Author name code: dravins ADS astronomy entries on 2022-09-14 author:"Dravins, Dainis" ------------------------------------------------------------------------ Title: CTA – the World's largest ground-based gamma-ray observatory Authors: Zanin, R.; Abdalla, H.; Abe, H.; Abe, S.; Abusleme, A.; Acero, F.; Acharyya, A.; Acin Portella, V.; Ackley, K.; Adam, R.; Adams, C.; Adhikari, S. S.; Aguado Ruesga, I.; Agudo, I.; Aguilera, R.; Aguirre Santaella, A.; Aharonian, F.; Alberdi, A.; Alfaro, R.; Alfaro, J.; Alispach, C.; Aloisio, R.; Alves Batista, R.; Amans, J. P.; Amati, L.; Amato, E.; Ambrogi, L.; Ambrosi, G.; Ambrosio, M.; Ammendola, R.; Anderson, J.; Anduze, M.; Anguner, E. O.; Antonelli, L. A.; Antonuccio, V.; Antoranz, P.; Anutarawiramkul, R.; Aragunde Gutierrez, J.; Aramo, C.; Araudo, A.; Araya, M.; Arbet Engels, A.; Arcaro, C.; Arendt, V.; Armand, C.; Armstrong, T.; Arqueros, F.; Arrabito, L.; Arsioli, B.; Artero, M.; Asano, K.; Ascasibar, Y.; Aschersleben, J.; Ashley, M.; Attina, P.; Aubert, P.; Singh, C. B.; Baack, D.; Babic, A.; Backes, M.; Baena, V.; Bajtlik, S.; Baktash, A.; Balazs, C.; Balbo, M.; Ballester, O.; Ballet, J.; Balmaverde, B.; Bamba, A.; Bandiera, R.; Baquero Larriva, A.; Barai, P.; Barbier, C.; Barbosa Martins, V.; Barcelo, M.; Barkov, M.; Barnard, M.; Baroncelli, L.; Barres de Almeida, U.; Barrio, J. A.; Bastieri, D.; Batista, P. I.; Batkovic, I.; Bauer, C.; Bautista González, R.; Baxter, J.; Becciani, U.; Becerra González, J.; Becherini, Y.; Beck, G.; Becker Tjus, J.; Bednarek, W.; Belfiore, A.; Bellizzi, L.; Belmont, R.; Benbow, W.; Berge, D.; Bernardini, E.; Bernardos, M. I.; Bernlöhr, K.; Berti, A.; Berton, M.; Bertucci, B.; Beshley, V.; Bhatt, N.; Bhattacharyya, S.; Bhattacharyya, W.; Bhattacharyya, S.; Bi, B. Y.; Bicknell, G.; Biederbeck, N.; Bigongiari, C.; Biland, A.; Bird, R.; Bissaldi, E.; Biteau, J.; Bitossi, M.; Blanch, O.; Blank, M.; Blazek, J.; Bobin, J.; Boccato, C.; Bocchino, F.; Boehm, C.; Bohacova, M.; Boisson, C.; Boix, J.; Bolle, J. P.; Bolmont, J.; Bonanno, G.; Bonavolontà, C.; Bonneau Arbeletche, L.; Bonnoli, G.; Bordas, P.; Borkowski, J.; Bose, R.; Bose, D.; Bosnjak, Z.; Bottacini, E.; Böttcher, M.; Botticella, M. T.; Boutonnet, C.; Bouyjou, F.; Bozhilov, V.; Bozzo, E.; Brahimi, L.; Braiding, C.; Brau Nogue, S.; Breen, S.; Bregeon, J.; Breuhaus, M.; Brill, A.; Brisken, W.; Brocato, E.; Brown, A. M.; Brügge, K.; Brun, P.; Brun, F.; Brunetti, L.; Brunetti, G.; Bruno, P.; Bruno, A.; Bruzzese, A.; Bucciantini, N.; Buckley, J. H.; Bühler, R.; Bulgarelli, A.; Bulik, T.; Bünning, M.; Bunse, M.; Burton, M.; Burtovoi, A.; Buscemi, M.; Buschjager, S.; Busetto, G.; Buss, J.; Byrum, K.; Caccianiga, A.; Cadoux, F.; Calanducci, A.; Calderon, C.; Calvo Tovar, J.; Cameron, R. A.; Campana, P.; Canestrari, R.; Cangemi, F.; Cantlay, B.; Capalbi, M.; Capasso, M.; Cappi, M.; Caproni, A.; Capuzzo Dolcetta, R.; Caraveo, P.; Cárdenas, V.; Cardiel, L.; Cardillo, M.; Carlile, C.; Caroff, S.; Carosi, R.; Carosi, A.; Carquin, E.; Carrere, M.; Casandjian, J. M.; Casanova, S.; Cassol, F.; Catalani, F.; Catalano, O.; Cauz, D.; Ceccanti, A.; Celestino Silva, C.; Cerny, K.; Cerruti, M.; Chabanne, E.; Chadwick, P.; Chai, Y.; Chambery, P.; Champion, C.; Chaty, S.; Chen, A.; Cheng, K.; Chernyakova, M.; Chiaro, G.; Chiavassa, A.; Chikawa, M.; Chitnis, V. R.; Chudoba, J.; Chytka, L.; Cikota, S.; Circiello, A.; Clark, P.; Colak, M.; Colombo, E.; Colonges, S.; Comastri, A.; Compagnino, A.; Conforti, V.; Congiu, E.; Coniglione, R.; Conrad, J.; Conte, F.; Contreras, J. L.; Coppi, P.; Cornat, R.; Coronado Blazquez, J.; Cortina, J.; Costa, A.; Costantini, H.; Cotter, G.; Courty, B.; Covino, S.; Crestan, S.; Cristofari, P.; Crocker, R.; Croston, J.; Cubuk, K.; Cuevas, O.; Cui, X.; Cusumano, G.; Cutini, S.; D'Amico, G.; D'Ammando, F.; D'Avanzo, P.; Da Vela, P.; Dadina, M.; Dai, S.; Dalchenko, M.; Dall'Ora, M.; Daniel, M. K.; Dauguet, J.; Davids, I.; Davies, J.; Dawson, B.; De Angelis, A.; de Araujo Carvalho, A. E.; de Bony de Lavergne, M.; De Cesare, G.; de Frondat, F.; de la Calle, I.; de Gouveia Dal Pino, E.; De Lotto, B.; De Luca, A.; De Martino, D.; de Naurois, M.; de Ona Wilhelmi, E.; De Palma Persio, F.; De Simone, N.; de Souza Valle, V.; Delagnes, E.; Deleglise Reznicek, G.; Delgado, C.; Delgado Giler, A. G.; Delgado Mengual Valle, J.; della Volpe, D.; Depaoli, D.; Devin, J.; Di Girolamo, T.; Di Giulio Pierro, C.; Di Venere, L.; Díaz, C.; Dib, C.; Diebold, S.; Digel, S.; Djannati Atai, A.; Djuvsland, J.; Dmytriiev, A.; Docher, K.; Domínguez, A.; Dominis Prester, D.; Donini, A.; Dorner, D.; Doro, M.; dos Anjos, R. d. C.; Dournaux, J. L.; Downes, T.; Drake, G.; Drass, H.; Dravins, D.; Duangchan, C.; Duara, A.; Dubus, G.; Ducci, L.; Duffy, C.; Dumora, D.; Dundas Mora, K.; Durkalec, A.; Dwarkadas, V. V.; Ebr, J.; Eckner, C.; Eder, J.; Edy, E.; Egberts, K.; Einecke, S.; Eleftheriadis, C.; Elsässer, D.; Emery, G.; Emmanoulopoulos, D.; Ernenwein, J. P.; Errando, M.; Escarate, P.; Escudero, J.; Espinoza, C.; Ettori, S.; Eungwanichayapant, A.; Evans, P.; Evoli, C.; Fairbairn, M.; Falceta Goncalves, D.; Falcone, A.; Fallah Ramazanı, V.; Falomo, R.; Farakos, K.; Fasola, G.; Fattorini, A.; Favre, Y.; Fedora, R.; Fedorova, E.; Feijen, K.; Feng, Q.; Ferrand, G.; Ferrara, G.; Ferreira, O.; Fesquet, M.; Fiandrini, E.; Fiasson, A.; Filipovic, M.; Fink, D.; Finley, J. P.; Fioretti, V.; Fiorillo, D. F. G.; Fiorini, M.; Flis, S.; Flores, H.; Foffano, L.; Fohr, C.; Fonseca, M. V.; Font, L.; Fontaine, G.; Fornieri, O.; Fortin, P.; Fortson, L.; Fouque, N.; Fraga, B.; Franceschini, A.; Franco, F. J.; Freixas Coromina, L.; Fresnillo, L.; Fugazza, D.; Fujita, Y.; Fukami, S.; Fukazawa, Y.; Fulla, D.; Funk, S.; Furniss, A.; Gabici, S.; Gaggero, D.; Galanti, G.; Galdemard, P.; Gallant, Y. A.; Galloway, D.; Gallozzi, S.; Gammaldi, V.; Garcia, R.; Garcia, E.; Garcia Lopez, E.; Gargano, F.; Gargano, C.; Garozzo, S.; Gascon, D.; Gasparetto, T.; Gasparrini, D.; Gasparyan, H.; Gaug, M.; Geffroy, N.; Gent, A.; Germani, S.; Ghalumyan, A.; Ghedina, A.; Ghirlanda, G.; Gianotti, F.; Giarrusso, S.; Giarrusso, M.; Giavitto, G.; Giebels, B.; Giglietto, N.; Gika, V.; Gillardo, F.; Gimenes, R.; Giordano, F.; Giro, E.; Giroletti, M.; Giuliani, A.; Gjaja, M.; Glicenstein, J. F.; Gliwny, P.; Goksu, H.; Goldoni, P.; Gomez, J. L.; Gonzalez, M. M.; Gonzalez, J. M.; Gothe, K. S.; Gotz Coelho, D.; Grabarczyk, T.; Graciani, R.; Grandi, P.; Grasseau, G.; Grasso, D.; Green, D.; Green, J.; Greenshaw, T.; Grespan, P.; Grillo, A.; Grondin, M. H.; Grube, J.; Guarino, V.; Guest, B.; Gueta, O.; Günduz, M.; Gunji, S.; Gyuk, G.; Hackfeld, J.; Hadasch, D.; Hagge, L.; Hahn, A.; Hajlaoui, J. E.; Halim, A.; Hamal, P.; Hanlon, W.; Harada, Y.; Hardcastle, M. J.; Collado, M. Harvey; Haubold, T.; Haupt, A.; Havelka, M.; Hayashi, K.; Hayashi, K.; Hayashida, M.; He, H.; Heckmann, L.; Heller, M.; Henault, F.; Henri, G.; Hermann, G.; Hernández Cadena, S.; Herrera Llorente, J.; Hervet, O.; Hinton, J.; Hiramatsu, A.; Hirotani, K.; Hnatyk, B.; Hnatyk, R.; Hoang, J. K.; Hoffmann, D. H. H.; Hoischen, C.; Holder, J.; Holler, M.; Hona, B.; Horan, D.; Horns, D.; Horvath, P.; Houles, J.; Hrabovsky, M.; Hrupec, D.; Huang, Y.; Huet, J. M.; Hughes, G.; Hull, G.; Humensky, T. B.; Hütten, M.; Iarlori, M.; Illa, J. M.; Imazawa, R.; Inada, T.; Incardona, F.; Ingallinera, A.; Inoue, S.; Inoue, T.; Inoue, Y.; Iocco, F.; Ioka, K.; Ionica, M.; Iovenitti, S.; Iriarte, A.; Ishio, K.; Ishizaki, W.; Iwamura, Y.; Jacquemier, J.; Jacquemont, M.; Jamrozy, M.; Janecek, P.; Jankowsky, F.; JardinBlicq, A.; Jarnot, C.; Martínez, P. Jean; Jocou, L.; Jordana, N.; Josselin, M.; JungRichardt, I.; Junqueira, F. J. P. A.; Juramy Gilles, C.; Kaaret, P.; Kadowaki, L. H. S.; Kagaya, M.; Kankanyan, R.; Kantzas, D.; Karas, V.; Karastergiou, A.; Karkar, S.; Kasperek, J.; Katagiri, H.; Kataoka, J.; Katarzynski, K.; Katsuda, S.; Kawanaka, N.; Kazanas, D.; Kerszberg, D.; Khélifi, B.; Kherlakian, M. C.; Kian, T. P.; Kieda, D. B.; Kihm, T.; Kim, S.; Kisaka, S.; Kissmann, R.; Kleijwegt, R.; Kluge, G.; Kluźniak, W.; Knapp, J.; Kobakhidze, A.; Kobayashi, Y.; Koch, B.; Kocot, J.; Kohri, K.; Komin, N.; Kong, A.; Kosack, K.; Krack, F.; Krause, M.; Krennrich, F.; Kubo, H.; Kudryavtsev, V. N.; Kunwar, S.; Kushida, J.; Kushwaha, P.; Parola, B.; La Rosa, G.; Lahmann, R.; Lamastra, A.; Landoni, M.; Landriu, D.; Lang, R. G.; Lapington, J.; Laporte, P.; Lason, P.; Lasuik, J.; Lazendic Galloway, J.; Le Flour, T.; Le Sidaner, P.; Leach, S.; Lee, S. H.; Lee, W. H.; Oliveira, S. Lee; Lemiere, A.; Lemoine Goumard, M.; Lenain, J. P.; Leone, F.; Leray, V.; Leto, G.; Leuschner, F.; Lindemann, R.; Lindfors, E.; Linhoff, L.; Liodakis, I.; Lipniacka, A.; Lobo, M.; Lohse, T.; Lombardi, S.; Lopez, A.; Lopez, M.; Lopez Coto, R.; Louis, F.; Louys, M.; Lucarelli, F.; Boudi, H. Ludwig; Luque Escamilla, P. L.; Maccarone, M. C.; Mach, E.; Maciejewski, A. J.; Mackey, J.; Maeght, P.; Maggio, C.; Maier, G.; Majumdar, P.; Makariev, M.; Mallamaci, M.; Malta Nunes de Almeida, R.; Malyshev, D.; Malyshev, D.; Mandat, D.; Maneva, G.; Manganaro, M.; Manigot, P.; Mannheim, K.; Maragos, N.; Marano, D.; Marconi, M.; Marcowith, A.; Marculewicz, M.; Marcun, B.; Marin, J.; Marinello, N.; Marinos, P.; Markoff, S.; Marquez, P.; Marsella, G.; Martin, J. M.; Martin, P. G.; Martinez, M.; Martinez, G.; Martinez, O.; Martinez Huerta, H.; Marty, C.; Marx, R.; Masetti, N.; Massimino, P.; Matsumoto, H.; Matthews, N.; Maurin, G.; Moerbeck, W. Max; Maxted, N.; Mazziotta, M. N.; Mazzola, S. M.; Mbarubucyeye, J. D.; Mc Comb, L.; McHardy, I.; McKeague, S.; McMuldroch, S.; Medina, E.; Medina Miranda, D.; Melandri, A.; Melioli, C.; Melkumyan, D.; Menchiari, S.; Mereghetti, S.; Merino Arevalo, G.; Mestre, E.; Meunier, J. L.; Meures, T.; Micanovic, S.; Miceli, M.; Michailidis, M.; Michalowski, J.; Miener, T.; Mievre, I.; Miller, J. D.; Mineo, T.; Minev, M.; Miranda, J. M.; Mitchell, A.; Mizuno, T.; Mode, B. A.; Moderski, R.; Mohrmann, L.; Molinari, E.; Montaruli, T.; Monteiro, I.; Moore, C.; Moralejo, A.; Morcuende Parrilla, D.; Moretti, E.; Mori, K.; Moriarty, P.; Morik, K.; Morris, P.; Morselli, A.; Mosshammer, K.; Mukherjee, R.; Muller, J.; Mundell, C.; Mundet, J.; Murach, T.; Muraczewski, A.; Muraishi, H.; Musella, I.; Musumarra, A.; Nagai, A.; Nagataki, S.; Naito, T.; Nakamori, T.; Nakashima, K.; Nakayama, K.; Nakhjiri, N.; Naletto, G.; Naumann, D.; Nava, L.; Nawaz, M. A.; Ndiyavala, H.; Neise, D.; Nellen, L.; Nemmen, R.; Neyroud, N.; Ngernphat, K.; Nguyen Trung, T.; Nicastro, L.; Nickel, L.; Niemiec, J.; Nieto, D.; Nigro, C.; Nikołajuk, M.; Ninci, D.; Noda, K.; Nogami, Y.; Nolan, S.; Norris, R. P.; Nosek, D.; Nöthe, M.; Novotny, V.; Nozaki, S.; Nunio, F.; O'Brien, P.; Obara, K.; Ohira, Y.; Ohishi, M.; Ohm, S.; Oka, T.; Okazaki, N.; Okumura, A.; Oliver, C.; Olivera, G.; Olmi, B.; Orienti, M.; Orito, R.; Orlandini, M.; Orlando, E.; Osborne, J. P.; Ostrowski, M.; Otte, N.; Ovcharov, E.; Owen, E.; Oya, I.; Ozieblo, A.; Padovani, M.; Pagliaro, A.; Paizis, A.; Palatiello, M.; Palatka, M.; Palazzi, E.; Panazol, J. L.; Paneque, D.; Panny, S.; Pantaleo, F. R.; Panter, M.; Paolillo, M.; Papitto, A.; Paravac, A.; Paredes, J. M.; Pareschi, G.; Parmiggiani, N.; Parsons, R. D.; Paśko, P.; Patel, S. R.; Patricelli, B.; Pavletic, L.; Pavy, S.; Peer, A.; Pecimotika, M.; Pellegriti, M. G.; Peñil Del Campo, P.; Pepato, A.; Perard, S.; Perennes, C.; Peresano, M.; Perez Aguilera, A.; Perez Romero, J.; Perez Torres, M. A.; Persic, M.; Petrucci, P. O.; Petruk, O.; Peyaud, B.; Pfrang, K.; Pian, E.; Piatteli, P.; Pietropaolo, E.; Pillera, R.; Pimentel, D.; Pintore, F.; Garcia, C. Pio; Pirola, G.; Piron, F.; Pita, S.; Pohl, M.; Poireau, V.; Pollo, A.; Polo, M.; Pongkitivanichkul, C.; Porthault, J.; Powell, J.; Pozo, D.; Prado, R. R.; Prandini, E.; Prast, J.; Pressard, K.; Principe, G.; Produit, N.; Prokhorov, D.; Prokoph, H.; Przybilski, H.; Pueschel, E.; Pühlhofer, G.; Puljak, I.; Pumo, M. L.; Punch, M.; Queiroz, F.; Quinn, J.; Quirrenbach, A.; Rajda, P. J.; Rando, R.; Razzaque, S.; Recchia, S.; Reichherzer, P.; Reimer, O.; Reisenegger, A.; Remy, Q.; Renaud, M.; Reposeur, T.; Reville, B.; Reymond, J. M.; Reynolds, J.; Ribeiro, D.; Ribo, M.; Richards, G.; Rico, J.; Rieger, F.; Riitano, L.; Riquelme, M.; Riquelme, D.; Rivoire, S.; Rizi, V.; Roache, E.; Roche, M.; Rodriguez, J.; Rodriguez Fernandez, G.; Rodriguez Ramirez, J. C.; Rodriguez Vazquez, J. J.; Rojas, G.; Romano, P.; Romeo Lobato, G.; Romoli, C.; Roncadelli, M.; Rosado, J.; Rosales de Leon, A.; Rowell, G.; Rugliancich, A.; Ruiz del Mazo, J. E.; Rulten, C.; Russell, C.; Russo Hatlen, F.; Safi Harb, S.; Saha, L.; Sahakian, V.; Sailer, S.; Saito, T.; Sakaki, N.; Sakurai, S.; Salina, G.; Salzmann, H.; Sanchez, D.; Sandaker, H.; Sandoval, A.; Sangiorgi, P.; Sanguillon, M.; Sano, H.; Santander, M.; Santangelo, A.; Santos Lima, R.; Sanuy, A.; Sapozhnikov, L.; Saric, T.; Sarkar, S.; Sasaki, H.; Sasaki, N.; Sato, Y.; Saturni, F. G.; Sawada, M.; Schaefer, J.; Scherer, A.; Scherpenberg, J.; Schipani, P.; Schleicher, B.; Schmoll, J.; Schneider, M.; Schoorlemmer, H.; Schovanek, P.; Schussler, F.; Schwab, B.; Schwanke, U.; Schwarz, J.; Sciacca, E.; Scuderi, S.; Seglar Arroyo, M.; Seitenzahl, I.; Semikoz, D.; Sergijenko, O.; Serna Franco, J. E.; Seweryn, K.; Sguera, V.; Shalchi, A.; Shang, R. Y.; Sharma, P.; Sidoli, L.; Sieiro, J.; Siejkowski, H.; Sillanpaa, A.; Singh, B. B.; Singh, K. K.; Sinha, A.; Siqueira, C.; Sitarek, J.; Sizun, P.; Sliusar, V.; Sobczynska, D.; Sobrinho, R. W.; Sol, H.; Sottile, G.; Spackman, H.; Spencer, S.; Spengler, G.; Spiga, D.; Springer, W.; Stamerra, A.; Stanic, S.; Starling, R.; Stawarz, Ł.; Stefanik, S.; Stegmann, C.; Steiner, A.; Steinmassl, S.; Stella, C.; Sternberger, R.; Sterzel, M.; Stevens, C.; Stevenson, B.; Stolarczyk, T.; Stratta, G.; Straumann, U.; Striskovic, J.; Strzys, M.; Stuik, R.; Suchenek, M.; Sunada, Y.; Suomijarvi, T.; Suric, T.; Suzuki, H.; Swierk, P.; Szepieniec, T.; Tachihara, K.; Tagliaferri, G.; Tajima, H.; Tajima, N.; Tak, D.; Takahashi, H.; Takahashi, M.; Takata, J.; Takeishi, R.; Tam, T.; Tanaka, M.; Tanaka, T.; Tanaka, S.; Tavani, M.; Tavecchio, F.; Tavernier, T.; Taylor, A. R.; Tejedor, L. A.; Temnikov, P.; Terauchi, K.; Terrazas, J. C.; Terrier, R.; Terzic, T.; Teshima, M.; Thibaut, D.; Thocquenne, F.; Tian, W.; Tibaldo, L.; Tiengo, A.; Tluczykont, M.; Todero Peixoto, C. J.; Toma, K.; Tomankova, L.; Tomastik, J.; Tornikoski, M.; Torres, D. F.; Torresi, E.; Tosti, G.; Tosti, L.; Tothill, N.; Toussenel, F.; Tovmassian, G.; Trichard, C.; Trifoglio, M.; Trois, A.; Truzzi, S.; Tsiahina, A.; Turk, B.; Tutone, A.; Uchiyama, Y.; Utayarat, P.; Vaclavek, L.; Vacula, M.; Vagelli, V.; Vagnetti, F.; Valdivia, J. A.; Valentino, M.; Valio, A.; Vallage, B.; Vallania Quispe, P.; van den Berg, A. M.; van Driel, W.; van Eldik, C.; van Rensburg, C.; van Soelen, B.; Vandenbroucke, J.; Vasileiadis, G.; Vassiliev, V.; Vazquez Acosta, M.; Vecchi, M.; Vega, A.; Veh, J.; Veitch, P.; Venter, C.; Ventura, S.; Vercellone, S.; Verguilov, V.; Verna, G.; Vernetto, S.; Verzi, V.; Vettolani, G. P.; Veyssiere, C.; Viale, I.; Viana, A.; Viaux, N.; Vignatti, J.; Vigorito, C. F.; Villanueva, J.; Vitale, V.; Vittorini, V.; Vodeb, V.; Vogel, N.; Voisin, V.; Vorobiov, S.; Vrastil, M.; Vuillaume, T.; Wagner, S. J.; Wagner, P.; Wakazono, K.; Wakely, S. P.; Ward, M.; Warren, D.; Watson, J.; Wechakama, M.; Wegner, P.; Weinstein, A.; Weniger, C.; Werner, F.; Wetteskind, H.; White, M. L.; Wierzcholska, A.; Wiesand, S.; Wijers, R.; Wilkinson, M.; Will, M.; Williams, J.; Williamson, T. J.; Wolter, A.; Wong, Y. W.; Wood, M.; Yamamoto, T.; Yamamoto, H.; Yamane, Y.; Yamazaki, R.; Yanagita, S.; Yang, L.; Yoo, S.; Yoshida, T.; Yoshikoshi, T.; Yu, P.; Yusafzai, A.; Zacharias, M.; Zaldivar, B.; Zampieri, L.; Zanin, R.; Zanmar Sanchez, R.; Zaric, D.; Zavrtanik, M.; Zavrtanik, D.; Zdziarski, A.; Zech, A.; Zechlin, H.; Zenin, A.; Zerwekh, A.; Ziętara, K.; Zink, A.; Ziolkowski, J.; Zivec, M.; Zmija, A. Bibcode: 2022icrc.confE...5Z Altcode: 2022PoS...395E...5Z No abstract at ADS Title: Astrometric radial velocities for nearby stars Authors: Lindegren, Lennart; Dravins, Dainis Bibcode: 2021A&A...652A..45L Altcode: 2021arXiv210509014L Context. Under certain conditions, stellar radial velocities can be determined from astrometry, without any use of spectroscopy. This enables us to identify phenomena, other than the Doppler effect, that are displacing spectral lines.
Aims: The change of stellar proper motions over time (perspective acceleration) is used to determine radial velocities from accurate astrometric data, which are now available from the Gaia and HIPPARCOS missions.
Methods: Positions and proper motions at the epoch of HIPPARCOS are compared with values propagated back from the epoch of the Gaia Early Data Release 3. This propagation depends on the radial velocity, which obtains its value from an optimal fit assuming uniform space motion relative to the solar system barycentre.
Results: For 930 nearby stars we obtain astrometric radial velocities with formal uncertainties better than 100 km s−1; for 55 stars the uncertainty is below 10 km s−1, and for seven it is below 1 km s−1. Most stars that are not components of double or multiple systems show good agreement with available spectroscopic radial velocities.
Conclusions: Astrometry offers geometric methods to determine stellar radial velocity, irrespective of complexities in stellar spectra. This enables us to segregate wavelength displacements caused by the radial motion of the stellar centre-of-mass from those induced by other effects, such as gravitational redshifts in white dwarfs. Title: Intensity Interferometry Authors: Dravins, Dainis Bibcode: 2021hai3.book...31D Altcode: No abstract at ADS Title: Spatially resolved spectroscopy across stellar surfaces. IV. F, G, and K-stars: Synthetic 3D spectra at hyper-high resolution Authors: Dravins, Dainis; Ludwig, Hans-Günter; Freytag, Bernd Bibcode: 2021A&A...649A..16D Altcode: 2021arXiv210303880D Context. High-precision stellar analyses require hydrodynamic 3D modeling. Such models predict changes across stellar disks of spectral line shapes, asymmetries, and wavelength shifts. For testing models in stars other than the Sun, spatially resolved observations are feasible from differential spectroscopy during exoplanet transits, retrieving spectra of those stellar surface segments that successively become hidden behind the transiting planet, as demonstrated in Papers I, II, and III.
Aims: Synthetic high-resolution spectra over extended spectral regions are now available from 3D models. Similar to other ab initio simulations in astrophysics, these data contain patterns that have not been specifically modeled but may be revealed after analyses to be analogous to those of a large volume of observations.
Methods: From five 3D models spanning Teff = 3964-6726 K (spectral types ~K8 V-F3 V), synthetic spectra at hyper-high resolution (λ/Δλ >1 000 000) were analyzed. Selected Fe I and Fe II lines at various positions across stellar disks were searched for characteristic patterns between different types of lines in the same star and for similar lines between different stars.
Results: Spectral-line patterns are identified for representative photospheric lines of different strengths, excitation potentials, and ionization levels, thereby encoding the hydrodynamic 3D structure. Line profiles and bisectors are shown for various stars at different positions across stellar disks. Absolute convective wavelength shifts are obtained as differences to 1D models, where such shifts do not occur.
Conclusions: Observable relationships for line properties are retrieved from realistically complex synthetic spectra. Such patterns may also test very detailed 3D modeling, including non-LTE effects. While present results are obtained at hyper-high spectral resolution, the subsequent Paper V examines their practical observability at realistically lower resolutions, and in the presence of noise. Title: Spatially resolved spectroscopy across stellar surfaces. V. Observational prospects: toward Earth-like exoplanet detection Authors: Dravins, Dainis; Ludwig, Hans-Günter; Freytag, Bernd Bibcode: 2021A&A...649A..17D Altcode: 2021arXiv210304996D Context. High-precision stellar analyses require hydrodynamic 3D modeling. Testing such models is feasible by retrieving spectral line shapes across stellar disks, using differential spectroscopy during exoplanet transits. Observations were presented in Papers I, II, and III, while Paper IV explored synthetic data at hyper-high spectral resolution for different classes of stars, identifying characteristic patterns for Fe I and Fe II lines.
Aims: Anticipating future observations, the observability of patterns among photospheric lines of different strength, excitation potential and ionization level are examined from synthetic spectra, as observed at ordinary spectral resolutions and at different levels of noise. Time variability in 3D atmospheres induces changes in spectral-line parameters, some of which are correlated. An adequate calibration could identify proxies for the jitter in apparent radial velocity to enable adjustments to actual stellar radial motion.
Methods: We used spectral-line patterns identified in synthetic spectra at hyper-high resolution in Paper IV from 3D models spanning Teff = 3964-6726 K (spectral types ~K8 V-F3 V) to simulate practically observable signals at different stellar disk positions at various lower spectral resolutions, down to λ/Δλ = 75 000. We also examined the center-to-limb temporal variability.
Results: Recovery of spatially resolved line profiles with fitted widths and depths is shown for various noise levels, with gradual degradation at successively lower spectral resolutions. Signals during exoplanet transit are simulated. In addition to Rossiter-McLaughlin type signatures in apparent radial velocity, analogous effects are shown for line depths and widths. In a solar model, temporal variability in line profiles and apparent radial velocity shows correlations between jittering in apparent radial velocity and fluctuations in line depth.
