337 research outputs found
Towards a new full-sky list of radial velocity standard stars
The calibration of the Radial Velocity Spectrometer (RVS) onboard the ESA
Gaia satellite (to be launched in 2012) requires a list of standard stars with
a radial velocity (RV) known with an accuracy of at least 300 m/s. The IAU
Commission 30 lists of RV standard stars are too bright and not dense enough.
We describe the selection criteria due to the RVS constraints for building an
adequate full-sky list of at least 1000 RV standards from catalogues already
published in the literature. A preliminary list of 1420 candidate standard
stars is built and its properties are shown. An important re-observation
programme has been set up in order to ensure within it the selection of objects
with a good stability until the end of the Gaia mission (around 2018). The
present list of candidate standards is available at CDS and usable for many
other projects.Comment: Astronomy & Astrophysics, in press, 8 pages, 8 figure
A Community of Procedure Scholars: Teaching Procedure and the Legal Academy
This article asks whether the way in which procedure is taught has an impact on the extent and accomplishments of a scholarly community of proceduralists. Not surprisingly, we find a strong correlation between the placement of procedure as a required course in an academic context and the resulting body of scholars and scholarship. Those countries in which more civil procedure is taught as part of a university degree — and in which procedure is recognized as a legitimate academic subject — have larger scholarly communities, a larger and broader corpus of works analyzing procedural issues, and a richer web of institutional support systems that inspire, fund, and shape the study of public justice
The catalog of radial velocity standard stars for the Gaia RVS: status and progress of the observations
A new full-sky catalog of Radial Velocity standard stars is being built for
the determination of the Radial Velocity Zero Point of the RVS on board of
Gaia. After a careful selection of 1420 candidates matching well defined
criteria, we are now observing all of them to verify that they are stable
enough over several years to be qualified as reference stars. We present the
status of this long-term observing programme on three spectrographs : SOPHIE,
NARVAL and CORALIE, complemented by the ELODIE and HARPS archives. Because each
instrument has its own zero-point, we observe intensively IAU RV standards and
asteroids to homogenize the radial velocity measurements. We can already
estimate that ~8% of the candidates have to be rejected because of variations
larger than the requested level of 300 m/s.Comment: Proceedings of SF2A2010, S. Boissier, M. Heydari-Malayeri, R. Samadi
and D. Valls-Gabaud (eds), 3 pages, 2 figure
Discovery of a nearby M9 dwarf
We report the discovery of a new M9.0 dwarf at only 8.2 pc, which we
identified in our search for nearby ultracool dwarf (I-J >= 3.0, later than
M8.0) in the DENIS database. We measure a very high proper motion of 2.5
arc-sec/yr. The PC3 index measured from its low-resolution spectrum gives a
spectrophotometric distance of 8.2 pc. This makes it the third closest M9.0
dwarf.Comment: revised version, accepted by MNRAS Letter
Recommended from our members
Encouraging Investors to Enable Corporate Sustainability Transitions: The Case of Responsible Investment in France
This paper studies the case of the socially responsible investment (SRI) industry in France. This case accounts for how the SRI category and practices have successfully moved from the margins of the industry in the late 1990s to become mainstream over two decades. We bring to the forefront the importance of three complementary factors in the process of causing corporations to transition toward more sustainable businesses: the role of investors and, in particular, institutional investors; the importance of the presence of a clear category definition and of intermediary organizations, providing ratings, scores, and other calculative devices; and the role of governments and regulators. With other studies, this case stresses the fundamental influence of investors in how corporations manage sustainability transitions
How Many CMEs Have Flux Ropes? Deciphering the Signatures of Shocks, Flux Ropes, and Prominences in Coronagraph Observations of CMEs
We intend to provide a comprehensive answer to the question on whether all
Coronal Mass Ejections (CMEs) have flux rope structure. To achieve this, we
present a synthesis of the LASCO CME observations over the last sixteen years,
assisted by 3D MHD simulations of the breakout model, EUV and coronagraphic
observations from STEREO and SDO, and statistics from a revised LASCO CME
database. We argue that the bright loop often seen as the CME leading edge is
the result of pileup at the boundary of the erupting flux rope irrespective of
whether a cavity or, more generally, a 3-part CME can be identified. Based on
our previous work on white light shock detection and supported by the MHD
simulations, we identify a new type of morphology, the `two-front' morphology.
