arXiv subjects

Ajit Kembhavi

Publications and source records attributed to Ajit Kembhavi.

27 records · Page 2Linked to original sources

arXiv2006

Astronomical Data Management

We present a summary of the major contributions to the Special Session on Data Management held at the IAU General Assembly in Prague in 2006. While recent years have seen enormous improvements in access to astronomical data, and the Virtual Observatory aims to provide astronomers with seamless access to on-line resources, more attention needs to be paid to ensuring the quality and completeness of those resources. For example, data produced by telescopes are not always made available to the astronomical community, and new instruments are sometimes designed and built with insufficient planning for data management, while older but valuable legacy data often remain undigitised. Data and results published in journals do not always appear in the data centres, and astronomers in developing countries sometimes have inadequate access to on-line resources. To address these issues, an 'Astronomers Data Manifesto' has been formulated with the aim of initiating a discussion that will lead to the development of a 'code of best practice' in astronomical data management.

astro-ph↗

arXiv2005

Photometric Scaling Relations for Bulges of Galaxies

We study the photometric parameters of the bulges of galaxies of different Hubble types including ellipticals, lenticulars, early and late type spirals and early type dwarf galaxies. Analyzing the distributions of various photometric parameters, and two- and three-dimensional correlations between them, we find that there is a difference in the correlations exhibited by bright (M_K < -22) and faint bulges, irrespective of their Hubble type. Importantly, the bright bulges, which include typically E/S0 galaxies and bulges of early type spirals, are tightly distributed around a common photometric plane (PP), while their fainter counter parts, mainly bulges of late type spirals and dwarf galaxies show significant deviation from the planar distribution. We show that the specific entropy, determined from the bulge structural parameters, systematically increases as we move from late to early Hubble types. We interpret this as evidence for hierarchical merging and passive evolution scenarios for bright and faint bulges respectively.

astro-ph↗

arXiv2002

A difference boosting neural network for automated star-galaxy classification

In this paper we describe the use of a new artificial neural network, called the difference boosting neural network (DBNN), for automated classification problems in astronomical data analysis. We illustrate the capabilities of the network by applying it to star galaxy classification using recently released, deep imaging data. We have compared our results with classification made by the widely used Source Extractor (SExtractor) package. We show that while the performance of the DBNN in star-galaxy classification is comparable to that of SExtractor, it has the advantage of significantly higher speed and flexibility during training as well as classification.

astro-ph↗

arXiv2000

A near infrared photometric plane for ellipticals and bulges of spirals

We report the existence of a single plane in the space of global photometric parameters describing elliptical galaxies and the bulges of early type spiral galaxies. The three parameters which define the plane are obtained by fitting the Sersic form to the brightness distribution obtained from near-infrared K band images. We find, from the range covered by their shape parameters, that the elliptical galaxies form a more homogeneous population than the bulges. Known correlations like the Kormendy relation are projections of the photometric plane. The existence of the plane has interesting implications for bulge formation models.

astro-ph↗

arXiv1999

Correlations among global photometric properties of disk galaxies

Using a two-dimensional galaxy image decomposition technique, we extract global bulge and disk parameters for a complete sample of early type disk galaxies in the near infrared K band. We find significant correlation of the bulge parameter n with the central bulge surface brightness $μ_b(0)$ and with effective radius r_e. Using bivar iate analysis techniques, we find that $\log n$, $\log r_e$ and $μ_b(0)$ are distributed in a plane with small scatter. We do not find a strong correlation of n with bulge-to-disk luminosity ratio, contrary to earlier reports. r_e and the disk scale length r_d are well correlated for these early type disk galaxies, but with large scatter. We examine the implications of our results to various bulge formation scenarios in disk galaxies.

astro-ph↗

arXiv1999

A Study of Quasar Radio Emission from the VLA FIRST Survey

Using the most recent (1998) version of the VLA FIRST survey radio catalog, we have searched for radio emission from 1704 quasars taken from the most recent (1993) version of the Hewitt and Burbidge quasar catalog. These quasars lie in the ~5000 square degrees of sky already covered by the VLA FIRST survey. Our work has resulted in positive detection of radio emission from 389 quasars of which 69 quasars have been detected for the first time at radio wavelengths. We find no evidence of correlation between optical and radio luminosities for optically selected quasars. We find indications of a bimodal distribution of radio luminosity, even at a low flux limit of 1 mJy. We show that radio luminosity is a good discriminant between radio loud and radio quiet quasar populations, and that it may be inappropriate to make such a division on the basis of the radio to optical luminosity ratio. We discuss the dependence of the radio loud fraction on optical luminosity and redshift.

astro-ph↗

arXiv1999

Effective Radii and Color Gradients in Radio Galaxies

We present de Vaucouleurs' effective radii in B and R bands for a sample of Molonglo Reference Catalogue radio galaxies and a control sample of normal galaxies. We use the ratio of the scale lengths in the two bands as an indicator to show that the radio galaxies tend to have excess of blue color in their inner region much more frequently than the control galaxies. We show that the scale length ratio is a useful indicator of radial color variation even when the conventional color gradient is too noisy to serve the purpose.

astro-ph↗

arXiv1997

Two dimensional bulge disk decomposition

We propose a two dimensional galaxy fitting algorithm to extract parameters of the bulge, disk, and a central point source from broad band images of galaxies. We use a set of realistic galaxy parameters to construct a large number of model galaxy images which we then use as input to our galaxy fitting program to test it. We find that our approach recovers all structural parameters to a fair degree of accuracy. We elucidate our procedures by extracting parameters for 3 real galaxies -- NGC 661, NGC 1381, and NGC 1427.

astro-ph↗

arXiv1995

A Dust Lane in the Radio galaxy 3C270

We present broad band surface photometry of the radio galaxy 3C270 (NGC~4261). We find a distinct dust lane in the $V-R$ image of the galaxy, and determine its orientation and size. We use the major axis profile of the galaxy to estimate the optical depth of the dust lane, and discuss the significance of the lane to the shape of the galaxy.

astro-ph↗