Conclusions: Spatially resolved spectroscopy using exoplanet transits is feasible for main-sequence stars. Overall line parameters of width, depth and wavelength position can be retrieved already with moderate efforts, but a very good signal-to-noise ratio is required to reveal the more subtle signatures between subgroups of spectral lines, where finer details of atmospheric structure are encoded. Fluctuations in line depth correlate with those in wavelength, and because both can be measured from the ground, searches for low-mass exoplanets should explore these to adjust apparent radial velocities to actual stellar motion. Title: Spatially Resolved Stellar Disk Spectra at Hyper-high Resolution: Toward Earth-like Exoplanet Detection Authors: Dravins, D.; Ludwig, H. Bibcode: 2020AAS...23613002D Altcode: High-precision spectroscopy might find 'truly' Earth-like exoplanets. Instrumental precisions are close to being achieved but limitations arise in the complexities of spectral-line formation. Spectral lines become somewhat asymmetric by being formed in dynamic gas flows. Radial-velocity signatures differ between different types of lines, change between stars, vary across stellar disks, and are modulated by magnetic activity. Spectroscopy across spatially resolved stellar disks has become possible by using transiting exoplanets as occulting spatial probes, permitting to test center-to-limb atmospheric hydrodynamics in stars also other than the Sun. Additional suitable target stars will likely be found in exoplanet surveys, and simulated observations are in progress to identify strategies for their near-future observations. From a grid of 3-D hydrodynamic CO5BOLD model atmospheres for solar-type stars, synthetic spectra have been computed at hyper-high spectral resolution (R greater than 1 million), for several center-to-limb locations across stellar disks. (The term 'hyper-high' is used since 'ultra-high' is already taken for lower-resolution data.) Such resolutions are required to fully resolve intrinsic line asymmetries. To segregate those from such arising due to blends, and also to obtain absolute wavelength shifts irrespective of errors in laboratory wavelengths, 3-D spectra are matched against similar data from 1-D models. There, unblended lines appear symmetric at their laboratory wavelength positions, and differences to 3-D profiles isolate effects arising in the dynamic photospheres. Synthetic spectra are surveyed for unblended lines with different strengths, excitation potentials, and ionization levels, each of which contribute characteristic signatures of line asymmetries and apparent Doppler shifts. The hyper-high resolution data are degraded to common spectrometer values to appreciate what signatures may realistically be observed. An adequate understanding of both line formation and of spectrometer performance should enable to disentangle effects from variable stellar atmospheres from those induced by even small Earth-like exoplanets. Title: State of the Profession: Intensity Interferometry Authors: Kieda, David; Anton, Gisela; Barbano, Anastasia; Benbow, Wystan; Carlile, Colin; Daniel, Michael; Dravins, Dainis; Griffin, Sean; Hassan, Tarek; Holder, Jamie; LeBohec, Stephan; Matthews, Nolan; Montaruli, Theresa; Produit, Nicolas; Reynolds, Josh; Walter, Roland; Zampieri, Luca Bibcode: 2019BAAS...51g.227K Altcode: 2019astro2020U.227K; 2019arXiv190713181K This paper describes validation tests of Stellar Intensity Interferometry (SII) in the laboratory and SII measurements on nearby stars that have been completed as a technology demonstrator. The paper describes current and future observatories that will advance the impact and increase the instrumental resolution of SII during the upcoming decade. Title: Science opportunities enabled by the era of Visible Band Stellar Imaging with sub-100 {\mu}arc-sec angular resolution Authors: Kieda, D.; Acosta, Monica; Barbano, Anastasia; Carlile, Colin; Daniel, Michael; Dravins, Dainis; Holder, Jamie; Matthews, Nolan; Montaruli, Teresa; Walter, Roland; Zampieri, Luca Bibcode: 2019arXiv190803164K Altcode: This white paper briefly summarizes stellar science opportunities enabled by ultra-high resolution (sub-100 {\mu} arc-sec) astronomical imaging in the visible (U/V) wavebands. Next generation arrays of Imaging Cherenkov telescopes, to be constructed in the next decade, can provide unprecedented visible band imaging of several thousand bright (m< 6), hot (O/B/A) stars using a modern implementation of Stellar Intensity Interferometry (SII). This white paper describes the astrophysics/astronomy science opportunities that may be uncovered in this new observation space during the next decade. Title: Science opportunities enabled by the era of Visible Band Stellar Imaging with sub-100 μarc-sec angular resolution. Authors: Kieda, David; Acosta, Monica; Barbano, Anastasia; Carlile, Colin; Daniel, Michael; Dravins, Dainis; Holder, Jamie; Matthews, Nolan; Montaruli, Teresa; Walter, Roland; Zampieri, Luca Bibcode: 2019BAAS...51c.275K Altcode: 2019astro2020T.275K This white paper briefly summarizes stellar science opportunities enabled by ultra-high resolution (sub-100 μarc-sec) astronomical imaging in the visible (U/V) wavebands. We describe the science impact of imaging of several thousand bright (m < 6), hot (O/B/A) stars using a modern implementation of Stellar Intensity Interferometry (SII). Title: Science with the Cherenkov Telescope Array Authors: Cherenkov Telescope Array Consortium; Acharya, B. S.; Agudo, I.; Al Samarai, I.; Alfaro, R.; Alfaro, J.; Alispach, C.; Alves Batista, R.; Amans, J. -P.; Amato, E.; Ambrosi, G.; Antolini, E.; Antonelli, L. A.; Aramo, C.; Araya, M.; Armstrong, T.; Arqueros, F.; Arrabito, L.; Asano, K.; Ashley, M.; Backes, M.; Balazs, C.; Balbo, M.; Ballester, O.; Ballet, J.; Bamba, A.; Barkov, M.; Barres de Almeida, U.; Barrio, J. A.; Bastieri, D.; Becherini, Y.; Belfiore, A.; Benbow, W.; Berge, D.; Bernardini, E.; Bernardini, M. G.; Bernardos, M.; Bernlöhr, K.; Bertucci, B.; Biasuzzi, B.; Bigongiari, C.; Biland, A.; Bissaldi, E.; Biteau, J.; Blanch, O.; Blazek, J.; Boisson, C.; Bolmont, J.; Bonanno, G.; Bonardi, A.; Bonavolontà, C.; Bonnoli, G.; Bosnjak, Z.; Böttcher, M.; Braiding, C.; Bregeon, J.; Brill, A.; Brown, A. M.; Brun, P.; Brunetti, G.; Buanes, T.; Buckley, J.; Bugaev, V.; Bühler, R.; Bulgarelli, A.; Bulik, T.; Burton, M.; Burtovoi, A.; Busetto, G.; Canestrari, R.; Capalbi, M.; Capitanio, F.; Caproni, A.; Caraveo, P.; Cárdenas, V.; Carlile, C.; Carosi, R.; Carquín, E.; Carr, J.; Casanova, S.; Cascone, E.; Catalani, F.; Catalano, O.; Cauz, D.; Cerruti, M.; Chadwick, P.; Chaty, S.; Chaves, R. C. G.; Chen, A.; Chen, X.; Chernyakova, M.; Chikawa, M.; Christov, A.; Chudoba, J.; Cieślar, M.; Coco, V.; Colafrancesco, S.; Colin, P.; Conforti, V.; Connaughton, V.; Conrad, J.; Contreras, J. L.; Cortina, J.; Costa, A.; Costantini, H.; Cotter, G.; Covino, S.; Crocker, R.; Cuadra, J.; Cuevas, O.; Cumani, P.; D'Aì, A.; D'Ammando, F.; D'Avanzo, P.; D'Urso, D.; Daniel, M.; Davids, I.; Dawson, B.; Dazzi, F.; De Angelis, A.; de Cássia dos Anjos, R.; De Cesare, G.; De Franco, A.; de Gouveia Dal Pino, E. M.; de la Calle, I.; de los Reyes Lopez, R.; De Lotto, B.; De Luca, A.; De Lucia, M.; de Naurois, M.; de Oña Wilhelmi, E.; De Palma, F.; De Persio, F.; de Souza, V.; Deil, C.; Del Santo, M.; Delgado, C.; della Volpe, D.; Di Girolamo, T.; Di Pierro, F.; Di Venere, L.; Díaz, C.; Dib, C.; Diebold, S.; Djannati-Ataï, A.; Domínguez, A.; Dominis Prester, D.; Dorner, D.; Doro, M.; Drass, H.; Dravins, D.; Dubus, G.; Dwarkadas, V. V.; Ebr, J.; Eckner, C.; Egberts, K.; Einecke, S.; Ekoume, T. R. N.; Elsässer, D.; Ernenwein, J. -P.; Espinoza, C.; Evoli, C.; Fairbairn, M.; Falceta-Goncalves, D.; Falcone, A.; Farnier, C.; Fasola, G.; Fedorova, E.; Fegan, S.; Fernandez-Alonso, M.; Fernández-Barral, A.; Ferrand, G.; Fesquet, M.; Filipovic, M.; Fioretti, V.; Fontaine, G.; Fornasa, M.; Fortson, L.; Freixas Coromina, L.; Fruck, C.; Fujita, Y.; Fukazawa, Y.; Funk, S.; Füßling, M.; Gabici, S.; Gadola, A.; Gallant, Y.; Garcia, B.; Garcia López, R.; Garczarczyk, M.; Gaskins, J.; Gasparetto, T.; Gaug, M.; Gerard, L.; Giavitto, G.; Giglietto, N.; Giommi, P.; Giordano, F.; Giro, E.; Giroletti, M.; Giuliani, A.; Glicenstein, J. -F.; Gnatyk, R.; Godinovic, N.; Goldoni, P.; Gómez-Vargas, G.; González, M. M.; González, J. M.; Götz, D.; Graham, J.; Grandi, P.; Granot, J.; Green, A. J.; Greenshaw, T.; Griffiths, S.; Gunji, S.; Hadasch, D.; Hara, S.; Hardcastle, M. J.; Hassan, T.; Hayashi, K.; Hayashida, M.; Heller, M.; Helo, J. C.; Hermann, G.; Hinton, J.; Hnatyk, B.; Hofmann, W.; Holder, J.; Horan, D.; Hörandel, J.; Horns, D.; Horvath, P.; Hovatta, T.; Hrabovsky, M.; Hrupec, D.; Humensky, T. B.; Hütten, M.; Iarlori, M.; Inada, T.; Inome, Y.; Inoue, S.; Inoue, T.; Inoue, Y.; Iocco, F.; Ioka, K.; Iori, M.; Ishio, K.; Iwamura, Y.; Jamrozy, M.; Janecek, P.; Jankowsky, D.; Jean, P.; Jung-Richardt, I.; Jurysek, J.; Kaaret, P.; Karkar, S.; Katagiri, H.; Katz, U.; Kawanaka, N.; Kazanas, D.; Khélifi, B.; Kieda, D. B.; Kimeswenger, S.; Kimura, S.; Kisaka, S.; Knapp, J.; Knödlseder, J.; Koch, B.; Kohri, K.; Komin, N.; Kosack, K.; Kraus, M.; Krause, M.; Krauß, F.; Kubo, H.; Kukec Mezek, G.; Kuroda, H.; Kushida, J.; La Palombara, N.; Lamanna, G.; Lang, R. G.; Lapington, J.; Le Blanc, O.; Leach, S.; Lees, J. -P.; Lefaucheur, J.; Leigui de Oliveira, M. A.; Lenain, J. -P.; Lico, R.; Limon, M.; Lindfors, E.; Lohse, T.; Lombardi, S.; Longo, F.; López, M.; López-Coto, R.; Lu, C. -C.; Lucarelli, F.; Luque-Escamilla, P. L.; Lyard, E.; Maccarone, M. C.; Maier, G.; Majumdar, P.; Malaguti, G.; Mandat, D.; Maneva, G.; Manganaro, M.; Mangano, S.; Marcowith, A.; Marín, J.; Markoff, S.; Martí, J.; Martin, P.; Martínez, M.; Martínez, G.; Masetti, N.; Masuda, S.; Maurin, G.; Maxted, N.; Mazin, D.; Medina, C.; Melandri, A.; Mereghetti, S.; Meyer, M.; Minaya, I. A.; Mirabal, N.; Mirzoyan, R.; Mitchell, A.; Mizuno, T.; Moderski, R.; Mohammed, M.; Mohrmann, L.; Montaruli, T.; Moralejo, A.; Morcuende-Parrilla, D.; Mori, K.; Morlino, G.; Morris, P.; Morselli, A.; Moulin, E.; Mukherjee, R.; Mundell, C.; Murach, T.; Muraishi, H.; Murase, K.; Nagai, A.; Nagataki, S.; Nagayoshi, T.; Naito, T.; Nakamori, T.; Nakamura, Y.; Niemiec, J.; Nieto, D.; Nikołajuk, M.; Nishijima, K.; Noda, K.; Nosek, D.; Novosyadlyj, B.; Nozaki, S.; O'Brien, P.; Oakes, L.; Ohira, Y.; Ohishi, M.; Ohm, S.; Okazaki, N.; Okumura, A.; Ong, R. A.; Orienti, M.; Orito, R.; Osborne, J. P.; Ostrowski, M.; Otte, N.; Oya, I.; Padovani, M.; Paizis, A.; Palatiello, M.; Palatka, M.; Paoletti, R.; Paredes, J. M.; Pareschi, G.; Parsons, R. D.; Pe'er, A.; Pech, M.; Pedaletti, G.; Perri, M.; Persic, M.; Petrashyk, A.; Petrucci, P.; Petruk, O.; Peyaud, B.; Pfeifer, M.; Piano, G.; Pisarski, A.; Pita, S.; Pohl, M.; Polo, M.; Pozo, D.; Prandini, E.; Prast, J.; Principe, G.; Prokhorov, D.; Prokoph, H.; Prouza, M.; Pühlhofer, G.; Punch, M.; Pürckhauer, S.; Queiroz, F.; Quirrenbach, A.; Rainò, S.; Razzaque, S.; Reimer, O.; Reimer, A.; Reisenegger, A.; Renaud, M.; Rezaeian, A. H.; Rhode, W.; Ribeiro, D.; Ribó, M.; Richtler, T.; Rico, J.; Rieger, F.; Riquelme, M.; Rivoire, S.; Rizi, V.; Rodriguez, J.; Rodriguez Fernandez, G.; Rodríguez Vázquez, J. J.; Rojas, G.; Romano, P.; Romeo, G.; Rosado, J.; Rovero, A. C.; Rowell, G.; Rudak, B.; Rugliancich, A.; Rulten, C.; Sadeh, I.; Safi-Harb, S.; Saito, T.; Sakaki, N.; Sakurai, S.; Salina, G.; Sánchez-Conde, M.; Sandaker, H.; Sandoval, A.; Sangiorgi, P.; Sanguillon, M.; Sano, H.; Santander, M.; Sarkar, S.; Satalecka, K.; Saturni, F. G.; Schioppa, E. J.; Schlenstedt, S.; Schneider, M.; Schoorlemmer, H.; Schovanek, P.; Schulz, A.; Schussler, F.; Schwanke, U.; Sciacca, E.; Scuderi, S.; Seitenzahl, I.; Semikoz, D.; Sergijenko, O.; Servillat, M.; Shalchi, A.; Shellard, R. C.; Sidoli, L.; Siejkowski, H.; Sillanpää, A.; Sironi, G.; Sitarek, J.; Sliusar, V.; Slowikowska, A.; Sol, H.; Stamerra, A.; Stanič, S.; Starling, R.; Stawarz, Ł.; Stefanik, S.; Stephan, M.; Stolarczyk, T.; Stratta, G.; Straumann, U.; Suomijarvi, T.; Supanitsky, A. D.; Tagliaferri, G.; Tajima, H.; Tavani, M.; Tavecchio, F.; Tavernet, J. -P.; Tayabaly, K.; Tejedor, L. A.; Temnikov, P.; Terada, Y.; Terrier, R.; Terzic, T.; Teshima, M.; Testa, V.; Thoudam, S.; Tian, W.; Tibaldo, L.; Tluczykont, M.; Todero Peixoto, C. J.; Tokanai, F.; Tomastik, J.; Tonev, D.; Tornikoski, M.; Torres, D. F.; Torresi, E.; Tosti, G.; Tothill, N.; Tovmassian, G.; Travnicek, P.; Trichard, C.; Trifoglio, M.; Troyano Pujadas, I.; Tsujimoto, S.; Umana, G.; Vagelli, V.; Vagnetti, F.; Valentino, M.; Vallania, P.; Valore, L.; van Eldik, C.; Vandenbroucke, J.; Varner, G. S.; Vasileiadis, G.; Vassiliev, V.; Vázquez Acosta, M.; Vecchi, M.; Vega, A.; Vercellone, S.; Veres, P.; Vergani, S.; Verzi, V.; Vettolani, G. P.; Viana, A.; Vigorito, C.; Villanueva, J.; Voelk, H.; Vollhardt, A.; Vorobiov, S.; Vrastil, M.; Vuillaume, T.; Wagner, S. J.; Wagner, R.; Walter, R.; Ward, J. E.; Warren, D.; Watson, J. J.; Werner, F.; White, M.; White, R.; Wierzcholska, A.; Wilcox, P.; Will, M.; Williams, D. A.; Wischnewski, R.; Wood, M.; Yamamoto, T.; Yamazaki, R.; Yanagita, S.; Yang, L.; Yoshida, T.; Yoshiike, S.; Yoshikoshi, T.; Zacharias, M.; Zaharijas, G.; Zampieri, L.; Zandanel, F.; Zanin, R.; Zavrtanik, M.; Zavrtanik, D.; Zdziarski, A. A.; Zech, A.; Zechlin, H.; Zhdanov, V. I.; Ziegler, A.; Zorn, J. Bibcode: 2019scta.book.....C Altcode: 2017arXiv170907997C The Cherenkov Telescope Array, CTA, will be the major global observatory for very high energy gamma-ray astronomy over the next decade and beyond. The scientific potential of CTA is extremely broad: from understanding the role of relativistic cosmic particles to the search for dark matter. CTA is an explorer of the extreme universe, probing environments from the immediate neighbourhood of black holes to cosmic voids on the largest scales. Covering a huge range in photon energy from 20 GeV to 300 TeV, CTA will improve on all aspects of performance with respect to current instruments. The observatory will operate arrays on sites in both hemispheres to provide full sky coverage and will hence maximize the potential for the rarest phenomena such as very nearby supernovae, gamma-ray bursts or gravitational wave transients. With 99 telescopes on the southern site and 19 telescopes on the northern site, flexible operation will be possible, with sub-arrays available for specific tasks. CTA will have important synergies with many of the new generation of major astronomical and astroparticle observatories. Multi-wavelength and multi-messenger approaches combining CTA data with those from other instruments will lead to a deeper understanding of the broad-band non-thermal properties of target sources. The CTA Observatory will be operated as an open, proposal-driven observatory, with all data available on a public archive after a pre-defined proprietary period. Scientists from institutions worldwide have combined together to form the CTA Consortium. This Consortium has prepared a proposal for a Core Programme of highly motivated observations. The programme, encompassing approximately 40% of the available observing time over the first ten years of CTA operation, is made up of individual Key Science Projects (KSPs), which are presented in this document. Title: Capabilities beyond Gamma Rays Authors: Bühler, R.; Dravins, D.; Egberts, K.; Hinton, J. A.; Parsons, R. D.; Cherenkov Telescope Array Consortium Bibcode: 2019scta.book..291B Altcode: Although designed as a gamma-ray observatory, CTA is a powerful tool for a range of other astrophysics and astroparticle physics. For example, CTA can make precision studies of charged cosmic rays in the energy range from ∼100 GeV up to PeV energies, and it can be used as an instrument for optical intensity interferometry, to provide unprecedented angular resolution in the optical for bright sources. Below, we briefly summarise these possibilities. Most of the topics we discuss can be explored in parallel with gamma-ray data-taking, without interfering with the major science operations of CTA. Those studies (such as intensity interferometry) which require specific observations can likely make use of bright moonlight time, thus enhancing the CTA science return without negative impact on the key science goals. Title: Spatially resolved spectroscopy across stellar surfaces. III. Photospheric Fe I lines across HD 189733A (K1 V) Authors: Dravins, Dainis; Gustavsson, Martin; Ludwig, Hans-Günter Bibcode: 2018A&A...616A.144D Altcode: 2018arXiv180600012D Context. Spectroscopy across spatially resolved stellar surfaces reveals spectral line profiles free from rotational broadening, whose gradual changes from disk center toward the stellar limb reflect an atmospheric fine structure that is possible to model by 3D hydrodynamics.
Aims: Previous studies of photospheric spectral lines across stellar disks exist for the Sun and HD 209458 (G0 V) and are now extended to the planet-hosting HD 189733A to sample a cooler K-type star and explore the future potential of the method.
Methods: During exoplanet transit, stellar surface portions successively become hidden and differential spectroscopy between various transit phases uncovers spectra of small surface segments temporarily hidden behind the planet. The method was elaborated in Paper I, in which observable signatures were predicted quantitatively from hydrodynamic simulations.
Results: From observations of HD 189733A with the ESO HARPS spectrometer at λ/Δλ 115 000, profiles for stronger and weaker Fe I lines are retrieved at several center-to-limb positions, reaching adequate S/N after averaging over numerous similar lines.
Conclusions: Retrieved line profile widths and depths are compared to synthetic ones from models with parameters bracketing those of the target star and are found to be consistent with 3D simulations. Center-to-limb changes strongly depend on the surface granulation structure and much greater line-width variation is predicted in hotter F-type stars with vigorous granulation than in cooler K-types. Such parameters, obtained from fits to full line profiles, are realistic to retrieve for brighter planet-hosting stars, while their hydrodynamic modeling offers previously unexplored diagnostics for stellar atmospheric fine structure and 3D line formation. Precise modeling may be required in searches for Earth-analog exoplanets around K-type stars, whose more tranquil surface granulation and lower ensuing microvariability may enable such detections. Title: Intensity Interferometry: Imaging Stars with Kilometer Baselines Authors: Dravins, Dainis Bibcode: 2018iss..confE...6D Altcode: Microarcsecond imaging will reveal stellar surfaces but requires kilometer-scale interferometers. Intensity interferometry circumvents atmospheric turbulence by correlating intensity fluctuations between independent telescopes. Telescopes connect only electronically, and the error budget relates to electronic timescales of nanoseconds (light-travel distances on the order of a meter), enabling the use of imperfect optics in a turbulent atmosphere. Once pioneered by Hanbury Brown and Twiss, digital versions have now been demonstrated in the laboratory, reconstructing diffraction-limited images from hundreds of optical baselines. Arrays of Cherenkov telescopes (primarily erected for gamma-ray studies) will extend over a few km, enabling an optical equivalent of radio interferometers. Resolutions in the tens of microarcseconds will resolve rotationally flattened stars with their circumstellar disks and winds, or possibly even the silhouettes of transiting exoplanets. Applying the method to mirror segments in extremely large telescopes (even with an incompletely filled main mirror, poor seeing, no adaptive optics), the diffraction limit in the blue may be reached. Title: Seeing Stars - Intensity Interferometry in the Laboratory & on the Ground Authors: Carlile, Colin; Dravins, Dainis Bibcode: 2018iss..confE...3C Altcode: In many ways it is a golden age for astronomy. Spectacular new discoveries, for example the detection of gravitational waves, are very dependent upon instrumental development. The specific instrument development we propose, Intensity Interferometry (II), aims toimprove the spatial resolution of optical telescopes by 100x to 50µas [1]. This is impractical to achieve by increasing the size of telescopes or by extending the capabilities of phase interferometry. II, if implemented on the Cherenkov Telescope Array (CTA) currently being installed in La Palma and Paranal, would record the light intensity - the photon train - from many different telescopes, up to 2 km apart, on a nanosecond timescale and compare them. The signal from the many pairs of telescopes would quantify the degree of correlation by extracting the second-order correlation function, and thus create an image. This is not a real space image. However we can invert the data by Fourier Transform and create a real image. The more telescopes, the better resolved and more physical is the image, enabling the study of sunspots on nearby stars; orbiting binary stars; or exoplanets traversing the disc of their own star. We understand the Sun well but we have little experimental knowledge of how representative it is of main sequence stars. To test the II method, at Lund Observatory we have set up a laboratory analogue comprising ten small telescopes observing an artificial star created by light from a laser. The method has been shown to work [2] and the telescope array has now been extended to two dimensions. We are in discussion with other groups to explore the possibility of implementing this method on real telescopes observing actual stars. We plan to do this with the prototype Small Size Telescopes being built by groups in Europe, and ultimately with the CTA itself. A Science Working Group for II has now been set up within the CTA Consortium, of which Lund University is an integral part. A Letter of Intent has been sent to CTA expressing these intentions. An attractive aspect of II is its complementarity to the principle goal of CTA - the exploration of high energy cosmic rays via the Cherenkov light they generate in the atmosphere. This can only be observed under the most demanding atmospheric conditions whereas II can be recorded when conditions are poor: with a bright Moon, during periods of turbulence; in hazy conditions; or after dusk and before dawn. Two further advantages of implementing an II option on CTA are the minimal marginal costs incurred to an already 400M€ investment and, secondly, that even a few telescopes would produce unique scientific results even in the early days when the CTA array is far from complete. [1] Dainis Dravins and Colin Carlile, SPIE Newsroom (2016), http://spie.org/newsroom/6504-kilometer-baseline-optical-intensity-interferometry-for-stellar-surface-observations [2] D. Dravins, T. Lagadec, P.D. Nuñez, Nature Communications 6, 6852 (2015) Title: Revealing Stellar Surface Structure Behind Transiting Exoplanets Authors: Dravins, Dainis Bibcode: 2018iss..confE...7D Altcode: During exoplanet transits, successive stellar surface portions become hidden and differential spectroscopy between various transit phases provide spectra of small surface segments temporarily hidden behind the planet. Line profile changes across the stellar disk offer diagnostics for hydrodynamic modeling, while exoplanet analyses require stellar background spectra to be known along the transit path. Since even giant planets cover only a small fraction of any main-sequence star, very precise observations are required, as well as averaging over numerous spectral lines with similar parameters. Spatially resolved Fe I line profiles across stellar disks have now been retrieved for HD209458 (G0V) and HD189733A (K1V), using data from the UVES and HARPS spectrometers. Free from rotational broadening, spatially resolved profiles are narrower and deeper than in integrated starlight. During transit, the profiles shift towards longer wavelengths, illustrating both stellar rotation at the latitude of transit and the prograde orbital motion of the exoplanets. This method will soon become applicable to more stars, once additional bright exoplanet hosts have been found. Title: Stellar atmospheres behind transiting exoplanets Authors: Dravins, D.; Ludwig, H. -G.; Dahlén, E.; Gustavsson, M.; Pazira, H. Bibcode: 2017EPSC...11...21D Altcode: Stellar surfaces are covered with brighter and darker structures, just like on the Sun. While solar surface details can be easily studied with telescopes, stellar surfaces cannot thus be resolved. However, one can use planets that happen to pass in front of distant stars as "shades" that successively block out small portions of the stellar surface behind. By measuring how the light from the star changes during such a transit, one can deduce stellar surface properties. Knowing those is required not only to study the star as such, but also to deduce the chemical composition of the planet that is passing in front of it, where some of the detected starlight has been filtered through the planet's atmosphere. Title: Cherenkov Telescope Array Contributions to the 35th International Cosmic Ray Conference (ICRC2017) Authors: Acero, F.; Acharya, B. S.; Acín Portella, V.; Adams, C.; Agudo, I.; Aharonian, F.; Samarai, I. Al; Alberdi, A.; Alcubierre, M.; Alfaro, R.; Alfaro, J.; Alispach, C.; Aloisio, R.; Alves Batista, R.; Amans, J. -P.; Amato, E.; Ambrogi, L.; Ambrosi, G.; Ambrosio, M.; Anderson, J.; Anduze, M.; Angüner, E. O.; Antolini, E.; Antonelli, L. A.; Antonuccio, V.; Antoranz, P.; Aramo, C.; Araya, M.; Arcaro, C.; Armstrong, T.; Arqueros, F.; Arrabito, L.; Arrieta, M.; Asano, K.; Asano, A.; Ashley, M.; Aubert, P.; Singh, C. B.; Babic, A.; Backes, M.; Bajtlik, S.; Balazs, C.; Balbo, M.; Ballester, O.; Ballet, J.; Ballo, L.; Balzer, A.; Bamba, A.; Bandiera, R.; Barai, P.; Barbier, C.; Barcelo, M.; Barkov, M.; Barres de Almeida, U.; Barrio, J. A.; Bastieri, D.; Bauer, C.; Becciani, U.; Becherini, Y.; Becker Tjus, J.; Bednarek, W.; Belfiore, A.; Benbow, W.; Benito, M.; Berge, D.; Bernardini, E.; Bernardini, M. G.; Bernardos, M.; Bernhard, S.; Bernlöhr, K.; Bertinelli Salucci, C.; Bertucci, B.; Besel, M. -A.; Beshley, V.; Bettane, J.; Bhatt, N.; Bhattacharyya, W.; Bhattachryya, S.; Biasuzzi, B.; Bicknell, G.; Bigongiari, C.; Biland, A.; Bilinsky, A.; Bird, R.; Bissaldi, E.; Biteau, J.; Bitossi, M.; Blanch, O.; Blasi, P.; Blazek, J.; Boccato, C.; Bockermann, C.; Boehm, C.; Bohacova, M.; Boisson, C.; Bolmont, J.; Bonanno, G.; Bonardi, A.; Bonavolontà, C.; Bonnoli, G.; Borkowski, J.; Bose, R.; Bosnjak, Z.; Böttcher, M.; Boutonnet, C.; Bouyjou, F.; Bowman, L.; Bozhilov, V.; Braiding, C.; Brau-Nogué, S.; Bregeon, J.; Briggs, M.; Brill, A.; Brisken, W.; Bristow, D.; Britto, R.; Brocato, E.; Brown, A. M.; Brown, S.; Brügge, K.; Brun, P.; Brun, P.; Brun, F.; Brunetti, L.; Brunetti, G.; Bruno, P.; Bryan, M.; Buckley, J.; Bugaev, V.; Bühler, R.; Bulgarelli, A.; Bulik, T.; Burton, M.; Burtovoi, A.; Busetto, G.; Buson, S.; Buss, J.; Byrum, K.; Caccianiga, A.; Cameron, R.; Canelli, F.; Canestrari, R.; Capalbi, M.; Capasso, M.; Capitanio, F.; Caproni, A.; Capuzzo-Dolcetta, R.; Caraveo, P.; Cárdenas, V.; Cardenzana, J.; Cardillo, M.; Carlile, C.; Caroff, S.; Carosi, R.; Carosi, A.; Carquín, E.; Carr, J.; Casandjian, J. -M.; Casanova, S.; Cascone, E.; Castro-Tirado, A. J.; Castroviejo Mora, J.; Catalani, F.; Catalano, O.; Cauz, D.; Celestino Silva, C.; Celli, S.; Cerruti, M.; Chabanne, E.; Chadwick, P.; Chakraborty, N.; Champion, C.; Chatterjee, A.; Chaty, S.; Chaves, R.; Chen, A.; Chen, X.; Cheng, K.; Chernyakova, M.; Chikawa, M.; Chitnis, V. R.; Christov, A.; Chudoba, J.; Cieślar, M.; Clark, P.; Coco, V.; Colafrancesco, S.; Colin, P.; Colombo, E.; Colome, J.; Colonges, S.; Conforti, V.; Connaughton, V.; Conrad, J.; Contreras, J. L.; Cornat, R.; Cortina, J.; Costa, A.; Costantini, H.; Cotter, G.; Courty, B.; Covino, S.; Covone, G.; Cristofari, P.; Criswell, S. J.; Crocker, R.; Croston, J.; Crovari, C.; Cuadra, J.; Cuevas, O.; Cui, X.; Cumani, P.; Cusumano, G.; D'Aì, A.; D'Ammando, F.; D'Avanzo, P.; D'Urso, D.; Da Vela, P.; Dale, Ø.; Dang, V. T.; Dangeon, L.; Daniel, M.; Davids, I.; Dawson, B.; Dazzi, F.; De Angelis, A.; De Caprio, V.; de Cássia dos Anjos, R.; De Cesare, G.; De Franco, A.; De Frondat, F.; de Gouveia Dal Pino, E. M.; de la Calle, I.; De Lisio, C.; de los Reyes Lopez, R.; De Lotto, B.; De Luca, A.; De Lucia, M.; de Mello Neto, J. R. 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M.; Mirzoyan, R.; Mitchell, A.; Mizuno, T.; Moderski, R.; Mohammed, M.; Mohrmann, L.; Molijn, C.; Molinari, E.; Moncada, R.; Montaruli, T.; Monteiro, I.; Mooney, D.; Moore, P.; Moralejo, A.; Morcuende-Parrilla, D.; Moretti, E.; Mori, K.; Morlino, G.; Morris, P.; Morselli, A.; Moscato, F.; Motohashi, D.; Moulin, E.; Mueller, S.; Mukherjee, R.; Munar, P.; Mundell, C.; Mundet, J.; Murach, T.; Muraishi, H.; Murase, K.; Murphy, A.; Nagai, A.; Nagar, N.; Nagataki, S.; Nagayoshi, T.; Nagesh, B. K.; Naito, T.; Nakajima, D.; Nakamori, T.; Nakamura, Y.; Nakayama, K.; Naumann, D.; Nayman, P.; Neise, D.; Nellen, L.; Nemmen, R.; Neronov, A.; Neyroud, N.; Nguyen, T.; Nguyen, T. T.; Nguyen Trung, T.; Nicastro, L.; Nicolau-Kukliński, J.; Niemiec, J.; Nieto, D.; Nievas-Rosillo, M.; Nikołajuk, M.; Nishijima, K.; Nishikawa, K. -I.; Nishiyama, G.; Noda, K.; Nogues, L.; Nolan, S.; Nosek, D.; Nöthe, M.; Novosyadlyj, B.; Nozaki, S.; Nunio, F.; O'Brien, P.; Oakes, L.; Ocampo, C.; Ochoa, J. 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E.; Rujopakarn, W.; Rulten, C.; Russo, F.; Saavedra, O.; Sabatini, S.; Sacco, B.; Sadeh, I.; Sæther Hatlen, E.; Safi-Harb, S.; Sahakian, V.; Sailer, S.; Saito, T.; Sakaki, N.; Sakurai, S.; Salek, D.; Salesa Greus, F.; Salina, G.; Sanchez, D.; Sánchez-Conde, M.; Sandaker, H.; Sandoval, A.; Sangiorgi, P.; Sanguillon, M.; Sano, H.; Santander, M.; Santangelo, A.; Santos, E. M.; Sanuy, A.; Sapozhnikov, L.; Sarkar, S.; Satalecka, K.; Sato, Y.; Saturni, F. G.; Savalle, R.; Sawada, M.; Schanne, S.; Schioppa, E. J.; Schlenstedt, S.; Schmidt, T.; Schmoll, J.; Schneider, M.; Schoorlemmer, H.; Schovanek, P.; Schulz, A.; Schussler, F.; Schwanke, U.; Schwarz, J.; Schweizer, T.; Schwemmer, S.; Sciacca, E.; Scuderi, S.; Seglar-Arroyo, M.; Segreto, A.; Seitenzahl, I.; Semikoz, D.; Sergijenko, O.; Serre, N.; Servillat, M.; Seweryn, K.; Shah, K.; Shalchi, A.; Sharma, M.; Shellard, R. C.; Shilon, I.; Sidoli, L.; Sidz, M.; Siejkowski, H.; Silk, J.; Sillanpää, A.; Simone, D.; Singh, B. B.; Sironi, G.; Sitarek, J.; Sizun, P.; Sliusar, V.; Slowikowska, A.; Smith, A.; Sobczyńska, D.; Sokolenko, A.; Sol, H.; Sottile, G.; Springer, W.; Stahl, O.; Stamerra, A.; Stanič, S.; Starling, R.; Staszak, D.; Stawarz, Ł.; Steenkamp, R.; Stefanik, S.; Stegmann, C.; Steiner, S.; Stella, C.; Stephan, M.; Sternberger, R.; Sterzel, M.; Stevenson, B.; Stodulska, M.; Stodulski, M.; Stolarczyk, T.; Stratta, G.; Straumann, U.; Stuik, R.; Suchenek, M.; Suomijarvi, T.; Supanitsky, A. D.; Suric, T.; Sushch, I.; Sutcliffe, P.; Sykes, J.; Szanecki, M.; Szepieniec, T.; Tagliaferri, G.; Tajima, H.; Takahashi, K.; Takahashi, H.; Takahashi, M.; Takalo, L.; Takami, S.; Takata, J.; Takeda, J.; Tam, T.; Tanaka, M.; Tanaka, T.; Tanaka, Y.; Tanaka, S.; Tanci, C.; Tavani, M.; Tavecchio, F.; Tavernet, J. -P.; Tayabaly, K.; Tejedor, L. A.; Temme, F.; Temnikov, P.; Terada, Y.; Terrazas, J. C.; Terrier, R.; Terront, D.; Terzic, T.; Tescaro, D.; Teshima, M.; Testa, V.; Thoudam, S.; Tian, W.; Tibaldo, L.; Tiengo, A.; Tiziani, D.; Tluczykont, M.; Todero Peixoto, C. J.; Tokanai, F.; Tokarz, M.; Toma, K.; Tomastik, J.; Tonachini, A.; Tonev, D.; Tornikoski, M.; Torres, D. F.; Torresi, E.; Tosti, G.; Totani, T.; Tothill, N.; Toussenel, F.; Tovmassian, G.; Trakarnsirinont, N.; Travnicek, P.; Trichard, C.; Trifoglio, M.; Troyano Pujadas, I.; Tsirou, M.; Tsujimoto, S.; Tsuru, T.; Uchiyama, Y.; Umana, G.; Uslenghi, M.; Vagelli, V.; Vagnetti, F.; Valentino, M.; Vallania, P.; Valore, L.; Van den Berg, A. M.; van Driel, W.; van Eldik, C.; van Soelen, B.; Vandenbroucke, J.; Vanderwalt, J.; Varner, G. S.; Vasileiadis, G.; Vassiliev, V.; Vázquez, J. R.; Vázquez Acosta, M.; Vecchi, M.; Vega, A.; Veitch, P.; Venault, P.; Venter, C.; Vercellone, S.; Veres, P.; Vergani, S.; Verzi, V.; Vettolani, G. P.; Veyssiere, C.; Viana, A.; Vicha, J.; Vigorito, C.; Villanueva, J.; Vincent, P.; Vink, J.; Visconti, F.; Vittorini, V.; Voelk, H.; Voisin, V.; Vollhardt, A.; Vorobiov, S.; Vovk, I.; Vrastil, M.; Vuillaume, T.; Wagner, S. J.; Wagner, R.; Wagner, P.; Wakely, S. P.; Walstra, T.; Walter, R.; Ward, M.; Ward, J. E.; Warren, D.; Watson, J. J.; Webb, N.; Wegner, P.; Weiner, O.; Weinstein, A.; Weniger, C.; Werner, F.; Wetteskind, H.; White, M.; White, R.; Wierzcholska, A.; Wiesand, S.; Wijers, R.; Wilcox, P.; Wilhelm, A.; Wilkinson, M.; Will, M.; Williams, D. A.; Winter, M.; Wojcik, P.; Wolf, D.; Wood, M.; Wörnlein, A.; Wu, T.; Yadav, K. K.; Yaguna, C.; Yamamoto, T.; Yamamoto, H.; Yamane, N.; Yamazaki, R.; Yanagita, S.; Yang, L.; Yelos, D.; Yoshida, T.; Yoshida, M.; Yoshiike, S.; Yoshikoshi, T.; Yu, P.; Zaborov, D.; Zacharias, M.; Zaharijas, G.; Zajczyk, A.; Zampieri, L.; Zandanel, F.; Zanin, R.; Zanmar Sanchez, R.; Zaric, D.; Zavrtanik, M.; Zavrtanik, D.; Zdziarski, A. A.; Zech, A.; Zechlin, H.; Zhdanov, V. I.; Ziegler, A.; Ziemann, J.; Ziętara, K.; Zink, A.; Ziółkowski, J.; Zitelli, V.; Zoli, A.; Zorn, J. Bibcode: 2017arXiv170903483A Altcode: 2017arXiv170903483C List of contributions from the Cherenkov Telescope Array Consortium presented at the 35th International Cosmic Ray Conference, July 12-20 2017, Busan, Korea. Title: Spatially resolved spectroscopy across stellar surfaces. II. High-resolution spectra across HD 209458 (G0 V) Authors: Dravins, Dainis; Ludwig, Hans-Günter; Dahlén, Erik; Pazira, Hiva Bibcode: 2017A&A...605A..91D Altcode: 2017arXiv170801618D Context. High-resolution spectroscopy across spatially resolved stellar surfaces aims at obtaining spectral-line profiles that are free from rotational broadening; the gradual changes of these profiles from disk center toward the stellar limb reveal properties of atmospheric fine structure, which are possible to model with 3D hydrodynamics.
Aims: Previous such studies have only been carried out for the Sun but are now extended to other stars. In this work, profiles of photospheric spectral lines are retrieved across the disk of the planet-hosting star HD 209458 (G0 V).
Methods: During exoplanet transit, stellar surface portions successively become hidden and differential spectroscopy provides spectra of small surface segments temporarily hidden behind the planet. The method was elaborated in Paper I, with observable signatures quantitatively predicted from hydrodynamic simulations.
Results: From observations of HD 209458 with spectral resolution λ/ Δλ 80 000, photospheric Fe I line profiles are obtained at several center-to-limb positions, reaching adequately high S/N after averaging over numerous similar lines.
Conclusions: Retrieved line profiles are compared to synthetic line profiles. Hydrodynamic 3D models predict, and current observations confirm, that photospheric absorption lines become broader and shallower toward the stellar limb, reflecting that horizontal velocities in stellar granulation are greater than vertical velocities. Additional types of 3D signatures will become observable with the highest resolution spectrometers at large telescopes. Title: Spatially resolved spectroscopy across stellar surfaces. I. Using exoplanet transits to analyze 3D stellar atmospheres Authors: Dravins, Dainis; Ludwig, Hans-Günter; Dahlén, Erik; Pazira, Hiva Bibcode: 2017A&A...605A..90D Altcode: 2017arXiv170801616D Context. High-precision stellar analyses require hydrodynamic modeling to interpret chemical abundances or oscillation modes. Exoplanet atmosphere studies require stellar background spectra to be known along the transit path while detection of Earth analogs require stellar microvariability to be understood. Hydrodynamic 3D models can be computed for widely different stars but have been tested in detail only for the Sun with its resolved surface features. Model predictions include spectral line shapes, asymmetries, and wavelength shifts, and their center-to-limb changes across stellar disks.
Aims: We observe high-resolution spectral line profiles across spatially highly resolved stellar surfaces, which are free from the effects of spatial smearing and rotational broadening present in full-disk spectra, enabling comparisons to synthetic profiles from 3D models.
Methods: During exoplanet transits, successive stellar surface portions become hidden and differential spectroscopy between various transit phases provides spectra of small surface segments temporarily hidden behind the planet. Planets cover no more than 1% of any main-sequence star, enabling high spatial resolution but demanding very precise observations. Realistically measurable quantities are identified through simulated observations of synthetic spectral lines.
Results: In normal stars, line profile ratios between various transit phases may vary by 0.5%, requiring S/N ≳ 5000 for meaningful spectral reconstruction. While not yet realistic for individual spectral lines, this is achievable for cool stars by averaging over numerous lines with similar parameters.
