15 research outputs found
Molecular outflows in the young open cluster IC348
We present a wide-field survey of the young open cluster IC348 for molecular
H2 outflows. Outflow activity is only found at its south-western limit, where a
new subcluster of embedded sources is in an early phase of its formation. If
the IC348 cluster had been built up by such subclusters forming at different
times, this could explain the large age-spread that Herbig (1998) found for the
IC348 member stars. In addition to several compact groups of H2 knots, our
survey reveals a large north-south oriented outflow, and we identify the newly
discovered far-infrared and mm-object IC348MMS as its source. New deep images
in the 1-0 S(1) line of molecular hydrogen trace the HH211 jet and counterjet
as highly-collimated chains of knots, resembling the interferometric CO and SiO
jets. This jet system appears rotated counter-clockwise by about 3 degrees with
respect to the prominent H2 bow shocks. Furthermore, we resolve HH211-mm as a
double point-like source in the mm-continuum.Comment: 10 pages, 9 figures, accepted for publication in Ap
A survey for variable young stars with small telescopes: III. Warm spots on the active star V1598Cyg
Magnetic spots on low-mass stars can be traced and characterised using multi-band photometric light curves. Here we analyse an extensive data set for one active star, V1598Cyg, a known variable K dwarf which is either pre-main sequence and/or in a close binary system. Our light curve contains 2854 photometric data points, mostly in V, Rc, Ic, but also in U, B and Hα, with a total baseline of about 4yr, obtained with small telescopes as part of the HOYS project. We find that V1598Cyg is a very fast rotator with a period of 0.8246 days and varying amplitudes in all filters, best explained as a signature of strong magnetic activity and spots. We fit the photometric amplitudes in V, Rc, Ic and use them to estimate spot properties, using a grid-based method that is also propagating uncertainties. We verify the method on a partial data set with high cadence and all five broad-band filters. The method yields spot temperatures and fractional spot coverage with typical uncertainties of 100K and 3-4%, respectively. V1598Cyg consistently exhibits spots that are a few hundred degrees warmer than the photosphere, most likely indicating that the light curve is dominated by chromospheric plage. The spot activity varies over our observing baseline, with a typical time scale of 0.5-1yr, which we interpret as the typical spot lifetime. Combining our light curve with archival data, we find a six year cycle in the average brightness, that is probably a sign of a magnetic activity cycle
HST/STIS Spectroscopy of the Optical Outflow from DG Tau: Indications for Rotation in the Initial Jet Channel
We have carried out a kinematical, high angular resolution (~ 0".1) study of
the jet from DG Tau within 0."5 from the source (or 110 AU along this flow). We
analysed line profiles extracted from a set of seven spectra taken with STIS on
board the Hubble Space Telescope, with the slits parallel to the jet axis but
displaced transversely every 0".07. For the flow of moderate velocity (-70
km/s), we have found systematic differences in the radial velocities of lines
emitted on alternate sides of the jet axis. The results are corrected for the
effects due to uneven illumination of the slit. The relative Doppler shifts
range from 5 to 20 km/s. If this is interpreted as rotation, the flow is then
rotating clockwise looking from the jet towards the source and the derived
toroidal velocities are in the range 6 - 15 km/s. Using recent estimates of the
mass loss rate, one obtains for the considered velocity regime, an angular
momentum flux of ~ 3.8x10E-5 M_sun/yr AU km/s. Our findings may constitute the
first detection of rotation in the initial channel of a jet flow. The derived
values appear to be consistent with the predictions of popular
magneto-centrifugal jet-launching models, although we cannot exclude transverse
outflow asymmetries other than rotation.Comment: aastex, 23 pages, 5 b/w figures, 3 color figures, ApJ in pres
Rotation of Jets from Young Stars: New Clues from the Hubble Space Telescope Imaging Spectrograph
We report findings from the first set of data in a current survey to
establish conclusively whether jets from young stars rotate. We observed the
bi-polar jets from the T Tauri stars TH28 and RW Aur, and the blue-shifted jet
from T Tauri star LkH321, using the Hubble Space Telescope Imaging
Spectrograph (HST/STIS). Forbidden emission lines (FELs) show distinct and
systematic velocity asymmetries of 10 -- 25 (+/- 5) km/s at a distance of 0".3
from the source, representing a (projected) distance of ~ 40 AU along the jet
in the case of RW Aur, ~ 50 AU for TH28, and 165 AU in the case of
LkH321. These velocity asymmetries are interpreted as rotation in the
initial portion of the jet where it is accelerated and collimated. For the
bi-polar jets, both lobes appear to rotate in the same direction. Values
obtained were in agreement with the predictions of MHD disk-wind models
(Bacciotti et al 2002, Anderson et al 2003, Dougados et al 2003, Pesenti et al
2003). Finally, we determine, from derived toroidal and poloidal velocities,
values for the distance from the central axis of the footpoint for the jet's
low velocity component of ~ 0.5 - 2 AU, consistent with the models of
magneto-centrifugal launching (Anderson et al 2003).Comment: 17 pages, 10 figures, Accepted by Ap
Multi-wavelength spectroscopy of the bipolar outflow from Cepheus E
Cepheus E is the site of an exceptional example of a protostellar outflow
with a very young dynamical age and extremely high near infrared luminosity. We
combine molecular spectroscopic data from the submillimeter to the near
infrared in order to interpret the rotational excitation of CO and the
ro-vibrational excitation of H2. We conclude that C-type shocks with a
paraboloidal bow shock geometry can simultaneously explain all the molecular
excitations. Extinction accounts for the deviation of the column densities from
local thermodynamic equilibrium. A difference in the extinction between the red
and blue-shifted outflow lobes may account for the measured flux difference.
