Vol. 6 No. 2 April 1, 2010

Journal of Double Star Observations

Page 152

A New Double Star from Lunar Occultations:
HIP 87306
Dave Herald, Canberra, Australia
M. Kashiwagura, Oe, Yamagata, Japan
Brian Loader, Darfield, New Zealand
Steve Messner, Northfield, MN, USA
Robert Sandy, Blue Springs, MO, USA
H. Togashi, Oe, Yamagata, Japan
International Occultation Timing Association (IOTA

Abstract: A lunar occultation of HIP 87306 (= ZC2564, star #2564 in Robertson’s Zodiacal
Catalog of 1940) observed on 2009 Aug 2 showed this star to be a double star with a separation of 0.086². Two video observations made in 2003 were subsequently identified and retrieved, enabling a measurement for that epoch to also be made.

Observation
On 2009 Aug 2 Messner and Sandy observed alunar occultation of HIP 87306 (=ZC 2564) using(respectively) a 45 cm and a 20 cm telescope andvideo. The occultation light curve of both observers
showed a clear step event, as shown in their light
curves, Figure 1.
Follow-up observations were made in Japan on
2009 Aug 29, by H. Togashi and M. Kashiwagura –with neither observer recording a step event.
A check of past occultation observations identified
a video observation by Herald on 2008 May 22 which
on review showed a probable short step event. (Thisobservation has not been used in this analysis; thelunar limb was aligned similar to the observations ofTogashi and Kashiwagura.) Also identified were video
observations by Sandy on 2003 May 18 and 2003 July
12. These were retrieved, and measured using current
measurement techniques. The vector angles for the2003 events differed by 85º, allowing for a good solution – assuming minimal change over the two months
between the occultations. {The solution below indicates the pair has been closing at a rate of 0.005"/year,with no change in position angle}
The double star characteristics were derived using

the standard analysis of the observations described by
Herald (2009). For the 2009 occultations, Figure 2
shows the location of the lunar limb relative to theprimary star at the time of the occultation of the secondary star. The image width is 0.30".
The derived double star solutions for the two epochs are:
StarHIP 87306 = ZC 2564 = HD
162083 = SAO 185826 = CD-27º
11991 = CPD-27º 5802
Coordinates (J2000)
17h 50m 21.14s, -27º 03’ 42.0²
Spectral type A3
Mag A
7.6 ±0.1 (V)Mag B
7.8 ±0.1 (V)Epoch2009.62
Separation
0.086" ±0.002²
Position Angle 195.30º ± 0.33º
Observers
S. Messner, R. Sandy, H. Togashi
and M. Kashiwagura
Epoch2003.44
Separation
0.116"
Position Angle : 196.0º
Observer
R SandyVol. 6 No. 2 April 1, 2010

Journal of Double Star Observations

Page 153

A New Double Star from Lunar Occultations: HIP 87306

Figure 1: Light curves of Messner and Sandy on 2009 Aug 2. The step event is at a height of about 2500 on Messner’s curve, and70 on Sandy’s curve.

The two solutions suggest the star is closing at arate of 0.005" per year, with no change in position angle.

References
Herald, D., 2009, "SAO97883 – A New Double star",
JDSO, 5, 208-210.
Robertson, J., 1940, "Catalog of 3539 Zodiacal Stars
for the Equinox 1950.0", Astronomical Papers prepared for the use of the American Ephemeris andNautical Almanac, Vol 10, Part II.

Figure 2: Plot of the lunar limb at the time of the 2009 occultations. (3) = Messner on July 12, (4) = Sandy on July 12. The othertwo lines are from Togashi and Kashiwagura on Aug 29.