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Vol. 6 No. 1 January 1, 2010 Journal of Double Star Observations Page 88 New Double Stars from Asteroidal Occultations, 1971 - 2008 Dave Herald, Canberra, Australia International Occultation Timing Association (IOTA) Robert Boyle, Carlisle, Pennsylvania, USA Dickinson College David Dunham, Greenbelt, Maryland, USA; Toshio Hirose, Tokyo, Japan; Paul Maley, Houston, Texas, USA; Bradley Timerson, Newark, New York, USA International Occultation Timing Association (IOTA) Tim Farris, Gallatin, Tennessee, USA Volunteer State Community College Eric Frappa and Jean Lecacheux, Paris, France Observatoire de Paris Tsutomu Hayamizu, Kagoshima, Japan Sendai Space Hall Marek Kozubal, Brookline, Massachusetts, USA Clay Center Richard Nolthenius, Aptos, California, USA Cabrillo College and IOTA Lewis C. Roberts, Jr., Pasadena, California, USA California Institute of Technology/Jet Propulsion Laboratory David Tholen, Honolulu, Hawaii, USA University of Hawaii E-mail: [email protected] Abstract: Observations of occultations by asteroids and planetary moons can detect double stars with separations in the range of about 0.3” to 0.001”. This paper lists all double stars detected in asteroidal occultations up to the end of 2008. It also provides a general explanation of the observational method and analysis. The incidence of double stars with a separation in the range 0.001” to 0.1” with a magnitude difference less than 2 is estimated to be about 1%. Vol. 6 No. 1 January 1, 2010 Journal of Double Star Observations Page 89 New Double Stars from Asteroidal Occultations, 1971 - 2008 tions. More detail about the method of analysis is set Introduction out in the Appendix. Asteroids and planetary moons will naturally oc- cult many stars as they move through the sky. The big- Results – 1971 to 2008 gest challenge in observing such occultations is to accu- Double stars have been detected in occultations by rately predict the time of the occultation event and the asteroids and planetary satellites since 1971. While location of the shadow path as it crosses the Earth. some of these detections have been published in the Since the Hipparcos mission, and the availability of literature, almost none are listed in the Interferometric catalogues like Tycho2 and UCAC2, predictions of oc- Catalogue or the Washington Double Star catalogue. cultations by asteroids and planetary moons with un- Table 1 presents the measures of all double stars ob- certainties of 100km in the path location have become served or discovered in these occultations up to the end routine. For the last few years almost 200 occultation of 2008 – whether or not they have been reported else- events per year have been observed around the world. where. They include the bright stars γ Gem (HIP In the early days of asteroidal occultations, most 31681), λ Vir (HIP 69974), β2 Sco (HIP 78821), 1 Vul observations were made visually. For the last several (HIP 78821) and 16 Psc (HIP 116495). References are years the great majority of observations are made us- given for those events known to have been published in ing video cameras with a time signal obtained from the the literature. GPS satellite system inserted into the video stream. At the time these observations were made, little Compared to visual observing, video provides enhanced attention was given to determining the star magni- time resolution, and a record that can be measured to tudes. Component magnitudes determined from photo- deduce accurate event times. Asteroid profiles can be electric recordings were published for the three events measured at the 1-km scale using small telescopes and listed below observed before 1983. Most of the other inexpensive video detectors, as has been illustrated by occultations listed were video recorded, but until re- Timerson [1]. cently there was no easy way to quantify the magni- In a typical occultation the asteroid is not visible. tudes of the component stars from video recordings. The occultation is recorded as the sudden disappear- The authors plan to digitize the older video recordings ance of the star, followed some seconds (or tens of sec- and publish a list of component magnitudes for most of onds) later with a sudden reappearance of the star. For the listed events in a future publication. a small number of events, the occultation may involve: There are three types of entries in Table 1: A partial drop in light, followed by a complete drop Single-line entry. The double star solution for in light. The order of the light change may be either these stars is unique and well determined. the same, or reversed, when the star reappears; or Single-line entry with a 3-point range (TYC There is simply a partial drop in light. 