Rahul Surendra Dave

Cosmological imprint of an energy component with general equation of state

We examine the possibility that a significant component of the energy density of the Universe has an equation of state different from that of matter, radiation, or cosmological constant ({Lambda} ). An example is a cosmic scalar field evolving in a potential, but our treatment is more general. Including this component alters cosmic evolution in a way that fits current observations well. Unlike {Lambda} , it evolves dynamically and develops fluctuations, leaving a distinctive imprint on the microwave background anisotropy and mass power spectrum. {copyright} {ital 1998} {ital The American Physical Society}

Resolving the cosmological missing energy problem

Some form of missing energy may account for the difference between the observed cosmic matter density and the critical density. Two leading candidates are a cosmological constant and quintessence (a time-varying, inhomogeneous component with negative pressure). We show that an ideal, full-sky cosmic background anisotropy experiment may not be able to distinguish the two, even when non-linear effects due to gravitational lensing are included. Because of this ambiguity, microwave background experiments alone may not determine the matter density or Hubble constant very precisely. We further show that degeneracy may remain even after considering classical cosmological tests and measurements of large scale structure. {copyright} {ital 1999} {ital The American Physical Society}

Finding outlier light curves in catalogues of periodic variable stars

We present a methodology to discover outliers in catalogues of periodic light curves. We use a cross-correlation as the measure of ‘similarity’ between two individual light curves, and then classify light curves with lowest average ‘similarity’ as outliers. We performed the analysis on catalogues of periodic variable stars of known type from the MACHO and OGLE projects. This analysis was carried out in Fourier space and we established that our method correctly identifies light curves that do not belong to those catalogues as outliers. We show how an approximation to this method, carried out in real space, can scale to large data sets that will be available in the near future such as those anticipated from the Panoramic Survey Telescope & Rapid Response System (Pan-STARRS) and Large Synoptic Survey Telescope (LSST).

Sensitivity of the Cosmic Microwave Background Anisotropy to Initial Conditions in Quintessence Cosmology

We analyze the evolution of energy density fluctuations in cosmological scenarios with a mixture of cold dark matter and quintessence, in which the quintessence field is modeled by a constant equation of state. We obtain analytic expressions for the time evolution of the quintessence perturbations in models with light fields. The fluctuations behave analogously to a driven harmonic oscillator, where the driving term arises from the inhomogeneities in the surrounding cosmological fluid. We demonstrate that the homogeneous solution, determined by the initial conditions, is completely sub-dominant to the inhomogeneous solution for physically realistic scenarios. Thus we show that the cosmic microwave background anisotropy predicted for such models is highly insensitive to the initial conditions in the quintessence field.

The Taiwanese-American Occultation Survey: The Multi-Telescope Robotic Observatory

The Taiwanese-American Occultation Survey (TAOS) operates four fully automatic telescopes to search for occultations of stars by Kuiper Belt Objects. It is a versatile facility that is also useful for the study of initial optical GRB afterglows. This paper provides a detailed description of the TAOS multi-telescope system, control software, and high-speed imaging.

TAOS: The Taiwanese–American Occultation Survey

The Taiwanese–American Occultation Survey (TAOS) seeks to determinethe number and size spectrum for small (∼3 km) bodies in the KuiperBelt. This will be accomplished by searching for the brief occultations of brightstars (R∼14) by these objects. We have designed and built a specialpurpose photometric monitoring system for this purpose. TAOS comprisesfour 50 cm telescopes, each equipped with a 2048×2048 pixel CCDcamera, in a compact array located in the central highlands of Taiwan. TAOSwill monitor up to 3,000 stars at 5 Hz. The system will go into scientificoperation at the end of 003.

Search for Small Trans-Neptunian Objects by the TAOS Project

The Taiwan-America Occultation Survey (TAOS) aims to determine the number of small icy bodies in the outer reach of the Solar System by means of stellar occultation. An array of 4 robotic small (D=0.5 m), wide-field (f/1.9) telescopes have been installed at Lulin Observatory in Taiwan to simultaneously monitor some thousand of stars for such rare occultation events. Because a typical occultation event by a TNO a few km across will last for only a fraction of a second, fast photometry is necessary. A special CCD readout scheme has been devised to allow for stellar photometry taken a few times per second. Effective analysis pipelines have been developed to process stellar light curves and to correlate any possible flux changes among all telescopes. A few billion photometric measurements have been collected since the routine survey began in early 2005. Our preliminary result of a very low detection rate suggests a deficit of small TNOs down to a few km size, consistent with the extrapolation of some recent studies of larger (30-100 km) TNOs.

Fast CCD Photometry in the Taiwan-America Occultation Survey

Abstract We describe the efforts of the Taiwan-America Occultation Survey (TAOS) project to develop a data acquisition and analysis scheme for fast CCD imaging photometry. The TAOS project aims to conduct a census of the Kuiper-belt objects (KBOs) by detecting chance stellar occultation events by these small bodies in the outer reach of the solar system. An array of telescopes, each with fast optics (f/2) of 0.5 m aperture and equipped with a 2K CCD camera (3 square degrees FOV), have been set up in central Taiwan to monitor a couple thousand stars simultaneously. By reading out the CCD chip sequentially a few rows of pixels at a time (pause-and-shift), it is possible to achieve stellar photometry with a sampling rate up to several hertz. Here we report how such a setup has been used to observe the SX Phoenicis type variable CY Aqr to illustrate the potential usefulness of the TAOS database in stellar variability studies.