Search

Your search keyword '"Witzke, Veronika"' showing total 28 results
Start Over Author "Witzke, Veronika"
28 results on '"Witzke, Veronika"'

1. The PLATO Mission

Author

Rauer, Heike, Aerts, Conny, Cabrera, Juan, Deleuil, Magali, Erikson, Anders, Gizon, Laurent, Goupil, Mariejo, Heras, Ana, Lorenzo-Alvarez, Jose, Marliani, Filippo, Martin-Garcia, Cesar, Mas-Hesse, J. Miguel, O'Rourke, Laurence, Osborn, Hugh, Pagano, Isabella, Piotto, Giampaolo, Pollacco, Don, Ragazzoni, Roberto, Ramsay, Gavin, Udry, Stéphane, Appourchaux, Thierry, Benz, Willy, Brandeker, Alexis, Güdel, Manuel, Janot-Pacheco, Eduardo, Kabath, Petr, Kjeldsen, Hans, Min, Michiel, Santos, Nuno, Smith, Alan, Suarez, Juan-Carlos, Werner, Stephanie C., Aboudan, Alessio, Abreu, Manuel, Acuña, Lorena, Adams, Moritz, Adibekyan, Vardan, Affer, Laura, Agneray, François, Agnor, Craig, Børsen-Koch, Victor Aguirre, Ahmed, Saad, Aigrain, Suzanne, Al-Bahlawan, Ashraf, Gil, M de los Angeles Alcacera, Alei, Eleonora, Alencar, Silvia, Alexander, Richard, Alfonso-Garzón, Julia, Alibert, Yann, Prieto, Carlos Allende, Almeida, Leonardo, Sobrino, Roi Alonso, Altavilla, Giuseppe, Althaus, Christian, Trujillo, Luis Alonso Alvarez, Amarsi, Anish, Eiff, Matthias Ammler-von, Amôres, Eduardo, Andrade, Laerte, Antoniadis-Karnavas, Alexandros, António, Carlos, del Moral, Beatriz Aparicio, Appolloni, Matteo, Arena, Claudio, Armstrong, David, Aliaga, Jose Aroca, Asplund, Martin, Audenaert, Jeroen, Auricchio, Natalia, Avelino, Pedro, Baeke, Ann, Baillié, Kevin, Balado, Ana, Balestra, Andrea, Ball, Warrick, Ballans, Herve, Ballot, Jerome, Barban, Caroline, Barbary, Gaële, Barbieri, Mauro, Forteza, Sebastià Barceló, Barker, Adrian, Barklem, Paul, Barnes, Sydney, Navascues, David Barrado, Barragan, Oscar, Baruteau, Clément, Basu, Sarbani, Baudin, Frederic, Baumeister, Philipp, Bayliss, Daniel, Bazot, Michael, Beck, Paul G., Bedding, Tim, Belkacem, Kevin, Bellinger, Earl, Benatti, Serena, Benomar, Othman, Bérard, Diane, Bergemann, Maria, Bergomi, Maria, Bernardo, Pierre, Biazzo, Katia, Bignamini, Andrea, Bigot, Lionel, Billot, Nicolas, Binet, Martin, Biondi, David, Biondi, Federico, Birch, Aaron C., Bitsch, Bertram, Ceballos, Paz Victoria Bluhm, Bódi, Attila, Bognár, Zsófia, Boisse, Isabelle, Bolmont, Emeline, Bonanno, Alfio, Bonavita, Mariangela, Bonfanti, Andrea, Bonfils, Xavier, Bonito, Rosaria, Bonomo, Aldo Stefano, Börner, Anko, Saikia, Sudeshna Boro, Martín, Elisa Borreguero, Borsa, Francesco, Borsato, Luca, Bossini, Diego, Bouchy, Francois, Boué, Gwenaël, Boufleur, Rodrigo, Boumier, Patrick, Bourrier, Vincent, Bowman, Dominic M., Bozzo, Enrico, Bradley, Louisa, Bray, John, Bressan, Alessandro, Breton, Sylvain, Brienza, Daniele, Brito, Ana, Brogi, Matteo, Brown, Beverly, Brown, David, Brun, Allan Sacha, Bruno, Giovanni, Bruns, Michael, Buchhave, Lars A., Bugnet, Lisa, Buldgen, Gaël, Burgess, Patrick, Busatta, Andrea, Busso, Giorgia, Buzasi, Derek, Caballero, José A., Cabral, Alexandre, Calderone, Flavia, Cameron, Robert, Cameron, Andrew, Campante, Tiago, Martins, Bruno Leonardo Canto, Cara, Christophe, Carone, Ludmila, Carrasco, Josep Manel, Casagrande, Luca, Casewell, Sarah L., Cassisi, Santi, Castellani, Marco, Castro, Matthieu, Catala, Claude, Fernández, Irene Catalán, Catelan, Márcio, Cegla, Heather, Cerruti, Chiara, Cessa, Virginie, Chadid, Merieme, Chaplin, William, Charpinet, Stephane, Chiappini, Cristina, Chiarucci, Simone, Chiavassa, Andrea, Chinellato, Simonetta, Chirulli, Giovanni, Christensen-Dalsgaard, Jorgen, Church, Ross, Claret, Antonio, Clarke, Cathie, Claudi, Riccardo, Clermont, Lionel, Coelho, Hugo, Coelho, Joao, Cogato, Fabrizio, Colomé, Josep, Condamin, Mathieu, Conseil, Simon, Corbard, Thierry, Correia, Alexandre C. M., Corsaro, Enrico, Cosentino, Rosario, Costes, Jean, Cottinelli, Andrea, Covone, Giovanni, Creevey, Orlagh L., Crida, Aurelien, Csizmadia, Szilard, Cunha, Margarida, Curry, Patrick, da Costa, Jefferson, da Silva, Francys, Dalal, Shweta, Damasso, Mario, Damiani, Cilia, Damiani, Francesco, Chagas, Maria Liduina das, Davies, Melvyn, Davies, Guy, Davies, Ben, Davison, Gary, de Almeida, Leandro, de Angeli, Francesca, de Barros, Susana Cristina Cabral, Leão, Izan de Castro, de Freitas, Daniel Brito, de Freitas, Marcia Cristina, De Martino, Domitilla, de Medeiros, José Renan, de Paula, Luiz Alberto, de Plaa, Jelle, De Ridder, Joris, Deal, Morgan, Decin, Leen, Deeg, Hans, Degl'Innocenti, Scilla, Deheuvels, Sebastien, del Burgo, Carlos, Del Sordo, Fabio, Delgado-Mena, Elisa, Demangeon, Olivier, Denk, Tilmann, Derekas, Aliz, Desidera, Silvano, Dexet, Marc, Di Criscienzo, Marcella, Di Giorgio, Anna Maria, Di Mauro, Maria Pia, Rial, Federico Jose Diaz, Díaz-García, José-Javier, Dima, Marco, Dinuzzi, Giacomo, Dionatos, Odysseas, Distefano, Elisa, Nascimento Jr., Jose-Dias do, Domingo, Albert, D'Orazi, Valentina, Dorn, Caroline, Doyle, Lauren, Duarte, Elena, Ducellier, Florent, Dumaye, Luc, Dumusque, Xavier, Dupret, Marc-Antoine, Eggenberger, Patrick, Ehrenreich, David, Eigmüller, Philipp, Eising, Johannes, Emilio, Marcelo, Eriksson, Kjell, Ermocida, Marco, Giribaldi, Riano Isidoro Escate, Eschen, Yoshi, Estrela, Inês, Evans, Dafydd Wyn, Fabbian, Damian, Fabrizio, Michele, Faria, João Pedro, Farina, Maria, Farinato, Jacopo, Feliz, Dax, Feltzing, Sofia, Fenouillet, Thomas, Ferrari, Lorenza, Ferraz-Mello, Sylvio, Fialho, Fabio, Fienga, Agnes, Figueira, Pedro, Fiori, Laura, Flaccomio, Ettore, Focardi, Mauro, Foley, Steve, Fontignie, Jean, Ford, Dominic, Fornazier, Karin, Forveille, Thierry, Fossati, Luca, Franca, Rodrigo de Marca, da Silva, Lucas Franco, Frasca, Antonio, Fridlund, Malcolm, Furlan, Marco, Gabler, Sarah-Maria, Gaido, Marco, Gallagher, Andrew, Galli, Emanuele, Garcia, Rafael A., Hernández, Antonio García, Munoz, Antonio Garcia, García-Vázquez, Hugo, Haba, Rafael Garrido, Gaulme, Patrick, Gauthier, Nicolas, Gehan, Charlotte, Gent, Matthew, Georgieva, Iskra, Ghigo, Mauro, Giana, Edoardo, Gill, Samuel, Girardi, Leo, Winter, Silvia Giuliatti, Giusi, Giovanni, da Silva, João Gomes, Zazo, Luis Jorge Gómez, Gomez-Lopez, Juan Manuel, Hernández, Jonay Isai González, Murillo, Kevin Gonzalez, Gorius, Nicolas, Gouel, Pierre-Vincent, Goulty, Duncan, Granata, Valentina, Grenfell, John Lee, Grießbach, Denis, Grolleau, Emmanuel, Grouffal, Salomé, Grziwa, Sascha, Guarcello, Mario Giuseppe, Gueguen, Loïc, Guenther, Eike Wolf, Guilhem, Terrasa, Guillerot, Lucas, Guiot, Pierre, Guterman, Pascal, Gutiérrez, Antonio, Gutiérrez-Canales, Fernando, Hagelberg, Janis, Haldemann, Jonas, Hall, Cassandra, Handberg, Rasmus, Harrison, Ian, Harrison, Diana L., Hasiba, Johann, Haswell, Carole A., Hatalova, Petra, Hatzes, Artie, Haywood, Raphaelle, Hébrard, Guillaume, Heckes, Frank, Heiter, Ulrike, Hekker, Saskia, Heller, René, Helling, Christiane, Helminiak, Krzysztof, Hemsley, Simon, Heng, Kevin, Hermans, Aline, Hermes, JJ, Torres, Nadia Hidalgo, Hinkel, Natalie, Hobbs, David, Hodgkin, Simon, Hofmann, Karl, Hojjatpanah, Saeed, Houdek, Günter, Huber, Daniel, Huesler, Joseph, Hui-Bon-Hoa, Alain, Huygen, Rik, Huynh, Duc-Dat, Iro, Nicolas, Irwin, Jonathan, Irwin, Mike, Izidoro, André, Jacquinod, Sophie, Jannsen, Nicholas Emborg, Janson, Markus, Jeszenszky, Harald, Jiang, Chen, Mancebo, Antonio José Jimenez, Jofre, Paula, Johansen, Anders, Johnston, Cole, Jones, Geraint, Kallinger, Thomas, Kálmán, Szilárd, Kanitz, Thomas, Karjalainen, Marie, Karjalainen, Raine, Karoff, Christoffer, Kawaler, Steven, Kawata, Daisuke, Keereman, Arnoud, Keiderling, David, Kennedy, Tom, Kenworthy, Matthew, Kerschbaum, Franz, Kidger, Mark, Kiefer, Flavien, Kintziger, Christian, Kislyakova, Kristina, Kiss, László, Klagyivik, Peter, Klahr, Hubert, Klevas, Jonas, Kochukhov, Oleg, Köhler, Ulrich, Kolb, Ulrich, Koncz, Alexander, Korth, Judith, Kostogryz, Nadiia, Kovács, Gábor, Kovács, József, Kozhura, Oleg, Krivova, Natalie, Kučinskas, Arunas, Kuhlemann, Ilyas, Kupka, Friedrich, Laauwen, Wouter, Labiano, Alvaro, Lagarde, Nadege, Laget, Philippe, Laky, Gunter, Lam, Kristine