We present details of the recent trade study on design changes to the Wide Field Optical Spectrometer (WFOS) for the Thirty Meter Telescope (TMT)[1]. WFOS is planned as a first light instrument and will provide highly efficient imaging and multi-slit spectroscopy over the wavelength range 0.31 to 1µm across a field of view of 8.3 by 3 arcminutes. The existing baseline prior to the trade study used a laser cut metal slit mask at the focal plane to enable observation of ~50 to 80 objects simultaneously. The masks would be cut in advance of observing and installed in a cassette, allowing a mechanism to select the mask and move it into place at the focal plane. Each multi-object observation requires a dedicated mask, with a more general single long slit mask remaining in the cassette permanently. The configurable slit unit (CSU) is an alternative approach, and a design that has previously been used in MOSFIRE and FORS. A CSU uses multiple knife edges mounted on computer-controlled bars to create and position slits at the focal plane. In the case of WFOS the CSU will be capable of creating 96 separate slits with the ability to reconfigure them on the fly to adapt to seeing conditions or to respond to targets of opportunity. We detail here the decision criteria, design, and science case analysis used by the WFOS team to decide to change the baseline design of WFOS to incorporate a CSU.
The Infrared Imaging Spectrograph (IRIS) is a diffraction-limited instrument designed for the Thirty Meter Telescope (TMT) through an international collaboration. IRIS works in tandem with the Narrow-Field InfraRed Adaptive Optics System (NFIRAOS) and covers a near-infrared spectral range of 0.84 to 2.4 microns. IRIS and NFIRAOS will be the instruments used to demonstrate first light at TMT. IRIS incorporates a wide-field Imager with a fixed plate scale of 4 milliarcseconds (mas), and an Integral Field Spectrograph (IFS) offering four plate scales that range from 4 mas to 50 mas. In 2021, the major subsystems of IRIS went through final design reviews. This paper provides an update on IRIS design and outlines the plan for its fabrication, integration, and delivery to TMT for first light.
We present the preliminary design for the configurable slit unit (CSU) for TMT’s Wide Field Optical Spectrometer (WFOS). The design consists of 96 bar pairs that can create an arbitrary pattern of focal plane slits. The large number of motorized mechanisms to drive the bars into position requires a high reliance on off the shelf components to reduce cost and design effort. A prototype was completed that shows the selected components will likely meet requirements. The current design nearing completion as WFOS ramps into a preliminary design review in 2025.
HISPEC is a new, high-resolution near-infrared spectrograph being designed for the W.M. Keck II telescope. By offering single-shot, R 100,000 spectroscopy between 0.98 – 2.5 μm, HISPEC will enable spectroscopy of transiting and non-transiting exoplanets in close orbits, direct high-contrast detection and spectroscopy of spatially separated substellar companions, and exoplanet dynamical mass and orbit measurements using precision radial velocity monitoring calibrated with a suite of state-of-the-art absolute and relative wavelength references. MODHIS is the counterpart to HISPEC for the Thirty Meter Telescope and is being developed in parallel with similar scientific goals. In this proceeding, we provide a brief overview of the current design of both instruments, and the requirements for the two spectrographs as guided by the scientific goals for each. We then outline the current science case for HISPEC and MODHIS, with focuses on the science enabled for exoplanet discovery and characterization. We also provide updated sensitivity curves for both instruments, in terms of both signal-to-noise ratio and predicted radial velocity precision.
At first light, the NIR instruments of TMT will be assisted by a multi-conjugate adaptive optics instrument, known as the Narrow Field Infrared Adaptive Optics System (NFIRAOS). NFIRAOS will use laser guide stars for distortion correction in a field of view of 2 arcmin diameter, but natural guide stars will be required for tip/tilt correction. A catalogue of guide stars with NIR magnitudes as faint as 22 mags in J band (Vega system), covering the TMT-observable sky will be a critical resource for the efficient operation of NFIRAOS and no catalogue currently exists with objects so faint and cover the entire TMT observable sky. Hence it is essential to develop such a catalogue by computing the expected NIR magnitudes of stellar sources, identified in deep optical sky surveys, by using their optical magnitudes. In this paper, we will discuss a road map created for the generation of the Infrared Guide Star Catalogue (IRGSC) for the TMT using the optical data of stellar sources from the Pan-STARRS observations and computing their NIR magnitudes by using stellar atmospheric models and Spectral Energy Distribution (SED) fits. We have validated the computed NIR magnitudes of the sources in some fields by using the available NIR data for those fields. We find our method to be satisfactory, thereby creating a path for the final production of the IRGSC using the Pan-STARRS and put forward the challenges that need to be overcome in the future development of IRGSC.
