34 research outputs found
Infrared interferometry to spatially and spectrally resolve jets in X-ray binaries
Infrared interferometry is a new frontier for precision ground based
observing, with new instrumentation achieving milliarcsecond (mas) spatial
resolutions for faint sources, along with astrometry on the order of 10
microarcseconds. This technique has already led to breakthroughs in the
observations of the supermassive black hole at the Galactic centre and its
orbiting stars, AGN, and exo-planets, and can be employed for studying X-ray
binaries (XRBs), microquasars in particular. Beyond constraining the orbital
parameters of the system using the centroid wobble and spatially resolving jet
discrete ejections on mas scales, we also propose a novel method to discern
between the various components contributing to the infrared bands: accretion
disk, jets and companion star. We demonstrate that the GRAVITY instrument on
the Very Large Telescope Interferometer (VLTI) should be able to detect a
centroid shift in a number of sources, opening a new avenue of exploration for
the myriad of transients expected to be discovered in the coming decade of
radio all-sky surveys. We also present the first proof-of-concept GRAVITY
observation of a low-mass X-ray binary transient, MAXI J1820+070, to search for
extended jets on mas scales. We place the tightest constraints yet via direct
imaging on the size of the infrared emitting region of the compact jet in a
hard state XRB.Comment: 12 Pages, 3 figures, accepted for publication in MNRA
Very high contrast IFU spectroscopy of AB Doradus C: 9 mag contrast at 0.2" without a coronagraph using spectral deconvolution
We present an extension of the spectral deconvolution method (Sparks & Ford
2002) to achieve very high contrast at small inner working radii. We apply the
method to the specific case of ground based adaptive optics fed integral field
spectroscopy (without a coronagraph). Utilising the wavelength dependence of
the Airy and speckle patterns, we make an accurate estimate of the PSF that can
be scaled and subtracted from the data cube. The residual noise in the
resulting spectra is very close to the photon noise from the starlight halo. We
utilise the technique to extract a very high SNR H & K band spectrum of AB Dor
C, the low mass companion to AB Dor A. By effectively eliminating all
contamination from AB Dor A, the extracted spectrum retains both continuum and
spectral features. The achieved 1 sigma contrast is 9 mag at 0.2", 11 mag at
0.5", in 20 mins exposure time, at an effective spectral bandwidth of 5.5 nm,
proving that the method is applicable even in low Strehl regimes.
The spectral deconvolution method clearly demonstrates the efficacy of image
slicer based IFUs in achieving very high contrast imaging spectroscopy at small
angular separations, validating their use as high contrast
spectrographs/imagers for extreme adaptive optics systems.Comment: 9 pages, 5 figures, accepted for publication in MNRAS. This is a
joint submission with astro-ph/0703564 by L. Close et a
The GRAVITY instrument software / High-level software
GRAVITY is the four-beam, near- infrared, AO-assisted, fringe tracking,
astrometric and imaging instrument for the Very Large Telescope Interferometer
(VLTI). It is requiring the development of one of the most complex instrument
software systems ever built for an ESO instrument. Apart from its many
interfaces and interdependencies, one of the most challenging aspects is the
overall performance and stability of this complex system. The three infrared
detectors and the fast reflective memory network (RMN) recorder contribute a
total data rate of up to 20 MiB/s accumulating to a maximum of 250 GiB of data
per night. The detectors, the two instrument Local Control Units (LCUs) as well
as the five LCUs running applications under TAC (Tools for Advanced Control)
architecture, are interconnected with fast Ethernet, RMN fibers and dedicated
fiber connections as well as signals for the time synchronization. Here we give
a simplified overview of all subsystems of GRAVITY and their interfaces and
discuss two examples of high-level applications during observations: the
acquisition procedure and the gathering and merging of data to the final FITS
file.Comment: 8 pages, 7 figures, published in Proc. SPIE 9146, Optical and
Infrared Interferometry IV, 91462
VLTI status update: a decade of operations and beyond
We present the latest update of the European Southern Observatory's Very
Large Telescope interferometer (VLTI). The operations of VLTI have greatly
improved in the past years: reduction of the execution time; better offering of
telescopes configurations; improvements on AMBER limiting magnitudes; study of
polarization effects and control for single mode fibres; fringe tracking real
time data, etc. We present some of these improvements and also quantify the
operational improvements using a performance metric. We take the opportunity of
the first decade of operations to reflect on the VLTI community which is
analyzed quantitatively and qualitatively. Finally, we present briefly the
preparatory work for the arrival of the second generation instruments GRAVITY
and MATISSE.Comment: 10 pages, 7 figures, Proceedings of the SPIE, 9146-1
The GRAVITY+ Project: Towards All-sky, Faint-Science, High-Contrast Near-Infrared Interferometry at the VLTI
The GRAVITY instrument has been revolutionary for near-infrared
interferometry by pushing sensitivity and precision to previously unknown
limits. With the upgrade of GRAVITY and the Very Large Telescope Interferometer
(VLTI) in GRAVITY+, these limits will be pushed even further, with vastly
improved sky coverage, as well as faint-science and high-contrast capabilities.
