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Cluster Members (cluster + member)
Selected AbstractsThe young open cluster Trumpler 3ASTRONOMISCHE NACHRICHTEN, Issue 3 2010G. Maciejewski Abstract We present a photometric and spectroscopic study of the poorly investigated open cluster Trumpler 3. Basic parameters such as the age of 70 ± 10 Myr, the color excess E (B , V) = 0.30 ± 0.02 mag, the distance of 0.69 ± 0.03 kpc and the limiting radius of 12, were redetermined and compared with previous preliminary studies. The distance of 0.65 ± 0.09 kpc was determined independently by spectral parallaxes. Simultaneously, our analysis allowed us to estimate a total number of members to be Ntot = 570 ± 90 and a total mass of the cluster to be Mtot = 270 ± 40 M,. We also determined a state of cluster's dynamical evolution. We conclude that Trumpler 3 is a young low-massive stellar ensemble with a typical mass function slope, located near to the outer edge of the Galaxy's Orion Spur. As a result of a wide-field search for short period variable stars, 24 variables were discovered in the cluster's area. Only one of them , a variable of the , -Dor type , was found to be a likely cluster member (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The Cepheid impostor HD 18391 and its anonymous parent clusterASTRONOMISCHE NACHRICHTEN, Issue 8 2009D.G. Turner Abstract New and existing photometry for the G0 Ia supergiant HD 18391 is analyzed in order to confirm the nature of the variability previously detected in the star, which lies off the hot edge of the Cepheid instability strip. Small-amplitude variability at a level of ,V = 0.016 ± 0.002 is indicated, with a period of P = 123d.04 ± 0d.06. A weaker second signal may be present at P = 177d.84 ± 0d.18 with ,V = 0.007 ± 0.002, likely corresponding to fundamental mode pulsation if the primary signal represents overtone pulsation (123.04/177.84 = 0.69). The star, with a spectroscopic reddening of EB,V = 1.02 ± 0.003, is associated with heavily-reddened B-type stars in its immediate vicinity that appear to be outlying members of an anonymous young cluster centered ,10, to the west and 1661 ± 73 pc distant. The cluster has nuclear and coronal radii of rn = 3.5, and Rc = 14,, respectively, while the parameters for HD 18391 derived from membership in the cluster with its outlying B stars are consistent with those implied by its Cepheid-like pulsation, provided that it follows the semi-period-luminosity relation expected of such objects. Its inferred luminosity as a cluster member is MV = ,7.76 ± 0.10, its age (9 ± 1) × 106 years, and its evolutionary mass ,19 M,. HD 18391 is not a classical Cepheid, yet it follows the Cepheid period-luminosity relation closely, much like another Cepheid impostor, V810 Cen (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Flare stars in the TW Hydrae association: the HIP 57269 system,ASTRONOMISCHE NACHRICHTEN, Issue 6 2003B. König Abstract We discuss a new member candidate of the TW Hydrae association (TWA) among the stars of the Gershberg et al. (1999) flare star catalog. TWA is one of the closest known associations of young stars at about 60 pc. Three supposedly young flare stars are located in the same region of the sky as TWA. One of them (HIP 57269) shows strong lithium absorption with spectral type K1/K2V and a high level of chromospheric and coronal activity. It is located at a distance of 48.7 ± 6.3 pc in common with the five TWA members observed with Hipparcos (46.7 to 103.9 pc). HIP 57268 A has a wide companion C which also shows lithium absorption at 6707 Å and which has common proper motion with HIP 57269, as well as a close companion resolved visually by Tycho. HIP 57269 A&C lie above the main sequence and are clearly pre-main-sequence stars. The UVW-space velocity is more consistent with the star system being a Pleiades super cluster member. The two other flare stars in the TWA sky region do not show lithium at all and are, hence, unrelated. