Eclipsing Binary in Young Subcluster NGC 1850A of Globular-Like
LMC Cluster NGC 1850 Discovery Page
Eclipsing Binary in Young Subcluster NGC 1850A of Globular-Like
LMC Cluster NGC 1850 Discovery Page
Still quick & dirty announcement page
pending publication of paper giving finding
of a 3.13 day period Eclipsing Binary Star in
the region of NGC 1850 A, a subcluster of
NGC 1850. NGC 1850A's age has been variously
measured from 4 to 6 Million Years (Myr),
and NGC 1850's age is similarly given from
60 to 80 Myr. NGC 1850 resembles a globular cluster
but is so much younger than Milky Way globular clusters
that it is a matter of considerable debate whether it
is a young globular cluster still in the early stages of
globular cluster formation, or whether it may not form
into a globular cluster and thus does not deserve the
designation of "globular cluster." With this uncertainty
in terminology acknowledged, for simplicity I will refer
to it as a globular cluster or GLC for Globular-Like Cluster. (11 June 2004)
Finder chart for 6 variables in region of the LMC cluster NGC 1850.
The detached eclisping binary that, if not a foreground star,
would be part of NGC 1850A, is labeled "6," for
"Variable #6" or "V6."
Another NGC 1850 candidate member found by the OGLE
collaboration to be an eclisping binary is labeled "1."
I say "in the region" because all of these stars are not
confirmed members of NGC 1850, but might be stars along the
same line-of-sight as NGC 1850.
Image subtraction discovery images of V6:
Image subtraction of central region of NGC 1850, including NGC 1850A,
in an 80 arcsecond square frame (north up, east left), in which
V6, V2, SW 17 stand out strongly and V4 is apparent as well.
This image is
near minima of V6 and V2 (which show as bright PSFs, from defining
the reference image as positive from which the individual image is
subtracted; thus, stars such as SW 17 and V4, which at this time are
brighter than in the reference image appear black and
stars dimmer than the reference image appear white).
Image subtraction of same NGC 1850 central region, when
variable 6 can be seen to be slightly darker than (and thus brighter)
the reference image. (V4 and V2 are also brighter than in the
reference image.)
I-band "reference" image of region of above image subtraction images:
Regular image of the central region of NGC 1850, including NGC 1850A,
in an 80 arcsecond square frame (north up, east left).
Light curve for 3.13 day period:
Difference magnitude for phased light curve variable 6, a newly-found
detached eclipsing binary in the central region
of the young subcluster of NGC 1850 referred to as NGC 1850A.
Still under construction, with light curves and linked credits to OGLE
(especially Andrzej Udalski), the image subtraction program ISIS,
and many others to come.
Acknowledgements from paper in preparation:
I am grateful to Alberto Miranda and the staff at the
National Science Foundation's Cerro Tololo Inter-American Observatory,
in particular Edgardo Cosgrove, Manuel Hernandez, and Malcolm Smith,
for their assistance. The generous encouragement and
support of research at
Georgia State University under Harold A. McAlister
is acknowledged. The support for using the CTIO 0.9 m
telescope by Todd Henry
and the SMARTS Consortium is also
gratefully acknowledged. CHARA members Doug Gies and William
Bagnuolo provided helpful discussion. Computer network support by
John McFarland, Rajesh Deo,
James P. Kinney III, and Ginny Mauldin-Kinney is appreciated.
This research was supported by a
Research Program Enhancement grant
from the Georgia State University Research Office.
This paper utilizes work from the OGLE project
(Udalski, 2003; Udalski et al. 1999; Wyrzykowski et al. 2003).
This paper utilizes public domain data originally obtained by the MACHO Project, whose work was performed under the joint auspices of the U.S. Department of Energy, National Nuclear Security Administration by the University of California, Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48, the National Science Foundation through the Center for Particle Astrophysics of the University of California under cooperative agreement AST-8809616, and the Mount Stromlo and Siding Spring Observatory, part of the Australian National University.
I appreciate the contributions of analysis code, OGLE data, and
valuable suggestions from
Kaspar von Braun, Michael Reid, Hans Bruntt, Barbara J. Mochejska,
Christophe Alard, and Andrzej Udalski.
Preprint as of 16 Jul 2004 (not yet for general dissemination):
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Last modified: 16 Jul 2004.