This upgrade includes the implementation of wide-field off-axis
fringe-tracking, new adaptive optics systems on all Unit Telescopes, and laser
guide stars in an upgraded facility. GRAVITY+ will open up the sky to the
measurement of black hole masses across cosmic time in hundreds of active
galactic nuclei, use the faint stars in the Galactic centre to probe General
Relativity, and enable the characterisation of dozens of young exoplanets to
study their formation, bearing the promise of another scientific revolution to
come at the VLTI.Comment: Published in the ESO Messenge
Simulation of Kalman-filter fringe tracking with on-sky measurements of the PRIMA Fringe Sensor Unit
International audienceGRAVITY is a second generation instrument for the VLTI that will combine four telescopes in the K band. To achieve astrometric precision of 10muas and angular resolution of 4mas for objects with magnitude up to K=16 in the science beam, its fringe tracker will stabilize fringes to 350nm rms on a reference star as faint as K=10. To efficiently correct both atmospheric piston and longitudinal vibrations, we developed a controller based on Kalman filtering, which is a predictive algorithm providing optimized commands based on a model of the disturbances. In order to validate the Kalman algorithm as a fringe tacker for GRAVITY, we performed numerical simulations of 2-telescope fringe tracking with a Kalman controller with on-sky measurements from the PRIMA Fringe Sensor Unit (FSU). We find that tracking with the Kalman controller is more efficient than with the PRIMA FSU for all archive data provided by ESO. We deduced an average gain of 170nm rms over the residual OPD using the PRIMA FSU
New Photometry and Spectra of AB Doradus C: An Accurate Mass Determination of a Young Low-Mass Object with Theoretical Evolutionary Tracks 1
We present new photometric and spectroscopic measurements for the unique, young, low-mass evolutionary track calibrator AB Dor C. While the new Ks photometry is similar to that previously published in Close et al. (2005) the spectral type is found to be earlier. Based on new H & K IFS spectra of AB Dor C (Thatte et al. 2007; paper I) we adopt a spectral type of M5.5 ± 1.0 for AB Dor C. This is considerably earlier than the M8 ± 1 estimated in Close et al. (2005) and Nielsen et al. (2005) yet is consistent with the M6 ± 1 independently derived by Luhman & Potter (2005). However, the spectrum presented in paper 1 and analyzed here is a significant improvement over any previous spectrum of AB Dor C. We also present new astrometry for the system which further supports a 0.090 ± 0.005M â mass for the system. Once armed with an accurate spectrum and Ks flux we find L = 0.0021 ± 0.0005L â and Teff = 2925 +170 â145K for AB Dor C. These values are consistent with a ⌠75 Myr 0.090 ± 0.005M â object like AB Dor C according to the DUSTY evolutionary tracks (Chabrier et al. 2000). Hence masses can be estimated from the HR diagram with the DUSTY tracks for young low-mass objects like AB Dor C. However, we cautiously note that underestimates of the mass from the tracks can occur if one lacks a proper (continuum preserved) spectra or is relying on NIR fluxes alone
GRAVITY: The AO assisted, two object beam combiner instrument for the VLTI.
International audienc