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Speckle Observations and Orbits of Multiple Stars 3 Draft version September 2, 2019 A Preprint typeset using LTEX style emulateapj v. 12/16/11 , SPECKLE OBSERVATIONS AND ORBITS OF MULTIPLE STARS Andrei Tokovinin Cerro Tololo Inter-American Observatory, Casilla 603, La Serena, Chile Mark E. Everett National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85719, USA Elliott P. Horch∗ Department of Physics, Southern Connecticut State University, 501 Crescent Street, New Haven, CT 06515, USA Guillermo Torres Center for Astrophysics — Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA David W. Latham Center for Astrophysics — Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA Draft version September 2, 2019 ABSTRACT We report results of speckle-interferometric monitoring of visual hierarchical systems using the newly commissioned instrument NESSI at the 3.5-m WIYN telescope. During one year, 390 measurements of 129 resolved subsystems were made, while some targets were unresolved. Using our astrometry and archival data, we computed 36 orbits (27 for the first time). Spectro-interferometric orbits of seven pairs are determined by combining positional measurements with radial velocities measured, mostly, with the Center for Astrophysics digital speedometers. For the hierarchical systems HIP 65026 (periods 49 and 1.23 years) and HIP 85209 (periods 34 and 1.23 years) we determined both the inner and the outer orbits using astrometry and radial velocities and measured the mutual orbit inclinations of 11◦.3±1◦.0 and 12◦.0±3◦.0, respectively. Four bright stars are resolved for the first time; two of those are triple systems. Several visual subsystems announced in the literature are shown to be spurious. We note that subsystems in compact hierarchies with outer separations less than 100 au tend to have less eccentric orbits compared to wider hierarchies. Keywords: binaries:visual 1. INTRODUCTION alternative channel of close-binary formation via dynam- We know that the majority of multi-planet systems ical evolution of misaligned triple systems, also rele- are co-planar (Fabrycky et al. 2014), as well the plan- vant for formation of hot Jupiters (Fabrycky & Tremaine ets found around eclipsing binaries (e.g. Kepler-1647, 2007), is not efficient enough. Kostov et al. 2016). Low-mass triple systems with outer The distribution of relative inclinations in triple sys- separations of the order of ∼50 au or less also have a tems is an essential input to those studies. Orbits of strong alignment trend, even though the typical relative binary and triple systems contain a fossil record of the angles between orbital planes are still substantial, ∼30◦ conditions prevailing during their formation. While mi- arXiv:1908.11445v1 [astro-ph.SR] 29 Aug 2019 (Tokovinin 2017). Formation of companions in a mas- gration in a disk produces quasi-coplanar systems, mis- sive circumstellar disc, their subsequent growth and in- aligned systems diagnose alternative formation mecha- ward migration seem to match the prevalent architecture nisms. For example, frequent dynamical interactions be- of compact “planetary-like” (i.e. quasi-coplanar) triple tween stars in dense clusters or accretion of misaligned systems. One of the natural outcomes of this scenario gas produce multiple systems with misaligned orbits, bi- are close (eclipsing) binaries surrounded by a remnant naries with misaligned stellar spins and, later, planetary disk, from which the circumbinary planets condense, as systems that are not confined to one plane. demonstrated by the Kepler discovery of such systems. Although stellar triples have been known for a long Recent modeling by Moe & Kratter (2018) shows that time, advances in the observational techniques have only recently given access to the most interesting close migration in a disc is also necessary for explaining the ∼ observed fraction of solar-type close binaries, while the and fast systems with spatial scales of 10 au, match- ing the typical size of discs and planetary systems. Electronic address: [email protected] For some of those, it has been possible to determine Electronic address: [email protected] both inner and outer orbits and their relative orienta- ∗Adjunct Astronomer, Lowell Observatory Electronic address: [email protected] tion (Tokovinin et al. 2015; Tokovinin & Latham 2017). Electronic address: [email protected] However, much work remains to be done. Ongoing high- Electronic address: [email protected] 2 Tokovinin et al. resolution surveys, particularly in the solar neighbor- right). Further information on NESSI is provided by hood, continue to discover compact hierarchical systems Scott et al. (2018). (Horch et al. 2019). Follow-up astrometric monitoring on a time scale from years to decades is needed to map 2.2. Observing procedure the orbital motion and to define the architecture of those On each target, we registered sub-frames of 256×256 systems. These data, in turn, will provide insights on the ′′ pixels (4. 