In the GRAVITY+ project, GRAVITY is presently undergoing a series of upgrades to enhance its performance, add wide field capability and thereby expand its sky coverage. Some aspects of these improvements have already been implemented and commissioned by the end of 2021, making them accessible to the community. The augmentation of sky coverage involves increasing the maximum angular separation between the celestial science object and the fringe tracking object from the previous 2 arcseconds (limited by the field of view of the VLTI) to 20 – 30 arcseconds (constrained by atmospheric conditions during observation). Phase 1 of GRAVITY+ Wide utilizes the earlier PRIMA Differential Delay Lines to compensate for the optical path length variation between the science and fringe tracking beams throughout an observation. In phase 2, we are upgrading the existing beam compressors (BC) to integrate optical path length difference compensation directly into the BC. This modification eliminates five optical reflections per beam, thereby enhancing the optical throughput of the VLTI–GRAVITY system and the bandwidth of the vibrational control. We will present the implementation of phase 2 and share preliminary results from our testing activities for GRAVITY+ Wide.
The GRAVITY+ project consists of instrumental upgrades to the Very Large Telescope Interferometer (VLTI) for faint-science, high-contrast, milliarcsecond interferometric imaging. As an integral part of the GRAVITY+ Adaptive Optics (AO) architecture, the Wavefront Sensor (WFS) subsystem corrects image distortions caused by the turbulence of Earth's atmosphere. We present the opto-mechanical design of the WFS subsystem and the design strategies used to implement two payloads positioned diagonally opposite each other - Natural Guide Star (NGS) and Laser Guide Star (LGS) - within a single compact design structure. We discuss the implementation of relative motions of the two payloads covering their respective patrol fields and a nested motion within the LGS Payload covering the complete Sodium layer profile in the Earth's atmosphere.
We present the Wavefront Sensor units of the Gravity Plus Adaptive Optics (GPAO) system, which will equip all 8m class telescopes of the VLTI and is an instrumental part of the GRAVITY+ project. It includes two modules for each Wavefront Sensor unit: a Natural Guide Star sensor with high-order 40×40 Shack-Hartmann and a Laser Guide Star 30×30 sensor. The state-of-the-art AO correction will considerably improve the performance for interferometry, in particular high-contrast observations for NGS observations and all-sky coverage with LGS, which will be implemented for the first time on VLTI instruments. In the following, we give an overview of the Wavefront Sensor units system after completion of their integration and characterization.
We present latest results and further development of the image reconstruction tool GRAVITY-RESOLVE (G^R), which is specifically designed for Galactic Center observations with the near-infrared phase-referencing VLTI instrument GRAVITY. We show deep images of the Galactic Center in recent years and movies in which the stellar motion around the central massive black hole SgrA* becomes apparent on yet unmatched scales. Moreover, we present a first result of the newly implemented mosaicing method in G^R to jointly reconstruct multiple datasets which have been separately recorded on sky.
The GRAVITY instrument has transformed the field of near-infrared interferometry and is redefining the limits of ground-based observations. In Galactic Center observations, this is shown by routinely achieving below 50 μas uncertainty on astrometric measurements within a 5-minute exposure and detecting stars fainter than 19th magnitude. Nevertheless, systematic effects are still limiting the instrument's performance. In this talk, I will introduce two observing modes to overcome these limitations: Pupil modulation to improve the astrometry and metrology attenuation to overcome SNR limitations. I will detail these two modes and show how significant the improvements are on examples of on-sky data.
MICADO is a first light instrument for the Extremely Large Telescope (ELT), set to start operating later this decade. It will provide diffraction limited imaging, astrometry, high contrast imaging, and long slit spectroscopy at near-infrared wavelengths. During the initial phase operations, adaptive optics (AO) correction will be provided by its own natural guide star wavefront sensor. In its final configuration, that AO system will be retained and complemented by the laser guide star multi-conjugate adaptive optics module MORFEO (formerly known as MAORY). Among many other things, MICADO will study exoplanets, distant galaxies and stars, and investigate black holes, such as Sagittarius A* at the centre of the Milky Way. After their final design phase, most components of MICADO have moved on to the manufacturing and assembly phase. Here we summarize the final design of the instrument and provide an overview about its current manufacturing status and the timeline. Some lessons learned from the final design review process will be presented in order to help future instrumentation projects to cope with the challenges arising from the substantial differences between projects for 8-10m class telescopes (e.g. ESO’s VLT) and the next generation Extremely Large Telescopes (e.g. ESO’s ELT). Finally, MICADO's expected performance will be discussed in the context of the current landscape of astronomical observatories and instruments. For instance, MICADO will have similar sensitivity as the James Webb Space Telescope (JWST), but with six times the spatial resolution.
ERIS (Enhanced Resolution Imager and Spectrograph) is a new adaptive optics instrument installed at the Cassegrain focus of the VLT-UT4 telescope at the Paranal Observatory in Chile. ERIS consists of two near infrared instruments: SPIFFIER, an integral field unit (IFU) spectrograph covering J to K bands, and NIX, an imager covering J to M bands. ERIS has an adaptive optics system able to work with both LGS and NGS. The Assembly Integration Verification (AIV) phase of ERIS at the Paranal Observatory was carried out starting in December 2021, followed by several commissioning runs in 2022. This contribution will describe the first preliminary results of the on-sky performance of ERIS during its commissioning and the future perspectives based on the preliminary scientific results.
