Fringe Packet Research Articles

Separated Fringe Packet Observations with the CHARA Array. III. The Very High-eccentricity Binary HR 7345

Abstract After an 11-year observing campaign, we present the combined visual–spectroscopic orbit of the formerly unremarkable bright star HR 7345 (HD 181655, HIP 94981, GJ 754.2). Using the Separated Fringe Packet method with the CHARA Array, we were able to determine a difficult-to-complete orbital period of 331.609 ± 0.004 days. The 11-month period causes the system to be hidden from interferometric view behind the Sun for three years at a time. Due to the high-eccentricity orbit of about 90% of a year, after 2018 January the periastron phase will not be observable again until late 2021. Hindered by its extremely high eccentricity of 0.9322 ± 0.0001, the double-lined spectroscopic phase of HR 7345 is observable for 15 days. Such a high eccentricity for HR 7345 places it among the most eccentric systems in catalogs of both visual and spectroscopic orbits. For this system, we determine nearly identical component masses of 0.941 ± 0.076 M ⊙ and 0.926 ± 0.075 M ⊙ as well as an orbital parallax of 41.08 ± 0.77 mas.

Long distance measurement using optical sampling by cavity tuning.

We experimentally demonstrate a method enabling absolute distance measurement based on optical sampling by cavity tuning. The cross-correlation patterns can be obtained by sweeping the repetition frequency of the frequency comb. The 114m long fiber delay line, working as the reference arm, is actively stabilized by using a feedback servo loop with 10-10 level stability. The unknown distance can be measured via the instantaneous repetition frequency corresponding to the peak of the fringe packet. We compare the present technique with the reference incremental interferometer, and the experimental results show an agreement within 3μm over 60m distance, corresponding to 10-8 level in relative.

SEPARATED FRINGE PACKET OBSERVATIONS WITH THE CHARA ARRAY. II. ω ANDROMEDA, HD 178911, AND ξ CEPHEI

When observed with optical long-baseline interferometers (OLBI), components of a binary star which are sufficiently separated produce their own interferometric fringe packets; these are referred to as Separated Fringe Packet (SFP) binaries. These SFP binaries can overlap in angular separation with the regime of systems resolvable by speckle interferometry at single, large-aperture telescopes and can provide additional measurements for preliminary orbits lacking good phase coverage, help constrain elements of already established orbits, and locate new binaries in the undersampled regime between the bounds of spectroscopic surveys and speckle interferometry. In this process, a visibility calibration star is not needed, and the separated fringe packets can provide an accurate vector separation. In this paper, we apply the SFP approach to {\omega} Andromeda, HD 178911, and {\xi} Cephei with the CLIMB three-beam combiner at the CHARA Array. For these systems we determine component masses and parallax of 0.963${\pm}$0.049 $M_{\odot}$ and 0.860${\pm}$0.051 $M_{\odot}$ and 39.54${\pm}$1.85 milliarcseconds (mas) for {\omega} Andromeda, for HD 178911 of 0.802${\pm}$0.055 $M_{\odot}$ and 0.622${\pm}$0.053 $M_{\odot}$ with 28.26${\pm}$1.70 mas, and masses of 1.045${\pm}$0.031 $M_{\odot}$ and 0.408${\pm}$0.066 $M_{\odot}$ and 38.10${\pm}$2.81 mas for {\xi} Cephei.

Spatially Resolving Spectroscopic Binaries with the CHARA Array: The SFP Project

When observed with optical long-baseline interferometers (OLBI), components of a binary star which are sufficiently separated such that their interferometric fringe packets do not overlap are referred to as Separated Fringe Packet (SFP) binaries. These SFP binaries extend out into the regime of systems resolvable by speckle interferometry at single, large-aperture telescopes and can provide additional measurements for preliminary orbits lacking good phase coverage, help constrain elements of already established orbits, and locate new binaries in the undersampled regime between the bounds of spectroscopic surveys and speckle interferometry. In this process, a visibility calibration star is not needed, and the separated fringe packets can provide an accurate vector separation. Presented here we describe the method, usage, and modified orbits for several systems used to validate the procedure.

Length and refractive index measurement by Fourier transform interferometry and frequency comb spectroscopy

In this paper we describe the progress we have made in our simultaneous length measurement and the femtosecond comb interferometric spectroscopy in a conventional arrangement with a moving mirror. Scanning and detection over an interval longer than the distance between two consecutive pulses of the frequency comb allow for a spectral resolution of the individual frequency modes of the comb. Precise knowledge of comb mode frequency leads to a precise estimation of the spectral characteristics of inspected phenomena. Using the pulse train of the frequency comb allows for measurement with highly unbalanced lengths of interferometer arms, i.e. an absolute long distance measurement. Further, we present a non-contact (double sided) method of measurement of the length/thickness of plane-parallel objects (gauge blocks, glass samples) by combining the fs comb (white light) with single frequency laser interferometry. The position of a fringe packet is evaluated by estimating the stationary phase position for any wavelength in the spectral band used. The repeatability of this position estimation is a few nanometres regardless of whether dispersion of the arms is compensated (transform limited fringe packet ∼10 fringes FWHM) or highly different (fringe packet stretched to >200 fringes FWHM). The measurement of steel gauge block by this method was compared with the standard method, and deviation (+13 ± 12) nm for gauge blocks (2 to 100) mm was found. The measurement of low reflecting ceramic gauges or clear glass samples was also tested. In the case of glass, it becomes possible to measure simultaneously both the thickness and the refractive index (and dispersion) of flat samples.