8 on the sky) with a short exposure of 40ms. formation history of stars and planets. The electron multiplication gain was adjusted depending The highly efficient speckle program at the South- on the star brightness. A sequence of 1000 such frames ern Astrophysical Research Telescope (SOAR) assigns (the data cube) is recorded in the FITS file. Auxiliary top priority to the study of orbital motions in resolved information (target name, coordinates, filters, and time triple systems (see Tokovinin et al. 2018, and references of observation) is kept in the text files of observing logs, therein). As a result, tens of triples already have new or one per night. We recorded from 2 to 8 sequential data updated accurate orbits while monitoring of other sys- cubes of the object and one data cube of the reference tems continues. We are extending this effort to the north- star, selected from the Bright Star Catalog in the vicinity ern sky using the recently commissioned NESSI instru- of the target. The bright star is used as a reference in ment on the 3.5-m WIYN telescope (Scott et al. 2018). the data processing. Our targets were selected from the current version of Forty hours of service observations were allocated to the Multiple-Star Catalog (Tokovinin 2018b). We ob- this program by the NASA-WIYN TAC (programs 18A- served resolved northern subsystems with unknown or- 0122 and 18B-0008). Our objects, reference stars, and bits and estimated orbital periods shorter than 100 yr. calibration binaries were observed together with other This speckle program at WIYN pursues three main goals. programs. The data used in this paper have been ob- • Determination or improvement of visual orbits for tained during 33 nights in the period from 2018 Febru- members of hierarchical systems, especially those ary 2 to 2019 January 30. A total of 2057 data cubes with short periods. Orbits contribute to the statis- were recorded, amounting to 23 hours of the open-shutter tics of periods, relative inclinations, and eccentric- time. ities. 2.3. Data processing and calibration • Positional measurements and relative photometry of subsystems with periods of a few decades for All NESSI data cubes are normally processed using the future orbit determinations. speckle image reconstruction pipeline (Scott et al. 2018). However, for multiple stars the image reconstruction is • Verification of uncertain subsystems. Identifica- not strictly necessary (images from the NESSI pipeline tion of spurious triple stars cleans the statistics and are used here for illustration). We adaptated the SOAR saves efforts for their future monitoring. speckle pipeline (see Tokovinin, Mason, & Hartkopf 2010; Tokovinin 2018a) written in IDL. The most In this paper we report speckle observations at the computer-intensive part of the pipeline is the calcula- WIYN telescope conducted during one year, from 2018 tion of the power spectra. After reading the image cube February to 2019 January. The instrument, observing into the memory, the code first determines the centroids procedure, and data reduction are covered in Section 2. in each frame, thresholded at 10 counts above the back- The results (new measurements and orbits) are presented ground (the threshold is less than one electron and there- in Section 3. Section 4 summarizes our work. fore does not distort the linearity). Frames where the star 2. OBSERVATIONS is too close to the edge are rejected. Then the power spec- 2.1. trum is accumulated, as well as re-centered images and The instrument the shift-and-add (SAA) images centered on the bright- The speckle camera at the WIYN telescope is called est pixel in each frame. The orientation of images in the NESSI for NASA-NSF Exoplanet Observational Research red channel is changed to match the blue channel. (NN-EXPLORE) Exoplanet Stellar Speckle Imager. This Further data processing uses only the two-dimensional is a dual-channel imaging instrument (Scott et al. 2018). images and power spectra. It is organized by means of The beam arriving from the telescope is collimated, di- the data structure that keeps all relevant parameters and vided into two color channels by a dichroic beamsplitter, the processing results for each data cube and each chan- and re-focused on two identical electron-multiplication nel, i.e. from 4 to 16 records for a given target and, typ- CCD cameras with a magnification of 1.5× or a pixel ically, two records for the reference star. The essential scale of 18.2 mas. Wavelengths longer than 673nm pass information is ingested from the text files of the observ- through the dichroic to the red channel, while shorter ing logs and complemented by calculation of additional wavelengths are reflected to the blue channel. Both chan- parameters such as the zenith distance and parallactic nels have additional filters. Here we used the 562.3/43.6 angle. Results of the data analysis (e.g. the signal level in nm filter in the blue channel and the 716.0/51.5 nm in the the power spectrum, estimates of the resolution and de- red channel (some observations were obtained instead in tection limits, and binary-star parameters) are also kept the 832.0/40.4 nm filter).
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