| 1. |
- Eyer, L., et al.
(författare)
-
Gaia Data Release 2 Variable stars in the colour-absolute magnitude diagram
- 2019
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 623
-
Tidskriftsartikel (refereegranskat)abstract
- Context. The ESA Gaia mission provides a unique time-domain survey for more than 1.6 billion sources with G less than or similar to 21 mag. Aims. We showcase stellar variability in the Galactic colour-absolute magnitude diagram (CaMD). We focus on pulsating, eruptive, and cataclysmic variables, as well as on stars that exhibit variability that is due to rotation and eclipses. Methods. We describe the locations of variable star classes, variable object fractions, and typical variability amplitudes throughout the CaMD and show how variability-related changes in colour and brightness induce "motions". To do this, we use 22 months of calibrated photometric, spectro-photometric, and astrometric Gaia data of stars with a significant parallax. To ensure that a large variety of variable star classes populate the CaMD, we crossmatched Gaia sources with known variable stars. We also used the statistics and variability detection modules of the Gaia variability pipeline. Corrections for interstellar extinction are not implemented in this article. Results. Gaia enables the first investigation of Galactic variable star populations in the CaMD on a similar, if not larger, scale as was previously done in the Magellanic Clouds. Although the observed colours are not corrected for reddening, distinct regions are visible in which variable stars occur. We determine variable star fractions to within the current detection thresholds of Gaia. Finally, we report the most complete description of variability-induced motion within the CaMD to date. Conclusions. Gaia enables novel insights into variability phenomena for an unprecedented number of stars, which will benefit the understanding of stellar astrophysics. The CaMD of Galactic variable stars provides crucial information on physical origins of variability in a way that has previously only been accessible for Galactic star clusters or external galaxies. Future Gaia data releases will enable significant improvements over this preview by providing longer time series, more accurate astrometry, and additional data types (time series BP and RP spectra, RVS spectra, and radial velocities), all for much larger samples of stars.
|
|
| 2. |
- Katz, D., et al.
(författare)
-
Gaia Data Release 2 Mapping the Milky Way disc kinematics
- 2018
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 616
-
Tidskriftsartikel (refereegranskat)abstract
- Context. The second Gaia data release (Gaia DR2) contains high-precision positions, parallaxes, and proper motions for 1.3 billion sources as well as line-of-sight velocities for 7.2 million stars brighter than G(RVS) = 12 mag. Both samples provide a full sky coverage. Aims. To illustrate the potential of Gaia DR2, we provide a first look at the kinematics of the Milky Way disc, within a radius of several kiloparsecs around the Sun. Methods. We benefit for the first time from a sample of 6.4 million F-G-K stars with full 6D phase-space coordinates, precise parallaxes (sigma((omega) over bar)/(omega) over bar <= 20%), and precise Galactic cylindrical velocities (median uncertainties of 0.9-1.4 km s(-1) and 20% of the stars with uncertainties smaller than 1 km s(-1) on all three components). From this sample, we extracted a sub-sample of 3.2 million giant stars to map the velocity field of the Galactic disc from similar to 5 kpc to similar to 13 kpc from the Galactic centre and up to 2 kpc above and below the plane. We also study the distribution of 0.3 million solar neighbourhood stars (r < 200 pc), with median velocity uncertainties of 0.4 km s(-1), in velocity space and use the full sample to examine how the over-densities evolve in more distant regions. Results. Gaia DR2 allows us to draw 3D maps of the Galactocentric median velocities and velocity dispersions with unprecedented accuracy, precision, and spatial resolution. The maps show the complexity and richness of the velocity field of the galactic disc. We observe streaming motions in all the components of the velocities as well as patterns in the velocity dispersions. For example, we confirm the previously reported negative and positive galactocentric radial velocity gradients in the inner and outer disc, respectively. Here, we see them as part of a non-axisymmetric kinematic oscillation, and we map its azimuthal and vertical behaviour. We also witness a new global arrangement of stars in the velocity plane of the solar neighbourhood and in distant regions in which stars are organised in thin substructures with the shape of circular arches that are oriented approximately along the horizontal direction in the U - V plane. Moreover, in distant regions, we see variations in the velocity substructures more clearly than ever before, in particular, variations in the velocity of the Hercules stream. Conclusions. Gaia DR2 provides the largest existing full 6D phase-space coordinates catalogue. It also vastly increases the number of available distances and transverse velocities with respect to Gaia DR1. Gaia DR2 offers a great wealth of information on the Milky Way and reveals clear non-axisymmetric kinematic signatures within the Galactic disc, for instance. It is now up to the astronomical community to explore its full potential.
