AAVSO publishes its VS of the Season
OK, I was reading my daily AAVSOnews feed (sad aren't I ) and saw this. I have unashamedly lifted it complete, (please contact my solicitor with any copyright issues) but thought this interesting enough to post here.
RU Virginis
The Mira variables undergo some of the most dramatic behavior among all of the variable stars. For just that reason, they were among the earliest variable stars discovered and followed by astronomers trying to understand how our universe works. Four centuries after their discovery, the Mira variables remain one of the most challenging variable star classes to understand. All Miras are "dying stars", soon to shed most of their mass, leaving only a white dwarf behind. To fully understand these objects, we have to understand late stellar evolution, the physics of high-amplitude pulsations and convection, mass loss and stellar winds, and all of the microphysics and chemistry that ties them all together. Individual Mira stars are themselves in transition, but they also represent another cosmic transition in progress. Because the Mira stars are in the stage of their evolution during which most of their mass is returned to the galaxy through stellar winds and mass loss, they are a key mechanism for cosmic chemical enrichment for new generations of stars. Our understanding of how our galaxy and the larger universe are evolving depends in part upon the study of Mira variables.
Visual magnitude estimates (25-day averages) of RU Virginis from theAAVSO International Database.
No two light curves look alike -- Miras light curves are really like snowflakes. And a few Miras have truly remarkable light curves, with lots of interesting behaviors going on at the same time. This quarter brings into view one of these curious Miras -- RU Virginis. RU Vir is one of many Miras in the AAVSO observing program whose light curve has hit the century mark, and more (and more varied) observations continue to be made. RU Vir has shown some perplexing behavior ever since its discovery, and this behavior may help to shed light on some fundamental physics of stars at the ends of their lives. This makes RU Virginis a deserving target of our Variable Star of the Season series.
A short history of RU Virginis
The recorded history of RU Vir dates to the late 19th Century, and the cartographic work then being done at the Dudley Observatory in Albany, New York. At the time, Dudley was under the directorship of Lewis Boss, compiler of the Preliminary General Catalogue of 6188 stars -- the first Boss Catalog -- and also the uncle of the AAVSO PEP pioneer Lewis J. Boss. The Boss catalogue was meant to be a more accurate and complete astrometric and proper motion survey than had been done before. Proper motion surveys require multiple observations of the same regions of sky many years apart, and so it's no surprise that such a survey might uncover some long period variable stars.
Leon Campbell with the AAVSO at HCO, 1915.In 1897, Arthur J. Roy, a staff astronomer of the Dudley Observatory, published a note on a star in Virgo found during observations for the Boss Catalogue that did not appear in the Bonner Durchmusterung published half a century earlier. Roy gave several magnitude estimates made between May 1895 and March 1897, and also noted that it was a very red star. Although he gave no suggestion as to the type of variable, a light curve of Roy's magnitude estimates could easily match that of a Mira. After Roy's discovery, several observers -- including early amateur observers Seth Chandler Jr. and Henry Parkhurst -- began recording the light curve of RU Vir, and it entered the AAVSO's published light curves with Leon Campbell's first observations in 1904, published in Harvard Annals.
The light curve of RU Vir began to show curious behavior almost immediately with a pronounced declining trend in average magnitude. Later photometric studies confirmed and clarified the red spectral type of this object, and by 1940 it was a known carbon star -- a star with pronounced spectral absorption features of carbon. By the end of the 20th Century, the long-term light variations of RU Vir proved to be cyclical, and the nature of this and similar stars were under intense scrutiny by the astronomical community. RU Vir and asymptotic giant branch (AGB) stars like it remain an interesting astrophysical puzzle, and theoretical studies of these stars continue.
Regards
RU Virginis
The Mira variables undergo some of the most dramatic behavior among all of the variable stars. For just that reason, they were among the earliest variable stars discovered and followed by astronomers trying to understand how our universe works. Four centuries after their discovery, the Mira variables remain one of the most challenging variable star classes to understand. All Miras are "dying stars", soon to shed most of their mass, leaving only a white dwarf behind. To fully understand these objects, we have to understand late stellar evolution, the physics of high-amplitude pulsations and convection, mass loss and stellar winds, and all of the microphysics and chemistry that ties them all together. Individual Mira stars are themselves in transition, but they also represent another cosmic transition in progress. Because the Mira stars are in the stage of their evolution during which most of their mass is returned to the galaxy through stellar winds and mass loss, they are a key mechanism for cosmic chemical enrichment for new generations of stars. Our understanding of how our galaxy and the larger universe are evolving depends in part upon the study of Mira variables.
Visual magnitude estimates (25-day averages) of RU Virginis from theAAVSO International Database.
No two light curves look alike -- Miras light curves are really like snowflakes. And a few Miras have truly remarkable light curves, with lots of interesting behaviors going on at the same time. This quarter brings into view one of these curious Miras -- RU Virginis. RU Vir is one of many Miras in the AAVSO observing program whose light curve has hit the century mark, and more (and more varied) observations continue to be made. RU Vir has shown some perplexing behavior ever since its discovery, and this behavior may help to shed light on some fundamental physics of stars at the ends of their lives. This makes RU Virginis a deserving target of our Variable Star of the Season series.
A short history of RU Virginis
The recorded history of RU Vir dates to the late 19th Century, and the cartographic work then being done at the Dudley Observatory in Albany, New York. At the time, Dudley was under the directorship of Lewis Boss, compiler of the Preliminary General Catalogue of 6188 stars -- the first Boss Catalog -- and also the uncle of the AAVSO PEP pioneer Lewis J. Boss. The Boss catalogue was meant to be a more accurate and complete astrometric and proper motion survey than had been done before. Proper motion surveys require multiple observations of the same regions of sky many years apart, and so it's no surprise that such a survey might uncover some long period variable stars.
Leon Campbell with the AAVSO at HCO, 1915.In 1897, Arthur J. Roy, a staff astronomer of the Dudley Observatory, published a note on a star in Virgo found during observations for the Boss Catalogue that did not appear in the Bonner Durchmusterung published half a century earlier. Roy gave several magnitude estimates made between May 1895 and March 1897, and also noted that it was a very red star. Although he gave no suggestion as to the type of variable, a light curve of Roy's magnitude estimates could easily match that of a Mira. After Roy's discovery, several observers -- including early amateur observers Seth Chandler Jr. and Henry Parkhurst -- began recording the light curve of RU Vir, and it entered the AAVSO's published light curves with Leon Campbell's first observations in 1904, published in Harvard Annals.
The light curve of RU Vir began to show curious behavior almost immediately with a pronounced declining trend in average magnitude. Later photometric studies confirmed and clarified the red spectral type of this object, and by 1940 it was a known carbon star -- a star with pronounced spectral absorption features of carbon. By the end of the 20th Century, the long-term light variations of RU Vir proved to be cyclical, and the nature of this and similar stars were under intense scrutiny by the astronomical community. RU Vir and asymptotic giant branch (AGB) stars like it remain an interesting astrophysical puzzle, and theoretical studies of these stars continue.
Regards
posted by Peter Little at
21:21
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