With more than a decade of design work behind them, the instrumentation program of each of the three Extremely Large Telescope (ELT)-class telescopes is now ready to lock-in the set of capabilities it will be able to offer to their respective community at first light. The Giant Magellan Telescope, the Thirty Meter Telescope, and the European Southern Observatory’s ELT have each followed a formal instrumentation prioritization process with input from the astronomical community, which resulted in extensive and complementary suites of instruments that will be divided into two generations. We present this process as well as the general scientific characteristics of every instrument currently being developed for the three observatories. We also present how these instruments will fit the operation models of the observatories.
Observatory end-to-end science operations is the overall process starting with a scientific question, represented by a proposal requesting observing time; ending with the analysis of observation data addressing that question; and including all of the intermediate steps needed to plan, schedule, obtain, and process these observations. Increasingly complex observing facilities demand a highly efficient science operations approach and at the same time must be user friendly to the astronomical user community and enable the highest possible scientific return. Therefore, this process is supported by a collection of tools. We describe the overall end-to-end process and its implementation for the three upcoming Extremely Large Telescopes (ELTs): European Southern Observatory’s ELT, the Thirty Meter Telescope, and the Giant Magellan Telescope.
The IRIS Exposure Time Calculator (ETC) was designed to be a publicly available aid to the astronomical community in the development of science cases for the Infrared Imaging Spectrograph (IRIS) and future proposal planning. The IRIS ETC is developed from the IRIS simulator in which the signal-to-noise calculation is done pixel-by-pixel for 2D and 3D data. The IRIS ETC makes use of simulated Narrow Field InfraRed Adaptive Optics System (NFIRAOS) point spread functions sampling the performance at key positions across the focal plane of the IRIS imager and Integral Field Spectrograph, with varying adaptive optics performances and atmospheric conditions. Like the IRIS simulator, we model the near-infrared background with variable OH emission lines and thermal emission from the atmosphere to provide accurate noise estimates. The IRIS ETC is designed to work with the hundreds of modes given the combination of filters and grating selection. The framework, developed in Python and making use of Astropy and Photutils, can handle any 2D or 3D data input and therefore can be easily adapted for any current or future near-infrared instrument.
The transition from construction to operations of the Thirty-Meter-Telescope (TMT) will happen over a phase of "early-operations” that will last several years to encompass the technical and science commissioning of its main systems, and will conclude when the facility enters "steady-state operations” (early 2030s according to the current schedule).
In this talk, we will present the current plan for technical and scientific operations of the Thirty-Meter-Telescope, including a description of its organizational structure, staffing and day-to-day activities. TMT's science operations model will be aimed at optimizing the science impact of the TMT and its operations efficiency, while providing a high-level of support to TMT users over all phases (submission, implementation and (post-)execution) of their science programs.
The TMT Early-Career Initiative (TECI) is an innovative, evolving program designed to support inclusion in the Thirty Meter Telescope (TMT) International Observatory (TIO) by engaging graduate students and postdocs in TIO projects, and preparing them with skills required to contribute to the project and advance in their careers. TECI has an annual cycle that begins with a workshop that includes project management, instrument design, and teamwork sessions, and engages participants in projects that could lead to visits and new collaborations. Project teams are led by the participants themselves, who consult with a member of the relevant technical team or project staff. In this paper we describe the components of TECI, our approach to designing it, and outcomes from our early piloting in 2016-17, as well as our first full program in 2018-19.
The Thirty Meter Telescope (TMT) is a future generation telescope proposed to be located in Mauna Kea, Hawaii or in La Palma in the Canary Islands. The telescope will have a segmented primary and an inclined tertiary mirror. The segmentation of the primary mirror and the inclination in the tertiary mirror can introduce significant polarization aberrations. Typically, the polarization aberrations, introduced due to the mirror coating and the high incident angles cause small modifications to the Point Spread Function (PSF). Here, we perform the polarization ray tracing for TMT using the optical design software Zemax for different input polarizations for a point source (on-axis). We calculate the diattenuation and retardance aberration maps for all the three mirrors of TMT. The coating induced astigmatism obtained from the retardance of the primary and secondary mirror is found to be of the order of 0.048 radians, whereas, the polarization induced tilt by the retardance of the tertiary mirror is in the order of 0.29 radians. The Jones pupil maps are estimated at two of the instrument ports, Wide Field Optical Spectrograph (WFOS) and Narrow Field Infrared Adaptive Optics System (NFIRAOS).The Amplitude Response Matrix (ARM) estimated at the WFOS port show the presence of ghost PSF's. The magnitude of the ghost PSF components is of the order of 2.5 x 10-5 at 1μm at WFOS port. The ARM and the Point Spread Matrix (PSM) are estimated at the focus of the NFIRAOS instrument. The Stokes PSF is shown for horizontal and vertical polarization as inputs. The Huygen's point spread function obtained from Zemax shows the variations in FWHM for unpolarized and polarized inputs. These estimations would help in the design aspects of a high contrast imaging instrument for the TMT in the future.
