kavan Ratnatunga - Academia.edu (original) (raw)
Papers by kavan Ratnatunga
National Science Foundation. – 2 – This study explores the space density and properties of active... more National Science Foundation. – 2 – This study explores the space density and properties of active galaxies to z≃0.8. We have investigated the frequency and nature of unresolved nuclei in galaxies at moderate redshift as indicators of nuclear activity such as Active Galactic Nuclei (AGN) or starbursts. Candidates are selected by fitting imaged galaxies with multi-component models using maximum likelihood estimate techniques to determine the best model fit. We select those galaxies requiring an unresolved point-source component in the galaxy nucleus, in addition to a disk and/or bulge component, to adequately model the galaxy light. We have searched 70 WFPC2 images primarily from the Medium Deep Survey for galaxies containing compact nuclei. In our survey of 1033 galaxies, the fraction containing an unresolved nuclear component ≥5 % of the total galaxy light is 9±1 % corrected for incompleteness. In this second of two papers in this series, we discuss the nature of the compact nuclei ...
The Astrophysical Journal, 1994
... Spectroscopy at the William Herschel Telescope has shown that this galaxy has a spectrum simi... more ... Spectroscopy at the William Herschel Telescope has shown that this galaxy has a spectrum similar to that of a classical H II region, with a redshift of z = 0.688 1 ± 0.0003 ; the blue com-' ponents thus seem to be supergiant H II regions undergoing starbursts (Glazebrook et al. ...
The Astrophysical Journal, 1999
![Research paper thumbnail of The Morphological Mix of Field Galaxies to [ITAL]m[/ITAL][TINF][ITAL]I[/ITAL][/TINF] = 24.25 Magnitudes ([ITAL]b[/ITAL][TINF][ITAL]J[/ITAL][/TINF] ∼ 26 Magnitudes) from a Deep [ITAL]Hubble Space Telescope[/ITAL] WFPC2 Image](https://attachments.academia-assets.com/89604626/thumbnails/1.jpg)
](The Astrophysical Journal, 1995
The Astronomical Journal, 1988
Coins, tokens or possibly amulets depicting turtles, terrapins and tortoises discovered from fiel... more Coins, tokens or possibly amulets depicting turtles, terrapins and tortoises discovered from fields around Tissamaharama, Southeastern Sri Lanka are discussed. The bad status of preservation of these objects could probably be due to the main metal used is lead, and the close proximity to the sea of the location where these objects were unearthed. The Brāhmī letters refer to a person and not the ruling monarchy which leads to the assumption that most of these coins are in reality amulets. Depicting turtles could perhaps be due to the lucrative trade in marine turtle scutes (scales of the carapace) and their products around southeast of the country from nd century BCE. Abbreviations: AdS= Anslem de Silva, ID = Indraneil Das, KR = Kavan Ratnatunga, OB = Osmand Boppearachchi, RW = Rajha Wickramasinghe, SM = Siri Munasinghe Fig. 1. Greek turtle coin, the silver stater. (Image courtesy: CNG https://en.wikipedia.org/wiki/Silver_stater_with_a_turtle#/media/File:Aegina_Stater_achaic.jpg) 12 ...
Astrophysical Journal, 1985
On decrit une technique permettant de trouver des geantes K du champ dans le halo galactique exte... more On decrit une technique permettant de trouver des geantes K du champ dans le halo galactique externe, de 10 a 40 kpc du centre galactique. On calcule les vitesses radiales de 150 de ces geantes du halo, et on montre que (1) le halo externe a une rotation plus lente et (2) la dispersion de la vitesse de ligne de vue dans les deux meilleurs champs etudies est approximativement constante avec la distance au soleil
Proceedings of the Astronomical Society of …, 1982
422 Contributions Proc. ASA 4(4)1982 -1.0 0.0 1.0 2.0 3.0 mug Author's V luminosity distance... more 422 Contributions Proc. ASA 4(4)1982 -1.0 0.0 1.0 2.0 3.0 mug Author's V luminosity distance modulus Figure 5. Distance moduli of 37 spirals in the five clusters derived through luminosity-HI width relations, using V luminosity and IV luminosity, are compared . ...