Wai Fun, Lambrechts, Michiel, Lammer, Helmut, Lanza, Antonino Francesco, Lanzafame, Alessandro, Martiz, Mariel Lares, Laskar, Jacques, Latter, Henrik, Lavanant, Tony, Lawrenson, Alastair, Lazzoni, Cecilia, Lebre, Agnes, Lebreton, Yveline, Etangs, Alain Lecavelier des, Leinhardt, Zoe, Leleu, Adrien, Lendl, Monika, Leto, Giuseppe, Levillain, Yves, Libert, Anne-Sophie, Lichtenberg, Tim, Ligi, Roxanne, Lignieres, Francois, Lillo-Box, Jorge, Linsky, Jeffrey, Liu, John Scige, Loidolt, Dominik, Longval, Yuying, Lopes, Ilídio, Lorenzani, Andrea, Ludwig, Hans-Guenter, Lund, Mikkel, Lundkvist, Mia Sloth, Luri, Xavier, Maceroni, Carla, Madden, Sean, Madhusudhan, Nikku, Maggio, Antonio, Magliano, Christian, Magrin, Demetrio, Mahy, Laurent, Maibaum, Olaf, Malac-Allain, LeeRoy, Malapert, Jean-Christophe, Malavolta, Luca, Maldonado, Jesus, Mamonova, Elena, Manchon, Louis, Mann, Andrew, Mantovan, Giacomo, Marafatto, Luca, Marconi, Marcella, Mardling, Rosemary, Marigo, Paola, Marinoni, Silvia, Marques, Érico, Marques, Joao Pedro, Marrese, Paola Maria, Marshall, Douglas, Perales, Silvia Martínez, Mary, David, Marzari, Francesco, Masana, Eduard, Mascher, Andrina, Mathis, Stéphane, Mathur, Savita, Figueiredo, Ana Carolina Mattiuci, Maxted, Pierre F. L., Mazeh, Tsevi, Mazevet, Stephane, Mazzei, Francesco, McCormac, James, McMillan, Paul, Menou, Lucas, Merle, Thibault, Meru, Farzana, Mesa, Dino, Messina, Sergio, Mészáros, Szabolcs, Meunier, Nadége, Meunier, Jean-Charles, Micela, Giuseppina, Michaelis, Harald, Michel, Eric, Michielsen, Mathias, Michtchenko, Tatiana, Miglio, Andrea, Miguel, Yamila, Milligan, David, Mirouh, Giovanni, Mitchell, Morgan, Moedas, Nuno, Molendini, Francesca, Molnár, László, Mombarg, Joey, Montalban, Josefina, Montalto, Marco, Monteiro, Mário J. P. F. G., Morales, Juan Carlos, Morales-Calderon, Maria, Morbidelli, Alessandro, Mordasini, Christoph, Moreau, Chrystel, Morel, Thierry, Morello, Guiseppe, Morin, Julien, Mortier, Annelies, Mosser, Benoît, Mourard, Denis, Mousis, Olivier, Moutou, Claire, Mowlavi, Nami, Moya, Andrés, Muehlmann, Prisca, Muirhead, Philip, Munari, Matteo, Musella, Ilaria, Mustill, Alexander James, Nardetto, Nicolas, Nardiello, Domenico, Narita, Norio, Nascimbeni, Valerio, Nash, Anna, Neiner, Coralie, Nelson, Richard P., Nettelmann, Nadine, Nicolini, Gianalfredo, Nielsen, Martin, Niemi, Sami-Matias, Noack, Lena, Noels-Grotsch, Arlette, Noll, Anthony, Norazman, Azib, Norton, Andrew J., Nsamba, Benard, Ofir, Aviv, Ogilvie, Gordon, Olander, Terese, Olivetto, Christian, Olofsson, Göran, Ong, Joel, Ortolani, Sergio, Oshagh, Mahmoudreza, Ottacher, Harald, Ottensamer, Roland, Ouazzani, Rhita-Maria, Paardekooper, Sijme-Jan, Pace, Emanuele, Pajas, Miriam, Palacios, Ana, Palandri, Gaelle, Palle, Enric, Paproth, Carsten, Parro, Vanderlei, Parviainen, Hannu, Granado, Javier Pascual, Passegger, Vera Maria, Pastor-Morales, Carmen, Pätzold, Martin, Pedersen, May Gade, Hidalgo, David Pena, Pepe, Francesco, Pereira, Filipe, Persson, Carina M., Pertenais, Martin, Peter, Gisbert, Petit, Antoine C., Petit, Pascal, Pezzuto, Stefano, Pichierri, Gabriele, Pietrinferni, Adriano, Pinheiro, Fernando, Pinsonneault, Marc, Plachy, Emese, Plasson, Philippe, Plez, Bertrand, Poppenhaeger, Katja, Poretti, Ennio, Portaluri, Elisa, Portell, Jordi, de Mello, Gustavo Frederico Porto, Poyatos, Julien, Pozuelos, Francisco J., Moroni, Pier Giorgio Prada, Pricopi, Dumitru, Prisinzano, Loredana, Quade, Matthias, Quirrenbach160, ndreas, Reina6, Julio Arturo Rabanal, Soares, Maria Cristina Rabello, Raimondo, Gabriella, Rainer, Monica, Rodón, Jose Ramón, Ramón-Ballesta, Alejandro, Zapata, Gonzalo Ramos, Rätz, Stefanie, Rauterberg, Christoph, Redman, Bob, Redmer, Ronald, Reese, Daniel, Regibo, Sara, Reiners, Ansgar, Reinhold, Timo, Renie, Christian, Ribas, Ignasi, Ribeiro, Sergio, Ricciardi, Thiago Pereira, Rice, Ken, Richard, Olivier, Riello, Marco, Rieutord, Michel, Ripepi, Vincenzo, Rixon, Guy, Rockstein, Steve, Rodríguez, María Teresa Rodrigo, Díaz, Luisa Fernanda Rodríguez, Garcia, Juan Pablo Rodriguez, Rodriguez-Gomez, Julio, Roehlly, Yannick, Roig, Fernando, Rojas-Ayala, Bárbara, Rolf, Tobias, Rørsted, Jakob Lysgaard, Rosado, Hugo, Rosotti, Giovanni, Roth, Olivier, Roth, Markus, Rousseau, Alex, Roxburgh, Ian, Roy, Fabrice, Royer, Pierre, Ruane, Kirk, Mastropasqua, Sergio Rufini, de Galarreta, Claudia Ruiz, Russi, Andrea, Saar, Steven, Saillenfest, Melaine, Salaris, Maurizio, Salmon, Sebastien, Saltas, Ippocratis, Samadi, Réza, Samadi, Aunia, Samra, Dominic, da Silva, Tiago Sanches, Carrasco, Miguel Andrés Sánchez, Santerne, Alexandre, Santoli, Francesco, Santos, Ângela R. G., Mesa, Rosario Sanz, Sarro, Luis Manuel, Scandariato, Gaetano, Schäfer, Martin, Schlafly, Edward, Schmider, François-Xavier, Schneider, Jean, Schou, Jesper, Schunker, Hannah, Schwarzkopf, Gabriel Jörg, Serenelli, Aldo, Seynaeve, Dries, Shan, Yutong, Shapiro, Alexander, Shipman, Russel, Sicilia, Daniela, Sanmartin, Maria Angeles Sierra, Sigot, Axelle, Silliman, Kyle, Silvotti, Roberto, Simon, Attila E., Napoli, Ricardo Simoyama, Skarka, Marek, Smalley, Barry, Smiljanic, Rodolfo, Smit, Samuel, Smith, Alexis, Smith, Leigh, Snellen, Ignas, Sódor, Ádám, Sohl, Frank, Solanki, Sami K., Sortino, Francesca, Sousa, Sérgio, Southworth, John, Souto, Diogo, Sozzetti, Alessandro, Stamatellos, Dimitris, Stassun, Keivan, Steller, Manfred, Stello, Dennis, Stelzer, Beate, Stiebeler, Ulrike, Stokholm, Amalie, Storelvmo, Trude, Strassmeier, Klaus, Strøm, Paul Anthony, Strugarek, Antoine, Sulis, Sophia, Švanda, Michal, Szabados, László, Szabó, Róbert, Szabó, Gyula M., Szuszkiewicz, Ewa, Talens, Geert Jan, Teti, Daniele, Theisen, Tom, Thévenin, Frédéric, Thoul, Anne, Tiphene, Didier, Titz-Weider, Ruth, Tkachenko, Andrew, Tomecki, Daniel, Tonfat, Jorge, Tosi, Nicola, Trampedach, Regner, Traven, Gregor, Triaud, Amaury, Trønnes, Reidar, Tsantaki, Maria, Tschentscher, Matthias, Turin, Arnaud, Tvaruzka, Adam, Ulmer, Bernd, Ulmer-Moll, Solène, Ulusoy, Ceren, Umbriaco, Gabriele, Valencia, Diana, Valentini, Marica, Valio, Adriana, Guijarro, Ángel Luis Valverde, Van Eylen, Vincent, Van Grootel, Valerie, van Kempen, Tim A., Van Reeth, Timothy, Van Zelst, Iris, Vandenbussche, Bart, Vasiliou, Konstantinos, Vasilyev, Valeriy, de Mascarenhas, David Vaz, Vazan, Allona, Nunez, Marina Vela, Velloso, Eduardo Nunes, Ventura, Rita, Ventura, Paolo, Venturini, Julia, Trallero, Isabel Vera, Veras, Dimitri, Verdugo, Eva, Verma, Kuldeep, Vibert, Didier, Martinez, Tobias Vicanek, Vida, Krisztián, Vigan, Arthur, Villacorta, Antonio, Villaver, Eva, Aparicio, Marcos Villaverde, Viotto, Valentina, Vorobyov, Eduard, Vorontsov, Sergey, Wagner, Frank W., Walloschek, Thomas, Walton, Nicholas, Walton, Dave, Wang, Haiyang, Waters, Rens, Watson, Christopher, Wedemeyer, Sven, Weeks, Angharad, Weingril, Jörg, Weiss, Annita, Wendler, Belinda, West, Richard, Westerdorff, Karsten, Westphal, Pierre-Amaury, Wheatley, Peter, White, Tim, Whittaker, Amadou, Wickhusen, Kai, Wilson, Thomas, Windsor, James, Winter, Othon, Winther, Mark Lykke, Winton, Alistair, Witteck, Ulrike, Witzke, Veronika, Woitke, Peter, Wolter, David, Wuchterl, Günther, Wyatt, Mark, Yang, Dan, Yu, Jie, Sanchez, Ricardo Zanmar, Osorio, María Rosa Zapatero, Zechmeister, Mathias, Zhou, Yixiao, Ziemke, Claas, and Zwintz, Konstanze

