The FRAM robotic telescope for atmospheric monitoring at the Pierre Auger Observatory Aab, A. Bueno Villar, Antonio Pierre Auger Collaboration Large detector systems for particle and astroparticle physics Real-time monitoring Optics Photon detectors for UV Visible and IR photons (solid-state) The successful installation, commissioning, and operation of the Pierre Auger Observatory would not have been possible without the strong commitment and effort from the technical and admin-istrative staff in Malargtie. We are very grateful to the following agencies and organizations for financial support: Argentina - Comision Nacional de Energia Atomica; Agencia Nacional de Promocion Cientffica y Tecnologica (ANPCyT) ; Consejo Nacional de Investigaciones Cientfficas y Tecnicas (CONICET) ; Gobierno de la Provincia de Mendoza; Municipalidad de Malargtie; NDM Holdings and Valle Las Leas; in gratitude for their continuing cooperation over land access; Australia - the Australian Research Council; Brazil - Conselho Nacional de Desenvolvi-mento Cientffico e Tecnologico (CNPq) ; Financiadora de Estudos e Projetos (FINEP) ; FundacAo de Amparo a Pesquisa do Estado de Rio de Janeiro (FAPERJ) ; SAo Paulo Research Foundation (FAPESP) Grants No. 2019/101512, No. 2010/07359-6 and No. 1999/054043; Ministerio da Ciencia, Tecnologia, Inovacoes e Comunicacoes (MCTIC) ; Czech Republic - Grant No. MSMT CR LTT18004, LM2015038, LM2018102, CZ.02.1.01/0.0/0.0/16_013/0001402,CZ.02.1.01/0.0/0.0/18_046/0016010 and CZ.02.1.01/0.0/0.0/17_049/0008422; France - Centre de Calcul IN2P3/CNRS; Centre National de la Recherche Scientifique (CNRS) ; Conseil Regional IledeFrance; Departement Physique Nucleaire et Corpusculaire (PNCIN2P3/CNRS) ; Departement Sciences de l'Univers (SDUINSU/CNRS) ; Institut Lagrange de Paris (ILP) Grant No. LABEX ANR-10-LABX-63 within the Investissements d'Avenir Programme Grant No. ANR11IDEX000402; Germany - Bundesministerium fur Bildung und Forschung (BMBF) ; Deutsche Forschungsgemeinschaft (DFG) ; Finanzministerium BadenWurttemberg; Helmholtz Alliance for Astroparticle Physics (HAP) ; Helmholtz-Gemeinschaft Deutscher Forschungszentren (HGF) ; Min-isterium fur Innovation, Wissenschaft und Forschung des Landes NordrheinWestfalen; Minis-terium fur Wissenschaft, Forschung und Kunst des Landes BadenWurttemberg; Italy - Isti-tuto Nazionale di Fisica Nucleare (INFN) ; Istituto Nazionale di Astrofisica (INAF) ; Ministero dell'Istruzione, dell'Universita e della Ricerca (MIUR) ; CETEMPS Center of Excellence; Minis-tero degli Affari Esteri (MAE) ; Mexico - Consejo Nacional de Ciencia y Tecnologia (CONACYT) No. 167733; Universidad Nacional Autonoma de Mexico (UNAM) ; PAPIIT DGAPAUNAM; The Netherlands - Ministry of Education, Culture and Science; Netherlands Organisation for Sci-entific Research (NWO) ; Dutch national e-infrastructure with the support of SURF Cooperative; Poland-Ministry of Science and Higher Education, grant No. DIR/WK/2018/11; National Sci-ence Centre, Grants No. 2013/08/M/ST9/00322, No. 2016/23/B/ST9/01635 and No. HARMONIA 5-2013/10/M/ST9/00062, UMO2016/22/M/ST9/00198; Portugal - Portuguese national funds and FEDER funds within Programa Operacional Factores de Competitividade through Fundacao para a Ciencia e a Tecnologia (COMPETE) ; Romania - Romanian Ministry of Education and Research, the Program Nucleu within MCI (PN19150201/16N/2019 and PN19060102) and project PNIIIP11.2PCCDI20170839/19PCCDI/2018 within PNCDI III; Slovenia - Slovenian Research Agency, grants P10031, P10385, I00033, N10111; Spain - Ministerio de Economia, Industria y Competitividad (FPA2017-85114-P and PID2019104676GBC32, Xunta de Galicia (ED431C 2017/07) , Junta de Andalucia (SOMM17/6104/UGR, P18-FR-4314) Feder Funds, RENATA Red Nacional Tematica de Astroparticulas (FPA2015-68783-REDT) and Maria de Maeztu Unit of Excel-lence (MDM20160692) ; U.S.A. - Department of Energy, Contracts No. DEAC0207CH11359, No. DEFR0204ER41300, No. DE-FG02-99ER41107 and No. DESC0011689; National Sci-ence Foundation, Grant No. 0450696; The Grainger Foundation; Marie CurieIRSES/EPLANET; European Particle Physics Latin American Network; and UNESCO. FRAM (F/Photometric Robotic Atmospheric Monitor) is a robotic telescope operated at the Pierre Auger Observatory in Argentina for the purposes of atmospheric monitoring using stellar photometry. As a passive system which does not produce any light that could interfere with the observations of the fluorescence telescopes of the observatory, it complements the active monitoring systems that use lasers. We discuss the applications of stellar photometry for atmospheric monitoring at optical observatories in general and the particular modes of operation employed by the Auger FRAM. We describe in detail the technical aspects of FRAM, the hardware and software requirements for a successful operation of a robotic telescope for such a purpose and their implementation within the FRAM system. 2021-10-21T09:44:25Z 2021-10-21T09:44:25Z 2021-07-26 journal article Published version: The Pierre Auger collaboration et al 2021 JINST 16 P06027 [https://doi.org/10.1088/1748-0221/16/06/P06027] http://hdl.handle.net/10481/71024 eng http://creativecommons.org/licenses/by-nc-nd/3.0/es/ open access Atribución-NoComercial-SinDerivadas 3.0 España IOP Publishing