An analytical model has been developed to estimate the polarization effects, such as instrumental polarization (IP), crosstalk (CT), and depolarization, due to the optics of the Thirty Meter Telescope. These are estimated for the unvignetted field-of-view and the wavelengths of interest. The model estimates an IP of 1.26% and a CT of 44% at the Nasmyth focus of the telescope at the wavelength of 0.6 μm at field angle zero with the telescope pointing to zenith. Mueller matrices have been estimated for the primary, secondary, and Nasmyth mirrors. It is found that some of the Mueller matrix elements of the primary and secondary mirrors show a fourfold azimuthal antisymmetry, which indicates that the polarization at the Cassegrain focus is negligible. At the inclined Nasmyth mirror, there is no azimuthal antisymmetry in the matrix elements, and this results in nonzero values for IP and CT, which would negatively impact the polarization measurements at the telescope focus. The averaged Mueller matrix is estimated at the Nasmyth focus at different instrument ports and various zenith angles of the telescope. The variation in the Mueller matrix elements for different coatings is also estimated. The impact of this polarization effect on the science case requirements has been discussed. This analysis will help in achieving precise requirements for future instruments with polarimetric capability.
The polarization introduced due to Thirty Meter Telescope (TMT) optics is calculated using an analytical model. Mueller matrices are also generated for each optical element using Zemax, based on which the instrumental polarization due to the entire system at the focal plane is estimated and compared with the analytical model. This study is significant in the estimation of the telescope sensitivity and also has great implications for future instruments.
The Thirty Meter Telescope (TMT) will be called upon to support a polarimetric observing capability. Many different observing programs covering a range of different science areas are being considered for the TMT and a model of the overall polarization characteristics is being developed. The instrument development program will provide a means for polarimetric instruments to be developed, however the telescope itself and the AO system must be able to support polarimetric instruments. As a first step to defining the necessary polarimetric technical requirements we have created an international working group to carry out a study in which technical and cost implications will be balanced with scientific impact; new requirements will be generated with supporting science cases. We present here initial results of the instrumental polarization sensitivity of TMT with NFIRAOS, the first-light adaptive optics system.
Dome and mirror seeing are critical effects influencing the optical performance of ground-based telescopes.
Computational Fluid Dynamics (CFD) can be used to obtain the refractive index field along a given optical path and
calculate the corresponding image quality utilizing optical modeling tools. This procedure is validated using
measurements from the Keck II and CFHT telescopes.
CFD models of Keck II and CFHT observatories on the Mauna Kea summit have been developed. The detailed models
resolve all components that can influence the flow pattern through turbulence generation or heat release. Unsteady
simulations generate time records of velocity and temperature fields from which the refractive index field at a given
wavelength and turbulence parameters are obtained.
At Keck II the Cn2 and l0 (inner scale of turbulence) were monitored along a 63m path sensitive primarily to turbulence
around the top ring of the telescope tube. For validation, these parameters were derived from temperature and velocity
fluctuations obtained from CFD simulations.
At CFHT dome seeing has been inferred from their database that includes telescope delivered Image Quality (IQ). For
this case CFD simulations were run for specific orientations of the telescope respect to incoming wind, wind speeds and
outside air temperature. For validation, temperature fluctuations along the optical beam from the CFD are turned to
refractive index variations and corresponding Optical Path Differences (OPD) then to Point Spread Functions (PSF) that
are ultimately compared to the record of IQ.
During the site testing campaign for the Thirty Meter Telescope (TMT) in addition to the optical conditions of the atmosphere, measurements of the soil surface properties were obtained also. The dust concentration in the air was measured by means of dust sensors which were mounted underneath the mount of the site monitoring telescopes. The ground head fluxes and soil temperatures were measured several centimeters into the ground. On Cerro Armazones it was also possible to conduct an experiment to measure heat conduction of the soil. In this paper, all of these measurements are described, the results and their potential use is summarized.