Subjects
Astrophysics - Instrumentation and Methods for Astrophysics, Astrophysics - Earth and Planetary Astrophysics, Astrophysics - Solar and Stellar Astrophysics
Abstract

PLATO (PLAnetary Transits and Oscillations of stars) is ESA's M3 mission designed to detect and characterise extrasolar planets and perform asteroseismic monitoring of a large number of stars. PLATO will detect small planets (down to <2 R_(Earth)) around bright stars (<11 mag), including terrestrial planets in the habitable zone of solar-like stars. With the complement of radial velocity observations from the ground, planets will be characterised for their radius, mass, and age with high accuracy (5 %, 10 %, 10 % for an Earth-Sun combination respectively). PLATO will provide us with a large-scale catalogue of well-characterised small planets up to intermediate orbital periods, relevant for a meaningful comparison to planet formation theories and to better understand planet evolution. It will make possible comparative exoplanetology to place our Solar System planets in a broader context. In parallel, PLATO will study (host) stars using asteroseismology, allowing us to determine the stellar properties with high accuracy, substantially enhancing our knowledge of stellar structure and evolution. The payload instrument consists of 26 cameras with 12cm aperture each. For at least four years, the mission will perform high-precision photometric measurements. Here we review the science objectives, present PLATO's target samples and fields, provide an overview of expected core science performance as well as a description of the instrument and the mission profile at the beginning of the serial production of the flight cameras. PLATO is scheduled for a launch date end 2026. This overview therefore provides a summary of the mission to the community in preparation of the upcoming operational phases.