With the upgrade from GRAVITY to GRAVITY+ the instrument will evolve to an all-sky interferometer that can observe faint targets, such as high redshift AGN. Observing the faintest targets requires reducing the noise sources in GRAVITY as much as possible. The dominant noise source, especially in the blue part of the spectrum, is the backscattering of the metrology laser light onto the detector. To reduce this noise we introduce two new metrology modes. With a combination of small hardware changes and software adaptations, we can dim the metrology laser during the observation without losing the phase referencing. For single beam targets, we can even turn off the metrology laser for the maximum SNR on the detector. These changes lead to a SNR improvement of over a factor of two averaged over the whole spectrum and up to a factor of eight in the part of the spectrum currently dominated by laser noise.
As part of the GRAVITY+ project, the near-infrared beam combiner GRAVITY and the VLTI are currently undergoing a series of significant upgrades to further improve the performance and sky coverage. The instrumental changes will be transformational, and for instance uniquely position GRAVITY to observe the broad line region of hundreds of Active Galactic Nuclei (AGN) at a redshift of two and higher. The increased sky coverage is achieved by enlarging the maximum angular separation between the celestial science object (SC) and the off-axis fringe tracking (FT) star from currently 2 arcseconds (arcsec) up to unprecedented 30 arcsec, limited by the atmospheric conditions. This was successfully demonstrated at the VLTI for the first time.
During the past years, the VLTI-instrument GRAVITY has made spectacular discoveries with phase-referenced interferometric imaging with milliarcsecond resolution and ten microarcsecond astrometry. Here, we report on the upgrade of the GRAVITY science spectrometer with two new grisms in October 2019, increasing the instrument throughput by a factor > 2. This improvement was made possible by using a high refractive index Germanium substrate, which reduces the grism and groove angles, and by successfully applying an anti-reflection coating to the ruled surface to overcome Fresnel losses. We present the design, manufacturing, and laboratory testing of the new grisms, as well as the results from the re-commissioning on sky.
Combining adaptive optics and interferometric observations results in a considerable contrast gain compared to single-telescope, extreme AO systems. Taking advantage of this, the ExoGRAVITY project is a survey of known young giant exoplanets located in the range of 0.1” to 2” from their stars. The observations provide astrometric data of unprecedented accuracy, being crucial for refining the orbital parameters of planets and illuminating their dynamical histories. Furthermore, GRAVITY will measure non-Keplerian perturbations due to planet-planet interactions in multi-planet systems and measure dynamical masses. Over time, repetitive observations of the exoplanets at medium resolution (R = 500) will provide a catalogue of K-band spectra of unprecedented quality, for a number of exoplanets. The K-band has the unique properties that it contains many molecular signatures (CO, H2O, CH4, CO2). This allows constraining precisely surface gravity, metallicity, and temperature, if used in conjunction with self-consistent models like Exo-REM. Further, we will use the parameter-retrieval algorithm petitRADTRANS to constrain the C/O ratio of the planets. Ultimately, we plan to produce the first C/O survey of exoplanets, kick-starting the difficult process of linking planetary formation with measured atomic abundances.
Instrumental polarization can have large effects on measurements with the VLTI, as it can alter measured polarization and introduce uncertainties. To understand these effects we measured and simulated the instrumental polarization of the VLTI and of GRAVITY. We are able to provide a calibration model for GRAVITY observations and quantify systematic uncertainties due to instrumental polarization. This work has shown to be crucial to measure the polarization of the galactic center black hole Sgr A* where we detect a swing in the polarization angle during flare events. While the analysis was done for GRAVITY, it also gives an important basis for the design of future near-infrared instruments at the VLTI.
We present the successful demonstration of world's first large-separation ~30" off-axis fringe tracking with four telescopes in October 2019. With this technique we increase the sky-coverage for optical interferometry by orders of magnitude compared to current technology. Following the early work at the Palomar Testbed Interferometer, the first demonstration of off-axis fringe tracking at the Keck Interferometer and with PRIMA at the ESO Very Large Telescope Interferometer, and the breakthrough with the GRAVITY Galactic Center observations, we enhanced the VLTI infrastructure for GRAVITY to take advantage of the PRIMA Star separators and Differential Delay Lines for off-axis fringe tracking. In our presentation we give an introduction to the subject, present the enhancements of the VLTI, and present our results from the first on-sky operation in October 2019, with observations of the Orion Trapezium Cluster, a field brown dwarf, and a high redshift quasar.
The GRAVITY instrument has revolutionized optical/IR interferometry: fringe-tracking and phase-referencing allow for 30 micro-arcsecond astrometry in a dual beam mode, and for spectro-differential astrometry better than 10 micro-arcseconds. The control of systematic effects is essential to fully exploit this technological advancement. Among those systematics are static phase aberrations, introduced along the instrument's optical path, which in particular affect the inferred separation of two unresolved objects within the same FOV. Here, we present how the aberrations can be measured, characterized by low-order Zernike polynomials and, most importantly, how their impact on the astrometry is corrected. The resulting astrometry corrections are verified with calibration observations of a binary before we discuss how they affect GRAVITY's measurement of the galactic center distance.
MICADO will enable the ELT to perform diffraction limited near-infrared observations at first light. The instrument’s capabilities focus on imaging (including astrometric and high contrast) as well as single object spectroscopy. This contribution looks at how requirements from the observing modes have driven the instrument design and functionality. Using examples from specific science cases, and making use of the data simulation tool, an outline is presented of what we can expect the instrument to achieve.
