PHASES High-Precision Differential Astrometry of δ Equulei

Muterspaugh, Matthew W.; Lane, Benjamin F.; Konacki, Maciej; Burke, B. F.; Colavita, M. M.; Kulkarni, S. R.; Shao, M.

doi:10.1086/497035

Cited by 28 publications

(29 citation statements)

References 68 publications

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“…Combining astrometric with spectroscopic, radial-velocity observations of planetary systems can yield the complete orbital solution, hence solve for the planets' mass (Benedict et al 2002;Bean et al 2007;Pravdo & Shaklan 2009). Similarly, astrometric observations can yield the components' masses of binary systems (Muterspaugh et al 2005(Muterspaugh et al , 2008Lane et al 2007) and can be used to explore the dynamics of the stellar cluster close to the galactic centre's black hole (Bartko et al 2008). …”

Section: Scientific Rationalementioning

confidence: 99%

The PRIMA fringe sensor unit

Ménardi¹,

Abuter²,

Accardo³

et al. 2009

A&A

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Context. The fringe sensor unit (FSU) is the central element of the phase referenced imaging and micro-arcsecond astrometry (PRIMA) dual-feed facility and provides fringe sensing for all observation modes, comprising off-axis fringe tracking, phase referenced imaging, and high-accuracy narrow-angle astrometry. It is installed at the Very Large Telescope Interferometer (VLTI) and successfully served the fringe-tracking loop during the initial commissioning phase. Aims. To maximise sensitivity, speed, and robustness, the FSU is designed to operate in the infrared K-band and to include spatial filtering after beam combination and a very-low-resolution spectrometer without photometric channels. It consists of two identical fringe sensors for dual-star operation in PRIMA astrometric mode. Methods. Unique among interferometric beam combiners, the FSU uses spatial phase modulation in bulk optics to retrieve real-time estimates of fringe phase after spatial filtering. The beam combination design accommodates a laser metrology for pathlength monitoring. An R = 20 spectrometer across the K-band makes the retrieval of the group delay signal possible. The calibration procedure uses the artificial light source of the VLTI laboratory and is based on Fourier transform spectroscopy to remove instrumental effects. Results. The FSU was integrated and aligned at the VLTI in July and August 2008. It yields phase and group delay measurements at sampling rates up to 2 kHz, which are used to drive the fringe-tracking control loop. During the first commissioning runs, the FSU was used to track the fringes of stars with K-band magnitudes as faint as m K = 9.0, using two VLTI auxiliary telescopes (AT) and baselines of up to 96 m. Fringe tracking using two Very Large Telescope (VLT) unit telescopes was demonstrated. Conclusions. The concept of spatial phase-modulation for fringe sensing and tracking in stellar interferometry is demonstrated for the first time with the FSU. During initial commissioning and combining stellar light with two ATs, the FSU showed its ability to improve the VLTI sensitivity in K-band by more than one magnitude towards fainter objects, which is fundamental for achieving the scientific objectives of PRIMA.

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Section: Scientific Rationalementioning

confidence: 99%

The PRIMA fringe sensor unit

Ménardi¹,

Abuter²,

Accardo³

et al. 2009

A&A

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“…There is no single system on the sky for which the separation at any given time can be predicted with microarcsecond accuracy and which could be used as standard star pair for PRIMA. (Rather accurate astrometric measurements of the visual binary δ Equ were presented by Muterspaugh et al 10 recently, with the median of the minor axis of the uncertainty ellipse only 26 µas and 465 µas for the major axis, but the separation of the components in this system is only 0.25 , too close for observations with PRIMA.) However, for many systems a reasonable rate of change of the separation can be predicted, especially after the first PRIMA measurements are available, so that -if a few pairs are observed every night with PRIMA -good standard star pairs should be available after commissioning.…”

Section: Standard Star Pairsmentioning

confidence: 85%

The PRIMA astrometric planet search: goals and prospects

Reffert

Ségransan²,

Launhardt

et al. 2006

Advances in Stellar Interferometry

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ESO's PRIMA (Phase-Referenced Imaging and Micro-arcsecond Astrometry) facility at the VLT Interferometer on Cerro Paranal in Chile is expected to be fully operational in only a couple of years from now. With PRIMA/VLTI, it will then be possible to perform relative astrometry with an accuracy of the order of 10 µas over angles of about 10 .The main science driver for this astrometric capability is the detection and characterization of extrasolar planets, including (1) the observation of known radial velocity planets and planetary systems to fully constrain their orbital geometry and accurately determine the mass of the planet(s), (2) a search for extrasolar planets around stars which are less suitable for the radial velocity method (for example young and active stars as well as early type stars), and (3) a systematic search around the most nearby stars to detect low mass planets (Uranus or Neptune masses).Preparatory observations of possible target stars, with the aim of identifying nearby suitable astrometric reference stars, have already started with SOFI at the NTT and are described. Furthermore, we compare the goals and prospects of the PRIMA Astrometric Planet Search to other projects aiming at detecting planets astrometrically, mostly from space.

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“…To properly weight the data set when doing a combined fit with previous astrometry and radial velocity data, we fit an orbital model to the PHASES astrometry by itself, and rescaled the formal uncertainties so as to yield a reduced 2 of unity; the resulting scale factor was 2.5, indicating a substantial amount of excess scatter beyond the internal error estimates. We do not believe this scatter to be due to the effect of starspots, given that the Hipparcos photometry of this system indicates a scatter of no more than 5 mmag; the resulting maximum starspot-induced astrometric noise would be $4 as (Muterspaugh et al 2006a). We have however identified possible instrumental sources of this systematic error and developed methods for reducing it; see M. W. Muterspaugh et al (2007, in preparation).…”

Section: Phases Astrometrymentioning

confidence: 88%

“…With the advent of long-baseline stellar interferometry, and more recently phase-referenced long-baseline interferometric astrometry (Lane & Muterspaugh 2004) capable of 10-20 as astrometric precision between pairs of stars with separations in the range 0.05 00 -1 00 , it has become possible to resolve the orbital motion of several interesting multiple systems ( Muterspaugh et al 2006a( Muterspaugh et al , 2006b). Here we report on astrometric and radial velocity measurements of the 88 Tau A system, which allow us to constrain the orbits of the 3.57 day, 7.89 day, and 18 yr components with improved precision, and for the first time provide a relative orientation of the orbits as well as component masses.…”

Section: Introductionmentioning

confidence: 99%

The Orbits of the Quadruple Star System 88 Tauri A from PHASES Differential Astrometry and Radial Velocity

Lane

Muterspaugh

Fekel

et al. 2007

ApJ

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We have used high-precision differential astrometry from the Palomar High-precision Astrometric Search for Exoplanet Systems (PHASES) project and radial velocity measurements covering a time span of 20 years to determine the orbital parameters of the 88 Tau A system. 88 Tau is a complex hierarchical multiple system comprising a total of six stars; we have studied the brightest four, consisting of two short-period pairs orbiting each other with an $18 yr period. We present the first orbital solution for one of the short-period pairs, and determine the masses of the components and distance to the system to the level of a few percent. In addition, our astrometric measurements allow us to make the first determination of the mutual inclinations of the orbits. We find that the subsystems are not coplanar.

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PHASES High-Precision Differential Astrometry of δ Equulei

Cited by 28 publications

References 68 publications

The PRIMA fringe sensor unit

The PRIMA fringe sensor unit

The PRIMA astrometric planet search: goals and prospects

The Orbits of the Quadruple Star System 88 Tauri A from PHASES Differential Astrometry and Radial Velocity

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