Published
2024

2. A roadmap for the atmospheric characterization of terrestrial exoplanets with JWST

Author

de Wit, Julien, Doyon, Rene, Rackham, Benjamin V, Lim, Olivia, Ducrot, Elsa, Kreidberg, Laura, Benneke, Bjoern, Ribas, Ignasi, Berardo, David, Niraula, Prajwal, Iyer, Aishwarya, Shapiro, Alexander, Kostogryz, Nadiia, Witzke, Veronika, Gillon, Michael, Agol, Eric, Meadows, Victoria, Burgasser, Adam J, Owen, James E, Fortney, Jonathan J, Selsis, Franck, Bello-Arufe, Aaron, de Beurs, Zoe, Bolmont, Emeline, Cowan, Nicolas, Dong, Chuanfei, Drake, Jeremy J, Garcia, Lionel, Greene, Thomas, Haworth, Thomas, Hu, Renyu, Kane, Stephen R, Kervella, Pierre, Koll, Daniel, Krissansen-Totton, Joshua, Lagage, Pierre-Olivier, Lichtenberg, Tim, Lustig-Yaeger, Jacob, Lingam, Manasvi, Turbet, Martin, Seager, Sara, Barkaoui, Khalid, Bell, Taylor J, Burdanov, Artem, Cadieux, Charles, Charnay, Benjamin, Cloutier, Ryan, Cook, Neil J, Correia, Alexandre CM, Dang, Lisa, Daylan, Tansu, Delrez, Laetitia, Edwards, Billy, Fauchez, Thomas J, Flagg, Laura, Fraschetti, Federico, Haqq-Misra, Jacob, Huang, Ziyu, Iro, Nicolas, Jayawardhana, Ray, Jehin, Emmanuel, Jin, Meng, Kite, Edwin, Kitzmann, Daniel, Kral, Quentin, Lafreniere, David, Libert, Anne-Sophie, Liu, Beibei, Mohanty, Subhanjoy, Morris, Brett M, Murray, Catriona A, Piaulet, Caroline, Pozuelos, Francisco J, Radica, Michael, Ranjan, Sukrit, Rathcke, Alexander, Roy, Pierre-Alexis, Schwieterman, Edward W, Turner, Jake D, Triaud, Amaury, and Way, Michael J

Subjects
Astronomical Sciences, Physical Sciences, Astronomical sciences, Particle and high energy physics, Space sciences
Published
2024

3. Stellar Surface Magnetic Fields Impact Limb Darkening

Author

Kostogryz, Nadiia M., Shapiro, Alexander I., Witzke, Veronika, Cameron, Robert H., Gizon, Laurent, Krivova, Natalie A., Ludwig, Hans-G., Maxted, Pierre F. L., Seager, Sara, Solanki, Sami K., and Valenti, Jeff

Subjects
Astrophysics - Solar and Stellar Astrophysics, Astrophysics - Earth and Planetary Astrophysics
Abstract

Stars appear darker at their limbs than at their disk centers because at the limb we are viewing the higher and cooler layers of stellar photospheres. Limb darkening derived from state-of-the-art stellar atmosphere models systematically fails to reproduce recent transiting exoplanet light curves from the Kepler, TESS, and JWST telescopes -- stellar brightness obtained from measurements drops less steeply towards the limb than predicted by models. All previous models assumed atmosphere devoid of magnetic fields. Here we use our new stellar atmosphere models computed with the 3D radiative magneto-hydrodynamic code MURaM to show that small-scale concentration of magnetic fields on the stellar surface affect limb darkening at a level that allows us to explain the observations. Our findings provide a way forward to improve the determination of exoplanet radii and especially the transmission spectroscopy analysis for transiting planets, which relies on a very accurate description of stellar limb darkening from the visible through the infrared. Furthermore, our findings imply that limb darkening allows measuring the small-scale magnetic field on stars with transiting planets., Comment: 19 pages, 6 figures This is the submission version of manuscript to Nature Astronomy

Published
2024

5. A roadmap for the atmospheric characterization of terrestrial exoplanets with JWST

Author

Initiative, TRAPPIST-1 JWST Community, de Wit, Julien, Doyon, René, Rackham, Benjamin V., Lim, Olivia, Ducrot, Elsa, Kreidberg, Laura, Benneke, Björn, Ribas, Ignasi, Berardo, David, Niraula, Prajwal, Iyer, Aishwarya, Shapiro, Alexander, Kostogryz, Nadiia, Witzke, Veronika, Gillon, Michaël, Agol, Eric, Meadows, Victoria, Burgasser, Adam J., Owen, James E., Fortney, Jonathan J., Selsis, Franck, Bello-Arufe, Aaron, de Beurs, Zoë, Bolmont, Emeline, Cowan, Nicolas, Dong, Chuanfei, Drake, Jeremy J., Garcia, Lionel, Greene, Thomas, Haworth, Thomas, Hu, Renyu, Kane, Stephen R., Kervella, Pierre, Koll, Daniel, Krissansen-Totton, Joshua, Lagage, Pierre-Olivier, Lichtenberg, Tim, Lustig-Yaeger, Jacob, Lingam, Manasvi, Turbet, Martin, Seager, Sara, Barkaoui, Khalid, Bell, Taylor J., Burdanov, Artem, Cadieux, Charles, Charnay, Benjamin, Cloutier, Ryan, Cook, Neil J., Correia, Alexandre C. M., Dang, Lisa, Daylan, Tansu, Delrez, Laetitia, Edwards, Billy, Fauchez, Thomas J., Flagg, Laura, Fraschetti, Federico, Haqq-Misra, Jacob, Huang, Ziyu, Iro, Nicolas, Jayawardhana, Ray, Jehin, Emmanuel, Jin, Meng, Kite, Edwin, Kitzmann, Daniel, Kral, Quentin, Lafrenière, David, Libert, Anne-Sophie, Liu, Beibei, Mohanty, Subhanjoy, Morris, Brett M., Murray, Catriona A., Piaulet, Caroline, Pozuelos, Francisco J., Radica, Michael, Ranjan, Sukrit, Rathcke, Alexander, Roy, Pierre-Alexis, Schwieterman, Edward W., Turner, Jake D., Triaud, Amaury, and Way, Michael J.

Subjects
Astrophysics - Earth and Planetary Astrophysics, Astrophysics - Instrumentation and Methods for Astrophysics, Astrophysics - Solar and Stellar Astrophysics
Abstract

Ultra-cool dwarf stars are abundant, long-lived, and uniquely suited to enable the atmospheric study of transiting terrestrial companions with JWST. Amongst them, the most prominent is the M8.5V star TRAPPIST-1 and its seven planets. While JWST Cycle 1 observations have started to yield preliminary insights into the planets, they have also revealed that their atmospheric exploration requires a better understanding of their host star. Here, we propose a roadmap to characterize the TRAPPIST-1 system -- and others like it -- in an efficient and robust manner. We notably recommend that -- although more challenging to schedule -- multi-transit windows be prioritized to mitigate the effects of stellar activity and gather up to twice more transits per JWST hour spent. We conclude that, for such systems, planets cannot be studied in isolation by small programs, but rather need large-scale, jointly space- and ground-based initiatives to fully exploit the capabilities of JWST for the exploration of terrestrial planets.