ERIS is an instrument that will both extend and enhance the fundamental diffraction limited imaging and spectroscopy capability for the VLT. It will replace two instruments that are now being maintained beyond their operational lifetimes, combine their functionality on a single focus, provide a new wavefront sensing module that makes use of the facility Adaptive Optics System, and considerably improve their performance. The instrument will be competitive with respect to JWST in several regimes, and has outstanding potential for studies of the Galactic Center, exoplanets, and high redshift galaxies. ERIS had its final design review in 2017, and is expected to be on sky in 2020. This contribution describes the instrument concept, outlines its expected performance, and highlights where it will most excel.
The use of optical fibers in astronomical instrumentation has been becoming more and more common. High transmission, polarization control, compact and easy routing are just a few of the advantages in this respect. But fibers also bring new challenges for the development of systems. During the assembly of the VLTI beam combiner GRAVITY different side effects of the fiber implementation had to be taken into account. In this work we summarize the corresponding phenomena ranging from the external factors influencing the fiber performance, like mechanical and temperature effects, to inelastic scattering within the fiber material.
Since its first light at the Very Large Telescope Interferometer (VLTI), GRAVITY has reached new regimes in optical interferometry, in terms of accuracy as well as sensitivity.1 GRAVITY is routinely doing phase referenced interferometry of objects fainter than K > 17 mag, which makes for example the galactic center black hole Sagittarius A*2 detectable 90 % of the times. However from SNR calculations we are confident that even a sensitivity limit of K ~ 19 mag is possible. We therefore try to push the limits of GRAVITY by improving the observations as well as the calibration and the data reduction. This has further improved the sensitivity limit to K > 18 mag in the beginning of this year. Here we present some work we are currently doing in order to reach the best possible sensitivity.
MICADO will equip the E-ELT with a first light capability for diffraction limited imaging at near-infrared wavelengths. The instrument’s observing modes focus on various flavours of imaging, including astrometric, high contrast, and time resolved. There is also a single object spectroscopic mode optimised for wavelength coverage at moderately high resolution. This contribution provides an overview of the key functionality of the instrument, outlining the scientific rationale for its observing modes. The interface between MICADO and the adaptive optics system MAORY that feeds it is summarised. The design of the instrument is discussed, focusing on the optics and mechanisms inside the cryostat, together with a brief overview of the other key sub-systems.
The VLTI instrument GRAVITY combines the beams from four telescopes and provides phase-referenced imaging as well as precision-astrometry of order 10 μas by observing two celestial objects in dual-field mode. Their angular separation can be determined from their differential OPD (dOPD) when the internal dOPDs in the interferometer are known. Here, we present the general overview of the novel metrology system which performs these measurements. The metrology consists of a three-beam laser system and a homodyne detection scheme for three-beam interference using phase-shifting interferometry in combination with lock-in amplifiers. Via this approach the metrology system measures dOPDs on a nanometer-level.
SPIFFI is an AO-fed integral field spectrograph operating as part of SINFONI on the VLT, which will be upgraded and reused as SPIFFIER in the new VLT instrument ERIS. In January 2016, we used new technology developments to perform an early upgrade to optical subsystems in the SPIFFI instrument so ongoing scientific programs can make use of enhanced performance before ERIS arrives in 2020. We report on the upgraded components and the performance of SPIFFI after the upgrade, including gains in throughput and spatial and spectral resolution. We show results from re-commissioning, highlighting the potential for scientific programs to use the capabilities of the upgraded SPIFFI. Finally, we discuss the additional upgrades for SPIFFIER which will be implemented before it is integrated into ERIS.
The VLTI instrument GRAVITY will provide very powerful astrometry by combining the light from four tele- scopes for two objects simultaneously. It will measure the angular separation between the two astronomical objects to a precision of 10 μas. This corresponds to a differential optical path difference (dOPD) between the targets of few nanometers and the paths within the interferometer have to be maintained stable to that level. For this purpose, the novel metrology system of GRAVITY will monitor the internal dOPDs by means of phase- shifting interferometry. We present the four-step phase-shifting concept of the metrology with emphasis on the method used for calibrating the phase shifts. The latter is based on a phase-step insensitive algorithm which unambiguously extracts phases in contrast to other methods that are strongly limited by non-linearities of the phase-shifting device. The main constraint of this algorithm is to introduce a robust ellipse fitting routine. Via this approach we are able to measure phase shifts in the laboratory with a typical accuracy of λ=2000 or 1 nm of the metrology wavelength.
KEYWORDS: Sensors, Process control, Control systems, Cameras, Telescopes, Signal detection, Data acquisition, Computing systems, Interferometers, Interfaces
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.
KEYWORDS: Sensors, Lamps, Camera shutters, Control systems, Analog electronics, Metrology, Detection and tracking algorithms, Optical fibers, Fiber lasers, Laser metrology
The GRAVITY Instrument Software (INS) is based on the common VLT Software Environment. In addition to the basic Instrument Control Software (ICS) which handles Motors, Shutters, Lamps, etc., it also includes three detector subsystems, several special devices, field bus devices, and various real time algorithms. The latter are implemented using ESO TAC (Tools for Advanced Control) and run at a frequency of up to 4 kHz. In total, the instrument has more than 100 ICS devices and runs on five workstations and seven vxWorks LCUs.
The laser metrology system in the GRAVITY instrument plays a crucial role in an attempt at high-precision narrow-angle astrometry. With a design goal of achieving 10 microarcseconds precision in astrometry, the system must measure the optical path difference between two beam combiners within GRAVITY to an accuracy of better than 5nm. However in its current design, some parts of the optical paths of the metrology system are not common to the optical paths of starlight (the science path) which it must measure with high accuracy. This state of the design is true for most but not all the baselines which will be used by the GRAVITY instrument. The additional non-common optical paths could produce inaccurate path length measurements and consequently inaccurate measurements of the differential phase between fringe packets of two nearby celestial objects, which is the main astrometric observable of the instrument. With reference to the stability and the sensitivity of the non-common paths, this paper describes the impact of a biased differential phase measurement on the narrowangle astrometry and the image reconstruction performance of the GRAVITY instrument. Several alternative designs are also discussed.