The outflow is deeply embedded in a clump of density 10^5cm^-3, yet a good
fraction of atomic hydrogen, about 40%, is required to explain the excitation
and statistical equilibrium. We propose that this atomic component arises,
self-consistently, from the dissociated gas at the apex of the leading bow
shocks and the relatively long molecule reformation time. At least 20 bow
shocks are required in each lobe, although these may be sub-divided into
smaller bows and turbulent shocked regions. The total outflow mechanical power
and cooling amounts to over 30L_\odot, almost half the source's bolometric
luminosity. Nevertheless, only about 6% of the clump mass has been set in
outward motion by the outflow, allowing a collapse to continue.Comment: 14 pages, 8 figures, accepted for publication in Ap
Further Indications of Jet Rotation in New Ultraviolet and Optical HST/STIS Spectra
We present survey results which suggest rotation signatures at the base of
T-Tauri jets. Observations were conducted with the Hubble Space Telescope
Imaging Spectrograph at optical and near ultraviolet wavelengths (NUV). Results
are presented for the approaching jet from DG Tau, CW Tau, HH 30 and the
bipolar jet from TH 28. Systematic asymmetries in Doppler shift were detected
across the jet, within 100 AU from the star. At optical wavelengths, radial
velocity differences were typically 10 to 25 (+/-5) km/s, while differences in
the NUV range were consistently lower at typically 10 (+/-5) km/s. Results are
interpreted as possible rotation signatures. Importantly, there is agreement
between the optical and NUV results for DG Tau. Under the assumption of steady
magnetocentrifugal acceleration, the survey results lead to estimates for the
distance of the jet footpoint from the star, and give values consistent with
earlier studies. In the case of DG Tau, for example, we see that the higher
velocity component appears to be launched from a distance of 0.2 to 0.5 AU from
the star along the disk plane, while the lower velocity component appears to
trace a wider part of the jet launched from as far as 1.9 AU. The results for
the other targets are similar. Therefore, if indeed the detected Doppler
gradients trace rotation within the jet then, under the assumption of steady
MHD ejection, the derived footpoint radii support the existence of magnetized
disk winds. However, since we do not resolved the innermost layers of the flow,
we cannot exclude the possibility that there also exists an X-wind or stellar
wind component.Comment: 22 pages, 21 figures, accepted by The Astrophysical Journa
HST/STIS Observations of the Bipolar Jet from RW Aurigae: Tracing Outflow Asymmetries Close to the Source
We have observed the bipolar jet from RW Aur A with STIS on board the HST.
After continuum subtraction, morphological and kinematic properties of this
outflow can be traced to within 0."1 from the source in forbidden emission
lines. The jet appears well collimated, with typical FWHMs of 20 to 30 AU in
the first 2" and surprisingly does not show a separate low-velocity component
in contrast to earlier observations. The systemic radial outflow velocity of
the blueshifted lobe is typically 50% larger than that of the redshifted one
with a velocity difference of about 65 km/s. Although such asymmetries have
been seen before on larger scales, our high spatial resolution observations
suggest that they are intrinsic to the "central engine" rather than effects of
the star's immediate environment. Temporal variations of the bipolar jet's
outflow velocities appear to occur on timescales of a few years. They have
combined to produce a 55% increase in the velocity asymmetry between the two
lobes over the past decade. In the red lobe estimated mass flux and momentum
flux values are around one half and one third of those for the blue lobe,
respectively. The mass outflow to mass accretion rate is 0.05, the former being
measured at a distance of 0."35 from the source.Comment: Accepted by ApJ, 16 pages, 5 figure
Proper Motions and Variability of the H Emission in the HH~46/47system
We report here on the first proper motion measurements of molecular hydrogen
emission features in the Herbig-Haro 46/47 outflow. Assuming a distance of 350
pc to this flow, the inferred tangential velocities range from a few tens to
almost 500 km/s . The highest velocities are observed for H2 knots either in,
or close to, the jet/counterjet axes. Knots constituting the wings of the large
scale H2 bow (see, for example, Eisl\"offel et al. 1994) are found to move much
more slowly. These results appear to be in agreement with recent numerical
simulations of H2 emission from pulsed jets. We also report the first detection
of variability in H2 features for a young stellar object (YSO) outflow. It was
found that several H2 knots significantly changed their luminosity over the 4
year timebase used to conduct our study. This is in line with current estimates
for the cooling time of gas radiating shocked H2 emission in YSO environments.Comment: 2 figure
Probing atmospheric electric fields in thunderstorms through radio emission from cosmic-ray-induced air showers
We present measurements of radio emission from cosmic ray air showers that took place during thunderstorms. The intensity and polarization patterns of these air showers are radically different from those measured during fair-weather conditions. With the use of a simple two-layer model for the atmospheric electric field, these patterns can be well reproduced by state-of-the-art simulation codes. This in turn provides a novel way to study atmospheric electric fields
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Far-infrared photometry of deeply embedded outflow sources
Unique new ISO data (covering the important and so far unobserved FIR part of the SED) of a number of young protostars was analysed in detail to determine their ages and masses. The properties of the inevitably connected molecular outflows were then used to test the consistency of the observational data and current evolutionary models of protostars. (Impact Factor: 5.325