Conclusions: For bright host stars of large transiting planets, spatially resolved spectroscopy is currently practical. More observable targets are likely to be found in the near future by ongoing photometric searches. Title: Contributions of the Cherenkov Telescope Array (CTA) to the 6th International Symposium on High-Energy Gamma-Ray Astronomy (Gamma 2016) Authors: CTA Consortium, The; :; Abchiche, A.; Abeysekara, U.; Abril, Ó.; Acero, F.; Acharya, B. S.; Adams, C.; Agnetta, G.; Aharonian, F.; Akhperjanian, A.; Albert, A.; Alcubierre, M.; Alfaro, J.; Alfaro, R.; Allafort, A. J.; Aloisio, R.; Amans, J. -P.; Amato, E.; Ambrogi, L.; Ambrosi, G.; Ambrosio, M.; Anderson, J.; Anduze, M.; Angüner, E. O.; Antolini, E.; Antonelli, L. A.; Antonucci, M.; Antonuccio, V.; Antoranz, P.; Aramo, C.; Aravantinos, A.; Araya, M.; Arcaro, C.; Arezki, B.; Argan, A.; Armstrong, T.; Arqueros, F.; Arrabito, L.; Arrieta, M.; Asano, K.; Ashley, M.; Aubert, P.; Singh, C. B.; Babic, A.; Backes, M.; Bais, A.; Bajtlik, S.; Balazs, C.; Balbo, M.; Balis, D.; Balkowski, C.; Ballester, O.; Ballet, J.; Balzer, A.; Bamba, A.; Bandiera, R.; Barber, A.; Barbier, C.; Barcelo, M.; Barkov, M.; Barnacka, A.; Barres de Almeida, U.; Barrio, J. A.; Basso, S.; Bastieri, D.; Bauer, C.; Becciani, U.; Becherini, Y.; Becker Tjus, J.; Beckmann, V.; Bednarek, W.; Benbow, W.; Benedico Ventura, D.; Berdugo, J.; Berge, D.; Bernardini, E.; Bernardini, M. G.; Bernhard, S.; Bernlöhr, K.; Bertucci, B.; Besel, M. -A.; Beshley, V.; Bhatt, N.; Bhattacharjee, P.; Bhattacharyya, W.; Bhattachryya, S.; Biasuzzi, B.; Bicknell, G.; Bigongiari, C.; Biland, A.; Bilinsky, A.; Bilnik, W.; Biondo, B.; Bird, R.; Bird, T.; Bissaldi, E.; Bitossi, M.; Blanch, O.; Blasi, P.; Blazek, J.; Bockermann, C.; Boehm, C.; Bogacz, L.; Bogdan, M.; Bohacova, M.; Boisson, C.; Boix, J.; Bolmont, J.; Bonanno, G.; Bonardi, A.; Bonavolontà, C.; Bonifacio, P.; Bonnarel, F.; Bonnoli, G.; Borkowski, J.; Bose, R.; Bosnjak, Z.; Böttcher, M.; Bousquet, J. -J.; Boutonnet, C.; Bouyjou, F.; Bowman, L.; Braiding, C.; Brantseg, T.; Brau-Nogué, S.; Bregeon, J.; Briggs, M.; Brigida, M.; Bringmann, T.; Brisken, W.; Bristow, D.; Britto, R.; Brocato, E.; Bron, S.; Brook, P.; Brooks, W.; Brown, A. M.; Brügge, K.; Brun, F.; Brun, P.; Brun, P.; Brunetti, G.; Brunetti, L.; Bruno, P.; Buanes, T.; Bucciantini, N.; Buchholtz, G.; Buckley, J.; Bugaev, V.; Bühler, R.; Bulgarelli, A.; Bulik, T.; Burton, M.; Burtovoi, A.; Busetto, G.; Buson, S.; Buss, J.; Byrum, K.; Cadoux, F.; Calvo Tovar, J.; Cameron, R.; Canelli, F.; Canestrari, R.; Capalbi, M.; Capasso, M.; Capobianco, G.; Caproni, A.; Caraveo, P.; Cardenzana, J.; Cardillo, M.; Carius, S.; Carlile, C.; Carosi, A.; Carosi, R.; Carquín, E.; Carr, J.; Carroll, M.; Carter, J.; Carton, P. -H.; Casandjian, J. -M.; Casanova, S.; Casanova, S.; Cascone, E.; Casiraghi, M.; Castellina, A.; Castroviejo Mora, J.; Catalani, F.; Catalano, O.; Catalanotti, S.; Cauz, D.; Cavazzani, S.; Cerchiara, P.; Chabanne, E.; Chadwick, P.; Chaleil, T.; Champion, C.; Chatterjee, A.; Chaty, S.; Chaves, R.; Chen, A.; Chen, X.; Chen, X.; Cheng, K.; Chernyakova, M.; Chiappetti, L.; Chikawa, M.; Chinn, D.; Chitnis, V. R.; Cho, N.; Christov, A.; Chudoba, J.; Cieślar, M.; Ciocci, M. A.; Clay, R.; Colafrancesco, S.; Colin, P.; Colley, J. -M.; Colombo, E.; Colome, J.; Colonges, S.; Conforti, V.; Connaughton, V.; Connell, S.; Conrad, J.; Contreras, J. L.; Coppi, P.; Corbel, S.; Coridian, J.; Cornat, R.; Corona, P.; Corti, D.; Cortina, J.; Cossio, L.; Costa, A.; Costantini, H.; Cotter, G.; Courty, B.; Covino, S.; Covone, G.; Crimi, G.; Criswell, S. J.; Crocker, R.; Croston, J.; Cuadra, J.; Cumani, P.; Cusumano, G.; Da Vela, P.; Dale, Ø.; D'Ammando, F.; Dang, D.; Dang, V. T.; Dangeon, L.; Daniel, M.; Davids, I.; Davids, I.; Dawson, B.; Dazzi, F.; de Aguiar Costa, B.; De Angelis, A.; de Araujo Cardoso, R. F.; De Caprio, V.; de Cássia dos Anjos, R.; De Cesare, G.; De Franco, A.; De Frondat, F.; de Gouveia Dal Pino, E. M.; de la Calle, I.; De Lisio, C.; de los Reyes Lopez, R.; De Lotto, B.; De Luca, A.; de Mello Neto, J. R. T.; de Naurois, M.; de Oña Wilhelmi, E.; De Palma, F.; De Persio, F.; de Souza, V.; Decock, G.; Decock, J.; Deil, C.; Del Santo, M.; Delagnes, E.; Deleglise, G.; Delgado, C.; Delgado, J.; della Volpe, D.; Deloye, P.; Detournay, M.; Dettlaff, A.; Devin, J.; Di Girolamo, T.; Di Giulio, C.; Di Paola, A.; Di Pierro, F.; Diaz, M. A.; Díaz, C.; Dib, C.; Dick, J.; Dickinson, H.; Diebold, S.; Digel, S.; Dipold, J.; Disset, G.; Distefano, A.; Djannati-Ataï, A.; Doert, M.; Dohmke, M.; Domínguez, A.; Dominik, N.; Dominique, J. -L.; Dominis Prester, D.; Donat, A.; Donnarumma, I.; Dorner, D.; Doro, M.; Dournaux, J. -L.; Downes, T.; Doyle, K.; Drake, G.; Drappeau, S.; Drass, H.; Dravins, D.; Drury, L.; Dubus, G.; Ducci, L.; Dumas, D.; Dundas Morå, K.; Durand, D.; D'Urso, D.; Dwarkadas, V.; Dyks, J.; Dyrda, M.; Ebr, J.; Edy, E.; Egberts, K.; Eger, P.; Egorov, A.; Einecke, S.; Eisch, J.; Eisenkolb, F.; Eleftheriadis, C.; Elsaesser, D.; Elsässer, D.; Emmanoulopoulos, D.; Engelbrecht, C.; Engelhaupt, D.; Ernenwein, J. -P.; Escarate, P.; Eschbach, S.; Espinoza, C.; Evans, P.; Fairbairn, M.; Falceta-Goncalves, D.; Falcone, A.; Fallah Ramazani, V.; Fantinel, D.; Farakos, K.; Farnier, C.; Farrell, E.; Fasola, G.; Favre, Y.; Fede, E.; Fedora, R.; Fedorova, E.; Fegan, S.; Ferenc, D.; Fernandez-Alonso, M.; Fernández-Barral, A.; Ferrand, G.; Ferreira, O.; Fesquet, M.; Fetfatzis, P.; Fiandrini, E.; Fiasson, A.; Filipčič, A.; Filipovic, M.; Fink, D.; Finley, C.; Finley, J. P.; Finoguenov, A.; Fioretti, V.; Fiorini, M.; Fleischhack, H.; Flores, H.; Florin, D.; Föhr, C.; Fokitis, E.; Fonseca, M. V.; Font, L.; Fontaine, G.; Fontes, B.; Fornasa, M.; Fornasa, M.; Förster, A.; Fortin, P.; Fortson, L.; Fouque, N.; Franckowiak, A.; Franckowiak, A.; Franco, F. J.; Freire Mota Albuquerque, I.; Freixas Coromina, L.; Fresnillo, L.; Fruck, C.; Fuessling, M.; Fugazza, D.; Fujita, Y.; Fukami, S.; Fukazawa, Y.; Fukuda, T.; Fukui, Y.; Funk, S.; Furniss, A.; Gäbele, W.; Gabici, S.; Gadola, A.; Galindo, D.; Gall, D. D.; Gallant, Y.; Galloway, D.; Gallozzi, S.; Galvez, J. A.; Gao, S.; Garcia, A.; Garcia, B.; García Gil, R.; Garcia López, R.; Garczarczyk, M.; Gardiol, D.; Gargano, C.; Gargano, F.; Garozzo, S.; Garrecht, F.; Garrido, L.; Garrido-Ruiz, M.; Gascon, D.; Gaskins, J.; Gaudemard, J.; Gaug, M.; Gaweda, J.; Gebhardt, B.; Gebyehu, M.; Geffroy, N.; Genolini, B.; Gerard, L.; Ghalumyan, A.; Ghedina, A.; Ghislain, P.; Giammaria, P.; Giannakaki, E.; Gianotti, F.; Giarrusso, S.; Giavitto, G.; Giebels, B.; Gieras, T.; Giglietto, N.; Gika, V.; Gimenes, R.; Giomi, M.; Giommi, P.; Giordano, F.; Giovannini, G.; Girardot, P.; Giro, E.; Giroletti, M.; Gironnet, J.; Giuliani, A.; Glicenstein, J. -F.; Gnatyk, R.; Godinovic, N.; Goldoni, P.; Gomez, G.; Gonzalez, M. M.; González, A.; Gora, D.; Gothe, K. S.; Gotz, D.; Goullon, J.; Grabarczyk, T.; Graciani, R.; Graham, J.; Grandi, P.; Granot, J.; Grasseau, G.; Gredig, R.; Green, A. J.; Green, A. M.; Greenshaw, T.; Grenier, I.; Griffiths, S.; Grillo, A.; Grondin, M. -H.; Grube, J.; Grudzinska, M.; Grygorczuk, J.; Guarino, V.; Guberman, D.; Gunji, S.; Gyuk, G.; Hadasch, D.; Hagedorn, A.; Hagge, L.; Hahn, J.; Hakobyan, H.; Hara, S.; Hardcastle, M. J.; Hassan, T.; Hatanaka, K.; Haubold, T.; Haupt, A.; Hayakawa, T.; Hayashida, M.; Heller, M.; Heller, R.; Helo, J. C.; Henault, F.; Henri, G.; Hermann, G.; Hermel, R.; Herrera Llorente, J.; Herrera Llorente, J.; Herrero, A.; Hervet, O.; Hidaka, N.; Hinton, J.; Hirai, W.; Hirotani, K.; Hnatyk, B.; Hoang, J.; Hoffmann, D.; Hofmann, W.; Holch, T.; Holder, J.; Hooper, S.; Horan, D.; Hörandel, J.; Hörbe, M.; Horns, D.; Horvath, P.; Hose, J.; Houles, J.; Hovatta, T.; Hrabovsky, M.; Hrupec, D.; Huet, J. -M.; Huetten, M.; Hughes, G.; Hui, D.; Humensky, T. B.; Hussein, M.; Iacovacci, M.; Ibarra, A.; Ikeno, Y.; Illa, J. M.; Impiombato, D.; Inada, T.; Incorvaia, S.; Infante, L.; Inome, Y.; Inoue, S.; Inoue, T.; Inoue, Y.; Iocco, F.; Ioka, K.; Iori, M.; Ishio, K.; Ishio, K.; Israel, G. L.; Iwamura, Y.; Jablonski, C.; Jacholkowska, A.; Jacquemier, J.; Jamrozy, M.; Janecek, P.; Janiak, M.; Jankowsky, D.; Jankowsky, F.; Jean, P.; Jegouzo, I.; Jenke, P.; Jimenez, J. J.; Jingo, M.; Jingo, M.; Jocou, L.; Jogler, T.; Johnson, C. A.; Jones, M.; Josselin, M.; Journet, L.; Jung, I.; Kaaret, P.; Kagaya, M.; Kakuwa, J.; Kalekin, O.; Kalkuhl, C.; Kamon, H.; Kankanyan, R.; Karastergiou, A.; Kärcher, K.; Karczewski, M.; Karkar, S.; Karn, P.; Kasperek, J.; Katagiri, H.; Kataoka, J.; Katarzyński, K.; Kato, S.; Katz, U.; Kawanaka, N.; Kaye, L.; Kazanas, D.; Kelley-Hoskins, N.; Kersten, J.; Khélifi, B.; Kieda, D. B.; Kihm, T.; Kimeswenger, S.; Kisaka, S.; Kishida, S.; Kissmann, R.; Klepser, S.; Kluźniak, W.; Knapen, J.; Knapp, J.; Knödlseder, J.; Koch, B.; Köck, F.; Kocot, J.; Kohri, K.; Kokkotas, K.; Kokkotas, K.; Kolitzus, D.; Komin, N.; Kominis, I.; Kong, A.; Konno, Y.; Kosack, K.; Koss, G.; Kossatz, M.; Kowal, G.; Koyama, S.; Kozioł, J.; Kraus, M.; Krause, J.; Krause, M.; Krawzcynski, H.; Krennrich, F.; Kretzschmann, A.; Kruger, P.; Kubo, H.; Kudryavtsev, V.; Kukec Mezek, G.; Kuklis, M.; Kuroda, H.; Kushida, J.; La Barbera, A.; La Palombara, N.; La Parola, V.; La Rosa, G.; Laffon, H.; Lahmann, R.; Lakicevic, M.; Lalik, K.; Lamanna, G.; Landriu, D.; Landt, H.; Lang, R. G.; Lapington, J.; Laporte, P.; Le Fèvre, J. -P.; Le Flour, T.; Le Sidaner, P.; Lee, S. -H.; Lee, W. H.; Lees, J. -P.; Lefaucheur, J.; Leffhalm, K.; Leich, H.; Leigui de Oliveira, M. A.; Lelas, D.; Lemière, A.; Lemoine-Goumard, M.; Lenain, J. -P.; Leonard, R.; Leoni, R.; Lessio, L.; Leto, G.; Leveque, A.; Lieunard, B.; Limon, M.; Lindemann, R.; Lindfors, E.; Linhoff, L.; Liolios, A.; Lipniacka, A.; Lockart, H.; Lohse, T.; Łokas, E.; Lombardi, S.; Longo, F.; Lopatin, A.; Lopez, M.; Loreggia, D.; Louge, T.; Louis, F.; Louys, M.; Lucarelli, F.; Lucchesi, D.; Lüdecke, H.; Luigi, T.; Luque-Escamilla, P. L.; Lyard, E.; Maccarone, M. C.; Maccarone, T.; Maccarone, T. J.; Mach, E.; Madejski, G. M.; Madonna, A.; Magniette, F.; Magniez, A.; Mahabir, M.; Maier, G.; Majumdar, P.; Majumdar, P.; Makariev, M.; Malaguti, G.; Malaspina, G.; Mallot, A. K.; Malouf, A.; Maltezos, S.; Malyshev, D.; Mancilla, A.; Mandat, D.; Maneva, G.; Manganaro, M.; Mangano, S.; Manigot, P.; Mankushiyil, N.; Mannheim, K.; Maragos, N.; Marano, D.; Marchegiani, P.; Marcomini, J. A.; Marcowith, A.; Mariotti, M.; Marisaldi, M.; Markoff, S.; Martens, C.; Martí, J.; Martin, J. -M.; Martin, L.; Martin, P.; Martínez, G.; Martínez, M.; Martínez, O.; Martynyuk-Lototskyy, K.; Marx, R.; Masetti, N.; Massimino, P.; Mastichiadis, A.; Mastroianni, S.; Mastropietro, M.; Masuda, S.; Matsumoto, H.; Matsuoka, S.; Matthews, N.; Mattiazzo, S.; Maurin, G.; Maxted, N.; Maxted, N.; Maya, J.; Mayer, M.; Mazin, D.; Mazziotta, M. N.; Mc Comb, L.; McCubbin, N.; McHardy, I.; Medina, C.; Mehrez, F.; Melioli, C.; Melkumyan, D.; Melse, T.; Mereghetti, S.; Merk, M.; Mertsch, P.; Meunier, J. -L.; Meures, T.; Meyer, M.; Meyrelles, J. L., jr; Miccichè, A.; Michael, T.; Michałowski, J.; Mientjes, P.; Mievre, I.; Mihailidis, A.; Miller, J.; Mineo, T.; Minuti, M.; Mirabal, N.; Mirabel, F.; Miranda, J. M.; Mirzoyan, R.; Mitchell, A.; Mizuno, T.; Moderski, R.; Mognet, I.; Mohammed, M.; Moharana, R.; Mohrmann, L.; Molinari, E.; Molyneux, P.; Monmarthe, E.; Monnier, G.; Montaruli, T.; Monte, C.; Monteiro, I.; Mooney, D.; Moore, P.; Moralejo, A.; Morello, C.; Moretti, E.; Mori, K.; Morris, P.; Morselli, A.; Moscato, F.; Motohashi, D.; Mottez, F.; Moudden, Y.; Moulin, E.; Mueller, S.; Mukherjee, R.; Munar, P.; Munari, M.; Mundell, C.; Mundet, J.; Muraishi, H.; Murase, K.; Muronga, A.; Murphy, A.; Nagar, N.; Nagataki, S.; Nagayoshi, T.; Nagesh, B. K.; Naito, T.; Nakajima, D.; Nakajima, D.; Nakamori, T.; Nakayama, K.; Nanni, J.; Naumann, D.; Nayman, P.; Nellen, L.; Nemmen, R.; Neronov, A.; Neyroud, N.; Nguyen, T.; Nguyen, T. T.; Nguyen Trung, T.; Nicastro, L.; Nicolau-Kukliński, J.; Niederwanger, F.; Niedźwiecki, A.; Niemiec, J.; Nieto, D.; Nievas-Rosillo, M.; Nikolaidis, A.; Nikołajuk, M.; Nishijima, K.; Nishikawa, K. -I.; Nishiyama, G.; Noda, K.; Noda, K.; Nogues, L.; Nolan, S.; Northrop, R.; Nosek, D.; Nöthe, M.; Novosyadlyj, B.; Nozka, L.; Nunio, F.; Oakes, L.; O'Brien, P.; Ocampo, C.; Occhipinti, G.; Ochoa, J. P.; OFaolain de Bhroithe, A.; Oger, R.; Ohira, Y.; Ohishi, M.; Ohm, S.; Ohoka, H.; Okazaki, N.; Okumura, A.; Olive, J. -F.; Olszowski, D.; Ong, R. A.; Ono, S.; Orienti, M.; Orito, R.; Orlati, A.; Osborne, J.; Ostrowski, M.; Ottaway, D.; Otte, N.; Öttl, S.; Ovcharov, E.; Oya, I.; Ozieblo, A.; Padovani, M.; Pagano, I.; Paiano, S.; Paizis, A.; Palacio, J.; Palatka, M.; Pallotta, J.; Panagiotidis, K.; Panazol, J. -L.; Paneque, D.; Panter, M.; Panzera, M. R.; Paoletti, R.; Paolillo, M.; Papayannis, A.; Papyan, G.; Paravac, A.; Paredes, J. M.; Pareschi, G.; Park, N.; Parsons, D.; Paśko, P.; Pavy, S.; Pech, M.; Peck, A.; Pedaletti, G.; Pe'er, A.; Peet, S.; Pelat, D.; Pepato, A.; Perez, M. d. C.; Perri, L.; Perri, M.; Persic, M.; Persic, M.; Petrashyk, A.; Petrucci, P. -O.; Petruk, O.; Peyaud, B.; Pfeifer, M.; Pfeiffer, G.; Piano, G.; Pieloth, D.; Pierre, E.; Pinto de Pinho, F.; García, C. Pio; Piret, Y.; Pisarski, A.; Pita, S.; Platos, Ł.; Platzer, R.; Podkladkin, S.; Pogosyan, L.; Pohl, M.; Poinsignon, P.; Pollo, A.; Porcelli, A.; Porthault, J.; Potter, W.; Poulios, S.; Poutanen, J.; Prandini, E.; Prandini, E.; Prast, J.; Pressard, K.; Principe, G.; Profeti, F.; Prokhorov, D.; Prokoph, H.; Prouza, M.; Pruchniewicz, R.; Pruteanu, G.; Pueschel, E.; Pühlhofer, G.; Puljak, I.; Punch, M.; Pürckhauer, S.; Pyzioł, R.; Queiroz, F.; Quel, E. J.; Quinn, J.; Quirrenbach, A.; Rafighi, I.; Rainò, S.; Rajda, P. J.; Rameez, M.; Rando, R.; Rannot, R. 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D.; Suric, T.; Sushch, I.; Sutcliffe, P.; Sykes, J.; Szanecki, M.; Szepieniec, T.; Szwarnog, P.; Tacchini, A.; Tachihara, K.; Tagliaferri, G.; Tajima, H.; Takahashi, H.; Takahashi, K.; Takahashi, M.; Takalo, L.; Takami, S.; Takata, J.; Takeda, J.; Talbot, G.; Tam, T.; Tanaka, M.; Tanaka, S.; Tanaka, T.; Tanaka, Y.; Tanci, C.; Tanigawa, S.; Tavani, M.; Tavecchio, F.; Tavernet, J. -P.; Tayabaly, K.; Taylor, A.; Tejedor, L. A.; Telezhinsky, I.; Temme, F.; Temnikov, P.; Tenzer, C.; Terada, Y.; Terrazas, J. C.; Terrier, R.; Terront, D.; Terzic, T.; Tescaro, D.; Teshima, M.; Teshima, M.; Testa, V.; Tezier, D.; Thayer, J.; Thornhill, J.; Thoudam, S.; Thuermann, D.; Tibaldo, L.; Tiengo, A.; Timpanaro, M. C.; Tiziani, D.; Tluczykont, M.; Todero Peixoto, C. J.; Tokanai, F.; Tokarz, M.; Toma, K.; Tomastik, J.; Tomono, Y.; Tonachini, A.; Tonev, D.; Torii, K.; Tornikoski, M.; Torres, D. F.; Torres, M.; Torresi, E.; Toso, G.; Tosti, G.; Totani, T.; Tothill, N.; Toussenel, F.; Tovmassian, G.; Toyama, T.; Travnicek, P.; Trichard, C.; Trifoglio, M.; Troyano Pujadas, I.; Trzeciak, M.; Tsinganos, K.; Tsujimoto, S.; Tsuru, T.; Uchiyama, Y.; Umana, G.; Umetsu, Y.; Upadhya, S. S.; Uslenghi, M.; Vagelli, V.; Vagnetti, F.; Valdes-Galicia, J.; Valentino, M.; Vallania, P.; Valore, L.; van Driel, W.; van Eldik, C.; van Soelen, B.; Vandenbroucke, J.; Vanderwalt, J.; Vasileiadis, G.; Vassiliev, V.; Vázquez, J. R.; Vázquez Acosta, M. L.; Vecchi, M.; Vega, A.; Vegas, I.; Veitch, P.; Venault, P.; Venema, L.; Venter, C.; Vercellone, S.; Vergani, S.; Verma, K.; Verzi, V.; Vettolani, G. P.; Veyssiere, C.; Viana, A.; Viaux, N.; Vicha, J.; Vigorito, C.; Vincent, P.; Vincent, S.; Vink, J.; Vittorini, V.; Vlahakis, N.; Vlahos, L.; Voelk, H.; Voisin, V.; Vollhardt, A.; Volpicelli, A.; von Brand, H.; Vorobiov, S.; Vovk, I.; Vrastil, M.; Vu, L. V.; Vuillaume, T.; Wagner, R.; Wagner, R.; Wagner, S. J.; Wakely, S. P.; Walstra, T.; Walter, R.; Walther, T.; Ward, J. E.; Ward, M.; Warda, K.; Warren, D.; Wassberg, S.; Watson, J. J.; Wawer, P.; Wawrzaszek, R.; Webb, N.; Wegner, P.; Weiner, O.; Weinstein, A.; Wells, R.; Werner, F.; Wetteskind, H.; White, M.; White, R.; Więcek, M.; Wierzcholska, A.; Wiesand, S.; Wijers, R.; Wilcox, P.; Wild, N.; Wilhelm, A.; Wilkinson, M.; Will, M.; Will, M.; Williams, D. A.; Williams, J. T.; Willingale, R.; Wilson, N.; Winde, M.; Winiarski, K.; Winkler, H.; Winter, M.; Wischnewski, R.; Witt, E.; Wojcik, P.; Wolf, D.; Wood, M.; Wörnlein, A.; Wu, E.; Wu, T.; Yadav, K. K.; Yamamoto, H.; Yamamoto, T.; Yamane, N.; Yamazaki, R.; Yanagita, S.; Yang, L.; Yelos, D.; Yoshida, A.; Yoshida, M.; Yoshida, T.; Yoshiike, S.; Yoshikoshi, T.; Yu, P.; Zabalza, V.; Zaborov, D.; Zacharias, M.; Zaharijas, G.; Zajczyk, A.; Zampieri, L.; Zandanel, F.; Zanmar Sanchez, R.; Zaric, D.; Zavrtanik, D.; Zavrtanik, M.; Zdziarski, A.; Zech, A.; Zechlin, H.; Zhao, A.; Zhdanov, V.; Ziegler, A.; Ziemann, J.; Ziętara, K.; Zink, A.; Ziółkowski, J.; Zitelli, V.; Zoli, A.; Zorn, J.; Żychowski, P. Bibcode: 2016arXiv161005151C Altcode: List of contributions from the Cherenkov Telescope Array (CTA) Consortium presented at the 6th International Symposium on High-Energy Gamma-Ray Astronomy (Gamma 2016), July 11-15, 2016, in Heidelberg, Germany. Title: Exoplanet Transits Enable High-Resolution Spectroscopy Across Spatially Resolved Stellar Surfaces Authors: Dravins, Dainis; Ludwig, Hans-Günter; Dahlén, Erik; Pazira, Hiva Bibcode: 2016csss.confE..66D Altcode: 2016arXiv160703489D Observations of stellar surfaces ndash; except for the Sun ndash; are hampered by their tiny angular extent, while observed spectral lines are smeared by averaging over the stellar surface, and by stellar rotation. Exoplanet transits can be used to analyze stellar atmospheric structure, yielding high-resolution spectra across spatially highly resolved stellar surfaces, free from effects of spatial smearing and the rotational wavelength broadening present in full-disk spectra. During a transit, stellar surface portions successively become hidden, and differential spectroscopy between various transit phases provides spectra of those surface segments then hidden behind the planet. The small area subtended by even a large planet (about 1% of a main-sequence star) offers high spatial resolution but demands very precise observations. We demonstrate the reconstruction of photospheric Fe I line profilesnbsp;at a spectral resolution R=80,000 across the surface of the solar-type star HD 209458. Any detailed understanding of stellar atmospheres requires modeling with 3-dimensional hydrodynamics. The properties predicted by such models are mapped onto the precise spectral-line shapes, asymmetries and wavelength shifts, and their variation from the center to the limb across any stellar disk. This method provides a tool for testing and verifying such models. The method will soon become applicable to more diverse types of stars, thanks to new spectrometers on very large telescopes, and since ongoing photometric searches are expected to discover additional bright host stars of transiting exoplanets.> Title: Intensity interferometry: optical imaging with kilometer baselines Authors: Dravins, Dainis Bibcode: 2016SPIE.9907E..0MD Altcode: 2016arXiv160703490D Optical imaging with microarcsecond resolution will reveal details across and outside stellar surfaces but requires kilometer-scale interferometers, challenging to realize either on the ground or in space. Intensity interferometry, electronically connecting independent telescopes, has a noise budget that relates to the electronic time resolution, circumventing issues of atmospheric turbulence. Extents up to a few km are becoming realistic with arrays of optical air Cherenkov telescopes (primarily erected for gamma-ray studies), enabling an optical equivalent of radio interferometer arrays. Pioneered by Hanbury Brown and Twiss, digital versions of the technique have now been demonstrated, reconstructing diffraction-limited images from laboratory measurements over hundreds of optical baselines. This review outlines the method from its beginnings, describes current experiments, and sketches prospects for future observations. Title: Spatially Resolved Spectroscopy Across HD189733 (K1V) Using Exoplanet Transits Authors: Gustavsson, Martin; Dravins, Dainis; Ludwig, Hans-Günter Bibcode: 2016csss.confE..53G Altcode: For testing 3-dimensional models of stellar atmospheres, spectroscopy across spatially resolved stellar surfaces would be desired with a spectral resolution of(R = 100,000) or more. Hydrodynamic models predict variations in line profile shapes, strengths, wavelength positions and asymmetries. These variations vary systematically between disk center and limb and as a function of line strength, excitation potential and wavelength region. However, except for a few supergiants and the Sun, current telescopes are not yet capable of resolving any stellar surfaces. One alternative method to resolve distant stellar surfaces, feasible already now, is differential spectroscopy of transiting exoplanet systems. By subtracting in-transit spectra from the spectrum outside of transit, the spectra from stellar surface portions temporarily hidden behind the planet can be disentangled. Since transiting planets cover only a small portion of the stellar surface, the method requires a very high signal-to-noise ratio, obtainable by averaging numerous similar spectral lines. We apply such differential spectroscopy on the 7.7 mag K1V star HD 189733 ('Alopex'*); its transiting planet covers ∼ 3% of its host star's surface, which is the deepest known transit among the brighter systems. Archival data from the ESO HARPS spectrometerare used to construct averaged profiles of photospheric Fe I lines, with the aim of comparing spatially resolved profiles to analogous synthetic line profiles computed from the 3-dimensional hydrodynamic CO5BOLD model.
* We refer to HD 189733 as 'Alopex' (from the Greek 'αλɛπού'), denoting a fox related to the one that gave name to its constellation of Vulpecula. Title: Stellar Intensity Interferometry over Kilometer Baselines: Optical aperture synthesis with electronically connected telescopes Authors: Dravins, Dainis; Lagadec, Tiphaine; Nuñez, Paul D. Bibcode: 2015IAUGA..2233727D Altcode: Diffraction-limited optical imaging over kilometer baselines will reveal stellar surfaces, perhaps even resolving the silhouettes of transiting exoplanets. An opportunity is opening up with arrays of air Cherenkov telescopes used for intensity interferometry, a technique once pioneered by Hanbury Brown and Twiss. Being essentially insensitive to atmospheric turbulence, this permits both very long baselines and observing at short optical wavelengths.System verifications have been made in a large optics laboratory. Artificial stars were observed by a group of small telescopes equipped with nanosecond-resolving photon-counting detectors, their outputs processed in a digital correlator. Numerous telescope pairs at different baseline lengths and orientations build up a two-dimensional map of the second-order spatial coherence of the source, from which its image can be extracted.From up to 180 baselines thus measured, full two-dimensional images were reconstructed. As far as we are aware, these are the first diffraction-limited images produced by an array of optical telescopes connected only electronically in software, with no optical connections between them. Since the electronic signal from any telescope can be freely copied without loss of signal, very many baselines can be built up between dispersed telescopes. Using arrays of air Cherenkov telescopes, this should enable the optical equivalent of interferometric aperture synthesis arrays currently operating at radio wavelengths. arxiv.org/abs/1407.5993, Nature Commun., in press (2015) Title: CTA Contributions to the 34th International Cosmic Ray Conference (ICRC2015) Authors: CTA Consortium, The; :; Abchiche, A.; Abeysekara, U.; Abril, Ó.; Acero, F.; Acharya, B. S.; Actis, M.; Agnetta, G.; Aguilar, J. A.; Aharonian, F.; Akhperjanian, A.; Albert, A.; Alcubierre, M.; Alfaro, R.; Aliu, E.; Allafort, A. J.; Allan, D.; Allekotte, I.; Aloisio, R.; Amans, J. -P.; Amato, E.; Ambrogi, L.; Ambrosi, G.; Ambrosio, M.; Anderson, J.; Anduze, M.; Angüner, E. O.; Antolini, E.; Antonelli, L. A.; Antonucci, M.; Antonuccio, V.; Antoranz, P.; Aramo, C.; Aravantinos, A.; Argan, A.; Armstrong, T.; Arnaldi, H.; Arnold, L.; Arrabito, L.; Arrieta, M.; Arrieta, M.; Asano, K.; Asorey, H. G.; Aune, T.; Singh, C. B.; Babic, A.; Backes, M.; Bais, A.; Bajtlik, S.; Balazs, C.; Balbo, M.; Balis, D.; Balkowski, C.; Ballester, O.; Ballet, J.; Balzer, A.; Bamba, A.; Bandiera, R.; Barber, A.; Barbier, C.; Barceló, M.; Barnacka, A.; Barres de Almeida, U.; Barrio, J. A.; Basso, S.; Bastieri, D.; Bauer, C.; Baushev, A.; Becciani, U.; Becherini, Y.; Becker Tjus, J.; Beckmann, V.; Bednarek, W.; Benbow, W.; Benedico Ventura, D.; Berdugo, J.; Berge, D.; Bernardini, E.; Bernhard, S.; Bernlöhr, K.; Bertucci, B.; Besel, M. -A.; Bhatt, N.; Bhattacharjee, P.; Bhattachryya, S.; Biasuzzi, B.; Bicknell, G.; Bigongiari, C.; Biland, A.; Billotta, S.; Bilnik, W.; Biondo, B.; Bird, T.; Birsin, E.; Bissaldi, E.; Biteau, J.; Bitossi, M.; Blanch Bigas, O.; Blasi, P.; Boehm, C.; Bogacz, L.; Bogdan, M.; Bohacova, M.; Boisson, C.; Boix Gargallo, J.; Bolmont, J.; Bonanno, G.; Bonardi, A.; Bonifacio, P.; Bonnoli, G.; Borkowski, J.; Bose, R.; Bosnjak, Z.; Bottani, A.; Böttcher, M.; Bousquet, J. -J.; Boutonnet, C.; Bouyjou, F.; Braiding, C.; Brandt, L.; Brau-Nogué, S.; Bregeon, J.; Bretz, T.; Briggs, M.; Brigida, M.; Bringmann, T.; Brisken, W.; Brocato, E.; Brook, P.; Brown, A. M.; Brun, P.; Brunetti, G.; Brunetti, L.; Bruno, P.; Bryan, M.; Buanes, T.; Bucciantini, N.; Buchholtz, G.; Buckley, J.; Bugaev, V.; Bühler, R.; Bulgarelli, A.; Bulik, T.; Burton, M.; Burtovoi, A.; Busetto, G.; Buson, S.; Buss, J.; Byrum, K.; Cameron, R.; Camprecios, J.; Canelli, F.; Canestrari, R.; Cantu, S.; Capalbi, M.; Capasso, M.; Capobianco, G.; Caraveo, P.; Cardenzana, J.; Carius, S.; Carlile, C.; Carmona, E.; Carosi, A.; Carosi, R.; Carr, J.; Carroll, M.; Carter, J.; Carton, P. -H.; Caruso, R.; Casandjian, J. -M.; Casanova, S.; Cascone, E.; Casiraghi, M.; Castellina, A.; Catalano, O.; Catalanotti, S.; Cavazzani, S.; Cazaux, S.; Cefalà, M.; Cerchiara, P.; Cereda, M.; Cerruti, M.; Chabanne, E.; Chadwick, P.; Champion, C.; Chaty, S.; Chaves, R.; Cheimets, P.; Chen, A.; Chen, X.; Chernyakova, M.; Chiappetti, L.; Chikawa, M.; Chinn, D.; Chitnis, V. R.; Cho, N.; Christov, A.; Chudoba, J.; Cieślar, M.; Cillis, A.; Ciocci, M. A.; Clay, R.; Cohen-Tanugi, J.; Colafrancesco, S.; Colin, P.; Colombo, E.; Colome, J.; Colonges, S.; Compin, M.; Conforti, V.; Connaughton, V.; Connell, S.; Conrad, J.; Contreras, J. L.; Coppi, P.; Corbel, S.; Coridian, J.; Corona, P.; Corti, D.; Cortina, J.; Cossio, L.; Costa, A.; Costantini, H.; Cotter, G.; Courty, B.; Covino, S.; Covone, G.; Crimi, G.; Criswell, S. J.; Crocker, R.; Croston, J.; Cusumano, G.; Da Vela, P.; Dale, Ø.; D'Ammando, F.; Dang, D.; Daniel, M.; Davids, I.; Dawson, B.; Dazzi, F.; de Aguiar Costa, B.; De Angelis, A.; de Araujo Cardoso, R. F.; De Caprio, V.; De Cesare, G.; De Franco, A.; De Frondat, F.; de Gouveia Dal Pino, E. M.; de la Calle, I.; De La Vega, G. A.; de los Reyes Lopez, R.; De Lotto, B.; De Luca, A.; de Mello Neto, J. R. T.; de Naurois, M.; de Oña Wilhelmi, E.; De Palma, F.; de Souza, V.; Decock, G.; Deil, C.; Del Santo, M.; Delagnes, E.; Deleglise, G.; Delgado, C.; della Volpe, D.; Deloye, P.; Depaola, G.; Detournay, M.; Dettlaff, A.; Di Girolamo, T.; Di Giulio, C.; Di Paola, A.; Di Pierro, F.; Di Sciascio, G.; Díaz, C.; Dick, J.; Dickinson, H.; Diebold, S.; Diez, V.; Digel, S.; Dipold, J.; Disset, G.; Distefano, A.; Djannati-Ataï, A.; Doert, M.; Dohmke, M.; Domainko, W.; Dominik, N.; Dominis Prester, D.; Donat, A.; Donnarumma, I.; Dorner, D.; Doro, M.; Dournaux, J. -L.; Doyle, K.; Drake, G.; Dravins, D.; Drury, L.; Dubus, G.; Dumas, D.; Dumm, J.; Durand, D.; D'Urso, D.; Dwarkadas, V.; Dyks, J.; Dyrda, M.; Ebr, J.; Echaniz, J. C.; Edy, E.; Egberts, K.; Egberts, K.; Eger, P.; Einecke, S.; Eisch, J.; Eisenkolb, F.; Eleftheriadis, C.; Elsässer, D.; Emmanoulopoulos, D.; Engelbrecht, C.; Engelhaupt, D.; Ernenwein, J. -P.; Errando, M.; Eschbach, S.; Etchegoyen, A.; Evans, P.; Fairbairn, M.; Falcone, A.; Fantinel, D.; Farakos, K.; Farnier, C.; Farrell, E.; Farrell, S.; Fasola, G.; Fegan, S.; Feinstein, F.; Ferenc, D.; Fernandez, A.; Fernandez-Alonso, M.; Ferreira, O.; Fesquet, M.; Fetfatzis, P.; Fiasson, A.; Filipčič, A.; Filipovic, M.; Fink, D.; Finley, C.; Finley, J. P.; Finoguenov, A.; Fioretti, V.; Fiorini, M.; Firpo Curcoll, R.; Fleischhack, H.; Flores, H.; Florin, D.; Föhr, C.; Fokitis, E.; Font, L.; Fontaine, G.; Fontes, B.; Forest, F.; Fornasa, M.; Förster, A.; Fortin, P.; Fortson, L.; Fouque, N.; Franckowiak, A.; Franco, F. J.; Frankowski, A.; Frega, N.; Freire Mota Albuquerque, I.; Freixas Coromina, L.; Fresnillo, L.; Fruck, C.; Fuessling, M.; Fugazza, D.; Fujita, Y.; Fukami, S.; Fukazawa, Y.; Fukuda, T.; Fukui, Y.; Funk, S.; Gäbele, W.; Gabici, S.; Gadola, A.; Galante, N.; Gall, D. D.; Gallant, Y.; Galloway, D.; Gallozzi, S.; Gao, S.; Garcia, B.; García Gil, R.; Garcia López, R.; Garczarczyk, M.; Gardiol, D.; Gargano, C.; Gargano, F.; Garozzo, S.; Garrecht, F.; Garrido, D.; Garrido, L.; Gascon, D.; Gaskins, J.; Gaudemard, J.; Gaug, M.; Gaweda, J.; Geffroy, N.; Gérard, L.; Ghalumyan, A.; Ghedina, A.; Ghigo, M.; Ghislain, P.; Giannakaki, E.; Gianotti, F.; Giarrusso, S.; Giavitto, G.; Giebels, B.; Giglietto, N.; Gika, V.; Gimenes, R.; Giomi, M.; Giommi, P.; Giordano, F.; Giovannini, G.; Giro, E.; Giroletti, M.; Giuliani, A.; Glicenstein, J. -F.; Godinovic, N.; Goldoni, P.; Gomez Berisso, M.; Gomez Vargas, G. A.; Gonzalez, M. M.; González, A.; González, F.; González Muñoz, A.; Gothe, K. S.; Gotz, D.; Grabarczyk, T.; Graciani, R.; Grandi, P.; Grañena, F.; Granot, J.; Grasseau, G.; Gredig, R.; Green, A. J.; Green, A. M.; Greenshaw, T.; Grenier, I.; Grillo, A.; Grondin, M. -H.; Grube, J.; Grudzinska, M.; Grygorczuk, J.; Guarino, V.; Guberman, D.; Gunji, S.; Gyuk, G.; Hadasch, D.; Hagedorn, A.; Hahn, J.; Hakansson, N.; Hamer Heras, N.; Hanabata, Y.; Hara, S.; Hardcastle, M. J.; Harris, J.; Hassan, T.; Hatanaka, K.; Haubold, T.; Haupt, A.; Hayakawa, T.; Hayashida, M.; Heller, M.; Heller, R.; Henault, F.; Henri, G.; Hermann, G.; Hermel, R.; Herrera Llorente, J.; Herrero, A.; Hervet, O.; Hidaka, N.; Hinton, J.; Hirai, W.; Hirotani, K.; Hoard, D.; Hoffmann, D.; Hofmann, W.; Hofverberg, P.; Holch, T.; Holder, J.; Hooper, S.; Horan, D.; Hörandel, J. R.; Hormigos, S.; Horns, D.; Hose, J.; Houles, J.; Hovatta, T.; Hrabovsky, M.; Hrupec, D.; Huet, J. -M.; Hütten, M.; Humensky, T. B.; Huovelin, J.; Huppert, J. -F.; Iacovacci, M.; Ibarra, A.; Idźkowski, B.; Ikawa, D.; Illa, J. M.; Impiombato, D.; Incorvaia, S.; Inome, Y.; Inoue, S.; Inoue, T.; Inoue, Y.; Iocco, F.; Ioka, K.; Iori, M.; Ishio, K.; Israel, G. L.; Jablonski, C.; Jacholkowska, A.; Jacquemier, J.; Jamrozy, M.; Janecek, P.; Janiak, M.; Jankowsky, F.; Jean, P.; Jeanney, C.; Jegouzo, I.; Jenke, P.; Jimenez, J. J.; Jingo, M.; Jingo, M.; Jocou, L.; Jogler, T.; Johnson, C. A.; Journet, L.; Juffroy, C.; Jung, I.; Kaaret, P. E.; Kagaya, M.; Kakuwa, J.; Kalekin, O.; Kalkuhl, C.; Kankanyan, R.; Karastergiou, A.; Kärcher, K.; Karczewski, M.; Karkar, S.; Karn, P.; Kasperek, J.; Katagiri, H.; Kataoka, J.; Katarzyński, K.; Katz, U.; Kaufmann, S.; Kawanaka, N.; Kawashima, T.; Kazanas, D.; Kelley-Hoskins, N.; Kellner-Leidel, B.; Kendziorra, E.; Kersten, J.; Khélifi, B.; Kieda, D. B.; Kihm, T.; Kisaka, S.; Kissmann, R.; Klepser, S.; Kluźniak, W.; Knapen, J.; Knapp, J.; Knödlseder, J.; Köck, F.; Kocot, J.; Kodakkadan, A.; Kodani, K.; Kohri, K.; Kojima, T.; Kokkotas, K.; Kolitzus, D.; Komin, N.; Kominis, I.; Konno, Y.; Kosack, K.; Koss, G.; Koul, R.; Kowal, G.; Koyama, S.; Kozioł, J.; Kraus, M.; Krause, J.; Krause, M.; Krawzcynski, H.; Krennrich, F.; Kretzschmann, A.; Kruger, P.; Kubo, H.; Kudryavtsev, V.; Kukec Mezek, G.; Kushida, J.; Kuznetsov, A.; La Barbera, A.; La Palombara, N.; La Parola, V.; La Rosa, G.; Laffon, H.; Lagadec, T.; Lahmann, R.; Lalik, K.; Lamanna, G.; Landriu, D.; Landt, H.; Lang, R. G.; Languignon, D.; Lapington, J.; Laporte, P.; Latovski, N.; Law-Green, D.; Le Fèvre, J. -P.; Le Flour, T.; Le Sidaner, P.; Lee, S. -H.; Lee, W. H.; Leffhalm, K.; Leich, H.; Leigui de Oliveira, M. A.; Lelas, D.; Lemière, A.; Lemoine-Goumard, M.; Lenain, J. -P.; Leonard, R.; Leoni, R.; Lessio, L.; Leto, G.; Leveque, A.; Lieunard, B.; Limon, M.; Lindemann, R.; Lindfors, E.; Liolios, A.; Lipniacka, A.; Lockart, H.; Lohse, T.; Loiseau, D.; Łokas, E.; Lombardi, S.; Longo, F.; Longo, G.; Lopatin, A.; Lopez, M.; López-Coto, R.; López-Oramas, A.; Loreggia, D.; Louge, T.; Louis, F.; Lu, C. -C.; Lucarelli, F.; Lucchesi, D.; Lüdecke, H.; Luque-Escamilla, P. L.; Luz, O.; Lyard, E.; Maccarone, M. C.; Maccarone, T. J.; Mach, E.; Madejski, G. M.; Madonna, A.; Mahabir, M.; Maier, G.; Majumdar, P.; Makariev, M.; Malaguti, G.; Malaspina, G.; Mallot, A. K.; Maltezos, S.; Mancilla, A.; Mandat, D.; Maneva, G.; Manigot, P.; Mankushiyil, N.; Mannheim, K.; Maragos, N.; Marano, D.; Marchegiani, P.; Marcomini, J. A.; Marcowith, A.; Mariotti, M.; Marisaldi, M.; Markoff, S.; Marszałek, A.; Martens, C.; Martí, J.; Martin, J. -M.; Martin, P.; Martínez, G.; Martínez, M.; Martínez, O.; Marx, R.; Massimino, P.; Mastichiadis, A.; Mastroianni, S.; Mastropietro, M.; Masuda, S.; Matsumoto, H.; Matsuoka, S.; Mattiazzo, S.; Maurin, G.; Maxted, N.; Maya, J.; Mayer, M.; Mazin, D.; Mazureau, E.; Mazziotta, M. N.; Mc Comb, L.; McCann, A.; McCubbin, N.; McHardy, I.; McKay, R.; McKinney, K.; Meagher, K.; Medina, C.; Mehrez, F.; Melioli, C.; Melkumyan, D.; Melo, D.; Melse, T.; Mereghetti, S.; Mertsch, P.; Meyer, M.; Meyrelles, J. L., jr; Miccichè, A.; Michałowski, J.; Micolon, P.; Mientjes, P.; Mignot, S.; Mihailidis, A.; Mineo, T.; Minuti, M.; Mirabal, N.; Mirabel, F.; Miranda, J. M.; Mirzoyan, R.; Mistò, A.; Mitchell, A.; Mizuno, T.; Moderski, R.; Mognet, I.; Mohammed, M.; Moharana, R.; Molinari, E.; Monmarthe, E.; Monnier, G.; Montaruli, T.; Monte, C.; Monteiro, I.; Moore, P.; Moralejo Olaizola, A.; Morello, C.; Moretti, E.; Mori, K.; Morlino, G.; Morselli, A.; Mottez, F.; Moudden, Y.; Moulin, E.; Mrusek, I.; Mueller, S.; Mukherjee, R.; Munar-Adrover, P.; Mundell, C.; Muraishi, H.; Murase, K.; Muronga, A.; Murphy, A.; Nagataki, S.; Nagayoshi, T.; Nagesh, B. K.; Naito, T.; Nakajima, D.; Nakamori, T.; Nakayama, K.; Naumann, D.; Nayman, P.; Nellen, L.; Nemmen, R.; Neronov, A.; Neustroev, V.; Neyroud, N.; Nguyen, T.; Nicastro, L.; Nicolau-Kukliński, J.; Niederwanger, F.; Niedźwiecki, A.; Niemiec, J.; Nieto, D.; Nievas, M.; Nikolaidis, A.; Nishijima, K.; Nishikawa, K. -I.; Noda, K.; Nogues, L.; Nolan, S.; Northrop, R.; Nosek, D.; Nozka, L.; Nunio, F.; Oakes, L.; O'Brien, P.; Occhipinti, G.; O'Faolain de Bhroithe, A.; Ogino, M.; Ohira, Y.; Ohishi, M.; Ohm, S.; Ohoka, H.; Okumura, A.; Olive, J. -F.; Olszowski, D.; Ong, R. A.; Ono, S.; Orienti, M.; Orito, R.; Orlati, A.; Orlati, A.; Osborne, J.; Ostrowski, M.; Otero, L. A.; Ottaway, D.; Otte, N.; Oya, I.; Ozieblo, A.; Padovani, M.; Pagano, I.; Paiano, S.; Paizis, A.; Palacio, J.; Palatka, M.; Pallotta, J.; Panagiotidis, K.; Panazol, J. -L.; Paneque, D.; Panter, M.; Panzera, M. R.; Paoletti, R.; Paolillo, M.; Papayannis, A.; Papyan, G.; Paravac, A.; Paredes, J. 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J.; Wakely, S. P.; Walter, R.; Walther, T.; Ward, J. E.; Ward, M.; Warda, K.; Warwick, R.; Wassberg, S.; Watson, J.; Wawer, P.; Wawrzaszek, R.; Webb, N.; Wegner, P.; Weinstein, A.; Weitzel, Q.; Wells, R.; Werner, F.; Werner, M.; Wetteskind, H.; White, M.; White, R.; Więcek, M.; Wierzcholska, A.; Wiesand, S.; Wijers, R.; Wild, N.; Wilhelm, A.; Wilkinson, M.; Will, M.; Williams, D. A.; Williams, J. T.; Willingale, R.; Winde, M.; Winiarski, K.; Winkler, H.; Wischnewski, R.; Wojcik, P.; Wolf, D.; Wood, M.; Wörnlein, A.; Wu, E.; Wu, T.; Yadav, K. K.; Yamamoto, H.; Yamamoto, T.; Yamazaki, R.; Yanagita, S.; Yang, L.; Yebras, J. M.; Yelos, D.; Yeung, W.; Yoshida, A.; Yoshida, T.; Yoshiike, S.; Yoshikoshi, T.; Yu, P.; Zabalza, V.; Zabalza, V.; Zacharias, M.; Zaharijas, G.; Zajczyk, A.; Zampieri, L.; Zandanel, F.; Zanin, R.; Zanmar Sanchez, R.; Zavrtanik, D.; Zavrtanik, M.; Zdziarski, A.; Zech, A.; Zechlin, H.; Zhao, A.; Ziegler, A.; Ziemann, J.; Ziętara, K.; Ziółkowski, J.; Zitelli, V.; Zoli, A.; Zurbach, C.; Żychowski, P. Bibcode: 2015arXiv150805894C Altcode: List of contributions from the CTA Consortium presented at the 34th International Cosmic Ray Conference, 30 July - 6 August 2015, The Hague, The Netherlands. Title: Long-baseline optical intensity interferometry. Laboratory demonstration of diffraction-limited imaging Authors: Dravins, Dainis; Lagadec, Tiphaine; Nuñez, Paul D. Bibcode: 2015A&A...580A..99D Altcode: 2015arXiv150605804D Context. A long-held vision has been to realize diffraction-limited optical aperture synthesis over kilometer baselines. This will enable imaging of stellar surfaces and their environments, and reveal interacting gas flows in binary systems. An opportunity is now opening up with the large telescope arrays primarily erected for measuring Cherenkov light in air induced by gamma rays. With suitable software, such telescopes could be electronically connected and also used for intensity interferometry. Second-order spatial coherence of light is obtained by cross correlating intensity fluctuations measured in different pairs of telescopes. With no optical links between them, the error budget is set by the electronic time resolution of a few nanoseconds. Corresponding light-travel distances are approximately one meter, making the method practically immune to atmospheric turbulence or optical imperfections, permitting both very long baselines and observing at short optical wavelengths.