KMOS is a multi-object near-infrared integral field spectrograph built by a consortium of UK and German institutes for
the ESO Paranal Observatory. We report on the on-sky performance verification of KMOS measured during three
commissioning runs on the ESO VLT in 2012/13 and some of the early science results.
LUCI (former LUCIFER) is the full cryogenic near-infrared multi-object spectrograph and imager at the LBT. It presently allows for seeing limited imaging and multi-object spectroscopy at R~2000-4000 in a 4x4arcmin2 FOV from 0.9 to 2.5 micron. We report on the instrument performance and the lessons learned during the first two years on sky from a technical and operational point of view. We present the upcoming detector upgrade to Hawaii-2 RG arrays and the operating modes to utilize the binocular mode, the LBT facility AO system for diffraction limited imaging as well as to use the wide-field AO correction afforded by the multi-laser GLAO System ARGOS in multi-object spectroscopy.
KMOS is a multi-object near-infrared integral field spectrograph being built by a consortium of UK and German
institutes. We report on the final integration and test phases of KMOS, and its performance verification, prior to
commissioning on the ESO VLT later this year.
SAMI, the SCAO module for the E-ELT adaptive optics imaging camera MICADO, could be used in the first
years of operation of MICADO on the telescope, until MAORY is operational and coupled to MICADO. We
present the results of the study made in the framework of the MICADO phase A to design and estimate the
performance of this SCAO module.
KEYWORDS: Point spread functions, Galactic astronomy, Stars, Adaptive optics, Kinematics, Photometry, Field spectroscopy, Deconvolution, Signal to noise ratio, Diffraction
We describe several projects addressing the growth of galaxies and massive black holes, for which adaptive optics
is mandatory to reach high spatial resolution but is also a challenge due to the lack of guide stars and long
integrations. In each case kinematics of the stars and gas, derived from integral field spectroscopy, plays a key
role. We explain why deconvolution is not an option, and that instead the PSF is used to convolve a physical
model to the required resolution. We discuss the level of detail with which the PSF needs to be known, and the
ways available to derive it. We explain how signal-to-noise can limit the resolution achievable and show there
are many science cases that require high, but not necessarily diffraction limited, resolution. Finally, we consider
what requirements astrometry and photometry place on adaptive optics performance and design.
ARGOS is the Laser Guide Star adaptive optics system for the Large Binocular Telescope. Aiming for a wide field
adaptive optics correction, ARGOS will equip both sides of LBT with a multi laser beacon system and corresponding
wavefront sensors, driving LBT's adaptive secondary mirrors. Utilizing high power pulsed green lasers the artificial
beacons are generated via Rayleigh scattering in earth's atmosphere. ARGOS will project a set of three guide stars above
each of LBT's mirrors in a wide constellation. The returning scattered light, sensitive particular to the turbulence close to
ground, is detected in a gated wavefront sensor system. Measuring and correcting the ground layers of the optical
distortions enables ARGOS to achieve a correction over a very wide field of view. Taking advantage of this wide field
correction, the science that can be done with the multi object spectrographs LUCIFER will be boosted by higher spatial
resolution and strongly enhanced flux for spectroscopy. Apart from the wide field correction ARGOS delivers in its
ground layer mode, we foresee a diffraction limited operation with a hybrid Sodium laser Rayleigh beacon combination.
GRAVITY is an adaptive optics assisted Beam Combiner for the second generation VLTI instrumentation. The
instrument will provide high-precision narrow-angle astrometry and phase-referenced interferometric imaging in the
astronomical K-band for faint objects. We describe the wide range of science that will be tackled with this instrument,
highlighting the unique capabilities of the VLTI in combination with GRAVITY. The most prominent goal is to observe
highly relativistic motions of matter close to the event horizon of Sgr A*, the massive black hole at center of the Milky
Way. We present the preliminary design that fulfils the requirements that follow from the key science drivers: It includes
an integrated optics, 4-telescope, dual feed beam combiner operated in a cryogenic vessel; near-infrared wavefrontsensing
adaptive optics; fringe-tracking on secondary sources within the field of view of the VLTI and a novel metrology
concept. Simulations show that 10 μas astrometry within few minutes is feasible for a source with a magnitude of
mK = 15 like Sgr A*, given the availability of suitable phase reference sources (mK = 10). Using the same setup, imaging of mK = 18 stellar sources in the interferometric field of view is possible, assuming a full night of observations and the corresponding UV coverage of the VLTI.
MICADO will be the IR imaging camera for the E-ELT. It has been designed to work in conjunction with both SCAO
(in the early phase) and LGS-MCAO system MAORY (for which it has been optimized) and delivers diffraction limited
quality over about 1 arcmin field of view covering the wavelength range from 0.8 to 2.5 micron. In this paper, we
describe the optical configurations and the observing modes, for both the primary and the auxiliary arms, of the current
baseline and we show the expected performances and how the optical path can be folded to fit the available limited space
in the cryo-chamber.
