158 research outputs found
Results of the ROTOR-program. I. The long-term photometric variability of classical T Tauri stars
We present a unique, homogeneous database of photometric measurements for
Classical T Tauri stars extending up to 20 years. The database contains more
than 21,000 UBVR observations of 72 CTTs. All the data were collected within
the framework of the ROTOR-program at Mount Maidanak Observatory (Uzbekistan)
and together they constitute the longest homogeneous, accurate record of TTS
variability ever assembled. We characterize the long term photometric
variations of 49 CTTs with sufficient data to allow a robust statistical
analysis and propose an empirical classification scheme. Several patterns of
long term photometric variability are identified. The most common pattern,
exhibited by a group of 15 stars which includes T Tau itself, consists of low
level variability (Delta(V)<=0.4mag) with no significant changes occurring from
season to season over many years. A related subgroup of 22 stars exhibits a
similar stable long term variability pattern, though with larger amplitudes (up
to Delta(V)~1.6 mag). Besides these representative groups, we identify three
smaller groups of 3-5 stars each which have distinctive photometric properties.
The long term variability of most CTTs is fairly stable and merely reflects
shorter term variability due to cold and hot surface spots. Only a small
fraction of CTTs undergo significant brightness changes on the long term
(months, years), which probably arise from slowly varying circumstellar
extinction.Comment: 16 pages, 11 figures. Astron. Astrophys., in pres
The Monitor Project: Stellar rotation at 13~Myr: I. A photometric monitoring survey of the young open cluster h~Per
We aim at constraining the angular momentum evolution of low mass stars by
measuring their rotation rates when they begin to evolve freely towards the
ZAMS, i.e. after the disk accretion phase has stopped. We conducted a
multi-site photometric monitoring of the young open cluster h Persei that has
an age of ~13 Myr. The observations were done in the I-band using 4 different
telescopes and the variability study is sensitive to periods from less than 0.2
day to 20 days. Rotation periods are derived for 586 candidate cluster members
over the mass range 0.4<=M/Msun<=1.4. The rotation period distribution
indicates a sligthly higher fraction of fast rotators for the lower mass
objects, although the lower and upper envelopes of the rotation period
distribution, located respectively at ~0.2-0.3d and ~10d, are remarkably flat
over the whole mass range. We combine this period distribution with previous
results obtained in younger and older clusters to model the angular momentum
evolution of low mass stars during the PMS. The h Per cluster provides the
first statistically robust estimate of the rotational period distribution of
solar-type and lower mass stars at the end of the PMS accretion phase (>10
Myr). The results are consistent with models that assume significant
core-envelope decoupling during the angular momentum evolution to the ZAMS.Comment: 39 pages, 19 figures, light curves in appendix, 1 long tabl
Another deep dimming of the classical T Tauri star RW Aur A
Context. RW Aur A is a classical T Tauri star (CTTS) with an unusually rich
emission line spectrum. In 2014 the star faded by ~ 3 magnitudes in the V band
and went into a long-lasting minimum. In 2010 the star suffered from a similar
fading, although less deep. These events in RW Aur A are very unusual among the
CTTS, and have been attributed to occultations by passing dust clouds. Aims. We
want to find out if any spectral changes took place after the last fading of RW
Aur A with the intention to gather more information on the occulting body and
the cause of the phenomenon. Methods. We collected spectra of the two
components of RW Aur. Photometry was made before and during the minimum.
Results. The overall spectral signatures reflecting emission from accretion
flows from disk to star did not change after the fading. However, blue-shifted
absorption components related to the stellar wind had increased in strength in
certain resonance lines, and the profiles and strengths, but not fluxes, of
forbidden lines had become drastically different. Conclusions. The extinction
through the obscuring cloud is grey indicating the presence of large dust
grains. At the same time, there are no traces of related absorbing gas. The
cloud occults the star and the interior part of the stellar wind, but not the
wind/jet further out. The dimming in 2014 was not accompanied by changes in the
accretion flows at the stellar surface. There is evidence that the structure
and velocity pattern of the stellar wind did change significantly. The dimmings
could be related to passing condensations in a tidally disrupted disk, as
proposed earlier, but we also speculate that large dust grains have been
stirred up from the inclined disk into the line-of-sight through the
interaction with an enhanced wind.Comment: 5 pages, 5 figures, Accepted for publication in A&
Effect of the Deposition Parameters on the Phase-Structure State, Hardness, and Tribological Characteristics of Mo2 N/CrN Vacuum - Arc Multilayer Coatings
A complex study has been performed of the effect of the technological parameters, which are responsible for the energy states of deposited particles, on the elemental, phase and structure compositions, hardness, and tribological characteristics of formed vacuum-arc multilayer Mo2N/CrN systems with a nanometric thickness. The formation of two phase and structure types has been defined in combined nitride layers: γ-Mo2N/CrN with the isostructural cubic crystalline lattices and γ-Mo2N/CrN with nonisostructural cubic and hexagonal lattice
Photonic Controlled-Phase Gates Through Rydberg Blockade in Optical Cavities
We propose a novel scheme for high fidelity photonic controlled phase gates
using Rydberg blockade in an ensemble of atoms in an optical cavity. The gate
operation is obtained by first storing a photonic pulse in the ensemble and
then scattering a second pulse from the cavity, resulting in a phase change
depending on whether the first pulse contained a single photon. We show that
the combination of Rydberg blockade and optical cavities effectively enhances
the optical non-linearity created by the strong Rydberg interaction and thereby
reduces the requirements for photonic quantum gates. The resulting gate can be
implemented with cavities of moderate finesse which allows for highly efficient
processing of quantum information encoded in photons. As a particular example
of this, we show how the gate can be employed to increase the communication
rate of quantum repeaters based on atomic ensembles.Comment: main manuscript 5 pages with 11 pages of supplementary informatio
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