scholarly journals COMMISSION 30: RADIAL VELOCITIES

2008 ◽  
Vol 4 (T27A) ◽  
pp. 316-325
Author(s):  
Stephane Udry ◽  
Guillermo Torres ◽  
Birgitta Nordström ◽  
Francis C. Fekel ◽  
Kenneth C. Freeman ◽  
...  

This three-year period has seen considerable activity in the Commission, with a wide range of applications of radial velocities as well as a significant push toward higher precision. The latter has been driven in large part by the exciting research on extrasolar planets. This field is now on the verge of detecting Earth-mass bodies around nearby stars, as demonstrated by recent work summarized below, and radial velocities continue to play a central role.

1998 ◽  
Vol 11 (1) ◽  
pp. 560-561
Author(s):  
M. Grenon

As a preparation to the HIPPARCOS mission, a large observing programme on NLTT stars (propermotion > 0.18 ″/yr) was started in Genevaphotometry. The original programme consists of 10047 stars brighter than mR = 11.5, or mR = 12.5 if of colour class m. Among them, 7813 targets could be included in the HIPPARCOS programme, selected according to their observability and internal priorities in favour of large parallaxe stars (photometric distances < 100 pc) and high-velocity stars. The bulk of new nearby, halo, mild-metal poor and SMR stars in the HIP Catalogue originates from this proposal (N° 139). No less than 208 new nearby stars with π ≥ 40 mas were discovered south of δ +10°, the closest has π(HIP)= 182 mas. Radial velocities were obtained with CORAVEL at OHP and ESO. Most aspects of the early evolution of the Galaxy may be addressed with this sample. Here we discuss, as examples, the ages of the thick disk and of the galactic bulge.


2018 ◽  
Vol 612 ◽  
pp. A108 ◽  
Author(s):  
A.-M. Lagrange ◽  
M. Keppler ◽  
N. Meunier ◽  
J. Lannier ◽  
H. Beust ◽  
...  

Context. The search for extrasolar planets has been limited so far to close orbit (typ. ≤5 au) planets around mature solar-type stars on the one hand, and to planets on wide orbits (≥10 au) around young stars on the other hand. To get a better view of the full giant planet population, we have started a survey to search for giant planets around a sample of carefully selected young stars. Aims. This paper aims at exploring the giant planet population around one of our targets, β Pictoris, over a wide range of separations. With a disk and a planet already known, the β Pictoris system is indeed a very precious system for studies of planetary formation and evolution, as well as of planet–disk interactions. Methods. We analyse more than 2000 HARPS high-resolution spectra taken over 13 years as well as NaCo images recorded between 2003 and 2016. We combine these data to compute the detection probabilities of planets throughout the disk, from a fraction of au to a few dozen au. Results. We exclude the presence of planets more massive than 3 MJup closer than 1 au and further than 10 au, with a 90% probability. 15+ MJup companions are excluded throughout the disk except between 3 and 5 au with a 90% probability. In this region, we exclude companions with masses larger than 18 (resp. 30) MJup with probabilities of 60 (resp. 90) %.


Author(s):  
Daniel Butt

This chapter examines the limitations of both command-and-control and market-based legal mechanisms in the pursuit of environmental justice. If the environment is to be protected to at least a minimally acceptable degree, approaches that focus on the coercive force of the state must be complemented by the development of an “ecological ethos,” whereby groups and individuals are motivated to act with non-self-interested concern for the environment. The need for this ethos means that the state is dependent on the cooperation of a wide range of non-state actors. Recent work on environmental governance emphasizes the delegation of aspects of governing to such actors and supports efforts to increase popular participation in governmental processes. The chapter therefore advocates a governance approach that seeks to rectify some of the limitations of state-led environmental law, while encouraging popular participation in a way that can encourage the development of an ecological ethos among the citizenry.


1986 ◽  
Vol 118 ◽  
pp. 247-249
Author(s):  
W. Gliese

At the General Assembly of the IAU at New Delhi van Altena reported on the new General Catalogue of Trigonometric Stellar Parallaxes (GCTSP) which was completed recently at the Yale Observatory. Time seems to be ripe now for the compilation of a Third Catalogue of Nearby Stars which will include all objects known to be nearer than 25 parsecs. This catalogue will contain positions, proper motions, radial velocities, spectral types, broad-band photometry, and parallaxes - quantities won by observations.


