Membership Criterion Research Articles

High-Resolution Spectroscopy in Tr 37: Gas Accretion Evolution in Evolved Dusty Disks

Using the Hectochelle multifiber spectrograph, we have obtained high-resolution (R ~ 34,000) spectra in the Hα region for a large number of stars in the 4 Myr old cluster Tr 37, containing 146 previously known members and 26 newly identified ones. We present the Hα line profiles of all members, compare them to our IR observations of dusty disks (Two Micron All Sky Survey JHK + IRAC + MIPS 24 μm), use the radial velocities as a membership criterion, and calculate the rotational velocities. We find a good correlation between the accretion-broadened profiles and the presence of protoplanetary disks, noting that a small fraction of the accreting stars presents broad profiles with Hα equivalent widths smaller than the canonical limit separating classical T Tauri stars (CTTSs) and weak-lined T Tauri stars (WTTSs). The number of strong accretors appears to be lower than in younger regions, and a large number of CTTSs have very small accretion rates ( ≤ 10-9 M⊙ yr-1). Taking into account that the spectral energy distributions are consistent with dust evolution (grain growth/settling) in the innermost disk, this suggests a parallel evolution of the dusty and gaseous components. We also observe that about half of the transition objects (stars with no IR excesses at λ ≤ 6 μm) do not show any signs of active accretion, whereas the other half is accreting with accretion rates ≤10-9 M⊙ yr-1. These zero or very low accretion rates reveal important gas evolution and/or gas depletion in the innermost disk, which could be related to grain growth up to planetesimal or even planet sizes. Finally, we examine the rotational velocities of accreting and nonaccreting stars, finding no significant differences that could indicate disk locking at these ages.

Resisting a genetic identity: the black Seminoles and genetic tests of ancestry.

In July 2000, the Seminole Nation of Oklahoma passed a resolution that would effectively expel a significant portion of its tribal members. The resolution amended the Nation's constitution by changing its membership criteria. Previously, potential members needed to show descent from an enrollee of the 1906 Dawes Rolls, the official American Indian tribal rolls established by the Dawes Commission to facilitate the allotment of reservation land. The amended constitution requires possession of one-eighth Seminole Indian blood, a requirement that a significant portion of the tribe's membership cannot fulfill. The members of the Nation who fail to meet this new membership criterion all have one thing in common: they are black.Descendents of former slaves who came to live among the Seminole Indians of Florida in the seventeenth and eighteenth centuries, the black Seminoles have been officially recognized by the U.S. government as members of the Seminole Nation of Oklahoma since 1866.

The Open Cluster NGC 2516. I. Optical Photometry

We present UBVI CCD photometry of the intermediate-age open cluster NGC 2516. From this new photometry we derive the cluster parameters [V0 - MV = 7.77 ± 0.11 mag, E(B-V) = 0.112 ± 0.024 mag], age [log (age) = 8.2 ± 0.1], and a photometric abundance ([Fe/H] = -0.10 ± 0.04) from a comparison with theoretical isochrones of the Padua group. We find that the X-ray bright stars [log LX(ergs s-1)29.0] are systematically bluer in B-V and U-B. It was necessary to modify the photometric membership criterion used by Sung & Bessell due to the UV excess of X-ray bright stars and due to the abrupt increase in the slope of the (MV, B-V) ZAMS relation at B-V1.4. A minimum binary frequency 40% (±5%) was estimated from the distribution of distance moduli of unevolved photometric members. The photometric abundance obtained in this study is similar to that of the Pleiades and therefore the lower metallicity is not the cause of strong X-ray emission of F-type stars in NGC 2516. We believe that this results from them being close binaries, as suggested by their different distribution of distance moduli compared to other cluster members and surmise that the tidal forces between the two stars must increase their X-ray activity.

Chiral Replacement Criterion for Characterizing Holotopic and Hemitopic Relationships

Abstract A chiral replacement criterion has been proposed to characterize stereochemical equivalence. This criterion is effective to determine holotopic and hemitopic relationships, which are sub-relationships of a homotopic relationship. The criterion has been shown to be complementary to the membership criterion based on the sphericity concept.

