Multiwavelength optical observations of chromospherically active binary systems V. FF UMa (2RE J0933+624): a system with orbital period variation

This is the fifth paper in a series aimed at studying the chromospheres of active binary systems using several optical spectroscopic indicators to obtain or improve orbital solution and fundamental stellar parameters. We present here the study of FF UMa (2RE J0933+624), a recently discovered, X-ray/EUV selected, active binary with strong H_alpha emission. The objectives of this work are, to find orbital solutions and define stellar parameters from precise radial velocities and carry out an extensive study of the optical indicators of chromospheric activity. We obtained high resolution echelle spectroscopic observations during five observing runs from 1998 to 2004. We found radial velocities by cross correlation with radial velocity standard stars to achieve the best orbital solution. We also measured rotational velocity by cross-correlation techniques and have studied the kinematic by galactic space- velocity components (U, V, W) and Eggen criteria. Finally, we have determined the chromospheric contribution in optical spectroscopic indicators, from Ca II H & K to Ca II IRT lines, using the spectral subtraction technique. We have found that this system presents an orbital period variation, higher than previously detected in other RS CVn systems. We determined an improved orbital solution, finding a circular orbit with a period of 3.274 days. We derived the stellar parameters, confirming the subgiant nature of the primary component and obtained rotational velocities (vsini), of 33.57 km/s and 32.38 km/s for the primary and secondary components respectively. From our kinematic study, we can deduce its membership to the Castor moving group. Finally, the activity study has given us a better understanding of the possible mechanisms that produce the orbital period variation.Comment: Latex file with 16 pages, 18 figures. Available at http://www.ucm.es/info/Astrof/invest/actividad/actividad_pub.html Accepted for publication in: Astronomy & Astrophysics (A&A

Dynamics of two interacting particles in classical billiards

The problem of two interacting particles moving in a d-dimensional billiard is considered here. A suitable coordinate transformation leads to the problem of a particle in an unconventional hyperbilliard. A dynamical map can be readily constructed for this general system, which greatly simplifies calculations. As a particular example, we consider two identical particles interacting through a screened Coulomb potential in a one-dimensional billiard. We find that the screening plays an important role in the dynamical behavior of the system and only in the limit of vanishing screening length can the particles be considered as bouncing balls. For more general screening and energy values, the system presents strong non-integrability with resonant islands of stability.Comment: REVTEX manuscript, 4 figures (1 ps + 3 gif, Postscript versions available upon request). Also available at http://www.phy.ohiou.edu/~ulloa/ulloa.htm

Force measurements with optical tweezers inside living cells

The force exerted by optical tweezers can be measured by tracking the momentum changes of the trapping beam, a method which is more general and powerful than traditional calibration techniques as it is based on first principles, but which has not been brought to its full potential yet, probably due to practical difficulties when combined with high-NA optical traps, such as the necessity to capture a large fraction of the scattered light. We show that it is possible to measure forces on arbitrary biological objects inside cells without an in situ calibration, using this approach. The instrument can be calibrated by measuring three scaling parameters that are exclusively determined by the design of the system, thus obtaining a conversion factor from volts to piconewtons that is theoretically independent of the physical properties of the sample and its environment. We prove that this factor keeps valid inside cells as it shows good agreement with other calibration methods developed in recent years for viscoelastic media. Finally, we apply the method to measuring the stall forces of kinesin and dynein in living A549 cells.Publisher PD

Reaching the boundary between stellar kinematic groups and very wide binaries. III. Sixteen new stars and eight new wide systems in the beta Pictoris moving group

Aims. We look for common proper motion companions to stars of the nearby young beta Pictoris moving group. Methods. First, we compiled a list of 185 beta Pictoris members and candidate members from 35 representative works. Next, we used the Aladin and STILTS virtual observatory tools, and the PPMXL proper motion and Washington Double Star catalogues to look for companion candidates. The resulting potential companions were subjects of a dedicated astro-photometric follow-up using public data from all-sky surveys. After discarding 67 sources by proper motion and 31 by colour-magnitude diagrams, we obtained a final list of 36 common proper motion systems. The binding energy of two of them is perhaps too small to be considered physically bound. Results. Of the 36 pairs and multiple systems, eight are new, 16 have only one stellar component previously classified as a beta Pictoris member, and three have secondaries at or below the hydrogen-burning limit. Sixteen stars are reported here for the first time as moving group members. The unexpected large number of high-order multiple systems, 12 triples and two quadruples among 36 systems, may suggest a biased list of members towards close binaries or an increment of the high-order-multiple fraction for very wide systems.Comment: A&A in pres