A SEARCH FOR SEPARATED FRINGE PACKET BINARIES USING THE CHARA ARRAY

We present the results of a comprehensive search for new companions to nearby solar-type stars using the separated fringe packet (SFP) technique at the Center for High Angular Resolution Astronomy (CHARA) Array. Our search included 636 observations of 186 stars, searching for companions with separations of approximately 8-80 mas and moderate brightness ratios ({Delta}K {approx}< 1.5). This survey was undertaken to support a comprehensive assessment of companions to solar-type stars within 25 pc. We detected separated fringe companions to two stars (HD 3196 and 79096) and found faint companion signatures to two more stars (HD 98231 and 137763). All of these companions are previously known by spectroscopic methods, and three of them have speckle interferometric observations as well. The faint companion seen to HD 98231 represents the first visual detection of this spectroscopic companion. Our null detection for new companions implies that the presumed gap between spectroscopic and visual techniques has largely been filled for nearby solar-type stars, thanks to systematic radial-velocity observations over multiple decades and a thorough coverage using visual techniques, especially speckle interferometric observations. We also generate simulated fringe packets to derive detection limits for SFP binaries using the CHARA Array.

AN INTERFEROMETRIC AND SPECTROSCOPIC ANALYSIS OF THE MULTIPLE STAR SYSTEM HD 193322

The star HD 193322 is a remarkable multiple system of massive stars that lies at the heart of the cluster Collinder 419. Here we report on new spectroscopic observations and radial velocities of the narrow-lined component Ab1 that we use to determine its orbital motion around a close companion Ab2 ($P = 312$ d) and around a distant third star Aa ($P = 35$ y).We have also obtained long baseline interferometry of the target in the $K^\prime$-band with the CHARA Array that we use in two ways. First, we combine published speckle interferometric measurements with CHARA separated fringe packet measurements to improve the visual orbit for the wide Aa,Ab binary. Second, we use measurements of the fringe packet from Aa to calibrate the visibility of the fringes of the Ab1,Ab2 binary, and we analyze these fringe visibilities to determine the visual orbit of the close system. The two most massive stars, Aa and Ab1, have masses of approximately 21 and $23 M_\odot$, respectively, and their spectral line broadening indicates that they represent extremes of fast and slow projected rotational velocity, respectively.

Robust determination of optical path difference: fringe tracking at the Infrared Optical Telescope Array interferometer

We describe the fringe-packet tracking system used to equalize the optical path lengths at the Infrared Optical Telescope Array interferometer. The measurement of closure phases requires obtaining fringes on three baselines simultaneously. This is accomplished by use of an algorithm based on double Fourier interferometry for obtaining the wavelength-dependent phase of the fringes and a group-delay tracking algorithm for determining the position of the fringe packet. A comparison of data acquired with and without the fringe-packet tracker shows a factor of approximately 3 reduction of the error in the closure-phase measurement. The fringe-packet tracker has been able so far to track fringes with signal-to-noise ratios as low as 1.8 for stars as faint as mH = 7.0.

Fringe beating effects induced by misalignment in a white-light interferometer

The profile of the interference fringe packet obtained in interferometry, especially in the topical area of white-light interferometry, may be dramatically altered by the presence of the so-called `fringe beating effect' due to the poor quality of the collimation lens or the misalignment of the optical arrangement. In the worst cases, the peak value of the central fringe will be equal to or even less than that of the other fringes and in consequence will give an erroneous result for the determination of the central fringe position in the visibility profile. This effect is considered using a simple computer simulation model and the results both from the computer simulation and from experiment are discussed and compared to find means of eliminating such effects.

Technique for obtaining visibility amplitudes from atmospherically disturbed interferograms

We describe the general data-reduction techniques that we developed to deal with stellar interferograms. The techniques that we describe here were used to obtain the fundamental visibility data from raw Earth-scanned interferograms obtained with the infrared Michelson array stellar interferometer. The reduced visibility data have resulted in new direct angular diameter measurements and effective temperature determinations for α Her, α Ori, and Mira. These astrophysical results were previously published. We point out that the data-reduction techniques described here are completely general in the sense that they can be used to reduce the data from any stellar interferometer that records the temporal data stream as the fringe packet is swept by the detectors.