Published
2023
Full Text
View/download PDF

6. Testing MURaM and MPS-ATLAS against the quiet solar spectrum

Author

Witzke, Veronika, Shapiro, Alexander I., Kostogryz, Nadiia M., Mauviard, Lucien, Bhatia, Tanayveer S., Cameron, Robert, Gizon, Laurent, Przybylski, Damien, Solanki, Sami K., Unruh, Yvonne C., and Yue, Li

Subjects
Astrophysics - Solar and Stellar Astrophysics, Astrophysics - Instrumentation and Methods for Astrophysics
Abstract

Three-dimensional (3D) radiative magnetohydrodynamics (MHD) simulations are the only way to model stellar atmospheres without any ad hoc parameterisations. Several 3D radiative MHD codes have achieved good quantitative agreement with observables for our Sun. We aim to validate the most up-to-date version of the MURaM code against well established quiet Sun measurements, in particular spatially averaged measurements that are relevant for stellar studies. This validation extends the number of solar observables that MURaM can reproduce with high precision. It is also an essential condition for using MURaM to accurately calculate spectra of other cool stars. We simulate the solar upper convection zone and photosphere harbouring a small-scale-dynamo. Using time series of 3D snapshots we calculate the spectral irradiance, limb darkening and selected spectral lines, which we compare to observations. The computed observables agree well with the observations, in particular the limb darkening of the quiet Sun is reproduced remarkably well., Comment: 9 Page, 7 figures, accepted in A&A

Published
2023
Full Text
View/download PDF

7. Spectral variability of photospheric radiation due to faculae II: Facular contrasts for cool main-sequence stars

Author

Norris, Charlotte M., Unruh, Yvonne C., Witzke, Veronika, Solanki, Sami K., Krivova, Natalie A., Shapiro, Alexander I., Cameron, Robert, and Beeck, Benjamin

Subjects
Astrophysics - Solar and Stellar Astrophysics, Astrophysics - Earth and Planetary Astrophysics
Abstract

Magnetic features on the surface of stars, such as spots and faculae, cause stellar spectral variability on time-scales of days and longer. For stars other than the Sun, the spectral signatures of faculae are poorly understood, limiting our ability to account for stellar pollution in exoplanet transit observations. Here we present the first facular contrasts derived from magnetoconvection simulations for K0, M0 and M2 main-sequence stars and compare them to previous calculations for G2 main-sequence stars. We simulate photospheres and immediate subsurface layers of main-sequence spectral types between K0 and M2, with different injected vertical magnetic fields (0 G, 100 G, 300 G and 500 G) using MURaM, a 3D radiation-magnetohydrodynamics code. We show synthetic spectra and contrasts from the UV (300 nm) to the IR (10000 nm) calculated using the ATLAS9 radiative transfer code. The calculations are performed for nine viewing angles to characterise the facular radiation across the disc. The brightness contrasts of magnetic regions are found to change significantly across spectral type, wavelength and magnetic field strength, leading to the conclusion that accurate contrasts cannot be found by scaling solar values. This is due to features of different size, apparent structure and spectral brightness emerging in the presence of a given magnetic field for different spectral types., Comment: 17 pages, 12 figures, to be published in MNRAS

Published
2023
Full Text
View/download PDF

8. Can 1D radiative equilibrium models of faculae be used for calculating contamination of transmission spectra?

Author

Witzke, Veronika, Shapiro, Alexander I., Kostogryz, Nadiia M., Cameron, Robert, Rackham, Benjamin V., Seager, Sara, Solanki, Sami K., and Unruh, Yvonne C.

Subjects
Astrophysics - Solar and Stellar Astrophysics, Astrophysics - Earth and Planetary Astrophysics
Abstract

The reliable characterization of planetary atmospheres with transmission spectroscopy requires realistic modeling of stellar magnetic features, since features that are attributable to an exoplanet atmosphere could instead stem from the host star's magnetic activity. Current retrieval algorithms for analysing transmission spectra rely on intensity contrasts of magnetic features from 1D radiative-convective models. However, magnetic features, especially faculae, are not fully captured by such simplified models. Here we investigate how well such 1D models can reproduce 3D facular contrasts, taking a G2V star as an example. We employ the well established radiative magnetohydrodynamic code MURaM to obtain three-dimensional simulations of the magneto-convection and photosphere harboring a local small-scale-dynamo. Simulations without additional vertical magnetic fields are taken to describe the quiet solar regions, while simulations with initially 100 G, 200 G and 300 G vertical magnetic fields are used to represent different magnetic activity levels. Subsequently, the spectra emergent from the MURaM cubes are calculated with the MPS-ATLAS radiative transfer code. We find that the wavelength dependence of facular contrast from 1D radiative-convective models cannot reproduce facular contrasts obtained from 3D modeling. This has far reaching consequences for exoplanet characterization using transmission spectroscopy, where accurate knowledge of the host star is essential for unbiased inferences of the planetary atmospheric properties., Comment: 7 pages, 2 figures, submitted to APJL

Published
2022
Full Text
View/download PDF

9. Small-scale Dynamo in Cool Stars: I. Changes in stratification and near-surface convection for main-sequence spectral types

Author

Bhatia, Tanayveer S., Cameron, Robert H., Solanki, Sami K., Peter, Hardi, Przybylski, Damien, Witzke, Veronika, and Shapiro, Alexander

Subjects
Astrophysics - Solar and Stellar Astrophysics
Abstract

Some of the small-scale solar magnetic flux can be attributed to a small-scale dynamo (SSD) operating in the near-surface convection. The SSD fields have consequences for solar granular convection, basal flux, as well as chromospheric heating. A similar SSD mechanism is expected to be active in the near-surface convection of other cool main-sequence stars, but this has never been investigated. We aim to investigate changes in stratification and convection due to inclusion of SSD fields for F3V, G2V, K0V and M0V spectral types in the near-surface convection. 3D magnetohydrodynamic (MHD) models of the four stellar boxes, covering the subsurface convection zone up to the lower photosphere in a small cartesian box, are studied using the \textit{MURaM} radiative-MHD simulation code. The SSD runs are compared against reference hydrodynamic runs. An SSD is found to efficiently produce magnetic field with energies ranging between 5\% to 80\% of the plasma kinetic energy at different depths. This ratio tends to be larger for larger $T_{\mathrm{eff}}$. The relative change in density and gas pressure stratification for the deeper convective layers due to SSD magnetic fields is negligible, except for the F-star. For the F-star, there is a substantial reduction in convective velocities due to Lorentz force feedback from magnetic fields, which, in turn, reduces the turbulent pressure. SSD in near-surface convection for cool main-sequence stars introduces small but significant changes in thermodynamic stratification (especially for the F-star) due to reduction in convective velocities., Comment: Update (20.07.2023): an errata (appendix D) has been included to correct a small error in the derivation of turbulent pressure in appendix B. In addition, the text has been updated with the published version. 10 pages, 7 figures, accepted for publication in A&A

Published
2022
Full Text
View/download PDF

11. Forward modelling of Kepler-band variability due to faculae and spots

Author

Johnson, Luke J., Norris, Charlotte N., Unruh, Yvonne C., Solanki, Sami K., Krivova, Natalie, Witzke, Veronika, and Shapiro, Alexander I.

