Speckle interferometry at SOAR

Speckle interferometry attains diffration-limited resolution by processing short-exposure images taken with high magnification. This method works on relatively bright stars. The High-Resolution Camera (HRCAM) at the SOAR 4.1-m telescope is used since 2008 for speckle interferometry. Presently it is mounted at the SOAR Adaptive Module (SAM). This is a restricted-use instrument supported by its PI Andrei Tokovinin.

Brief description. The figure below shows the HRCAM (see also the instrument manual ). The data are transmitted by an extended USB link to a PC and registered as image cubes, typically 400 frames of 200x200 pixels each ( speckle movie ). The data are procesed by IDL programs to compute power spectrum and auto-correlation function, ACF. A binary star is detected by "fringes" in the power spectrum or by symmetric peaks in the ACF. Its parameters are measured by fitting a model to the data. Details of the data processing are explained in the paper.

speckle data flow

Capabilities. Most observations are made in the Stroemgren y or Cousins I filters with resolution of 25 mas and 36 mas, respectively. The maximum detectable magnitude difference can reach 6 mag at 1 arcsecond, it is less at smaller separations (in the Figure below, asterisks are detections of simulated binaries, squares are non-detections, and the curve is the estimated limiting magnitude difference) and in the I filter. The limiting magnitude strongly depends on the seeing and is deeper in the I band. Stars as faint as V=12 mag were observed under good seeing, but V=10 mag is a more realistic limit under median seeing. Typically, some 100 to 150 stars per night are observed. The effficiency is determined by the telescope pointing and target acquisition time, the data cubes are collected for only a few seconds. The raw data are processed by A. Tokovinin using his software. The data products are measurements of resolved binary and triple stars and the detection limits at 0.15 and 1 arcsec separation for unresolved targets.

In March 2017, the failed Luca-S detector was replaced by the iXon-888 camera, on loan from the UNC (courtecy N. Law). It has a higher quantum efficiency, so a gain of ~1 magnitude in sensitivity is expected.

dynamic range

Example. HIP 83716 is a 1-arcsec visual binary star known since 1881. Its secondary component is itself a close pair Ba,Bb discovered at SOAR in 2009. Further monitoring at SOAR revealed the fast orbital motion, allowing to compute the orbit of Ba,Bb with a period of 6.5yr and semi-major axis of 70 mas. See also the NOAO press release with animation.

TOK 52

Publications. More than 8000 measurements of binary stars were made at SOAR by 2017, several dozens of new multiple systems were discovered. The list of publications below is in chronological order. Please, take note of the study of systematic errors of HRCAM. Typically they are less then 0.1 deg in angle and 0.2% in scale; small systematic errors in the published data can be corrected using this document.

  1. Tokovinin A., Cantarutti R. First speckle-interferometry at SOAR telescope with electron multiplictaion CCD. 2008, PASP, 120, 170-177 [PDF, 338K]
  2. Tokovinin A., Mason B.D., Hartkopf W.I. Speckle interferometry at Blanco and SOAR telescopes in 2008 and 2009. AJ, 2010, 139, 743-756. [PDF, 937K] . Electronic tables (ASCII): table4 (measurements), table5 (unresolved stars), table7 (notes).
  3. Mason B.D., Hartkopf W.I., Tokovinin A. Binary Star Orbits. IV. Orbits for 18 Southern Interferometric Pairs. 2010, AJ, 140, 735-743.
  4. Tokovinin A. Cantarutti R., Tighe R., Schurter P., van der Bliek N., Martinez M., Mondaca E. High-resolution imaging at the SOAR telescope. 2010, PASP, 122, 1483-1494 [PDF, 421K] ArXiv: 1010.4176
  5. Hartkopf, W.I., Tokovinin, A., Mason, B.D. Speckle Interferometry at SOAR in 2010 and 2011: Measures, Orbits, and Rectilinear Fits. 2012, AJ, 143, 42 [PDF, 1.2M]
  6. Tokovinin, A. Speckle interferometry and orbits of "fast" visual binaries. 2012, AJ, 144, 56 [PDF, 298K] ArXiv:1206.1882
  7. Tokovinin, A. Kappa Fornaci, a triple radio-star. 2013, AJ, 145, 76 [PDF, 250K] ArXiv:1301.1352
  8. Tokovinin, A. From binaries to multiples I: Data on F and G dwarfs within 67 pc of the Sun. AJ, 2014, 147, 86 [PDF, 371K] The electronic tables are available here. ArXiv:1401.6825
  9. Tokovinin, A., Mason, B. D., Hartkopf, W. I. Speckle interferometry at SOAR in 2012 and 2013. 2014, AJ, 147, 123. ArXiv:1403.4970
  10. Tokovinin, A. Gorynya, N.A., Morrell, N.I. The quadruple system ADS 1652. 2014, MNRAS, 443 (2): 3082-3089 [PDF, 192K]
  11. Tokovinin, A. Imaging survey of subsystems in secondary components to nearby southern dwarfs. 2014, AJ, 148, 72 [PDF, 228K] , ArXiv:1407.6045
  12. Tokovinin, A., Latham, D. W., Mason, B. D. The unusual quadruple system HD 91962 with a "planetary" architecture. 2015, AJ, 149, 195 [PDF, 184K] ArXiv: 1504.06535
  13. Tokovinin, A., Mason, B.D., Hartkopf, W.I., Mendez, R.A., Horch, E.P. Speckle interferometry at SOAR in 2014. 2015, AJ, 150, 50 [PDF, 338K] , ArXiv: 1506.05718
  14. Schmitt, J. R., Tokovinin, A., Wang, Ji, Fischer, D. A., Kristiansen, M. R., LaCourse, D. M., Gagliano, R., Tan, A. J. V., Schwengeler, H. M., Omohundro, M. R., Venner, A., Terentev, I., Schmitt, A. R., Jacobs, T. L., Winarski, T., Sejpka, J., Jek, K., Boyajian, T. S., Brewer, J. M., Ishikawa, S. T., Lintott, C., Lynn, S., & Weiksna, A. Planet hunters X: searching for nearby neighbors of 75 planet and eclipsing binary candidates from the K2 Kepler extended mission. 2016, AJ, 151, 159
  15. Tokovinin, A., Mason, B.D., Hartkopf, W.I., Mendez, R.A., Horch, E.P. Speckle interferometry at SOAR in 2015. AJ, 151, 153
  16. Tokovinin, A. Orbits of subsystems in four hierarchical multiple stars. 2016, AJ, 152, 10
  17. Tokovinin, A. Orbits of four young triple-lined multiple systems. 2016, AJ, 152, 11
  18. Tokovinin, A. New orbits based on speckle interferometry at SOAR. 2016, AJ, 152, 138
  19. Tokovinin, A. The triple system Zeta Aquarii. 2016, ApJ, 831, 151
  20. Tokovinin, A. & Latham, D. W. Relative orbit orientation in several resolved multiple systems. 2017, ApJ, 838, 54
  21. Gomez, J., Docobo, J. A., Campo, P. P., Mendez, R. A Orbits of 12 Southern Binaries Based on Soar Speckle Observations. 2016, AJ, 152, 216
  22. Briceno, C. & Tokovinin, A. New binaries in the \epsilon Cha association. 2017, AJ, in preparation.

Updated: Apr 11, 2017 A. Tokovinin