2021, Hill, Gary J., Lee, Hanshin, MacQueen, Phillip J., Kelz, Andreas, Drory, Niv, Vattiat, Brian L., Good, John M., Ramsey, Jason, Kriel, Herman, Peterson, Trent, DePoy, D. L., Gebhardt, Karl, Marshall, J. L., Tuttle, Sarah E., Bauer, Svend M., Chonis, Taylor S., Fabricius, Maximilian H., Froning, Cynthia, Häuser, Marco, Indahl, Briana L., Jahn, Thomas, Landriau, Martin, Leck, Ron, Montesano, Francesco, Prochaska, Travis, Snigula, Jan M., Zeimann, Greg, Bryant, Randy, Damm, George, Fowler, J. R., Janowiecki, Steven, Martin, Jerry, Mrozinski, Emily, Odewahn, Stephen, Rostopchin, Sergey, Shetrone, Matthew, Spencer, Renny, Mentuch Cooper, Erin, Armandroff, Taft, Bender, Ralf, Dalton, Gavin, Hopp, Ulrich, Komatsu, Eiichiro, Nicklas, Harald, Ramsey, Lawrence W., Roth, Martin M., Schneider, Donald P., Sneden, Chris, Steinmetz, Matthias

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.

2020, Ahumada, Romina, Prieto, Carlos Allende, Almeida, Andrés, Anders, Friedrich, Anderson, Scott F., Andrews, Brett H., Anguiano, Borja, Arcodia, Riccardo, Armengaud, Eric, Aubert, Marie, Avila, Santiago, Garcia, Rafael A., García-Hernández, D.A., Oehmichen, Luis Alberto Garma, Ge, Junqiang, Maia, Marcio Antonio Geimba, Geisler, Doug, Gelfand, Joseph, Goddy, Julian, Gonzalez-Perez, Violeta, Grabowski, Kathleen, Avila-Reese, Vladimir, Green, Paul, Grier, Catherine J., Guo, Hong, Guy, Julien, Harding, Paul, Hasselquist, Sten, Hawken, Adam James, Hayes, Christian R., Hearty, Fred, Hekker, S., Badenes, Carles, Hogg, David W., Holtzman, Jon A., Horta, Danny, Hou, Jiamin, Hsieh, Bau-Ching, Huber, Daniel, Hunt, Jason A. S., Chitham, J. Ider, Imig, Julie, Jaber, Mariana, Balland, Christophe, Angel, Camilo Eduardo Jimenez, Johnson, Jennifer A., Jones, Amy M., Jönsson, Henrik, Jullo, Eric, Kim, Yerim, Kinemuchi, Karen, Kirkpatrick IV, Charles C., Kite, George W., Klaene, Mark, Barger, Kat, Kneib, Jean-Paul, Kollmeier, Juna A., Kong, Hui, Kounkel, Marina, Krishnarao, Dhanesh, Lacerna, Ivan, Lan, Ting-Wen, Lane, Richard R., Law, David R., Le Goff, Jean-Marc, Barrera-Ballesteros, Jorge K., Leung, Henry W., Lewis, Hannah, Li, Cheng, Lian, Jianhui, Lin, Lihwai, Long, Dan, Longa-Peña, Penélope, Lundgren, Britt, Lyke, Brad W., Ted Mackereth, J., Basu, Sarbani, MacLeod, Chelsea L., Majewski, Steven R., Manchado, Arturo, Maraston, Claudia, Martini, Paul, Masseron, Thomas, Masters, Karen L., Mathur, Savita, McDermid, Richard M., Merloni, Andrea, Bautista, Julian, Merrifield, Michael, Mészáros, Szabolcs, Miglio, Andrea, Minniti, Dante, Minsley, Rebecca, Miyaji, Takamitsu, Mohammad, Faizan Gohar, Mosser, Benoit, Mueller, Eva-Maria, Muna, Demitri, Beaton, Rachael L., Muñoz-Gutiérrez, Andrea, Myers, Adam D., Nadathur, Seshadri, Nair, Preethi, Nandra, Kirpal, do Nascimento, Janaina Correa, Nevin, Rebecca Jean, Newman, Jeffrey A., Nidever, David L., Nitschelm, Christian, Beers, Timothy C., Noterdaeme, Pasquier, O’Connell, Julia E., Olmstead, Matthew D., Oravetz, Daniel, Oravetz, Audrey, Osorio, Yeisson, Pace, Zachary J., Padilla, Nelson, Palanque-Delabrouille, Nathalie, Palicio, Pedro A., Benavides, B. Izamar T., Pan, Hsi-An, Pan, Kaike, Parker, James, Paviot, Romain, Peirani, Sebastien, Ramŕez, Karla Peña, Penny, Samantha, Percival, Will J., Perez-Fournon, Ismael, Pérez-Ràfols, Ignasi, Bender, Chad F., Petitjean, Patrick, Pieri, Matthew M., Pinsonneault, Marc, Poovelil, Vijith Jacob, Povick, Joshua Tyler, Prakash, Abhishek, Price-Whelan, Adrian M., Raddick, M. Jordan, Raichoor, Anand, Ray, Amy, Bernardi, Mariangela, Rembold, Sandro Barboza, Rezaie, Mehdi, Riffel, Rogemar A., Riffel, Rogério, Rix, Hans-Walter, Robin, Annie C., Roman-Lopes, A., Román-Zúñiga, Carlos, Rose, Benjamin, Ross, Ashley J., Bershady, Matthew, Rossi, Graziano, Rowlands, Kate, Rubin, Kate H. R., Salvato, Mara, Sánchez, Ariel