Aims: Previous theoretical modeling has shown that full images should be possible to retrieve from observations with such telescope arrays. This project aims at verifying diffraction-limited imaging experimentally with groups of detached and independent optical telescopes.
Methods: In a large optics laboratory, artificial stars (single and double, round and elliptic) were observed by an array of small telescopes. Using high-speed photon-counting solid-state detectors and real-time electronics, intensity fluctuations were cross-correlated over up to 180 baselines between pairs of telescopes, producing coherence maps across the interferometric Fourier-transform plane.
Results: These interferometric measurements were used to extract parameters about the simulated stars, and to reconstruct their two-dimensional images. As far as we are aware, these are the first diffraction-limited images obtained from an optical array only linked by electronic software, with no optical connections between the telescopes.
Conclusions: These experiments serve to verify the concepts for long-baseline aperture synthesis in the optical, somewhat analogous to radio interferometry. Title: Stellar Spectroscopy during Exoplanet Transits: Revealing structures across stellar surfaces Authors: Dravins, Dainis; Ludwig, Hans-Günter; Dahlén, Erik Bibcode: 2015IAUGA..2233688D Altcode: Exoplanet transits permit to study stellar surface portions that successively become hidden behind the planet. Differential spectroscopy between various transit phases reveals spectra of those stellar surface segments that were hidden. The deduced center-to-limb behavior of stellar spectral line shapes, asymmetries and wavelength shifts enables detailed tests of 3-dimensional hydrodynamic models of stellar atmospheres, such that are required for any precise determination of abundances or seismic properties. Such models can now be computed for widely different classes of stars (including metal-poor ones and white dwarfs), but have been feasible to test and verify only for the Sun with its resolved surface structure. Exoplanet transits may also occur across features such as starspots, whose magnetic signatures will be retrieved from spectra of sufficient fidelity.Knowing the precise background stellar spectra, also properties of exoplanet atmospheres are better constrained: e.g., the Rossiter-McLaughlin effect becomes resolved as not only a simple change of stellar wavelength, but as a variation of the full line profiles and their asymmetries.Such studies are challenging since exoplanets cover only a tiny fraction of the stellar disk. Current work, analyzing sequences of high-fidelity ESO UVES spectra, demonstrate that such spatially resolved stellar spectra can already be (marginally) retrieved in a few cases with the brightest host stars. Already in a near future, ongoing exoplanet surveys are likely to find further bright hosts that will enable such studies for various stellar types. http://arxiv.org/abs/1408.1402 Title: Optical aperture synthesis with electronically connected telescopes Authors: Dravins, Dainis; Lagadec, Tiphaine; Nuñez, Paul D. Bibcode: 2015NatCo...6.6852D Altcode: 2015NatCo...6E6852D; 2015arXiv150404619D Highest resolution imaging in astronomy is achieved by interferometry, connecting telescopes over increasingly longer distances and at successively shorter wavelengths. Here, we present the first diffraction-limited images in visual light, produced by an array of independent optical telescopes, connected electronically only, with no optical links between them. With an array of small telescopes, second-order optical coherence of the sources is measured through intensity interferometry over 180 baselines between pairs of telescopes, and two-dimensional images reconstructed. The technique aims at diffraction-limited optical aperture synthesis over kilometre-long baselines to reach resolutions showing details on stellar surfaces and perhaps even the silhouettes of transiting exoplanets. Intensity interferometry circumvents problems of atmospheric turbulence that constrain ordinary interferometry. Since the electronic signal can be copied, many baselines can be built up between dispersed telescopes, and over long distances. Using arrays of air Cherenkov telescopes, this should enable the optical equivalent of interferometric arrays currently operating at radio wavelengths. Title: Stellar Spectroscopy During Exoplanet Transits: Dissecting Fine Structure Across Stellar Surfaces Authors: Dravins, Dainis; Ludwig, Hans-Gunter; Dahlen, Erik; Pazira, Hiva Bibcode: 2015csss...18..853D Altcode: 2014arXiv1408.1402D Differential spectroscopy during exoplanet transits permits to reconstruct spectra of small stellar surface portions that successively become hidden behind the planet. The center-to-limb behavior of stellar line shapes, asymmetries and wavelength shifts will enable detailed tests of 3-dimensional hydrodynamic models of stellar atmospheres, such that are required for any precise determination of abundances or seismic properties. Such models can now be computed for widely different stars but have been feasible to test in detail only for the Sun with its resolved surface structure. Although very high quality spectra are required, already current data permit reconstructions of line profiles in the brightest transit host stars such as HD 209458 (G0 V). Title: Stellar intensity interferometry over kilometer baselines: laboratory simulation of observations with the Cherenkov Telescope Array Authors: Dravins, Dainis; Lagadec, Tiphaine Bibcode: 2014SPIE.9146E..0ZD Altcode: 2014arXiv1407.5993D A long-held astronomical vision is to realize diffraction-limited optical aperture synthesis over kilometer baselines. This will enable imaging of stellar surfaces and their environments, show their evolution over time, and reveal interactions of stellar winds and gas flows in binary star systems. An opportunity is now opening up with the large telescope arrays primarily erected for measuring Cherenkov light in air induced by gamma rays. With suitable software, such telescopes could be electronically connected and used also for intensity interferometry. With no optical connection between the telescopes, the error budget is set by the electronic time resolution of a few nanoseconds. Corresponding light-travel distances are on the order of one meter, making the method practically insensitive to atmospheric turbulence or optical imperfections, permitting both very long baselines and observing at short optical wavelengths. Theoretical modeling has shown how stellar surface images can be retrieved from such observations and here we report on experimental simulations. In an optical laboratory, artificial stars (single and double, round and elliptic) are observed by an array of telescopes. Using high-speed photon-counting solid-state detectors and real-time electronics, intensity fluctuations are cross correlated between up to a hundred baselines between pairs of telescopes, producing maps of the second-order spatial coherence across the interferometric Fourier-transform plane. These experiments serve to verify the concepts and to optimize the instrumentation and observing procedures for future observations with (in particular) CTA, the Cherenkov Telescope Array, aiming at order-of-magnitude improvements of the angular resolution in optical astronomy. Title: Intensity Interferometry with Cherenkov Telescope Arrays: Prospects for submilliarcsecond optical imaging Authors: Dravins, D. Bibcode: 2014ipco.conf...19D Altcode: Intensity interferometry measures the second-order coherence of light. Very rapid (nanosecond) fluctuations are correlated between separate telescopes, without any optical connection. This makes the method insensitive to atmospheric turbulence and optical imperfections, permitting observations over long baselines, and at short wavelengths. The required large telescopes are becoming available as those primarily erected to study gamma rays: the planned Cherenkov Telescope Array (https://www.cta-observatory.org/) envisions many tens of telescopes distributed over a few square km. Digital signal handling enables very many baselines to be simultaneously synthesized between many pairs of telescopes, while stars may be tracked across the sky with electronic time delays, synthesizing an optical interferometer in software. Simulations indicate limiting magnitudes around m(v)=8, reaching a resolution of 30 microarcseconds in the violet. Since intensity interferometry provides only the modulus (not phase) of any spatial frequency component of the source image, image reconstruction requires phase retrieval techniques. As shown in simulations, full two-dimensional images can be retrieved, provided there is an extensive coverage of the (u,v)-plane, such as will be available once the number of telescopes reaches numbers on the order of ten. Title: A Community Science Case for E-ELT HIRES Authors: Maiolino, R.; Haehnelt, M.; Murphy, M. T.; Queloz, D.; Origlia, L.; Alcala, J.; Alibert, Y.; Amado, P. J.; Allende Prieto, C.; Ammler-von Eiff, M.; Asplund, M.; Barstow, M.; Becker, G.; Bonfils, X.; Bouchy, F.; Bragaglia, A.; Burleigh, M. R.; Chiavassa, A.; Cimatti, D. A.; Cirasuolo, M.; Cristiani, S.; D'Odorico, V.; Dravins, D.; Emsellem, E.; Farihi, J.; Figueira, P.; Fynbo, J.; Gansicke, B. T.; Gillon, M.; Gustafsson, B.; Hill, V.; Israelyan, G.; Korn, A.; Larsen, S.; De Laverny, P.; Liske, J.; Lovis, C.; Marconi, A.; Martins, C.; Molaro, P.; Nisini, B.; Oliva, E.; Petitjean, P.; Pettini, M.; Recio Blanco, A.; Rebolo, R.; Reiners, A.; Rodriguez-Lopez, C.; Ryde, N.; Santos, N. C.; Savaglio, S.; Snellen, I.; Strassmeier, K.; Tanvir, N.; Testi, L.; Tolstoy, E.; Triaud, A.; Vanzi, L.; Viel, M.; Volonteri, M. Bibcode: 2013arXiv1310.3163M Altcode: Building on the experience of the high-resolution community with the suite of VLT high-resolution spectrographs, which has been tremendously successful, we outline here the (science) case for a high-fidelity, high-resolution spectrograph with wide wavelength coverage at the E-ELT. Flagship science drivers include: the study of exo-planetary atmospheres with the prospect of the detection of signatures of life on rocky planets; the chemical composition of planetary debris on the surface of white dwarfs; the spectroscopic study of protoplanetary and proto-stellar disks; the extension of Galactic archaeology to the Local Group and beyond; spectroscopic studies of the evolution of galaxies with samples that, unlike now, are no longer restricted to strongly star forming and/or very massive galaxies; the unraveling of the complex roles of stellar and AGN feedback; the study of the chemical signatures imprinted by population III stars on the IGM during the epoch of reionization; the exciting possibility of paradigm-changing contributions to fundamental physics. The requirements of these science cases can be met by a stable instrument with a spectral resolution of R~100,000 and broad, simultaneous spectral coverage extending from 370nm to 2500nm. Most science cases do not require spatially resolved information, and can be pursued in seeing-limited mode, although some of them would benefit by the E-ELT diffraction limited resolution. Some multiplexing would also be beneficial for some of the science cases. (Abridged) Title: CTA contributions to the 33rd International Cosmic Ray Conference (ICRC2013) Authors: CTA Consortium, The; :; Abril, O.; Acharya, B. S.; Actis, M.; Agnetta, G.; Aguilar, J. A.; Aharonian, F.; Ajello, M.; Akhperjanian, A.; Alcubierre, M.; Aleksic, J.; Alfaro, R.; Aliu, E.; Allafort, A. J.; Allan, D.; Allekotte, I.; Aloisio, R.; Amato, E.; Ambrosi, G.; Ambrosio, M.; Anderson, J.; Angüner, E. O.; Antonelli, L. A.; Antonuccio, V.; Antonucci, M.; Antoranz, P.; Aravantinos, A.; Argan, A.; Arlen, T.; Aramo, C.; Armstrong, T.; Arnaldi, H.; Arrabito, L.; Asano, K.; Ashton, T.; Asorey, H. G.; Aune, T.; Awane, Y.; Baba, H.; Babic, A.; Baby, N.; Bähr, J.; Bais, A.; Baixeras, C.; Bajtlik, S.; Balbo, M.; Balis, D.; Balkowski, C.; Ballet, J.; Bamba, A.; Bandiera, R.; Barber, A.; Barbier, C.; Barceló, M.; Barnacka, A.; Barnstedt, J.; Barres de Almeida, U.; Barrio, J. A.; Basili, A.; Basso, S.; Bastieri, D.; Bauer, C.; Baushev, A.; Becciani, U.; Becerra, J.; Becerra, J.; Becherini, Y.; Bechtol, K. C.; Becker Tjus, J.; Beckmann, V.; Bednarek, W.; Behera, B.; Belluso, M.; Benbow, W.; Berdugo, J.; Berge, D.; Berger, K.; Bernard, F.; Bernardino, T.; Bernlöhr, K.; Bertucci, B.; Bhat, N.; Bhattacharyya, S.; Biasuzzi, B.; Bigongiari, C.; Biland, A.; Billotta, S.; Bird, T.; Birsin, E.; Bissaldi, E.; Biteau, J.; Bitossi, M.; Blake, S.; Blanch Bigas, O.; Blasi, P.; Bobkov, A.; Boccone, V.; Böttcher, M.; Bogacz, L.; Bogart, J.; Bogdan, M.; Boisson, C.; Boix Gargallo, J.; Bolmont, J.; Bonanno, G.; Bonardi, A.; Bonev, T.; Bonifacio, P.; Bonnoli, G.; Bordas, P.; Borgland, A.; Borkowski, J.; Bose, R.; Botner, O.; Bottani, A.; Bouchet, L.; Bourgeat, M.; Boutonnet, C.; Bouvier, A.; Brau-Nogué, S.; Braun, I.; Bretz, T.; Briggs, M.; Brigida, M.; Bringmann, T.; Britto, R.; Brook, P.; Brun, P.; Brunetti, L.; Bruno, P.; Bucciantini, N.; Buanes, T.; Buckley, J.; Bühler, R.; Bugaev, V.; Bulgarelli, A.; Bulik, T.; Busetto, G.; Buson, S.; Byrum, K.; Cailles, M.; Cameron, R.; Camprecios, J.; Canestrari, R.; Cantu, S.; Capalbi, M.; Caraveo, P.; Carmona, E.; Carosi, A.; Carosi, R.; Carr, J.; Carter, J.; Carton, P. -H.; Caruso, R.; Casanova, S.; Cascone, E.; Casiraghi, M.; Castellina, A.; Catalano, O.; Cavazzani, S.; Cazaux, S.; Cerchiara, P.; Cerruti, M.; Chabanne, E.; Chadwick, P.; Champion, C.; Chaves, R.; Cheimets, P.; Chen, A.; Chiang, J.; Chiappetti, L.; Chikawa, M.; Chitnis, V. R.; Chollet, F.; Christof, A.; Chudoba, J.; Cieślar, M.; Cillis, A.; Cilmo, M.; Codino, A.; Cohen-Tanugi, J.; Colafrancesco, S.; Colin, P.; Colome, J.; Colonges, S.; Compin, M.; Conconi, P.; Conforti, V.; Connaughton, V.; Conrad, J.; Contreras, J. L.; Coppi, P.; Coridian, J.; Corona, P.; Corti, D.; Cortina, J.; Cossio, L.; Costa, A.; Costantini, H.; Cotter, G.; Courty, B.; Couturier, S.; Covino, S.; Crimi, G.; Criswell, S. J.; Croston, J.; Cusumano, G.; Dafonseca, M.; Dale, O.; Daniel, M.; Darling, J.; Davids, I.; Dazzi, F.; de Angelis, A.; De Caprio, V.; De Frondat, F.; de Gouveia Dal Pino, E. M.; de la Calle, I.; De La Vega, G. A.; de los Reyes Lopez, R.; de Lotto, B.; De Luca, A.; de Naurois, M.; de Oliveira, Y.; de Oña Wilhelmi, E.; de Palma, F.; de Souza, V.; Decerprit, G.; Decock, G.; Deil, C.; Delagnes, E.; Deleglise, G.; Delgado, C.; della Volpe, D.; Demange, P.; Depaola, G.; Dettlaff, A.; Di Girolamo, T.; Di Giulio, C.; Di Paola, A.; Di Pierro, F.; di Sciascio, G.; Díaz, C.; Dick, J.; Dickherber, R.; Dickinson, H.; Diez-Blanco, V.; Digel, S.; Dimitrov, D.; Disset, G.; Djannati-Ataï, A.; Doert, M.; Dohmke, M.; Domainko, W.; Dominis Prester, D.; Donat, A.; Dorner, D.; Doro, M.; Dournaux, J. -L.; Drake, G.; Dravins, D.; Drury, L.; Dubois, F.; Dubois, R.; Dubus, G.; Dufour, C.; Dumas, D.; Dumm, J.; Durand, D.; Dwarkadas, V.; Dyks, J.; Dyrda, M.; Ebr, J.; Edy, E.; Egberts, K.; Eger, P.; Einecke, S.; Eleftheriadis, C.; Elles, S.; Emmanoulopoulos, D.; Engelhaupt, D.; Enomoto, R.; Ernenwein, J. -P.; Errando, M.; Etchegoyen, A.; Evans, P. A.; Falcone, A.; Faltenbacher, A.; Fantinel, D.; Farakos, K.; Farnier, C.; Farrell, E.; Fasola, G.; Favill, B. W.; Fede, E.; Federici, S.; Fegan, S.; Feinstein, F.; Ferenc, D.; Ferrando, P.; Fesquet, M.; Fetfatzis, P.; Fiasson, A.; Fillin-Martino, E.; Fink, D.; Finley, C.; Finley, J. P.; Fiorini, M.; Firpo Curcoll, R.; Flandrini, E.; Fleischhack, H.; Flores, H.; Florin, D.; Focke, W.; Föhr, C.; Fokitis, E.; Font, L.; Fontaine, G.; Fornasa, M.; Förster, A.; Fortson, L.; Fouque, N.; Franckowiak, A.; Franco, F. J.; Frankowski, A.; Fransson, C.; Fraser, G. W.; Frei, R.; Fresnillo, L.; Fruck, C.; Fugazza, D.; Fujita, Y.; Fukazawa, Y.; Fukui, Y.; Funk, S.; Gäbele, W.; Gabici, S.; Gabriele, R.; Gadola, A.; Galante, N.; Gall, D.; Gallant, Y.; Gámez-García, J.; Garczarczyk, M.; García, B.; Garcia López, R.; Gardiol, D.; Gargano, F.; Garrido, D.; Garrido, L.; Gascon, D.; Gaug, M.; Gaweda, J.; Gebremedhin, L.; Geffroy, N.; Gerard, L.; Ghedina, A.; Ghigo, M.; Ghislain, P.; Giannakaki, E.; Gianotti, F.; Giarrusso, S.; Giavitto, G.; Giebels, B.; Giglietto, N.; Gika, V.; Giomi, M.; Giommi, P.; Giordano, F.; Girard, N.; Giro, E.; Giuliani, A.; Glanzman, T.; Glicenstein, J. -F.; Godinovic, N.; Golev, V.; Gomez Berisso, M.; Gómez-Ortega, J.; Gonzalez, M. M.; González, A.; González, F.; González Muñoz, A.; Gothe, K. S.; Grabarczyk, T.; Gougerot, M.; Graciani, R.; Grandi, P.; Grañena, F.; Granot, J.; Grasseau, G.; Gredig, R.; Green, A.; Greenshaw, T.; Grégoire, T.; Grillo, A.; Grimm, O.; Grondin, M. -H.; Grube, J.; Grudzinska, M.; Gruev, V.; Grünewald, S.; Grygorczuk, J.; Guarino, V.; Gunji, S.; Gyuk, G.; Hadasch, D.; Hagedorn, A.; Hagiwara, R.; Hahn, J.; Hakansson, N.; Hallgren, A.; Hamer Heras, N.; Hara, S.; Hardcastle, M. J.; Harezlak, D.; Harris, J.; Hassan, T.; Hatanaka, K.; Haubold, T.; Haupt, A.; Hayakawa, T.; Hayashida, M.; Heller, R.; Henault, F.; Henri, G.; Hermann, G.; Hermel, R.; Herrero, A.; Hervet, O.; Hidaka, N.; Hinton, J. A.; Hirotani, K.; Hoffmann, D.; Hofmann, W.; Hofverberg, P.; Holder, J.; Hörandel, J. R.; Horns, D.; Horville, D.; Houles, J.; Hrabovsky, M.; Hrupec, D.; Huan, H.; Huber, B.; Huet, J. -M.; Hughes, G.; Humensky, T. B.; Huovelin, J.; Huppert, J. -F.; Ibarra, A.; Ikawa, D.; Illa, J. M.; Impiombato, D.; Incorvaia, S.; Inoue, S.; Inoue, Y.; Iocco, F.; Ioka, K.; Israel, G. L.; Jablonski, C.; Jacholkowska, A.; Jacquemier, J.; Jamrozy, M.; Janiak, M.; Jean, P.; Jeanney, C.; Jimenez, J. J.; Jogler, T.; Johnson, C.; Johnson, T.; Journet, L.; Juffroy, C.; Jung, I.; Kaaret, P.; Kabuki, S.; Kagaya, M.; Kakuwa, J.; Kalkuhl, C.; Kankanyan, R.; Karastergiou, A.; Kärcher, K.; Karczewski, M.; Karkar, S.; Kasperek, J.; Kastana, D.; Katagiri, H.; Kataoka, J.; Katarzyński, K.; Katz, U.; Kawanaka, N.; Kazanas, D.; Kelley-Hoskins, N.; Kellner-Leidel, B.; Kelly, H.; Kendziorra, E.; Khélifi, B.; Kieda, D. B.; Kifune, T.; Kihm, T.; Kishimoto, T.; Kitamoto, K.; Kluźniak, W.; Knapic, C.; Knapp, J.; Knödlseder, J.; Köck, F.; Kocot, J.; Kodani, K.; Köhne, J. -H.; Kohri, K.; Kokkotas, K.; Kolitzus, D.; Komin, N.; Kominis, I.; Konno, Y.; Köppel, H.; Korohoda, P.; Kosack, K.; Koss, G.; Kossakowski, R.; Koul, R.; Kowal, G.; Koyama, S.; Kozioł, J.; Krähenbühl, T.; Krause, J.; Krawzcynski, H.; Krennrich, F.; Krepps, A.; Kretzschmann, A.; Krobot, R.; Krueger, P.; Kubo, H.; Kudryavtsev, V. A.; Kushida, J.; Kuznetsov, A.; La Barbera, A.; La Palombara, N.; La Parola, V.; La Rosa, G.; Lacombe, K.; Lamanna, G.; Lande, J.; Languignon, D.; Lapington, J. S.; Laporte, P.; Laurent, B.; Lavalley, C.; Le Flour, T.; Le Padellec, A.; Lee, S. -H.; Lee, W. H.; Lefèvre, J. -P.; Leich, H.; Leigui de Oliveira, M. A.; Lelas, D.; Lenain, J. -P.; Leoni, R.; Leopold, D. J.; Lerch, T.; Lessio, L.; Leto, G.; Lieunard, B.; Lieunard, S.; Lindemann, R.; Lindfors, E.; Liolios, A.; Lipniacka, A.; Lockart, H.; Lohse, T.; Lombardi, S.; Longo, F.; Lopatin, A.; Lopez, M.; López-Coto, R.; López-Oramas, A.; Lorca, A.; Lorenz, E.; Louis, F.; Lubinski, P.; Lucarelli, F.; Lüdecke, H.; Ludwin, J.; Luque-Escamilla, P. L.; Lustermann, W.; Luz, O.; Lyard, E.; Maccarone, M. C.; Maccarone, T. J.; Madejski, G. M.; Madhavan, A.; Mahabir, M.; Maier, G.; Majumdar, P.; Malaguti, G.; Malaspina, G.; Maltezos, S.; Manalaysay, A.; Mancilla, A.; Mandat, D.; Maneva, G.; Mangano, A.; Manigot, P.; Mannheim, K.; Manthos, I.; Maragos, N.; Marcowith, A.; Mariotti, M.; Marisaldi, M.; Markoff, S.; Marszałek, A.; Martens, C.; Martí, J.; Martin, J. -M.; Martin, P.; Martínez, G.; Martínez, F.; Martínez, M.; Massaro, F.; Masserot, A.; Mastichiadis, A.; Mathieu, A.; Matsumoto, H.; Mattana, F.; Mattiazzo, S.; Maurer, A.; Maurin, G.; Maxfield, S.; Maya, J.; Mazin, D.; Mc Comb, L.; McCann, A.; McCubbin, N.; McHardy, I.; McKay, R.; Meagher, K.; Medina, C.; Melioli, C.; Melkumyan, D.; Melo, D.; Mereghetti, S.; Mertsch, P.; Meucci, M.; Meyer, M.; Michałowski, J.; Micolon, P.; Mihailidis, A.; Mineo, T.; Minuti, M.; Mirabal, N.; Mirabel, F.; Miranda, J. M.; Mirzoyan, R.; Mistò, A.; Mizuno, T.; Moal, B.; Moderski, R.; Mognet, I.; Molinari, E.; Molinaro, M.; Montaruli, T.; Monte, C.; Monteiro, I.; Moore, P.; Moralejo Olaizola, A.; Mordalska, M.; Morello, C.; Mori, K.; Morlino, G.; Morselli, A.; Mottez, F.; Moudden, Y.; Moulin, E.; Mrusek, I.; Mukherjee, R.; Munar-Adrover, P.; Muraishi, H.; Murase, K.; StJ. Murphy, A.; Nagataki, S.; Naito, T.; Nakajima, D.; Nakamori, T.; Nakayama, K.; Naumann, C.; Naumann, D.; Naumann-Godo, M.; Nayman, P.; Nedbal, D.; Neise, D.; Nellen, L.; Neronov, A.; Neustroev, V.; Neyroud, N.; Nicastro, L.; Nicolau-Kukliński, J.; Niedźwiecki, A.; Niemiec, J.; Nieto, D.; Nikolaidis, A.; Nishijima, K.; Nishikawa, K. -I.; Noda, K.; Nolan, S.; Northrop, R.; Nosek, D.; Nowak, N.; Nozato, A.; Oakes, L.; O'Brien, P. T.; Ohira, Y.; Ohishi, M.; Ohm, S.; Ohoka, H.; Okuda, T.; Okumura, A.; Olive, J. -F.; Ong, R. A.; Orito, R.; Orr, M.; Osborne, J. P.; Ostrowski, M.; Otero, L. 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J.; Wierzcholska, A.; Wiesand, S.; Wilhelm, A.; Wilkinson, M. I.; Williams, D. A.; Willingale, R.; Winde, M.; Winiarski, K.; Wischnewski, R.; Wiśniewski, Ł.; Wojcik, P.; Wood, M.; Wörnlein, A.; Xiong, Q.; Yadav, K. K.; Yamamoto, H.; Yamamoto, T.; Yamazaki, R.; Yanagita, S.; Yebras, J. M.; Yelos, D.; Yoshida, A.; Yoshida, T.; Yoshikoshi, T.; Yu, P.; Zabalza, V.; Zacharias, M.; Zajczyk, A.; Zampieri, L.; Zanin, R.; Zdziarski, A.; Zech, A.; Zhao, A.; Zhou, X.; Zietara, K.; Ziolkowski, J.; Ziółkowski, P.; Zitelli, V.; Zurbach, C.; Zychowski, P. Bibcode: 2013arXiv1307.2232C Altcode: Compilation of CTA contributions to the proceedings of the 33rd International Cosmic Ray Conference (ICRC2013), which took place in 2-9 July, 2013, in Rio de Janeiro, Brazil Title: Introducing the CTA concept Authors: Acharya, B. S.; Actis, M.; Aghajani, T.; Agnetta, G.; Aguilar, J.; Aharonian, F.; Ajello, M.; Akhperjanian, A.; Alcubierre, M.; Aleksić, J.; Alfaro, R.; Aliu, E.; Allafort, A. J.; Allan, D.; Allekotte, I.; Amato, E.; Anderson, J.; Angüner, E. O.; Antonelli, L. A.; Antoranz, P.; Aravantinos, A.; Arlen, T.; Armstrong, T.; Arnaldi, H.; Arrabito, L.; Asano, K.; Ashton, T.; Asorey, H. G.; Awane, Y.; Baba, H.; Babic, A.; Baby, N.; Bähr, J.; Bais, A.; Baixeras, C.; Bajtlik, S.; Balbo, M.; Balis, D.; Balkowski, C.; Bamba, A.; Bandiera, R.; Barber, A.; Barbier, C.; Barceló, M.; Barnacka, A.; Barnstedt, J.; Barres de Almeida, U.; Barrio, J. A.; Basili, A.; Basso, S.; Bastieri, D.; Bauer, C.; Baushev, A.; Becerra, J.; Becherini, Y.; Bechtol, K. C.; Becker Tjus, J.; Beckmann, V.; Bednarek, W.; Behera, B.; Belluso, M.; Benbow, W.; Berdugo, J.; Berger, K.; Bernard, F.; Bernardino, T.; Bernlöhr, K.; Bhat, N.; Bhattacharyya, S.; Bigongiari, C.; Biland, A.; Billotta, S.; Bird, T.; Birsin, E.; Bissaldi, E.; Biteau, J.; Bitossi, M.; Blake, S.; Blanch Bigas, O.; Blasi, P.; Bobkov, A.; Boccone, V.; Boettcher, M.; Bogacz, L.; Bogart, J.; Bogdan, M.; Boisson, C.; Boix Gargallo, J.; Bolmont, J.; Bonanno, G.; Bonardi, A.; Bonev, T.; Bonifacio, P.; Bonnoli, G.; Bordas, P.; Borgland, A.; Borkowski, J.; Bose, R.; Botner, O.; Bottani, A.; Bouchet, L.; Bourgeat, M.; Boutonnet, C.; Bouvier, A.; Brau-Nogué, S.; Braun, I.; Bretz, T.; Briggs, M.; Bringmann, T.; Brook, P.; Brun, P.; Brunetti, L.; Buanes, T.; Buckley, J.; Buehler, R.; Bugaev, V.; Bulgarelli, A.; Bulik, T.; Busetto, G.; Buson, S.; Byrum, K.; Cailles, M.; Cameron, R.; Camprecios, J.; Canestrari, R.; Cantu, S.; Capalbi, M.; Caraveo, P.; Carmona, E.; Carosi, A.; Carr, J.; Carton, P. -H.; Casanova, S.; Casiraghi, M.; Catalano, O.; Cavazzani, S.; Cazaux, S.; Cerruti, M.; Chabanne, E.; Chadwick, P.; Champion, C.; Chen, A.; Chiang, J.; Chiappetti, L.; Chikawa, M.; Chitnis, V. R.; Chollet, F.; Chudoba, J.; Cieślar, M.; Cillis, A.; Cohen-Tanugi, J.; Colafrancesco, S.; Colin, P.; Colome, J.; Colonges, S.; Compin, M.; Conconi, P.; Conforti, V.; Connaughton, V.; Conrad, J.; Contreras, J. L.; Coppi, P.; Corona, P.; Corti, D.; Cortina, J.; Cossio, L.; Costantini, H.; Cotter, G.; Courty, B.; Couturier, S.; Covino, S.; Crimi, G.; Criswell, S. J.; Croston, J.; Cusumano, G.; Dafonseca, M.; Dale, O.; Daniel, M.; Darling, J.; Davids, I.; Dazzi, F.; De Angelis, A.; De Caprio, V.; De Frondat, F.; de Gouveia Dal Pino, E. M.; de la Calle, I.; De La Vega, G. A.; de los Reyes Lopez, R.; De Lotto, B.; De Luca, A.; de Mello Neto, J. R. T.; de Naurois, M.; de Oliveira, Y.; de Oña Wilhelmi, E.; de Souza, V.; Decerprit, G.; Decock, G.; Deil, C.; Delagnes, E.; Deleglise, G.; Delgado, C.; Della Volpe, D.; Demange, P.; Depaola, G.; Dettlaff, A.; Di Paola, A.; Di Pierro, F.; Díaz, C.; Dick, J.; Dickherber, R.; Dickinson, H.; Diez-Blanco, V.; Digel, S.; Dimitrov, D.; Disset, G.; Djannati-Ataï, A.; Doert, M.; Dohmke, M.; Domainko, W.; Dominis Prester, D.; Donat, A.; Dorner, D.; Doro, M.; Dournaux, J. -L.; Drake, G.; Dravins, D.; Drury, L.; Dubois, F.; Dubois, R.; Dubus, G.; Dufour, C.; Dumas, D.; Dumm, J.; Durand, D.; Dyks, J.; Dyrda, M.; Ebr, J.; Edy, E.; Egberts, K.; Eger, P.; Einecke, S.; Eleftheriadis, C.; Elles, S.; Emmanoulopoulos, D.; Engelhaupt, D.; Enomoto, R.; Ernenwein, J. -P.; Errando, M.; Etchegoyen, A.; Evans, P.; Falcone, A.; Fantinel, D.; Farakos, K.; Farnier, C.; Fasola, G.; Favill, B.; Fede, E.; Federici, S.; Fegan, S.; Feinstein, F.; Ferenc, D.; Ferrando, P.; Fesquet, M.; Fiasson, A.; Fillin-Martino, E.; Fink, D.; Finley, C.; Finley, J. P.; Fiorini, M.; Firpo Curcoll, R.; Flores, H.; Florin, D.; Focke, W.; Föhr, C.; Fokitis, E.; Font, L.; Fontaine, G.; Fornasa, M.; Förster, A.; Fortson, L.; Fouque, N.; Franckowiak, A.; Fransson, C.; Fraser, G.; Frei, R.; Albuquerque, I. F. M.; Fresnillo, L.; Fruck, C.; Fujita, Y.; Fukazawa, Y.; Fukui, Y.; Funk, S.; Gäbele, W.; Gabici, S.; Gabriele, R.; Gadola, A.; Galante, N.; Gall, D.; Gallant, Y.; Gámez-García, J.; García, B.; Garcia López, R.; Gardiol, D.; Garrido, D.; Garrido, L.; Gascon, D.; Gaug, M.; Gaweda, J.; Gebremedhin, L.; Geffroy, N.; Gerard, L.; Ghedina, A.; Ghigo, M.; Giannakaki, E.; Gianotti, F.; Giarrusso, S.; Giavitto, G.; Giebels, B.; Gika, V.; Giommi, P.; Girard, N.; Giro, E.; Giuliani, A.; Glanzman, T.; Glicenstein, J. -F.; Godinovic, N.; Golev, V.; Gomez Berisso, M.; Gómez-Ortega, J.; Gonzalez, M. M.; González, A.; González, F.; González Muñoz, A.; Gothe, K. S.; Gougerot, M.; Graciani, R.; Grandi, P.; Grañena, F.; Granot, J.; Grasseau, G.; Gredig, R.; Green, A.; Greenshaw, T.; Grégoire, T.; Grimm, O.; Grube, J.; Grudzinska, M.; Gruev, V.; Grünewald, S.; Grygorczuk, J.; Guarino, V.; Gunji, S.; Gyuk, G.; Hadasch, D.; Hagiwara, R.; Hahn, J.; Hakansson, N.; Hallgren, A.; Hamer