Subjects
Astrophysics - Solar and Stellar Astrophysics
Abstract

Variability observed in photometric lightcurves of late-type stars (on timescales longer than a day) is a dominant noise source in exoplanet surveys and results predominantly from surface manifestations of stellar magnetic activity, namely faculae and spots. The implementation of faculae in lightcurve models is an open problem, with scaling typically based on spectra equivalent to hot stellar atmospheres or assuming a solar-derived facular contrast. We modelled rotational (single period) lightcurves of active G2, K0, M0 and M2 stars, with Sun-like surface distributions and realistic limb-dependent contrasts for faculae and spots. The sensitivity of lightcurve variability to changes in model parameters such as stellar inclination, feature area coverage, spot temperature, facular region magnetic flux density and active band latitudes is explored. For our lightcurve modelling approach we used actress, a geometrically accurate model for stellar variability. actress generates 2-sphere maps representing stellar surfaces and populates them with user-prescribed spot and facular region distributions. From this, lightcurves can be calculated at any inclination. Quiet star limb darkening and limb-dependent facular contrasts were derived from MURaM 3D magnetoconvection simulations using ATLAS9. 1D stellar atmosphere models were used for the spot contrasts. We applied actress in Monte-Carlo simulations, calculating lightcurve variability amplitudes in the Kepler band. We found that, for a given spectral type and stellar inclination, spot temperature and spot area coverage have the largest effect on variability of all simulation parameters. For a spot coverage of 1%, the typical variability of a solar-type star is around 2 parts-per-thousand. The presence of faculae clearly affects the mean brightness and lightcurve shape, but has relatively little influence on the variability., Comment: 17 pages, 16 figures. Accepted for publication in MNRAS 22 April 2021

Published
2021
Full Text
View/download PDF

12. Where have all the solar-like stars gone? Rotation period detectability at various inclinations and metallicities

Author

Reinhold, Timo, Shapiro, Alexander I., Witzke, Veronika, Nèmec, Nina-E., Işık, Emre, and Solanki, Sami K.

Subjects
Astrophysics - Solar and Stellar Astrophysics
Abstract

The plethora of photometric data collected by the Kepler space telescope has promoted the detection of tens of thousands of stellar rotation periods. However, these periods are not found to an equal extent among different spectral types. Interestingly, early G-type stars with near-solar rotation periods are strongly underrepresented among those stars with known rotation periods. In this study we investigate whether the small number of such stars can be explained by difficulties in the period determination from photometric time series. For that purpose, we generate model light curves of early G-type stars with solar rotation periods for different inclination angles, metallicities and (magnitude-dependent) noise levels. We find that the detectability is determined by the predominant type of activity (i.e. spot or faculae domination) on the surface, which defines the degree of irregularity of the light curve, and further depends on the level of photometric noise. These two effects significantly complicate the period detection and explain the lack of solar-like stars with known near-solar rotation periods. We conclude that the rotation periods of the majority of solar-like stars with near-solar rotation periods remain undetected to date. Finally, we promote the use of new techniques to recover more periods of near-solar rotators., Comment: 14 pages, 7 figures, accepted for publication in ApJL

Published
2021
Full Text
View/download PDF

13. The influence of metallicity on stellar differential rotation and magnetic activity

Author

Karoff, Christoffer, Metcalfe, Travis S., Santos, Angela R. G., Montet, Benjamin T., Isaacson, Howard, Witzke, Veronika, Shapiro, Alexander I., Mathur, Savita, Davies, Guy R., Lund, Mikkel N., Garcia, Rafael A., Brun, Allan S., Salabert, David, Avelino, Pedro P., van Saders, Jennifer, Egeland, Ricky, Cunha, Margarida S., Campante, Tiago L., Chaplin, William J., Krivova, Natalie, Solanki, Sami K., Stritzinger, Maximilian, and Knudsen, Mads F.

Subjects
Astrophysics - Solar and Stellar Astrophysics
Abstract

Observations of Sun-like stars over the last half-century have improved our understanding of how magnetic dynamos, like that responsible for the 11-year solar cycle, change with rotation, mass and age. Here we show for the first time how metallicity can affect a stellar dynamo. Using the most complete set of observations of a stellar cycle ever obtained for a Sun-like star, we show how the solar analog HD 173701 exhibits solar-like differential rotation and a 7.4-year activity cycle. While the duration of the cycle is comparable to that generated by the solar dynamo, the amplitude of the brightness variability is substantially stronger. The only significant difference between HD 173701 and the Sun is its metallicity, which is twice the solar value. Therefore, this provides a unique opportunity to study the effect of the higher metallicity on the dynamo acting in this star and to obtain a comprehensive understanding of the physical mechanisms responsible for the observed photometric variability. The observations can be explained by the higher metallicity of the star, which is predicted to foster a deeper outer convection zone and a higher facular contrast, resulting in stronger variability., Comment: Submitted to ApJ

Published
2017
Full Text
View/download PDF

14. Shear instabilities in stellar objects : linear stability and non-linear evolution

Author

Witzke, Veronika

Subjects
516, QA Mathematics
Abstract

Shear flows have a significant impact on the dynamics in various astrophysical objects, including accretion discs and stellar interiors. Due to observational limitations the complex dynamics in stellar interiors that result in turbulent motions, mixing processes, and magnetic field generation, are not entirely understood. It is therefore necessary to investigate the inevitable small-scale dynamics via numerical calculations. In particular a thin region with strong shear at the base of the convection zone in the Sun, the tachocline, is believed to play an important role in the Sun's interior dynamics and magnetic field generation. Velocity measurements suggest a stable tachocline. However, helioseismology can only provide large-scale time-averaged measurements, so small scale turbulent motions can still be present. Therefore, studying the stability of shear flows and their non-linear evolution in a fully compressible polytropic atmosphere provides a fundamental understanding of potential motion in stellar interiors and is the main focus of this thesis. To commence the investigations a linear stability analysis of a stratified system in a two-dimensional Cartesian geometry is performed to study the effect of compressibility and thermal diffusivity on the stability threshold. In addition, this first investigation provides a reference for subsequent non-linear calculations. Focusing on a local model of unstable shear flows, direct numerical calculations are used to first compare numerical forcing methods to sustain a shear flow against viscous dissipation; and then to study the effect of key parameters on the saturated quasi-steady regime. Finally, magnetic fields are included and the full set of MHD equations is solved to study a potential kinematic dynamo in shear-driven turbulence.

Published
2017

15. Small-scale dynamo in cool stars

Author

Bhatia, Tanayveer S., primary, Cameron, Robert H., additional, Solanki, Sami K., additional, Peter, Hardi, additional, Przybylski, Damien, additional, Witzke, Veronika, additional, and Shapiro, Alexander, additional

Published
2023
Full Text
View/download PDF

16. Magnetic field affects stellar limb darkening

Author

Kostogryz, Nadiia, Shapiro, Aleksandr, Witzke, Veronika, Cameron, Robert, Gizon, Laurent, Krivova, Natalie, Maxted, Pierre F. L., Seager, Sara, Solanki, Sami K., and Valenti, Jeff

Abstract

Transit light curves are affected by host star darkening towards the limb, impacting transit profile and depth. Thus, accurate determination of planetary radii and atmospheric composition requires solving the problem of limb darkening for stars with different parameters. However, there is a conundrum: multiple observations show significantly brighter stellar limbs as compared to all available stellar models. We propose that neglecting surface stellar magnetic fields is the main issue in models of the limb darkening. Magnetic fields form within stars and emerge on their surface. Here, we focus on small-scale concentrations of surface magnetic field that create a rather uniform network on stellar surface. We simulated it using 3D radiative magnetohydrodynamics (MHD) code MURaM and radiative transfer code MPS-ATLAS. We found that including this network in our simulations allows reproducing stellar limb darkening deduced from the observations of Kepler and TESS transits, thus reconciling models and observations. The dependence of limb darkening on stellar surface magnetic field offers a fascinating prospect for measuring magnetization of stars with transiting planets. This method is especially promising since it is sensitive to small-scale fields, which in the exemplary case of the Sun play a crucial role in the total magnetic flux, and, thus, are important for comprehending stellar dynamo and star-planet interaction. All in all, the limb darkening approach presents an intriguing possibility to measure stellar magnetic fields using the upcoming PLATO mission, which is projected to discover numerous transiting planets. &nbsp

