Observation and analysis of R2987 on Jun. 1 and Aug. 22, 2010 (UTC)

Nov. 27, 2010
Kazuhisa Miyashita



H. Karasaki(Nerima, Tokyo) observed two events of this star on Jun. 1 and Aug. 22. E. Katayama(Mitaka, Tokyo), K. Ushizaka(Sendai, Miyagi), M. Ishida(Moriyama, Shiga) also observed on Aug. 22.
An astrometric solution of this double star's components was made by B. Loader who is the IOTA double star coordinator. As a result of the solution, an accurate position of component was obtained.

Separation Position angle
  Otained    1.615+/-0.017"    192.02+/-0.23  degrees
  From orbit    1.641"    189.89 degrees 

Ishida's observation doesn't have a step. The slope of the lunar limb of the event is from -5 to -10 degrees. If it is geven -4 degree for the limb, Ishida's obervation fit to this solution very well.

The catalogue's detail of R2987

Catalogue details
 XZ 28475 = SAO 163614 = ZC 2987 = rho Capricorni
 RA =  20 28 51.6114   PM = -0.00106s
Dec = -17 48 49.433    PM = -0.0116"
 Mv = 4.86, Mb = 0.00, Mr = 0.00    Spectrum F3    Dia: .0000" [Estimated]

Star is the mean position of AB
Name    Cmpt   Yr1  Yr2: PA1   PA2  :   Sep1   Sep2  :  Mag1  Mag2:     #1      #2  mean
SHJ 323 AB    1782 2004: 174.0 194.0:   3.000   1.300:  4.97  6.88: R  2987 X174647 mean
BU   61 AC    1871 1998: 135.0 150.0:  30.000  54.600:  4.97 13.30: R  2987  ------
SHJ 323 AD    1800 2001: 150.0 150.0: 228.200 258.700:  4.97  6.68: R  2987 R  2990
BU   61 BC    1898 1915: 150.0 148.0:  52.800  53.100:  6.88 13.20: X174647  ------
DOB  13 DE    1913 1998: 106.0  96.0:  59.400  54.300:  6.55      : R  2990  ------

WDS Discoverer codes
BU   Burnham, S.W.                       
DOB  Doberck, W.A.                       
SHJ  South, J. & Herschel, J.            

Orbital elements
Name  Cmpt     Period       a"        i       node      T        e       peri
SHJ 323 AB     278.00000  1.877000 113.3000 162.0000 1965.00000 0.91000 144.5000
Year   PA    Sep
2008 190.68  1.56
2009 190.38  1.59
2010 190.09  1.62
2011 189.81  1.65
2012 189.54  1.68
-------------------------------------------------------------------------------------------
Interferometric catalogue entries

202851.62-174849.2  ADS 13887                 SHJ 323AB                 HD 194943    HIP 101027        
 20289-1749 N O
    Date       PA              Sep                  M1             M2
  1982.7598   204.8     .      0.760      .          .      .       .      .              n  3.8   1  Hrt2000a Sch    
  1983.4258   205.6     .      0.784      .          .      .       .      .       549  22   3.8   1  McA1987b Sch    
  1991.25     198.6     .      1.013      .         5.01    .      7.06    .       550       0.3   1  HIP1997a Thp    
  1991.25        .      .       .         .         5.007  0.003   7.059  0.020    511 222   0.3   1  HIP1997f Thp    
  1991.25        .      .       .         .         4.99    .      6.94   0.01     505  97   0.3   1  Fab2000a Thp    
  1991.25        .      .       .         .         5.36    .      7.64   0.01     435  70   0.3   1  Fab2000a Thp    
  1991.3903   198.9     .      1.014      .          .      .       .      .       549  22   4.0   1  Hrt1993  Sch    
  1991.67     201.9     .      1.079      .         4.97    .      6.88    .       530 100   1.4   1  TYC2000a Tty    
  1991.7151   198.8     .      1.026      .          .      .       .      .       549  22   4.0   1  Hrt1996b Sch    
  1994.5246   198.7     .      1.163      .          .      .       .      .       503  40   0.8   1  Hor2006c Spe    
  1994.5246   198.2    0.5     1.196     0.008       .      .       .      .       503  40   0.8   1  Hor1996  Spe    
  1999.       195.      .      1.23       .          .      .      1.30    .      2100       3.6   1  Boc2001  Uds    
  1999.7672   195.1     .      1.26       .          .      .       .      .       541  88   0.6   1  Hor2000  Spe    
  1999.7836   194.4     .      1.27       .          .      .       .      .       541  88   0.6   1  Hor2000  Spe    
  2002.644    193.6     .      1.34       .          .      .       .      .       550  24   0.7   4  WSI2004a Sus    
  2004.669    193.9     .      1.30       .          .      .       .      .       550  24   0.7   1  WSI2006a Sus    


Observation and orbit




Double star solution by IOTA coordinator



Comment from Brian Loader (double star coordinator).
With 4 positive observations from Japan this year I have combined them to get a solution for the pair. They give a separation of 1.615+/-0.017" at PA 192.02+/-0.23 degrees. This is strongly dependent on Karasaki-san's observation of 2010 June 1 as those on August 22 are close in position on the moon. The result is quite close to the calculated 1.641" at 189.89 degrees.

Using Dave Herald's earlier observation of 2009 September 1 reduces the separation to 1.505" but makes little difference to the PA. I think my observation of the same date should be dropped. The seeing conditions were very poor and I while I think there is a step, its start is too uncertain.

Light curve and explanation


i) Karasaki's observation on Jun. 1, 2010
Raw light curve.






The CCD image of this star is slightly saturated. It isn't suitable for accurate photometry of components.


ii) Karasaki's observation on Aug. 22, 2010
Raw light curve.









This Karasaki-san's observation has very small noise. The light of bright star and stable air make this analysis an accurate measurement on time and on magnitude. The _raw light curve_ is Karasaki-san's own analysis with field by field measurement. It also has rather small noise.
From above, I think the event time which obtained from diffraction fitting has a small error less than several milli-seconds. So, I describe this report on event time with milli-second accuracy.
ii) Katayama's observation on Aug. 22, 2010
Raw light curve.



Katayama-san uses SONY TRV900 camcorder which has _progressive mode_. The progressive mode is same as two frames integration. So, this report on timing has 1/15 second accuracy.

iii) Ushizaka's observation on Aug. 22, 2010
Light curve with diffraction simulation.



As a result of Limovie analysis, very small but quite obvious step was appeared on the light-curve.

iv) Ishida's observation on Aug. 22, 2010
Light curve with diffraction simulation.



This Ishida-san's observation has no-instantaneous light-change. And the light curve well fit to diffraction simulation.