The HETDEX Instrumentation: Hobby–Eberly Telescope Wide-field Upgrade and VIRUS

The Hobby–Eberly Telescope (HET) Dark Energy Experiment (HETDEX) is undertaking a blind wide-field low-resolution spectroscopic survey of 540 deg2 of sky to identify and derive redshifts for a million Lyα-emitting galaxies in the redshift range 1.9 < z < 3.5. The ultimate goal is to measure the expansion rate of the universe at this epoch, to sharply constrain cosmological parameters and thus the nature of dark energy. A major multiyear Wide-Field Upgrade (WFU) of the HET was completed in 2016 that substantially increased the field of view to 22′ diameter and the pupil to 10 m, by replacing the optical corrector, tracker, and Prime Focus Instrument Package and by developing a new telescope control system. The new, wide-field HET now feeds the Visible Integral-field Replicable Unit Spectrograph (VIRUS), a new low-resolution integral-field spectrograph (LRS2), and the Habitable Zone Planet Finder, a precision near-infrared radial velocity spectrograph. VIRUS consists of 156 identical spectrographs fed by almost 35,000 fibers in 78 integral-field units arrayed at the focus of the upgraded HET. VIRUS operates in a bandpass of 3500−5500 Å with resolving power R ≃ 800. VIRUS is the first example of large-scale replication applied to instrumentation in optical astronomy to achieve spectroscopic surveys of very large areas of sky. This paper presents technical details of the HET WFU and VIRUS, as flowed down from the HETDEX science requirements, along with experience from commissioning this major telescope upgrade and the innovative instrumentation suite for HETDEX.

Review of potential astronomical optical observatory sites in the Philippines

The Philippines is an archipelago of more than 7,600 islands with many geographical features such as mountain ranges, seas, and plains. The country has fairly developed cities that are now experiencing various kinds of pollution at different levels and intensities. Highly developed urban areas are brightly lit and are currently experiencing worsening light pollution. Despite this, the two biggest telescopes in the country are still installed in two observatories right in the country’s capital city where light pollution is at its worst. This paper aims to identify several locations away from light pollution in the islands of Luzon, the biggest island in the Philippines, and the island of Palawan, where optical astronomical observatories may be built. The locations are chosen by studying the comparative light pollution scales in the various locations. The topography of the place and meteorological data such as temperature, humidity, and precipitation are likewise studied and considered as factors. Included in these factors is the fact that both the islands of Luzon and Palawan experience several typhoons every year, while earthquakes occur anywhere in the archipelago. For this reason, the observatories to be built must be designed to withstand Category 5 typhoons and strong magnitude 7 to 8 earthquakes. The results of the study identify the places on the island of Palawan and in northern Luzon which are good dark sites for the establishment of optical astronomy observatories. These locations can be declared as protected and developed as dark-sky sites dedicated to the study of Astronomy.

Development of an optical photon-counting imager with a monolithic Geiger Avalanche Photodiode array

We have developed a sensor system based on an optical photon-counting imager with high timing resolution, aiming for highly time-variable astronomical phenomena. The detector is a monolithic Geiger-mode avalanche photodiode array customized in a Multi-Pixel Photon Counter with a response time on the order of nanoseconds. This paper evaluates the basic performance of the sensor and confirms the gain linearity, uniformity, and low dark count. We demonstrate the system’s ability to detect the period of a flashing light-emitting diode, using a data acquisition system developed to obtain the light curve with a time bin of 100 μs. The Crab pulsar was observed using a 35-cm telescope without cooling, and the equipment detected optical pulses with a period consistent with the data from the radio ephemeris. Although improvements to the system will be necessary for more reliability, the system has been proven to be a promising device for exploring the time-domain optical astronomy.

Observations of astronomical objects using radio (Irbene RT-32 telescope) and optical (Baldone Schmidt) methods

Institute of Astronomy (University of Latvia) with Ventspils International Radio Astronomy Centre (Ventspils University of Applied Sciences) participation is implementing the scientific project "Complex investigations of the small bodies in the Solar system" which is related to the research of the small bodies in the Solar system (mainly focusing on asteroids and comets) using methods of radio and optical astronomy and signal processing.To detect the rotation period and other physical characteristics of NEO objects using optical methods, 566 positions and photo-metric observations of NEO objects 2006 VB14 = Y5705 = 345705 (hereafter 2006 VB14) and 1986 DA = 6178 (hereafter 1986 DA) were obtained with Baldone Schmidt telescope in 2018. A Fourier transform was applied to determine the rotation period for asteroid 1986 DA. Value 3.12 0.02 h was obtained. Observations confirm the previously obtained rotation period P = 3.25 h for 2006 VB14. To detect weak (~0.1 Jy) OH maser of astronomical objects using radio methods, a researcher group in VIRAC adapted Irbene RT-32 radio telescope working at 1665.402 and 1667.359 MHz frequencies. Novel data processing methods were used to acquire weak signals. Spectral analysis using Fourier transform and continuous wavelet transform were applied to radio astronomical data from multiple observations related to weak OH maser detection. Successful observations of multiple galactic masers were carried out in 2019 and adapted Irbene RT32 radio telescope is ready for the observations of comets in the near future.

Phase-shift mask fabrication at micrometric scale by ion-exchange in glass for astronomical wavefront sensors

Photolithography combined with ion-exchange in glass is a well-known technology that can be applied to develop many different optical devices. In this work, we present the complete procedure to generate small circular phase-shift masks with diameters of only a few microns and high control in the phase change produced. It is a strategic element in applications such as optical astronomy.

The origin of the elements and other implications of gravitational wave detection for nuclear physics

The neutron-star collision revealed by the event GW170817 gave us a first glimpse of a possible birthplace of most of our heavy elements. The multi-messenger nature of this historical event combined gravitational waves, a gamma-ray burst and optical astronomy of a “kilonova”, bringing the first observations of rapid neutron capture (r process) nucleosynthesis after 60 years of speculation. Modeling the r process requires a prodigious amount of nuclear-physics ingredients: practically all the quantum state and interaction properties of virtually all neutron-rich nuclides, many of which may never be produced in the laboratory! Another essential contribution of nuclear physics to neutron stars (and their eventual coalescence) is the equation of state (EoS) that defines their structure and composition. The EoS, combined with the knowledge of nuclear binding energies, determines the elemental profile of the outer crust of a neutron star and the relationship between its radius and mass. In addition, the EoS determines the form of the gravitational wave signal. This article combines a tutorial presentation and bibliography with recent results that link nuclear mass spectrometry to gravitational waves via neutron stars.