The LUCIFER-MOS unit is the full cryogenic mask-exchange unit for the near-infrared multi-object spectrograph
LUCIFER at the Large Binocular Telescope. We present the design and functionality of this unique device. In LUCIFER
the masks are stored, handled, and placed in the focal plane under cryogenic conditions at all times, resulting in very low
thermal background emission from the masks during observations. All mask manipulations are done by a novel
cryogenic mask handling robot that can individually address up to 33 fixed and user-provided masks and place them in
the focal plane with high accuracy. A complete mask exchange cycle is done in less than five minutes and can be run in
every instrument position and state reducing instrument setup time during science observations to a minimum. Exchange
of old and new MOS masks is likewise done under cryogenic conditions using a unique exchange drive mechanism and
two auxiliary cryostats that attach to the main instrument cryostat.
MICADO is the adaptive optics imaging camera for the E-ELT. It has been designed and optimised to be mounted
to the LGS-MCAO system MAORY, and will provide diffraction limited imaging over a wide (~1 arcmin) field
of view. For initial operations, it can also be used with its own simpler AO module that provides on-axis
diffraction limited performance using natural guide stars. We discuss the instrument's key capabilities and
expected performance, and show how the science drivers have shaped its design. We outline the technical
concept, from the opto-mechanical design to operations and data processing. We describe the AO module,
summarise the instrument performance, and indicate some possible future developments.
KMOS is a near-infrared multi-object integral-field spectrometer which is one of a suite of second-generation
instruments under construction for the VLT. The instrument is being built by a consortium of UK and German
institutes working in partnership with ESO and is now in the manufacture, integration and test phase. In this paper
we present an overview of recent progress with the design and build of KMOS and present the first results from the
subsystem test and integration.
FIFI LS is the German far-infrared integral field spectrometer for the SOFIA airborne observatory. The instrument consists
of two independent integral field spectrometers for two different wavelength bands (45-110 μm and 100-200 μm). A
dichroic filter enables simultaneous observation of two different spectral lines in the same field-of view. This allows very
efficient mapping of extended regions with FIFI LS in many important far-infrared cooling lines with line ratios sensitive to
temperature and density.
FIFI LS will become a facility instrument for SOFIA. In the next two years it will become a fully commissioned facility
instrument. After its commission, FIFI LS will be available for general observing with a large science potential. In this
paper, we will also discuss the science of FIFI LS.
We present the second-generation VLTI instrument GRAVITY, which currently is in the preliminary design phase.
GRAVITY is specifically designed to observe highly relativistic motions of matter close to the event horizon of Sgr A*,
the massive black hole at center of the Milky Way. We have identified the key design features needed to achieve this
goal and present the resulting instrument concept. It includes an integrated optics, 4-telescope, dual feed beam combiner
operated in a cryogenic vessel; near infrared wavefront sensing adaptive optics; fringe tracking on secondary sources
within the field of view of the VLTI and a novel metrology concept. Simulations show that the planned design matches
the scientific needs; in particular that 10µas astrometry is feasible for a source with a magnitude of K=15 like Sgr A*,
given the availability of suitable phase reference sources.
The Phase-Referenced Imaging and Micro-arcsecond Astrometry (PRIMA) facility is scheduled for installation
in the Very Large Telescope Interferometer observatory in Paranal, Chile, in the second half of 2008. Its goal
is to provide an astrometric accuracy in the micro-arcsecond range. High precision astrometry can be applied
to explore the dynamics of the dense stellar cluster. Especially models for the formation of stars near super
massive black holes or the fast transfer of short-lived massive stars into the innermost parsec of our galaxy can
be tested. By measuring the orbits of stars close the the massive black hole one can probe deviations from a
Keplerian motion. Such deviations could be due to a swarm of dark, stellar mass objects that perturb the point
mass solution. At the same time the orbits are affected by relativistic corrections which thus can be tested. The
ultimate goal is to test the effects of general relativity in the strong gravitational field. The latter can be probed
with the near infrared flares of SgrA* which are most likely due to accretion phenomena onto the black hole.
We study the expected performance of PRIMA for astrometric measurements in the Galactic Center based on
laboratory measurements and discuss possible observing strategies.
FIFI-LS is a Field-Imaging Line Spectrometer designed for the SOFIA airborne observatory. The instrument will
operate in the far infrared (FIR) wavelength range from 42 to 210 μm. Two spectrometers operating between
42-110 μm and 110-210 μm allow simultaneous and independent diffraction limited 3D imaging over a field of
view of 6" × 6" and 12" × 12" respectively. We have developed a telescope simulator to test the imaging and
spectral performance of FIFI-LS in the FIR. Here, we present the telescope simulator as well as the performance
verification of FIFI-LS using the simulator. Finally we compare the measurements with the theoretical expected
performance of FIFI-LS.
Laser guide star adaptive optics and interferometry are currently revolutionizing ground-based near-IR astronomy, as
demonstrated at various large telescopes. The Large Binocular Telescope from the beginning included adaptive optics in
the telescope design. With the deformable secondary mirrors and a suite of instruments taking advantage of the AO
capabilities, the LBT will play an important role in addressing major scientific questions. Extending from a natural guide
star based system, towards a laser guide stars will multiply the number of targets that can be observed. In this paper we
present the laser guide star and wavefront sensor program as currently being planned for the LBT. This program will
provide a multi Rayleigh guide star constellation for wide field ground layer correction taking advantage of the multi
object spectrograph and imager LUCIFER in a first step. The already foreseen upgrade path will deliver an on axis
diffraction limited mode with LGS AO based on tomography or additional sodium guide stars to even further enhance
the scientific use of the LBT including the interferometric capabilities.
FIFI LS is a far-infrared integral field spectrometer for the SOFIA airborne observatory. The instrument is designed to maximize the observing efficiency by simultaneous and nearly independent imaging of the field-of-view in two medium spectral resolution bands. We present a summary of the FIFI LS design and the current status of instrument development. Its unique features as the large far-infrared photoconductor detectors, its integral field concept, and control system will be highlighted. Special attention will be given to the Extended Observing Opportunity Program, which will allow general access to FIFI LS on SOFIA.
