Observations of Binary Stars With the Differential Speckle Survey Instrument. Iii. Measures Below the Diffraction Limit of the Wiyn Telescope

Abstract

In this paper, we study the ability of CCD-and electron-multiplying-CCD-based speckle imaging to obtain reliable astrometry and photometry of binary stars below the diffraction limit of the WIYN 3.5 m Telescope. We present a total of 120 measures of binary stars, 75 of which are below the diffraction limit. The measures are divided into two groups that have different measurement accuracy and precision. The first group is composed of standard speckle observations, that is, a sequence of speckle images taken in a single filter, while the second group consists of paired observations where the two observations are taken on the same observing run and in different filters. The more recent paired observations were taken simultaneously with the Differential Speckle Survey Instrument, which is a two-channel speckle imaging system. In comparing our results to the ephemeris positions of binaries with known orbits, we find that paired observations provide the opportunity to identify cases of systematic error in separation below the diffraction limit and after removing these from consideration, we obtain a linear measurement uncertainty of 3-4 mas. However, if observations are unpaired or if two observations taken in the same filter are paired, it becomes harder to identify cases of systematic error, presumably because the largest source of this error is residual atmospheric dispersion, which is color dependent. When observations are unpaired, we find that it is unwise to report separations below approximately 20 mas, as these are most susceptible to this effect. Using the final results obtained, we are able to update two older orbits in the literature and present preliminary orbits for three systems that were discovered by Hipparcos.

HAT-P-67b: An Extremely Low Density Saturn Transiting an F-subgiant Confirmed via Doppler Tomography∗

“…In order to detect possible neighboring stars that may be diluting the photometric transits, we obtained optical and nearinfrared imaging of HAT-P-67 using the Clio2 near-IR imager (Freed et al 2004) on the MMT 6.5 m telescope on Mt.Hopkins in Arizona; together with the Differential Speckle Survey Instrument (DSSI; Howell et al 2011;Horch et al 2012Horch et al , 2011; and the WIYN High-Resolution Infrared Camera (WHIRC), both of which are on the WIYN3.5 m telescope 15 at Kitt Peak National Observatory in Arizona.…”

“…These images were searched for companions, but none were detected. Based on this, the s 5 lower limits on the differential magnitude between a putative companion and the primary star were determined as a function of angular separation as described in Horch et al (2011). Based on these observations, we exclude neighbors with D < m 2.56 at 692 nm or D < m 2.80 at 880 nm down to a limiting separation of  0.…”

Observations of Binary Stars With the Differential Speckle Survey Instrument. V. Toward an Empirical Metal-Poor Mass–luminosity Relation

“…Table 1 have separations below the diffraction limit. We have discussed this type of situation in Horch et al (2006a) and Horch et al (2011b), where we find in the latter reference that comparing the results in the two channels of the instrument allows us the ability to distinguish between elongation of speckles due to residual atmospheric dispersion and that due to the presence of an unresolved companion. For the measures below the diffraction limit in Table 1, the consistency in the separation determination between both channels of the instrument gives good that we are indeed measuring the presence of an unresolved companion.…”

Observations of Binary Stars with the Differential Speckle Survey Instrument. VII. Measures from 2010 September to 2012 February at the WIYN Telescope

“…This program has contributed a large amount of relative astrometry and photometry data as well as about two dozen orbits and total mass estimates. Some of the smallest separation systems that we have successfully observed at WIYN have had separations below the diffraction limit of ∼50 mas at 692 nm (Horch et al 2011b), which has led to follow-up observations at larger telescopes and the determination of a handful of short-period orbits, with periods of a few months to a few years (Horch et al 2015a). In the area of exoplanet host star observations, we have developed a methodology for companion detection from reconstructed images obtained from speckle data (Horch et al 2011;Howell et al 2011), and used this to estimate the fraction of Kepler exoplanet hosts that also have a stellar companion .…”