Long-Baseline Interferometric Multiplicity Survey of the Sco-Cen OB Association

We present the first multiplicity-dedicated long baseline optical interferometric survey of the Scorpius-Centaurus-Lupus-Crux association. We used the Sydney University Stellar Interferometer to undertake a survey for new companions to 58 Sco-Cen B- type stars and have detected 24 companions at separations ranging from 7-130mas, 14 of which are new detections. Furthermore, we use a Bayesian analysis and all available information in the literature to determine the multiplicity distribution of the 58 stars in our sample, showing that the companion frequency is F = 1.35 and the mass ratio distribution is best described as a power law with exponent equal to -0.46, agreeing with previous Sco-Cen high mass work and differing significantly from lower-mass stars in Tau-Aur. Based on our analysis, we estimate that among young B-type stars in moving groups, up to 23% are apparently single stars. This has strong implications for the understanding of high-mass star formation, which requires angular momentum dispersal through some mechanism such as formation of multiple systems.Comment: 7 figures, 5 tables, accepted for publication in MNRA

The Palomar Testbed Interferometer

The Palomar Testbed Interferometer (PTI) is a long-baseline infrared interferometer located at Palomar Observatory, California. It was built as a testbed for interferometric techniques applicable to the Keck Interferometer. First fringes were obtained in July 1995. PTI implements a dual-star architecture, tracking two stars simultaneously for phase referencing and narrow-angle astrometry. The three fixed 40-cm apertures can be combined pair-wise to provide baselines to 110 m. The interferometer actively tracks the white-light fringe using an array detector at 2.2 um and active delay lines with a range of +/- 38 m. Laser metrology of the delay lines allows for servo control, and laser metrology of the complete optical path enables narrow-angle astrometric measurements. The instrument is highly automated, using a multiprocessing computer system for instrument control and sequencing.Comment: ApJ in Press (Jan 99) Fig 1 available from http://huey.jpl.nasa.gov/~bode/ptiPicture.html, revised duging copy edi

Modeling the Infrared Bow Shock at delta Velorum: Implications for Studies of Debris Disks and lambda Bootis Stars

We have discovered a bow shock shaped mid-infrared excess region in front of delta Velorum using 24 micron observations obtained with the Multiband Imaging Photometer for Spitzer (MIPS). The excess has been classified as a debris disk from previous infrared observations. Although the bow shock morphology was only detected in the 24 micron observations, its excess was also resolved at 70 micron. We show that the stellar heating of an ambient interstellar medium (ISM) cloud can produce the measured flux. Since delta Velorum was classified as a debris disk star previously, our discovery may call into question the same classification of other stars. We model the interaction of the star and ISM, producing images that show the same geometry and surface brightness as is observed. The modeled ISM is 15 times overdense relative to the average Local Bubble value, which is surprising considering the close proximity (24 pc) of delta Velorum. The abundance anomalies of lambda Bootis stars have been previously explained as arising from the same type of interaction of stars with the ISM. Low resolution optical spectra of delta Velorum show that it does not belong to this stellar class. The star therefore is an interesting testbed for the ISM accretion theory of the lambda Bootis phenomenon.Comment: 11 pages, 1 table and 13 figures, emulateapj; Accepted for publication in The Astrophysical Journa

A new concept for the combination of optical interferometers and high-resolution spectrographs

The combination of high spatial and spectral resolution in optical astronomy enables new observational approaches to many open problems in stellar and circumstellar astrophysics. However, constructing a high-resolution spectrograph for an interferometer is a costly and time-intensive undertaking. Our aim is to show that, by coupling existing high-resolution spectrographs to existing interferometers, one could observe in the domain of high spectral and spatial resolution, and avoid the construction of a new complex and expensive instrument. We investigate in this article the different challenges which arise from combining an interferometer with a high-resolution spectrograph. The requirements for the different sub-systems are determined, with special attention given to the problems of fringe tracking and dispersion. A concept study for the combination of the VLTI (Very Large Telescope Interferometer) with UVES (UV-Visual Echelle Spectrograph) is carried out, and several other specific instrument pairings are discussed. We show that the proposed combination of an interferometer with a high-resolution spectrograph is indeed feasible with current technology, for a fraction of the cost of building a whole new spectrograph. The impact on the existing instruments and their ongoing programs would be minimal.Comment: 27 pages, 9 figures, Experimental Astronomy; v2: accepted versio

Activation of endogenous p53 by combined p19Arf gene transfer and nutlin-3 drug treatment modalities in the murine cell lines B16 and C6