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Distributed end-host multicast algorithms for the Knowledge GridCONCURRENCY AND COMPUTATION: PRACTICE & EXPERIENCE, Issue 15 2007Wanqing Tu Abstract The Knowledge Grid built on top of the peer-to-peer (P2P) network has been studied to implement scalable, available and sematic-based querying. In order to improve the efficiency and scalability of querying, this paper studies the problem of multicasting queries in the Knowledge Grid. An m -dimensional irregular mesh is a popular overlay topology of P2P networks. We present a set of novel distributed algorithms on top of an m -dimensional irregular mesh overlay for the short delay and low network resource consumption end-host multicast services. Our end-host multicast fully utilizes the advantages of an m -dimensional mesh to construct a two-layer architecture. Compared to previous approaches, the novelty and contribution here are: (1) cluster formation that partitions the group members into clusters in the lower layer where cluster consists of a small number of members; (2) cluster core selection that searches a core with the minimum sum of overlay hops to all other cluster members for each cluster; (3) weighted shortest path tree construction that guarantees the minimum number of shortest paths to be occupied by the multicast traffic; (4) distributed multicast routing that directs the multicast messages to be efficiently distributed along the two-layer multicast architecture in parallel, without a global control; the routing scheme enables the packets to be transmitted to the remote end hosts within short delays through some common shortest paths; and (5) multicast path maintenance that restores the normal communication once the membership alteration appears. Simulation results show that our end-host multicast can distributively achieve a shorter delay and lower network resource consumption multicast services as compared with some well-known end-host multicast systems. Copyright © 2006 John Wiley & Sons, Ltd. [source] Molecular characterization of microbial community in nitrate-removing activated sludgeFEMS MICROBIOLOGY ECOLOGY, Issue 2 2002Han-Woong Lee Abstract The microbial community composition and dominant denitrifying populations in high-nitrate-removing (CR-I) and low-nitrate-removing (CR-II) activated sludge from continuous bioreactors were investigated with most probable number (MPN) enumeration, fluorescence in situ hybridization (FISH) and 16S rDNA characterization. MPNs of nitrate-reducing bacteria of sludge CR-I and sludge CR-II were 2.82×107 and 2.69×104 colony-forming units ml,1, respectively. Eight denitrifying bacteria and two nitrate-reducing bacteria were isolated from sludge CR-I, and four denitrifying bacteria and three nitrate-reducing bacteria from sludge CR-II. Small subunit rDNA characterization of the isolates showed that the majority belonged to the genus Pseudomonas. By using FISH up to 76% (CR-I) and 52% (CR-II) of total 4,6-diamidino-2-phenylindole cell counts hybridized to the bacterial probe EUB338. Members of ,-Proteobacteria were the most abundant proteobacterial group in both sludges, accounting for up to 41.6% and 37.1% of those detected by EUB338, respectively, whereas a higher number of Cytophaga,Flexibacter cluster members were observed in CR-I sludge compared to CR-II sludge. In contrast with culture-based results, the numbers of rRNA group I Pseudomonads accounted for less than 0.01% of those detected by EUB338 in both sludges. Ribosomal DNA clone library analysis showed that the ,-Proteobacteria were also dominant in both sludges. In CR-I sludge, they were related to Zooglorea ramigera, Alcaligenes defragrans, denitrifying Fe-oxidizing bacteria and Dechlorimonas sp., whereas in CR-II sludge, they were related to Nitrosomonas sp. and Dechlorimonas agitatus. When this reactor was operated under anaerobic and anoxic conditions, nitrifying bacteria could adapt to the anoxic environment. We inferred that anaerobic ammonium oxidation and nitrite oxidation may occur in low-nitrate-removing sludge CR-II and inhibit denitrification. [source] Prospective Follow-Up of Empirically Derived Alcohol Dependence Subtypes in Wave 2 of the National Epidemiologic Survey on Alcohol and Related Conditions (NESARC): Recovery Status, Alcohol Use Disorders and Diagnostic Criteria, Alcohol Consumption Behavior, Health Status, and Treatment SeekingALCOHOLISM, Issue 6 2010Howard B. Moss Background:, We have previously reported on an empirical classification of Alcohol Dependence (AD) individuals into subtypes using nationally representative general population data from the 2001 to 2002 Wave 1 of the National Epidemiologic Survey on Alcohol and Related Conditions (NESARC) and latent class analysis. Our results suggested a typology of 5 separate clusters based upon age of onset of AD, multigenerational familial AD, rates of antisocial personality disorder (ASPD), endorsement of specific AD and Alcohol Abuse (AA) criteria, and the presence of comorbid mood, anxiety, and substance use disorders (SUD). In this report, we focus on the clinical follow-up of these cluster members in Wave 2 of the NESARC (2004 to 2005). Methods:, The mean interval