G., Sánchez-Menguiano, Laura, Sánchez-Gallego, José R., Sayres, Conor, Schaefer, Adam, Schiavon, Ricardo P., Beutler, Florian, Schimoia, Jaderson S., Schlafly, Edward, Schlegel, David, Schneider, Donald P., Schultheis, Mathias, Schwope, Axel, Seo, Hee-Jong, Serenelli, Aldo, Shafieloo, Arman, Shamsi, Shoaib Jamal, Bidin, Christian Moni, Shao, Zhengyi, Shen, Shiyin, Shetrone, Matthew, Shirley, Raphael, Aguirre, Víctor Silva, Simon, Joshua D., Skrutskie, M.F., Slosar, Anže, Smethurst, Rebecca, Sobeck, Jennifer, Bird, Jonathan, Sodi, Bernardo Cervantes, Souto, Diogo, Stark, David V., Stassun, Keivan G., Steinmetz, Matthias, Stello, Dennis, Stermer, Julianna, Storchi-Bergmann, Thaisa, Streblyanska, Alina, Stringfellow, Guy S., Bizyaev, Dmitry, Stutz, Amelia, Suárez, Genaro, Sun, Jing, Taghizadeh-Popp, Manuchehr, Talbot, Michael S., Tayar, Jamie, Thakar, Aniruddha R., Theriault, Riley, Thomas, Daniel, Thomas, Zak C., Blanc, Guillermo A., Tinker, Jeremy, Tojeiro, Rita, Toledo, Hector Hernandez, Tremonti, Christy A., Troup, Nicholas W., Tuttle, Sarah, Unda-Sanzana, Eduardo, Valentini, Marica, Vargas-González, Jaime, Vargas-Magaña, Mariana, Blanton, Michael R., Vázquez-Mata, Jose Antonio, Vivek, M., Wake, David, Wang, Yuting, Weaver, Benjamin Alan, Weijmans, Anne-Marie, Wild, Vivienne, Wilson, John C., Wilson, Robert F., Wolthuis, Nathan, Boquien, Médéric, Wood-Vasey, W. M., Yan, Renbin, Yang, Meng, Yèche, Christophe, Zamora, Olga, Zarrouk, Pauline, Zasowski, Gail, Zhang, Kai, Zhao, Cheng, Zhao, Gongbo, Borissova, Jura, Zheng, Zheng, Zheng, Zheng, Zhu, Guangtun, Zou, Hu, Bovy, Jo, Brandt, W. N., Brinkmann, Jonathan, Brownstein, Joel R., Bundy, Kevin, Bureau, Martin, Burgasser, Adam, Burtin, Etienne, Cano-Díaz, Mariana, Capasso, Raffaella, Cappellari, Michele, Carrera, Ricardo, Chabanier, Solène, Chaplin, William, Chapman, Michael, Cherinka, Brian, Chiappini, Cristina, Doohyun Choi, Peter, Chojnowski, S. Drew, Chung, Haeun, Clerc, Nicolas, Coffey, Damien, Comerford, Julia M., Comparat, Johan, da Costa, Luiz, Cousinou, Marie-Claude, Covey, Kevin, Crane, Jeffrey D., Cunha, Katia, Ilha, Gabriele da Silva, Dai, Yu Sophia, Damsted, Sanna B., Darling, Jeremy, Davidson, James W., Davies, Roger, Dawson, Kyle, De, Nikhil, de la Macorra, Axel, De Lee, Nathan, Queiroz, Anna Bárbara de Andrade, Deconto Machado, Alice, de la Torre, Sylvain, Dell’Agli, Flavia, du Mas des Bourboux, Hélion, Diamond-Stanic, Aleksandar M., Dillon, Sean, Donor, John, Drory, Niv, Duckworth, Chris, Dwelly, Tom, Ebelke, Garrett, Eftekharzadeh, Sarah, Davis Eigenbrot, Arthur, Elsworth, Yvonne P., Eracleous, Mike, Erfanianfar, Ghazaleh, Escoffier, Stephanie, Fan, Xiaohui, Farr, Emily, Fernández-Trincado, José G., Feuillet, Diane, Finoguenov, Alexis, Fofie, Patricia, Fraser-McKelvie, Amelia, Frinchaboy, Peter M., Fromenteau, Sebastien, Fu, Hai, Galbany, Lluís

This paper documents the 16th data release (DR16) from the Sloan Digital Sky Surveys (SDSS), the fourth and penultimate from the fourth phase (SDSS-IV). This is the first release of data from the Southern Hemisphere survey of the Apache Point Observatory Galactic Evolution Experiment 2 (APOGEE-2); new data from APOGEE-2 North are also included. DR16 is also notable as the final data release for the main cosmological program of the Extended Baryon Oscillation Spectroscopic Survey (eBOSS), and all raw and reduced spectra from that project are released here. DR16 also includes all the data from the Time Domain Spectroscopic Survey and new data from the SPectroscopic IDentification of ERosita Survey programs, both of which were co-observed on eBOSS plates. DR16 has no new data from the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey (or the MaNGA Stellar Library "MaStar"). We also preview future SDSS-V operations (due to start in 2020), and summarize plans for the final SDSS-IV data release (DR17).