5614-00026-1 and HIP 38465). For these stars These are characteristics of the star being a double the data is insufficient to provide a unique so- star – with the changes of light occurring as the two lution, but are constrained by the geometry of stars are sequentially hidden by the asteroid. When the event. The values given are the extreme this occurs, a double star is typically ‘discovered’. If values in PA (where the separation is also there are several observers at spaced locations, it is greatest) - and the intermediate value of PA possible to combine the observations in a way that al- where the separation is least. If the asteroid lows the PA and separation to be solved. The typical profile is significantly elliptical, the range in measurement accuracy obtained is a milli-arcsec in PA can be significantly greater than 180 de- separation, and a few degrees in PA. grees. The values are given in order of increas- The practical minimum separation detectable by ing PA. this method is about 1 milli-arcsec – a limit arising Double-line entry (TYC 1808-00641-1 and HIP from the time resolution of the video cameras being 69974). For these stars there are two well- used, and Fresnel diffraction. The maximum separa- determined solutions. The observations are tion detectable is limited by the apparent diameter of insufficient to resolve the ambiguity, or associ- the asteroid involved. If the diameter is less than the ate a formal uncertainty with the solution. separation, an occultation of only one star might occur – with there being no data to measure the separation On the night following the occultation of TYC 1879 from the second star, but these cases usually involve (Continued on page 91) doubles already known from visual or other observa- Vol. 6 No. 1 January 1, 2010 Journal of Double Star Observations Page 90 New Double Stars from Asteroidal Occultations, 1971 - 2008 Table 1: Double stars discovered or measured in asteroidal occultations: 1971 - 2008 Star number, Position Angle Angular Separa- Publ J2000 RA/Dec (PA) Date Asteroid tion (masec) Ref WDS/4thInterfer. ID (degrees) TYC 0622-00932-1 2005 Nov 11 01 46 51.55 +08 16 08.3 248.7 ± 2.5 18.8 ± 1.1 116 Sirona - 2005.865 - TYC 1808-00641-1 278.1 or 5.1 or 2008 Jan 14 03 53 33.26 +27 18 06.1 1258 Sicilia - 272.1 25.1 2008.034 - TYC 1879-02151-1 2006 Sep 19 06 31 17.55 +22 47 50.9 240.0 ± 0.5 261.9 ± 1.5 144 Vibilia - 2006.715 COU 581 TYC 1908-00844-1 2006 Nov 29 07 14 41.22 +29 52 38.7 302.9 ± 0.1 170.4 ± 0.3 578 Happelia - 2006.909 - TYC 1947-00293-1 2006 Dec 18 08 25 01.65 +28 33 55.3 105.6 106.3 87 Sylvia 2 2006.961 - TYC 2411-01645-1 1996 Nov 25 05 31 33.75 +35 01 45.8 248.7 ± 0.5 6.3 ± 0.1 93 Minerva - 1996.899 - TYC 2916-02502-1 1999 Sep 21 05 52 44.43 +40 10 45.0 70.4 ± 3.9 57.5 ± 2.3 375 Ursula - 1999.719 - TYC 5614-00026-1 41.0 - 7.0 - 2002 May 10 15 54 10.20 -09 44 49.8 165 - 270 - 36 638 Moira - 16.0 2002.353 - TYC 6154-00401-1 2003 Apr 21 14 41 45.96 -16 36 09.2 81.9 ± 1.4 5.4 ± 0.2 210 Isabella - 2003.301 - HIP 26902 2005 Dec 1 05 42 41.48 +36 08 59.4 30.3 ±19.7 1.1 ± 0.3 99 Dike 3 2005.915 - HIP 30570 2001 Sep 7 06 25 32.94 +23 19 37.8 344.9 ± 1.3 36.5 ± 3.7 9 Metis 4 2001.682 MCA 26 HIP 31681 1991 Jan 13 06 37 42.70 +16 23 57.3 126.3 ± 4.7 63.4 ± 1.0 381 Myrrha 5 1991.032 BUP 90A HIP 31694 1978 Dec 11 06 37 51.49 +06 40 59.7 26.1 ± 1.4 45.9 ± 2.1 18 Melpomene 6 1978.942 HD 47239 HIP 32525 2007 Mar 28 06 47 13.67 +16 55 34.9 70.9 ± 1.9 9.7 ± 0.3 72 Feronia - 2007.235 - HIP 34452 1974 Aug 29 Saturn 5 07 08 30.95 +21 59 09.4 89.0 39.0 7 1974.657 (Rhea) OCC 337; HIP 36189 2003 Mar 23 704 Interam- 07 27 09.12 +11 57 18.0 230.7 ± 2.5 12.8 ± 0.5 - 2003.221 nia HD 58686 Table continued on next page. Vol. 6 No. 1 January 1, 2010 Journal of Double Star Observations Page 91 New Double Stars from Asteroidal Occultations, 1971 - 2008 Table 1 (continued): Double stars discovered or measured in asteroidal occultations: 1971 - 2008 Star number, Position Angle Angular Separa- Publ J2000 RA/Dec (PA) Date Asteroid tion (masec) Ref WDS/4thInterfer.
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