between NESARC Wave 1 and NESARC Wave 2 interviews was 36.6 (SD = 2.6) months. For these analyses, we utilized a Wave 2 NESARC sample that was comprised of a total of 1,172 individuals who were initially ascertained as having past-year AD at NESARC Wave 1 and initially subtyped into one of 5 groupings using latent class analysis. We identified these subtypes as: (i) Young Adult, characterized by very early age of onset, minimal family history, and low rates of psychiatric and SUD comorbidity; (ii) Functional, characterized by older age of onset, higher psychosocial functioning, minimal family history, and low rates of psychiatric and SUD comorbidity; (iii) Intermediate Familial, characterized by older age of onset, significant familial AD, and elevated comorbid rates of mood disorders SUD; (iv) Young Antisocial, characterized by early age of onset and elevated rates of ASPD, significant familial AD, and elevated rates of comorbid mood disorders and SUD; (v) Chronic Severe, characterized by later onset, elevated rates of ASPD, significant familial AD, and elevated rates of comorbid mood disorders and SUD. In this report, we examine Wave 2 recovery status, health status, alcohol consumption behavior, and treatment episodes based upon these subtypes. Results:, Significantly fewer of the Young Adult and Functional subtypes continued to meet full DSM-IV AD criteria in Wave 2 than did the Intermediate Familial, the Young Antisocial, and the Chronic Severe subtypes. However, we did not find that treatment seeking for alcohol problems increased over Wave 1 reports. In Wave 2, Young Antisocial and Chronic Severe subtypes had highest rates of past-year treatment seeking. In terms of health status, the Intermediate Familial, the Young Antisocial, and the Chronic Severe subtypes had significantly worse mental health scores than the Young Adult and Functional subtypes. For physical health status, the Functional, Intermediate Familial, Young Antisocial, and the Chronic Severe subtypes had significantly worse scores than the Young Adult subtype. In terms of alcohol consumption behavior, the Young Adult, Functional, and Young Antisocial subtypes significantly reduced their risk drinking days between Wave 1 and Wave 2, whereas the Intermediate Familial and the Chronic Severe subtypes did not. Discussion:, The results suggest that the empirical AD typology predicts differential clinical outcomes 3 years later. Persistence of full AD, treatment seeking, and worse mental health status were associated most strongly with those subtypes manifesting the greatest degree of psychiatric comorbidity. Reductions in alcohol consumption behavior and good physical health status were seen among the 2 younger subtypes. Overall, the least prevalent subtype, the Chronic Severe, showed the greatest stability in the manifestations of AD, despite having the highest rate of treatment seeking. [source] Long-term monitoring in IC4665: fast rotation and weak variability in very low mass objectsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2009Alexander Scholz ABSTRACT We present the combined results of three photometric monitoring campaigns targeting very low mass (VLM) stars and brown dwarfs in the young open cluster IC4665 (age ,40 Myr). Each of our observing runs covers time-scales of ,5 d in the seasons 1999, 2001 and 2002, respectively. In all three runs, we observe ,100 cluster members, allowing us for the first time to put limits on the evolution of spots and magnetic activity in fully convective objects on time-scales of a few years. For 20 objects covering masses from 0.05 to 0.5 M,, we detect a periodic flux modulation, indicating the presence of magnetic spots co-rotating with the objects. The detection rate of photometric periods (,20 per cent) is significantly lower than in solar-mass stars at the same age, which points to a mass dependence in the spot properties. With two exceptions, none of the objects exhibits variability and thus spot activity in more than one season. This is contrary to what is seen in solar-mass stars and indicates that spot configurations capable of producing photometric modulations occur relatively rarely and are transient in VLM objects. The rotation periods derived in this paper range from 3 to 30 h, arguing for a lack of slow rotators among VLM objects. The periods fit into a rotational evolution scenario with pre-main sequence contraction and moderate (40,50 per cent) angular momentum losses due to wind braking. By combining our findings with literature results, we identify two regimes of rotational and magnetic properties, called