Heras, N.; Hara, S.; Hardcastle, M. J.; Harris, J.; Hassan, T.; Hatanaka, K.; Haubold, T.; Haupt, A.; Hayakawa, T.; Hayashida, M.; Heller, R.; Henault, F.; Henri, G.; Hermann, G.; Hermel, R.; Herrero, A.; Hidaka, N.; Hinton, J.; Hoffmann, D.; Hofmann, W.; Hofverberg, P.; Holder, J.; Horns, D.; Horville, D.; Houles, J.; Hrabovsky, M.; Hrupec, D.; Huan, H.; Huber, B.; Huet, J. -M.; Hughes, G.; Humensky, T. B.; Huovelin, J.; Ibarra, A.; Illa, J. M.; Impiombato, D.; Incorvaia, S.; Inoue, S.; Inoue, Y.; Ioka, K.; Ismailova, E.; Jablonski, C.; Jacholkowska, A.; Jamrozy, M.; Janiak, M.; Jean, P.; Jeanney, C.; Jimenez, J. J.; Jogler, T.; Johnson, T.; Journet, L.; Juffroy, C.; Jung, I.; Kaaret, P.; Kabuki, S.; Kagaya, M.; Kakuwa, J.; Kalkuhl, C.; Kankanyan, R.; Karastergiou, A.; Kärcher, K.; Karczewski, M.; Karkar, S.; Kasperek, J.; Kastana, D.; Katagiri, H.; Kataoka, J.; Katarzyński, K.; Katz, U.; Kawanaka, N.; Kellner-Leidel, B.; Kelly, H.; Kendziorra, E.; Khélifi, B.; Kieda, D. B.; Kifune, T.; Kihm, T.; Kishimoto, T.; Kitamoto, K.; Kluźniak, W.; Knapic, C.; Knapp, J.; Knödlseder, J.; Köck, F.; Kocot, J.; Kodani, K.; Köhne, J. -H.; Kohri, K.; Kokkotas, K.; Kolitzus, D.; Komin, N.; Kominis, I.; Konno, Y.; Köppel, H.; Korohoda, P.; Kosack, K.; Koss, G.; Kossakowski, R.; Kostka, P.; Koul, R.; Kowal, G.; Koyama, S.; Kozioł, J.; Krähenbühl, T.; Krause, J.; Krawzcynski, H.; Krennrich, F.; Krepps, A.; Kretzschmann, A.; Krobot, R.; Krueger, P.; Kubo, H.; Kudryavtsev, V. A.; Kushida, J.; Kuznetsov, A.; La Barbera, A.; La Palombara, N.; La Parola, V.; La Rosa, G.; Lacombe, K.; Lamanna, G.; Lande, J.; Languignon, D.; Lapington, J.; Laporte, P.; Lavalley, C.; Le Flour, T.; Le Padellec, A.; Lee, S. -H.; Lee, W. H.; Leigui de Oliveira, M. A.; Lelas, D.; Lenain, J. -P.; Leopold, D. J.; Lerch, T.; Lessio, L.; Lieunard, B.; Lindfors, E.; Liolios, A.; Lipniacka, A.; Lockart, H.; Lohse, T.; Lombardi, S.; Lopatin, A.; Lopez, M.; López-Coto, R.; López-Oramas, A.; Lorca, A.; Lorenz, E.; Lubinski, P.; Lucarelli, F.; Lüdecke, H.; Ludwin, J.; Luque-Escamilla, P. L.; Lustermann, W.; Luz, O.; Lyard, E.; Maccarone, M. C.; Maccarone, T. J.; Madejski, G. M.; Madhavan, A.; Mahabir, M.; Maier, G.; Majumdar, P.; Malaguti, G.; Maltezos, S.; Manalaysay, A.; Mancilla, A.; Mandat, D.; Maneva, G.; Mangano, A.; Manigot, P.; Mannheim, K.; Manthos, I.; Maragos, N.; Marcowith, A.; Mariotti, M.; Marisaldi, M.; Markoff, S.; Marszałek, A.; Martens, C.; Martí, J.; Martin, J. -M.; Martin, P.; Martínez, G.; Martínez, F.; Martínez, M.; Masserot, A.; Mastichiadis, A.; Mathieu, A.; Matsumoto, H.; Mattana, F.; Mattiazzo, S.; Maurin, G.; Maxfield, S.; Maya, J.; Mazin, D.; Mc Comb, L.; McCubbin, N.; McHardy, I.; McKay, R.; Medina, C.; Melioli, C.; Melkumyan, D.; Mereghetti, S.; Mertsch, P.; Meucci, M.; Michałowski, J.; Micolon, P.; Mihailidis, A.; Mineo, T.; Minuti, M.; Mirabal, N.; Mirabel, F.; Miranda, J. M.; Mirzoyan, R.; Mizuno, T.; Moal, B.; Moderski, R.; Mognet, I.; Molinari, E.; Molinaro, M.; Montaruli, T.; Monteiro, I.; Moore, P.; Moralejo Olaizola, A.; Mordalska, M.; Morello, C.; Mori, K.; Mottez, F.; Moudden, Y.; Moulin, E.; Mrusek, I.; Mukherjee, R.; Munar-Adrover, P.; Muraishi, H.; Murase, K.; Murphy, A.; Nagataki, S.; Naito, T.; Nakajima, D.; Nakamori, T.; Nakayama, K.; Naumann, C.; Naumann, D.; Naumann-Godo, M.; Nayman, P.; Nedbal, D.; Neise, D.; Nellen, L.; Neustroev, V.; Neyroud, N.; Nicastro, L.; Nicolau-Kukliński, J.; Niedźwiecki, A.; Niemiec, J.; Nieto, D.; Nikolaidis, A.; Nishijima, K.; Nolan, S.; Northrop, R.; Nosek, D.; Nowak, N.; Nozato, A.; O'Brien, P.; Ohira, Y.; Ohishi, M.; Ohm, S.; Ohoka, H.; Okuda, T.; Okumura, A.; Olive, J. -F.; Ong, R. A.; Orito, R.; Orr, M.; Osborne, J.; Ostrowski, M.; Otero, L. A.; Otte, N.; Ovcharov, E.; Oya, I.; Ozieblo, A.; Padilla, L.; Paiano, S.; Paillot, D.; Paizis, A.; Palanque, S.; Palatka, M.; Pallota, J.; Panagiotidis, K.; Panazol, J. -L.; Paneque, D.; Panter, M.; Paoletti, R.; Papayannis, A.; Papyan, G.; Paredes, J. M.; Pareschi, G.; Parks, G.; Parraud, J. -M.; Parsons, D.; Paz Arribas, M.; Pech, M.; Pedaletti, G.; Pelassa, V.; Pelat, D.; Perez, M. d. C.; Persic, M.; Petrucci, P. -O.; Peyaud, B.; Pichel, A.; Pita, S.; Pizzolato, F.; Platos, Ł.; Platzer, R.; Pogosyan, L.; Pohl, M.; Pojmanski, G.; Ponz, J. D.; Potter, W.; Poutanen, J.; Prandini, E.; Prast, J.; Preece, R.; Profeti, F.; Prokoph, H.; Prouza, M.; Proyetti, M.; Puerto-Gimenez, I.; Pühlhofer, G.; Puljak, I.; Punch, M.; Pyzioł, R.; Quel, E. J.; Quinn, J.; Quirrenbach, A.; Racero, E.; Rajda, P. J.; Ramon, P.; Rando, R.; Rannot, R. C.; Rataj, M.; Raue, M.; Reardon, P.; Reimann, O.; Reimer, A.; Reimer, O.; Reitberger, K.; Renaud, M.; Renner, S.; Reville, B.; Rhode, W.; Ribó, M.; Ribordy, M.; Richer, M. G.; Rico, J.; Ridky, J.; Rieger, F.; Ringegni, P.; Ripken, J.; Ristori, P. R.; Riviére, A.; Rivoire, S.; Rob, L.; Roeser, U.; Rohlfs, R.; Rojas, G.; Romano, P.; Romaszkan, W.; Romero, G. E.; Rosen, S.; Rosier Lees, S.; Ross, D.; Rouaix, G.; Rousselle, J.; Rousselle, S.; Rovero, A. C.; Roy, F.; Royer, S.; Rudak, B.; Rulten, C.; Rupiński, M.; Russo, F.; Ryde, F.; Sacco, B.; Saemann, E. O.; Saggion, A.; Sahakian, V.; Saito, K.; Saito, T.; Saito, Y.; Sakaki, N.; Sakonaka, R.; Salini, A.; Sanchez, F.; Sanchez-Conde, M.; Sandoval, A.; Sandaker, H.; Sant'Ambrogio, E.; Santangelo, A.; Santos, E. M.; Sanuy, A.; Sapozhnikov, L.; Sarkar, S.; Sartore, N.; Sasaki, H.; Satalecka, K.; Sawada, M.; Scalzotto, V.; Scapin, V.; Scarcioffolo, M.; Schafer, J.; Schanz, T.; Schlenstedt, S.; Schlickeiser, R.; Schmidt, T.; Schmoll, J.; Schovanek, P.; Schroedter, M.; Schultz, C.; Schultze, J.; Schulz, A.; Schure, K.; Schwab, T.; Schwanke, U.; Schwarz, J.; Schwarzburg, S.; Schweizer, T.; Schwemmer, S.; Segreto, A.; Seiradakis, J. -H.; Sembroski, G. H.; Seweryn, K.; Sharma, M.; Shayduk, M.; Shellard, R. C.; Shi, J.; Shibata, T.; Shibuya, A.; Shum, E.; Sidoli, L.; Sidz, M.; Sieiro, J.; Sikora, M.; Silk, J.; Sillanpää, A.; Singh, B. B.; Sitarek, J.; Skole, C.; Smareglia, R.; Smith, A.; Smith, D.; Smith, J.; Smith, N.; Sobczyńska, D.; Sol, H.; Sottile, G.; Sowiński, M.; Spanier, F.; Spiga, D.; Spyrou, S.; Stamatescu, V.; Stamerra, A.; Starling, R.; Stawarz, Ł.; Steenkamp, R.; Stegmann, C.; Steiner, S.; Stergioulas, N.; Sternberger, R.; Sterzel, M.; Stinzing, F.; Stodulski, M.; Straumann, U.; Strazzeri, E.; Stringhetti, L.; Suarez, A.; Suchenek, M.; Sugawara, R.; Sulanke, K. -H.; Sun, S.; Supanitsky, A. D.; Suric, T.; Sutcliffe, P.; Sykes, J.; Szanecki, M.; Szepieniec, T.; Szostek, A.; Tagliaferri, G.; Tajima, H.; Takahashi, H.; Takahashi, K.; Takalo, L.; Takami, H.; Talbot, G.; Tammi, J.; Tanaka, M.; Tanaka, S.; Tasan, J.; Tavani, M.; Tavernet, J. -P.; Tejedor, L. A.; Telezhinsky, I.; Temnikov, P.; Tenzer, C.; Terada, Y.; Terrier, R.; Teshima, M.; Testa, V.; Tezier, D.; Thuermann, D.; Tibaldo, L.; Tibolla, O.; Tiengo, A.; Tluczykont, M.; Todero Peixoto, C. J.; Tokanai, F.; Tokarz, M.; Toma, K.; Torii, K.; Tornikoski, M.; Torres, D. F.; Torres, M.; Tosti, G.; Totani, T.; Toussenel, F.; Tovmassian, G.; Travnicek, P.; Trifoglio, M.; Troyano, I.; Tsinganos, K.; Ueno, H.; Umehara, K.; Upadhya, S. S.; Usher, T.; Uslenghi, M.; Valdes-Galicia, J. F.; Vallania, P.; Vallejo, G.; van Driel, W.; van Eldik, C.; Vandenbrouke, J.; Vanderwalt, J.; Vankov, H.; Vasileiadis, G.; Vassiliev, V.; Veberic, D.; Vegas, I.; Vercellone, S.; Vergani, S.; Veyssiére, C.; Vialle, J. P.; Viana, A.; Videla, M.; Vincent, P.; Vincent, S.; Vink, J.; Vlahakis, N.; Vlahos, L.; Vogler, P.; Vollhardt, A.; von Gunten, H. -P.; Vorobiov, S.; Vuerli, C.; Waegebaert, V.; Wagner, R.; Wagner, R. G.; Wagner, S.; Wakely, S. P.; Walter, R.; Walther, T.; Warda, K.; Warwick, R.; Wawer, P.; Wawrzaszek, R.; Webb, N.; Wegner, P.; Weinstein, A.; Weitzel, Q.; Welsing, R.; Werner, M.; Wetteskind, H.; White, R.; Wierzcholska, A.; Wiesand, S.; Wilkinson, M.; Williams, D. A.; Willingale, R.; Winiarski, K.; Wischnewski, R.; Wiśniewski, Ł.; Wood, M.; Wörnlein, A.; Xiong, Q.; Yadav, K. K.; Yamamoto, H.; Yamamoto, T.; Yamazaki, R.; Yanagita, S.; Yebras, J. M.; Yelos, D.; Yoshida, A.; Yoshida, T.; Yoshikoshi, T.; Zabalza, V.; Zacharias, M.; Zajczyk, A.; Zanin, R.; Zdziarski, A.; Zech, A.; Zhao, A.; Zhou, X.; Ziętara, K.; Ziolkowski, J.; Ziółkowski, P.; Zitelli, V.; Zurbach, C.; Żychowski, P.; CTA Consortium Bibcode: 2013APh....43....3A Altcode: 2013APh....43....3C The Cherenkov Telescope Array (CTA) is a new observatory for very high-energy (VHE) gamma rays. CTA has ambitions science goals, for which it is necessary to achieve full-sky coverage, to improve the sensitivity by about an order of magnitude, to span about four decades of energy, from a few tens of GeV to above 100 TeV with enhanced angular and energy resolutions over existing VHE gamma-ray observatories. An international collaboration has formed with more than 1000 members from 27 countries in Europe, Asia, Africa and North and South America. In 2010 the CTA Consortium completed a Design Study and started a three-year Preparatory Phase which leads to production readiness of CTA in 2014. In this paper we introduce the science goals and the concept of CTA, and provide an overview of the project. Title: Optical intensity interferometry with the Cherenkov Telescope Array Authors: Dravins, Dainis; LeBohec, Stephan; Jensen, Hannes; Nuñez, Paul D.; CTA Consortium Bibcode: 2013APh....43..331D Altcode: 2012arXiv1204.3624D With its unprecedented light-collecting area for night-sky observations, the Cherenkov Telescope Array (CTA) holds great potential for also optical stellar astronomy, in particular as a multi-element intensity interferometer for realizing imaging with sub-milliarcsecond angular resolution. Such an order-of-magnitude increase of the spatial resolution achieved in optical astronomy will reveal the surfaces of rotationally flattened stars with structures in their circumstellar disks and winds, or the gas flows between close binaries. Image reconstruction is feasible from the second-order coherence of light, measured as the temporal correlations of arrival times between photons recorded in different telescopes. This technique (once pioneered by Hanbury Brown and Twiss) connects telescopes only with electronic signals and is practically insensitive to atmospheric turbulence and to imperfections in telescope optics. Detector and telescope requirements are very similar to those for imaging air Cherenkov observatories, the main difference being the signal processing (calculating cross correlations between single camera pixels in pairs of telescopes). Observations of brighter stars are not limited by sky brightness, permitting efficient CTA use during also bright-Moon periods. While other concepts have been proposed to realize kilometer-scale optical interferometers of conventional amplitude (phase-) type, both in space and on the ground, their complexity places them much further into the future than CTA, which thus could become the first kilometer-scale optical imager in astronomy. Title: Stellar intensity interferometry: Prospects for sub-milliarcsecond optical imaging Authors: Dravins, Dainis; LeBohec, Stephan; Jensen, Hannes; Nuñez, Paul D. Bibcode: 2012NewAR..56..143D Altcode: 2012arXiv1207.0808D Using kilometric arrays of air Cherenkov telescopes at short wavelengths, intensity interferometry may increase the spatial resolution achieved in optical astronomy by an order of magnitude, enabling images of rapidly rotating hot stars with structures in their circumstellar disks and winds, or mapping out patterns of nonradial pulsations across stellar surfaces. Intensity interferometry (once pioneered by Hanbury Brown and Twiss) connects telescopes only electronically, and is practically insensitive to atmospheric turbulence and optical imperfections, permitting observations over long baselines and through large airmasses, also at short optical wavelengths. The required large telescopes (∼10 m) with very fast detectors (∼ns) are becoming available as the arrays primarily erected to measure Cherenkov light emitted in air by particle cascades initiated by energetic gamma rays. Planned facilities (e.g., CTA, Cherenkov Telescope Array) envision many tens of telescopes distributed over a few square km. Digital signal handling enables very many baselines (from tens of meters to over a kilometer) to be simultaneously synthesized between many pairs of telescopes, while stars may be tracked across the sky with electronic time delays, in effect synthesizing an optical interferometer in software. Simulated observations indicate limiting magnitudes around mV = 8, reaching angular resolutions ∼30 μarcsec in the violet. The signal-to-noise ratio favors high-temperature sources and emission-line structures, and is independent of the optical passband, be it a single spectral line or the broad spectral continuum. Intensity interferometry directly provides the modulus (but not phase) of any spatial frequency component of the source image; for this reason a full image reconstruction requires phase retrieval techniques. This is feasible if sufficient coverage of the interferometric (u, v)-plane is available, as was verified through numerical simulations. Laboratory and field experiments are in progress; test telescopes have been erected, intensity interferometry has been achieved in the laboratory, and first full-scale tests of connecting large Cherenkov telescopes have been carried out. This paper reviews this interferometric method in view of the new possibilities offered by arrays of air Cherenkov telescopes, and outlines observational programs that should become realistic already in the rather near future. Title: Design concepts for the Cherenkov Telescope Array CTA: an advanced facility for ground-based high-energy gamma-ray astronomy Authors: Actis, M.; Agnetta, G.; Aharonian, F.; Akhperjanian, A.; Aleksić, J.; Aliu, E.; Allan, D.; Allekotte, I.; Antico, F.; Antonelli, L. A.; Antoranz, P.; Aravantinos, A.; Arlen, T.; Arnaldi, H.; Artmann, S.; Asano, K.; Asorey, H.; Bähr, J.; Bais, A.; Baixeras, C.; Bajtlik, S.; Balis, D.; Bamba, A.; Barbier, C.; Barceló, M.; Barnacka, A.; Barnstedt, J.; Barres de Almeida, U.; Barrio, J. A.; Basso, S.; Bastieri, D.; Bauer, C.; Becerra, J.; Becherini, Y.; Bechtol, K.; Becker, J.; Beckmann, V.; Bednarek, W.; Behera, B.; Beilicke, M.; Belluso, M.; Benallou, M.; Benbow, W.; Berdugo, J.; Berger, K.; Bernardino, T.; Bernlöhr, K.; Biland, A.; Billotta, S.; Bird, T.; Birsin, E.; Bissaldi, E.; Blake, S.; Blanch, O.; Bobkov, A. A.; Bogacz, L.; Bogdan, M.; Boisson, C.; Boix, J.; Bolmont, J.; Bonanno, G.; Bonardi, A.; Bonev, T.; Borkowski, J.; Botner, O.; Bottani, A.; Bourgeat, M.; Boutonnet, C.; Bouvier, A.; Brau-Nogué, S.; Braun, I.; Bretz, T.; Briggs, M. S.; Brun, P.; Brunetti, L.; Buckley, J. H.; Bugaev, V.; Bühler, R.; Bulik, T.; Busetto, G.; Buson, S.; Byrum, K.; Cailles, M.; Cameron, R.; Canestrari, R.; Cantu, S.; Carmona, E.; Carosi, A.; Carr, J.; Carton, P. H.; Casiraghi, M.; Castarede, H.; Catalano, O.; Cavazzani, S.; Cazaux, S.; Cerruti, B.; Cerruti, M.; Chadwick, P. M.; Chiang, J.; Chikawa, M.; Cieślar, M.; Ciesielska, M.; Cillis, A.; Clerc, C.; Colin, P.; Colomé, J.; Compin, M.; Conconi, P.; Connaughton, V.; Conrad, J.; Contreras, J. L.; Coppi, P.; Corlier, M.; Corona, P.; Corpace, O.; Corti, D.; Cortina, J.; Costantini, H.; Cotter, G.; Courty, B.; Couturier, S.; Covino, S.; Croston, J.; Cusumano, G.; Daniel, M. K.; Dazzi, F.; de Angelis, A.; de Cea Del Pozo, E.; de Gouveia Dal Pino, E. M.; de Jager, O.; de La Calle Pérez, I.; de La Vega, G.; de Lotto, B.; de Naurois, M.; de Oña Wilhelmi, E.; de Souza, V.; Decerprit, B.; Deil, C.; Delagnes, E.; Deleglise, G.; Delgado, C.; Dettlaff, T.; di Paolo, A.; di Pierro, F.; Díaz, C.; Dick, J.; Dickinson, H.; Digel, S. W.; Dimitrov, D.; Disset, G.; Djannati-Ataï, A.; Doert, M.; Domainko, W.; Dorner, D.; Doro, M.; Dournaux, J. -L.; Dravins, D.; Drury, L.; Dubois, F.; Dubois, R.; Dubus, G.; Dufour, C.; Durand, D.; Dyks, J.; Dyrda, M.; Edy, E.; Egberts, K.; Eleftheriadis, C.; Elles, S.; Emmanoulopoulos, D.; Enomoto, R.; Ernenwein, J. -P.; Errando, M.; Etchegoyen, A.; Falcone, A. D.; Farakos, K.; Farnier, C.; Federici, S.; Feinstein, F.; Ferenc, D.; Fillin-Martino, E.; Fink, D.; Finley, C.; Finley, J. P.; Firpo, R.; Florin, D.; Föhr, C.; Fokitis, E.; Font, Ll.; Fontaine, G.; Fontana, A.; Förster, A.; Fortson, L.; Fouque, N.; Fransson, C.; Fraser, G. W.; Fresnillo, L.; Fruck, C.; Fujita, Y.; Fukazawa, Y.; Funk, S.; Gäbele, W.; Gabici, S.; Gadola, A.; Galante, N.; Gallant, Y.; García, B.; García López, R. J.; Garrido, D.; Garrido, L.; Gascón, D.; Gasq, C.; Gaug, M.; Gaweda, J.; Geffroy, N.; Ghag, C.; Ghedina, A.; Ghigo, M.; Gianakaki, E.; Giarrusso, S.; Giavitto, G.; Giebels, B.; Giro, E.; Giubilato, P.; Glanzman, T.; Glicenstein, J. -F.; Gochna, M.; Golev, V.; Gómez Berisso, M.; González, A.; González, F.; Grañena, F.; Graciani, R.; Granot, J.; Gredig, R.; Green, A.; Greenshaw, T.; Grimm, O.; Grube, J.; Grudzińska, M.; Grygorczuk, J.; Guarino, V.; Guglielmi, L.; Guilloux, F.; Gunji, S.; Gyuk, G.; Hadasch, D.; Haefner, D.; Hagiwara, R.; Hahn, J.; Hallgren, A.; Hara, S.; Hardcastle, M. J.; Hassan, T.; Haubold, T.; Hauser, M.; Hayashida, M.; Heller, R.; Henri, G.; Hermann, G.; Herrero, A.; Hinton, J. A.; Hoffmann, D.; Hofmann, W.; Hofverberg, P.; Horns, D.; Hrupec, D.; Huan, H.; Huber, B.; Huet, J. -M.; Hughes, G.; Hultquist, K.; Humensky, T. B.; Huppert, J. -F.; Ibarra, A.; Illa, J. M.; Ingjald, J.; Inoue, Y.; Inoue, S.; Ioka, K.; Jablonski, C.; Jacholkowska, A.; Janiak, M.; Jean, P.; Jensen, H.; Jogler, T.; Jung, I.; Kaaret, P.; Kabuki, S.; Kakuwa, J.; Kalkuhl, C.; Kankanyan, R.; Kapala, M.; Karastergiou, A.; Karczewski, M.; Karkar, S.; Karlsson, N.; Kasperek, J.; Katagiri, H.; Katarzyński, K.; Kawanaka, N.; Kȩdziora, B.; Kendziorra, E.; Khélifi, B.; Kieda, D.; Kifune, T.; Kihm, T.; Klepser, S.; Kluźniak, W.; Knapp, J.; Knappy, A. R.; Kneiske, T.; Knödlseder, J.; Köck, F.; Kodani, K.; Kohri, K.; Kokkotas, K.; Komin, N.; Konopelko, A.; Kosack, K.; Kossakowski, R.; Kostka, P.; Kotuła, J.; Kowal, G.; Kozioł, J.; Krähenbühl, T.; Krause, J.; Krawczynski, H.; Krennrich, F.; Kretzschmann, A.; Kubo, H.; Kudryavtsev, V. A.; Kushida, J.; La Barbera, N.; La Parola, V.; La Rosa, G.; López, A.; Lamanna, G.; Laporte, P.; Lavalley, C.; Le Flour, T.; Le Padellec, A.; Lenain, J. -P.; Lessio, L.; Lieunard, B.; Lindfors, E.; Liolios, A.; Lohse, T.; Lombardi, S.; Lopatin, A.; Lorenz, E.; Lubiński, P.; Luz, O.; Lyard, E.; Maccarone, M. C.; Maccarone, T.; Maier, G.; Majumdar, P.; Maltezos, S.; Małkiewicz, P.; Mañá, C.; Manalaysay, A.; Maneva, G.; Mangano, A.; Manigot, P.; Marín, J.; Mariotti, M.; Markoff, S.; Martínez, G.; Martínez, M.; Mastichiadis, A.; Matsumoto, H.; Mattiazzo, S.; Mazin, D.; McComb, T. J. L.; McCubbin, N.; McHardy, I.; Medina, C.; Melkumyan, D.; Mendes, A.; Mertsch, P.; Meucci, M.; Michałowski, J.; Micolon, P.; Mineo, T.; Mirabal, N.; Mirabel, F.; Miranda, J. M.; Mirzoyan, R.; Mizuno, T.; Moal, B.; Moderski, R.; Molinari, E.; Monteiro, I.; Moralejo, A.; Morello, C.; Mori, K.; Motta, G.; Mottez, F.; Moulin, E.; Mukherjee, R.; Munar, P.; Muraishi, H.; Murase, K.; Murphy, A. Stj.; Nagataki, S.; Naito, T.; Nakamori, T.; Nakayama, K.; Naumann, C.; Naumann, D.; Nayman, P.; Nedbal, D.; Niedźwiecki, A.; Niemiec, J.; Nikolaidis, A.; Nishijima, K.; Nolan, S. J.; Nowak, N.; O'Brien, P. T.; Ochoa, I.; Ohira, Y.; Ohishi, M.; Ohka, H.; Okumura, A.; Olivetto, C.; Ong, R. A.; Orito, R.; Orr, M.; Osborne, J. P.; Ostrowski, M.; Otero, L.; Otte, A. N.; Ovcharov, E.; Oya, I.; Oziȩbło, A.; Paiano, S.; Pallota, J.; Panazol, J. L.; Paneque, D.; Panter, M.; Paoletti, R.; Papyan, G.; Paredes, J. M.; Pareschi, G.; Parsons, R. D.; Paz Arribas, M.; Pedaletti, G.; Pepato, A.; Persic, M.; Petrucci, P. O.; Peyaud, B.; Piechocki, W.; Pita, S.; Pivato, G.; Płatos, Ł.; Platzer, R.; Pogosyan, L.; Pohl, M.; Pojmański, G.; Ponz, J. D.; Potter, W.; Prandini, E.; Preece, R.; Prokoph, H.; Pühlhofer, G.; Punch, M.; Quel, E.; Quirrenbach, A.; Rajda, P.; Rando, R.; Rataj, M.; Raue, M.; Reimann, C.; Reimann, O.; Reimer, A.; Reimer, O.; Renaud, M.; Renner, S.; Reymond, J. -M.; Rhode, W.; Ribó, M.; Ribordy, M.; Rico, J.; Rieger, F.; Ringegni, P.; Ripken, J.; Ristori, P.; Rivoire, S.; Rob, L.; Rodriguez, S.; Roeser, U.; Romano, P.; Romero, G. E.; Rosier-Lees, S.; Rovero, A. C.; Roy, F.; Royer, S.; Rudak, B.; Rulten, C. B.; Ruppel, J.; Russo, F.; Ryde, F.; Sacco, B.; Saggion, A.; Sahakian, V.; Saito, K.; Saito, T.; Sakaki, N.; Salazar, E.; Salini, A.; Sánchez, F.; Sánchez Conde, M. Á.; Santangelo, A.; Santos, E. M.; Sanuy, A.; Sapozhnikov, L.; Sarkar, S.; Scalzotto, V.; Scapin, V.; Scarcioffolo, M.; Schanz, T.; Schlenstedt, S.; Schlickeiser, R.; Schmidt, T.; Schmoll, J.; Schroedter, M.; Schultz, C.; Schultze, J.; Schulz, A.; Schwanke, U.; Schwarzburg, S.; Schweizer, T.; Seiradakis, J.; Selmane, S.; Seweryn, K.; Shayduk, M.; Shellard, R. C.; Shibata, T.; Sikora, M.; Silk, J.; Sillanpää, A.; Sitarek, J.; Skole, C.; Smith, N.; Sobczyńska, D.; Sofo Haro, M.; Sol, H.; Spanier, F.; Spiga, D.; Spyrou, S.; Stamatescu, V.; Stamerra, A.; Starling, R. L. C.; Stawarz, Ł.; Steenkamp, R.; Stegmann, C.; Steiner, S.; Stergioulas, N.; Sternberger, R.; Stinzing, F.; Stodulski, M.; Straumann, U.; Suárez, A.; Suchenek, M.; Sugawara, R.; Sulanke, K. H.; Sun, S.; Supanitsky, A. D.; Sutcliffe, P.; Szanecki, M.; Szepieniec, T.; Szostek, A.; Szymkowiak, A.; Tagliaferri, G.; Tajima, H.; Takahashi, H.; Takahashi, K.; Takalo, L.; Takami, H.; Talbot, R. G.; Tam, P. H.; Tanaka, M.; Tanimori, T.; Tavani, M.; Tavernet, J. -P.; Tchernin, C.; Tejedor, L. A.; Telezhinsky, I.; Temnikov, P.; Tenzer, C.; Terada, Y.; Terrier, R.; Teshima, M.; Testa, V.; Tibaldo, L.; Tibolla, O.; Tluczykont, M.; Todero Peixoto, C. J.; Tokanai, F.; Tokarz, M.; Toma, K.; Torres, D. F.; Tosti, G.; Totani, T.; Toussenel, F.; Vallania, P.; Vallejo, G.; van der Walt, J.; van Eldik, C.; Vandenbroucke, J.; Vankov, H.; Vasileiadis, G.; Vassiliev, V. V.; Vegas, I.; Venter, L.; Vercellone, S.; Veyssiere, C.; Vialle, J. P.; Videla, M.; Vincent, P.; Vink, J.; Vlahakis, N.; Vlahos, L.; Vogler, P.; Vollhardt, A.; Volpe, F.; von Gunten, H. P.; Vorobiov, S.; Wagner, S.; Wagner, R. M.; Wagner, B.; Wakely, S. P.; Walter, P.; Walter, R.; Warwick, R.; Wawer, P.; Wawrzaszek, R.; Webb, N.; Wegner, P.; Weinstein, A.; Weitzel, Q.; Welsing, R.; Wetteskind, H.; White, R.; Wierzcholska, A.; Wilkinson, M. I.; Williams, D. A.; Winde, M.; Wischnewski, R.; Wiśniewski, Ł.; Wolczko, A.; Wood, M.; Xiong, Q.; Yamamoto, T.; Yamaoka, K.; Yamazaki, R.; Yanagita, S.; Yoffo, B.; Yonetani, M.; Yoshida, A.; Yoshida, T.; Yoshikoshi, T.; Zabalza, V.; Zagdański, A.; Zajczyk, A.; Zdziarski, A.; Zech, A.; Ziȩtara, K.; Ziółkowski, P.; Zitelli, V.; Zychowski, P. Bibcode: 2011ExA....32..193A Altcode: 2011ExA...tmp..121A; 2010arXiv1008.3703C Ground-based gamma-ray astronomy has had a major breakthrough with the impressive results obtained using systems of imaging atmospheric Cherenkov telescopes. Ground-based gamma-ray astronomy has a huge potential in astrophysics, particle physics and cosmology. CTA is an international initiative to build the next generation instrument, with a factor of 5-10 improvement in sensitivity in the 100 GeV-10 TeV range and the extension to energies well below 100 GeV and above 100 TeV. CTA will consist of two arrays (one in the north, one in the south) for full sky coverage and will be operated as open observatory. The design of CTA is based on currently available technology. This document reports on the status and presents the major design concepts of CTA. Title: Gravitational redshifts in main-sequence and giant stars Authors: Pasquini, L.; Melo, C.; Chavero, C.; Dravins, D.; Ludwig, H. -G.; Bonifacio, P.; de La Reza, R. Bibcode: 2011A&A...526A.127P Altcode: 2010arXiv1011.4635P Context. Precise analyses of stellar radial velocities is able to reveal intrinsic causes of the wavelength shifts of spectral lines (other than Doppler shifts due to radial motion), such as gravitational redshifts and convective blueshifts.
Aims: Gravitational redshifts in solar-type main-sequence stars are expected to be some 500 m s-1 greater than those in giants. We search for this difference in redshifts among groups of open-cluster stars that share the same average space motion and thus have the same average Doppler shift.
Methods: We observed 144 main-sequence stars and cool giants in the M 67 open cluster using the ESO FEROS spectrograph and obtained radial velocities by means of cross-correlation with a spectral template. Binaries and doubtful members were not analyzed, and average spectra were created for different classes of stars.
Results: The M 67 dwarf and giant radial-velocity distributions are each well represented by Gaussian functions, which share the same apparent average radial velocity to within ≃100 m s-1. In addition, dwarfs in M 67 appear to be dynamically hotter (σ = 0.90 km s-1) than giants (σ = 0.68 km s-1).
Conclusions: We fail to detect any difference in the gravitational redshifts of giants and MS stars. This is probably because of the differential wavelength shifts produced by the different hydrodynamics of dwarf and giant atmospheres. Radial-velocity differences measured between unblended lines in averaged spectra vary with line-strength: stronger lines are more blueshifted in dwarfs than in giants, apparently removing any effect of the gravitational redshift. Synthetic high-resolution spectra are computed from three dimensional (3D) hydrodynamic model atmospheres for both giants and dwarfs, and synthetic wavelength shifts obtained. In agreement with observations, 3D models predict substantially smaller wavelength-shift differences than expected from gravitational redshifts only. The procedures developed could be used to test 3D models for different classes of stars, but will ultimately require high-fidelity spectra for measurements of wavelength shifts in individual spectral lines.

Based on observations collected at ESO, La Silla, Chile, during the agreement between the Observatorio Nacional at Rio de Janeiro and ESO.Table 1 is available in electronic form at http://www.aanda.org and also at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/526/A127 Title: VizieR Online Data Catalog: Velocities of M67 main-sequence and giant stars (Pasquini+, 2011) Authors: Pasquini, L.; Melo, C.; Chavero, C.; Dravins, D.; Ludwig, H. -G.; Bonifacio, P.; de La, Reza R. Bibcode: 2011yCat..35260127P Altcode: 2011yCat..35269127P We observed 144 main-sequence stars and cool giants in the M67 open cluster using the ESO FEROS spectrograph and obtained radial velocities by means of cross-correlation with a spectral template. Binaries and doubtful members were not analyzed, and average spectra were created for different classes of stars.

