988 research outputs found
Chandra/ACIS-I study of the X-ray properties of the NGC 6611 and M16 stellar population
Mechanisms regulating the origin of X-rays in YSOs and the correlation with
their evolutionary stage are under debate. Studies of the X-ray properties in
young clusters allow to understand these mechanisms. One ideal target for this
analysis is the Eagle Nebula (M16), with its central cluster NGC6611. At 1750
pc from the Sun, it harbors 93 OB stars, together with a population of low-mass
stars from embedded protostars to disk-less Class III objects, with age <=
3Myrs. We study an archival 78 ksec Chandra/ACIS-I observation of NGC6611, and
two new 80ksec observations of the outer region of M16, one centered on the
Column V, and one on a region of the molecular cloud with ongoing
star-formation. We detect 1755 point sources, with 1183 candidate cluster
members (219 disk-bearing and 964 disk-less). We study the global X-ray
properties of M16 and compare them with those of the Orion Nebula Cluster. We
also compare the level of X-ray emission of Class II and Class III stars, and
analyze the X-ray spectral properties of OB stars. Our study supports the lower
level of X-ray activity for the disk-bearing stars with respect to the
disk-less members. The X-ray Luminosity Function (XLF) of M16 is similar to
that of Orion, supporting the universality of the XLF in young clusters. 85% of
the O stars of NGC6611 have been detected in X-rays. With only one possible
exception, they show soft spectra with no hard component, indicating that
mechanisms for the production of hard X-ray emission in O stars are not
operating in NGC 6611.Comment: Accepted in Ap
X-rays from HH210 in the Orion nebula
We report the detection during the Chandra Orion Ultradeep Project (COUP) of
two soft, constant, and faint X-ray sources associated with the Herbig-Haro
object HH210. HH210 is located at the tip of the NNE finger of the emission
line system bursting out of the BN-KL complex, northwest of the Trapezium
cluster in the OMC-1 molecular cloud. Using a recent Halpha image obtained with
the ACS imager on board HST, and taking into account the known proper motions
of HH210 emission knots, we show that the position of the brightest X-ray
source, COUP703, coincides with the emission knot 154-040a of HH210, which is
the emission knot of HH210 having the highest tangential velocity (425 km/s).
The second X-ray source, COUP704, is located on the complicated emission tail
of HH210 close to an emission line filament and has no obvious optical/infrared
counterpart. Spectral fitting indicates for both sources a plasma temperature
of ~0.8 MK and absorption-corrected X-ray luminosities of about 1E30 erg/s
(0.5-2.0 keV). These X-ray sources are well explained by a model invoking a
fast-moving, radiative bow shock in a neutral medium with a density of ~12000
cm^{-3}. The X-ray detection of COUP704 therefore reveals, in the complicated
HH210 region, an energetic shock not yet identified at other wavelengths.Comment: 5 pages, 3 figures; accepted for publication in A&A Letter
A 1.3 cm wavelength radio flare from a deeply embedded source in the Orion BN/KL region
Aims: Our aim was to measure and characterize the short-wavelength radio
emission from young stellar objects (YSOs) in the Orion Nebula Cluster and the
BN/KL star-forming region. Methods: We used the NRAO Very Large Array at a
wavelength of 1.3 cm and we studied archival X-ray, infrared, and radio data.
Results: During our observation, a strong outburst (flux increasing >10 fold)
occurred in one of the 16 sources detected at a wavelength of 1.3cm, while the
others remained (nearly) constant. This source does not have an infrared
counterpart, but has subsequently been observed to flare in X-rays. Curiously,
a very weak variable double radio source was found at other epochs near this
position, one of whose components is coincident with it. A very high extinction
derived from modeling the X-ray emission and the absence of an infrared
counterpart both suggest that this source is very deeply embedded.Comment: 7 pages, 5 figures, accepted for publication in A&
Simultaneous X-ray, radio, near-infrared, and optical monitoring of Young Stellar Objects in the Coronet cluster
Multi-wavelength (X-ray to radio) monitoring of Young Stellar Objects (YSOs)
can provide important information about physical processes at the stellar
surface, in the stellar corona, and/or in the inner circumstellar disk regions.
