U Ophiuchi (HD156247)

Aim of the campaign

U Ophiuchi is a triple star system in which the third star induces periodic variations in the observed times of eclipses as it orbits the eclipsing pair. The initial aim is to determine accurate Time of Minimum for several primary and secondary eclipses. We will repeat TOM measurements each season in order to determine the Light Travel Time (LTT) effect and apsidal motion caused by the third star.

{tab Data}

STAR	V Max	RA 2000	BRNO epoch (HJD)	BRNO period	Primary / secondary
U Oph	5.84	17h16m31.7s	2444416.3864	1.6773462	p
			2444417.2251	1.6773462	s
	V Min	DEC 2000	Krakow epoch (HJD)	Krakow period
	6.56	+01° 12′ 8″	2452501.1880	1.6773395

Recent data: 2455751.041740 (0.000111) TOM for secondary eclipse (M. Blackford)

{tab Light Curve}

From Shobbrook, R.R., The Journal of Astronomical Data 10, 1 (2004)

{tab Observing Notes}

No bright field stars close enough to interfere with measurements.

{tab Finder Chart}

The field of U Oph is shown in the plot below.

{tab Comparison Star Data}

Please use the four comparison stars labled on the chart and catalogue values listed below.

Comp Star	Name	RA (J2000)	DEC (J2000)	V	B-V	V-Rc
1	HD155646	17 12 54.42	+00 21 07.9	6.644	0.493	0.251
2	HD155231	17 10 15.56	+00 28 53.8	6.818	0.964	0.473
3	HD156458	17 17 36.98	+01 44 33.1	6.855	0.399	0.336
4	HD157347	17 22 51.34	-02 23 19.3	6.278	0.688	0.358

{tab Preliminary Results}

The plot below shows a secondary minimum observed by Mark Blackford at HJD 2455751.041740 (0.000111) as determined using PERANSO which is 6min 26sec earlier than the BRNO prediction and 12min 11sec later than the Krakow prediction.

{/tabs}