5,620 research outputs found
Periodic variations in the colours of the classical T Tauri star RW Aur A
The classical T Tauri star RW Aur A is an irregular variable with a large
amplitude in all photometric bands. In an extended series of photometric data
we found small-amplitude periodic variations in the blue colours of the star,
with a period of 2.64 days. The period was relatively stable over several
years. The amplitude of the periodic signal is 0.21 mag in U-V, 0.07 mag in
B-V, and about 0.02 mag in V-R and V-I. No periodicity was found in the V
magnitude. The relevance of this photometric period to the recently discovered
periodicity in spectral features of the star is discussed, and the hypothesis
of a hot spot is critically considered.Comment: 5 pages, 8 figures, uses new aa.cls, accepted for publication in
Astronomy and Astrophysic
Canton de Revel
Date de l'opération : 1989 (PR) Inventeur(s) : Calvet J.-P Les prospections entreprises sur quatre communes ont révélé plusieurs sites inédits : Saint-Félix, La Grange et Cadenac (gisements du Ier s. avant J.-C., avec amphores vinaires italiques Dr. 1) ; Revel, Chemin de la Sabière (établissement gallo-romain) ; Saint-Julien, En Coque (souterrain aménagé de type monocellulaire) ; Roumens, le Village (dépotoir constitué de céramiques du XVIe s. et d’ossements humains)
Quantitative features of multifractal subtleties in time series
Based on the Multifractal Detrended Fluctuation Analysis (MFDFA) and on the
Wavelet Transform Modulus Maxima (WTMM) methods we investigate the origin of
multifractality in the time series. Series fluctuating according to a qGaussian
distribution, both uncorrelated and correlated in time, are used. For the
uncorrelated series at the border (q=5/3) between the Gaussian and the Levy
basins of attraction asymptotically we find a phase-like transition between
monofractal and bifractal characteristics. This indicates that these may solely
be the specific nonlinear temporal correlations that organize the series into a
genuine multifractal hierarchy. For analyzing various features of
multifractality due to such correlations, we use the model series generated
from the binomial cascade as well as empirical series. Then, within the
temporal ranges of well developed power-law correlations we find a fast
convergence in all multifractal measures. Besides of its practical significance
this fact may reflect another manifestation of a conjectured q-generalized
Central Limit Theorem
Linking Signatures of Accretion with Magnetic Field Measurements - Line Profiles are not Significantly Different in Magnetic and Non-Magnetic Herbig Ae/Be Stars
Herbig Ae/Be stars are young, pre-main-sequence stars that sample the
transition in structure and evolution between low- and high-mass stars,
providing a key test of accretion processes in higher-mass stars. Few Herbig
Ae/Be stars have detected magnetic fields, calling into question whether the
magnetospheric accretion paradigm developed for low-mass stars can be scaled to
higher masses. We present He I 10830 \AA\ line profiles for 64 Herbig Ae/Be
stars with a magnetic field measurement in order to test magnetospheric
accretion in the physical regime where its efficacy remains uncertain. Of the 5
stars with a magnetic field detection, 1 shows redshifted absorption,
indicative of infall, and 2 show blueshifted absorption, tracing mass outflow.
The fraction of redshifted and blueshifted absorption profiles in the
non-magnetic Herbig Ae/Be stars is remarkably similar, suggesting that the
stellar magnetic field does not affect gas kinematics traced by He I 10830 \AA.
Line profile morphology does not correlate with the luminosity, rotation rate,
mass accretion rate, or disk inclination. Only the detection of a magnetic
field and a nearly face-on disk inclination show a correlation (albeit for few
sources). This provides further evidence for weaker dipoles and more complex
field topologies as stars develop a radiative envelope. The small number of
magnetic Herbig Ae/Be stars has already called into question whether
magnetospheric accretion can be scaled to higher masses; accretion signatures
are not substantially different in magnetic Herbig Ae/Be stars, casting further
doubt that they accrete in the same manner as classical T Tauri stars.Comment: accepted to ApJ; 17 pages, 4 figures, 3 table
- …