Vol. 2 No. 3 Summer 2006 Journal of Double Star Observations Page 79 Divinus Lux Observatory Bulletin: Report #5 Dave Arnold Program Manager for Double Star Research 2728 North Fox Fun Drive Flagstaff, AZ 86004 E-mail: [email protected] Abstract: This report contains theta/rho measurements from 94 different double star systems. The time period spans from 2005.351 to 2005.479. All measurements were obtained using a 20-cm Schmidt- Cassegrain telescope and an illuminated reticle micrometer. This report represents a portion of the work that is currently being conducted in double star astronomy at Divinus Lux Observatory in Flagstaff, Ari- zona. how well current measurements agree with the com- Introduction puted orbit. The systems mentioned above are all When one is interested in regularly making theta/ fairly bright, thereby enabling one to use an illumi- rho measurements of double stars, which are known nated measuring device if that is desired. to be binary in nature, the thought may be that a As in previous articles, the selected double star large telescope, with expensive accessories, is a pre- systems, which appear in this report, have been taken requisite for engaging in such efforts. While it is true from the 2001.0 version of the WDS CATALOG, with that the majority of binaries, which have had orbital published measurements that are no more recent than elements determined, might be out of reach for those ten years ago. Exceptions to this stipulation include who employ modest instrumentation, there are sev- STF 2140 Aa-B and STF 2272 AB, because the theta/ eral binary systems that can be regularly monitored rho shifts for these visual binaries are large enough to and measured with a small telescope. I am aware of at warrant more frequent measurements. There are also least four systems that have separations of over 10 some noteworthy items that are mentioned in refer- seconds, which could be regularly studied. Addition- ence to the following table. ally, there are another dozen or so that are within As has been reported in previous articles, this one reach of a medium sized telescope. These binaries can lists double stars that have displayed significant be located in SKY CATALOGUE 2000.0, volume 2, in theta/rho shifts, because of the effects of proper mo- the visual binaries section. The four systems with 10+ tion, by one or both of the components. To begin with, seconds of separation are listed in Table 1 below for WFC 310 has undergone a 5 % decrease in separation the convenience of the reader who might like to get and an increase of 2 degrees in position angle, since started with this type of research program. 1970, because of proper motion by the reference point SKY CATALOGUE 2000.0 also provides an star. A large proper motion by the reference point star ephemeris for each listed system, so one can check on has also caused major theta/rho shifts for WFC 359. Since 1902, the separation has increased by 45” and the position angle has increased by 27 degrees. Both of these dou- Name Coordinates Theta Rho Year Measured ble stars have been neglected, and STF 60 AB 00491+5749 318 degrees 12.7 seconds 1999 there is a great need for addi- STF 296 AB 02442+4914 308 degrees 20.5 seconds 1996 tional measurements by others. STF 1321 AB 09144+5241 92 degrees 17.3 seconds 1997 An extremely large proper mo- tion by the reference point star, in STF 275 AB 21069+3845 150 degrees 30.7 seconds 2000 BUP 176, has caused theta/rho shifts of 7 degrees and 16 seconds Table 1: Four binary systems with separation over 10 arc seconds. since the last published measure- Vol. 2 No. 3 Summer 2006 Journal of Double Star Observations Page 80 Divinus Lux Observatory Bulletin: Report #5 ments in 1984. In a like manner, a large proper mo- Four additional double stars, bearing the “WFC” tion shift by the “BC” components, in STN 41 A-BC, prefix, are in need of additional measurements be- has caused theta/rho shifts of 14 degrees and 6.5 sec- cause only a few theta/rho recordings currently exist. onds since 1991. A proper motion shift is also noted As a consequence, the theta/rho measurements for for HLM 7 AB. Since 1983, the theta value has in- WFC 341 (18518-0505) vary by 6 degrees in p.a. and creased by almost 2 degrees, while the rho value has 1” in separation since the first measurements were decreased by 2.7%. SMA 79 has also displayed a note- made in 1892. There are no trends of increasing or de- worthy proper motion shift. Since 1991, the rho value creasing values for either