Mitochondrial DNA marker EST00083 is not associated with high vs. average IQ in a German sample

In a recent report in this journal (Plomin & Petrill, 1997), a mitochondrial DNA marker (EST00083) yielded significant associations with high vs. low IQ in two population-based samples of children in the U.S. The present study tested this allelic association for German adults with high vs. average IQ scores. The high IQ adults ( N=47) were members of Mensa, an organization whose membership criterion is an IQ score above 130. Their EST00083 allelic frequencies were compared to the allelic frequencies for a control group of adults ( N=77) whose IQ scores were less than 110 as estimated from short-term memory and speed-of information-processing tests. Although the differences between the two studies are considerable, the present results do not provide support for the hypothesis that EST00083 is associated with high IQ.

A proper-motion study of the open cluster NGC 3680

view Abstract Citations (56) References (25) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Proper-Motion Study of the Open Cluster NGC 3680 Kozhurina-Platais, Vera ; Girard, Terrence M. ; Platais, Imants ; van Altena, William F. ; Ianna, Phillip A. ; Cannon, Russell D. Abstract Relative proper motions and cluster membership probabilities have been determined for 2711 stars in a region containing the old open cluster NGC 3680. The Yale-Columbia 26 in. refractor plates used in this study contain significant magnitude equation as well as color equation. A procedure is developed for transforming the measures from each of the plates into a common magnitude/color equation system, thus yielding differential positions from plate to plate, (i.e., proper motions) which are free of these systematic errors. For well measured stars the mean standard error of the proper motions is +/- 0.35 mas/yr. Three different membership calculation techniques are described in detail. The best fit to the proper-motion distributions yields 74 cluster members. Almost all known red giants are cluster member according to the proper motion membership criterion. The luminosity function of NGC 3680 shows a characteristic turnover at Mupsilon approximately equals +3 mag and an essentially flat faint end. Monte-Carlo simulations are used in order to explore the mutual dependence of the luminosity function and membership probabilities. The bimodality of the upper main sequence found in earlier photometric studies probably still exists even after eliminating proper-motion nonmembers. Publication: The Astronomical Journal Pub Date: February 1995 DOI: 10.1086/117310 Bibcode: 1995AJ....109..672K Keywords: Color-Magnitude Diagram; Image Processing; Open Clusters; Radial Velocity; Stellar Motions; Astronomical Photometry; Monte Carlo Method; Red Giant Stars; Statistical Analysis; Stellar Color; Stellar Luminosity; Stellar Magnitude; Astronomy; OPEN CLUSTERS AND ASSOCIATIONS: INDIVIDUAL: NGC 3680 full text sources ADS | data products SIMBAD (2711) CDS (1) Related Materials (1) Catalog: 1995yCat.1212....0K

Flare Activity and Cluster Membership Probability of Flare Stars

Mirzoyan (1976) showed that the concentration of flare stars around the center of the Pleiades cluster (Alcyone) was the same, irrespective of their proper motions. At that time, however, proper motions of only a few flare stars were known. The result was confirmed on the basis of more extensive observational material (Chavushian 1979, Mirzoyan 1983). Photographic observations of stellar flares in the general galactic field during 181 hours yielded the detection of only a single flare, i.e. the percentage of flare stars in the general galactic field is about 10% of the total number of flare stars detected in the regions of stellar clusters and associations (Chavushian 1979, Mirzoyan et al. 1988).This result shows that flare activity can be considered as a definitive cluster membership criterion, which appears to be a better one than the cluster membership probability, which is based on proper motions. To prove this, cluster membership probabilities (Stauffer et al. 1991) for 408 Pleiades cluster flare stars from the catalogue by Haro et al. (1982), are used (Table 1).

Studies of Coma cluster of galaxies 5. Dynamical problems

We use the radial velocity data for 414 galaxies in the Coma cluster region provided by Kent and Gunn and the results of applying a membership criterion to carry out a discussion on the dynamical aspects of the Coma cluster. Our analysis shows that the Coma cluster has no bulk rotation that is clearly a dynamical effect. Fitting with the King-Mitchie model we find a core radius of 5.2′ or 210 kpc at H 0 = 50(km/s)/Mpc and a characteristic velocity dispersion of 935 km/s. Viewed dynamically, there is clear morphological segregation, and there is evidence that substructure exists in the central region.