Published
2023
Full Text
View/download PDF

17. A roadmap to the efficient and robust characterization of temperate terrestrial planet atmospheres with JWST

Author

Initiative, TRAPPIST-1 JWST Community, de Wit, Julien, Doyon, René, Rackham, Benjamin V., Lim, Olivia, Ducrot, Elsa, Kreidberg, Laura, Benneke, Björn, Ribas, Ignasi, Berardo, David, Niraula, Prajwal, Iyer, Aishwarya, Shapiro, Alexander, Kostogryz, Nadiia, Witzke, Veronika, Gillon, Michaël, Agol, Eric, Meadows, Victoria, Burgasser, Adam J., Owen, James E., Fortney, Jonathan J., Selsis, Franck, Bello-Arufe, Aaron, Bolmont, Emeline, Cowan, Nicolas, Dong, Chuanfei, Drake, Jeremy J., Garcia, Lionel, Greene, Thomas, Haworth, Thomas, Hu, Renyu, Kane, Stephen R., Kervella, Pierre, Koll, Daniel, Krissansen-Totton, Joshua, Lagage, Pierre-Olivier, Lichtenberg, Tim, Lustig-Yaeger, Jacob, Lingam, Manasvi, Turbet, Martin, Seager, Sara, Barkaoui, Khalid, Bell, Taylor J., Burdanov, Artem, Cadieux, Charles, Charnay, Benjamin, Cloutier, Ryan, Cook, Neil J., Correia, Alexandre C. M., Dang, Lisa, Daylan, Tansu, Delrez, Laetitia, Edwards, Billy, Fauchez, Thomas J., Flagg, Laura, Fraschetti, Federico, Haqq-Misra, Jacob, Huang, Ziyu, Iro, Nicolas, Jayawardhana, Ray, Jehin, Emmanuel, Jin, Meng, Kite, Edwin, Kitzmann, Daniel, Kral, Quentin, Lafrenière, David, Libert, Anne-Sophie, Liu, Beibei, Mohanty, Subhanjoy, Morris, Brett M., Murray, Catriona A., Piaulet, Caroline, Pozuelos, Francisco J., Radica, Michael, Ranjan, Sukrit, Rathcke, Alexander, Roy, Pierre-Alexis, Schwieterman, Edward W., Turner, Jake D., Triaud, Amaury, Way, Michael J., Initiative, TRAPPIST-1 JWST Community, de Wit, Julien, Doyon, René, Rackham, Benjamin V., Lim, Olivia, Ducrot, Elsa, Kreidberg, Laura, Benneke, Björn, Ribas, Ignasi, Berardo, David, Niraula, Prajwal, Iyer, Aishwarya, Shapiro, Alexander, Kostogryz, Nadiia, Witzke, Veronika, Gillon, Michaël, Agol, Eric, Meadows, Victoria, Burgasser, Adam J., Owen, James E., Fortney, Jonathan J., Selsis, Franck, Bello-Arufe, Aaron, Bolmont, Emeline, Cowan, Nicolas, Dong, Chuanfei, Drake, Jeremy J., Garcia, Lionel, Greene, Thomas, Haworth, Thomas, Hu, Renyu, Kane, Stephen R., Kervella, Pierre, Koll, Daniel, Krissansen-Totton, Joshua, Lagage, Pierre-Olivier, Lichtenberg, Tim, Lustig-Yaeger, Jacob, Lingam, Manasvi, Turbet, Martin, Seager, Sara, Barkaoui, Khalid, Bell, Taylor J., Burdanov, Artem, Cadieux, Charles, Charnay, Benjamin, Cloutier, Ryan, Cook, Neil J., Correia, Alexandre C. M., Dang, Lisa, Daylan, Tansu, Delrez, Laetitia, Edwards, Billy, Fauchez, Thomas J., Flagg, Laura, Fraschetti, Federico, Haqq-Misra, Jacob, Huang, Ziyu, Iro, Nicolas, Jayawardhana, Ray, Jehin, Emmanuel, Jin, Meng, Kite, Edwin, Kitzmann, Daniel, Kral, Quentin, Lafrenière, David, Libert, Anne-Sophie, Liu, Beibei, Mohanty, Subhanjoy, Morris, Brett M., Murray, Catriona A., Piaulet, Caroline, Pozuelos, Francisco J., Radica, Michael, Ranjan, Sukrit, Rathcke, Alexander, Roy, Pierre-Alexis, Schwieterman, Edward W., Turner, Jake D., Triaud, Amaury, and Way, Michael J.

Abstract

Ultra-cool dwarf stars are abundant, long-lived, and uniquely suited to enable the atmospheric study of transiting terrestrial companions with JWST. Amongst them, the most prominent is the M8.5V star TRAPPIST-1 and its seven planets, which have been the favored targets of eight JWST Cycle 1 programs. While Cycle 1 observations have started to yield preliminary insights into the planets, they have also revealed that their atmospheric exploration requires a better understanding of their host star. Here, we propose a roadmap to characterize the TRAPPIST-1 system -- and others like it -- in an efficient and robust manner. We notably recommend that -- although more challenging to schedule -- multi-transit windows be prioritized to constrain stellar heterogeneities and gather up to 2$\times$ more transits per JWST hour spent. We conclude that in such systems planets cannot be studied in isolation by small programs, thus large-scale community-supported programs should be supported to enable the efficient and robust exploration of terrestrial exoplanets in the JWST era.

Published
2023

18. Spectral variability of photospheric radiation due to faculae – II. Facular contrasts for cool main-sequence stars.

Author

Norris, Charlotte M, Unruh, Yvonne C, Witzke, Veronika, Solanki, Sami K, Krivova, Natalie A, Shapiro, Alexander I, Yeo, Kok Leng, Cameron, Robert, and Beeck, Benjamin

Subjects
MAIN sequence (Astronomy), MAGNETIC flux density, STELLAR magnetic fields, RADIATION, RADIATIVE transfer, SOLAR photosphere, STELLAR atmospheres, STELLAR photospheres
Abstract

Magnetic features on the surface of stars, such as spots and faculae, cause stellar spectral variability on time-scales of days and longer. For stars other than the Sun, the spectral signatures of faculae are poorly understood, limiting our ability to account for stellar pollution in exoplanet transit observations. Here we present the first facular contrasts derived from magnetoconvection simulations for K0, M0, and M2 main-sequence stars and compare them to previous calculations for G2 main-sequence stars. We simulate photospheres and immediate subsurface layers of main-sequence spectral types between K0 and M2, with different injected vertical magnetic fields (0 G, 100 G, 300 G, and 500 G) using MURaM, a 3D radiation-magnetohydrodynamics code. We show synthetic spectra and contrasts from the UV (300 nm) to the IR (10 000 nm) calculated using the ATLAS9 radiative transfer code. The calculations are performed for nine viewing angles to characterize the facular radiation across the disc. The brightness contrasts of magnetic regions are found to change significantly across spectral type, wavelength, and magnetic field strength, leading to the conclusion that accurate contrasts cannot be found by scaling solar values. This is due to features of different size, apparent structure and spectral brightness emerging in the presence of a given magnetic field for different spectral types. [ABSTRACT FROM AUTHOR]

Published
2023
Full Text
View/download PDF

20. Small-scale dynamo in cool stars

Author

Bhatia, Tanayveer S., primary, Cameron, Robert H., additional, Solanki, Sami K., additional, Peter, Hardi, additional, Przybylski, Damien, additional, Witzke, Veronika, additional, and Shapiro, Alexander, additional

Published
2022
Full Text
View/download PDF

21. Modelling Solar Ca II H&K Emission Variations

Author

Sowmya, Krishnamurthy, Shapiro, Alexander I., Witzke, Veronika, Nèmec, Nina-E., Chatzistergos, Theodosis, Yeo, Kok Leng, Krivova, Natalie A., Solanki, Sami K., and Wolk, Scott

Subjects
The Sun and the Heliosphere, Solar chromosphere, 13. Climate action, Physics::Space Physics, Solar activity, Astrophysics::Solar and Stellar Astrophysics, Astrophysics::Earth and Planetary Astrophysics, Stellar activity
Abstract

The emission in the near ultraviolet Ca II H&K lines, often quantified via the S-index, has been serving as a prime proxy of solar and stellar magnetic activity. Despite the broad usage of the S-index, the link between the coverage of a stellar disk by magnetic features and Ca IIH&K emission is not fully understood. In order to fill this gap we developed a physics-based model to calculate the solar S-index. To this end, we made use of the distributions of the solar magnetic features derived from the simulations of magnetic flux emergence and surface transport, together with the Ca IIH&K spectra synthesized using a non-local thermodynamic equilibrium (non-LTE) radiative transfer code. We show that the value of the solar S-index is influenced by the inclination angle between the solar rotation axis and the observer’s line-of-sight, i.e. the solar S-index values obtained by an out-of-ecliptic observer are different from those obtained by an ecliptic-bound observer. This is important for comparing the magnetic activity of the Sun to other stars. We computed time series of the S-index as they would be observed at various inclinations dating back to 1700. We find that depending on the inclination and period of observations, the activity cycle in solar S-index can appear weaker or stronger than in stars with a solar-like level of magnetic activity. We show that there is nothing unusual about the solar chromospheric emission variations in the context of stars with near-solar magnetic activity.