theta or rho because of the has decreased by 3% and the theta value has in- paucity of the data. The theta/rho values listed in the creased by 3 degrees. table match up fairly closely with those that are given An extended length of time, amounting to several in the Hipparcos/Tycho data for this common proper decades since the last published catalog measure- motion pair. ments, has contributed to detectable proper motion The lack of measurements has placed WFC 335 shifts in five additional double stars. As a conse- (18344+0853) is in a similar situation with WFC 341. quence, ES 2664 has displayed a 3.3% decrease in the In this case, the separation value has been recorded rho value since 1934. Similarly, HJ 2823 has shown a with a variance of 1.2" over the past several decades, 4.1% decrease in the rho value since 1922. Also of note with no obvious trend among prior measurements. is the fact that the 1879 theta value for HJ 2823 The rho listing in the table does not match up closer matches the theta value listed in this report more than 5% with any other values in the WDS CATALOG closely than the value reported in 1922. The Hippar- or with Hipparcos/Tycho data. This double star is also cos/Tycho data seems to confirm this finding. Thirdly, a common proper motion pair. the rho value for STF 2057 AC has increased by 10” Similarly, only a few theta/rho measurements ex- since the last published measurements in 1906. ist for WFC 192 (12021+1521) and WFC 348 Fourthly, regarding BUP 177AC, the theta value has (19125+4447). As in the above cases, the theta/rho decreased by 4.5 degrees and the rho value has in- values show a random scattering with no apparent creased by over 7 seconds, since 1912. Finally, for trends. Specifically, for WFC 192, the theta value has HZG 13, a large proper motion by both components been recorded with a variance of 4 degrees, while the has caused a 29 degrees increase in the theta value rho value for WFC 348 has been recorded with a 6.7% and a 5” increase in the rho value, since 1946. variance. These two double stars are also common The fact that older measurements seem to reflect proper motion pairs, and all four of these “WFC” pairs more accuracy than more recent measurements, in have been neglected for many decades. some cases, is relevant to the situation regarding Vat I might also mention that there are discrepancies 2. For this double star, the 1916 measurements ap- in how the WFC double stars are listed in the WDS pear to match more closely with the measurements in CATALOG. The listings that are appearing in my re- this article, and with the Hipparcos/Tycho data, than ports have been taken from the 2001.0 web site cata- do the measurements that were reported in 1941. If log, but the USNO Double Star CD 2001.0 lists a dif- the 1916 measurements have a high degree of reliabil- ferent numerical sequence for the “WFC” doubles. To ity, then this double star would appear to be a rela- avoid confusion, the reader may wish to refer to these tively fixed system. double stars with their coordinates. Orbital motion may be the cause of theta/rho Additionally, WFC 351 (19212-1146) and WFC shifts in some common proper motion pairs that are 363 (19533+0820), which appear in this report, are not listed in the table. STF 2128 might be one such pair, listed in the main catalog of the double star CD. This which has apparently displayed a large enough mo- should probably be addressed because these double tion of this type that can be measured. Since 1995, the stars represent more neglected pairs that are in great separation has increased by 4.4%. Likewise, orbital need of additional measurements. The web site cata- motion might have contributed to a 3 degrees decrease log lists only one previous set of measurements for in the theta value for STF 2228, which also seems to both of these pairs, which were done in 1969 and 1957 be suggested by the Hipparcos/ Tycho data. However, respectively. For WFC 363, as an example, this article the situation for STF 2228 needs further study be- reports a 9 degrees increase in the theta value and a cause the last published catalog measurements were 4% decrease in the rho value since the 1957 measure- in 1905 ments were published. Vol. 2 No. 3 Summer 2006 Journal of Double Star Observations Page 81 Divinus Lux Observatory Bulletin: Report #5 Three measurement listings in the WDS catalog were obtained for this report, while the listing for appear to be anomalous. In regards to BU 242 AD 1990 appears to deviate.