KEYWORDS: Actuators, Mirrors, Turbulence, Servomechanisms, Adaptive optics, Telescopes, Data modeling, Systems modeling, Wind energy, Control systems design
The principal dynamic disturbances acting on a telescope segmented primary mirror are unsteady wind pressure
(turbulence) and narrowband vibration from rotating equipment. Understanding these disturbances is essential
for the design of the segment support assembly (SSA), segment actuators, and primary mirror control system
(M1CS). The wind disturbance is relatively low frequency, and is partially compensated by M1CS; the response
depends on the control bandwidth and the quasi-static stiffness of the actuator and SSA. Equipment vibration is
at frequencies higher than the M1CS bandwidth; the response depends on segment damping, and the proximity
of segment support resonances to dominant vibration tones. We present here both disturbance models and
parametric response. Wind modeling is informed by CFD and based on propagation of a von Karman pressure
screen. The vibration model is informed by analysis of accelerometer and adaptive optics data from Keck. This
information is extrapolated to TMT and applied to the telescope structural model to understand the response
dependence on actuator design parameters in particular. Whether the vibration response or the wind response
is larger depends on these design choices; "soft" (e.g. voice-coil) actuators provide better vibration reduction
but require high servo bandwidth for wind rejection, while "hard" (e.g. piezo-electric) actuators provide good
wind rejection but require damping to avoid excessive vibration transmission to the primary mirror segments.
The results for both nominal and worst-case disturbances and design parameters are incorporated into the TMT
actuator performance assessment.
In order to validate various assumptions about the operating environment of the Thirty Meter Telescope (TMT),
to validate the modeling packages being used to guide the design work for the TMT and to directly investigate
the expected operation of several subsystems we have embarked on an extensive campaign of environmental
measurements at the Keck telescopes. We have measured and characterized the vibration environment around
the observatory floor and at certain locations on the telescope over a range of operating conditions. Similarly the
acoustic environment around the telescope and primary mirror has been characterized for frequencies above 2 Hz.
The internal and external wind and temperature fields are being measured using combined sonic anemometer
and PRT sensors. We are measuring the telescope position error and drive torque signals in order to investigate
the wind induced telescope motions. A scintillometer mounted on the telescope is measuring the optical
turbulence inside the telescope tube. This experimental work is supplemented by an extensive analysis of telescope
and engineering sensor log files and measurements, primarily those of accelerometers located on the main
telescope optics, primary mirror segment edge sensor error signals (residuals), telescope structure temperature
measurements and the telescope status information.
Between February and April 2009 a number of ultrasonic anemometers, temperature probes and dust sensors were
operated inside the CTIO Blanco telescope dome. These sensors were distributed in a way that temperature and
3 dimensional wind speeds were monitored along the line of sight of the telescope. During telescope operations,
occasional seeing measurements were obtained using the Mosaic CCD imager and the CTIO site monitoring MASS-DIMM
system. In addition, also a Lunar Scintillometer (LuSci) was operated over the course of a few nights inside the
dome. We describe the instrumental setup and first preliminary results on the linkage of the atmospheric conditions
inside the dome to the overall image quality.
Atmospheric optical turbulence is the main driver of wavefront distortions which affect optical telescope performance.
Therefore, many techniques have been developed to measure the optical turbulence strength along the line of sight.
Based on data collected with the MASS (Multi Aperture Scintillation Sensor), we show that a large sample of such
measurements can be used to assess the average three dimensional turbulence distribution above ground.
The use of, and a more sophisticated instrumental setup for, such turbulence tomography will be discussed.
With the development of increasingly larger and more complex telescopes and instrumentation, site testing and
characterization efforts also increase in both magnitude and complexity. This happens because the investment
into larger observatories is higher and because new technologies, such as adaptive optics, require knowledge about
parameters that did not matter previously, such as the vertical distribution of turbulence. We present examples
of remaining questions which, to date, are not generally addressed by "standard" site characterization efforts,
either because they are technically not (yet) feasible or because they are impractical. We center our observations
around the experience gained during the Thirty Meter Telescope (TMT) site testing effort with an emphasis
on turbulence measurements, but our findings are applicable in general to other current and future projects as
well.
The ground layer turbulence at Dome C is the cause for more than 90% of the total turbulence column. While the height
of this layer has been currently measured to be approximately 30m, no long term statistics is available from this part of
the atmosphere. In order to plan the construction of future telescope at this site temperature site, temperature, wind speed
and turbulence measurements are also necessary. Using fast sonicanemometers we present, a preliminary set of data
covering January to October 2007 sampling these quantities at heights of 8, 16 and 28 meters.
All Sky Cameras were deployed at all Thirty Meter Telescope (TMT) candidate sites. The images gathered
by these cameras were used to assess the cloud statistics for each site. We describe two methods that were
developed to do this, a manual method based on inspection of blue and red movies, and an automated method
based on photometric analysis of the images.