The aim of this survey is to locate samples of very distant field halo stars, to study the kinema... more The aim of this survey is to locate samples of very distant field halo stars, to study the kinematics and metal abundance distribution in the outer regions of the galactic halo. Field halo K giants were chosen for the study, as they are intrinsically bright stars whose evolution is well understood. Halo K giants, near the tip of the giant branch and between 10 and 40 kpc from the sun, will have apparent magnitudes in the range 13 < V < 18, and colours (B-V) < 0.9.
The Astrophysical Journal Supplement Series, 1986
... Printed in USA WIDE BINARIES IN THE DIRECTION OF ANDROMEDA JOHN N. BAHCALL Institute for Adva... more ... Printed in USA WIDE BINARIES IN THE DIRECTION OF ANDROMEDA JOHN N. BAHCALL Institute for Advanced Study, Princeton, New Jersey ... Davis, Hut, and Muller (1984) and Whitmire and Jackson (1984) suggested that the presence of wide binaries in the Galaxy ...
We discuss the procedures adopted to optimize the calibration of the Hubble Space Telescope Wide ... more We discuss the procedures adopted to optimize the calibration of the Hubble Space Telescope Wide Field Camera and to improve quantitative measurement of faint images. We use exposures of random sky fields that were taken in parallel mode when another detector was being used on a primary target extending two or more orbits. The observations are part of the Medium-Deep Survey, which will generate an object catalog that is useful for statistical studies in both Galactic and extra-galactic astronomy. We present improved flatfields for use with the F555W and F785LP filters. The flatfields constructed by creating a skyflat from all suitable WFC data taken between August 1992 and July 1993 allow for a single zero-point for all 4-CCDs and achieve a rms error of order 2%.
Publications of the Astronomical Society of Australia
The aim of this study is to investigate the spheroidal halo around our Galaxy, that is, the outer... more The aim of this study is to investigate the spheroidal halo around our Galaxy, that is, the outer extentions of the central bulge. The kinematics and variations in metal abundance in the halo are important astrophysical parameters for any theory which models the formation and evolution of our galaxy. Attempts to determine these parameters have so far used a particular class of stars which can be easily identified as members of the halo.
International Astronomical Union Colloquium
A model for the kinematic distribution function of our Galaxy can be used as an independent confi... more A model for the kinematic distribution function of our Galaxy can be used as an independent confirmation that a reference system is free of Earth motions and retains the true kinematics of the stars. Maximum likelihood can simultaneously estimate the parameters required to calibrate distances to the stars, represent the kinematic distribution function, and check on residual Earth rotations in the proper-motion system. The global maximum-likelihood analysis uses all available information: photometry, trigonometric parallax, proper motion, and line-of-sight velocity for a well-defined catalog of stars. Awaiting observations from HIPPARCOS, preliminary testing of the algorithm on available ground-based observations is discussed.
Transactions of the International Astronomical Union, 2001
Small developing countries may not have a dark site with good seeing for an astronomical observat... more Small developing countries may not have a dark site with good seeing for an astronomical observatory or be able to afford the financial commitment to set up and support such a facility. Much of astronomical research today is however done with remote observations, such as from telescopes in space, or obtained by service observing at large facilities on the ground. Cutting-edge astronomical research can now be done with low-cost computers, with a good Internet connection to get on-line access to astronomical observations, journals and most recent preprints. E-mail allows fast easy collaboration between research scientists around the world. An international program with some short-term collaborative visits, could mine data and publish results from available astronomical observations for a fraction of the investment and cost of running even a small local observatory. Students who have been trained in the use of computers and software by such a program would also be more employable in th...
The Astrophysical Journal, Mar 30, 1985
The Astrophysical Journal, Aug 10, 1990
... [AlO]), the distribution in distance will peak at a smaller distance, about 75 pc; also the o... more ... [AlO]), the distribution in distance will peak at a smaller distance, about 75 pc; also the overall probability will be significantly reduced ... In a related application, Ratnatunga and Yoss (1989) have recently shown the usefulness of the likelihood ratio test to decide how many ...