(1 data file). Title: Stellar intensity interferometry: experimental steps toward long-baseline observations Authors: LeBohec, Stephan; Adams, Ben; Bond, Isobel; Bradbury, Stella; Dravins, Dainis; Jensen, Hannes; Kieda, David B.; Kress, Derrick; Munford, Edward; Nuñez, Paul D.; Price, Ryan; Ribak, Erez; Rose, Joachim; Simpson, Harold; Smith, Jeremy Bibcode: 2010SPIE.7734E..1DL Altcode: 2010arXiv1009.5585L; 2010SPIE.7734E..40L Experiments are in progress to prepare for intensity interferometry with arrays of air Cherenkov telescopes. At the Bonneville Seabase site, near Salt Lake City, a testbed observatory has been set up with two 3-m air Cherenkov telescopes on a 23-m baseline. Cameras are being constructed, with control electronics for either off- or online analysis of the data. At the Lund Observatory (Sweden) and in Technion (Israel) and at the University of Utah (USA), laboratory intensity interferometers simulating stellar observations have been set up and experiments are in progress, using various analog and digital correlators, reaching 1.4 ns time resolution, to analyze signals from pairs of laboratory telescopes. Title: Stellar intensity interferometry: astrophysical targets for sub-milliarcsecond imaging Authors: Dravins, Dainis; Jensen, Hannes; LeBohec, Stephan; Nuñez, Paul D. Bibcode: 2010SPIE.7734E..0AD Altcode: 2010arXiv1009.5815D; 2010SPIE.7734E...9D Intensity interferometry permits very long optical baselines and the observation of sub-milliarcsecond structures. Using planned kilometric arrays of air Cherenkov telescopes at short wavelengths, intensity interferometry may increase the spatial resolution achieved in optical astronomy by an order of magnitude, inviting detailed studies of the shapes of rapidly rotating hot stars with structures in their circumstellar disks and winds, or mapping out patterns of nonradial pulsations across stellar surfaces. Signal-to-noise in intensity interferometry favors high-temperature sources and emission-line structures, and is independent of the optical passband, be it a single spectral line or the broad spectral continuum. Prime candidate sources have been identified among classes of bright and hot stars. Observations are simulated for telescope configurations envisioned for large Cherenkov facilities, synthesizing numerous optical baselines in software, confirming that resolutions of tens of microarcseconds are feasible for numerous astrophysical targets. Title: Stellar intensity interferometry: optimizing air Cherenkov telescope array layouts Authors: Jensen, Hannes; Dravins, Dainis; LeBohec, Stephan; Nuñez, Paul D. Bibcode: 2010SPIE.7734E..1TJ Altcode: 2010SPIE.7734E..54J; 2010arXiv1009.5828J Kilometric-scale optical imagers seem feasible to realize by intensity interferometry, using telescopes primarily erected for measuring Cherenkov light induced by gamma rays. Planned arrays envision 50-100 telescopes, distributed over some 1-4 km2. Although array layouts and telescope sizes will primarily be chosen for gamma-ray observations, also their interferometric performance may be optimized. Observations of stellar objects were numerically simulated for different array geometries, yielding signal-to-noise ratios for different Fourier components of the source images in the interferometric (u, v)-plane. Simulations were made for layouts actually proposed for future Cherenkov telescope arrays, and for subsets with only a fraction of the telescopes. All large arrays provide dense sampling of the (u, v)-plane due to the sheer number of telescopes, irrespective of their geographic orientation or stellar coordinates. However, for improved coverage of the (u, v)-plane and a wider variety of baselines (enabling better image reconstruction), an exact east-west grid should be avoided for the numerous smaller telescopes, and repetitive geometric patterns avoided for the few large ones. Sparse arrays become severely limited by a lack of short baselines, and to cover astrophysically relevant dimensions between 0.1-3 milliarcseconds in visible wavelengths, baselines between pairs of telescopes should cover the whole interval 30-2000 m. Title: Stellar intensity interferometry: imaging capabilities of air Cherenkov telescope arrays Authors: Nuñez, Paul D.; LeBohec, Stephan; Kieda, David; Holmes, Richard; Jensen, Hannes; Dravins, Dainis Bibcode: 2010SPIE.7734E..1CN Altcode: 2010arXiv1009.5599N; 2010SPIE.7734E..39N Sub milli-arcsecond imaging in the visible band will provide a new perspective in stellar astrophysics. Even though stellar intensity interferometry was abandoned more than 40 years ago, it is capable of imaging and thus accomplishing more than the measurement of stellar diameters as was previously thought. Various phase retrieval techniques can be used to reconstruct actual images provided a sufficient coverage of the interferometric plane is available. Planned large arrays of Air Cherenkov telescopes will provide thousands of simultaneously available baselines ranging from a few tens of meters to over a kilometer, thus making imaging possible with unprecedented angular resolution. Here we investigate the imaging capabilities of arrays such as CTA or AGIS used as Stellar Intensity Interferometry receivers. The study makes use of simulated data as could realistically be obtained from these arrays. A Cauchy-Riemann based phase recovery allows the reconstruction of images which can be compared to the pristine image for which the data were simulated. This is first done for uniform disk stars with different radii and corresponding to various exposure times, and we find that the uncertainty in reconstructing radii is a few percent after a few hours of exposure time. Finally, more complex images are considered, showing that imaging at the sub-milli-arc-second scale is possible. Title: High-fidelity spectroscopy at the highest resolutions Authors: Dravins, D. Bibcode: 2010AN....331..535D Altcode: 2010arXiv1002.1190D High-fidelity spectroscopy presents challenges for both observations and in designing instruments. High-resolution and high-accuracy spectra are required for verifying hydrodynamic stellar atmospheres and for resolving intergalactic absorption-line structures in quasars. Even with great photon fluxes from large telescopes with matching spectrometers, precise measurements of line profiles and wavelength positions encounter various physical, observational, and instrumental limits. The analysis may be limited by astrophysical and telluric blends, lack of suitable lines, imprecise laboratory wavelengths, or instrumental imperfections. To some extent, such limits can be pushed by forming averages over many similar spectral lines, thus averaging away small random blends and wavelength errors. In situations where theoretical predictions of lineshapes and shifts can be accurately made (e.g., hydrodynamic models of solar-type stars), the consistency between noisy observations and theoretical predictions may be verified; however this is not feasible for, e.g., the complex of intergalactic metal lines in spectra of distant quasars, where the primary data must come from observations. To more fully resolve lineshapes and interpret wavelength shifts in stars and quasars alike, spectral resolutions on order R=300 000 or more are required; a level that is becoming (but is not yet) available. A grand challenge remains to design efficient spectrometers with resolutions approaching R=1 000 000 for the forthcoming generation of extremely large telescopes. Title: Division Iv: Stars Authors: Spite, Monique; Corbally, Christopher; Dravins, Dainis; Allen, Christine; d'Antona, Francesca; Giridhar, Sunetra; Landstreet, John; Parthasarathy, Mudumba Bibcode: 2010IAUTB..27..188S Altcode: During the General Assembly in Rio de Janeiro the Division IV meeting, and the meetings of the participating working groups and commissions, were held on thursday 6th (session 1 and 2) and friday 7th (sessions 1, 2, 3, 4). Title: Towards a Square-Kilometer Optical Telescope: The Potential of Intensity Interferometry Authors: Dravins, D. Bibcode: 2010RMxAC..38...17D Altcode: Kilometric-scale optical baselines are required for imaging features across stellar disks. Ground-based intensity interferometry is insensitive to both atmospheric turbulence and to imperfections in telescope optics, permitting long-baseline observations even at short optical wavelengths. Its required large flux collectors are becoming available as arrays of atmospheric Cherenkov telescopes set up for studying energetic gamma rays. High-speed detectors and digital signal handling enable very many baselines to be synthesized in software between numerous pairs of telescopes in a digital revival of a technique once pioneered by Hanbury Brown & Twiss. Title: High Time Resolution Astrophysics in the Extremely Large Telescope Era : White Paper Authors: Shearer, A.; Kanbach, G.; Slowikowska, A.; Barbieri, C.; Marsh, T.; Dhillon, V.; Mignani, R.; Dravins, D.; Gouiffes, c.; MacKay, C.; Bonanno, G.; Collins, S. Bibcode: 2010htra.confE..54S Altcode: 2010PoS...108E..54S; 2010arXiv1008.0605S High Time Resolution Astrophysics (HTRA) concerns itself with observations on short scales normally defined as being lower than the conventional read-out time of a CCD. As such it is concerned with condensed objects such as neutron stars, black holes and white dwarfs, surfaces with extreme magnetic reconnection phenomena, as well as with planetary scale objects through transits and occultations. HTRA is the only way to make a major step forward in our understanding of several important astrophysical and physical processes; these include the extreme gravity conditions around neutron stars and stable orbits around stellar mass black holes. Transits, involving fast timing, can give vital information on the size of, and satellites around exoplanets. In the realm of fundamental physics very interesting applications lie in the regime of ultra-high time resolution, where quantum-physical phenomena, currently studied in laboratory physics, may be explored. HTRA science covers the full gamut of observational optical/IR astronomy from asteroids to {\gamma}-rays bursts, contributing to four out of six of AstroNet's fundamental challenges described in their Science Vision for European Astronomy. Giving the European-Extremely Large Telescope (E-ELT) an HTRA capability is therefore importance. We suggest that there are three possibilities for HTRA and E-ELT. These are, firstly giving the E-ELT first light engineering camera an HTRA science capability. Secondly, to include a small HTRA instrument within another instrument. Finally, to have separate fibre feeds to a dedicated HTRA instrument. In this case a small number of fibres could be positioned and would provide a flexible and low cost means to have an HTRA capability. By the time of E-ELT first light, there should be a number of significant developments in fast detector arrays, in particular in the infra-red (IR) region. Title: High-Fidelity Spectroscopy at the Highest Resolution Authors: Dravins, Dainis Bibcode: 2010RvMA...22..191D Altcode: No abstract at ADS Title: Towards the Intensity Interferometry Stellar Imaging System Authors: Daniel, M.; de Wit, W. J.; Dravins, D.; Kieda, D.; LeBohec, S.; Nunez, P.; Ribak, E. Bibcode: 2009arXiv0906.3276D Altcode: The imminent availability of large arrays of large light collectors deployed to exploit atmospheric Cherenkov radiation for gamma-ray astronomy at more than 100GeV, motivates the growing interest in application of intensity interferometry in astronomy. Indeed, planned arrays numbering up to one hundred telescopes will offer close to 5,000 baselines, ranging from less than 50m to more than 1000m. Recent and continuing signal processing technology developments reinforce this interest. Revisiting Stellar Intensity Interferometry for imaging is well motivated scientifically. It will fill the short wavelength (B/V bands) and high angular resolution (< 0.1mas) gap left open by amplitude interferometers. It would also constitute a first and important step toward exploiting quantum optics for astronomical observations, thus leading the way for future observatories. In this paper we outline science cases, technical approaches and schedule for an intensity interferometer to be constructed and operated in the visible using gamma-ray astronomy Air Cherenkov Telescopes as receivers. Title: New Astrophysical Opportunities Exploiting Spatio-Temporal Optical Correlations Authors: Barbieri, C.; Daniel, M. K.; de Wit, W. J.; Dravins, D.; Jensen, H.; Kervella, P.; Le Bohec, S.; Malbet, F.; Nunex, P.; Ralston, J. P.; Ribak, E. N. Bibcode: 2009astro2010S..61B Altcode: 2009arXiv0903.0062B; 2009astro2010S..61D The space-time correlations of streams of photons can provide fundamentally new channels of information about the Universe. Today's astronomical observations essentially measure certain amplitude coherence functions produced by a source. The spatial correlations of wave fields has traditionally been exploited in Michelson-style amplitude interferometry. However the technology of the past was largely incapable of fine timing resolution and recording multiple beams. When time and space correlations are combined it is possible to achieve spectacular measurements that are impossible by any other means. Stellar intensity interferometry is ripe for development and is one of the few unexploited mechanisms to obtain potentially revolutionary new information in astronomy. As we discuss below, the modern use of stellar intensity interferometry can yield unprecedented measures of stellar diameters, binary stars, distance measures including Cepheids, rapidly rotating stars, pulsating stars, and short-time scale fluctuations that have never been measured before. Title: Highest-resolution spectroscopy at the largest telescopes? Authors: Dravins, Dainis Bibcode: 2009MmSAI..80..614D Altcode: 3-D models of stellar atmospheres predict spectral-line shapes with asymmetries and wavelength shifts, but the confrontation with observations is limited by blends, lack of suitable lines, imprecise laboratory wavelengths, and instrumental imperfections. Limits can be pushed by averaging many similar lines, thus averaging small random blends and wavelength errors. In non-solar cases, any detailed verification of 3-D hydrodynamics requires spectra of resolutions R = lambda /Delta lambda ≈ 300,000, soon to become available. An issue is the optical interface of high-resolution spectrometers to [very] large telescopes with their [very] large image scales, possibly requiring adaptive optics. The next observational frontier may be spectroscopy across spatially resolved stellar disks, utilizing optical interferometers and extremely large telescopes. Title: Division IV: Stars Authors: Spite, Monique; Corbally, Christopher J.; Dravins, Dainis; Allen, Christine; d'Antona, Francesca; Giridhar, Sunetra; Landstreet, John D.; Parthasarathy, Mudumba Bibcode: 2009IAUTA..27..193S Altcode: IAU Division IV organizes astronomers studying the characteristics, interior and atmospheric structure, and evolution of stars of all masses, ages, and chemical compositions. Title: ``Ultimate'' information content in solar and stellar spectra. Photospheric line asymmetries and wavelength shifts Authors: Dravins, Dainis Bibcode: 2008A&A...492..199D Altcode: 2008arXiv0810.2533D Context: Spectral-line asymmetries (displayed as bisectors) and wavelength shifts are signatures of the hydrodynamics in solar and stellar atmospheres. Theory may precisely predict idealized lines, but accuracies in real observed spectra are limited by blends, few suitable lines, imprecise laboratory wavelengths, and instrumental imperfections.
Aims: We extract bisectors and shifts until the “ultimate” accuracy limits in highest-quality solar and stellar spectra, so as to understand the various limits set by (i) stellar physics (number of relevant spectral lines, effects of blends, rotational line broadening); by (ii) observational techniques (spectral resolution, photometric noise); and by (iii) limitations in laboratory data.
Methods: Several spectral atlases of the Sun and bright solar-type stars were examined for those thousands of “unblended” lines with the most accurate laboratory wavelengths, yielding bisectors and shifts as averages over groups of similar lines. Representative data were obtained as averages over groups of similar lines, thus minimizing the effects of photometric noise and of random blends.
Results: For the solar-disk center and integrated sunlight, the bisector shapes and shifts were extracted for previously little-studied species (Fe II, Ti I, Ti II, Cr II, Ca I, C I), using recently determined and very accurate laboratory wavelengths. In Procyon and other F-type stars, a sharp blueward bend in the bisector near the spectral continuum is confirmed, revealing line saturation and damping wings in upward-moving photospheric granules. Accuracy limits are discussed: “astrophysical” noise due to few measurable lines, finite instrumental resolution, superposed telluric absorption, inaccurate laboratory wavelengths, and calibration noise in spectrometers, together limiting absolute lineshift studies to ≈50-100 m s-1.
Conclusions: Spectroscopy with resolutions λ/Δλ ≈ 300 000 and accurate wavelength calibration will enable bisector studies for many stars. Circumventing remaining limits of astrophysical noise in line-blends and rotationally smeared profiles may ultimately require spectroscopy across spatially resolved stellar disks, utilizing optical interferometers and extremely large telescopes of the future.

Tables are only available in electronic form at http://www.aanda.org Title: Toward a revival of stellar intensity interferometry Authors: LeBohec, Stephan; Barbieri, Cesare; de Wit, Willem-Jan; Dravins, Dainis; Feautrier, Philippe; Foellmi, Cédric; Glindemann, Andreas; Hall, Jeter; Holder, Jamie; Holmes, Richard; Kervella, Pierre; Kieda, David; Le Coarer, Etienne; Lipson, Stephan; Malbet, Fabien; Morel, Sébastien; Nuñez, Paul; Ofir, Aviv; Ribak, Erez; Saha, Swapan; Schoeller, Markus; Zhilyaev, Boriz; Zinnecker, Hans Bibcode: 2008SPIE.7013E..2EL Altcode: 2008SPIE.7013E..72L Building on technological developments over the last 35 years, intensity interferometry now appears a feasible option by which to achieve diffraction-limited imaging over a square-kilometer synthetic aperture. Upcoming Atmospheric Cherenkov Telescope projects will consist of up to 100 telescopes, each with ~100m2 of light gathering area, and distributed over ~1km2. These large facilities will offer thousands of baselines from 50m to more than 1km and an unprecedented (u,v) plane coverage. The revival of interest in Intensity Interferometry has recently led to the formation of a IAU working group. Here we report on various ongoing efforts towards implementing modern Stellar Intensity Interferometry. Title: Toward a diffraction-limited square-kilometer optical telescope: digital revival of intensity interferometry Authors: Dravins, Dainis; LeBohec, Stephan Bibcode: 2008SPIE.6986E..09D Altcode: 2008SPIE.6986E...9D Much of the progress in astronomy follows imaging with improved resolution. In observing stars, current capabilities are only marginal in beginning to image the disks of a few, although many stars will appear as surface objects for baselines of hundreds of meters. Since atmospheric turbulence makes ground-based phase interferometry challenging for such long baselines, kilometric space telescope clusters have been proposed for imaging stellar surface details. The realization of such projects remains uncertain, but comparable imaging could be realized by ground-based intensity interferometry. While insensitive to atmospheric turbulence and imperfections in telescope optics, the method requires large flux collectors, such as being set up as arrays of atmospheric Cherenkov telescopes for studying energetic gamma rays. High-speed detectors and digital signal handling enable very many baselines to be synthesized between pairs of telescopes, while stars may be tracked across the sky by electronic time delays. First observations with digitally combined optical instruments have now been made with pairs of 12-meter telescopes of the VERITAS array in Arizona. Observing at short wavelengths adds no problems, and similar techniques on an extremely large telescope could achieve diffraction-limited imaging down to the atmospheric cutoff, achieving a spatial resolution significantly superior by that feasible by adaptive optics operating in the red or near-infrared. Title: Photon Correlation Spectroscopy for Observing Natural Lasers Authors: Dravins, Dainis; Germanà, Claudio Bibcode: 2008AIPC..984..216D Altcode: 2007arXiv0710.1756D Natural laser emission may be produced whenever suitable atomic energy levels become overpopulated. Strong evidence for laser emission exists in astronomical sources such as Eta Carinae, and other luminous stars. However, the evidence is indirect in that the laser lines have not yet been spectrally resolved. The lines are theoretically estimated to be extremely narrow, requiring spectral resolutions very much higher (R~108) than possible with ordinary spectroscopy. Such can be attained with photon-correlation spectroscopy on nanosecond timescales, measuring the autocorrelation function of photon arrival times to obtain the coherence time of light, and thus the spectral linewidth. A particular advantage is the insensitivity to spectral, spatial, and temporal shifts of emission-line components due to local velocities and probable variability of `hot-spots' in the source. A laboratory experiment has been set up, simulating telescopic observations of cosmic laser emission. Numerically simulated observations estimate how laser emission components within realistic spectral and spatial passbands for various candidate sources carry over to observable statistical functions. Title: Intrinsic Lineshifts in Astronomical Spectra Authors: Dravins, Dainis Bibcode: 2008psa..conf..139D Altcode: Spectral-line displacements away from the wavelengths naively expected from the Doppler shift due to radial motion may originate as convective shifts (correlated velocity and brightness patterns), as gravitational redshifts, or be induced by wave motions. Convective shifts are important tools for testing 3-dimensional stellar hydrodynamics; analogous shifts may be expected even in intergalactic absorption lines (convection driven by AGNs in clusters of galaxies). Title: Photonic Astronomy and Quantum Optics Authors: Dravins, Dainis Bibcode: 2008ASSL..351...95D Altcode: 2007astro.ph..1220D Quantum optics potentially offers an information channel from the Universe beyond the established ones of imaging and spectroscopy. All existing cameras and all spectrometers measure aspects of the first-order spatial and/or temporal coherence of light. However, light has additional degrees of freedom, manifest in the statistics of photon arrival times, or in the amount of photon orbital angular momentum. Such quantum-optical measures may carry information on how the light was created at the source, and whether it reached the observer directly or via some intermediate process. Astronomical quantum optics may help to clarify emission processes in natural laser sources and in the environments of compact objects, while high-speed photon-counting with digital signal handling enables multi-element and long-baseline versions of the intensity interferometer. Time resolutions of nanoseconds are required, as are large photon fluxes, making photonic astronomy very timely in an era of large telescopes. Title: Division Iv: Stars Authors: Dravins, Dainis; Spite, Monique; Barbuy, Beatriz; Corbally, Christopher; Dziembowski, Wojciech; Hartkopf, William I.; Sneden, Christopher Bibcode: 2007IAUTB..26..145D Altcode: Division IV organizes astronomers studying the characterization, interior and atmospheric structure of stars of all masses, ages and chemical compositions. Title: Commission 36: Theory of Stellar Atmospheres Authors: Spite, Monique; Landstreet, John D.; Asplund, Martin; Ayres, Thomas R.; Balachandran, Suchitra C.; Dravins, Dainis; Hauschildt, Peter H.; Kiselman, Dan; Nagendra, K. N.; Sneden, Christopher; Tautvaišiené, Grazina; Werner, Klaus Bibcode: 2007IAUTB..26..160S Altcode: The business meeting of Commission 36 was held during the General Assembly in Prague on 16 August. It was attended by about 15 members. The issues presented included a review of the work made by members of Commission 36, and the election of the new Organising Committee. We note that a comprehensive report on the activities of the commission during the last triennium has been published in Reports on Astronomy, Transactions IAU Volume XXVIA. The scientific activity of the members of the commission has been very intense, and has led to the publication of a large number of papers. Title: Commission 30: Radial Velocities Authors: Nordström, Birgitta; Udry, Stéphane; Tokovinin, Andrei A.; Dravins, Dainis; Fekel, Francis C.; Glushkova, Elena V.; Levato, Hugo; Pourbaix, Dimitri; Smith, Myron A.; Szabados, Laszlo; Torres, Guillermo Bibcode: 2007IAUTB..26..197N Altcode: The president welcomed all the participants of the Business Meeting and remarked that several of the major ongoing and planned Radial Velocity projects were well represented. Title: Wolfe Creek Crater in Western Australia Authors: Dravins, Dainis Bibcode: 2007S&T...114d.102D Altcode: No abstract at ADS Title: Searching for Optical Lasers in Emission-Line Stars Authors: Dravins, Dainis; Germano, Claudio Bibcode: 2007jena.confE..26D Altcode: Natural laser emission may be produced whenever radiative mechanisms overpopulate suitable atomic energy levels. Well-studied cases are optical emission lines from gas ejecta around the extremely luminous star Eta Carinae. Theoretically expected linewidths are very narrow, requiring spectral resolution around 100 million, far beyond classical spectroscopy. Such resolutions are feasible with nanosecond-resolution photon-correlation spectroscopy, a quantum-optical method of analyzing the autocorrelation function of photon arrival times. Observations with large telescopes are simulated both numerically, and in a laboratory experiment measuring narrow emission lines with photon-counting avalanche photodiodes. Further discussion: http://www.astro.lu.se/~dainis/ Title: Very fast photon counting photometers for astronomical applications: from QuantEYE to AquEYE Authors: Naletto, Giampiero; Barbieri, Cesare; Occhipinti, Tommaso; Tamburini, Fabrizio; Billotta, Sergio; Cocuzza, Silvio; Dravins, Dainis Bibcode: 2007SPIE.6583E..0BN Altcode: 2007SPIE.6583E...9N In the great majority of the cases, present astronomical observations are realized analyzing only first order spatial or temporal coherence properties of the collected photon stream. However, a lot of information is "hidden" in the second and higher order coherence terms, as details about a possible stimulated emission mechanism or about photon scattering along the travel from the emitter to the telescope. The Extremely Large Telescopes of the future could provide the high photon flux needed to extract this information. To this aim we have recently studied a possible focal plane instrument, named QuantEYE, for the 100 m OverWhelmingly Large Telescope of the European Southern Observatory. This instrument is the fastest photon counting photometer ever conceived, with an array of 100 parallel channels operating simultaneously, to push the time tagging capabilities toward the pico-second region. To acquire some experience with this novel type of instrumentation, we are now in the process of realizing a small instrument prototype (AquEYE) for the Asiago 182 cm telescope, for then building a larger instrument for one of the existing 8-10 m class telescopes. We hope that the results we will obtain by these instruments will open a new frontier in the astronomical observations. Title: Commission 36: Theory of Stellar Atmospheres Authors: Spite, Monique; Landstreet, John; Asplund, M.; Ayres, T.; Balachandran, S.; Dravins, D.; Hauschildt, P.; Kiselman, D.; Nagendra, K. N.; Sneden, C.; Tautvaišiené, G.; Werner, K. Bibcode: 2007IAUTA..26..215S Altcode: Commission 36 covers all the physics of stellar atmospheres. The scientific activity in this large field has been very intense during the last triennium and led to the publication of a large number of papers which makes an exhaustive report practically not feasible. As a consequence we decided to keep the format of the preceding report: first a list of areas of current research, then web links for obtaining further information. Title: Commission 12: Solar Radiation & Structure Authors: Bogdan, Thomas. J.; Martínez Pillet, Valentin; Asplund, M.; Christensen-Dalsgaard, J.; Cauzzi, G.; Cram, L. E.; Dravins, D.; Gan, W.; Henzl, P.; Kosovichev, A.; Mariska, J. T.; Rovira, M. G.; Venkatakrishnan, P. Bibcode: 2007IAUTA..26...89B Altcode: Commission 12 covers research on the internal structure and dynamics of the Sun, the "quiet" solar atmosphere, solar radiation and its variability, and the nature of relatively stable magnetic structures like sunspots, faculae and the magnetic network. There is considerable productive overlap with the other Commissions of Division II as investigations move progressively toward the fertile intellectual boundaries between traditional research disciplines. In large part, the solar magnetic field provides the linkage that connects these diverse themes. The same magnetic field that produces the more subtle variations of solar structure and radiative output over the 11 yr activity cycle is also implicated in rapid and often violent phenomena such as flares, coronal mass ejections, prominence eruptions, and episodes of sporadic magnetic reconnection.The last three years have again brought significant progress in nearly all the research endeavors touched upon by the interests of Commission 12. The underlying causes for this success remain the same: sustained advances in computing capabilities coupled with diverse observations with increasing levels of spatial, temporal and spectral resolution. It is all but impossible to deal with these many advances here in anything except a cursory and selective fashion. Thankfully, the Living Reviews in Solar Physics; has published several extensive reviews over the last two years that deal explicitly with issues relevant to the purview of Commission 12. The reader who is eager for a deeper and more complete understanding of some of these advances is directed to http://www.livingreviews.org for access to these articles. Title: Division IV: Stars Authors: Dravins, Dainis; Barbuy, Beatriz; Corbally, Christopher; Dziembowski, Wojciech; Hartkopf, William; Sneden, Christopher; Spite, Monique Bibcode: 2007IAUTA..26..191D Altcode: The IAU Division IV (`Stars') organizes astronomers studying the characteristics, interior and atmospheric structure, and evolution of stars of all masses, ages, and chemical compositions. Title: COMMISSION 30: Radial Velocities* Authors: Nordström, Birgitta; Udry, Stephane; Dravins, D.; Fekel, F.; Glushkova, E.; Levato, H.; Pourbaix, D.; Smith, M. A.; Szabados, L.; Torres, G. Bibcode: 2007IAUTA..26E...1N Altcode: This report from Commission 30 covers the salient areas in which major progress has been made in the triennium covered by the present volume. The principal scientific areas are: The Milky Way, star clusters, spectroscopic binaries, extrasolar planets, pulsating stars and stellar oscillations. Following these, an account is given of the progress in techniques and methodology for radial velocity determinations. Finally, a summary is given of the progress made by the working groups of the Commission, followed by a list of key papers in the triennium. A more extensive report also covering extragalactic work, which due to unforeseen circumstances could not be included here, can be found at the web page of Commission 30 (http://www.iau.org/IAU/Organization/divcom/). Title: Astronomical applications of quantum optics for extremely large telescopes Authors: Barbieri, C.; Dravins, D.; Occhipinti, T.; Tamburini, F.; Naletto, G.; da Deppo, V.; Fornasier, S.; D'Onofrio, M.; Fosbury, R. A. E.; Nilsson, R.; Uthas, H. Bibcode: 2007JMOp...54..191B Altcode: No abstract at ADS Title: QuantEYE: a quantum optics instrument for extremely large telescopes Authors: Naletto, Giampiero; Barbieri, Cesare; Dravins, Dainis; Occhipinti, Tommaso; Tamburini, Fabrizio; Da Deppo, Vania; Fornasier, Sonia; D'Onofrio, Mauro; Fosbury, Robert A. E.; Nilsson, Ricky; Uthas, Helena; Zampieri, Luca Bibcode: 2006SPIE.6269E..1WN Altcode: 2006SPIE.6269E..62N We have carried out a conceptual study for an instrument (QuantEYE) capable to detect and measure photon-stream statistics, e.g. power spectra or autocorrelation functions. Such functions increase with the square of the detected signal, implying an enormously increased sensitivity at the future Extremely Large Telescopes, such as the OverWhelmingly Large (OWL) telescope of the European Southern Observatory (ESO). Furthermore, QuantEYE will have the capability of exploring astrophysical variability on microsecond and nanosecond scales, down to the quantum-optical limit. Expected observable phenomena include instabilities of photon-gas bubbles in accretion flows, p-mode oscillations in neutron stars, and quantum-optical photon bunching in time. This paper describes QuantEYE, an instrument aimed to realize the just described science, proposed for installation at the ESO OWL telescope focal plane. The adopted optical solution is relatively simple and possible with actual technologies, the main constraint essentially being the present limited availability of very fast photon counting detector arrays. Also some possible alternative designs are described, assuming a future technology development of fast photon counting detector arrays. Title: Astronomical quantum optics with Extremely Large Telescopes Authors: Dravins, D.; Barbieri, C.; Fosbury, R. A. E.; Naletto, G.; Nilsson, R.; Occhipinti, T.; Tamburini, F.; Uthas, H.; Zampieri, L. Bibcode: 2006IAUS..232..502D Altcode: Modern optics focuses on photonics and quantum optics, studying individual photons and statistics of photon streams. Those can be complex and carry information beyond that recorded by imaging, spectroscopy, polarimetry or interferometry. Since [almost] all astronomy is based upon the interpretation of subtleties in the light from astronomical sources, quantum optics has the potential of becoming another information channel from the Universe. The observability of quantum statistics increases rapidly with telescope size making photonic astronomy very timely in an era of very large telescopes. Title: QuantEYE, the quantum optics instrument for OWL Authors: Barbieri, C.; da Deppo, V.; D'Onofrio, M.; Dravins, D.; Fornasier, S.; Fosbury, R. A. E.; Naletto, G.; Nilsson, R.; Occhipinti, T.; Tamburini, F.; Uthas, H.; Zampieri, L. Bibcode: 2006IAUS..232..506B Altcode: A brief description of the QuantEYE instrument proposed as a focal plane instrument for OWL is given. This instrument is dedicated to the very high speed observation of many active phenomena with a photon counting capability of up to 1GHz. The system samples the beam in 10×10 subpupils, each focused on a fast photon counting detector. Title: QuantEYE: The Quantum Optics Instrument for OWL Authors: Dravins, D.; Barbieri, C.; Fosbury, R. A. E.; Naletto, G.; Nilsson, R.; Occhipinti, T.; Tamburini, F.; Uthas, H.; Zampieri, L. Bibcode: 2005astro.ph.11027D Altcode: QuantEYE is designed to be the highest time-resolution instrument on ESO:s planned Overwhelmingly Large Telescope, devised to explore astrophysical variability on microsecond and nanosecond scales, down to the quantum-optical limit. Expected phenomena include instabilities of photon-gas bubbles in accretion flows, p-mode oscillations in neutron stars, and quantum-optical photon bunching in time. Precise timescales are both variable and unknown, and studies must be of photon-stream statistics, e.g., their power spectra or autocorrelations. Such functions increase with the square of the intensity, implying an enormously increased sensitivity at the largest telescopes. QuantEYE covers the optical, and its design involves an array of photon-counting avalanche-diode detectors, each viewing one segment of the OWL entrance pupil. QuantEYE will work already with a partially filled OWL main mirror, and also without [full] adaptive optics. Title: Report by the ESA-ESO Working Group on Extra-Solar Planets Authors: Perryman, M.; Hainaut, O.; Dravins, D.; Leger, A.; Quirrenbach, A.; Rauer, H.; Kerber, F.; Fosbury, R.; Bouchy, F.; Favata, F.; Fridlund, M.; Gilmozzi, R.; Lagrange, A. -M.; Mazeh, T.; Rouan, D.; Udry, S.; Wambsganss, J. Bibcode: 2005astro.ph..6163P Altcode: Various techniques are being used to search for extra-solar planetary signatures, including accurate measurement of radial velocity and positional (astrometric) displacements, gravitational microlensing, and photometric transits. Planned space experiments promise a considerable increase in the detections and statistical knowledge arising especially from transit and astrometric measurements over the years 2005-15, with some hundreds of terrestrial-type planets expected from transit measurements, and many thousands of Jupiter-mass planets expected from astrometric measurements. Beyond 2015, very ambitious space (Darwin/TPF) and ground (OWL) experiments are targeting direct detection of nearby Earth-mass planets in the habitable zone and the measurement of their spectral characteristics. Beyond these, `Life Finder' (aiming to produce confirmatory evidence of the presence of life) and `Earth Imager' (some massive interferometric array providing resolved images of a distant Earth) appear as distant visions. This report, to ESA and ESO, summarises the direction of exo-planet research that can be expected over the next 10 years or so, identifies the roles of the major facilities of the two organisations in the field, and concludes with some recommendations which may assist development of the field. The report has been compiled by the Working Group members and experts over the period June-December 2004. Title: ESA-ESO Working Group on "Extra-solar Planets" Authors: Perryman, M.; Hainaut, O.; Dravins, D.; Leger, A.; Quirrenbach, A.; Rauer, H.; Kerber, F.; Fosbury, R.; Bouchy, F.; Favata, F.; Fridlund, M.; Gilmozzi, R.; Lagrange, A. -M.; Mazeh, T.; Rouan, D.; Udry, S.; Wambsganss, J. Bibcode: 2005ewg1.rept.....P Altcode: No abstract at ADS Title: Wavelength shifts in solar-type spectra Authors: Dravins, D.; Lindegren, L.; Ludwig, H. -G.; Madsen, S. Bibcode: 2005ESASP.560..113D Altcode: 2004astro.ph..9212D; 2005csss...13..113D Spectral-line displacements away from the wavelengths naively expected from the Doppler shift caused by stellar radial motion may originate as convective shifts (correlated velocity and brightness patterns in the photosphere), as gravitational redshifts, or perhaps be induced by wave motions. Absolute lineshifts, in the past studied only for the Sun, are now accessible also for other stars thanks to astrometric determination of stellar radial motion, and spectrometers with accurate wavelength calibration. Comparisons between spectroscopic apparent radial velocities and astrometrically determined radial motions reveal greater spectral blueshifts in F-type stars than in the Sun (as theoretically expected from their more vigorous convection), further increasing in A-type stars (possibly due to atmospheric shockwaves). An important near-future development to enable a further analysis of stellar surface structure will be the study of wavelength variations across spatially resolved stellar disks, e.g., the center-to-limb wavelength changes along a stellar diameter, and their spatially resolved time variability. Title: Intrinsic Wavelength Shifts in Stellar Spectra Authors: Dravins, D.; Lindegren, L.; Ludwig, H. -G.; Madsen, S. Bibcode: 2004AAS...20517004D Altcode: 2004BAAS...36.1624D Wavelengths of stellar spectral lines do not have the precise values `naively' expected from laboratory wavelengths merely Doppler-shifted by stellar radial motion. Slight displacements may originate as convective shifts (correlated velocity and brightness patterns in the photosphere), as gravitational redshifts, or perhaps be induced by wave motions. Intrinsic lineshifts thus reveal stellar surface structure, while possible periodic changes (during a stellar activity cycle, say) need to be segregated from variability induced by orbiting exoplanets.

Absolute lineshifts can now be studied also in some stars other than the Sun, thanks to astrometric determinations of stellar radial motion. Comparisons between spectroscopic apparent radial velocities and astrometrically determined radial motions reveal greater spectral blueshifts in F-type stars than in the Sun (as theoretically expected from their more vigorous convection), further increasing in A-type stars (possibly due to atmospheric shockwaves).

Solar spectral atlases, and high-resolution spectra (from UVES on ESO VLT) of a dozen solar-type stars are being surveyed for `unblended' photospheric lines of most atomic species with accurate laboratory wavelengths available. One aim is to understand the ultimate information content of stellar spectra, and in what detail it will be feasible to verify models of stellar atmospheric hydrodynamics. These may predict line asymmetries (bisectors) and shifts for widely different classes of lines, but there will not result any comparison with observations if such lines do not exist in real spectra.

