Astrometric orbit of a low-mass companion to an ultracool dwarf

Sahlmann, J.; Lazorenko, P. F.; Ségransan, D.; Martín, E. L.; Queloz, D.; Mayor, M.; Udry, S.

doi:10.1051/0004-6361/201321871

Cited by 62 publications

(78 citation statements)

References 75 publications

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“…In June 2012, it became clear that the standard astrometric model is not sufficient to explain the motion of DE0630−18, and we initiated follow-up observations. We followed the same strategy and procedures for the adjustment of an additional Keplerian motion that is described in Sahlmann et al (2013). A genetic algorithm was used to efficiently explore the large parameter space and to identify the most promising model parameters.…”

Section: Observations and Data Reductionmentioning

confidence: 99%

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Astrometric planet search around southern ultracool dwarfs

Lazorenko

Ségransan

Martín

et al. 2015

A&A

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Using astrometric measurements obtained with the FORS2/VLT camera, we are searching for low-mass companions around 20 nearby ultracool dwarfs. With a single-measurement precision of ∼0.1 milli-arcsec, our survey is sensitive to a wide range of companion masses from planetary companions to binary systems. Here, we report the discovery and orbit characterisation of a new ultracool binary at a distance of 19.5 pc from Earth that is composed of the M8.5-dwarf primary DE0630−18 and a substellar companion. The nearly edge-on orbit is moderately eccentric (e = 0.23) with an orbital period of 1120 d, which corresponds to a relative separation in semimajor axis of approximately 1.1 AU. We obtained a high-resolution optical spectrum with UVES/VLT and measured the system's heliocentric radial velocity. The spectrum does not exhibit lithium absorption at 670.8 nm, indicating that the system is not extremely young. A preliminary estimate of the binary's physical parameters tells us that it is composed of a primary at the stellar-substellar limit and a massive brown-dwarf companion. DE0630−18 is a new very low-mass binary system with a well-characterised orbit.

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Section: Observations and Data Reductionmentioning

confidence: 99%

“…The project is described in Sahlmann et al (2014b), and its first result, the discovery of a low-mass companion to an L dwarf, is reported in Sahlmann et al (2013) and updated by Sahlmann et al (2014c). Details on the astrometric reduction methods are given in Lazorenko et al (2014).…”

Section: Introductionmentioning

confidence: 99%

Astrometric planet search around southern ultracool dwarfs

Lazorenko

Ségransan

Martín

et al. 2015

A&A

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“…The target list (Paper I) contains 20 southern M/L dwarfs, which were monitored for two years starting in November 2010, each with approximately 4-6 epochs per year with one-month spacing in the visibility period. In the third year, a few more follow-up observations were obtained for some targets, for example the binary DE0823−49 (Sahlmann et al 2013b). Because the targets are red dwarfs, we observed with the I-Bessel filter with a central wavelength at 768 nm.…”

Section: Observations and Initial Data Reductionmentioning

confidence: 99%

“…and used them to recover S astrometric parameters ξ s of the target by fitting their change in time t with the model νξ + Ψ(t) = ΔX (Lazorenko et al 2011), which, in the general case, includes the orbital motion Ψ(t) of the target and is solved as described by Sahlmann et al (2013b). For the field stars with Ψ(t) = 0, the solution of this model provides the residuals x m and parameters ξ s which refer to the system of reference stars set by Eq.…”

Section: Deriving Astrometric Parameters For the Target Starmentioning

confidence: 99%

“…In this paper, we present the latest optimisations of the astrometric methods for the reduction of FORS2 observations described in PL09. These methods were already successfully used A&A 565, A21 (2014) for the detection of a close 28 Jupiter-mass (M J ) companion of an L1.5 dwarf (Sahlmann et al 2013b) and are implemented for the planet search survey (Paper I).…”

Section: Introductionmentioning

confidence: 99%

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Astrometric planet search around southern ultracool dwarfs

Lazorenko

Ségransan

Martín

et al. 2014

A&A

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Aims. We describe the astrometric reduction of images obtained with the FORS2/VLT camera in the framework of an astrometric planet search around 20 M/L-transition dwarfs. We present the correction of systematic errors, the achieved astrometric performance, and a new astrometric catalogue containing the faint reference stars in 20 fields located close to the Galactic plane. Methods. Remote reference stars were used both to determine the astrometric trajectories of the nearby planet search targets and to identify and correct systematic errors. Results. We detected three types of systematic errors in the FORS2 astrometry: the relative motion of the camera's two CCD chips, errors that are correlated in space, and an error contribution of as yet unexplained origin. The relative CCD motion probably has a thermal origin and typically is 0.001-0.010 px (∼0.1-1 mas), but sometimes amounts to 0.02-0.05 px (3-6 mas). This instability and space-correlated errors are detected and mitigated using reference stars. The third component of unknown origin has an amplitude of 0.03-0.14 mas and is independent of the observing conditions. We find that a consecutive sequence of 32 images of a well-exposed star over 40 min at 0.6 seeing results in a median rms of the epoch residuals of 0.126 mas. Overall, the epoch residuals are distributed according to a normal law with a χ 2 value near unity. We compiled a catalogue of 12 000 stars with I-band magnitudes of 16-22 located in 20 fields, each covering ∼2 × 2 . It contains I-band magnitudes, ICRF positions with 40-70 mas precision, and relative proper motions and absolute trigonometric parallaxes with a precision of 0.1 mas/yr and 0.1 mas at the bright end, respectively. Conclusions. This work shows that an astrometric accuracy of ∼100 micro-arcseconds over two years can be achieved with a large optical telescope in a survey covering several targets and varying observing conditions.

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