Flare activity of stars as a cluster membership criterion

Flare activity of stars as a cluster membership criterion

Equivalence of K-functional and modulus of smoothness of functions on the sphere

In the present note certain fundamental estimates of the constructive theory of functions on the sphere Sn ⊂ Rn+1, n ≥ 1, are sharpened on the basis of the equivalence of the K-functional and the modulus of smoothness of functions. In particular a Bernshtein-type inequality for spherical polynomials is made more precise. The estimates obtained are applied to deduce a membership criterion for the function f e Lp(Sn), 1 ≤ p ≤ ∞, to the space Hr HrωLp(Sn) depending on the growth of the norm of derivatives of best approximation polynomials of the function f, which is an analog of a result found by S. B. Stechkin related to continuous periodic functions.

Integral means of ?-subharmonic functions and classes of entirely regular growth

Classes Λδ of functions of finite λ-type δ-subharmonic in ℝm are investigated. A membership criterion that defines when a function belongs to the class Γδ expressed in terms of its integral q-means is established. Classes of entirely regular growth of functions that are δ-subharmonic in ℝm are introduced and the behavior of these functions at infinity and the distribution of Riesz-associated measures are studied.

Overextension of conjunctive concepts: Evidence for a unitary model of concept typicality and class inclusion.

Four experiments investigated how people judge both the typicality and membership of items in conjunctive concepts such as school furniture or sports which are games. Judgments of membership in conjunctions were overextended, and there was asymmetry between the constituent concepts in their influence on relative conjunctive concept membership. The results are discussed in the light of recent theoretical disputes about the modeling of concept representations and the process of forming conjunctions (Cohen & Murphy, 1984; Osherson & Smith, 1981, 1982; Smith & Osherson, 1984). A theory is proposed in which constituent intensions are combined to form a composite prototype for the conjunction. Membership in both single and conjunctive concepts is then determined in the same unitary fashion, by placing a membership criterion on the perceived similarity of possible exemplars to the prototype. An important issue in the study of natural language concepts is the way in which common semantic concepts combine to form conjunctions. For a wide range of concepts, two very reliable phenomena have been established: One, members of concept categories vary in their representativeness, and two, for many concepts the boundary around the class of concept members is unclear or fuzzy. However, to date few empirical studies have considered what happens when two of these fuzzy concepts are placed in conjunction. Do conjunctions show similar typicality and fuzziness phenomena? If so, how can they be related to typicality in the constituent concepts? Do fuzzy concepts follow the same logical rules for conjunction as well-defined concepts? The first aim of this article is to provide empirical evidence that may begin to answer these questions. The current interest in concept conjunctions comes largely from their relevance to the basic question of concept definitions: that is, how a concept picks out an extensional set of concept members. A second aim of this research is therefore to use the study of conceptual combination to provide important constraints on models of conceptualization. In particular, it will be argued that evidence on conjunctions can have theoretical implications for distinguishing the following two opposing accounts of concept definitions.

LUMINOSITY CLASSIFICATION WITH THE WASHINGTON SYSTEM.

ABSTRACT The DDO 51 filter has been added to the Washington photometric system. The strong surface gravity sensitivity of the Mg I "b" triplet and MgH bands which it monitors allows the system to easily discriminate between dwarfs and giants of late G and K spectral type. The system is especially suited as a membership criterion for abundance studies of distant cluster giants. The Mg index is insensitive to surface gravity variations among G giants. The metallicity sensitivity among giants is also relatively weak. Population I and II giants can be distinguished but no further differentiation is evident.

Les affinités électives

Le Nouvel Observateur. This article seeks to establish the characteristics of the functionning of a social group, the group of «friends» of the weekly magazine Le Nouvel Observateur, which is not defined by any formal membership criterion. By means of counting procedures, the author has endeavoured to construct the system of relations to the group (which can also be treated as a system of relations to the publishing firm). Adjustment to the specific constraints of journalistic practice is only of the principles accounting for the constitution of the group. Collective integration takes place, and a native («NouvelObs») ranking principle is generated, through the phenomenal (and loudly proclaimed) diversity of the classificatory principles.