|
|
| 3. |
- Spoto, F., et al.
(författare)
-
Gaia Data Release 2 : Observations of solar system objects
- 2018
-
Ingår i: Astronomy and Astrophysics. - : EDP SCIENCES S A. - 0004-6361 .- 1432-0746. ; 616
-
Tidskriftsartikel (refereegranskat)abstract
- Context: The Gaia spacecraft of the European Space Agency (ESA) has been securing observations of solar system objects (SSOs) since the beginning of its operations. Data Release 2 (DR2) contains the observations of a selected sample of 14,099 SSOs. These asteroids have been already identified and have been numbered by the Minor Planet Center repository. Positions are provided for each Gaia observation at CCD level. As additional information, complementary to astrometry, the apparent brightness of SSOs in the unfiltered G band is also provided for selected observations.Aims: We explain the processing of SSO data, and describe the criteria we used to select the sample published in Gaia DR2. We then explore the data set to assess its quality.Methods: To exploit the main data product for the solar system in Gaia DR2, which is the epoch astrometry of asteroids, it is necessary to take into account the unusual properties of the uncertainty, as the position information is nearly one-dimensional. When this aspect is handled appropriately, an orbit fit can be obtained with post-fit residuals that are overall consistent with the a-priori error model that was used to define individual values of the astrometric uncertainty. The role of both random and systematic errors is described. The distribution of residuals allowed us to identify possible contaminants in the data set (such as stars). Photometry in the G band was compared to computed values from reference asteroid shapes and to the flux registered at the corresponding epochs by the red and blue photometers (RP and BP).Results: The overall astrometric performance is close to the expectations, with an optimal range of brightness G similar to 12 - 17. In this range, the typical transit-level accuracy is well below 1 mas. For fainter asteroids, the growing photon noise deteriorates the performance. Asteroids brighter than G similar to 12 are affected by a lower performance of the processing of their signals. The dramatic improvement brought by Gaia DR2 astrometry of SSOs is demonstrated by comparisons to the archive data and by preliminary tests on the detection of subtle non-gravitational effects.
|
|
| 4. |
|
|
| 5. |
|
|
| 6. |
|
|
| 7. |
- Dujon, B, et al.
(författare)
-
The nucleotide sequence of Saccharomyces cerevisiae chromosome XV
- 1997
-
Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 387:6632, s. 98-102
-
Tidskriftsartikel (refereegranskat)abstract
- Chromosome XV was one of the last two chromosomes of Saccharomyces cerevisiae to be discovered(1). It is the third-largest yeast chromosome after chromosomes XII and IV, and is very similar in size to chromosome VII. It alone represents 9% of the yeast genome (8% if ribosomal DNA is included). When systematic sequencing of chromosome XV was started, 93 genes or markers were identified, and most of them were mapped(2). However, very little else was known about chromosome XV which, in contrast to shorter chromosomes, had not been the object of comprehensive genetic or molecular analysis. It was therefore decided to start sequencing chromosome XV only in the third phase of the European Yeast Genome Sequencing Programme, after experience was gained on chromosomes III, XI and II (refs 3-5). The sequence of chromosome XV has been determined from a set of partly overlapping cosmid clones derived from a unique yeast strain, and physically mapped at 3.3-kilobase resolution before sequencing. As well as numerous new open reading frames (ORFs) and genes encoding tRNA or small RNA molecules, the sequence of 1,091,283 base pairs confirms the high proportion of orphan genes and reveals a number of ancestral and successive duplications with other yeast chromosomes.
|
|
| 8. |
- Majchrzak, P., et al.
