The fourth generation of the Sloan Digital Sky Survey (SDSS-IV) began observations in 2014 July. It pursues three core programs: the Apache Point Observatory Galactic Evolution Experiment 2 (APOGEE-2), Mapping Nearby Galaxies at APO (MaNGA), and the Extended Baryon Oscillation Spectroscopic Survey (eBOSS). As well as its core program, eBOSS contains two major subprograms: the Time Domain Spectroscopic Survey (TDSS) and the SPectroscopic IDentification of ERosita Sources (SPIDERS). This paper describes the first data release from SDSS-IV, Data Release 13 (DR13). DR13 makes publicly available the first 1390 spatially resolved integral field unit observations of nearby galaxies from MaNGA. It includes new observations from eBOSS, completing the Sloan Extended QUasar, Emission-line galaxy, Luminous red galaxy Survey (SEQUELS), which also targeted variability-selected objects and X-ray-selected objects. DR13 includes new reductions of the SDSS-III BOSS data, improving the spectrophotometric calibration and redshift classification, and new reductions of the SDSS-III APOGEE-1 data, improving stellar parameters for dwarf stars and cooler stars. DR13 provides more robust and precise photometric calibrations. Value-added target catalogs relevant for eBOSS, TDSS, and SPIDERS and an updated red-clump catalog for APOGEE are also available. This paper describes the location and format of the data and provides references to important technical papers. The SDSS web site, http://www.sdss.org, provides links to the data, tutorials, examples of data access, and extensive documentation of the reduction and analysis procedures. DR13 is the first of a scheduled set that will contain new data and analyses from the planned similar to 6 yr operations of SDSS-IV.

We use photometric and spectroscopic observations of four detached eclipsing binaries in the globular cluster NGC 3201 to derive masses, radii, and luminosities of the component stars. Spanning across almost three magnitudes in the colour-magnitude diagram, the components offer a unique possibility to test the theory of stellar evolution. Their masses, radii, and luminosities range from 0.66 to 0.84 M-circle dot, 0.68 to 2.46 R-circle dot, and 0.38 to 5.56 L-circle dot, respectively. The distance to the cluster measured from the distance moduli of the component stars amounts to 4.54(-0.14)(+0.11) kpc and agrees with the recent estimate based on Gaia parallaxes. By comparing the M - R and M - L diagrams of the component stars and the colour-magnitude diagram of NGC 3201 to Dartmouth model isochrones, we estimate the most probable age of the cluster to be 11.5 +/- 0.5 Gyr. This estimate is based on three binaries only, as the fourth one seems to evolve along a different path, probably due to non-standard chemical composition and/or history. We confirm the tendency, observed in earlier CASE papers, for the age indicated by the M - R diagram to be younger than that implied by the colour-magnitude diagram.

We develop a machine learning based algorithm using a convolutional neural network (CNN) to identify low H I column density Ly alpha absorption systems (log N-H I/cm(-2) < 17) in the Ly alpha forest, and predict their physical properties, such as their H I column density (log N-H I/cm(-2)), redshift (z(H I)), and Doppler width (b(H I)). Our CNN models are trained using simulated spectra (S/N similar or equal to 10), and we test their performance on high quality spectra of quasars at redshift z similar to 2.5-2.9 observed with the High Resolution Echelle Spectrometer on the Keck I telescope. We find that similar to 78 per cent of the systems identified by our algorithm are listed in the manual Voigt profile fitting catalogue. We demonstrate that the performance of our CNN is stable and consistent for all simulated and observed spectra with S/N greater than or similar to 10. Our model can therefore be consistently used to analyse the enormous number of both low and high S/N data available with current and future facilities. Our CNN provides state-of-the-art predictions within the range 12.5 <= log N-H I/cm(-2) < 15.5 with a mean absolute error of Delta(log N-H (I)/cm(-2) = 0.13, Delta(z(H I)) = 2.7 x 10(-5), and Delta(b(H I)) = 4.1 km s(-1). The CNN prediction costs < 3 min per model per spectrum with a size of 120 000 pixels using a laptop computer. We demonstrate that CNNs can significantly increase the efficiency of analysing Ly alpha forest spectra, and thereby greatly increase the statistics of Ly alpha absorbers.

We present the design of Henrietta, is a wide-band (0.6 - 2.4 mu m) low resolution spectrograph located at the 1-m Swope Telescope in Las Campanas Observatory. Henrietta is designed to routinely suppress instrumental variations in spectrophotometric flux in order to reach the photon noise limit. The primary way Henrietta achieves this is by employing a wide-slit at the telescope focal plane to mitigate time-dependent slit losses; employing a diffusing optical element to broaden the shape of the PSF and mitigate flux variations due to the intra-pixel quantum efficiency variations; a wide field-of-view for access to reference stars with similar brightness and spectral type; and minimizing the number of optical elements to keep throughput high across a wide spectral range. Henrietta is currently in the integration and testing phase and will begin science operations in early 2023.

PHANGS-HST is an ultraviolet-optical imaging survey of 38 spiral galaxies within similar to 20 Mpc. Combined with the PHANGS-ALMA, PHANGS-MUSE surveys and other multiwavelength data, the data set will provide an unprecedented look into the connections between young stars, H ii regions, and cold molecular gas in these nearby star-forming galaxies. Accurate distances are needed to transform measured observables into physical parameters (e.g. brightness to luminosity, angular to physical sizes of molecular clouds, star clusters and associations). PHANGS-HST has obtained parallel ACS imaging of the galaxy haloes in the F606W and F814W bands. Where possible, we use these parallel fields to derive tip of the red giant branch (TRGB) distances to these galaxies. In this paper, we present TRGB distances for 10 PHANGS galaxies from similar to 4 to similar to 15 Mpc, based on the first year of PHANGS-HST observations. Four of these represent the first published TRGB distance measurements (IC 5332, NGC 2835, NGC 4298, and NGC 4321), and seven of which are the best available distances to these targets. We also provide a compilation of distances for the 118 galaxies in the full PHANGS sample, which have been adopted for the first PHANGS-ALMA public data release.