Spectral and UBV Data for 583 Stars (Supergiants and Foreground Stars) in the Direction of the Large Magellanic Cloud

The stars observed are mainly from the Catalogue by Fehrenbach and Duflot. Some other stars – overexposed on the objective-prism plates, faint blue stars in H ii regions, stars with overlapping objective-prism spectra – have been added.The photoelectric UBV photometry was done with the 1-m telescope at La Silla. The UBV filters have always been those recommended by Johnson. Normally 3 measurements or more on different nights have been made for each star. For a single observation of a program star the internal standard deviations are The spectra have been taken with a Cassegrain spectrograph mounted on the 1.52-m telescope at La Silla. The dispersion is 73 Å mm−1, the spectral range 3250-5000 Å, and the limiting resolution 1.3 Å.As a result of our observations, we present 409 stars as members of the LMC, 42 as possible members and 132 as galactic foreground stars (19 of these having high radial velocity). Remarkable features regarding velocities, spectra, magnitudes and colors are noted and commented.All stars down to B = 11.5 have been observed spectrographically as well as photometrically. This is also the case for the majority of the high-velocity stars down to B = 12.0. For fainter objects the photometry is quite representative, whereas the spectroscopy is more scarce. The limiting magnitude is B = 14.0.As radial velocities were used as membership criterion, our data do not suffer from any spectral type selection effects.It was easy to apply the MK criteria to our dispersion using the Yerkes atlas and the Bidelman list of supergiants. A continuous series of supergiant standards in the LMC has been established from 06 to G2. Comparison with Radcliffe data and with recent results of Divan gives a dispersion in spectral type of less than one tenth of a spectral class. Also the luminosity classification shows good agreement.In the classification several difficulties were met:(1) The LMC stars are very luminous objects. In the Galaxy we do not have many corresponding stars. This is especially so for later spectral types.(2) With the dispersion used, the differences between IaO and la are not very pronounced, especially not for F-G type stars.(3) Many of the LMC supergiants are P Cygni stars. They show very sharp, often asymmetric line profiles with a sharp rise to the long wavelength side. This might cause erroneous classification, and also affect radial velocities.(4) The presence of an extended atmosphere, causing dilution effects, can give spurious spectral classification.We have found 8 A type high-velocity stars. The UBV results confirm their classification. 11 G-K type stars have been found to be high-velocity stars, among which are two subdwarfs earlier discussed by Fehrenbach and Thackeray. The number of late type high-velocity stars is quite high.Full accounts have been given in Astron. Astrophys. Suppl.6 (1972), 249.

Logical structure of adaptive systems: I. Microevolution, conditioning and their decision problems

First, the scope of the project and its motivation are presented. Arguments are offered in support of the contention that the theoretical description presented in the body of the paper is a non-trivial one which possibly characterizes the phenomena described. Second, microevolution and conditioning are described as analogous adaptive processes that construct symbolic models of the environment by assembling classes of messages. Potential class members originating as statistically determinate memory unit variability, are tested by a two-part membership criterion. Those potential class members which satisfy formal (i.e. syntactic) criteria specified by a machine-like part of the adaptive system are messages. Messages which survive an environmentally-specified test of function are efficacious messages. Genes-in-a-population and the engrams of conditional stimuli, discriminative stimuli, and operant responses are classes of efficacious messages. Each of these classes has a size parameter (a gene's frequency; an engram's strength) whose material basis is the number of message-instances comprising the class. As a result of natural selection and reinforcement, the amount of this “message redundancy” reflects the efficacy of the messages constituting the class. Third, by reference to experimental results, it is demonstrated that decisions within adaptive systems which appear to be based upon an evaluation of the efficacy of individual message-instances are in actuality based upon message redundancy in one way or another. A scheme for a learning machine is presented which illustrates how secondary reinforcement and chaining may be simulated by measuring message redundancy. Fourth, having established as an empirical generalization that efficacy is evaluated within an adaptive system in terms of message redundancy, the logic underlying microevolution and conditioning is examined. It is demonstrated that, because of the two-part membership criterion, the efficacy of individual message-instances is undecidable within an adaptive system and, therefore, that indirect evaluation of efficacy is unavoidable. Four theorems which delineate the decision problems of microevolution and conditioning are demonstrated, and their scopes illustrated by application to the learning machine. Analogies are drawn between the decision problems of microevolution and conditioning and those of two deductive systems. Fifth, a natural extension of the theoretical description to more complex processes than microevolution and conditioning is considered. A hypothetical mechanism is suggested to account for the ability of adaptive systems to build upon the environmentally specified information they accumulate. In terms of the mechanism partial copies (complements) of efficacious messages are used as autonomous names in the construction of messages about messages. The freezing of coding structures, hierarchy formation, and self reference are briefly discussed in the light of this. An interpretation is suggested for the phyletic and intragenome polynucleotide sequence redundancies observed in genetic systems. Finally, conclusions are drawn.