolution optical spectroscopy obtained
with 2.2m MPG/ESO FEROS. We use complementary ground-based photometry,
previously performed by us, to place these stars in the Hertzsprung-Russel
diagram. We derive their masses and ages by interpolation from evolutionary
models. The average ages and age spread of the most massive stars are found to
be in general comparable with those previously derived for the cluster from its
low mass PMS stars. We use the masses of the 5 sample stars to extend to the
high-mass end the stellar initial mass function of LH 95 previously established
by us. We find that the initial mass function follows a Salpeter relation down
to the intermediate-mass regime at 2 Msun. The second most massive star in LH
95 shows broad Balmer line emission and infrared excess, which are compatible
with a classical Be star. The existence of such a star in the system adds a
constrain to the age of the cluster, which is well covered by our age and age
spread determinations. The most massive star, a 60-70 Msun O2 giant is found to
be younger (<1 Myr) than the rest of the population. Its mass in relation to
the total mass of the system does not follow the empirical relation of the
maximum stellar mass versus the hosting cluster mass, making LH 95 an exception
to the average trend.Comment: 15 pages, 9 figures, MNRAS accepte
A benchmark for multi-conjugated AO: VLT-MAD observations of the young massive cluster Trumpler 14
MAD is the first multi-conjugated adaptive optics system at the VLT. We
present H and Ks observations of the young massive cluster Trumpler 14
revealing the power of MCAO systems by providing a homogeneous Strehl ratio
over a large field of view. Mean Strehl ratios of 6.0 and 5.9 per cent with
maximum Strehl ratios of 9.8 and 12.6 per cent in H and Ks, respectively, show
significant improvement of the spatial PSF stability compared to
single-conjugated adaptive optics systems. Photometry of our observations cover
a dynamic range of ~10 mag including 2-3 times more sources than comparable
seeing-limited observations. The colour-magnitude diagram reveals that the
massive cluster originated in a recent starburst-like event 1+/-0.5 Myr ago. We
tentatively detect hints for an older population of 3 Myr suggesting that low
intensity star formation might have been going on in the HII region for a few
Myr. We derive the luminosity function and mass function between 0.1 M_sun and
3.2 M_sun and identify a change of the power law slope of the mass function at
m_c~0.53(+0.12/-0.10) M_sun. The MF appears shallow with power law slopes of
Gamma1=-0.50+/-0.11 above m_c and Gamma2=0.63+/-0.32 below m_c.Comment: Accepted for publication in MNRAS, 12 pages, 10 figures, 2 table
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