The processes of star formation and feedback, regulating the cycle of matter between gas and stars on the scales of giant molecular clouds (GMCs; similar to 100 pc), play a major role in governing galaxy evolution. Measuring the time-scales of GMC evolution is important to identify and characterize the specific physical mechanisms that drive this transition. By applying a robust statistical method to high-resolution CO and narrow-band H alpha imaging from the PHANGS survey, we systematically measure the evolutionary timeline from molecular clouds to exposed young stellar regions on GMC scales, across the discs of an unprecedented sample of 54 star-forming main-sequence galaxies (excluding their unresolved centres). We find that clouds live for about 1-3 GMC turbulence crossing times (5-30 Myr) and are efficiently dispersed by stellar feedback within 1-5 Myr once the star-forming region becomes partially exposed, resulting in integrated star formation efficiencies of 1-8 per cent. These ranges reflect physical galaxy-to-galaxy variation. In order to evaluate whether galactic environment influences GMC evolution, we correlate our measurements with average properties of the GMCs and their local galactic environment. We find several strong correlations that can be physically understood, revealing a quantitative link between galactic-scale environmental properties and the small-scale GMC evolution. Notably, the measured CO-visible cloud lifetimes become shorter with decreasing galaxy mass, mostly due to the increasing presence of CO-dark molecular gas in such environment. Our results represent a first step towards a comprehensive picture of cloud assembly and dispersal, which requires further extension and refinement with tracers of the atomic gas, dust, and deeply embedded stars.

We developed control software for an enclosure system of the SDSS-V Local Volume Mapper (LVM) which provides a contiguous 2,500 deg2 integral-field survey. The LVM enclosure, located at the Las Campanas Observatory in Chile, is a building that hosts the LVM instruments (LVM-I). The enclosure system consists of four main systems: 1) a roll-off dome, 2) building lights, 3) a Heating, Ventilation, and Air Conditioning (HVAC) system, and 4) a safety system. Two Programmable Logic Controllers (PLCs) as middleware software directly operate complex mechanisms of the dome and the HVAC via the Modbus protocol. The LVMECP is implemented by Python 3.9 following the SDSS software framework which adopted a protocol, called CLU, with message passing based on the RabbitMQ and Advanced Message Queuing Protocol (AMQP). Also, we applied asynchronous programming to our system to process multiple requests simultaneously. The Dome PLC system remotely sends commands for the operation of a roll-off dome and enclosure lights. The HVAC PLC system keeps track of changing environmental values of the HVAC system in real-time. This software provides observers with remote access by high-level commands.

The Carnegie Observatories in 2019 celebrated 50 years since Las Campanas in northern Chile was chartered as the site for its large telescopes. Since that time Carnegie has deployed four telescopes, the Swope 1 meter, the du Pont 2.5 meter and, on behalf of the Magellan consortium, the two Magellan 6.5 meter. All telescopes are routinely used producing world class science. In this paper we will review the current science operations that are mainly performed in a classical observing mode, and then present the future strategies needed across the observatory to operate in survey, remote and robotic mode.

This paper presents an update on the construction, testing, and commissioning of the SDSS-V Local Volume Mapper (LVM) telescope system. LVM is one of three surveys that form the fifth generation of the Sloan Digital Sky Survey, and it will employ a coordinated network of four, 16-cm telescopes feeding three fiber spectrographs at the Las Campanas Observatory. The goal is to spectrally map approximately 2500 square degrees of the Galactic plane with 37 '' spatial resolution and R similar to 4000 spectral resolution over the wavelength range 360-980 nm. LVM will also target the Magellanic Clouds and other Local Group galaxies.

The Local Volume Mapper (LVM) project is one of three surveys that form the Sloan Digital Sky Survey V. It will map the interstellar gas emission in a large fraction of the southern sky using wide-field integral field spectroscopy. Four 16-cm telescopes in siderostat configuration feed the integral field units (IFUs). A reliable acquisition and guiding (A&G) strategy will help ensure that we meet our science goals. Each of the telescopes hosts commercial CMOS cameras used for A&G. In this work, we present our validation of the camera performance. Our tests show that the cameras have a readout noise of around 5.6 e- and a dark current of 21 e-/s, when operated at the ideal gain setting and at an ambient temperature of 20 degrees C. To ensure their performance at a high-altitude observing site, such as the Las Campanas Observatory, we studied the thermal behaviour of the cameras at different ambient pressures and with different passive cooling solutions. Using the measured properties, we calculated the brightness limit for guiding exposures. With a 5 s exposure time, we reach a depth of similar to 16.5 Gaia gmag with a signal-to-noise ratio (SNR) > 5. Using Gaia Early Data Release 3, we verified that there are sufficient guide stars for each of the similar to 25 000 survey pointings. For accurate acquisition, we also need to know the focal plane geometry. We present an approach that combines on-chip astrometry and using a point source microscope to measure the relative positions of the IFU lenslets and the individual CMOS pixels to around 2 mu m accuracy.