77 research outputs found
Rotation in NGC 2264: a study based on CoRoT photometric observations
Rotation is one of the key stellar parameters which undergo substantial
evolution during the stellar lifetime, in particular during the early stages.
Stellar rotational periods can be determined on the basis of the periodic
modulation of starlight produced by non-uniformities on the surface of the
stars, due to manifestation of stellar activity. We present the results of an
extensive search for rotational periods among NGC 2264 cluster members, based
on photometric monitoring using the CoRoT satellite, with a particular
attention to the distribution of classical and weak-line T-Tauri stars. NGC
2264 is one of the nearest and best studied star forming region in the solar
neighbourhood, with an estimated age of 3 Myr, and is the object of a recent
simultaneous multiband campaign including a new CoRoT observation with the aim
to assess the physical origin of the observed variability. We find that the
rotational distributions of classical and weak-line T-Tauri star are different,
suggesting a difference in the rotational properties of accreting and
non-accreting stars.Comment: 15 pages, 10 figure
Recent X-ray studies of stellar cycles and long-term variability
AbstractWe discuss recent X-ray studies of stellar cycles and long-term variability
Discovery of X-ray emission from the proto-stellar jet L1551 IRS5 (HH 154)
We have for the first time detected X-ray emission associated with a
proto-stellar jet, on the jet emanating from L1551 IRS5. The IRS5 proto-star is
hidden beyond a very large absorbing column density, making the direct
observation of the jet's emission possible. The observed X-ray emission is
likely associated with the shock ``working surface'', i.e. the interface
between the jet and the circumstellar medium. The X-ray luminosity emanating
from the jet is moderate, at LX ~ 3 times 10^29 erg/s, a significant fraction
of the luminosity normally associated with the coronal emission from young
stars. The spectrum of the X-ray emission is compatible with thermal emission
from a hot plasma, with T ~ 0.5 MK, fully compatible with the temperature
expected (on the basis of the jet's velocity) for the shock front produced by
the jet hitting the circumstellar medium.Comment: To appear in "Stellar Coronae in the Chandra and XMM Era", ASP
Conference Series in press, F. Favata & J. Drake ed
X-ray Flares of EV Lac: Statistics, Spectra, Diagnostics
We study the spectral and temporal behavior of X-ray flares from the active
M-dwarf EV Lac in 200 ks of exposure with the Chandra/HETGS. We derive flare
parameters by fitting an empirical function which characterizes the amplitude,
shape, and scale. The flares range from very short (<1 ks) to long (10 ks)
duration events with a range of shapes and amplitudes for all durations. We
extract spectra for composite flares to study their mean evolution and to
compare flares of different lengths. Evolution of spectral features in the
density-temperature plane shows probable sustained heating. The short flares
are significantly hotter than the longer flares. We determined an upper limit
to the Fe K fluorescent flux, the best fit value being close to what is
expected for compact loops.Comment: 9 pages; 9 figures; latex/emulateapj style; Submitted to The
Astrophysical Journa
Detailed diagnostics of an X-ray flare in the single giant HR 9024
We analyze a 96 ks Chandra/HETGS observation of the single G-type giant HR
9024. The high flux allows us to examine spectral line and continuum
diagnostics at high temporal resolution, to derive plasma parameters. A
time-dependent 1D hydrodynamic model of a loop with half-length cm (), cross-section radius
cm, with a heat pulse of 15 ks and ~erg cm s
deposited at the loop footpoints, satisfactorily reproduces the observed
evolution of temperature and emission measure, derived from the analysis of the
strong continuum emission. For the first time we can compare predictions from
the hydrodynamic model with single spectral features, other than with global
spectral properties. We find that the model closely matches the observed line
emission, especially for the hot ( K) plasma emission of the FeXXV
complex at \AA. The model loop has and aspect
ratio as typically derived for flares observed in active stellar
coronae, suggesting that the underlying physics is the same for these very
dynamic and extreme phenomena in stellar coronae independently on stellar
parameters and evolutionary stage.Comment: 26 pages. Accepted for publication on the Astrophysical Journa
TTauri Stars in the Large Magellanic Cloud: a combined HST and VLT effort
The combination of the unprecedented spatial resolution attainable with WFPC2
on board HST and of the large collecting area of the VLT makes it possible to
study in detail the low mass pre-Main Sequence stars in galaxies other than our
own.
Here we present the results of our studies of two star forming environments
in our closest galactic neighbor, the Large Magellanic Cloud: the region around
Supernova 1987A and the double cluster NGC 1850.Comment: To appear in "The Origins of Stars and Planets: the VLT View", eds.
Joao Alves and Mark McCaughrean. Nomenclature confusion between alpha and
Gamma as IMF exponent fixe
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