C- and I-sequence. Main properties on the C-sequence are fast rotation, weak wind braking, H, emission and saturated activity levels, while the I-sequence is characterized by slow rotation, strong wind braking, no H, emission and linear activity-rotation relationship. Rotation rate and stellar mass are the primary parameters that determine in which regime an object is found. We outline a general scheme to understand rotational evolution for low-mass objects in the context of these two regimes and discuss the potential as well as the problems of this picture. [source] The Monitor project: rotation periods of low-mass stars in M50MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2009Jonathan Irwin ABSTRACT We report on the results of a time-series photometric survey of M50 (NGC 2323), a ,130 Myr open cluster, carried out using the Cerro Tololo Inter-American Observatory (CTIO) 4-m Blanco telescope and Mosaic-II detector as part of the Monitor project. Rotation periods were derived for 812 candidate cluster members over the mass range 0.2 ,M/M,, 1.1. The rotation period distributions show a clear mass-dependent morphology, statistically indistinguishable from those in NGC 2516 and M35 taken from the literature. Due to the availability of data from three observing runs separated by ,10 and 1 month time-scales, we are able to demonstrate clear evidence for evolution of the photometric amplitudes, and hence spot patterns, over the 10 month gap. We are not able to constrain the time-scales for these effects in detail due to limitations imposed by the large gaps in our sampling, which also prevent the use of the phase information. [source] The Monitor project: the search for transits in the open cluster NGC 2362MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2008Adam A. Miller ABSTRACT We present the results of a systematic search for transiting planets in a ,5 Myr open cluster, NGC 2362. We observed ,1200 candidate cluster members, of which ,475 are believed to be genuine cluster members, for a total of ,100 h. We identify 15 light curves with reductions in flux that pass all our detection criteria, and six of the candidates have occultation depths compatible with a planetary companion. The variability in these six light curves would require very large planets to reproduce the observed transit depth. If we assume that none of our candidates are, in fact, planets then we can place upper limits on the fraction of stars with hot Jupiters (HJs) in NGC 2362. We obtain 99 per cent confidence upper limits of 0.22 and 0.70 on the fraction of stars with HJs (fp) for 1,3 and 3,10 d orbits, respectively, assuming all HJs have a planetary radius of 1.5RJup. These upper limits represent observational constraints on the number of stars with HJs at an age ,10 Myr, when the vast majority of stars are thought to have lost their protoplanetary discs. Finally, we extend our results to the entire Monitor project, a survey searching young, open clusters for planetary transits, and find that the survey as currently designed should be capable of placing upper limits on fp near the observed values of fp in the solar neighbourhood. [source] Probing galactic dark matter in dense environments: on the strong lensing efficiency of galaxies in rich clustersMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2007Lindsay J. King ABSTRACT The recent detection by Limousin et al. of five new strong lensing events dominated by galaxy cluster members in Abell 1689, and outside the critical regime of the cluster itself, offers a way to obtain constraints on the cluster mass distribution in a region inaccessible to standard lensing analysis. In addition, modelling such systems will provide another window on the dark matter haloes of galaxies in very dense environments. Here, it is shown that the boost in image separation due to the external shear and convergence from a smooth cluster component means that more numerous, less massive galaxies have the potential to create multiple images with detectable separations, relative to isolated field galaxies. This comes in addition to a potential increase in their lensing (source plane) cross-section. To gain insight into the factors involved and as a precursor to a numerical study using N -body simulations, a simple analytic model of a cluster at z= 0.3 lensing background galaxies at z= 2 is considered here. The fiducial model has cluster members with isothermal density profiles and luminosities L, distributed in a Schechter function (faint-end slope ,=,1.25), related to their velocity dispersions , via the Faber,Jackson scaling