The Thirty Meter Telescope (TMT) project has been collecting data on five candidate sites since 2003. This paper
describes the site testing portion of the TMT site selection program and the process and standards employed
by it. This includes descriptions of the candidate sites, the process by which they were identified, the site
characterization instrument suite and its calibration and the available results, which will be published shortly.
One of the main tools used in the TMT site testing campaign is the turbulence profiler MASS. We describe
empirical investigations and a side by side comparison of two MASS systems which were performed in order to
identify the accuracy of MASS turbulence data and its dependence on the instrument calibration. The accuracy
of the total seeing delivered by the TMT MASS systems is found to be better than 0"05. The combination of
MASS and DIMM allows to observe the seeing within the first few hundred meters of the atmosphere and can be
used to investigate possible correlations with meteorological parameters measured close to the ground. We also
compare the detection of clouds and cirrus by means of MASS data (LOSSAM method) with measurements of
the thermal emission of clouds using a net radiation sensor. These methods are compared with the visual cloud
detection using all sky cameras.
Seeing stability is an important criterion of site characterization. Two sites, with the same seeing statistics, could in
principle differ in their temporal stability and hence have their observatories perform differently. Temporal variability
can, however, be defined in several ways, all of which may determine the performance of the observatories in different
manner. In this paper, we propose three methods to measure variability each focusing on different applications: Selection
(maximization of observation time), Image quality (seeing variation within a given integration time) and finally
Scheduling (prediction of seeing fluctuation on a given time scale). We apply these methods to the seeing of the TMT
candidate sites to determine their stability properties.
Light pollution can create difficulties for astronomers attempting to observe faint objects in the night sky. Light
from a local small town can be just as intrusive as light from a large city in the distance. As the population
of the Earth increases, light pollution will become more of a problem, even in remote areas. The Thirty Meter
Telescope site testing program has measured light pollution at the candidate sites by using all sky cameras;
an analysis procedure enhances the all sky camera images to make the determination of the effects of the light
pollution. This paper summarizes the light pollution analysis procedure and current results, which are that light
pollution is currently unimportant for TMT to select a site for the final telescope location.
Differential Image Motion Monitors (DIMMs) have become the industry standard for astronomical site characterization.
The calibration of DIMMs is generally considered to be routine, but we show that particular care
must be paid to this issue if high accuracy measurements are to be achieved. In a side by side comparison of
several DIMMs, we demonstrate that with proper calibration we can characterize the seeing to better than ±0.02
arcseconds.
The Thirty Meter Telescope (TMT) project is currently testing six remote sites as candidates for the final location
of the telescope. Each site has several instruments, including seeing monitors, weather stations, and turbulence
profile measuring systems, each of which is computer controlled. As the sites are remote (usually hours from
the nearest town), they requires a system that can control the operations of all the varied subsystems, keep the
systems safe from damage and recover from errors during operation. The robotic system must also be robust
enough to operate without human intervention and when internet connections are lost. It is also critical that a
data archiving system diligently records all data as gathered. This paper is a discussion of the TMT site testing
robotic computer system as implemented.
The Thirty Meter Telescope (TMT) site testing programme is evaluating the use of sonic anemometers as a means
of measuring the optical turbulence at the level of its MASS/DIMM telescopes (7m). Tests were performed where
sonic anemometers were directly compared against a differenced fine wire thermocouple system. We also show
here that fine wire thermocouples produce turbulence measurements comparable to those from a traditional
microthermal probe system.
The Thirty Meter Telescope (TMT) site testing team are developing a suite of instruments to measure the atmospheric and optical characteristics of candidate TMT sites. Identical sets of robotically operating instruments will be placed at each candidate site. The fully developed system will comprise of a combined MASS/DIMM. a SODAR, tower mounted thermal probes and a portable DIMM. These instruments have overlapping altitude coverage and provide a measure of the C2n profile from the ground up with sufficient resolution to make conclusions about the ground layer and high altitude turbulence characteristics. The overlapping altitude coverage is essential to ensure consistency between these very different instruments. In addition to checking for consistency in the overlap regions, procedures are being used to cross check between instruments, i.e. the calculation of the isoplanatic angle from both the MASS and DIMM and that the integrals of the C2n profiles from the MASS, SODAR and 30m tower gives the same r0 value as measured by the DIMM.
We discuss a variation of the traditional DIMM system in which we employ a continuous drift mode readout technique giving a maximum of nearly 300 samples per second.
Findings of our major equipment testing campaigns and first field deployment are presented that demonstrate our progress in developing a rigorous approach to site testing.
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