While coronal processes should mainly cause variations in the X-ray and radio
bands, accretion processes may be traced by time-correlated variability in the
X-ray and optical/infrared bands. Several multi-wavelength studies have been
successfully performed for field stars and approx. 1-10 Myr old T Tauri stars,
but so far no such study succeeded in detecting simultaneous X-ray to radio
variability in extremely young objects like class I and class 0 protostars.
Here we present the first simultaneous X-ray, radio, near-infrared, and optical
monitoring of YSOs, targeting the Coronet cluster in the Corona Australis
star-forming region, which harbors at least one class 0 protostar, several
class I objects, numerous T Tauri stars, and a few Herbig AeBe stars. [...]
Seven objects are detected simultaneously in the X-ray, radio, and
optical/infrared bands; they constitute our core sample. While most of these
sources exhibit clear variability in the X-ray regime and several also display
optical/infrared variability, none of them shows significant radio variability
on the timescales probed. We also do not find any case of clearly
time-correlated optical/infrared and X-ray variability. [...] The absence of
time-correlated multi-wavelength variability suggests that there is no direct
link between the X-ray and optical/infrared emission and supports the notion
that accretion is not an important source for the X-ray emission of these YSOs.
No significant radio variability was found on timescales of days.Comment: 11 pages, 11 figures, accepted for publication in A&A (06 Dec 2006
Multi-wavelength observing of a forming solar-like star
V2129 Oph is a 1.35 solar mass classical T Tauri star, known to possess a
strong and complex magnetic field. By extrapolating from an observationally
derived magnetic surface map, obtained through Zeeman-Doppler imaging, models
of V2129 Oph's corona have been constructed, and used to make predictions
regarding the global X-ray emission measure, the amount of modulation of X-ray
emission, and the density of accretion shocks. In late June 2009 we will under
take an ambitious multi-wavelength, multi-observing site, and near
contemporaneous campaign, combining spectroscopic optical, nIR, UV, X-ray,
spectropolarimetric and photometric monitoring. This will allow the validity of
the 3D field topologies derived via field extrapolation to be determined.Comment: 4 pages, proceedings of the 3rd MSSL workshop on High Resolution
X-ray Spectroscopy: towards IX
Radio and X-ray variability of Young Stellar Objects in the Coronet Cluster
The Coronet Cluster in the nearby R CrA dark cloud offers the rare
opportunity to study at least four "class I" protostellar sources as well as
one candidate "class 0" source, a Herbig Ae star, and a candidate brown dwarf
within a few square arcminutes - most of them detected at radio- and X-ray
wavelengths. These sources were observed with the Very Large Array (VLA) at
3.5cm on nine occasions in 1998, spread over nearly four months. The source IRS
5, earlier shown to emit circularly polarized radio emission, was observed to
undergo a flux increase accompanied by changes in its polarization properties.
Comparison with VLA measurements taken in January 1997 allows for some analysis
of longer-term variability. In addition to this radio monitoring, we analyze
archival Chandra and XMM-Newton X-ray data of these sources. Three class I
protostars are bright enough for X-ray spectroscopy, and we perform a
variability analysis for these sources, covering a total of 154 ksec spread
over more than two and a half years. Also in X-rays, IRS 5 shows the most
pronounced variability, whilst the other two class I protostars IRS 1 and IRS 2
have more stable emission. X-ray data is also analyzed for the recently
identified candidate class 0 source IRS 7E, which shows strong variability as
well as for the Herbig Ae star R CrA for which we find extremely hot
X-ray-emitting plasma. For IRS 1,2 and 5, the hydrogen column densities derived
from the X-ray spectra are at about half the values derived with near-infrared
techniques, a situation similar to what has been observed towards some other
young stellar objects.Comment: 17 pages, 11 figures, accepted for publication in A&
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