L,,4. Just outside the critical regime of the cluster, the scale of galaxy-dominated image separations is significantly increased. Folding in the fact that less massive galaxies present a lower lensing cross-section, and that the cross-section can itself be enhanced in an external field leads to a factor of a few times more detected events relative to field galaxies. These values will be higher closer to the critical curve. Given that the events in Abell 1689 were detected over a very small region of the cluster where ACS data were available, this motivates the search for such events in other clusters. [source] Dust-enshrouded star formation in XMM-LSS galaxy clustersASTRONOMISCHE NACHRICHTEN, Issue 9-10 2009S. Temporin Abstract In recent years, infrared studies of individual galaxy clusters at intermediate redshifts led to the identification of several luminous infrared galaxies (LIR > 1011 L,). These findings were interpreted as an evidence ofvigorous, dust-enshrouded star formation activity, hinting at the presence of an infrared Butcher-Oemler effect. In order to explore this effect, we have undertaken a statistical investigation based on a cluster sample drawn from the XMM-Newton Large Scale Structure survey (XMM-LSS) and exploiting the contiguous coverage of the XMM-LSS field by the Spitzer SWIRE legacy survey. We adopted a stacking technique to investigate the distribution of 24- , m sources out to the cluster periphery and compare it with the distribution of sources in a sample of control fields. Among putative cluster members, selected by means of photometric redshifts, we identified surprisingly high numbers of bright 24- , m sources toward intermediate redshift clusters (z > 0.3). Our analysis indicates the presence of an excess of bright mid-IR sources at redshift z > 0.3 at clustercentric radii ,200,500 kpc (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Magnetic survey of emission line B-type stars with FORS 1 at the VLT,ASTRONOMISCHE NACHRICHTEN, Issue 7 2009S. Hubrig Abstract We report the results of our search for magnetic fields in a sample of 16 field Be stars, the binary emission-line B-type star , Sgr, and in a sample of fourteen members of the open young cluster NGC3766 in the Carina spiral arm. The sample of cluster members includes Be stars, normal B-type stars and He-strong/He-weak stars. Nine Be stars have been studied with magnetic field time series obtained over ,1 hour to get an insight into the temporal behaviour and the correlation of magnetic field properties with dynamical phenomena taking place in Be star atmospheres. The spectropolarimetric data were obtained at the European Southern Observatory with the multi-mode instrument FORS1 installed at the 8m Kueyen telescope. We detect weak photospheric magnetic fields in four field Be stars, HD 62367, , Cen, o Aqr, and , Tuc. The strongest longitudinal magnetic field, ,Bz, = 117 ± 38 G, was detected in the Be star HD 62367. Among the Be stars studied with time series, one Be star, , Eri, displays cyclic variability of the magnetic field with a period of 21.12 min. The binary star , Sgr, in the initial rapid phase of mass exchange between the two components with strong emission lines in the visible spectrum, is a magnetic variable star, probably on a timescale of a few months. The maximum longitudinal magnetic field ,Bz, = ,102 ± 10 G at MJD 54333.018 was measured using hydrogen lines. The cluster NGC3766 seems to be extremely interesting, where we find evidence for the presence of a magnetic field in seven early B-type stars out of the observed fourteen cluster members (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Photometric study of the OB star clusters NGC 1502 and NGC 2169 and mass estimation of their members at the University Observatory Jena,ASTRONOMISCHE NACHRICHTEN, Issue 5 2009M.M. Hohle Abstract In this work we present detailed photometric results of the trapezium like galactic nearby OB clusters NGC 1502 and NGC 2169 carried out at the University Observatory Jena. We determined absolute BVRI magnitudes of the mostly resolved components using Landolt standard stars. This multi colour photometry enables us to estimate spectral type and absorption as well as the masses of the components, which were not available for most of the cluster members in the literature so far, using models of stellar evolution. Furthermore, we investigated the optical spectrum of the components ADS 2984A and SZ Cam of the sextuple system in NGC 1502. Our spectra clearly confirm the multiplicity of these components, which is the first investigation of this kind at