The declination degeneracy in interferometric astrometry

Buscher, David F.

doi:10.1051/0004-6361/201118393

“…However, not only the maximum baseline, but also the u-v coverage determines the quality of the reconstructed maps (i.e. Buscher 2012). For further information about ALMA configurations and CASA see http:// almascience.eso.org/.…”

Section: Appendix A: Atacama Large (Sub)millimeter Arraymentioning

confidence: 99%

Tracing large-scale structures in circumstellar disks with ALMA

Ruge

¹

,

Wolf

²

,

Uribe

³

et al. 2013

A&A

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Context. Planets are supposed to form in circumstellar disks. The additional gravitational potential of a planet perturbs the disk and leads to characteristic structures, i.e. spiral waves and gaps, in the disk's density profile. Aims. We perform a large-scale parameter study of the observability of these planet-induced structures in circumstellar disks in the (sub)mm wavelength range for the Atacama Large (Sub)Millimeter Array (ALMA). Methods. On the basis of hydrodynamical and magneto-hydrodynamical simulations of star-disk-planet models, we calculated the disk temperature structure and (sub)mm images of these systems. These were used to derive simulated ALMA images. Because appropriate objects are frequent in the Taurus-Auriga region, we focused on a distance of 140 pc and a declination of ≈20 • . The explored range of star-disk-planet configurations consists of six hydrodynamical simulations (including magnetic fields and different planet masses), nine disk sizes with outer radii ranging from 9 AU to 225 AU, 15 total disk masses in the range between 2.67 × 10 −7 M and 4.10 × 10 −2 M , six different central stars, and two different grain size distributions, resulting in 10 000 disk models.Results. On almost all scales and in particular down to a scale of a few AU, ALMA is able to trace disk structures induced by planet-disk interaction or by the influence of magnetic fields on the wavelength range between 0.4 and 2.0 mm. In most cases, the optimum angular resolution is limited by the sensitivity of ALMA. However, within the range of typical masses of protoplanetary disks (0.1-0.001 M ) the disk mass has a minor impact on the observability. It is possible to resolve disks down to 2.67 × 10 −6 M and trace gaps induced by a planet with Mp M = 0.001 in disks with 2.67 × 10 −4 M with a signal-to-noise ratio greater than three. The central star has a major impact on the observability of gaps, as well as the considered maximum grainsize of the dust in the disk. In general, it is more likely to trace planet-induced gaps in our magnetohydrodynamical disk models, because gaps are wider in the presence of magnetic fields. We also find that zonal flows resulting from magneto-rotational instability (MRI) create gap-like structures in the disk's re-emission radiation, which are observable with ALMA. Conclusions. Through the unprecedented resolution and sensitivity of ALMA in the (sub)mm wavelength range, the expected detailed observations of planet-disk interaction and global disk structures will deepen our understanding of the planet formation and disk evolution process.

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“…(14) allows for the non-degenerate solution for the three components of B Wide (e.g. Shao et al 1990;Buscher 2012). The pivot point of an ideal telescope is defined as the intersection between the altitude and azimuth axes and remains at a fixed position in the horizontal coordinate system at all times.…”

Section: Wide-angle Astrometric Baselinementioning

confidence: 99%

The ESPRI project: astrometric exoplanet search with PRIMA

Henning

¹

,

Queloz

²

,

Quirrenbach³

et al. 2013

A&A

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Context. The ESPRI project relies on the astrometric capabilities offered by the PRIMA facility of the Very Large Telescope Interferometer for discovering and studying planetary systems. Our survey consists of obtaining high-precision astrometry for a large sample of stars over several years to detect their barycentric motions due to orbiting planets. We present the operation's principle, the instrument's implementation, and the results of a first series of test observations. Aims. We give a comprehensive overview of the instrument infrastructure and present the observation strategy for dual-field relative astrometry in the infrared K-band. We describe the differential delay lines, a key component of the PRIMA facility that was delivered by the ESPRI consortium, and discuss their performance within the facility. This paper serves as reference for future ESPRI publications and for the users of the PRIMA facility. Methods. Observations of bright visual binaries were used to test the observation procedures and to establish the instrument's astrometric precision and accuracy. The data reduction strategy for the astrometry and the necessary corrections to the raw data are presented. Adaptive optics observations with NACO were used as an independent verification of PRIMA astrometric observations. Results. The PRIMA facility was used to carry out tests of astrometric observations. The astrometric performance in terms of precision is limited by the atmospheric turbulence at a level close to the theoretical expectations and a precision of 30 µas was achieved. In contrast, the astrometric accuracy is insufficient for the goals of the ESPRI project and is currently limited by systematic errors that originate in the part of the interferometer beamtrain that is not monitored by the internal metrology system. Conclusions. Our observations led to defining corrective actions required to make the facility ready for carrying out the ESPRI search for extrasolar planets.

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“…The wide-angle astrometric baseline can be determined by measuring the metrology delays w 1...k when observing a set of 1...k stars with coordinates s 1...k , selected such that the resulting system of equations 14 allows for the non-degenerate solution for the three components of B Wide (e.g. Shao et al 1990;Buscher 2012).…”

Section: Wide-angle Astrometric Baselinementioning

confidence: 99%

The ESPRI project: astrometric exoplanet search with PRIMA I. Instrument description and performance of first light observations

Sahlmann,

Henning,

Queloz

et al. 2012

Preprint

0

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Context. The ESPRI project relies on the astrometric capabilities offered by the PRIMA facility of the Very Large Telescope Interferometer for discovering and studying planetary systems. Our survey consists of obtaining high-precision astrometry for a large sample of stars over several years to detect their barycentric motions due to orbiting planets. We present the operation's principle, the instrument's implementation, and the results of a first series of test observations. Aims. We give a comprehensive overview of the instrument infrastructure and present the observation strategy for dual-field relative astrometry in the infrared K-band. We describe the differential delay lines, a key component of the PRIMA facility that was delivered by the ESPRI consortium, and discuss their performance within the facility. This paper serves as reference for future ESPRI publications and for the users of the PRIMA facility. Methods. Observations of bright visual binaries were used to test the observation procedures and to establish the instrument's astrometric precision and accuracy. The data reduction strategy for the astrometry and the necessary corrections to the raw data are presented. Adaptive optics observations with NACO were used as an independent verification of PRIMA astrometric observations. Results. The PRIMA facility was used to carry out tests of astrometric observations. The astrometric performance in terms of precision is limited by the atmospheric turbulence at a level close to the theoretical expectations and a precision of 30 µas was achieved. In contrast, the astrometric accuracy is insufficient for the goals of the ESPRI project and is currently limited by systematic errors that originate in the part of the interferometer beamtrain that is not monitored by the internal metrology system. Conclusions. Our observations led to defining corrective actions required to make the facility ready for carrying out the ESPRI search for extrasolar planets.

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The declination degeneracy in interferometric astrometry

Cited by 3 publications

References 11 publications

Tracing large-scale structures in circumstellar disks with ALMA

Tracing large-scale structures in circumstellar disks with ALMA

The ESPRI project: astrometric exoplanet search with PRIMA

The ESPRI project: astrometric exoplanet search with PRIMA I. Instrument description and performance of first light observations

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