FIFI LS is a Field-Imaging Line Spectrometer designed for the SOFIA airborne observatory. The instrument will operate in the far infrared wavelength range between 42 to 210 microns. Two spectrometer bands from 42 - 110 microns ('blue' channel) and 110 - 210 microns ('red' channel) allow simultaneous and independent diffraction limited 3D imaging over a field of view of 6 x 6 and 12 x 12 arcseconds respectively. Both spectrometer channels use Littrow mounted diffraction gratings, a set of anamorphic collimators, and a reflective integral field unit. Two large scale 25 x 16 pixel Ge:Ga detector arrays are utilized, axially stressed in the red channel and only slightly stressed in the blue channel. The spectral resolution of the instrument varies between R = 1400 to 6500 depending on wavelength. The sensitivity of the instrument will allow background limited performance over the entire wavelength range. We present test results for the components in the optical path of FIFI LS including grating efficiencies, filter characteristics, detector performance, and optical throughput. Based on our measurements we characterized and optimized the overall system performance to maximize observing efficiency - one of the major instrument design criteria.
We present the adaptive optics assisted, near-infrared VLTI instrument - GRAVITY - for precision narrow-angle astrometry and interferometric phase referenced imaging of faint objects. Precision astrometry and phase-referenced interferometric imaging will realize the most advanced vision of optical/infrared interferometry with the VLT. Our most ambitious science goal is to study motions within a few times the event horizon size of the Galactic Center massive black hole and to test General Relativity in its strong field limit. We define the science reference cases for GRAVITY and derive the top level requirements for GRAVITY. The installation of the instrument at the VLTI is planned for 2012.
KMOS is a near-infrared multi-object integral field spectrometer which has been selected as one of a suite of second-generation instruments to be constructed for the ESO VLT in Chile. The instrument will be built by a consortium of UK and German institutes working in partnership with ESO and is currently at the end of its preliminary design phase. We present the design status of KMOS and discuss the most novel technical aspects and the compliance with the technical specification.
Using adaptive optics on the Keck Telescope and the VLT, we are able to probe the dynamics and star formation in Seyfert and QSO nuclei on spatial scales better than 0.1" in the H- and K-bands. Such spectroscopic data are essential for studying the link between AGN and star formation, understanding how gas is driven into the
nucleus, and measuring the black hole mass. In this contribution we present some of our recent results, and consider what an astronomer needs from an adaptive optics system for extragalactic work, as well as what is realistic to expect. We discuss why deconvolution is not appropriate in this context; and examine the scientifically more useful alternative of convolving a model with an estimate of the PSF, describing what level of detail and reliability can actually be achieved in the various methods of measuring the PSF.
FIFI LS is a far-infrared integral field spectrometer for the SOFIA airborne observatory. The instrument is designed to maximize the observing efficiency by simultaneous and nearly independent imaging of the field of view in two medium spectral resolution bands. Both spectral channels - covering a wavelength range of 42 to 110 microns and 110 to 210 microns respectively - allow diffraction limited spectral imaging. Reflective image slicers rearrange the 5x5 pixel field of view into the 1x25 pixel entrance slit of a grating spectrograph. Littrow mounted gratings with anamorphic collimators are used for spectral multiplexing with a spectral resolution between R = 1400 - 6500, depending on observing wavelength. Each spectral band employs two large format 25x16 pixel Ge:Ga detector arrays, axially stressed for the long wavelength band to achieve a longer wavelength response and slightly stressed for the short wavelength band. For each of the 25 spatial pixels, we are able to cover a velocity range of approximately 1500 km/s around a selected far-infrared line. This arrangement provides good spectral coverage with high responsivity. We present a summary of the FIFI LS design and the current status of instrument integration.
SPIFFI (SPectrometer for Infrared Faint Field Imaging) is a fully cryogenic, near-infrared imaging spectrograph built at the Max-Planck-Institute for Extraterrestrial Physics (MPE) and upgraded with a new detector and spectrograph camera by ASTRON/NOVA, ESO and MPE. The upgraded instrument will become a facility instrument for the ESO VLT in summer 2004 as part of the SINFONI (SINgle Faint Object Near-IR Investigation) project, which is the combination of SPIFFI and ESOs adaptive optics module MACAO (Multiple Application Curvature Adaptive Optics), at the Cassegrain focus of Yepun (UT4). In spring 2003 we had the opportunity to observe with SPIFFI as a guest instrument without the AO-module at the Cassegrain focus of UT2 of the VLT. In this paper we discuss the performance of SPIFFI during the guest-instrument phase. First we summarize the technical performance of SPIFFI like the spatial and spectral resolution, the detector performance and the instruments throughput. Afterwards we illustrate the power of integral field spectroscopy by presenting data and results of the Galactic Center.
We describe the design of a 2nd generation instrument for the ESO VLT which will deliver a unique multiple deployable integral field capability in the near-infrared (1-2.5μm). The science drivers for the instrument are presented and linked to the functional specification. The baseline instrument concept is described with emphasis on technological innovations. Detailed discussions of specific technologies, and ongoing prototype studies, are described in separate papers.