An expected near-future development in stellar physics is spatially resolved spectroscopy across stellar disks, enabled by optical interferometry and adaptive optics on very large telescopes. Stellar surface structure manifests itself in the center-to-limb wavelength changes along a stellar diameter, and their spatially resolved time variability, diagnostics which already now can be theoretically modeled. Title: Absolute Wavelength Shifts- A New Diagnostic for Rapidly Rotating Stars Authors: Dravins, D. Bibcode: 2004IAUS..215...27D Altcode: 2003astro.ph..2592D Accuracies reached in space astrometry now permit the accurate determination of astrometric radial velocities, without any use of spectroscopy. Knowing this true stellar motion, spectral shifts intrinsic to stellar atmospheres can be identified, for instance gravitational redshifts and those caused by velocity fields on stellar surfaces. The astrometric accuracy is independent of any spectral complexity, such as the smeared-out line profiles of rapidly rotating stars. Besides a better determination of stellar velocities, this permits more precise studies of atmospheric dynamics, such as possible modifications of stellar surface convection (granulation) by rotation-induced forces, as well as a potential for observing meridional flows across stellar surfaces. Title: Intrinsic spectral blueshifts in rapidly rotating stars? Authors: Madsen, Søren; Dravins, Dainis; Ludwig, Hans-Günter; Lindegren, Lennart Bibcode: 2003A&A...411..581M Altcode: 2003astro.ph..9346M Spectroscopic radial velocities for several nearby open clusters suggest that spectra of (especially earlier-type) rapidly rotating stars are systematically blueshifted by 3 km s-1 or more, relative to the spectra of slowly rotating ones. Comparisons with astrometrically determined radial motions in the Hyades suggests this to be an absolute blueshift, relative to wavelengths naively expected from stellar radial motion and gravitational redshift. Analogous trends are seen also in most other clusters studied (Pleiades, Coma Berenices, Praesepe, alpha Persei, IC 2391, NGC 6475, IC 4665, NGC 1976 and NGC 2516). Possible mechanisms are discussed, including photospheric convection, stellar pulsation, meridional circulation, and shock-wave propagation, as well as effects caused by template mismatch in determining wavelength displacements. For early-type stars, a plausible mechanism is shock-wave propagation upward through the photospheric line-forming regions. Such wavelength shifts thus permit studies of certain types of stellar atmospheric dynamics and - irrespective of their cause - may influence deduced open-cluster membership (when selected from common velocity) and deduced cluster dynamics (some types of stars might show fortuitous velocity patterns). Title: The fundamental definition of ``radial velocity'' Authors: Lindegren, Lennart; Dravins, Dainis Bibcode: 2003A&A...401.1185L Altcode: 2003astro.ph..2522L Accuracy levels of metres per second require the fundamental concept of ``radial velocity'' for stars and other distant objects to be examined, both as a physical velocity, and as measured by spectroscopic and astrometric techniques. Already in a classical (non-relativistic) framework the line-of-sight velocity component is an ambiguous concept, depending on whether, e.g., the time of light emission (at the object) or that of light detection (by the observer) is used for recording the time coordinate. Relativistic velocity effects and spectroscopic measurements made inside gravitational fields add further complications, causing wavelength shifts to depend, e.g., on the transverse velocity of the object and the gravitational potential at the source. Aiming at definitions that are unambiguous at accuracy levels of 1 m s-1, we analyse different concepts of radial velocity and their interrelations. At this accuracy level, a strict separation must be made between the purely geometric concepts on one hand, and the spectroscopic measurement on the other. Among the geometric concepts we define kinematic radial velocity, which corresponds most closely to the ``textbook definition'' of radial velocity as the line-of-sight component of space velocity; and astrometric radial velocity, which can be derived from astrometric observations. Consistent with these definitions, we propose strict definitions also of the complementary kinematic and astrometric quantities, namely transverse velocity and proper motion. The kinematic and astrometric radial velocities depend on the chosen spacetime metric, and are accurately related by simple coordinate transformations. On the other hand, the observational quantity that should result from accurate spectroscopic measurements is the barycentric radial-velocity measure. This is independent of the metric, and to first order equals the line-of-sight velocity. However, it is not a physical velocity, and cannot be accurately transformed to a kinematic or astrometric radial velocity without additional assumptions and data in modelling the process of light emission from the source, the transmission of the signal through space, and its recording by the observer. For historic and practical reasons, the spectroscopic radial-velocity measure is expressed in velocity units as czB, where c is the speed of light and zB is the observed relative wavelength shift reduced to the solar-system barycentre, at an epoch equal to the barycentric time of light arrival. The barycentric radial-velocity measure and the astrometric radial velocity are defined by recent resolutions adopted by the International Astronomical Union (IAU), the motives and consequences of which are explained in this paper. Title: Absolute Lineshifts - a New Diagnostic for Stellar Hydrodynamics Authors: Dravins, D. Bibcode: 2003IAUS..210P..E4D Altcode: 2003astro.ph..2591D For hydrodynamic model atmospheres, absolute lineshifts are becoming an observable diagnostic tool beyond the classical ones of line-strength, -width, -shape, and -asymmetry. This is the wavelength displacement of different types of spectral lines away from the positions naively expected from the Doppler shift caused by stellar radial motion. Caused mainly by correlated velocity and brightness patterns in granular convection, such absolute lineshifts could in the past be studied only for the Sun (since the relative Sun-Earth motion, and the ensuing Doppler shift is known). For other stars, this is now becoming possible thanks to three separate developments: (a) Astrometric determination of stellar radial motion; (b) High-resolution spectrometers with accurate wavelength calibration, and (c) Accurate laboratory wavelengths for several atomic species. Absolute lineshifts offer a tool to segregate various 2- and 3-dimensional models, and to identify non-LTE effects in line formation. Title: Commission 36: Theory of stellar atmospheres (Théorie des atmosphères stellaires) Authors: Dravins, Dainis Bibcode: 2003IAUTA..25..242D Altcode: 2003IAUTr..25A.242D No abstract at ADS Title: Critical science for the largest telescopes: science drivers for a 100m ground-based optical-IR telescope Authors: Hawarden, Timothy G.; Dravins, Dainis; Gilmore, Gerard F.; Gilmozzi, Roberto; Hainaut, Olivier; Kuijken, K.; Leibindgut, Bruno; Merrifield, Michael; Queloz, Didier; Wyse, Rosie Bibcode: 2003SPIE.4840..299H Altcode: Extremely large filled-aperture ground-based optical-IR telescopes, or ELTs, ranging from 20 to 100m in diameter, are now being proposed. The all-important choice of the aperture must clearly be driven by the potential science offered. We here highlight science goals from the Leiden Workshop in May 2001 suggesting that for certain critical observations the largest possible aperture - assumed to be 100m (the proposed European OverWhelmingly Large telescope (OWL) - is strongly to be desired. Examples from a long list include: COSMOLOGY: * Identifying the first sources of ionisation in the universe, out to z >=14 * Identifying and stufdying the first generation of dusty galaxies * More speculatively, observing the formation of the laws of physics, via the evolution of the fundamental physical contants in the very early Universe, by high-resolution spectroscopy of very distant quasars. NEARER GALAXIES: *Determining detailed star-formation histories of galaxies out to the Virtgo Cluster, and hence for all major galaxy types (not just those available close to the Local Group of galaxies). THE SOLAR SYSTEM: A 100-m telescope would do the work of a flotilla of fly-by space probes for investigations ranging from the evolution of planetary sutfaces and atmospheres to detailed surface spectroscopy of Kuiper Belt Objects. (Such studies could easily occupy it full-time.) EARTHLIKE PLANETS OF NEARBY STARS: A propsect so exciting as perhaps to justify the 100-m telescope on its own, is that of the direct detection of earthlike planets of solar-type stars by imaging, out to at least 25 parsecs (80 light years) from the sun, followed by spectroscopic and photometric searches for the signature of life on the surfaces of nearer examples. Title: HARPS: ESO's coming planet searcher. Chasing exoplanets with the La Silla 3.6-m telescope Authors: Pepe, F.; Mayor, M.; Rupprecht, G.; Avila, G.; Ballester, P.; Beckers, J. -L.; Benz, W.; Bertaux, J. -L.; Bouchy, F.; Buzzoni, B.; Cavadore, C.; Deiries, S.; Dekker, H.; Delabre, B.; D'Odorico, S.; Eckert, W.; Fischer, J.; Fleury, M.; George, M.; Gilliotte, A.; Gojak, D.; Guzman, J. -C.; Koch, F.; Kohler, D.; Kotzlowski, H.; Lacroix, D.; Le Merrer, J.; Lizon, J. -L.; Lo Curto, G.; Longinotti, A.; Megevand, D.; Pasquini, L.; Petitpas, P.; Pichard, M.; Queloz, D.; Reyes, J.; Richaud, P.; Sivan, J. -P.; Sosnowska, D.; Soto, R.; Udry, S.; Ureta, E.; van Kesteren, A.; Weber, L.; Weilenmann, U.; Wicenec, A.; Wieland, G.; Christensen-Dalsgaard, J.; Dravins, D.; Hatzes, A.; Kürster, M.; Paresce, F.; Penny, A. Bibcode: 2002Msngr.110....9P Altcode: An extensive review of past, present and future research on extrasolar planets is given in the article “Extrasolar Planets” by N. Santos et al. in the present issue of The Messenger. Here we want to mention only that the search for extrasolar planets and the interpretation of the scientific results have evolved in recent years into one of the most exciting and dynamic research topics in modern astronomy. Title: Astrometric radial velocities. III. Hipparcos measurements of nearby star clusters and associations Authors: Madsen, Søren; Dravins, Dainis; Lindegren, Lennart Bibcode: 2002A&A...381..446M Altcode: 2001astro.ph.10617M Radial motions of stars in nearby moving clusters are determined from accurate proper motions and trigonometric parallaxes, without any use of spectroscopy. Assuming that cluster members share the same velocity vector (apart from a random dispersion), we apply a maximum-likelihood method on astrometric data from Hipparcos to compute radial and space velocities (and their dispersions) in the Ursa Major, Hyades, Coma Berenices, Pleiades, and Praesepe clusters, and for the Scorpius-Centaurus, alpha Persei, and ``HIP 98321'' associations. The radial motion of the Hyades cluster is determined to within 0.4 km s-1 (standard error), and that of its individual stars to within 0.6 km s-1. For other clusters, Hipparcos data yield astrometric radial velocities with typical accuracies of a few km s-1. A comparison of these astrometric values with spectroscopic radial velocities in the literature shows a good general agreement and, in the case of the best-determined Hyades cluster, also permits searches for subtle astrophysical differences, such as evidence for enhanced convective blueshifts of F-dwarf spectra, and decreased gravitational redshifts in giants. Similar comparisons for the Scorpius OB2 complex indicate some expansion of its associations, albeit slower than expected from their ages. As a by-product from the radial-velocity solutions, kinematically improved parallaxes for individual stars are obtained, enabling Hertzsprung-Russell diagrams with unprecedented accuracy in luminosity. For the Hyades (parallax accuracy 0.3 mas), its main sequence resembles a thin line, possibly with wiggles in it. Although this main sequence has underpopulated regions at certain colours (previously suggested to be ``Böhm-Vitense gaps''), such are not visible for other clusters, and are probably spurious. Future space astrometry missions carry a great potential for absolute radial-velocity determinations, insensitive to the complexities of stellar spectra. Based on observations by the ESA Hipparcos satellite. Extended versions of Tables \ref{tab1} and \ref{tab2} are available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.125.8) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/381/446 Title: VizieR Online Data Catalog: Astrometric Radial Velocities. III. (Madsen+, 2002) Authors: Madsen, S.; Dravins, D.; Lindegren, L. Bibcode: 2001yCat..33810446M Altcode: Astrometrically determined kinematic data are given for nearby clusters and associations, including astrometric radial velocities and kinematically improved parallaxes for individual stars. The astrometric radial velocities are determined independent of spectroscopy. Table 1 gives the space velocities and internal velocity dispersions of the clusters and associations. The electronic Table1 (Table1.dat) is an extended version of Table 1 in the journal paper, now including the full covariances of the space velocity components as well as the space motion in spherical coordinates. Table 2 gives the astrometric radial velocities and kinematically improved parallaxes for the individual stars. The electronic Table 2 is an extended version of Table 2 in the journal paper, now including all clusters and associations studied; results using data from both the Hipparcos and Tycho-2catalogues, as well as the standard errors for all deduced quantities. The electronic Table 2 is divided into 10 sub-tables (table1a.dat through table2j.dat), one for each cluster or association. (11 data files). Title: The Velocity Dispersion of the Hyades as a Function of Mass and Radius Authors: Madsen, S.; Lindegren, L.; Dravins, D. Bibcode: 2001ASPC..228..506M Altcode: 2001dscm.conf..506M No abstract at ADS Title: Quantum-Optical Signatures of Stimulated Emission Authors: Dravins, D. Bibcode: 2001ASPC..242..339D Altcode: 2001ecom.conf..339D No abstract at ADS Title: Division IV: Stars Authors: Barbuy, Beatriz; Cram, L.; Dravins, D.; Evans, T. L.; Mathys, G.; Scarfe, C.; VandenBerg, D. Bibcode: 2001IAUTB..24..157B Altcode: No abstract at ADS Title: Absolute Lineshifts as Signatures of Stellar Surface Convection (CD-ROM Directory: contribs/dravins) Authors: Dravins, D. Bibcode: 2001ASPC..223..778D Altcode: 2001csss...11..778D No abstract at ADS Title: Avalanche diodes as photon-counting detectors in astronomical photometry Authors: Dravins, Dainis; Faria, Daniel; Nilsson, Bo Bibcode: 2000SPIE.4008..298D Altcode: Photon-counting silicon avalanche photo-diodes (APDs) offer very high quantum efficiency, and might eventually replace photocathode detectors in high-speed photometry of astronomical objects. Laboratory studies have been performed on both passively and actively quenched APDs. Peculiarities of APDs include that the dark signal may exhibit bistability, with the count rate jumping between discrete levels. Following any photon detection, the detector itself emits some light, which might be confusing under certain conditions. Deadtimes and after pulsing properties appear favorable, but the small physical size of APDs causes challenges in optically matching them to the entrance pupils of large telescopes. Title: Astrometric radial velocities. II. Maximum-likelihood estimation of radial velocities in moving clusters Authors: Lindegren, Lennart; Madsen, Søren; Dravins, Dainis Bibcode: 2000A&A...356.1119L Altcode: Accurate proper motions and trigonometric parallaxes of stars in nearby open clusters or associations permit to determine their space motions relative to the Sun, without using spectroscopy for their radial-velocity component. This assumes that the member stars share the same mean velocity vector, apart from a (small) random velocity dispersion. We present a maximum-likelihood formulation of this problem and derive an algorithm for estimating the space velocity and internal velocity dispersion of a cluster using astrometric data only. As a by-product, kinematically improved parallaxes and distances are obtained for the individual cluster stars. The accuracy of the method, its robustness, and its sensitivity to internal velocity fields, are studied through Monte Carlo simulations, using the Hyades as a test case. From Hipparcos data we derive the centroid velocity and internal velocity dispersion of the Hyades cluster. The astrometric radial velocities are obtained with a standard error of 0.47 km s-1 for the cluster centroid, increasing to about 0.68 km s-1 for the individual stars due to their peculiar velocities. If known binaries are removed, this improves to 0.60 km s-1. Based (in part) on observations by the ESA Hipparcos satellite Title: Magnetic deformation of the white dwarf surface structure Authors: Fendt, C.; Dravins, D. Bibcode: 2000AN....321..193F Altcode: 2000astro.ph..7387F The influence of strong, large-scale magnetic fields on the structure and temperature distribution in white dwarf atmospheres is investigated. Magnetic fields may provide an additional component of pressure support, thus possibly inflating the atmosphere compared to the non-magnetic case. Since the magnetic forces are not isotropic, atmospheric properties may significantly deviate from spherical symmetry. In this paper the magnetohydrostatic equilibrium is calculated numerically in the radial direction for either for small deviations from different assumptions for the poloidal current distribution. We generally find indication that the scale height of the magnetic white dwarf atmosphere enlarges with magnetic field strength and/or poloidal current strength. This is in qualitative agreement with recent spectropolarimetric observations of Grw+10o -8247. Quantitatively, we find for e.g. a mean surface poloidal field strength of 100 MG and a toroidal field strength of 2-10 MG an increase of scale height by a factor of 10. This is indicating that already a small deviation from the initial force-free dipolar magnetic field may lead to observable effects. We further propose the method of finite elements for the solution of the two-dimensional magnetohydrostatic equilibrium including radiation transport in the diffusive approximation. We present and discuss preliminary solutions, again indicating on an expansion of the magnetized atmosphere. Title: Main sequences of nearby open clusters and OB associations from kinematic modelling of Hipparcos data Authors: Madsen, S.; Lindegren, L.; Dravins, D. Bibcode: 2000ASPC..198..137M Altcode: 2000scac.conf..137M No abstract at ADS Title: Commission 12: Solar Radiation and Structure (Radiation et Structure Solaires) Authors: Foukal, Peter; Solanki, Sami; Mariska, J.; Baliunas, S.; Dravins, D.; Duvall, T.; Fang, C.; Gaizauskas, V.; Heinzel, P.; Kononovich, E.; Koutchmy, S.; Melrose, D.; Stix, M.; Suematsu, Y.; Deubner, F. Bibcode: 2000IAUTA..24...73F Altcode: No abstract at ADS Title: Commission 36: Theory of Stellar Atmospheres: (Theorie des Atmospheres Stellaires) Authors: Pallavicini, R.; Dravins, D.; Barbuy, B.; Cram, L.; Hubeny, I.; Owocki, S.; Saio, H.; Sasselov, D.; Spite, M.; Stepien, K.; Wehrse, R. Bibcode: 2000IAUTA..24..219P Altcode: No abstract at ADS Title: Beyond imaging, spectroscopy and interferometry: Quantum optics at the largest telescopes Authors: Dravins, D. Bibcode: 2000ESOC...57...36D Altcode: 2000elt..conf...36D No abstract at ADS Title: Astrometric radial velocities. I. Non-spectroscopic methods for measuring stellar radial velocity Authors: Dravins, Dainis; Lindegren, Lennart; Madsen, Søren Bibcode: 1999A&A...348.1040D Altcode: 1999astro.ph..7145D High-accuracy astrometry permits the determination of not only stellar tangential motion, but also the component along the line-of-sight. Such non-spectroscopic (i.e. astrometric) radial velocities are independent of stellar atmospheric dynamics, spectral complexity and variability, as well as of gravitational redshift. Three methods are analysed: (1) changing annual parallax, (2) changing proper motion and (3) changing angular extent of a moving group of stars. All three have significant potential in planned astrometric projects. Current accuracies are still inadequate for the first method, while the second is marginally feasible and is here applied to 16 stars. The third method reaches high accuracy (<1 km s(-1) ) already with present data, although for some clusters an accuracy limit is set by uncertainties in the cluster expansion rate. Based (in part) on observations by the ESA Hipparcos satellite Title: Exactly What Is Stellar 'Radial Velocity'? Authors: Lindegren, L.; Dravins, D.; Madsen, S. Bibcode: 1999ASPC..185...73L Altcode: 1999IAUCo.170...73L; 1999psrv.conf...73L Accuracy levels of metres per second require the fundamental concept of 'radial velocity' to be examined, in particular due to relativistic velocity effects, and spectroscopic measurements made inside gravitational fields. Naively, 'radial velocity' equals the line-of-sight component of the stellar velocity vector, measured by the Doppler shifts of stellar spectral lines. Although many physical effects in stellar atmospheres contribute to the line shifts, those could in principle be corrected for, leaving the 'true' (centre-of-mass) velocity. However, also this concept becomes ambiguous at accuracy levels around 10-100 m/s. Radial velocity is the change in distance with respect to 'time'. But is this the time of light emission (at the star) or light reception (at the observer)? The former seems natural if radial velocity is considered a 'property' of the star, while the latter is more natural for the observer. The difference is of second order in velocity (v*v/c), exceeding 100 m/s for v > 173 km/s. Similar differences exist between the classical and the relativistic Doppler formulae, and depend on how the transverse Doppler effect is treated. Thus, the determination of the radial velocity component cannot be separated from the determination of the transverse one, requiring knowledge also of the stellar proper motion, and distance. Gravitational redshift caused by the Sun diminishes with distance as 1/r. At the solar surface (r = Ro), it is 636 m/s, diminishing to 3 m/s at the Earth's distance (215 Ro). Thus, in principle, all stars will have such a blueshift component, if measured near the Earth. A general-relativistic treatment introduces additional complications, e.g. that the numerical velocities depend on the chosen metric. Also, variable relativistic delay along the light path would introduce line shifts, e.g. during microlensing events. Among the effects influencing the measurement of accurate line shifts, only local ones can be reliably calculated. These depend on the motion and gravitational potential of the observer relative to the desired reference frame, usually the solar system barycentre. We argue that the barycentric fractional wavelength shift z is therefore the proper observational quantity to be derived from spectroscopic measurements. However, this barycentric shift cannot be uniquely interpreted as a radial motion of the object. If velocity units are desired, this shift can be expressed as cz, analogous to the case in cosmology. Title: Radial Velocities without Spectroscopy Authors: Madsen, S.; Lindegren, L.; Dravins, D. Bibcode: 1999ASPC..185...77M Altcode: 1999IAUCo.170...77M; 1999psrv.conf...77M Accuracies in space astrometry now permit accurate determination of stellar radial velocity without using spectroscopy or invoking the Doppler principle. Already Hipparcos data permit accuracies of 100 m/s in some cases, while future space astrometry missions will enable such determinations for a broad range of stars. Fundamental radial-velocity standards have hitherto been limited to solar-system objects, in particular asteroids, whose space motions can be derived with very high accuracy without the use of spectroscopic data. Astrometric techniques are now extending the realm of such geometrically determined radial velocities to many nearby stars. Among astrometric measures for radial-velocity determination, the most direct is the secular change in trigonometric parallax due to the radial displacement of a star. Although this requires extremely accurate measurements over years or decades, it should become feasible with planned space missions. For Barnard's star (parallax 549 mas, V_r = -110 km/s), the expected parallax change is 34 microarcsec/year. Assuming that a star moves uniformly through space, its velocity can also be derived from the secular change in its proper motion (which varies due to the observer). For astrometric missions now being planned, this method should yield space velocities to better than 100 m/s for several nearby high-velocity stars. A third astrometric method that already has been applied using data from the Hipparcos mission, concerns the secular change of the angular extent of moving star clusters. Since all cluster stars share the same (average) velocity vector, the cluster's apparent size changes as it moves in the radial direction. This relative change (revealed by the proper-motion vectors towards the cluster apex) corresponds to the relative change in distance. Since the individual stellar distances are known from parallaxes, their radial velocities follow. Applying this moving-cluster method to Hipparcos data, radial velocities have now been derived for many stars in the Hyades and in the Ursa Major clusters, reaching accuracies between 100-400 m/s. The comparison of these values with precise spectroscopic measurements reveals wavelength shifts not caused by stellar motion, as discussed elsewhere in this colloquium. Title: Astrometric versus Spectroscopic Radial Velocities Authors: Dravins, D.; Gullberg, D.; Lindegren, L.; Madsen, S. Bibcode: 1999ASPC..185...41D Altcode: 1999IAUCo.170...41D; 1999psrv.conf...41D The radial velocity of a star, as deduced from wavelength shifts, does not merely contain the true velocity of the stellar center of mass but also components arising from dynamics in the star's atmosphere, gravitational redshifts, and other effects. For the Sun, the segregation of such effects has been possible because the relative Sun-Earth motion is accurately known from planetary system dynamics, and does not have to be deduced from asymmetric and shifted line profiles. For other stars, accurate determinations of their true radial motion have only recently become feasible with space astrometry. Data from Hipparcos permit accurate such determinations for stars in nearby moving clusters such as Ursa Major and the Hyades (Dravins et al., in Proc. Hipparcos - Venice '97, ESA SP-402, p.733, 1997). When a star cluster (whose stars share the same velocity vector) moves in the radial direction, its angular size changes, as measured by stellar proper-motion vectors. This rate of change equals the time derivative of the [known] distance, i.e. the radial velocity. Future astrometric missions will extend astrometric radial-velocity determinations also to individual field stars with measurable changes in parallax and proper motion. For these stars with astrometric radial-velocity determinations, a parallel spectroscopic program has recently been completed at Haute-Provence Observatory, using its ELODIE radial-velocity spectrometer. Almost 100 program stars of many different spectral types were observed under very good signal-to-noise conditions. Work is in progress to compare the spectroscopic radial velocities with the astrometric values, and to search for systematic line shift differences between groups of different spectral lines (with respect to line-strength, excitation potential, or wavelength region). The overall stability of ELODIE spectra reaches 10 m/s; the expected spectroscopic precision for groups of 100 selected lines in any one star is about 50 m/s; the accuracy in astrometric radial velocity reaches 200 m/s, while hydrodynamic models of stellar atmospheres predict differences on the order of 1 km/s in convective line shifts between different stars. Gravitational redshifts are of comparable magnitude. This program thus aims at identifying signatures of stellar surface structure from line shift patterns, at finding differences in gravitational redshift between different spectral types, and at improving the absolute calibration of velocity values for stars of different rotational velocity and spectral complexity. The program includes not only Hyades and Ursa Major stars, but also IAU radial-velocity standards, metal-deficient stars, and others. For a further discussion, see: <A HREF="http://www.astro.lu.se/dainis/HTML/ASTROMET.html"> Discussion </A> Title: Stellar Surface Convection, Line Asymmetries, and Wavelength Shifts Authors: Dravins, D. Bibcode: 1999ASPC..185..268D Altcode: 1999IAUCo.170..268D; 1999psrv.conf..268D When observed under sufficient resolution, practically all stellar spectral lines prove to be slightly asymmetric. Absorption lines in cooler stars form in inhomogeneous atmospheres, affected by surface convection (stellar granulation). Asymmetries and wavelength shifts originate from correlated velocity and brightness patterns: rising ( = blueshifted) elements are hot (=bright), and convective blueshifts result from a larger contribution of such blueshifted photons than of redshifted ones from the sinking and cooler (=darker) gas. For the Sun, the effect is around 300 m/s. High-excitation lines form predominantly in the hottest elements and show a more pronounced blueshift. The effects are predicted to be greater in F-type stars, and in giants. In the presence of magnetic fields, convection is disturbed and granules do not develop to equally large size or velocity amplitude, resulting in smaller blueshifts (by perhaps 10% or 30 m/s) during the years around activity maximum in the 11-year solar cycle. Such activity-cycle induced lineshift variations must of course be segregated from stellar velocity signals in searches for exoplanets with comparable periods. While line asymmetries and shifts may appear as a noise source in determining stellar motions, they are an important observational signature for constraining three-dimensional (magneto-) hydrodynamic models of stellar atmospheres. These are capable of predicting not only line-widths and shapes, but also second-order quantities such as asymmetries and shifts. A high measuring precision reveals properties of the stellar surface structure also through the temporal variability of stellar line wavelengths. On the visible solar disk, there are on the order of 10**6 granules, each with a velocity amplitude of some 2 km/s, evolving over some 10 min. In integrated sunlight, this amplitude is reduced by a factor of about sqrt(10**6) to perhaps 2 m/s. Stars with larger velocity amplitudes and/or fewer granules will show correspondingly greater fluctuations, observable already with current techniques. Until the present, wavelength-shift observations have generally been for unresolved (i.e. spatially averaged) stellar disks. A major future development will be the study of wavelength variations across spatially resolved stars, e.g. the center-to-limb changes along the equatorial and polar diameters, and their spatially resolved time variability. Adaptive optics on very large telescopes, long-baseline optical interferometry, and optical aperture synthesis will soon open up new vistas of stellar atmospheric physics through radial-velocity observations. Title: Atmospheric Intensity Scintillation of Stars (PASP, 110, 610 [1998]). Authors: Dravins, Dainis; Lindegren, Lennart; Mezey, Eva; Young, Andrew T. Bibcode: 1998PASP..110.1118D Altcode: In the paper ``Atmospheric Intensity Scintillation of Stars. III. Effects for Different Telescope Apertures'' by Dainis Dravins, Lennart Lindegren, Eva Mezey, and Andrew T. Young (PASP, 110, 610 [1998]), there is a typographical error on page 625, column (2), 17 lines from bottom. The expression giving the frequencies for which the previous equation (10) is valid has the superfluous characters ``3D'' on its right-hand side, which thus should read only ``1 Hz.'' The error was caused in proof stage from inconsistencies in e-mail sending and receiving ``standards.'' Title: Atmospheric Intensity Scintillation of Stars. III. Effects for Different Telescope Apertures Authors: Dravins, Dainis; Lindegren, Lennart; Mezey, Eva; Young, Andrew T. Bibcode: 1998PASP..110..610D Altcode: Stellar intensity scintillation in the optical was extensively studied at the astronomical observatory on La Palma (Canary Islands). Atmospheric turbulence causes ``flying shadows'' on the ground, and intensity fluctuations occur both because this pattern is carried by winds and is intrinsically changing. Temporal statistics and time changes were treated in Paper I, and the dependence on optical wavelength in Paper II. This paper discusses the structure of these flying shadows and analyzes the scintillation signals recorded in telescopes of different size and with different (secondary-mirror) obscurations. Using scintillation theory, a sequence of power spectra measured for smaller apertures is extrapolated up to very large (8 m) telescopes. Apodized apertures (with a gradual transmission falloff near the edges) are experimentally tested and modeled for suppressing the most rapid scintillation components. Double apertures determine the speed and direction of the flying shadows. Challenging photometry tasks (e.g., stellar microvariability) require methods for decreasing the scintillation ``noise.'' The true source intensity I(lambda) may be segregated from the scintillation component DeltaI(t,lambda,x,y) in postdetection computation, using physical modeling of the temporal, chromatic, and spatial properties of scintillation, rather than treating it as mere ``noise.'' Such a scheme ideally requires multicolor high-speed (<~10 ms) photometry on the flying shadows over the spatially resolved (<~10 cm) telescope entrance pupil. Adaptive correction in real time of the two-dimensional intensity excursions across the telescope pupil also appears feasible, but would probably not offer photometric precision. However, such ``second-order'' adaptive optics, correcting not only the wavefront phase but also scintillation effects, is required for other critical tasks such as the direct imaging of extrasolar planets with large ground-based telescopes. Title: Beta Hydri (G2 IV): a revised age for the closest subgiant Authors: Dravins, D.; Lindegren, L.; Vandenberg, D. A. Bibcode: 1998A&A...330.1077D Altcode: The secular evolution of solar-type atmospheres may be studied through comparisons of the current Sun with old solar-type stars of known age. Among the few such stars in the solar Galactic neighborhood, beta Hydri (G2 IV) stands out as a normal single star with an advanced age. Previous age determinations ( =~ 9.5 Gy) were based on the old ground-based parallax of 153 mas. The new Hipparcos value of 133.78+/- 0.51 mas implies an absolute magnitude M_V=3.43 +/- 0.01, 0.3 mag brighter than previously believed. New evolutionary calculations produce best-fit models with ages around 6.7 Gy. Although the Hipparcos data thus lead to a significant reduction of its estimated age, beta Hyi remains an old star. Based on observations made with the ESA Hipparcos astrometry satellite Title: Astrometric Radial Velocities from HIPPARCOS Authors: Dravins, D.; Lindegren, L.; Madsen, S.; Holmberg, J. Bibcode: 1998HiA....11..564D Altcode: No abstract at ADS Title: Spectroscopic Radial Velocities: Photospheric Lineshifts Calibrated by HIPPARCOS Authors: Gullberg, D.; Dravins, D. Bibcode: 1998HiA....11..564G Altcode: No abstract at ADS Title: Beta Hydri (G2 IV): A Revised Age for the Closest Subgiant Authors: Dravins, D.; Lindegren, L.; Vandenberg, D. A. Bibcode: 1997ESASP.402..397D Altcode: 1997hipp.conf..397D The secular evolution of solar-type atmospheres may be studied through comparisons of the current Sun with old solar-type stars of known age. Among the few such stars in the solar Galactic neighborhood, beta Hydri (G2 IV) stands out as a normal single star with an advanced age. Previous age determinations (~= 9.5 Gy) were based on the old ground-based parallax of 153 mas. The new Hipparcos value of 133.78 +/- 0.51 mas implies an absolute magnitude M_V=3.43 +/- 0.01, 0.3 mag brighter than previously believed. New evolutionary calculations produce best-fit models with ages around 6.7 Gy. Although the Hipparcos data thus lead to a significant reduction of its age, beta Hyi remains an old star. Title: Astrometric Radial Velocities from HIPPARCOS Authors: Dravins, D.; Lindegren, L.; Madsen, S.; Holmberg, J. Bibcode: 1997ESASP.402..733D Altcode: 1997hipp.conf..733D Space astrometry now permits accurate determinations of stellar radial motion, without using spectroscopy. Using Hipparcos data, this is possible for stars in nearby moving clusters, where all stars share nearly the same space velocity. A maximum-likelihood method has been developed to yield kinematic cluster parameters (including the internal velocity dispersion) purely from parallaxes and proper motions. The deduced astrometric radial velocities of the Ursa Major open cluster and the Hyades have inaccuracies of 0.3 and 0.4 km/s, respectively, and the internal cluster velocity dispersions are found to be 0.66 +/- 0.10 and 0.25 +/- 0.04 km/s (consistent with random stellar motions). Remaining errors arise from uncertainties in excluding binary stars. The errors get worse for the more distant Coma Berenices cluster. The fitting of cluster parameters includes all individual stellar distances. The constraint of a uniform average cluster velocity markedly improves the parallax precisions (roughly by a factor two), compared with Hipparcos data for individual stars. The HR diagram for the Hyades now reveals a very narrow main sequence line (not band), even suggesting some wiggles in it. Discrepancies between astrometric and spectroscopic radial velocities reveal effects (other than stellar motion) that affect wavelength positions of spectral lines. Such are caused by stellar pulsation, surface convection, and by gravitational redshifts. A parallel programme is obtaining and analysing high-precision spectroscopic radial velocities for different classes of spectral lines in these programme stars. Title: Atmospheric Intensity Scintillation of Stars. II. Dependence on Optical Wavelength Authors: Dravins, D.; Lindegren, L.; Mezey, E.; Young, A. T. Bibcode: 1997PASP..109..725D Altcode: Atmospheric intensity scintillation of stars on milli- and microsecond time scales was extensively measured at the astronomical observatory on La Palma (Canary Island). Scintillation statistics and temporal changes were discussed in Paper I, while this paper shows how scintillation depends on optical wavelength. Such effects originate from the changing refractive index of air, and from wavelength-dependent diffraction in atmospheric inhomogeneities. The intensity variance \sigma2/I increases for shorter wavelengths, at small zenith distances approximately consistent with a theoretical \lambda $^{-7/6}$ slope, but with a tendency for a somewhat weaker dependence. Scintillation in the blue is more rapid than in the red. The increase with wavelength of autocorrelation time scales (roughly proportional to $sqrt{\lambda}$ is most pronounced in very small apertures, but was measured up to \o 20 cm. Scintillation at different wavelengths is not simultaneous: atmospheric chromatic dispersion stretches the atmospherically induced 'flying shadows' into 'flying spectra' on the ground. As the 'shadows' fly past the telescope aperture, a time delay appears between fluctuations at different wavelengths whenever the turbulence-carrying winds have components parallel to the direction of dispersion. These effects increase with zenith distance (reaching \approx 100 ms cross-correlation delay between blue and red at Z = 60°), and also with increased wavelength difference. This time delay between scintillation in different colors is a property of the atmospheric flying shadows, and thus a property that remains unchanged even in very large telescopes. However, the wavelength dependence of scintillation amplitude and time scale is 'fully' developed only in small telescope apertures (less than about 5 cm), the scales where the 'flying shadows' on the Earth's surface become resolved. Although these dependences rapidly vanish after averaging in larger apertures, an understanding of chromatic effects may still be needed for the most accurate photometric measurements. These will probably require a sampling of the [stellar] signal with full spatial, temporal and chromatic resolution to segregate the scintillation signatures from those of astrophysical variability. (SECTION: Atmospheric Phenomena and Seeing) Title: Atmospheric Intensity Scintillation of Stars, I. Statistical Distributions and Temporal Properties Authors: Dravins, Dainis; Lindegren, Lennart; Mezey, Eva; Young, Andrew T. Bibcode: 1997PASP..109..173D Altcode: Stellar intensity scintillation in the optical was extensively studies at the astronomical observatory on La Palma (Canary Islands). Photon-counting detectors and digital signal processors recorded temporal auto-and cross-correlation functions, power spectra, and probability distributions. This first paper of a series treats the temporal properties of scintillation, ranging from microseconds to seasons of year. Previous studies, and the mechanisms producing scintillation are reviewed. Atmospheric turbulence causes 'flying shadows' on the ground, and intensity fluctuations occur both because this pattern is carried by winds, and is intrinsically changing. On very short timescales, a break in the correlation functions around 300 mus may be a signature of an inner scale (approx. 3 mm in the shadow pattern at windspeeds of ms -1). On millisecond timescales, the autocorrelation decreases for smaller telescope apertures until approx. 