eclipsing variable star

or eclipsing binary

Binary star in an orbit whose plane passes through or very near Earth. An observer on Earth sees one star pass periodically in front of the other and diminish its light through an eclipse. The star Algol, in the constellation Perseus, was the first such star recognized (1782); thousands are now known. By combining the brightness variations with spectroscopic information for both stars, astronomers can determine the mass and size of each star. Seealso variable star.

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The Sagittarius Window Eclipsing Extrasolar Planet Search, or SWEEPS, was a 2007 project using the Hubble Space Telescope's Advanced Camera for Surveys wide field channel to monitor 180,000 stars for seven days to detect extrasolar planets via the transit method. The stars were located in the Sagittarius-I Window region 27,000 light years from Earth near the Milky Way's central bulge, a region of the galaxy that had not previously been systematically searched for exoplanets before.

Sixteen candidate planets were discovered with orbital periods ranging from 0.6 to 4.2 days. Planets with orbital periods less than 1.2 days have not previously been detected, and have been dubbed "ultra-short period planets" (USPPs) by the search team. USPPs were discovered only around low-mass stars, suggesting that larger stars destroyed any planets orbiting so closely or that planets were unable to migrate as far inward around larger stars.

Planets were found with roughly the same frequency of occurrence as in the local neighborhood of Earth.

SWEEPS-4 and SWEEPS-11 orbited stars that were sufficiently visually distinct from their neighbors that followup observations using the radial velocity method were possible, allowing their masses to be determined.

Planet	Period (days)	Mass (MJ)	Radius (RJ)
SWEEPS-01	1.56		1.01 ± 0.13
SWEEPS-02	0.912		1.37 ± 0.25
SWEEPS-03	1.27		0.87 ± 0.11
SWEEPS-04	4.20	<3.8	0.81 ± 0.1
SWEEPS-05	2.313		1.09 ± 0.1
SWEEPS-06	3.039		0.82 ± 0.21
SWEEPS-07	1.747		0.9 ± 0.11
SWEEPS-08	0.868		0.98 ± 0.09
SWEEPS-09	1.617		1.01 ± 0.12
SWEEPS-10	0.425	>1.6	1.24 ± 0.23
SWEEPS-11	1.796	9.7 ± 5.6	1.13 ± 0.21
SWEEPS-12	2.952		0.91 ± 0.11
SWEEPS-13	1.684		0.78 ± 0.12
SWEEPS-14	2.965		0.93 ± 0.09
SWEEPS-15	0.541		1.37 ± 0.3
SWEEPS-16	0.969		1.4 ± 0.18

References