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Dive into the research topics where Michael G. Richer is active.

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Featured researches published by Michael G. Richer.


The Astronomical Journal | 2003

Uncovering Additional Clues to Galaxy Evolution. II. The Environmental Impact of the Virgo Cluster on the Evolution of Dwarf Irregular Galaxies

Henry Lee; Marshall L. McCall; Michael G. Richer

The impact of the cluster environment on the evolution of dwarf galaxies is investigated by comparing the properties of a sample of dwarf irregular galaxies (dI’s) in the Virgo Cluster with a control sample of nearby (‘‘ field ’’) dI’s having oxygen abundances derived from [O iii] � 4363 measurements and measured distances from resolved stellar constituents. Spectroscopic data are obtained for H ii regions in 11 Virgo dI’s distributed in the central and outer regions of the cluster. To ensure that oxygen abundances are derived in a homogeneous manner, oxygen abundances for field and Virgo dI’s are computed using the bright-line method and compared with abundances directly obtained from [O iii] � 4363, where available. They are found to agree to within about 0.2 dex, with no systematic offset. At a given optical luminosity, there is no systematic difference in oxygen abundance between the sample of Virgo dI’s and the sample of nearby dI’s. However, five of the 11 Virgo dI’s exhibit much lower baryonic gas fractions than field dI’s at comparable oxygen abundances. Using field dI’s as a reference, a gas-deficiency index for dI’s is constructed, making it possible quantitatively to identify which galaxies have lost gas. For the Virgo sample, some of the dwarfs are gas-deficient by a factor of 30. The gas deficiency correlates roughly with the X-ray surface brightness of the intracluster gas. Ram pressure stripping can best explain the observed gas-poor dI’s in the cluster sample. Together with the lack of significant fading and reddening of the gas-poor dI’s compared with gas-normal dI’s, these observations suggest that the gas-poor dI’s in Virgo have recently encountered the intracluster medium for the first time. Faded remnants of gas-poor dI’s in Virgo will resemble bright dwarf elliptical galaxies currently seen in the cluster core.


Archive | 2007

PN and HII regions of West and East of NGC 3109 (Pena+, 2007)

M. A. Pena; Michael G. Richer; Grazyna Stasinska


Archive | 2007

Resolving the dusty discs around post-AGB binaries

Gaghik H. Tovmassian; John A. Tomsick; R. Napiwotzki; Lev R. Yungelson; Grazyna Stasinska; M. A. Pena; Michael G. Richer


Archive | 2005

Pinning down the composition of the extraordinary planetary nebula PNG 135.9+55.9

Grazyna Stasinska; Corinne Charbonnel; R. Napiwotzki; Miriam Peña; Michael G. Richer; R. Szczerba; Gaghik H. Tovmassian


Symposium - International Astronomical Union | 2003

Oxygen Abundances for the Planetary Nebulae in M32, NGC 185, and NGC 205

Michael G. Richer; Marshall L. McCall


Proceedings of The International Astronomical Union | 2003

Planetary Nebulae as Traces of Chemical Evolution in External Galaxies (invited review)

Marshall L. McCall; Michael G. Richer


Archive | 2003

PN G 135.9+55.9, the Most Oxygen-Poor Planetary Nebula

Grazyna Stasinska; Gaghik H. Tovmassian; Michael G. Richer


Archive | 2002

The Current Health of Dwarf Irregular Galaxies in the Virgo Cluster

Heejo Lee; Marshall L. McCall; Michael G. Richer


Archive | 1998

PN abundances in five galaxies (Stasinska+ 1998)

Grazyna Stasinska; Michael G. Richer; Marshall L. McCall


Archive | 1996

Planetary Nebulae in M31: Oxygen Abundances and Comparison with the Bright Planetary Nebulae in the LMC

Michael G. Richer; Grazyna Stasinska; Marshall L. McCall

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Gaghik H. Tovmassian

National Autonomous University of Mexico

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R. Napiwotzki

University of Hertfordshire

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Miriam Peña

National Autonomous University of Mexico

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Lev R. Yungelson

Russian Academy of Sciences

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