The Astrophysical Journal, Jul 30, 1991
ABSTRACT
National Science Foundation. – 2 – This study explores the space density and properties of active... more National Science Foundation. – 2 – This study explores the space density and properties of active galaxies to z≃0.8. We have investigated the frequency and nature of unresolved nuclei in galaxies at moderate redshift as indicators of nuclear activity such as Active Galactic Nuclei (AGN) or starbursts. Candidates are selected by fitting imaged galaxies with multi-component models using maximum likelihood estimate techniques to determine the best model fit. We select those galaxies requiring an unresolved point-source component in the galaxy nucleus, in addition to a disk and/or bulge component, to adequately model the galaxy light. We have searched 70 WFPC2 images primarily from the Medium Deep Survey for galaxies containing compact nuclei. In our survey of 1033 galaxies, the fraction containing an unresolved nuclear component ≥5 % of the total galaxy light is 9±1 % corrected for incompleteness. In this second of two papers in this series, we discuss the nature of the compact nuclei ...
The Astrophysical Journal, 1994
... Spectroscopy at the William Herschel Telescope has shown that this galaxy has a spectrum simi... more ... Spectroscopy at the William Herschel Telescope has shown that this galaxy has a spectrum similar to that of a classical H II region, with a redshift of z = 0.688 1 ± 0.0003 ; the blue com-&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#x27; ponents thus seem to be supergiant H II regions undergoing starbursts (Glazebrook et al. ...
The Astrophysical Journal, 1999
The Astrophysical Journal, 1995
The Astronomical Journal, 1988
Coins, tokens or possibly amulets depicting turtles, terrapins and tortoises discovered from fiel... more Coins, tokens or possibly amulets depicting turtles, terrapins and tortoises discovered from fields around Tissamaharama, Southeastern Sri Lanka are discussed. The bad status of preservation of these objects could probably be due to the main metal used is lead, and the close proximity to the sea of the location where these objects were unearthed. The Brāhmī letters refer to a person and not the ruling monarchy which leads to the assumption that most of these coins are in reality amulets. Depicting turtles could perhaps be due to the lucrative trade in marine turtle scutes (scales of the carapace) and their products around southeast of the country from nd century BCE. Abbreviations: AdS= Anslem de Silva, ID = Indraneil Das, KR = Kavan Ratnatunga, OB = Osmand Boppearachchi, RW = Rajha Wickramasinghe, SM = Siri Munasinghe Fig. 1. Greek turtle coin, the silver stater. (Image courtesy: CNG https://en.wikipedia.org/wiki/Silver_stater_with_a_turtle#/media/File:Aegina_Stater_achaic.jpg) 12 ...
Astrophysical Journal, 1985
On decrit une technique permettant de trouver des geantes K du champ dans le halo galactique exte... more On decrit une technique permettant de trouver des geantes K du champ dans le halo galactique externe, de 10 a 40 kpc du centre galactique. On calcule les vitesses radiales de 150 de ces geantes du halo, et on montre que (1) le halo externe a une rotation plus lente et (2) la dispersion de la vitesse de ligne de vue dans les deux meilleurs champs etudies est approximativement constante avec la distance au soleil
Proceedings of the Astronomical Society of …, 1982
422 Contributions Proc. ASA 4(4)1982 -1.0 0.0 1.0 2.0 3.0 mug Author's V luminosity distance... more 422 Contributions Proc. ASA 4(4)1982 -1.0 0.0 1.0 2.0 3.0 mug Author's V luminosity distance modulus Figure 5. Distance moduli of 37 spirals in the five clusters derived through luminosity-HI width relations, using V luminosity and IV luminosity, are compared . ...