(författare)
-
Switching of the electron-phonon interaction in 1T-VSe2 assisted by hot carriers
- 2021
-
Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 103:24
-
Tidskriftsartikel (refereegranskat)abstract
- We apply an intense infrared laser pulse in order to perturb the electronic and vibrational states in the three-dimensional charge density wave material 1T-VSe2. Ultrafast snapshots of the light-induced hot carrier dynamics and nonequilibrium quasiparticle spectral function are collected using time- and angle-resolved photoemission spectroscopy. The hot carrier temperature and time-dependent electronic self-energy are extracted from the time-dependent spectral function, revealing that incoherent electron-phonon interactions heat the lattice above the charge density wave critical temperature on a timescale of (200±40) fs. Density functional perturbation theory calculations establish that the presence of hot carriers alters the overall phonon dispersion and quenches efficient low-energy acoustic phonon scattering channels, which results in a new quasiequilibrium state that is experimentally observed.
|
|
| 9. |
- Peibst, R., et al.
(författare)
-
PECVD grown Ge nanocrystals embedded in SiO(2) : From disordered to templated self-organization
- 2009
-
Ingår i: MICROELECTRONICS JOURNAL. - : Elsevier BV. - 0026-2692. ; 40:4-5, s. 759-761
-
Tidskriftsartikel (refereegranskat)abstract
- We present a new "templated self-organization" method for the preparation of Ge nanocrystals in SiO(2) that combines a bottom-up with a top-down approach for nanostructuring. Ge nanocrystals are formed by self-organization induced by thermal annealing of thin Ge films embedded ill SiO(2) whose areas are predefined by nanoimprint patterning. Thus Much smaller Structure sizes call be achieved than by pure nanostructuring and touch more regular structures call be prepared than by pure self-organization. in particular, the method enables the generation of Ge nanocrystals of equal size at predefined vertical and lateral positions thus facilitating the fabrication of nanoscaled devices due to the Suppression of Structural fluctuations.
|
|
| 10. |
- Vacassy, R., et al.
(författare)
-
Synthesis of controlled spherical zinc sulfide particles by precipitation from homogeneous solutions
- 1998
-
Ingår i: Journal of The American Ceramic Society. - : American Ceramic Society. - 0002-7820 .- 1551-2916. ; 81:10, s. 2699-2705
-
Tidskriftsartikel (refereegranskat)abstract
- Zinc sulfide (ZnS) powders have been obtained by precipitation from homogeneous solutions of various zinc salt compounds with S 2- as precipitating anion, formed by decomposition of thioacetamide. Spherical particles with a very narrow size distribution can be obtained by controlling; the synthesis parameters. The particle sizes are influenced by the nature of the associated anion. For example nanometer-sized ZnS particles are formed using acetate or acetylacetonate anions under acidic pH conditions, controlled by the addition of acetic acid. Although the nucleation is accelerated by the use of acetic acid, limited particle growth occurs because of the formation of complexes with zinc cations that lowers the concentration of free cations in the solution. Also, the complexing-attachment phenomena of the ZnS particles with acetate and acetylacetonate anions lead to the arrest of particle growth processes. The presence of complexed Zn 2+ species in the acidic solution is demonstrated both theoretically, using a model based on the calculations of the solubility isotherms of the soluble species, and by Fourier-transform infrared techniques. The nanostructured ZnS particles may provide a suable semi-conductor nanocluster material for optoelectronic applications as well as a phosphor suitable for application in flat-panel display technology.
|
|