SINFONI is an adaptive optics assisted near-infrared integral field spectrometer for the ESO VLT. The Adaptive OPtics Module (built by the ESO Adaptive Optics Group) is a 60-elements curvature-sensor based system, designed for operations with natural or sodium laser guide stars. The near-infrared integral field spectrometer SPIFFI (built by the Infrared Group of MPE) provides simultaneous spectroscopy of 32 x 32 spatial pixels, and a spectral resolving power of up to 3300. The adaptive optics module is in the phase of integration; the spectrometer is presented tested in the laboratory. We provide an overview of the project, with particular emphasis on the problems encountered in designing and building an adaptive optics assisted spectrometer.
We describe a proposed 2nd generation instrument (KMOS) for the ESO VLT which will deliver a unique multiple integral field capability in the near-infrared (1-2.5 μm). The science drivers for such an instrument are presented and linked to the functional specification. The overall instrument concept is discussed in the context of two proposed solutions for delivering a deployable integral field capability. Detailed discussions of these two approaches, and ongoing prototype studies, are described in separate papers.
FIFI LS is a far-infrared integral field spectrometer for SOFIA that
maximizes observing efficiency by spectrally imaging fields in two
medium velocity resolution bands simultaneously and nearly independently. Although the two observing bands, Red (110-210 microns) and Blue (42-110 microns), share some common fore-optics, the Field-Imaging Far-Infrared Line Spectrometer (FIFI LS) can observe diffraction-limited spectra at R = 1400 to 6500, depending on wavelength, with two separate Littrow mounted spectrometers. To further increase the observing efficiency, we employ an integral field technique that allows multiplexing spatially. This is achieved by utilizing slicer mirrors to optically re-arrange the 2D field into a single slit for a standard long slit spectrometer. Effectively,
a 5 × 5 pixel spatial field of view is imaged to a 25 × 1 pixel slit and dispersed to a 25 × 16 pixel, 2D detector array. The detectors are two large format Ge:Ga arrays, axially stressed in the Red channel to achieve a longer wavelength response and slightly stressed in the Blue channel. Overall, for each of the 25 spatial pixels in each band, the instrument can cover a velocity range of approximately 1500 km/s with an estimated sensitivity of 2 × x 10-15 W Hz1/2 per pixel. This arrangement provides good spectral coverage with high responsivity. With this scheme FIFI LS will have advantages over single-slit spectrometers in detailed morphological studies of the heating and cooling of galaxies, star formation, the ISM under low-metalicity conditions as found in dwarf galaxies, active galactic nuclei and their environment, starbursts, and merging/interacting galaxies.
We present the optical system of the Field-Imaging Far-Infrared Line Spectrometer (FIFI LS) for the SOFIA airborne observatory. The instrument is designed to allow diffraction limited integral field spectroscopy in the far infrared wavelength range 42 to 210 microns. Two parallel wavelength channels (42 - 110 microns and 110 - 210 microns) employ Littrow mounted diffraction gratings with anamorphic collimators. Mirror image slicers in each channel rearrange the 5 × 5 pixel field of view along the 1 × 25 entrance slit of the grating spectrograph. The spectral resolution varies in the range of R = 1400 - 6500, depending on observing wavelength. The optical components in the image slicer is comprised of several mirrors with physical dimensions on the order of a few tens of wavelength. Consequently diffraction effects are a serious concern in the design of the optical system. Substantial effort in modeling diffraction effects throughout the optical system and its impact upon the expected performance of the instrument have been made. The results of the scalar diffraction analysis carried out with a commercial software package has been confirmed by a full vectorial analysis, showing negligible dependence of the diffraction effects on the polarization properties of the electromagnetic field.
Using ISAAC on VLT-ANTU and UVES on VLT-KUEYEN we have begun a program to measure stellar velocity dispersions of young star clusters in merging and interacting galaxies. In this contribution, we present results for clusters in two interacting galaxies - NGC 4038/39 and NGC 1487. Combining the measured velocity dispersions with sizes of the clusters estimated from Hubble Space Telescope imaging data resulted in the first determinations of dynamical masses of stellar clusters in galaxy mergers. Due to the faintness of the clusters and the high spectral resolution required, these results could only be obtained in with 10m class telescopes.
Our results suggest that masses, sizes and concentrations of the light distributions are comparable to those of globular clusters, supporting the idea that part of the globular cluster population in elliptical galaxies is formed as a result of a merger event between to gas-rich spiral galaxies. However, the initial mass function (IMF) of the stars in the clusters seems to vary with environment: In some regions (dust-rich?), the IMF is more biased towards low-mass stars than in other (dust-poor) regions. There is a long-standing and substantial controversy in the literature whether or not their exists a "universal IMF". Our results for clusters in merging galaxies support the notion that the IMF depends on the birth environment of the cluster or perhaps some other variable. The relative content of low mass stars also influences the survival probability of stellar clusters. For their masses and light concentrations, some of the clusters have sufficiently shallow IMFs that it is likely that they will dissolve within a Hubble time, while for others, the IMF is sufficiently steep that they are likely to survive but undergo significant mass loss during their evolution.
We present a progress report on the design and construction of the Field-Imaging Far-Infrared Line Spectrometer (FIFI LS) for the SOFIA airborne observatory. The design of the instrument is driven by the goal of maximizing observing efficiency, especially for observations of faint, extragalactic objects. Thus, FIFI LS utilizes an integral field technique that uses slicer mirrors to optically re- arrange the 2D field into a single slit for a long slit spectrometer. Effectively, a 5 X 5 pixel spatial field of view is imaged to a 25 X 1 pixel slit and dispersed to a 25 X 16 pixel, 2D detector array, providing diffraction- limited spatial and spectral multiplexing. In this manner, the instrument employs two parallel, medium resolution (R approximately 2000) grating spectrometers for simultaneous observations in two bands: a short wavelength band (42 to 110 micrometers ) and a long wavelength band (110 to 210 micrometers ). Overall, for each of the 25 spatial pixels, the instrument can cover a velocity range of approximately 1500 km/s around selected far-infrared lines with an estimated sensitivity of 2 X 10-15 W Hz1/2 per pixel. This arrangement provides good spectral coverage with high responsivity.
