28 research outputs found
The first CCD photometric study of the open cluster NGC 2126
We present the first CCD photometric observations of the northern open
cluster NGC 2126. Data were taken on eight nights in February and December 2002
with a total time span of ~57 hours. Almost 1000 individual V-band frames were
examined to find short-period variable stars. We discovered six new variable
stars, of which one is a promising candidate for an eclipsing binary with a
pulsating component. Two stars were classified as delta Scuti stars and one as
Algol-type eclipsing binary. Two stars are slow variables with ambiguous
classification. From absolute VRI photometry we have estimated the main
characteristics of the cluster: m-M=11.0+/-0.5, E(V-I)=0.4+/-0.1,
E(V-R)=0.08+/-0.06 (E(B-V)=0.2+/-0.15) and d=1.3+/-0.6 kpc. Cluster membership
is suggested for three variable stars from their positions on the
colour-magnitude diagram.Comment: 7 pages, 10 figures, accepted for publication in A&
Planet Hunters IX. KIC 8462852-where's the flux?
Over the duration of the Kepler mission, KIC 8462852 was observed to undergo irregularly shaped, aperiodic dips in flux of up to similar to 20 per cent. The dipping activity can last for between 5 and 80 d. We characterize the object with high-resolution spectroscopy, spectral energy distribution fitting, radial velocity measurements, high-resolution imaging, and Fourier analyses of the Kepler light curve. We determine that KIC 8462852 is a typical main-sequence F3 V star that exhibits no significant IR excess, and has no very close interacting companions. In this paper, we describe various scenarios to explain the dipping events observed in the Kepler light curve. We confirm that the dipping signals in the data are not caused by any instrumental or data processing artefact, and thus are astrophysical in origin. We construct scenario-independent constraints on the size and location of a body in the system that are needed to reproduce the observations. We deliberate over several assorted stellar and circumstellar astrophysical scenarios, most of which have problems explaining the data in hand. By considering the observational constraints on dust clumps in orbit around a normal main-sequence star, we conclude that the scenario most consistent with the data in hand is the passage of a family of exocomet or planetesimal fragments, all of which are associated with a single previous break-up event, possibly caused by tidal disruption or thermal processing. The minimum total mass associated with these fragments likely exceeds 10(-6) M-circle plus, corresponding to an original rocky body of > 100 km in diameter. We discuss the necessity of future observations to help interpret the system.Peer reviewe
Binarity and multiperiodicity in high-amplitude delta Scuti stars
We have carried out a photometric and spectroscopic survey of bright
high-amplitude delta Scuti (HADS) stars. The aim was to detect binarity and
multiperiodicity (or both) in order to explore the possibility of combining
binary star astrophysics with stellar oscillations. Here we present the first
results for ten, predominantly southern, HADS variables. We detected the
orbital motion of RS Gru with a semi-amplitude of ~6.5 km/s and 11.5 days
period. The companion is inferred to be a low-mass dwarf star in a close orbit
around RS Gru. We found multiperiodicity in RY Lep both from photometric and
radial velocity data and detected orbital motion in the radial velocities with
hints of a possible period of 500--700 days. The data also revealed that the
amplitude of the secondary frequency is variable on the time-scale of a few
years, whereas the dominant mode is stable. Radial velocities of AD CMi
revealed cycle-to-cycle variations which might be due to non-radial pulsations.
We confirmed the multiperiodic nature of BQ Ind, while we obtained the first
radial velocity curves of ZZ Mic and BE Lyn. The radial velocity curve and the
O-C diagram of CY Aqr are consistent with the long-period binary hypothesis. We
took new time series photometry on XX Cyg, DY Her and DY Peg, with which we
updated their O-C diagrams.Comment: 15 pages, 16 pages, accepted for publication in MNRA
Neighbourhood Reduction in Global and Combinatorial Optimization: The Case of the p-Centre Problem
Neighbourhood reductions for a class of location problems known as the vertex (or discrete) and planar (or continuous) p-centre problems are presented. A brief review of these two forms of the p-centre problem is first provided followed by those respective reduction schemes that have shown to be promising. These reduction schemes have the power of transforming optimal or near optimal methods such as metaheuristics or relaxation-based procedures, which were considered relatively slow, into efficient and exciting ones that are now able to find optimal solutions or tight lower/upper bounds for larger instances. Research highlights of neighbourhood reduction for global and combinatorial optimisation problems in general and for related location problems in particular are also given
A922 Sequential measurement of 1 hour creatinine clearance (1-CRCL) in critically ill patients at risk of acute kidney injury (AKI)
Meeting abstrac
European Commission, Standards, Measurement and Testing Programme. Project SMT4-CT95-7501: intercomparison of impulse charge measurement
Consiglio Nazionale delle Ricerche - Biblioteca Centrale - P.le Aldo Moro, 7, Rome / CNR - Consiglio Nazionale delle RichercheSIGLEITItal
A Multiobjective Model for Locating Public Facilities on an Uncongested Transportation Network
A Multiobjective model for the location of public facilities on an uncongested transportation network is presented. The model combines the Mini-Max and Mini-Sum objectives and considers capacity constraints for the location of the facilities. The problem of locating health care centers in a rural area of Greece is used to display the capabilities of the proposed model