Published
2021
Full Text
View/download PDF

22. Small-scale dynamo in an F-star: effects on near-surface stratification, convection and intensity

Author

Bhatia, Tanayveer, Cameron, Robert, Solanki, Sami, Peter, Hardi, Przybylski, Damien, Witzke, Veronika, Shapiro, Alexander, and Bhatia, Tanayveer

Subjects
Cool Stars on the main sequence, Small-scale dynamo, Near-surface convection, Astrophysics::Solar and Stellar Astrophysics, Simulation
Abstract

The emission from the photosphere of stars shows a systematic center-to-limb variation. In cool main-sequence stars, the near-surface convection has an impact on this variation, with implications for lightcurves of stars during planetary transits. In the Sun, there is strong evidence for a small-scale dynamo (SSD) maintaining the small-scale magnetic flux. We aim to investigate what additional effects such a field would play for other cool main-sequence stars. In our work we first concentrate on F-stars. This is because they have sonic velocities near the surface, implying a rough equipartition between internal and kinetic energies. In addition, an SSD might create a significant magnetic energy density to impact the results. We investigate the interplay between internal, kinetic and magnetic energies in 3D cartesian box MHD models of a F3V-star in the near-surface convection, using the MURaM radiative-MHD simulation code. Along with a reference hydrodynamic run, two MHD models with self-consistently generated magnetic fields with two different lower boundary conditions are considered. We find that the SSD process creates a magnetic field with energy within an order of magnitude of the internal and the kinetic energy. Compared to the hydrodynamic run, we find slight (~1-3%) but significant deviations in density, gas pressure and temperature stratification. At the surface, this corresponds to a temperature difference of ~130 K. As expected, there is a significant reduction in kinetic energy flux once the SSD is operational. The changes in intensity are more subtle, both in total intensity and granulation pattern. From this we conclude that the presence of an SSD will have a significant impact on the atmospheric structure and intensity characteristics seen at the surface. This makes it clear that it would be important to consider the spatially and temporally averaged effects of the SSD also for global stellar models.

Published
2021
Full Text
View/download PDF

23. Predictions of astrometric jitter for sun-like stars. II. dependence on ınclination, metallicity, and active-region nesting

Author

Krishnamurthy, Sowmya, Nemec, Nina Elisabeth, Shapiro, Alexander, Işık, Emre, Witzke, Veronika, Mints, Alexey, Krivova, Natalie, Solanki, Sami, TAÜ, Mühendislik Fakültesi, Bilgisayar Mühendisliği Bölümü, and Işık, Emre

Subjects
Güneş Işınımı, Cycles, Astrophysics::Instrumentation and Methods for Astrophysics, Solar Irradiance, Astrophysics::Solar and Stellar Astrophysics, Astrophysics::Earth and Planetary Astrophysics, Fahrräder, Reconstruction, Yeniden Yapılanma, Wiederaufbau, Astrophysics::Galaxy Astrophysics, Sonneneinstrahlung
Abstract

Ultra-precise astrometry from the Gaia mission is expected to lead to astrometric detections of more than 20,000 exoplanets in our Galaxy. One of the factors that could hamper such detections is the astrometric jitter caused by the magnetic activity of the planet host stars. In our previous study, we modeled astrometric jitter for the Sun observed equator-on. In this work, we generalize our model and calculate the photocenter jitter as it would be measured by the Gaia and Small-JASMINE missions for stars with solar rotation rate and effective temperature, but with various values of the inclination angle of the stellar rotation axis. In addition, we consider the effect of metallicity and of nesting of active regions (i.e., the tendency of active regions to emerge in the vicinity of each other). We find that, while the jitter of stars observed equator-on does not have any long-term trends and can be easily filtered out, the photocenters of stars observed out of their equatorial planes experience systematic shifts over the course of the activity cycle. Such trends allow the jitter to be detected with continuous measurements, in which case it can interfere with planet detectability. An increase in the metallicity is found to increase the jitter caused by stellar activity. Active-region nesting can further enhance the peak-to-peak amplitude of the photocenter jitter to a level that could be detected by Gaia.

Published
2021

27. The Influence of Metallicity on Stellar Differential Rotation and Magnetic Activity

Author

Karoff, Christoffer, primary, Metcalfe, Travis S., additional, Santos, Ângela R. G., additional, Montet, Benjamin T., additional, Isaacson, Howard, additional, Witzke, Veronika, additional, Shapiro, Alexander I., additional, Mathur, Savita, additional, Davies, Guy R., additional, Lund, Mikkel N., additional, Garcia, Rafael A., additional, Brun, Allan S., additional, Salabert, David, additional, Avelino, Pedro P., additional, Saders, Jennifer van, additional, Egeland, Ricky, additional, Cunha, Margarida S., additional, Campante, Tiago L., additional, Chaplin, William J., additional, Krivova, Natalie, additional, Solanki, Sami K., additional, Stritzinger, Maximilian, additional, and Knudsen, Mads F., additional

Published
2018
Full Text
View/download PDF

28. Modelling Solar Ca II H&K Emission Variations

Author

Sowmya, Krishnamurthy, Shapiro, Alexander I., Witzke, Veronika, Nèmec, Nina-E., Chatzistergos, Theodosis, Yeo, Kok Leng, Krivova, Natalie A., and Solanki, Sami K.

Subjects
The Sun and the Heliosphere, Solar chromosphere, 13. Climate action, Physics::Space Physics, Solar activity, Astrophysics::Solar and Stellar Astrophysics, Astrophysics::Earth and Planetary Astrophysics, Stellar activity
Abstract

The emission in the near ultraviolet Ca II H&K lines, often quantified via the S-index, has been serving as a prime proxy of solar and stellar magnetic activity. Despite the broad usage of the S-index, the link between the coverage of a stellar disk by magnetic features and Ca II H&K emission is not fully understood. In order to fill this gap we developed a physics-based model to calculate the solar S-index. To this end, we made use of the distributions of the solar magnetic features derived from the simulations of magnetic flux emergence and surface transport, together with the Ca II H&K spectra synthesized using a non-local thermodynamic equilibrium (non-LTE) radiative transfer code. We show that the value of the solar S-index is influenced by the inclination angle between the solar rotation axis and the observer’s line-of-sight, i.e. the solar S-index values obtained by an out-of-ecliptic observer are different from those obtained by an ecliptic-bound observer. This is important for comparing the magnetic activity of the Sun to other stars. We computed time series of the S-index as they would be observed at various inclinations dating back to 1700. We find that depending on the inclination and period of observations, the activity cycle in solar S-index can appear weaker or stronger than in stars with a solar-like level of magnetic activity. We show that there is nothing unusual about the solar chromospheric emission variations in the context of stars with near-solar magnetic activity.

Catalog

Books, media, physical & digital resources
See catalog results