48 research outputs found
The star formation history of RCW 36
Recent studies of massive-star forming regions indicate that they can contain
multiple generations of young stars. These observations suggest that star
formation in these regions is sequential and/or triggered by a previous
generation of (massive) stars. Here we present new observations of the star
forming region RCW 36 in the Vela Molecular Ridge, hosting a young cluster of
massive stars embedded in a molecular cloud complex. In the periphery of the
cluster several young stellar objects (YSOs) are detected which produce bipolar
jets (HH 1042 and HH 1043) demonstrating that these objects are still actively
accreting. The VLT/X-shooter spectrum of the jet structure of HH 1042 provides
detailed information on the physical conditions and kinematical properties of
the jet plasma. From this information the YSO's accretion history can be
derived. Combining the photometric and spectroscopic observations of RCW 36
gives insight into the formation process of individual stars and the star
formation history of this young massive-star forming region.Comment: 10 pages, 5 figures, to appear in the proceedings of the ESO workshop
"Circumstellar Dynamics at High Resolution", Foz do Iguacu (Br), Feb 2012,
eds. A. Carciofi and T. Riviniu
The Discovery of a Very Massive Star in W49
Very massive stars (M>100 M) are very rare objects, but have a
strong influence on their environment. The formation of this kind of objects is
of prime importance in star formation, but observationally still poorly
constrained. We report on the identification of a very massive star in the
central cluster of the star-forming region W49. We investigate near-infrared
K-band spectroscopic observations of W49 from VLT/ISAAC together with JHK
images obtained with NTT/SOFI and LBT/LUCI. We derive a spectral type of
W49nr1, the brightest star in the dense core of the central cluster of W49. On
the basis of its K-band spectrum, W49nr1 is classified as an O2-3.5If* star
with a K-band absolute magnitude of -6.270.10 mag. The effective
temperature and bolometric correction are estimated from stars of similar
spectral type. After comparison to the Geneva evolutionary models, we find an
initial mass between 100 M and 180 M. Varying the
extinction law results in a larger initial mass range of 90 - 250 M.Comment: 5 pages, 3 figures, 1 table, accepted for publication in A&A Letter
On the contribution of ULXs to stellar feedback: an intermediate mass black hole candidate and the population of ULXs in the low-metallicity starburst galaxy ESO 338-4
X-ray radiation from accreting compact objects is an important part of
stellar feedback. The metal-poor galaxy ESO 338-4 has experienced vigorous
starburst during the last 40 Myr and contains some of the most massive super
star clusters in the nearby Universe. Given its starburst age and its
star-formation rate, ESO 338-4 is one of the most efficient nearby manufactures
of neutron stars and black holes, hence providing an excellent laboratory for
feedback studies. We compared X-ray images and spectra obtained by XMM-Newton
and Chandra telescopes with integral field spectroscopic VLT MUSE observations
in the optical to constrain the nature of strong X-ray emitters. X-ray
observations uncover three ultraluminous X-ray sources (ULXs) in ESO 338-4. The
brightest among them, ESO 338~X-1, has X-ray luminosity in excess of 10^{40}
erg/s. We speculate that ESO 338-4 is powered by accretion on an
intermediate-mass (~300Msun) black hole. We show that X-ray radiation from ULXs
and hot superbubbles strongly contributes to HeII ionization and general
stellar feedback in this template starburst galaxy.Comment: A&A, in pres
Massive pre-main sequence stars in M17
The formation process of massive stars is still poorly understood. Massive
young stellar objects (mYSOs) are deeply embedded in their parental clouds,
they are rare and thus typically distant, and their reddened spectra usually
preclude the determination of their photospheric parameters. M17 is one of the
best studied HII regions in the sky, is relatively nearby, and hosts a young
stellar population. With X-shooter on the ESO Very Large Telescope we have
obtained optical to near-infrared spectra of candidate mYSOs, identified by
Hanson et al. (1997), and a few OB stars in this region. The large wavelength
coverage enables a detailed spectroscopic analysis of their photospheres and
circumstellar disks. We confirm the pre-main sequence (PMS) nature of six of
the stars and characterise the O stars. The PMS stars have radii consistent
with being contracting towards the main sequence and are surrounded by a
remnant accretion disk. The observed infrared excess and the (double-peaked)
emission lines provide the opportunity to measure structured velocity profiles
in the disks. We compare the observed properties of this unique sample of young
massive stars with evolutionary tracks of massive protostars by Hosokawa &
Omukai (2009), and propose that these mYSOs near the western edge of the HII
region are on their way to become main-sequence stars (
) after having undergone high mass-accretion rates ( ). Their spin
distribution upon arrival at the zero age main sequence (ZAMS) is consistent
with that observed for young B stars, assuming conservation of angular momentum
and homologous contraction.Comment: Accepted for publication in A&A. Appendixes A and B have been
truncated due to size limitations, the full version will be available on A&
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
Different Evolutionary Stages in the Massive Star Forming Region W3 Main Complex
We observed three high-mass star-forming regions in the W3 high-mass star
formation complex with the Submillimeter Array and IRAM 30 m telescope. These
regions, i.e. W3 SMS1 (W3 IRS5), SMS2 (W3 IRS4) and SMS3, are in different
evolutionary stages and are located within the same large-scale environment,
which allows us to study rotation and outflows as well as chemical properties
in an evolutionary sense. While we find multiple mm continuum sources toward
all regions, these three sub-regions exhibit different dynamical and chemical
properties, which indicates that they are in different evolutionary stages.