2019 ◽  
Vol 2 (1) ◽  
pp. 137-146
Author(s):  
Rory Smead ◽  
Patrick Forber

AbstractSpite (in the biological or evolutionary sense) is behavior that harms others at a cost to the actor. The presence of spite in human and animal populations presents an evolutionary puzzle. Recent work has suggested small populations and pre-play signaling can have a significant effect on the evolution of spite. Here, we use computational methods to explore these factors in fluctuating populations that may go extinct. We find that the presence of spite can make a population significantly more likely to go extinct, but that this does not preclude the possibility of spite reliably evolving. Additionally, we find that the stochastic effects of small fluctuating populations allow for the evolution and predominance of signal-mediated conditional spite across a wide range of conditions. These results suggest that directed harm, even if costly, can play a significant early role in the evolution of social behaviors and this provides a possible origin for punishment.


2020 ◽  
Vol 493 (4) ◽  
pp. 5520-5531 ◽  
Author(s):  
Fred C Adams ◽  
Konstantin Batygin ◽  
Anthony M Bloch ◽  
Gregory Laughlin

ABSTRACT Motivated by the trends found in the observed sample of extrasolar planets, this paper determines tidal equilibrium states for forming planetary systems – subject to conservation of angular momentum, constant total mass, and fixed orbital spacing. In the low mass limit, valid for super-Earth-class planets with masses of order mp ∼ 10 M⊕, previous work showed that energy optimization leads to nearly equal mass planets, with circular orbits confined to a plane. The present treatment generalizes previous results by including the self-gravity of the planetary bodies. For systems with a sufficiently large total mass $m_{\scriptstyle \rm T}$ in planets, the optimized energy state switches over from the case of nearly equal mass planets to a configuration where one planet contains most of the material. This transition occurs for a critical mass threshold of approximately $m_{\scriptstyle \rm T}\gtrsim m_{\scriptstyle \rm C}\sim 40\,{\rm M_\oplus}$ (where the value depends on the semimajor axes of the planetary orbits, the stellar mass, and other system properties). These considerations of energy optimization apply over a wide range of mass scales, from binary stars to planetary systems to the collection of moons orbiting the giant planets in our Solar system.


Author(s):  
Keith J. Topping

Both peer tutoring and cooperative learning are types of peer assisted learning; they involve people from similar social groupings who are not professional teachers helping each other to learn and learning themselves by teaching. Peer tutoring usually involves pairs of students, one in the role of tutor and the other as tutee, with the more able or experienced member helping the other to learn material which is new to the tutor but not to the tutee. By contrast, cooperative learning is usually done in small groups of perhaps four students, often of mixed ability. The group works toward a consensus on a problem. Because it is easier to dominate or hide in a group, roles are often assigned to each group member. Earlier perspectives tended to use the theories of Piaget and Vygotsky, perhaps with some consideration of Bandura and Dewey. Chi, King, and Graesser have been prominent in more recent work. However, a theoretical perspective is offered that integrates these elements with more practical issues. In general, both peer tutoring and cooperative learning “work”— in a wide range of curricular subjects and with a wide range of ages. Given the appropriate form of organization, cognitive gains ensue for both helpers and those who are helped. This is not the main research issue, which is exploring how and why these practices work, in order to improve effectiveness. There are several meta-analyses (a statistical procedure for combining data from multiple studies) which are relevant, and beyond this, key individual papers of specific importance are highlighted. Over the years, we have become wiser about some of the key issues. In peer tutoring, same-ability tutoring has appeared in recent years, sometimes reciprocal, and we need to know under what conditions it works. Cooperative learning has issues regarding the most effective roles for group members and how these integrate with student ability and personality. There has also been much recent work in online peer tutoring which raises different issues. The existing literature is well-developed since these are not new methods. Future research should include more tightly defined studies focusing on more minor variables of context and organization. Many teachers will say they use both peer tutoring and cooperative learning, but very often they overestimate how often anything like good practice takes place. Simply putting students together and hoping for the best will not do, although it might have mild effects. Teachers using these methods need to be clear about what organizational parameters are vital in their context with their type of peer assisted learning. These features then need to be maximized in practice and an eye must be kept on implementation fidelity throughout. Education administrators need to organize professional development for teachers which is thorough, including initial instruction and practice followed up by support and monitoring in the classroom.