5 cm, when the 'flying shadows' become resolved. During any night, timescales and amplitudes evolve on scales of tens of minutes. In good summer conditions, the flying-shadow patterns are sufficiently regular and long-lived to show anti-correlation dips in autocorrelation functions, which in winter are smeared out by apparent wind shear. Recordings of intensity variance together with stellar speckle images suggest some correlation between good [angular] seeing and large scintillation. Near zenith, the temporal statistics (with up to 12:th order moments measured)is best fitted by a Beta distribution of the second kind (F-distribution), although it is well approximated by log-normal functions, evolving with time. (SECTION: Atmospheric Phenomena and Seeing) Title: Astrometric Radial Velocities from HIPPARCOS Authors: Dravins, D.; Lindegren, L.; Madsen, S.; Holmberg, J. Bibcode: 1997IAUJD..14E..33D Altcode: Space astrometry now permits accurate determinations of stellar radial motion, without using spectroscopy. Although the feasibility of deducing astrometric radial velocities from geometric projection effects was realized already by Schlesinger (1917), only with Hipparcos has it become practical. Such a program has now been carried out for the moving clusters of Ursa Major, Hyades, and Coma Berenices. Realized inaccuracies reach 500 m/s, or slightly better (Dravins et al. 1997). Discrepancies between astrometric and spectroscopic radial velocities reveal effects (other than stellar motion) that affect wavelength positions of spectral lines. Such are caused by stellar surface convection, and by gravitational redshifts. A parallel program (Gullberg & Dravins 1997) is analyzing high-precision spectroscopic radial velocities for different spectral lines in these stars, using the ELODIE radial-velocity instrument at Haute-Provence. Title: Spectroscopic Radial Velocities: Photospheric Lineshifts Calibrated by HIPPARCOS Authors: Gullberg, D.; Dravins, D. Bibcode: 1997IAUJD..14E..32G Altcode: Stellar wavelengths depend not only on the star's motion. Until recently, accurate studies of shifts not caused by radial motion were feasible only for the Sun. Solar lineshifts are interpreted as gravitational redshift (636 m/s) and convective blueshifts (~400 m/s; caused by velocity-brightness correlations). In other stars, such effects may be greater (Dravins & Nordlund 1990). Accurate astrometric radial velocities are now available from Hipparcos (Dravins et al. 1997a; 1997b), permitting studies of such shifts also in some other stars. For such stars in the open clusters of Hyades, Ursa Major and Coma Berenices, a spectroscopic program is in progress, analyzing wavelength shifts in groups of lines with different strengths, excitation potentials, etc., using the ELODIE high-precision radial-velocity instrument (Baranne et al., 1996) at Haute-Provence. Baranne, A. et al., 1996, A&AS 119, 373 Dravins, D., Nordlund, AA., 1990, A&A 228, 203 Dravins, D., Lindegren, L., Madsen, S., Holmberg, J., 1997a, in ESA SP-402, Hipparcos Symposium, Venice Dravins, D., Lindegren, L., Madsen, S., Holmberg, J., 1997b, IAU General Assembly, Kyoto Title: Observed and computed spectral line profiles Authors: Dravins, D. Bibcode: 1996IAUS..176..519D Altcode: No abstract at ADS Title: Optical Observations on Milli-, Micro-, and Nanosecond Timescales Authors: Dravins, D.; Lindegren, L.; Mezey, E. Bibcode: 1995LNP...454..129D Altcode: 1995flfl.conf..129D Instrumentation and observing methods are developed for optical high-speed astrophysics, aiming at exploring milli-, micro-, and nanosecond variability. Such rapid fluctuations can be expected from instabilities in accretion flows, and in the fine structure of photon emission. For the optical, we have constructed a dedicated instrument, whose first version was tested on La Palma to study atmospheric scintillation on very short timescales. A second version is now under development, using photon-counting avalanche photodiodes as detectors. Title: Observational Astrophysics on Milli-, Micro-, and Nanosecond Timescales Authors: Dravins, D.; Lindegren, L.; Mezey, E. Bibcode: 1995svlt.conf..139D Altcode: No abstract at ADS Title: Spectroscopic measurements of stellar rotation Authors: Dravins, D. Bibcode: 1995HiA....10..403D Altcode: No abstract at ADS Title: Astrophysics on its shortest timescales. Authors: Dravins, D. Bibcode: 1994Msngr..78....9D Altcode: The VLT will permit enormously more sensitive searches for high-speed phenomena in astrophysics. Title: Optical astronomy on milli-, micro-, and nanosecond timescales Authors: Dravins, Dainis; Hagerbo, Hans O.; Lindegren, Lennart; Mezey, Eva; Nilsson, Bo Bibcode: 1994SPIE.2198..289D Altcode: Instrumentation and observing methods are being developed for a program in optical high-speed astrophysics, an exploratory project entering the domains of milli-, micro-, and nanosecond variability. Current studies include accretion flows around compact objects, stellar scintillation, and astronomical quantum optics. To study such rapid phenomena is not possible everywhere in the spectrum (e.g., X-ray studies are constrained by the photon count rates feasible with current spacecraft). The ground- based optical is a promising region, for which we have constructed a dedicated instrument, QVANTOS ('Quantum-Optical Spectrometer'). It was designed for real-time handling of large amounts of data, for observing also faint sources, and with a time resolution that can be extended to reveal quantum properties of light, such as the bunching of photons in time. Its first version was used to study atmospheric scintillation on timescales between 100 milli- and 100 nsec, utilizing some 25 full nights at a telescope on La Palma (Canary Islands). An understanding of the atmosphere is required to segregate astrophysical variability from terrestial effects, and to find optimal observing strategies. For very high time resolution, light curves are of little use, and statistical functions of variability have to be measured. The noise in such functions decreases dramatically with increased light collecting power, making very large telescopes much more sensitive for the study of rapid variability than ordinary-sized ones. Title: Instrumental effects in stellar spectroscopy Authors: Dravins, D. Bibcode: 1994ASIC..436..269D Altcode: 1994iltm.conf..269D No abstract at ADS Title: The Distant Future of Solar Activity: A Case Study of beta Hydri. II. Chromospheric Activity and Variability Authors: Dravins, D.; Linde, P.; Fredga, K.; Gahm, G. F. Bibcode: 1993ApJ...403..396D Altcode: A detailed comparison of the present sun with the very old star Beta Hyi (G2 IV) is presented in order to study the secular evolution of solar-type chromospheres, with emphasis placed on chromospheric features and their time variability. High-resolution Ca II H and K profiles show the emission to be about half that for the sun, but with the same sense of violet-red asymmetry. The emission's wavelength width is slightly broader, consistent with the Wilson-Bappu relation for this slightly more luminous star. Mg II h and k profiles also exhibit an emission weaker than the sun, but with the opposite sense of asymmetry, probably altered by absorption in a nearby interstellar cloud. The emission variations are small and are characterized by smooth and systematic change in the line profiles from year to year, suggesting continuous changes in the chromospheric structure, rather than the sudden emergence of growth of active regions. Title: Atmospheric Intensity Scintillation of Stars on Millisecond and Microsecond Time Scales Authors: Dravins, D.; Lindegren, L.; Mezey, E. Bibcode: 1993spct.conf..113D Altcode: 1993IAUCo.136..113D No abstract at ADS Title: The Distant Future of Solar Activity: A Case Study of beta Hydri. I. Stellar Evolution, Lithium Abundance, and Photospheric Structure Authors: Dravins, D.; Lindegren, L.; Nordlund, A.; Vandenberg, D. A. Bibcode: 1993ApJ...403..385D Altcode: A detailed comparison of the current sun (G2 V) with the very old solar-type star Beta Hyi (G2 IV) is presented in order to study the postmain-sequence evolution of stellar activity and of nonthermal processes in solar-type atmospheres. Special attention is given to general stellar properties and the deeper atmosphere of Beta Hyi. A critical review of data from various sources is presented, and the age of Beta Hyi is determined from evolutionary models to 9.5 +/- 0.8 Gyr. The relatively high lithium abundance may be a signature of the early subgiant stage, when lithium that once diffused to beneath the main-sequence convection zone is dredged up to the surface as the convection zone deepens. Numerical simulations of the 3D photospheric hydrodynamics show typical granules to be significantly larger (a factor of about 5) than solar ones. Title: The Distant Future of Solar Activity: A Case Study of beta Hydri. III. Transition Region, Corona, and Stellar Wind Authors: Dravins, D.; Linde, P.; Ayres, T. R.; Linsky, J. L.; Monsignori-Fossi, B.; Simon, T.; Wallinder, F. Bibcode: 1993ApJ...403..412D Altcode: The paper investigates the secular decay of solar-type activity through a detailed comparison of the present sun with the very old solar-type star, Beta Hyi, taken as a proxy of the future sun. Analyses of successive atmospheric layers are presented, with emphasis of the outermost parts. The FUV emission lines for the transition zone are among the faintest so far seen in any solar-type star. The coronal soft X-ray spectrum was measured through different filters on EXOSAT and compared to simulated X-ray observations of the sun seen as a star. The flux from Beta Hyi is weaker than that from the solar corona and has a different spectrum. It is inferred that a thermally driven stellar wind can no longer be supported, which removes the mechanism from further rotational braking of the star through a magnetic stellar wind. Title: High Resolution Spectroscopy of Stellar Velocity Signatures Authors: Dravins, D. Bibcode: 1992ESOC...40...55D Altcode: 1992hrsw.conf...55D No abstract at ADS Title: The distant future of solar activity: a case study of beta Hydri (abstract) Authors: Dravins, D.; Linde, P.; Ayres, T. R.; Fredga, K.; Gahm, G.; Lindegren, L.; Linsky, J. L.; Monsignori-Fossi, B.; Nordlund, Å.; Simon, T.; Vandenberg, D.; Wallinder, F. Bibcode: 1992sccw.conf..105D Altcode: No abstract at ADS Title: The rotationally broadened line profiles of Sirius. Authors: Dravins, D.; Lindegren, L.; Torkelsson, U. Bibcode: 1990A&A...237..137D Altcode: Photospheric Fe I and Fe II absorption line profiles in Sirius are analyzed. The Fourier transforms of the line profiles reveal several sidelobes consistent with line broadening from rigid stellar rotation at V sin i = 15.3 + or - 0.3 km/s. The Fourier transforms are fitted, leading to deduced parameters of line profiles and stellar rotation. These profiles are remarkably similar to Gaussians with FWHM at about 8 km/s and resemble synthetic line profiles computed from hydrodynamic model atmospheres by Gigas (1989). The 'superposition' of neighboring absorption lines occasionally produces spectral features that are much narrower than the widths of individual rotationally broadened profiles. The widths of such 'subrotational' features may approach these of the 'intrinsic' line profiles, illustrating the need for very high spectral resolution to fully resolve the spectra also of rapidly rotating stars. Title: Stellar activity cycles Authors: Dravins, D. Bibcode: 1990ESASP.310...61D Altcode: 1990eaia.conf...61D No abstract at ADS Title: Enhancing IUE spectrophotometry: a case study of Beta Hydri Authors: Linde, P.; Dravins, D. Bibcode: 1990ESASP.310..605L Altcode: 1990eaia.conf..605L No abstract at ADS Title: The distant future of solar activity - A case study of Beta Hydri Authors: Dravins, D.; Linde, P.; Ayres, T. R.; Fredga, K.; Gahm, G.; Lindegren, L.; Linsky, J. L.; Monsignori-Fossi, B.; Nordlund, A.; Simon, T.; Vandenberg, D.; Wallinder, F. Bibcode: 1990ESASP.310..323D Altcode: 1990eaia.conf..323D No abstract at ADS Title: The archival reprocessing of IUE data: I. An accurate registration technique for distorted images Authors: de La Pena, M. D.; Shaw, R. A.; Linde, P.; Dravins, D. Bibcode: 1990ESASP.310..617D Altcode: 1990eaia.conf..617D No abstract at ADS Title: Stellar granulation. IV. Line formation in inhomogeneous stellar photospheres. Authors: Dravins, D.; Nordlund, A. Bibcode: 1990A&A...228..184D Altcode: Synthetic images of stellar granulation and photospheric Fe line profiles are computed in model atmospheres obtained from detailed numerical simulations of stellar surface convection. Models corresponding to Procyon (F5 IV-V), α Cen A (G2V), β Hyi (G2IV), and β Cen B (K1V) are studied (5200 ≤Teff≤6600 K). The broadening, wavelength shift and asymmetry of spatially and temporally resolved line profiles follows from radiative transfer in explicitly computed three- dimensional and time-variable velocity fields, and no adjustable - fitting parameters (such as e. g. "turbulence") are used. Synthetic white-light and monochromatic images illustrate the intensity contrast on stellar surfaces, its center-to-limb variation and the morphology of line formation. Spatially resolved and spatially averaged profiles illustrate line broadening through the Doppler effect in photospheric velocity fields. An increase in the velocity spread of spatially resolved lines near the stellar limbs reflects the larger amplitudes of horizontal velocities in line-forming layers. Time variability of spatially averaged line profiles and of their continuum flux levels reflects time evolution of convective patterns larger than individual granules. Spatially and temporally averaged data identify how different shapes, asymmetries and shifts among lines of different strength, excitation potential, ionization level, and wavelength region, map the detailed physical properties throughout the photo sphere. The properties of averaged profiles (in particular their asymmetries) are not at all typical for individual points on the stellar surface, but rather reflect the statistical distribution of photospheric inhomogeneities. Only very strong lines have sufficiently extended depths of formation for their asymmetry to be significantly influenced also by the depth-variation of photospheric flow velocities. Effects of the (non-LTE) radiative ionization of iron are not large but visible as a weakening of blueshifted Fe I line components above especially hot and bright granules. Convective blueshifts, originating from correlations between local brightness and local Doppler shift, vary between ∼=200 and 1000 ms-1 at disk center in different stars. Since such correlations change throughout the atmosphere, already small differences in line formation conditions for lines of different strength or excitation potential may result in different asymmetries and wavelength shifts. For example, the lower surface gravity on the solar near-twin α Cen A permits larger velocity amplitudes in the high photosphere, causing noticeable differences to the Sun in the asymmetries of its stronger photospheric lines. Title: Stellar granulation. V. Synthetic spectral lines in disk-integrated starlight. Authors: Dravins, D.; Nordlund, A. Bibcode: 1990A&A...228..203D Altcode: Numerical simulations of stellar photo spheric structure have provided line profiles at different positions across stellar disks. Using these data, synthetic Fe line profiles in disk-integrated flux are computed (including their asymmetries and wavelength shifts) for models corresponding to Procyon (F 5 IV-V), α Cen A (G2V), β Hyi (G2IV) and α Cen B (K1V). The line profiles are computed without any adjustable physical parameters besides that of stellar rotation, and the model atmospheres contain no classical parameters such as "mixing-length" nor "turbulence". Since line strength, width, asymmetry, rotational broadening, and limb darkening change with disk position, the disk-integrated profiles reflect these properties in a complex manner. This intercoupling might allow determinations of not only stellar rotation, but also line profile variations across stellar disks, using observations of similar stars with different rotation. Grids of "observed" synthetic line profiles and bisectors illustrate effects of finite spectral resolution. Comparisons with observations show good agreement, and the stellar rotation can be independently determined from the symmetric line broadening, and from the bisector patterns. For the well observed stars Procyon and α Cen A, we estimate V sin i≃2.9 and 1.8 km s-1, respectively. For the solar near-twin α Cen A, the profile and bisector fits are almost perfect, and permit the identification of subtle differences against the Sun, apparently reflecting changes in solar-type granulation during some billion years of stellar evolution. The bisector fit for Procyon is excellent, but some absorption is missing in the flanks of the intensity profiles outside about ±5 km s-1. This, and a similar effect in the subgiant β Hyi, is believed to be an artifact of the hydrodynamically anelastic atmospheric model, which excludes sound waves and absorption by features moving at near-sonic speeds. Different stars have different line asymmetries, and in each star there is a systematic dependence on line-strength. The excitation-potential and wavelength-region dependences are smaller. The convective blueshift of spectral lines ranges between ≃200 km s-1 in K dwarfs to ≃1000 m s-1 in F stars. Such effects may limit the accuracies possible in spectroscopic determinations of stellar radial velocities. Title: Stellar granulation. VI. Four-component models and non-solar-type stars. Authors: Dravins, Dainis Bibcode: 1990A&A...228..218D Altcode: A series of relatively simple empirical models of inhomogeneous stellar surfaces that allow granulation properties to be estimated also in stars for which detailed hydrodynamic models cannot yet be computed (e.g., the stars of spectral types A,F,G and K, reproducing observed line asymmetries) are presented. In these models, the stellar surface is divided into four components of different brightness and velocity, and the integrated stellar line profile is obtained as a summation of profiles from different components. By matching the synthetic and observed bisector patterns, estimates of the velocity and brightness amplitudes of stellar granulation can be obtained without a major computational effort. Title: Stellar granulation. III. Hydrodynamic model atmospheres. Authors: Nordlund, A.; Dravins, D. Bibcode: 1990A&A...228..155N Altcode: Detailed models for the three-dimensional, time-dependent and radiation-coupled hydrodynamics of solar granular convection have been adapted to stellar conditions, and extensive numerical simulations have been carried out to model four different stars in the vicinity of the sun in the H-R diagram. The results from the simulations, showing the three-dimensional structure and time evolution of temperature, velocity, and pressure features in stellar photospheres, are presented. They are then used as sets of temporally and spatially varying model atmospheres in which radiative transfer computations are made of the continuum and line radiation leaving the stars. Synthetic images show the optical appearance of stellar surface structure at different positions across stellar disks. Synthetic spectral line profiles are computed for different locations and times, and the buildup of average line profiles is examined for lines of different strength, excitation potential, ionization level, and wavelength region. The average line profiles are then used as an input to synthesize the disk-integrated flux of photospheric Fe lines for stars of different rotational velocities in order to predict observable spectral line shapes, asymmetries, and wavelength shifts. Title: Stellar Granulation Authors: Dravins, Dainis Bibcode: 1990ASPC....9...27D Altcode: 1990csss....6...27D Numerical simulations of the three-dimensional structure and time evolution of stellar surface convection are now feasible. Using the output from such simulations as sets of spatially and temporally varying model atmospheres, synthetic images of the stellar surface structure (granulation) as well as photospheric line profiles can be computed, and compared to observations. Such models are free from the classical ad hoc parameters of 'mixing-length', 'micro-' or 'macro-turbulence'. Challenges for the future include detailed modeling of early-type, giant, and other nonsolar type stars. Signatures of stellar granulation are primarily observed as asymmetries and wavelength shifts in photospheric absorption lines. Observational challenges include identifying such asymmetries and shifts throughout the HR-diagram, monitoring lineshift variations during stellar activity cycles, and ultimately achieving spectroscopy across spatially resolved stellar disks. Title: Observing, Modeling, and Understanding Stellar Granulation Authors: Dravins, D. Bibcode: 1990IAUS..138..397D Altcode: No abstract at ADS Title: The rotationally broadened line profiles of Sirius. Authors: Dravins, D.; Lindegren, L.; Torkelsson, U. Bibcode: 1990apsu.conf...19D Altcode: No abstract at ADS Title: Enhancing IUE spectrophotometry: a case study of Beta Hydri. Authors: Linde, P.; Dravins, D. Bibcode: 1990apsu.conf...45L Altcode: No abstract at ADS Title: The distant future of solar activity - a case study of Beta Hydri. Authors: Dravins, D.; Linde, P.; Ayres, T. R.; Fredga, K.; Gahm, G.; Lindegren, L.; Linsky, J. L.; Monsignori-Fossi, B.; Nordlund, Å.; Simon, T.; Vandenberg, D.; Wallinder, F. Bibcode: 1990apsu.conf...17D Altcode: No abstract at ADS Title: Enhancing IUE spectrophotometry: a case study of Beta Hydri. Authors: Linde, P.; Dravins, D. Bibcode: 1990nba..meet..181L Altcode: 1990taco.conf..181L A technique for improved processing of data from the IUE satellite has been developed. A correlation scheme is used to directly measure the geometric displacement of the raw image, which enables the necessary geometric transformation to be carried out with subpixel accuracy. The resulting improvement in photometric calibration allows the subsequent data extraction to give spectra with significantly lower noise than with standard reduction methods. In an on-going search for chromospheric variability in the solar-type star β Hydri, nearly 100 IUE exposures have been reduced with the new method. Title: Atmospheric intensity scintillation of stars on milli- and microsecond time scales. Authors: Dravins, D.; Lindegren, L.; Mezey, E. Bibcode: 1990apsu.conf...18D Altcode: No abstract at ADS Title: Stellar granulation. Authors: Dravins, Dainis Bibcode: 1990MmSAI..61..513D Altcode: The spectroscopic features that can be interpreted as signatures of stellar granulation are described. Special attention is given to theoretical models of stellar granulation and synthetic photospheric line profiles in solar-type stars. Problems involved in observing subtle photospheric line asymmetries caused by stellar granulation are illustrated, and indirect methods that can be used for imaging stellar surfaces are discussed. Title: A Cross Correlation Technique for Improved IUE Image Registration Authors: de La Peña, M. D.; Shaw, R. A.; Linde, P.; Dravins, D. Bibcode: 1989BAAS...21.1073D Altcode: No abstract at ADS Title: Absolute flux calibration of the H and K lines of CA II : chromospheric radiative losses in F and G-type stars. Authors: Pasquini, L.; Pallavicini, R.; Dravins, D. Bibcode: 1989A&A...213..261P Altcode: Ca II H and K spectra of 81 (mainly Southern) F and G stars are analyzed using two different calibration methods. It is shown that, for spectra of sufficiently high resolution, and for stars of relatively low rotation rates, the calibrations of Linsky et al. (1979) and of Pasquini et al. (1988) give essentially the same results. These calibrations are used to derive absolute surface fluxes in the H and K lines of Ca II for 64 stars. It is shown that several late-F and early-G giants and supergiants have Ca II H and K fluxes in excess of about 10 to the 6th erg/sq cm s, much larger than those typically observed for normal giants of later spectral types. Title: Stellar Granulation: Modeling of Stellar Surfaces and Photospheric Line Asymmetries Authors: Dravins, D. Bibcode: 1989ASIC..263..493D Altcode: 1989ssg..conf..493D No abstract at ADS Title: Challenges and Opportunities in Stellar Granulation Observations Authors: Dravins, D. Bibcode: 1989ASIC..263..153D Altcode: 1989ssg..conf..153D No abstract at ADS Title: The Lunde observatory method for IUE spectral image processing Authors: Linde, Peter; Dravins, Dainis Bibcode: 1988ESASP.281b.345L Altcode: 1988uvai....2..345L; 1988IUE88...2..345L A method for IUE data processing and spectrum extraction is described. The geometric transformation of the raw image is made by identifying fixed patterns in the background outside spectral orders. By correlating these with patterns in the flat-field calibration exposures, geometric correction to within a fraction of one pixel appears possible. The photometric calibration thus avoids the pixel-to-pixel fixed-pattern noise ordinarily present, and the subsequent spectrum extraction may give spectra with significantly lower noise than ordinary reduction methods. Title: Stellar Granulation and Photospheric Line Asymmetries Authors: Dravins, D. Bibcode: 1988IAUS..132..239D Altcode: Numerical simulations of stellar surface convection in different stars have now been carried out, and such three-dimensional and time-dependent models predict the detailed stellar line profiles (including asymmetries and wavelength shifts), thus enabling a direct confrontation between observations and theory. Title: The Lund Observatory method for IUE spectral image processing. Authors: Linde, P.; Dravins, D. Bibcode: 1988EIUEN..29....9L Altcode: Since 1978 the authors have used the International Ultraviolet Explorer (IUE) satellite to monitor the solar-type star β Hydri (G2 IV) in order to detect long-term variations in chromospheric activity. The indicators they use are the Mg II h and k emission lines near 280 nm. β Hydri is estimated to be about twice as old as the sun. Current astrophysical theory predicts that this should result in a lowered overall magnetic- and chromospheric activity. This also implies that any variations of the Mg II emission line intensities are expected to be small. Preliminary data reductions, basically using the standard IUE software package, have shown this to be correct. Title: The Lund Observatory method for IUE spectral image processing. Authors: Linde, P.; Dravins, D. Bibcode: 1988IUEEN..29....1L Altcode: No abstract at ADS Title: Stellar Granulation Authors: Dravins, D. Bibcode: 1987MitAG..70...64D Altcode: No abstract at ADS Title: Stellar granulation. I - The observability of stellar photospheric convection Authors: Dravins, Dainis Bibcode: 1987A&A...172..200D Altcode: The application of astrophysical techniques, data analysis methods, and theoretical tools to investigate the stellar equivalent of solar granulation is considered. The aim is to study stellar photospheric convection patterns, the ensuing atmospheric inhomogeneities, and their effects on other observable parameters. Through experimental observations of sunlight, the ESO coude echelle spectrometer (in the special double-pass scanner mode) has been shown to be adequate for this task. The spectrometer, its performance, and its mode of operation are described. The selection of spectral lines is discussed for seven program stars (Sirius, Canopus, Procyon, Beta Hydri, Alpha Cen A, Alpha Cen B, and Arcturus). Examples are shown of observed stellar line profiles and the asymmetry of these line profiles is described by the computed line bisectors. The stellar bisector patterns for differently strong lines turn out to constitute a characteristic signature for each spectral type. Title: Stellar granulation. II. Stellar photospheric line asymmetries. Authors: Dravins, D. Bibcode: 1987A&A...172..211D Altcode: A search for a spectral signature of stellar granulation is made in seven stars of spectral types A, F, G, and K. Very high quality absorption line profiles have been obtained for Fe lines, using the ESO coude echelle spectrometer double-pass photoelectric scanner at a resolution λ/Δλ ≃ 200,000. Intrinsic line asymmetries are seen in all stars, with marked differences among different spectral types. The asymmetries are described by average bisectors for groups of similar spectral lines. A typical bisector amplitude is ≃ 300 m/s, a few percent of the line width. The characteristic solar granulation signature of progressively changing bisector slopes with changing line-strength is clearly indicated, in particular in the best-studied stars αCen A and Procyon. A survey of the Procyon spectral atlas is also made, and the asymmetries of 233 unblended Fe lines analyzed. This larger sample agrees very well with the photoelectric measurements and also shows additional trends, such as decreased bisector slope for lines at longer wavelengths. Title: Photospheric Structure in Solar-Type Stars (Abstract) Authors: Dravins, D. Bibcode: 1987LNP...292...72D Altcode: 1987ssp..conf...72D No abstract at ADS Title: Stellar Granulation: Photospheric Line Asymmetries and Hydrodynamic Model Atmospheres Authors: Dravins, D.; Nordlund, A. Bibcode: 1986BAAS...18.1002D Altcode: No abstract at ADS Title: Solar Fe II line asymmetries and wavelength shifts. Authors: Dravins, D.; Larsson, B.; Nordlund, A. Bibcode: 1986A&A...158...83D Altcode: Convective motions of solar granulation are manifest in the spatially unresolved spectrum as slight asymmetries and wavelength shifts of photospheric spectral lines. In a previous paper (Dravins et al., 1981) that dependence for Fe I lines with line strength, excitation potential and wavelength region was analyzed. This paper extends that work to Fe II lines, examining bisector shapes and wavelength shifts of "unblended" Fe II lines both at disk center and in integrated sunlight. Fe II lines form predominantly in the hotter and denser regions of the deep photosphere, and these different line formation conditions for Fe II manifest themselves in well-defined differences from Fe I: the average Fe II bisectors show a more articulated curvature and a larger convective blueshift. Synthetic spectral lines, computed from a three-dimensional time-dependent hydrodynamic simulation of solar photospheric convection confirm the observed behavior. Title: Stellar Activity Cycle in Beta Hydri Authors: Dravins, D. Bibcode: 1986iue..prop.2585D Altcode: No abstract at ADS Title: Stellar activity cycles Authors: Dravins, D. Bibcode: 1986HiA.....7..393D Altcode: Stellar activity cycles in the corona, chromosphere, photosphere, and deeper layers are examined. Observational problems related to the study of magnetic flux variations during solar cycle, of changes in the deeper layer and convective zone, and of ancient sun activity are described. Chromospheric activity cycles in ordinary stars, irradiance cycles in spotted stars, and flare frequency cycles in flare stars are considered. The need for the analysis of magnetic cycles in stellar activity and of cyclic activity in ordinary stars, and direct imaging of stellar surfaces is discussed. Title: Stellat Activity Cycle in Beta Hydri Authors: Dravins, D. Bibcode: 1986iue..prop.2574D Altcode: No abstract at ADS Title: Stellar Activity Cycle in Beta Hydri Authors: Dravins, D. Bibcode: 1985iue..prop.2301D Altcode: No abstract at ADS Title: Stellar Lineshifts Induced by Photospheric Convection Authors: Dravins, Dainis Bibcode: 1985srv..conf..311D Altcode: 1985IAUCo..88..311D; 1985srv..proc..311D; 1985LDP.....5..311D Effects of stellar atmospheres on measured radial velocities are examined. Surface convection ("stellar granulation") causes photospheric line asymmetries and wavelength shifts of ≅ 100 - 500 m/s. Cyclic changes in the convection patterns, such as observed during the solar 11-year cycle, may mimic radial velocity variations of perhaps 30 m/s. The study of stellar atmospheres would benefit from accurate (< 100 m/s) differential radial velocity measurements among lines of different parameters (strength, excitation potential, wavelength region) in the same star. Title: High resolution spectroscopy of alpha Centauri. I. Lithium depletion near one solar mass. Authors: Soderblom, D. R.; Dravins, D. Bibcode: 1984A&A...140..427S Altcode: The lithium (Li) abundance of Alpha-Centauri A was measured and an upper limit was found for Li in Alpha Centauri B using the ESO Coude Echelle Spectrometer. The measurements were made in the 670.7 nm region in single-pass mode. The signal to noise ratio was not less than about 300 and was limited by the properties of the recorder. For Alpha-Centauri A the measured abundance was log N(Li) = 1.28, on a scale where log N(H) = 12.00. The upper limit for Li abundance in Alpha Centauri B was 0.7. It is shown that these abundances are consistent with the probable evolutionary age of the stars, given a mass of 1.1 solar mass for Alpha Centauri A. The lithium depletion e-folding time for that mass is therefore about 1.4 Gyr, compared to 1.1 Gyr at 1.0 solar mass. It is shown that the accuracy of estimates of the ages of individual stars based on Li abundances is limited when the masses are not precisely known. The age-related properties of solar-type stars that depend on Li abundances are discussed. Title: Solar Fe II Line Asymmetries and Wavelength Shifts Authors: Dravins, D.; Larsson, Birgitta Bibcode: 1984ssdp.conf..306D Altcode: Asymmetries are studied for 32 apparently unblended Fe II photospheric absorption lines in the solar disk center spectrum, and in the spectrum of integrated sunlight. Average bisectors have been computed for groups of similar lines, and the bisector variation is shown as function of line-strength and of excitation potential. The same trends as previously known from Fe I are present, although Fe II line shapes show subtle differences. Title: Observing Stellar Granulation (Keynote) Authors: Dravins, D.; Lind, J. Bibcode: 1984ssdp.conf..414D Altcode: Granulation-induced photospheric spectrum line asymmetries can be detected with high-resolution stellar spectrometers. Such stellar line asymmetries are well respresented by bisectors which show changing shapes for lines of different strengths. The solar near-twin α Cen A shows a bisector pattern very similar to that of the Sun. F- and K-type main-sequence stars have line asymmetries reminiscent of solar ones, but very different from those of F- and K-type giants. Stellar bisector patterns are presented from very high-resolution (λ/Δλ ≅ 200,000) observations made with the ESO double-pass coudé echelle spectrometer, and the observability of stellar bisectors also at moderate resolutions (≅ 100,000) is shown. Title: Stellar granulation: evidence for stellar surface convection from photospheric line asymmetries. Authors: Dravins, D.; Lind, J. Bibcode: 1983PASP...95R.588D Altcode: No abstract at ADS Title: Stellar Granulation and the Structure of Stellar Surfaces Authors: Dravins, D. Bibcode: 1983Msngr..32...15D Altcode: Convection in Stars Stellar convection is a central but poorly understood parameter In the construction of stellar models and the determination of stellar ages, influencing both the energy transport through the atmosPh.ere and the replenishment 01 nuclear fuels in the core. The motlons in stellar convection zones probably supply the energy for generating magnetic fields, heating stellar chromospheres and coronae, driving stellar winds, and for many other nonthermal phenomena. The inhomogeneous structure of velocity fields on stellar surfaces complicates the accurate determination of stellar radial velocities. Further, the temperature inhomogeneities on stellar surfaces induce molecular abundance inhomogeneities and entangle the accurate determination of chemical abundances. Title: High Resolution Spectroscopy - the Need for Larger Telescopes Authors: Dravins, D. Bibcode: 1983ESOC...17..107D Altcode: 1983vlt..work..107D No abstract at ADS Title: Solar Activity 5 Billion Years in the Future - A Case Study of Beta Hydri Authors: Dravins, D.; Linde, P.; Fredga, K.; Gahm, G. Bibcode: 1983BAAS...15..698D Altcode: No abstract at ADS Title: Spectrograph Instrumental Profiles - Dependence on Dispersion Authors: Andersen, J.; Dravins, D. Bibcode: 1982PASP...94..390A Altcode: Spectrograph instrumental profiles (including stray light far away from the central peak) have been measured in blue and red light for the three cameras in the coudé spectrograph of the 1.52-m telescope at Observatoire de Haute-Provence. The different dispersions 0.7, 1.2, and 2.0 nm mm-1 are obtained using the same ruled diffraction grating. On a linear distance scale in the focal plane the profiles are rather similar down to a 10-3 intensity level, but on a wavelength scale the profiles improve with increasing dispersion, indicating the presence of a stray light component other than that caused by diffraction by grating irregularities. The effects of these instrumental profiles on observed spectra are illustrated by numerical convolutions with the solar spectrum. Title: Convection in stellar atmospheres. Authors: Dravins, D.; Lind, J. Bibcode: 1982ROLun..18..109D Altcode: No abstract at ADS Title: Measurements of Photon Statistics with Nanosecond Resolution Authors: Dravins, D. Bibcode: 1982ASSL...92..229D Altcode: 1982IAUCo..67..229D; 1982ialo.coll..229D No abstract at ADS Title: Photospheric spectrum line asymmetries and wavelength shifts Authors: Dravins, D. Bibcode: 1982ARA&A..20...61D Altcode: Results of studies on the asymmetries of spectral lines that have hitherto been regarded as symmetric are discussed. The discrepancy between solar and laboratory wavelengths is summarized, including the limb effect. Solar line profiles have been accurately measured, revealing intrinsic asymmetries in the lines. The causes of asymmetries and shifts can be traced back to photospheric inhomogeneities, so that high spatial resolution images and spectra of the solar granulation are needed to understand their origins. Recent theoretical developments in time-dependent and hydrodynamic solar and stellar model atmospheres incorporating convection permit predictions and interpretations of observed asymmetries and shifts. The asymmetries are also visible in integrated sunlight and the corresponding phenomena have been seen for a few bright stars. Title: CA II and K chromospheric emission in F-and G-type stars. Authors: Dravins, D. Bibcode: 1981A&A....98..367D Altcode: A survey of representative Ca II H and K line profiles (the most pronounced chromospheric indicators observable from the ground) is presented to illustrate the chromospheric emission of different types of F and G stars. Of the 90 stars observed, a typical one is selected for each spectral type, leaving a sample of 47. The spectral types are taken from Jaschek (1978), except when superseded by Keenan and Pitts (1980). For BS 3591 the Bright Star Catalog classification of F 8 III is retained, and data for the sun (G 2 V) refer to observations of skylight, which is almost equal to integrated sunlight. General trends in the changing appearance of chromospheric emission, as well as the physical scatter of chromospheric activity levels among stars of similar photospheric properties, are presented. It is shown that the sun's level of chromospheric activity does not deviate much from what is typical for field stars of a similar spectral class. Title: Nanosecond Resolution Observations: Quantum-Optical Spectroscopy and Intensity Interferometry Authors: Dravins, D. Bibcode: 1981siwn.conf..253D Altcode: No abstract at ADS Title: Search for chromospheres in A-type stars. Authors: Dravins, D. Bibcode: 1981A&A....96...64D Altcode: A search for chromospheric emission in the Ca II H and K lines was made for eight main-sequence A-stars in the young clusters C 0838-528 (IC 2391) and in the Hyades, where (at least later-type) stars have generally enhanced chromospheric activity, making possible emission easier to detect. No evidence for emission was found in these stars and nor in Sirius (A 1 V). Title: Solar granulation - Influence of convection on spectral line asymmetries and wavelength shifts Authors: Dravins, D.; Lindegren, L.; Nordlund, A. Bibcode: 1981A&A....96..345D Altcode: The observed shapes and shifts of 311 Fe I lines in the spectrum of solar disk center and also of integrated sunlight are investigated. Line shapes are described using bisectors, and the dependence of these on line strength, excitation potential, and wavelength region is analyzed. A theoretical model atmosphere incorporating radiation-coupled, time-dependent hydrodymamics of solar convection is used to compute synthetic photospheric spectral lines. These lines exhibit asymmetries and wavelength shifts, and the observed bisector behavior can be closely reproduced. The detailed properties of, for example, convective motions and changing granulation constrast with wavelength manifest themselves in the detailed bisector shapes. It is confirmed that convection is the principal cause of solar line shifts, and errors in other suggested explanations are pointed out. It is concluded that the study of line shapes and shifts is a powerful tool for the analysis of solar photospheric convection. Title: Possible applications of long-baseline intensity interferometry. Authors: Dravins, D. Bibcode: 1981siha.conf..295D Altcode: Atmospheric phase distortions presently limit ground-based optical phase interferometers to baselines of the order of 100 m. Intensity interferometry, however, avoids both atmospheric and instrumental phase distortion problems and permits the operation of optical interferometers with baselines of more than 10 km between existing large telescopes. Such baselines may make feasible the search for stellar surface inhomogeneities, and although only very bright objects could be observed, the angular resolution of about 0.000001 arcsec obtained would permit the study of fine structure on the surfaces of nearby stars. Title: Photometric Properties of the IUE Flat-Field Calibration Exposures Authors: Dravins, D.; Linde, P. Bibcode: 1980idr..conf...85D Altcode: No abstract at ADS Title: Methods for accurate photographic stellar spectrophotometry using the solar spectrum as calibration Authors: Lind, J.; Dravins, D. Bibcode: 1980A&A....90..151L Altcode: Methods for photographic spectrophotometry using single-pass spectrographs are developed with the purpose of obtaining stellar spectra of sufficiently high quality to allow detailed spectral line studies over extended wavelength regions. The spectrograph instrumental profile and photographic development effects are investigated, and the corresponding MTFs are determined by measuring the modulation experienced by a calibration spectrum of skylight and moonlight which is exposed side by side with the stellar spectrum on each plate. Either of these calibration spectra is very similar to the accurately known spectrum of integrated sunlight, whose modulation in the observing/recording/measuring process is then determined. Title: Search for Spectral Line Polarization in the Solar Vacuum Ultraviolet Authors: Stenflo, J. O.; Dravins, D.; Wihlborg, N.; Bruns, A.; Prokofev, V. K.; Zhitnik, I. A.; Biverot, H.; Stenmark, L. Bibcode: 1980SoPh...66...13S Altcode: An instrument designed to record polarization in the region 120-150 nm of the solar spectrum was launched on the satellite Intercosmos-16, July 27, 1976. The aim was to search for resonance-line polarization that is caused by coherent scattering. Oblique reflections at gold- and aluminium-coated mirrors in the instrument were used to analyze the polarization. The average polarization of the Lα solar limb was found to be less than 1%. It is indicated how future improved VUV polarization measurements may be a diagnostic tool for chromospheric and coronal magnetic fields and for the three-dimensional geometry of the emitting structures. Title: Observed Solar Spectral Line Asymmetries and Wavelength Shifts due to Convection Authors: Dravins, D. Bibcode: 1980LNP...114...51D Altcode: 1980IAUCo..51...51D; 1980sttu.coll...51D No abstract at ADS Title: Comments on solar chromospheric activity compared to that of other stars (These comments were intended to be presented during the discussion but it was not possible for shortage of time.) Authors: Dravins, D. Bibcode: 1980fsoo.conf..266D Altcode: No abstract at ADS Title: The far-UV spectrum of the T Tauri star RU Lupi. Authors: Gahm, G. F.; Fredga, K.; Liseau, R.; Dravins, D. Bibcode: 1979A&A....73L...4G Altcode: The spectrum of the T Tauri star RU Lupi from 1150 to 3100 A has been observed from the IUE satellite. It is rich in emission lines, seen superimposed on a background continuum and traceable from Ly-alpha to 3100 A. The region from 2000 to 3100 A is dominated by metal line emission of the same nature as previously observed in the optical region. The resonance lines of Mg II at 2795 and 2780 A are exceedingly strong. In the region from 1150 to 2000 A the most conspicuous features are the very strong emission lines of C IV, Si IV and Si III, indicating that regions of very high temperature (50,000 to 100,000 K) exist around the star. Title: Comments on solar chromospheric activity compared to that of other stars. Authors: Dravins, D. Bibcode: 1979MmArc.106..266D Altcode: No abstract at ADS Title: Holography at the telescope - an interferometric method for recording stellar spectra in thick photographic emulsions. Authors: Lindegren, L.; Dravins, D. Bibcode: 1978A&A....67..241L Altcode: Low-resolution spectra (resolving power of no more than about 100) are recorded without any dispersive optics by direct focal-plane Lippmann photography using thick holographic emulsions. These record the Fourier transforms of the spectra, enabling spectrum reconstruction by reflected light and analysis with a microspectrophotometer. Since the spectral information is stored inside the emulsion and perpendicular to the holographic plate surface, problems with overlapping spectrograms in dense star fields are eliminated. Spectral resolution is set by emulsion thickness and is independent of seeing and telescope guiding. The holographic storage format appears suitable for automated spectral searches, and the future feasibility of a holographic spectral sky survey with Schmidt telescopes is suggested. Theoretical and experimental work is presented, and practical and theoretical limitations discussed. Title: High-dispersion astronomical spectroscopy with holographic and rules diffraction gratings. Authors: Dravins, D. Bibcode: 1978ApOpt..17..404D Altcode: Holographic gratings cause much less stray light and spectral degradation than classically ruled gratings. Their high groove densities enable high dispersion in first diffraction order and a high spectrograph throughput comparable to the best echelles. Their lower reflective efficiency is compensated by the avoidance of cross dispersers, enabling efficient high-fidelity spectroscopy with single-pass spectrographs. Instrumental profiles of the ESO coude spectrograph with large holographic and ruled gratings have been studied in detail, and their effects on astronomical spectra are discussed and compared to those of other instruments. Title: Holographic gratings for astronomical spectroscopy. Authors: Dravins, D. Bibcode: 1978sss..meet...E5D Altcode: No abstract at ADS Title: Diffraction Gratings - Holographic and Ruled Authors: Dravins, D. Bibcode: 1978hrs..conf..221D Altcode: No abstract at ADS Title: Comments on solar chromospheric activity compared to that of other stars Authors: Dravins, D. Bibcode: 1978fsoo.conf..266D Altcode: No abstract at ADS Title: Beryllium in Alpha Centauri A and constraints on beryllium formation. Authors: Dravins, D.; Hultqvist, L. Bibcode: 1977A&A....55..463D Altcode: The equivalent width of the Be II 313.1-nm line in Alpha Cen A (G2 V) is determined to be 1.25 times the solar value, leading to a Be/H abundance ratio of 2.5 by 10 to the -11th power. The age of Alpha Cen A is estimated to 8 billion years. This, together with observed Be in the old stars Delta Eri (K0 IV) and Mu Her A (G5 IV), indicates that beryllium existed in significant amounts relatively early in the history of the Galaxy. Title: Observations of resonance-line polarization in the solar EUV. Authors: Stenflo, J. O.; Dravins, D.; Öhman, Y.; Wihlborg, N.; Bruns, A.; Prokof'ev, V. K.; Severnyj, A.; Severny, A.; Zhitnik, I. A.; Biverot, H.; Stenmark, L. Bibcode: 1977ROLun..12..147S Altcode: No abstract at ADS Title: Chromospheric activity and atmospheric dynamics in Rho Puppis and other Delta-Scuti stars. Authors: Dravins, D.; Lind, J.; Sarg, K. Bibcode: 1977A&A....54..381D Altcode: Summary. The Scuti pulsating variable Pup (P = 0d 14) is studied using simultaneous spectrographic and photometric observations. A transient Ca ii K chromospheric emission is seen at a phase near maximum outward acceleration, shock waves are identified from radial velocity behavior at different atmospheric levels, a secondary minimum is seen in radial velocity and phase- shifts are detected between light-curves for different wavelengths. The latter permit a stellar radius determination through a phase-matching method. In addition, four other a Scuti stars have been studied for K emission. Key words: variable stars - stellar chromospheres shock waves - stellar radii uvby photometry Title: Spectrograph Instrumental Profiles--A Comparison between Holographic and Ruled Gratings. Authors: Dravins, D. Bibcode: 1976BAAS....8..517D Altcode: No abstract at ADS Title: Chromospheric Activity in f- and G-Stars Authors: Dravins, D. Bibcode: 1976IAUS...71..469D Altcode: No abstract at ADS Title: Observation of convection in stellar atmospheres Authors: Dravins, D. Bibcode: 1976pmas.conf..459D Altcode: No abstract at ADS Title: a Self-Scanned Silicon Diode Array for Astronomical Photometry Authors: Dravins, D. Bibcode: 1975ASSL...54...97D Altcode: 1975ipta.proc...97D No abstract at ADS Title: Physical limits to attainable accuracies in stellar radial velocities. Authors: Dravins, D. Bibcode: 1975A&A....43...45D Altcode: It is shown that true stellar radial velocities cannot be obtained from spectral lines with a precision of better than 0.5 km/sec unless detailed knowledge of small-scale inhomogeneities in the line-formation region is available. Two models are calculated which demonstrate that convection-cell velocity patterns in particular cause line asymmetries and average wavelength shifts that depend critically on many unknown parameters and are likely to vary from star to star. It is suggested that more accurate radial velocities might be obtained from strong lines that form in layers above both the convection zone and the region of convective overshoot. The Na I D(1) line at 5896 A is recommended as the best line to use for this purpose, although it may be contaminated by chromospheric emission as well as circumstellar and interstellar absorption. Title: Height Dependence of Horizontal Velocities in the Photosphere Authors: Dravins, D. Bibcode: 1975BAAS....7..363D Altcode: No abstract at ADS Title: Horizontal Velocities in the Solar Photosphere Authors: Dravins, D. Bibcode: 1975SoPh...40...53D Altcode: Horizontal macroscopic velocities Vhor in the photosphere are studied. High-resolution spectrograms of quiet regions are analyzed for center-limb variation of rms Doppler shifts. The data are treated to assure that the observed velocities refer to constant size volumes on the Sun (800 × × 3000 × 250 km), independent of μ. Using known height variation of vertical velocities and calculated line formation heights, the height dependence of «Vhor» is obtained. From a value around 450 m s−1 it decreases rapidly with increasing height. To study also small-scale velocities, the time evolution of subarcsecond size elements in the photospheric network (solar filigree) is studied on filtergrams. It is concluded that they show proper motions implying «Vhor» about 1 km s−1. Title: Instrument profiles in stellar spectrography. Authors: Dravins, D. Bibcode: 1975ROLun...5..241D Altcode: No abstract at ADS Title: Measurements in stellar spectra: Lectures at the Lund Observatory Nordic Summer School 1975 Authors: Ardeberg, A.; Larsson-Leander, G.; Lynga, G.; Dravins, D.; Andersen, J. Bibcode: 1975STIN...7634081A Altcode: Transcripts of five lecture series given during the 1975 summer are given. These deal with the following subjects: measurement of stellar continuous spectra, measurement of spectral lines, automatic evaluation methods, instrument profiles in stellar spectrographs, and modern spectrograph design. Title: Convection in the photosphere of Arcturus Authors: Dravins, D. Bibcode: 1974A&A....36..143D Altcode: Convective motions in stellar atmospheres involve hot gases that rise, cool off and then sink back. High-excitation spectral lines are preferentially formed in the hot, rising and thus locally blue-shifted elements while low-excitation lines are preferentially formed in the cooler, sinking and red-shifted elements. By comparing accurate wavelengths for spectral lines in Arcturus with laboratory values, a relation is found, such that high-excitation lines are systematically blue-shifted relative to low-excitation lines. This relation is very similar to the one previously known for the sun and is interpreted as the existence of convection cells, similar to the solar granulation, in the photosphere of Arcturus. Title: Magnetic Field and Electric Current Structure in the Chromosphere Authors: Dravins, D. Bibcode: 1974SoPh...37..323D Altcode: Three dimensional vector magnetic field structure throughout the chromosphere above an active region is deduced by combining high resolution Hα filtergrams with a simultaneous digital magnetogram. An analog model of the field is made with 400 metal wires representing fieldlines which are assumed to outline the Hα structure. The height extent of the field is determined from vertical field gradient observations around sunspots, from observed fibril heights and from an assumption that the sources of the field should be largely local. After digitization the magnetic field H matrix is retrieved. Electric current densities j are computed from j=curl H. The currents (typically 10 mA m−2) flow in patterns not similar to observed features and not parallel to magnetic fields. Lorentz forces are computed from {ie0323-01}. The force structures correspond to observed solar features and a series of observed dynamics may be expected: downward motion in bipolar areas in lower chromosphere, an outflow of the outer chromosphere into the corona with radially outward flow above bipolar plage regions (where coronal streamers are observed) and motions of arch filament systems. Observed current structure and magnitude agree well with previous vector magnetograph observations but disagree with theoretical current-free or force-free concepts. A dynamic chromosphere with electromagnetic forces in action is thus inferred from observations. Title: Evolution of Structures in the Bright Hα Network Authors: Dravins, D. Bibcode: 1974IAUS...56..257D Altcode: No abstract at ADS Title: A Possible Solar Electrograph Authors: Dravins, Dainis Bibcode: 1973ApL....13..243D Altcode: No abstract at ADS Title: Solen sedd i väteljus. Authors: Dravins, D. Bibcode: 1973ATi.....6..100D Altcode: No abstract at ADS Title: Magnetic Fields, Electric Currents and Lorentz Forces in the Chromosphere. Authors: Dravins, D. Bibcode: 1972BAAS....4Q.309D Altcode: No abstract at ADS Title: Ballongastronomi. Authors: Dravins, D. Bibcode: 1970ATi.....3...53D Altcode: No abstract at ADS