<p>Abstract</p> <p>Background</p> <p>Reactivation of p53 by either gene transfer or pharmacologic approaches may compensate for loss of p19Arf or excess mdm2 expression, common events in melanoma and glioma. In our previous work, we constructed the pCLPG retroviral vector where transgene expression is controlled by p53 through a p53-responsive promoter. The use of this vector to introduce p19Arf into tumor cells that harbor p53wt should yield viral expression of p19Arf which, in turn, would activate the endogenous p53 and result in enhanced vector expression and tumor suppression. Since nutlin-3 can activate p53 by blocking its interaction with mdm2, we explored the possibility that the combination of p19Arf gene transfer and nutlin-3 drug treatment may provide an additive benefit in stimulating p53 function.</p> <p>Methods</p> <p>B16 (mouse melanoma) and C6 (rat glioma) cell lines, which harbor p53wt, were transduced with pCLPGp19 and these were additionally treated with nutlin-3 or the DNA damaging agent, doxorubicin. Viral expression was confirmed by Western, Northern and immunofluorescence assays. p53 function was assessed by reporter gene activity provided by a p53-responsive construct. Alterations in proliferation and viability were measured by colony formation, growth curve, cell cycle and MTT assays. In an animal model, B16 cells were treated with the pCLPGp19 virus and/or drugs before subcutaneous injection in C57BL/6 mice, observation of tumor progression and histopathologic analyses.</p> <p>Results</p> <p>Here we show that the functional activation of endogenous p53wt in B16 was particularly challenging, but accomplished when combined gene transfer and drug treatments were applied, resulting in increased transactivation by p53, marked cell cycle alteration and reduced viability in culture. In an animal model, B16 cells treated with both p19Arf and nutlin-3 yielded increased necrosis and decreased BrdU marking. In comparison, C6 cells were quite susceptible to either treatment, yet p53 was further activated by the combination of p19Arf and nutlin-3.</p> <p>Conclusions</p> <p>To the best of our knowledge, this is the first study to apply both p19Arf and nutlin-3 for the stimulation of p53 activity. These results support the notion that a p53 responsive vector may prove to be an interesting gene transfer tool, especially when combined with p53-activating agents, for the treatment of tumors that retain wild-type p53.</p

Modern optical astronomy: technology and impact of interferometry

The present `state of the art' and the path to future progress in high spatial resolution imaging interferometry is reviewed. The review begins with a treatment of the fundamentals of stellar optical interferometry, the origin, properties, optical effects of turbulence in the Earth's atmosphere, the passive methods that are applied on a single telescope to overcome atmospheric image degradation such as speckle interferometry, and various other techniques. These topics include differential speckle interferometry, speckle spectroscopy and polarimetry, phase diversity, wavefront shearing interferometry, phase-closure methods, dark speckle imaging, as well as the limitations imposed by the detectors on the performance of speckle imaging. A brief account is given of the technological innovation of adaptive-optics (AO) to compensate such atmospheric effects on the image in real time. A major advancement involves the transition from single-aperture to the dilute-aperture interferometry using multiple telescopes. Therefore, the review deals with recent developments involving ground-based, and space-based optical arrays. Emphasis is placed on the problems specific to delay-lines, beam recombination, polarization, dispersion, fringe-tracking, bootstrapping, coherencing and cophasing, and recovery of the visibility functions. The role of AO in enhancing visibilities is also discussed. The applications of interferometry, such as imaging, astrometry, and nulling are described. The mathematical intricacies of the various `post-detection' image-processing techniques are examined critically. The review concludes with a discussion of the astrophysical importance and the perspectives of interferometry.Comment: 65 pages LaTeX file including 23 figures. Reviews of Modern Physics, 2002, to appear in April issu

Asteroseismology and Interferometry

Asteroseismology provides us with a unique opportunity to improve our understanding of stellar structure and evolution. Recent developments, including the first systematic studies of solar-like pulsators, have boosted the impact of this field of research within Astrophysics and have led to a significant increase in the size of the research community. In the present paper we start by reviewing the basic observational and theoretical properties of classical and solar-like pulsators and present results from some of the most recent and outstanding studies of these stars. We centre our review on those classes of pulsators for which interferometric studies are expected to provide a significant input. We discuss current limitations to asteroseismic studies, including difficulties in mode identification and in the accurate determination of global parameters of pulsating stars, and, after a brief review of those aspects of interferometry that are most relevant in this context, anticipate how interferometric observations may contribute to overcome these limitations. Moreover, we present results of recent pilot studies of pulsating stars involving both asteroseismic and interferometric constraints and look into the future, summarizing ongoing efforts concerning the development of future instruments and satellite missions which are expected to have an impact in this field of research.Comment: Version as published in The Astronomy and Astrophysics Review, Volume 14, Issue 3-4, pp. 217-36