the University Observatory Jena (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Brown dwarf candidates in the Serpens cloud core,ASTRONOMISCHE NACHRICHTEN, Issue 1 2006C. Eiroa Abstract The Serpens cloud core is populated by a young, low-mass stellar cluster with members in many different evolutionary stages. We revisit the near-IR properties of the cluster in this contribution. A total of 188 near-IR sources are identified, including new members suggested in this work. Near-IR colour-magnitude and colour-colour diagrams allow us to suggest 42 objects among the cluster members as brown dwarf candidates. A considerable fraction of them present near-IR excesses which indicates that many of these very low mass objects are still surrounded by prominent dust accretion disks. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Do maternity care provider groups have different attitudes towards birth?BJOG : AN INTERNATIONAL JOURNAL OF OBSTETRICS & GYNAECOLOGY, Issue 12 2004Birgit Reime Objective To compare family physicians', obstetricians' and midwives' self-reported practices, attitudes and beliefs about central issues in childbirth. Design Mail-out questionnaire. Setting/Population All registered midwives in the province, and a sample of family physicians and obstetricians in a maternity care teaching hospital. Response rates: 91% (n= 50), 69% (n= 97) and 89% (n= 34), respectively. Methods A postal survey. Main outcome measures Twenty-three five-point Likert scale items (strongly agree to strongly disagree) addressing attitudes toward routine electronic fetal monitoring, induction of labour, epidural analgesia, episiotomy, doulas, vaginal birth after caesarean section (VBACs), birth centres, provision educational material, birth plans and caesarean section. Results Cluster analysis identified three distinct clusters based on similar response to the questions. The ,MW' cluster consisted of 100% of midwives and 26% of the family physicians. The ,OB' cluster was composed of 79% of the obstetricians and 16% of the family physicians. The ,FP' cluster was composed of 58% the family physicians and 21% the obstetricians. Members of the ,OB' cluster more strongly believed that women had the right to request a caesarean section without maternal/fetal indications (P < 0.001), that epidurals early in labour were not associated with development of fetal malpositions (P < 0.001) and that increasing caesarean rates were a sign of improvement in obstetrics (P < 0.001). The ,OB' cluster members were more likely to say they would induce women as soon as possible after 41 3/7 weeks of gestation (P < 0.001) and were least likely to encourage the use of birth plans (P < 0.001). The ,MW' cluster's views were the opposite of the ,OBs' while the ,FP' cluster's views fell between the ,MW' and ,OB' clusters. Conclusions In our environment, obstetricians were the most attached to technology and interventions including caesarean section and inductions, midwives the least, while family physicians fell in the middle. While generalisations can be problematic, obstetricians and midwives generally follow a defined and different approach to maternity care. Family physicians are heterogeneous, sometimes practising more like midwives and sometimes more like obstetricians. [source] Implementing chemicals policy: leaders or laggards?BUSINESS STRATEGY AND THE ENVIRONMENT, Issue 6 2004J. P. Richards Prioritization of regulatory agency resources remains a key issue in the management of industrial pollution. This is likely to become increasingly important as a new EC chemicals policy is implemented and measures are introduced to achieve the OSPAR zero emissions target. The Environment Agency (England and Wales) has updated the Operator Pollution and Risk Assessment (OPRA) scheme, but it still includes no quantitative measurement of operator attitudes towards environmental regulation. This is important because regulated firms' attitudes are known to affect regulatory behaviour. This study explores the attitudes of environmental managers from 142 chemical sector companies regulated under Integrated Pollution Control. Analysis of responses from a questionnaire survey revealed a number of regulatory typologies. A ,conservative' cluster exhibited satisfaction with the current regulatory system and rejected change. ,Progressive' cluster members recognized shortcomings and welcomed change. This methodology could be used alongside OPRA to support decisions necessary to prioritize regulatory resources. Copyright © 2004 John Wiley & Sons, Ltd and ERP Environment. [source] | |||||||||||||