2019 ◽  
Vol 375 (1792) ◽  
pp. 20190164 ◽  
Author(s):  
Lei Zhao ◽  
Yuqing Hou ◽  
Nathan A. McNeill ◽  
George B. Witman

Nearly all motile cilia and flagella (terms here used interchangeably) have a ‘9+2’ axoneme containing nine outer doublet microtubules and two central microtubules. The central pair of microtubules plus associated projections, termed the central apparatus (CA), is involved in the control of flagellar motility and is essential for the normal movement of ‘9+2’ cilia. Research using the green alga Chlamydomonas reinhardtii , an important model system for studying cilia, has provided most of our knowledge of the protein composition of the CA, and recent work using this organism has expanded the number of known and candidate CA proteins nearly threefold. Here we take advantage of this enhanced proteome to examine the genomes of a wide range of eukaryotic organisms, representing all of the major phylogenetic groups, to identify predicted orthologues of the C. reinhardtii CA proteins and explore how widely the proteins are conserved and whether there are patterns to this conservation. We also discuss in detail two contrasting groups of CA proteins—the ASH-domain proteins, which are broadly conserved, and the PAS proteins, which are restricted primarily to the volvocalean algae. This article is part of the Theo Murphy meeting issue ‘Unity and diversity of cilia in locomotion and transport’.


1984 ◽  
Vol 88 ◽  
pp. 231-239
Author(s):  
Wayne Osborn ◽  
D.J. MacConnell

The possibility of determining stellar radial velocities for large numbers of stars from objective-prism plates was recognized soon after objective-prism spectroscopy became a common observational technique ; (Pickering, 1887). However, the initial investigations quickly revealed a serious practical problem: how does one determine the rest wavelength position in slitless spectra? This difficulty caused the objective-prism method of obtaining radial velocities to be neglected for many years. It was not until the second half of this century that the method saw a large-scale application. This was the work of Fehrenbach who developed a technique based on a specially designed zero-deviation prism, and successfully used it to isolate members of the Large Magellanic Cloud from foreground field stars (Fehrenbach 1947a, 1947b, 1948; Fehrenbach and Duflot 1970). The Fehrenbach technique has since been applied in a number of other studies; one can mention, as examples, recent work on spectroscopie binaries (Gieseking and Karimie 1982), on cluster membership (Gieseking 1980), and on velocity dispersions at intermediate galactic latitudes (Fehrenbach and Burnage 1982).


2008 ◽  
Vol 4 (S253) ◽  
pp. 263-271 ◽  
Author(s):  
Eliza Miller-Ricci ◽  
Sara Seager ◽  
Dimitar Sasselov

AbstractExtrasolar super-Earths (1-10 M⊕) are likely to exist with a wide range of atmospheres. While a number of these planets have already been discovered through radial velocities and microlensing, it will be the discovery of the firsttransitingsuper-Earths that will open the door to a variety of follow-up observations aimed at characterizing their atmospheres. Super-Earths may fill a large range of parameter space in terms of their atmospheric composition and mass. Specifically, some of these planets may have high enough surface gravities to be able to retain large hydrogen-rich atmosphseres, while others will have lost most of their hydrogen to space over the planet's lifetime, leaving behind an atmosphere more closely resembling that of Earth or Venus. The resulting composition of the super-Earth atmosphere will therefore depend strongly on factors such as atmospheric escape history, outgassing history, and the level of stellar irradiation that it receives. Here we present theoretical models of super-Earth emission and transmission spectra for a variety of possible outcomes of super-Earth atmospheric composition ranging from hydrogen-rich to hydrogen-poor. We focus on how observations can be used to differentiate between the various scenarios and constrain atmospheric composition.


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