SINFONI, the SINgle Faint Object Near-IR Investigation, is an instrument for the very large telescope, designed to provide spectroscopy at the telescope diffraction limit in the near-IR. This unique capability is achieved by combining two state-of-the-art developments, an integral field spectrometer and a curvature sensor based adaptive optics system. SINFONI is a collaborative effort by the Max-Planck- Institut fuer extraterrsetrische Physik and the European Southern Observatory.
The powerful tools of integral field spectroscopy and adaptive optics have made great contributions to the progress in astronomy in recent years. The combined use of these techniques now enables spectroscopy in the near IR close to the telescope diffraction limit. This will provide new and interesting insights into a variety of objects such as AGNs, QSOs, circumstellar disks around highly extincted YSOs, etc. Spectroscopy at or close to the telescope diffraction limit has some caveats which one has to be aware of when designing the instruments so as to maintain the maximum possible throughput and to optimize spectral resolution. Astronomical campaigns with our H- and K-band integral field array spectrograph 3D in combination with the laser guide star adaptive optics system ALFA at the 3.5-m telescope at Calar Alto require special observational techniques in order to make the most efficient use of the observing time available. Chopping by moving the telescope to do background subtraction makes it necessary to relock the A.O. system on the guide star after moving the telescope back to source. This procedure is usually rather time consuming. The aperture interchange module (AIM), which we present here, enables us to perform chopping between source and black sky while keeping the telescope fixed at a certain point in the sky. For this purpose AIM uses two different optical channels. The ON channel always points to the center of the 3'ALFA FOV, picking off a FOV of roughly 4 inch by 4 inch. With the OFF channel one can choose any off-center position within the ALFA FOV except a central obscuration of 36 inch diameter. The AIM optics are designed in such a way that the optical pathlengths for the on- and off-axis positions are kept equal. AIM also includes a scale changer which magnifies the scale from 0.25 inch/pix to 0.07 inch pix. The 3D spectrometer itself is equipped with two interchangeable grisms, so that one can choose between H- and K-bands and between spectral resolutions of 1100 and 2100. The commissioning run of AIM together with 3D and ALFA took place in July 1997 at the 3.5m Calar Alto telescope.
3D, the next generation near-IR spectrometer developed at the MPE, offers, in a single integration, the opportunity to image an 8" x 8" field with a pixel scale of 0.5" or 0.3" across the entire K- or H-band simultaneously at a spectral resolution of R equals 1000 or R equals 2000 (K). Combining the advantages of imaging and spectroscopy increases the observing efficiency on small extended objects (e.g., galactic nuclei) by such a large factor over existing grating or Fabry-Perot spectrometers that subarcsecond near-IR spectroscopy on faint Seyferts, starbursts, quasars, or distant galaxies clusters becomes feasible for the first time on 4 m class telescopes. 3D, including a NICMOS III FPA at 25 e-/single read, has been successfully operated at telescopes such as the 4.2 m WHT, 3.5 m Calar Alto, and 2.2 m La Silla. An additional tip-tilt seeing corrector for 3D called ROGUE correcting on up to 18th mag stars at 4 m-class-telescopes was successfully commissioned in the summer of 1994. The optical and electronic design of 3D as well as recent results are presented.
Near infrared imaging spectroscopy at spatial resolutions of 0.5 arc seconds will fundamentally change our understanding of active galactic nuclei. This long desired capability has been achieved for the first time by the latest generation of MPE instruments, ROGUE and 3D. ROGUE, the rapid off-axis guider experiment, is a low order adaptive optics system performing tip-tilt correction in the near infrared using natural guide stars. Three-dimensional is the MPE near infrared imaging spectrometer capable of simultaneous imaging and spectroscopy of the entire H and K atmospheric windows. ROGUE is capable of tip-tilt correction at 40 Hz in a 4 arc-minute diameter isokinetic patch using natural guide stars as faint as 18th magnitude. We discuss the design of the instrument, present the first astronomical results, and outline future efforts to incorporate variable image scales.
We present the first astronomical results from the new 3D near IR imaging array spectrometer. These include K band (1.95 to 2.45 micrometers ) spectra and images of nearby starburst galaxies and active galactic nuclei with a spectral resolution of 1000. A special image slicer allows simultaneous spectra and imaging of an 8 arc second field of view. The background limited performance achieved by this instrument represents an order of magnitude reduction in integration time over existing near IR cameras and spectrometers. In addition, subtraction of atmospheric OH lines may be performed with far higher accuracy. We discuss the data reconstruction procedure, with special emphasis on flat fielding and calibration of the detector. This is complicated by the scrambled image format, which results in adjacent image pixels being widely separated on the detector. Small non linearities of the optical elements must also be dealt with carefully. We also discuss future improvements to instrument performance, including a low order adaptive optics system for compensating atmospheric turbulence.
The Very Large Telescope Interferometer (VLTI) is one of the operating modes of the VLT. In addition to consisting of the four stationary 8-meter-diameter telescopes, it includes a number of movable Auxiliary Telescopes which both complement the (u,v) plane coverage of the large telescopes and provide a powerful interferometric facility by itself (available 100 percent of the time). The current plans for the implementation of the VLTI are described. These plans will be finalized after the choice of the VLT site in 1990.
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