Even within each subregion, massive cores of different ages are found, e.g. in
SMS2, sub-sources from the most evolved UCHII region to potential starless
cores exist within 30 000 AU of each other. Outflows and rotational structures
are found in SMS1 and SMS2. Evidence for interactions between the molecular
cloud and the HII regions is found in the 13CO channel maps, which may indicate
triggered star formation.Comment: Accepted for publication in ApJ, 22 pages, 23 figure
The Lyman alpha reference sample. VII. Spatially resolved H kinematics
We present integral field spectroscopic observations with the Potsdam Multi
Aperture Spectrophotometer of all 14 galaxies in the Lyman Alpha
Reference Sample (LARS). We produce 2D line of sight velocity maps and velocity
dispersion maps from the Balmer (H) emission in our data
cubes. These maps trace the spectral and spatial properties of the LARS
galaxies' intrinsic Ly radiation field. We show our kinematic maps
spatially registered onto the Hubble Space Telescope H and Lyman
(Ly) images. Only for individual galaxies a causal connection
between spatially resolved H kinematics and Ly photometry can
be conjectured. However, no general trend can be established for the whole
sample. Furthermore, we compute non-parametric global kinematical statistics --
intrinsic velocity dispersion , shearing velocity ,
and the ratio -- from our kinematic maps. In
general LARS galaxies are characterised by high intrinsic velocity dispersions
(54\,km\,s median) and low shearing velocities (65\,km\,s
median). values range from 0.5 to 3.2 with an
average of 1.5. Noteworthy, five galaxies of the sample are dispersion
dominated systems with and are thus
kinematically similar to turbulent star forming galaxies seen at high redshift.
When linking our kinematical statistics to the global LARS Ly
properties, we find that dispersion dominated systems show higher Ly
equivalent widths and higher Ly escape fractions than systems with
. Our result indicates that turbulence in
actively star-forming systems is causally connected to interstellar medium
conditions that favour an escape of Ly radiation.Comment: 26 pages, 15 figures, accepted for publication in A&
CLusters in the Uv as EngineS (CLUES). II. Sub-kpc scale outflows driven by stellar feedback
We analyze the far-ultraviolet spectroscopy of 20 young and massive star
clusters (YSCs) in 11 nearby star-forming galaxies. We probe the interstellar
gas intervening along the line of sight, detecting several metal absorption
lines of a wide range of ionization potentials, from 6.0 eV to 77.5 eV.
Multiple-component Voigt fits to the absorption lines are used to study the
kinematics of the gas. We find that nearly all targets in the sample feature
gas outflowing from 30 up to 190 km per second, often both in the neutral and
ionized phase. The outflow velocities correlate with the underlying stellar
population properties directly linked to the feedback: the mass of the YSCs,
the photon production rate and the instantaneous mechanical luminosity produced
by stellar winds and SNe. We detect a neutral inflow in 4 targets, which we
interpret as likely not associated with the star cluster but tracing larger
scale gas kinematics. A comparison between the outflows energy and that
produced by the associated young stellar populations suggests an average
coupling efficiency of 10 per cent with a broad scatter. Our results extend the
relation found in previous works between galactic outflows and the host galaxy
star-formation rate to smaller scales, pointing towards the key role that
clustered star formation and feedback play in regulating galaxy growth.Comment: Accepted for publication on the Astronomical Journal on 14th February
2024. 32 pages, 13 figure