It consists of a faint front followed by diffuse emission and the bright
loop-like CME leading edge. We show that the faint front is caused by density
compression at a wave (or possibly shock) front driven by the CME. We also
present high-detailed multi-wavelength EUV observations that clarify the
relative positioning of the prominence at the bottom of a coronal cavity with
clear flux rope structure. Finally, we visually check the full LASCO CME
database for flux rope structures. In the process, we classify the events into
two clear flux rope classes (`3-part', `Loop'), jets and outflows (no clear
structure). We find that at least 40% of the observed CMEs have clear flux rope
structures. We propose a new definition for flux rope CMEs (FR-CMEs) as a
coherent magnetic, twist-carrying coronal structure with angular width of at
least 40 deg and able to reach beyond 10 Rsun which erupts on a time scale of a
few minutes to several hours. We conclude that flux ropes are a common
occurrence in CMEs and pose a challenge for future studies to identify CMEs
that are clearly not FR-CMEs.Comment: 26 pages, 9 figs, to be published in Solar Physics Topical Issue
"Flux Rope Structure of CMEs
Spectroscopic survey of the Galaxy with Gaia I. Design and performance of the Radial Velocity Spectrometer
The definition and optimisation studies for the Gaia satellite spectrograph,
the Radial Velocity Spectrometer (RVS), converged in late 2002 with the
adoption of the instrument baseline. This paper reviews the characteristics of
the selected configuration and presents its expected performance. The RVS is a
2.0 by 1.6 degree integral field spectrograph, dispersing the light of all
sources entering its field of view with a resolving power R=11 500 over the
wavelength range [848, 874] nm. The RVS will continuously and repeatedly scan
the sky during the 5 years of the Gaia mission. On average, each source will be
observed 102 times over this period. The RVS will collect the spectra of about
100-150 million stars up to magnitude V~17-18. At the end of the mission, the
RVS will provide radial velocities with precisions of ~2 km/s at V=15 and
\~15-20 km/s at V=17, for a solar metallicity G5 dwarf. The RVS will also
provide rotational velocities, with precisions (at the end of the mission) for
late type stars of sigma_vsini ~5 km/s at V~15 as well as atmospheric
parameters up to V~14-15. The individual abundances of elements such as Silicon
and Magnesium, vital for the understanding of Galactic evolution, will be
obtained up to V~12-13. Finally, the presence of the 862.0 nm Diffuse
Interstellar Band (DIB) in the RVS wavelength range will make it possible to
derive the three dimensional structure of the interstellar reddening.Comment: 17 pages, 9 figures, accepted for publication in MNRAS. Fig. 1,2,4,5,
6 in degraded resolution; available in full resolution at
http://blackwell-synergy.com/links/doi/10.1111/j.1365-2966.2004.08282.x/pd
Stellar Encounters with the Beta Pictoris Planetesimal System
We use data from the Hipparcos Catalog and the Barbier-Brossat & Figon (2000)
catalog of stellar radial velocities to test the hypothesis that the Beta Pic
planetesimal disk was disrupted by a close stellar encounter. We trace the
space motions of 21,497 stars and discover 18 that have passed within 5 pc of
Beta Pic in the past 1 Myr. Beta Pic's closest encounter is with the K2III star
HIP 27628 (0.6 pc), but dynamically the most important encounter is with the
F7V star HIP 23693 (0.9 pc). We calculate the velocity and eccentricity changes
induced by the 18 perturbations and conclude that they are dynamically
significant if planetesimals exist in a Beta Pic Oort cloud. We provide a
first-order estimate for the evolutionary state of a Beta Pic Oort cloud and
conclude that the primary role of these stellar perturbations would be to help
build a comet cloud rather than destroy a pre-existing structure. The stellar
sample is 20% complete and motivates future work to identify less common close
interactions that would significantly modify the observed circumstellar disk.
For future radial velocity study we identify six stars in the Hipparcos Catalog
that may have approached Beta Pic to within 0.1 pc and therefore remain as
candidate disk perturbers.Comment: 23 pages, 5 figures, Accepted for publication in Ap
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