The aim of this survey is to locate samples of very distant field halo stars, to study the kinema... more The aim of this survey is to locate samples of very distant field halo stars, to study the kinematics and metal abundance distribution in the outer regions of the galactic halo. Field halo K giants were chosen for the study, as they are intrinsically bright stars whose evolution is well understood. Halo K giants, near the tip of the giant branch and between 10 and 40 kpc from the sun, will have apparent magnitudes in the range 13 < V < 18, and colours (B-V) < 0.9.
The Astrophysical Journal Supplement Series, 1986
... Printed in USA WIDE BINARIES IN THE DIRECTION OF ANDROMEDA JOHN N. BAHCALL Institute for Adva... more ... Printed in USA WIDE BINARIES IN THE DIRECTION OF ANDROMEDA JOHN N. BAHCALL Institute for Advanced Study, Princeton, New Jersey ... Davis, Hut, and Muller (1984) and Whitmire and Jackson (1984) suggested that the presence of wide binaries in the Galaxy ...
We discuss the procedures adopted to optimize the calibration of the Hubble Space Telescope Wide ... more We discuss the procedures adopted to optimize the calibration of the Hubble Space Telescope Wide Field Camera and to improve quantitative measurement of faint images. We use exposures of random sky fields that were taken in parallel mode when another detector was being used on a primary target extending two or more orbits. The observations are part of the Medium-Deep Survey, which will generate an object catalog that is useful for statistical studies in both Galactic and extra-galactic astronomy. We present improved flatfields for use with the F555W and F785LP filters. The flatfields constructed by creating a skyflat from all suitable WFC data taken between August 1992 and July 1993 allow for a single zero-point for all 4-CCDs and achieve a rms error of order 2%.
Publications of the Astronomical Society of Australia
The aim of this study is to investigate the spheroidal halo around our Galaxy, that is, the outer... more The aim of this study is to investigate the spheroidal halo around our Galaxy, that is, the outer extentions of the central bulge. The kinematics and variations in metal abundance in the halo are important astrophysical parameters for any theory which models the formation and evolution of our galaxy. Attempts to determine these parameters have so far used a particular class of stars which can be easily identified as members of the halo.
International Astronomical Union Colloquium
A model for the kinematic distribution function of our Galaxy can be used as an independent confi... more A model for the kinematic distribution function of our Galaxy can be used as an independent confirmation that a reference system is free of Earth motions and retains the true kinematics of the stars. Maximum likelihood can simultaneously estimate the parameters required to calibrate distances to the stars, represent the kinematic distribution function, and check on residual Earth rotations in the proper-motion system. The global maximum-likelihood analysis uses all available information: photometry, trigonometric parallax, proper motion, and line-of-sight velocity for a well-defined catalog of stars. Awaiting observations from HIPPARCOS, preliminary testing of the algorithm on available ground-based observations is discussed.
Transactions of the International Astronomical Union, 2001
Small developing countries may not have a dark site with good seeing for an astronomical observat... more Small developing countries may not have a dark site with good seeing for an astronomical observatory or be able to afford the financial commitment to set up and support such a facility. Much of astronomical research today is however done with remote observations, such as from telescopes in space, or obtained by service observing at large facilities on the ground. Cutting-edge astronomical research can now be done with low-cost computers, with a good Internet connection to get on-line access to astronomical observations, journals and most recent preprints. E-mail allows fast easy collaboration between research scientists around the world. An international program with some short-term collaborative visits, could mine data and publish results from available astronomical observations for a fraction of the investment and cost of running even a small local observatory. Students who have been trained in the use of computers and software by such a program would also be more employable in th...
The Astrophysical Journal, Mar 30, 1985
The Astrophysical Journal, Aug 10, 1990
... [AlO]), the distribution in distance will peak at a smaller distance, about 75 pc; also the o... more ... [AlO]), the distribution in distance will peak at a smaller distance, about 75 pc; also the overall probability will be significantly reduced ... In a related application, Ratnatunga and Yoss (1989) have recently shown the usefulness of the likelihood ratio test to decide how many ...
The Astrophysical Journal, Jul 30, 1991
ABSTRACT